CHEMICAL. ENGINEERING FACTORS IN THE PREPARATION OF UREA FROM CAR BONYL SULFIDE AND ANHYDROUS AMMONIA
Dissertation
Presented in Partial Fulfillment of the Requirements for the Doctor of Philosophy Degree in the Graduate School of The Ohio State University
By
FELICE JOSEPH CELLI, B. Ch. E. , M. Sc. The Ohio State University 1953
Approved by:
L. Ker Herndon, Adviser TABLE OF CONTENTS
Page
Acknowledgement 1
Statement of Problem 2
Scope of Problem 3
Indications
Batch System 6
Flow System 8
Historical 10
Manufacture of Urea from COz and NH3
Once Through Process 13 Solution Recycle Process 14 Hot Gas Recycle Process 14
Oil Slurry Process (Pechiney) 1 6
Preparation of Urea from COS and NH3 17
Theoretical 19
Raw Materials
Ammonia 24 Carbonyl Sulfide 25 Absolute Alcohol 28
Analysis of Product 29
Experimental Program 33
i BATCH SYSTEM
Page
Equipment 34
Effect of Order of Condensation of Reactants on Yield of Urea 36
Effect of Reactants Weight Charge / Reactor-Volume on Yield 39
Effect of Reaction Time on Yield 43
Ratio of Reactants vs. Yield 47
Effect of Temperature on Yield
No Supplementary .Liquid Phase 52 Ethanol as Reacting Medium 56
Effect of CS2 on Yield 6 0
SUMMARY 64
FLOW SYSTEM
Reactor Design 6 6
Heat Transfer Fluid for Reactor 69
Flowmeter 71
Calibration of Flowmeters
Ammonia 7 8 Nitrogen 79 Carbonyl Sulfide 81
Recovery of Urea from Catalyst 8 6
Operational Procedure 8 8
Li Page
Nature of Catalyst vs. Yield 91
Ratio of Reactants vs. Yield
Effect of Temperature on Yield 101
Effect of Space Velocity on Yield 104
SUMMARY
Temperature - Yield
Space-Velocity - Yield 1 0 6
Space-time-yield vs. Space Velocity 111
Catalyst Loading 115
Catalyst Loading vs. Space Velocity 120
Catalyst Life 123
Material Balance 125
SUMMARY 126
APPENDIX
Sample Data Sheet - Batch System 128
Sample Data Sheet - Batch System 129
Sample Data Sheet - Flow System 13 0
AUTOBIOGRAPHY 131
ILL ACKNOWLEDGEMENT
The author wishes to extend his appreciation to
Dr. L.Kermit Herndon, Professor of Chemical Engineering, for his advice and criticism during the course of this work and also for his extramural professional guidance. STATEMENT OF PROBLEM
The problem was to investigate the effect of the process variables, using both batch and flow processes, on the yield of urea when the latter is prepared according to the following reaction
COS + 2 NH3 = CO(NH2 ) 2 + HZS carbonyl sulfide ammonia urea hydrogen sulfide SCOPE OF PROBLEM
The problem of the preparation of urea from carbonyl sulfide and anhydrous ammonia was divided into two phases -- a batch system investigation and a flow system investigation. Equip ment was designed and constructed to carry out these studies.
In the batch system the variables studied were as follows:
1.) The effect of the ratio of the weight or volume of charge to the reactor volume on the yield of urea. The range was from 0.25 gram- mole of carbonyl sulfide and 0. 50 gram-mole of ammonia to 1.25 gram-moles of carbonyl sulfide and 2.50 gram-moles of ammonia per 245 ml. of reactor volume.
2. ) The order of condensation of the reactants into the autoclave and its effect on the yield of urea.
3.) Effect of the time of reaction on the yield.
4.) Effect of the temperature of the reaction on the yield of urea. The temperature range was from 30° to 143°C.
a. Using a liquid reacting medium, absolute ethanol.
b. Using no liquid reacting medium but condensing the
gases directly into the autoclave.
5.) The effect of the molar ratio of reactants, NH3 /COS, on the yield. The range was from 0 to 300 molar per cent escess ammonia and 0 to
163 molar per cent excess carbonyl sulfide.
6 .) The effect of carbon disulfide on the yield. The range of carbon
disulfide was from 0 to 18 parts per 1 0 0 parts of carbonyl sulfide.
Carbon disulfide was an impurity in the raw carbonyl sulfide before
purification.
In the flow system the process variables studied and their
effect on the yield of urea were as follows:
1 .) Nature of catalyst. Those catalysts employed were activated
charcoal, bone charcoal, wood charcoal, activated alumina, anhydrous
calcium sulfate, anhydrous calcium chloride, a.nd glass wool.
2.) Effect of temperature. The temperature range was from 25° to
193°C. for three of the above catalysts.
3.) Effect of space velocity, from 1. 56 min. - 1 to 7. 50 min. at S. T.P for activated charcoal as the catalyst.
4.) The effect of varying both space velocity and temperature respecti vely through the ranges given in (2j and (3) above.
5.) Space-time-yield versus space velocity at constant temperature
as given in( 2 ). 6 .) Ratio of reactants from 4. 0 moles ammonia per mole of carbonyl
sulfide to 0 . 5 mole of ammonia per mole of carbonyl sulfide, i. e. , up to 100 molar per cent excess ammonia and up to 300 molar per cent molar excess carbonyl sulfide.
7.) Catalyst life.
8 . ) Catalyst loading versus yield
a. At constant space velocities and variable time.
b. At constant time and variable space velocities. -6 INDICATIONS
BATCH SYSTEM
1. When absolute ethanol is used as a supplementary liquid phase
with the carbonyl sulfide and ammonia reactants, a yield of urea
of 76 per cent may be realized at a temperature of 76°C. If the
temperature is raised the yield drops to 60 per cent at 110°C.. and
from this point follows the same increase with increase in tem pera
ture as when no supplementary liquid phase is used. From ilO°C.
the maximum yield of 65 per cent is reached at approximately the
melting point of urea. Using ethanol at this low temperature is
equivalent to using a 40 molar per cent excess ammonia or 90 molar
per cent excess carbonyl sulfide. Another big advantage is that the
corrosion is greatly reduced at a low temperature and pressure.
2. When no supplementary liquid is introduced with the reactants
the yield increases steadily with temperature and reaches a maximum
of 64 per cent in the vicinity of the melting point of urea, 132°C.
3. The time for the reaction of stoichiometric quantities of carbonyl
sulfide and ammonia to reach completion, using 93°C. as the basis,
is approximately 1 2 0 minutes.
4. At 105°C. using an excess of carbonyl sulfide of 100 molar per cent a maximum yield of urea of 78 per cent may be obtained. 5. At 105°C. using ammonia in excess of 150 molar per cent a
maximum yield of 8 8 per cent of urea may be obtained. Ammonia has a greater driving force than does the carbonyl sulfide in the for mation of urea from these two reactants.
6 . In the range of ratios of reactants weight charge to volume of reactor studied, 0.10 to 0.48 gr. per ml. of reactor volume, no effect was noted on the yield of urea.
7. The order of condensing the reactant gases into the autoclave has no effect on the yield of urea.
8 . Carbon disulfide, a possible impurity of carbonyl sulfide, does not decrease the yield of urea but rather increases it slightly. The product, however, is oily and would have to be purified before it could be sold on the market.
9. Excess ammonia is more corrosive than excess carbonyl sulfide on 18-8 stainless steel 316 reactor. FLOW SYSTEM
1. Since the urea remains on the catalyst, catalyst loading and de
activation play one of the leading factors in the flow system.
2. Catalyst loading increases with space velocity at equivalent gas throughput.
3. Activated charcoal gave the best yields of any catalyst used.
Activated alumina and bone charcoal followed.
4. Increase in space velocity results in a decrease in yield at all tempe iqtur e s.
5. Using activated charcoal and stoichiometric quantities of reac tants the best yields at all space velocities is at 125°C.
6 . The yield of urea drops off sharply above 125°C. (Urea decom poses above its melting point (132. 7°C)).
7. The highest space-time-yields are obtained at 125°C. The data show that there no major side reactions in the formation of urea from carbonyl sulfide and ammonia.
8 . Ammonia has a greater driving force in the formation of urea from carbonyl sulfide and ammonia than does the carbonyl sulfide. 9. At 1 2 9 °C. and space velocity of 2.41 min. a molar excess of ammonia of 50 per cent raises the yield of urea from 56 to a maximum of 75 per cent.
10. At 129°C. and space velocity of 2.41 min. a molar excess of carbonyl sulfide of 100 per cent raises the yield from 56 to a maximum of 65 per cent.-
11. At 121 °C. and space velocity of 2.41 min. an excess of carbo nyl sulfide has essentially no effect on yield.
12. At 121°C. and space velocity of 2.41 min. an excess of am monia of 80 molar per cent raises the yield from 20 to 36 per cent maximum.
13. A greater excess of ammonia is needed to attain a maximum yield of urea as the temperature drops from the 125-129°C. range.
14. The catalyst, activated charcoal, may be re-used. Its activity does not decrease with re-use after having been subjected to extrac tion process. -/< ? - HISTORICAL
It was in the year 1828 that Wohler, on checking a mixture from an experiment he had performed and set aside four years earlier, found some crystals had developed. He identified these as urea. He was very much surprised at the results because he had taken typical inorganic substances and synthesized a typical organic substance.
Pb(OCN ) 2 + (NH4)2 S0 4 ------► PbS0 4 + 2 NH^OCN lead cyanate ammonium lead ammonium sulfate sulfate cyanate
NHjOCN CO(NH2)2 'l+ urea
This finding was so contrary to the thinking of that period that he repeated his experiments several times. The barrier between organic and inorganic matter was thus broken. The "vital force" doctrine no longer held and so, thoroughly convinced of his findings, he wrote to his friend Berzelius as follows, "I must tell you that I can prepare urea without requiring a kidney, either man or dog. "
This preparation may well be considered as the forerunner of the field of synthetic organic chemistry.
-H- Liebig and Wohler in 1831 demonstrated that ammonium cyanate was quite different in properties from urea thus ending the belief that they were one and the same substance. -//-
At first it was difficult for Berzelius and other contemporary
chemists to divorce themselves from the ”vital force” concepts but
eventually they abandoned their idea after subsequent similar experi
ments were reported.
Actually it was Rouelle in 1773 who discovered urea in urine and some twenty-six years later Fourcroy and Vanquelin obtained urea in a comparatively pure crystalline form from the same source
and recognized it as being a new compound and gave it the name UREE.
It was Prout who in 1824 made the first accurate analysis of urea and determined its emperical formula.
Davy in 1812 synthesized urea from phosgene and ammonia according to the reaction
COCl2 + 4 NH3 >CO(NH 2 ) 2 + 2 NH^Cl phosgene ammonia urea ammonium chloride
although credit is usually given to Regnault
(lS^) for the preparation of urea by this reaction.
Numerous methods have been postulated for the synthesis of urea but only a few have attracted interest industrially the most popular being hydrolysis of cyanamide and the interaction of carbon dioxide and ammonia.
It was J. Basaroff (Ann. Chem. Pharm. 146, 142 (1868)) who first suggested the synthesis of urea from carbon dioxide and- ammonia showing that both ammonium carbamate and carbonate when heated in a sealed tube.
Before 1935 the world market for urea was controlled by Germany. In 1935 Imperial .Chemical Industries Ltd. of England began production of urea on a small scale and duPont began the first commercial production of synthetic solid urea in the United
States.
A description of the carbon dioxide - ammonia processes now in use are described in later section. -/ 5-
MANUFACTURE OF UREA FROM CARBON DIOXIDE AND AMMONIA
There are several processes now in use for the manu facture of urea from carbon dioxide and ammonia. Essentially these processes consist of the following steps:- a.) compression of the carbon dioxide b.) compression and liquification of ammonia c.) introduction of these reactants into the reaction system under pressure d. ) the release of pressure and the decomposition of the unconverted ammonium carbamate into carbon dioxide and ammonia e.) the recovery of urea.
ONCE THROUGH PROCESS
Process Conditions: The compressed carbon dioxide and ammonia
are fed at stoichiometric ratio (1 :2 ) into the reactor which is at tem perature of 160-180°C. and at a pressure of 150-200 atmospheres depending on the various manufacturing modifications. The carbamate- urea solution is then sent to a flash stripper where the carbamate under goes decomposition to ammonia and carbon dioxide and the urea remains in solution. In the stripping operation the temperature drops to about
95°C. The ammonia, is recovered as ammonium sulfate or some other s alt.
Process Economics: The conversion depends on the conditions used and varies from 30-60 per cent. Actually the urea is very pure as noted by fact that the yield based on the reactants consumed is very nearly theo- - I 4 - - retical. Corrosion is a big problem and the reactor must be lined with lead. The recovery of the ammonia is a must.
