EA040386B1 - ABSORBENT AND METHOD FOR SELECTIVE REMOVAL OF HYDROGEN SULFIDE - Google Patents

Description

The present invention relates to an absorbent useful for selectively removing hydrogen sulfide from a fluid stream over carbon dioxide. The present invention also relates to a process for selectively removing hydrogen sulfide from a fluid stream over carbon dioxide.

The removal of acid gases, such as CO2, H2S, SO2, CS2, HCN, COS, or mercaptans, from fluid streams such as natural gas, refinery gas, or synthesis gas is beneficial for various reasons. Sulfur compounds in natural gas can form corrosive acids, particularly when reacting with water, which is often entrained in natural gas. Therefore, for the transport of natural gas in a pipeline or for further processing in a natural gas liquefaction plant (LNG = liquefied natural gas), certain restrictions on the amount of sulfur-containing impurities must be observed. In addition, various sulfur compounds are toxic and have an unpleasant odor even at low concentrations.

It is necessary to remove carbon dioxide from natural gas, as the calorific value of the gas decreases at high concentrations of CO2. Moreover, CO2 combined with moisture can cause corrosion in pipes and valves.

Known methods for removing acid gases include scrubbing operations with aqueous absorbent solutions of inorganic or organic bases. When acid gases dissolve in the absorbent, ions are formed from the bases. Regeneration of the absorbent can be carried out by low pressure decompression and/or by desorption, whereby the ionic species are reversed, released and/or desorbed by an inert fluid, eg steam. After the regeneration process, the absorbent can be reused.

The method in which almost complete removal of CO2 and H2S occurs is called complete absorption. While removal of CO2 may be necessary in order to avoid corrosion and provide the required calorific value of the gas to the consumer, in some cases it is necessary or desirable to treat acid gas mixtures containing CO ₂ and H ₂ S in such a way that a selective removal of H ₂ S from the mixture with minimal removal of CO ₂ . For example, due to the technical characteristics of natural gas pipelines, there are more stringent restrictions on the level of H ₂ S compared to the level of CO ₂ , since H ₂ S is more toxic and corrosive than CO ₂ : in accordance with such characteristics for public natural gas pipelines, the H2S content should generally not exceed 4 ppm. by volume, while the requirements for CO2 content are less stringent - 2 vol.%. Often, selective H2S removal is desirable so that the H2S content of the feed stream to the sulfur recovery unit, eg the downstream Claus process unit, can be higher.

Sterically hindered secondary amines such as 2-(2-tert-butylaminoethoxy)ethanol (TBAEE) and tertiary amines such as methyldiethanolamine (MDEA) exhibit kinetic selectivity for H2S over CO2. Thus, such amines are suitable for the selective removal of H ₂ S over CO ₂ from gas mixtures containing CO ₂ and H ₂ S, as a rule, they are used in the form of aqueous mixtures. These amines do not react directly with CO2 - the reaction of CO2 with the amine and water to produce the bicarbonate ion is slow. The reaction kinetics allow H ₂ S to react more rapidly directly with the amine groups of the sorbent to form a hydrosulfide ion in aqueous solution.

The use of hydroxy-substituted amines (alkanolamines), such as those mentioned above, is well known, since the presence of hydroxyl groups improves the solubility of the reaction products of the absorbent and acid gas in widely used aqueous solvent systems, while also improving the circulation of the solvent through a conventional absorption column/ regeneration column by suppressing phase separation. The presence of hydroxyl groups can also reduce the volatility of the amine and therefore reduce the loss of the amine during operation.

However, such advantages in some cases may be associated with certain problems. While alkanolamines are effective at removing acid gases at higher pressures, it is expected that H ₂ S removal selectivity will decrease markedly due to direct physical adsorption of CO ₂ into the liquid solvent and due to reaction with the hydroxyl groups of the amine compound. Although CO ₂ preferentially reacts with the amine nitrogen, at higher pressures it reacts with oxygen, and at higher pressures the bicarbonate/hemicarbonate/carbonate reaction products that form from the reaction at the hydroxyl center are stabilized, with an increase in pressure, there is a progressive decrease in selectivity for H2S.

Also, while the presence of hydroxyl groups positively affects the solubility of amines in water, the hydroxyl groups impart surfactant properties to the absorbent/acid gas reaction products, which can result in foaming problems during operation of the gas treatment unit.

Another well-known problem with the use of aqueous amine mixtures in the absorption treatment of gas mixtures is that separation into several phases can occur at temperatures in

- 1 040386 regeneration temperature range for aqueous mixtures of amines, which are usually in the range

50-170°C.

US 2015/0027055 A1 describes a process for the selective removal of H ₂ S from a gas mixture containing CO ₂ using an absorbent containing sterically hindered alkanolamines containing an ether end group. It has been found that ether-terminating the alkanolamines and the exclusion of water results in higher H2S selectivity.

US 2010/003775 A1 describes an acid gas absorbent containing an alkylaminoalkyloxy alcohol monoalkyl ether and a process for the selective removal of H2S from gas mixtures containing H2S and CO2 using an absorbent solution containing said monoalkyl ether.

WO 2013/181245 A1 describes an absorbent composition that can be used for the selective removal of H2S, said absorbent composition comprising an aqueous amine mixture, which is an amination reaction product of tert-butylamine and a mixture of polyethylene glycol, and an organic co-solvent selected from sulfones. , sulfone derivatives and sulfoxides, as well as a strong acid to suppress phase separation.

WO 2014/001664 A1 describes compounds of the formula below and their use in acid gas removal:

R1-R4 are selected from H and alkyl, and R5 and _R6 are alkyl, or R5 and _R6 together form a cycle. These compounds contain only tertiary amino groups, each of which contains a basic nitrogen atom.

US 2013/0011314 A1 describes compounds of the formula below and their use for the selective removal of H2S from a gas containing H2S and CO2:

R1 and R2 are alkyl or may together form a heterocycle such as piperidine, pyrrolidine or morpholine, and _R3 and R7 are selected from H, alkyl and alkoxy groups. The compounds described in US 2013/0011314 A1 include a secondary amino group and a tertiary amino group, each of which has a basic nitrogen atom.

There is a need to develop new and improved absorbents suitable for the selective removal of hydrogen sulfide over carbon dioxide from a fluid stream containing carbon dioxide and hydrogen sulfide. Such absorbents should have a reduced tendency to phase separation at temperatures in the normal regeneration temperature range for aqueous amine blends. Said absorbents should exhibit low volatility in aqueous solvents. Also provided is a method for selectively removing hydrogen sulfide from a fluid stream over carbon dioxide.

The purpose of the present invention is achieved by an absorbent for selectively removing hydrogen sulfide over carbon dioxide from a fluid, the absorbent comprising an aqueous solution containing an amine of formula (I) and/or an amine of formula (II)

- 2 040386 where

UVW is CH-O-CHR ⁵ , N-CO-CHR ⁵ or N-CO-NR ⁵ ;

U'-V'-W' is CO-CR ⁵ ;

R ¹ is independently C1- _C5 alkyl;

R ² is selected from hydrogen and C1- _C5 alkyl;

R ³ is independently selected from hydrogen and C1- _C5 alkyl;

R ⁴ is independently selected from hydrogen and C1- _C5 alkyl;

R ⁵ is selected from hydrogen, C1-C ₅ -alkyl, (C ₁ -C ₅ -alkoxy)-C ₁ -C ₅ -alkyl and hydroxy-C1-C ₅ -alkyl; and x is an integer from 1 to 10.

Such absorbents have a reduced tendency to phase separation at regeneration temperatures. The absorbents of the present invention, as a rule, form a single phase (and do not show phase separation) up to a temperature of 130°C, preferably up to 140°C, for example, 36 wt.% aqueous solution.

Amines of general formula (I) and (II) include a secondary amino group immediately adjacent to the group CR ¹ R ¹ R ² . Thus, at least one secondary or tertiary carbon atom is directly adjacent to the nitrogen atom in said secondary amino group, hence such an amine is sterically hindered.

