Thermochemical cycle for splitting hydrogen sulfide

Abstract

A thermochemical cycle for the recovery of hydrogen and sulfur by splitting hydrogen sulfide, based upon initial reactions between the hydrogen sulfide and carbon dioxide or carbon monoxide. The cycle exists in three versions, two utilizing the initial reaction of hydrogen sulfide and carbon dioixide. One of these versions utilizes high temperature for the initial step for production of carbon monoxide for use in the shift reaction to produce hydrogen. The other conducts the initial step of moderate temperature in the presence of a desiccant to increase the yields of carbonyl sulfide and carbon disulfide, which are subsequently subjected to high temperature reactions to produce the carbon monoxide for the shift reaction. The third version employs the reaction of hydrogen sulfide with carbon monoxide at moderate temperatures producing original hydrogen and fractions including carbonyl sulfide and carbon disulfide, which are later reacted at high temperatures for production of carbon monoxide and sulfur, the carbon monoxide being recycled to the initial reaction.

Description

BACKGROUND OF THE INVENTION

1. Field:

The field of the invention is methods for recovery of hydrogen and sulfur by breakdown of gaseous hydrogen sulfide (H.sub.2 S)

2. State of the Art:

Over a period of several decades, many chemical process workers have studied methods for the decomposition of hydrogen sulfide to yield hydrogen and elemental sulfur. The reason for these efforts has been the very large quantities of hydrogen and elemental sulfur contained in the noxious hydrogen sulfide, H.sub.2 S, produced in the refining of petroleum and the purifying of natural gas. At present, H.sub.2 S is partially oxidized to produce sulfur dioxide (SO.sub.2), which reacts with residual H.sub.2 S to form elemental sulfur and water. This method is known as the Claus process. Kalina and Maas.sup.5 noted that, in 1982, conversion of hydrogen sulfide by this method yielded 4.2.times.10.sup.6 long tons of sulfur, approximately 50% of the sulfur produced in the United States that year. Also noted was the fact that recovery of the stoichiometric amount of hydrogen associated with this sulfur could, if recovered, provide a very significant portion of the hydrogen required for heavy crude oil upgrading, and for coal liquefying and gasifying.

The following H.sub.2 S decomposition methods have been studied and described in recent papers:

direct, high temperature thermal decomposition, with separation of the resultant gases by means of pressure swing absorption of H.sub.2 S.sup.1 ; direct high temperature thermal decomposition, with high temperature separation of gases by means of porous ceramic membranes.sup.6 ; thermochemical cycles involving the reaction of H.sub.2 S with a metal or metal sulfide to form a higher sulfide and evolve hydrogen, followed by thermal decomposition of the higher sulfide.sup.8 ; electrochemical processes for H.sub.2 S decomposition.sup.4,5 ; and photolytic decomposition of H.sub.2 S via the irradiation of semiconductor electrodes or treated particles with light.sup.2.

All of these methods, with the possible exception of the photon based processes, appear to offer possibilities for development of practical approaches for recovery of both S.sub.2 and H.sub.2. However, none have been developed sufficiently nor widely adopted by the petroleum industry, which remains in need of a practical, economical method.

REFERENCES

1. Bandermann, F. and K.-B. Harder. Production of H.sub.2 Via Thermal Decomposition of H.sub.2 S and Separation of H.sub.2 and H.sub.2 S by Pressure Swing Adsorption. Int. J. Hydrogen Energy. Vol. 7, No. 6, pp. 471-475, 1982. 2. Barbeni, M., E. Pelizzetti, E. Borgarello, N. Serpone, M. Gratzel L. Balducci and M. Visca. Hydrogen From Hydrogen Sulfide Cleavage. Improved Efficiency Via Modification of Semiconductor Particulates. Int. J. Hydrogen Energy, Vol. 10, No. 4, pp. 249-253, 1985. 3. Chivers, T. and C. Lau. The Thermal Decomposition of Hydrogen sulfide Over Alkali Metal Sulfides and Polysulfides. Int. J. Hydrogen Energy, Vol. 10. No. 1, pp. 21-25. 1985. 4. Kalina, D. W. and E. T. Maas, Jr. (1985-1). Indirect Hydrogen Sulfide Conversion--1. An Acidic Electrochemical Process. Int. J. Hydrogen Energy, Vol. 10. No. 3, pp. 157-162, 1985. 5. Kalina, D. W. and E. T. Maas, Jr. (1985-2). Indirect Hydrogen Sulfide Conversion--II. A Basic Electrochemical Process. Int. J. Hydrogen Energy, Vol. 10, No. 3, pp. 163-167, 1985. 6. Kameyama, T., M. Dokiya, M. Fujishige, H. Yokokawa and K. Fukuda. Possibility For Effect Production of Hydrogen From Hydrogen Sulfide by Means of a Porous Vycor Glass Membrane. Ind. Eng. Chem. Fund., 20, pp. 97, 1981 7. Kameyama, T., M. Dokiya, M. Fujishige, H. Yokogawa and K. Fukuda. Production of Hydrogen From Hydrogen sulfide by Porous Ceramic Membrane. Kagikenpou, 77, pp. 627, 1982. 8. Kiuchi, H., T. Nakamura, K. Funaki and T. Tanaka. Recovery of Hydrogen From Hydrogen Sulfide With Metals of Metal Sulfides. Int. J. Hydrogen Energy, Vol. 7, No. 6, pp. 477-482, 1982. 9. Naman, S. A., S. M. Aliwi and K. Al-Emara. Hydrogen Production From Splitting H S By Visible Light Irradiation of Vanadium Sulfides Dispersion Loaded With RuO.sub.2. Int. J. Hydrogen Energy, Vol. 11, No. 1, pp. 33-38, 1986. 10. Terres, E. and H. Wesemann. Angew. Chem.45, pp. 795-803, 1932. 11. Fukudu, et al, J. of Catalysis, 49, 379 (1977); Bul. of Chemistry for Japan, 51, 150 (1973); U.S. Pat. No. 3,856,925.

BRIEF SUMMARY OF THE INVENTION

With the foregoing in mind, the present invention eliminates or substantially alleviates the disadvantages of prior art methods of splitting H.sub.2 S, by providing a thermochemical process based on selected initial reactions of H.sub.2 S with carbon dioxide (CO.sub.2) or carbon monoxide (CO). The invention may be carried out by use of any one of three variations of the basic process, each characterized by use of individually selected starting (reactor inlet) gas compositions, reaction pressures, and reaction sequences. Two of the process variations utilize the well known water gas shift reaction to yield hydrogen (H.sub.2) after production of sulfur (S.sub.2) by the initial CO.sub.2 reaction described above. The third evolves H.sub.2 in the initial CO reaction, described above. The sulfur is obtained by subsequent thermal decomposition of carbonyl sulfide (COS) and carbon disulfide (CS.sub.2), which are products of the initial reactions. Each of the three processes also incorporates separation steps for the recovery of the H.sub.2 and S.sub.2, as well as necessary intermediate separation measures. Each process may be conducted at temperatures and pressures selected over a considerable range, as necessary for desirable results with individual process equipment variables, such as size and temperature capability.

It is therefore the object of the present invention to provide a process for complete recovery of hydrogen and sulfur by splitting of hydrogen sulfide.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which represent the best modes presently contemplated for carrying out the invention,

FIG. I-B graphically illustrates the variation in the proportions of carbon dioxide and hydrogen after the shift reaction, and the variation in the hydrogen sulfide+carbonyl sulfide fractions per mole of hydrogen, as functions of reaction temperatures,

FIG. 1-C graphically illustrates the variation in the proportions of carbon dioxide and hydrogen after the shift reaction, and the variation in the proportions of the hydrogen sulfide+carbonyl sulfide fraction and hydrogen, as a function of the proportion of carbon dioxide and hydrogen sulfide in the inlet gases,

FIG. I-D graphically indicates the variations in the proportions of carbon dioxide and hydrogen after the shift reaction, and the variations in the proportions of the hydrogen sulfide+carbonyl sulfide fraction and hydrogen, as a function of reaction pressures,

FIG. 1-A is a flow diagram of Version I of the thermochemical cycle of the invention,

FIG. 2-A is a flow diagram of Version II of the thermochemical cycle of the invention, and

FIG. 3-A is a flow diagram of Version III of the thermochemical cycle of the invention.