SOLUTION RECYCLE PROCESS
Process Conditions: The process differs from the previous in that the ammonia and carbon dioxide is recycled as an aqueous solution of ammonium carbamate. The source of water is from the reaction and of course the presence of so much water in the system tends to lower the conversion. The duPont process is essentially this one and the way they overcome this is by using higher temperatures on the
order of 2 0 0 °C. and using an excess of 3-5 moles of ammonia. The reactor pressure is then about 400 atmospheres. The reactor is self- cooling since the high excess of ammonia in the system is stripped away from the solution and recycled as liqid ammonia.
Process Economics: Higher temperatures tend to increase the cor rosion problem and consequently silver-lined reaction equipment is used which in turn means a higher plant investment. An overall yield
of 9 0 based on ammonia and 80 based on carbon dioxide is realized.
HOT GAS RECYCLE PROCESS
Process Conditions: This process is/was used in Germany by I. G.
Farbenindustrie at Oppau. The unconverted gases can be to the process or used for the manufacture of other products. In the recycle process the gas mixture is compressed to 170 atmospheres in a 5 stage recycle - / £ ~ gas compressor with air cooling between stages. These gases are injected at 260°C. into the header at the point of mixing of fresh carbon dioxide and ammonia. It is necessary to maintain the return ed gases at a high temperature during their compression in order to prevent the formation of solid carbamate and also corrosion in the com pressor. The recycle of the hot gases requires a two stage r e actor to control the reaction at the desired temperature of 160-170°C.
Water inside the tubes under pressure carries off the heat. In order to prevent excessive corrosion in the high pressure reaction vessels all sulfur compounds and traces of oxygen are removed. The com- o pressed carbon dioxide at 45 C. is passed through an activated carbon tower in which the sulfur is removed. It is necessary to inject into the tower about 3.5 grams of ammonia per cu. m. of gas as well as sufficient air to give an amount of oxygen slightly in excess of stoichio metric proportion with the sulfur content. The oxygen is completely removed by passing the gas at 220-230°C. over a nickel copper catalyst.
Process Economics: An overall yield of 93 per cent based on ammonia and 83. 5 per cent based on carbon dioxide is reported. Maintenance is high and operation of the plant is difficult. The recycle compression and lead covered tubes contribute to high plant investment. At the present time this process cannot compete with others. -/6-
OIL SLURRY PROCESS (Pechiney Process)
Process Conditions: In the Pechiney process the reactions take place
in a neutral oil which is circulated continuously through the process
equipment. The carbon dioxide are charged to a reactor operating at 200 atmospheres and 180°C. These mix with slurry made up of finely dispersed ammonium carbamate in the neutral oil and react to form additional carbamate. At the top of the reactor the mixture is flashed to a low pressure where the unconverted carbamate decomposes to ammonia and carbon dioxide. The decomposition is carried out to
completion by addition heat. The remaining oil-urea mixture is sepa
rated by decantation, the oil flowing to reactors where the ammonia and carbon dioxide from the carbamate decomposition step recombine in it to form the ammonium carbamate slurry (ca 45°C.) which is then sent back to the synthesis reactor. The oil helps control the tempera ture by absorbing the heat liberated by the reaction. The heat is par tially released in the stripper.
Process Economics: A yield of 93 per cent based on ammonia is ob tained when carbon dioxide of 98 per cent purity is used. Higher yields are obtained with more pure carbon dioxide. Corrosion is minimized by the presence of the oil. Actually the corrosion conditions due to high tem peratures accur only in the reactor which is lead lined. PREPAHATION OF UREA FROM CARBONYL SULFIDE AND AMMONIA
M. Berthelot reported in the literature (Ann. 148 , 266
(1868))that ammonium thiocarbamate was formed from carbonyl sulfide and ammonia gases. E. Kretzschmar (Journ. fur prakt. Chemie (2) 1_,
474 (l873))in order to show or prove the formula for ammonium thio- carbamate heated it to 13d~140°C. under pressure and obtained urea and hydrogen sulfide. He started with pure dry solid ammonium thio- carbamate which he prepared by passing carbonyl sulfide into absolute alcohol saturated with dry ammonia. E. Fleischer (Ber. 9, 436 (1876)) proved the formula by desulfurizing ammonium thiocarbamate with mercuric oxide.
A. Klemenc (Z. fur anorg. u. allg. Chemie 191, 246 (1930)) made some thermodynamic calculations which showed that it might be
possible to realize a yield of urea better than 9 0 % by using carbonyl sulfide and ammonia.
Several patents have been issued on the preparation of urea from carbonyl sulfide and ammonia.
A. Klemenc and S. Scholler (German Patent 537, 765 (1931));
U.S. Patent 1,808,465 (1931) and British Patent 327, 026 (l930))assigned to I. G. Farbenindustrie)) suggested the preparation of urea without the isolation of the ammonium thiocarbamate by liquifying the carbonyl -/a- sulfide and ammonia either simultaneously or while mixed with each other and then heating the mixture to 80-12 0°C.
A. Zieren (German Patent 579,567 (1933)) passed carbonyl sulfide and ammonia in stoichiometric quantities over ac tivated carbon at 100-140°C. and obtained urea. He also suggested
(French (Patent 803, 141 (1936)) that gaseous ammonia and carbonyl sulfide be passed into a molten bath of urea under pressure and with drawing urea formed.
S. Oda (Japanese Patent 94, 859 (1933)) made urea from ammonia and carbonyl sulfide in methanol and ethanol with and without metallic oxides under pressure.
I. Kitawaki, S. Hou and M. Shinoda (Japanese Patent
100, 812 (1933)) also made urea from carbonyl sulfide and ammonia.
S. Oda (Japanese Patent 95,663) passed chlorine through an alcohol solution of NHjCOSNH* and obtained urea along with hydrogen- chloride and sulfur as the by-products. THEORETICAL
Carbonyl sulfide and ammonia react to give urea and hydrogen sulfide by way of an intermediate product, ammonium thiocarbamate
,NH2 n h 2
COS + 2NH 3 ^ 0 = C ^ 0 = C y + H2S (1) SNH* X NH2 ammoni um thiocarbamate
Selivanova and Syrkin (Acta Physicochimica U, S. S, S. 11, 647 (1939)) in their kinetics study believe the reaction proceeds in two stages.
The first of these , which determines the kinetics, is a slow stage.
COS + NH3 = COSNH3 (slow) (2)
COSNH3 + NH3 = NH2 COSNH4 (rapid) (3)
A reaction rate equation of the second order represented their experi mental results better than any equation of any order. The reaction is heterogenous.
The ammonium thiocarbamate as it is formed is a white crystalline compound but on standing at room temperature in air, it undergoes decomposition and turns yellow. The reaction is slightly
reversible when the mixture is cooled to dry ice-acetone temperature.-
The overall reaction (l) is exothermic-. The heat of feaction at 18°C. as calcukied from the heats of formation from Bichowski and - £ 0 ~
Hossini heats of formation
Reactants Products
COS = 35.0 CO(NH2)2 =78.5 2 NH3 =22.0 H2S = 5.3 57.0 83.8 then
heat of reaction = 83. 8 - 57. 0 = 26. 8 kcal./gr. mole of urea = 48,240 BTU/lb.mole of urea
The heat of reaction at 18°C. for the synthesis of urea from carbon dioxide and ammonia
COz + 2 NH3 = CO(NH2 ) 2 + h 2o
is 1 9 . 8 kcal. /gr. mole of urea or
35,640 BTU/lb.mole of urea.
There are no thermodynamic objections tc the synthesis of uraa from carbonyl sulfide and ammonia. The free energy of the reaction may be calculated as follows:
Carbonyl sulfide
C (/3-graphite) + 0. 5 Sz(g) + 0.5 Oz = COS^g)
aF° = 50, 630 - 5. 08 T log T + 0. 00118 T 2 + 74, 600 T " 1 + 12. 65 T
Hydrogen sulfide
H2 + 0 .5 S 2fg) = H2 S^g)
aF° = -19,405 - 7. 70 T log T - 0..001033 T 2 -12. 51 T
Ammonia
aF9= _ 9 , 500 + 4. 96 T In T + 0 . 03 5 7 5 Tz - 0. 0685 T3 -9 .6 1 T -at- Urea
at 298. 1°K a H° = -79,639 a F° = -47, 120 C° = 22.26 P Assume that at 25 to 130°C. , for the solid urea, the specific heat does
not vary, then
C = 22.26 a = 22. 2 6 P
AH° =/*Ho + aff = H 0 * 22.26 T
at 298. 1 ° »*H0 =aH° _ 22. 26 T = -79, 639 - 2 2 . 2 6 x 298. 1 = -86,267
*F° = a Ho - a T In T + I T
at 298.1° -47,120 = -86,267 - 37,747 + 1 x 298.1
then I = 258
Therefore the free energy for solid urea is
F° = -86,267 - 51.2 T log T + 258 T.
