WO2014114862A2

WO2014114862A2 - Absorbent solution based on a tertiary or hindered amine and on a particular activator and process for removing acidic compounds from a gas effluent

Info

Publication number: WO2014114862A2
Application number: PCT/FR2014/050083
Authority: WO
Inventors: Thierry Huard; Laurent Renaudot; Bruno Delfort
Original assignee: IFP Energies Nouvelles
Priority date: 2013-01-24
Filing date: 2014-01-16
Publication date: 2014-07-31
Also published as: FR3001157A1; FR3001157B1; WO2014114862A3

Abstract

- An absorbent solution for removing acidic compounds contained in a gas effluent, comprising: - water; - at least one absorbent compound chosen from tertiary amines and sterically hindered amines; - at least one activator chosen from the substituted piperidine or cyclohexylamine family. - A process for removing acidic compounds from a gas effluent using the absorbent solution.

Description

ABSORBENT SOLUTION BASED ON TERTIARY OR CONTAINER AMINE AND A PARTICULAR ACTIVATOR AND METHOD FOR REMOVING ACIDIC COMPOUNDS FROM A GASEOUS EFFLUENT

The present invention relates to the removal of acidic compounds in a gaseous effluent.

The present invention relates in particular to the treatment of acid gases (H ₂ S, CO ₂ , COS, CS ₂ , mercaptans, etc.) by means of an aqueous solution of tertiary amine or sterically hindered, formulated with a secondary amine of the family of cyclohexylamines such as N-methylcyclohexylamine, N-isopropylcyclohexylamine, N-butylcyclohexylamine, dicyclohexylamine, or in admixture with a secondary amine derived from piperidine, such as 4-methylpiperidine or 2-methyl-5-ethylpiperidine or perhydroisoquinoline.

The invention is advantageously applicable to the treatment of natural gas and gas of industrial origin.

Treatment of industrial gases

The nature of the gaseous effluents to be treated is diverse, and one can cite without limitation the synthesis gases, the combustion fumes, the refinery gases, the gases obtained in the tail of the Claus process, the fermentation gases of biomass , cement gases and blast furnace gases.

All of these gases contain acidic compounds such as carbon dioxide (CO ₂ ), hydrogen sulfide (H ₂ S), carbon oxysulfide (COS), carbon disulfide (CS ₂ ) and mercaptans (RSH). ), mainly methyl mercaptan (CH ₃ SH), ethyl mercaptan (CH ₃ CH ₂ SH) and propylmercaptans (CH ₃ CH ₂ CH ₂ SH).

For example, in the case of combustion fumes, CO ₂ is the acid compound that is to be removed. Indeed, carbon dioxide is one of the greenhouse gases largely produced by different human activities and has a direct impact on air pollution. In order to reduce the quantities of carbon dioxide emitted into the atmosphere, it is possible to capture the C0 ₂ contained in a gaseous effluent.

Natural gas treatment In the case of natural gas, three main treatment operations are considered: deacidification, dehydration and degassing. The first step, which is deacidification, aims to eliminate acid compounds such as carbon dioxide (CO ₂ ), but also hydrogen sulfide (H ₂ S), carbon oxysulfide (COS), carbon disulfide (CS ₂ ) and mercaptans (SH), mainly methyl mercaptan (CH ₃ SH), ethyl mercaptan (CH ₃ CH ₂ SH) and propyl mercaptans (CH ₃ CH ₂ CH ₂ SH). The generally accepted specifications for the deacidified gas are 2% of C0 ₂ or 50 ppm of C0 ₂ to subsequently liquefy the natural gas; 4 ppm H ₂ S, and 10 to 50 ppm volume of total sulfur. The dehydration step then controls the water content of the deacidified gas against transport specifications. Finally, the degassing stage of natural gas ensures the dew point of hydrocarbons in natural gas, again depending on transport specifications.