DETAILED DESCRIPTION OF PROCESS VERSIONS

Three versions of a new thermochemical cycle are described, each for recovery of hydrogen and elemental sulfur by splitting of hydrogen sulfide. The versions vary, in that each is based on individually selected temperatures and mixtures of inlet gases for its initial process reactions. The versions are herein designated Versions I, II and III. The high temperature step in Version I involves the reaction of CO.sub.2 with H.sub.2 S, the high temperature enhancing the direct formation of CO for subsequent reaction with water for hydrogen formation. High temperature is utilized in Versons II and III for decomposition of carbonyl sulfide (COS) to form gaseous CO and sulfur, S.sub.2 (g), for sulfur recovery. In Versions II and III, mixtures of COS and CS.sub.2 may also be decomposed by the application of high temperatures to again form CO+S.sub.2 (g).

Equilibrium products of the CO.sub.2, CO, H.sub.2 S reactions produce mixtures of several gaseous species. Various reactions which occur to define the final gas composition include:

CO.sub.2 +H.sub.2 S=COS+H.sub.2 O COS=CO+0.5S.sub.2 (g) COS+H.sub.2 S=CS.sub.2 +H.sub.2 O CO+H.sub.2 O=CO.sub.2 +H.sub.2 CO+H.sub.2 S=COS+H.sub.2 CO.sub.2 +0.75S.sub.2 =COS+0.5SO.sub.2 CO.sub.2 +CS.sub.2 =2COS At equilibrium, the different reactant species exist in a range of concentrations, depending on reaction pressure, temperature and composition of the initial reactant inlet gases.

VERSION I

Version I is the first preferred variation of the new H.sub.2 S splitting methods, and is based on the reaction of H.sub.2 S with CO.sub.2 at the highest practical temperatures, in order to enhance the direct yield of CO without intermediate formation of COS. Version I includes the following steps, which are illustrated in a flow diagram in FIG. I-A.

1. The high temperature reaction of H.sub.2 S with CO.sub.2 : CO.sub.2 +H.sub.2 S=CO+H.sub.2 O=0.5S.sub.2 (I- 1) 2. Separation of S.sub.2 (G) by condensation. 3. Separation of H.sub.2 O(g) by condensation. 4. Separation of CO.sub.2 +CO+H.sub.2 fraction (after reaction I-1) from the residual H.sub.2 S+COS+CS.sub.2 fraction. (The CS.sub.2 is almost negligible). This is the primary separation step of Version I. It can probably best be effected by dissolving the sulfur bearing species in a solvent in which CO and CO.sub.2 are not soluble, such as liquid CS.sub.2. The separated H.sub.2 S+COS+CS.sub.2 is mixed with CO.sub.2 from step 6 and additional H.sub.2 S to constitute the inlet gas for a repetition of the cycle. 5. Formation of H.sub.2 by reaction of CO+H.sub.2 O: CO+H.sub.2 O=CO.sub.2 +H.sub.2 (I- 2) This reaction is commonly called the water-gas shift reaction. 6. Separation of the H.sub.2 from CO.sub.2 by methods now used commercially for the water-gas shift process, such as condensation/evaporation and absorption/desorption.

As stated above, compositions of the product gases will vary with pressure, temperature, and composition of the inlet gases. Equilibrium compositions computed for a variety of pressures, temperatures and inlet gas compositions are presented in I-A through I-D below. Computations were based where possible on data listed in the Joint Army Navy Air Force (JANAF) Thermochemical Tables. For COS, experimental data was used from studies by Terres and Wesemann (1932).sup.10.

