chlorofluoro- and chlorofluorohydrocyclohexanes. I t is evident that when these hydrogen-containing compounds are present, a higher temperature is needed for complete aromatization. This resistance to aromatization is shown to a n even greater extent by the saturated fluorohydrocyclohexanes ; for example a mixture of cyclic CsFloHz isomers yielded only starting material when defluorinated at 500’ C. in the reactor described. At 630‘ C. it decomposed almost completely, and no fluorobenzenes were isolated. I t is therefore evident that the presence of chlorine in the hydrogen-containing fluorocyclohexanes allows aromatization to occur a t lower temperatures, perhaps initially by loss of chlorine, ClF, or even HCI, and both perfiuorobenzene and pentafluorobenzene are readily obtainable. The infrared spectra of all of the material, described in Table I\- as other fluorobenzenes, from every dehalogenated fraction were almost identical. S o significant absorption \vas present in the t n o regions 1777 to 1734 c m . 3 and 1741 to 1635 c m . 3 quoted by Burdon and Whiffen ( 5 ) for fluorinated cyclic hexadienes. Neither did the material affect the color of a dilute solution of permanganate in acetone. Some spectra of various fluorinated benzenes were available, and the presence of 1,2,4-trifluorobenzene, 1.3.5-trifluorobenzene, 1.3-difluorobenzene, and 1.2.4.5-tetrafluorobenzenewas indicated. Remaining absorptions are thought to be caused by other fluorobenzenes.
(2) Barbour, A. K., Barlow, G. B., Tatlow, J. C., J . Appl. Chem. (London) 2, 127 (1952). (3) Birchall. J. M.. Haszeldine. R. N.. J . Chem. Soc. 1959. D. 13. (4) Birchall, J. M’,?Haszeldine. R. ~ , Parkinson. , .A. R . . Ibid., 1961, p. 2204. (5) Burdon, J., IVhiffen. D. H.. Spectrochim. Acta 12, 139 (1358). (6) Coe, P. L.,Patrick, C. R.. Tatlow, J. C., Tetrahedron 9, 240 (1 960). (7) Dtsirant, Y . , Bull. Classe Sci.iicad. roy. Belq. 41, 759 (1955). (8) Feeney. .J.. Sutcliffe, L. H., Trans. Faraday Soc. 5 6 , 1553 (1960). (9)’ Finger. G. C.. Reed. F. H., Burness. D. M..Fort. D. M., Blough. R. R., J . ‘4m. Chem. Soc. 73, 145 (1951). (IO) Gething, R., Patrick, C. R.. Stacev, M.. Tatlow, J. C., ’ .vatwe 1 85,588 (1959) (11) Gething, R.:Patrick, C. R., Tatlow, J. C., Banks, R. E., Barbour, A. K., Tipping, A. E., Ibid., 183, 586 (1959). (12) Hellman, M.?Peters, E., Pummer. \V. J., \2;all, L. A , J . Am. Chem. Sac. 79, 5654 (1957). (13) Johncock, P., Musgrave. LV. E;. R.: Feeney, J.. Sutcliffe, L.H.:Chem. 2nd. (London) 1959, p. 1314. (14) Leffler, A. J., J . Org. Chem. 24, 1132,2074 (1959). (15) Ligett, I V . B., McBee, E. T., Lindgren, V. V., U. S. Patent 2,432,997 (Dec. 23,1947); 2,480,080 (.4ug. 23,1949). (16) McBee. E. T.. Lindgren, V. V.. Ligett, \V. B.! IND.ENG. CHEM.39, 378 (1947). (17) McBee, E. T.. Lindgren, V. V.: Ligett, \V. B.. V. S. Patent 2,489,969 (Nov. 29,1949). (18) Rochow, E. G., Kukin, I.: J . .4m. C h m . Soc. 74, 1615 (1952). (19) Roylance, J.. Tatlow, J . C., Worthington? R. E., J . Chem. Sac. 1954, p. 4426.
literature Cited
Division of Industrial and Engineering Chemistry. 138th Meeting, hCS, New York, September 1960. A preliminary note has appeared in Chem. Ind. (London) 1961, p. 1268. \Vork supported in part by a Department of Scientific and Industrial Research maintenance grant to R. H. Mobbs.
