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Masters Theses Student Theses and Dissertations

1928

Solubility of paraffins in lower molecular weight

Ruth Veino Goodhue

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Recommended Citation Goodhue, Ruth Veino, "Solubility of solid paraffins in lower molecular weight drhy ocarbons" (1928). Masters Theses. 4710. https://scholarsmine.mst.edu/masters_theses/4710

This thesis is brought to you by Scholars' Mine, a service of the Missouri S&T Library and Learning Resources. This work is protected by U. S. Copyright Law. Unauthorized use including reproduction for redistribution requires the permission of the copyright holder. For more information, please contact [email protected]. SOLUBILITY OF SOLID PARAFFINS IN LOWER MOLECULAR WEIGHT HYDROCARBONS

by

Ruth Veino Goodhue, B. S.

SUBMITTED IN PARTIAL FULFILMENT OF THE

REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN CHEMICAL ENGINEERING

in the

SCHOOL OF MINES AND METALLURGY UNIVERSITY OF MISSOURI.

Rolla Missouri 1928.

:)4492 ~araffins 08 SO~U.bilitY t' ~oliu 001 ThJsis: f 'Q.p.. lin lowerllmolecula weight llydro- • 0 ,carbons. Goodhue 1928 I I! I Ii i I, I·

PREFACE The writer wishes to express her sincere appreciation to Dr. H. L. Dunlap for his valuable assistance and suggestions in the development of this research. TABLE OF CONTENTS

Introduction ------1. Frevious Work ------2. Preparation and Purification of the

Solid and Liquid Hydrocarbons ------4.

Procedure ------7. Tabulated Data and Graphs ------10. Discussion of Data ------20. SllIllmary ------.------·------27. Suggestions for Future Work ------28. THE SOLUBILITY OF SOLID PARAFFINS IN LOWER

MOLECULAR WEIGHT HYDROCARBOl-lS.

INTRODUCTION The solubility of solid paraffins in the lower mol­ ecular weight liquid ~rdrocarbons offers a problem of some considerable commercial import~~ce since it is by use of these low boiling hydrocarbons that the un­ desirable paraffin are removed from lUbricating oils 1n the Sharples process. Little data is to be fotmd 1n the literature on the solubility of the paraffin waxes. and that which is available is of a very general nature. Ordinary commercial paraffins are mixtures of higher hydrocarbons containing twenty or more carbon atoms to the molecule. These paraffins are rendered less soluble in lUbricating oils by a process known industrially as ,. cracking" but which should more properly be termed Htelescopingd of the straight chain hydrocarbons. This "cracking" or "telescoping" is brought about by redistilling the at a relatively high temperature in a current of steam. The mechanism of this process is not lmderstood but the wax is made less soluble in lubricating oil and the lower hydrocarbons by this distillation with steam. This work was undertaken for the purpose of finding if possible, what effect this "cracking" or "teles­ coping" process has on the solubility of the paraffins in the liquid hydrocarbons.

PREVIOUS WORK Sakhanov and Vassilievl determined the solubility of solid paraffins and the solidifying temperatures of materials containing them. They used as . . acetic acid, liquid paraffins. machine oil and alcohols. Sachanen2 determined the solubility of a solid paraffin in various gasol1nes, , solar oil, paraffin Oil, fuel oil, benzene, alcohols and acetic acid. He found that at their melting points the paraffins were soluble in all proportions

in the various oils, benzene. alcohol. ~tc. Sullivan. KcGill and French3 determined the solu­ bility of various paraffins, ranging in melting points from 1090 to 1410 Fahrenheit in a number of oils varying from ether to a 333-viscosity oil

obtained by redistillation of a twenty per cent

1. Solubility of solid paraffins and the solidifying temperatures of material containing them. A.N. Sakhanov and N.A. Vassiliev. Neftjanoe slancevoe ChozjajstYQ, ~ 820-37 (1924) 2. Solubility of paraffin and the solidification of paraffin containing products. A.Sachanen, Petroleum Z. 21, 735-40 (1925) 3. -Solubility of paraffin wax in oil. Sullivan, KcGill and French, Industrial and Engineering Chemistry, ~t 1042 (1927) bottom from the fractional distillation of a wax free distillate. Weber and Dunlapl determined the solubility of a solid paraffin in pentane, hexane, heptane, octane and isodecane. Results of these solubility tests indicate that the following are true in general:-

~. The solubility of a solid paraffin increases with decrease in of the paraffin. 2. The solubility decreases with increasing molecular weight of the or with increasing viscosity and density of the solvent. 3. The difference in solubility due to difference in melting point of the paraffin and increasing density of the solvent decreases with decrease in concentration of the solution. 4. The solubility of a solid paraffin in liquid hydrocarbons increases rapidly with rise in temp- erature. These authors used paraffins which eVidently were highly telescoped or in other words the paraffin had been distilled with steam 50 as to render it as insoluble as possible.