For the reaction, the free anergy may be obtained as follows: /
^F° .- AF° .. =-36,042 -61.2 T log T - 1. 266 x 1 0 ^3 T2 reaction ’ 6 + 0. O5 1 17 T 3 - 0. 746 x 10 5 T - 1 + 253 T The equilibrium constant may be calculated from the free energy according to the following relationship .aF0 = - R T In K At low pressures for the reaction COS + 2 NH3 = CO(NH2 ) 2 + h 2s Assume COS = 1 mole NH3 = 2 moles CO(NH2 ) 2 formed = x then at I atmosphere and 1 0 0 °C. K x______=2.54 ^ ( 1 -x) ( 2 - 2 x) 2 solving x = 90% conversion At 10 atmospheres x r, 91% conversion. Actually, as was found in the course of this study, unless the filling ratio of the autoclave is very small , there will always be pressures higher than 1 0 atmospheres in the autoclave. Effect of heat on u rea: Urea undergoes decomposition when heated above its melting point, 132. 7°C. For example, if it is heated slowly to 150-60°C. , biuret forms H2 N-CO-NH2 + H2 N-CO.NH2 = H2 N-CO-NH-CO-NH2 + n h 3 biuret If the heating is more rapid and the temperature raised then cyanic acid results H2 N-CO.NH2 = NCOH + NH3 cyanic acid However the cyanic acid polymerizes readily to the cyanuric acid - £ 3 - C-OH 3 NCOH = ) 1! HO - C C-OH cyanuric acid Also'formed are ammelide, ammelinj&, and melamine which are mono-, di-, and tri- substituted compounds of the cyanuric acid as the amides. - 2 4 ~ RAW MATERIALS Ammonia ,1 The ammonia used as the starting material was anhydrous ammonia. A "lecture size" (Mathescn) cylinder of ammonia was required for the batch system studies since the amount of ammonia used had to be measured by weighing the cylinder periodically until the right amount had been transferred into the reactor. The use of this size cylinder dictated a refilling every so often and this was done by immersing the small cylinder inco an acetone-dry ice bath and connecting the valve directly by pressure tuftung to the valve of the larger cylinder of anhydrous ammonia which was at room temperature. The valve of the small cylinder was opened completely while that of the large cylinder was used as the control valve and was usually opened slightly. The ammonia condensed in the small bottle and it was moisture freet: The following CAUTION was adhered to very rigidly. The valves on the two cylinders were closed and the small cylinder was disconnected from the assembly. The small cylinder was weighed immediately and AMMONIA BLED OFF UNTIL THE WEIGHT WAS EQUAL TO OR LESS THAN THE WEIGHT OF THE FILLED CYLINDER AS IT WAS RECEIVED FROM THE MATHESON COMPANY. This precaution had to be taken to prevent an explosion from taking place i when the cylinder would be filled with liqid cold and then warmed to room temperature. - a s - Carbonyl sulfide 1. Preparation The starting material, carbonyl sulfide, used in both the batch system and flow system had to be prepared in the laboratory since it could not be purchased. Briefly, the carbonyl sulfide was prepared as follows: - Meterdd quantities of sulfur dioxide and car bon monoxide were passed continuously over a bed of wood charcoal maintained above 800^C. and in the absence of moisture and air. The wood charcoal was first calcined to remove hydrocarbons and moisture which would ultimately lead to the formation of hydrogen sulfide. The exit gas was bubbled through a sulfur trap to remove some of the sulfur and thence sent to a packed scrubbing tower where it met a countercurrent stream of sodium hydroxide solution. Some hydrolysis of the carbonyl sulfide took place resulting a loss of yield. The sodium hydroxide removed all of the carbon dioxide and hydrogen sulfide and some of the sulfur carried along as fog. The exit gas was passed over Drierite (anhydrous calcium sulfate) to re move the moisture and some of the sulfur fog and then sent to a tube maintained at acetone-dry ice temperature to condense out the carbonyl sulfide. Carbon monoide, some carbonyl sulfide, and still some of the remaining sulfur fog were vented. 2. purification and Storage. The carbonyl sulfide as was prepared by the above method - < 3 6 - contained some water in the ice form (some of this water coming from condensation on the neck of the storage flask previous to trans ferring) and earbon disulfide in the maximum range of 5 parts per 100 parts of carbonyl sulfide. Since the boiling point of carbonyl sulfide is -50.2°C.76o and that of carbon disulfide +46. 3°C. the sepa ration was easily affected. The flask containing the mixture was removed from the dry ice-acetone bath and connected to the "lecture size" cy linder, which had the valve assembly removed and had been cooled for some time in an acetone-dry ice Dewar. The gas was allowed to distill over on its own. The gas leaving the flask was passed through drying tubes containing anhydrous calcium sulfate and then a capillary tube (3 mm. O, D. - 1 mm, I. D. ) which fitted trough the opening in the cylinder. (For this reason Matheson Co. cylinder was used since it could be refilled; Ohio Chemical could not be used as such). The distillation was a very slow process since the flask containing the carbonyl sulfide became heavily frosted on the outside from the atmos pheric moisture depositing. Actually this was advantageous since it meant a better separation and easier condensation on the other end since not so much came over at one time, then too, the moisture was removed more easily in the drying tubes as the contact time was longer. If by chance any moisture did find its way through the drying tube then capillary tube would ice up and plug causing a back pressure in the lines and result in a blow-off of the rubber tubing and a loss of carbonyl sulfide. -27- The valve assembly was placed back on the cylinder and the valve shut. The same precaution was taken with the carbonyl sulfide as with the ammonia, namely, not to get too much cold liquid into the cylinder for danger of an explosion upon warming. The cy linder used for storing the carbonyl sulfide was one that had contained hydrogen sulfide. The vapor pressure and corrosiveness of carbonyl sulfide is very close to that of hydrogen sulfide. Actually in filling the cylinder only about 400 grams were transferred; this was consi derably below the comparable weight of hydrogen sulfide which the cylinder contained originally. When the cylinder had warmed to room temperature and shaken one could hear the liquid sloshing inside; if the sloshing sound was not too audible then it meant that the cylinder was too full. It was found that the carbonyl sulflide could be kept for long periods of time in these cylinders since it was very pure and moisture free. In practice the gas was used up to within a month from the time it was transferred but on several occasions some cylinders were not used for several months but the carbonyl sulfide was found to be perfectly all right. - a e Absolute Alcohol The absolute alcohol was prepared as follows: - 14 grams of sodium were dissolved in 1 liter of ethanol that was very nearly water free and the mixture refluxed; 40 grams of ethyl formate were added and the mixture heated to boiling and refluxed. The smallest amount of water hydrolyzes the ethyl formate and sodium formate which is very insoluble in water precipitates. The excess ester decomposes completely to carbon dioxide and ethanol in about two hours as was indicated by ceasing of the carbon- dioxide evolution. The reflux condenser was replaced by the distilla tion head and the absolute alcohol distilled. The first 100 ml. were descarded; the next 200 ml. contain 0. 001 % ester; the next part only 0. 00015 %. Further fractionation does not make it better. The water content amounts to 0. 03 %. -23 ANALYSIS OF PRODUCT The first products were analyzed for urea nitrogen by the Kjeldahl method as set forth by the A. O. A. C. This not only proved to be fastidious, as was to be expected, but also the results on duplicate samples were inconsistent. Therefore the literature was checked for other possible procedures in analyzing the samples for nitrogen or more specifically, urea itself. There is available an enzyme called UREASE, obtained from extraction of the Jack Bean (Canavalia ensiformis) which has the specific property of being able to hydrolyze urea into ammonia and carbon dioxide. The brand name of the urease used for the analyses was Urease-Arlington manufactured by the Arlington Chemical Company, Yonkers, N. Y. This urease is a very fine off-white powder which is extremely water soluble and highly reactive. The manufacturer claims that their product is ammonia free and it will keep if kept at room tempe rature, tightly corked, dry and out of strong light. They claim that after three years, no deterioration is shown. The manufacture also recom mended that a stock solution not be prepared since bacterial decomposi tion starts readily and ammonium compounds are soon formed. The solution may be kept in the refrigerator for several days but the rate of decomposition is so variable that it is far safer to prepare the solution fresh each time before iising. -30 Procedure for Urea Nitrogen by the Urease Method The procedure used for analyzing for urea nitrogen was a modification of the A. O. A. C. - Urea and Ammoniacal Nitrogen (Official and Tentative Methods of Analysis of the Association of Official Agricul tural Chemists, A .O .A .C ., Franklin Station, Washington, D.C. (1945)). Reagents: 1. N/lO Hydrochloric acid 2. N/lO Sodium hydroxide 3. Indicator - Fleisher methyl purple (manuf. by Fleisher Chem. Co. , Benjamin Franklin Station, Washington 4, D.C.) 4. Calcium chloride solution - dissolve 25 gr.of CaCl2 in 100 ml. of HzO. 5. Magnesium oxide (heavy type). (Schaar and Co.) 6 . Urease powder (The Arlington Chemical Co. , Yonkers, N. Y.) Procedure: An aliquot of the urea sample containing up to0 . 1 gr. of urea was placed into a Kjeldahl flask containing 300 ml. of water. Urease was added to the mixture (0. 1 gr/50 ml of HzO - neutral) and the flask stoppered tightly and allowed to stand at room temperature for one hour. Two grams of MgO (heavy type) and 1 ml. of CaCl 2 solution were added to the flask. The flask was connected to the condenser through the Kjeldahl bulb and heat applied. About 200 ml. were distilled into an Erlenmeyer flakk containing 50 ml. of N/lO HC1. The acid was back- titrated using 5 drops of Fleisher Methyl Purple indicator (pH-4.8 , green; pH-5.1, grey; pH-5.4, red) and N/lO NaOH. - 3 7 - Sample calculation: Weight of sample = 1. 000 Aliquot = 25/250 Volume HC1 =50. 0 ml. Normality HC1 = 0. 1001 Volume NaOH Normality NaOH = 0.1015 Blank = 49. 0 ml. Sample = 17. 0 Urease = 0.1 gram/50 ml. gr. of Urea = (49. 0 - 17. 0) x 0. 1015 x 2 NH 3 x CO(NH2 ) 2► x 250 2000 2 NH3 25 = 0.974 = 97.4% - J £ - K oeldakl IHCCSTtOt* RACK S' Gr a d u a t e t CYUHOCA K j c l m h l ARLMNtHEYER FLASK FLASK VOLUMSTRJC FLASK ttJKfe BURETTE. CMMP MfO MtASURtNS IAOUE INDICATOR. CALCIUtA U*£ASE MASMASIUM CHtaiuoe ottos $O LN. FIG. 2 5 EQUIPMENT POP. UREA DETERMINATION -35 EXPERIMENTAL PROGRAM The experimental program was divided into several sections. In the batch system,suitable methods and equipment had to be developed for condensing the reactant gases and heating the reactor. Procedures for the recovery and analysis of the urea were formulated. Finally the process bariables were studied. In the flow process, equipment had to be designed and adapted for metering the reactant gases. This equipment had to befcalibrated. Methods for working up the urea had to be devised. The process variables were then studied. BATCH SYSTEM -34~ EQUIPMENT The reactor used in the batch system studies was an Aminco Micro Reaction Vessel as shown in Figure 1. The material of construction was 18-8 Stainless Steel 316. The reactor was equipped with liners made from oversize 3 8 mm. Pyrex tubing thus providing a close fit. The heating jacket consisted of a copper sheeting which fitted snugly around the reactor and it was wound with asbestos tape and Nichrome heating wire in three separate circuits. Transformers were used to control the voltage. In some studies the reactor was kept at constant tempe rature by using a steam-water bath. The temperature of the reactor was measured by a thermo couple arrangement. -3S- F/g u r e / A utoclave, r e a c t o r . -36 EFFECT OF ORDER OF CONDENSATION OF REACTANTS INTO AUTOCLAVE ON THE YIELD OF UREA The method finally selected for introducing the ammonia and carbonyl sulfide into the reactor was a direct condensation of the gases from their respective cylinders into the autoclave maintained at dry ice-acetone temperature (-78.5°C.). The carbonyl sulfide is the more volatile of the two gases, having a boiling point of -50.2°C. and a melting point of -138.2°C. as compared to -33.4°C. and-77. 