WO2018009497A1

WO2018009497A1 - Method of reducing hydrogen sulfide levels in liquid or gaseous mixtures

Info

Publication number: WO2018009497A1
Application number: PCT/US2017/040646
Authority: WO
Inventors: Runyu TAN; H. Robert Goltz
Original assignee: Dow Global Technologies Llc
Priority date: 2016-07-06
Filing date: 2017-07-05
Publication date: 2018-01-11

Abstract

The present invention relates to a method for reducing or eliminating hydrogen sulfide and other objectionable sulfides from a liquid or gaseous stream comprising hydrogen sulfide, preferably a hydrocarbon stream. More particularly, the method of the present invention comprises the steps of first contacting the hydrogen sulfide comprising stream with a triazine compound providing a reduced hydrogen sulfide comprising stream, followed by the step of passing the resultant reduced hydrogen sulfide comprising stream through an absorption media to provide a further reduced hydrogen sulfide comprising stream.

Description

METHOD OF REDUCING HYDROGEN SULFIDE LEVELS IN LIQUID OR GASEOUS

MIXTURES

FIELD OF THE INVENTION

The present invention relates to a method for reducing hydrogen sulfide and other objectionable sulfides from a liquid or gaseous stream comprising hydrogen sulfide, in particularly a hydrocarbon stream. More particularly, the method of the present invention comprises the steps of first contacting the hydrogen sulfide comprising stream with a triazine compound providing a reduced hydrogen sulfide comprising stream, followed by the step of passing the resultant reduced hydrogen sulfide comprising stream through an absorption media to provide a further reduced hydrogen sulfide comprising stream. BACKGROUND OF THE INVENTION

In the drilling, production, transport, storage, and processing of crude oil, including waste water associated with crude oil production, and in the storage of residual fuel oil, hydrogen sulfide and mercaptans are often encountered. The presence of hydrogen sulfide and mercaptans is objectionable because they often react with other hydrocarbons or fuel system components. Further, hydrogen sulfide and mercaptans are often highly corrosive as well as emit highly noxious odors. Uncontrolled emissions of hydrogen sulfide gives rise to severe health hazards. Burning of such vapors neither solves toxic gas problems nor is economical since light hydrocarbons have significant value.

Furthermore, hydrogen sulfide and mercaptans, as well as other sulfhydryl compounds, are often present in the underground water removed with the crude oil, in the crude oil itself and in the gases associated with such water and oil. When the water and oil are separated from each other, they emit foul odors. For instance, hydrogen sulfide is emitted as a gas which is associated with water and hydrocarbon vapors. Natural gases further often contain sulfhydryl compounds.

Treatments for removal of sulfhydryl compounds, such as hydrogen sulfide and mercaptans, from hydrocarbons and other substrates include the use of various reactive organic compounds. For example, USP 6,063,346 discloses the use of a combination of maleimides, formaldehydes, amines, carboxamides, alkylcarboxyl-azo compounds and cumine-peroxide compounds for the removal of hydrogen sulfide and mercaptan contaminants from a fluid. Further, USP 5,128,049 discloses the use of certain morpholino and amino derivatives for the removal of hydrogen sulfide content from fluids. In addition, USP 6,063,346; 5,128,049; and 8,734,637 disclose the use of triazines to remove hydrogen sulfide.

Alternatively, treatments for the removal of sulfhydryl compounds include contacting the feedstock stream with a bed of particles of a suitable adsorbent, for example zinc oxide, USP 4,861,566, iron chelates, USP 4,876,075, and ion exchange resins, USP 4,988,807 and US Patent Publication No. 2016/0145517 and 2016/0122671.

There is a continuing need for alternatives which may be useful in the removal and/or reduction of hydrogen sulfide and other sulfhydryl compounds from liquid and gaseous hydrocarbon streams. Such alternatives include the development of new method which exhibit high efficiency for removing sulfhydryl compounds. SUMMARY OF THE INVENTION

The present invention is a method of reducing H2S in a liquid or gaseous stream comprising H2S which comprises the steps of: (A) contacting the stream comprising H2S with an aqueous sulfide-scavenging composition comprising a triazine compound to provide a reduced H2S stream, preferably have an H2S level equal to or less than 1% and (B) passing the reduced H2S stream through an adsorbent bed comprising one or more absorption media to provide a loaded adsorbent and a further reduced H2S stream, preferably have an H2S level equal to or less than 150 ppm.

One embodiment of the method disclosed herein above further comprises the step (C) regenerating the loaded adsorbent.

