DE102015004342A1 - Method for absorbing CO2 from a gas mixture - Google Patents

Abstract

The invention relates to a method for the absorption of CO2 from gas mixtures, which can be used in particular in the treatment of biogas to biogas, but also for example in the treatment of combustion gases or other CO2-containing gas mixtures. The invention has for its object to find physically selective absorption media for the separation of CO2 from biogas or flue gases, which have a high CO2 absorption capacity, do not require low temperature levels for the absorption of CO2 and are not toxic. The technical object is achieved in that Isopropylidenglycerin (4-hydroxymethyl-2,2-dimethyl-1,3-dioxolane) and / or glycerol formal (4-hydroxymethyl-1,3-dioxolane) and / or glycerol carbonate (4-hydroxymethyl 1,3-dioxolan-2-one) are used as absorption medium in the absorption process.

Description

The invention relates to a process for the absorption of CO ₂ from gas mixtures, which can find application especially in the treatment of biogas to biogas, but also, for example, in the treatment of combustion gases or other CO ₂ -containing gas mixtures.

The absorptive separation of CO ₂ from CO ₂ -containing gas streams such as biogas, natural gas or combustion gases of fossil energy production is done so far either by chemical absorption or by physical absorption. On an industrial scale, aqueous solutions of alkanolamines are usually used as the absorption medium for chemical absorption. The loaded absorption medium is regenerated by heating, depressurization to a lower pressure or by stripping, whereby the CO _{2 is} desorbed. After the regeneration process, the absorption medium is recirculated. These methods are in Rolke, J .; Arlt, W .: "Separation of carbon dioxide from flue gases by absorption" in Chemie Ingenieur Technik 2006, 78, p. 416 ff as in Cabbage, AL; Nielsen, RB: "Gas Purification", 5th ed., Gulf Publishing, Housten 1997 described. In contrast to purely physical absorption, the CO ₂ reacts with the absorption medium during chemical absorption and thus binds reversibly. Although this significantly increases the selectivity and the capacity of the solvent compared with the physisorption, the chemical compound must, however, be dissolved again in the regeneration step. The CO _{2 is} expelled from the loaded solvent by evaporation. The energy required for this desorption step is very high.

The physical CO ₂ absorption preferably proceeds at elevated pressure. This increases the absorption capacity of the CO ₂ solvent. In Table 1, industrially relevant physical absorption processes for CO ₂ separation, as in Cabbage, AL; Nielsen, RB: "Gas Purification", 5th ed., Gulf Publishing, Housten 1997 described, compiled. The absorbents used in the physical absorption of CO ₂ generally have a lower capacity and selectivity than chemically acting absorbents.

Disadvantages of the absorption processes are environmental effects due to solvent losses as a result of the required high vapor pressures of the partly toxic solvents. Furthermore, partly low temperature levels below the ambient temperature are necessary for the absorption of the CO ₂ , which requires a high energy input. Table 1: Industrial solvents for physical CO ₂ absorption process name Used absorbent Water scrubbing water Fluorine solvent propylene carbonate selexol Mixture dimethyl ether / polyethylene glycol Purisol N-methyl-2-2-pyrrolidone (NMO) Rectisol® methanol Sepasolv MPE MPE (mixture of glycol ethers) Estasolvan Tri-n-bytylphosphat

The invention has for its object to find physically selective absorption media for the separation of CO ₂ from biogas or flue gases, which have a high CO ₂ uptake capacity, do not require low temperature levels for the absorption of CO ₂ and are not toxic.

The technical object is achieved in that Isopropylidenglycerin (4-hydroxymethyl-2,2-dimethyl-1,3-dioxolane) and / or glycerol formal (4-hydroxymethyl-1,3-dioxolane) and / or glycerol carbonate (4-hydroxymethyl 1,3-dioxolan-2-one) are used as absorption medium in the absorption process. The absorption medium is contacted in cocurrent or countercurrent, and preferably at elevated pressure, with the CO ₂ -containing gas stream in a process contact apparatus such as columns, flash tanks, membrane contactors or similar apparatus. By means of suitable surface-enlarging internals (packing or packings, as well as trays), the mass, energy and momentum transport is intensified, so that, due to a driving potential gradient, the CO ₂ passes into the receiving liquid phase. The absorbent according to the invention has the intrinsic property, much CO ₂ and to be able to take up little CH ₄ . In addition, the gases dissolve quickly in the absorbent, which has small dimensions of the contact apparatus used for the absorption result. The absorbent according to the invention has a low vapor pressure, which, inter alia, given a very good regeneration and the solvent loss in the circulation process is low. The absorbent is environmentally friendly as it consists of non-toxic, non-corrosive biogenic solvents.

embodiment

The solubility of CO ₂ and CH ₄ in the solvents isopropylidene glycerol, glycerol formal and glycerol carbonate were measured experimentally at 25 ° C and described on the basis of the meaningful for the gas solution Henry coefficients. Comparisons with the commercially used propylene carbonate show that the selectivity but also the capacity of the investigated solvents, in particular for the glycerol formal is comparable. The experimental results are set forth in Table 2.

The pressure and temperature range to be set for the absorption and desorption with these solvents largely corresponds to those of pressurized water washing, an industrially used process for biogas treatment in which water is used as solvent. Table 2: Physical properties of the investigated solvents solvent Henry coefficient CO ₂ [bar] Henry coefficient CH ₄ [bar] selectivity isopropylidene 67 741 11 glycerol 112 2174 19 glycerol 208 No data - propylene carbonate 76 1864 25

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• Rolke, J .; Arlt, W .: "Separation of carbon dioxide from flue gases by means of absorption" in Chemie Ingenieur Technik 2006, 78, p. 416 ff [0002]
• Cabbage, AL; Nielsen, RB: "Gas Purification", 5th ed., Gulf Publishing, Housten 1997 [0002]
• Cabbage, AL; Nielsen, RB: "Gas Purification", 5th ed., Gulf Publishing, Housten 1997 [0003]

Claims (1)

Process for absorbing CO ₂ from a gas mixture by contacting the gas mixture with an absorption medium, characterized in that isopropylideneglycerol (4 hydroxymethyl-2,2-dimethyl-1,3-dioxolane) and / or glycerol formal (4 hydroxymethyl) is used as the absorption medium. 1,3-dioxolane) and / or glycerol carbonate (4-hydroxymethyl-1,3-dioxolan-2-one).