Deacidification is therefore often carried out first, in particular in order to eliminate toxic acid gases such as H ₂ S in the first stage of the process chain and to avoid the pollution of the different unit operations by these acidic compounds. including the dehydration section and the heavier hydrocarbon condensation and separation section.

Elimination of acidic compounds by absorption

Deacidification of gaseous effluents, such as for example natural gas and combustion fumes, as well as synthesis gases, refinery gases, bottoms gases from the Claus process, biomass fermentation gases, process gases cement and blast furnace gases, is usually carried out by washing with an absorbent solution. The absorbent solution makes it possible to absorb the acidic compounds present in the gaseous effluent. In general, for the treatment of acidic effluents comprising acidic compounds such as, for example, H ₂ S, mercaptans, CO ₂ , COS, SO ₂ , CS ₂ , the use of separation agents comprising amine functions is interesting, because of their performance and their ease of implementation in aqueous solution.

An essential aspect of industrial gas treatment operations or industrial fumes is the absorption step. For example, in the case of C0 ₂ capture, the absorbed C0 ₂ reacts with the amine present in solution according to a reversible exothermic reaction, well known to those skilled in the art and leading to the formation of hydrogenocarbonates, carbonates and / or carbamates, allowing CO ₂ removal in the gas to be treated. Similarly, for the removal of H ₂ S in the gas to be treated, the absorbed H ₂ S reacts with the amine present in solution according to a reversible exothermic reaction, well known to those skilled in the art and leading to the formation of hydrogen sulfide.

Another essential aspect of industrial gas treatment operations or industrial fumes is the step of regeneration of the separating agent. Depending on the type of absorption (physical and / or chemical), regeneration by expansion, and / or distillation and / or entrainment by a vaporized gas called "stripping gas" is generally envisaged.

Aqueous solutions of tertiary amines are generally preferred by those skilled in the art for the removal of acidic compounds present in a gas, as they generally have a large acidic gas capture capacity, and high stability.

It is well known to those skilled in the art that tertiary amines or sterically hindered amines have a kinetics of C0 ₂ and COS capture slower than unconfined primary or secondary amines. In a 1987 review, Sartori et al, Sep. and Purification Methods, 16 (2), 171-200 have shown the benefits of various hindered amines, both in terms of harvesting capacity C0 ₂ for moderately hindered amines or lowering vis-reactivity of C0 ₂ for severely congested amines. Severely clogged amines, such as tertiary amines, have an advantage when the CO ₂ and COS concentrations are below the desired specifications because their low CO ₂ reactivity is used to achieve selective removal of the H ₂ S. Nevertheless, when the C0 ₂ and COS are above the desired specifications, the use of a tertiary or confined aqueous amine solution may be unsatisfactory because it would require gigantic absorption column sizes to meet the specifications. . To remedy this problem, WO 89/11327 proposes mixing the tertiary amines with a primary amine to activate the absorption of C0 ₂ .

This primary or secondary amine makes it possible to boost the C0 ₂ capture kinetics in the top of the absorption column, where the partial pressure of C0 ₂ and or of COS is the lowest (references: Aroonwilas, A.; Veawab AT. ; Characterization and Comparison of the C0 ₂ Absorption Performance in Single and Blended Alkanolamines in a Packed Column; Ind. Eng. Chem. Res. 43, 2228-2237 & van Loo, S.; van Elk, EP; Versteeg, GF; The removal of carbon dioxide with activated solutions of methyl-diethanol-amine; Journal of Petroleum Science and Engineering 55 (2007) 135-145). Thus, the addition of a few% by weight of activator considerably reduces the size of the absorption columns, while maintaining the thermodynamic and physicochemical properties of the tertiary amine or congested amine solution.

