WO2018067298A1

WO2018067298A1 - Selective removal of hydrogen sulfide from a gas stream using a quarternary ammonium amine functionalized cross-linked macroporous polymer

Info

Publication number: WO2018067298A1
Application number: PCT/US2017/052125
Authority: WO
Inventors: Runyu TAN; Ajay N. BADHWAR; H. Robert Goltz; Yujun Liu; Marvin H. Tegen
Original assignee: Dow Global Technologies Llc
Priority date: 2016-10-06
Filing date: 2017-09-19
Publication date: 2018-04-12

Abstract

A pressure swing adsorption (PSA) process is disclosed for the removal of hydrogen sulfide (H2S) from natural. This PSA process provides for passing a fluid stream, preferably a natural gas feedstream comprising H2S though a regenerable adsorbent media which adsorbs H2S to provide an H2S-lean natural gas product and H2S. The regenerable adsorbent media of the present invention is a quaternary amine functionalized crosslinked macroporous polymeric adsorbent media.

Description

SELECTIVE REMOVAL OF HYDROGEN SULFIDE FROM A GAS STREAM USING A QUATERNARY AMMONIUM AMINE FUNCTIONALIZED CROSSLINKED

MACROPOROUS POLYMER

FIELD OF THE INVENTION

The present invention relates generally to adsorbents useful for the extraction of acid gases from gas well streams. More specifically, the invention relates to a quaternary ammonium functionalized crosslinked macroporous polymer adsorbent and method for the removal of hydrogen sulfide gas from a natural gas stream.

BACKGROUND OF THE INVENTION

Fluid streams derived from natural gas reservoirs, petroleum or coal, often contain a significant amount of acid gases, for example carbon dioxide (CO2), hydrogen sulfide (H2S), sulfur dioxide (SO2), carbon disulfide (CS₂), hydrogen cyanide (HCN), carbonyl sulfide (COS), or mercaptans as impurities. These fluid streams may be gas, hydrocarbon gases from shale pyrolysis, synthesis gas, and the like or liquids such as liquefied petroleum gas (LPG) and natural gas liquids (NGL).

In natural gas processing, it is often desirable to remove sulfur compounds from the feedstream in order to satisfy some requirement, for example natural gas pipeline ¾S concentration limits are typically set at or less than 4 parts per million (ppm).

Various compositions and processes for removal of acid gasses are known and described in the literature. Depending on the flow rate of the gas and the ¾S concentration in the gas stream, different technologies have been applied in ¾S removal for optimized economics. Conventional gas resources typically have very large gas flow rates (e.g., greater than 500 million standard cubic feet per day (MMSCFD)), in which cases liquid alkanolamine units are used. Typically, the aqueous amine solution contacts the gaseous mixture comprising the acidic gases counter currently at low temperature or high pressure in an absorber tower. The overall ¾S treating cost is very low (a few cents per pound of sulfur removal) due to the economy of scale, however, such amine treating units usually require large capital expense and operational expense. Recently, unconventional resources, such as those from shale, have emerged. These gas resources typically have small gas flow (e.g., less than 100 MMSCFD) and contain relatively low concentration of ShS (e.g., less than 2000 ppm) and low concentration of CO2 (e.g. less than 2 percent).

Activated carbon has been used for acid gas removal in the hydrocarbon stream but it is not selective. The selective removal of H2S over CO2 and other components is desirable since it will reduce the overall adsorption unit and also make it easier to deal with the concentrated H2S stream.

One approach to selectively removing ¾S in such applications has been the use of disposable ¾S scavengers (liquid triazine or iron sponge) because of their low capital expense and selectivity towards ¾S. However, the overall sulfur treating cost is relatively high (more than $10 per pound of sulfur removal) because of the excessive scavenger consumption. They also create hazardous waste requiring special disposing procedure. Caustic treating is also known in the industry but due to removal of all acidic components it is reserved for ¾S and mercaptan removal where there is a low level of ¾S or where there are no other options.

Zinc oxide has also been used for removing sulfur compounds from hydrocarbon streams. However, its high cost and substantial regeneration costs make it generally uneconomical to treat hydrocarbon streams containing an appreciable amount of sulfur compound impurities on a volume basis. So too, the use of zinc oxide and other

chemisorption material similar to it disadvantageously generally require the additional energy expenditure of having to heat the sulfur containing fluid stream prior to its being contacted with the stream in order to obtain a desirable sulfur compound loading characteristic.

