ES2673740B2 - Aqueous absorbent composition - Google Patents

Abstract

Aqueous absorbent composition. # The invention relates to an absorbent composition for capturing CO {sub, 2} or any other acid gas from a gas stream by regenerative chemical absorption based on an optimized adjustment of the cyclic working capacity of the absorbent.

Description

5

10

fifteen

twenty

25

30

Aqueous absorbent composition DESCRIPTION

The present invention relates to an aqueous absorbent composition and its use in a process of separation of CO2 from a gas stream by regenerative chemical absorption, based on the optimization of the cyclic capacity of operation of the absorbent. Therefore, the present invention is framed in the area of environmental technology and chemical processes. In particular, it is included in the sector of the capture of C02 from stationary emission sources in industrial combustion facilities, but is applicable to other industrial processes where a separation of C02 and / or acid gases from any compound process stream is required by a mixture of gases.

STATE OF THE TECHNIQUE

The process of separation of acid gases from a gas stream by regenerative chemical absorption has been used since the 30s of the last century in numerous industrial processes, such as the treatment of synthesis gas. In recent years, these processes have aroused great interest at the industrial level thanks to the possibility of being used within C02 capture and storage technologies (W01995 / 021683 A1).

The general scheme of the process of separation of COz by chemical absorption was patented by R. R Bottoms (US1783901 A). Said invention describes a system composed of an absorber, in which the gases to be treated are brought into contact, in countercurrent, with an absorbent solution that separates the acid gases (C02, H2S and S02) from the main stream by dissolution and chemical reaction. , and a regenerator, where the operating conditions are opposed to the absorber, the acid compound being separated from the absorbent, this being available for reincorporation into the absorption process. Numerous absorbents have been proposed to be used in this process, the majority being amino-based compounds: monoethanolamine (MEA), triethanolamine (TEA), methyldiethanolamine (MDEA), diisopropanolamine (DIPA) and diglylamine (DGA) were the first compounds used in aqueous solution to separate acid gases selectively

5

10

fifteen

twenty

25

30

35

in process streams. These compounds had to be diluted in aqueous solution because they generate important corrosion problems. From the 50s, several chemical companies such as DOW, BASF or UOP developed proprietary formulations in industrial property of absorbent mixtures which included, in addition to common absorbents, corrosion inhibitors, defoamers, buffers and promoters, which enhanced the operational capabilities of these units thanks to a significant increase in the concentrations of absorbent in the aqueous solution. The main problems associated with the use of chemical absorbents for the separation of CO2 are the high energy consumption associated with the regeneration of the absorbent, the emissions of absorbent and derivatives, due to its high volatility and / or drag of the gas phase, and in the degradation that it suffers due to oxidative and thermal mechanisms that occurs during the process of absorption of CO2 and regeneration of the absorbent.

The application of C02 chemical absorption processes to separate it from combustion gases from the combustion of fossil fuels and / or industrial processes requires the development of absorbent mixtures specifically formulated to operate in these operating conditions. These absorbent mixtures are intended to optimize the performance of traditional absorbents in terms of load capacity (mol of C02 per mol of absorbent), degradation resistance, low volatility, rapid kinetics and low enthalpy of C02 solubility and can operate optimally For each case.

The application of chemical absorption in C02 capture processes has resulted in new absorbent formulations based on mixtures of primary / secondary amines with tertiary amines or salts such as potassium carbonate, so that they have an intermediate functionality between their components, as well such as the use of sterically hindered amines that facilitate the release of absorbed CO2 by the formation of weakened bonds by the presence of large functional groups in the vicinity of the amino groups. The use of amines with spherical impairment was initially proposed by Sartori et. to the. (US4112050A). There are numerous patents based on 2-amine-2-methyl-1-propanol, 2-methylaminoethanol, 2-ethylaminoethanol and 2-piperidine ethanol as hindered amine (US6036931A). Other innovative absorbents are called ionic liquids, amino acid salts with high melting points, high viscosity and low

5

10

fifteen

twenty

25

30

kinetics, even in laboratory scale study {Galán Sánchez, L. M., G Meindersma, A Dehaan. 2007, Chemical Engineering Research and Design 85: 31-39).

The use of piperazine mixtures (PZ) and derivatives with different types of low absorption kinetics absorbents has also been proposed. The use of PZ as an absorbent (CA2651265A1) has been proposed primarily as a promoter of slow kinetic absorbent mixtures such as piperazine and monodiethanolamine (MDEA) (US2009 / 0211446A1), piperazine and potassium carbonate (US4581209A), piperazine and alcohols (US8388855B2). All of them showed excellent results compared to MEA 30% w / w, while solving the problems associated with problems of solubility piperacin in aqueous solution.

On the other hand, numerous configurations of the basic process have been developed over the last years with the aim of optimizing the overall C02 separation process and, in particular, significantly reducing the energy consumption mainly associated with the regeneration of the absorbent . Different variants have been proposed on the traditional arrangement of the absorber, (US8192530B2) and modifications on the regenerator, such as, for example, energy use of the sensible heat of the regenerator output current (US4798910A), preheating of the condensates at the regenerator inlet. (W02007 / 107004A1), partial evaporation of the poor amine at the outlet of the regenerator so that the total energy supply to the reboiler of the regeneration unit is minimized (W02008 / 063079A2), pressurization of the upper section of the regenerator to decrease the ratio water / C02 in the stripping current of the regeneration unit (W02008 / 063082A2). Many of them have led to significant energy reductions in the regeneration of the absorbent compared to the traditional arrangement.

