Hydrogen Sulfide from Sulfur Dioxide and Methane. - Industrial


Reduction of sulfur dioxide with methane over selected transition metal sulfides. Industrial & Engineering Chemistry Research. Mulligan, Berk. 1989 28...
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Hydrogen Sulfide from v Sulfur Dioxide and Methane J

Equilibrium calculations froin r&tiiig data gisc a c l e a r picture of the effect of certain \ariables on the reaction of' sulfur dioxide and methane. The ratio of reactant*. Y(SO2) '(CH,), is an important factor in the yield of hydrogen sulfide and other reaction products. Experimental confirmation of the conditions predicted by these calculatioris is reasonably satisfactory. The rate of the ober-all reaction within the range 850-1000" C. appears to he controlled by the rate of reaction or decomposition of methane: the effect of temperature on o*er-all rate i* appreciahle.

4 ) f ' 11) drogrii ~ullrclein(.rt~asing n ith temperact urv. I he effrc*tof space b e l o c i t y within the range for V ' C , a b f 660-1320, temperature 850-1000° (:., and ,V = 0.5 appear. t o be negligible. Sulfur, formation is encountered either .it high talues of X , high rates of flow, or low temperature. i t \ = 0.3, temperature range of 850-1000° C., and flou rates I I; of 660-1320, high jields of hydrogen sulfide raii he produced b j the reaction of sulfur dioxide and methanr. i t 1000" C. and F'/C'c of 880, the value of A' can he iaried f r o m 0.5 to 1.0 without affecting hydrogen sulfidr jield.

I tit* 1 it-lcl

T"

.wvt~ralratio, llesirable to make tn-o indepentlc~nt oalculations of equilibrium orie with excess carbon present, t h t x other kvith no polid carboii. 3, in addition to the equilihrirliii \laterial balances on the c~leinr~nt information, will tlictatc t h v r.orn*ct i-omposition Cor any V : M ,

FIGURE I

FRACTION 0.ot

907

T h e e iudependent equittioiis are thus obtained from thih iiiaterial idance, The final equation is, a,s before, the sum of the molc i'ractions in a gas mixture. The solution of this case is even niore complex than i n W ~ C1, : i i i r l makes use of the three final equations. TIT-oiiitlip~ndcnt (quations in three variables were obtained from t h o origiriiil niiw : i r i t l wsr? solved by trial solution at. various coiwtaiit v:ilut>- oi i l i i ( ~ . The vnlucv rommon to both equations, detcrminttl gral)i i~ ~ : i, l\r-ercl lj thcn ~ubstitutcdin thc. tenth (,quation as hoforc, to o i l The rcsults of these equilibririni c d c u i i i i i i tht' i'orrect holution. 1:iticIn- a i ( ' given in Tahle I1 and are presented in FigunSa 1 and 2 . Ttic w o r k involvcd in tlic calculations preventid the tL(,t(ariiliti:tI ion of I I I I J W points:. .is thr length of the work hecainc ap~iiirtwt, i t was ,juclgrd to bc most advantageous to find the effcrt of vari:tt)le.\-at coilstant temperature. Thcchoiccof727'"C. (1000°K.) may not have been the best, as later experimental ivorli had t ( ~hc ronducted at approximately 100-300" C. higher. At the t iine of calculation, this appeared to be a logical starting point, t):wti o n the temperatures disclosed in the patents. It is beti, however, that there is little change in the gas coniposition for this variation in temperature. One point a t 1000" C'. I 1273" IC.) is shown to support this belief. I n the figures presented, the mole fractions a t each point are [)laced on a common basis by calculating each one as a fraction a total element~---i.c.,x ( C ) , ZiO,), etc. T h r w fractions or ~-ific~irncir+ are givcn in T a h k 111.