(1) Banks, R. E.? Johncock? P., Mobbs, R. H., Musgrave, W. K. R., IND. ENG. CHEM., PROCESS DESIGNDEVELOP.1, 262 (1962).
RECEIVED for review August 21, 1961 ACCEPTED March 1, 1962
SYNTHESIS OF MERCAPTANS H l L L l S 0. FOLKINS AND ELMER L. M I L L E R Research Center, The Pure Oil Co., Crystal Lake, Ill.
Catalyst systems consisting of alkali metal oxides and carbonates and the alkali metal salts of acids of Group VI metals supported on activated alumina have been studied for activity in the synthesis of aliphatic mercaptans b y the reaction of alcohols and hydrogen sulfide. The best catalyst was found to b e 10% potassium tungstate on activated alumina. At 400” C., atmospheric pressure, 0.4 liquid volume hourly space velocity, and 2.0 mole ratio hydrogen sulfide to methanol, the optimum catalyst gave 91 mole yield of methanethiol with a selectivity of 98%. By-products were small amounts of dimethyl sulfide and dimethyl ether. Higher alcohols respond similarly at lower temperatures.
70
THE Pure Oil Co. process for the manufacture of aliphatic mercaptans is baged on a n old reaction, discovered by Sabatier in 1910 (73). adapted to a new process and an active and selective catalyst. The process involves the reaction of aliphatic monohydric alcohols and hydrogen sulfide to form corresponding mercaptans at high yields and selectivities per pass according to the reaction ROH
+ H&
+
RSH
+ H20
Kramer and Reid in 1921 (77) found that the reaction of alcohols and hydrogen sulfide progressed over thoria-type catalysts. However, the reaction system had disadvantages Deceased.
in that yields and selectivities were low, and the catalyst was sensitive to moderate temperature changes. I n developing the process for methyl mercaptan (methanethiol) production, efforts were concentrated on formulating catalyst compositions which would be highly active for the conversion of methanol and hydrogen sulfide to methyl mercaptan a t high selectivity. As a result, a catalyst and process have been developed and proved in pilot plant operation in which methyl mercaptan is produced in molal yields of over 90% per pass with selectivities of around 9570. T h e minor by-products are dimethyl sulfide and dimethyl ether, which may be recycled, if desired, for further conversion to the mercaptan. VOL.
1
NO. 4 O C T O B E R 1 9 6 2
271
Although the process was developed primarily for methyl mercaptan production, the catalyst performs equally well in the conversion of higher alcohols such as ethanol. butanol. and octanol into their corresponding mercaptans. Process conditions vary to only a small degree as higher molecular weight alcohols are used as the charge stocks.
Until a few years ago, mercaptans were classed as unwanted materials, particularly when present in petroleum fractions. Refiners developed processes for sweetening naphthas by conversion of the mercaptans to disulfides. T h e main use for mercaptans was as a n odorant for odorless gases, such as natural gas. n ’ o ~o.n~the other hand, methyl mercaptan has been used as a raw material in the chemical synthesis of the amino acid, methionine, ivhich is used as a poultry food supplement. Methionine production involves the interaction of methyl mercaptan and acrolein. O t h e r indicated uses include the incorporation of mercaptan in the synthesis of polymers and plastics. Similarly. methyl mercaptan may serve as the raw material for the synthesis of dimethyl sulfoxide. a versatile solvent. through the intermediate of dimethyl sulfide. Reactions Involved
Several over-all reactions are possible when alcohols and hydrogen sulfide are contacted over solid catalysts a t elevated temperature. Thus? methanol and hydrogen sulfide react readily to form methyl mercaptan and/or dimethyl sulfide according to Reactions 1 and 2. CHaOH
+ H?S + H?S
+ H20 + 2H2O
+
CH8SH
+
(CHs)?S
(1) (2)
Other possible reactions which may lead to the formation of either mercaptans or sulfides, depending upon rates and equilibrium. may be represented as folloivs: 2CHjSH
ic
(CH.i)tS
+ H2S
(3)
Equilibrium Conversions ( x ) for Equations 1 and 2 in terms of moles CHpOH conversion per mole of CHsOH charged)
Table 1. (x
~___127 227
..