The appearance of new configurations of the separation process of C02 and / or acid gases requires the use of specifically designed absorbents that allow a wide range of operation and a maximization of the performance of each of the new technologies. In this way, significant reductions in energy consumption of the global C02 capture process can be obtained.

DESCRIPTION OF THE INVENTION

The present invention provides a new absorbent composition formulated to capture C02 and / or an acid gas from a gas stream by regenerative chemical absorption, and particularly by regenerative chemical absorption operated in an alternative configuration to the traditional C02 separation system of a gas flow through chemical absorption, based on the optimization of the cyclic operating capacity of the absorbent used through a particular arrangement of the currents involved in the absorption-desorption process of 10 C02 and a very exhaustive control of the operating conditions of the currents of

Regenerator input, mainly in terms of temperature and distribution of feed flow to the equipment. This procedure is protected by the Spanish patent application P201600519 (see example 1 and FIGs 1 to 3), which can comprise the following steps:

fifteen

a) absorption of CO2 from a gaseous stream to be treated at a temperature preferably below 60 ° C and a pressure in a range of between 1 and 1.5 bar, by bringing an absorber of said current into contact with a current absorbent solution to which the CO2 is to be retained;

twenty

b) recirculation of up to 75% of the current comprising the absorbent solution rich in C02 from stage a) to the lower bed of the absorption system. The operation under these conditions allows optimally adjusting the range of cyclic working capacity of the absorbent during the operation;

25

c) desorption of C02 in a current regenerator comprising the absorbent solution rich in C02 from stage a) not recirculated to stage b) at a temperature between 80'C and 120 "C, a pressure between 1 , 5 and 5 bar and a steam flow rate of between 10 and 90% by volume with respect to the desorbed C02 flow,

30 where said current is divided into at least two streams by a train of heat exchangers, prior to the regenerator input;

d) recovery of the absorbent solution resulting from stage c) to the absorber of stage a).

5

10

fifteen

twenty

25

30

35

In a preferred embodiment, the CO2 is absorbed from the current to be treated in step a) of the process of the Invention in the absorber unit from the gas phase to the liquid phase, where it is dissolved and chemically bonded with the absorbent or absorbent solution . Absorbents that operate only with physical, and non-chemical, absorption mechanisms can also be used.

From this basic configuration, the procedure first proposes the incorporation of a recycle line aimed at the absorber that constitutes a derivation of the output of the absorbent solution rich in C02, which is partially redirected to the absorber in order to optimize the capacity of C02 absorption of the absorbent used. Secondly, the procedure incorporates a particular train of heat exchangers that apart from thermally conditioning the solution rich in C02 divides it into at least two streams that are introduced into the regenerator in areas located at different heights, stratifying the feed to the regenerator, which causes a decrease in the temperature profile of the regenerator.

This chemical absorption process allows an efficient operation of the regenerator at a lower thermal level than those proposed in traditional modes of operation and, therefore, significantly reduces the specific consumption associated with the regeneration of the absorbent. With this, it is possible to work with a greater load or concentration of C02 in the regenerated absorbent and, thus, move the cyclic capacity of operation to areas where the energy consumption associated with the desorption of C02 is lower. Likewise, the decrease obtained in the temperature profile of the regenerator reduces the degradation rate of the absorbent associated with thermal mechanisms.

The mixture of absorbents aims to optimize the performance of this configuration due to a greater load capacity thereof, so that a better adjustment of the operating conditions is possible and, therefore, a lower flow of absorbent solution is required and lower energy consumption in the global capture process.

The absorbent composition of the present invention is characterized by a high load capacity and flexibility of operation that maximizes the performance of the absorption-desorption process with a significant reduction in consumption

5

10

fifteen

twenty

25

30

energy compared to the same operation of the C02 capture unit using 30% w / w monoethanolamine as absorbent (reference absorbent).

Therefore, a first aspect of the present invention relates to an aqueous acid gas absorbent composition comprising:

i. a saturated heterocyclic amine, which acts as a promoter or as an absorber of high kinetics and with a high loading capacity;

ii. an amine with steric hindrance, which reduces the heat of absorption of the overall acid gases of the system;

iii. an organic diamine, which adjusts the kinetics and loading capacity of the absorbent composition, and

iv. Water.

By "saturated heterocyclic amine" is meant that organic compound comprising at least one heterocyclic ring consisting of 3 to 10 carbon atoms, which is saturated or partially saturated, and containing at least one N atom forming part of the ring. These compounds Amines are amines without steric hindrance Preferably the heterocyclic amine is saturated In a preferred embodiment the saturated heterocyclic amine is of the general formula (I):

where: X is selected from NR2 and CR3R4; preferably X is NR2 and more

preferably X is NH;

R, and R2 are each independently selected from hydrogen, (Ci-C5) alkyl, optionally substituted by an amino terminal group (-NH2);

R3 and R4 are each independently selected from hydrogen and alkyl (CrC5), preferably selected from hydrogen and methyl; Y

n is 0 or 1, formed a ring of five or six members respectively, preferably n is 1.

image 1

image2

N

(D

5

10

fifteen

twenty

25

30

35

The term "alkyl" refers, in the present invention, to saturated, linear or branched hydrocarbon chains having 1 to 5 carbon atoms, for example, methyl, ethyl, n-propyl, i-propyl, n-butyl , tere-butyl, sec-butyl or n-pentyl Preferably the alkyl group has between 1 and 4 carbon atoms.