Selective physical adsorption of sulfur impurities is also known. As used herein, a "physical adsorbent" is an adsorbent which does not chemically react with the impurities that it removes. Both liquid phase and vapor phase processes have been developed. One such approach comprises passing a sulfur-containing hydrocarbon stream through a bed of crystalline zeolitic molecular sieves or a bed of a molecular sieve adsorbent having a pore size large enough to adsorb the sulfur impurities, recovering the non-adsorbed effluent hydrocarbon until a desired degree of loading of the adsorbent with sulfur-containing impurities is obtained, and thereafter purging the adsorbent mass of hydrocarbon and regenerating the adsorbent by desorbing the sulfur-containing compounds therefrom. Conventionally, the adsorbent regenerating operation is a thermal swing or combined thermal and pressure swing-type operation in which the heat input is supplied by a hot gas substantially inert toward the hydrocarbons, the molecular sieve adsorbents and the sulfur-containing adsorbate. When treating a hydrocarbon in the liquid phase, such as propane, butane or liquefied petroleum gas (LPG), natural gas is ideally suited for use in purging and adsorbent regeneration, provided that it can subsequently be utilized in situ as a fuel wherein it constitutes an economic balance against its relatively high cost. Frequently, however, the sweetening operation requires more natural gas for thermal-swing

regeneration than can advantageously be consumed as fuel, and therefore, constitutes an inadequacy of the regeneration gas. The result is a serious impediment to successful design and operation of sweetening processes, especially when desulfurization is carried out at a location remote from the refinery, as is frequently the case.

However, crystalline zeolitic molecular sieves and/or molecular sieves have low adsorption capacity for ¾S and it is generally difficult to get complete sulfur-compound removal when utilizing such a physical adsorbent.

There is a need for regenerable adsorbent (solid-gas contact) for ¾S separation from a natural gas stream which process is more economical and efficient than the prior art techniques discussed above. SUMMARY OF THE INVENTION

The present invention is a process for removing, preferably selectively removing, hydrogen sulfide (¾S) from a fluid feedstream, preferably a natural gas feedstream, comprising ¾S and optional one or more impurity, comprising the steps of:

(a) providing an adsorbent comprising a quaternary amine functionalized crosslinked macroporous polymeric adsorbent media, wherein said adsorbent media adsorbs ¾S;

(b) contacting the fluid feedstream through the quaternary amine functionalized crosslinked macroporous polymeric adsorbent to provide a H2S-lean fluid stream and a hydrogen sulfide-loaded quaternary amine functionalized crosslinked macroporous polymeric adsorbent media, preferably the crosslinked macroporous polymeric adsorbent has a surface area greater than 50 m²/g; (c) further treating, recovering, transporting, liquefying, flaring, or using I hS-lean fluid stream for another process,

(d) regenerating the loaded quaternary amine functionalized crosslinked macroporous polymeric adsorbent media for reuse by desorbing the adsorbed H2S using a pressure swing adsorption (PSA) process,

and

(e) discharging the ¾S to be collected, flared, neutralized by caustic, converted to elemental sulfur, reinjected, disposed of, sent to other unit for processing, or converted to sulfuric acid.

One embodiment of the present invention is the process disclosed herein above wherein the quaternary amine functionalized crosslinked macroporous polymeric adsorbent is a polymer of a monovinyl aromatic monomer crosslinked with a polyvinylidene aromatic compound, preferably the monovinyl aromatic monomer comprises from 92% to 99.25% by weight of said polymer, and said polyvinylidene aromatic compound comprises from 0.75% to 8% by weight of said polymer.

Another embodiment of the present invention is the process disclosed herein above wherein the quaternary amine functionalized crosslinked macroporous polymeric adsorbent is a polymer of a member selected from the group consisting of styrene, vinylbenzene, vinyltoluene, ethylstyrene, and t-butylstyrene; and is crosslinked with a member selected from the group consisting of divinylbenzene, trivinylbenzene, and ethylene glycol dimethacrylate, preferably a polymer of a member selected from the group consisting of styrene, vinylbenzene, vinyltoluene, ethylstyrene, and t-butylstyrene, more preferably styrene; and is crosslinked with a member selected from the group consisting of divinylbenzene, trivinylbenzene, and ethylene glycol dimethacrylate, more preferably divinylbenzene; and preferably the crosslinked macroporous resin has a total porosity of from 0.5 to 1.5 cc/g, a surface area of from 150 to 2100 m²/g as measured by nitrogen adsorption, and an average pore diameter of from 10 Angstroms to 100 Angstroms.

Another embodiment of the present invention is the process disclosed herein above wherein the quaternary amine functionalized crosslinked macroporous polymeric is produced by first chloromethylating a macroporous copolymer, post-crosslinking the copolymer, and then aminating the chloromethylated post-crosslinked copolymer with a tertiary amine represented by the following formula: ^RV^R2

R³

wherein R¹, R², and R³ are independently selected from a Ci to C20 straight or branched chain alkyl group, optionally comprising one or more O and/or N atom present in the chain. Suitable tertiary amines include, but not limited to, trimethylamine, triethylamine, methyldiethylamine, ethyldimethylamine, tripropylamine, tri-n-butylamine, tri-i- butylamine, triphenylamine, dimethylphenylamine, N-methyldiethanolamine, N,N- dimethylethanolamine, triethanolamine, Ν,Ν,Ν',Ν' -tetramethylethylene diamine, tertiary amines represented by the following formula:

R₂N-(CH2CH2N(R))n(CH2CH₂NR2) wherein each R is independently H or -CH3 and n is from 0 to 4, more preferably bis(hexamethylene)triamine, or an alkylated linear or branched polyethyleneimine (PEI) having a molecular weight between 600 to 6,000,000.

In another embodiment of the present invention, the process disclosed herein above is continuous.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a pressure swing adsorption (PSA) process according to the present invention.