711
CH:jOH 0.99 0 . 9 8
1 3
1.00
1.00
2CH.iOH 1.00
0.5 where
t/i =
1.00
Temperature, 327 427
+ H2S
0.97 1.00
F?
CHsSH 0.95 1.00
C. 527
627
727
0.93 1.00
0.91 0.99
0.99
+ H20
0.89
+ H?S * (CH3)aS + 2H20 1.00
1.00
0.99
0.98
0.96
moles HsS/mole CHJOH in charge.
Table II. Equilibrium Molal Ratios of Methyl Mercaptan and Dimethyl Sulfide in Products Assuming Total Conversion of Methanol Temperature. C. ____ vi 127 227 327 427 527 627 727 1 n n? n 07 o i n o 14 o 17 o 20 o 23 0 38 0 415 0 40 y 0 485 0 465 0 45 0 43 046 036 041 0 1 5 0 2 2 0 2 9 3 x 007 0 295 0 27 y 0 465 0 425 0 39 0 355 0 32 wheie 2 = moles of C H S H in product per mole CHiOH in
272
b
=
?/I
=
F’ (CH,)?S
+ H20
(4)
Other reactions may also occur. Thus, dimethyl ether may be formed by the decomposition of methanol. 2CH.iOH + (CH,i)!O
+ H20
(5)
If formed, the ether may be converted to either methyl mercaptan or dimethyl sulfide according to the reactions:
Uses of Methyl Mercaptan
2CH.iOH
CHsSH f CHsOH
charge moles of (CHl)tS in product per mole C H 8 0 H in charze moles of HrS /mole CH iOH in charge
I & E C PROCESS D E S I G N A N D D E V E L O P M E N T
+ 2H2S 2CH3SH + H a 0 (CHs)zO + H?S * (CH:i)*S+ H?O
(CH:q)*O or
(6)
+
(7)
Aside from the above reactions, which may be desirable in the catalytic reaction of methanol and hydrogen sulfide to form methyl mercaptan. there are other potential reactions to form carbon monoxide or carbon disoide. These may be represented as: CH.qOH
CO
2CH:jOH + C o t
+ 2H2
18)
+ CHI $- 2H?
(9)
Fortunately: the occurrence of these two reactions under conditions described in this process is negligible. Earlier studies on the synthesis of methyl mercaptan from methanol and hydrogen sulfide have shown that the three principal reactions occurring over solid catalysts were those represented by Equations 1> 2> and 5. I t was the purpose of this study to develop a catalyst which would selectively promote methyl mercaptan formation to the exclusion of the potentially competing reactions 2 and 5. Thermodynamic Considerations
Equilibrium calculations have been made for various known reactions Lvhich occur when alcohols, particularly methanol, are brought in contact with hydrogen sulfide over active catalysts. Fundamental data were obtained from various sources (2, 7>9, 70, 72, 74). Results of these calculations, on the basis of atmospheric pressure, are presented in Tables I to 111. T h e values in Table I show that the formation of methyl mercaptan and methyl sulfide is thermodynamically favorable over a \vide temperature range and at varying ratios of reactants. Table I1 shows equilibrium ratios of methyl mercaptan and methyl sulfide that would exist, assuming complete reaction of the methanol. While increase in hydrogen sulfide-methanol ratio and temperature favors a higher mercaptan concentration, thermodynamics still indicates a mixture of the ttvo products. Thus: the need is evident for an active catalyst to accelerate selectively the rate of the desired reaction without accelerating th? equilibrium reaction between the mercaptan and sulfide. This is also borne out in the data presented in Table 111: where the possibility of recycling by-product dimethl-l sulfide to form methyl mercaptan is inferred. The reaction is thermody-
Table 111. [x
Equilibrium Conversions for Reaction
+
*
(CHa)zS HaS 2CH3SH in terms of moles of (CHa)2Sconversion per mole of (CH3)yS charged]
Temperature, C. __ 527 627 427 227 327 127 0.10 0.14 0.17 0.20 0.07 0.03 0.41 0.22 0.29 0.36 0.15 0.07 where m = moles of H*S/mole ( C H Z ) ~inS charge. m 1 5
727 0.23 0.46
namically unfavorable a t low concentrations of hydrogen sulfide in the reactants. Increase of hydrogen sulfide partial pressures favors mercaptan formation, but even a t a mole ratio of 5 to 1 the equilibrium for mercaptan formation at 427' C . is only around 30%. Thus, in practice, a large excess of hydrogen sulfide or dimethyl sulfide would be required in recycle operation. This would, of course, put extra demands on the recovery system. Other reactions that have been considered from a thermodynamic equilibrium standpoint include those of dimethyl ether, which occurs as an intermediate in the reaction or which may serve as a reactant for the production of methyl mercaptan or methyl sulfide. Thermodynamic equilibrium conversion of methanol to yield dimethyl ether 2CH30H
