AMINE COMPOUNDS FOR SELECTIVELY REMOVING HYDROGEN SULPHIDE

Abstract

A compound of the general formula (I)

##STR00001##

in which R.sub.1 to R.sub.8, x, y and z are as defined in the description. Also described is an absorbent comprising a solution of the compound, and the use thereof and a process for removing acid gases from a fluid stream, wherein the fluid stream is contacted with the absorbent. The compounds of the general formula (I) are notable for thermal stability and low volatility. Absorbents based on the compounds are notable for high loading capacity, high cyclic capacity and good regeneration capacity. The solutions of the compounds in nonaqueous solvents are notable for low viscosities.

Claims

1: A compound of the general formula (I): ##STR00007## wherein: R.sub.1 and R.sub.2 are independently C.sub.1-C.sub.4-alkyl; R.sub.3, R.sub.4, R.sub.5 and R.sub.6 are independently selected from the group consisting of hydrogen and C.sub.1-C.sub.4-alkyl; R.sub.7 and R.sub.8 are independently C.sub.1-C.sub.4-alkyl; x and y are integers from 2 to 4; and z is an integer from 1 to 3.

2: A compound according to claim 1, which is selected from the group consisting of 2-(2-tert-butylaminoethoxy)ethyl-N,N-dimethylamine, 2-(2-tert-butylaminoethoxy)ethyl-N,N-diethylamine, 2-(2-tert-butylaminoethoxy)ethyl-N,N-dipropyl amine, 2-(2-isopropylaminoethoxy)ethyl-N,N-dimethylamine, 2-(2-isopropylaminoethoxy) ethyl-N,N-diethylamine, 2-(2-isopropylaminoethoxy)ethyl-N,N-dipropylamine, 2-(2-(2-tert-butylaminoethoxy)ethoxy)ethyl-N,N-dimethylamine, 2-(2-(2-tert-butylaminoethoxy)ethoxy) ethyl-N,N-diethylamine, 2-(2-(2-tert-butylaminoethoxy) ethoxy)ethyl-N,N-dipropylamine, 2-(2-tert-amylaminoethoxy)ethyl-N,N-dimethylamine, and 2-(2-(1-methyl-1-ethylpropylamino) ethoxy)ethyl-N,N-dimethylamine.

3: An absorbent, comprising a solution of a compound according to claim 1 for removal of acid gases from a fluid stream.

4: The absorbent according to claim 3, wherein the absorbent is an aqueous solution.

5: The absorbent according to claim 4, further comprising an acid.

6: The absorbent according to claim 3, further comprising an organic solvent.

7: The absorbent according to claim 6, wherein the organic solvent is selected from the group consisting of a C.sub.4-C.sub.10 alcohol, a ketone, an ester, a lactone, a lactam, a sulfone, a sulfoxide, a glycol, a cyclic urea, a thioalkanol, and mixtures thereof.

8: The absorbent according to claim 7, wherein the organic solvent is selected from the group consisting of a sulfone and a glycol.

9: The absorbent according to claim 3, further comprising a tertiary amine or highly sterically hindered amine other than the compound of the general formula (I).

10: A process, comprising removing at least one acid gas from a fluid stream by contacting the fluid stream with the absorbent of claim 3.

11: The process of claim 10, comprising selectively removing hydrogen sulfide from a fluid stream comprising carbon dioxide and hydrogen sulfide.

12: The process of claim 10, wherein the process forms a treated fluid stream and a laden absorbent.

13: The process according to claim 12, comprising selectively removing hydrogen sulfide from a fluid stream comprising carbon dioxide and hydrogen sulfide.

14: The process according to claim 12, wherein the laden absorbent is regenerated by at least one of heating, decompressing and stripping the laden absorbent with an inert fluid.

15: The absorbent according to claim 6, wherein the organic solvent is selected from the group consisting of a polyalkylene glycol, a di- or mono-(C1-4-alkyl ether) glycol, and mixtures thereof.

16: The absorbent according to claim 6, wherein the organic solvent is selected from the group consisting of a di- or mono-(C1-4-alkyl ether) glycol, a di- or mono-(C1-4-alkyl ether) polyalkylene glycol, and mixtures thereof.

Description

[0081] The invention is illustrated in detail by the appended drawing and the examples which follow.

[0082] FIG. 1 is a schematic diagram of a plant suitable for performing the process of the invention.

[0083] According to FIG. 1, via the inlet Z, a suitably pretreated gas comprising hydrogen sulfide and carbon dioxide is contacted in countercurrent, in an absorber A1, with regenerated absorbent which is fed in via the absorbent line 1.01. The absorbent removes hydrogen sulfide and carbon dioxide from the gas by absorption; this affords a hydrogen sulfide- and carbon dioxide-depleted clean gas via the offgas line 1.02.

