Патент USA US3078650код для вставки
United States Patent O?tice 3,078,641 Patented Feta. 26, 1963 1 2 Zeolite X exhibits adsorptive properties that are unique 3,078,641 among known adsorbents. The common adsorbents, like SEPARATKQN @F SULFUR CQOMPGUND§ FRGM ‘VAPGR MlXTUlisEd chorcoal and silica gel, show adsorption selectivities based primarily on the boiling point or critical temperature of the adsorbate. Activated zeolite X, on the other hand, exhibits a selectivity based on the size and shape of the adsorbate molecule. Among those adsorbate molecules Robert M. Milton, Buffalo, N.Y., assignor to Union ‘Carbide Corporation, a corporation of New Yuri: No Drawing. Filed Dec. 31, 1959, Ser. No. 863,104 8 Claims. (til. 55--73) whose size and shape are such as to permit adsorption This invention relates to a method for adsorbing ?uids by zeolite X, a very strong preference is exhibited toward and separating a mixture of ?uids into its component 10 those that are polar, polarizable, and unsaturated. An parts. More particularly, the invention relates to a other property of zeolite X that contributes to its unique method of separating hydrogen sul?de from a vapor mixture thereof with hydrogen and/or alkanes contain position among adsorbents is that of adsorbing large quantities of adsorbate at either very low pressures, at ing less than six carbons per molecule. Still more par very low partial pressures, or at very low concentrations. ticularly, the invention relates to a method for preferen 15 One or a combination of one or more of these adsorption tially adsorbing hydrogen sulfide from fuel gases. characteristics or others can make zeolite X useful for This application is a continuation-in-part of copending numerous gas or liquid separation processes where adsorb ‘patent application Serial No. 400,386, ?led December ents are not now employed. 24, 1953, now abandoned. ' Illustrating the utility of this invention, it may, for example, be desirable to remove hydrogen sul?de from mits more ef?cient and more economical operation of numerous processes now employing other absorbents. fuel gases such as natural gas. Hydrogen sul?de is a common undesirable impurity in such fuels which con ‘exhibit any appreciable molecular sieve action, whereas sist primarily of alkanes and hydrogen. Such fuel gases may be “sweetened,” i.e., have the undesirable hydrogen sul?de removed therefrom, by the present adsorption In the tables which follow, the term “Weight % adsorbed” refers to the percentage increase in the weight The use of zeolite X per Common adsorbents like silica gel and charcoal do not the various forms of zeolite X do. of the adsorbent. The adsorbent was activated by heat process. ing it at a reduced pressure to remove adsorbed mate Broadly, the invention comprises mixing molecules, rials. Throughout the speci?cation the activation tem in a fluid state, of the materials to be adsorbed or sepa perature for zeolite X was 350° C., and the pressure at rated with a crystalline synthetic dehydrated zeolite X, 30 which it was ‘heated was less than about 0.1 millimeter and effecting the adsorption of the adsorbate by the of mercury absolute unless otherwise speci?ed. Like zeolite. wise, the pressure given for each adsorption is the pres Zeolite X, and the methods for making zeolite X, sure of the adsorbate under the adsorption conditions are described in detail and claimed in US. patent appli unless the contrary is speci?ed. cation Serial No. 400,389, ?led December 24, 1953, now 35 The present process for separating hydrogen sul?de U.S. Patent No. 2,882,244, issued April 14, 1959, in the from certain vapor mixtures depends upon the selectivity name of R. M. Milton. of the internal surfaces of the zeolite X crystal towards It is the principal object of the present invention to this strongly polar compound as compared with the al provide a process for the selective adsorption of mole kanes and hydrogen. Zeolite X is capable of adsorbing cules from ?uids. A further object of the invention is 40 all of