VS. N

E O U I L / B R / U M CALCULAT/ONS

TEMP. 727.C. CtOOO'K.) EACESS SOLID CARBON PRESENT

. -

-~ *

-

1.0

._*

-

1

,

( .A*E 1, SOLIDCARBOXPEEJEST. I'nder tiles(. conditiuii> rilere are ten variables (the fugacity of solid carbon was assumcvl wiistant) so that ten independent equations are necessary for H

d i t i o n . Seven independent equations for the eleven componrntz were developed from the corresponding equilibrium expres*iotis. Equilibrium constant K , is in terms of mole fractions, ~ i i t lr refers to the numbered equations in Tahle I. The total pressure was assumed to be one atmosphere. In the mixture of reactants the ratio of SO2to CHI is defined a.V, where N is a constant. As the ratio of their mole fractions i i ~ I R N, O material balances on the elements can he expresed as S(S) = V(0:)

= 2(Oi)

$

2

= '!:.YV(HZ)

wlitre Z(S), for example, is the sum of the mole fractions of sulfur-bearing components. Kot,e, too, that carbon is assumed present in excess. Two further independent equations are obrained from this material balance. The final equation necessary 16 otitained by remembering that the sum of mole fractions in a gas mixture is unity. Reducing these ten equations to one equation containing on(' unknown is complicated. Solution was simplified by combiniug the first nine equations into one equation in t,wo variables, ( C 0 2 )and (SO2). This equation was then solved by trial wlution, and the various values of the corresponding components were substituted into the tenth equation to obtain the corrwt solution. ( ~ A S E2, NO SOLID CARBOSPKESENT. I n this case there are ttw components (no solid carbon) and ten variables. Six independent equations are developed, as in case 1, from the equilibrium constant expressions. Here t'oo (SO,)/(CH,) = .Y by definition. The materixl balances now containing carbon are:

X(S)

0.1

SV(c') = I j ? S X ( H g )

0.01

EQUIL t&Q/UM CALCULA T/ONS

rEw

7 ~ 7 " ~~t 0. 0 0 ' K . )

0.002 0.5

1.0

1.5

2.0

&\I 1' = 727" C'. and S = 0.5, when excess carbon is present, the S Z(C'j in the gas phase is less than 1/tLVZ(H2). This indicates that, a t equilibrium, solid carbon is being deposited from methane. This point is, t,hen, common to the equilibrium conditions where carbon is added only as methane. All other points of this group with solid carbon present show excess caarhon in the gas phase ovw that which canit' from methant,.

INDUSTRIAL AND ENGINEERING CHEMISTRY

908

I 2

0.2528

0 5

0 0338 0 1864 0 4080 0 0676 0 2620 0 . 2 2 5 2 0 098.5 o 2806 o o m o in30 o.zo2n o 0212

I

I i

0.3380 o.0009 0 4730 0.4810

7'705

2

0.1.523 0.3170 0.1688 0.2550 0 . 1 4 9 1 0 0016

I

0 1370

1

0 3180

0.005-1 0.0202 0.0818 0.2020

n o m

0 0473 0 0183 o 0052

0.2-18~ .... 0.3621 . ... O . I ~ 0.0003 0 . 4 m

....

0.0003 o.0030 0.0185

n.0017

,. I

Iic.

E. F. 6. H. I.

J. K. 1,.

0.1921 0.1Y20 0.2825 0.2828 0 . 3 6 ~ 2 0.3711

0.4330

0.4m

0.IiIL 0.4MCI i.2~1;

7.1oii

~ ~ l l i ~ ~ i tof~ i iiict yi l i ~ a i i i ~ i01i tlie reduring agents, f 1 2

;iiid (',

rnixturo. Although the siiliur dioxide--methane ratio of 1.33, sirggwt ~ i i tly I{~)wnstcin( I S ) from thv equation,