1. Solubility of paraffin in liquid hydrocarbons. Weber and Dunlap. Industrial and Engineering Chemistry. ~. 383 {1928} PREPARATION AND PURIFICATION OF THE SOLID Al~ LIQUID HYDROCARBONS. As has been stated, the commercial paraffins con­ sist of hydrocarbons containing twenty or more carbon atoms to the m~lecule, usually telescoped to a greater or less extent. It was desirable to obtain for this type of work a paraffin containing as few individual members as possible and these in a normal or straight chain condition. For their work Weber and Dunlap took an ordinary commercial paraffin, dissolved it in warm benzene and allowed crystallization to take place. The part which crystallized out was filtered off and redissolved in benzene. This process was repeated three times. The last traces of benzene were removed from the final product by distillation under reduced pressure. The paraffin obtained amounted to about twenty five per cent of the original sample and had a melting point of 56°0. For the work under discussion in this paper a part of the paraffin prepared as stated above was treated in a somewhat different way. It was dissolved in warm benzene and the solution allowed to cool down slightly. The paraffin which crystallized out was discarded and the filtratetchilled. This crystallized more paraffin which was then filtered off and redissolved in benzene. This process was repeated three times and the last of the benzene distilled off under reduced pressure. About forty per cent of the sample was recovered and had a melting point of 50.5° to 51°C. Stra.ight run gasoline was carefully fractionated to obtain the liquid hydrocarbons used for the solvents. A three foot fractionating column. welter cooled for the lower boiling and air cooled for the higher boiling hydrocarbons was used. The gasoline was first roughly cut at the desired temperatures and ea.,ch fraction was then fractionated carefully three times. The product was washed with concen­ trated sulfuric acid until no yellow color appeared, then washed with distilled water and sodium carbonate solution, dried over calcium chloride and distilled from metallic sodium. Only the portion which boiled within half a degree on either side of the boiling points listed in International Critical Tables (I.C.T.) was used, except in the case of isopentane. I.C.T. give the of isopentane as 28°0. Gas from two sources was used for obtaining the isopentane and neither gave more than a very small quantity distilling at this tempera.ture. They did give considerable quantities distilling at the previously accepted value of 31° and this fraction was used as the pure ieopentane. It is difficult to obtain completely pure hydro­ carbons from gasoline by this method. Brown and Carr in a bUlletin, "Pure Hydrocarbons from Petroleum", using an elaborate system of fractionating columns. one 18 feet high packed with modified Raschig rings 1/2 inch in diameter, a second 10 feet high with 1/4 inch rings and a third 5 feet high with 1/8 inch rings, found that five fractionations were suffici- ent to separate cyclopentane, cyclohexane, benzene and toluene from the pentanes and hexanes. Additional fractionations were necessary to obtain pure fractions of the liquid hydrocarbons. It was not possible to use such a complicated system in this work a.nd for that reason the solvents used were not perfectly pure. No practical method is known for separating the cyclo compounds from the normal straight chain compounds, and some of these cycla compounds are close in boiling points to the stra.ight chain com­ pounds. but are much higher in specific gravity. While the boiling points of the solvents used check the values given in I.C.T. within the limits given before, the specific gravities in some cases are high, probably due to traces of the cyclo compounds.

The benzene used for purifying the solid paraffin and for running solubility data. on the paraffin WB.a purified by the same method and its boiling point and specific gravity checked the values given in I.C.T. 7.

Hydrocarbon B.P. Sp.gr. Sp.gr. obsv. I.C.T. ~~~--~~------~~--~----~--~----~---~-~-----~-~- Pentane 36°_37° .626 .631 Isopentane 30.5°-31.50 .620 .621 Hexane 68.5°-69.50 .680 .660 Diisopropyl 57.6°_58.6° .659 .666 3-methyl pentane 63.5°_64.5° .669 .668 3,3-dimethyl pentane86.5g-87.5° .710 .711 2,4-dimethy1 pentane83.4 -84.4° .707 .681 Heptane 980 _99 0 .723 .684 2,2,3-trimethyl butane .699 .695 2-methy1 hexane .716 .707 ~-~~--~------~~------~------~------~----~----~--