FIG. 2 shows the pressure histories during four cycles of a PSA process of the present invention.

FIG. 3 shows temperature histories at three different locations of the adsorbent bed in the first five cycles of a PSA process of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Fluid streams derived from natural gas reservoirs, petroleum or coal, often contain a significant amount of acid gases, for example carbon dioxide (CO2), hydrogen sulfide

(H2S), sulfur dioxide (SO2), carbon disulfide (CS2), hydrogen cyanide (HCN), carbonyl sulfide (COS), or mercaptans as impurities. These fluid streams may be gas, hydrocarbon gases from shale pyrolysis, synthesis gas, and the like or liquids such as liquefied petroleum gas (LPG) and natural gas liquids (NGL).

Raw natural gas comes from three types of wells: oil wells, gas wells, and condensate wells. Natural gas that comes from oil wells is typically termed "associated gas". This gas can exist separate from oil in the formation (free gas), or dissolved in the crude oil (dissolved gas). Natural gas from gas and condensate wells, in which there is little or no crude oil, is termed "non-associated gas". Gas wells typically produce raw natural gas by itself, while condensate wells produce free natural gas along with a semi-liquid hydrocarbon condensate. Whatever the source of the natural gas, once separated from crude oil (if present) it commonly exists as methane in mixtures with other hydrocarbons;

principally ethane, propane, butane, and pentanes and to a lesser extent heavier

hydrocarbons.

Raw natural gas often contain a significant amount of impurities, such as water or acid gases, for example carbon dioxide (CO2), hydrogen sulfide (¾S), sulfur dioxide (SO2), carbon disulfide (CS₂), hydrogen cyanide (HCN), carbonyl sulfide (COS), or mercaptans as impurities. The term "natural gas feedstream" as used in the process of the present invention includes any natural gas source, raw or raw natural gas that has been treated one or more times to remove water and/or other impurities.

Suitable adsorbents are solids having a microscopic structure. The internal surface of such adsorbents is preferably between 100 to 2000 m²/g, more preferably between 500 to 1500 m²/g, and even more preferably 1000 to 1300 m²/g. The nature of the internal surface of the adsorbent in the adsorbent bed is such that C2 and heavier hydrocarbons are adsorbed. Suitable adsorbent media include materials based on silica, silica gel, alumina or silica- alumina, zeolites, activated carbon, polymer supported silver chloride, copper-containing resins. Most preferred adsorbent media is a porous crosslinked polymeric adsorbent or a partially pyrolized macroporous polymer.

In one embodiment, the present invention is the use of an adsorbent media to extract H2S from a fluid stream, preferably a natural gas stream comprising ¾S and optionally one or more impurity. The mechanism by which the macroporous polymeric adsorbent extracts the H2S from the natural gas stream is a combination of adsorption and absorption; the dominating mechanism at least is believed to be adsorption. Accordingly, the terms "adsorption" and "adsorbent" are used throughout this specification, although this is done primarily for convenience. The invention is not considered to be limited to any particular mechanism.

When an adsorbent media has adsorbed any amount of ¾S it is referred to as "loaded". Loaded includes a range of adsorbance from a low level of ¾S up to and including saturation with adsorbed ¾S.

The term "macroporous" is used in the art interchangeably with "macroreticular" and refers in general to pores with diameters of about 500 A or greater. "Mesopores" are characterized as pores of between 50 A and larger but less than 500 A. "Micropores" are characterized as pores of less than 50 A. The engineered distribution of these types of pores gives rise to the desired properties of high adsorption capacity for ¾S and ease of desorption of ¾S under convenient/practical chemical engineering process modifications (increase in temperature or reduced pressure [vacuum]). The process giving rise to the distribution of micropores, mesopores and macropores can be achieved in various ways, including forming the polymer in the presence of an inert diluent or other porogen to cause phase separation and formation of micropores by post cross-linking.

In one embodiment, the adsorbent media of the present invention is a quaternary amine functionalized crosslinked macroporous polymeric adsorbent. Preferably, said quaternary amine functionalized crosslinked macroporous polymeric adsorbent is engineered to have high surface area, high pore volume and high adsorption capacities as well as an engineered distribution of macropores, mesopores and micropores. Preferably, the macroporous polymeric adsorbent of the present invention is hypercrosslinked and/or methylene bridged having the following characteristics: a BET surface area of equal to or greater than 50 m²/g, preferably equal to or greater than 100 m²/g, preferably equal to or greater than 150 m²/g, more preferably equal to or greater than 200 m²/g and preferably equal to or less than 2,100 m²/g, preferably equal to or less than 1,500 m²/g, more preferably equal to or less than 1,000 m²/g and having a particle size of 300 microns to 1500 microns, preferably 500 to 1200 microns.

Examples of monomers that can be polymerized to form macroporous polymeric adsorbents useful are styrene, alkylstyrenes, halostyrenes, haloalkylstyrenes, vinylphenols, vinylbenzyl alcohols, vinylbenzyl halides, and vinylnaphthalenes. Included among the substituted styrenes are ortho-, meta-, and para-substituted compounds. Specific examples are styrene, vinyltoluene, ethylstyrene, t-butylstyrene, and vinyl benzyl chloride, including ortho-, meta-, and para-isomers of any such monomer whose molecular structure permits this type of isomerization. Further examples of monomers are polyfunctional compounds. One preferred class is polyvinylidene compounds, examples of which are divinylbenzene, trivinylbenzene, ethylene glycol dimethacrylate, divinylsulfide and divinylpyridine.

