DE102010008846A1 - Absorbent, useful for absorption of acid gases e.g. carbon dioxide, from a fluid stream, comprises 2-(2-aminoethoxy)ethanol, an activator comprising e.g. 2-aminoethanol, and an additive comprising sucrose and/or magnesium carbonate - Google Patents

Abstract

Absorbent, where the absorbent is an aqueous solution, comprises 5-65 wt.% of 2-(2-aminoethoxy)ethanol, 0.001-20 wt.% of an activator comprising 2-aminoethanol and/or piperazine, and 0-20 wt.% of an additive comprising sucrose and/or magnesium carbonate. An independent claim is included for deacidifying a fluid stream containing the acid gases as impurities, comprising (a) contacting the fluid stream with the absorbent in at least one absorption step, where the absorbent loaded with acid gases and a purified fluid stream are formed, and (b) separating the fluid stream purified by acid gases and absorbent loaded with acid gases from one another.

Description

The present invention relates to an absorbent for deacidifying a fluid stream containing acid gases as an impurity, in particular a smoke or reaction gas stream containing carbon dioxide. Furthermore, the invention relates to a method for deacidifying a fluid stream containing acid gases as an impurity, wherein the absorbent according to the invention is used.

In many industrial processes, for example in the chemical industry or in power generation, fluid flows occur which contain acid gases such as CO ₂ , H ₂ S, SO ₂ , CS ₂ , HCN, COS or mercaptans as impurities. These fluid streams can be, for example, gas streams such as natural gas, synthesis gas, refinery gas, flue gases or reaction gases formed during the composting of organic substances containing waste materials. For example, flue gases are produced by burning coal, oil, natural gas or organic waste.

The removal of acid gases is of particular importance for a variety of reasons. For example, it is desirable to purify the reaction and flue gases of acid gases resulting from the oxidation of organic materials, such as organic wastes, coal, natural gas, or petroleum, or in the composting of organic substances, to reduce the emission of gases that damage the environment Climate can prevent, prevent. When extracting natural gas, the content of sulfur compounds must be reduced by suitable treatment measures directly at the source of natural gas, because the sulfur compounds in the water, which is often contained in natural gas, form acids which have a corrosive effect on the transport pipelines. In a similar manner, carbon dioxide, in conjunction with water frequently carried in fluid streams, can result in corrosion of pipes and fittings.

Numerous methods have already been developed for removing sour gas constituents from fluid streams. In the most widely used process, the acid mixture containing the acid gases is brought into contact with an organic solvent or an aqueous solution of an organic solvent in a so-called gas scrubbing or a liquid / liquid extraction.

Basically, you can distinguish between two different types of absorption or solvents in gas scrubbing:
On the one hand, so-called physical solvents are used in which, after absorption, the dissolved acid gases are present in molecular form.

On the other hand, chemical solvents are used whose mode of action is based on chemical reactions in which, after absorption, the dissolved acid gases are present in the form of chemical compounds. For example, the acid gases are dissolved as ions in the aqueous solutions of inorganic bases (eg potassium carbonate in the Benfield process), which are used most frequently on an industrial scale as chemical solvents, or organic bases (eg alkanolamines). This step is called an absorption step and may consist of several substeps.

The solvent loaded with acid gases can then be regenerated in a further step, for example by depressurization to a lower pressure or stripping, the ionic species reacting back to acid gases and / or stripped off by means of steam. This step is also called a desorption step. After the regeneration process, the solvent can be reused.

For the economics of such purification processes, it is important that the absorbent per unit volume under the conditions of the absorption step can absorb the largest possible amount of acid gas. Since during regeneration, depending on the absorbent and regeneration conditions, a different residual amount of sour gas remains in the absorbent, this value can sometimes be significantly different from the amount of gas that can be absorbed by an absorbent that is completely free of acid gases.

Of further importance is the speed with which the acid gases contained in the fluid stream are absorbed by the absorbent.

Furthermore, the corrosivity of the absorbent over the steels commonly used in the apparatus industry is problematic, so it is desirable to use an absorbent with the least possible corrosivity to steels.

In addition, the rate of degradation of the absorbent used also plays an essential role. It is desirable to use an absorbent which has the lowest possible rate of degradation.

For the removal of sour gas impurities in fluid streams, especially organic bases, and in particular alkanolamines, are used today. Commonly used alkanolamines include, for example, monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), Diethylethanolamine (DEEA), diisopropylamine (DIPA), aminoethoxyethanol (AEE) and methyldiethanolamine (MDEA).