Thus, the absorbent solutions composed of a tertiary amine and a few% by weight of activator are commonly used. For example, US Pat. No. 6,852,144 describes a method for removing acidic compounds from hydrocarbons. The method uses a water-methyldiethanolamine or water-triethanolamine absorbent solution containing a proportion of a compound belonging to the following group: piperazine and / or methylpiperazine and / or morpholine. We can also cite JP08257353 which describes a method for removing CO ₂ in the flue gases. The method uses a water-bis (2-dimethylaminoethyl) ether absorbent solution containing, for example, 2-methylaminoethanol or piperazine.

Another important aspect to take into account is the stability of the activators. During deacidification of the gaseous effluents, the absorbing solution, and in particular the activator, is degraded either by thermal degradation or by secondary reaction with the acid gases to be captured, but also with other compounds contained in the gaseous effluent, such as oxygen, SOx and NOx, contained in industrial fumes.

These degradation reactions are detrimental to the proper functioning of the process: reduction of the effectiveness of the absorbing solution, corrosion, foaming, etc. Due to these degradations, it is necessary to carry out a purification of the absorbing solution by distillation and / or ion exchange, and to make amine additions. By way of example, amine bonds in a post-combustion CO ₂ capture process, using a 30% by weight absorbent solution of MonoEthanolAmine, represent 1.4 kg of amine per tonne of CO ₂ captured, significantly increasing the operating costs of a capture unit (reference: Chapel, DG, Mariz, CL, Recovery of C0 ₂ from Flue Gases: Commercial Trends, presented at The Canadian Society of Chemical Engineers annual meeting, October 4-6, 1999, Saskatoon, Saskatchewan, Canada). It is hard to find for an aqueous solution of a tertiary or hindered amine, an activator compound which added to several% by weight greatly increases the kinetics of uptake of the C0 ₂ and COS, thereby removing acidic compounds below specifications at lower cost in any type of effluent. In addition, it is difficult to find an activator compound that has high stability.

The object of the invention relates to an absorbent solution for absorbing acidic compounds contained in a gaseous effluent, comprising an activator that combines good chemical stability with an excellent ability to accelerate the absorption of C0 ₂ and COS within a formulation containing tertiary amines and / or sterically hindered amines.

Another subject of the invention relates to a process for the absorption of the acidic compounds contained in a gaseous effluent, in which the absorbing solution according to the invention is used.

In general, the invention relates to an absorbent solution for removing acidic compounds contained in a gaseous effluent, the solution comprising:

- some water ;

at least one absorbent compound chosen from tertiary amines and sterically hindered amines;

at least one activator chosen from the family of cyclohexylamines or substituted piperidines.

The activator may be chosen from the following substituted piperidines:

N methylcyclohexylamine;

perhydroisoquinoline;

N-isopropylcyclohexylamine;

N-n-butylcyclohexylamine;

dicyclohexylamine;

4 Methylpiperidine; or

2-methyl-5-ethylpiperidine.

substituted piperidines.

According to the invention, the solution may comprise an amount of less than 50% by weight of said activator, preferably less than 30% by weight of said activator, very preferably less than 15% by weight of said activator. The absorbent solution may comprise between 10% and 90% by weight of said absorbent compound, preferably between 20% and 60% by weight, very preferably between 30% and 50% by weight. Finally, the absorbent solution may comprise between 10% and 90% by weight of water.

According to the invention, the absorbent compound may be chosen from the following amines:

diethylethanolamine,

- DiMethylEthanolAmine,

diisopropanolamine,

- MethylDiEthanolAmine,

- TriEthanolAmine,

2-Amino-2-methylpropan-l-ol,

bis (2-dimethylaminoethyl) ether

TetraMethyl-1,2-EthaneDiAmine,

TetraMethyl-1,3-propane-diamine

Pentamethyldipropylenetriamine.

The invention also relates to a process for removing acidic compounds contained in a gaseous effluent, in which a step of absorption of the acidic compounds is carried out by contacting the effluent with an absorbent solution according to the invention.

According to the invention, it is possible to perform a regeneration operation of the absorbent solution loaded with acidic compounds obtained at the end of the absorption step, the regeneration step comprising at least one of the following operations:

- Relaxing the absorbent solution loaded with acid compounds,

- Heating the absorbent solution.