ihou!tl givt. the I I ~ : L Y ~ I ~ L U I yield II of hydrogen sulfide as tv(>il maximum utilization oi' thc V and HZ, a t his recommended ternp c ~ a t i i r eo f 700-1000" C.the equilibrium calculations, assumilia. no carbori present, indicat,e that it is i m p w i hle t o obtain only these three reduction p r i r c l ucts. The conversion of sulfur to hydrogwi sulfide is lower here than at lesser ratios of .Y, I I O v. TO and considerable sulfur vapor is likely to lw produced. Tushkevich et al. (22, 23, 24) seem to 1i:ivv :i i n i i c h better conception of the products to be expected at specified conditions than do other.. They :icmirately point out the effect of t t m pt.r:rture on increasing the formation of c m boil monoxide and HP. Although their hiy!, yic'lds of sulfur at S = 2.3 cannot be ~ c i i r:itt,ly checked by the calculations, they are cvrt:iiiily in the range indicated. The incomplct~* i,i.actiori of methane reported may he due p:trtly to !c)vv reaction rate, but equilibrium alone n-ill :ic*count for some of the excess. The figures reveal the trend of each coinpoiient Kith .V. With the production of hydi,oFIGURE 3 geii sulfide from sulfur dioxide and methario i i i FLOW SHEET mind, t,he usc of carbon as an ,xlditional Y I P ducing agcnt does not appear justified. It is truts that :it .\- = 2 the hydrogen sulfide yii,ltl o n tiit:tl sulfur, for this c Liquid aulfur dioxide cllinder Methane gas holder, a n 18-liter bottle with eonstant-hem1 Htandpipc. t h a n with no carbon presen Flowmeter. ome sulfur is converted to unw:mtcd S,nr Electric furnace, equipped with GI0 Bar rceistorr. carbonyl sulfide. Catalyst tube (I-inch fused quartz) I n the range d i e r e N = 0.5-1.0 and tlie iiyThermocouple in quartz protection tube Millivoltmeter (li.og(111sulfide yield is high, the presencri of Sulfur condensers with bayonet heaters c*arhim has less effect. If the value of citrboi~ Trap, water-filled in methme [vas high with respect to that iu Bubblers containing sodium hydroxide solution some solid form (coke), the iiso of carbiin Gas storage bottle, with e x i t line as shown and a t t s c h r d Ie\eling I m t t l c Volumetric flask and opcration at S of 2-4 might k~e w x ~

C.

...

0.1921 0.2825 0.3692 0.4330

sulfidt~,n.ater, :tiid ritrboti dioxide, but with solid carbori prerciit the amount of n-:iter and c:rrt)on dioxidc must of necessity bc lit\\. LYlnier (14) and H,trtmmn (?), n-ho used coke and steam 01' :I mixturc of Hzand carhon morioxide, could attain the same cquilih\v

1.21)7

1.280 1,200 1.047

0 ,5310

0 3975 0.1932 0 0!Jlj9

0.0987 0.1451 0.1569 0 1330

909

ANALYSES

Gas. A 100-cc. portion of the gas sample was drawn iiito a gas buret, using mercury as the leveling fluid. The analyses were conducted by the stxridard technique for each component. Briefly, in order of determination, these were as follows: Carbonyl sulfide was absorbed in alcoholic potassium hydroxide; if any alcohol remained in the gas phase, it was removed in concentrated siilfiiric arid. Oxygen was absorbed by :ilk:tlinc pyrogallol. (':trhon nion(isid~~ \vas removcd by contacting the g:is with :tc.id cuprous chloride wlution. Hydr determined by combustion. S It is to he noted thnt the anal inclurit* any carbon disulfide pr Howcvi:r, the lattrr w:t$ [lever found by colorimcttric tests. LIQIYD. The acidic gsscbs hydrogen sulfide, carbon dioxide, :ind sulfur dioxide were absorbed in the caustic solution. Hcatiiig coils were p1:tced on the gas sample lines t o prcvixnt ivater condensstion there, as the reaction between hydrogf~risulfide and sulfur dioxide is known to take place in witer solution. There is n o reaction between these t\vo in alkaline liquid. The c.austic solution (a mixture of sodium sulfide, sulfite, carbonate, :ind hydroxide) was made up to one liter (the master sample). .4 portion of this sample was titrated with hydrochloric. acid, using methyl orange indicator. This determines the alkali as rodium hydroside, carbonate, sulfide, and half the sodium wlfite. The second detchrmination on the sample was titration with hydrochloric acid and phenolphthalein indicator, giving sodium hydroxide, halt' the sodium carbonate and half the wdium sulfide. T o :t portion of the originnl sample, barium chloride solution v a s added: barium sulfite and barium csrbonatc precipitated out and were t h r n titrated (without filtering) with hydrochloric wid arid pheriolphthalein to give t,he sodium hydroxide arid half the sodium sulfide. The total sodium sulfide and sulfite were determined by adding x i excess of standard iodine to the sample, acidifying, and titrating the excess iodine x i t h standard sodium thiosulfatc,. Sodium sulfite was determined b v addinn alkalinc zinc chloridt le and titrating a measured portion of this solution, nc sulfide precipitate with standard iodine. These ere then combined to determine each of the compo-

