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An Investigation of the Reaction i > ci>:' Between Dioxide and in a Fluidised Catalyst Bed

By

Robert W. Bell »■ and

Howard W. Strauss

A THESIS

Submitted in partial fulfillment of the requirements for degrees of

BASTER OF SCIENCE

Department of Chemical Engineering The Rice Institute

August^ 19h9

;-v. v', ACKB0M3GEMKJ

Tiie authors wish to express their appreciation to all those who have aided in this investigation# In particular* they wish to thank the follot/ing:

Dr. G* T. McBride, Jr., for his continued interest and advice*

Professor A. J. Hartsook for the opportunity of carrying out this

investigation.

The Pan American Refining Corporation and Dr. R. H. Eric© for the

financial assistance which made this work possible*

Dr. John T. Smith and the Shell Oil Company for a spectrographic

analysis 13

TABLE OF CONTENTS

Page I. SUMMARY i II. INTRODUCTION g

A. Purpose of Investigation g

B. Theory of Heterogeneous Reactions g

1. Effects of Mass Transfer g

2. Adsorption of a Reactant Rate Controlling g

3* Desorption of a Product Rate Controlling 7

L» Surface Reaction Rate Controlling f

$m Effects of Temperature 8

C. Work of Other Investigators 8

III. APPARATUS AHD PROCEDURE ■ * 13

A. Apparatus £3

B« Materials jg

G. Procedure 16

1. Catalyst Preparation 15

2* Run Technique • 18

3* Analyses 19

a. 19

b. Oxygen 19

c* ■ 20

IV. EXPERIMENTAL RESULTS 21

A. Preliminary Data 21

B. Investigation Proper 20

V. INTERPRETATION OP DATA 43 lli

i! flags

A. Differential Rate Equations Developed for the Theory 48 V of Activated Adsorption.

1. Adsorption of Sulfur Dioxide Rate Controlling. 48

2. Adsorption of Oxygen Rate Controlling. Si

3. Desorption of Sulfur Trioxide Rate Controlling. 62

i*. Surface Reaction Rate Controlling. GS

5. Effects of Mass Transfer. 66

B. Empirical Equations 67

C. Integrated Equations 67

VI. CONCLUSIONS 62

VII. APPENDICES 65

A. Summary of Experimental and Calculated Data 64

1* Original Data 6$

2* Calculated Reaction Rates 76

B. Details of Apparatus 60

1. Purification of Gases 61

2» Metering of Gases 61

3* Preheater 81

iio Reactor 8$

5* Solids Separator 07

6. Photograph of Apparatus 88

C. Chemical Analysis of Silica Gel 60

D» Sulfur Dioxide Analysis Technique gg

E. Calculation of Conversion gg

F. Reaction Equilibrium Constant Versus Temperature Go Nomenclature

II. Literature Cited

I. Location of Original Data INDEX TO FIGURES

No* Title Page

1. Schematic Flow Diagram 14

2. Typical Temperature Gradients in Empty Reactor 17

3* Typical Temperature Gradients in Loaded Reactor IS

It* Conversion Gradients in Empty Reactor 25

$» Conversion Versus Time 30

6. Conversion Versus Reciprocal Space Velocity - Series A 52

7» Conversion Versus Reciprocal Space Velocity - Series B gg

8* Conversion Versus Reciprocal Space Velocity - Series C 34

9» Reaction Rate Versus Reciprocal Space Velocity at U00°C gg

10, Reaction Rate Versus Reciprocal Space Velocity at i*5G°C 37

11. Reaction Rate Versus Reciprocal Space Velocity at £Q0°C gg

12* Product Composition Versus Reciprocal Space Velocity - 39

Series A at )400°C

13. Product Composition Versus Reciprocal Space Velocity - 40

Series A at ii50°C lit. Product Composition Versus Reciprocal Space Velocity - 41

Series A at 5>00°C

1$. Product Composition Versus Reciprocal Space Velocity - 42

Series B at itOO°C

16* Product Composition Versus Reciprocal Space Velocity - 45

Series B at bS0°0

17. Product Composition Versus Reciprocal Space Velocity - 44

Series B at 500°C

18. Product Composition Versus Reciprocal Space Velocity -

Series C at iiG0°C ■trl

No. Title Page

19. Product Composition Versus Reciprocal Space Velocity - 40

Series C at itSO°C

20. Product Composition Versus Reciprocal Space Velocity - m

Series C at £00°C

21. Reaction Rate Versus Reciprocal Temperature - Series A ss

22. Reaction Rate Versus Reciprocal Temperature - Series R m

23. Reaction Rate Versus Reciprocal Temperature - Series C m

21* • Orifice Calibration, Oxygen 0-1 82

2£. Orifice Calibration, Oxygen 0-3 as

26. Orifice Calibration, 8-3 84

2?. Reactor Desigd Details 86

28. Photograph of the Apparatus 89

29. Reaction Equilibrium Constant Versus Temperature 99 yii

IMDEX TO TABLES

Ho. Title Rige

1. Silica Gel Particle Size Distribution IS

II. Original Investigation of Catalytic Activity of Empty 2S

Reactor and Unplatinised Silica Gel

III. Comparison of Reactor Wall Activity at Beginning and End 24

of Investigation Proper

17. Conversion Gradient in Empty Reactor 26

7. Investigation of Effect of Reducing the Reactor Wall 20

tilth

■ VI. Effect of Time on Conversion 31

VII. Average Feed Compositions 29

VIII. Initial Compositions and Reaction Rates 00

IX. Constants for the Surface Reaction as the Rate Controlling gg

Step

X. Summary of Experimental Data - Series A 33

XI. Summary of Experimental Data - Series B @©

XII. Summary of Experimental Data - Series C fg

XIII. Reaction Bates and Partial Pressures at ijOQ0C fg

XIV. Reaction Rates and Partial Pressures at h$0°G 77

XV. Reaction Rates and Partial Pressures at 5GG°C 73

XVI. Reaction Rates at Constant Product Composition 70 I. SUMMARY

Date are presented on the rate or oxidation of sulfur dioxide on a platinized silicia gel catalyst in a batch fluidised bed* The variables investigated were feed composition, space velocity, and temperature*

The pressure was approximately one atmosphere.

The data indicate that the rate of mss transfer was a substantial portion of the total resistance to reaction. The lack of suitable data for isolating the respective effects of mss transfer and chemical re¬ action prevented a correlation of the data*

An apparent activational energy of 23,500 calories per granwaol was established from reaction rate data alone* This compares with a value of 20,000 calories per graia-mol reported by other investigators. II. IRTEODUGTJOH

A» Purpose of Investigation

It was the purpose of this investigation to study the kinetic rela¬ tionships in the oxidation of sulfur dioxide to sulfur trioxide over an active catalyst by employing a wide-range of temperature, feed composition, and space velocity* In view of the highly exothermic na¬ ture of the reaction, a batch fluidised system was chosen for the pur¬ pose of maintaining isothermal conditions.

B. Theory of Heterogeneous Reactions

It is a generally accepted hypothesis that when catalysed by a solid, a gas phase chemical reaction actually occurs on the surface of the catalyst and involves the reaction of molecules or atoms which are chemically adsorbed on the active centers of the surface. In this re¬ spect the catalyst functions to increase the rate of reaction through its ability to adsorb the reactant gases in such a form that the activa¬ tion energy necessary for reaction is reduced below that required for the uncatalysed reaction.

The development of rate equations based upon this theory of activa¬ ted adsorption has been adequately summarized by Hougen and batson (1).

The succeeding equations have been taken from the work of these authors.

If the chemical change in a heterogeneous reaction occurs between molecules or atoms on the active centers of a catalyst,the overall pro¬ cess of converting reactant gases to product gases may be classified in¬ to five separate steps (1): a

1® The mass transfer of reactants from the main gas phase to

the surface of the catalyst®

2® The activated adsorption of the reactants on the active

centers of the catalyst®

3® The surface reaction of adsorbed reactants to fora adsorbed

products.

h» The desorption of the product®

5® The mass transfer of products from the surface of the cat¬

alyst to the Gain gas phase®

The rate at which each of these steps occurs is important in deter¬ mining the overall rate, but it is generally sufficient to assume that the rate is controlled by one of the above steps, all others being considered at equilibrium®

1. Effects of Mass Transfer

The rate of mass transfer of the reactant and product

molecules to and from the surface of the catalyst is de¬

termined by the flow characteristics of the system such as

mass velocity of the main fluid stream, catalyst particle

3ise, and the diffusions! characteristics of the fluid.

In the batch fluid catalytic process the velocity of i flow is limited because of catalyst carryover® The mass

velocities, in general, are comparable to those in a fixed-

bed system operating at low mass velocity® Such a situa¬

tion is particularly conducive to large mass transfer

effects, especially if the rate of the surface reaction is

high® The rate of transfer of a component from the main fluid stream to the catalyst interface my be expressed (2) by the equations

rA = ApG^PA (i)

a(BTU)J^ Pgf where = rate of mass transfer of component A, mols per unit mass of catalyst per unit time Ap - gross external area of the catalyst per unit mass G = mass velocity per total unit cross-section

^pA = Difference in partial pressure of component A in main gas phase and at the catalyst surface, % z Mean molecular freight of the gases = log-mean partial pressure of gases other than component A in the gas film a s interfacial area per unit volume of packing HTU s height of a transfer unit Values of a(HTU) have been correlated as function of ir the diffusing component for relatively large particles

(3S its 5)s but no data are available for the particle size range generally encountered in fluid-bed work, thereby rendering the calculation of interfacial partial pressures impossible® • It is, in general, sufficient to compare reaction rates at two or more different values of oass velocity at constant apace velocity to determine if the rate of mss transfer is a significant portion of the resistance to reaction* In the operation of a bench scale fluid unit* however* the varia¬ tion in reaction rate resulting from differences in cat¬ alyst-gas mixing characteristics at different mass veloci¬ ties obscures the mass transfer effects* Although it has been reported (6) that gas back-mixing is not likely to. be a serious factor in small fluidized beds with large length to disaster ratios* the mixing effect cannot entirely b© ignored*

In general, the degree of back-mixing varies with the mass velocity of the main fluid stream* catalyst particle size distribution* and catalyst loading. Therefore* con¬ centration gradients can exist to varying degrees and the magnitude of such gradients has a profound effect upon the rate of reaction*

Previous experience has indicated that the depth of catalyst bed is an important factor to be considered with respect to back-mixing* Therefore, for this investigation a constant solids holdup was mintained in the reactor at all times* This was done by diluting the active catalyst with inert material* Although, the superficial gas velo¬ city varied with temperature? the mass velocity was prac¬ tically constant in all work'

Under conditions such that the degree of back-mixing is constant or negligible, the effects of mass transfer can be, in general, reflected in the temperature coeffi¬ cient of reaction* That is to say, for a reaction con¬ trolled by the rate of chemical processes, the logarithm of the temperature coefficient should be a linear function of the reciprocal absolute temperature according to the

Arrhenius equation® If the rate of mss transfer is of importance, this equation is not valid because the diffu¬ sion coefficient is a function of the square root of tire absolute temperature*

For mazy reactions, however, the resistance to mss transfer is negligible and the partial pressure of a com¬ ponent in the main gas stream can be taken as that at the surface of the catalyst without appreciable error*

#

Adsorption of a Reactant Rate Controlling

If for a bimolecular — mono-molecular reaction

A + B a the assumption is made that the reaction takes place be¬ tween adjacently adsorbed molecules, it can be shown (2) that for the adsorption of a reactant as the rate con¬ trolling step that r - % k (1 + % + %j % + »Hi % + aji

aBi K

All activities are interfacial activities* 7

It can be seen from equation (2) that the initial rate

of the reaction, where ajy. s 0, is decreased by increased

activity of component B.