The amines of general formula (I) and (II) contain a five-membered ring structure which, depending on the nature of the UVW or U'-V'-W' structural unit, is a furan, tetrahydrofuran, pyrrolidone or 2-imidazolidone structure. These structures have been found to effectively increase the water solubility of both the amine and the amine/acid gas reaction products without affecting absorption efficiency and absorbent selectivity. As is understood, the structure of pyrrolidone or 2-imidazolidone contains one or two amido groups. Due to the electron withdrawing effect of the carbonyl group, said amido groups are essentially non-basic. It is assumed that due to the lack of basicity, these amido groups do not contribute to the absorption of acid gases and, therefore, essentially do not affect the selectivity of the absorbent containing amines of General formula (I) and (II), in relation to H ₂ S.

Preferably R ¹ is methyl. Preferably R ² is Ci-C ₅ alkyl, in particular methyl. Preferably R ³ is hydrogen. Preferably R ⁴ is hydrogen. Preferably x is an integer from 1 to 6. More preferably x is a number from 1 to 3, in particular 1 or 2. Preferably, UVW is N-CO-CR ⁵ or CH-O-CHR ⁵ , in particular N- CO-CHR ⁵ .

When UVW is N-CO-CHR ⁵ or N-CO-NR ⁵ , R ⁵ is preferably hydrogen or C1-C5 alkyl, in particular hydrogen. When UVW is CH-O-CHR ⁵ , R ⁵ is preferably (C1-C ₅ -alkoxy)-C ₁ -C ₅ -alkyl or hydroxy-C1-C ₅ -alkyl, particularly preferably (C ₁ -C ₅ -alkoxy)-C ₁ -C ₅ -alkyl, for example methoxy-C 1 -C ₅ -alkyl, such as methoxymethyl.

In the amines of formula (II), R ⁵ is preferably (C ₁ -C ₅ -alkoxy)-C ₁ -C ₅ -alkyl, for example methoxy-C ₁ -C ₅ -alkyl, such as methoxymethyl.

When UVW is N-CO-CHR ⁵ or N-CO-NR ⁵ , x is preferably an integer from 2 to 10, more preferably from 2 to 6, in particular 2 or 3.

In those embodiments where UVW is CH-O-CHR ⁵ or U'V'-W' is CO-CR ⁵ , preferably R ¹ is methyl, R ² is C1-C ₅ - alkyl, R ³ is hydrogen, R ⁴ is hydrogen, and x is an integer from 1 to 6, such as 1 to 3. More preferably R ¹ and R ² are methyl, R ³ and R ⁴ are hydrogen and x represents 1 or 2.

In those embodiments where UVW is N-CO-CHR ⁵ or NCO-NR ⁵ , preferably R ¹ is methyl, R ² is C1-C ₅ alkyl, R ³ is hydrogen, R ⁴ is hydrogen and x is an integer from 2 to 6, such as 2 or 3. More preferably, R ¹ and R ² are methyl, R ³ and R ⁴ are hydrogen, and x is 2 or 3.

The term alkyl includes branched and straight chain saturated aliphatic hydrocarbon groups with a specified number of carbon atoms. This also applies to alkyl groups contained in other possible substituents, such as alkoxy substituents.

In a preferred embodiment, the absorbent contains an amine of formula (I). In yet another embodiment of the invention, the absorbent contains an amine of formula (II). In yet another embodiment of the invention, the absorbent contains a mixture of amines of general formula (I) and (II).

- 3 040386

Suitable amines of formula (I) include:

- [2-(tert-butylamino)ethyl] pyrrolidin-2-one,

- [2-(tert-butylamino)propyl] pyrrolidin-2-one, 1-[2-(isopropylamino)ethyl]pyrrolidin-2-one, 1-[2-(isopropylamino)propyl]pyrrolidin-2-one, 2 -methyl-M-(tetrahydrofuran-2-ylmethyl)propan-2-amine, 2-methyl-M-(tetrahydrofuran-2-ylethyl)propan-2-amine, N(tetrahydrofuran-2-ylmethyl)propan-2-amine , M-(tetrahydrofuran-2-ylethyl)propan-2-amine, [5-[(tert-butylamino)methyl]tetrahydrofuran-2-yl]methanol, [5-[(tert-butylamino)ethyl]tetrahydrofuran-2- yl]methanol, [5-[(isopropylamino)methyl]tetrahydrofuran-2-yl]methanol, [5-[(isopropylamino)ethyl]tetrahydrofuran-2-yl]methanol, N-[[5-(methoxymethyl)tetrahydrofuran-2 -yl] methyl] -2-methyl-propan-2-amine, N- [ [5 - (methoxymethyl) tetrahydrofuran-2-yl] ethyl] -2-methyl-propan-2-amine, N- [ [5 - (methoxymethyl)tetrahydrofuran-2-yl]methyl]propan-2-amine, M-[[5-(methoxymethyl)tetrahydrofuran-2-yl]ethyl]propan-2-amine, 1-[2-(tert-butylamino) ethyl]imide azolidin-2-one, 1-[2-(tert-butylamino)propyl]imide azolide in-2-one, and 1-[2-(isopropylamino)ethyl]imidazolidin-2-one, and 1-[ 2-(isopropyl mino)propyl]imidazolidin-2-one.

Suitable amines of formula (II) include: M-(2-furylmethyl)-2-methyl-propan-2-amine, N-(2-furylethyl)-2-methyl-propan-2-amine, M-(2-furylmethyl )propan-2-amine, M-(2-furylethyl)propan-2-amine, [5-[(tert-butylamino)methyl]-2-furyl] methanol, [5-[(tert-butylamino)ethyl] -2-furyl]methanol, [5-[(isopropylamino)methyl]-2-furyl]methanol, [5-[(isopropylamino)ethyl]-2-furyl]methanol, N-[[5-(methoxymethyl)-2 -furyl] methyl] -2-methyl-propan-2-amine, N- [ [ 5 -(methoxymethyl)-2-furyl] ethyl] -2-methyl-propan-2-amine, N- [ [ 5 -( methoxymethyl)-2-furyl]methyl]propan-2-amine, and M-[[5-(methoxymethyl)-2-furyl]ethyl]propan-2-amine.

- 4 040386

In a preferred embodiment, the absorbent comprises an amine of formula (I) and/or an amine of formula (II) selected from:

- [2-(tert-butylamino)ethyl]pyrrolidin-2-one, 1-[2-(isopropylamino)ethyl]pyrrolidin-2-one, and-(2-furylmethyl)-2-methyl-propan-2-amine , X-(2-furylmethyl)propan-2-amine, [5-[(tert-butylamino)methyl]-2-furyl]methanol, [5-[(isopropylamino)methyl]-2-furyl]methanol, N - [[5-(methoxymethyl)-2-furyl]methyl]-2-methyl-propan-2-amine, N methyl-M-(tetrahydrofuran-2-ylmethyl)propan-2-amine, M-(tetrahydrofuran-2-ylmethyl)propan-2-amine, [5-[(tert-butylamino)methyl]tetrahydrofuran-2-yl]methanol , [5-[(isopropylamino)methyl]tetrahydrofuran-2-yl]methanol, N-[[5-(methoxymethyl)tetrahydrofuran-2-yl]methyl]-2-methyl-propan-2-amine, N-[[ 5-(methoxymethyl)tetrahydrofuran-2-yl]methyl]propan-2-amine, 1-[2-(tert-butylamino)ethyl]imidazolidin-2-one, and 1-[2-(isopropylamino)ethyl]imidazolidin- 2-she.