The. hydrogen sulfide, carbon dioxide, and sulfur dioxide tvere then converted t o volumetric units under the conditions colht:n combined with those implete gas analysis of the

a of the experimental n.ork V/'t*c, in cubic fevt per 25" C. arid 1 :itniospherc* cntdyst, \vas nstd tci i ~ s l ) r w ttrt, s r:iti. o f fli>v

per cubic. f i i c ~ t ( i t tlir(1Ilgli t h l ~c3t:lly.t h t l .

HESUL?'S

t s ( ~ the f investigation are prosented in 'r:tl)lc~I\' and res 4 and 5 . Table I V gives the composite gas compositioii, dry h i s , of cach run as computcd from t,he combined

0.1758 0.2393 0.267 0.238

0.028! 0 071,) 0 222 0 407

0 0158 0 0433 0.1302 0 2603

0.2427 0.463 0.751 0 923

0.Yil 0.927 0.762: 0.467

0.1992 0.0333 0.0025

....

INDUSTRIAL AND ENGINEERING CHEMISTRY

910

4 5

0.36 7 . 7 5 9 . 1 3 1 0 . 7 2 1 0 . 6 0 30.63 1 3 . 5 7 17.27 1.76 18.00 22.56 26.40 0.15 7.65 13.85 9 . 6 2 1.82 1 6 . 3 0 25.10 22.25 0.29 7 . 0 0 1 6 . 9 5 10.30 1 . 4 0 1 5 . 5 0 27.22 19.15 7 0.60 6.00 1 9 . 3 0 10.83 1 . 7 1 20.90 1 7 . 1 5 37.90 8 0.94 6.75 8.62 5.98 1OA 1 . 6 1 18.10 23.90 27.50 5 . 3 6 13.61 0.23 9.78 2 . 1 9 20.82 27.30 28.30 0.42 1OB 5 . 2 3 13.54 2.16 1 . 9 2 25.80 11.1 0.61 9 . 7 5 3 4 , 2 0 . 4 . 4 5 20.60 2.63 11B 2 . 0 2 26.40 12.50 3 2 , 5 0 6 . 7 7 1 8 . 4 5 0.40 1.00 12 1.91 2 5 . 2 1 1 1 . 6 1 38.61 9.00 12.60 0.85 0.17 8 . 4 6 40.48 1 . 9 4 26.21 6 . 7 6 14.20 13A 0.68 1.24 7.85 40,20 1 . 7 3 26.80 7 . 0 9 14 55 13B 0.72 1.03 6 . 2 8 39.81 2.60 26,20 7.19 14.87 2.43 14 0.62 15 0.66 19.18 5 . 0 6 34.70 1 4 , 3 9 1 . 3 0 21.60 3.10 16 27.25 11.00 48.12 1.22 13.60 4.79, 19 1:63 27.76 3 . 9 2 40.62 6 . 5 2 13.91 2.50 1.14 20 1.29 25.98 2 . 7 2 31.59 3 . 0 8 26.20 1.69 7.45 a No SO2 was found in the samples, 4 i r ( 0 2 and Nz) found in samples uii. present in sample lines, bubblers, etc. b No sample for runs 1 2 3 9 17 a n d 18. Air leak calculated 0; a h k r g e b h .

6

Vol. 38, No. 9

fide i n tho connectirig lines; however, iiu sulfur dioxide wa8 found in the caustic solution. This reaction can occur in the gaa phase (16, 20) but a t temperatures lower than that of the catalyst bed; starting at about 400" C., the yield increases as temperature decreases. The rate decreases until reaction becomes negligible near 150-100" C. Thus, the gas-phase reaction must have occurred occasionally and was probably encouraged by the residence a t 400-200" C. in the heated sulfur condensers. This ivas the most probable cause of sulfur fog under certain conditions. Thus the use of the elements Hz, 02,or S was eliminated :is a basic balance for calculations, and carbon remained the only I !ne availablr.