Preferred polyvinylidene compounds are di- and tri vinyl aromatic compounds.

Polyfunctional compounds can also be used as crosslinkers for the monomers of the first group.

Preferred mono vinyl aromatic monomers are styrene and its derivatives, such as alpha-methylstyrene and vinyl toluene: vinyl naphthalene; vinylbenzyl chloride and vinylbenzyl alcohol. Crosslinking monomers broadly encompass the polyvinylidene compounds listed in USP 4,382,124. Preferred crosslinking monomers are divinylbenzene (commercially available divinylbenzene containing less than about 45 weight percent ethylvinylbenzene), trivinylbenzene, and ethylene glycol diacrylate.

A preferred macroporous polymeric adsorbent comprises a copolymer of a monovinyl aromatic monomer and an aromatic polyvinylidene monomer. A most preferred macroporous polymeric adsorbent comprises a copolymer of styrene and divinyl benzene.

One preferred method of preparing the polymeric adsorbent is by swelling the polymer with a swelling agent, then crosslinking the polymer in the swollen state, either as the sole crosslinking reaction or as in addition to crosslinking performed prior to swelling. When a swelling agent is used, any pre-swelling crosslinking reaction will be performed with sufficient crosslinker to cause the polymer to swell when contacted with the swelling agent rather than to dissolve in the agent. The degree of crosslinking, regardless of the stage at which it is performed, will also affect the porosity of the polymer, and can be varied to achieve a particular porosity. Given these variations, the proportion of crosslinker can vary widely, and the invention is not restricted to particular ranges. Accordingly, the crosslinker can range from about 0.25% of the polymer to about 45%. Best results are generally obtained with about 0.75% to about 8% crosslinker relative to the polymer, the remaining (noncrosslinking) monomer constituting from about 92% to about 99.25% (all percentages are by weight).

Other macroporous polymeric adsorbents useful in the practice of this invention are copolymers of one or more monoaromatic monomers with one or more nonaromatic monovinylidene monomers. Examples of the latter are methyl acrylate, methyl methacrylate and methylethyl acrylate. When present, these nonaromatic monomers preferably constitute less than about 30% by weight of the copolymer. The macroporous polymeric adsorbent is prepared by conventional techniques, examples of which are disclosed in various United States patents. Examples are USP 4,297,220; 4,382,124; 4,564,644; 5,079,274; 5,288,307; 4,950,332; and 4,965,083. The disclosures of each of these patents are incorporated herein by reference in their entirety.

For polymers that are swollen and then crosslinked in the swollen state, the crosslinking subsequent to swelling can be achieved in a variety of ways, which are further disclosed in the patents cited above. One method is to first haloalkylate the polymer, and then swell it and crosslink by reacting the haloalkyl moieties with aromatic groups on neighboring chains to form an alkyl bridge. Haloalkylation is achieved by conventional means, an example of which is to first swell the polymer under non-reactive conditions with the haloalkylating agent while including a Friedel-Crafts catalyst dissolved in the haloalkylating agent. Once the polymer is swollen, the temperature is raised to a reactive level and maintained until the desired degree of haloalkylation has occurred. Examples of haloalkylating agents are chloromethyl methyl ether, bromomethyl methyl ether, and a mixture of formaldehyde and hydrochloric acid. After haloalkylation, the polymer is swelled further by contact with an inert swelling agent. Examples are dichloroethane, chlorobenzene, dichlorobenzene, ethylene dichloride, methylene chloride, propylene dichloride, and nitrobenzene. A Friedel-Crafts catalyst can be dissolved in the swelling agent as well, since the catalyst will be used in the subsequent crosslinking reaction. The temperature is then raised to a level ranging from about 60°C to about 85°C in the presence of the catalyst, and the bridging reaction proceeds. Once the bridging reaction is complete, the swelling agent is removed by solvent extraction, washing, drying, or a combination of these procedures.

In one embodiment of the present invention, the crosslinked macroporous copolymer of the present invention is functionalized with a quaternary amine. Preferably, the macroporous copolymer is functionalized by first chloromethylating the copolymer, post-crosslinking the copolymer and then aminating the chloromethylated post-crosslinked copolymer with a tertiary amine, suitable tertiary amines are represented by the following formula:

^RV^R2

R³ wherein R¹, R², and R³ are independently selected from a Ci to C20 straight or branched chain alkyl group, optionally comprising one or more O and/or N atom present in the chain.

Suitable tertiary amines include, but not limited to, trimethylamine, triethylamine, methyldiethylamine, ethyldimethylamine, tripropylamine, tri-n-butylamine, tri-i- butylamine, triphenylamine, dimethylphenylamine, N-methyldiethanolamine, N,N- dimethylethanolamine, triethanolamine, Ν,Ν,Ν',Ν'-tetramethylethylene diamine, tertiary amines represented by the following formula:

Most preferably, the post-crosslinked macroporous copolymer is functionalized by animating the chloromethylated copolymer with trimethyl amine.

