CN1962032A - Solvent and method for simultaneous removal of hydrogen sulphide and carbon dioxide - Google Patents

Abstract

A solvent and method for simultaneously removing hydrogen sulfide and carbon dioxide belong to the technical field of gas purification. Using some amines with special structures and MDEA to form a mixed aqueous solution, and using these mixed aqueous solutions to contact the gas to be treated can maintain the advantages of traditional MDEA mixed solvents while overcoming their shortcomings.

Description

A solvent and method for simultaneous removal of hydrogen sulfide and carbon dioxide

Technical field:

The invention belongs to the technical field of gas purification, and in particular relates to a solvent and a method used in the process of simultaneously removing hydrogen sulfide and carbon dioxide.

Background technique:

Industrial gases usually contain harmful impurities such as H ₂ S and CO ₂ , which must be removed before further use. So far, there are no less than a hundred technologies applied to gas desulfurization and decarbonization, and there are several widely used ones. Ten, but the dominant method is the alcohol amine method.

Amine desulfurization uses chemically active substances such as alkylolamines. Solvents such as monoethanolamine (MEA), diethanolamine (DEA), diglycolamine (DGA), and diisopropanolamine (DIPA) were first developed and used abroad. These solvents have high efficiency in removing CO ₂ and H ₂ S, but have poor efficiency in selective removal of H ₂ S and organic sulfur, and the desulfurization energy consumption and operating costs are high, and solvent degradation and equipment corrosion are serious. Since 1980, methyldiethanolamine (MDEA) aqueous solution has been widely used in the natural gas processing industry due to its advantages of high selectivity, high acid gas load, low energy consumption and corrosiveness.

However, due to the slow reaction rate between MDEA and CO ₂ , conventional MDEA solvents are not suitable for occasions that require deep desulfurization and large amount of CO ₂ removal. Therefore, a mixed solvent composed of a certain amount of MEA or DEA has appeared in MDEA. This type of solvent activates MDEA by using the rapid reaction of MEA or DEA to react with _CO2 to generate carbamate, thereby overcoming the MDEA solvent. The defects of desulfurization and decarburization have achieved good results. However, in such solvents, MEA or DEA and CO ₂ form stable carbamate, which requires more heat to decompose during the regeneration process, resulting in high energy consumption for regeneration. At the same time, carbamate is highly corrosive to equipment and will form scale. In addition, carbamate also intensifies the degradation reaction of alkanolamine and CO ₂ , resulting in a series of problems such as increased loss of alkanolamine, decreased decarburization performance, and increased corrosion.

Invention content:

The purpose of the present invention is to adopt some amines with special structures and MDEA to form a mixed solvent, which can keep the advantages of the aforementioned mixed solvents and overcome their disadvantages simultaneously.

The amines with special structure used in the present invention are secondary amines. The special structure means that the alkyl group connected to the amino group in the molecule has a significant steric hindrance effect, and the carbamate R ₁ R ₂ of them reacts with CO ₂ In NCOOH, due to the steric hindrance effect of R ₁ or R ₂ , the connection between -COO ^- and N atom is extremely unstable, thus greatly reducing the stability of carbamate. Thus, problems arising from the stability of carbamates are overcome.

The amines with special structure adopted in the present invention are selected as: isopropylaminoethanol (IPAE), isopropylaminoisopropanol (IPAIP), isobutylaminoethanol (IBAE), isobutylaminopropanol (IBAP), isopropylaminopropanol (IBAP), Butylaminoisopropanol (IBAIP), tert-butylaminopropanol (TBAP), tert-butylaminoisopropanol (TBAIP), etc.

When the amine with special structure used in the present invention is mixed with MDEA, the suitable ratio is: amine with special structure: MDEA=1:1.2-6.5 (molar ratio), preferably 1:2-5.

In the mixed amine aqueous solution used in the present invention, the suitable total amine concentration is: 20-70% (wt), but preferably 30-50% (wt).

Additives such as corrosion inhibitors, defoamers and the like may also be contained in the mixed amine aqueous solution used in the present invention. Typically, the concentration of these additives ranges from 0.01% to 5% (wt), and the use of these additives is well known to those skilled in the art.

Any gas containing both _H2S and _CO2 in significant amounts can be treated in accordance with the present invention. The gas source is not critical to the invention and includes, for example, natural gas, synthesis gas, and various refinery gases. Typically, these gas streams contain a large amount of H ₂ S and CO ₂ at the same time, wherein the content of H ₂ S is about 5%-90% (mol), and the content of CO ₂ is about 5%-50% (mol).

_H2S and _CO2 in the gas stream are removed by contact with the aqueous mixed amine solution of the present invention. Simultaneously the spent absorbent is regenerated to remove all or part of the absorbed _H2S and _CO2 before recycling to the absorption step. Any equipment known in the art can be used for the absorption, regeneration and other steps.

Detailed ways:

The present invention will be further described below in conjunction with the implementation examples, but it does not limit the protection scope of the present invention.

The embodiment is a typical process for deep desulfurization and large amount of _CO2 removal according to the present invention.

The bottom of the gas absorption tower containing a large amount of H ₂ S and CO ₂ is in contact with the mixed amine aqueous solution from the upper part of the absorption tower, the H ₂ S and CO ₂ in the gas flow are removed, and the product gas that meets the requirements enters the next process. The mixed amine aqueous solution rich in H ₂ S and CO ₂ is discharged from the bottom of the absorption tower.