Also, it can be shown (2) that where a component is

dissociated upon adsorption, equation (2) as well as the

succeeding equations can be modified to account for such

dissociation by taking the square root of the activities

and adsorption-equilibrium constants wherever either ap¬

pears in the equation,

3, Desorption of a Product Rate Controlling

For the desorption of a product as the rate controlling

step, the rate of reaction can be expressed by the equation:

(3) In this case the overall equilibrium constant appears in both

numerator and denominator of the multiplying fraction.

Under conditions favorable for the forward reaction, where

K is large, the rate becomes essentially independent of

the activities of reactants or products, approaching lcR l/KR

as a limit.

!i. Surface Reaction'Rate Controlling

For the rate of the surface reaction as the rate con¬

trolling step the follor/ing equation has been developed: $• Effects of Temperature

Each of the equilibrium and velocity constants of

the previous rats equations is a function of temperature

and can, in general, be represented (2) by the equations

In K = -4H° +. />S° (S) ~w ~ir

The standard enthalpy change A H°, and the standard

entropy change A $° may be considered constant over narrow

temperature ranges.

The reaction velocity constant can be represented by

the Arrhenius equation (7)

d (ln k) _ Ea_ (6) dT RT2

where Ea is the apparent energy of activation. For the

case of no retardation by the products, the minimum energy

an adsorbed molecule must acquire before it can react is

given by:

E = Ea+V (7)

where A is the heat evolved when one mol of the reactant

gas is adsorbed. If a product has a retarding influence

then

/

E = Ea + /\-A (8)

/ where A is the heat of adsorption of the retarding gas. Thus* the influence of temperature on the velocity of a

heterogeneous reaction is dependent on the heats of ad¬

sorption as well as the energy of activation* Consequent¬

ly* the rate may decrease with an increase in teuperature

when the energy of adsorption of the reactants is high*

* 0* Work of Other Investigators

Early in the twentieth century Bodenetein (8) investigated the me¬

chanism of the reactions

2SC2 + C^ZSO (?)

occuring at the surface of the platinum catalyst* It was found experi-

' mentally that the above reaction did not proceed according to a trimo-

lecular reactions but that the velocity of Hie reaction was proportional

to the sulfur dioxide concentration* inversely proportional to the square

root of the sulfur trioxide concentration* and independent of the oxygen

concentration according to the equation

(10) where a a sulfur dioxide originally present* mols/liter

X «r sulfur trioxide converted in t minutes

k a reaction velocity constant

A variation in catlyst activity did not change this relationship. At very low oxygen concentrations the rate of the reaction v/as found to

decrease in a manner inconsistent with the above equation*

The early work of Kneitsch on the rate of oxidation of sulfur dioxide lias been discussed and interpreted by Lewis and Rios {?)*

Realising the inadequacy of existing data, these sane authors obtained

new data (10) on this system using a platinum catalyst* Previous reac¬

tion rate equations were found to be incapable of interpreting the new

data* 1'he new equation

(11) dt

where

—- ® time rate of decrease of sulfur dioxide dt

b - reaction velocity constant

re * ratio of concentration of sulfur trioxide to sulfur

dioxide at equilibrium

r = ratio of sulfur trioxide to sulfur dioxide at time t

x « sulfur dioxide concentration at time t

was shown to represent the data accurately* Mo attempt was made to ex¬

plain the mechanism of the reaction*

The data upon which Lewis and Hies based the above equation were

analyzed by Uyohara and Batson (11) according to principles of the theory

of activated adsorption for chemical reactions catalysed by solids*

These investigators invalidated all previous data as material for the

development of a general rate equation because in each case a system was

employed in which diffusional concentrations and temperature differences

were difficult to predict® The data of Lewis and Rios* however, were

found to be well represented by an equation of the type li

-AH° ^Ole “ /p S' -

1 + 2 ( J \ \ * %o3 ho) \

This type of equation is based upon the assumption that the rate control¬ ling step is the surface reaction between adsorbed sulfur dioxide and atomic oxygen.

Several references have appeared in the literature to Russian,

Chinese, and Japanese investigations of the rate of the catalytic oxida¬ tion of sulfur dioxide on various catalysts. Boreskov (12) established the equation as _ % /xy°*2g) % /§££_ (13) dt y gO»S J I y0»25

where time is expi’essed by t, and X, X, and % are respectively the partial pressures of sulfur dioxide, oxygen, and sulfur trioxide. This equation is accounted for by assuming the rate of adsorption of sulfur dioxide by platinum to be the rate controlling step.

In the presence of catalysts this same investigator found the rate to be expressed by

d3 „ KX dt g0.8 m

Since in this equation the rate was directly proportional to the oxygen concentration, and sulfur dioxide and sulfur trioxide had equal and oppo¬ site effects, it was assumed that the adsorption of oxygen was the rate controlling step. Krichevskaya (13) developed a rate equation for the oxidation of sulfur dioxide over a pure vanadium pentoxids catalyst. His equation was of the type

a W /302ft /pgft ^ K2 /^ft x (15) dt ft°3) /sojji

The rate was found to be determined by the rate of surface reaction between adsorbed sulfur dioxide and adsorbed oxygen.

Hung-Yuan Chang and Te~Eui (Hi) found that the mechanism of the sulfur dioxide oxidation reaction in the presence of a vanadium cat-

1 alyst differed from that in the presence of a platinum catalyst.

These investigators proposed the equation

(16)

to correlate the vanadium oxidation data. This differs from the equation for the oxidation in the presence of platinum only in the exponent of the sulfur dioxide term. The terms **e and r have the same meaning as those in equation (11) as proposed by lewis and liies.

Hurt (15) has correlated sulfur dioxide oxidation data including a term for mass transfer effects.

The proposed correlations and postulated reaction mechanisms show the inconsistency and state of uncertainty surrounding ^he system under coib- sideration. Moreover, all reported investigations have been carried out in static or fixed-bed flow systems. In no reported case has a fluid-bed unit been used for this particular system. ±3

m. APPARATUS AM0 PROCEDURE

A. Apparatus

The experimental equipment used in this investigation consisted of an electrically heated 2" I*P.3* iypa 310 steel reactor with attendant

gas metering, preheating, and sampling devices* Temperatures in the reactor were recorded by a Leeds and Uorbhrup Company ten point Speedosax.

The temperature readings could bo estimated to one degree Centigrade, but were readable to only t 3 degrees Centigrade basis the manufacturer’s

specifications*

A schematic flow diagram is shown in Figure 1, The gases were metered with calibrated capillary orifices, preheated in an electrically

tested stainless steal coil, passed into the reactor, then into a solids

separator, and sampled prior to venting to the atmosphere* Details and a photograph of the apparatus are given in Appendix B, pages to gg .

B« Materials

Sulfur Dioxide ? Obtained from the latheson Chemical Company? 1*>0 pounds of liquid, industrial grade specified to be 99*90$ sulfur dioxide,

0.10:1 tsiter.

Gxgrgens Houston Oxygen Corapary Incorporated? analysed 99*$% oxygen*

Hitrogent Houston Oxygen Coatary Incorporated, and the Magnolia Airco

Gas Products Company? analysed 98.7 to 99*99$ nitrogen,

l?ra>latinised Silica Gals Davison Chemical Company? Grade Code 12,

28*»20O mesh ground to particle sis® distribution specified in fable 1* 14 Table I Silica Gel Particle 3i.se Distribution Tyler Screen Heah Weight % ~35 to +B 0.9 - ltd to + 69 k.9 - 69 to +100 35.0 -100 to + 1#0 37*9 -150 to + 200 21.3 100.0 Ota saaaufaeturer claims that there is no change in sise or shape of the particles as they adsorb vapors. She chemical composition of the gel is given in Appendix C3 page . . Platinised Silica Pelt The above silica gel was impregnated with approximately 0.3 wight percent platinum by the J. T. Baker Company. The particle siae distribution was the same as shovm in Table I.

C6 Procedure 1. Catalyst Preparation The unplat inis ed/ait d platinised silica gel wore dried over¬

night at 115°0. The SQESB total weight of the platinised and unplatinised gel was used in all runs* Therefore, the proper amount of platinised gel for a given space velocity was weighed out and onou#i of the inert gel added to bring the total weight up to the arbitrarily chosen value of J60 grams. 2* Run Technique The reactor was charged by dropping the solids through the l/2M I.P.3, pipe extending from the top of the reactor into a snail stream of nitrogen at iiOO°C, The catalyst and inert gel was then dried at 500°C for one hour. IS

After the drying period, the proper gas composition was metered into the reactor, and the necessary temperature

and pressure adjustments were made* The pressure on the system was maintained at nearly a constant value by adjust¬ ment of a control valve on the product vent line. However,

the pressure control was not sufficiently exact to enable

duplication of feed composition using the capillary orifice method of controlling flew*

The temperature was controlled by manual adjustment of

the auto-transforaers* Typical temperature gradient curves

for the empty and leaded reactor are shown in Figures 2 and

3. In Figure 3 the constant temperature points are positions

in the bed*

After the reactor had bean at constant temperature with

the proper feed gas composition for ten to twenty minutes,

samples of feed arid product gases wore taken and analysed

simultaneously for sulfur dioxide content* At the same tins

a sample of the product gas was scrubbed free of sulfur

dioxide and sulfur trioxide in caustic solution and retained

for oxygen analysis* The requisite readings and samples were

taken in fifteen to thirty minutes*

An attempt was made to make all runs for a given space

velocity in a period of ten to twelve hours in order to mini¬

mise the effects of changes in catalyst activity* Usually

runs were made at *?00oS, Iif?0°G, and hOO°C, the high temperature

runs for the various feed compositions being Bade first* The 17

FIGURE 2

TYPICAL TEMPERATURE GRADIENTS IN EMPTY REACTOR FIGURE 3

TYPICAL TEMPERATURE GRADIENTS IN LOADED REACTOR

550

w~A 500 1/ — o “4

9

^4 450 Jk . . 4k A

4 ^ ~ 9 —c ‘ 400 Mk. ft . ... 4k . ii

350

1

300 0 10 20 30 40 50 60

DISTANCE FROM INLET OF REACTOR, INCHES space velocity was changed by varying the weight of active

catalyst, keeping the feed rate constant.

After each ran the small amount of 3olid material which

had been blown over into the solids separator was returned to

tl’io reactor.

. At the termination of a scries of runs tho catalyst was

dropped out of tho reactor by removing the l/2n plug from tho

* nipple extending below tbs reactor inlet.

3* > Analyses

a. Sulfur Dioxide

The well known Reich test was used for the analysis of

sulfur dioxide in both the feed and product gases, Tho

Reich test consists of titration of an solution

with sulfur dioxide ©is which is free of sulfur trioxide

using a starch-iodide indicator. A detailed description

of the technique used is given in Appendix D, pages gg

94 . Work by Drags and Greenan (16) indicates that the

test is ideally suited for the low concentrations used in

tMs work. Their results showed a reproducibility of 0.1$

for 12% sulfur dioxide* However, in this investigation

the repeatability of analyses appeared to be better than

0.1# for such concentrations.