The pore size distribution and related properties of the finished adsorbent can vary widely and no particular ranges are critical to the invention. In most applications, best results will be obtained at a porosity (total pore volume) within the range of from about 0.5 to about 1.5 cc/g of the polymer. A preferred range is about 0.7 to about 1.3 cc/g. Within these ranges, the amount contributed by macropores (i.e., pores having diameters of 500 A or greater) will preferably range from about 0.025 to about 0.6 cc/g, and most preferably from about 0.04 to about 0.5 cc/g. The surface area of the crosslinked macroporous polymer, as measured by nitrogen adsorption methods such as the well-known BET method, will in most applications be within the range of about 150 to about 2100 m²/g, and preferably from about 200 to about 1400 m²/g. The average pore diameter will most often range from about 10 A to about 100 A.

The form of the macroporous polymeric adsorbent is likewise not critical and can be any form which is capable of containment and contact with a flowing compressed air stream. Granular particles and beads are preferred, ranging in size from about 50 to about 5,000 microns, with a range of about 500 to about 3,000 microns particularly preferred.

Contact with the adsorbent can be achieved by conventional flow configurations of the gas, such as those typically used in vessels, columns, fluidized beds, or packed beds. The adsorbent can also be enclosed in a cartridge for easy removal and replacement and a more controlled gas flow path such as radial flow.

The macroporous polymeric adsorbent can function effectively under a wide range of operating conditions. The temperature will preferably be within any range which does not cause further condensation of vapors or any change in physical or chemical form of the adsorbent. Preferred operating temperatures are within the range of from 5°C to 75 °C, and most preferably from 10°C to 50°C. In general, operation at ambient temperature or between ambient temperature and 10°C to 15°C above ambient will provide satisfactory results. The pressure of the natural gas stream contacting the adsorbent can vary widely as well, preferably extending from 2 psig (115 kPa) to 1000 psig (7000 kPa). The pressure will generally be dictated by the plant unit where the product gas will be used. A typical pressure range is from 100 psig (795 kPa) to 300 psig (2170 kPa). The minimum residence time of the natural gas stream in contact with the adsorbent will be 0.02 second and a longer residence time is recommended. The space velocity of the natural gas stream through the adsorbent will most often fall within the range of 0.1 foot per second to 5 feet per second, with a range of 0.3 foot per second to 3 feet per second preferred. Finally, the relative humidity can have any value up to 100%, although a lower relative humidity is preferred.

The quaternary amine functionalized crosslinked macroporous polymeric adsorbents of the present invention described herein above can be used to selectively adsorb hydrogen sulfide from natural gas comprising ¾S and one or more other impurities.

The separation process of the present invention comprises contacting a gas stream, preferably a natural gas stream, comprising ¾S with the adsorbent(s) of the invention, wherein the adsorbent may be present in a vessel, column, bed, or other suitable means. Preferably, the ¾S which is selectively adsorbed, can be readily desorbed either by lowering the pressure of the adsorber vessel, column, or bed resulting in a regenerated adsorbent.

The adsorption step and/or the regeneration step of process of the present invention may operate in as a batch process, a semi-continuous process, a continuous process, or combination thereof. For instance in one embodiment of the present invention, both the adsorption step and the regeneration step may operate in the batch mode. In another embodiment of the present invention both the adsorption step and the regeneration step may operate in the semi-continuous mode. In yet another embodiment of the present invention both the adsorption step and the regeneration step may operate in the continuous mode. Alternatively, in one embodiment of the present invention the adsorption step may operate in a batch, semi-continuous, or continuous mode while the regeneration step operates in a different mode than that of the adsorption step. For example, in one embodiment of the present invention the adsorption step may operate in a batch mode while the regeneration step operates in a continuous mode. In another embodiment of the present invention the adsorption step may operate in a continuous mode while the regeneration step operates in a continuous mode. All possible combinations of batch, semi-continuous, and continuous modes for the adsorption step and regeneration step are considered within the scope of the present invention.

Adsorption is in many situations a reversible process. The practice of the present invention, removing volatiles from the adsorption media is accomplished by reducing the pressure over the media. The desired outcome is to re- volatilize the trapped ¾S, and subsequently remove them from the adsorbent so that it can be reused to capture additional ¾S. Preferably, the adsorption media of the present invention when regenerated, desorbs adsorbed ¾S in an amount equal to or greater than 0.1 percent of the amount adsorbed, more preferably equal to or greater than 1 percent, more preferably equal to or greater than 5 percent, more preferably equal to or greater than 10 percent, and more preferably equal to or greater than 15 percent. Preferably, the adsorption media of the present invention when regenerated, desorbs adsorbed ¾S in an amount equal to or less than 90 percent of the amount adsorbed, more preferably equal to or less than 75 percent, more preferably equal to or less than 60 percent, and more preferably equal to or less than 50 percent.