In a more preferred embodiment, the absorbent contains an amine of formula (I) selected from:

- [2-(tert-butylamino)ethyl]pyrrolidin-2-one, 1-[2-(isopropylamino)ethyl]pyrrolidin-2-one, 2-methyl-M-(tetrahydrofuran-2-ylmethyl)propan-2- amine, and-(tetrahydrofuran-2-ylmethyl)propan-2-amine, [5-[(tert-butylamino)methyl]tetrahydrofuran-2-yl]methanol, [5-[(isopropylamino)methyl]tetrahydrofuran-2-yl ] methanol, N- [ [5 - (methoxymethyl) tetrahydrofuran-2-yl] methyl] -2-methyl-propan-2-amine, N- [ [5 - (methoxymethyl) tetrahydrofuran-2-yl] methyl] propan- 2-amine, 1-[2-(t-butylamino)ethyl]imidazolidin-2-one, and 1-[2-(isopropylamino)ethyl]imidazolidin-2-one.

In a particularly preferred embodiment, the absorbent comprises an amine of formula (I) selected from:

- [2-(tert-butylamino)ethyl]pyrrolidin-2-one, 1-[2-(isopropylamino)ethyl]pyrrolidin-2-one, 2-methyl-M-(tetrahydrofuran-2-ylmethyl)propan-2- amine, and N-[[5-(methoxymethyl)tetrahydrofuran-2-yl]methyl]-2-methyl-propan-2-amine.

Most preferably, the amine of formula (I) contained in the absorbent is 1[2-(tert-butylamino)ethyl]pyrrolidin-2-one.

The total amount of amine of general formulas (I) and (II) contained in the absorbent is preferably 10-70 wt.%, more preferably 15-65 wt.%, most preferably 20-60 wt.% based on the total weight of the absorbent.

In one embodiment, the absorbent contains an acid. The acid promotes the regeneration of the absorbent to low loading values and increases the efficiency of the process. A proton equilibrium is formed between the acid and the amine of formula (I) or (II). The equilibrium position is temperature dependent, and at higher temperatures the equilibrium shifts towards the free oxonium ion and/or amine salt with lower enthalpy of protonation. At the relatively low temperatures that prevail in the absorption step, the higher pH promotes efficient absorption of acid gases, while at the relatively high temperatures that prevail in the desorption step, the lower pH supports the release of absorbed acid gases.

Surprisingly, it has been found that the presence of acid in the absorbent of the invention can also lead to higher H ₂ S selectivity.

- 5 040386

Preferably the acid has a pKA value of less than 6, in particular less than 5, when measured at 25°C. In the event that acids have more than one dissociation step and, accordingly, more than one pKA value, this requirement is met if one of the pKA values is in the indicated range. The acid is suitably selected from protic acids (Brönsted acids).

The acid is preferably added in such an amount that the pH of the aqueous solution, measured at 120° C., is from 7.9 to less than 9.5, preferably from 8.0 to less than 8.8, more preferably from 8.0 to less than 8.5, most preferably 8.0 to values less than 8.2.

In accordance with one embodiment, the amount of acid is 0.1-5.0 wt.%, preferably 0.2-4.5 wt.%, more preferably 0.5-4.0 wt.%, most preferably 1.0 -2.5 wt.% based on the total weight of the absorbent.

The acid is selected from organic and inorganic acids. Suitable organic acids include, for example, phosphonic acids, sulfonic acids, carboxylic acids and amino acids. In a particular embodiment of the invention, the acid is a polybasic acid.

Suitable acids are, for example, mineral acids such as hydrochloric acid, sulfuric acid, amidosulfuric acid, phosphoric acid, partial esters of phosphoric acid, for example mono- and dialkyl phosphates and mono- and diarmyl phosphates, such as tridecyl phosphates, dibutyl phosphates, diphenyl phosphates and bis( 2-ethyl)phosphates; boric acid; carboxylic acids, e.g. saturated aliphatic monocarboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, isovaleric acid, pivalic acid, caproic acid, n-heptanoic acid, caprylic acid, 2-ethylhexanoic acid , pelargonic acid, caproic acid, neodecanoic acid, undecanoic acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, margaric acid, stearic acid, isostearic acid, arachidic acid, behenic acid; saturated aliphatic polycarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid; cycloaliphatic mono- and polycarboxylic acids such as cyclohexanecarboxylic acid, hexahydrophthalic acid, tetrahydrophthalic acid, resin acids, naphthenic acids; aliphatic hydroxycarboxylic acids such as glycolic acid, lactic acid, mandelic acid, hydroxybutyric acid, tartaric acid, malic acid, citric acid; halogenated aliphatic carboxylic acids such as trichloroacetic acid or 2-chloropropionic acid; aromatic mono- and polycarboxylic acids such as benzoic acid, salicylic acid, gallic acid, positionally isomeric toluic acids, methoxybenzoic acids, chlorobenzoic acids, nitrobenzoic acids, phthalic acid, terephthalic acid, isophthalic acid; technical mixtures of carboxylic acids, such as versatic acids; sulfonic acids such as methylsulfonic acid, butylsulfonic acid, 3-hydroxypropylsulfonic acid, sulfoacetic acid, benzenesulfonic acid, rtoluenesulfonic acid, p-xylenesulfonic acid, 4-dodecylbenzenesulfonic acid, 1-naphthalenesulfonic acid, dinonylnaphthalenesulfonic acid and dinonylnaphthalenesulfonic acid, trifluoromethyl- or nonafluoro-n acid, camphorsulfonic acid, 2-(4-(2hydroxyethyl)-1-piperazine ethanesulfonic acid (HEPES); organic phosphonic acids, e.g. phosphonic acids of formula (III)

R ⁶ -PO ₃ H (III), where R ⁶ represents C ₁ . ₁₈ αkyl optionally substituted with four or less substituents independently selected from carboxyl, carboxamido, hydroxyl and amino.

These include alkylphosphonic acids such as methylphosphonic acid, propylphosphonic acid, 2-methylpropylphosphonic acid, t-butylphosphonic acid, n-butylphosphonic acid, 2,3-dimethylbutylphosphonic acid, octylphosphonic acid; hydroxyalkylphosphonic acids such as hydroxymethylphosphonic acid, 1-hydroxyethylphosphonic acid, 2hydroxyethylphosphonic acid; arylphosphonic acids such as phenylphosphonic acid, tolylphosphonic acid, xylylphosphonic acid, aminoalkylphosphonic acids such as aminomethylphosphonic acid, 1-aminoethylphosphonic acid, 1-dimethyl-aminoethylphosphonic acid, 2-aminoethylphosphonic acid, 2-(N-methylamino)ethylphosphonic acid, 3-aminopropylphosphonic acid acid, 2-aminopropylphosphonic acid, 1-aminopropylphosphonic acid, 1-aminopropyl-2chloropropylphosphonic acid, 2-aminobutylphosphonic acid, 3-aminobutylphosphonic acid, 1-aminobutylphosphonic acid, 4-aminobutylphosphonic acid, 2-aminopentylphosphonic acid, 5aminopentylphosphonic acid, 2-aminohexylphosphonic acid acid, 5-amino-hexylphosphonic acid, 2-aminooctylphosphonic acid, 1-aminooctylphosphonic acid, 1-aminobutylphosphonic acid; amidoalkyl phosphonic acids such as 3-hydroxymethylamino-3-oxopropylphosphonic acid; and phosphonocarboxylic acids such as 2-hydroxyphosphonoacetic acid and 2-phosphonobutane 1,2,4-tricarboxylic acid;

- 6 040386 phosphonic acids of formula (IV)

RO ₃ H ₂

R---Q

PO ₃ H ₂ where R ⁷ is H or C1-C6 alkyl, Q is H, OH or NR ⁸ 2 and R ⁸ is H or CH2PO3H2, for example 1-hydroxyethane-1,1-diphosphonic acid;

phosphonic acids of formula (V)