In one embodiment of the method disclosed herein above, the triazine compound is represented by the formula:

R¹

wherein R¹, R², and R³ are independently selected from a Ci to C20 straight or branched chain alkyl group,

wherein R⁴, R⁵, and R⁶ are independently selected from a Ci to C₆ alkyl group and wherein R⁷, R⁸, and R⁹ are independently selected from hydrogen or a Ci to C₆ alkyl group, or a mixture thereof, preferably the triazine compound is 1, 3, 5-trimethyl-hexahydro-l, 3, 5- triazine, 1, 3, 5-tris(2-hydroxyethyl)hexahydro-s-triazine, or mixtures thereof.

In one embodiment of the method disclosed herein above, the absorption media is silica gel, alumina, silica-alumina, zeolites, activated carbon, molecular sieves, polymer supported silver chloride, copper-containing resin, a metal oxide, a metal chelate, an ion exchange resin, a macroporous cross-linked polymer, a pyrolized macroporous polymer, mixtures thereof.

In one embodiment of the method disclosed herein above, the absorption media is a weak-base anion exchange resin, a strong-base anion exchange resin, or a gel-type anion exchange resin.

In one embodiment of the method disclosed herein above, the absorption media is an anion exchange resin derived from an epoxy resin polymer, an acrylic based copolymer, or a copolymer composition of styrene-divinylbenzene.

In one embodiment of the method disclosed herein above, the absorption media is a cross-linked macroporous polymer, a pyrolized macroporous polymer, or mixtures thereof.

In one embodiment of the method disclosed herein above, the adsorption media is a caustic solution, sodium carbonate solution, or mixtures thereof

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing of the apparatus used in the examples.

FIG. 2 is a plot showing the H2S reduction in a gas for an example of the method of the present invention and of example of a method not of the present invention. DETAILED DESCRIPTION OF THE INVENTION

In the method of the present invention, in a first step, a liquid or hydrocarbon stream comprising H2S is brought into contact with a hydrogen sulfide scavenger. As used herein, the term "hydrogen sulfide scavenger" shall include those scavengers useful in the treatment of liquid and hydrocarbon substrates that are rendered "sour" by the presence of sulfhydryl compounds. The term shall include, in addition to hydrogen sulfide and mercaptans, thiols, thiol carboxylic acids and dithio acids as well as other sulfhydryl compounds. The liquid stream may be a liquid hydrocarbon stream or an aqueous substrate. As used herein, the term "aqueous substrate" refers to any sour aqueous substrate, including waste water streams in transit to or from municipal waste water treatment facilities, tanning facilities, and the like.

The term "hydrocarbon substrate" may include both liquid and gaseous streams and is meant to include unrefined and refined hydrocarbon products, including natural gas, derived from petroleum or from the liquefaction of coal, both of which contain hydrogen sulfide or other sulfur-containing compounds. Thus, particularly for petroleum-based fuels, the term hydrocarbon substrate includes, but is not limited to, wellhead condensate as well as crude oil which may be contained in storage facilities at the producing field.

Hydrocarbon substrate also includes the same materials transported from those facilities by barges, pipelines, tankers, or trucks to refinery storage tanks, or, alternately, transported directly from the producing facilities through pipelines to the refinery storage tanks. The term hydrocarbon substrate also includes refined products, interim and final, produced in a refinery, including distillates such as gasolines, distillate fuels, oils, and residual fuels and to vapors produced by the foregoing materials.

The invention defined herein is therefore applicable to a wide variety of fluid streams, including liquefied petroleum gas as well as crude oil and petroleum residual fuel, heating oil, etc. In addition, the invention is applicable to gaseous hydrocarbon streams. For instance, the scavenger may be contacted with wet or dry gaseous mixtures of hydrogen sulfide and/or mercaptan and hydrocarbon vapors, such as is found, for instance, in natural gas or obtained in the drilling, removal from the ground, storage, transport, and processing of crude oil.

The hydrogen sulfide scavenger useful in the first step of the present invention is preferably an aqueous solution comprising one or more triazine compound. Triazine compounds and methods to make them are well known, for example see USP 5,744,024, which is incorporated by reference herein in its entirety. Suitable triazine compounds include alkyl hexahydro triazines, alkoxy-hexahydro triazines, and hydroxyalkyl-hexahydro triazines.

Suitable alkyl hexahydro-triazines have the following formula:

where R¹, R², and R³ are the same or different and are independently selected from a Ci to C20 straight or branched chain alkyl group, preferably a Ci to C₆ straight or branched chain alkyl group, and more preferably a Ci to C₄ straight or branched chain alkyl group. The preferred alkyl hexahydro-triazine is l,3,5-trimethyl-hexahydro-l,3,5-triazine where R¹, R², and R³ are all a Ci alkyl group.

Suitable alkyl hexahydro-triazines have the following formula:

where R⁴, R⁵, and R⁶ may be the same or different and are independently selected from a Ci to C₆ alkyl group, preferably Ci to C₄. The preferred triazine of this group is l,3,5-tri-(2- hexahydroethyl)-hexahydro-5-triazine where R⁴, R⁵, and R⁶ are all a C2 alkyl group.