Traditional means of regenerating adsorbent media for the purpose of removing adsorbed volatiles that utilize conventional heating systems such as heated gas (air or inert gas), or radiant heat contact exchangers are suitable for use in the present ¾S separation process as part of the adsorbent media regeneration step, for example, a temperature swing adsorption (TSA) process, or a combination of TSA with PSA.

One embodiment of the process of the present invention is only a PSA process, in other words there is no heat used to regenerate adsorbent either alone (TSA) or in combination with pressure (TSA combined with PSA).

In one embodiment, the H2S adsorption/desorption separation process of the present invention is performed within a pressure swing adsorption (PSA) unit comprising one or more vessel containing an adsorbent material comprising one or more quaternary amine functionalized crosslinked macroporous polymeric adsorbent media and is followed by an adsorbent regeneration sequence comprising the steps of depressurizing/venting the adsorption vessel down to low pressure followed by purging the adsorbent-containing vessel with a portion of the purified gas stream the repressurizing the adsorbent-containing vessel with the feed mixture back to the pressure level at which the gas stream was initially contacted with the adsorbent.

Also preferably, the depressurization is partly performed via one or more pressure equalization steps with other PSA vessels undergoing said repressurizing, FIG. 1.

In one type of PSA, the depressurizing is performed down to vacuum pressure levels by connecting the adsorption vessel to a vacuum pump (i.e. vacuum swing adsorption or VSA). The skilled practitioner will appreciate that this will improve the adsorbent's rejection of the adsorbed impurities during the depressurization step, albeit at the expense of power.

Also preferably, the adsorbent is purged or rinsed with a portion of the purified gas stream subsequent to said depressurization step and prior to said repressurization step. The skilled practitioner will appreciate that this will further improve the adsorbent's rejection of the adsorbed impurities, albeit at the expense of methane recovery. Note however that in a typical PSA process, the purge step is performed at 1 atm pressure. By lowering the purge pressure to 0.1 atm, one can obtain the same degree of purging with about 10% of the gas required at 1 atm.

Batch, semi-continuous, and continuous processes and apparatuses for separating

¾S from natural gas feedstreams are well known. FIG. 1 shows one embodiment of a separation process of the present invention. FIG. 1 depicts a continuous PSA process 1. The first step, the adsorption step, in the continuous process is to feed a gaseous mixture comprising ¾S, or feed gas, which is compressed to a pressure, preferably between 4-10 bar, through line 2 into line 3 with valves 11, 13, 14, 24, and 22 open and valves 12, 23, and 21 closed. The pressurized gaseous mixture comprising ¾S flows through line 3 passes through open valve 11 into the first vessel 10 at a first pressure Pi where it contacts the absorbent, a quaternary amine functionalized crosslinked macroporous polymeric adsorbent media, which will selectively retain ¾S. The ¾S lean gaseous mixture, or product gas, flows from the top of the vessel 10 into line 4 through valve 13 and exits through line 30 with a pressure drop.

A portion of the ¾S lean gaseous mixture leaving the top of vessel 10 is used as purge gas to regenerate the adsorbent in a second vessel 20. The purge gas flows through line 6 and open valves 14 and 24 into the top of vessel 20 which is at a second pressure P2', where P2' is less than Pi. The adsorption of ¾S is reversible from the quaternary amine functionalized crosslinked macroporous polymeric adsorbent media and ¾S desorbs from the adsorbent in vessel 20 into the purge gas, forming an H2S loaded purge gas which passes out the bottom of vessel 20 through line 5, open valve 22, and out through line 40 as loaded purge gas, resulting in vessel 20 containing a regenerated quaternary amine functionalized crosslinked macroporous polymeric adsorbent media.

After the adsorption step in vessel 10 is completed, the adsorbent in vessel 10 needs to be regenerated. In the second step of the continuous PSA process, vessel 10 will be depressurized and vessel 20 will be repressurized. During this step, valves 11, 13, 14, 22, 23, and 24 are closed and valves 12 and 21 are open. The pressure Pi in the first vessel 10 is lowered to Pi' (optionally to vacuum) by gas withdrawal through valve 12 to line 40. The compressed feed gas is fed through line 2 into line 3 and valve 21 to repressurize vessel 20 from the low pressure P2' to the high adsorption pressure P2 (i.e., P2 > P2').

In the third step of the continuous PSA process, valves 11, 13, and 22 remain closed and valves 12 and 21 remain open but valves 14, 23, and 24 are opened. The compressed feed gas is fed through line 2 into line 3 with valves 21, 23, 24, 14, and 12 open and valves 11, 13, and 22 closed. The pressurized gaseous mixture comprising H2S flows through line 3 passes through open valve 21 into the second vessel 20 at the pressure P2where it contacts the regenerated quaternary amine functionalized crosslinked macroporous polymeric adsorbent media. The product gas, or H2S lean gaseous mixture, flows from the top of the vessel 20 into line 4 through valve 23 and exits through line 30 with a pressure drop.