. I .

analysis. Before these gas compositions, however, can bc directly compared, they must be reduced to a common basis. Thib was done by expressing each gas in the mixture as a fract,ion of ant' { i f its element components. Table V presents these ratios of coniponent t.o element, or fraction efficiencies, as well as the additional variables of temperature, rate of gas flow, and ratio of reactant* S02,'CHI or N (both as measured by flowmeters and as calciiLatrd from analytical data). Table V is the master sheet for t h cwnstruction of the figures and should be considered the tabulation of usable data. There are three sets of runs: ( a ) 4-llB, where the carbon riirixide analysis is likely to be in error; ( b ) 12-18, where the carboii iliox4de error is probably small; and (c) qualitative runs, 111' moasured data. The analysis of carbon dioxide in the caustic solution wa. a troublesome feature. A probable error was the transitory e i i t i point due to the action of sulfide on the indicators. After ruii 11B an attempt was made to reduce this by the addition of an indrpendent determination of carbon dioxide. It is believed that the accuracy, with few exceptions, is within 10% of the correi-l value. Every precaution was taken to prevent condensation of water and the subsequent reaction of sulfur dioxide and hydrogen sul-

4 5 6 7 8

1OA

10B

11A 11B 12 13-4 13B 14 15 16 19 20 17 18 1 2 3

848 840 845 847 910 850 850 848 848 980 970 970 970 1000 985 1020 940 1010 1010 775 775 850

660 660 991 1320 660 660 660 330 330 705 660 660 1320 882 882 772 882 882 1320 1000 1000 660

0.5 0.5 0.5 0.5 0.5 0.5 0.5 0 . $5 0.5 0.455 0.5 0.5 0.5 1.0 0.5 0.525 0.75 1.33 1 .00 1 00 1 00 0 5

u

460 0 191 0 198 0 200 0 133 0.188 0 043 0 068 0.025 0 021 0 034 0 028 0 069 0 362 0 108 0 071 0 197 lPlP

0.967 0.518 0.494 0.487 0.476 0.513 0.318 0.47 0.42 0.361 0 427 0 435 0 520 0 980 0 552 0 566 0 753

KFFECT OF N ON RATIO OF COiMPONENTS TO ELEMEYTR

Figure 4 shows the effect of .V, the volumetric ratio of sulfur ilioxide to methane entering the catalyst bed, on the reduction wmponents a t constant temperature (approximately 1000" V.) :ind constant rate of flow ( V / V , = 880 approximately). Comparison with the equilibrium calculations indicates t tir -ame trends for each constituent. Figure 6 is that portion of the tquilibrium curves covering this range, the scale being the same i n both cases. Although the equilibrium calculations were for 727" C. and t,he experimental temperature was 1000" C., it i p cbvident that the variation in temperature makes only a slight change in the position of the curves but does not change the gelr1.ra1shape. Table VI compares the equilibrium values of ,V = 1, 1000" and 727" C., with theexperimerital point N = 1,1000"C. The similarity of the equilibrium and the experimental curve* iiidicates that the gases are at or near equilibrium. Certainly I his is the case with those of the n-ater gas reaction, as the agrtvrnent between its equilibrium constant from experimental data :ind the accepted values is goad (Table V). There are certain marked twnds with the variation of S. Tiit. yields of carbon dioxide and water increase its N increases, wherea* rwbon monoxide and hydrogen decrease. This shifting of water :rnd carbon dioxide, as the amourit of oxygen from sulfur dioxide i q increased per unit of methane, is both compatible with thc *toichiometry and the assumption of equilibrium for the watur gas renrstion. Examination of the equilibrium expression,

0.01 0.006 0.012 0.023 0.044 0.009 0,026 0.033 0 024 0 012 0,044 0.046 0,034 0.08 0 0.5 0 0.5; 0 060

0 181 0 13U 0 163 0 178 0 096 0 131 0 133 0 266 0.22Y

374 0 532 0 6i2 0 732 0 403 0 610 0 84.5 1.13 I ,085

0 . 166 0.194 0,200 0.209 0.437

0 91Y 0 908 0 919 0 805 0 893

IJ

0 556 0 790 0 920

0.154

0 , 2263 0 . 346

0.391 0 152 0 140 0 142 0.102 0.145 0.049 0,042 0.058 0 017 0 021 0 032 0 054 0 306 0.122 0 089 0 178

lPll , ,

., .Sulfur fog . . . . ,Sulfur f o g . . . . . . .

