CN105617819A - Method for absorbing carbon dioxide in synthesis gas at low temperature with ionic liquid - Google Patents

Abstract

A method for low-temperature absorption of carbon dioxide in synthesis gas by ionic liquid. The invention belongs to the technical field of gas separation and purification. The absorbent can be a single ionic liquid or a mixed solution of several ionic liquids. In the present invention, the absorption tower is operated at a temperature of -45-0°C and a pressure of 0.3-10 MPa, and the number of theoretical plates is 11-30. The raw material gas is fed from the bottom of the absorption tower, and the ionic liquid is added from the top of the tower as an absorbent, and the raffinate phase rich in ionic liquid at the bottom of the tower enters the flash tank to remove carbon dioxide in the ionic liquid. When the ionic liquid and its mixed solvent are used to absorb _CO2 in the syngas, it has a good absorption effect, and at the same time, the ionic liquid is neutral, which can avoid the corrosion of the compressor, and avoid the high consumption and environment caused by the use of traditional solvents to absorb gas. Pollution and other issues, simple equipment, less investment, low energy consumption.

Description

A method for absorbing carbon dioxide in synthesis gas by ionic liquid at low temperature

technical field

The invention relates to a method for absorbing _CO2 in synthesis gas at low temperature by using ionic liquid as an absorbent, and belongs to the technical field of gas separation and purification.

Background technique

As a greenhouse gas, carbon dioxide has an important impact on global warming. In order to reduce the negative impact of the greenhouse effect on society and economy, CO ₂ absorption is an important part of the gas treatment process. However, China's CO ₂ industrial emissions mainly come from two types: one is the flue gas produced by the combustion of fossil fuels such as coal, and the other is the synthesis gas produced in the chemical industry. Syngas chemical industry occupies a very important position in the modern chemical industry, such as synthesis of ammonia, synthesis of olefins, Fischer-Tropsch synthesis and hydrogen production from synthesis gas. According to different follow-up processes, industrial separation and purification requirements for syngas are also different, sometimes very strict (removal must be below 20ppm), for example, for ammonia synthesis process, CO ₂ is not only a poison of ammonia synthesis catalyst, but also causes Subsequent processes produce NH ₄ HCO ₃ or (NH ₄ ) ₂ CO ₃ crystallization and cause blockage of pipelines and equipment.

Ionic liquids refer to organic salts composed of organic cations or organic anions, usually in a liquid state at or near room temperature. Ionic liquids have the characteristics of good thermal stability, difficulty in volatilization, easy separation and recovery, reproducible recycling, and functional designability. These special structures and physical properties have brought broad development space for the application of ionic liquids, especially the "non-volatility" of ionic liquids themselves and the unique ability to dissolve _CO2 in large quantities, so that they can be used in the fixed conversion and utilization of _CO2 It has great application potential.

Contents of the invention

The purpose of the present invention is to provide a method for ionic liquid to absorb gas at low temperature. The method adopts ionic liquid as absorbent to absorb _CO2 in the synthesis gas at low temperature, so that the content of _CO2 in the synthesis gas is less than 2000ppm, and the ionic liquid can Recycling.

A method for absorbing carbon dioxide in synthesis gas by ionic liquid at low temperature, characterized in that raw material gas containing carbon dioxide is fed from the bottom of the absorption tower, ionic liquid is added from the top of the tower as an absorbent, and the operating temperature of the absorption tower is -45-0°C , operating under a pressure of 0.3-10MPa, the number of theoretical plates is 11-30; the raw material gas is fed from the bottom of the absorption tower, and the raffinate phase rich in ionic liquid at the bottom of the tower enters the flash tank to remove carbon dioxide in the ionic liquid, flash The ionic liquid extracted from the bottom of the steamer is recycled.

The content of carbon dioxide in the feed gas containing carbon dioxide is 0.02-0.30 (mol fraction), and the solvent ratio is 2.7-80 (the solvent ratio is the ratio of IL entering the absorption tower to the mass flow rate of the feed gas).

The flash tank operates at a temperature of 50-200°C and a pressure of 1 atm.

The carbon dioxide-enriched ionic liquid flowing out from the bottom of the absorption tower is firstly heated by a heat exchanger before entering the flash tank.

The mole fraction content of _CO2 in the feed gas containing carbon dioxide is 0.02-0.30, and the content of _CO2 in the synthesis gas obtained from the top of the tower is less than 2000ppm.