In a preferred embodiment, the saturated heterocyclic amine is 1- (2-aminoC1-C, -C5)) -piperazine, more preferably 1- (2-amino ethyl) -piperazine.

In another preferred embodiment, the saturated heterocyclic amine has a loading capacity expressed in moles C02 per mole of absorbent close to or greater than 1 and is at a concentration of at least 1% w / w solution, more preferably at a concentration of between 5% w / w and 50% w / w in solution.

By "steric hindered amines" are defined the compounds that structurally contain at least one primary amine attached to a tertiary carbon atom or a secondary amine attached to a secondary or tertiary carbon atom and at least one water solubilization group. Water solubilization groups are groups that help or permit the dissolution of the compound in water and can be selected from carboxylic acid (COOH), sulfonic acid (S03H), hydroxyl (OH), sulfinic acid (S02H), sulfate (- OSO3H), among other groups In a preferred embodiment the amine with aesthetic impairment is an alkanolamine, as for example but not limited to 2-amino-2-methyl-1-propanol, 2-amino-2-methyl-1-butanol , 3- amino-3-methyl-1-butanol, 3-amino-3-methyl-2-butanol, 2-ethanol piperidine, 2-methanol piperidine, among others.

In a preferred embodiment, the steric hindered amine is amino-2-methyl-propanol.

In another preferred embodiment, the steric hindered amine is in a concentration of at least 1% w / w, being limited by the maximum solubility in aqueous solution and the viscosity of the absorbent system, more preferably between 5% w / w 50% w / w solution.

By "organic diamine" is meant in the present invention two groups of primary amines (-NH2) linked by a linear or cyclic chain of saturated or unsaturated hydrocarbons. Where the linear chain can be branched and contain

5

10

fifteen

twenty

25

30

between 2 to 20 carbon atoms, preferably 6 to 12, and the cyclic chain of 4 to 18 carbon atoms, preferably 5 to 15, and may be optionally substituted. Non-limiting examples are 1,2-diaminoethane, 1,1-dimethylletylenediamine, 1,3-diaminopropane, 1,4-diaminobutane, diaminocyclohexane, o-phenylenediamine, isophorondiamine, among others.

In a preferred embodiment the diamine is selected from a compound of formula (II)

H2N-R-NH2

(II)

where: R is an alkylene group, branched or not, C2-C2o, preferably C6-C12,

or R is an optionally substituted cycloalkyl group, preferably C4-C18 cycloafkyl, more preferably C5-C15.

In a preferred embodiment, the diamine is isophorondiamine or any of its derivatives, more preferably the diamine is isophorondiamine.

By "isoforondamine derivatives" are understood the compounds of formula (Illa) or (IHb):

image3

image4

(Illa) (lllb)

where: R-, is hydrogen or an alkyl group (CVC.,); preferably it is hydrogen or methyl;

R2 and R3, each independently selected from hydrogen or a (C1-C4) alkyl group, preferably are hydrogen;

each R4 is an alkyl group (CrC4); preferably a methyl; n is between 1 and 8, preferably 1, 2 or 3; more preferably 1 and m is between 1 and 9, preferably 2 or 3, more preferably 2

5

10

fifteen

twenty

25

30

35

In a preferred embodiment, the diamine has a loading capacity expressed in moles of C02 per mole of absorbent greater than 1 and is in a concentration of up to 5% w / w in solution.

In a more preferred embodiment, the composition of the invention comprises 1- (2- amino ethyl) -piperazine, 2-amino-2-methyl-1-propanol and isophorondiamine. More preferably, the composition of the invention comprises 1- (2-amino ethyl) -piperazine in 20% w / w, 2-amino-2-methyl-1-propanol in 15% w / w and isophorondiamine in 1, 5% w / w, in aqueous solution.

In another even more preferred embodiment, the absorbent composition of the invention further comprises additives selected from promoters for the adjustment of the kinetics of the absorption process, of adjuvant agents, anti-foaming agents, corrosion inhibitors, oxidative degradation inhibitors or Any of your combinations. Examples of these additives can be selected, without being limited to arsenious anhydride, selenium or tellurium acids, protids, amino acids, such as glycine, vanadium oxides or chromates, among others. All these additives can be found in the composition in amounts suitable for proper functionality and operability of the absorbent in a CO2 separation process by means of the chemical absorption described in the present invention, amounts known to one skilled in the art.

The acid gas separation process, in particular C02, by chemical absorption is based on an optimization of the cyclic charge capacity in operation of the absorbent, understood as the difference between the C02 charge of the rich absorbent composition at the exit of the absorber and poor absorbent composition at the outlet of the regenerator, so that the energy requirements in the reboiler associated with the regeneration process of the absorbent are minimized.

The displacement of the cyclic load capacity of C02 in operation of the absorbent allows an operation in a region of lower enthalpy of solubility of C02, whereby a decrease in energy consumption in the regenerator is obtained compared to a conventional operation. The optimization of the cyclic load capacity is done by adjusting the degree of regeneration required by the absorbent. This adjustment is achieved by entering the current of

absorbent composition rich in CO2 obtained at the outlet of the absorber at different heights of the regenerator and / or by adjusting the temperature of the absorbent composition streams rich in CO2 at the inlet of the regenerator.