TABLE I-A__________________________________________________________________________ CO2*/ H2S/ COS/T % CO2 % H2S % COS % H2O % CO % CS2 % H2 % S2 H2* H2* H2*__________________________________________________________________________Inlet: 0.67 atm. CO2, 0.33 atm. H2S. 900 59.68 26.34 3.72 5.96 2.14 0.05 0.49 1.31 23.52 10.14 1.421000 56.10 23.57 3.54 8.29 4.65 0.05 0.99 2.82 10.77 4.18 0.631100 51.65 19.74 2.97 11.05 8.00 0.04 1.70 4.85 6.15 2.04 0.311200 46.92 15.57 2.30 13.97 11.61 0.03 2.53 7.07 4.14 1.10 0.161300 42.54 11.65 1.69 16.67 14.95 0.02 3.35 9.15 3.14 0.64 0.09Inlet: 0.6 atm. CO2, 0.4 atm. H2S. 900 52.74 32.92 3.90 6.21 2.18 0.07 0.59 1.39 19.81 11.87 1.411000 49.03 29.58 3.73 8.63 4.77 0.07 1.21 2.99 9.00 4.95 0.621100 44.43 25.35 3.16 11.49 8.23 0.05 2.12 5.17 5.09 2.45 0.311200 39.50 20.63 2.47 14.53 12.00 0.04 3.23 7.62 3.38 1.35 0.161300 34.89 16.01 1.83 17.38 15.50 0.02 4.41 9.97 2.53 0.80 0.09Inlet: 0.5 atm. CO2, 0.5 atm. H2S. 900 42.63 42.57 4.00 6.34 2.17 0.09 0.75 1.46 15.33 14.57 1.371000 38.91 38.94 3.83 8.77 4.76 0.09 1.55 3.16 6.92 6.17 0.611100 34.31 34.24 3.26 11.63 8.23 0.07 2.77 5.50 3.87 3.11 0.301200 29.42 28.84 2.55 14.63 11.98 0.05 4.37 8.17 2.53 1.76 0.161300 24.89 23.35 1.90 17.41 15.44 0.03 6.17 10.81 1.87 1.08 0.09Inlet: 0.4 atm. CO2, 0.6 atm. H2S. 900 32.84 52.48 3.89 6.19 2.09 0.11 0.91 1.50 11.65 17.51 1.301000 29.29 48.67 3.72 8.54 4.57 0.11 1.91 3.24 5.23 7.52 0.571100 24.98 43.65 3.15 11.17 7.84 0.09 3.48 5.66 2.90 3.86 0.281200 20.51 37.72 2.45 13.89 11.30 0.07 5.61 8.46 1.88 2.23 0.141300 16.50 31.48 1.81 16.32 14.42 0.05 8.15 11.28 1.37 1.39 0.08__________________________________________________________________________ CO2* and H2* refer to quantities after the shift reaction. TABLE I-B__________________________________________________________________________ CO2*/ H2S/ COS/T % CO2 % H2S % COS % H2O % CO % CS2 % H2 % S2 H2* H2* H2*__________________________________________________________________________Inlet: 2 atm. CO2, 1 atm. H2S. 900 60.23 27.15 4.01 5.69 1.56 0.06 0.34 0.95 32.49 14.27 2.111000 57.22 24.60 4.05 7.72 3.54 0.07 0.69 2.12 14.35 5.81 0.961100 53.38 21.41 3.63 10.13 6.39 0.06 1.20 3.80 7.87 2.82 0.481200 49.07 17.79 3.00 12.78 9.69 0.04 1.85 5.77 5.09 1.54 0.261300 44.81 14.14 2.34 15.38 12.98 0.03 2.55 7.76 3.72 0.91 0.15Inlet: 1.8 atm. CO2, 1.2 atm. H2S. 900 53.32 33.47 4.20 5.94 1.59 0.08 0.41 1.00 27.43 16.72 2.101000 50.20 30.73 4.25 8.05 3.63 0.08 0.84 2.23 12.05 6.88 0.951100 46.22 27.24 3.84 10.55 6.56 0.07 1.49 4.02 6.56 3.39 0.481200 41.74 23.21 3.20 13.31 9.99 0.06 2.33 6.16 4.20 1.88 0.261300 37.28 19.03 2.52 16.03 13.43 0.04 3.30 8.37 3.03 1.14 0.15Inlet: 1.5 atm. CO2, 1.5 atm. H2S. 900 43.20 43.19 4.29 6.07 1.59 0.10 0.52 1.05 21.29 20.53 2.041000 40.06 40.23 4.36 8.20 3.63 0.11 1.07 2.35 9.30 8.57 0.931100 36.07 36.42 3.95 10.71 6.56 0.10 1.94 4.25 5.02 4.29 0.461200 31.61 31.91 3.30 13.44 9.99 0.08 3.11 6.55 3.18 2.44 0.251300 27.21 27.09 2.60 16.12 13.41 0.06 4.54 8.97 2.26 1.51 0.15Inlet: 1.2 atm. CO2, 1.8 atm. H2S. 900 33.38 53.16 4.17 5.94 1.53 0.12 0.63 1.08 16.20 24.68 1.941000 30.37 50.09 4.23 7.98 3.48 0.14 1.32 2.40 7.05 10.44 0.881100 26.61 46.07 3.82 10.34 6.27 0.13 2.42 4.35 3.78 5.30 0.441200 22.48 41.23 3.17 12.85 9.48 0.10 3.97 6.72 2.38 3.07 0.241300 18.52 35.91 2.48 15.23 12.60 0.08 5.92 9.26 1.68 1.94 0.13__________________________________________________________________________ CO2* and H2* refer to quantities after the shift reaction. TABLE I-C__________________________________________________________________________ CO2*/ H2S/ COS/T % CO2 % H2S % COS % H2O % CO % CS2 % H2 % S2 H2* H2* H2*__________________________________________________________________________Inlet: 4 atm. CO2, 2 atm. H2S. 900 60.01 27.39 4.16 5.56 1.27 0.07 0.27 0.77 39.74 17.76 2.701000 57.81 25.11 4.33 7.43 2.95 0.07 0.55 1.75 17.36 7.17 1.241100 54.34 22.27 4.04 9.64 5.46 0.07 0.96 3.21 9.31 3.47 0.631200 50.35 19.00 3.48 12.10 8.51 0.06 1.50 5.01 5.88 1.90 0.351300 46.25 15.60 2.82 14.59 11.69 0.04 2.11 6.90 4.20 1.13 0.20Inlet: 3.6 atm. CO2, 2.4 atm. H2S. 900 53.60 33.73 4.35 5.81 1.30 0.08 0.33 0.81 33.85 20.80 2.681000 50.80 31.28 4.55 7.75 3.02 0.09 0.67 1.84 14.61 8.49 1.231100 47.21 28.20 4.27 10.05 5.61 0.09 1.19 3.40 7.78 4.15 0.631200 43.06 24.60 3.69 12.61 8.77 0.07 1.88 5.33 4.87 2.31 0.351300 38.79 20.75 3.01 15.20 12.09 0.05 2.71 7.40 3.44 1.40 0.20Inlet: 3 atm. CO2, 3 atm. H2S. 900 43.48 43.48 4.44 5.94 1.29 0.11 0.41 0.85 26.31 25.55 2.611000 40.66 40.05 4.65 7.92 3.02 0.12 0.85 1.93 11.30 10.36 1.201100 37.05 37.51 4.38 10.22 5.60 0.12 1.54 3.57 5.98 5.26 0.611200 32.91 33.52 3.80 12.77 8.77 0.10 2.49 5.63 3.70 2.98 0.341300 28.69 29.17 3.11 15.33 12.07 0.08 3.69 7.88 2.59 1.85 0.20Inlet: 2.4 atm. CO2, 3.6 atm. H2S. 900 33.65 53.48 4.32 5.82 1.24 0.13 0.50 0.87 20.05 30.74 2.481000 30.94 50.77 4.52 7.72 2.90 0.15 1.04 1.97 8.58 12.88 1.151100 27.52 47.27 4.23 9.90 5.37 0.15 1.92 3.64 4.51 6.49 0.581200 23.66 43.04 3.65 12.25 8.35 0.13 3.17 5.76 2.78 3.74 0.321300 19.82 38.31 2.97 14.56 11.39 0.10 4.78 8.08 1.93 2.37 0.18__________________________________________________________________________ CO2* and H2* refer to quantities after the shift reaction. TABLE I-D__________________________________________________________________________ CO2*/ H2S/ COS/T % CO2 % H2S % COS % H2O % CO % CS2 % H2 % S2 H2* H2* H2*__________________________________________________________________________Inlet: 8 atm. CO2, 4 atm. H2S. 900 60.74 27.58 4.34 5.38 1.04 0.07 0.21 0.63 49.27 21.99 3.461000 58.30 25.52 4.65 7.11 2.46 0.09 0.43 1.45 21.00 8.82 1.611100 55.18 23.00 4.48 9.13 4.66 0.08 0.77 2.71 11.04 4.24 0.831200 51.52 20.07 3.98 11.41 7.43 0.07 1.21 4.32 6.83 2.32 0.461300 47.66 16.94 3.34 13.77 10.44 0.05 1.72 6.08 4.78 1.39 0.27Inlet: 7.2 atm. CO2, 4.8 atm. H2S. 900 53.83 33.95 4.55 5.61 1.06 0.09 0.26 0.66 41.62 25.74 3.451000 51.30 31.74 4.88 7.40 2.52 0.11 0.52 1.52 17.68 10.42 1.601100 48.07 29.01 4.72 9.51 4.78 0.11 0.94 2.86 9.24 5.07 0.821200 44.26 25.80 4.23 11.88 7.65 0.09 1.51 4.58 5.67 2.82 0.461300 40.24 22.31 3.56 14.35 10.78 0.07 2.20 6.49 3.93 1.72 0.27Inlet: 6 atm. CO2, 6 atm. H2S. 900 43.71 43.72 4.66 5.72 1.06 0.12 0.32 0.69 32.32 31.56 3.361000 41.15 41.37 5.01 7.54 2.53 0.14 0.67 1.60 13.68 12.95 1.571100 37.90 38.43 4.86 9.66 4.80 0.14 1.21 3.01 7.10 6.39 0.811200 34.10 34.92 4.35 12.03 7.68 0.13 1.98 4.83 4.32 3.61 0.451300 30.10 31.03 3.67 14.47 10.80 0.10 2.97 6.88 2.97 2.25 0.27Inlet: 4.8 atm. CO2, 7.2 atm. H2S. 900 33.86 53.74 4.55 5.58 1.03 0.14 0.39 0.71 24.60 37.90 3.211000 31.40 51.33 4.88 7.32 2.44 0.17 0.82 1.63 10.38 15.75 1.501100 28.30 48.28 4.72 9.33 4.61 0.18 1.51 3.06 5.37 7.88 0.771200 24.74 44.59 4.20 11.54 7.34 0.16 2.51 4.92 3.26 4.53 0.431300 21.07 40.41 3.52 13.76 10.24 0.13 3.82 7.03 2.23 2.87 0.25__________________________________________________________________________ CO2* and H2* refer to quantities after the shift reaction.

Equilibrium constants were measured for the CO.sub.2 +H.sub.2 S: reaction over the temperature range of 623.degree.-873.degree. K. The experimental success of these early studies, made to determine thermochemical parameters, confirms the practicality of the basic reactions of the present invention, given proper conditions.

The calculations for Tables I-A, I-B, I-C and I-D are based on the assumption that the inlet gas is composed of only CO.sub.2 and H.sub.2 S. However, in practice, steady state concentrations of COS and CS.sub.2 would be recycled from step 4, resulting in a small net increase in the calculated CO yields. At equilibrium, very small amounts of SO.sub.2 would also be formed, not listed in the tables being less than 0.1%. As stated in footnotes to the tables, CO.sub.2 * and H.sub.2 * refer to the quantities in the system that exist after the shift reaction. Thus, the ratio CO.sub.2 */H.sub.2 * is the number of moles of CO.sub.2 to be separated from H.sub.2 after the shift reaction step per mole of H.sub.2 produced in the overall process. The ratios H.sub.2 S/H.sub.2 * and COS/H.sub.2 * are the moles of each of these gases to be separated from the CO.sub.2 +CO+H.sub.2 fraction, after reaction (I-1), per mole of H.sub.2 product.

It is desirable to minimize the quantities of gases that must be separated by condensation/evaporation or by absorption/desorption. From the tables, it is apparent that several variables can be adjusted to optimize the overall process.