The absorbent can be an ionic liquid or a mixed solution of several ionic liquids. The cations of the ionic liquids can be imidazoles, pyridines, quaternary ammonium salts, etc., and the anions can be bistrifluoromethanesulfonylimide, tetrafluoroboric acid Root, hexafluorophosphate, acetate, diethyl sulfate, etc. The imidazole ionic liquid cations used are 1-octyl-3-methylimidazolyl and 1-ethyl-3-methylimidazolyl, and the anion is bistrifluoromethanesulfonimide, but not limited to the above-mentioned cations and anion.

The raw material gas containing carbon dioxide is a mixed gas containing _CO2 , or pure _CO2 gas.

Compared with the existing technology, the ionic liquid has a strong ability to absorb carbon dioxide at low temperature, and the effect is good. At the same time, the ionic liquid is neutral, which avoids the corrosion of equipment, and avoids the problems of high energy consumption and environmental pollution caused by the use of traditional solvents to absorb gas. The equipment is simple, the investment is small, and the energy consumption is low.

Description of drawings

Accompanying drawing 1 is the process flow diagram of ionic liquid absorbing _CO in syngas.

Among them: B1—absorption tower; B2—flash tank; S—ionic liquid feed, F—raw material gas feed; D—overhead product; G1—CO ₂ desorption gas; W—recovered ionic liquid.

detailed description

The present invention uses the following examples to illustrate the effect of adopting ionic liquids to remove carbon dioxide in synthesis gas, but the present invention is not limited to the following examples. Under the scope of not departing from the purpose described before and after, the variation examples are all included in the scope of the present invention within the technical range.

As shown in Figure 1, the present invention adopts an absorption process comprising an absorption tower and a solvent flash tank. The absorbent enters from the top of the absorption tower, and the synthesis gas enters from the bottom of the absorption tower. The stream extracted from the bottom of the absorption tower enters the flash tank, and the flash tank removes the carbon dioxide in the ionic liquid, and the high-purity ionic liquid is extracted from the bottom of the flash tank and can be recycled.

Example 1

The absorption process shown in Figure 1. The operating conditions of the absorption tower are temperature-10°C, pressure 3MPa, the absorption tower has 17 theoretical trays, and the _CO content in the synthesis gas is 0.3 (mol fraction), fed from the bottom of the tower, and the mass flow rate is 100kg/h. Ionic liquid [EMIM] ⁺ [Tf ₂ N] ^- (1-ethyl-3-methylimidazole bistrifluoromethanesulfonimide) is added from the top of the tower as the absorbent, and the mass flow rate is 1000kg/h, and the top of the tower gets The CO ₂ content in the syngas is 20ppm, and the raffinate phase rich in [EMIM] ⁺ [Tf ₂ N] ^- at the bottom of the tower enters the flash tank, and the [EMIM] ⁺ [Tf ₂ N] ^- produced at the bottom of the flash tank is recycled use.

Change the theoretical plate number of the absorption tower to 18, and keep other conditions constant, and the _CO content in the synthesis gas obtained at the top of the tower is 11ppm.

Change the theoretical plate number of the absorption tower to 19, and keep other conditions constant, and the _CO content in the synthesis gas obtained at the top of the tower is 6ppm.

Example 2

The absorption process shown in Figure 1. The operating conditions of the absorption tower are temperature 0°C, pressure 3MPa, the absorption tower has 25 theoretical plates, the _CO content in the synthesis gas is 0.3 (mol fraction), feeds from the bottom of the tower, and the mass flow rate is 100kg/h, expressed as ions Liquid [EMIM] ⁺ [Tf ₂ N] ^- (1-ethyl-3-methylimidazole bistrifluoromethanesulfonimide) is added from the top of the tower as the absorbent, and the mass flow rate is 1000kg/h, and the top of the tower is synthesized The CO ₂ content in the gas is 16ppm, and the raffinate phase rich in [EMIM] ⁺ [Tf ₂ N] ^- at the bottom of the tower enters the flash tank, and the [EMIM] ⁺ [Tf ₂ N] ^- extracted from the bottom of the flash tank is recycled .

Change the theoretical plate number of the absorption tower to 26, and keep other conditions constant, and the _CO content in the synthesis gas obtained at the top of the tower is 11ppm.

Change the theoretical plate number of the absorption tower to 27, and keep other conditions constant, and the _CO content in the synthesis gas obtained at the top of the tower is 7ppm.