According to one embodiment, the absorption step of the acidic compounds is carried out at a pressure of between 1 bar and 120 bar, and at a temperature of between 30 ° C. and 90 ° C.

According to one embodiment, the regeneration step is carried out at a pressure of between 1 bar and 10 bar and a temperature of between 100 ° C. and 180 ° C.

According to one embodiment, the gaseous effluent comprises one of the following elements: natural gas, synthesis gases, combustion fumes, gases Refinery gas, tail gas Claus process, biomass fermentation gas, cement gas, incinerator fumes.

Finally, according to the invention, the acidic compounds may comprise at least one of the compounds: CO ₂ and COS.

The present invention is of interest for reducing absorption column sizes when seeking to remove CO ₂ and / or COS contained in a gas.

Other characteristics and advantages of the invention will be better understood and will become clear from reading the description given hereinafter with reference to FIG. 1, appended and given by way of example, and showing a diagram of FIG. principle of a process for treating acid gas effluents.

The present invention proposes to eliminate the acidic compounds of a gaseous effluent by using aqueous solutions of tertiary amines or sterically hindered amines activated by an amine chosen from the family of cyclohexylamines or substituted piperidines such as N methylcyclohexylamine, perhydroisoquinoline, N-isopropylcyclohexylamine, N-n-butylcyclohexylamine, dicyclohexylamine, 4-methylpiperidine or 2-methyl-5-ethylpiperidine.

Nature of gaseous effluents

The absorbent solutions according to the invention can be used to deacidify the following gaseous effluents: natural gas, synthesis gases, combustion fumes, refinery gases, gases obtained at the bottom of the Claus process, the gases of fermentation of biomass, cement gas, incinerator fumes. These gaseous effluents contain one or more of the following acidic compounds: C0 ₂ , H ₂ S, mercaptans, COS, CS ₂ .

The combustion fumes are produced in particular by the combustion of hydrocarbons, biogas, coal in a boiler or for a combustion gas turbine, for example for the purpose of producing electricity. These fumes have a temperature of between 20 and 60 ° C., a pressure of between 1 and 5 bar and can comprise between 50 and 80% of nitrogen, between 5 and 40% of carbon dioxide, between 1 and 20% of oxygen, and some impurities as SOx and NOx, if they have not been removed downstream of the deacidification process.

Natural gas consists mainly of gaseous hydrocarbons, but may contain several of the following acidic compounds: C0 ₂ , H ₂ S, mercaptans, COS, CS ₂ . The content of these acidic compounds is very variable and can be up to 40% for C0 ₂ and H ₂ S, up to 1000 ppm for COS. The temperature of the natural gas can be between 20 ° C and 100 ° C. The pressure of the natural gas to be treated may be between 10 and 120 bar.

Composition of the absorbent aqueous solution

The absorbent solution advantageously comprises from 10 to 90% by weight of tertiary amine or a sterically hindered amine, preferably from 20 to 60% by weight, and very preferably from 30 to 50% by weight of tertiary amine or from sterically hindered amine.

Preferably, the tertiary amine or sterically hindered amine is selected from the group consisting of:

diethylethanolamine,

- DiMethylEthanolAmine,

diisopropanolamine,

- MethylDiEthanolAmine,

- TriEthanolAmine,

2-Amino-2-methylpropan-l-ol,

bis (2-dimethylaminoethyl) ether

TetraMethyl-1,2-EthaneDiAmine,

TetraMethyl-1,3-propane-diamine

Pentamethyldipropylenetriamine.

The absorbent solution comprises a non-zero and less than 50% by weight, preferably less than 30% by weight, very preferably less than 15% by weight of an activator chosen from the family of cyclohexylamines or piperidines such as N methylcyclohexylamine, perhydroisoquinoline, N-isopropylcyclohexylamine, N-n-butylcyclohexylamine, dicyclohexylamine, 4-methylpiperidine or 2-methyl-5-ethylpiperidine.