1. The number of moles of the different process gases to be separated and recirculated, per mole of H.sub.2 produced, decreases quite rapidly with increasing temperature. A practical process can probably operate at temperatures below 1300.degree. K. However, the higher relative yield of H.sub.2 with an increase in temperature may well justify the use of expensive materials that can be used at even higher temperatures. 2. The CO.sub.2 /H.sub.2 S ratio in the inlet gas can be adjusted to minimize the overall problem of the separation of gases. For example, at 1300.degree. K. and an operating pressure of 3 atm., the CO.sub.2 */H.sub.2 * ratio decreases from 3.72 with 66.7% CO.sub.2 in the inlet gas to 1.68 with 40% CO.sub.2 in the inlet gas. The (H.sub.2 S+COS)H.sub.2 * ratio increases from 1.06 to 2.07 over the same composition range. 3. The relative yield of H.sub.2 decreases with increased operating pressure. For example, at a temperature of 1300.degree. K. and equimolar CO.sub.2 -H.sub.2 S at the inlet, the CO.sub.2 */H.sub.2 * ratio increases from 1.87 for a pressure of 1 atm. to 2.97 for a pressure of 12 atm. The (H.sub.2 S+COS)/.sub.- H.sub.2 * ratio increases from 1.17 to 2.52 over the same pressure range. The relative amount of the H.sub.2 S+COS fraction increases somewhat with increasing pressure. It is emphasized, however, that several advantages accrue to operating a practical system at high pressure. Costs per unit output are lowered for heat exchangers, and pressures of the product gases will probably more nearly approximate the pressure at which they will subsequently be used. The higher pressures also simplify gas separation.

The effects of temperature, composition of inlet gases and pressure are illustrated in FIGS. I-B, I-C and I-D.

At 1200.degree. K., reaction (I-1) is endothermic by about 29.5 kcal. However, some H.sub.2 is formed simultaneously in reaction (I-2) which is exothermic by about 7.9 kcal. At a temperature of 1200.degree. K., 50% CO.sub.2 in the inlet gas and a pressure of 3 atm., reaction (I-2) would be about 25% complete. Thus, the overall heat requirement for the two reactions would be about 27.5 kcal. Condensation of 0.5 mole of S.sub.2 at about 700.degree. K. would yield 13.4 kcal. of high quality heat. Heat from the condensation of 0.75 mole of H.sub.2 O might be useful for some low temperature applications.

VERSION II

In Version II, the initial reaction of CO.sub.2 with H.sub.2 S is conducted at intermediate temperatures. A suitable desicant is used to reduce pressures of H.sub.2 O to shift reaction equilibria to maximize the yields of COS and CS.sub.2. The important reactions are:

CO.sub.2 +H.sub.2 S=COS+H.sub.2 O (II-1) COS+H.sub.2 S=CS.sub.2 +H.sub.2 O (II-2). The following reaction also controls relative amounts of CO.sub.2, COS and CS.sub.2. CO.sub.2 +CS.sub.2 =2COS (II-3) Relatively small amounts of CO, S.sub.2 and H.sub.2 are also produced. Computed equilibrium product compositions over a temperature range of 600.degree.-900.degree. K. for various pressures, compositions of inlet gas and assumed H.sub.2 O pressures are presented in Tables II-A to II-F below. Practical pressures must be selected during set up of the process, a wide range of H.sub.2 O pressures having been used in the claculations. Many of the well characterized desiccants are effective only at temperatures below those required for practical yields in reactions II-1 and II-2. The listed H.sub.2 pressures represent equilibria for the given CO, CO.sub.2 and H.sub.2 O pressures. Recirculation of steady state compositions of CO and H.sub.2 is probably desirable in the operating process. This would suppress both COS decomposition into CO and S.sub.2 and hydrogen formation during successive cycles. Slightly enhanced yields of COS and CS.sub.2 would result. TABLE II-A__________________________________________________________________________(PH2O = 0.01 atm)(YLD = COS + 2CS2) YLD/ COS/ YLD/T % CO2 % H2S % COS % H2O % CO % CS2 % H2 % S2 CO2 H2S H2S__________________________________________________________________________Inlet: 2 atm. CO2, 1 atm. H2S.600 62.23 28.95 7.51 0.33 0.44 0.21 0.07 0.26 0.13 0.26 0.27700 57.06 24.01 15.33 0.33 1.46 0.95 0.08 0.77 0.30 0.64 0.72800 52.14 18.89 23.26 0.33 1.93 2.40 0.05 0.99 0.54 1.23 1.49900 45.84 14.08 27.04 0.33 5.92 3.68 0.10 3.01 0.75 1.92 2.44Inlet: 1.5 atm. CO2, 1.5 atm. H2S.600 45.02 44.98 8.44 0.33 0.47 0.36 0.10 0.29 0.20 0.19 0.20700 39.17 39.16 17.17 0.33 1.50 1.73 0.12 0.81 0.53 0.44 0.53800 33.36 32.72 25.77 0.33 2.05 4.60 0.09 1.07 1.05 0.79 1.07900 26.35 26.67 29.43 0.33 6.24 7.58 0.18 3.21 1.69 1.10 1.67Inlet: 1 atm. CO2, 2 atm. H2S.600 28.86 62.05 7.47 0.33 0.42 0.45 0.14 0.28 0.29 0.12 0.13700 23.57 56.60 14.93 0.33 1.40 2.18 0.19 0.79 0.82 0.26 0.34800 18.39 50.41 21.89 0.33 1.82 6.03 0.14 0.98 1.85 0.43 0.67900 12.62 44.72 23.63 0.33 5.33 10.21 0.33 2.83 3.49 0.53 0.99Inlet: 4 atm. CO2, 2 atm. H2S.600 59.40 26.05 12.90 0.17 0.52 0.65 0.04 0.28 0.24 0.50 0.55700 52.82 19.41 22.94 0.17 1.53 2.30 0.05 0.79 0.52 1.18 1.42800 47.72 13.72 30.93 0.17 1.86 4.64 0.03 0.94 0.84 2.25 2.93900 42.25 9.51 33.65 0.17 5.45 6.18 0.05 2.75 1.09 3.54 4.84Inlet: 3 atm. CO2, 3 atm. H2S.600 41.75 41.54 14.47 0.17 0.55 1.15 0.06 0.31 0.40 0.35 0.40700 34.10 33.34 25.45 0.17 1.63 4.38 0.08 0.85 1.00 0.76 1.03800 27.90 25.65 33.79 0.17 1.96 9.47 0.05 1.01 1.89 1.32 2.06900 21.69 19.79 35.95 0.17 5.68 13.74 0.10 2.89 2.92 1.82 3.21Inlet: 2 atm. CO2, 4 atm. H2S.600 25.91 58.88 12.72 0.17 0.50 1.44 0.09 0.29 0.60 0.22 0.26700 19.03 51.00 21.73 0.17 1.45 5.72 0.12 0.79 1.74 0.43 0.65800 13.48 43.20 27.50 0.17 1.70 12.97 0.09 0.89 3.96 0.64 1.24900 8.61 37.43 26.99 0.17 4.65 19.52 0.21 2.43 7.67 0.72 1.76__________________________________________________________________________ TABLE II-B__________________________________________________________________________(PH2O = 0.01 atm)(YLD = COS + 2CS2) YLD/ COS/ YLD/T % CO2 % H2S % COS % H2O % CO % CS2 % H2 % S2 CO2 H2S H2S__________________________________________________________________________Inlet: 8 atm. CO2, 4 atm. H2S.600 55.44 21.78 20.14 0.08 0.56 1.68 0.02 0.29 0.42 0.92 1.08700 48.31 14.18 30.67 0.08 1.48 4.49 0.02 0.75 0.82 2.16 2.80800 43.92 8.97 37.21 0.08 1.67 7.29 0.01 0.84 1.18 4.15 5.77900 39.69 5.81 38.60 0.08 4.75 8.66 0.02 2.38 1.41 6.64 9.62Inlet: 6 atm. CO2, 6 atm. H2S.600 37.09 36.29 22.45 0.08 0.60 3.13 0.04 0.32 0.77 0.62 0.79700 28.57 26.25 33.58 0.08 1.57 9.10 0.04 0.80 1.81 1.28 1.97800 22.93 18.41 39.88 0.08 1.75 16.03 0.03 0.89 3.14 2.17 3.91900 17.98 13.38 40.31 0.08 4.88 20.84 0.05 2.46 4.56 3.01 6.13Inlet: 4 atm. CO2, 8 atm. H2S.600 21.68 53.85 19.47 0.08 0.53 4.03 0.06 0.30 1.27 0.36 0.51700 14.04 43.78 27.51 0.08 1.36 12.43 0.08 0.72 3.73 0.63 1.20800 9.05 35.27 30.14 0.08 1.44 23.22 0.06 0.75 8.46 0.85 2.17900 5.44 29.91 27.26 0.08 3.73 31.51 0.13 1.93 16.60 0.91 3.02Inlet: 16 atm. CO2, 8 atm. H2S.600 50.84 16.57 28.11 0.04 0.56 3.58 0.01 0.28 0.69 1.70 2.13700 44.40 9.33 37.07 0.04 1.34 7.14 0.01 0.67 1.16 3.97 5.50800 41.21 5.34 41.56 0.04 1.43 9.69 0.01 0.72 1.48 7.78 11.41900 38.18 3.28 41.91 0.04 3.98 10.61 0.01 2.00 1.65 12.78 19.25Inlet: 12 atm. CO2, 12 atm. H2S.600 31.55 29.47 31.01 0.04 0.59 7.02 0.02 0.31 1.43 1.05 1.53700 23.48 18.95 29.83 0.04 1.40 15.57 0.02 0.71 2.60 1.57 3.22800 19.07 12.10 43.56 0.04 1.47 23.01 0.01 0.74 4.70 3.60 7.40900 15.44 8.27 42.79 0.04 4.03 27.37 0.03 2.03 6.32 5.17 11.79Inlet: 8 atm. CO2, 16 atm. H2S.600 16.62 47.02 26.07 0.04 0.52 9.41 0.04 0.28 2.70 0.55 0.95700 9.48 35.82 30.39 0.04 1.16 22.47 0.05 0.60 7.95 0.85 2.10800 5.64 27.62 29.44 0.04 1.13 35.52 0.04 0.58 17.82 1.07 3.64900 3.24 23.01 24.98 0.04 2.80 44.41 0.08 1.44 35.12 1.09 4.95__________________________________________________________________________ TABLE II-C__________________________________________________________________________(PH2O = 0.05 atm)(YLD = COS + 2CS2) YLD/ COS/ YLD/T % CO2 % H2S % COS % H2O % CO % CS2 % H2 % S2 CO2 H2S H2S__________________________________________________________________________Inlet: 2 atm. CO2, 1 atm. H2S.600 64.84 31.41 1.70 1.67 0.14 0.01 0.11 0.12 0.03 0.05 0.05700 63.12 29.84 4.22 1.67 0.58 0.07 0.15 0.36 0.07 0.14 0.15800 60.85 27.74 7.97 1.67 0.92 0.24 0.11 0.51 0.14 0.29 0.30900 56.49 24.30 11.67 1.67 3.32 0.55 0.23 1.78 0.23 0.48 0.53Inlet: 1.5 atm. CO2, 1.5 atm. H2S.600 48.05 47.90 1.92 1.67 0.15 0.02 0.15 0.15 0.04 0.04 0.04700 46.13 46.09 4.76 1.67 0.62 0.11 0.21 0.41 0.11 0.10 0.11800 43.55 32.66 8.98 1.67 0.98 0.43 0.16 0.57 0.23 0.27 0.30900 38.84 39.75 12.93 1.67 3.53 0.99 0.35 1.94 0.38 0.33 0.38Inlet: 1 atm. CO2, 2 atm. H2S.600 31.52 64.62 1.70 1.67 0.13 0.02 0.19 0.16 0.06 0.03 0.03700 29.81 62.94 4.20 1.67 0.54 0.14 0.29 0.42 0.15 0.07 0.07800 27.50 60.76 7.89 1.67 0.88 0.62 0.23 0.55 0.33 0.13 0.15900 23.35 57.07 11.16 1.67 3.16 1.23 0.52 1.84 0.58 0.20 0.24Inlet: 4 atm. CO2, 2 atm. H2S.600 64.38 31.02 3.33 0.83 0.19 0.04 0.07 0.13 0.05 0.11 0.11700 61.54 28.36 7.81 0.83 0.72 0.23 0.09 0.41 0.13 0.28 0.29800 58.09 24.95 13.69 0.83 1.06 0.75 0.06 0.56 0.26 0.55 0.61900 52.95 20.73 18.39 0.83 3.61 1.47 0.13 1.87 0.40 0.89 1.03Inlet: 3 atm. CO2, 3 atm. H2S.600 47.48 47.41 3.75 0.83 0.20 0.07 0.10 0.15 0.08 0.08 0.08700 44.28 44.33 8.79 0.83 0.77 0.40 0.14 0.45 0.22 0.20 0.22800 40.32 40.29 15.34 0.83 1.14 1.35 0.10 0.62 0.45 0.38 0.45900 34.59 35.26 20.43 0.83 3.85 2.78 0.21 2.03 0.75 0.58 0.74Inlet: 2 atm. CO2, 4 atm. H2S.600 31.05 64.24 3.33 0.83 0.18 0.08 0.14 0.16 0.11 0.05 0.05700 28.19 61.41 7.75 0.83 0.69 0.49 0.19 0.44 0.31 0.13 0.14800 24.62 57.68 13.41 0.83 1.02 1.69 0.15 0.58 0.68 0.23 0.29900 19.62 52.96 17.40 0.83 3.41 3.56 0.34 1.87 1.25 0.33 0.46__________________________________________________________________________ TABLE II-D__________________________________________________________________________(PH2O = 0.05 atm.)