(V) where Z is C ₂ -C 6 alkylene, cycloalkanediyl, phenylene, or C ₂ -C ₆ alkylene opened with cycloalkanediyl or phenylene, Y is CH 2 PO 3 H 2 , am is a number from 0 to 4, e.g. methylenephosphonic acid), diethylenetriaminepenta(methylenephosphonic acid) and bis(hexamethylene)triaminepenta-(methylenephosphonic acid);

phosphonic acids of formula (VI)

where R ⁹ is C ₁ -C ₆ alkyl, C ₂ -C ₆ hydroxyalkyl or R ¹⁰ and R ¹⁰ is CH2PO3H2 such as nitrilotris(methylenephosphonic acid) and 2-hydroxyethyliminobis(methylenephosphonic acid);

aminocarboxylic acids with tertiary amino groups or amino groups with at least one secondary or tertiary carbon atom immediately adjacent to the amino group, e.g. N,Ndimethylglycine (dimethylaminoacetic acid), Ν,N-diethylglycine, alanine (2-aminopropionic acid), N-methylalanine (2-(methylamino)propionic acid), N,N-dimethylalanine, N-ethylalanine, 2methylalanine (2-aminoisobutyric acid), leucine (2-amino-4-methylpentano-1-oic acid), N-methylleucine, N,N-dimethylleucine, isoleucine (1-amino-2-methylpentanoic acid), N-methylisoleucine, N,N-dimethylisoleucine, valine (2-aminoisovaleric acid), α-methylvaline (2-amino-2methylisovaleric acid), N-methylvaline (2-methylaminoisovaleric acid), N,Ndimethylvaline, proline (pyrrolidine-2-carboxylic acid), N-methylproline, N-methylserine , N, Nd imethylserine, 2-(methylamino)isobutyric acid, piperidine-2-carboxylic acid, N-methylpiperidine2-carboxylic acid, β-aminocarboxylic acids with tertiary amino groups or amino groups with at least one secondary or tertiary carbon atom immediately adjacent to the amino group, for example 3-dimethyl-iminopropionic acid, N-methyliminodipropionic acid, N-methylpiperidine-3-carboxylic acid, γ-amino acids with tertiary amino groups or amino groups with at least one secondary or tertiary carbon atom immediately adjacent to the amino group, for example 4dimethylaminobutyric acid, or aminocarboxylic acids with tertiary amino groups or amino groups with at least one secondary or tertiary carbon atom immediately adjacent to the amino group, for example N-methylpiperidine-4-carboxylic acid.

Of the inorganic acids, phosphoric acid and phosphoric acid, in particular phosphoric acid, are preferred.

Of the carboxylic acids, formic acid, acetic acid, benzoic acid, succinic acid and adipic acid are preferred.

Of the sulfonic acids, methanesulfonic acid, rtoluenesulfonic acid and 2-(4-(2-hydroxyethyl)-1-piperazinyl)ethanesulfonic acid (HEPES) are preferred.

Of the phosphonic acids, 2-hydroxyphosphonoacetic acid, 2phosphonobutane-1,2,4-tricarboxylic acid, 1-hydroxyethane-1,1-diphosphonic acid, ethylenediaminetetra(methylenephosphonic acid), diethylenetriaminepenta(methylenephosphonic acid), bis(hexamethylene)triaminepenta( methylenephosphonic acid) (HDTMP) and nitrilotris(methylenephosphonic acid), of which 1-hydroxyethane-1,1-diphosphonic acid is particularly preferred.

Of the aminocarboxylic acids with tertiary amino groups or amino groups with at least one secondary or tertiary carbon atom immediately adjacent to the amino group, N,N-dimethylglycine and N-methylalanine are preferred.

More preferably, the acid is an inorganic acid.

In accordance with one of the embodiments of the invention, the absorbent contains a tertiary

- 7 040386 an amine or a highly hindered primary amine and/or a highly hindered secondary amine other than the amines of general formulas (I) and (II). The term highly sterically hindered means that the tertiary carbon atom is directly adjacent to the primary or secondary nitrogen atom. According to this embodiment, the absorbent contains a tertiary amine or a highly hindered amine other than the compounds of general formula (I), generally in an amount of 5-50% by weight, preferably 10-40% by weight, more preferably 20-40 wt.% based on the total weight of the absorbent.

Suitable tertiary amines in particular include:

1) tertiary alkanolamines such as bis(2-hydroxyethyl)methylamine (methyldiethanolamine, MDEA), tris(2-hydroxyethyl)amine (triethanolamine, TEA), tributanolamine, 2-diethylaminoethanol (diethylethanolamine, DEEA), 2-dimethylaminoethanol (dimethylethanolamine, DMEA), 3-dimethylamino-1-propanol (N,Ndimethylpropanolamine), 3-diethylamino-1-propanol, 2-diisopropylaminoethanol (DIEA), N,N-6uc(2hydroxypropyl)-methylamine (methyldiisopropanolamine, MDIPA);

2) tertiary amino esters such as 3-methoxypropyldimethylamine;

3) tertiary polyamines, for example bis-tertiary diamines such as N,N,N',N'tetramethylethylenediamine, N,N-diethyl-N',N'-dimethylethylenediamine, N,N,N',N'-tetraethylethylenediamine, N,N,N',N'-tetramethyl-1,3-propanediamine (TMPDA), N,N,N',N'-tetraethyl-1,3-propanediamine (TEPDA), N,N,N',N '-tetramethyl-1,6-hexanediamine, N,N-dimethyl-N',N'-diethylethylenediamine (DMDEEDA), 1dimethylamino-2-dimethylaminoethoxyethane (bis[2-(dimethylamino)-ethyl]ether), 1,4- diazabicyclo[2.2.2]octane (TEDA), tetramethyl-1,6-hexanediamine;

and their mixtures.

In general, tertiary alkanolamines are preferred, i. e. amines having at least one hydroxyalkyl group bonded to the nitrogen atom. A particularly preferred compound is methyldiethanolamine (MDEA).

Particularly useful highly hindered amines (i.e., amines in which the tertiary carbon atom is directly adjacent to the primary or secondary nitrogen atom) other than the compounds of general formula (I) include:

1) highly sterically hindered secondary alkanolamines such as 2-(2-tert-butylaminoethoxy)ethanol (TBAEE), 2-(2-tert-butylamino)-propoxyethanol, 2-(2-tert-amylaminoethoxy)ethanol, 2-( 2-(1-methyl-1-ethylpropylamino)ethoxy)ethanol, 2-(tert-butylamino)ethanol, 2-tert-butylamino-1-propanol, 3-tert-butylamino-1-propanol, 3-tert-butylamino-1- butanol, and 3-aza-2,2-dimethylhexane1,6-diol, 2-N-methylaminopropan-1-ol, 2-M-methylamino-2-methylpropan-1-ol;

2) highly hindered primary alkanolamines such as 2-amino2-methylpropanol (2-AMP); 2-amino-2-ethylpropanol; and 2-amino-2-propylpropanol;

3) highly hindered amino esters such as 1,2-bis(t-butylaminoethoxy)ethane, bis(t-butylaminoethyl) ether;

and their mixtures.

Generally, highly hindered secondary alkanolamines are preferred. Especially preferred are 2-(2-t-butylaminoethoxy)ethanol and 2-(2t-butylaminoethoxyethoxy)ethanol.

Typically, the absorbent does not contain sterically unhindered primary or sterically unhindered secondary amines. The term unhindered primary amine means compounds with primary amino groups to which only hydrogen atoms or primary or secondary carbon atoms are bonded. The term sterically unhindered secondary amine means compounds with secondary amino groups to which only hydrogen atoms or primary carbon atoms are bonded. Spatially unhindered primary or secondary amines act as strong CO ₂ absorption activators. Their presence in the absorbent can cause the absorbent to lose H2S selectivity.

In accordance with one of the embodiments of the invention, the absorbent contains at least one non-aqueous organic solvent. It may be desirable to limit the maximum water content of the absorbent to, for example, 20% or 10%, preferably 5% or 2% by weight. Limiting the water content of the absorbent can improve the selectivity of the absorbent for H ₂ S over CO ₂ .