The absorbent solution may contain between 10% and 90% by weight of water.

This type of formulation is particularly interesting in the case of capture of C0 ₂ in industrial fumes, or treatment of natural gas containing COS above the desired specification. Indeed, for this type of applications, it is sought to increase the sensing kinetics of the COS, in order to reduce the height of the absorption columns.

In one embodiment, the absorbent solution may comprise other organic compounds. Thus, the absorbent solution according to the invention may contain organic compounds which are not reactive with respect to acidic compounds (commonly called "physical solvents"), which make it possible to increase the solubility of at least one or more acidic compounds of the gaseous effluent. For example, the absorbent solution may comprise between 5% and 50% by weight of physical solvent such as alcohols, glycol ethers, lactams, N-alkylated pyrrolidones, N-alkylated piperidones, cyclotetramethylenesulphone, N-alkylformamides. , N-alkylacetamides, ethers-ketones or alkyl phosphates and their derivatives. By way of example and without limitation, it may be methanol, tetraethylene glycol-dimethyl ether, sulfolane or N-formyl morpholine.

Process for removing acidic compounds in a gaseous effluent (Fiq.1)

The implementation of an absorbent solution according to the invention for deacidifying a gaseous effluent is carried out schematically by performing an absorption step followed by a regeneration step. The absorption step consists in bringing the gaseous effluent (~ 1) into contact with the absorbing solution (~ 4). During contact, the organic compounds provided with an amine function of the absorbent solution react with the acidic compounds contained in the effluent so as to obtain a gaseous effluent depleted in acidic compounds (~ 2) and an acid-enriched absorbent solution. (~ 3). The regeneration step consists in particular in heating and, optionally, in expanding, the absorbent solution enriched in acidic compounds in order to release the acidic compounds in gaseous form (~ 7). The regenerated absorbent solution, that is to say depleted in acid compounds (~ 6) is recycled to the absorption step.

The absorption step of the acidic compounds can be carried out at a pressure of between 1 bar and 120 bar, preferably between 20 bar and 100 bar for the treatment of a natural gas, preferably between 1 and 3 bar for the treatment of industrial fumes, and at a temperature between 20 and 100 ° C, preferably between 30 ° C and 90 ° C. The regeneration step of the process according to the invention can be carried out by thermal regeneration, optionally supplemented by one or more expansion steps.

The regeneration can be carried out at a pressure of between 1 bar and 5 bar, or even up to 10 bar and at a temperature of between 100 ° C. and 180 ° C., preferably between 130 ° C. and 170 ° C.

Examples: Activation for COS Absorption

By way of example, the rate of absorption of COS can be compared between solutions based on MethylDiEthanolAmine activated by N-methylcyclohexylamine, perhydroisoquinoline or 4-methylpiperidine.

These tests are compared with absorbent solutions comprising, in aqueous solutions, MethylDiEthanolAmine activated by Piperazine, an activator well known to those skilled in the art for its COS elimination performance (see US Pat. No. 6,852,144, for example). These tests are also compared with a solution of N, N'DiMethyl-6Hexanediamine-activated MDEA, a molecule studied by Singh et al (Chemical Engineering Science, 66 (2011) 4521-4532) in a stirred reactor for the absorption of C02.

For each test, the absorption flux of COS is measured by the aqueous solution in a closed reactor, Lewis cell type. 200 g of solution are introduced into the closed reactor, regulated at a temperature of 40 ° C. Four successive injections of carbon oxysulfide of 100 to 200 mbar are carried out in the vapor phase of the reactor having a volume of 200 cm ³ . The gas phase and the liquid phase are stirred at 100 revolutions / minute and fully characterized from the hydrodynamic point of view. For each injection, the absorption rate of the carbon oxysulfide is measured by variation of pressure in the gas phase. An overall transfer coefficient Kg is thus determined by an average of the results obtained on the four injections.