7°C. for the ammonia. At the autoclave temperature the ammonia condensed and solidified. Also the carbonyl sulfide and ammonia formed a solid, i presumably ammonium thiocarbamate, NH 2 COSNH4 , and it was thought that a localized excess of one of the reactants around or occluded in this compound might result in a reduction of the urea yield. There fore it was decided to study the effect of the order of condensation of the reactants on hhe yield of urea. It was found that no difference in the yield of urea was obtained. A definite order of condensing the gases was adopted, however., F irst the carbonyl sulfide was condensed and then the ammonia. The reason for this choice was as follows: -37~ The carbonyl sulfide was the more difficult of the two gases to condense therefore it was condensed first. The feed tube was placed up against the very bottom of the autoclave liner and the gas condensed easily as it came up against the cold surface. The feed tube was inserted through a rubber stopper which fitted snugly on the reactor liner to keep moisture from entering the liner itself. From this stopper was also another short tube which was attached to a small test tube to act as a trap so as to condense any gases which had not condensed in the autoclave. This trap was placed in the dry ice - acetone next to the autoclave. If any gas condensed in this tube then the feed rate was adjusted so that all input gas remained in the reactor. When the right amount of the gas had been transferred as noted by the weight difference then the feed was switched to the ammonia feed cylinder. If the tube were allowed to remain below the liquid carbonyl sulfide whfcch had condensed then, when the ammonia was introduced, aJter a short time a solid would form, either or both NH3^ and NH2 OCSNH4 , This would result in plugging if the feed rate slowed down enough to keep the liquid from coming up: . the tube and meeting the ammonia and forming a solid in there. It was difficult to maintain a perfectly steady gas feed to prevent plugging. - 3 3 - Therefore the tube was initially raised above the liquid carbonyl sulfide and, since the reactor was about some 45°C. below the condensation temperature of ammonia, the ammonia condensed easily after it left the feed tube. No plugging occurred. If however the reverse order was used in condensing the gases then the rate of carbonyl feed had to be extremely small in order that sill of it would condense when the feed tube was not touching the cold surface directly. It was easy to condense the first gas but the second gas gave a little more trouble and especially carbonyl sulfide as pointed out. If the lines became plugged and a slight leak occurred one could smell the ammonia whereas it was not so with the carbonyl sulfide unless it had first hydrolized to the hydrogen sulfide. -39 EFFECT OF REACTANTS WEIGHT CHARGE / REACTOR - VOLUME ON YIELD OF UREA An important factor which had to be established before undertaking any of the other variables studies was the relationship between the yield of urea and the volume or weight charge of the reactants introduced into the autoclave. The gases, carbonyl sulfide and ammonia, combine to give ammonium thiocarbamate as one of the products of reaction. This compound is a solid which undergoes the splitting-off of hydro gen sulfide yielding a urea solid. By increasing the weight, and consequently the volume, of charge the free space in the reactor is decreased. When the autoclave is heated then the mixture gases exert their own partial pressure which probably passes through some maximum when the temperature is raised or their volume decreased. The effect of this on the yield of urea was stugdjied by charging into the reactor different weights of carbonyl sulfide and ammonia in stoichiometric ratio. The range was from 0. 10 to 0.48 grams carbonyl sulfide plus ammonia per unit volume of the reacto r, The data are tabulated in Table 1 and represented graphically in Figure 2. -40- It can be seen from the figure that, within the range of "Reactants Weight Charge Reactor Volume” studied the yield is independent of this ratio. And since this is the range in which all runs were made, no adjustment of reactants weights and volume had to be carried out. In the ammonium carbamate - urea - water system the yield is definitely a function of this ratio and increases with an increase in ratio (Clark, Gaddy, and Rist, Ind. and Eng. Chem. 25, 1092 (1933)). TABLE 1 EFFECT OF REACTANTS WEIGHT CHARGE / REACTOR VOLUME ON YIELD OF UREA Temperature - 107°C. Run Max. COS COS nh3 nh3 NH3/COS Total Reactor « /0 % Yiel Press. g*. moles gr. moles COS + NH3 Volume psig. gr. 0 a 33 260 15.6 0.26 9.0 0.53 2. 0 24.6 245 0.100 65.4 32 475 30.2 0.50 17.1 1.00 2.0 47.3 245 0.193 60.0 34 450 30.5 0.51 17.3 1/02 2.0 47.8 245 0.195 58.5 30 725 61.2 1.02 35.1 2V06 2.0 96.3 245 0.393 58. 0 31 75.0 1.25 43.4 2.55 2.0 118.4 245 0.483 64.5 %> Yi£LD m . e r m F " 1 W 17 0 - ~r - * 2 Effect of React s ne/ Charse/ m onYi ij> ie Y n o /m u > H r o t c a e /r e s r a h C t h /g e n ts n ta c a e R f o t c e f f E . 1 ‘ ^ fUO tflU Q 0 t a *7H lb t M llbU &*C7tHZ 1 * ‘ * r 040 r. j .M |r 1 ■ OSO f MO m loo -4-3- EFFECT OF TIME OF REACTION ON YIELD OF UREA An important factor in any reaction is the time necessary for equilibrium conditions to be attained. Studies were made to determine the effects of heating time on the yield of urea when stoichiometric quantities of carbonyl sulfide and ammonia were used. The method of carrying out the study was as follows: - the carbonyl suj/tide and the ammonia were condensed into the auto clave as was described previously. The sealed autoclave was allowed to warm up to room temperature overnight. A water bath heated by steam passing through a copper coil and having an air tube for keeping the water mixed and at a constant temperature throughout was brought up to 93°C. The autoclave was introduced into the bath and was wholly submerged. The time was noted. The bath was of sufficient capacity that the temperature drop was about 4° at the most when the reactor was first introduced and the temperature of 93oC. was re-attained within 3 minutes. At the chosen time the autoclave was removed from the bath and immediately plunged into an ice water bath in which the autoclave could be completely submerged. After half an hour the autoclave was taken from the bath and the contents removed and -44- worked up for the urea formed. The results are given in the accompanying table and chart. The yield rose steadily with time and the curve began to flatten after approximately 100 minutes. At this temperature of 93°C, the maximum converaion of 63 per cent was reached at approximately two hours. TABLE 2 EFFECT OF TIME OF REACTION ON YIELD OF UREA (Autoclave - Water bath heated) Run Time Temp. COS COS NH3 NH3 NH3/COS Yield ______(min.)______°C.______gr.______moles gr. moles ______^ ______ 35 0 room 30.8 0.51 17.9 1.05 2.00 9.74 T-3 10 93 30. 1 0.50 17.5 1.03 2.06 31.4 J $ T-2 30 93 30.0 0.50 17.0 1.00 2.00 45.6 | T-l 60 93 31.0 0.52 17.6 1.04 2.00 56.1 T-7 1 0 0 93 30. 3 0 . 51 17.2 1 . 0 1 2 . 0 0 62.7 T - 6 180 93 30.4 0. 51 17.5 1. 03 2. 00 63.4 a y c p ' 2 0 40 60 80 100 1 2 0 140 160 180 Tim e , (m in ) F m n f. 3 Effect of Hemm Time on T/elo -4-7- RATIO OF REACTANTS vs. YIELD The effect on the yield of urea by an excess of carbonyl sulfide and of ammonia over the stoichiometric was determined at a reactor temperature of approximately 105°C. (autoclave was elec trically heated and temperature measured by thermocouple). The range of molar ratio of reactants, NH3 /COS, was from 0. 76 to 8 . 14 or from 164 molar per cent excess carbonyl sulfide to 300 molar per cent excess ammonia. The data are given in Table 3 and represented graphi cally in Figure 4 and Figure 5. These figures clearly show that ammonia has a greater driving force in getting the urea to form than does the carbonyl sulfide. This has one advantage, namely, that industrially the am monia would be favored cost-wise. The pressure would also be slightly lower when ammonia would be used. There is one big dis advantage, however, and that is the corrosion problem involved. When the above runs were made, using an excess of carbonyl sulfide there was hardly any corrosion to speak of; when operating on the ammonia side the corrosion was high. A black powdery scale formed. The reactor was made of 18-8 stainless steel $16. At this temperature of approximately 105°C. using an -46' excess of carbonyl sulfide a maximum yield of some 78 per cent was realized at about a 100 molar per cent excess(2 moles of NH3/ 2 moles of COS). Using ammonia in excess of 150 molar per cent (5 moles of NH3/l mole of COS) about 8 8 per cent yield was obtained as a maximum yield. At stoichiometric quantities (2 moles of NH3 /I mole of COS) the yield was 60. 0 per cent.. TABLE 3 RATIO OF REACTANTS VS YIELD Run Temp. COS COS NH3 NH3 NH3/COS % % % Yield °C. gr. moles gr. moles Excess Excess based on based on NH3 COS______COS______NH3 40 103-8 4,8 0 . 08 1 1 . 1 0.65 8.14 300 89.1 21.9 46 104-8 19.8 0.33 29.9 1.76 5.33 167 83.0 31.2 42 164.5 34.4 9.57 29.8 1.75 3. 05 52 79.0 51.8 4+32 1 0 6 30.2 0.50 17.1 1 . 0 0 2 . 0 0 s toichiometr ic 6 0 . 0 60.0 0 0 ++34 107 30.5 0.51 17.3 1 . 0 2 2 . 0 0 0 0 58.5 58.5 43 114 43.2 0.72 18. 0 1.06 1.47 38.5 52.8 71. 0 45 1 0 1 30.0 0.50 8 . 6 0.51 1 . 0 0 1 0 0 39.3 77. 7 48 108 50.3 0.84 1 0 . 8 0.64 0.76 163 28.8 75. 5 -H- Stoichiometric COS + 2 NH3 = CO(NH2 ) 2 + H2S to £0 SO 40 50 60 70 M o le f/m o ■M /cos Meu^e 4-. Rfrn OF ^Emms *>■ Yield (Batch System) 0^0 fitu> on cos 3 £ 8 f e lt BfiS& ON NHS ISO 300 3 0 0250 % M o u n ( E x c e s s J H j t r O R Fig u r e 6 . Ef f e c t o f E x c e s s j / h3 * -C 0 S o n T/e l o (Batch System ) EFFECT OF TEMPERATURE ON YIELD OF UREA 1. Straight Reactants Feed with No Supplementary Liquid Phase in the Reactor The yield of urea was studied as a function of the tempera ture of the reaction. Stoichiometric quantities of carbonyl sulfide and ammonia were condensed per se into the autoclave held at dry-ice acetone temperature. The temperature was varied from 30° to 143°C. by heating the reactor electrically and measuring the temperature by a thermocouple. The data are presented in Table 4 and Figure 6 . The yield increases with temperature and reaches a max imum of 64 per cent approximately at the melting point of urea, 132. 7°C. A plot of the log of the temperature versus the yield gives a straightline up to the break-point where the maximupi conversion attained corresponds as mentioned. The equation for the yield versus temperature up to the melting point of urea may be expressed by Yield = 78. 7-log (temp.) -100 TABLE 4 TEMPERATURE - YIELD (reactor - electrically heated) Run Tem p. COS COS NH3 NH3 NH3/COS % Y ield ______°C .______gr._____ m oles______gr.______m oles______ 35 2 6 30.8 0.51 17.9 1.05 2 . 0 9.74 36 38 32.2 0.54 19.4 1.14 2 . 1 24.94 38 82 30.7 0.51 17.4 1 . 0 2 2 . 0 49.9 32 1 0 6 30.2 0.50 17.1 1 . 0 0 2 . 0 60.0 34 107 30.5 0.51 17.3 1 . 0 2 2 . 0 58.5 39 143 31.5 0.53 17.9 1.05 2 . 0 64.0 % Y/£L£> too F t e U R E . 6 . Effect of Tmpewture. on on m 0 2 1 Yield % % Yield too 0 4 0 3 0 3 0 3 caj T Efp£ct of T&vpa^TufE. feu> u e tf > a o . E f u T ^ a p v & T f o t c £ p f E 7T a j^ a /c f 0 8 ) c * ( e z t m g & p m k T 0 4 0 3 - T 2 J - SO SO /CO 0 8 0 7 0 0 0 0 8 ~36- 2. Reactants with Absolute Ethanol as Reacting Medium When the reactants, carbonyl snlfide and ammonia, are condensed into the autoclave at dry ice-acetone temperature, a solid mass with no uniform composition forms as well as some liquid phase. It was decided to introduce a liquid phase into the reactor to act as a medium for reaction or possibly a catalyst and to aid as a heat transfer agent. Absolute ethanol, prepared as described elsewhere in this paper, was chosen as the liquid. There were several reasons for its selection. It has a great affinity for water, much greater than either the carbonyl sulfide ar ammonia. The carbonyl sulfide under goes hydrolysis slowly in the presence of moisture thus lowering the possible yield. Also the water would tend to hydrolyze the urea when at high temperatures and pressure as is the case in the conventional manufacture of urea from carbon dioxide and ammonia. Although every precaution was taken to exclude any moisture from getting itto the reactor still some traces did get in when the reactants feed tube was removed and the autoclave capped. Another reason for choosing ethanol was its comparatively inertness to reaction with the products and reactants. The range of temperatures used in the study was from 30° to 132°C. The data are given in the following table and plotted in - S 7 - Figure 8 . The results obtained were very interesting . Initially (30°C.) the yield is higher than using no alcohol since probably the liquid medium has facilitated the coming together of the reactants to form the ammonium thiocarbamate. The yield does not change for the next 30 degrees and then within the next 15 degeees it climbs approxi mately 47 per cent to'75,3 per cent . This is a higher yield than any obtained in the temperature studies using no alcohol medium. The yield then drops off slowly uhtil the curve parallels that of the regular "no liquid medium" runs and follows on out. Industrially it would be very convenient to operate a reactor at such a low temperature and pressure and get a 76 per cent yield. The corrosion is at a minimum at low temperature and pressure. T A B L E 5 TEMPERATURE - YIELD Using Ethanol as Reacting Medium (reactor - electrically heated) Run Temp. COS COS n h 3 nh 3 nh 3/ cos Absolute % Yiel °c. gr - moles gr. moles Ethanol cc. A-2 30 31.6 0.53 1 6 . 