Primary and secondary alkanolamines are particularly suitable for gas scrubbing in which the purified gas must have a very low CO ₂ content (eg 10 ppm _V CO ₂ ). The absorption of the carbon dioxide is carried out by direct reaction of the nitrogen of the primary and secondary alkanolamines to form soluble carbamate. In the aqueous amine solution, the carbamate is in equilibrium with bicarbonate. For regeneration of the amine solution, a two-stage regeneration process is often used in industrial applications, wherein the loaded solvent is first expanded in one or more flash columns, so that a portion of the absorbed CO ₂ evaporates from the solution. Residual carbon dioxide and possibly other absorbed acid gases are then removed by stripping with steam. Solvents containing primary and secondary alkanolamines, however, require more regeneration effort because decomposition of the carbamate requires a greater amount of vapor than tertiary amines and therefore correspondingly much heat energy.

Unlike primary and secondary alkanolamines, tertiary alkanolamines do not react directly with carbon dioxide since the amine is fully substituted. Rather, carbon dioxide is reacted with the tertiary alkanolamine and with water to bicarbonate in a low reaction rate reaction. Since there is no direct bond between tertiary alkanolamines and carbon dioxide, the amine solution can be regenerated very economically. In many cases, a flash regeneration with one or more relaxation levels is sufficient. An optional additional thermal regeneration requires much less energy than in the case of solutions of primary or secondary alkanolamines. A disadvantage of the use of tertiary alkanolamines, however, is that because of the lower reaction rate of the carbon dioxide, the washing process must be carried out with a very high residence time. The required absorption and desorption columns are therefore very high compared to systems where either primary or secondary alkanolamines are used.

Object of the present invention is therefore to provide an improved absorbent for deacidifying a fluid stream containing acid gases as impurities by gas scrubbing, wherein acid gases, in particular CO ₂ , can be effectively removed from the fluid stream. In addition, it is also an object of the present invention to provide an improved process for deacidifying a fluid stream containing acid gases as impurities, in particular for deacidifying a flue gas stream as it z. B. arises in the combustion of coal, oil or natural gas in power plants for power generation.

This object is achieved by the absorbent according to the present claim 1 and the method according to the present claim 5.

The present invention therefore provides an absorbent for deacidifying a fluid stream containing acid gases such as CO ₂ , H ₂ S, COS, CS ₂ , mercaptans, SO ₃ , SO ₂ , hydrogen halide, HCN or mixtures thereof as impurities, wherein the absorbent an aqueous solution containing, based on the absorbent, 5-65% by weight of an alkanolamine, namely 2- (2-aminoethoxy) ethanol (AEE), 0.001-20% by weight of an activator selected from 2-aminoethanol ( MEA), piperazine and mixtures thereof, and 0-20 wt .-% of an additive selected from sucrose, magnesium carbonate and mixtures thereof.

In one embodiment, the residual component of the absorbent (ad 100% by weight) is water. The water may in particular be deionized water.

In one embodiment, the concentration of 2- (2-aminoethoxy) ethanol (AEE) based on the absorbent is 15-65 wt%, 40-65 wt% or about 50 wt%.

The sum of the concentrations of all activators contained in the absorbent selected from 2-aminoethanol (MEA) and / or piperazine is, based on the absorbent, 0.1-15% by weight or 0.4-7% by weight. -%. In this case, the absorbent according to the invention 2-aminoethanol and piperazine in any mixing ratio, d. H. 0-100 wt .-% piperazine and 0-100 wt .-% 2-aminoethanol (MEA) based on the total amount of the activator. In certain embodiments of the invention, the proportion of piperazine in the total amount of activator is 20-80, 30-70 or 40-60% by weight.

In one embodiment of the invention, the absorbent contains 2-6% by weight of piperazine. In another embodiment, the absorbent contains 2-6% by weight of 2-aminoethanol.

In a further preferred embodiment, the absorbent of the invention contains an activator selected from sucrose and magnesium carbonate or mixtures thereof, said activator being in an amount of 0.001-20% by weight, based on the absorbent, of 0.1 -15 wt .-% or 0.4-7 wt .-% is included.

In certain embodiments of the invention, the absorbent may contain other customary auxiliaries and additives. These are known to the person skilled in the art.

The above information refers to the ready-to-use washing liquid, d. H. the absorbent according to the invention. The absorbent of the invention is usually prepared as a concentrate, which is diluted by the user by the addition of water to the final concentration.

The absorbent of the present invention can be used to deacidify a fluid stream, preferably a gas stream, more preferably a flue gas stream, most preferably for CO ₂ scrubbing a flue gas stream.