The results obtained are shown in Table 1 as the relative absorption rate of the reference formulation MethylDiEthanolAmine 40% by weight activated by piperazine at 3.3% by weight, this relative absorption rate being defined by the ratio of the transfer coefficient. of the formulation tested on the overall transfer coefficient of the reference formulation. Composition of the aqueous absorbent liquid

Amine Activator

Speed

Concentration Concentration

Nature Nature of absorption

(% wt) (% wt) relative to the

COS

MDEA 40 Piperazine 3.3 1.00

MDEA 40 N Methyl - Cyclohexylamine 4.3 1.07

MDEA 40 Ν, Ν 'DiMethyl -1.6 Hexanediamine 5.5 1.12

MDEA 40 Perhydroisoquinoline 5.3 1.38

MDEA 40 4Methyl-Piperidine 3.8 1.41

Table 1

Examination of the results in Table 1 shows the speed of absorption of the COS presented by the absorbent liquids according to the invention improved between 7% and 40% for the molecules derived from the family of benzylamines or piperidines compared to the MethylDiEthanolAmine solution. -Piperazine known to those skilled in the art.

Claims

claims

1. Absorbent solution for removing acidic compounds contained in a gaseous effluent, the solution comprising:

- some water ;

The absorbent solution of claim 1, wherein the activator is selected from the following substituted piperidines:

N methylcyclohexylamine;

perhydroisoquinoline;

N-isopropylcyclohexylamine;

N-n-butylcyclohexylamine;

dicyclohexylamine;

4 Methylpiperidine; or

2-methyl-5-ethylpiperidine.

substituted piperidines.

3. Absorbent solution according to one of the preceding claims, comprising an amount less than 50% by weight of said activator, preferably less than 30% by weight of said activator, very preferably less than 15% by weight of said activator.

4. Absorbent solution according to one of the preceding claims, comprising between 10% and 90% by weight of said absorbent compound, preferably between 20% and 60% by weight, very preferably between 30% and 50% by weight.

5. Absorbent solution according to one of the preceding claims, comprising between 10% and 90% by weight of water.

6. Absorbent solution according to one of the preceding claims, wherein the absorbent compound is selected from the following amines:

diethylethanolamine,

- DiMethylEthanolAmine,

diisopropanolamine,

- MethylDiEthanolAmine,

- TriEthanolAmine, 2-Amino-2-methylpropan-l-ol,

bis (2-dimethylaminoethyl) ether

TetraMethyl-1,2-EthaneDiAmine,

TetraMethyl-1,3-propane-diamine

Pentamethyldipropylenetriamine.

7. A process for removing the acidic compounds contained in a gaseous effluent, in which an absorption step of the acidic compounds is carried out by contacting the effluent with an absorbent solution according to any one of claims 1 to 6.

8. The absorption process according to claim 7, wherein a regeneration operation of the absorbent solution loaded with acidic compounds obtained at the end of the absorption step is carried out, the regeneration step comprising at least one following operations:

- Relaxing the absorbent solution loaded with acid compounds,

- Heating the absorbent solution.

9. Method according to one of claims 7 and 8, wherein the step of absorption of the acidic compounds is carried out at a pressure between 1 bar and 120 bar, and at a temperature between 30 ° C and 90 ° C .

10. Method according to one of claims 7 to 9, wherein the regeneration step is carried out at a pressure between 1 bar and 10 bar and a temperature between 100 ° C and 180 ° C.

11. Method according to one of claims 7 to 10, wherein the gaseous effluent comprises one of the following elements: natural gas, synthesis gas, combustion fumes, refinery gases, gases obtained in the tail of Claus process, biomass fermentation gases, cement gases, incinerator fumes.

12. Method according to one of claims 7 to 11, wherein the acidic compounds comprise at least one of the compounds: CO ₂ and COS.