* (CHz)zO + HzO
is around 877, at 400' C. 4 t the same temperature the reactions (CHa)20 and
+ 2HzS * 2CHaSH + HzO
+
( C H P I ~ O HzS
* (CH3)zS + H z 0
as its main objective the development of a catalyst possessing high activity and selectivity, ruggedness, long process life, and properties that would allow it to be readily regenerable. After evaluating many catalyst compositions and methods of preparation, an efficient class of catalysts was developed. I n general, suitable catalysts consisted of alkali metal oxides, alkali metal carbonates, etc., or alkali metal salts of acids of Group V I metals on activated alumina or similar high surface area supports (3-6). The most effective compositions are those in which about 5 to 109; of selected promoters are deposited on a gammaalumina support having a surface area of around 100 to 200 sq. meters per gram. This catalyst was developed to operate in both fixed- and fluid-bed type reactors and it has been proved in extended pilot plant runs to give one-pass yields of methyl mercaptan of around 85 to 90 mole % at selectivities of 95% or higher. The catalyst has long process life and is readily regenerated to full activity and selectivity, if fouled. Actual maximum process cycle periods betlveen regenerations have not been determined, but they should exceed 3 months. Process Conditions
are 100% favorable for the formation of methyl mercaptan and dimethyl sulfide at hydrogen sulfide-dimethyl ether ratios of 1 or greater. If the relative reaction rates for the formation of mercaptan and sulfide are faster than the formation of the ether from methanol, no buildup of ether for recycle should occur. Again, the direction of product formation should reside in the preferential catalytic acceleration in rate of the desired reaction. Choice of Catalyst
Kramer and Reid ( 7 7 ) had shown that a thoria-on-pumice catalyst was effective in converting methanol and hydrogen sulfide to methyl mercaptan. Experimental work carried out in the present study confirmed that work but showed that catalysts of this type possessed certain disadvantages which ~ o u l dbe detrimental to their commercial use. Catalytic activity was destroyed a t temperatures slightly above those used in the reaction. T h e thoria-pumice catalyst, because of its tendency for physical erosion, was not suitable for fluid-bed operation, T h e catalyst showed relatively low conversions and selectivities under practical reaction conditions. Loss of activity was experienced with time on stream and the catalyst failed to respond to regeneration. \Vork was carried out also using activated alumina as the catalyst. However, this catalyst is sensitive to reactant ratios and high HzS/CH30H mole ratios in the order of 5 to 1 must be used to maintain high selectivities for methyl mercaptan production. The present catalytic process evolved from a program having
The process may be carried out in a fixed catalyst bed arrangement, or a fluidized bed may be employed to aid in reactor temperature control, since the reaction is exothermic (8). The reaction for methyl mercaptan production proceeds in the temperature range of 340' to 430' C., temperatures of 375' to 410' C. being optimum. The effect of temperature upon the reaction carried out over an alumina-potassium tungstate catalyst is shown in Table IV. Results obtained over alumina, alone, are included for comparison. Operating conditions were: Pressure, atmospheric LVHSV, 0.39 H?S/methanol (mole)?2.00 Lower temperatures are employed in the adaptation of the process to higher molecular weight mercaptan formation. The reaction is rather insensitive to pressure, but yields are increased somewhat by pressure application, because of increased residence time. Yields a t atmospheric pressure and a t 100 p.s.i.g, are shorvn in Table V for a catalyst similar to, but less active and selective than, that used in the process. Although most of the research work involved in the development of the catalyst \vas done at atmospheric pressure, pilot plant work for the establishment of the process was carried out a t 100 p.s.i.g. to simplify separation and recovery procedures. Hydrogen sulfide-methanol ratios are not critical lvith the catalyst employed, since it is relatively insensitive to ratio effect on selectivity. This is shown in Table V I , where the process
Table V.