PROCEDURE Weber and Dunlap used weight method determina.tions for finding the amount of paraffin soluble in a given solvent at a given temperature. This method has several drawbacks, the most objectionable perhaps. being the fact that the solubility, as determined in this way varies with the excess of paraffin present. While all samples taken from the same run give close checks, no two runs check very closely. ' In the present work the cloud point method was

used. This method was employed by Sullivan, KcGill and French in their work and was found to be satis­ factory. Solutions of varying known concentrations were made up in 8 inch test tubes. A thermometer reading to tenths of a degree and a magnetic stirrer were lowered into the solution and the test tube lowered into the cooling bath. The continuous

stirring by the magnetic stirrer prevented any super­ cooling and at the same time this type of stirrer permits the test tube to be closely stoppered thereby 8. preventing appreciable evaporation of the volatile solvents. The solutions were cooled with continuous stirring to the point where the cloud appeared. This point was very clear and distinct in almost all cases although at the low concentrations (2 grams paraffin per 100 grams solvent) it was more difficult to see. After reading the cloud temperature the test tube wa.s put into a ba.th of we.rm water which served to quickly cause the paraffin to redissolve. The solution was then again cooled down to the cloud point and the temperature read. Five readings were taken on each solution and the variation in cloud temperature was never more than one tenth of a degree either way. Some care is neoessary in having the temperature of the cooling bath not less than one nor more than two degrees cooler than the cloud point of the sol­ ution. Too cool a bath results in a cloud point which is too high and which cannot be checked while a ba.th too warm produces an indefinite cloud if any at all. In order to check the cloud points more closely in several cases the temperature at which the cloud disappeared was read and found to check the point at which it appeared. Cooling curves were also made in a few cases. These resulted in lag points two or three tenths of a degree below the cloud point. This ie probably due to the fact that the paraffin used was not an absolutely pure paraffin consisting of only one individual type of moleCUles but wa,s instead a mixture of several members. The cloud temperature is then the temperature at which the least soluble paraffin settles out while the lag temperature gives the point where the average of the paraffins present settles out. Weight method determinations were also run to find out how closely the weight and cloud methods check. Points were taken from the cloud point curves and solutions made up which had a slight excess of paraffin over that indicated by the curve as the solUbility at that temperature. These solutions were put in 250 co. flasks with a condenser attached. The f11- tering arrangement was a. small Soxhlet thimble. The whole apl:'aratus was patterned after that used by Weber and Dunlap1. The solutions were :put in a thermostat and agitated at a constant temperature for three hours. A sample was then taken, weighed. the solvent evaporated off and the sample dried to constant weight. A second sample was t~ken two hours after the first. These samples checked each other closely but ran about --~~-~----~---~---~--~------~---_.~~~~~--~-~~~- 1. Apparatus for filtering saturated liqUids at a constant temperature. Palll Weber and H.L. Dunlap, Ind. and Eng. Chem. 12.. 481 (1927) 10. two and one half per cent lower than the solubility as indicated by the cloud point ~ethod.

TABULATED DATA The solutions used in the cloud point determinations were made up by weight and from this the concentrations were calculated in terms of grams paraffin per 100 grams of solvent, grams paraffin per mole of solvent, and per cent by weight. The curves are plotted in terms of grams paraffin per mole of solvent since this method gives curves which are more widely separated and easier to read. On Plates I, II. III, IV. V and VI the curve for the paraffin melting at 50.5° to 51° in isopentane is used as a reference curve. Plates I. II and III show the solubility of the paraffin melting at 50.5° to 51° in various solvents. Plate IV shows the solubility of the distilled paraffin having a melting range of 50° to 50.5°0. Plate V shows the 8ol.ubility of the telescoped pa.raffin mel.ting at 52.5° to 53°0. On Plate VI are the curves for the telescoped, distilled paraffin which mel.ted at 51.5° to 52°0. Plate VII gives comparison curves for the paraffin melting at 50.5° to 5100 and for the paraffin melting at 52.50 to 53°0 in pentane, hexane and heptane. Plate VIII gives curves for the solubility of the Standard Oil paraffin melting at 60.60 C (1.41 0 F) in pentane hexane and heptane. 11.

