DE102011079811A1 - Separation of carbon dioxide - Google Patents

Abstract

The invention relates to a method for separating carbon dioxide, which is carried out with the aid of polyvinylpyrrolidone, PVP, and / or a derivative thereof. A carbon dioxide separator (1) has a process vessel (4) filled with an aqueous PVP solution (3), which has an inlet (5) for carbon dioxide-containing medium (6), and a regeneration device (7) for regenerating the carbon dioxide storage material. The invention also relates to a power generation plant (2) with such a carbon dioxide separator (1). The invention can be used in particular for a combustion plant for carbonaceous energy sources, in particular for gas, oil or coal power plants.

Description

The invention relates to a method for separating or fixing carbon dioxide (CO ₂ ). The invention also relates to a use of the method for power generation plants. The invention further relates to a carbon dioxide separator and a power generation plant with a carbon dioxide separator. The invention can be used in particular for separating carbon dioxide originating from a combustion of carbonaceous energy carriers, in particular for gas, oil or coal power plants.

Forty percent of global energy needs are currently met by the burning of coal. A corresponding percentage of the anthropogenic carbon dioxide input into the atmosphere is currently from coal-fired power plants, and the concentration of the greenhouse gas carbon dioxide has increased with concern from 1958 with 315 ppm to 390 ppm in 2007. For a secure energy supply and a further increase in global energy consumption, the share of coal in the energy mix will remain at almost the same level over the next decades.

However, in order to reduce carbon dioxide emissions, technologies for the capture and storage of carbon dioxide from combustion gases are used, in particular by coal-fired power plants. With the help of current carbon capture and storage technologies (e.g., CCS, "Carbon Capture and Storage"), carbon dioxide emissions from combustion gases from coal power plants can be reduced by 85 to 95%. For this purpose, aqueous media of amino acid salts, amines, alkanolamines and ammonia are used. These media are highly alkaline (pH> 10), often not sufficiently resistant to oxidation, have a strong corrosive effect and are energy-intensive due to carbamate formation and high desorption energies. In addition, the equipment required by additional washing processes to minimize emissions of conditionally combustible ammonia is high. Also, cooling in the carbon dioxide absorption to a range between 2 ° C and 10 ° C in the so-called "chilled ammonia process" increases the costs by additional investment and further deteriorates the efficiency of the CCS concepts.

It is the object of the present invention to overcome the disadvantages of the prior art, at least in part, and in particular to provide a way to deposit or fix carbon dioxide with an improved energy balance.

This object is achieved according to the features of the independent claims. Preferred embodiments are in particular the dependent claims.

The object is achieved by a method for separating carbon dioxide, wherein the deposition by means of polyvinylpyrrolidone (hereinafter abbreviated as PVP), and / or a derivative thereof is performed.

The polymer polyvinylpyrrolidone finds versatile applications in the pharmaceutical, cosmetic, detergent, textile, food and beverage industries. Due to its polar structure, it dissolves well in polar organic solvents such as propylene glycol, in monohydric and polyhydric alcohols, e.g. also in higher boiling polyethylene glycol 400 and water. PVP is toxicologically harmless. Aqueous PVP solutions have a pH around 4, are slightly acidic and stable over a wide pH range. It is also noteworthy that the viscosity of PVP is almost independent of electrolytic contaminants. Furthermore, PVP is chemically as well as biologically inert and acts in aqueous solution via carbonyl functions of its lactam structural unit as a complexing agent in H donors, such as phenols. In particular, this property as a complexing agent in H donors can cause a CO2 bond through the polyvinylpyrrolidone and thus deposition. The deposition of carbon dioxide from a starting medium may correspond analogously to a fixation or binding of carbon dioxide with the aid of polyvinylpyrrolidone (or a derivative thereof).