Suitable alkoxy-hexahydro triazines have the following formula:

R⁴-OR⁷

where R⁴, R⁵, and R⁶ are described herein above and R⁷, R⁸, and R⁹ are independently selected from a Ci to C₆ alkyl group, preferably Ci.

The preferred hexahydro-triazine is l,3,5-tri-methoxypropyl-hexahydro-l,3,5- triazine (MOPA hexahydro-triazine).

The MOPA-hexahydro-triazine is prepared by the condensation of methoxypropyl amine (MOPA) with formalin or a lower aldehyde such as formaldehyde. As noted above, the hexahydro-triazine scavenger can be used as manufactured (water solution). For use in oil base formulations, the scavenger can be used in neat form or dissolved in a suitable solvent.

Although the preferred hexahydro-triazine is the MOPA hexahydro-triazine, other hexahydro-triazines within the scope of Formula III include 1,3,5-tri-methoxyethyl- hexahydro-l,3,5-triazine (from 2-methoxyethyl amine); l,3,5-tri-(3-ethoxypropyl)- hexahydro-l,3,5-triazine (from 3-ethoxypropylamine); l,3,5-tri-(3-isopropoxypropyl)- hexahydro- 1,3,5 -triazine(from 3 -ethoxypropyl amine) ; 1 , 3 , 5 - (3 -butoxy-propyl)-hexahydro- 1,3,5-triazine (from 3 butoxypropylamine); l,3,5-tri-(3-butoxypropyl)-hexahydro-l,3,5- triazine (from 3 -butoxypropylamine); and l,3,5-tri-(5-methoxypentyl)-hexahydro-l,3,5- triazine (from 5-methoxypentylamine).

The triazine compound is used in the aqueous sulfide-scavenging composition in an amount equal to or greater than 5 weight percent, preferably equal to or greater than 15 weight percent, more preferably equal to or greater than 25 weight percent, and more preferably equal to or greater than 35 weight percent based on the total weight of the aqueous sulfide-scavenging composition. The triazine compound is used in the aqueous sulfide-scavenging composition in an amount equal to or less than 90 weight percent, preferably equal to or less than 80 weight percent, more preferably equal to or less than 60 weight percent, and more preferably equal to or less than 40 weight percent based on the total weight of the aqueous sulfide-scavenging composition.

Optionally, the aqueous sulfide-scavenging composition used in the method of present invention may comprise an amine, an anionic surfactant, an alcohol, a glycol ether, or mixtures thereof. The compositions provide excellent sulfide scavenging in the context of sulfide removal from oil liquid or gas streams, and in the treatment of oil or gas transmission lines or equipment. The compositions are capable of scavenging a wide variety of sulfur-bearing compounds, such as sulfhydryl compounds including hydrogen sulfide and organic sulfides (e.g., mercaptans, thiols, and sulfur-bearing carboxylic acids). Suitable amines include, but not limited to, monoethanolamine, diethanolamine, Ν,Ν-diethylethanolamine, monoisopropanolamine, diisopropanolamine, tri- isopropanolamine, triethanolamine, N-methyldiethanolamine, N,N-dimethylethanolamine, monomethylethanolamine, (2-(2-aminoethoxy)ethanol, 3-(dimethylamino)- 1 ,2-propanediol, 3-(diethylamino)-l,2-propanediol, 2-amino-2-methyl-l-propanol, 2-dimethylamino-2- methyl-l-propanol, 2-amino-2-hydroxymethyl-l,3-propanediol, 2-dimethylamino-2- hydroxymethyl- 1,3 -propanediol, piperazine, l-(2-hydroxyethyl)piperazine, l,4-bis(2- hydroxylethyl)piperazine, methylamine, ethylamine, n-propylamine, isopropyl amine, n- butylamine, isobutylamine, sec-butylamine, and t-butylamine, dimethylamine,

diethylamine, methylethylamine, isopropylmethylamine, isopropylethylamine,

diisopropylamine, and isobutylmethylamine, trimethylamine, triethylamine, tri(n- propyl)amine, ethyldimethylamine, n-propyldimethylamine, isobutyldimethylamine, diisopropylmethylamine, choline hydroxide and combinations thereof.

Anionic surfactants are well known, for example see USP 4,426,303, in which an anionic surfactant alkylated diaromatic sulfonate is used in enhanced oil recovery processes. USP 8,828,124 disclosed the use of an anionic surfactant for biogas purification.

WO 2014116309 discloses the use of anionic surfactants and polyalkylenimine for sweep efficiency improvement of a fluid flood of a reservoir.