Solvent Cone. Per cent Cone. Temp. g/100g. by weight g,Imole ~~~--~~~~~~--~---~~~---~~~--~------~--~----~-~~-----

Pentane 1.99 1.95 1.44 -3.3 3.87 3.73 2.80 1.5 4.51 4.32 3.25 2.8 6.27 5.90 4.53 5.4 7.53 7.00 5.43 6.9 9.26 8.47 6.67 8.7 10.05 9.13 7.25 9.3 10.94 9.87 7.89 10.0 14.32 12.53 10.33 12.1 20.20 16.81 14.57 14.9 23 0 25 18.86 16.76 16.0 26.61 21.02 19.19 17.1 27.25 21.41 19.65 17.4

Isopentane 2.01 1.97 1.45 -2.6 2.76 2.69 1.99 -0.3 2.81 2.73 2.03 -0.2 3.43 3.32 2.47 1.3 4.12 3.96 2.97 2.6 5.04 4.80 3.64 4.5 6.47 6.08 4.66 6.4 7.08 6.61 5.11 7.1 7.48 6.96 5.40 7.5 8.18 7.56 5.90 8.1 10.92 9.85 7.87 10.4 14.42 12.61 10.40 12.6 17.96 15.23 12.95 14.5 18.30 15.47 13.20 14.7 19.77 16.54 14.26 15.5 25.33 20.22 18.27 17.9 __ --.-e;'_'-' _-.'.__ .-- ..... _~...... ,', .....-:.-"'_ ..... _-~-_- ....'~._' ~ ... _-...... ~ ... .-,_ ...... __ ...... _

Hexane 1.81 1.78 1.56 -5.0 2.13 2.09 1.83 -3.7 3.04 2.95 2.62 -0.9 4.66 4.44 3.93 2.4 6.70 6.28 5.77 5.5 11.22 10.01 9.66 9.7 14.90 12.97 12.83 12.0 19.69 16.45 .16.96 14.7 20.97 17.33 18.06 15.2 24.58 19.73 21.17 16.7 25.52 20.33 21.99 16.8 ---~----~--~- -~~~~---~~--~-~~-~-----~~~-~---~--~-~-~ 12.

50.5° - 51 0 m.p. Paraffin Solvent Cone. Per cent Gonc. Temp. g/100g. by weight g/mo1e ~~-~---~~-~~-~~-~--~~,~--~~~-~--~~---~-~-~~~~---~-~--~-

3-methy1 1.96 1.92 1.69 -3.6 pentane 3.04 2.95 2.62 -0.3 3.78 3.64 3.26 1.5 6.14 5.79 5.29 5.5 8.86 8.14 7.63 8.4 12.66 11.24 10.91 11.3 16.53 14.19 14.24 13.7 18.84 15.85 16.23 14.6 20.14 16.76 17.35 15.3 25.02 20.01 21.55 17.1 --~~-~--~~~--~~~--~--~~~~---~~~------~~-~-~------... - Diisopropy1 2.03 1.98 1.75 -3.5 2.93 2.85 2.52 -0.9 3.98 3.83 3.43 1.6 6.24 5.87 5.37 5.1 11.54 10.34 9.94 10.2 15.22 13.21 13.11 12.5 19.48 16.30 16.78 14.5 23.76 19.20 20.47 16.4 26.94 21-.22 23.21 17.6 28.86 21.89 24.86 18.0 -~~-~~~~----~~~-~--~-~--~----~--~--~~~------~--~----~

Heptane ~.Ob G.Ol 2.06 -3.8 2.84 2.'76 2.83 -1.0 2.98 2.90 2.99 -0.9 3.43 3.32 3.44 0.9 4.53 4.34 4.54 2.8 7:06 6.59 7.07 6.4 10.80 9.'75 10.82 10.0 15.13 13.14 15.16 12.9 18.42 15.56 18.45 14.5 23.59 19.09 23.63 16.8

2.4-dimethyl 2.37 2.32 2.37 -2.7 pentane 3.41 3.30 3.41 0.1 4.18 4.01 4.18 2.2 6.84 6.40 6.85 5.9 9.87 8.98 9~89 8.8 13.42 11.83 13.44 11.4 17.69 15.03 17.?2 13.8 22.72 18.51 22.76 15.9 13.