Table IV. Catalyst
.-\luminaKzFV04
Alumina
Methyl Mercaptan Production
Temp., Conwr- Yield, Selectivity, yo O C. sion, % Mole % C H P S H (CH3)nS (CH3)zO 373 400 413 427 400
84.7 92.7 89.2 87.7 68.7
80.5 90 9 87.7 87.0 47.1
905. 98 1 98.3 99.1 68 6
2.9 1 0 1.7 0.9 31.4
2.1 0.9 0.0 0.0 0.0
Effect of Pressure on Methyl Mercaptan Yields from Methanol and Hydrogen Sulfide (Development catalyst, not final catalyst of process) Temp., O C. 400 400 Pressure Atmospheric 100 p.s.i.g. Mole ratio, HzS/CH,OH 1.1 1.1 GHSV (methanol) 21 0 210 Conversion, % 72 89 Mercaptan yield, mole yo 63 75 Selectivity, % a7 85
VOL.
1
NO. 4
OCTOBER 1 9 6 2
273
-
n Table VI.
Comparison of Catalysts in Respect to Selectivity with Change in Ratio of Reactants Methyl Mercaptan Production Mole Ratio, Yield, Selectivity, Catalyst H,S/CH,OH mole % %
COMPRESSOR
I
I 1 i l ABSORBER
Process catalyst A Process catalyst B Activated alumina
2.0 1.1 1.1 0.8 2.0 0.6
90 86 78 67 47 9
97 87 85 80 69 10
CHiOH
catalyst is compared with one that shows a high selectivity response as ratios are lowered. However, H 2 S / C H 3 0 H ratios of stoichiometric or greater proportions are desired to maintain high selectivity and activity. Generally a ratio of 1.1 to 1 is considered optimum for maintaining suitable selectivity compatible with less load on the recovery system. Throughput rates can be varied widely according to the operating conditions employed (principally temperature). Since the catalyst operates most efficiently in the neighborhood of 375' to 410' C., throughput rates are generally in the order of 0.3 to 1.0 volume of methanol per volume of catalyst per hour. Figure 1 is a simplified flowsheet of the process as applied to methyl mercaptan production. Methanol, containing around 0.5 to 1.0% of water, and hydrogen sulfide are preheated and pass to the catalytic reactor, which may be of a fixed-bed type with suitable design for heat transfer, or to a fixed or circulating fluidized bed of catalyst. Since catalyst selectivity is not appreciably affected by pressure change, the choice of process pressure is governed by recovery efficiency and reactor size. A suitable pressure is around 100 p.s.i.g. The reactor effluent is stabilized to remove the hydrogen sulfide (for recycle) and a small amount of mercaptan which is subsequently absorbed, stripped, and returned to the stabilizer. T h e absorber overhead hydrogen sulfide is recompressed and preferably dried for recycle to the reactor. The stabilized bottoms consisting of mercaptan, water, unreacted methanol, and by-product methyl sulfide is stabilized to remove methanol and water as bottoms. T h e overhead mixture of mercaptan and dimethyl sulfide is fractionated to give a product mercaptan and a by-product or recycle dimethyl sulfide. Water and methanol are separated by distillation and the overhead methanol is recycled to the reactor. Production of Higher Molecular Weight Mercaptans
While the discussion of the process has been directed mainly toward the production of methyl mercaptan, the process is also equally adaptable to the synthesis of higher molecular weight alkyl mercaptans. Thus, ethyl mercaptan can be readily produced from ethanol and hydrogen sulfide a t high yields and selectivities at temperatures of 370' C. and lower. Preferred temperatures are around 315' C. As in the case of
Table VII.
