EP2106283A2

EP2106283A2 - Method for separating gaseous co2 contained in a gas mixture

Info

Publication number: EP2106283A2
Application number: EP08761801A
Authority: EP
Inventors: Alain Seron; Fabian Delorme; Christain Fouillac
Original assignee: Bureau de Recherches Geologiques et Minieres BRGM
Current assignee: Bureau de Recherches Geologiques et Minieres BRGM
Priority date: 2007-01-24
Filing date: 2008-01-24
Publication date: 2009-10-07
Also published as: WO2008110676A2; JP2010516607A; AU2008225736A1; ZA200905077B; WO2008110676A3; BRPI0807440A2; CA2676345A1; CN101754793A; FR2911517B1; AU2008225736A8; RU2009128585A; US20100061917A1; FR2911517A1

Abstract

The invention relates to a method for separating the gaseous CO2 contained in a gas mixture, that comprises: the step of suspending in a liquid phase a solid absorbent capable of trapping the gaseous CO2; the step of dispersing the gas mixture into the liquid phase, said step being carried out at a temperature ranging from the liquid phase solidification temperature to the evaporation temperature, with the limits excluded, and under a pressure ranging from the atmospheric pressure to 10 bars, with the limits included.

Description

PROCESS FOR SEPARATING CO ₂ GAS FROM A MIXTURE

GAS

The present invention relates to a process for separating gaseous CO ₂ contained in a gas mixture.

The separation of gaseous CO ₂ contained in a gas mixture is of interest in many fields of application. In particular, we can mention the fight against global warming, an area for which greenhouse gas trapping is essential. We can still mention the purification of CO ₂ for its commercialization as well as the depollution of gaseous industrial discharges.

Various methods are known, whether these are of a physical or chemical type, making it possible to ensure the separation of CO ₂ from a gas mixture, in particular for trapping and / or purifying it. A widespread technique is based on the use of amines and more specifically on the use of the monoethanolamine solvent (see US-4,477,419). This method, interesting as it is, has drawbacks in terms of transport because of the nature of the solvent used. On the other hand, many impurities such as NO _x and SO _x degrade the amines thus decreasing the yield of the process.

It has also been proposed to use mineral traps whose ability to promote the physisorption or even the capillary condensation of gaseous CO ₂ in a suitable gas phase porosity (see Yong et al., Separation and Purification Technology 26 ( 2002) 195-205). These traps consist in particular of aluminas, zeolites, active carbons or hydrotalcite-type minerals. A problem of this technique is however to require the implementation of high pressures and high temperatures that are necessary for the realization of capillary condensation and desorption phenomena. A recent technique, antisublimation, in which the operation is carried out at atmospheric pressure by the direct passage of the vapor phase to the solid phase of CO ₂ on the outer surface of the refrigeration exchangers, has also been used. temperatures between -80 ^° C. and -110 ^° C. (see FR-2,820,052 and FR-2,851,936). This process also requires the implementation of significant energy.

It has also been proposed to cross the flow of gaseous mixture from which it is desired to separate some of the constituents through a membrane made of a material having a permeability which is a function of the component that it is desired to isolate during this passage.

(see Vallières and Favre, Journal of Membrane Science 244 issues 1-2 (2004) 17-23). It has been used to constitute such a membrane to many mineral and polymeric materials. This technique has the disadvantage of only allowing the effective treatment of low gas flows. US Pat. No. 2,823,765 discloses a process for separating gaseous mixture containing one or more gases that can be adsorbed by an adsorbent. This method comprises contacting the gas mixture with an adsorbent suspended in a liquid at high pressure. The adsorbent is incompatible with the liquid and is in particular activated carbon; carbon dioxide is mentioned as a gas to which the process can be applied.

Finally, the Applicant has proposed in patent FR 2,893,516 to separate and / or purify gases, some of which are capable of forming anionic species in the aqueous phase by HDL-type solids (Hydroxydes Double Lamellar) or mixed oxides from heat treatment of HDL.

The present invention aims to overcome the disadvantages of known techniques, by providing an efficient and low cost method for the separation of gaseous CO ₂ contained in a gaseous mixture.

To this end, the subject of the present invention is a process for separating gaseous CO ₂ contained in a gas mixture comprising: a step of suspending in a liquid phase an absorbent solid capable of capturing the gaseous CO ₂ , and

a step of dispersing the gas mixture in the liquid phase, said step being carried out at a temperature between the solidification temperature and the vaporization temperature of the liquid phase, excluding the limits, and at a pressure comprised between atmospheric pressure and 10 bars, terminals included.