Suitable anionic surfactants include carboxylates, sulfonates, di-sulfonates, petroleum sulphonates, alkylbenzenesulphonates, naphthalenesulphonates, olefin sulphonates, alkyl sulphates, sulphates, sulphated natural oils and fats, sulphated esters, sulphated alkanolamides, alkylphenols, ethoxylated alkylphenols, and sulphated

alkylphenols.

If present, the anionic surfactant is used in the aqueous sulfide-scavenging composition in an amount equal to or greater than 0.1 weight percent, preferably equal to or greater than 1 weight percent, preferably equal to or greater than 2 weight percent, and more preferably equal to or greater than 3 weight percent based on the total weight of the aqueous sulfide-scavenging composition. The anionic surfactant is used in the aqueous sulfide- scavenging composition in an amount equal to or less than 50 weight percent, preferably equal to or less than 30 weight percent, preferably equal to or less than 20 weight percent, preferably equal to or less than 10 weight percent, and more preferably equal to or less than 5 weight percent based on the total weight of the aqueous sulfide-scavenging composition. In one embodiment of the present invention, the scavenging composition comprises a glycol ether. The glycol ethers usable in the compositions of the invention are preferably selected from the group consisting of glycol mono-, di-, and tri-alkylene ethers, glycol aryl ethers, derivatives of the foregoing, and mixtures thereof, where the alkylene groups may be straight or branched chain and the aryl groups may be any aromatic species, such as mono- or poly-phenyls. The derivatives may again be any form of the foregoing ethers, such as the acetates, acrylates, amides, and nitriles. The single most preferred glycol ether for use in the invention is glycol butyl ether, also known as 2-butoxy ethanol. However, other glycol ethers may also be used, alone or in combination, for example: ethylene glycol

monomethyl ether (EGME) or 2-methoxyethanol, ethylene glycol monoethyl ether (EGEE) or 2-ethoxyethanol, ethylene glycol monoethyl ether acetate (EGEEA) or 2-ethoxyethanol acetate, ethylene glycol monobutyl ether acetate (EGBEA) or 2-butoxyethanol acetate, ethylene glycol monopropyl ether (EGPE) or 2-propoxyethanol, ethylene glycol monophenyl ether (EGPhE) or 2-phenoxyethanol, ethylene glycol monohexyl ether or 2- hexyloxyethanol, ethylene glycol mono 2-ethylhexyl ether or 2-(2-ethylhexyloxy) ethanol.

The glycol component is normally present in the compositions of the invention at a level of from 0 to 90 percent by volume, and more preferably from 0 to 50 percent by volume.

In one embodiment of the present invention, the scavenging composition comprises an alcohol component. The alcohol component, when used, is preferably an organic mono- or poly-alcohol including a Ci to Ci₈ organic moiety. More preferably, the alcohol is a Ci to C₆ mono-alcohol, where the Ci to C₆ group is a straight or branched chain alkyl group. The most preferred alcohols are selected from methanol, ethanol, propanol, isopropanol, butanol, and mixtures thereof, with methanol normally being used.

The alcohol component is normally present in the compositions of the invention at a level of from 0 to 90 percent by volume, and more preferably from 0.1 to 20 percent by volume.

The balance of the aqueous sulfide-scavenging composition is water, typically from 0.1 to 90 percent by volume, preferably from 1 to 80 percent by volume.

The scavenging compositions of the invention can be used in a variety of ways in order to reduce or substantially eliminate H2S and other objectionable sulfides from hydrocarbon streams (e.g., crude oil or natural gas), and to scavenge hydrocarbon transmission lines or equipment (e.g., well heads, separators, glycol units, coolers, and compressors).

Preferably, the scavenging compositions used in the first step of the method of the present invention are used in a ¾S scrubber or bubble tower, or in chemical solvent processes. In each of these systems, towers are used to increase the contact time between the scavenging compositions and the ¾S containing stream being treated.

In scrubber/bubble tower systems, the scavenging compositions are preferably used without further dilution, or with additional alcohol or other non-aqueous solvents. The H2S containing stream, such as a hydrocarbon stream, is delivered to the bottom of the tower and passes upwardly through the scavenging composition to affect the desired result. Such tower systems are the preferred apparatus in which to sweeten hydrocarbon streams, owing to the high efficiencies and relatively low capital investments of such systems. Use of the present composition permits gas sweetening without carryover of water vapor, which minimizes and eliminates corrosion in downstream equipment.

In chemical solvent processes, the sulfides are stripped from the scavenging compositions after the sweetening reaction. Accordingly, in such systems, the compositions may be part of continuous, recirculating processes, and may be regenerated and reused. The amounts of the scavenging compositions are variable depending upon the particular application (e.g., the tower sizes and the amounts of sulfides present, etc.).