5 This configuration of the regenerative absorption process of C02 concludes with the reintroduction of the poor current in C02 to the output of the regenerator in the absorber, to again produce the absorption of C02 and / or acid gases, these being retained within the absorbent. To produce an increase in the C02 charge of the absorbent during the absorption process, part of the charged current of C02 at the outlet of the absorber is partially recirculated after prior cooling. This results in an increase in the overall CO2 load of the absorbent at the outlet of the absorber. The operation under these conditions allows optimally adjusting the range of cyclic working capacity of the absorbent during the operation. Thus, this procedure has allowed a significant reduction in the specific consumption associated with the regeneration of the absorbent compared to a conventional configuration of the absorption system.

Therefore, another aspect of the present invention relates to a process for separating acid gases from a gas stream based on chemical absorption, comprising the following steps:

a) absorption of acid gases from the gaseous stream to be treated at a temperature of between 40 ° C and 60 ° C and a pressure in a range of between 1 and 1.5 bar, by bringing into contact in an absorber of said stream with an absorbent solution in which the acid gases are to be retained, where the

Absorbent solution is an absorbent composition of the present invention;

b) recirculation to the absorber of up to 75% of the current comprising the absorbent solution rich in acid gas from step (a);

c) desorption of the acid gas in a current regenerator comprising the absorbent solution rich in acid gas, preferably C02, from the

30 stage (a) not recirculated to stage (b) at a temperature between 80 ° C and 120 ° C,

a pressure of between 1.5 and 5 bar and a steam flow rate of between 10 and 90% by volume with respect to the flow of desorbed acid gas, where said current is divided into at least two streams by a heat exchanger train , prior to the regenerator input; and 35 d) recovery of the absorbent solution resulting from step (c) to the absorber

of stage (a).

5

10

fifteen

twenty

25

30

35

In a preferred embodiment of the process of the invention the acid gas of the gas stream to be treated in step (a) is transferred to the liquid phase where it is dissolved and chemically bonded to the absorbent.

In a preferred embodiment of the process of the invention the recirculated flow rate of stage (b) reaches between 25% and 75% of the total acid-rich solution from stage (a).

In a preferred embodiment of the process of the invention the recirculation of the current from stage (b) takes place in the lower bed of the absorber of stage (a).

In a preferred embodiment of the process of the invention the currents from stage (c) are introduced into areas located at different heights of the regenerator of stage (d).

In a preferred embodiment of the process of the invention, prior to step (c), a train of heat exchangers is incorporated, through which the current comprising the absorbent solution rich in acid gas, preferably C02, is introduced from step ( a) not recirculated to step (b). This train of exchangers apart from thermally conditioning the absorbent solution rich in C02 divides it into at least two currents that are introduced into the regenerator in areas located at different heights, stratifying the feed to the regenerator, which causes a decrease in the temperature profile of the regenerator.

The absorbent composition of the present invention is suited to this process of separation of CO2 and / or acid gases from a gas stream. The improvement of the performance of the process from the use of the absorbent composition described in this invention is based on the following characteristics, which have been corroborated in the examples:

a) High load capacity of C02, expressed as moles of C02 per mole of absorbent in aqueous solution: This characteristic gives it a better adaptation to the operating conditions imposed by the procedure described.

5

10

fifteen

twenty

25

30

35

b) High kinetic absorption ratios of C02, expressed as a mass flow rate of C02 per unit of time, which leads to a reduction of the absorbent flow rate required to achieve a given separation performance of C02 and, therefore, to a decrease in the investment, by reducing the size of the equipment and lines of the separation unit of C02.

c) Both characteristics described above entail a lower requirement of the operating L / G ratio to achieve a given separation performance of C02. This implies a lower circulation of liquid absorbent solution and, therefore, a lower consumption in impulse of the absorbent.

d) The use of the absorbent composition described in this invention in the process of the invention makes it possible to significantly reduce the energy consumption associated with the regeneration of the absorbent.

Another aspect of the present invention relates to the use of the composition of the invention for the absorption of acid gases.

By "acid gas" we mean in the present invention any of the following: C02, H2S and S02, or mixtures thereof, preferably the acid gas to be separated in the process of the present invention is C02.

The application of this C02 capture procedure can be for gases or gaseous streams from stationary sources of combustion, such as electrical production systems, cement, oil refineries or steel, and can also be extended to a gas stream from any industrial process where the separation of C02 and / or acid gases is required, such as the production of synthesis gas. The process of separation of C02 in a gas stream under these conditions is highly favored when C02 has a high concentration of C02.

Throughout the description and the claims the word "comprises" and its variants are not intended to exclude other technical characteristics, additives, components or steps. For those skilled in the art, other objects, advantages and features of the invention will be derived partly from the description and partly from the practice of the invention. The following examples and figures are provided by way of illustration, and are not intended to be limiting of the present invention.

5

10

fifteen

twenty

25

30

DESCRIPTION OF THE FIGURES

FIG. 1: Shows a diagram of a C02 absorption-desorption system by means of a process for optimizing the cyclic capacity of the absorbent to operate.

FIG. 2: Shows a detail of the heat exchanger train.

FIG. 3: It shows a graph representing the enthalpy of solubility of C02 as a function of the absorbent load expressed in moles of C02 per mole of absorbent (generic absorbent). The cyclic capacity of operation for a conventional configuration and an optimization configuration of the cyclic capacity of operation of the absorbent are generically indicated.