7 8 9 10 11
274
Alumina-KtW04 Alumina-KZW 0 4 Alumina-KzWO4 Alumina-KpWO4 Alumina
289 318 360 382 317
STRIPPER
HEATERS
c
RECYCLE
HZ0
Figure
1.
Methyl
mercaptan
process
flowsheet
the methyl mercaptan process, the choice of catalyst is important if high selectivity for mercaptan formation is to be attained. Table VI1 summarizes results obtained in the processing of ethanol and hydrogen sulfide and the data show the superiority of the potassium tungstate-supported catalyst over an alumina catalyst. Operating conditions were Temperature, variable Pressure, atmospheric H*S/ethanol (mole), 2.86 LVHSV, 0.35 Various reactions are possible for the reaction of ethanol and hydrogen sulfide. CzHjOH
+ H?S
2CzHsOH
+ HzS
-
CzHjSH $- HzO
(CzHs)zS
+ HzO
(CzHs)zO 4- HzO
2CzHsOH C2HsOH
CZH4
+ HzO
CHZCHO
CzH50H
+ Hz
The results in Table VI1 show that temperatures of around 315' C. are optimum for yields and for high selectivity for mercaptan formation. The main losses in selectivity a t higher temperatures are due to the formation of ether and dehydration of the alcohol to olefins. The superiority of the potassium tungstate catalyst over alumina in minimizing these reactions is shown also in this table. The potassium tungstate catalyst has also shown high activity and selectivity in the production of mercaptans higher in the homologous series, Thus, 1-octanol and hydrogen sulfide react readily to form the corresponding mercaptan at temperatures as low as 230' C.
Ethyl Mercaptan Production
60.1 83.4 83.1 82.3 93.0
I&EC PROCESS DESIGN A N D DEVELOPMENT
55.9 68.7 66.9 64.1 42.6
93.0 82.4 80.5 78.0 45.8
2.5 6.0 4.1 3.6 1.7
4.3 9.3 7.5 6.6 13.5
0.2 2.3 7.6 11.5 38.8
0.3 0.3 0.2
Table VIM. Octyl Mercaptan Production Temp., Conversion, Yield, O 0 /O Mole 70 ’ CsH1;SH
Calalyst
1 2 3 4 5
Alumina-KzWO4 Alumina-KzW04 Alumina-KzWOa Alumina-KzWO4 Alumina
235 260 287 318 317
48.0 81.6 100 100 100
Table VI11 shows the results obtained in the octanol-H*S reaction over the potassium tungstate catalyst as compared to that over alumina. Reaction conditions were: Temperature, variable Pressure, atmospheric LVHSV, 0.39 HnS/octanol (mole), 7.73 The optimum temperature is around 290’ C . for yields without much sacrifice in selectivity. This reaction varies from that with ethanol as the reactant, in that little sulfide or ether was formed. The product under the heading “Other” is probably mostly octyl aldehyde (inferred from the infrared absorption a t 10.3 microns, the odor, and the work of Kramer and Reid). Effect
of Feed Impurities
The mercaptan synthesis catalyst is resistant to impurities that might be present in fresh or recycle feeds. I n a pilot plant life test run impurities consisting of 0.5y0 carbon disulfide and 0.5% diethanolamine were added to the methanol charge during a 60-hour process period. N o loss in activity or selectivity resulted because of these impurities. I n another test, 1070 carbon dioxide was added to the hydrogen sulfide feed. Again catalyst performance was not impaired. Bell (7) noted that small amounts of water in the charge prevented deactivation of thoria-type catalysts used in this reaction. A slow deactivation of the catalysts described here also
Table IX.