[0084] Via the absorbent line 1.03, the heat exchanger 1.04 in which the CO.sub.2- and H.sub.2S-laden absorbent is heated up with the heat from the regenerated absorbent conducted through the absorbent line 1.05, and the absorbent line 1.06, the CO.sub.2- and H.sub.2S-laden absorbent is fed to the desorption column D and regenerated.

[0085] Between the absorber A1 and heat exchanger 1.04, one or more flash vessels may be provided (not shown in FIG. 1), in which the CO.sub.2- and H.sub.2S-laden absorbent is decompressed to, for example, 3 to 15 bar.

[0086] From the lower part of the desorption column D, the absorbent is conducted into the boiler 1.07, where it is heated. The steam that arises is recycled into the desorption column D, while the regenerated absorbent is fed back to the absorber A1 via the absorbent line 1.05, the heat exchanger 1.04 in which the regenerated absorbent heats up the CO.sub.2- and H.sub.2S-laden absorbent and at the same time cools down itself, the absorbent line 1.08, the cooler 1.09 and the absorbent line 1.01. Instead of the boiler shown, it is also possible to use other heat exchanger types for energy introduction, such as a natural circulation evaporator, forced circulation evaporator or forced circulation flash evaporator. In the case of these evaporator types, a mixed-phase stream of regenerated absorbent and steam is returned to the bottom of the desorption column D, where the phase separation between the vapor and the absorbent takes place. The regenerated absorbent to the heat exchanger 1.04 is either drawn off from the circulation stream from the bottom of the desorption column D to the evaporator or conducted via a separate line directly from the bottom of the desorption column D to the heat exchanger 1.04.

[0087] The CO.sub.2- and H.sub.2S-containing gas released in the desorption column D leaves the desorption column D via the offgas line 1.10. It is conducted into a condenser with integrated phase separation 1.11, where it is separated from entrained absorbent vapor. In this and all the other plants suitable for performance of the process of the invention, condensation and phase separation may also be present separately from one another. Subsequently, the condensate is conducted through the absorbent line 1.12 into the upper region of the desorption column D, and a CO.sub.2- and H.sub.2S-containing gas is discharged via the gas line 1.13.

[0088] The invention is illustrated in detail by the examples which follow.

[0089] The following abbreviations were used:

[0090] MDEA: methyldiethanolamine

[0091] TBAEE: 2-(2-tert-butylaminoethoxy)ethanol

[0092] TBAAE DA: 2-(2-tert-butylaminoethoxy)ethyl-N,N-dimethylamine

EXAMPLE 1: PREPARATION OF 2-(2-TERT-BUTYLAMINOETHOXY)ETHYL-N,N-DIMETHYLAMINE (TBAEEDA)

[0093] An oil-heated glass reactor having a length of 0.9 m and an internal diameter of 28 mm was charged with quartz wool. The reactor was charged with 200 mL of V2A mesh rings (diameter 5 mm), above that 100 mL of a copper catalyst (support: alumina) and finally 600 mL of V2A mesh rings (diameter 5 mm).

[0094] Subsequently, the catalyst was activated as follows: Over a period of 2 h, at 160 C., a gas mixture consisting of H.sub.2 (5% by volume) and N.sub.2 (95% by volume) was passed over the catalyst at 100 L/h. Thereafter, the catalyst was kept at a temperature of 180 C. for a further 2 h. Subsequently, at 200 C. over a period of 1 h, a gas mixture consisting of H.sub.2 (10% by volume) and N.sub.2 (90% by volume) was passed over the catalyst, then, at 200 C. over a period of 30 min, a gas mixture consisting of H.sub.2 (30% by volume) and N.sub.2 (70% by volume) and finally, at 200 C. over a period of 1 h, H.sub.2.

[0095] 50 g/h of a mixture of tert-butylamine (TBA) and 2-[dimethylamino(ethoxy)]ethan-1-ol (DMAEE, CAS 1704-62-7, Sigma-Aldrich) in a TBA:DMAEE weight ratio=4:1 were passed over the catalyst at 200 C. together with hydrogen (40 L/h). The reaction output was condensed by means of a jacketed coil condenser and analyzed by means of gas chromatography (column: 30 m Rtx-5 Amine from Restek, internal diameter: 0.32 mm, d.sub.f: 1.5 m, temperature program 60 C. to 280 C. in steps of 4 C./min). The following analysis values are reported in GC area percent.

[0096] The GC analysis shows a conversion of 96% based on DMAEE used, and 2-(2-tert-butylaminoethoxy)ethyl-N,N-dimethylamine (TBAEEDA) was obtained in a selectivity of 73%. The crude product was purified by distillation. After the removal of excess tert-butylamine under standard pressure, the target product was isolated at a bottom temperature of 95 C. and a distillation temperature of 84 C. at 8 mbar in a purity of >97%.

