US005413627A United States Patent 19 11 Patent Number: 5,413,627 Landeck et al. (45) Date of Patent: May 9, 1995 54 PROCESS FOR THE SELECTIVE REMOVAL OF NORGANIC AND/OR ORGANIC FOREIGN PATENT DOCUMENTS SULFUR COMPOUNDS 8449 3/1950 European Pat. Off. ......... 423/242.6 471592 2/1992 European Pat. Off. ........ 423/242.6 75 Inventors: Heiner Landeck, Munich; Gerhard 1471541 1/1967 France................................ 423/226 Ranke, Pocking, both of Germany 2545378 11/1984 France. 4027239 3/1992 Germany .............................. 95/235 73 Assignee: Linde Aktiengesellschaft, Wiesbaden, 4027297 3/1992 Germany .............................. 95/235 Germany 1132922 11/1968 United Kingdom ................ 423/226 21 Appl. No.: 34,798 Primary Examiner-Gary P. Straub Assistant Examiner-Timothy C. Vanoy 22 Filed: Mar. 1, 1993 Attorney, Agent, or Firm-Millen, White, Zelano & 30 Foreign Application Priority Data Branigan Aug. 29, 1990 (DEI Germany ................... 40 27 239.7 57 ABSTRACT For the selective removal of sulfur from gases, a physi 51 int. Cl'.............................................. C01B 17/00 cal scrubbing agent is used, comprising a heterocycle 52 U.S.C. ...................................... 95/235; 423/210; having five or more ring atoms, which contains two 423/220; 423/226; 423/242.1; 423/242.6; heteroatoms, one of which is nitrogen and the other of 423/245.2 which is oxygen or nitrogen; and the heteroatoms in the 58 Field of Search ............... 423/210, 220, 226, 227, rings of even member number of atoms occupy; one of 423/242.1, 242.6, 245.2; 95/235 the positions from 1,2 to 1,n/2 and, in the rings of un even member number of atoms occupy one of the posi 56) References Cited tions from 1,2 up to 1, (n-1)/2. Further, the nitrogen U.S. PATENT DOCUMENTS heteroatom(s) present in the ring is/are either double 4,094,957 6/1978 Sartori et al. ....................... 423/223 bonded or single bonded but, if single bonded, the nitro 4,217,238 8/1980 Sartori et al. ....................... 252/192 gen is organo-Substituted. 4,624,838 11/1986 Pan et al. ............................ 423/226 5,098,681 3/1992 Christiansen et al. .............. 423/243 34 Claims, 2 Drawing Sheets 3 U.S. Patent May 9, 1995 Sheet 1 of 2 5,413,627 U.S. Patent May 9, 1995 Sheet 2 of 2 5,413,627 f) S. 5,413,627 2 called hybrid scrubbing agents. This type of scrubbing PROCESS FOR THE SELECTIVE REMOVAL OF agent uses the advantages of the chemical as well as NORGANIC AND/OR ORGANIC SULFUR those of the physical scrubbing agents. Thus, by the COMPOUNDS presence of purely physical scrubbing agent compo nents, organic sulfur compounds can also be scrubbed CROSS-REFERENCE TO RELATED out, which with a purely chemical scrubbing agent is APPLICATION possible only in a limited way. This application is a continuation-in-part of Interna To increase the selectivity between CO2 and H2S in tional Application PCT/EP91/01622, filed Aug. 26, these processes, i.a., advantage is taken of the fact that 1991, now WO4204102-A published on 19 Mar. 1992 O in aqueous solutions, the electrolytic and chemical reac designating the United States, based on German Prior tions of CO2 are partly kinetically hindered and occur at ity Application P 40 27 239.7, filed Aug. 29, 1990. a substantially slower rate than those of H2S. But since H2S must be scrubbed out to a residual content of a few BACKGROUND OF THE INVENTION ppm, normally 20 to 30% of the CO2 contained in the The invention relates to a process for the selective 15 crude gas is also scrubbed out. removal of inorganic and/or organic sulfur compounds, With the known physical scrubbing agents, a substan such as H2S, COS, CS2, thiols, and the like, from gases tial disadvantage exists insofar as besides H2S and less which contain, in addition, at least one of the compo volatile sulfur components (for example, thiols, CS2, nents H2, N2, Ar, CO2, CO, and aliphatic hydrocarbons etc.) there are also scrubbed out a considerable part of by scrubbing with a physical scrubbing agent, i.e., a 20 the CO2 as well as higher hydrocarbons. In most cases, scrubbing agent which does not depend on a chemical reaction with the absorbed compound. it is also necessary to conduct an at least partial separa For the selective removal of sulfur compounds from tion of these additional components from the sulfur gases which, besides H2S, can contain other inorganic components to obtain a sulfur-rich fraction amenable-to and organic sulfur compounds, such as, for example, 25 the requisite conversion reactions to elementary sulfur COS, CS2, thiols, etc., physical, as well as chemical, in a relatively problem-free manner. In many cases this scrubbing agents have been used for many years. not only results in complicating the scrubbing process A detailed discussion of various scrubbing processes but also increases the consumption and the investment can be found, for example, in A. L. Kohl, F. C. Riesen costs. Corresponding to the vapor pressure of the scrub feld: “Gas Purification,’ 4th ed, Gulf Publishing Co., 30 bing agent, both the scrubbed product gas and the sulfur Houston, Tex. (1985); S. A. Newman (Editor): "Acid component fraction contain undesirable scrubbing and Sour Gas Treating Processes,” Gulf Publishing Co., agent components, which, on the one hand, increase the Houston, Texas (1985); as well as in R. N. Maddox: investment and operation costs of the system and, on the "Gas Conditioning and Processing,” Vol. IV, Campbell other hand, represent possibly troublesome impurities in Petroleum Series, Norman, Okla. (1982). 