Conversions based upon inlet and outlet concentrations

were calculated according to the procedure outlined in

Appendix B.

b. Oxygen

The oxygen content of the product gases was determined 'by Qrsat analysis of samples free of sulfur dioxide

and sulfur tricedde* These gases were removed from

tbs sample by bubbling the product gas through an

aqueous sodi.ua hydroxide solution containing a trace

of stannous chloride. The scrubbed samples warn

collected over aa aqueous 20$ - 5$

solution. A precision type Fisher

analyser with sorcery as the confining liquid was used

for the analyses5 the oxygen being absorbed in Qxsorbent

a costaerelal preparation.

. Sulfur Trioxida

Ho analyses were mde for sulfur tricesl.de because

no simple* rapid method is knosm for the analysis of

snail amounts of sulfur trioxido in the presence of

sulfur dioxide* IV. EXPBEBSIITAL RESULTS

This section lias been subdivided into two parts, preliminary data and the investigation proper.

A* Preliminary Data

Preliminary investigations, using fluidisation equipment constructed of glass, indicated that silica gal of the petiole size range previously specified in Table I, could be satisfactorily fluidised at superficial velocities from 0»h to 0.7 feet per second.

A ground and sized commercially available vanadium catalyst was found to be unsuitable for fluidization purposes because of an agglomeration of the particles.

In view of the fact that most previous laboratory investigations of the rate of the catalytic oxidation of sulfur dioxide had been made using platinum catalysts, a platinized silica gel catalyst was selected for the present work. Moreover, silica gel alone had been reported (17) to lave no catalytic activity for this reaction.

Prior to the introduction of the platinised catalyst into the reactor, runs were made to determine the extent of conversion produced by the empty reactor and the unplatinized silica gel. These data are in Table II. The conversion was negligible in aH but the run at S>Q0°C. As previously noted

Holmes ot al (17) had found silica gel to have no catalytic activity, and the extent of the uncatalyzed reaction at temperatures of hOO to 0O°G is known to be very small.

After the termination of the investigation reported in the following section, a recheck was made on the data reported in Table II. Hie latter data shaved an appreciable conversion at a temperature as low as I|00°G in the empty reactor. Hie date indicate that during the period of operation TABLE II

ORIGINAL INVESTIGATION OF CATALYTIC ACTIVITY OP

EMPTY REACTOR AND UNPLATINIZED SILICA GEL

Empty Reactor UMplatlnized Silica Gal

Ran No* 1 1 2 3 Temperature* °G 38U koo U51 503

Pressure at Outlet, ATM. 1.06 1.06 1.06 1.06

Pressure at Inlet, ATM. 1.06 1.10 1.10 1,10

Feed Composition, Mol % 5.0? h.9h 5.06 U.99 15.5 15.7 15.5 15.8

N2 7 9.U 79.3 79.5 79.3 Total Mols Feod/Hr* .0501 .0510 .0506 .050? Conversion, % 0.2 0 0.2 1.3

Product Composition, Mol %

so3 0.01 0.0 0.01 0.06

so2 5.06 h.% 5.05 U.93 Og 15.5 15.7 15.5 15.8 % 7 9.k 79.3 79.5 79.3 Mols SO2 Converted/Mol Feed .0001 0.0 •0001 •0006

Mol % 02 (SOj-SOgj Free), Calculated 16.3 16,5 16.3 16.6 Mol % Og (SO3-SO12 Free), Analysis 16.6 16.U 16.6 16.2 following tbo initial addition of platinum to the reactor, the reactor walls had acquired catalytic activity for the oxidation reaction.

There was no evidence to indicate that this activity had been accumula¬

tive, nor was it possible to predict when the activation occurred. Con¬ sequently, check runs were made on one of the runs initially made for the investigation reported in the next section. The results of these runs are sham in Bible III. These data indicate that the activity of the reactor

«a31 must have remained essentially constant over the period of tic© during which the bull: of the reported data were taken.

An investigation was then made to determine the approximates location

of the caialyiically -active substance* Figure k and Table IF show the results of an attempt to establish a conversion gradient in the empty reactor . Although these data hare the disadvantage of non-iso thermal conditions they indicate that only the lower portion of the reactor had appreciable activity.

ifext an Investigation was made to determine the cause of the activity

The possibility of an coating on the reactor wall was first con¬ sidered. Talley (18) found that raild steel which had been oxidised at

60G°C for 2h hours was an appreciably active catalyst. In his work, how¬ ever, the oxide film was thick enough to be easily visible. In the present work, inspection of the thermowells which had extended into the reactor revealed no visible oxide.

Gulbranoen (24?) studied the oxidation of polished 18/Q stainless steel at 55Q°C and found that the major portion of the oxidation recurred witW.ii twenty minutes and subsequent oxidation occurred very slowly. Ho - studies of Type 310 stainless steel, the reactor material, were found in the literature. Basis Gulbranaen,s work, however, it is believed that TABLE III

COMPARISON OP REACTOR WALL ACTIVITY AT BEGINNING AMD END OF INVESTIGATION PROPER

mir Run No. A-2-a* h-2~a A~2~a's^:~

Temperature 5, °C 800 800 800

Pressure at outlet, ate. 1.03 1.01 1.01

Pressure at inlet, atm. 1.0? 1.05 1.05

Feed Composition, Mol %

SOg 5.1*1 5.61 5.72

02 15.8 15.8 15.9

% 78.8 78,6 ?8.8

Total Mols Feed/Hr* .0516 .0513 .0514

Superficial Velocity, Ft./ Sec. 0.52 0.52 0.52

Weight of Platinized Gel., Lbs. 0.155 0.155 0.155

Conversion, % 17.6 18.2 m.o

Product Composition, Mol %

SO3 0,95 1.03 0.80

so2 1*48 8.61 8.98

°2 15.8 15*8 15.6

N2 79.2 79.0 78.7

Mols S02 Converted/Mol. Feed .0G?5 .0102 0.0080

Mol % Og (SO3 - SOjj Free), Calculated 16.3 16.3 16.5

Mol % 02 (SO3 - SOg Free), Analysis 16.1 16.3 16.3

% run initially made for the investigation proper. ^Ituns made at the end of the investigation proper. MOLS S02 CONVERTED/MOL FEED AVERAGE FEEDCOMPOSITION-MOL% DISTANCE FROMINLET OF REACTOR,INCHES CONVERSION GRADIENT EMPTY REACTOR N 78.6% S02 9.037S 02 12.4% 2 FIGURE 4 IN 25 TABLE IV

CONVERSION GRADIENT IN EHETO REACTOR

Sample Point No,* 1 2 3 U 5 6

Sample Point Temperature, °C 1*11 1*80 505 510 $2h

Pressure at outlet, atm. 1.02 1.02 1.02 1.02 1.02 1.02

Pressure at inlet, atm. 1.03 1.03 1.03 1.03 1.03 1.03

Feed Composition, Mol %

SOg 9.05 9.01* 9.00 9.00 9.03 9.09

°2 12,1*. 12.1* 12.1* 12.1* 12.2* 12.1*

N2 78.6 78.6 78.6 78.6 78.5 78.5 Total Mols Feed/Hr, .0501* .0505 .0503 .0503 .0502 .0502

Conversion, % 2.3 8.5 9.2 19.3 20.1 22.5

Product Composition, Mol %

SO3 0.21 0.78 0.83 1.72 1.81* 2.07

so2 8.81* 8.30 8.20 7.35 7.28 7.U

°2 12,1* 12.0 12.0'11.6 11.6 11.5 % 78.6 78.9 78.9 79.3 79.3 79.3

Mols S02 Converted/iiol Feed .0021 .0077 .0083 .0171 .0182 .0205

Mol^OgCSQ-j - SC^ Free), Calculated 13.6 13.2 13.2 12.8 12.8 12.7

Mol^G2(S03 ■» SOg Free), Analysis 13.5 13.2 13.1 12.6 12.5 12.1*

* Sampling Points* 1.- Preheater Downstream. 2. At Thermocouple No. 6 (Lowest Thermocouple in reactor) 3, At Thermocouple No. 5 It. At Thermocouple No. 1* 5. At Thermocouple No. 3 6. At approximately Thermocouple No. 1 Position, Internal Sampling.* larger conversions would have been observed in the empty reactor during the original runs if an aside film ted teen the active catalyst. More¬ over, reduction of the reactor wall with hydrogen at £>OG°C for as long as twenty hours had no effect on the activity observed. In view of these data, which are shown in Table ¥, and the fact that no conversion was observed in the original runs, it was concluded that unless an oxide fils had foraed extremely rapidly during the runs immediately following the hytlrogori treatment, ted no observable catalytic effect.

The possibility of a platinum deposition on the reactor walls was next considered. It was realised that platinum could have been removed from the surface of the catalyst tgr attrition. It is possible, but not probable, that such platinum would diffuse into the - alloy.

However, a spectrographic analysis of the surface metal of two thermo¬ wells which ted extended into the catalyst bed revealed a platinum con¬ tent of 0«006£ by weight, or the equivalent of ,00$ iag/c*a.® of thermowell surface. A semi-quantitative estimation of the platinum content based upon the data alone indicated the equivalent of 0.016 mg./cm. of surface considering only the lower section of the reactor. In view of the fact that the analysis was specified to bo accurate to one-fourth or four times the reported value, it is believed that the presence of platinum was responsible for the observed activity. Furthermore, it is believed that the amount of platinum was essentially constant throughout the investiga¬ tion proper.

All runs with a particular batch of catalyst wore made within a period of ten to twelve hours, fo determine the stability of the activity of the catalyst over this short period, a 3©ries of runs were made inter- 28

TABLE V.

1HVESTIGATI0N OF EFFECT OF REDUCING

THE REACTOR WALL WITH HYDROGEN*

Rim Mo.^ 1-b 2-a 2-b

Temperature, °C $00 500 500 500

Pressure at outlet, atm. 1.02 1.02 1.02 1,02

Pressure at inlet, ate. 1.06 1.06 1.06 1.06

Feed Composition, Mol %

so2 8.86 8.72 8.73 8.61*

°2 11.8 11.8 11.8 11.8

% 79.3 79.5 79.5 79.6 Total Mols Feed/Hr. •0509 .0507 .0510 .0512

Conversion, % 16*$ 18.3 16.1* 18.2

Product Composition, Mol $

SO3 1.1*7 1.61 1.14* 1.58

so2 7.1*6 7.18 7.35 7.12

°2 11.2 11.1 11.2 11.1

% 79.9 80.1 80.0 80.2

Mols S02 Converted/Mol Feed .011*6 .0160 .011*3 .0157

Mol % 02 (SO3 - SGg Free), Calculated 12.3 12.2 12.3 12*1

Mol % Og (SO3 - SOg Free), Analysis 12.0$ 12.0 - 12.0

AH Runs made with unplatinized silica gel Tor good temperature control.

** Run Mo. t 1. Runs before introduction of ijydrogen.

2-a. Run after passing small rate of pure hydrogen through reactor foi one hour.