After contact of the liquid or gaseous stream, preferably a hydrocarbon stream, comprising H2S with the aqueous sulfide-scavenging composition comprising a triazine compound a reduced H2S stream is attained. The level of H2S in the reduced H2S stream is preferably equal to or less than 1%, more preferably equal to or less than 5000 ppm, more preferably equal to or less than 1000 ppm, more preferably equal to or less than 500 ppm, more preferably equal to or less than 150 ppm, more preferably equal to or less than 100 ppm, more preferably equal to or less than 50 ppm, and more preferably equal to or less than 10 ppm.

In the second step of the method of the present invention, the reduced H2S stream is passing through an adsorbent bed comprising one or more absorption media to provide a loaded adsorbent and a further reduced H2S stream. The adsorbent media is any adsorbent that can adsorb H2S. Suitable adsorbent media may be a solid or in solution and include, but are not limited to, caustic solutions, silica gel, alumina, silica-alumina, zeolites, activated carbon, molecular sieves, metal-organic frameworks (MOFs), polymer supported silver chloride, copper-containing resins, metal oxides, such as iron (II) and (III) oxides, zinc oxide, calcium oxide, magnesium oxide, and mixtures thereof, metal chelates, preferably iron chelates, ion exchange resins, macroporous cross-linked polymers, pyrolized macroporous polymers, or mixtures thereof.

Suitable ion exchange resins are produced from aromatic and/or aliphatic monomers to provide a preferred class of starting polymers for production of porous adsorbtion media used in the present invention. The ion exchange resin may also contain a functional group selected from cation, anion, strong base, weak base, sulfonic acid, carboxylic acid, oxygen containing, halogen and mixtures of the same. Further, such ion exchange resins may optionally contain an oxidizing agent, a reactive substance, sulfuric acid, nitric acid, acrylic acid, or the like at least partially filling the macropores of the polymer before heat treatment.

The synthetic polymer may be impregnated with a filler such as carbon black, charcoal, bonechar, sawdust or other carbonaceous material prior to pyrolysis. Such fillers provide an economical source of carbon which may be added in amounts up to about 90% by weight of the polymer.

The starting polymers, when ion exchange resins, may optionally contain a variety of metals in their atomically dispersed form at the ionic sites. These metals may include iron, copper, silver, nickel, manganese, palladium, cobalt, titanium, zirconium, sodium, potassium, calcium, zinc, cadmium, ruthenium, uranium and rare earths such as lanthanum. By utilizing the ion exchange mechanism it is possible for the skilled technician to control the amount of metal that is to be incorporated as well as the distribution.

Although the incorporation of metals onto the resins is primarily to aid their ability to serve as catalytic agents, useful adsorbents may also contain metal.

Synthetic polymers, ion exchange resins whether in the acid, base or metal salt form are commercially available.

A preferable ion exchange resin is an anion exchange resin. Anion exchange resins are well known, for example see USP 4,988,807, which is incorporated in its entirety herein by reference. By "anion exchange resin" is meant a solid polymeric material that has a positively charged matrix and exchangeable negative ions or anions.

In one embodiment, anion exchange resins that are useful in the method of the present invention herein are functionalized copolymer beads or copolymer beads that have been pulverized. Preferably, the anion exchange resin is employed in the bead form of the resin. The polymer beads from which anion exchange resins are derived can be prepared from epoxy resin-based polymers, (e.g., an epoxy-amine polymer); acrylic copolymers (e.g., an acrylic-divinylbenzene copolymer); and copolymer compositions of styrene- divinylbenzene. Anionic exchange resins are typically prepared via suspension

polymerization of comonomers and are then functionalized with groups that can exchange anions. To functionalize the copolymer beads, the beads can be chloromethylated with chloromethylmethylether (CMME) and then aminated with a dimethylamine to provide weak-base functionality or a trimethylamine to provide a strong-base functionality.

In another embodiment, a useful resin which could be employed in the method of the present invention herein is an adsorptive, porous, post-crosslinked resin in bead form. The adsorptive, porous post-crosslinked resin is prepared by contacting a functionalized resin in a swollen state with a Friedel-Craft catalyst under conditions effective to catalyze the post- crosslinking and rearrangement of the swollen functionalized resin. Examples of these polymeric post-crosslinked adsorbent resins are taught in USP 4,263,407, which is incorporated in its entirety herein by reference.

The anion exchange resin useful in the method of the present invention herein typically has a substituent that is either a strong-base quaternary ammonium group or a weak-base amino group. If the substituent is an alkyl quaternary ammonium salt, the material is known in the industry as a strong-base anion exchange resin. If the substituent is an amine or alkyl amine group, the material is known as a weak-base resin. The weak-base resins are effective in the unaltered or free-base form; whereas, the strong-base resin is effective with a chloride or hydroxide counterion, also known in the ion exchange art as the chloride or hydroxide ion form.