50.5° - 510 m.p. Paraffin Solvent Cone. Per cent Cone. Temp. g/100g. by weight g/mole ~~~~--~~----'~~~~--~-~'~---~~-~--~~-~~---~_.... -- ... _--- ... - 3,3-dimethyl 3.82 3.68 3.82 1.2 pentane 5.34 5.07 5.35 3.8 5.85 5.53 5.86 4.4 7.70 7.15 7.72 6.7 9.81 8.94 9.83 8.7 11.24 10.10 11.25 9.8 13.12 11.60 121.14 11.2 15.65 13.53 15.67 12.7 19.41 16.26 19.43 14.7

2-methy1 4.63 4.43 4.63 2.9 hexane 5.79 5.47 5.80 4.5 7.66 7.12 7.67 6.9 9.53 8.70 9.54 8.7 13.86 11.90 13.88 11.8 25.91 20.58 25.95 17.3 ------~-~---~~-~-~~~~------~-~~-~~-~-~---~~~~~-~-- 2,2,3-tri 4.87· 4.64 4.88 2.8 methyl 6.78 6.35 6.79 5.5 butane 8.87 8.15 8.89 7.8 11.99 10.71 12.01 10.3 17.54 14.93 17.57 13.6

Pentane and 3.99 3.84 2.88 2.5 isopentane 5.17 4.91 3.73 4.4 mixture, 50­ 5.63 5.33 4.06 5.2 50 by vol. 6.71 6.29 4.84 6.4 8.91 8.18 6.43 8.7 9.96 9.06 7.19 9.6 12.66 11.23 9.13 11.4 16.86 14.42 '12.16 13.7 17.08 14.59 12.32 13.8 20.42 16.96 14.73 15.2 22.92 18.65 16.53 16.2 23.11 18.77 16.67 16.3 50.5° - 51° m.p. Paraffin

Solvent Cone. Per cent Cone. Temp. g/100g. by weight g/mo1e

----.-._-- -_ • .- ---._... --... .-_...... ---'_ .. ------... - - -.------... _... Benzene 2.81 2.73 2.19 7.1 4.11 3.95 3.21 9.5 5.06 4.81 3.93 10.7 6.42 6.03 5.02 12.1 6.80 6.37 5.31 12.4 8.04 7.45 6.28 13.5 8.65 7.96 6.75 13.8 9.26 8.47 7.23 14.3 11.87 10.61 9.27 15.9 13.28 11.72 10.37 16.6 14.98 13.03 11.70 17.0 --~-~----~~~--~~----~~~~~~~------~~~------~-~~~----~- 15.

Distilled Paraffin. m.p. 50° - 50.5° Solvent Cone. Per cent Cone. Temp. sllOOg. bY weight g/mole ---~~-~-~-~--~~-~~~~-~-~--~------~-~-~------

Pentane 3.95 3.80 2.85 0.5 4.76 4.65 3.43 1.9 5.52 5.23 3.98 2.9 5.60 5.30 4.04 ~.O 8.38 7.73 6.04 6.2 10.0? 9.10 7.26 7.5 12.96 11.52 9.15 9.5 15.83 13.67 11.42 11.3 21.76 17.87 15.69 14.0 21.96 18.01 15.84 14.4 24.95 19.97 18.00 15.1 ~~-~~---'~-'-~'~~~-~~~.~~~-~-~~~~------~--~--~~-~-----~~

IBopentane 4.01 3.86 2.89 1.1 5.00 4.76 3.61 2.6 5.19 4.93 3.75 3.0 7.53 7.00 5.43 5.9 10.15 9.22 7.32 B.2 13.18 11.65 9.51 10.3 17.10 14.60 12.30 12.4 18.55 15.65 13.38 13.1 23.09 18.75 16.65 15.0 25.63 20.40 18.49 15.7

3-methyl 5.30 5.03 4.56 2.6 pentane 5.94 5.61 5.11 3.6 6.70 6.28 5.77 4.4 9.48 8.66 8.17 7.3 10.81 9.76 9.32 8.4 13.13 11.36 11.31 10.0 16.72 14.32 14.40 12.2 20.18 16.79 17.38 13.5 20.99 17.35 18.08 13.9 16.

Telescoped Paraffin. m.p. 52.50_53°

Solvent Cone. Per cent Cone. Temp. g;'100g. by weight g/mole -~-~-~-~--~~-----~~~----~~---~--~-~----~~--~------~~~

Pentane 3.83 3.69 2.76 1.9 4.47 4.28 3.22 3.4 7.34 6.84 5.29 7.1 7.51 ?15 5.42 7.2 9.07 8.32 6.54 8.7 9.71 8.85 7.00 9.2 12.24 10.90 8.83 11.2 14:.09 12.35 10.16 12.3 19.01 15.97 13.74 15.3 -~---~-~~~--~-----~~----~---~---~-~--~-----~~---~--- Isopenta.ne 3.94 3.79 2.84 2.7 4.36 4.18 3.14 3.6 4.79 4.57 3.46 4.3 5.78 5.46 4.17 6.0 7.28 6.94 5.25 7.8 8.41 7.76 6.06 8.8 8.63 7.96 6.22 9.0 8.99 8.25 6.48 9.3 12.02 10.73 8.67 11.5 15.10 13.12 10.89 13.4 18.42 15.55 13.28 15.0 18.82 15.84 13.57 15.2 23.03 18.72 16.61 16.8