2-b. Run after passing small rate of pure hydrogen through reactor for twenty hours. slttontly at UOO°G with ona feed composition using ona batch of catalyst ever a period of £*> hours* Figure $ is a plot of conversion versus time* Table VI contains the tabulated data* Although the data are erratic, tie activity appears to have remained constant for at least 25 hours and probably longer* In fact, the date indicate teat dropping out and re¬ charging the catalyst ted little or no effect upon the activity. It is realised teat temperatures higher than hOO°C might cause a decrease in activity in a shorter time, but subsequent data showed no evidence of this* B* Investigation proper Tm runs in this investigation can be grouped into three series each having a different feed composition as shown in Table VII*

Tables VXI Average Feed Compositions, Mol % Series A B 0 '

so2 5.65 8.80 13.71 °2 16.0 11.8 7.18 h2 78.6 79 di 79.1

tech series was run at five space velocities and at temperatures of !;(%)<, 1*50 and 500°C. The average pressure was l.OU atmospheres. Both calculated and observed date for these runs are included in

Appendix A, pages 64 to 74. In Figures 6 to 8 the conversion, expressed as raols of sulfur dioxide converted per mol of feed is plotted versus reciprocal space velocity* Reciprocal space velocity is defined as pounds of catalyst per mol of feed per hour. These plots show temperature as a parameter and include - CONVERSION VERSUS TIME \5$. cb M @ COO$25 O CM O rHfc*- O O)COCM O I'iflOO) H g I CM 9 § a CO § 3 to to W O W £ 9 o 1 iH O rH CM o A o o o (EKM TXO/dBS.'SSMqOZOS S10H u 0 rH O o 0 o o 0 o o 00 o u A J * o CO

° ORIGINAL CHARGE o s

• ORIGINAL CATALYST RECHARGED o CM o AFTER BEING DROPPED OUT 1 CM o to o o in o CO O b- o 30 EFFECT OF TIME ON CONVERSION 1 H p£# §j Sw M r n o n a, % 0 en-o n b vo caCM Pi HN- os « :• xnos i <6 ❖ & £ V0 M3 xn 3 XA lA CO XA 04 CM ca cn Os CM o\ Os o cn CM rn m ft CM 3 •«tf •s 3 •d fH P *§ 0 O o PHH Pi H Pi rH Pi HrH Pi rlH 4Hrl Pi HIrH 4H H P rlH GO o \A rH CO o CM O C\ •« 0S • OS o O • P 0 fi B £«J P« 0CO ^ CDG> , HXA CM XA CM VO CM tA HXn H 1A r o *H 0 •d •5l §<5^ m P CM0 0 1 I a \ § .33 0 d v s vO NHOIAA O ••VAH® vO XAOV\H Pt HC"—®O-CT 4Hh- «O •PF H£■*-•O -PCD \AO\AtA PH N®OH 03NCMO tAsO PHN •OCM PHN •OCM PT Hc-•OCM caAOOlAA PCVH OXAXA \A rH•OH XAH C—•OCM XA HN•O XAH N«OCM CD •«IAH® \AHN •OH lA ®®1AH 'MNHN •OCM XA Hc—•OH IAH iN®OH U\HN •OH CM NAO\ACs Os ••XAH® CM OsOBXA CM CDOXApj- 5-* CDCAOXAH H •»XAH H •\A® O •®\AH OsC-CAOlAtA rH ®XA» N ®•XAH O ®®ir\H• C— •PtH*• NOHOIAO 0\ •XAH 0s OvOsOXA NC\U\H XAPT m OSPIOsXACM Os OsHHXA o •®inH Q •XAH O ®XAH• O •tlAH • tAONO®\A • VAOsO«CD « XAOsO®v0 • XAOsOcA • XAOSO®vQ • XAOsOvQ ® \AOsOvQ otAOs O*Os • XAOSO • XAOsO4A ® XAOSO•H • XAcaO*XA • \AOsOCM •vO OsO*P • XAOSON ® XAOsO•vQ . HXA vO XA CO iA PJXA XA1A Pt XA CO lA OS tA CA\A ON XA Os XA CAXA O XA mxn 1 o. H I 5 ♦HI u O p ft T3 o w 0 O co VI QFACM *§° £ O jn aCO VI H ♦H 'd H P P S 0 o a 0 O PUO O 9 s PlvO fAXACOCMXA vO OsCMCDHOXA PfrvO PtXA^CMXA CD CM•O CO CM•O® CD CAvOCMC-PlvO CO N•O® CO H•O® OPlPtvO HCMvD DCDvOpOpp CD CA•O XA CAr—COt^-p^vO CD CMXAvOHfAO H OsCAt—FAXA CM HCD• O •H CM PlvOqXA OsO •O CNOsptfptt-PtXA A- 03«•O H FAr*—• HplACO OsCMxn HAHN •H HN •H Os CMPiXAO Os 0\XAOsCOCMXA (A £'■*-COPjfAXAvD H CO«•® HPH N•H HtnHN •H H

CO

CM rH

EH CO a Q W EH « O O

O

CO w& o o CO

HHg ow P-* CO

CO o o

M O

CM

O IDo K**o o tO oCM o rH o O • • « e e •

aaaa im/asimMoo so3 snow 33

CO H

CM

en CO o w % w O o 3 3 o

w o o *3 00 wg o £ CO

<3 o CO o # P-*

CM

O O CO CO ^ CM o rH O O O O o • • o • N •

aaaa low/aaiHaMoo 2os snow CO

CM

EH CO a Q < W EH W o

PQ o

EH o CO S g pq o

<3 CO o o AS p* M O w

CM

O co co ^ CM O o o o O O • • • aaai loK/asiHaMoo 2os siow. the eqtiilibrium degree of conversion., as calculated from thermodynamic relationships* for each feed composition and temperature. The overall equilibrium constant (20) for the reaction '

SOg 1/2 Og *=^S0j is included in Appendix F» page 0? * In no case was equilibrium con¬ version approached experimentally* She slopes of these curves represent the rate of* oxidation of sulfur dioxide (mols of sulfur dioxides converted per hour per pound of catalyst)* 7m rate of oxidation as determined by graphical differentiation'is plotted versus reciprocal space velocity in

Figures iSk tollifor each taaperature with feed composition as a para¬ meter.

Product gas coiaposition3, expressed as mol fractionss are shown as a function of reciprocal space velocity in Figures 12 to 20 for each feed composition and each temperature*

It is possible with these curves to determine the instantaneous re¬ action rates and corresponding gas compositions at a specified reciprocal space velocity*

It should bo noted that in each of the above mentioned figures the curves have been extrapolated to conditionsof zero conversion* The vertical dotted lines in each case correspond to conditions observed as a result of platinum deposited on the reactor wall, the observed space velocities are thereby adjusted to include this residual wall effect* FIGURE 9

REACTION RATE VERSUS RECIPROCAL SPACE VELOCITY

TEMPERATURE 400° C

il

g o o CVIO O CO 3

3

M S3

LBS. CATALYST RECIPROCAL SPACE VELOCITY w&ymyBBT FIGURE 10

REACTION RATE VERSUS RECIPROCAL SPACE VELOCITY

TEMPERATURE 450 C

RECIPROCAL SPACE VELOCITY LBS. CATALYST MOLS PEED/HR 38

FIGURE 11

REACTION RATE VERSUS RECIPROCAL SPACE VELOCITY

TEMPERATURE 500° C

LBS. CATALYST RECIPROCAL SPACE VELOCITY, MOLS FEED/Effi. FIGURE 12

• PRODUCT COMPOSITION VERSUS RECIPROCAL SPACE VELOCITY

SERIES A - 400° C

LBS. CATALYST RECIPROCAL SPACE VELOCITY, ISLS PEEtyta. FIGURE 13

PRODUCT COMPOSITION VERSUS RECIPROCAL SPACE VELOCITY

SERIES A - 450° C

Ool8 n 1 -

0.16< t 1 o S fsb.

u ~° °2 0.14 r 1

0.12 -1 1

1 | 0.10 e-* 1 o

&■ ij § 0.08

1 0.06 1 <

0.04 r

1 o

1 X o CO c? 1 «> o 1 1 o 0.02 0 "1 / o -o S0 1 / 2 1/

n l 0 2 4 6 8 10 12 14

RECIPROCAL SPACE VELOCITY. ^LS FIGURE 14 ,

PRODUCT COMPOSITION • ■VERSUS RECIPROCAL SPACE VELOCITY

SERIES A - 500°C 0.18 1 • 1 1 0.16< Si 1 o ° 0.14 —0 /Cv °2 1 1 0.12 I * 1 * 1 1 • S S o.io 1 O 1 3 1 1 § 0.08 1 1 -

0.06 < > \ o -© s05 0.04 LV o - 0.02 / 0

2 4 6 8 10 ' 12 14

RECIPROCAL SPACE VELOCITY, FEED/HRT 48 FIGURE 16

PRODUCT COMPOSITION VERSUS RECIPROCAL SPACE VELOCITY

SERIES B - 450°C

LBS. CATALYST RECIPROCAL SPACE VELOCITY, MOLS FEED/HR. FIGURE 17

PRODUCT COMPOSITION VERSUS RECIPROCAL SPACE VELOCITY

SERIES B - 500°C

I >

FIGURE 19

PRODUCT COMPOSITION VERSUS RECIPROCAL SPACE VELOCITY

SERIES C - 450°C

IjriLj A I# M L M 1 j I LJ ^ RECIPROCAL SPACE VELOCITY, M0LS FEED7HR*

a FIGURE 20

PRODUCT COMPOSITION VERSUS RECIPROCAL SPACE VELOCITY

SERIES C - 500°C

LBS. CATALYST RECIPROCAL SPACE VELOCITY, MOLS FEED/HR* Vo IHTERrMTATION OF DATA

A. Differential Rate Equations Developed for toe Theory of Activated

Adsorption*

1® Adsorption of Sulfur Dioxide Rate Controlling

If the adsorption of sulfur dioxide were rate controlling, equation

(2) could be written as

ks L PSo r = °2 /l>S02 _ 3 ) (17) 1 1 ( *JPOe «o2 + PBO3 %O2 - - PS03 Kso;) '

J^2 K for the surface reaction of atomic oxygen and molecular sulfur dioxide*

If too surface reaction occurred between molecular sulfur dioxide and molecular oxygen, considering a dual site mechanism, equation (17) could be modified by merely raising to the first power the activity and adsorp¬

tion equilibrium constant of oxygen wherever either appears in toe equa¬

tion* In view .of the work of other investigators showing that nitrogen had no effect upon the reaction rate, the nitrogen term has been omitted* < Equation (1?) can b© rearranged to

PS02 - p303

+ JP5"2 K 1 (1+'/PO^ K0 PS0 %0g + PSOj *saJ 2 3 (18) C L K S02 ' yf$Q2 '

or R a a + b fg^ + c pSQ + d p, SO, (19) >TP^ 49

-.there

p PsoP so3 ■Ifop- a 1 b kSOg L

%03 %03 s d k L so2

For the initial rate, where the partial pressure of sulfur trioxide

is zero, equation (19) becomes

R * —^ m a+ b'fP^ (20) r 2

Thus for the initial conditions, R should be a linear function of the square

root of the oxygen partial pressure. It is a requirement of the theory

upon which equation (18) and successive equations of this type are based

that the constants have positive or zero values. Since for each tempera-

ture the value of R decreases as s| increases the constant b must have

a negative value, therefore, the adsorption of sulfur dioxide is not

rate controlling. Values of R, J pg , and pg for the initial conditions Cm Cm are shown in Table VIII.