Example 3

The absorption process shown in Figure 1. The operating conditions of the absorption tower are temperature-45°C, pressure 3MPa, the absorption tower has 12 theoretical plates, the _CO content in the syngas is 0.3 (mol fraction), feeds from the bottom of the tower, and the mass flow rate is 100kg/h, with Ionic liquid [OMIM] ⁺ [Tf ₂ N] ^- (1-octyl-3-methylimidazole bistrifluoromethanesulfonimide) is added from the top of the tower as the absorbent, and the mass flow rate is 2000kg/h, and the top of the tower gets The CO ₂ content in the synthesis gas is 13ppm, and the raffinate phase rich in [OMIM] ⁺ [Tf ₂ N] ^- at the bottom of the tower enters the flash tank, and the [OMIM] ⁺ [Tf ₂ N] ^- produced at the bottom of the flash tank is recycled use.

Change the theoretical plate number of the absorption tower to 13, and keep other conditions unchanged, and the _CO content in the synthesis gas obtained at the top of the tower is 6ppm.

Change the theoretical plate number of the absorption tower to 14, and keep other conditions constant, and the _CO content in the synthesis gas obtained at the top of the tower is 5ppm.

Example 4

The absorption process shown in Figure 1. The operating conditions of the absorption tower are temperature-30°C, pressure 3MPa, the absorption tower has 11 theoretical trays, the _CO content in the synthesis gas is 0.3 (mol fraction), feeds from the bottom of the tower, and the mass flow rate is 100kg/h. Ionic liquid [OMIM] ⁺ [Tf ₂ N] ^- (1-octyl-3-methylimidazole bistrifluoromethanesulfonimide) is added from the top of the tower as the absorbent, and the mass flow rate is 2000kg/h, and the top of the tower gets The CO ₂ content in the synthesis gas is 12ppm, and the raffinate phase rich in [OMIM] ⁺ [Tf ₂ N] ^- at the bottom of the tower enters the flash tank, and the [OMIM] ⁺ [Tf ₂ N] ^- produced at the bottom of the flash tank is recycled use.

Change the theoretical plate number of the absorption tower to 12, and keep other conditions constant, and the _CO content in the synthesis gas obtained at the top of the tower is 5ppm.

Change the theoretical plate number of the absorption tower to 13, and keep other conditions constant, and the _CO content in the synthesis gas obtained at the top of the tower is 3ppm.

Example 5

The absorption process shown in Figure 1. The operating conditions of the absorption tower are temperature-20°C, pressure 3MPa, the absorption tower has 13 theoretical plates, the _CO content in the synthesis gas is 0.3 (mol fraction), feeds from the bottom of the tower, and the mass flow rate is 100kg/h, with Ionic liquid [OMIM] ⁺ [Tf ₂ N] ^- (1-octyl-3-methylimidazole bistrifluoromethanesulfonimide) is added from the top of the tower as the absorbent, and the mass flow rate is 2000kg/h, and the top of the tower gets The CO ₂ content in the synthesis gas is 12ppm, and the raffinate phase rich in [OMIM] ⁺ [Tf ₂ N] ^- at the bottom of the tower enters the flash tank, and the [OMIM] ⁺ [Tf ₂ N] ^- produced at the bottom of the flash tank is recycled use.

Change the theoretical plate number of the absorption tower to 14, and keep other conditions unchanged, and the _CO content in the synthesis gas obtained at the top of the tower is 6ppm.

Change the theoretical plate number of the absorption tower to 15, and keep other conditions constant, and the _CO content in the synthesis gas obtained at the top of the tower is 3ppm.

Example 6

The absorption process shown in Figure 1. The operating conditions of the absorption tower are temperature-10°C, pressure 3MPa, the absorption tower has 14 theoretical trays, the _CO content in the synthesis gas is 0.3 (mol fraction), feeds from the bottom of the tower, and the mass flow rate is 100kg/h. Ionic liquid [OMIM] ⁺ [Tf ₂ N] ^- (1-octyl-3-methylimidazole bistrifluoromethanesulfonimide) is added from the top of the tower as the absorbent, and the mass flow rate is 2000kg/h, and the top of the tower gets The CO ₂ content in the synthesis gas is 12ppm, and the raffinate phase rich in [OMIM] ⁺ [Tf ₂ N] ^- at the bottom of the tower enters the flash tank, and the [OMIM] ⁺ [Tf ₂ N] ^- produced at the bottom of the flash tank is recycled use.

Change the theoretical plate number of the absorption tower to 15, and keep other conditions constant, and the _CO content in the synthesis gas obtained at the top of the tower is 7ppm.

Change the theoretical plate number of the absorption tower to 16, and keep other conditions constant, and the _CO content in the synthesis gas obtained at the top of the tower is 3ppm.