(YLD = COS + 2CS2) YLD/ COS/ YLD/T % CO2 % H2S % COS % H2O % CO % CS2 % H2 % S2 CO2 H2S H2S__________________________________________________________________________Inlet: 8 atm. CO2, 4 atm. H2S.600 63.04 29.71 6.25 0.42 0.24 0.14 0.05 0.15 0.10 0.21 0.22700 58.70 25.46 13.38 0.42 0.84 0.70 0.06 0.45 0.25 0.53 0.58800 54.12 20.67 21.13 0.42 1.14 1.91 0.04 0.59 0.46 1.02 1.21900 48.70 16.00 26.10 0.42 3.64 3.23 0.07 1.86 0.67 1.63 2.04Inlet: 6 atm. CO2, 6 atm. H2S.600 45.93 45.88 7.03 0.42 0.26 0.25 0.07 0.16 0.16 0.15 0.16700 40.98 40.87 14.99 0.42 0.90 1.26 0.09 0.49 0.43 0.37 0.43800 35.63 34.94 23.51 0.42 1.21 3.59 0.06 0.64 0.86 0.67 0.88900 29.46 29.05 28.67 0.42 3.86 6.44 0.13 1.99 1.41 0.99 1.43Inlet: 4 atm. CO2, 8 atm. H2S.600 29.68 62.89 6.22 0.42 0.23 0.30 0.09 0.16 0.23 0.10 0.11700 25.22 58.24 13.15 0.42 0.81 1.58 0.13 0.47 0.65 0.23 0.28800 20.38 52.56 20.23 0.42 1.09 4.64 0.09 0.59 1.45 0.38 0.56900 15.07 46.89 23.68 0.42 3.36 8.58 0.21 1.79 2.71 0.51 0.87Inlet: 16 atm. CO2, 8 atm. H2S.600 60.61 27.23 11.01 0.21 0.29 0.46 0.03 0.16 0.20 0.40 0.44700 54.70 21.16 20.72 0.21 0.90 1.81 0.03 0.47 0.44 0.98 1.15800 49.61 15.50 29.04 0.21 1.12 3.93 0.02 0.57 0.74 1.87 2.38900 44.67 11.09 33.19 0.21 3.40 5.69 0.04 1.72 1.00 2.99 4.02Inlet: 12 atm. CO2, 12 atm. H2S.600 43.13 42.95 12.36 0.21 0.31 0.82 0.04 0.18 0.32 0.29 0.33700 36.27 35.54 23.08 0.21 0.96 3.39 0.05 0.51 0.82 0.65 0.84800 30.13 28.06 31.94 0.21 1.19 7.83 0.03 0.61 1.58 1.14 1.70900 24.35 21.97 35.85 0.21 3.57 12.17 0.07 1.82 2.47 1.63 2.74Inlet: 8 atm. CO2, 16 atm. H2S.600 27.16 60.20 10.91 0.21 0.28 1.01 0.06 0.17 0.48 0.18 0.21700 20.94 53.13 19.92 0.21 0.87 4.37 0.08 0.48 1.37 0.37 0.54800 15.40 45.63 26.54 0.21 1.04 10.58 0.06 0.55 3.10 0.58 1.05900 10.57 39.49 27.96 0.21 3.00 17.07 0.14 1.57 5.88 0.71 1.57__________________________________________________________________________ TABLE II-E__________________________________________________________________________(PH2O = 0.10 atm.)(YLD = COS + 2CS2) YLD/ COS/ YLD/T % CO2 % H2S % COS % H2O % CO % CS2 % H2 % S2 CO2 H2S H2S__________________________________________________________________________Inlet: 2 atm. CO2, 1 atm. H2S.600 64.50 31.03 0.83 3.33 0.08 0.00 0.12 0.10 0.01 0.03 0.03700 63.57 30.15 2.14 3.33 0.35 0.02 0.17 0.26 0.03 0.07 0.07800 62.26 29.00 4.26 3.33 0.59 0.07 0.13 0.36 0.07 0.15 0.15900 59.39 26.68 6.64 3.33 2.24 0.17 0.29 1.27 0.12 0.25 0.26Inlet: 1.5 atm. CO2, 1.5 atm. H2S.600 47.48 47.57 0.95 3.33 0.08 0.00 0.16 0.12 0.02 0.02 0.02700 46.74 46.54 2.43 3.33 0.37 0.03 0.25 0.31 0.05 0.05 0.05800 45.25 45.23 4.83 3.33 0.62 0.12 0.19 0.41 0.11 0.11 0.11900 42.09 42.53 7.50 3.33 2.39 0.31 0.44 1.42 0.19 0.18 0.19Inlet: 1 atm. CO2, 2 atm. H2S.600 31.18 64.24 0.84 3.33 0.07 0.01 0.21 0.14 0.03 0.01 0.01700 30.27 63.25 2.14 3.33 0.32 0.04 0.33 0.32 0.07 0.03 0.04800 28.95 62.11 4.24 3.33 0.55 0.14 0.27 0.41 0.16 0.07 0.07900 26.17 59.50 6.52 3.33 2.12 0.37 0.62 1.37 0.28 0.11 0.12Inlet: 4 atm. CO2, 2 atm. H2S.600 64.86 31.46 1.70 1.67 0.11 0.01 0.08 0.10 0.03 0.05 0.05700 63.23 29.93 4.24 1.67 0.46 0.07 0.12 0.29 0.07 0.14 0.15800 61.01 27.83 8.02 1.67 0.73 0.24 0.08 0.41 0.14 0.29 0.31900 57.10 24.64 11.78 1.67 2.66 0.56 0.18 1.42 0.23 0.48 0.52Inlet: 3 atm. CO2, 3 atm. H2S.600 48.08 47.96 1.92 1.67 0.12 0.02 0.12 0.12 0.04 0.04 0.04700 46.25 46.20 4.78 1.67 0.49 0.11 0.17 0.33 0.11 0.10 0.11800 43.72 43.78 9.04 1.67 0.78 0.43 0.13 0.45 0.23 0.21 0.23900 39.38 40.04 13.21 1.67 2.84 1.02 0.28 1.56 0.39 0.33 0.38Inlet: 2 atm. CO2, 4 atm. H2S.600 31.54 64.69 1.70 1.67 0.10 0.02 0.15 0.13 0.06 0.03 0.03700 29.91 63.07 4.22 1.67 0.43 0.14 0.23 0.33 0.15 0.07 0.07800 27.65 60.89 7.95 1.67 0.70 0.53 0.18 0.44 0.33 0.13 0.15900 23.82 57.38 11.45 1.67 2.53 1.27 0.41 1.47 0.59 0.20 0.24__________________________________________________________________________ TABLE II-F__________________________________________________________________________(PH2O = 0.10 atm.)(YLD = COS + 2CS2) YLD/ COS/ YLD/T % CO2 % H2S % COS % H2O % CO % CS2 % H2 % S2 CO2 H2S H2S__________________________________________________________________________Inlet: 8 atm. CO2, 4 atm. H2S.600 64.41 31.06 3.34 0.83 0.15 0.04 0.06 0.11 0.05 0.11 0.11700 61.67 28.44 7.85 0.83 0.58 0.23 0.07 0.32 0.13 0.28 0.29800 58.27 25.03 13.77 0.83 0.85 0.75 0.05 0.45 0.26 0.55 0.61900 53.47 20.93 18.74 0.83 2.90 1.52 0.10 1.50 0.41 0.90 1.04Inlet: 6 atm. CO2, 6 atm. H2S.600 47.52 47.46 3.76 0.83 0.16 0.07 0.08 0.12 0.08 0.08 0.08700 44.42 44.43 8.83 0.83 0.61 0.04 0.11 0.36 0.20 0.20 0.20800 40.50 40.38 15.44 0.83 0.91 1.36 0.08 0.49 0.45 0.38 0.45900 35.11 35.45 20.85 0.83 3.10 2.86 0.17 1.63 0.76 0.59 0.75Inlet: 4 atm. CO2, 8 atm. H2S.600 31.08 64.30 3.33 0.83 0.14 0.08 0.11 0.12 0.11 0.05 0.05700 28.31 61.52 7.79 0.83 0.55 0.49 0.15 0.35 0.31 0.13 0.14800 24.77 57.77 13.52 0.83 0.82 1.71 0.12 0.47 0.68 0.23 0.29900 20.03 53.12 17.83 0.83 2.75 3.66 0.26 1.51 1.26 0.34 0.47Inlet: 16 atm. CO2, 8 atm. H2S.600 63.09 29.75 6.26 0.42 0.19 0.14 0.04 0.12 0.10 0.21 0.22700 58.83 25.53 13.45 0.42 0.67 0.71 0.04 0.36 0.25 0.53 0.58800 54.29 20.72 21.25 0.42 0.91 1.92 0.03 0.47 0.46 1.03 1.21900 49.17 16.11 26.54 0.42 2.92 3.30 0.06 1.49 0.67 1.65 2.06Inlet: 12 atm. CO2, 12 atm. H2S.600 45.98 45.92 7.04 0.42 0.21 0.25 0.05 0.13 0.16 0.15 0.16700 41.12 40.95 15.07 0.42 0.71 1.27 0.07 0.39 0.43 0.37 0.43800 35.79 35.00 23.66 0.42 0.97 3.62 0.05 0.51 0.86 0.68 0.88900 29.91 29.12 29.18 0.42 3.10 6.57 0.10 1.60 1.41 1.00 1.45Inlet: 8 atm. CO2, 16 atm. H2S.600 29.72 62.94 6.24 0.42 0.18 0.30 0.07 0.13 0.23 0.10 0.11700 25.34 58.31 13.23 0.42 0.64 1.59 0.10 0.37 0.65 0.23 0.28800 20.51 52.60 20.38 0.42 0.87 4.68 0.07 0.47 1.45 0.39 0.57900 15.40 46.90 24.20 0.42 2.71 8.77 0.17 1.44 2.71 0.52 0.89__________________________________________________________________________