A portion of the H2S lean gaseous mixture leaving the top of vessel 20 is used as purge gas to regenerate the adsorbent in the first vessel 10. The purge gas flows through line 6 and open valves 14 and 24 into the top of vessel 10 which is at a second pressure Pi', where Pi' is less than P2. The H2S desorbs from the adsorbent in vessel 10 into the purge gas, forming a loaded purge gas which passes out the bottom of vessel 10 through line 5, open valve 12, and out through line 40 as loaded purge gas, resulting in vessel 10 containing a regenerated quaternary amine functionalized crosslinked macroporous polymeric adsorbent media.

After the adsorption step in vessel 20 is completed, the adsorbent in vessel 20 needs to be regenerated. In the fourth step of the continuous PSA cycle, vessel 20 is depressurized and vessel 10 is repressurized. During this step, valves 21, 23, 24, 12, 13, and 14 are closed and valves 11 and 22 are open. The pressure P2 in vessel 20 is lowered to P2' (optionally to vacuum) by gas withdrawal through valve 22 to line 40. The compressed feed gas is fed through line 2 into line 3 and valve 11 to repressurize vessel 10 from the low pressure Pi' to the high adsorption pressure Pi (i.e., Pi > Pi'). When vessel 10 pressure reaches Pi, the PSA process will go to next cycle beginning with the first step.

Although a particular preferred embodiment of the invention is disclosed in FIG. 1 for illustrative purposes, it will be recognized that variations or modifications of the disclosed process lie within the scope of the present invention. For example, in another embodiment of the present invention, there may be multiple adsorbent vessels, columns, or beds and/or the adsorbent vessel(s), column(s), or bed(s) may be regenerated in-place as exemplified by USP 3,458,973, which is incorporated herein by reference in its entirety.

The process of the present invention may be found useful in the treatment of gaseous mixtures, such as raw natural gas as well as refining and treating the outlet gas from an amine unit.

EXAMPLES

Syntheses of Adsorbent Materials.

Adsorbent materials, Examples 1 to 6 and Comparative Examples A and B, are made from a macroporous copolymer of styrene monomer crosslinked with divinylbenzene which is chloromethylated and post-crosslinked in the swollen state in the presence of a Friedel-Crafts catalyst at 50°C (Example 1), 60°C (Example 2), 70°C (Example 3) and 80°C (Examples 4 to 9) with post-capping of residual chloromethyl groups with trimethylamine to give a quaternary amine site (Examples 1 to 9), dimethylamine (Comparative Example A), or diethylene triamine (Comparative Example B). The differences between the adsorbent materials lie in the cross-linking reaction time. The cross-linking times, surface area and the total ion exchange capacity for each of the adsorbents are listed in Table 1.

The following is a typical reaction scheme: Chloromethylated Beads (CMB) are swollen in EDC (1,2-dichloroethane) for two hours without stirring. The excess EDC is withdrawn using a suction wand and fresh EDC is added and the beads are soaked for 30 minutes before the excess EDC is withdrawn. The addition of EDC and swelling is repeated and the excess EDC withdrawn. The EDC swollen CMB are slurried in about 1000 ml of fresh EDC and transferred to a 2L three-necked round bottom flask that had been outfitted with a heating mantle, overhead stirrer and a distillation head and with receiver. The CMB/EDC slurry is heated to reflux and reflux is continued as the EDC/methanol/water azeotrope is removed and the temperature of the pot slowly rose to 80°C. An additional distillate is removed at 80°C and the heating is stopped and the flask and contents allowed to cool. Additional EDC is added, if needed, to maintain an easily mixable slurry.

Once the flask contents had cooled back down, anhydrous FeCb is added and the mixture allowed to stir at room temperature. The flask is heated to 80°C over 30 minutes and samples were removed at 50, 60 and 70°C. The flask is then held at 80°C and samples were taken at various reaction time at 80°C.

Each of the samples of bridged resin are mixed with methanol to hydrolyze the FeCb and then washed with DI water, which is then placed into a heavy walled animation bottle with water and 25% trimethyl amine (TMA) is added. The bottle is shaken to mix the contents and then left in the hood over several days at room temperature. The bottles are opened and the animation liquors removed. The samples are then washed with water and 5% HC1 and then washed with water until the effluent water is pH neutral.

Table 1

Example

Cross-linking Surface Area Total Ion Exchange Time (min) (m²/g) Capacity (meq/ml) Comparative Example

1 30 223 0.75

2 30 384 0.7

3 30 473 0.6

4 30 599 0.53

5 60 710 0.38

6 90 973 0.34

7 120 901 0.33

8 150 884 0.32

9 210 1219 0.19

A 180 989 0.2

B 180 744 0.38 ¾S Breakthrougli Desorption.

The adsorbent materials are dried in the oven at 70°C overnight and are fully loaded in a 3/8 inch by 8 inch stainless steel column and exposed to 1000 ppm ¾S in nitrogen gas stream at 75 psig with a flow rate of 500 seem. The hydrogen sulfide (¾S) breakthrough is monitored using ultraviolet spectroscopy. The adsorption is continued until full breakthrough and the materials are regenerated by nitrogen purging through. Multiple cycles are repeated and the materials tested could all be fully regenerated determined by essentially identical breakthrough time. Key properties as well as ¾S breakthrough time are listed in Table 2.