these compounds based on a consideration of the to provide a method whereby certain molecules may be zeolite X pore size and critical molecular dimensions of adsorbed and separated by crystalline synthetic zeolite the compounds. For example, the pores of zeolite X'are X from ?uid mixtures of these molecules and other 31 sufficiently large and in fact do receive methane, octane molecules. and hydrogen molecules. The formula for zeolite X may be Written as follows: 45 Based on these considerations, one skilled in the art would logically conclude that zeolite X would not possess any particular‘ selectivity for hydrogen sul?de in D. In this formula “1* ” represents a metal, "11” its valence, and “Y” may be any value up to 8 depending on the ’ , preference to the other constituents of the present vapor mixture. Contrary to these expectations, it has been discovered that zeolite X possesses an extremely strong selectivity for hydrogen sul?de to the substantial exclu sion of alkanes and hydrogen. One reason for this identity of the metal and the degree of hydration of the crystal. X-ray diffraction data may be employed to de selectivity is the highly polar nature of hydrogen sul?de ?ne the crystal structure of zeolite X. Such information as compared with the other possible constituents of the and processes for synthesizing zeolite X, are provided in 55 vapor mixture. Since the lower molecular Weight al- p U.S. Patent No. 2,882,244. kanes and hydrogen are the major components of fuel The adsorbents contemplated herein include not only ‘gases such as natural gas, an adsorption process utilizing the sodium form of zeolite X which is a common form zeolite X as the adsorbent is quite effective for the produced, but also crystalline materials obtained from sweetening of such fuel gases. Table I contains data such a zeolite by partial or complete replacement of the 60 showing the percent of the various gases adsorbed by sodium ion with other cations. Sodium cations can zeolite X. In Table I, all of the adsorptions were car~ be replaced, in part or entirely, by other ions. For ex ried out at 25° C. ample, this may be accomplished by ion exchange tech An important characteristic of zeolite X is its property niques. of adsorbing large amounts of adsorbates at low adsorb 3,078,641 A. 3 ate pressures, partial pressures, or concentrations. drated zeolite X. This The ?ow is stopped as soon as hydro gen sul?de is detected in the etlluent. At this point, the property makes zeolite X useful in the removal of adsorb~ etlluent is substantially free of hydrogen sul?de contami~ able impurities from gas and liquid mixtures, since it has nation. If large amounts are tolerable, the adsorption a relatively high adsorption capacity even when the mate rial being adsorbed from a mixture is present in very low 5 can be continued until the hydrogen sul?de level reaches the predetermined value. concentrations. E?icient recovery of minor components of mixtures is also possible. High degrees of adsorption Example 11 at low pressures on zeolite X is also illustrated in Table I. TABLE I Adsorhatc 111$ ...................... ._ Adsorbent NaiX ..... .. Pressure Wt. percent mm. Hg adsorbed 0.5 11.5 11 400 22. 6 35. 0 (EN; ...................... .- N?zX _____ _. 500 Less than 1 CQI'IG _____________________ N NBQX _____ ._ 5 O. 2 25 300 700 0. 8 8. 3 10. 2 1 0. 8 5 4 25 3. l 2. G ll. 1 700 14. 6 700 17. 3 710 729 17. (i 17. 6 C515 ..................... ._ NnzX ..... __ Xl-Cqllm ................... _- NZMX ..... _. i-Cqll’w ___________________ __ N?gX _____ .. 11-05111: ___________________ _. B43511" ................... .. Xl~CaH1z ___________________ __ t Natural gas, containing principally methane, ethane, 10 propane, hydrogen and lesser amounts of the butanes, 0.2 2.4: 5. 5 400 11. 5 18. 4 205 18. 4 224 19. 3 O. 18 4. 8 0. 22 20 20 20 20 20 20 10. 2 19. 2 18. 3 15. 8 17. 9 l9. 2 16. l 11.0 30 2. 3 5. 0 2. 3 20. 8 20. 8 14. 2 5. 0 14. 