Selectivity, Octene 1 .o 7.7 8.4 18.1 6.7
c.
Run
Methyl Mercaptan Production from Methanol and from Dimethyl Ether
Operating conditions Temperature, 400’ C. STP space velocity (gaseous, on dimethyl ether or methanol), 210 Mole ratio of HzS to dimethvl ether or methanol, 2.0 Pressure, atmospheric Reactant CHBOH (CH3)zO Catalyst K2W04 K2WO4 Conversion, % 93 71 Methyl mercaptan yield, mole % 90 69.5 97 98 Selectivity, yo
47.5 75.3 91.3 77.4 34.3
99 .O 92.3 91.3 77.4 34.3
% Other 0.0 0.0 0.3 4.5 59.0
occurs if no moisture is present in the reactant feed. Thus to maintain constant yield levels over long periods of time water is added, in 0.6 weight concentration, to the alcohol feed. Under these conditions, no deactivation of the catalyst has occurred in life tests approaching 400 hours. Dimethyl Ether as Reactant
Although the methyl mercaptan process was primarily designed to operate with methanol as the reactant, the catalyst effects almost equal conversion and selectivity for mercaptan formation when dimethyl ether is employed as reactant (5). IVork along the line of converting dimethyl ether to mercaptan \vas clone initially to determine how effectively any ether formed in the process would be converted to mercaptan on recycle operation. Yields and selectivities were so good as to propose methyl ether as the initial reactant. Table IX compares yields and selectivities obtained using the two reactants under the same conditions of operation. \Vhile conversions are not so high with dimethyl ether as with methanol, the same high selectivity for mercaptan formation is maintained. Catalyst Regeneration
Under normal operation of the process no decline in catalyst activity over long processing periods is envisaged. However, under certain operating conditions, including the charging of dry feeds and processing at temperatures considerably higher than the optimum, a slow deactivation of the catalyst may occur. T o investigate the regenerative potential of the catalyst, several catalyst compositions which had been employed under adverse conditions with resultant decline in activity were subjected to a simple regenerative procedure, which consisted simply of air oxidation under mild combustion conditions. This treatment completely restored the catalyst to its original activity. Table X shows results on the regeneration of a catalyst fouled after 140 hours of continuous process cycle. Economic Considerations
Cost estimates for the methyl mercaptan process have been made o n the basis of a 5,000,000-pound-per-year plant a t a
Table X.
Catalyst History New Used 140 hours
Regeneration of Methyl Mercaptan Catalyst Activity Test Conversion, Yield, Regeneration Treatment % 5% CH.,SH None 86.4 84.9 98.3 None 82.4 79.8 96.8 2 hours, air at 450 C. 87.3 84.0 96.2 18 hours, air at 550 ’ C . 88.6 85.5 96.5
VOL.
1
Selectivity, yo ( CHd 2 s 1.5 2.4 2.3 2.1
( CHd 2 0
0.2 0.8 1.5 1.4
NO. 4 O C T O B E R 1 9 6 2
275
Table XI.
Cost Estimate for Methyl Mercaptan from Methanol
(5,000,000 pounds per year) Capital cost
$644,000 Pounds per Year
Products Methyl mercaptan Dimethyl sulfide Direct costs Operating labor Supervision and maintenance Methanol at 29 cents/gal. Hydrogen sulfide at 0.142 cent/lb. Catalyst and miscellaneous supplies Utilities Total
5,000,000 98,000 Cents/Lb . CHISH
1.63 0.56 3.55 0.13 0.48 0.44 6.79
costs are somewhat less with dimethyl ether, because of a simpler recovery section. However, this is to a large degree nullified by lower mercaptan yields per pass and the need for pressure storage to accommodate the ether. Thus the over-all cost of the process is about the same for either reactant. literature Cited
(1) Bell, R. T. (to Pure Oil Go.), U. S. Patent 2,685,605 (1954). (2) Binder, J. L., J . Chem. Phys. 18, 78 (1950). (3) Folkins, H. 0. (to Pure Oil Co.), U. S. Patent 2,786,079 (1957). (4)' Folkins, H. O., Miller, E. L. (to Pure Oil Co.), Ibid., 2,820,060 (1958).