FIG. 4: Evolution of C02 absorption ratios obtained in laboratory tests

The absorption rate of C02 is plotted as a function of the experimental time after the execution of each test, expressed as mL of C02 absorbed per minute (mL C02 / min). The tests performed with the new absorbent mixture are represented,

using 60% v / v C02 (* *) and 15% v / v C02 (...........) in the gas phase. If

of MEA, the absorption ratios obtained for 60% v / v C02 (

“) And 15% v / v C02 () in the gas phase.

FIG. 5: C02 capture performance obtained for each L / G ratio using the new absorbent mixture (■) and the reference absorbent (A) using a current of 40% v / v C02 in a chemical absorption unit of C02 operating

through a process of optimization of the cyclic capacity of the absorbent.

The capture performance of C02 is represented, defined as the difference in mass flow of C02 in the gas phase between the output and the input of the C02 absorption unit. The percentage capture yield is expressed based on the mass flow rate of C02 at the input of the absorption unit. This parameter has been represented as a function of the L / G ratio of each test, expressed as mass flow rate of liquid phase absorbent (kg / h) versus mass flow of gas to be treated (kg / h). The essays

5

10

fifteen

twenty

25

30

35

performed using the new absorbent mixture are represented by (■), while tests performed using MEA are represented by (A).

FIG. 6: Specific consumption of the regeneration of the absorbent obtained for each L / G ratio using the new absorbent mixture (■) and the reference absorbent (A) using a current of 40% v / v C02 in a chemical absorption unit of C02 operating through a process of optimization of the cyclic capacity of the absorbent.

The specific consumption associated with the regeneration of the absorbent, expressed in energy units per unit mass of C02 (GJ / t C02) is represented. This parameter has been represented as a function of the L / G ratio of each test, expressed as mass flow of absorbent in liquid phase (kg / h) versus mass flow of gas to be treated (kg / h). Tests performed using the new absorbent mixture are represented by (■), while tests performed using MEA are represented by (A).

EXAMPLES

The invention will now be illustrated by tests carried out by the inventors, which shows the effectiveness of the absorbent composition of the invention and more specifically the improvements in the performance of the separation process by means of an optimization process of the cyclic capacity of operation of the absorbent (Spanish patent application P201600519), associated with the use of this composition, in combination with a chemical absorption unit of C02.

Example 1: Preferred embodiment of the optimization system of the cyclic capacity of the absorbent.

Specifically in FIG 1 the absorption-desorption system of C02 has been represented, which includes the elements described below:

1. - Gas stream to be treated

2. - Absorber

3. - Clean gas

5

10

fifteen

twenty

25

30

35

4. - Exit absorbent solution rich in C02

5. - First drive pump

6 - C02 rich absorbent solution

7. - Recirculated C02-rich absorbent solution

8. A.- First heat exchanger

8. B.- Second heat exchanger

9. - Train exchangers

10. - Primary current

11 Heat exchanger for energy use of the gas stream at the regenerator outlet

12. - Main input current to the regenerator of absorbent solution rich in

co2

13. - Secondary current

14. - Alternative input currents to the regenerator of absorbent solution rich in CO2

15 - Regenerator

16. - Regenerator outlet gas current

17. - Condensate separator

18. - High concentration gas stream of C02

19. - Condensate stream

20 - Calderin

21 - Poor regenerated absorbent solution

22, - Second drive pump

23. - Input current of regenerated absorbent solution

As can be seen in FIG 1, the system incorporates an absorber (2) comprising a filler column that can be both structured and unstructured, and a lower bed, where the gas stream to be treated (1) arrives that will enter in contact in the absorber (2) with an absorbent liquid that is used to retain the CO2 of the gas to be treated (1). The absorber (2) incorporates an outlet of exit absorbent solution rich in C02 (4), an input for the inlet stream of regenerated absorbent solution (23), a stream of recycled absorbent solution rich in C02 (7) and a outlet through which the clean gas (3) free of C02 is evacuated.

5

10

fifteen

twenty

25

30

35

The input stream of regenerated absorbent solution (23) from the regenerator (15) is at a temperature that has been adjusted to values close to that of the gas stream to be treated (1) by using a second heat exchanger. heat (8B).

On the other hand, the absorber (2) incorporates an inlet of a recirculation line of recirculated C02-rich absorbent solution (7), which is redirected to the lower bed of the absorber (2) in order to increase the load thereof, with intermediation of a first heat exchanger (8A) that cools its temperature.

In a preferred embodiment, the design of the absorber (2) requires an increase in the section in the lower bed with respect to the rest of the column, as shown in FIG. one.

It is also observed in FIG. 1 that the absorbent outlet solution rich in C02 (4) is extracted from the absorber (2) from the bottom thereof and driven by a first drive pump (5) that drives the absorbent outlet solution rich in C02 (4) to then separate into the recirculated C02-rich absorbent solution (7) and a C02-rich absorbent solution (6), which is previously introduced into the heat exchanger train (9).

The heat exchanger train (9) receives the above-mentioned absorbent solution rich in COz (6), where the temperature of this current is optimally adjusted before being divided and directed towards the regenerator (15), as well as it arrives a poor regenerated absorbent solution (21) from the regenerator (15), and the regenerated absorbent solution inlet stream (23) directed to the absorber (2) leaves the train of heat exchangers (9), as well as leaves, consequence of the said division of the absorbent solution rich in CO2 (6), a primary current (10) and a secondary current (13).

