Premix for producing an absorption agent for removing acid gases from a fluid flow

Abstract

A premixture for producing an absorbent for removing acid gases from a fluid stream containing a) at least a tertiary amine and/or a sterically hindered secondary amine; b) a dicarboxylic acid in an amount, calculated as neutralization equivalent based on the protonatable nitrogen atoms in a), of at least 30%, wherein the dicarboxylic acid has a solubility in water at a temperature of 20° C. of not more than 15 g of dicarboxylic acid per 100 g of water; and c) 20 to 80 wt % of water. Also described is a process for producing an absorbent from the premixture. The premixture is a transportable and readily handleable solution of a dicarboxylic acid having poor solubility in water for producing an absorbent for removing acid gases from a fluid stream.

Claims

1. A premixture, comprising a) a tertiary amine which is at least one alkanolamine selected from bis(2-hydroxyethyl)methylamine, tributanolamine, 2-diethylaminoethanol, 2-dimethylaminoethanol, 3-dimethylamino-1-propanol, 3-diethylamino-1-propanol, 2-diisopropylaminoethanol, and N,N-bis(2-hydroxypropyl)methylamine; b) a dicarboxylic acid in an amount, calculated as neutralization equivalent based on protonatable nitrogen atoms in the tertiary amine, of at least 30%, wherein the dicarboxylic acid has a solubility in water at a temperature of 20° C. of not more than 15 g of dicarboxylic acid per 100 g of water; and c) from 20 to 80 wt % of water, wherein the premixture is suitable for producing an absorbent for removing acid gases from a fluid stream, and wherein the dicarboxylic acid is at least one selected from the group consisting of succinic acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid.

2. The premixture according to claim 1, wherein the amount of the dicarboxylic acid, calculated as neutralization equivalent based on the protonatable nitrogen atoms in a), is from 30% to 400%.

3. The premixture according to claim 1, wherein the dicarboxylic acid is selected from the group consisting of succinic acid and adipic acid.

4. A process for producing an absorbent for removing acid gases from a fluid stream, the process comprising: mixing the premixture of claim 1 with an amine and optionally with water, wherein the amount of the dicarboxylic acid in the premixture, calculated as neutralization equivalent based on the protonatable nitrogen atoms of the tertiary amine, is greater than in the absorbent.

5. The process of claim 4, wherein the absorbent comprises the dicarboxylic acid in an amount, calculated as neutralization equivalent based on the protonatable nitrogen atoms of the tertiary amine, of from 0.5% to 15%.

6. The process of claim 4, wherein the absorbent is free from sterically unhindered primary amines and sterically unhindered secondary amines.

Description

EXAMPLES

(1) The following abbreviations are used:

(2) AA adipic acid

(3) SA succinic acid

(4) MDEA methyldiethanolamine

(5) TBAEE 2-(2-tert-butylaminoethoxy)ethanol

Reference Example 1

(6) This example analyzed the solubility of succinic acid/adipic acid in various amines at 23.5° C.

(7) 100 g of MDEA were admixed with 2 g of succinic acid and stirred with a magnetic stirrer. An insoluble sediment was formed. The solubility of succinic acid in MDEA is less than 2 g/100 g.

(8) 100 g of TBAEE were admixed with 1.7 g of succinic acid and stirred with a magnetic stirrer. An insoluble sediment was formed. The solubility of succinic acid in TBAEE is less than 1.7 g/100 g.

(9) 100 g of MDEA were admixed with 2 g of adipic acid and stirred with a magnetic stirrer. An insoluble sediment was formed. The solubility of adipic acid in MDEA is less than 2 g/100 g.

Example 1

(10) This example analyzed the solubility of succinic acid/adipic acid in aqueous amine solutions at 23.5° C.

(11) This was achieved by adding with stirring carboxylic acid to aqueous amine solutions (starting solutions) as per the table which follows until an insoluble precipitate was formed. The compositions of the aqueous amine solutions at the solubility limit are reported in the table which follows.

(12) TABLE-US-00002 starting solution solubility limit composition MDEA TBAEE MDEA TBAEE acid [wt %] [wt %] [wt %] [wt %] wt % neutr. eq.* 20.0 — 15.5 — SA 23.0 299% 60.0 — 35.8 — SA 40.6 229% — 20.0 — 15.9 SA 20.5 352% — 60.0 — 37.5 SA 37.6 274% 20.0 — 16.7 — AA 17.6 172% 60.0 — 40.2 — AA 33.4 135% *neutr. eq. = neutralization equivalent based on the nitrogen atoms in MDEA/TBAEE

Reference Example 2

(13) This example analyzed the stability of MDEA in the presence of various carboxylic acids.

(14) Aqueous amine solutions comprising 30 wt % of MDEA, 15 wt % of TBAEE and various carboxylic acids were produced according to the table which follows by mixing. The thus obtained solutions were laden with 20 m.sup.3 (STP)/t of CO.sub.2 and 20 m.sup.3 (STP)/t of H.sub.2S. This was achieved by initially charging the aqueous absorbents into a glass cylinder at 40° C. and 1 bar and passing H.sub.2S/CO.sub.2 through the solution for about 3 h. The CO.sub.2/H.sub.2S loading was determined by titration and a loading of 20 m.sup.3 (STP)/t of CO.sub.2 and 20 m.sup.3 (STP)/t of H.sub.2S established by subsequent dilution with unladen absorbent. The thus acid-gas-laden solutions were transferred into a nitrogen-filled autoclave. The sealed autoclaves were heated in an oil bath to 160° C. and held at this temperature for 5 days.

(15) After cooling of the autoclaves the samples were removed and the acid gases (CO.sub.2 and H.sub.2S) stripped with nitrogen. This was achieved by transferring the samples into a glass flask fitted with a cooler and passing N.sub.2 through the fully refluxing samples at 100° C. over 4 h. The solutions substantially freed of acid gases were then analyzed for their amine content by gas chromatography. While the TABEE content was virtually unchanged for all samples, marked differences were observed for MDEA depending on the acids employed. The results are shown in the table which follows.

(16) TABLE-US-00003 acid content acid wt % neutr. eq.* MDEA loss formic acid 1.10 6.9% 6.14 wt % acetic acid 1.26 6.1% 6.35 wt % succinic acid 1.42 7.0% 4.95 wt % adipic acid 1.66 6.6% 2.44 wt % *neutr. eq. = neutralization equivalent based on the nitrogen atoms in MDEA/TBAEE