The invention is based on the surprising finding, verified experimentally by the inventors, that, during the dispersion of a gas mixture in a liquid phase, the amount of CO ₂ trapped by an absorbent solid suspended in a liquid phase is much higher than that retained by the same solid in the gas phase. The process according to the invention is furthermore particularly advantageous in that it displays a high yield at ambient temperature and pressure conditions, or close to ambient conditions, and therefore is economically very advantageous. In a preferred manner, the dispersion of the solid is carried out: in an aqueous solution; for example pure water or a saline solution,

- in an alcohol; for example ethanol, propanol, ethylene glycol - or in a ketone; for example, acetone.

According to an advantageous characteristic of the invention, the dispersion of the gas mixture is carried out in the form of bubbles in the liquid. The finer the dispersion, the better the homogenization and the diffusion of the gases in the liquid.

Preferably, the dispersion step is carried out at a temperature of between 0 ^° C. and 30 ^° C. and at a pressure, inclusive, between atmospheric pressure (Patm) and 3 bars, more preferably between Patm and 1.5. bars, even more preferably between Patm and 1.2 bars (so with a slight overpressure). Advantageously, the dispersion is carried out at conditions of ambient temperature and pressure.

In particular, the absorbent solid is indifferently chosen from: a carbonaceous material, such as, for example, an activated carbon or carbon nanotubes; an oxide, for example silicates such as zeolites, clays, mesoporous silicas, manganese oxides, pumice, perlite or diatomite; phosphate or phosphonate; a hydroxide, such as for example Lamellar Double Hydroxides, such as a 3T quintinite or a hydrotalcite.

Advantageously, the process comprises an additional step of recovering the gaseous CO ₂ captured. The combination of the trapping and recovery steps allows CO ₂ purification.

This recovery step preferably comprises a step of lowering the partial pressure of the gas to be trapped introduced into the liquid phase, this step being obtainable either by lowering the partial pressure of CO ₂ (in particular by recirculation in the saturated reactor in CO ₂ , a gas stream depleted in CO ₂ , from a capture reactor in use) or by using a low vacuum at most equal to 0.2 bar with respect to the capture pressure or by stopping the circulation of the gas containing the CO ₂ . Recovery of captured CO ₂ can also be obtained by a step of raising the temperature of the liquid phase, preferably at most 30 ^° C. above the temperature at which the capture has been carried out, without bringing the liquid to boiling.

Finally, the process may comprise iteratively the cycle formed of a dispersing step of the gas mixture and a recovery step. The following will be described by way of nonlimiting example, various embodiments of the present invention, with reference to the accompanying drawing in which: Figure 1 is a diagram schematically showing the method according to the invention, - Figure 2 is a curve representing, as a function of time, the concentration of CO ₂ in the exit gas stream during capture and release phases by activated carbon,

FIG. 3 is a curve representing, as a function of time, the concentration of CO ₂ in the exit gas stream during capture and release phases by a material rich in zeolite, FIG. 4 is a curve representing, as a function of time, the concentration of CO ₂ in the exit gas stream during capture and release phases repeated iteratively by a quintinite 3T which is a hydroxide type material Double Lamellar (HDL),

FIG. 5 is a curve representing, as a function of time, the concentration of CO ₂ in the exit gas stream during capture phases by a calcium carbonate type material, and FIG. 6 is a curve representing in FIG. a function of time, the concentration of CO ₂ in the exit gas stream during capture phases by a diatomite type material.

According to the invention and as shown diagrammatically in FIG. 1, there is a mixture of several gases, one of which is CO ₂ that it is desired to extract from the mixture in order to trap it and, if appropriate, to subsequently return it under purified form.

For this, the method comprises a first step 2 in which an absorbent solid suitable for trapping CO ₂ is suspended in a liquid medium. It comprises a second step 4 in which the gaseous mixture is dispersed in the liquid medium. In practice, the liquid medium is placed in a reactor comprising an inlet for admitting the gas mixture and an outlet for extracting the uncaptured gas mixture after treatment or carbon dioxide after liberation.

The first two stages 2 and 4 make it possible to trap the CO ₂ contained in the gas mixture. In an advantageous embodiment, the method may comprise a third step 6 for recovering CO ₂ . The release of CO ₂ entrapped in the trap material can be obtained by reducing the CO ₂ partial pressure at the inlet of the reactor, and / or by raising the temperature of the solid suspension and / or or by lowering the total pressure in the capture reactor. In the case where it is desired to extract purified CO ₂ , it is essential to completely close the gas inlet of the reactor, the gas leaving the reactor then comprising only carbon dioxide.

In the context of an industrial process, the two steps 4 and 6 are repeated iteratively, as indicated by the arrow 8, by opening and closing the reactor gas inlet to produce at the outlet of the reactor, when the gas inlet is closed, pure CO ₂ .