Example 7

The absorption process shown in Figure 1. The operating conditions of the absorption tower are temperature 0°C, pressure 3MPa, the absorption tower has 15 theoretical plates, the _CO content in the synthesis gas is 0.3 (mol fraction), feeds from the bottom of the tower, and the mass flow rate is 100kg/h, expressed as ions Liquid [OMIM] ⁺ [Tf ₂ N] ^- (1-octyl-3-methylimidazole bistrifluoromethanesulfonimide) is added from the top of the tower as the absorbent, and the mass flow rate is 2000kg/h, and the top of the tower is synthesized The CO ₂ content in the gas is 13ppm, and the raffinate phase rich in [OMIM] ⁺ [Tf ₂ N] ^- at the bottom of the tower enters the flash tank, and the [OMIM] ⁺ [Tf ₂ N] ^- extracted from the bottom of the flash tank is recycled .

Change the theoretical plate number of the absorption tower to 16, and keep other conditions constant, and the _CO content in the synthesis gas obtained at the top of the tower is 8ppm.

Change the theoretical plate number of the absorption tower to 17, and keep other conditions unchanged, and the _CO content in the synthesis gas obtained at the top of the tower is 4ppm.

Example 8

The absorption process shown in Figure 1. The operating conditions of the absorption tower are temperature-45°C, pressure 0.3MPa, the absorption tower has 30 theoretical trays, the _CO content in the synthesis gas is 0.02 (mol fraction), feeds from the bottom of the tower, and the mass flow rate is 100kg/h, Use ionic liquid [OMIM] ⁺ [Tf ₂ N] ^- (1-octyl-3-methylimidazole bistrifluoromethanesulfonimide) as absorbent to add from the top of the tower, the mass flow rate is 7600kg/h, the top of the tower The _CO2 content in the synthesis gas obtained is 10ppm, and the raffinate phase rich in [OMIM] ⁺ [Tf ₂ N] ^- at the bottom of the tower enters the flash tank, and the [OMIM] ⁺ [Tf ₂ N] ^- extracted from the bottom of the flash tank recycle.

Change the absorption tower pressure to 10MPa and the absorbent flow rate to 270kg/h, and keep other conditions constant, and the _CO content in the synthesis gas obtained at the top of the tower is 10ppm.

Claims (7)

1. the method for carbon dioxide in an ionic liquid low temperature absorption synthesis gas, it is characterized in that, unstripped gas containing carbon dioxide is from absorption tower bottom feed, ionic liquid adds from tower top as absorbent, the operation temperature on absorption tower is-45-0 DEG C, operating under pressure 0.3-10MPa, theoretical cam curve is 11-30; Entering flash tank rich in the raffinate phase of ionic liquid at the bottom of tower, the carbon dioxide in elimination ionic liquid, the ionic liquid of extraction bottom flash tank recycles.

2. the method for carbon dioxide in a kind of ionic liquid low temperature absorption synthesis gas described in claim 1, it is characterised in that in the unstripped gas containing carbon dioxide, the molar fraction content of carbon dioxide is 0.02-0.30, solvent is than for 2.7-80.

3. the method for carbon dioxide in a kind of ionic liquid low temperature absorption synthesis gas described in claim 1, it is characterized in that, absorbent is a kind of ionic liquid or the mixed solution of several ionic liquid, ionic liquid cation is selected from imidazoles, pyridines or quaternary ammonium salt, and anion is selected from bis-trifluoromethylsulfoandimide root, tetrafluoroborate, hexafluoro-phosphate radical, acetate or dithyl sulfate root.

4. the method for carbon dioxide in a kind of ionic liquid low temperature absorption synthesis gas described in claim 1, it is characterised in that flash tank temperature 50-200 DEG C, pressure 1atm when operation.

5. the method for carbon dioxide in a kind of ionic liquid low temperature absorption synthesis gas described in claim 1, it is characterised in that the carbonated ionic liquid of richness flowed out bottom absorption tower is preferentially heated by heat exchanger, enters back into flash tank.

6. the method for carbon dioxide in a kind of ionic liquid low temperature absorption synthesis gas described in claim 1, it is characterised in that CO in the unstripped gas containing carbon dioxide₂Molar fraction content is 0.02-0.30, CO in the synthesis gas that tower top obtains₂Content is less than 2000ppm.

7. the method for carbon dioxide in a kind of ionic liquid low temperature absorption synthesis gas described in claim 1, it is characterised in that the unstripped gas containing carbon dioxide is containing CO₂Mixing gas or pure CO₂Gas.