The non-aqueous solvent is preferably selected from the following compounds:

C ₄ -C ₁₀ alcohols such as n-butanol, n-pentanol and n-hexanol;

ketones such as cyclohexanone;

esters such as ethyl acetate and butyl acetate;

lactones such as γ-butyrolactone, δ-valerolactone and ε-caprolactone;

amides such as tertiary carboxamides, for example N,N-dimethylformamide; or N-formylmorpholine and N-acetylmorpholine;

- 8 040386 lactams such as γ-butyrolactam, δ-valerolactam and ε-caprolactam and N-methyl-2-pyrrolidone (NMP);

sulfones such as sulfolane;

sulfoxides such as dimethyl sulfoxide (DMSO);

glycols such as ethylene glycol (EG) and propylene glycol;

polyalkylene glycols such as diethylene glycol (DEG) and triethylene glycol (TEG);

di- or mono(C1- _C4 alkyl ether) glycols such as ethylene glycol monomethyl or dimethyl ether;

di- or mono(C1- _C4 -alkyl ether)polyalkylene glycols such as diethylene glycol dimethyl ether, dipropylene glycol monomethyl ether and triethylene glycol dimethyl ether;

cycloureas such as N,N-dimethylimidazolin-2-one and dimethylpropyleneurea (DMPU);

thioalkanols such as ethylenedithioethanol, thiodiethylene glycol (thiodiglycol, TDG) and methylthioethanol;

and their mixtures.

More preferably the non-aqueous solvent is selected from sulfones, glycols and polyalkylene glycols. Most preferably the non-aqueous solvent is selected from sulfones. The preferred non-aqueous solvent is sulfolane.

The absorbent may also contain additives such as anti-corrosion agents, enzymes, antifoam agents, and the like. In general, the amount of such additives is in the range of about 0.005-3% based on the total weight of the absorbent.

Amines of formula (I) are known to those skilled in the art or can be synthesized by reacting an alcohol of formula (VII)

with a primary amine H ₂ N(CR1R1R ² ), for example tert-butylamine, in the presence of an appropriate amination catalyst at elevated temperature and pressure in the presence of hydrogen.

Similarly, amines of formula (II) are known to those skilled in the art or can be synthesized by reacting an alcohol of formula (VIII)

with a primary amine H ₂ N(CR1R1R ² ), for example tert-butylamine, in the presence of an appropriate amination catalyst at elevated temperature and pressure in the presence of hydrogen.

UVW, U'-V'-W', R ¹ , R ² , R ³ , R ⁴ , R ⁵ and x are as defined above.

Preferably, the primary amine H ₂ N(CR1R1R ² ) is used in the course of the reaction in a molar excess compared to the molar amount of the alcohols of formula (VII) or (VIII). In a preferred embodiment, the molar amount of primary amine exceeds the molar amount of alcohol at the start of the reaction by 5-5000 mole %, preferably 50-1000 mole %, based on the amount of alcohol.

Preferably, the reaction is carried out in the presence of a hydrogenation/dehydrogenation catalyst, for example a copper-containing hydrogenation/dehydrogenation catalyst. The catalyst may be supported on a support, such as an alumina-based support.

In accordance with one embodiment, a hydrogenation/dehydrogenation catalyst containing copper, nickel and cobalt is used, while the catalytically active catalyst material contains oxygen compounds of aluminum, copper, nickel and cobalt before reduction with hydrogen, and 0.2-5.0 wt. % oxygen compounds of tin, which are calculated on the basis of SnO. According to a preferred embodiment, a catalyst is used according to the catalysts claimed in WO 2011/067199, in particular the catalyst according to WO 2011/067199, example 5.

The catalyst loading may vary in the range of 0.01-2 kg/(lh), preferably in the range of 0.1-1.0 kg/(lh), in a particularly preferred embodiment in the range of 0.2-0.8 kg/(lh) of an alcohol of formula (VII) or (VIII).

In a preferred embodiment, the reaction is carried out at a temperature of 150-260°C.

- 9 040386

In a particularly preferred embodiment, the reaction is carried out at a temperature of 170240°C. In the most preferred embodiment, the reaction is carried out at a temperature

190-220°C.

The reaction can be carried out at pressures in the range of 5-300 bar in liquid or vapor phase. In accordance with a preferred embodiment of the invention, the reaction is carried out at a pressure of 60-200 bar (abs.). In accordance with a particularly preferred embodiment of the invention, the reaction is carried out at a pressure of 70-130 bar (abs.).

The reaction can be carried out using mechanically stirred reactors, fixed bed tubular reactors and multitubular reactors. The reaction can be carried out in batch, semi-continuous and continuous modes, with recirculation of the crude reaction mixture and without recirculation. According to a preferred embodiment, the reaction is carried out continuously in a fixed bed tubular reactor.

According to a preferred embodiment, the excess primary amine H ₂ N(CR1R1R ² ) is separated from the reaction product by a single distillation. The term single-stage distillation means distillation with one separation stage, as in the case of a simple distillation unit, in which the vapors generated in the reboiler are sent directly to the condenser. In contrast, distillation columns, for example, have several separation steps and are fractional distillation. Preferably, the separated excess of primary amine (III) is recycled for further production of amine (I) or (II).

In addition to the amine (I) or (II), the alcohol (VII) or (VIII), and the primary amine H ₂ N(CR1R1R ² ), the reaction product contains various other substances. Typically, the reaction product contains water and by-products such as ether derivatives of alcohols (VII) or (VIII).

In a preferred embodiment, water and by-products are separated from the reaction product. According to a particularly preferred embodiment, water and by-products as well as excess primary amine still remaining in the reaction product after the one-step distillation as described above are removed from the reaction product by a second one-step distillation. This step is preferably carried out at a pressure of approximately 90 mbar. Any suitable reboiler may be used at this stage. A falling film evaporator or a thin film evaporator may be used. In particular, a Sambay-type thin film evaporator can be used, and the generated gas is condensed at room temperature.

After the processing steps, the resulting product can be mixed with water to obtain the absorbent of the invention. Additional substances may be added as described above.

Alternatively, after the processing steps, the resulting product may be transported to an acid gas absorbent disposal facility, such as a gas scrubber, and there mixed with water to form the absorbent of the invention. Additional substances may also be added at such a facility as described above.

Also provided is a process for selectively removing hydrogen sulfide over carbon dioxide from a fluid stream containing hydrogen sulfide and carbon dioxide, wherein the fluid stream is contacted with an absorbent in accordance with any of the embodiments described above, thereby obtaining a loaded absorbent and a stream treated fluid.

In the context of the present invention, the term selectivity for hydrogen sulfide over carbon dioxide means the following ratio:

mole (H2S)

----- (liquid phase) mol (CO2) mol (H2S)

------ (gas phase) mol (CO2) where mol (H2S) z % > >

-----, (liquid phase) mol (CO2) means the molar ratio of H ₂ S/CO ₂ in the liquid phase that is in contact with the gas phase, and mol (H2S) ( _{gas phase} ) mol (CO2) means the molar ratio H ₂ S/CO ₂ in the gas phase. In a typical gas scrubbing process, the liquid phase is the loaded absorbent at the bottom of the absorption unit, and the gas phase is the fluid stream being treated.

The process is considered to be selective for H ₂ S over CO ₂ when the value of the above coefficient is greater than 1. In the context of the process of the present invention, the term selectivity for hydrogen sulfide over carbon dioxide is preferably at least 1.1, even more preferably at least 2 and most preferably at least 4, such as at least 6.

The absorbent of the invention can be used to treat all kinds of fluids. Fluids are primarily gases such as natural gas, synthesis gas, coke oven gas, cracking gas, coal gasification gas, cycle gas, organic waste gas and combustion gases, and secondarily liquids , which are practically immiscible with the absorbent, such as LPG (liquefied hydrocarbon gas) or NGL (broad fraction of light hydrocarbons). The process of the invention can be used to treat hydrocarbon fluid streams. The hydrocarbons present are, for example, aliphatic hydrocarbons such as C ₁ -C ₄ hydrocarbons such as methane, unsaturated hydrocarbons such as ethylene or propylene, or aromatic hydrocarbons such as benzene, toluene or xylene.