35 the product gas. With physical scrubbing agents, because of the differ The most important disadvantages in chemical Scrub ent specific physical intermolecular interactions be bing processes are that the selectivity between H2S and tween individual functional groups of the scrubbing CO2 is small and the energy consumption in the regen agent or of the scrubbing agent molecule in its struc eration of the loaded scrubbing agent is relatively high. tural composition as a whole, individual gas compo Further, in chemical scrubbing processes, loading of the nents are preferably absorbed from gas mixtures. The scrubbing agent is dependent on the chemical equilib specific solubility characteristics are also affected by rium. Since the chemical equilibriums are only slightly different arrangements of the same functional groups in dependent on pressure, chemical scrubbing processes the scrubbing agent molecule, since the different loca are preferably used at low pressures. tions of the functional groups cause different electron 45 Conversely, with sulfur-containing synthesis gases at configurations. In these processes, the most important high pressures and with a higher CO2 content, in which process steps, i.e., absorption of the components to be CO2 can or is to remain in the scrubbed gas and the scrubbed out and regeneration of the scrubbing agent, sulfur components are to be lowered to a few ppm, the are determined by the specific physical solubility char use of physical scrubbing agents is significantly more acteristics of the individual gas components. As physi 50 advantageous in comparison with chemical scrubbing cal scrubbing agents in known processes, there can be agents. mentioned, for example, methanol, N-methylpyrroli done (NMP) and polyethylene glycol dialkyl ether SUMMARY OF THE INVENTION (PGE), among others. An object of this invention is to make available a Acid gas removal by chemical scrubbing agents is 55 scrubbing agent for selective sulfur removal, which, on based on a completely different principle which takes the one hand, exhibits a relatively high selectivity be advantage of the fact that specific chemical or electro tween H2S and CO2 and, on the other hand, offers the lytic reactions take place between individual solvent possibility of also removing COS and organic sulfur components and the acid gas components to be scrub compounds, and which, further, has a low vapor pres bed out'-'. In chemical scrubbing processes for the sure, so that the scrubbing can be performed at close to selective removal of sulfur, there have been used prefer ambient temperature. ably tertiary amines, e.g., methyldiethanolamine Another object is to provide a process for selective (MDEA), in aqueous solutions, with the water content sulfur removal. being usually more than 40% by weight. With these processes, besides the physical, chemical and electrolytic Upon further study of the specification and appended balances, the kinetics and the transport processes are thus the dominant 65 claims, further objects and advantages of this invention valves. will become apparent to those skilled in the art. It is also known to remove sulfur components by both To achieve these objects, a heterocyclic compound is physically and chemically active scrubbing agents, so used as a scrubbing agent having a number n of at least 5,413,627 3 4. 5 atoms in the heterocyclic ring, of which 2 atoms are heteroatoms, i.e., a ring of at least 3 carbon atoms, with O (4) the heteroatoms being either nitrogen or oxygen, of which at least one heteroatom is nitrogen. The nitrogen / \ N atom or atoms are either single bonded or double 5 bonded, but if single bonded, the remaining hydrogen is substituted. The two heteroatoms in rings of an even number of atoms occupy the 1,2-positions, up to the 3H-1,2-Diazopine (5) 1,n/2 positions. In rings of an uneven number of atoms 10 the two heteroatoms occupy the positions 1,2 up to the N S. N (5) 1,On-1)/2 positions. For the sake of simplicity, the basic structures ac cording to the invention are designated below as hetero cycles in which, besides nitrogen, oxygen can also 15 occur as one heteroatom.