• (a) der Fluidstrom in mindestens einem Absorptionsschritt mit einem Absorptionsmittel der Erfindung in Kontakt gebracht wird, wobei ein mit Sauergasen beladenes Absorptionsmittel und ein gereinigter Fluidstrom entsteht; und
• (b) der von Sauergasen gereinigte Fluidstrom und das mit Sauergasen beladene Absorptionsmittel voneinander getrennt werden.

In another aspect, the present invention relates to a process for deacidifying a fluid stream containing acid gases as impurities, characterized in that

• (a) contacting the fluid stream in at least one absorption step with an absorbent of the invention to form an acid gas laden absorbent and a purified fluid stream; and
• (B) the sour gas-cleaned fluid stream and the acid gas-laden absorbent are separated from each other.

In one embodiment of the process, in a further step (c), the adsorbed acid laden in step b) is regenerated and then brought into contact again with the fluid stream in step (a).

In a further embodiment of the method, the absorption step is carried out in a plurality of successive substeps, wherein the acid gas-containing fluid stream in each of the substeps is brought into contact with a respective partial stream of the absorbent. In this case, the partial streams of the absorbent can be obtained after each successive substeps of the regeneration process of the absorbent, so that the partial streams of the absorbent have a decreasing load of acid gases.

In a particular embodiment of the invention, the fluid stream which is freed from acid gases is a gas stream, in particular a stream of reaction or flue gas, which is formed by the oxidation of gas, coal, petroleum or organic waste. This oxidation may be, for example, the combustion of gas, coal, petroleum or organic waste. In a particular embodiment, this gas stream is flue gas from a coal, oil or gas power plant.

As already mentioned above, the absorbent according to the invention or process according to the invention is suitable for removing acid gases from fluid streams which are acid gases CO ₂ , H ₂ S, COS, mercaptans, SO ₃ , SO ₂ , CS ₂ , hydrogen halide, HCN, or mixtures contain the aforementioned sour gases. In one embodiment of the invention, the acid gas removed from the fluid stream essentially comprises, ie, at least about 80-90% by volume, based on the total amount of sour gases, of carbon dioxide.

The content of CO ₂ in the fluid stream is generally 0.5-99 vol .-%, in the case of flue gas about 80-99 vol .-%.

The absorbent according to the invention also allows a substantial removal of sulfur-containing gases from the gas stream.

The process according to the invention can be carried out using the customary washing devices used in gas scrubbing. Suitable washing devices which ensure intimate contact between the fluid stream and the washing liquid in an absorption zone are, for example, packed, packed and tray columns, radial flow scrubbers, jet scrubbers, venturi scrubbers and rotary scrubbers, preferably packed, packed and tray columns.

As already mentioned above, the method according to the invention can be carried out in one step or in several successive substeps. In the latter case, the fluid stream containing the acid gas components is brought into contact with a partial stream of the absorbent in each partial step. For example, at different locations of the absorption zone, i. H. of the region in which the fluid stream is brought into contact with the absorbent, a partial stream of the absorbent can be supplied.

The absorbent laden with acid gas components and the purified gas are separated from each other and discharged from the absorption zone. The absorbent can then be regenerated and subsequently returned to the absorption zone with reduced loading. Typically, during regeneration, a pressure release of the loaded absorption solution is carried out from a higher pressure prevailing in the absorption zone to a lower pressure. Pressure release can be done for example by means of a throttle valve. Additionally or alternatively, the absorbent can be passed through an expansion turbine, with a Generator powered and electrical energy can be recovered. The energy thus removed from the absorbent during the relaxation can also be used, for example, to drive liquid pumps in the circulation of the absorbent.

The release of the acidic gas constituents can be carried out during regeneration of the absorbent, for example in a flash column, for example a vertically or horizontally installed flash tank and a countercurrent column with internals. Several relaxation columns can be connected in series, in which, at different pressures, is regenerated.

With the help of a preferably also provided stripping with an inert fluid further sour gases can be removed from the absorbent in the regeneration. For this purpose, the absorbent and a stripping agent, preferably a hot inert gas, nitrogen or steam are preferred, passed in countercurrent through a provided with packing, packings or bottoms desorption. Preferably, the stripping pressure is 1 to 3 bar absolute and the temperature is 90-130 ° C.

A regeneration of the absorbent / the washing liquid in several successive substeps, wherein the loading of the absorbent decreases with sour gas components with each step, is for example in the US 4,336,233 described. Thereafter, a coarse wash with pure relaxation circuit is carried out without stripping, wherein the loaded absorbent is expanded via an expansion turbine and regenerated stepwise in a full voltage column and a main relaxation column.