This absorbent can be used to selectively remove hydrogen sulfide from a fluid stream containing hydrogen sulfide and carbon dioxide, which process provides high selectivity for H2S removal at a low solvent circulation rate. The absorbent can be used in the tail gas treatment unit of a sulfur recovery plant, in acid gas enrichment processes to improve the quality of the lean off-gas from the treatment units to produce a high quality feed stream for a Claus plant or for the treatment of associated gases and refinery gases.

In addition to selective removal of H2S (and concomitant removal of CO2), other acid gases that may be present in the fluid stream can also be removed, such as SO ₃ , SO2, CS2, HCN, COS and mercaptans. SO ₃ and SO 2 tend to form heat-resistant salts with amines and are not removed during regeneration.

In the method of the invention, the fluid stream is contacted with the absorbent during the absorption step in the absorption device, resulting in at least partial removal of carbon dioxide and hydrogen sulfide. This results in a fluid stream free of CO2 and H2S and an absorbent containing large amounts of CO2 and H2S.

The absorber used is a scrubbing device used in conventional gas scrubbing processes. Suitable scrubbers are, for example, irregular packing, structured packing and tray columns, membrane contact filters, radial scrubbers, jet scrubbers, tube scrubbers and dynamic wet scrubbers, preferably structured packing and tray columns, more preferably tray and irregular fittings. The fluid stream is preferably treated with an absorbent in a countercurrent column. The fluid is generally fed to the bottom of the column and the absorbent to the top. The tray columns contain sieve trays, cap trays, or valve trays through which the fluid flows. Irregular packing columns can be filled with bodies of various shapes. With an increase in the surface due to bodies of various shapes, as a rule, with a size of approximately 25-80 mm, an improvement in heat and mass transfer occurs. Notable examples are the Raschig ring (hollow cylinder), Pahl ring, Hyflow ring, Intalox saddle and other similar bodies. Irregular packing may be placed in the column in an ordered manner or in a random manner (as a layer). Possible materials include glass, ceramic materials, metal and plastic. Structured packings are a further development of ordered irregular packings. They have an ordered structure. As a result, the pressure drop in the gas stream can be reduced. There are various designs of structured packings, such as braided packings or metal sheet packings. Materials such as metal, plastic, glass and ceramics can be used.

The temperature of the absorbent during the absorption step is typically around 30-100°C, and when using a column, for example 30-70°C at the top of the column and 50-100°C at the bottom of the column.

The method of the present invention may include one or more, in particular two successive absorption steps. The absorption may be carried out in several successive steps, in which case the raw gas containing the acid gas components is contacted with the absorbent substream in each step. The absorbent with which the raw gas comes into contact may already partially contain acid gases; this means that said absorbent may have previously been recycled from the downstream absorption stage to the first absorption stage, or may be a partially regenerated absorbent. The two-stage absorption process is described in EP 0159495, EP 0190434, EP 0359991 and WO 00100271.

The person skilled in the art is able to achieve a high level of hydrogen sulfide removal with a certain selectivity by varying the conditions in the absorption step, in particular, for example conditions such as the ratio of absorbent flow to fluid flow, the height of the absorber column, the type of internal elements of the absorber in contact with the absorbent, such as irregular packings, plates or structured packings, and/or residual loading of regenerated absorbent.

Since CO2 absorption is slower than H2S absorption, a longer treatment time will absorb more CO2 than a shorter treatment time. Therefore, with longer treatment times, there is a tendency to decrease the H2S selectivity. Therefore, using a taller column results in less selective absorption. Trays or structured packings with relatively high liquid accumulation also provide less selective absorption. The thermal energy supplied to the regeneration step can be used to correct the residual load of the regenerated absorbent. In the case of a lower residual load of regenerated absorbent, improved absorption is provided.

Preferably, the method includes the step of regenerating an absorbent containing large amounts of CO2 and H2S. The regeneration step removes CO2 and H2S and, if necessary, other acid gas components from the absorbent containing large amounts of CO2 and H2S to form a regenerated absorbent. The regenerated absorbent is preferably then recycled to the absorption step. In general, the regeneration step includes at least one of the following: heating, decompression, and desorption with an inert fluid.

The regeneration step preferably includes heating the absorbent containing large amounts of acid gas components, for example with a boiler, natural circulation evaporator, forced circulation evaporator or forced circulation flash evaporator. Desorption of the absorbed acid gases is carried out using steam obtained by heating the solution. Instead of steam, an inert fluid such as nitrogen can also be used. The absolute pressure in the stripper is generally 0.1-3.5 bar, preferably 1.0-2.5 bar. Typically, the temperature is in the range of 50-170°C, preferably 70-140°C, more preferably 110-135°C. The regeneration temperature depends on the regeneration pressure.

Alternatively or in addition, the regeneration step may include decompression. This concerns at least one decompression step of an absorbent containing large amounts of acid gases when its pressure, which is high in the absorption step, is reduced to a lower pressure. Decompression can be carried out, for example, using a throttle valve and/or a decompression turbine. A regeneration process with a decompression step is described, for example, in US 4,537,753 and US 4,553,984.

The acid gas components may be removed during the regeneration step, for example, by means of a decompression column, such as a flash vessel mounted vertically or horizontally, or a countercurrent column with internals.

Similarly, the regeneration column may be an irregular packing, structured packing or trays column. At the bottom of the recovery column is a heater, such as a forced circulation evaporator with a circulation pump. In the upper part of the regeneration column there is an outlet for removing the released acid gases. The entrained vapors of the absorption medium are condensed in the condenser and recycled to the column.

It is possible to connect several decompression columns in series, in which regeneration is carried out at different pressures. For example, the pre-decompression column may be regenerated at high pressure, typically about 1.5 bar above the partial pressure of the acid gas components in the absorption step, and the main decompression column at low pressure, such as 1-2 bar abs. . A regeneration process with two or more decompression steps is described, for example, in US 4,537,753, US 4,553,984, EP 0159495, EP 0202600, EP 0190434 and EP 0121109.

The present invention is explained in more detail in the accompanying drawings and the following examples.

In FIG. 1 shows a schematic diagram of a plant for carrying out the method according to the invention.

According to FIG. 1, through the inlet Z, in the absorber A1, the suitably pre-treated gas containing hydrogen sulfide and carbon dioxide is contacted in countercurrent with the regenerated absorbent, which is fed through the absorbent line 1.01. With the help of the absorbent, hydrogen sulfide and carbon dioxide are removed by absorption from the gas; the result is a purified gas that does not contain hydrogen sulfide and carbon dioxide, which enters the exhaust gas line 1.02.

Through the absorbent line 1.03, the heat exchanger 1.04, in which the absorbent containing large amounts of CO ₂ and H ₂ S is heated, with the help of heat from the regenerated absorbent, which passes through the absorbent line 1.05 and the absorbent line 1.06, the absorbent containing large amounts of CO ₂ and H2S is fed into desorption column D and regenerated there.

Between the absorber A1 and the heat exchanger 1.04, one or more evaporation tanks (not shown in Fig. 1) can be located, where the absorbent containing large amounts of CO2 and H2S is decompressed, for example, to a pressure in the range of 3-15 bar.

From the bottom of the desorption column D, the absorbent is fed into the boiler 1.07, where it is heated. The resulting vapor is recycled to desorption column D, while the regenerated absorbent is fed back to absorber A1 through absorbent line 1.05, heat exchanger 1.04, in which the regenerated absorbent heats the absorbent containing large amounts of CO ₂ and H ₂ S and cools down.

- 12 040386 itself, through absorbent line 1.08, cooler 1.09 and absorbent line 1.01. Instead of the boiler shown in the drawing, other types of heat exchange devices can also be used for supplying energy, such as, for example, a natural circulation evaporator, a forced circulation evaporator or a forced circulation flash evaporator. In the case of these types of evaporator, the regenerated absorbent and vapor mixed phase flow is returned to the bottom of the desorption column D, where the vapor and absorbent phases are separated. The regenerated absorbent entering the heat exchanger 1.04 is either removed from the circulating stream from the bottom of the desorption column D to the evaporator or fed through a separate line directly from the bottom of the desorption column D to the heat exchanger 1.04.