8 0.99 1.87 75 29.3 A-10 30 30.0 0.50 18.1 1 . 0 6 2 . 1 2 75 28.4 A -ll 50 30.1 0.50 17.1 1 . 0 0 2 . 0 0 75 26.3 & A- 8 58 30.1 0.50 17.0 1 . 0 0 2 . 0 0 75 29.4 A-13 65 30.0 0.50 17.0 1 . 0 0 2 . 0 0 75 47.4 A-3 76 31.3 0.52 17.4 1 . 0 2 1.96 75 75.3 A-5 82 31.1 0.52 17,6 1.04 2 . 0 0 75 71.0 A - 6 92 30.7 0.51 17.4 1 . 0 2 2 . 0 0 75 6 8 . 1 A-l 109 32.8 0.55 17.9 1.05 1.91 75 59.9 A-4 131 27. 1 0.45 14.5 0.85 1.89 75 65.4 A-9 132 33.0 0.55 18.9 1 . 1 1 2 . 0 0 75 69.5 % % Y i e l d BO $0 O S 0 4 0 6 0 7 0 1 0 eo F gure r u ig s " x y / 8 E 8 0 4 0 J , 1 ' / f o / T e r u t a r e p m e M ) C * ( E R U T A R E P M E T b o 1 c t fc i I 1 1 1 1 1 1 1 um iu d e 3 s«# « 's n o Y eld l ie ng in s u l o n a h t e 1 1 1 1 1 1 1 1 1 1 1 1 1 I 1 t 1 1 1 1 0 4 1 X-1 1 so /s - 6 0 - EFFECT OF CARBON DISULFIDE ON THE YIELD OF UREA When carbonyl sulfide is prepared as previously desoibed one of the impurities is carbon disulfide. The usual range of carbon disulfide in the laboratory preparation of carbonyl sulfide is about 5 parts per 100 parts of COS. If commercially, the carbonyl sulfide gas, as it left the COS-converter, were sent directly to the urea manufacturing plant without the removal of the impurity, then it would be desirable to know what the effect, if any, this impurity would have on the urea production and yield. The carbonyl sulfide was condensed into the autoclave and a weighed amount of carbon disulfide added. The carbon disulfide was weighed as follows:- a small vial was weighed empty and then with carbon disulfide which had previously been chilled slightly. The vial was left uncovered to allow evaporation and when the desired weight had been reached the vial was immediately placed into dry ice. After cooling the vial was lowered into the liquid carbonyl sulfide and the contents discharged and the vial removed. From this point the procedure was the same as in a straight run. The reactor was heated in a water bath at 93°C. for ap proximately 8 hours. In this study the range of carbon disulfide was varied from 0 to 18 parts per 1 0 0 parts of carbonyl sulfide. After the reaction had taken place the autoclave contents were washed out with absolute alcohol into a beaker and the contents steam-heated to recover the urea. The products crystallized out after repeated heatings with portions of alcohol but the crystals were oily in nature. There was enough liquid phase in the 18 parts of CS2 / 100 parts of COS run that the urea would go into solution at 100°C. but as soon as the heat was removed the whole mass would solidify crystalline. Initially the products also had a bad odor but after several heatings this odor dis appeared. From Table 6 and Figure 9 it can be seen that the yield of urea is increased if anything up to 5 parts of CSg and then decreases slightly. Therefore if in a commercial process the carbonyl sulfide is manufactured as was in this study and carbon disulfide is present in the gas stream then the yield of urea will not be lowered but the crystals would be oily. A purity of 90 per cent was obtained in the laboratory study. This figure is low since the crystals had picked up considerable moisture while on the steam bath. T' A B L E 6 EFFECT OF CARBON DISULFIDE ON YIELD (reactor heated in water bath) Run Tem p. COS COS n h 3 n h 3 NH3/COS CS2 gr. CS2 % Y ield °C . gr. m oles gr. m oles gr. 100 gr COS T -6 93 30.4 0.51 17.5 1.03 2.00 0 0 63.4 f t T -7 93 30.3 0.51 17.2 1.01 2.00 0 0 62.7 C -6 93 30.3 0.51 17.2 1.01 2.00 1.8 6 75.5 C-12 93 30.6 0.52 17.7 1.05 2.00 3.6 12 69.4 C-18 93 36.6 0.52 17.4 1.03 2.00 5.4 18 67.2 63 too 9 0 8 0 7 0 6 0 2 0 2 0 F/g u r e 9 . E f f e c t o f CSa o n Y/e l o -64- SUMMARY Batch. System In a batch system used to manufacture urea from carbonyl sulfide and ammonia according to the following equation: COS + 2 NH3 CO(NH2 ) 2 + H2S using no supplementary liquid phase and no pressure above that developed by the constituents, a maximum yield of 64 per cent may be attained at a temperature near the melting point of urea. When an additional liquid is introduced together with the reactants the yield may be increased. A maximum yield of 76 per cent may be obtained at 76°C. if absolute ethanol is used as the medium. The yield may also be increased by using an excess of either carbonyl sulfide or ammonia. The ammonia is the better in this respect. At 105°C. , for example, the yield of urea may be raised from 60 per cent to 8 8 per cent using 150 molar per cent excess am monia. The maximum excess, industrially, would have to be determined economically. Using an excess of ammonia, however, presents a prob lem of corrosion which means contamination of the product as well as damage to the equipment. -6S- If the carbonyl sulfide were manufactured as was in the laboratory and if the gases from the process were sent directly to the urea plant then one of the impurities would be carbon disulfide up to 5 parts per 100 parts of carbonyl sulfide. The carbon disulfide does not lower the yield of urea but in the range of 5 parts /100 parts the yield is.actually increased. The product, however, is on the oily side, and would have to be purified further which would mean another step in the process. The carbon disulfide could be easily removed from the carbonyl sulfide by cooling the gases slightly. The two com pounds have widely separated boiling points. The weight of charge to reactor volume ratio in the range studied, 0 . 10 to 0.48 gr. per ml. , has no effect on the yield of urea. This is not so in the process for manufacturing urea from carbon di oxide and ammonia. FLOW SYSTEM -66- REACTOR DESIGN FOR FLOW SYSTEM Design No. 1 Initially the reactor for the flow system consisted of two concentric glass tubes, the inner being for the support of the catalyst and the outer to serve as a heating jacket. The outer was wound with 22 gauge Nichrome wire in three separate sections which could be used individually or connected in series. The control of voltage and current input was by three transformers. The inner tube was equipped with thermocouples at several places along its height. These thermocouples were of iron-constantin with the junc tions silver soldered. These joints were heated and cooled several times to remove stresses. A cold junction of 0°C. was used as a reference junction. The change in e.m. f. was measured with a Leeds northrup potentiometer. Several runs were made using this set up but the measurements and the various controls involved to main - tain a steady and even temperature throughout the height of the reactor were cumbersome. It was thus decided to alter the design of the re actor. Design No. 2 The reactor used throughout the various studies was of a design as shown in the following figure. Essentially it consisted of an inner tube for holding the catalyst and was surrounded by a concentric -67- tube thus establishing an annular space between the two through which heat transfer fluid could be circulated. The inside tube had the dimensions of 49. 5 cm x 8 mm. at the catalyst holding section. The reasons for choosing such a small diameter was to facilitate the heat transfer from the fluid in the outer jacket and thus establish a uniform temperature throughout the cata lyst bed. Also if the tube had been chosen of a larger diameter of the order of several times that of the current design then there would be a possibility of channeling of the gases as they passed through the re action bed and thus lead to some erroneous results. The outer jacket glass tube was 53. 5 cm. in overall height and 32 mm. in diameter. A thermometer well with a standard taper joint was provided at the midheight such that the tip of a standard thermometer would just protrude into the annular space. To this jacket was attached a heating and circulating tubing arrangement as shown in the diagram. The upper tube was at tached at right angle while the lower was at approximately 15°. The angle served the purpose of allowing the heated liquid and vapor to leave the lower tube without any difficulty. With the lower tube at right angle, vapor locks formed and when they finally left, a "hammer effect" would occur. The reactor vibrated and the catalyst in the bed settled - 68- and became compact when some fine catalysts were used. A 3? 14/35 joint for a condenser was provided in the side arm assembly. It was found during the operation of the reactor that it was not necessary to circulate water in the jacket continuously. The inlet line to the jacket was sealed and the annular space filled half or three-fourths with water. This provided enough cooling to condense the vapors of the heat transfer fluid and still made it possible to reach a temperature close to the boiling point of the medium and maintain an evenly distributed temperature throughout the reactor. An exit line lead from the condenser exit to a flask which caught any fluid that boiled over and also helped condense any of the vapors which escaped the condenser itself. The heating of the heat transfer fluid was done electri cally by wrapping the lower arm and the lower half of the reactor with 22 gauge Nichrome wire and passing current through the circuit. The input current was regulated by a transformer arrangement. Since the liquid in the jacket was maintained at its boiling point or slightly lower, then the bubbling which took place kept the liquid mixed and very uniform tem perature throughout the reactor. The temperature was measured by the thermometer in the jacket. - 6 9 - HEAT TRANSFER FLUID IN CONSTANT TEMPERATURE REACTOR There were several considerations to be made in choosing a heat transfer fluid for the reactor. The first was the temperature at which the reaction was to be run. The handbook was checked for liquids boiling in the range desired. The liquid chosen had to be stable at the boiling point and its vapors not toxic. The vapors could not be explosive at this temperature. Since the reactor was of an all glass construction the corrosion problem, was not of any importance as would be commercially. A pure compound was more desirable than a mixture since one could always obtain more of the pure and thus have the same temperature of boiling whereas in the case where a mixture was used as a fluid then the boiling point would not always be the same if some of the liquid would boil out of the reactor. For several studies a certain temperature was desired in which case a mixture of liquids blended to give this tem perature was used successfully. A low su r face tension liquid was desirable but not necessary. Water, for example, caused a ’’water hammer” effect when it reached within ten degrees of its boiling pointy «i CATAlfST % * i 1 / f Figure 10. R eacto r. - 77- FLOWMETER The flowmeter used in measuring the flow rates of the carbonyl sulfide and ammonia gases introduced into the reactor is pictured in the following figure. In principle this type of meter is no different from several now on the market but there are some design features whose combination are worthy of mention here. The flowmeter is an all glass apparatus and fairly simple to construct by one possessing some limited skill in glass- blowing. The all glass construction is ideal from the corrosion standpoint and thus is adaptable to use with many gases. In addi tion, the whole of the m eter can be seen both interiofLy and exterior ly at all times and any obstruction in any part may be easily detected. The glass feature does present a drawback in that the meter may be easily broken. A wide range of gas flow rates may be had by the inter change of the capillary flow tips of different diameter and/or length. Each capillary is calibrated and it will maintain its accuracy indefi nitely providing, of course, some obstruction of the hole does not take place. If such does happen, it may be detected visually and cleaned. the calibrations would not be the same because of the difference of the molecular weights of the gases and consequently viscocity differences. It is possible to calculate approximately the flow of various gases through the same capillary by making use of Graham's Law of Dif fusion' tj and t2 are the times of passage of each gas under a given pressure through an orifice, Cj and c2, dL and d2, Mj and M2 are the root mean square velocities, densities, and molecular weights of the two gases under consideration. At least with such a calculation one would know if a certain capillary would be in the right range and could calibrate for the specific gas if desired rather to go through some analytic mani pulations over and over again with different flow tips until one in the range is found. Each capillary flow tip is good for a limited range of flows which is indicated by the calibration curve. The accuracy is dependent on the skill with which it was calibrated. The overall accuracy is probably the same but the signi ficant figure within this range is a variable. -X?