Similar reasoning can be applied in the case of the reaction of

molecular oxygon. TABLE VIII

INITIAL COMPOSITIONS AND REACTION RATES

Temperature Series r %02_ PQ2 R H« l*Q0 A .0059 ,0565 008 .166 9.57 69.2 B ,0052 .0915 .351 .123 17.0 67.5 C ,0050 .026 .273 .071*5 28.52 0.6 -a* CD O h$o A ,0230• .0565 .166 2 05 17.73 B ,0210 .0915 .351 .123 lt.35 16.71 C ,0170 .026 .273 .071*5 8.38 16.05 5oo A ,0520 .0565 008 .166 1.09 7.0 B ,090 .0915 .351 .123 1.87 7.16

C 060 .026 .273 .071*5 3.10 5.93 2» Adsorption of Oxygen Rate Controlling

If the adsorption of oxygen were the rate controlling step, equation

(2) could be written for the reaction of atomic oxygen and molecular

sulfur dioxide as

k(3o k r = °a_S2^/ (a, f1 *■ pSOg %Qfc + PSO3 +• PsOj Ksa^) Psoj K Psog K '

Rearranging equation (21) 1

>/%> PS0,

p K so2 ® —3t— [1 + PsOg %0 + pS

02* Rf » b1 pgQ f o1 —"■** f df (23) p Pso so2 ' ’ 3

For the initial conditions, where pgQ^ = 0? equation (23) can b© written

as

„ R’ “ —- » a* + b» p3^ (21},)

It can be seen from table VIII that R1 decreases as pg^ increases.

Therefore, the constant bj. has a negative value, and the adsorption of

oxygen cannot be the rate controlling step. 58

Again similar reasoning would apply for the reaction of molecular oxygen and molecular sulfur dioxide.

3« Desorption of Sulfur frioxide Rate Controlling

If the desorption of sulfur trioxide were rate controlling, equa¬ tion (3) could be written as

PS02'/^02 pSCb (25) p P K K (1 *■ S02 %02 + SOr/K)2 %03 )

Since the thermodynamic equilibrium constant appears in both the numer¬ ator and denominator of the multiplying fraction, and is large, for the data at UCO and J|5Q°C in particular, the rate approaches k^g L / Kgg 3 3 as a limit thus indicating that the rate would be essentially indepen¬ dent of the concentration of reactants or products. Since the initial rate was a function of the feed composition, the desorption of sulfur trioxide was not rate controlling.

U* Surface Reaction Rate Controlling

If the surface reaction were rate controlling equation (i*) could be written as

k s t. K,S0 PSQo J^Ckp p K 2 *2 ’ Qjg> S03 (26) r e K 1+ K ( PSOg %Q2 +7PO2 02 + PSO^ %03) 53

Rearranging:

(27)

or R» = a" <- b” pS02+ + d" pg^ (28)

Since the total number of mols before and after reaction is essentially constant it is possible to write

P P S0 = %0g “ 80 3 O 2 (2 9)

Substituting in equation (2?) and simplifying, equation (28) can be mitten

R» = (*« * d-jpg^ + (v - d") pS02 (30)

(31)

Equation (31) is valid for a constant inlet partial pressure of sulfur dioxide*

It was necessary to solve for the constants in equation (31) by the method of simultaneous equations* the constants, as determined by the method of least squares, for each feed composition and each temperature 54 are shown in table IX. As required by theory the constants A and C must have positive values. Moreover, the constants 2 and C should have the

sane value for each series at constant temperature. Since this is not the

case, the surface rate of reaction between aolecularly adsorbed sulfur dioxide and atomically adsorbed osygen is not the rate controlling step*

If the surface reaction between nolecularly adsorbed sulfur dioxide and molecular oxygen were rate controlling, equation (26) could be written

k 3 L K _ G2 %O2

1 + E p K + K l %02 S0g * 02 0g %Oj 30

Upon simplification, equation (32) becomes

p p p . so2 o2 so3

1 + p K p K + p K S02 SOg * Og 0g S03 %0 yjks LKQ^ %O2

(33)

m or = a + b«“pS02+ c«»p02 + d'"?^ (31*)

Prom the relation (29) and

p p 1 2 p Qg “ 02o - / - S02] (35)

equation (3U) can be reduced to the linear form

Sm M *• H (36) TABLE IX

CONSTANTS FOR SURFACE REACTION AS

RATE CONTROLLING STEP

CONSTANTS Temperature Series A B 0

UOG A + 6.2$l6 - 75,599 + .01468 B +35.15 -12.36 '92.39 •

V

1*50 A + l*.313 - 71.87 + .2657

B - 98.12 - 61* .1*1* *■ 318.5 C + 5.91*9 - 38.963 + 2.983 500 A + 2.519 - 1*9.95 * 1.197

B + 3.055 - 23.31 - 3.810 C + 5.575 - 7.397 - 11* .23 56

Thus for each series of runs at constant temperature and constant feed composition* R,M should be a linear function of the sulfur dioxide partial pressure* Under no conditions did this relation exist* There¬ fore, the surface reaction between aolecularly adsorbed sulfur dioxide and aolecularly adsorbed oxygen was not the rate controlling step.

$» Mass Transfer Effects

As previously discussed, the mass transfer resistance was neglected in the above attempts to correlate the data, and if the assumption ofgoro diffusions! resistance was not valid the equations certainly would not apply* When it is possible to correlate data, the effects of mass trans¬ fer can be detected by plotting the logarithm of the temperature coeffi¬ cient of reaction versus the reciprocal absolute temperature* Basis the theory of Arrhenius a linear relation should exist if mass transfer effects are negligible* In the absence of the absolute values of such coefficients, however, reaction rates proportional to these values can be obtained if the assumption is made that the rate of reaction is some function of the product composition, i.e*

r (3?)

and that the reaction mechanism is independent of temperature* It can be seen from equation 3? that for a constant feed composition and con¬ stant outlet sulfur dioxide partial pressure, the rate of reaction is direct¬ ly proportional to the constant k, the temperature coefficient of reaction.

Thus a plat of reaction rate versus reciprocal absolute temperature on a semi-logarithmic scale should result in a straight line if diffusions! resistance is negligible® This procedure has been, followed for the re¬ ported data and the results are shown in Figures 21, 22, and 23® In all but one case a definite curvature existed thus indicating that the mass transfer resistance was a substantial portion of the total resistance to reaction*

It can be noted in Figures 21 to 23 that product sulfur dioxide con¬ centration has been included as a parameter and that the curvature of the lines is less for higher concentrations of sulfur dioxide as would be expected when the rate of mass transfer is significant®

The apparent activational energy calculated on the basis of the straight line data shown in Figure 23 was 23,500 calories per gram-mol®

This is in agreement with the value of 20,000 calories per graswaol re¬ ported recently by Hall and Smith (21).

B. Empirical Equations

fhe empirical correlations of other investigators, in particular those of Lewis and Ries (10) and Krichevskaya (13) (Equations (11) and

(lit) respectively) were found to be Incapable of representing the data*

Other types of empirical equations were used in the differential form, but also were found to be incapable of interpreting the data®

C® Integrated Equations

In view of the fact that there is an inherent possibility for error in obtaining instantaneous reaction rates by graphical differentiation. FIGURE 21

REACTION RATE VERSUS RECIPROCAL TEMPERATURE SERIES A

RECIPROCAL TEMPERATURE, PER DEGREE KELVIN RATE x 10^, LB« MOLS SO2 CONVERTED/HR . LB. CATALYST RECIPROCAL TEMPERATURE, PERDEGREEKELVIN RECIPROCAL TEMPERATURE REACTION RATE FIGURE 22 SERIES B VERSUS RATE x 10^| I*U* MOLS SO2 CONV ERTED/HR• LB. CATALYST RECIPROCAL TEMPERATURE,PERDEGREE KELVIN RECIPROCAL TEMPERATURE REACTION RATE FIGURE 23 SERIES C VERSUS 61

an attempt was mads to correlate the data at U50°C by an integrated fora of equation. The problem was complicated by the large number of possible differential equations, so only three in particular were investigated.

These equations were*

d n KL PSOg PS03

d w ~ kz k3 Pso^

dn _ * PS°2 P°2 (3?) 1 + p «” *2 POj'- *53 so2

d n _ 111 Psa2 0*0) d w 1 +• ^2 POg + PsOj

The integrated forms of these equations have not been included be¬

cause of their complexity. However, none of the above equations were applicable to the data. VI. COMCEUBIGHB

1. It ms found that the rate of mass transfer ms a. si&otsntlal portion of the overall resistance to reaction.

2. An extensive effort to correlate the data wo made, out tbs present flats together irilth available literature data vere insufficient to permit the evaluation of the separate effects of chemical and diffu¬ sions! resistances to reaction. 63

VII. APfflIIDICISS APJRBMDIX A

SUMMMU' Of EXPERIMENTAL AS®

CALCULATED DATA 65

1. ORIGIKAL DATA TABLE X,

SUMMARY OF EXPERIMENTAL LATA

SERIES A

Run Uo. A-2-0 A-2-a A-2-a A-2-a A-2-a A-2-b A-2-c A-2-d A«*2**0 Am*2m»o

Temperature, °C LOO LOO Loo Loo Loo Loo LOO Loo Loo LOO

Pressure at outlet, atm. 1.03 1.03 1.01 1.02 1.01 1.02 1.02 1.03 1.03 1.02 Pressure at inlet, atm. 1.06 1.07 1.00 1.00 1.00 1.06 3a .06 1.07 1.07 1.06

Feed Composition, mol %

so2 0.69 0.1*1 5.61 0.17 0.72 0.LL 0.20 0.37 0.Lo 0.60

°2 19.9 10.8 10.8 16.0 10.9 10,8 16 »L 10.9 10.8 10.8

% 78.L ?8.8 78.6 78.8 78.L 78.8 78.L 78.7 78.8 78.6 Total mols feed/hr .0522 .0016 .0013 .0010 .003)* .001? .0009 .0011* .0013 0.0020 •Si- , Superficial -velocity,ft/sec. 0.53 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.03

Weight'of platinised gel.lbs 0.000 0.100 0.100 0.100 0.100 0.310 O.L60 0.620 .0610 .0610 lb. mols feed/hr Space velocity, lb. catalyst 6.000 0.333 0.331 0.332 0.332 0.167 0.100 0.0820 .81*1 .802 Reciprocal space velocity - 3.00 3.02 3.01 3.01 0.99 9.1? 12.1 1.19 1.17 Adjusted reciprocal space velocity 0.1*0 3.1*0 3-1*2 3*Ll 3.L1 6.39 9.07 12.0 1.09 1.07 Conversion, $ L.7 17.6 18.2 37.8 1L.0 36.0 L3.9 L0.6 23.0 11.2

Product Composition, mol %

so3 0.2? 0.00 1.03 1.07 0.80 2.01 2.33 2.20 1.20 0.63

so2 0.L3 L.L8 L.61 3.20 L.9L 3.L9 2.98 3.23 L.19 L.99

62 15.8 10.L 10.L 10.2 10.6 1L.9 15.L 10.0 10.3 10.0 N 78.0 70.2 79.0 70.6 '78.7 79.0 79.3 79.6 79.3 78.9 2 4 Mols SOg Converted / mol feed l.0027 .0000 .0102 .0190 0.0080 .0199 .0230 .0218 .012L .0063

Mol % 02(803-3% free) calculated 16.8 16.3 16.3 16.0 16.0 10.8 16.3 10.9 16.2 16. L

Mol % GgtSQ^-SQg free) analysis l6.lt 16.1 16,3 10.7 16.3 10.6 16.3 10.8 16.3 16.3

Based upon inlet compositions 6*7

TABLE X. (Cont’d)

SUMMARY OF EXPERIMENTAL BATA

SERIES A

Run Mo. A-3“0 A-3-a A-3-to A-3-c A-3-d

Temperatures °C 850 850 850 850 850 851

Pressure at Outlets Atm. 1.02 1.03 1.02 1.02 1.03 1.03

Pressure at Inlets Ate. 1.06 1.07 1.06 1.06 1.07 1.06

Feed Composition, Mol %

S02 ■ 5.57 5.22 5.35 5.37 5.36 5.88

°2 15.9 15.? 15.9 16.8 15.9 15.9 % 73.5 78.9 78.8 77.9 78.7 78.7 Total Isols Feed / Hr. . 1)517 .0515 .0516 .0516 .0517 .0513