The gas containing CO2 and H2S that was liberated in the desorption column D leaves the desorption column D through the off-gas line 1.10. It is fed into a condenser 1.11 with integrated phase separation, where it is separated from the vapor entrained in the absorbent. In such an installation and in other installations suitable for carrying out the method according to the invention, condensation and phase separation can also be carried out separately. The condensate is then fed through the absorbent line 1.12 to the top of the desorption column D, and the gas containing CO2 and H2S is removed through the gas line 1.13.

The following abbreviations have been used in the description of the examples:

HEP: hydroxyethylpyrrolidone,

M3ETB: (2-(2-(2-tert-butylaminoethoxy)ethoxy)ethyl)methyl ester,

MDEA: methyldiethanolamine,

TBA: tert-butylamine,

TBAEE: 2-(2-tert-butylaminoethoxy)ethanol,

TWAEM: tert-butylaminoethoxyethylmorpholine,

TBAEPY: 1-[2-(tert-butylamino)ethyl]pyrrolidin-2-one,

TWAEM: tert-butylaminoethylmorpholine.

Example 1 Synthesis of 1-[2-(tert-butylamino)ethyl]pyrrolidin-2-one (TBAEPY)

Synthesis of 1-[2-(tert-butylamino)ethyl]pyrrolidin-2-one (TBAEPY) was carried out by reacting hydroxyethylpyrrolidone (HEP) and tert-butylamine (TBA) using a high-pressure laboratory plant with continuous operation. The setup consisted of two oil-heated reactors 100 cm long and 12 mm in internal diameter. The reactors were arranged in series and connected to high pressure feed pumps for two liquid feed ports and a high pressure hydrogen feed port. A remote-controlled valve was installed at the outlet of the reactors, adjusted to the required pressure to be maintained in the reactors. The crude reaction mixture was collected in a low pressure phase separator and the exhaust gas was connected to a fume hood.

Each of the reactors was loaded with a crumb of reduced and passivated catalyst, which includes Ni, Co, Cu, Sn on Al ₂ O ₃ (obtained in accordance with WO 2011/067199, example 5). The catalyst was activated as follows: 10 l of hydrogen/l of catalyst were passed through the reactors at 260° C. for 20 h at normal pressure. The pressure was then increased to 70 bar and at a hydrogen flow rate of 10 standard liters/l of catalyst per hour, and at a temperature of 188°C, TBA and hydroxyethylpyrrolidone were pumped into the reactors at a molar ratio of 3:1. The loading of the reactor relative to hydroxyethylpyrrolidone was 0.2 kg/l/h of the catalyst. Thus carried out the conversion of approximately 1000 g of HEP using 1694 g of TBA. The crude reaction product was analyzed by gas chromatography (GC). The product was identified by GC-MS (peak molecular weight at 184 amu) using electron ionization and ion ionization.

GC method: column used: type RTX5 Amin, length 30 m; diameter 0.32 mm; layer thickness 1.5 µm. Temperature program: injection at 60°C, immediately followed by a temperature gradient of 4°C/min. to 280°C, then 35 min at 280°C.

The product was analyzed by GC-MS, and the mass spectrum was recorded using electron and chemical ionization (EI and CI, respectively). Conditions for EI: mass range: 25-785 amu; ionization energy: 70 eV. Conditions for CI: mass range: 50-810 amu

The conversion rate for HEP was 73.6% and the selectivity for TBAEPY was 96.8%. First, excess TBA was removed in a rotary evaporator and then the product was isolated by distillation on a 30 cm column at 1 mbar.

The boiling point was 146° C. at 1 mbar. The purity determined by GC after distillation was >99%.

Peaks are listed below with exact mass divided by charge and intensity relative to the most intense signal in brackets. In addition, where possible, peaks are assigned molecular moieties. m/z=184 (<1%, M ⁺ ); 169 (20%); 127 (15%); 112 (100%, M - HN-C3H9); 99 (58%, M C ₄ H6NO)+H); 98 (25%); 86 (72%); 84 (37%, M - CH2CH2-NC3H9); 70 (17%, M - NCH2CH2NHC4H9); 69 (20%); 57 (40%, Gftf); 56 (13%); 44 (17%); 43 (17%); 42 (25%); 41 (36%); 30 (96%).

The predicted molar peak M ⁺ was found. The structure was confirmed by fragmentation mass spectrum.

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Example 2. pK _A values.

The pK _A values of MDEA and TBAPD were determined by titration. An aqueous solution with an amine concentration of 0.005 mol/l amine was used, it was titrated using aqueous hydrochloric acid (0.1 mol/l) at 20°C.

The results are presented in the following table:

MDEA TBAEPY pK _A (20 °C) 8.7 9.6

TBAEPY shows a higher pK _A value compared to MDEA. It is believed that high pK _A values at relatively low temperatures (such as 20° C.) during the absorption step promote efficient absorption of acid gas.

Example 3. Load and cycle capacity.

A loading experiment was carried out, followed by a desorption experiment.

A glass condenser was attached to a glass cylinder with a temperature-controlled jacket and operated at 5°C. This ensured the distortion of the test results due to the evaporation of the absorbent. Initially, about 100 ml of an acid-free absorbent (an aqueous amine solution, 30% by weight) was placed in a glass cylinder.

To determine the absorption capacity at normal pressure and at 40°C 8 Nl/h. CO ₂ or H ₂ S was passed through the absorption liquid through the inlet filter for approximately 4 hours. Then the content of CO 2 or H 2 S was determined as follows.

Determination of H ₂ S was carried out by titration using a solution of silver nitrate. For this purpose, the analyzed sample was measured into an aqueous solution together with about 2 wt.% sodium acetate and about 3 wt.% ammonia. The H2S content was then determined by potentiometric titration using silver nitrate. At the critical point, H2S is completely bound as Ag ₂ S. CO2 content was determined as total inorganic carbon content (TOCV Series Shimadzu analyzer).

Desorption of a solution containing a large amount of acid gases was carried out by heating in a device with a similar design to 80°C. After supplying a solution containing a large amount of acid gases, its desorption was carried out using an N2 flow (8 Nl/h). After 60 minutes, a sample was taken, the determination of the content of CO2 or H2S in the absorbent was carried out in accordance with the description above.

The difference between the content at the end of the loading run and the content at the end of the stripping run gives the corresponding cyclic capacity.

The results are presented in the following table. Aqueous TBAEPY has a CO ₂ and H ₂ S loading capacity similar to corresponding known H2S selective absorbents.

Absorbent CO2 capacity [molsog/molamine] CO2 cycling capacity [molsog/molamine] H2S capacity [MOL bH2s/MOLamine] H2S cycling capacity [MOL bH2s/MOLamine] No. p / p Compound after loading after desorption after loading after desorption 1* 30% wt.% MDEA + 70 wt% H2O 0.77 0.05 0.72 0.68 0.11 0.57 2* 30% wt.% TWAEE + 70% wt%H2O 0.97 0.24 0.73 0.92 0.25 0.67 3 30% wt.% TBAEPY + 70% wt.% HgO 1.02 0.13 0.89 0.85 0.24 0.61

* comparative example.

Example 4 Volatility

The volatility of several amines in aqueous solutions of 30 wt.% was investigated.

The same device was used as in example 3, except that the condensate obtained in the glass condenser was not returned to the glass condenser, but separated, and after the end of the experiment, its composition was analyzed using gas chromatography and Karl Fischer titration . The temperature of the glass cylinder was adjusted to 50° C., in each case 200 ml of absorbent was introduced. During the experiment lasting 8 hours 30 n.l/h. N2 was passed through the absorbent at normal pressure.