- The flowmeter manometer fluid may be varied for reasons of differential pressure drop span or also, as was the case in this research problem, the common fluid - water - could not be used since no water vapor could be present in the inlet gases. The manometer fluid can be easily changed by draining and refilling through stopcock M. The calibrations using a certain manometer fluid may be easily translated to another by a density relationship. The differential scale is easily visible and any convenient unit may be used. If the meter is set at a differential it will hold fairly steady when it is used in conjunction with a constant head trap des cribed below. The fluctuations are practically eliminated by incorpo rating a constriction or a capillary tube of reasonable size in one leg of the manometer. APPARATUS FOR DELIVERING LOW CONSTANT PRESSURE GAS TO FLOWMETER When it is desired to use gases from steel cylinders or air from compressed sources in conjunction with the flowmeter des cribed, then one must cut down the pressure and also take care of the n r FiGURg.ll- Fl o w m e t e r . - 7 S - fluctuations in pressure. This may be accomplished by using a trap arrangement as shown in Figure 1 2 . The bottled gas, contained in some suitable cylinder is reduced to a lower pressure ,?pcV by the main valve and needle valve on the cylinder. This is not suitable for the flowmeter since the pres sure fluctuates and also the adjustment is not fine enough. The gas reaches the point ftDM and divides seeking the lowest backpressure to escape. By choosing a liquid of a certain density and adjusting the height of this liquid in the trap the pressure to the flowmeter may be had at ,fKrt since any pressure above "pk is released by the gas bubbling out at MF,T and leaving through "H” and vented at nJ”. By adjusting the bubbling in the trap and the flowmeter stopcock the desired differential of the flowmeter may be had without any difficulty. The needle valve of the cylinder is then re-adjusted until the bubbling in the trap is approximately one bubble per second. OPERATION OF FLOWMETER The previously throttled gas, as described, enters the flowmeter at "A" (please refer to Figure 11) where the flow through the meter is regulated by stopcock ,TBTt. The gas passes through to point "C" where it exerts its pressure on the manometer liquid, -76- <3 »s /vwr 3-^- \ a < +i.. To To Phrtm eter f a c to r 5 + :t -if "TT o i* S C,2 J jq u a > ^ GAS C f U N O E J ^ F u m m E T B R ^ TRAP F/g u r e /2 . L o n Pr e s s u r e Co n s t a n t Ga s Fe e s A p p a ^ t u s. thence through "D" and the capillary flow tip "EM to point MFM, thence to MG” and "L" and out at MPM. The pressure at MLiM is lower then at "C" by the amount equal to the pressure drop across the ca pillary. This differential in pressure is noted by the liquid levels in the two legs of the manometer. Fluctuations in pressure are dampened by the constriction at "J”. As pointed out previously the liquid in the manometer may be changed as the need arises. - 7 8 - CALIBRATION OF FLOWMETERS There are several methods at one’s disposal for cali brating the flowmeters or actually the flowmeter capillary tips. Two such methods were used. a. direct 1.- chemical 2 . physical b. dilution 1. Calibration of Ammonia Capillaries The capillary flowmeter tips for use with anhydrous am monia were calibrated by direct chemical means. Anhydrous ammonia, after being throttled down to a constant low pressure, was passed through the meter. The flow through the tip was changed and the differential noted. The ammonia leaving the flowmeter was passed into gas washing bottles containing a known quantity of standard hydro chloric acid for a period of time. The acid was backtitrated with standard sodium hydroxide. Actually a stream of nitrogen was passed along with the ammonia after the latter left the flowmeter to keep the acid in the washing bottle from being sucked back into the ammonia lines. Sample calculation: Differential = 22. 1 vol. HC1 = 110. 0 cc. Meq. = 55. 1 Time = 11.0 min. vol. NaOH = 26.2 Meq. = 13.1 A Meq. 42. 0 - 73- NH3 c c/ min = Meq, x 22. 4 _ 42.0 x 22.4 = 85. 6 cc/m in. 11.0 l i .o TABLE 7 Calibration of Ammonia Capillary Tip DIFFEBENTIAL NH3 cc. /m in. (Mineral Oil) 3.4 25. 1 3.5 25. 2 11.5 55. 6 11.5 57. 2 11.6 57. 5 23. 5 88. 8 21. 8 84. 8 22. 1 85. 6 35. 2 114. 6 53. 3 145. 2 53. 3 145. 3 2 . Calibration of Nitrogen Capillaries It was necessary to calibrate capillaries for use with nitrogen since in the dilution method for calibrating the carbonyl sulfide ca pillaries, a known flow of nitrogen was necessary. Nitrogen from, a cylinder was throttled down through the con stant head trap as previously described. The flow through the meter was varied and the differential noted. The volume of nitrogen was ob- -SO- r n too 4 0 so o to 4 0 eo DtFFEfEAlnAL ( i "uh / ts - ritnero/&t) Fi g u r e / 3 . J 0 t5 C a p u l a k y F w n Ti p OAusQtrnorf -81' tained by passing the gas leaving the flowmeter through a wet test gas meter which had been saturated several hours with nitrogen gas. Sample calculation: Differential = 20. 0 Atmos, pressure = 755 mm. Temperature = 27.5°C. Vapor pressure of H20 Gas m etrr volume = 3. 00 liters at 27. 5°C. = 27. 5 mm. Time = 8 . 14 min. N2 cc/min. = 3,000 x 273.1 x 755. 0 - 27. 5 x 1 = 322 300.6 760 8.14 TABLE 8 Calibration of Nitrogen Capillary Tip DIFFERENTIAL DIFFERENTIAL n 2 (Water) (Mineral Oil) cc. /min. 6 . 0 6.9 1 6 1 1 1 . 0 1 2 . 6 229 1 6 . 0 18.3 283 2 0 . 0 22.9 322 Calibration of Carbonyl Sulfide Capillaries The carbonyl sulfide capillary tips were calibrated by dilution method. Gas flows were set at different values as noted by the diffirentials. The carbonyl sulfide leaving meter was mixed with a known flow of nitrogen from another flowmeter and passed through -aa- 3 3 0 2 3 0 ISO / 0 0 SO 2 0 F ig u r e M: J z Coptu/HgF l o p T/p Cp l ib p p t / oN —& 3 ~~ a gas holder of known volume. The flow was continued for a period of time to insure a complete purge of the air from the gas holder and replacement by the carbonyl sulfide - nitrogen mixture. The filled gas holder was connected to a levelling bottle con taining a concentrated solution of potassium hydroxide. The solution was introduced into the holder. Before the holder would accept any more fresh solution it had to be shaken to allow theCOS to react with the KOH. This was continued until no more solution would go in. The contents of the holder were made up to a volume and an aliquot taken for analysis. The aliquot was transferred to a beaker containing crushed ice and the solution made acid. A know quantity of standard iodine solution was added and backtitrated with standard sodium thiosulfate using starch as the indicator. Sample calculation: Differentials COS = 52. 1 N2 = 10.3 (200 cc/min at S. T. P.) Gas holder volume = 333 ml. Temperature = 27.5°C. Aliquot = 50/250 I2 = 25.0 cc. Meq. I2 = 2.44 Thio = 9.1 cc. Meq. Thio =0.91 A Meq = L53 - G 4 ~ COS = 1. 53 X 11. 2 X 250/50 = 85. 7 cc. Gas holder volume (S. T. P .) = 333 x 273. l/300. 6 = 302 cc. then Nz = 3 0 2 - 85. 7 = 2 1 6 cc. COS cc/min. = 85. 7 x 200/216 = 79.3 TABLE 9 Calibration of Carbonyl Sulfide Capillary Tip DIFFERENTIAL COS (Mineral Oil) cc./min. 12.0 31.2 28. 8 29.9 30. 3 29. 0 54.5 53. 6 52. 1 79.3 75. 5 % * - 66- r e c o v e r y OF UREA FROM CATALYST In the flow system studies the urea had to be recovered from the catalyst in and on which it was formed. The catalyst was removed from the reactor and placed in a 25 x 80 extraction thimble which was in turn placed in a Soxhlet extractor. Approximately 250 ml. of ab solute ethyl alcohol was placed in the flask together with some boiling chips and the extraction was carried on for a period of not less than five hours. Actually the urea is very soluble in hot ethyl alcohol but to insure the leaching out of all the urea from the voids of the catalyst the extraction duration was as stated. Actually the extraction took place while some other phase of research was being carried out and also since the extraction needed no supervision this period of time was found very convenient. The rate at which thed:hyl alcohol was refluxed and allowed to dripoimto the contents in the extraction thimble was ad justed such that the filling cycle of the thimble, was approximately 3.5 minutes. This would mean that not less than 100 extractions of the catalyst took place. WOBK-UP OF THE UREA FROM THE EXTRACT The urea and the impurities, mostly sulfur which had dis solved in the hot extracting ethyl alcohol and some fine pieces of carbon which washed over with the extracting liquid, were recovered from the extract by transferring the liquid to a beaker which was set up for steam -67- heating, A current of nitrogen or air was passed over the solution to hasten the removal of the solvent from the solid residue. UREA RECOVERY CHECK In an experiment to determine the recovery percentage of urea, activated charcoal was impregnated with c. p. urea by dis solving the urea in absolute alcohol and mixing the alcohol and solid until all of the liquid had been adsorbed by the charcoal. It was found that all of the urea could be recovered from the solid catalyst by the procedure described above. -88- O PE RATIONAL PROCEDURE - Flow System Reactor: The selected heat transfer fluid, meeting the specifications as brought out in a previous discussion, was introduced into the reac tor heating jacket. The jacket was not filled completely to allow for expansion of the fluid upon heating; the trap would catch any liquid coming over but usually practically the whole amount of liquid would siphon necessitating a temporary shutdown to refill the jacket. The characteristics of the thermal expansion of the liquid dictated the initial amount to be added. The reactor was wired in sections with 22 Nichrome to permit flexibility. Leads were run from the winding (usually the heating section included the whole lower side arm and one-fourth the height of the jacket) to the transform er. At first the heating was very slow to prevent ’'bumping” and strains.in the glass; when vapor bubbles first started to form the voltage input was raised and finally adjusted to maintain an even boiling. The transform er could not operate at more than five amperes therefore, if the liquid required more than this amperage to maintain a boil, then the circuit was changed so that the voltage could be raised and the amperage lowered. The circuit was never selected so that the wire operated at red heat. -89- Catalyst; When the reactor had reached a temperature near the desired value, the catalyst was added to the proper height.. In some runs the ca talyst was preheated in an oven at 110°C. for over five hours to drive out any moisture. This was especially true of the runs below 1 0 0 °C. in v/hich charcoals were used. The catalyst bed was heated for at least two hours. This was more than enough time to bring the tempe rature up uniformly throughout the bed. A stream of nitrogen gas was passed through the tube to sweep out any moisture and oxygen and to help the temperature distribution. Actually when the charcoal cata lysts were used the moisture was driven out within several minutes after the nitrogen was introduced. COS and NH3 Flowmeter Adjustment: While the catalyst temperature was being brought up to the heating fluid temperature the COS and NH3 flowmeters were adjusted to the selected differentials. Initially the respective flowmeter stopcocks, the tank needle valves, and the tank main valves were closed. In starting up, first the tank main valves were opened, then the needle valves until bubbling started in the ’’constant head traps”; the flowmeter stopcocks were opened and adjusted to the approximate desired differentials. The excess flow through the traps was cut back at the needle valves until the bubbling was about one bubble per second. The fine adjustments were made with the flowmeter stop cocks . - 3 0 - When all of the desired conditions were right the gases were introduced simultaneously into the top of the catalyst bed. Provisions were made for preheating the gases but since the temperature used in the studies was low and the gas volumes were small this was eliminated. The gases could not be premixed because they reacted and the product deposited on the tube wall. The time, differentials, and temperature were noted at the start of the run. During the course of the run these were checked and noted. Usually the flowmeters held steady over the entire time as did the temperature. There some fluctuations and ad justments had to be made. Care was taken to see that the carbonyl sulfide leaving the trap was vented to the hood. Usually the gases leaving the reactor were vented but in some studies these were condensed as is discussed later. Processing Catalyst to Remove the Product: At the end of the run the heat was cut off and the catalyst removed from the reactor