,

,

.. . .. . . Fimt analysis, error? in gas analysis, n o S f o x Equilibrium constants

727 850 910 loo0

08.

. .

..

temperature (from Kelley, 9,10, 1 1 ) :

0.645 1.06 1.30 1.71

19.5 360

"00

14000

0 . 809 0,587 0,576 0.550 0,426 0 . ,565 0,309 0.180 0.27.;

0,092 0.101 0 . Id9 0.207 0.623 0.441

0.314 0,472

INDUSTRIAL AND ENGINEERING CHEMISTRY

September, 1946

shows that it i i possible for these oxygen-carrying gases to i i i c1ea-e in amount and yet retain the same equilibrium value. However, there is far too much methane present for the a\wmption of complete gaseous equilibrium. This is evident whrn one compares the equilibrium values of K , = (CO)z(HJd (CH,) (CO) from Kelley with those calculated irom the expcsi Imental data of this work (Table 111). Thus, at the conditionof lato, temperature, and range of S invrTtigated. the metli,iiii did not rvnrt completely (?, 8,17, 1 9 ) .

This, however, is somewhat surprising when it is considered that the total amount of H1 referred to the sulfur dioxide is decreasing iincreasing A'), and the fraction of Hz converted to water is inweesing. It must be that the increased amount of sulfur with its tcmdency for hydrogen sulfide formation has as strong an influence 1111the distribution of the hydrogen as do the elements C and 0 2 . The trend of the Larbonyl sulfide formation shows little change ocer this range of A', and as its value here is small, it has little eft cvt on Ion ering the efficiency of qnlfiir cnnversion to hydrogvn -1ilfide.

1. C

si:

EFFECT OF TEMPERATURE ON RATIO OF COMPONENTS Ti) ELEMENTS

111 Figure 5 , runs 5, 8, 10-4,and 13, a t constant N = 0.5 aud rate, V / V , = 660, show the effect of temperature on the fraction of the components to elements. Actually run 8, the only det,ermitiation a t 910' C., is in error but is added because no other run was made at a third temperature. Inasmuch as there are insufficirnl iiata to establish the actual shape of the Curves, they are drawii :I.sfmight lines and represent trends only. In general, these trends are as would be expected from a study c i i the equilibrium calculations. The increase of carbon monoxide :I tid the decrease of carbon dioxide with increase in temperature :I t'c consistent with known equilibrium relations. The deereast, of 1nt:thane with increase of temperature at, cwnstant rate of flow is indicated both from its decomposition equilibria and from thtwte of its decomposition. The observed change of hydrogen qiilfidr yicxld is, however, not indicst,rd by the equilibrium calt*ii1;itions.

0.1

I-/

c,

$

:i:j

FffAcr;: :,- -'