In FIG. 2 the train of heat exchangers (9) comprising the following elements is observed:

6.- Absorber solution rich in C02 9 - Train of exchangers 10.- Primary current

5

10

fifteen

twenty

25

30

35

13.- Secondary current

13.A.- Alternative of extraction of the first secondary current exchanger of

C02 rich absorbent solution regenerator input

13.B- Alternative extraction of the second secondary current exchanger

input to the regenerator of absorbent solution rich in C02

13.C.- Alternative extraction of successive current exchangers

secondary input to the regenerator of absorbent solution rich in C02

21.- Poor regenerated absorbent solution

21.A.- Alternative supply of regenerated absorbent solution to successive exchangers in the exchange train

21.B.- Alternative supply of regenerated absorbent solution to the second exchanger in the exchange train

21.C.- Alternative supply of regenerated absorbent solution to the first exchanger in the exchange train

23. - Input current to the regenerated solution absorber

24. - First internal exchanger of the exchange train

25. - Second interchanger of the interchange train

26. - Successive interchangers train exchangers

The exchanger train (9) shown in FIG. 2 comprises a series of N internal heat exchangers (24, 25, 26), preferably from 2 to 4 heat exchangers, where the absorbent solution rich in C02 (6) is heated to different levels by using the solution poor regenerated absorbent (21) from the bottom of the regenerator (15). The stream of absorbent solution rich in CO2 (6) is divided into two main streams. The primary current (10) is heated by the use of all internal heat exchangers (24, 25, 26), while the secondary current (13) can be extracted at the output of each of the internal exchangers, giving place at internal currents (13A, 13B, 13C). The poor regenerated absorbent solution stream (21) can in turn be divided into different subcurrents, called (21 A, 21B, 21C), to achieve an even more precise adjustment of! thermal level of the primary stream of rich solution (10) and, therefore, of the temperature profile of the regenerator (15).

The distribution of the C02-rich absorbent solution (6) between the primary current (10) and the secondary current (11) is preferably set in the range of 0.25

5

10

fifteen

twenty

25

30

35

and 0.75. The primary current (10) is then preheated in a second indirect contact exchanger (11) using the regenerator output current (16), at a temperature greater than 100 "C, resulting in a main input current to the regenerator (12).

The absorber current (2) reaches different heights and temperatures at the regenerator (15), so that the degree of regeneration of the absorbent is optimally adjusted.

The main input current to the regenerator (12) is introduced in the upper part of the regenerator (15). On the other hand, the secondary current (13) is introduced at a temperature lower than that set for the primary current (10) in an intermediate bed of the regenerator (15), achieving a temperature profile that optimizes the energy requirements of! global capture process. The secondary current (13) can in turn be divided into another additional current (14) to be fed at different heights of the regenerator (15).

This configuration allows to obtain a partial regeneration of the absorbent, displacing the cyclic capacity of the same towards areas of lower energy requirement of the desorption of C02. The energy necessary for regeneration of the absorbent to occur is supplied to the regenerator (15) by means of a boiler (20) preferably using steam as a working fluid.

On the other hand, the output current (16) from the top of the regenerator, mainly composed of C02 and water vapor, is introduced into a separator.

(17), where the high concentration stream of C02 saturated in water is obtained

(18) and a condensate stream (19), which is subsequently recirculated to the regenerator (15).

Finally, the poor regenerated absorbent solution (21) is extracted from the lower part of the regenerator (15) and driven by a second pump (22) to the train of exchangers (9) prior to its return to the absorption system (23) .

The regenerator (15) preferably works in a pressure range between 1.5 and 5 bar, and at a maximum temperature below 12CTC, more

preferably, in a temperature range between 100 ° C and 120 ° C, so that less degradation of the absorbent is guaranteed.

Particularly, a process of separation of C02 from a synthetic gas stream 5 was carried out in a laboratory-scale unit based on two operating configurations that correspond on the one hand to a conventional configuration and on the other to a configuration according to the described system .

In this way, a synthetic gas flow rate of 7 L / min has been used, with a composition of 60% v / v C02, saturated in water vapor and completed with N2. Monoethanolamine in 30% w / w aqueous solution has been used as an absorbent, as it is a reference absorbent. The total amount of absorbent used in the system is 2 L. The absorption of C02 is carried out at a pressure of 1 atm and temperature of 50'C in a column of 3 cm in diameter and 2 m high using as an absorption bed 15 6 mm Raschig ceramic rings. The regeneration of the absorbent is carried out at a pressure of 2 bar on a column 3 cm in diameter and 1 m high using 6 mm 316L stainless steel Raschig rings.

The conventional configuration has consisted of having a recirculation rate 20 in the absorber of 0 (7), a single internal heat exchanger (24) composes the train of exchangers (9) and the power supply to! Regenerator (15) is performed by using a single primary current (10) introduced by the top of the regenerator (15). The absorbent flow rate was set at 7.01 kg / h, which corresponds to an L / G ratio equal to 12, the absorber inlet temperature being 49 ° C.

25

The configuration of the invention has employed a partial recirculation of the stream of recirculated C02-rich absorbent solution (7), a train of exchangers (9) composed of internal heat exchangers (24, 25), and the current has been distributed Input to the regenerator in two currents: a primary current (10) in the upper part of the regenerator (15) and a secondary current (13) in the intermediate zone of the regenerator (15). This secondary current (13) was extracted at the exit of the first internal heat exchanger (24) of the exchanger train (9). The absorbent flow rate was set at 8.18 kg / h, which corresponds to an L / G ratio equal to 14, the gas inlet temperature being to the absorber 47 "C.