Hexane 3.89 3.74 3.35 1.6 4.70 4.49 4.05 3.4 5.54 5.25 4.?8 4.6 7.09 6.62 6.10 6.8 7.89 7.31 6.80 7.4 9.02 8.27 7.?? 8.? 12.71 11.28 10.95 11.4 28.48 22.17 24.54 18.5

Heptane 3.55 3.43 3.55 1.2

4 0 76 4.54 4.77 3.7 5.77 5.45 5.78 5.1 7.90 ?32 7.91 7.7 9.63 8.58 9.65 9.4 12.53 11.14 12.55 11.7 16.31 14.02 16.34 14.0 l?

Telescoped Paraffin, m.p. 52.50 _53° Solvent Cone. Per cent Cone. Temp. g/lOOg. by weight g/mole

Benzene 2.86 2.78 2.24 7.5 3.5.4 3.42 2.77 9.0 4.23 4.06 3.46 10.4 5.02 4.78 3.92 11.0 6.68 6.26 5.22 13.0 7.34 6.84 5.73 13.6 10.35 9.38 8.08 15.6 18.

0 51.5 - 52° m.p. Paraffin

Solvent Cortc. Per cent Cone. Temp. g,!100g. by weight gfmole

Pentane 3.85 3.71 2.77 2.0 4.59 4.39 3.31 3.5 5.82 5.14 4.20 5.3 5.98 5.65 4.31 5.3 8.07 7.47 5.82 7.8 10 0 23 9.28 7.38 9.6 10.86 9.81 7.83 10.1 13.21 11.68 9.53 11.7 15.71 13.58 11.33 13.2 17.23 14.70 12.43 13.8 19.52 16.34 14.08 14.9 23.86 19.26 17.21 16.5 -~----~--~~-'-~~-~--~~----~~---~------~~-,~~----

Isopentane 3.76 3.62 2.71 2.3 4.90 4.6? 3.54 4.6 5.68 5.38 4.09 5.4 8.09 7.49 5.84 8.3 9.80 8.93 7.07 9.7 13.33 11.76 9.62 12.2 15.55 13.46 11.21 13.4 18.13 15.35 13.07 14.6 23.88 19.28 17.22 16.6

Hexane 4.60 4.40 3.96 3.1 5.68 5.38 4.90 4.6 6.24 5.87 5.38 5.5 11.19 9.99 9.64 10.1

Heptane 5.62 5.32 5.63 4.7 7.64 7.10 7.65 7.2 8.21 7.58 8.23 7.8 10.89 9.82 10.91 10.3 12.65 11.22 12.67 11.4 14.85 12.93 14.87 12.8 19.44 16.23 19.47 15.1 23.24 18.85 23.28 16.6 19.

Standa.rd Oil rc:raffin, m.p. 60.6° G. Solvent Cone. Per cent Cone. Temp. g/lOOg. by weight g/mole -~~~~~--~~~~~-~-~-~---~~-~-~~-~---~~-~----~--~--~~~-~

Pentane 3.55 3.43 2.56 13.8 4.37 4.19 3.15 15 .. 8 4.77 4.55 3.36 16.4 5.77 5.45 4.16 18.0 7.54 7.01 5.43 19.9 10.81 9.76 7.79 22.3 14.51 '12.67 10.46 24.6 17.80 15.11 12.84 25.9

Hexane 3.96 3.81 3.41 14.8 4.59 4.39 3.95 15.5 5.66 5.36 4.88 17.3 7.68 7 • .13 6.62 19.5 11.84 10.59 10.20 23.1 ~~~-~~-~~~~~~--~-~~---~~~-----~------~-~-~~------~-

Heptane 3.66 3.53 3.66 14.1 5.80 5.12 5.81 17.6 8.26 7.63 8.28 20.4 9.44 8.63 9.45 21.3 10.1? 9.23 10.19 22.0 o------~ .' \t) ~ ~--~:------l------I ~ ~ l4J () ~ ~ ~

20.