Table 2

In Table 2, the following adsorbents that are not examples of the invention are compared as Comparative Examples C to F:

Comparative Example C is a macroporous copolymer of styrene and divinylbenzene functionalized with dimethylamine with low surface area;

Comparative Example D is a macroporous copolymer of styrene and divinylbenzene functionalized with dimethylamine and trimethylamine with low surface area;

Comparative Example E is a macroporous copolymer of styrene and divinylbenzene functionalized with trimethylamine with low surface area;

and

Comparative Example F is a microporous crosslinked styrene and divinylbenzene functionalized with dimethylamine.

Pressure Swing Adsorption.

A single-column PSA system is used with the conventional Skarstrom type, 4-step cycle using Example 8. The four steps in a cycle include (I) co-current feed pressurization; (II) high-pressure adsorption with feed gas; (III) countercurrent blowdown; and (IV) countercurrent low-pressure desorption with light product purge. The apparatus is fully automated with Siemens software. The H2S concentration in the purified gas (PSA light product stream) is monitored real-time by an OMA-206-R Process Analyzer and is checked intermittently with a gas chromatography equipped with a Sulfur Chemiluminescence Detector.

PSA experiments are run under different operating conditions. Table 3 shows one set of PSA operating conditions along with the adsorbent bed properties. This experiment is run for 55 hours (413 cycles) and reached the cyclic steady state long before its shutdown. A purge-to-feed ratio of 6 is needed to produce a purified gas stream containing less than 4 ppmv H2S. No H2S is detected in the light product at cyclic steady state. FIG. 2 shows a representative pressure histories in randomly selected 4 cycles. FIG. 3 shows the temperature histories at three different locations of the adsorbent bed in the first several cycles. Table 3

Claims

What is claimed is:

1. A process for removing hydrogen sulfide (¾S) from a fluid feedstream comprising ¾S comprising the steps of:

(a) providing an adsorbent comprising a quaternary amine functionalized

5 crosslinked macroporous polymeric adsorbent media, wherein said adsorbent media adsorbs ¾S;

(b) contacting the fluid feedstream with the quaternary amine functionalized crosslinked macroporous polymeric adsorbent to provide a I hS-lean fluid stream and a hydrogen sulfide-loaded quaternary amine functionalized crosslinked o macroporous polymeric adsorbent media;

(c) further treating, recovering, transporting, liquefying, flaring, or using the I hS-lean fluid stream for another process,

(d) regenerating the loaded quaternary amine functionalized crosslinked macroporous polymeric adsorbent media for reuse by desorbing the adsorbed ¾S5 using a pressure swing adsorption (PSA) process,

and

(e) discharging the ¾S to be collected, flared, neutralized by caustic, converted to elemental sulfur, reinjected, disposed of, sent to other unit for processing, or converted to sulfuric acid,

0 wherein the crosslinked macroporous polymeric adsorbent has a surface area of greater than 50 m²/g.

2. The process of Claim 1 wherein the fluid feedstream is a natural gas feedstream.

3. The process of Claim 1 wherein the fluid stream comprises, in addition to ¾S, one or more impurity wherein the ¾S is selectively removed from the gas stream in the5 presence of one or more impurity.

4. The process of Claim 1 wherein the quaternary amine functionalized crosslinked macroporous polymeric adsorbent is a polymer of a monovinyl aromatic monomer crosslinked with a polyvinylidene aromatic compound.

5. The process in of Claim 3 wherein the monovinyl aromatic monomer comprises0 from 92% to 99.25% by weight of said polymer, and said polyvinylidene aromatic

compound comprises from 0.75% to 8% by weight of said polymer.

6. The process of Claim 1 wherein the quaternary amine functionalized crosslinked macroporous polymeric adsorbent is a polymer of a member selected from the group consisting of styrene, vinylbenzene, vinyltoluene, ethylstyrene, and t-butylstyrene; and is crosslinked with a member selected from the group consisting of divinylbenzene, trivinylbenzene, and ethylene glycol dimethacrylate.

7. The process of Claim 5 wherein the quaternary amine functionalized crosslinked macroporous polymeric adsorbent has a total porosity of from 0.5 to 1.5 cc/g, a surface area of from 150 m²/g to 2100 m²/g as measured by nitrogen adsorption, and an average pore diameter of from 10 Angstroms to 100 Angstroms.

8. The process of Claim 1 wherein the quaternary amine functionalized crosslinked macroporous polymeric adsorbent is a polymer of styrene and is crosslinked with divinylbenzene.

9. The process of Claim 1 wherein the process is continuous.

10. The process of Claim 1 wherein the quaternary amine functionalized macroporous copolymer is produced by first chloromethylating a macroporous copolymer, post- crosslinking the copolymer, and then aminating the chloromethylated post-crosslinked copolymer with a tertiary amine selected from trimethylamine, triethylamine,

methyldiethylamine, ethyldimethylamine, tripropylamine, tri-n-butylamine, tri-i- butylamine, triphenylamine, dimethylphenylamine, N-methyldiethanolamine, N,N- dimethylethanolamine, triethanolamine, Ν,Ν,Ν' ,Ν' -tetramethylethylene

diamine,bis(hexamethylene)triamine, or a per alkylated polyethyleneimine.