EXAMPLE 2: PK.SUB.A .VALUES AND TEMPERATURE DEPENDENCE OF THE PK.SUB.A .VALUES

[0097] The pKa values of the two amino groups of 2-(2-tert-butylaminoethoxy)ethyl-N,N-dimethylamine (TBAEEDA) were determined by means of titration with hydrochloric acid at 20 C. The pK.sub.A of the tertiary amine MDEA is reported for comparison.

[0098] The temperature dependence of the pK.sub.A of TBAEEDA as compared with MDEA was also examined. The temperature dependence of the pK.sub.A of aqueous amine solutions was determined in the temperature range from 20 C. to 120 C. A pressure apparatus was used, in which the pK.sub.A can be measured up to 120 C. The concentrations of the solutions were 0.010 mol/L.

[0099] The results are shown in the following table:

TABLE-US-00001 TBAEEDA MDEA* pK.sub.A1 10.4 8.7 pK.sub.A2 8.4 pK.sub.A1 (120-20 C.) 2.4 1.8

[0100] The result of a marked temperature dependence of the pKa is that, at relatively low temperatures as exist in the absorption step, the higher pK.sub.A promotes efficient acid gas absorption, whereas, at relatively high temperatures as exist in the desorption step, the lower pK.sub.A supports the release of the absorbed acid gases. It is expected that a great pK.sub.A differential for an amine between absorption and desorption temperature will result in a comparatively small regeneration energy.

EXAMPLE 3: LOADING CAPACITY AND CYCLIC CAPACITY

[0101] A loading experiment and then a stripping experiment were conducted.

[0102] A glass condenser, which was operated at 5 C., was attached to a glass cylinder with a thermostated jacket. This prevented distortion of the test results by partial evaporation of the absorbent. The glass cylinder was initially charged with about 100 mL of unladen absorbent (30% by weight of amine in water). To determine the absorption capacity, at ambient pressure and 40 C., 8 L (STP)/h of CO.sub.2 or H.sub.2S were passed through the absorption liquid via a frit over a period of about 4 h. Subsequently, the loading of CO.sub.2 or H.sub.2S was determined as follows:

[0103] The determination of H.sub.2S was effected by titration with silver nitrate solution. For this purpose, the sample to be analyzed was weighed into an aqueous solution together with about 2% by weight of sodium acetate and about 3% by weight of ammonia. Subsequently, the H.sub.2S content was determined by a potentiometric turning point titration by means of silver nitrate. At the turning point, the H.sub.2S is fully bound as Ag.sub.2S. The CO.sub.2 content was determined as total inorganic carbon (TOC-V Series Shimadzu).

[0104] The laden solution was stripped by heating an identical apparatus setup to 80 C., introducing the laden absorbent and stripping it by means of an N.sub.2 stream (8 L (STP)/h). After 60 min, a sample was taken and the CO.sub.2 or H.sub.2S loading of the absorbent was determined as described above.

[0105] The difference in the loading at the end of the loading experiment and the loading at the end of the stripping experiment gives the respective cyclic capacity.

[0106] The results are shown in table 1. It is clear that the inventive compound TBAEEDA has both a higher CO.sub.2 loading capacity and a higher H.sub.2S loading capacity. The cyclic CO.sub.2 and H.sub.2S capacities are also higher than those in the comparative examples.

EXAMPLE 4: H.SUB.2.S:CO.SUB.2 .LOADING CAPACITY RATIO

[0107] The same apparatus as in example 3 was used. Amine solutions having an amine content of 10% by weight and various solvents were used. The difference in the loading at the end of the loading experiment and the loading at the end of the stripping experiment gives the respective cyclic capacity. The H.sub.2S:CO.sub.2 loading capacity ratio was calculated as the quotient of the H.sub.2S loading divided by the CO.sub.2 loading and serves as an indication of the expected H.sub.2S selectivity. The results are shown in table 2.

[0108] It is clear from the comparison of example 4 with comparative example 5 that the inventive compound TBAEEDA has an elevated H.sub.2S:CO.sub.2 loading capacity ratio compared to TBAEE and hence tends to bring about an elevated H.sub.2S selectivity in a sulfolane solution.