Superficial Velocity, Ft. / Sec* 0.56 0.56 0.56 0.56 0.56 O.56

Weight of Platinised Gel, Lbs« 0.00 0.155 0.310 0.865 0.620 0.06I

Space VA^nni tys ^bvkols Peed/Hr. Lb. Catalyst. 0.332 0.166 0.111 0.0838 0.881

Reciprocal Space Velocity 0.00 3.01 6.02 9.00 12.0 1.19

Adjusted Reciprocal Space Velocity O.hO 3.81 6.82 9.82 12.8 1.59

Conversion, % 12.3 89.8 66.7 59.7 68.8 80.3

Product Composition, Mol %

SO, 0.65 2.61 3 3*68 3.26 3.78 2.21 so2 8.90 2.68 1.81 2.20 1.72 3.29

02 15.7 18.8 18.8 15.8 18 »8 15.0 78.8 80.1 h 79.9 79.1 80.2 79.5 Mols SQg Converted / Mol Feed .0065 .0258 .0357 .0321 .0367 .0219

Mol % Og (SO^ ~ S02 Free), Calculated 16.7 15.6 15.2 16.3 15.2 15.8

Mol % Og (SO3 - SOg Free), Analysis 16.5 1U.8 15.2 15.95 15.2 15.6 68

TABUS X. (Cont'd)

SUMMAHX JF EXffiEIMEMTAL DATA

SERIES A

J&r Run !lo. A-it-b A-li-c A-li~d” A-4tr&

Temperature, °C 500 k?9 . 500 500 501 500 500

Rfessiffe at outlets atn. 1.02 1.03 1.02 1.03 1.03 1.03 1.03

Pressure at inlet, atcu 1.06 1.07 1.06 1,06 1.07 1.07 1.07

Feed Composition, Mol %

so2 543 541* 0.50 5.23 3.37 540 5.27

02 16.0 15.9 15.9 16.7 15.9 15.9 15.9

Hg 78 4 78.6 78.6 78.1 78.8 78.7 78.8 O O Total Mols feed/Hr.9 • .0517 .0516 .0516 .0517 0.0516 ,0516

Superficial Velocity, Ft./Sec. 0.60 0.60 0.60 0,60 0.60 0.60 0.60

Weight of Platinized Gel, Lbs# 0.00 0.155 0.310 0.1*65 0.620 0.620 .061

Space Velocity, .%?. 0.333 0.166 .311 .0832 .0832 .81*6 ■ Ih. Catalyst. Reciprocal Space Velocity 0.00 3.00 6.02 9.00 12,0 12.0 1.10

Adjusted Reciprocal Space Velocity 0.1*0 340 6.1*2 9.1*2 12.1* 124 1.58

Conversion, % 17.6 60.9 79.1 80.0 80.7 79.8 59.5

Product Composition, Mol %

SO^ 0,99 3.37 845 li.27 1*43 1*41 3.19

SOg U.66 2.18 1.17 1.07 1.06 1.11 2.16

o2 15.6 HA .5 4,0 4.9 Hi.o 3i*.0 4.5

Hg 78.8 80.0 80.1* 79.8 80.5 80.5 80,1

Mols SOg Converted/ Mol Peed .0099 .0331 .0835 .0118 .433 .01*31 .034

Mol % O2 (SO^-Si^Free), Calculated 16.5 15.3 Hi.8 19.7 4.8 H*.8 154

Mol % O2 (SO^-SQgEree), Analysis 16.15 4.5 Hi. 8 15.0 4.85 4.7 15.3

* First Run of a Series. Fourth Run of a Series m

TABIE XI.

SUMHARST OF EXPERIMENTAL DATA

SERIES B

Run No. B~2~a B-2-b B-&-0 B-2-e Temperature, °C hOO i*oo U00 2(01 1(00 1(00 1(00

Pressure at outlet, atm. 1.02 1.03 1.02 1.02 1.02 1.03 1.02 Measure at inlet, atm. 1.06 1.07 1.06 1.06 1.06 1.07 1.06 Feed Composition, Mol %

SO2 9.00 8.80 8.86 8.88 8.96 8.77 8.77 a. 11,8 11.7 11.8 11.6 12.5 11.7 11,6 % 79.2 79.5 79.U 79.5 78.6 79.6 79.6 Total Mols Feed/Hr. .0516 .0509 .0509 .0510 .0506 .0511 .0507 Superficial Velocity, Ft,/Sec. 0.52 0.52 0.52 0.52 0.52 0.52 0.52 Weight or Platinized Cel, Das. 0.00 .155 .195 0.310 •U65 .620 .061

Space Velocity,J .^3 Feed/Hr. 0.328 .328 .165 *109 •082l( * £b. Catalyst .831

Reciprocal Space Velocity 0.00 3.05 3.05 6.06 9.17 12.1 1.20 Adjusted Reciprocal Space Velocity 0.1*0 3.1(5 3.U5 6.1(6 9.57 12.5 1.60 Conversion, % 1.8 12.5 15.9 27.5 29.8 33.1 6.5 Product Composition, Mol %

so3 0.16 1.11 1,1^2 2.1(7 2.71 2.9!( 0.57 S02 8.85 7.7ii 7.50 6.52 6.38 5.96 6.22

°2 11,7 11.2 11.1 10.5 11.3 10.3 11.3 H2 79.3 80.0 80,0 80.5 79.7 80.8 79.9 Mols SQg Converted/ Mol Feed .0016 .0110 .011(1 •Q2hh .0267 .0290 .0057

Mol %f QziSQy&Cfe Free), Calculated 12.9 12.2 12.2 11.6 12 .U 11. u 12 .U

Mol %t O2(SO^-SQg Free), Analysis 12.55 11,7 12.0 11.0 12.1 10.8 12.05 TABLE Si, (Confc’d)

SUMMART OF EXFERIMEMTAL DATA SERIES B

Run Ho. B-3-0 B-3«*b B-3-c B-3~d B-3-e Temperature, °C 450 450 1*50 450 450 450 treasure at outlet, atm. 1.02 1.03 1.02 1.02 1.03 1.03 Pressure at inletj atm. 1.06 l.o? 1.06 1.06 1.07 1.07 Feed Compositions Mol$

S02 8.76 8.65 8.61* 8.85 8.77 8.71 °2 11.8 11.7 n.6 12.4 11.7 11.6 % 7 9.4 75.6 75.8 78.7 79.6 79.7 Total Hols Feed/Hr. .0515 .0505 .0508 .0513 .0511 .0508 Superficial Velocity, Ft./Sec. 0,56 0.56 0.56 0.56 0.56 0.56 Weight of Platinized Gel, Lbs* 0.00 .155 0.310 .465 .620 .061 Space Velocity. Mi.*.,..1. .328 1.64 .110 .0824 .833 Lo* Catalyst* Reciprocal Space Velocity 0.00 3.05 6.10 9.05 12.1 1.20 Adjusted Reciprocal Space Velocity 0.40 3.1*5 6.50 5.45 12.5 1.60

Conversion, % 8.5 35.8 53.8 55.7 61.8 28.7

Product Composition, Mol %

BQj 0.78 3.86 4.76 5.08 5.57 2.53

so2 8.02 5.32 4.05 4.04 3.44 6.29 °2 11.5 10.1 5.4 10.2 9.2 10.4

N2 75.8 81.0 81.7 8O.7 81.8 80.7

Mols S02 Converted/Mol Feed ,00?8 .0356 *0465 .0455 .0542 .0250 Mol % O2 (SO3 - SOg Freo), Calculated 12.55 11.1 10.3 11.2 10.2 11,4

Mol % 02 (SO3 - S02 Free), Analysis 12.2 10.8 10.05 10.55 9.8 11.15 TABLE XI* (Cont*d)

SUMMfVRI OF EXPERIMENTAL BATA

SERIES B

Run Ho* B-U-0 ■ B-4*-a. B-4-b B-4~d B-4-e Tespsratur®, °C 500 500 500 500 499 Pressure at outlet, ata. 1*02 1.04 1.02 1.03 1.03 Pressure at inlet, atm* 1*06 1.07 1.06 1.07 1.07 Feed Composition, Mol %

sofc ' 8.99 8.60 8.63 8.92 8.72 °2 11.8 n.7 11.6 11.7 11.6 % 79.2 79.7 79.8 7 9.h 79.7 Total Mole Feed/Hr* .0511 .0510 .0509 .0511 .0510 Superficial Velocity, Ft ./Sec. 0.59 0.59 0.59 0.59 0.59 Weight of Platinised Gel, IBs* 0.00 .155 .310 .620 .0610 .329 .164 •0824 .836 Reciprocal Space Velocity 0.00 3.0b 6.10 12.1 1.2Q Adjusted Reciprocal Space Velocity 0.40 3.44 6.50 12.5 1.70 Conversion, % 16.6 59.0 68.5 74.3 45.9 Produet Composition, Mol % SO3 1.50 5.20 6.09 6.86 4.08 SO2 7.55 3.62 2.80 2.37 4.82

>2 11.2 9.4 8.9 8.7 9.8 % 79.8 81.7 82.2 82.1 81.3 Hols S02 Converted/Mol Feed .0149 .0507 .0591 .0663 •0400 Mol % O2 (SOj - SOg Free), Calculated 12.3 10.3 9.7 9.6 10.6 Mol % O2 (SOj - SOg Free), Analysis 11.95 9-7- 9.4 9.15 10.4 72

TABIE XII

SUBMAHX OF EXPERIMENTAL DATA

SERIES C

Run !io. C-2-0 C-2-a G**2*-Si C~2«d 0—2-*0 Temperature, °C 1*00 1*00 1*01 1*00 1*00 1*00 1*00 1*00 Pressure at outlet, atm* 1.02 1.03 1.01 1.02 1,02 1.03 1.02 1.02 Pressure at inlet, atm. 1.06 1.07 1.05 1.06 1.06 1.07 1.06 1.06

Feed. Composition, Mol %

SO, 13.86 13.79 13.75 13.60 13.77 13.87 13.66 13.52

o2 7.01* 7.00 7.16 7.01 7.81* 7.07 7.01* 7.12 % 79.1 79.2 79.1 79.1* 78.1* 79.1 79.3 79.1* Total Mols Peed/Hr* .0519 .0513 .0510 .0512 .0508 .0516 .0510 .0517 Superficial Velocity, Ft./sec.O»52 0*52 0.52 0.52 0.52 0.52 0.52 0.52 Weight of Platinised Gel,Lbs* 0.00 .155 -155 1*310 .1*65 .620 .061 .061 Space -J31 .329 .165 .109 .0832 .836 .81*8 Reciprocal Space Velocity 0.00 3.02 3.01* 6.06 9.17 12.0 1.20 1.18 Adjusted Reciprocal Space Velocity 0.1*0 3.1*2 3.1*1* 6.1*6 9.57 12.1* 1.60 1.58 Conversion, % 1.8 10.0 7.6 16.2 25.1* 23.3 9.98 9.97 Product Composition, Mol % so3 0.25 1.39 1.05 2.22 3.56 3.28 X.37 1.36 sog 13.63 12.50 12.77 H.53 10.1*5 10.81 12.38 12.25

°2 6.52 6.35 6.6 ? 5.98 6.20 5.51* 6.1*0 6.1*8 % 79.2 79.8 79.5 80.3 79.8 80.1* 79.8 79.9