• 1) CO₂ (gasförmig) ⇔ CO₂ (H₂O)
• 2) CO₂ (H₂O) + H₂O ⇔ H₂CO₃ (langsam)
• 3) H₂CO₃ ⇔ HCO₃ ^– + H⁺ (Bicarbonatbildung, schnell, pH < 8)
• 4) HCO₃ ^– ⇔ CO₃ ^2– + H⁺ (schnell, pH > 10)

It is an embodiment that carbon dioxide is bound in an aqueous PVP solution. This can be effectively mixed with carbon dioxide and provides a particularly high absorption capacity for carbon dioxide. When water or the aqueous solution is mixed with the carbon dioxide, the following equilibrium reactions 1 to 4 apply:

• 1) CO ₂ (gaseous) ⇔ CO ₂ (H ₂ O)
• 2) CO ₂ (H ₂ O) + H ₂ O ⇔ H ₂ CO ₃ (slow)
• 3) H ₂ CO ₃ ⇔ HCO ₃ ^- + H ⁺ (bicarbonate formation, fast, pH <8)
• 4) HCO ₃ ^- ⇔ CO ₃ ^2- + H ⁺ (fast, pH> 10)

As a result of the complex formation of the H ions at the C = O functions of adjacent pyrrolidone units, the equilibrium system according to reaction 3) is shifted to the left side during bicarbonate formation, so that more CO _{2 is} extracted from the combustion exhaust gases and through the polyvinylpyrrolidone or the aqueous solution is bound. The lone pair of electrons on the nitrogen atom of the polyvinylpyrrolidone can nucleophilically attack the electrophilic carbon atom in the carbon dioxide and thus continue to contribute to carbon dioxide fixation. Technologically and energetically, it is particularly advantageous that no carbamate formation takes place.

The aqueous polyvinylpyrrolidone (washing solution) can be regenerated following, in particular, e.g. by desorption in a regeneration device, e.g. in a stripper. The displacement may be accomplished, for example, by direct introduction of carbon dioxide into the aqueous PVP solution or e.g. by spraying a carbon dioxide-containing gas with the PVP solution (e.g., in a spray tower). In particular, it is of advantage in this case that the viscosity of PVP is virtually independent of electrolytic impurities, since this allows a particularly simple handling and effective deposition during a deposition process.

It is still an embodiment that the aqueous PVP solution is acidic, in particular has a pH of about 4. Because it has been shown that the binding ability of an aqueous PVP solution depends on its pH and is provided with an acidic solution, a particularly high absorption capacity for carbon dioxide. In contrast, at least for a 20 percent aqueous polymer solution based on polyvinylpyrrolidone "PVP 40" from Sigma Aldrich (having a molecular weight of 40000 g / mol average) for a pH of 7, a lower carbon dioxide uptake capacity than for a pH of 4.

It is still another embodiment that the aqueous PVP solution has a proportion of PVP between 5 percent by weight (wt .-%) and 50 weight percent, in particular between about 5 weight percent and about 25 weight percent, in particular of about 20 weight percent. In particular, these proportions provide a high absorption capacity for carbon dioxide at a low viscosity at the same time. The low viscosity is particularly advantageous for spraying the PVP solution.

It is also an embodiment that the PVP has a molecular weight between 2,000 and 2.5 million g / mol, in particular between 40,000 g / mol and 360,000 g / mol.

Another embodiment is that the carbon dioxide separation at (working) temperatures of the PVP solution in a range up to about 80 ° C, in particular of about 80 ° C, is performed. In other words, it is preferred that the PVP solution has a working temperature of up to about 80 ° C. This makes it possible for the carbon dioxide-to-be-cleaned, typically hot gas, in particular carbon dioxide-containing exhaust gas, to be cooled down less.

This allows a more energy-efficient operation. However, the method is not limited to this temperature range.

If the process is to be carried out at an even higher working temperature, it is advantageous to use a PVP solution with a mixture of water and glycol ether as the solvent. Here, a ratio of water to glycol ether of 10: 1 to 2: 1 is preferred. However, such a mixture can also be used at working temperatures of 80 ° C and less.

The object is also achieved by using the method for separating carbon dioxide from energy production plants, in particular incinerators for fossil fuels, in particular gas, oil or coal power plants.

The object is also achieved by a carbon dioxide separator, comprising a filled with carbon dioxide storage material process vessel having an inlet for carbon dioxide-containing medium (in particular gas), and in particular a regeneration means for regenerating the carbon dioxide storage material, wherein the carbon dioxide storage material polyvinylpyrrolidone and / or a derivative thereof in particular an aqueous PVP solution. Thereby, the same advantages are achieved as by the method, and the carbon dioxide separator can also be configured the same. The process vessel may be, for example, a spray tower. The regeneration device may, for example, have a stripper.