and the urea extracted from the catalyst by absolute alcohol as described elsewhere in this paper. -3t~ NATURE OF CATALYSTS vs. YIELD It was desired to find a catalyst that would give a reasonable yield of urea. The only reference in the literature to a flow system process for preparing urea from carbonyl sulfide and ammonia was the German Patent 579,567 issued to Alphonse Zieren in 1933. He used activated charcoal as the catalyst. Ammonium chloride, calcium chlo ride, and silica gel have been used in catalizing urea formation from ammonia and carbon dioxide. In this research several materials were investigated as possible catalysts. Those tried were: 1 . Activated Charcoal 2 . Bone Charcoal 3. Wood Charcoal 4. Activated Alumina 5. Anhydrous Calcium Sulfate 6 . Glass wool 7. Anhydrous Calcium Chloride The conditions were kept constant for each experiment as indicated in the accompanying table. The calcium chloride was too difficult to separate from the urea therefore it was not used through the range of the variables studied. In exploratory runs at 129°C. at a space velocity of 2.41 -, 92- min. it was found that the activated charcoal, bone charcoal, and activated alumina gave the best yield, therefore these three were investi gated further through the temperature range and space velocity. The bone charcoal gave practically no increase in yield with an increase of bed temperature. A slight increase did occur between 120 and 130°C. with the maximum of 30.4 occurring at 125°C. The activated alumina gave the greatest initial yield of the three but apparently became slightly deactivated as the temperature was increased. The alumina went through various color changes at the top section of the bed - from white to yellow white , to a green, to a blue. This was probably due to sulfur formation. Activated alumina is known to be a good catalyst for the formation of sulfur from sulfur gases. At 125°C. the yield rose sharply reaching a maximum of 47.4 per cent at 129°C. after which it dropped off rapidly. By far the best of the catalysts investigated was activated qharcoal. From room temperature to 121°C. there was essentially no change in the yield but then the yield rose sharply to 125° and then commenced to drop off. Within a short span of 5°rise the yield increased some 40 per cent to 6 0 . 6 per cent. TABLE 1 0 NATURE OF CATALYST vs. YIELD Space Velocity =2.41 m in. Temperature Bone Activated Wood Activated Anhydrous °^* Charcoal Alumina Charcoal Charcoal Calcium Sulfate 25 - - - 17.5 - 90 27.6 46.1 - 21.9 - 121 28. 0 42.7 - 20. 0 - 125 30.4 40.3 - 60. 6 - 129 28.3 ' 47.4 8. 0 56,5 10.4 137 25.9 39.6 - 49.7 - 193 7. 1 -34 § yi£U > **>• Omu/sr O s . . Jfante op 16 91 F ig u re . % < T 7 3 H 9 6 RATIO OF REACTANTS vs. YIELD AT CONSTANT TEMPERATURES Flow System The effect of the mole ratio of the carbonyl sulfide and am monia gas feed on the yield of urea was studied at temperatures of 121° and 129°C. using activated charcoal as the catalyst and a space velocity (S. T. P .) of 2. 41 min. . Table 11 gives the volumes of the reactants used in the va rious ratio runs. These values were calculated as follows: Basis: Space velocity = 2.41 miri. Catalyst bed = 24 cc. Mole feed ratio NH3/COS = 3.0 then Volume of gas feed = 2.41 x 24 = 57. 9 cc. /min. Volume of NH3 = 57.9 x 3. 0/4.0 = 43. 4 cc. /min. Volume of COS = 57.9 - 43.4 = 14. 5 cc. /min. The yields of urea at 121° and 129°C. at the various mole feed ratios are presented in Table 12. The yields were calculated as follows: Run 21. Mole ratio of feed NH3/COS = 3.0 NH3 = 43 . 4 cc. /m in. COS = 14. 5 cc. /min. Grams of urea obtained by analysis = 0. 709 Then according to the equation COS + 2 NH3 = CO(NH2 ) 2 + H2S one mole of carbonyl - 3 6 - sulfide and two moles of ammonia should give theoretically one mole or 6 0 gr. of urea. Yield based on NH 3 = Gr. of urea produced x 100 = 0.709 x 1 0 0 x 22,400 Vol. of NH3 NH^ CO(NH2 ) 2 43.4 x 30 22,400 2 NH3 = 20.32 % Yield based on COS = °- x 22,400 x 1 0 0 = 3 0 43 % 14. 5 x 60 It can be seen from the graph that an excess of ammonia has more of a driving force toward the formation of urea than does the carbo nyl sulfide. This would be advantageous if this process were used industri ally because the ammonia would no doubt be cheaper than the carbonyl sulfide. At 121°C. the maximum conversion is obtained in the vicinity of 3. 6 moles of NH3 per mole of COS or an excess of NH3 of 80 per cent based on the 2:1 stoichiometric ratio. The curve flattens out and reaches a maximum yield of 35. 9 per cent based on the COS and about 20% based on the NH3. As would be expected from the other studies, a higher yield may be realized by raising the temperature of the activated T A B L E 11 GAS FEED IN RATIO OF REACTANTS STUDIES Tx = 121° T2 = 129° ------Catalyst COS NH 3 Total Space NH3 COS RUN cc/min. cc/min. Feed Velocity COS nh 3 M 57 24 1 1 . 6 46.3 57.9 2.41 4. 0 0.25 2 1 58 24 14.5 43.4 57.9 2.41 3.0 0.33 4 14 32 24 19.3 38. 6 57.9 2.41 2 . 0 0.25 24 59 24 24.8 33.1 57.9 2.41 1.33 0.75 2 2 6 0 24 23.9 + 23.9 + 57.9 2.41 1 . 0 1 . 0 23 24 38.6 19.3 57.9 2.41 6.5 2 . 0 - 3 6 * charcoal bed to the 125-129°C. range. At 129°C. the yield jumps some 40 per cent at the stoichio metric ratio and maintains this differential over the 121°C. runs quite consistently. The maximum yield at 129°C. is reached at a lower excess NH3 at a NH3/COS ratio of 3. 0 (about 50 per cent excess). The maximum yield obtained at this higher temperature was 74. 7 per cent based on COS and 49. 9 per cent based on the NH3. Whereas in the 121° series an excess of carbonyl sulfide resulted in essentially no increase in yield of urea in the 1 2 9 ° series, the yield is raised some 1 0 per cent over the stoichiometric when a 100% excess of carbonyl sulfide is used. Nevertheless the ammonia still has the greater driving force. From observations made on previous runs in which stoichio metric ratio of the reactants were used, and comparing with the 1 2 9 °C. values it would appear that at 125°C. the maximum yield would be approximately 80 per cent at less than 50 per cent excess ammonia. TABLE 12 RATIO OF REACTANTS vs. YIELD AT CONSTANT TEMPERATURES - 1 Space Velocity = 2.41 min. Duration of Run = 1. 0 hr. Tx = 121°C Mole Ratio T2 = 129°C Run % Yield nh 3 COS % Yield Rim based on COS based on NH 3 COS nh 3 based on COS based on NH 3 2 0 35.9 17.9 4. 0 0.25 72.9 36.5 57 2 1 30.4 20.3 3.0 0.33 74.7 49.9 58 14 2 0 . 0 20.0 -H- 2 . 0 0.5 56. 5 56.5 32 24 12.9 19.4 1. 33 0.75 40. 8 61.13 59 2 2 1 0 . 2 20.4 1 . 0 1 . 0 32.3 64.7 6 0 23 5.5 2 2 . 0 0.5 2 . 0 - - - -H- Stoichiometric COS + 2 NH3 CO(NH2 ) 2 + H2S {M9(S*Q M id) •idnifajw zi jjwisncq iv EFFECT OF TEMPERATURE ON YIELD OF UREA It was found from previous catalytic studies that the best yields were obtained when activated charcoal was used as the catalyst, therefore it was used throughout the whole studies of the process variables. TABLE 13 TEMPERATURE-YIELD Catalyst: Activated Charcoal Gas Feed: COS = 19.3 cc./m in. NH3 = 38.3 cc./min. Volume of Catalyst: 24 cc. Space Velocity: 2.41 min. Time of Runs: 1. 0 hr. Run Temperature % Yield °C. 16 25 17.5 1 2 90 2 1 . 9 14 1 2 1 2 0 . 0 42 125 60. 6 32 129 56. 5 53 137 49. 7 19 193 7. 1 -/ 02 - The effect of tem perature of catalyst bed on the yield of urea was investigated through a range of 25° to 193°C. The tempera ture of the catalyst bed was kept constant by surrounding the catalyst tube with a boiling liquid as described elsewhere in this report. The data are presented in Table 13. For all. practical purposes the yield does not change between room temperature and 1 2 1 °C. but within the next 4° the yield jumps some 40 per cent and then begins to drop off steadily (max. yield = 6 0 . 6 % at 125°C.). This was the case with other catalysts studied also as pointed out in a previous section under nature of catalyst. It would appear, therefore, that the urea actually begins to decompose before it reaches its melting point (132. 7°C.); or probably the ammonia and carbonyl sulfide form the ammonium thio- carbamate. Hydrogen sulfide splits off with the formation of some urea but at temperatures close to and above the melting point, the forces which tend to break down the urea start to take affect. Thus the yield goes down steadily. Some urea does manage to survive but in due time, if held above the melting point , it too would decompose. The summary of temperature vs. yield at various space velocities is given in Table 15. /OO 3 0 $ 0 C atalyst Activated Charcoal 70 Space Velocity' 3 4 / mm:1 OuZflT/QN OF RuHS ‘t ohr. 0 0 I* 3 0 k 4 0 3 0 ZO / 0 0 20 40 CO 30 700 /20 /40 /00 /80 200 7&*PB&TU{£ fc ) F /6U ZE 18.Ef f e c t o f TEMPEKffwpa o n Y/e u > t -/Q4- EFFECT OF SPACE VELOCITY ON YIELD OF UREA A convenient unit for expressing the relationship between the feed rate volume and the volume of the reactor, or better, the volume of the reactor occupied by the catalyst, is the "volume-space velocity." Volume-space velocity is defined as the volume of the gas or liquid feed at standard temperature and pressure passing through a given volume of catalyst space per unit time. Weight-space velocity, by analogy, is defined as the weight of feed per unit time per unit weight of catalyst. The unit has the dimensions of reciprocal time usually ex pressed in hours. In this paper the space velocity is expressed in reciprocal minutes. The fact that space velocity is independent of all units except time has made it used extensively. Activated charcoal again was used as the catalyst in the space velocity studies. It was found that the best yields of urea, using the activated charcoal, were obtained at the temperature of 125°C. Data for this temperature are presented below in Table 14. The yield of urea decreases with increasing space velocity. -JOS*- TABLE 14 EFFECT OF SPACE VELOCITY ON YIELD OF UREA Catalyst:-Activated charcoal Temperature: 125°C. Run Gas Volumes Catalyst Space % Yield COS NH3 Volume Velocity cc cc cc (min. “■*■) min min 41 12. 5 25. 0 24 1. 56 6 6 . 5 42 19.3 38.6 24 2.41 60. 6 43 25. 0 50. 0 24 3. 13 55. 7 44 40. 0 80. 0 24 5. 00 49.2 45 6 0 . 0 1 2 0 . 0 24 7. 50 41. 5 The space velocity was varied by changing the moles of input carbonyl sulfide and ammonia. Actually the space velocity could be varied by changing the bed depth instead. This was done in the 121° . series in order to get higher space velocities and the values followed the curve. All variables except the space velocity were kept constant, e.g. temperature of the reactor, duration of the runs, stoichiometric ratio of input gases, (bed depth). -/ 0 6 - SUMMARY TEMPERATURE vs. YIELD (Constant Space Velocities) SPACE VELOCITY vs. YIELD (Constant Temperatures) A series of runs was made in which the temperature was varied and the space velocities were kept constant and in another series the temperatures were kept constant and the space velocity was varied. The range of temperatures was from 25° to 193°C. ; the range of space velocities was from 1.56 to 7.50 minutes-*. Summary data are. presented in Table 15 and Table 1 6 . Yield of urea decreases with increasing space velocity. At all space velocities and using activated charcoal as the catalyst the best yields are obtained near 125°C. - / 0 7 - TABLE 15 SUMMARY TEMPERATURE vs. YIELD AT CONSTANT SPACE VELOCITIES CATALYST : Activated Charcoal Ru Space Velocity Temperature % Yield min. ~ ^______°C.______ 11 1.56 90 20.0 28 1.56 121 15.6 41 1.56 125 66.5 33 1.56 129 64.4 48 1. 56 137 50.4 16 2.41 25 17.5 12 2.41 90 21.9 14 2.41 121 20.0 42 2.41 125 60.6 32 2.41 129 56.5 53 2.41 137 49.7 19 2.41 ' 193 7.1 13 3.13 90 22.3 29 3.13 121 19.8 43 3.13 125 55.7 49 3.13 137 41.3 44 5.00 125 49.2 35 5.00 129 43.2 50 5.00 137 38.1 30 7.50 121 15.1 45 7.50 125 41.5 36 7.50 129 40.5 51 7.50 137 32.7 -/ c o n s t a n t a S § ft ield Y on e m p e r a t u r e § T of e l o o t y V f f e c t pace E S /A . /A ig u r e F S S S < r m u % -/09- TABLE 16 SUMMARY SPACE VELOCITY vs. YIELD AT CONSTANT TEMPERATURES CATALYST : Activated Charcoal Rt Temperature Space Velocity % Yield °C. min. " ^ 16 25 2.41 17.5 11 90 1. 56 2 0 . 0 12 90 2.41 21.9 13 90 3. 13 22. 3 28 1 2 1 1. 56 15. 6 14 1 2 1 2.41 2 0 . 0 29 1 2 1 3. 13 19. 8 30 1 2 1 7. 50 15. 1 41 125 1. 56 66.5 42 125 2.41 6 0 . 6 43 125 3. 13 55. 7 44 125 5. 00 49.2 45 125 7. 50 41. 5 33 129 1. 56 64.4 32 129 2.41 56. 5 35 129 5. 00 43.2 36 129 7.50 40. 5 48 137 1.56 50.4 53 137 2.41 49.7 49 137 3. 13 41. 3 50 137 5. 00 38. 1 51 137 7. 50 32. 