Mols S02 Oonverted/liol Feed .0025 .0138 .Old* .0220 .0350 .0323 .0136 .0135

Mol % 02 (SOo-SOgFree), Calculated 8.03 7*38 7.75 6.93 7.21 6,1*5 7.1*2 7.51 Mol % Og (SO^-SOgFree)Analysis 8*0 7*1 7.6 6.1* 7.1* 6.2 7.5 7.6 TABLE XII. (Cont'd)

SUMHAHX OF EXH5EIMEHTAL BATA

SERIES C

Run riQ* C-3-Q C-3-a C~3~b C-3~c C-3~d G-3~8

Temperature, °C 450 hh9 450 450 450 450

Pressure at outlet, atm. 1.02 1.04 1.02 1.02 1.03 1.03

Pressure at Inlet, atm. 1.06 1.07 1.06 1.06 1.07 1.07

Feed Composition, Mol %

so2 13.77 13.60 13.65 13.6? 13.80 13.52

7.88 7.06 °2 7.20 7.02 7.01 7.09

B2 79.0 79.4 79.3 78.8 79.1 79.4

Total Bole Feed/iir. .0518 .0512 .0512 .0513 .0517 .0511

Superficial Velocity, Ft./Sec. 0.56 0.56 0.56 u.56 0.56 0.56

Weight of Platinised Gel, Lbs. 0.00 .155* .310. .465 0.620 .0610

Space Velocity, .330 1.65 •no .0834 .838

Reciprocal Space Velocity 0.00 3.03 6.06 9.09 12.0 1.19

Adjusted Reciprocal Space Velocity 0.I4O 3.43 6.46 9.49 12.4 1.59

Conversion, % 4.8 24.3 32.7 38.5 40.0 14.6

Product Goaaposition, Mol %

0*66 3.36 4.56 5.38 5.68 1.99

so2 13.16 10.47 9.40 8.60 8.52 11.6? °2 6.89 5.46 4.89 5.37 4.42 6.16 79.3 8O.7 81.1 80.6 81.4 80.2 «2

Mols S02 Converted / Mol Feed .0066 .0330 .0446 .0526 .0552 .0197

Mol % 02 (30^ - SO2 Free),Calculated 8.00 6.33 5.69 6.24 5.16 7.13

Mol % O2 (SO3 ~ SOg Free),Analysis 7.8 6.2 5.35 6.1 4.8 6.55 TABUS XU. (Cont’d)

SUMH&KX OF EXPERIMENTAL DATA

SERIES C

Run Ho. Q-li-0 C*4i**a C*4i~c C-8-e Temperature, °C 5(X) 500 500 5G0 899 899

Pressure at outlet, atm* 1.03 1.03 1.03 1.03 1.03 1.03 Pressure at inlet, atm. 1.06 1.07 1.06 1.06 1,07 1.07 Peed Composition, Mol %

SOg 13.76 13.66 13.62 13.73 13.83 13.67

°2 7.1? 7.02 7.00 7.81 7.05 7.06 % 79.0 79.3 79.h 78.5 79.1 79.3 Total liols Feed/Hr. 0.0515 .0512 .0513 .0517 .0513 .0513 Superficial Velocity, Ft./Sec. 0.60 0.60 0.60 0.60 0.60 0.6C

Weight of Platinised Gel, lbs. 0.00 .159 .310 .865 .0620 .061 Space Velocity, £oe,$/}?£,9, .330 .ill .0827 Lb. Catalyst .165 .881 Reciprocal Space Velocity 0.00 3.03 6.06 9.01 12.1 1.1? Adjusted Reciprocal Space Velocity 0.80 3.83 6.86 9.1*1 12.5 1.59 Conversion, % 9.3 39.2 li9.6 56.0 55.0 29.5 Product Composition, Mol %

S03 1.29 5.50 7.00 8.00- 7.91 8.11 SOg 12.57 8.58 7.10 6.28 6.87 9.88

°z 6.60 8.86 3.75 It.12 3*37 5.18 Hg 79.$ 81.5 82.2 81.6 82.3 80.9

Mols SOg Converted/Mol Feed .0126 .0535 .06? 6 .0679 . .0761 .0803 Mols % Og (SO3 - SOg Free),Calculated 7.66 5.19 it .36 1*.80 3.93 5.98 Mol % Og(SOj — SOg Free), Analysis 7.6 5.1 8.8 8.0 3.7 5.8 2. CALGUIATBD REACTION RATES 7B

TABLE XIII

REACTION RATES AMD PARTIAL PRESSURES TEMPERATURE - 1+00°C

Lb.-Mols 302 Converted/Hr./ Series A ^Catalyst Atmospheres Adjusted Space r p p so o Pso p Velocity 2 2 3 »2

0.0 0.0059 0.0565 0.166 0.0 0.818

1,0 0.0036 0.0530 0.162 0.0056 0.820

2.0 0.0030 0.01+96 0.160 0.G092 0.822

1+.0 0.0022 Q.ol+3? 0.158 G.0U+7 0.821+

6.0 0.001? 0.0389 0.158 0.0179 0.825

8.0 0.0012 0.0351+ 0.15? 0.0211+ 0.826

Series B

0.0 0.0052 0.0915 0.123 0.00 0.826

1.0 0.001+5 0.0873 0.119 0.0050 0.829

2.0 0.0039 0.0830 0.117 0.0091+ 0.831

l+.Q 0.0031 0.0756 0.113 0.0168 0.835

6.0 0.0023 0.0699 0.110 0.0221+ 0.838

8.0 0.0016 0.0658 0.109 0.0265 0.839

Series C

0.0 0.0050 0.11+26 0.071+5 0.00 0.823

1.0 O.GGI+5 0.1391+ 0.0692 0.0057 0.826

2.0 O.OOlil 0.1356 0.0657 0.0109 0.828

l+.o 0.QQ3I+ 0.1280 0.0629 0.0193 0.830

6.0 0.0028 0.1219 0.0619 0.0253 0.831

8.0 0.0021 0.1173 0.0608 0.0297 0.833 77

TABLE XIV „

REACTION RATES AND PARTIAL PRESSURES

TEMPERATURE - 1*5Q°C

Iib«~MolS SQg Comrerfced/Hr./ Series A ^Catalyst Ataaospherea

Adjusted Space %0g Velocity r - % 0.0 0.0230 0.0565 0.166 0.00 0.818 1*0 0.0101 0.0U2 0.160 0.0151 0.822* 2.0 0.0060 0.0331 0.156 0.0232 0.828 2*.0 0.0021 0.0262 0.152 0.0305 0.831

6.0 0.0012 0.0225 0.150 0.0337 0.83U 8.0 0.0008 0.0211 0.150 0.0359 0.833

Series B

0.0 0.1210 0.0515 0.123 0.00 0.826

1.0 0.0137 0.0707 0.133 0.0182 0.838

2.0 0.0085 0.0623 0.108 0.0305 0.839 1*«0 0.0038 0.0523 0.101 0.01*18 0.81*1* 6.0 0.0025 0.01*58 0.0987 0*01*81* 0.81*8

8.0 0.0021 0.0M36 0.0572 0.0530 0.850

Series C

0.0 0.0170 0.11*26 0.072*5 0.00 0.823 1.0 0.0112 0.1265 0.0669 0.011*5 0.832

2.0 0.0085 0.1175 0.0621 0.0251 0.835 1*.0 0.00U6 0.1071 0.0555 0.0371* 0.81*0

6.0 0.0031 0.0556 0.0513 0.01*56 0.81*3 8.0 0.0022 0.0939 0.01*97 0.0518 0.81*1* 78

TABLE XV. KEACTIQH RATES AMD PARTIAL PRESSURES

TEBfisRATURE - 500°C

Lb.-Mols S% Converted/fir./ Series A lOatalyst Atmospheres

Adjusted Space P P Velocity r S02 % », 0*0 0.0520 0.0565 0.166 0.00 0.818

1,0 0.0126 0.0335 0.158 0.0257 0.823 2.0 0.0053 0.021*1 0.152 0.031*0 0.830

l*.o O.OOll* 0.0173 0.11*7 0.01*01* 0.835 6.0 0.0010 0.011*2 0.11*7 0.01*28 0.836 6*0 0.0008 0.0123 G.H*? o.oy*6 0.836

Series B

0.0 0.GU50 0.0915 0,123 0.00 0.826

1.0 0.0177 0.0605 0.108 0.0322 0.839 2.0 0.0087 0.01*66 0.102 0.01*58 0.81*6

i*»0 0.0032 0.0360 0.0956 0.0561* 0.81*8

6.0 0.0017 0.0306 0.0932 0.0621* 0.851*

8.0 0.0008 0.0268 0.0921* 0.0668 0.851*

Series C

0.0 0,Ql*6Q 0.11*26 0.071*5 0.00 0.823

1.0 0.0192 0.1125 0.0598 0.0312 0.837 2.0 0.0102 0.0983 0.0522 0.01*72 0.81*2

ii.O 0.001*8 0.081*0 0.01*1*2 0.0613 0.851

6.0 0.0029 0.0751* 0.0397 0.0707 0.85U 6.0 0.0021 0.0706 0.0380 0.0771 0.851* 79

TABI& XVI.

REACTION RATES AT CONSTANT PRODUCT COMPOSITION

SERIES A

Lb.-Mole SOp Converted/Hr. Rato, Product SOp Atm* Temperature, °C Lb. Catalyst

0.0335 400 .00068 0*0335 450 .00608 0*0335 500 .0126

.0450 4oo .00245 .0450 450 .0121 .0450 500 .0230

SERIES B Lb.-Mds SO2 Gonverted/Hr. Product SQg Atm. Temperature, °C Pvate, Lb. Catalyst

.0615 400 .00118 .0615 450 .0076 .0615 500 .0182

.0730 400 .00308 .0730 450 .0146 .0730 500 .0308

SERIES C Lb.-Mols SO2 Converted/Hr. Product 502s Atm. , Temperature, °C Rate, LB. Catalyst .111*5 400 .0014 .1145 450 .0071 .1145 500 .020?