TABLE-US-00002 TABLE 1 CO.sub.2 loading H.sub.2S loading [m.sup.3 (STP)/t] Cyclic [m.sup.3 (STP)/t] Cyclic Absorbent after after CO.sub.2 capacity after after H.sub.2S capacity # Composition loading stripping [m.sup.3 (STP)/t] loading stripping [m.sup.3 (STP)/t] 1* 30% by wt. of MDEA + 43.4 2.7 40.7 38.7 6.7 32 70% by wt. of water 2* 30% by wt. of TBAEE + 40.6 9.9 30.7 38.5 10.4 28.1 70% by wt. of water 3 30% by wt. of 67.5 11.1 56.4 64.9 11.5 53.4 TBAEEDA + 70% by wt. of water *comparative example

TABLE-US-00003 TABLE 2 CO.sub.2 loading H.sub.2S loading [m.sup.3 (STP)/t] Cyclic [m.sup.3 (STP)/t] Cyclic Absorbent after after CO.sub.2 capacity after after H.sub.2S capacity H.sub.2S:CO.sub.2 loading # Composition loading stripping [m.sup.3 (STP)/t] loading stripping [m.sup.3 (STP)/t] capacity ratio 1* 10% by wt. of TBAEEDA + 22.2 4.7 17.5 22.0 3.2 18.8 1.0 90% by wt. of water 2 10% by wt. of TBAEEDA + 14.9 1.3 13.6 17.0 2.5 14.5 1.1 90% by wt. of ethylene glycol 3 10% by wt. of TBAEEDA + 5.3 0.7 4.6 17.0 3.0 14.0 3.2 90% by wt. of triethylene glycol 4 10% by wt. of TBAEEDA + 1.4 1.3 1.1 9.2 1.7 7.5 6.6 90% by wt. of sulfolane 5* 10% by wt. of TBAEE + 0.9 0.1 0.8 4.2 0.6 3.6 4.7 90% by wt. of sulfolane *comparative example

EXAMPLE 5: VOLATILITY

[0109] The volatility of TBAEEDA and dimethylamino-1-propanol (DIMAP), an amine customary in acid gas scrubbing, in 30% by weight aqueous solutions was examined.

[0110] The same apparatus as in example 3 was used, except that the condensate obtained in the glass condenser was not returned to the glass condenser but was separated and analyzed for its composition after the experiment had ended. The glass cylinder thermostated to 50 C., and 100 mL of the absorbent were introduced in each case. Over an experimental duration of 8 h, 50 L (STP)/h of N.sub.2 were passed through the absorbent at ambient pressure.

[0111] The results are shown in the following table:

TABLE-US-00004 Amount of Water DIMAP TBAEEDA condensate [g/ [g/ [g/ Solution [g] 100 g] 100 g] 100 g] 30% by wt. of 30.4 98.3 1.7 TBAEEDA + 70% by wt. of water 30% by wt. of 24.8 94.3 5.7 DIMAP + 70% by wt. of water* *comparative example

[0112] It is clear that the inventive compound TBAEEDA has a lower volatility compared to the comparative compound DIMAP.

EXAMPLE 6: THERMAL STABILITY

[0113] A Hastelloy cylinder (10 mL) was initially charged with the absorbent (30% by weight amine solution, 8 mL) and the cylinder was closed. The cylinder was heated to 160 C. for 125 h. The acid gas loading of the solutions was 20 m.sup.3 (STP)/t.sub.solvent of CO.sub.2 and 20 m.sup.3 (STP)/t.sub.solvent of H.sub.2S. The decomposition level of the amines was calculated from the amine concentration measured by gas chromatography before and after the experiment. The results are shown in the following table:

TABLE-US-00005 Decomposition Absorbent level 30% by wt. of MDEA + 70% by wt. of water* 15% 30% by wt. of TBAEEDA + 70% by wt. of water 9% *comparative example

[0114] It is clear that TBAEEDA has a higher thermal stability than MDEA.

EXAMPLE 7: VISCOSITY

[0115] The dynamic viscosities of TBAEE, MDEA and TBAEEDA were measured at various temperatures in a viscometer (Anton Paar Stabinger SVM3000 viscometer. The results are shown in the following table:

TABLE-US-00006 Dynamic viscosity [mPa .Math. s] Temperature [ C.] TBAEE* MDEA* TBAEEDA 20 58.4 102.2 5.4 40 16.9 34.1 2.5 60 6.9 14.4 1.6 80 3.6 7.2 1.1 *comparative example

[0116] It is clear that the dynamic viscosity of TBAEEDA is much lower at all the temperatures examined than that of the comparative examples.

[0117] In addition, the dynamic viscosities of various absorbents (without acid gas loading) were measured in the same instrument.

[0118] The results are shown in the following table:

TABLE-US-00007 Absorbent Amine Solvent Dynamic viscosity (30% by wt.) (70% by wt.) [mPa .Math. s] MDEA* sulfolane 8.2 TBAEEDA sulfolane 5.5 *comparative example

[0119] It is clear that the dynamic viscosity of the inventive absorbent is much lower than that of the comparative example.