DISCUSSION OF DATA All previous work on the solubility of solid para­ ffins tends to the belief that the solubility of a solid paraffin in a, lower molecular weight liquid decreases with increase in molecular weight of the solvent hydrocarbon. In most cases,

however. no infor~~tion is given as to the paraffin used, that is whether it was a highly telescoped paraffin or not. It is known that Sullivan. McGill and French and Weber and Dunlap all used more or less highly telescoped paraffins in their work. According to the general relations thought to exist between organic compounds of the same type we should expect to find that a solid paraffin was more soluble in the liquid paraffin as the molecular weight of the solvent increases. An examination of the curves given in Plates I, II, III, IV, V and VI show that this was found to be the case in this work

contrary to the order given by other workers. A peculiar result 1s shown in Plate VIII. Solu­ bility tests on the 141°F (60.6°0.) m.p. paraffin used by Sullivan, McGill and French in their work were run over short ranges of concentration in pentane, hexane and heptane. This sample was much less soluble than the paraffin used in the greater part of this work but the order was that.found with the other paraffin, i.e. the solubility increased with increase in molecular weight of the solvent. 21.

This data was plotted in terms of grams paraffin per mole solvent. An explanation was sought for this apparently wide discrepancy in results and it was found that if the data was plotted in terms of per cent paraffin by weight the order was reversed and be­ came that which Sullivan. McGill and French had observed. They worked, as ha.s been stated with heavy oils which are mixtures of hi.gher molecular weight liquid hydro­ carbons and as we shall see from the explanation about to be offered it is highly probable that the solubility in these cases may decrease more rapidly with increase of molecu1ar weight of the solvent than is the case in the solvents like pentane, hexane and hept~~e and a few higher. Several factors enter into this solubility problem. First we must consider the configuration of the solvent and solute paraffins. Here in the case of solid paraffins we must also remember that the paraffins used have in no case been absolutely pure. that is they have not been composed of only one type of molecules, as for instance, the straight chain thirty carbon atom molecule. They have been mixtures containing molecules which probably vary over a range of several carbon atoms to the molecule. Then, too, they have all been telescoped to a greater or less extent, thereby reducing the length of the chain and increasing the number of side chains. Temperature also enters the problem, as a molecule stably solvated at a low temperature may not be at a temperature a 22.

few degrees higher. Here we have analogy with hydrated

cupric sulfate o

Simple distillation of the paraffin in the absence of steam gave a paraffin which had a melting range half a degree lower than the original paraffin and

whose solubility was about t'wenty one per cent greater

than the o'riginal paraffin. It is probable that by this process the lower molecular weight members were distilled over leaving the heavier, higher melting fraction behind. This result confir~9 one conclusion of other workers. namely that the solubility increases with decrease in melting point of the paraffin. Curves for this paraffin are shown in Plate IV. The distilled paraffin was then heated to about 300°0 in a current of steam but it was not distilled over. The paraffin recovered from the flask had a melting point of 52.5° - 53°0 which was two degrees higher than the original. The change in solubility of this paraffin in pentane. hexane and heptane varied. The decrease in solubility in pentane was about two per cent and in hexane and. heptane four to five per cent. Comparison curves for the original paraffin and this telescoped paraffin in pentane, hexane and heptane are shown in Plate VII. A third treatment was then applied to the paraffin which consisted in distilling the paraffin in a current of steam. This time observations were made on the per cent of paraffin lost and it was found that about 84 per cent was recovered. The amount lost included th&t left in the condenser as well as that in thp, flask which did not distill over. The melting range of this :pa.raffin wa.s 51.5° to 52° and its solubility was less than that of the original lot but was greater than that 0f the paraffin which !lad been treated with steam but not distilled. It will be seen from the compclrison curves that with telescoping tl'1e difference in solubility in pentane t hexane and heptane de creases quita me,rkedly and the curves come closer toeether. D1.l€ t.o insuffici­ ent time further telescoping experiments could not be carried out. No paraffin used in this set of ex­

~eriments had a melting point as high as the one used by Weber in his work although both were derived from the same lot. It is difficult to reconcile two sets of data which give such very different results. However from the da.ta at hand the most logical explanation s~ems to rest in the telescoping process. What the action of steam in this process is, seems to be un­ known but without the presence of steam telescoping evidently does not take place. Telescoping a paraffin means that the length of the hydrocarbon chain is decreased and side chains ap~ear. It appears that