The effective yield in terms of CO available for the shift reaction is equal to the sum of one mole of COS plus two moles of CS.sub.2. The effective yield increases with pressure and also with temperature. Low H.sub.2 O pressure is expected to be practical at the higher temperatures, since several hydrates evolve their last molecule of water at rather high temperatures. Ce.sub.2 (SO.sub.4) 3.8H.sub.2 O evolves the eighth water of hydration at 900.degree. K., e.g.

The complete cycle of Version II includes the following steps, the first one of which may be selectively conducted in one of two modes.

1. Mode A: Conduct reactions II-1 and II-2 in the presence of a desiccant that absorbs H.sub.2 O. Mode B: Raise the reactor temperature to evolve H.sub.2 O and reconstitute the desiccant. The reactors could be used in parallel and the operational modes alternated. Or, Mode B could be operated intermittently with Mode A with the same reactor. 2. Separate COS and CS.sub.2 from the CO.sub.2 +CO+H.sub.2 fraction. It would not be necessary to separate unreacted H.sub.2 S from the CO.sub.2 fraction. However, some H.sub.2 S would probably included with COS, so that a step to separate H.sub.2 from COS might be desirable. 3. Add CO.sub.2 (from the shift reaction) to equal the CS.sub.2 in the COS+CS.sub.2 fraction and heat to high temperature to produce CO and S.sub.2 (g). 4. Condense the S.sub.2 (g) to S.sub.2 (l). 5. Separate the small quantities of COS and CS.sub.2 residual from step 3. Add to inlet gases for repetition of step 3 of the next cycle. 6. Use separated CO and the shift reaction to produce H.sub.2 from H.sub.2 O. 7. Separate the H.sub.2 from CO.sub.2 by methods now used commercially for the shift process and use this CO.sub.2 plus the CO.sub.2 fraction from step 2, together with the required quantity of H.sub.2 S, as inlet gas to repeat the cycle.

A flow diagram for Version II is presented in FIG. II-A.

Table II-G presents concentrations of the various product gases formed at different pressures when COS is heated to 800.degree.-1300.degree. K.

TABLE II-G______________________________________THE THERMAL DECOMPOSITION OF COS % % CO2 CO/ CO/ COS/T % CO % S2 COS & CS2 COS CO2 CS2______________________________________Inlet: 1 atm. COS. 800 4.52 2.26 47.55 22.84 0.10 0.20 2.08 900 11.55 5.77 42.17 20.26 0.27 0.57 2.081000 22.39 11.20 33.93 16.24 0.66 1.38 2.091100 34.77 17.39 24.46 11.69 1.42 2.97 2.091200 45.57 22.78 16.20 7.73 2.81 5.90 2.101300 53.27 26.64 10.29 4.90 5.18 10.87 2.101400 58.16 29.08 6.54 3.11 8.89 18.70 2.10Inlet: 5 atm. COS. 800 2.69 1.35 48.94 23.51 0.05 0.11 2.08 900 7.11 3.55 45.57 21.88 0.16 0.32 2.081000 14.59 7.30 39.91 19.10 0.37 0.76 2.091100 24.50 12.25 32.34 15.46 0.76 1.58 2.091200 34.96 17.48 24.34 11.61 1.44 3.01 2.101300 44.11 22.05 17.33 8.26 2.55 5.34 2.101400 51.04 25.52 12.02 5.71 4.25 8.94 2.11Inlet: 10 atm. COS. 800 2.15 1.08 49.36 23.71 0.04 0.09 2.08 900 5.73 2.86 46.62 22.39 0.12 0.26 2.081000 11.97 5.98 41.92 20.06 0.29 0.60 2.091100 20.62 10.31 35.31 16.88 0.58 1.22 2.091200 30.37 15.18 27.87 13.29 1.09 2.29 2.101300 39.56 19.78 20.82 9.92 1.90 3.99 2.101400 47.08 23.54 15.06 7.16 3.13 6.58 2.10Inlet: 15 atm. COS. 800 1.88 0.94 49.56 23.88 0.04 0.08 2.08 900 5.04 2.52 47.15 22.64 0.11 0.22 2.081000 10.62 5.31 42.95 20.56 0.25 0.52 2.091100 18.55 9.27 36.90 17.64 0.50 1.05 2.091200 27.78 13.89 29.86 14.24 0.93 1.95 2.101300 36.84 18.42 22.91 10.91 1.61 3.38 2.101400 44.57 22.29 16.99 8.08 2.62 5.52 2.10______________________________________

Heat Requirements for Version II. At temperatures of 600.degree.-900.degree. K., reactions II-1 and II-2 are each endothermic by about 8.3 kcal. However, each reaction produces H.sub.2 O(g) that will react with desiccant and evolve heat. Although a specific desiccant has not been selected, this quantity of heat can be estimated. The characteristic entropy change at 298.degree. K. (.DELTA.S.sup.o (298)) for the evolution of one mole of H.sub.2 O(g) from a hydrate (or hydroxide) is approximately 36 cal. Mole.sup.-1 deg..sup.-1. A selected dissociation pressure at the reaction temperature also establishes a corresponding .DELTA.G.sup.o. One can then estimate a value for .DELTA.H.sup.o (298) from the approximate expression .DELTA.G.sup.o (T)=.DELTA.H.sup.o (298-.DELTA.T S.sup.o (298). For an H.sub.2 O pressure of 0.10 atm. at 600.degree. K., the .DELTA.H.sup.o (298) would be about 24.3 kcal. For a pressure of 0.01 atm. at 700.degree. K., .DELTA.H.sup.o (298) would be about 32.4 kcal. Thus, the hydration reaction associated with reactions II-1 and II-2 would evolve about 28.3 kcal. of heat and combined reactions would yield about 20 kcal. of heat per mole of CO eventually produced in step 2 above. The overall high temperature dissociation reactions would require about 27.5 kcal. The condensation of 0.5 mole of S.sub.2 (at about 700.degree. K.) would yield 13.4 kcal. The evolution of H.sub.2 O from the desiccant (step 7 above) would require about 28 kcal. Since the overall shift reaction is nearly thermally neutral (with liquid H.sub.2 O), one can summarize a heat balance as follows:

______________________________________1. Endothermic dissociation (.DELTA.H = +27.5 kcal.) reaction at 1200-1300.degree. K.2. Endothermic dehydration (.DELTA.H = +28.5) reaction at 900-1000.degree. K.3. Endothermic reactions (.DELTA.H + -20.0) (II-1, II-2, etc.) at 700.degree. K.4. Exothermic S.sub.2 condensation (.DELTA.H = -13.4) at about 700.degree. K.______________________________________

The net 23 kcal heat requirement is not excessive. Further, the exothermic steps occur at sufficiently high temperatures for the heat to be readily usable. However, this exothermic heat must be used efficiently for some purpose for Version II to be practical.

VERSION III

This version is based on the following steps:

1. The reaction of CO with H.sub.2 S to form H.sub.2 and COS and also CS.sub.2 via the simultaneous reactions: CO+H.sub.2 S=COS+H.sub.2 (III- 1) 2COS=CS.sub.2 +CO.sub.2 (III- 2) The equilibrium production of CS.sub.2 is very important, since it essentially doubles the final yields of CO and H.sub.2 which would occur from the formation of COS only. 2. Separation of the H.sub.2 S+COS+CS.sub.2 fraction from the CO+H.sub.2 +CO.sub.2 fraction. 3. Separation of COS+CS.sub.2 from H.sub.2 S, as by use of membranes or molecular sieves. 4. Separation of H.sub.2 from CO+CO.sub.2, in similar manner. 5. Separation of CO.sub.2 from CO, in similar manner 6. Thermal decomposition of COS and of CS.sub.2 via the reactions: COS=CO+0.5S.sub.2 (g) (III-3) CS.sub.2 +CO.sub.2 =2CO+S.sub.2 (g) (III-4) 7. Recovery of the sulfur by condensation.

A flow diagram of Version III is presented in FIG. III-A.