It has also been found useful to use the ammonium salt form of the weak-base resin which is formed by the interaction of a weak-base resin with any suitable mineral acid. The mineral acids could include hydrochloric acid and sulfuric acid, with hydrochloric acid being preferred.

While any anion exchange resin will serve to reduce the H2S level in the reduced H2S stream, a macroporous resin is preferred over a gel-type resin. Preferable resins have a styrene-divinylbenzene matrix, a strong-base gel resin, a weak-base macroporous resin, or a strong-base macroporous resin.

Other suitable resins could include the following resins: a resin having a styrene- divinylbenzene matrix, a weak-base macroreticular styrene-divinylbenzene resin, an acrylicdivinylbenzene matrix, a strong-base macroreticular acrylic-divinylbenzene resin, an epoxy resin-based polymer, or an intermediate base resin with an epoxy amine matrix. The preferred anion exchange resins for use in the method of the present invention are a weak- base macroporous resin or a strong-base macroporous resin.

In addition to using particular anionic resins, some of which are described hereinabove, mixed bed resins can also be useful in the invention, for example a combination of a strong-base gel styrene-divinylbenzene resin and a strong acid cation exchange styrene-divinylbenzene resin.

If the anion exchange resin is a strong-base resin or the ammonium salt of a weak- base resin, then a counterion or anion will be present in the system. This counterion may be a chloride, hydroxide, or sulfate anion.

In one embodiment 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 H2S, mercaptans, thiols, thiol carboxylic acids and dithio acids as well as other sulfhydryl compounds are adsorbed. Examples of such absorption media include materials based on silica, silica gel, alumina or silica-alumina, zeolites, activated carbon, polymer supported silver chloride, copper-containing resins. Preferably, the internal surface of the adsorbent is non-polar.

In one embodiment the adsorbtion media is a macroporous cross-linked polymeric adsorbent, for example see US Patent Publication No. 2016/0145517, incorporated by reference herein in its entirety and/or a partially pyrolized macroporous polymer, for example see US Patent Publication No. 2016/0122671, incorporated by reference herein in its entirety.

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 trivinyl aromatic compounds.

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

Most preferred are copolymers of styrene, divinylbenzene, and ethyl vinylbenzene. 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 (noncros slinking) 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.

In another embodiment, the adsorbent media of the present invention is a pyrolized macroporous polymeric adsorbent media. Pyrolized macroporous polymeric adsorbent media are well known, for instance see USP 4,040,990, incorporated by reference herein in its entirety. Partially pyrolyzed particles, preferably in the form of beads or spheres, produced by the controlled decomposition of a synthetic polymer of specific initial porosity. In a preferred embodiment, the pyrolyzed particles are derived from the thermal decomposition of macroreticular ion exchange resins containing a macroporous structure. The absorption media may comprise iron chelates such as those disclosed in USP 4,876,075, which is incorporated in its entirety herein by reference. The iron chelates employed include coordination complexes in which irons form chelates with an acid having the formula

wherein from two to four of the groups Y are selected form acetic and propionic acid groups, from zero to two of the groups Y are selected from 2-hydroxyethyl, 2- hydroxypropyl, and

X CHnCH.N / ^v

\ X

R¹⁰ is ethylene, propylene or isopropylene or alternatively cyclohexane or benzene where the two hydrogen atoms replaced by nitrogen are in the 1,2-position, and mixtures thereof, and the solubilize ferrous chelate is a ferrous chelate of said acid or acids,

and

X is selected from acetic acid and propionic acid groups.

The iron chelates are supplied in solution as solubilized species, such as the ammonium or alkali metal salts (or mixtures thereof) of the iron chelates. As used herein, the term "solubilized" refers to the dissolved iron chelate or chelates, whether as a salt or salts of the aforementioned cation or cations, or in some other form, in which the iron chelate or chelates exist in solution. Where solubility of the chelate is difficult, and higher concentrations of chelates are desired, the ammonium salt may be utilized. However, the invention may also be employed with more dilute solutions of the iron chelates, wherein the steps taken to prevent iron chelate precipitation are not critical. Exemplary chelating agents for the iron include aminoacetic acids derived from ethylenediamine, diethylenetriamine, 1,2-propylenediamine, and 1,3-propylenediamine, such as EDTA (ethylenediamine tetraacetic acid), HEEDTA (N-2-hydroxy ethyl ethylenediamine triacetic acid), DETPA (diethylenetriamine pentaacetic acid); amino acetic acid derivatives of cyclic, 1,2-diamines, such as 1,2-diamino cyclohexane-N,N-tetraacetic acid, and l,2-phenylene-diamine-N,N- tetraacetic acid, and the amides of polyamino acetic acids disclosed in USP 3,580,950.