EXPERIMENTAL

FIGURE

4 1

0.01 0.5

0.6

0.7

0.6

1

0.9

1.0

Since the evidence points to the Fact that must u i the s u l i u ~ ~ dioxide has reacted at the low values of -?I' shown in Figuro -lS and since other gases are in equilibrium, it is possible that thu methane present acts mainly as a diluent. Since it appears that the water gas equilibrium is reached quickly, a slight change in the amount of methane reacting would cause only a shifting in the position of the curves but no change in their trends. These points cxould have been correlated with a calculated value of *?I7 on a residual methane-free basis, but the change in t'he position of t,ho curves would appear to be very slight. It is concluded that, while some methane is present in excess of that necessary foi, comp1et.e equilibrium, the experiment a1 curves represent :tpproximate equilibrium conditions for all other components and substantiate the trends found by the calculations. The fraction of total sulfur converted to hydrogen sulfidr shows very little change over the range of A' studied at these conditions of temperature and rate. However, &s indicated in Figure 1, a continued increase in hr should produce a sharper decrease in the yield of hydrogen sulfide. A run ( S o . 17) carritd out a t the same temperature and rate as shown on Figure 4 but with N = 1.33 (the ratio which would satisfy the equatioo, 4SO2 3CH4 + 4H2S 3 C 0 2 2 H 1 0 ) showed large amounts of sulfur fog. This sulfur may hsvr been that present at equilihrium under these conditions (Table 111, S = 2, no solid C present, S/ZS = 0.558) or may have been caused by the excess sulfur dioxide passing through the catalyst bed unreacted and thew uniting with hydrogen sulfide a t a lower temperature level. In ally event, experiment confirmed t h a t a t this rate a n d this temperature the yield of hydrogen sulfide it; drrreased by an increase i i i ratio N . The fraction of hydrogen which enters as methane and appears as hydrogen sulfide increases with S, as might be expected from the fact that, the fraction of total hydrogen as HS decreases.

+

911

+

+

TEUPERA TURE .*e.

Study of the magnitude of all the trends, even though in t l i v 1:rcct direction, shows that they are too large to be explaiiied mtirely by change in equilibrium with temperature. Thts ch tnges are more probably due to increased reaction rate at the higher temperatures. At these higher temperatures more melt hm e will be decomposed (cracked), and hence the yield of all elmponents will be changed accordingly. Less unreacted sulfur dioside should be present, and therefore a higher hydrogen sulfiil(~ c

912

INDUSTRIAL AND ENGINEERING CHEMISTRY

yield should result; consequently, less sulfur should be formed from the subsequent reaction of these two compounds. The fact that the samples represent only the over-all reactions, both a t the catalyst and any that might follow in the lines, prevented the confirmation of this cause of the iiicrease in hydiogen sulfide, but it appears logical in view of the experimental evidence. The conclusion is, then, that the effect of temperature on reactioii rate is appreciable under the conditions here measured; and the yield of hydrogen sulfide, based both on tot.al H1 and total S,is increased a,t t.he higher teniperaturtx

Vol. 38, No, 9

The first reaction which could take place is either that of sulfur dioxide with methane or simply methane decomposition. .4fter this, equilibrium among the reaction products is attained quickly, :ti indicated by the water gas reaction. Thus the rate of all rex t i o n s involving the decomposition or reaction products of sulfur dioxide or methane appears to be adequate to a s s h e the equilibrium n.hosth result is hydrogen sulfide.

EFFECT O F SPACE VELOCITY ON KATIO O F COi\ll'ONEh'IS TO ELE.MENTS

The effect of space velocity on yields \vas considered in the runs a t 850 * 10" C., A: = 0.5, and a t 980 * 10" C., = 0.5, where the rate V / V , (cubic feet of gas at 25" C. and 1 atmosphere per cubic foot of catalyst) varied from 660 t o 1320. In both cases there appears to be no significant variation with velocity over the range studied. When the slight irregularities due to errors are ignored, it appears safe to conclude that, at N = 0.5 in the temperature range 850" to 1000° C., little change in yield of products is produced by a variat'ion of rate from I7/VTc = 660 to 1300. 1.0

FIGURE 6 _iT/ON

,

I 1 '

VS. N

E Q U / L / B R / U M CALCUL.4 TIONS

0.952 0,045 0.137 0.500 0 . 2.54 0 268 0.478 0.634

0.6

0.7

0.8

0.893 0,080 0.362 0 . ,544 0.241

0.306 0.437 0.605

11 13auiii, li. I,'., nti,l Boe, 12. S . , ISD. Exc;. CHEY.,37, 4tiY (1945) . Soc., 93, 1197 (1905).

~

2,133,000 (July 5 , 1WS). F.,and Bradley, IT. E., IND. ENO. C H E J I . , 36, 829 (1944). 8 5 , G a m e r , J. €3.. and Clayton, H. L),,U. S , Pnteiit 1,175,566 ( F e b 29, 1916).