As an alternate sequence the CO+CO.sub.2 from step 4 could be mixed with the CO and CS.sub.2 (with some COS) remaining from step 7 and then combined with H.sub.2 S to constitute the inlet gas for step 1 to repeat the cycle. Recycled gases eventually reach steady-state compositions for a net yield of H.sub.2 +0.5S.sub.2, completing the cycle. Small amounts of H.sub.2 O would also be produced during step 1 via the reaction:

H.sub.2 S+COS=CS.sub.2 +H.sub.2 O (III-5) Computed equilibrium product compositions are given in Table III-A, for various temperatures and mixtures of inlet gases. TABLE III-A__________________________________________________________________________ COS + % CO2 COS/ CS2/ CS2/ 2CS2/T % CO % H2S % COS % H2 % CS2 % H2O H2/CO H2S COS H2S H2S__________________________________________________________________________Inlet: 67% CO, 33% H2S.500 55.80 22.46 5.56 10.87 2.66 .00 0.19 0.25 0.48 0.12 0.48600 56.57 23.24 5.15 10.10 2.47 0.02 0.18 0.22 0.48 0.11 0.43700 56.99 23.66 4.93 9.67 2.37 0.04 0.17 0.21 0.48 0.10 0.41800 57.22 23.88 4.82 9.45 2.32 0.09 0.17 0.20 0.48 0.10 0.40900 57.33 24.00 4.76 9.33 2.29 0.16 0.16 0.20 0.48 0.10 0.39Inlet: 50% CO, 50% H2S.500 38.26 38.26 6.00 11.75 2.87 0.01 0.31 0.16 0.48 0.08 0.31600 39.11 39.11 5.55 10.90 2.67 0.03 0.28 0.14 0.48 0.07 0.28700 39.57 39.57 5.32 10.43 2.55 0.07 0.26 0.13 0.48 0.06 0.26800 39.82 39.82 5.19 10.18 2.49 0.15 0.26 0.13 0.48 0.06 0.26900 39.95 39.95 5.13 10.05 2.46 0.27 0.25 0.13 0.48 0.06 0.25Inlet: 33% CO, 67% H2S.500 22.46 55.80 5.56 10.87 2.66 0.01 0.48 0.10 0.48 0.05 0.19600 22.24 56.57 5.15 10.10 2.47 0.04 0.45 0.09 0.48 0.04 0.18700 23.66 56.99 4.93 9.67 2.37 0.10 0.41 0.09 0.48 0.04 0.17800 23.88 57.22 4.82 9.45 2.32 0.22 0.40 0.08 0.48 0.04 0.17900 24.00 57.33 4.76 9.33 2.29 0.38 0.39 0.08 0.48 0.04 0.16__________________________________________________________________________

It is apparent that relatively low reaction temperature would be advantageous for step 1. Catalysts may be used if necessary to achieve adequate reaction rates. Fukudu.sup.11. describes the use of various metal sulfides which promise to be practical. U.S. Pat. No. 4,500,505 also discloses a class of catalysts based on combination of numerous elemental metals. The chosen catalysts must be such as to not also promote the disproportionation of CO.sub.2 through the reaction:

2CO=CO.sub.2 +C (III-6) For thermochemical equilibrium, this reaction must always occur at low temperature. However, it usually does not occur during the many processes that are conducted in commercial operations involving CO.

Yields for step 1 would not be penalized by highpressure operation, being essentially independent of pressure. This would facilitate the complex gas separation steps of Version III. Inlet gas compositions may also be varied to change relative composition of gases in the different separation steps.

At 800.degree. K., reaction (III-1) is exothermic by about 0.54 kcal. Reaction (III-2) is almost thermally neutral. The combined reactions should evolve about 0.5 kcal of heat. At a temperature of 1200.degree. K., reaction (III-3) is endothermic by about 21.4 kcal. The reaction of CO.sub.2 with CS.sub.2 to produce COS is almost thermally neutral. Thus, this cycle variation would require about 21.5 kcal of high temperature heat. Condensation of 0.5 mole of S.sub.2 at 700.degree.-800.degree. K. would yield about 13.4 kcal of high quality heat.

COMPARISON OF VERSIONS

Of the three methods for splitting H.sub.2 S, Version I is probably more easily developed. Some of the steps in this cycle are somewhat similar to those now practiced in the petroleum industry for producing H.sub.2 by steam reforming of hydrocarbons and for producing sulfur by the previously mentioned Claus process. Assuming (CH.sub.2).sub.x or (CH.sub.1.5).sub.x to be the hydrocarbon for the steam reforming step and also the fuel to produce combustion heat, and considering only the heat required for high temperature endothermic steps, Version I would save about 25% of the hydrocarbon needed for the steam reforming process. However, less valuable hydrocarbons would actually be used. Also, heat from the exothermic Claus process probably saves only less valuable fuel. Further analysis is needed of various fuel costs to establish actual monetary savings by use of Version I.

Version II is an interesting method for shifting equilibria in chemical reactions. The separation steps can probably be performed with good efficiency. However, the process will be advantageous only if heat from the exothermic steps can be used to good advantage in companion processes.

Version II requires less high temperature than the other two processes. The initial separation step presents no problems. Rapid progress has been made with membranes and molecular sieves used for adjusting gas compositions and for making gas separations, so that cycle Version III can undoubtedly be practically developed.

The invention may be embodied in still other specific versions and forms without departing from the spirit or essential characteristics thereof. The present embodiments and versions are, therefore, to be considered as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing descriptions, and all changes that come within the meaning and range of equivalency of the claims are, therefore, intended to be embraced therein.

Claims

1. A method of recovery of sulfur and hydrogen from hydrogen sulfide, comprising the steps:

initially reacting carbon dioxide with a portion of the hydrogen sulfide at temperatures not lower than approximately 900.degree. K.;

condensing the resultant gaseous sulfur to liquid sulfur;

condensing the resultant steam to liquid water;

separating the carbon dioxide+carbon monoxide+hydrogen fraction from the initial reaction leaving the sulfur bearing hydrogen sulfide+carbonyl sulfide+carbon disulfide fraction as a residual;

reacting water with the carbon monoxide of the carbon dioxide+carbon monoxide+hydrogen fraction, resulting in hydrogen and additional carbon dioxide; and

separating the hydrogen from the carbon dioxide.

2. The method of claim 1, comprising the further steps:

recycling the residual separated hydrogen sulfide+carbonyl sulfide+carbon disulfide fraction to the initial step; and

recycling the separated carbon dioxide to the step wherein carbon dioxide is reacted with hydrogen sulfide at temperatures not lower than approximately 900.degree. K.

3. A method of recovery of sulfur and hydrogen from hydrogen sulfide, comprising the steps:

initially reacting carbon dioxide with a portion of the hydrogen sulfide at a temperature below approximately 900.degree. K., in the presence of a desiccant to absorb water resulting from the reaction, to increase yields of carbonyl sulfide and carbon disulfide;

separating carbonyl sulfide and carbon disulfide from the carbon dioxide+carbon monoxide+hydrogen fraction from the initial reaction;

adding carbon dioxide to carbonyl sulfide+carbon disulfide fraction and heating to a temperature not lower than approximately 800.degree. K., to produce carbon monoxide and gaseous sulfur, along with residual carbonyl sulfide and carbon disulfide;

condensing said sulfur;

separating the residual carbonyl sulfide+carbon disulfide fraction;

reacting water with the remaining carbon monoxide to produce hydrogen and carbon dioxide; and

separating the hydrogen from the carbon dioxide.

4. The method of claim 3, comprising the further step:

recycling the separated carbonyl sulfide+carbon disulfide fraction and the separated carbon dioxide to the step wherein carbon dioxide is reacted with carbonyl sulfide+carbon disulfide fraction at a temperature not lower than approximately 800.degree. K.

5. The method of claim 3, wherein:

the initial step is conducted in a reactor which is periodically raised to temperatures sufficient to evolve gaseous water from the desiccant, said water being removed from the reactor.

6. A method of recovery of sulfur and hydrogen from hydrogen sulfide, comprising the steps:

initially reacting carbon monoxide with a portion of the hydrogen sulfide, producing carbonyl sulfide and hydrogen, accompanied by the simultaneous conversion of a portion of the carbonyl sulfide into carbon dioxide and equilibrium amounts of carbon disulfide;

separating the hydrogen sulfide+carbonyl sulfide+carbon disulfide fraction of the initial reaction from the carbon monoxide+hydrogen+carbon dioxide fraction thereof;

separating the carbonyl sulfide and carbon disulfide together from the hydrogen sulfide, and the hydrogen from the carbon monoxide and carbon dioxide together;

separating the carbon dioxide from the carbon monoxide;

reacting the carbonyl sulfide, carbon dioxide and carbon disulfide at a temperature not lower than approximately 800.degree. K., producing carbon monoxide and gaseous sulfur; and

condensing the sulfur.

7. The method of claim 6, wherein:

the separated carbon monoxide and hydrogen sulfide are recycled for use in the initial reaction.