The most relevant operating conditions and results obtained are summarized in Table 1. The operation by the method of the invention allowed to increase the cyclic capacity of the absorbent and the separation efficiency of C02 during the separation operation thanks to a greater load of the absorbent Rich in the stage of 5 absorption. This increase in load is mainly due to the recirculation of part of the absorbent solution rich in recirculated CO2 (7). The stratification of the feed in the regenerator (15) caused a decrease in the temperature profile in the regenerator (15) and, therefore, a poor solution more loaded in C02. This shift in the cyclic capacity of the absorbent 10 allowed the use of the new configuration to achieve a 11% reduction in the specific energy consumption associated with the regeneration of the absorbent, producing a net benefit with respect to the traditional configuration of this type of processes. In addition, the lower thermal level obtained in the regenerator favors the reduction of the degradation of the absorbent associated with thermal mechanisms.

fifteen

 Table 1

       Setting

 Conventional Units System FIG.1

 Operational Parameters

 Absorber

 Ratio L / G kg / kg 12 14

 Recirculation Rate

 % - twenty

 Depth temperature ° C 120 118

 Primary feed Flow rate kg / h 7.01 5.73

 Regenerate or

 Temperatures at ° C 112 108

 Feed

 Flow kg / h - 2.45

 Secondary ón Temperatur a ”C - 100

 Cast by train (21C / 21B)

 - 100/0 80/20

 Results

 Poor absorbent load

 mol C02 / mol absorbent 0.15 0.19

 Rich absorbent load

 mol C02 / mol absorbent 0.34 0.41

 Cyclic capacity

 mol C02 / mol absorbent 0.19 0.22

 C02 capture performance

 % 96 98

 Specific consumption of captured CO2

 GJ / t C02 4.55 4.05

5

10

fifteen

twenty

25

30

Example 2:

Different tests were performed in a laboratory assembly operating in semi-continuous regime to produce saturation of a known amount of the absorbent mixture proposed in this invention. For this, 250 ml_ of absorbent solution was placed in a reactor where 2 L / min of a gas stream of known composition was introduced until saturation. The test temperature was set at 50‘C. Upon completion of the test, the loading of the equilibrium absorbent mixture was determined, expressed in moles of C02 per mole of absorbent, using an inorganic carbon analyzer. Table 2 collects the results obtained for the tests carried out using absorbent mixture 1: comprising 1- (2-amino ethyl) -piperazine in 20% w / w, 2-amino-2-methyl-1-propanol in a 15% w / w and isoforondiamine in 1.5% w / w in aqueous solution and its comparison with the reference absorbent (MEA 30% w / w aqueous solution).

Table 2. Summary absorbent load in equilibrium at different concentrations of

C02 in gas phase

 Absorbent

 Test at 15% v / v C02 Test at 40% v / v co2

 Absorbent mixture 1

 0.889 0.955

 MEA 30% w / w

 0.535 0.584

The absorbent mixture 1 achieves up to 65% more loading capacity of C02 compared to the reference absorbent. In turn, the absorbent mixture has a high loading capacity, very close to 1 mol of CO2 per mol of absorbent in solution. In this way, the new absorbent mixture has a greater flexibility of operation and adaptation to the optimization system of the cyclic capacity of the absorbent (example 1).

Example 3:

From the tests described in example 2, it was possible to determine the absorption ratios measured in the gas phase for each of the tests performed. Figure 4 summarizes the results obtained in these tests, representing the evolution of the C02 absorption ratios obtained in the laboratory tests.

The absorption ratios increase significantly with an increase in the concentration of C02 in the gas phase. In addition, the absorbent mixture 1 has

5

10

fifteen

twenty

25

30

35

higher absorption rates of C02 than those obtained with the reference absorbent (30% w / w aqueous solution of MEA) for the same concentration of C02 in the gas phase, demonstrating a better kinetic behavior for an operation based on the system of optimization of the cyclic capacity of absorbent operation (example 1).

Example 4:

A process of separation of C02 from a stream of synthetic gas in a laboratory-scale unit was carried out based on an operation according to the optimization system of the cyclic capacity of the absorbent (example 1), using the absorbent mixture 1 and MEA 30 % w / w as reference absorbent. In the exemplary embodiment, a synthetic gas flow rate of 7 L / min was used, with a composition of 40% v / v C02, saturated in water and balanced with N2. The total amount of absorbent used in the system was 2 L. The absorption of C02 was performed at 1 atm and 50 "C on a column 3 cm in diameter and 2 m high using 6 mm Raschig ceramic rings.

The regeneration of the absorbent took place at 2 bar in a column 3 cm in diameter and 1 m high using a filling of 6 mm 316L stainless steel Raschig rings. The average operating temperature in the regeneration unit was 118 ° C for the MEA tests 30% w / w and 117 ° C for the absorbent mixture tests, operating according to the procedure for optimizing the cyclic capacity of the absorbent. The L / G ratio varied for each absorbent to reach a capture yield of 100%. Figure 5 shows the C02 capture yields obtained according to the L / G ratio used in each test.

The tests carried out demonstrate the greater absorption capacity and flexibility of operation of the absorbent mixture 1 with respect to the reference absorbent. The L / G ratios obtained are lower than those required by the reference absorbent for a defined C02 capture performance. In particular, the new absorbent system requires an L / G ratio of 7.3 while MEA 30% w / w requires an L / G ratio of 10 in the case of obtaining a C02 capture yield of 90% using a gas stream with a concentration of 40% v / v C02.