.1325 4co .0030 .1325 450 *0130 .1325 500 .0370 APPENDIX B

DETAILS OF APPARATUS 1, Purification of Gases

The metered oxygen and nitrogen ware dried over chloride be¬ fore passing into a feed raising bottle. Since -toe sulfur dioxide con¬ tained oil and water as impurities, it was bubbled through 98$ sulfuric acid and dried .over pentoxide before being sobered*

2* Metering of Gases

Orifices constructed from capillary glass tubing were used for me¬ tering all feed gasesj however, the orifice calibration for the sulfur dioxide was not used in calculations because a more accurate sulfur diox¬ ide analysis was made on the feed gas*

The oxygen and nitrogen orifices were calibrated using the gas v/±th which they were to be used by passing the gas first through the orifice and then through either a wet or dry test meter depending upon the flow range. The technique of J, 0, Whitwrell as quoted by Dodge (22) of plot¬

ting Q versus All on a log-log scale was used in making the orifice

calibration curves* Q is the flow in cubic feet per hour at orifice up¬

stream conditions, P is the upstream pressure in millimeters of ,

M is the molecular weight of the gas, T is the temperature in degrees

Kelvin, andZHf is the orifice differential in centimeters of water. These

calibration curves are in Figures 2k to 26*

3* Preheater

The metered gases were conducted through the mixing bottle into the preheater* The preheater consisted of twelve feet of l/fy* 25-20 steel tubing wiiich had been formed around 1” barstock* This tubing was enclosed ORIFICE CALIBRATION OXYGEN 0-1 CM in co O to to «H CM O o o to o in o o to

AH, INCHES H20 82 i 88

FIGURE RS

ORIFICE CALIBRATION 84

\

FIGURE 26

ORIFICE CALIBRATION NITROGEN H-J5

AHc INCHES HZ0 85

in a twelve inch section of 1-1/2" I.P.S. steel pipe. Preparatory to the installation of the heating element which was designed for 110 volts A~C, the 1-1/2" pipe was coated with about 1/6" of Alundum refrac¬ tory cement. A twenty-two foot length of #22 Hoskin’s Chromel "A" wire was coiled the full length of the pipe. The coil was covered with a second

1/8" layer of Alundum cement. Finally the whole assembly was insulated with

1" Magnesia pipe covering which was covered with canvas and a coating of asbestos finishing mix. A thermocouple was inserted in the center of the coil.

it. Reactor

A detailed drawing of the reactor is shown in Figure 2?. Before in¬ stalling the heating elements* the reactor ms coated with about 1/8" of

Alundum refractory cement. An eighty-five foot length of #17 Hoskin’s

Chromel "A" wire was coiled the full length of the reactor. After another application of cement, two forty-two foot lengths of #22 Chromel "A" wire were coiled on the reactor, one on the lower half and one on the upper half. A second coating of cement was applied over these elements. The coils were designed for 220 volts A-Cj however, the upper coil was opera¬ ted on 110 volts.

The reactor was supported only by a clamp and "tack" weld near the screw cap, thus allowing for thermal expansion. The reactor was suspended in a 13-1/2" x 13-1/2" sheet metal shell, and the annular space between the reactor and shell was filled with Johns-Manville’s Sil - 0 - Cel

C-3 insulation. FIGURE 27

REACTOR DESIGN DETAILS

SPECIFICATIONS:

1. ALL MATERIAL 25-20 CR-NI EXCEPT WHERE NOTED 2. CAP - 18-8 CR-NI * MACHINE THREADS 3. MAIN TUBE 2" IPS 4. NIPPLES IPS 6o TEE - 18-8 CR-NI 6. SUPPORTS - C STEEL ANGLE 87

The chroael-alumel thermocouples protected by porcelain insulators

n vmi’o sheathed in thirteen inch thermowells constructed from l/h 2$~20

n steel tubing® The thermowell was inserted through a l/h pipe plug and

secured by a soldered joint. The plug was screwed into a coupling

tt on the l/h pip© nipples welded on the reactor wall thereby suspending the thermowell and placing the tip in the center of the reactor tube.

Solids Separator

The solids separator consisted of a fourteen inch section of UH

I.P.3. carbon steel pipe capped with 1/8” sheet metal* the bottom portion

of the separator being cone-shaped. In preliminary runs in the equipment*

it was found necessary to place a heating element on the separator and

the 1/2“ pipe ejstanding from the top of the reactor. The units were coat¬

ed with Alundum cement* wound with twenty feet of #22 Chromel "A" wire* and recoated with cement. Finally* the units were insulated with 1"

Magnesia covering* The heating element was operated on 110 volts. A

thermocouple was inserted in the 1/2'* pipe. 6. PHOTOGRAPH OP APPARATUS

FIGURE 28

APPENDIX C

CHEMICAL ANALYSIS OF SILICA GEL The manufacturer gives the chemical composition (dry basis) of the unplatiniued silica gel ass

Silica as Si02 99.71 %

Iron as FegQ^ .03

Aluminum as AlgO^ .10

Titanium as TiOg .09

Calcium as CaO .01

Sodium as HagQ .02

Zirconium as ZrOg .01

Trace- elements .03

100.00 % APIEHDIX D

SU1F0E DIOXIDE AHAEISIS TECHNIQUE The sample of the feed gas ms taken from the mixing bottle in the feed line and run directly into a Belch test apparatus. The product gas sample was bubbled through 9$% sulfuric acid (which had previously been saturated with SOg) in order to remove the SQ^ before flowing into another

Reich test apparatus. The Belch test apparatus consisted of a Reich bot¬ tle, a Woulff bottle, and a beaker. In the Reich bottle, approximately

10 cc. of 0.1 M iodine solution (containing k% £1. and a drop of starch solution) in 100 cc. of distilled water was titrated with the sample gas until the starch-iodide indicator was decolorised. The Reich bottle was shaken during the course of the titration to insure complete absorption of the SOg. The sample gas, free of SOg, was collected in the Whulff bottle thereby displacing its volume in water through a siphon tube into a beaker. The weight and temperature of the water, the negative pres¬ sure of a siphon tube, and the barometric pressure were recorded for calculation of the volume of the residual gases.

The iodine solutions used in these analyses were standardized against standard arsenious acid solutions. /

A typical data sheet with the necessary calculations for a complete analysis is given below*

Weight of water, g. 185.5

Temp, of water, °C 28,3

Specific volume of water, ce./g. l.Od*

Volume of water, cc. 186.2

Barometric pressure, mm. of mercury 757.7

Siphon negative pressure, mm. of mercury b.U

Vapor pressure of water, mm. of mercury 28.8

Corrected pressure of residual gas, mm. of mercury, 757.7 - k.i* - 28.8 s 721.5 94

Volume of residual gas* ec. at standard conditions,

186.2 x^ 72U.5x ^ 273.2 - 160.8 301.5

Normality of iodine solution 0.0875 Volume of iodine solution, cc« 9.97 Volume of SOg equivalent to iodine solution, ec. at standard conditions,

9*5$

Volume percent of SQg in inlet gas

9*55 x 100 = 5*61 160.8 + 9*5^ APPENDIX E

CAICUIATIOS OF COHVBESIQ?* For the reaction

302 * i°o 30,J'3 one and one-half volumes of two different gases combine to fora one volume of the tliird gas (23). If & be designated as the volume fraction of SOg in the feed gas and c the fraction of SO2 converted., then 3/2ac represents the volume of feed consumed to form SO^. Since the SO3 is completely removed from theproduct gas in the Reich test, the remaining fraction of the volume of total feed gas is represented by l-3/2ac. Since the stripped exit gas contains b fractional volume of S(^, the vol¬ ume of SOg in the exit gas is b(l - 3/gac) and the volume converted is a - b (1 - 3/gac). ^hs fraction converted is therefore expressed by the equation c = a - b (1-3/pac) a Oil) which reduces to - 2a - 2b 2a - 3ab (1*2)

Equation (1+2) was used in all conversion calculations using the volume fractions obtained from Reich tests of feed and product gases APPENDIX F

REACTION EQUILIBRIUM CONSTANT

Versus

TEMPERATURE FIGURE 29

REACTION EQUILIBRIUM CONSTANT VERSUS TEMPERATURE

S02 + *202 = S03

GAS ACTIVITIES IN ATMOSPHERES

TEMPERATURE t DEGREES KELVIN APffiMDIX G

NOMEKCIATUHB 100

activities of components A, B, etc., at catalyst interface, a%> ctc# G overall rate constant, E i catalyst effectiveness factor* k Reaction velocity constant, ki empirical constant, kg empirical constant, k, empirical constant.

adsorption velocity constant of component A. eR adsorption velocity constant of component R. kQg adsorption velocity constant of oxygen* k adsorption velocity constant of sulfur dioxide, S02 K thermodynamic reaction equilibrium constant,

% empirical constant, empirical constant,

K, empirical constant.

K^, Kjjj ©tC« adsorption equilibrium constants of components A, B, etc.

It adsorption equilibrium constant of oxygen. % K adsorption equilibrium constant of sulfur dioxide. ■SO.J2 K. adsorption equilibrium constant of sulfur trioxide. SO, L number of active centers per unit mass. n Hole of sulfur dioxide flowing across a differential mass of eatalyst per trait time.

POg partial pressure of oxygen in atmospheres. Subscript sera refers to feed composition. pS02 partial pressure of sulfur dioxide in atmospheres. Subscript aero refers to feed composition.

%03 partial pressure of sulfur trioxide. r reaction rate, quantity reacted per unit time per unit mass of catalyst.

E gas law constant s number of equidistant active centers adjacent to each center. 101

time® temperature, degrees absolute* mass of catalyst. ±02

APFEIffilX H

LITERATURE CITED 108

10 Hougen, 0o A®, and Matson, K® Mo, Ind® Engo Chea® 30, 029-SI*3- (1943)°

20 Hougen, Oo A., and Watson, B® M®, ‘'Chemical Process ft*inciples - Part Three", John Wiley and Sons, Inc®, Mew York, 1948° 3o Resnick, W® and White, R® R®, Chea® Eng® Progress US, 377-390 (19H9)® H® Gamson, B® ?/«, Thodos, 0. and Hougen, 0® A®, Trans® As® Inst® Chea® Engrs® 39, 1-30 (3$l*3).

S® Wilke, C® E®, and Hougen, 0® A®, Trans® An® Inst. Chen® Bngrs® Hi, 440-401 (1940)° 6® Gilliland, E® R®, and Hasan, E® A®, Ind® Eng® Chea® HI,1191-1196, (391*9). 7® Glasstono, 3®, “Test-Book of Physical Cheoistry", li® Van Mostrand Co®, Inc®, .New York, 19H0, pp. 1067-1069, 1102-1103® 8® Fairlie, A. M®, "Sulfuric Acid Manufacture", Rainhold Publishing Corp®, Mew fork®, 1936, pp® 331-332°

9® Lewis, W® Ko, and Hies, E® D®, Ind® Eng® Chea® 17, 093-598 (1920)® 10® Lewis, IT® K®, find Hies, E® D®, Ind® Eng® Chea® 19, 830-837 (192?)® 11® Uyehara, 0. A. and Watson, K® M®, Ind. Eng® Chea® 30, 041-040 (19H3)® 12. C® A® HO, 29H3 (1946)®

13® C® A® Hi, 6121 (19H7). • IH® C® A® 31, 3217 (1937)® 15® Hurt, 0® M®, Ind® Eng. Chea. 3g» 022-028 (19H3)® 16® Bragt, G®, and Greenan, K. W®, Ind. Eng® Chea® (Anal® Ed®) Hi, 883-880 (191*2). 17® Holmes, H. H® Ramsey, J®, and Elder, A® L®, Ind® Eng® Chea® 21, 800-803 (1929). 18® Tolley, G®, J® Soc® Chea® Ind® 67, 369? H01-H07 (19H8)®

19® Gulbransen, I® A®, Trans® Electrochemical Soc® 91, 073-602 (19H?)® 20® Hougen, 0® A®, and Watson, K® II®, "Chemical Process Principles Charts,1' John Wiley and Sons, Inc®, Mew York, 19H8, Figure 106®

21. Hall, R® E®, and Smith, J® M®, Chea® Bngo Process 45? 409~47GO (19H9) 22® Dodge, B® F®, "Chemical Engineering Thermodynamics," McGraw-Hill JBook Co®, Inc®, Hew York, 1944, p® 336® 23® Fairlie, A® M®, "Sulfuric Acid Manufacture," Reinhold Publishing Corp®, Mew York, 1936, pp® 496-497 . ±04

APPENDIX I

LOCATION OF ORIOINAL DATA The original data of this investigation are in Research notebook No. I, pp. 1, 3, 5-a, 7, 21, 39-U3, $2-56, 69-72, and

Research Notebook No. .11, pp. 1-37* These notebooks are titled as followss An Investigation of the Reaction Between Sulfur Dioxide and Oxygen in a Fluidised Catalyst Bed.