- 14 040386

The experiments were repeated three times. The average values obtained are presented in the following table:

Solution: Condensate [ml] Water [wt%] Amine [wt%] 30 wt.% MZETV + 70 wt.% H2O* 30.1 99.2 0.7 30 wt.% TBAEE + 70 wt.% H ₂ O * 30.0 99.3 0.7 30 wt% MDEA + 70 wt% H ₂ O* 27.1 99.4 0.7 30 wt.% TVAEEM + 70 wt.% H ₂ O * 30.5 99.6 0.2 30 wt.% TWAEM + 70 wt.% H ₂ O * 34.8 98.0 1.6 30 wt.% TBAEPY + 70 wt.% H ₂ O 28.8 99.5 0.2

* comparative example.

It is clear that TBAEPY has a lower volatility than MZETB, TBAEE, MDEA and TBAEM and also has a volatility comparable to TBAEM.

Example 5. Phase separation.

A mixing unit was used to determine the critical temperature of the solution. This setup makes it possible to measure the temperature at which phase separation occurs (the critical temperature of the solution).

The miscibility measuring apparatus included a vessel with a viewing window with a manometer and a thermocouple. A heater was used to supply heat to the container. Measurements are possible up to a temperature of 140°C. A possible phase separation can be visually observed through the sight glass. The following table shows the measured critical solution temperatures for aqueous amine mixtures.

Water solution Critical solution temperature 36 wt.% MZETV* 107°C 36 wt% TWAEM* 131°С 30 wt% TWAEM* 115 - 120°C 36 wt% TBAEPY

* comparative example, ** no phase separation was observed up to 140°C.

Obviously, the aqueous solution containing TBAEPY has a higher critical solution temperature than the solution in the comparative examples.

Example 6 Selectivity for H2S over CO2.

The experiments were carried out in an absorption plant, which is a system with semi-continuous operation and includes a stirred autoclave, which can be supplied with gas in an upward flow, and a condenser. The autoclave is equipped with a manometer and a type J thermocouple. A rupture safety disc is placed in the upper part of the autoclave. To supply heat to the autoclave, a heater with high power ceramic fiber was used. The gas flow rate was controlled using mass flow controllers (manufactured by Brooks Instrument) and the condenser temperature was maintained using a cooler. The maximum operating pressure and temperature was 1000 psi. inch (69 bar) and 350°C respectively.

During the experiments at atmospheric pressure, the pH of the solution was monitored in situ using a pH probe (manufactured by Cole-Parmer) which was installed at the bottom of the autoclave. The maximum temperature and pressure limits for this pH sensor are 135°C and 100 psi. inch respectively. Therefore, before carrying out experiments at a pressure above atmospheric pressure (higher pressure), the pH sensor was removed and the autoclave was closed with a lid. In both cases (experiments at atmospheric pressure and experiments at pressure above atmospheric pressure), liquid samples were taken by connecting directly to the sampling system: a vial (atmospheric pressure) or a stainless steel cylinder filled with caustic soda (superatmospheric pressure). To control the operation of the absorption unit and to obtain experimental data (temperature, pressure, stirrer speed, pH (at atmospheric pressure), gas flow rate and off-gas composition), a specially designed Lab VIEW program was used.

- 15 040386

The gas mixture used in the examples had the following properties:

Composition of the gas feed stream 10 mol.% CO2, 1 mol.% H2S, 89 mol.% N2

Gas flow rate:

Temperature:

Pressure:

Volume:

154 cu. cm/min

40.8 °C bar ml (τ = 0.1 min.)

200 rpm

Stirring speed:

The experiments were carried out by passing gas mixtures as described above through an autoclave. The autoclave was preloaded with an appropriate aqueous amine solution (amine concentration: 2.17M). The acid gas mixture was fed to the bottom of the reactor. The gases leaving the autoclave were passed through a condenser kept at 10° C. in order to remove the trapped liquid. The exhaust gas stream leaving the condenser was fed to a gas microchromatograph (manufactured by Inficon) for analysis while the main gas stream passed through the scrubber. After the breakthrough, nitrogen was used to flush the system.

The analysis of the discharged off-gas stream was carried out using a specially manufactured gas microchromatograph. The gas microchromatograph is a refinery gas analyzer, it includes four columns (molecular sieve, PLOT U, OV-1, PLOT Q) and four thermal conductivity detectors. A portion of the off-gas was injected into the gas microchromatograph approximately every 2 minutes. A small internal vacuum pump was used to transfer the sample to the gas microchromatograph. The rated output of the pump was approximately 20 ml/min. to provide 10 times the flush volume of the line between the sample and the gas microchromatograph. The actual amount of gas that was fed into the gas microchromatograph was approximately 1 μl. A PLOT U column was used to separate and identify H2S and CO2, and a thermal conductivity microdetector was used to quantify H2S and CO2.

The change in selectivity for H2S versus CO2 was determined as a function of acid gas loading. The results are shown in FIG. 2.

As used throughout this document, the term acid gas loading refers to the concentration of H2S and CO2 gases that are physically dissolved and chemically combined in the absorbent solution, expressed as moles of gas per mole of amine.

The maximum selectivity of an aqueous solution of TBAEPY (2.17 M) was approximately 13.0 at approximately 0.15 mol loading and decreased at higher H2S and CO2 loadings. This value is significantly higher than the maximum selectivity of aqueous TBAEEM, aqueous M3ETB, aqueous TBAE and aqueous MDEA.

Claims (8)

CLAIM 1. A process for selectively removing hydrogen sulfide over carbon dioxide from a fluid stream, wherein the fluid stream is brought into contact with an absorbent to produce a loaded absorbent and a treated fluid stream, wherein the absorbent comprises an aqueous solution containing an amine of formula (I ) Where UVW is N-CO-CHR ⁵ ; R ¹ is methyl; R ² is selected from hydrogen and C ₁ -C ₅ -alkyl; R ³ is hydrogen; R ⁴ is hydrogen; R ⁵ is selected from hydrogen and C ₁ -C ₅ alkyl; and x is an integer from 1 to 3, and the absorbent contains a total amount of 15-70 wt.% amine of formula (I) based on the total weight of the absorbent; and the fluid stream is selected from hydrocarbon gases, synthesis gases, acid off-gas from the tail gas treatment unit of the sulfur production plant, and acid off-gas from the acid gas upgrade process. - 16 040386 2. The method according to claim 1, characterized in that the amine is selected from 1-[2-(tert-butylamino)ethyl]pyrrolidin-2-one, 1-[2-(tert-butylamino)propyl]pyrrolidin-2-one , 1-[2-(isopropylamino)ethyl]pyrrolidin-2-one, and 1-[2-(isopropylamino)propyl]pyrrolidin-2-one. 3. Process according to claim 2, wherein the amine is selected from 1-[2-(t-butylamino)ethyl]pyrrolidin2-one and 1-[2-(isopropylamino)ethyl]pyrrolidin-2-one. 4. The method according to claim 3, wherein the amine is 1-[2-(tert-butylamino)ethyl]pyrrolidin-2-one. 5. The method according to any one of the preceding claims, characterized in that the absorbent further comprises an acid having a _pKA value of less than 6, in such an amount that the pH of the aqueous solution, when measured at 120°C, is from 7.9 to less than 9.5. 6. The method according to any one of the preceding claims, characterized in that the absorbent further comprises a tertiary alkanolamine and/or a highly hindered secondary alkanolamine. 7. The method according to any of the preceding claims, characterized in that the absorbent contains a non-aqueous organic solvent selected from lactams, sulfones, glycols, polyalkylene glycols, di- or mono-(C1-C ₄ -alkylether) glycols, di- or mono (C1 -C ₄ -alkylether)-polyalkylene glycols, thioalkanols and mixtures thereof. 8. The method according to any of the preceding claims, characterized in that the regeneration of the loaded absorbent is carried out by at least one of the following actions: heating, decompression and desorption using an inert fluid medium. mol(COg + HgZumolAmin Fig. 2 - 17Eurasian Patent Organization, EAPO Russia, 109012, Moscow, Maly Cherkassky per., 2