The iron chelates also include those in which iron chelates of nitrilotriacetic acid are present in solution as a solubilized species, for example, solubilized ammonium or alkali metal salts of the iron chelates. As used herein, the term solubilized refers to the dissolved iron chelates mentioned, whether as a salt of the aforementioned cations, or in some other form, in which the iron chelates exist in solution. However, the invention may also be employed with more dilute solutions of the iron chelates, wherein the steps taken to prevent iron precipitation are not critical.

The regeneration of the reactant is preferably accomplished by the utilization of oxygen, preferably as air. As used herein, the term "oxygen" is not limited to "pure" oxygen, but includes air, air enriched with oxygen, or other oxygen-containing gases. The oxygen will accomplish two functions, the oxidation of ferrous iron of the reactant to the ferric state, and the stripping of any residual dissolved gas (if originally present) from the aqueous admixture. The oxygen (in whatever form supplied) is supplied in a stoichiometric equivalent or excess with respect to the amount of solubilized iron chelate to be oxidized to the ferric state. Preferably, the oxygen is supplied in an amount of from about 20 percent to about 500 percent excess. Electrochemical regeneration may also be employed.

After passing the liquid or gaseous stream, preferably a hydrocarbon stream, with reduced ¾S from the primary adsorber through the secondary adsorber having a bed with an absorption media a further reduced ¾S stream is attained. The level of ¾S in the further reduced ¾S stream is preferably equal to or less than 150 ppm, more preferably equal to or less than 100 ppm, more preferably equal to or less than 50 ppm, more preferably equal to or less than 25 ppm, more preferably equal to or less than 15 ppm, more preferably equal to or less than 10 ppm, more preferably equal to or less than 5 ppm, and more preferably equal to or less than 4 ppm.

The first step of the process of the present invention comprises passing a liquid or gaseous stream, preferably a hydrocarbon stream containing ¾S and optionally other sulfur compound impurities through a primary adsorber, such as a scrubber or bubble tower or pipelines containing the aqueous sulfide-scavenging composition comprising the triazine compound. Preferably towers are used to increase the contact time between the scavenging compositions and the liquid or gaseous stream. In scrubber/bubble tower systems, the aqueous sulfide-scavenging composition may be used without further dilution, or with additional alcohol, or other non-aqueous solvents. The raw, untreated hydrocarbon stream comprising ¾S to be sweetened is delivered to the bottom of the tower and passes upwardly through the scavenging composition to provide a hydrocarbon stream with a reduced level of ¾S as compared to the raw, untreated hydrocarbon stream. Such tower systems are the preferred apparatus in which to carry out the first step, owing to the high efficiencies and relatively low capital investments of such systems. In pipeline applications, triazine can be injected counter- or co-current of the hydrocarbon stream. In such systems, the scavenging compositions comprising a triazine compound may be part of continuous, recirculating processes, and may be regenerated and reused. The amounts of the scavenging compositions are variable depending upon the particular application (e.g., the tower sizes and the amounts of sulfides present, etc.).

This flow scheme continues until the H2S concentration within the aqueous sulfide- scavenging composition in the primary adsorber progressively increases to a maximum peak value at which time there begins to be a breakthrough of sulfur compounds in the hydrocarbon stream with a reduced level of H2S. At this time, the second phase of the cycle begins. The hydrocarbon stream with a reduced level of H2S contains a predetermined concentration of sulfur compounds which is higher than that required to be in the ultimate product.

At this point, the hydrocarbon stream having a reduced level of H2S exits the primary adsorber and passes into a secondary adsorber. The secondary adsorber contains an absorption bed comprising an absorption media which is selective for the absorption of H2S and other sulfur compounds which are still present in the hydrocarbon stream having a reduced level of H2S leaving the primary adsorber. After passing through the absorption bed comprising an absorption media a treated hydrocarbon stream having a further reduced level of H2S is provided wherein the produced product stream is substantially lower, preferably free of sulfur compounds.

The adsorbent bed contains an adsorbent capable of adsorbing the sulfur compound impurities when the adsorbent bed is in the adsorption mode, and providing the hydrocarbon stream having a further reduced level of H2S, preferably substantially free of sulfur compound impurities.

In one embodiment of the method of the present invention, the absorption media can be regenerated. In one embodiment, the adsorption media can be regenerated by washing with caustic solutions.

In one embodiment, a portion of this hydrocarbon stream having a further reduced level of H2S, or some other suitable gas, is used without heating or desirably heated and used as a regeneration medium to regenerate another secondary adsorption bed containing sulfur compound loaded adsorbent which is in the desorption mode.

In one embodiment, the hydrocarbon stream having a further reduced level of H2S leaving the adsorbent bed undergoing regeneration is allowed to leave the overall process and is utilized as fuel, flared, or the like.