\
Gulf Coast location (Table XI). Total direct operating costs have been estimated a t 6.79 cents per pound for producing methyl mercaptan from methanol as the reactant. The capital cost will be dependent upon the specific conditions under consideration, such as tankage, H2S recovery facilities available, etc. Since availability of H2S will be governed by the location of the plant, its cost may vary from that included here. Because some chemical companies may have a supply of by-product dimethyl ether, estimates have been made also on the basis of the ether as a n alternative reactant. Investment
,
trand, New'York, 1947. ' (8) Hennig, H. (to Pure Oil Co.), U. S. Patent 2,819,313 (1958). (9) Kelley, K. K., "Thermodynamic Properties of Sulfur and Its Inorganic Compounds," Bur. Mines Bull. 406 (1937). (10) Kistiakowsky, G. B., Rice, W. W., J . Chem. Phys. 8, 618 (1940). (11) Kramer, R. L., Reid, E. E., J . A m . Chem. Soc. 43, 880 (1921). (12) Natl. Bur. Standards, "Tables of Selected Values of Thermodynamic Properties," Circ. 500 (1952). (13) Sabatier, P., Comfit. rend. 150, 1217 (1910). (14) West, J. R., Chem. Eng. Progr. 44, 287 (1948). RECEIVED for review September 14, 1961 ACCEPTEDMarch 19, 1962 Division of Petroleum Chemistry, 140th Meeting, ACS, Chicago, Ill., September 1961.
P R E P A R A T ION OF LOW FREEZING JET FUELS B Y ISOCRACKI NG R. H. KOZLOWSKI, H . F. MASON,AND J . W . SCOTT California Research Gorp., Richmond, Calif.
Gas oils boiling in the range of 550" to 850" F. were lsocracked in the laboratory to evaluate the products as jet fuel components. Processing at 60% per pass conversion and 500" to 525" F. recycle cut point gave about a 20 to 40% yield of kerosine-type jet fuel with freezing points below -60" F. Produced in addition to the jet fuel were butanes, high octane light gasoline, and naphthenic reformer feed giving a total C4+ liquid yield of about 1 17%. Neither the yields nor the low freezing points of the synthetic jet fuels produced appear to be significantly affected by feed properties. The very low freezing points are attributed to very low normal paraffin content. Low freezing kerosine-type jet fuel components of high quality can be produced from heavy, lower value distillates by Isocracking. HE fastest growing major petroleum product today is Tkerosine-type jet engine fuel. If forecasts of continuing growth are correct, the demand for these fuels will exceed the petroleum industry's ability to supply them from straight-run fractions. Specifications (3) rather than volume of kerosine distillates will limit production. I n general, the freezing point and smoke point specifications represent the most important limits. Problems arising from high freezing points are the most difficult to overcome. Present solvent or urea dewaxing processes are effective for this purpose but Are not a t present economical. Molecular Sieve treatment or isomerization processes are possibly applicable, but their commercial feasibility has not been proved. O n the other hand, solvent extraction, acid treatment, and hydrofining have been used to correct
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smoke point, as well as polynuclear aromatic content, sulfur content, and stability. Such processes cannot correct both freezing point and smoke point problems in one step, however. I n addition, these processes use relatively valuable stocks already in the jet fuel boiling range. Isocracking can be used to produce kerosine-type jet fuel fractions from heavy distillates of lower value (75). Isocracking (72-74, 77) is a commercial low temperature hydrocracking process-a method of cracking in the presence of hydrogen and a catalyst. The jet fractions produced possess very low freezing points even when produced from paraffinic feed stocks. I n addition, they possess low total aromatic content and are substantially free of polynuclear aromatics, nitrogen and sulfur compounds, and other impurities. High quality gasoline is produced simultaneously.