Example 5:

From the tests described in the previous example, the specific consumptions associated with the regeneration of the absorbent for each test performed have been obtained, modifying the L / G ratio. Figure 6 represents the evolution of this parameter for each test performed, using the two absorbers indicated above.

As demonstrated from the results indicated in Figure 6 and in table 3 (summary), the absorbent mixture 1 provides a lower energy consumption of the regeneration of the absorbent in an operation to optimize the cyclic capacity 10 of the absorbent operation . The absorbent mixture proposed in this invention manages to reduce energy consumption up to 24% compared to the reference absorbent.

Table 3. Summary of energy consumption and capture yields associated with it obtained in an operation to optimize the cyclic capacity of the absorbent (see example 1).

 Absorbent

 Ratio L / G Specific consumption (GJ / t C02) Capture yield {%)

 Absorbent mixture 1

 8 4.59 93.1

 MEA 30% w / w

 12 6.03 91.8

Claims (17)

5 10 fifteen twenty 25 1. Aqueous absorbent composition comprising: i. a saturated heterocyclic amine of general formula (I): image 1 I Ri (D where: X is selected from NR2 and CR3R4; R, and R2 are each independently selected from hydrogen, alkyl (CrC5), optionally substituted by an amine group; R3 and R4 are each independently selected from hydrogen and (C1-C5) alkyl; and n is 0 or 1; I. an amine with steric hindrance, iii. an organic diamine that is selected from isoforondamine or its derivatives selected from a compound of formula (Illa) or (lllb): image2 or (Illa) (lllb) where: Rt is hydrogen or a (Ci-C4) alkyl group, R2 and R3, each independently selected from hydrogen or an alkyl group (CrC4), each R4 is an alkyl group (CrC4), n is between 1 and 8, and m is between 1 and 9, and image3 5 10 fifteen twenty 25 30 35 iv. Water. 2. Composition according to claim 1, wherein the saturated heterocyclic amine is in a concentration of at least 1% w / w in solution, preferably in a concentration between 5% w / w and 50% w / w in solution. 3. A compound according to any one of claims 1 or 2, wherein the saturated heterocyclic amine is 1- (2-amino ethyl) -piperazine. 4. Composition according to any one of claims 1 to 3, wherein the steric hindered amine is in a concentration of at least 1% w / w in solution, preferably between 5% w / w and 50% w / w in solution . 5. Composition according to any one of claims 1 to 4, wherein the steric hindered amine is amine-2-methyl-1-propanol. 6. Composition according to any of claims 1 to 5, wherein the diamine is in a concentration of up to 5% w / w in solution. 7. Composition according to any one of claims 1 to 6, wherein the diamine is isophorondiamine. 8. Composition according to any one of claims 1 to 7, wherein the composition comprises 1- (2-amino ethyl) -piperazine, 2-amino-2-methyl-1-propanol and isophorondiamine. 9. Composition according to any one of claims 1 to 8, wherein the composition comprises 1- (2-amino ethyl) -piperazine in 20% w / w, 2-amino-2-methyl-1-propanol in 15% w / py isoforondiamine in 1.5% w / w, in aqueous solution. 10. Composition according to any one of claims 1 to 9, wherein it further comprises promoters for the adjustment of the kinetics of the absorption process, of adjuvant agents, anti-foaming agents, corrosion inhibitors and oxidative degradation inhibitors. 11. Method of separation of acid gases from a gas stream based on chemical absorption, comprising the following steps: a) absorption of acid gases from the gaseous stream to be treated at a temperature of between 40 ° C and 60 ° C and a pressure in a range of between 1 and 1.5 bar, by bringing into contact in an absorber of said stream with an absorbent solution in which the acid gases are to be retained, where the Absorbent solution is a composition described in any of the claims 1 to 10; b) recirculation to the absorber of up to 75% of the current comprising the absorbent solution rich in acid gas from step (a); c) desorption of the acid gas in a current regenerator comprising the 10 absorbent solution rich in CO2 from stage (a) not recirculated to the step (b) at a temperature of between 80 ° C and 120 ° C, a pressure of between 1.5 and 5 bar and a steam flow rate of between 10 and 90% by volume with respect to the flow of desorbed acid gas, where said current is divided into at least two currents by a train of heat exchangers, prior to the input of the regenerator; Y d) recovery of the absorbent solution resulting from step (c) ai absorber of step (a). 12. Method according to claim 11 wherein the acid gas of the stream The gas to be treated in step (a) is transferred to the liquid phase where it dissolves and It is chemically bound to the absorbent. 13. The method according to any of claims 11 or 12, wherein the recirculated flow rate of stage (b) reaches between 25% and 75% of the total solution 25 rich in acid gas from step (a). 14. The method according to any of claims 11 to 13, wherein the recirculation of the current from stage (b) takes place in the lower bed of the absorber of stage (a). 30 15. Method according to any of claims 11 to 14, wherein the currents from stage (c) are introduced into areas located at different heights of the regenerator of stage (d). A method according to any one of claims 11 to 15, wherein prior to step (c), the absorbent solution rich in acid gas from step (a) not recirculated to stage (b) is passed through a train of heat exchangers, which divides said current into at least two currents that are introduced into the regenerator of stage (c) into areas at different heights. 5. A method according to any of claims 11 to 16, wherein the gas acid comprises C02. 18. Use of the composition according to any of claims 1 to 10, for the absorption of acid gases. 10 19. Use according to the preceding claim, wherein the acid gas comprises C02.