7 19 193 2.41 t o o Catalyst: M w xkd , s o Charcoal Du&t/on of fytts - to hr. S m m o m w c e o 7 0 6 0 s o 4 0 A3 7 ° i 3 0 2 0 to 0 3 4 S Space Velocity (mm-') F w & E O - E f f e c t o f Space . Ve l o c it y o n Yie l d a t Co n s t a n t t e m p e ^ t t u p e -///- SPACE-TIME-YIELD vs. SPACE VELOCITY The yield of desired product in unit time per unit volume of the catalyst per passage is the "space-time-yield1’. This is the product of the fractional conversion by the space velocity. The significance of a space-time-yield vs. space velocity diagram is discussed in Chemical Engineers Handbook, 3d edition, page 330 as follows: "The initial portion of the curve represents the low space velocity region in which equilibrium conditions are always attained, the space-time-, yield here being directly proportional to the space velocity.. At higher space velocities equilibrium conditions are not attained and the fractional con version becomes a function of the space velocity. It decreases with increasing space velocity, how ever, at a rate which is less than the increase of the latter. Consequently, the space-time-yield continues to increase, but at a slower rate. At very high space velocities the space-time-yield tends to become independent of space velocity and approaches a constant steady value deter - mined by the nature of the catalyst surface and its temperature. Where consecutive or side re actions are involved, the desired product being formed as an intermediate step in the series of reactions the space-time-yield space velo city curve referred to this product may pass through a maximum, the yield of this product diminishing at too high space velocities. This is due to the diverging effect of contact time on the relative over-all rates of the several compe ting reactions. This cannot be the case where only a single reaction is taking place. In cases -//a- where the reaction is retarded by the products, a relatively greater increase of space-time - yield with space velocity is to be expected than in cases where the reaction is not so retarded. " It would appear from the accompanying graph that there are no other significant reactions taking place except the formation of urea. -i/3- TABLE 17 SUMMARY SPACE - TIME - YIELD vs. SPACE VELOCITY AT CONSTANT TEMPERATURE CATALYST : Activated Charcoal Run Temperature Space Velocity Space °C. Time Yield 1 6 25 2 . 41 42.2 1 1 90 1 . 56 31.2 1 2 90 2. 41 52. 8 13 90 3. 13 69. 8 28 1 2 1 1. 56 24. 3 14 1 2 1 2.41 48. 2 29 1 2 1 3. 13 6 2 . 0 30 1 2 1 7. 50 113. 3 41 125 1. 56 103. 7 42 125 2.41 146. 0 43 125 3. 13 174. 3 44 125 5. 00 246. 0 45 125 7. 50 311=3 33 129 1. 56 100. 5 32 129 2.41 136. 2 35 129 5. 00 216. 0 36 129 7. 50 303. 8 48 137 1. 56 78. 6 53 137 2.41 119. 8 49 137 3. 13 129. 3 50 137 5. 00 190. 5 51 137 7. 50 245. 3 19 193 2.41 17. 1 -//*- •c- so s o & 0 S p a c e Ve l o c it y (m in -*) F ig u r e 2 1 . s p a c e Ye m c h t #*• s#>ce n/*E v e u > A T OO tlSTArfT 'TEJ9IPE/&TUICE -us- CATALYST LOADING In the ordinary flow system catalytic process where the feed is in the gaseous tate, the product formed at the bed temperature is itself usually gaseous. It is true that in certain petrochemical pro cesses by-products of a polymeric carbonaceous nature form and deposit on the catalyst. In this study of reacting gaseous ammonia and carbonyl sulfide, the urea formed is in the solid phase and does not leave the catalyst but rather remains impregnated on it. This results in the loading of the catalyst and a subsequent reduction in yield of urea. It was thus desirable to conduct an investigation on the loading of the catalyst. In runs made previously, in which the duration of the run was one hour, the high load, weight-wise, on the catalyst was obtained at the highest space velocity used (7. 50 min. ”^) and at temperatures of 125 to 1 2 9 °C. The yield of urea was lower at a lower space velocity - - at 129° the yield was 40. 5% at 7. 50 min. as com pared to 64. 4% at 1. 56 min. . In order to accelerate the test on loading, the higher space velocity was used. The results are given in Table 18. -// 6- TABLE 18 CATALYST LOADING Catalyst: Activated charcoal Temperature: 129°C. Feed: COS = 60 cc./min. NH3 = 120 cc./min. Space Velocity: 7. 50 min. Run Duration of Run Grams of Urea % Yield min. Theoretical Produced 36 6 0 9 . 62 3. 90 40. 5 62 1 2 0 19.24 5.48 28.4 64 , 180 28. 8 6 6 . 18 21.4 63 240 38. 48 6 . 84 17. 7 The values from the above table are plotted in Figure 2 2 . As was to be expected the yield of urea goes down as the catalyst becomes more and more impregnated with the product. The two curves in Figure 22 show that the formation of urea decreases approximating a parabolic function thereby indicating that the whole of the catalyst does not become coated at one time. This would result in the curve for "grams of urea formed" levelling off immediate ly and the yield dropping off sharply to zero. It would appear that the catalyst underwent both fouling and deactivation. A semi-log plot, Fig. 23, for the above data gives straight lines. An interesting ob servation was that the activated charcoal when removed from the re actor did not appear coated on the surface. The top portion next to the gas inlet did show a slight grayish cast. The majority of the urea was inside the granules. In Hun 63, for example, the 24 cc. of acti vated charcoal weighing 13.55 grams carried 6 . 84 grams of 100 % urea, over 50 per cent its own weight. - //< ? - too Catalyst: fctiYrfed C harcoa/ 90 IkM re& rrutE>- y-pa: r $&m $&m titpwCED QfUfSA 0 /GO /50 7/aa £ ( /* //* ) Figur£ .2 £ . Ef f e c t o f Ca t a l y s t Lo a d in g o n Yie l d -// 9- CATAiXST: /}ct/V € 0 4 0 JO G&0S G&0S OF (J&fi T fyw ceo JO SO J O 4 0 JO SO 70 » 3 6 /0 0 soo F / 6 u ^ e E 3 . E f f e c t o p Cf t j r l y s t L o a o j n g o n Y/e l d -/ao- CATALYST LOADING vs. SPACE VELOCITY The previous study on catalyst loading was carried out at a high space velocity (7. 50 min. “^) at which the greatest weight of urea was formed per unit time. In this study a low space velocity (1. 56 min. "*) was used and the duration of run was varied so that a comparison of yield could be made with the studies in which the duration of runs was constant but the space velocities were varied, i. e. , the total volume of carbonyl sulfide and ammonia passed over the catalyst could be used as the basis of comparison. From the accompanying figure it can seen that a lower space velocity gives a slightly higher yield. The product at the low space velocity contains some sulfur which imparts a yellow color to it. TA BLE 19 CATALYST LOADING vs. SPACE VELOCITY CATALYST : Activated Charcoal TEMPERATURE : 129°C. Run COS n h 3 Space Velocity Time COS nh 3 % Yield cc/min. cc/min. min. ~ ^ min. Total Total cc cc I 36 60.0 1 2 0 . 0 7.50 6 0 3600 7200 40.5 \ 35 40. 0 80. 0 5. 00 6 0 2400 4800 43.2 32 19.3 38. 6 2.41 6 0 1158 2 2 1 6 56=5 33 12. 5 25. 0 1.56 6 0 750 1500 64.4 70 12. 5 25. 0 1. 56 1 2 0 1500 3000 55.1 67 12. 5 25. 0 1.56 288 3600 7200 44.9- i too Ca t a l y s t : Qdm tcd Charcoal T&»P£%ATUf£ i /29*C. SV- 241mm-1 - 3 & - Tme - 6C>m 'n . ------^-S^-S-Oomin-i 1200 mo 2400 3000 3600 Total a. COS 0 1200 2400 3600 4600 6000 7200 Tim. Figure 24. Ca t a l y s t Ohad/m s m - S pace V e lo c ity t -/23~ CATALYST LIFE An important factor in a catalytic reaction is the life of the catalyst. A catalyst may be deactivated or fouled or both. Re activation and regeneration are two terms that are often interchanged. Reactivation may involve chemical treatment to remove poisons or to restore some lost constituent, or may consist of alternate oxida tions and reduction or solution and precipitation to restore the sur face structure of the catalyst. Regeneration removes the catalysts deposits formed by fouling. In the "catalyst loading” studies it was pointed out that the activated charcoal catalyst became both fouled and deactivated. In this particular series the catalyst used was the activated charcoal used in the other runs. The catalyst was used in one run and then extracted for several hours in a Soxhlet extractor using ab solute ethanol as the liquid. After extraction the catalyst was air-dried and then placed back into the reactor. The bed was brought up to temperature and the bed continuously swept with nitrogen gas. The operations were repeated. From the following table it can be seen that the catalyst activity is essentially the same in the three runs. The alcohol used -/24' T A B L E 20 CATALYST LIFE Catalyst: Activated charcoal Temperature: 1 2 9 °C. Feed: COS = 19.3 cc./min. NH3 = 38.6 cc./min. Space Velocity: 2.41 min. “ Time of Run: 1 hr. Run Number of Times % Yield ______Catalyst Used ______ 32 1 56. 5 65 2 52. 1 6 6 3 55. 0 in the extractions dissolved the urea and any other impurites from the catalyst and restored the activity. -/2S- MATERIAL BALANCE Flow System Input COS = 19. 3 cc x 6q min> x 1 mole x 60 gr = 3.10 grams min. 22,400 cc mole NH-3 6 0 ^ 38.6 cc^ x min> x 1 mole x 17 gr = 1.76 grams mm. 22.400 cc mole T otal : 4. 8 6 grams Output wt. of charcoal + deposit = 13.77 wt. of charcoal = 1 2 . 0 1 deposit 1. 76 g r. Recovery of solid charcoal by extraction = 1.820 grc still contains some alcohol and moisture Analysis of extraction product = 96.4% urea = 1.75 gr. weight of solid (NH^COSNH^) condensed in ice bath trap = 1.66 gr. weight of gas (H2 S, COS, NH3) leaving ice bath = 4. 8 6 - (1. 6 6 + 1. 75) = 1.45 According to the equation COS + 2 NH3 — CO (NH2 ) 2 + H2S H2S formed = 1.75 x 34 = 0.99 gr. 60 Wt. of COS and NH3 leaving ice bath unreacted = 1.45 - 0. 99 = 0.46 gr, SUMMARY IN OUT COS = 3. 10 gr. CO(NH2 ) 2 = 1.75 gr. NH3 = 1.76 NH2COSNH4 = 1.66 (H2 S, COS,NH3) = 1.45 4 . 86 gr i 4 . 8 6 gr, - / < s e - SUMMARY Flow System In the strictest sense of the word any flow system used to manufacture urea from carbonyl sulfide and ammonia according to the equation COS + 2 NH3 CO(NH2 ) 2 + h2s would not be a continuous one but rather semi-continuous. The urea formed does not leave the catalyst but remains impregnated and must be leached out by some solvent. In this work ethanol was used as the solvent. After extraction the catalyst regains its activity and the ethanol may be recovered and recycled. The urea formed is of a very high' purity (above 98%). Of the catalysts studied activated charcoal (14 mesh) was found to give the best yields with the maximum at all space velocities studied (1.56 to 7.50 min.-^) occurring at a temperature of 125°C. Above this temperature the yield decreases probably due to the break down of urea when maintained in the vicinity of its melting point or above. Lower space velocities favor higher yields. An economic cycle would have to be established as to maximum catalyst loading per mitted. Not all of the carbonyl sulfide and ammonia combine on the catalyst surface but some pass through the bed and combine later to form the ammonium thiocarbamate. This could be converted to the urea but it would take an autoclave system. The hydrogen sulfide formed as the product of the reaction could be converted back to the carbonyl sulfide on a commercial basis. Using an excess of carbonyl sulfide has not too much effect on increasing the yield whereas ammonia does. At a space velocity of 2.41 min.-^ and at catalyst temperatures of 125-129°C. the yield may be raised from 56 to 75 per cent at an excess of 50 molar per cent of ammonia. APPENDIX )* 7«. -/< 2 8 ~ SAMPLE SHEET ’ BATCH SYSTEM Autoclave - Electrically Heated Run No. 32 Temperature = 106°C. COS = 30.2 gr. = 0.50 moles NH3 = 17. 1 gr. =1.00 moles NH3 /COS = 2.0 % Yield = 60. 0 TABLE 2 1 Time Thermocouple Temperature Pressure iron-constantan °C. psis. ref. 0 °C. 0 1.50 rnv. 2 9 . 0 - 15 min. 2.53 48. 5 - 30 3.48 6 6 . 5 = 45 3.98 76. 0 - 6 0 4.40 84. 0 - 75 4.65 8 8 . 5 158 90 4.98 95. 0 2 0 0 105 5.10 97. 0 245 1 2 0 4. 33 1 0 1 . 0 275 130 5.42 163. 5 300 145 5. 53 104.5 310 150 5.55 105,0 335 1 6 0 5. 64 106. 5 350 170 5. 6 8 107. 0 375 180 5. 73 108. 0 385 195 5.68 167. 0 390 215 5.61 1 0 6 . 0 400 232 5.64 106. 5 400 240 5. 64 106. 5 400 1 1 hrs. 5. 64 106. 5 450 2 6 5.45 103. 0 475 50 5.64 106. 5 475 ~/29- SAMPLE SHEET BATCH SYSTEM Autoclave - Waterbath Heated Run No. T-2 Temperature = 93°C, COS = 30. 0 gr. = 0. 50 moles NH3 = 17. 0 gr. = 1. 00 moles NH3/COS = 2..0 % Yield = 45. 6 TABLE 22 Time Temperature min. °c. 0 93 0. 67 91 1.0 91 2. 0 91 3. 0 91. 5 4. 0 91. 5 5. 0 92 6. 0 92 7.0 93 8. 0 93 9.0 93 13.0 93 14. 0 93 15. 0 93 24. 0 93 30. 0 93 /JO SAMPLE SHEET FLOW SYSTEM Run No. 67 Temperature = 129°C. COS = 12.5 cc./min. = NH3 = 25,0 cc. /min. NH3 /COS = 2, 0 Space Velocity = 1.56 min. % Yield = 44, 9 TABLE 23 Time Temp. Flowmeter Differential V olume( cc/min hr. °c. COS n h 3 COS n h 3 0 129 3.4 3. 1 12. 5 25. 0 0. 5 129 3.4 . 3. 1 12. 5 25. 0 1.0 129 3.4 3. 1 12. 5 25. 0 1.5 129 3.4 3. 1 12. 5 25. 0 2. 0 129 3.4 3. 1 12. 5 25. 0 2.5 129 3.4 3. 1 12. 5 25. 0 3. 0 129 3.4 + 3. 1 12. 5 + 25. 0 3. 5 129 3.4 + 3. 1 12.5 + 25. 0 4. 0 129 3.4 + 3. 1 12. 5 + 25. 0 4. 75 129 3.4 3. 1 12. 5 25. 0 -/?/- AUTOBIOGRAPHY I, Felice Joseph CEL.L.I, was born on March 19a 1923 in Vastogirardi, Province of Campobasso, Italy. I received two years of elementary education in Italy and came to the United States in December, 1930. I continued my education through the high school at Grandview Heights Schools, Columbus, Ohio and graduated in June, 1941= I entered The Ohio State University where I obtained the Bachelor of Chemical Engineering degree in 1945 and the Master of Science degree in 1947. From 1944 to the present I have been employed by The Ohio State University Research Foundation.