Several examples of implementation of the method according to the invention will be described below.

EXAMPLE 1: Activated carbon

A capture and release test of CO ₂ from a stream of an N _{2 /} CO ₂ gas mixture was carried out by a trap formed of activated carbon suspended in an aqueous medium. The activated carbon used has a surface area of 1500 m ² / g

The initially introduced gas mixture had an initial CO _{2 content} of 19% by volume which was then raised to 76% by volume. The treatment was carried out at a temperature of 15 ° C and at atmospheric pressure.

The CO ₂ content in the reactor outlet mixture is shown in FIG. 2.

During a period between t0 (initial time) and t2, the CO ₂ content in the input gas mixture is 19% by volume. During this period, it is found that the CO ₂ content in the exit gas increases slowly from 0% at time t 0 to 19% until a time t 1, which indicates capture of CO ₂ by the trap, then stabilizes at 19% between t1 and t2, indicating that equilibrium is reached.

At time t2, the composition of the input gas mixture is modified by raising the CO ₂ content to 76% by volume up to a time t4. This modification of the CO ₂ content is carried out in the context of a laboratory test. In an industrial process, it is generally not possible to proceed with such a modification of the gas mixture. It can be seen that, as during the period t0-t2, the output CO ₂ content increases slowly between t2 and an instant t3, marking a capture of CO ₂ , and then stabilizes at 76% by volume from t3 when new balance is achieved. The volumes of CO ₂ captured at a CO ₂ content of 19 and 76% respectively represent 0.5 mole of CO ₂ / kg of activated carbon and 0.77 mole of CO ₂ / kg of activated carbon.

It is thus noted that the capture is even better than the partial pressure of CO ₂ in the gas mixture is important.

At time t4, we stop supplying CO ₂ into the reactor (nitrogen supply alone). At the outlet of the reactor, the liberation of the captured CO ₂ is observed until a time t5. The amount of gas released is of the order of 3.3 moles of CO ₂ / kg of activated carbon. This quantity is greater than that captured during the two capture phases. This is most likely due to the release of oxygenated groups present on the activated carbon surface prior to testing. When the temperature is raised to 60 ^° C., an additional release of 0.18 mol of residual CO ₂ / kg of activated carbon is observed (see period t5-t6). EXAMPLE 2 Zeolite

A similar test to the previous one was conducted by replacing the activated carbon with a zeolite-rich material whose specific surface area is close to 70 m ² / g. As can be seen in FIG. 3, the same type of curve is observed as in the previous test for the CO ₂ output content: tθ-t ₂ period: N _{2 /} CO ₂ mixture at 19% CO ₂ , reactor at 15 ° C; capture of CO ₂ until an equilibrium is reached; period t2-t4: mixture N _{2 /} CO ₂ at 76% CO ₂ , reactor at 15 ^° C. additional capture of CO ₂ until a new equilibrium is reached, period t4-t5: no CO ₂ input, reactor at 15 ^° C .; release of CO ₂ ,

- Period t5-T6: no CO _{2 supply} , reactor at 60 ⁰ C; additional release of CO ₂ .

In this example, the volumes of CO ₂ captured for CO ₂ levels of 19 and 76% were respectively 0.54 mol CO ₂ / kg of zeolite and 2.08 mol CO ₂ / kg of zeolite, an total amount of 2.62 moles of CO ₂ / kg of zeolite. At time t5, a release of 2.65 moles of CO ₂ / kg of zeolite is observed, which corresponds substantially to the portion collected. An additional release of 0.39 mole CO ₂ / kg of zeolite is observed when the reactor is heated to a temperature of 60 ^° C.

EXAMPLE 3: Quintinite 3T

The 3T quintinite is a material of the type Double Lamellar Hydroxide (HDL).

The test was carried out with an absorbent solid having a specific surface area of 80 m ² / g placed in aqueous suspension in a reactor at 30 ^° C. and under pressure. atmospheric. The input gas is an N _{2 /} CO ₂ mixture, the CO ₂ content being 9% by volume.

During the supply of the gas mixture (period t0-t1 in Figure 4), the CO ₂ is captured until a balance is reached. Under the conditions of the test, 0.49 mole

CO ₂ / kg of quintinite 3T is captured. Then, in the absence of CO ₂ input (period tl-t2 in Figure 4), the CO ₂ captured is released. A release of 0.49 mol

CO ₂ / kg of quintinite 3T, which corresponds to the captured part.

In this test, the capture step was repeated by feeding the reactor back with the gas mixture. There is a catch of 0.67 mole CO ₂ / kg of 3T quintinite.