As a result of this integration of the primary and secondary adsorbers containing their respective disparate sorbents, one of the primary advantages obtained is the ability to use less of the triazine compound in the primary adsorber than would ordinarily be required. Although at first, this reduction in the amount of adsorbent in the primary adsorber might not seem unusual inasmuch as a secondary adsorber is also being utilized in the present invention, what is surprising and clearly advantageous is that the amount of the reduction of such adsorbent inventory is much more than would be expected.

The overall integrated process of the present invention provides a more attractive economical system when considering such factors as operating costs and initial capital installation costs for the treatment of a particular fluid stream as contrasted to the use of either of the sorbents contained within the primary or secondary adsorbers alone for the treatment of the same fluid streams.

The present invention provides for a unique, simple and elegant method for removing sulfur compounds from a fluid streams in a most economical and efficient manner.

EXAMPLES

The apparatus used in Comparative Example A and Example 1 is shown in FIG. 1. Comparative Example A.

In a 500 mL modified graduated cylinder equipped with a sparger is loaded 100 g of 1, 3, 5-tris(2-hydroxyethyl)hexahydro-s-triazine (40 wt% active) scavenger. The cylinder is wrapped with heating tape to regulate the temperature of the solution. A 1 % H2S in N2 is bubbled through the solution which is heated at 60°C at lL/min at atmospheric pressure. The ¾S concentration of the outlet is monitored by gas chromatography every hour using the following procedure: 10 mL of the gas from the outlet is transferred via a syringe to a sealed GC vial, which is then placed on the Agilent 7679A Headspace autosampler tray. The GC analysis is done using an Agilent 7890 Gas Chromatograph equipped with a capillary GC column (Restek Rt-Q-Bond 0.53 mm diameter, 30m - P/N 19742)) and a Pulsed Discharge Detector. The ¾S concentration versus time for Comparative Example A is shown in FIG. 2. Example 1.

The same set up as used in Comparative Example A is further connected with a ¼" stainless steel tube loaded with 10 g of AMBERJET™ 9000 OH Resin is a uniform particle size, macroporous, strong base anion (quaternary ammonium) exchange resin available from The Dow Chemical Company. The ion exchange resin is pre-dried at 60°C in an oven overnight. The ¾S breakthrough experiment is then repeated following the same procedure as for Comparative Example A. The ¾S concentration versus time for Example 1 is shown in FIG. 2.

Claims

What is claimed is:

1. A method of reducing ¾S in a liquid or gaseous stream comprising ¾S comprising the steps of:

(A) contacting the stream comprising ¾S with an aqueous sulfide-scavenging composition comprising a triazine compound to provide a reduced ¾S stream and

(B) passing the reduced ¾S stream through an adsorbent bed comprising one or more absorption media to provide a loaded adsorbent and a further reduced ¾S stream.

2. The method of Claim 1 wherein the triazine compound is represented by the formula:

(a)

(b)

R⁴-OR⁷

wherein R⁴, R⁵, and R⁶ are independently selected from a Ci to Ce alkyl group and wherein R⁷, R⁸, and R⁹ are independently selected from hydrogen or a Ci to C₆ alkyl group,

or

(c) a mixture of (a) and (b).

2. The method of Claim 1 wherein the triazine compound is 1, 3, 5-trimethyl- hexahydro-1, 3, 5-triazine, 1, 3, 5-tris(2-hydroxyethyl)hexahydro-5-triazine, or mixtures thereof.

3. The method of Claim 1 wherein the absorption media is silica gel, alumina, silica- alumina, zeolites, activated carbon, molecular sieves, polymer supported silver chloride, copper-containing resin, a metal oxide, a metal chelate, an ion exchange resin, a macroporous cross-linked polymer, a pyrolized macroporous polymer, or mixtures thereof. 5 4. The method of Claim 1 wherein the absorption media is a weak-base anion

exchange resin, a strong-base anion exchange resin, or a gel-type anion exchange resin.

5. The method of Claim 1 wherein the absorption media is an anion exchange resin derived from an epoxy resin polymer, an acrylic based copolymer, or a copolymer composition of styrene-divinylbenzene.

o

6. The method of Claim 1 wherein the absorption media is a cross-linked

macroporous polymer, a pyrolized macroporous polymer, or mixtures thereof.

7. The method of Claim 1 wherein the adsorption media is a caustic solution, sodium carbonate solution, or mixtures thereof.

8. The method of Claim 1 wherein the reduced ¾S stream provided by step (A) has5 an ¾S level equal to or less than 1% and the further reduced ¾S stream provided by step

(B) has an ¾S level equal to or less than 150 ppm.

9. The method of Claim 1 further comprising the step:

(C) regenerating the loaded adsorbent.