The absorption tower is equipped with suitable trays or packings, and the specific devices involved in the absorption tower are well known to those skilled in the art. The typical operating temperature of the absorption tower is about 25 to 90 ° C, and the pressure is about 0.1 to 11 MPa.

The mixed amine aqueous solution rich in _H2S and _CO2 can pass through one or more flash tanks, a part of the absorbed _H2S and _CO2 is separated from the mixed amine aqueous solution and discharged from the top of the flash tank. The mixed amine aqueous solution after flash evaporation enters the regeneration tower and is regenerated in the regeneration tower.

The specific devices involved in the use of regeneration columns are well known to those skilled in the art. The typical operating temperature of the regeneration column is about 100 to 130°C, and the pressure is about 0.1 to 0.4MPa.

The desorbed H ₂ S and CO ₂ in the regeneration tower are discharged from the top of the tower, and the regenerated mixed amine aqueous solution is discharged from the bottom of the tower, and after cooling, it enters the absorption tower for reuse.

Implementation example one:

The performance of specific absorbents is measured directly on a test rig. The inner diameter of the absorption tower used in the test is 50mm, with a built-in φ6×6×1 porcelain Raschig ring, the inner diameter of the regeneration tower is 70mm, with a built-in φ8×8×1 porcelain Raschig ring, and a reboiler is installed at the bottom of the regeneration tower.

The prepared raw material gas (containing H ₂ S 14%, CO ₂ 9%) enters the bottom of the absorption tower and contacts the solution entering the top of the tower countercurrently, the acid gas in the gas is absorbed, and the purified gas comes out of the top of the tower and enters the gas-liquid separation The trap recovers the entrained droplets and then vents.

The rich liquid that has absorbed the acid gas is drawn from the bottom of the absorption tower to the top of the regeneration tower, and is regenerated by countercurrent contact with the rising steam in the regeneration tower. The regenerated lean liquid is sent to the top of the absorption tower for absorption after being cooled. The gas from the top of the regeneration tower enters the regeneration gas cooler to recover the water vapor in the gas, and the regeneration gas is separated and then emptied.

At a certain gas flow rate, the operability of absorbents composed of different amines mixed with MDEA is shown in Table 1.

Table 1: Operational properties of different absorbent blends

Absorbent Composition H ₂ S in the purified gas: ppmv CO ₂ in the purified gas: v%  Solution circulation volume: L/h Reboiler load: kw MDEA3.8mol/l+MEA0.8mol/l 20 0.4 20.0 2.20 MDEA2.0mol/l+IPAE0.8mol/l 20 0.3 19.8 2.10 MDEA3.3mol/l+IPAIP0.8mol/l 18 0.3 18.3 1.95 MDEA1.5mol/l+IBAE0.3mol/l 20 0.4 19.8 2.04 MDEA1.8mol/l+IBAP0.7mol/l 19 0.4 19.6 1.98 MDEA2.8mol/l+IBAIP0.8mol/l 20 0.3 19.0 2.07 MDEA3.0mol/l+TBAP0.6mol/l 19 0.3 18.4 1.88 MDEA4.2mol/l+TBAIP0.7mol/l 20 0.4 19.6 2.00

The data in Table 1 shows that using the absorbent composition of the present invention, its absorption performance is equivalent to the mixture of MDEA and MEA, but the regeneration energy consumption is reduced.

Implementation example two:

This test measures the corrosion of carbon steel by solution. A ₃ carbon steel coupon is used. After polishing, purification, drying and weighing, the coupon is immersed in an amine aqueous solution at 100°C, and H ₂ S is bubbled into the solution at a certain speed. The continuous test time is 72 Hours, take out the coupons afterwards, purify, dry and weigh the coupons, and measure the weight loss of the coupons. Corrosion of carbon steel by solutions with different compositions is shown in Table 2.

Table 2. Corrosion rate comparison

Solution composition MDEA3.5mol/l+MEA0.8mol/l MDEA3.5mol/l+TBAP0.8mol/l MDEA3.5mol/l+IPAE0.8mol/l MDEA3.5mol/l+TBAIP0.8mol/l Corrosion rate mm/a 0.058 0.043 0.032 0.038

The data in Table 2 demonstrate the reduction in corrosivity using the absorbent composition of the present invention.

Claims (5)

1. A solvent for simultaneously removing hydrogen sulfide and carbon dioxide is characterized in that some amines with special structures and MDEA are used to form a mixed aqueous solution. The amines with special structures used are: isopropylaminoethanol (IPAE), Isopropylaminopropanol (IPAIP), Isobutylaminoethanol (IBAE), Isobutylaminopropanol (IBAP), Isobutylaminopropanol (IBAIP), Tert-Butylaminopropanol (TBAP), Tert-Butylaminopropanol isopropyl alcohol (TBAIP). 2. The solvent according to claim 1, characterized in that when the amine with a special structure and MDEA are used in combination, the molar ratio used is: amine with a special structure: MDEA = 1: 1.2-6.5. 3. The solvent according to claim 1, characterized in that when the amine with special structure and MDEA are used in combination, the molar ratio used is: amine with special structure: MDEA = 1:2-5. 4. The solvent according to claim 1, characterized in that the weight ratio of total amine concentration in the mixed aqueous solution used is 30-60%. 5. A method for simultaneously removing hydrogen sulfide and carbon dioxide, which comprises contacting the gas to be treated with the mixed aqueous solution as claimed in claim 1.