An experiment was also carried out with the same adsorbent, with a temperature of 15 ^° C. and at atmospheric pressure. The input gas was a N 2 / CO 2 mixture, the CO 2 content being 16% by volume. A similar catch curve was observed with a capture rate of 7.8 moles CO ₂ / kg equilibrium adsorbent. EXAMPLE 4 PCC Calcium Carbonate

The test was carried out with a solid of precipitated calcium carbonate (PCC) type placed in aqueous suspension in a reactor at 15 ° C. and at atmospheric pressure. The input gas is a N ₂ / CO _{2 /} CO ₂ content in the initially being 16% by volume was then increased to 60%.

The measurement results are reported in FIG.

The volumes of CO ₂ captured represent respectively

1.07 and 1.21 moles of CO ₂ / kg carbonate, ie a total of 2.27 moles of CO ₂ captured per kg of carbonate.

As with other solids, it has been shown that lowering the CO ₂ partial pressure leads to a quantitative release of CO ₂ initially captured.

EXAMPLE 5 Diatomite

The test was carried out with a diatomite-type solid placed in an aqueous suspension in a reactor.

15 ° C and at atmospheric pressure. The input gas is a N ₂ / CO _{2 #} the CO ₂ content initially being 60% by volume.

The measurement results are reported in FIG. 6. The volume of CO ₂ captured represents 1.38 moles of CO ₂ per kg of diatomite. As for other solids, it has been shown that a lowering of the CO ₂ partial pressure leads to a quantitative release of the CO ₂ initially captured.

Thus, in the context of an industrial use of the process, it is found that by a succession of capture / release cycles, each cycle comprising a step of supplying a mixture of gases followed by a step without the addition of CO ₂ , even without the addition of a gas mixture, it is possible to extract CO ₂ from a gas mixture while purifying it.

In the tests described above, carried out in the laboratory, the nitrogen is continuously supplied to the reactor, this to better highlight in Figures 2 to 6 the decreasing CO _{2 content} at the outlet of the reactor, which reflects its release .

In the context of industrial use, the process may be exploited either to generate a pure CO ₂ stream or to generate a gas stream enriched in CO ₂ . If a stream of pure CO ₂ is sought, the release of the captured gas will be obtained by raising the temperature at most equal to 30 ^° C. or lowering the pressure, the supply of the initial gas mixture having been interrupted. If a gaseous stream enriched in CO ₂ is sought, while the circulation of the gaseous mixture to be treated is maintained, an increase in the temperature of the suspension at most equal to 30 ⁰ C will be sufficient to release the CO ₂ initially captured.

Among the various absorbents that can be used in the process according to the invention, the Double Lamellar Hydroxydes (HDL) are particularly effective. In addition to the examples of the quintinite 3T and the hydrotalcite, one skilled in the art can advantageously refer to the patent FR 2882549 which describes other examples of HDL and a method of synthesizing such materials.

The process according to the invention is therefore particularly interesting from an industrial point of view. Indeed, it allows the trapping of CO ₂ reversibly without implementing energy-intensive processes

(High temperature rise, evaporation of a liquid phase, solid / liquid separation, ...) and without any manipulation of the suspension constituting the trap which remains in place in the capture / release reactor for the duration of the cycles. Moreover, the process is carried out under conditions of ambient pressure and temperature or near ambient conditions, a slightly higher temperature favoring the release of CO ₂ .

Claims

1. A process for separating gaseous CO ₂ contained in a gas mixture comprising: a step of suspending in a liquid phase an absorbent solid capable of capturing gaseous CO ₂ , a step of dispersing the gas mixture in the liquid phase, said step being carried out at a temperature between the solidification temperature and the vaporization temperature of the liquid phase, limits excluded, and at a pressure between atmospheric pressure and 10 bars, inclusive.

2. A process according to claim 1, wherein the dispersing step is carried out at a temperature between 0 ⁰ C and 30 ⁰ C.

3.- Method according to one of claims 1 or 2, wherein the absorbent solid is indifferently chosen from: a carbon material, such as an activated carbon or carbon nanotubes; an oxide, for example silicates such as zeolites, clays, mesoporous silicas, manganese oxides, pumice, perlite or diatomite; phosphate or phosphonate; a hydroxide, such as for example Lamellar Double Hydroxides, such as 3T quintinite or hydrotalcite.

4. A process according to one of claims 1 to 3, comprising an additional step of recovering gaseous CO ₂ captured.

5. A process according to claim 4, wherein said recovery step comprises a step of lowering the partial pressure of the gas to be trapped. introduced into the liquid phase and / or the depression of the capture reactor.

6. Method according to one of claims 4 or 5, wherein said recovery step comprises a step of raising the temperature of the liquid phase.

7. A process according to claim 4, wherein it is repeated iteratively the cycle formed of a dispersion step and a recovery step.