In a further preferred embodiment of the method according to the invention, the partial streams of the washing liquid used in successive substeps of the washing or absorption process are obtainable by successive substeps of the regeneration process and have a decreasing loading of acidic gas constituents. In particular, a method is preferred in which the gas containing the acidic constituents in succession with a first partial flow of the washing liquid, after partial regeneration in a flash column and before the stripping, and a second partial flow of the washing liquid, which is obtained after the stripping, in intimate Contact is brought.

For example, as in US 4,336,233 described, the absorption step in two steps, a coarse and a fine wash, and the regeneration step are carried out stepwise by pressure release in an expansion turbine, a Vorentspannungskolonne and a Hauptentspannungskolonne, and by subsequent stripping. In this case, the partial flow of the scrubbing liquid for the coarse wash may originate from the stripping column and the scrubbing substream may originate from the stripping.

The regenerated absorbent is usually passed through a heat exchanger before being fed into the absorption zone and brought to the temperature required for the washing process. For example, the regenerated absorbent leaving the stripping column can be deprived of heat and fed to the absorbent still containing sour gas components prior to its entry into the stripping column.

The inventive method can be carried out with typical equipment used for gas scrubbing and subsequent regeneration of the scrubbing liquid system configuration, as for example in US 4,336,233 for a single-stage or two-stage washing process and particularly detailed in EP 0322924 for a one-step washing process with relaxation and stripping step are described.

In a particular embodiment of the invention, the described method can be used to deacidify a fluid stream for CO ₂ scrubbing a flue gas stream from a combustion power plant. It may, for example, with other methods for gas scrubbing, for example, in the German patent application DE 10 2007 043 331 A1 be combined described cooled NaOH flue gas scrubber.

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 patent literature

• US 4336233 [0038, 0040, 0042]
• EP 0322924 [0042]
• DE 102007043331 A1 [0043]

Claims (13)

Absorbent for the absorption of acid gases from a fluid stream, characterized in that the absorbent is an aqueous solution containing, based on the absorbent: (i) 5-65 wt .-% 2- (2-aminoethoxy ) ethanol (AEE); (ii) 0.001-20% by weight of an activator selected from 2-aminoethanol (MEA), piperazine and mixtures thereof; and (iii) 0-20% by weight of an additive selected from sucrose, magnesium carbonate and mixtures thereof. Absorbent according to claim 1, characterized in that the concentration of 2- (2-Aminoexthoxy) ethanol (AEE), based on the absorbent, 15-65 wt .-% or 40-65 wt .-% is. Absorbent according to claim 1 or 2, characterized in that the concentration of 2-aminoethanol (MEA) and / or piperazine, based on the absorbent, 0.1-15 wt .-% or 0.4-7 wt .-% is , Absorbent according to one of claims 1-3, characterized in that the concentration of sucrose and / or magnesium carbonate, based on the absorbent, 0.001-20 wt .-%, 0.1-15 wt .-% or 0.4-7 Wt .-% is. A process for deacidifying a fluid stream containing acid gases as impurities, characterized in that (A) the fluid stream in at least one absorption step is brought into contact with an absorbent according to any one of claims 1-4, wherein a sour gas-laden absorbent and a purified fluid stream arise; and (B) the sour gas-cleaned fluid stream and the acid gas-laden absorbent are separated from each other. A method according to claim 5, characterized in that the separated in step (b), loaded with acid gases absorbent is regenerated and then brought again in step (a) with the fluid stream in contact. A method according to claim 5 or 6, characterized in that the absorption step is carried out in several successive substeps, wherein the sour gas-containing fluid stream in each of the substeps is brought into contact with a respective partial stream of the absorbent. A method according to claim 7, characterized in that the partial streams of the absorbent are obtained after each successive substeps of the regeneration process of the absorbent, so that the partial streams of the absorbent have a decreasing load of acid gases. Method according to one of claims 5-8, characterized in that it is the fluid stream is a gas stream. A method according to claim 9, characterized in that it is the gas stream is formed by the oxidation of gas, coal, petroleum or organic waste reaction or flue gas. Method according to one of claims 5-10, characterized in that it is the sour gas is carbon dioxide. Method according to one of claims 5-11, characterized in that the purified fluid stream contains <500 ppm by weight of carbon dioxide. Use of the absorbent according to any one of claims 1-4 for the absorption of acid gases from a fluid stream.