2 An advantage that may be taken of this high adsorp tion capacity at low pressures is the operation of adsorp— pentanes and hexanes, together with sulfur impurities, chie?y hydrogen sul?de and the lower boiling mercaptans, particularly methyl mercaptan, is passed through a bed of dehydrated sodium zeolite X. The ef?uent is sub 15 stantially depleted in hydrogen sul?de and the mercap tans. If the process is stopped as soon as sulfur com pounds are detected in the e?iuent, the effluent will be almost completely free of contamination. Zeclite X may be used as an adsorbent for the purposes 20 indicated above in any suitable form. For example, a column of powdered crystalline material has given excel lent results as has a pelleted form obtained by pressing into pellets a mixture of zeolite X and a suitable binding agent such as clay. What is claimed is: 25 1. A process ‘for the separation of hydrogen sul?de from a vapor mixture thereof with at least one gas se lected from the group consisting of hydrogen and alkanes containing less than six carbon atoms which comprises 30 intimately contacting said vapor mixture with crystalline, synthetic, at least partially dehydrated zeolite X whereby said hydrogen sul?de is preferentially adsorbed from said mixture, and separating the hydrogen sul?de-depleted 35 vapor mixture from said zeolite X. 2. A process in accordance with claim 1 wherein said zeolite X is sodium zeolite X. y 3. A process according to claim 1 in which said vapor mixture contains hydrogen sul?de and methane. 4. A process according to claim 1 in which said vapor mixture contains hydrogen sul?de and ethane. , tion processes at higher temperatures than are normally 40 5. A process according to claim 1 in which said vapor used with common adsorbents. The adsorption power mixture contains hydrogen sul?de and propane. of physical adsorbents usually decreases with increasing 6. A process according to claim 1 in which said vapor temperature, and therefore while the adsorption capacity mixture contains hydrogen sul?de and butane. of many adsorbents in a certain separation may be suf? 7. A process according to claim 1 in which said vapor cient if operated at one temperature, the capacity may 45 mixture contains hydrogen sul?de and pentane. not be suflicient to make operation feasible at a higher 8. A process according to claim 1 in which said vapor temperature. With strongly adsorbing zeolite X, how~ ever, substantial capacity is retained at higher tempera tures. The present separation is preferably eifected at a temperature below 973“ K., since the crystal structure of zeolite X will be disrupted or damaged with conse quent loss of adsorption capacity and reduction in pore size. For maximum efficiency this adsorption process is performed at temperatures less than 616° K. but higher mixture contains hydrogen sul?de and hydrogen. References Cited in the ?le of this patent UNITED STATES PATENTS 2,270,058 2,882,244 Jones ________________ __ Jan. 13, 1942 Milton ______________ .._ Apr. 14, 1959 OTHER REFERENCES than 283° K. This is for the reason that above such 55 Separation of Mixtures Using Zeolites as Molecular range, the hydrocarbon constituents of the vapor feed Sieves, Parts I, II, III, Barrer, J. Soc. Chem. Ind., vol. stream in contact with zeolite X will tend to isomerize, 64, May 1945, pages 130—135. hydrogenate, aromatize and polymerize, all of which‘ will Molecular-Sieve Action of Solids, Barrer, Quarterly clog the pores and cause loss of capacity of zeolite X molecular sieve. Also, to employ adsorption tempera 60 Review (1949), Chem. Society, London, pages 293-320. Crystalline Zeolites, I, The Properties of a New Syn tures below about 283° K., a refrigerating system would thetic Zeolite, Type A. Breck'et al., J.A.C.S., vol. 78, No. 23, Dec. 8, 1956, pages 596345971. Examine These Ways To Use Selective Adsorption, Example I 65 Linde Co., Petroleum Re?ner, vol. 36, No. 7, July 1957, A mixture of propane containing about 0.1 mole frac pages 136-140. tion of hydrogen sul?de is passed through a bed of dehy be required which increases the complexity and expense of operation.