N O CARBON PRESENT

0.5

951 048 410 542 230 233 477 586

1It.tliane, hu\vcver, i j kriu\vri to h a w :+ slow ciecouipositiou rate ( 2 , 8,2 7 , 19), and the presence of an excess over that expected at equilibrium confirms this. It is prob3ble, t h c q that t,he fartor controlling the over-all rate of sulfur dioxide and meth:in? reaction is the slow methnne decomposition. It is :~lsopossible that the reaction of sulfur dioxide is likewise cess sulfur dioxide is indicated by sulfur formation sulfur dioxide and hydrogen sulfide) in several runs a t .Y = I . However, under the % m e conditions of N and temperaturc but :it a lower rate of flow, sulfur formation was negligible aince the increased contact time must have decomposed enough methane ior complete sulfur dioxide reaction. It is true that a t liiyh rate,;. low temperature, or high values of S,sulfur is formed ( i ther by tlie p:tssage of sulfur dioxide through the catalyst bed or by the :ictus1 forniittiori of sulfur at this point. (The equilibrium caloulations for S = 2 and 727" C. show that 55.8% of the total sulfur entering is present ns Szand that the sulfur dioxide is This form:ition, howevcr, in all cases can be considered 11(irto inwlfficient methane or t n lack of its ienct,iori.

TEMP. 72 7 "C. (/COO *U.>

0.01

0 0 0 0 0 0 0 0

0.0

Hilllows, It. L., private communication. Hartmarin, H., D i n a h ' s Journal, 237, 143 (1880). 1x1 Kahozev, Kashtanov, and Kobrin, J . Gen. Chem. (U.Y.S.R.). 5, 143-8 (1935). !JJ Kelley, K. K., U. S.Bur. Mines, Bull. 406 (1937).

I. 0

)

i

Qualitative run 18 was made a t 1000" C., A' = 1, utid 1'1 I', = 1320. This is to be compared with run 14. carried o u t :tt the same teniperature and rate but Kith S = 0.5. The presence of large amounts of sulfur fog rendered analysis of t,he gas mixture meaningless, but this sulfur does indicate that at, the high rate of .~ t /6,= 1320 and temperature of 1000" C., A' cariiiot aafcly- he raised as high as unity without a decrease in hydrogen sulfide yield. Qualitative runs 1 and 2 at 775' C., S = 1.0, :tnd I.'/T-, = 1000, where large amounts of sulfur were produced, were, in the light of other runs, also at the extremes of permissible riite, temperature, and ratio N . The individual reactions vhich actually occur to make up the over-all reaction between sulfur dioxide and methane a t these conditions of rate of flow, temperature, and ratio A' cannot, he determincd. However, some idea of the possible mechanism c ~ n be drawn from the experimental and calculated obserwtioiis.

10) Ihid., 407 (1937).

111) Kellev. K. K.. and Anderson. C. T.. Ibid.. 334 (1935). (12) L&e, R , INU.Evc;. CHBY.,33, 92 (1935). fI.3) It~id.,32, 910 (1940). 1-1) Alaier, C. G , and Dean, R. S., U. S. Patent 1,941,702 (Jan. 2 1934). (15) Mattlien%, E.. J . Chern. SOC.,1926, 2270. (16) hlerriam. H. F.,C . S . Patent 2,043,202 (June 2 , 1936). (17) Padorani, C.. Chirnie &- i n d u i t r i e , Special No., 255 (March. 191;2). 18) liosenstcin, L., C. S.P a t e n t s 1,967,263-4 (.July 24, 1934). 119) Slater, h l . , J . C.'hcm. Soc., 109, 160 (1916). ( 2 0 ) Taylor. H. .i., and T e d e y . IT. .i.,,I. Ph~yq.C h e m . . 31, 216 [

(1927). (911 Tliac~kcr.C .

AI., a i d Miller, I,:., ISD. I,Csti. CHEY.,35, 182 (1944). arid Avdeeva, .I. L'him. I d . (U.S.-

I 22) Yiistikovic.11,'Karshavin,

$ . I t , ) , 1932, So. 3, 17. ( 2 3 1 5-iid1kevii.h.

Karzharin. .lvdee\.a.

and Krechetov.

Ibid.,

1933, So. S, 50. (24) Y u i h kevich , K nrahar-i ri , .i~ d e e v amid , Niuol's kaya, Ibid., 1934, Yr).2 , :K%,