The object is also achieved by a power generation plant with a carbon dioxide separator, wherein the carbon dioxide is a carbon dioxide separator as described above. In particular, the power generation plant may be a combustion plant for carbonaceous energy carriers, in particular gas, oil or coal power plants.

The above-described characteristics, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more clearly understood in connection with the following schematic description of an embodiment which will be described in detail in conjunction with the drawings. In this case, the same or equivalent elements may be provided with the same reference numerals for clarity.

The figure shows sketchy and greatly simplified a carbon dioxide 1 a power plant in the form of a coal power plant 2 ,

The carbon dioxide separator 1 indicates an aqueous solution of PVP 3 filled or pressurized process vessel in the form of a spray tower 4 on. The spray tower 4 has an inlet 5 for carbon dioxide-containing medium, for example, for purified and cooled exhaust gases 6 a combustion chamber of the coal power plant 2 , In the spray tower 4 becomes the exhaust 6 with the aqueous PVP solution 3 sprayed, taking the aqueous PVP solution 3 Carbon dioxide binds.

To regenerate the polyvinylpyrrolidone, the carbon dioxide separator comprises 1 one with a catchment area of the spray tower 4 in which the aqueous PVP solution 3 collects, fluidly connected regeneration device with a stripper 7 in which the carbon dioxide is recovered from the aqueous PVP solution 3 is discharged, in particular desorbed, is. The thus recycled aqueous PVP solution 3 Following is back in the spray tower 4 directed and sprayed there.

Especially for the spraying method is an aqueous PVP solution 3 with a proportion of PVP between 5 percent by weight and 25 percent by weight, in particular of about 20 percent by weight, is preferred, since this results in a high absorption capacity for carbon dioxide with a simultaneously low viscosity. A high absorption capacity is also achieved by a pH of about 4 of the aqueous PVP solution 3, wherein the PVP has a molecular weight between 40,000 g / mol and 360,000 g / mol.

While the invention has been further illustrated and described in detail by the illustrated embodiment, the invention is not so limited and other variations can be derived therefrom by those skilled in the art without departing from the scope of the invention.

Thus, instead of or in addition to polyvinylpyrrolidone, a suitable derivative thereof may also be used.

Claims (10)

A method for separating carbon dioxide, characterized in that the deposition is carried out with the aid of polyvinylpyrrolidone, PVP, and / or a derivative thereof. Process according to claim 1, wherein carbon dioxide in an aqueous PVP solution ( 3 ) is bound. Process according to claim 2, wherein the aqueous PVP solution ( 3 ) is acidic, in particular has a pH of less than 7, in particular of about 4. Method according to one of claims 2 or 3, wherein the aqueous PVP solution ( 3 ) has a content of PVP between 5% by weight and 50% by weight, in particular of about 20% by weight. A process according to any one of the preceding claims, wherein the PVP has a molecular weight between 2,000 and 2.5 million g / mol, in particular between 40,000 g / mol and 360,000 g / mol. Method according to one of the preceding claims, wherein the PVP solution has a working temperature of up to about 80 ° C. Method according to one of claims 1 to 5, wherein the PVP solution has a working temperature of about about 80 ° C and having as solvent a mixture of water and glycol ether, in particular in a ratio between 2: 1 and 10: 1. Use of the method for separating carbon dioxide from energy production plants ( 2 ). Carbon dioxide separator ( 1 ), comprising - a process vessel filled with carbon dioxide storage material ( 4 ), which has an inlet ( 5 ) for carbon dioxide-containing medium ( 6 ), and - a regeneration device ( 7 ) for regenerating the carbon dioxide storage material, characterized in that - the carbon dioxide storage material comprises polyvinylpyrrolidone and / or a derivative thereof, in particular an aqueous PVP solution ( 3 ). Power generation plant ( 2 ) with a carbon dioxide separator, characterized in that the carbon dioxide separator is a carbon dioxide separator ( 1 ) according to claim 9.

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