Bufficient telescoping would reverse the order oi solubility of a highly telescoped paraffin in the liquid hydrocarbons. Evidence would seem to warrant the assumption that the solubility of a solid paraffin in a Ij.quid 24. hydrocarbon depends on the degree of solvation of the paraffin molecule. With this assumption as a basis th~ following theory may explain the very different results obtained by various workers on this problem. Let us consider first a straight chain paraffin molecule of thirty or more carbon atoms and also deal with straight chain solvent molecules. ASSUIne now that the maximum amount of solvation of the solid paraffin molecule with any normal solvent hydrocarbon will be ten molecules of solvent to one molecule of paraffin. That is. the ten molecules of solvent can find reom to orl.entate themselves about the paraffin molecule without crowding. Let us 8a~r that six solvated solvent molecules is the IIlinimum numrJer possible to produoe the same order of solubility as the ten 801va.ted molecules. Thus. call the degree of solubility for a paraffin molecule solvated with six molecules of pentane, hexane or heptane, 10 in a.ll theBe solvents. For a molE~cule solva.ted with ten solvent molecules it might be said to be 15. Reducing the solvation :reduces the solubility and below the critical solvation point according to our theory the solubility must decrease more rapidly in the higher solvents than in the lower. If the paraffin molecules solvate ten molecules of the various solvents. pentane, hexane, heptane, etc., the degree of solutdlity will be the sa'!l€ f1.nd VY€ get increasing solu'bility with increasing molecula.r 20. weight of the solvent. This is the order to be expected in a case of this kind. Now suppose the tllirty carbon atom paraffin be partially telescoped, say to the extent of producin~ a chain of twenty seven carbon atoms with three side chaine. Here there will be leas room for solvated molecules to add on. We must now begin to consider the 'size of the solvent molecule as well aR the con­ figuration of the.paraffin molecule. The pentane molecule with five carbon atoms will occuDY less space than the hexane or heptane molecules with six and seven carbon atoms. Our telescoped paraffin may then be able to solvate nine molecluee of pentane while it can take on only eight of hexane. This reduced number of solva.ted molecules will reduce the sOlubility in both pentane and hexane but it will reduce it more in hexane since in that it lost two solvated molecules while it lost only one in pentane. However the lower limit of six solvated molecules has not yet been reached so the order of solubili.ty will remain the same. On further telescoping let us assume that the paraffin can solvate seven pentane molecules but only five hexane due to the larger size of the hexane molecule. The hexane solution has now passed the critical ~olvation point and the solubility of the paraffin in hexane will thus decrease more rapidly 26. in hex8.ne than in penta.ne. Here the reversal of order of solubility appears. If the paraffin should be telescoped to the point where it could solvate only five molecules of pentane and thus reduce the solubility in this solvent con­ siderably, there would not be another reversal back to the original order because at this degree of telescoping only one or two hexane molecules could be solvated and this would make it less soluble. It is unlikely, however, that a paraffin could be sufficiently telescoped to render it entirely in­ soluble. So far we have dealt entirely with straight chain solvent molecules. Considering the curves given it is apparent that the solubility in a telescoped solvent is considerably less in all cases than in the straight chain solvent. This should be expected since the telescoped solvent molecule should occupy more space than the straight chain Aolvent molecules. Now this splitting off of solvent molecules described above may be not only an effect of telescoping but may also be a temperature effect with paraffins not so highly telescoped. Thus with the paraffin partially telescoped but still with sufficient room to hold six molecules of solvent if no particular strain is introduced, the solubility order will not be changed. Suppose now that the temperature is raised. This tends to activate the solvated molecules, particularly the one which may be held moat loosely bound due to 27. the configuration of the telescoped moleclue. and at a critical temperature this slight bond will be ruptured and the paraffin mole Clue will be left without its necessa.rjT quota of s j.x S01vated molecules and the solubility will at once suddenly increase while the solvent curve above and adjacent increases at the regular rate and the order will be reversed. 28.

SUGGESTIONS FOR FUTURE WORK If at some future time some one wishes to further investigate this very interesting problem, it is hoped that the following suggestions may be of value. 1. A pure paraffin of known molecular weight should be synthesized1 if possible in large enough quantities

60 that various methods of-heating could be tried upon it. 2. If this proves impossible an untelescoped paraffin should be obtained from a paraffin base crude oil and used for testing the heat effects on the solid paraffin. 3. Solvents used should be synthesized. 4. The paraffin should be heated in bombs with varying quantities of water and also without water, to various temperatures. not however high enough to crack the paraffin. 5. In the case that the paraffin used is a mixture obtained from a crude 011 the average molecular weight of the paraffin should be determined. 6. Solubilities as obtained by the weight method should be carefully investigated to determine the effeot of the presence of excess paraffin.

1. Uber die Synthese hochmolekularer Paraffin­ Kohlenw8sseretoffe aus Kohlenoxyd. Franz Fischer und Hans Tropsch. Ber. £.Q.. 1330-35 (1921)