USE OF MORPHOLINE-BASED HINDERED AMINE COMPOUNDS FOR SELECTIVE REMOVAL OF HYDROGEN SULFIDE

Abstract

A process for removing acid gases from a fluid stream, wherein the fluid stream is contacted with an absorbent comprising a compound of the general formula (I), wherein R.sub.1 and R.sub.2 are independently C.sub.1-C.sub.4-alkyl; R.sub.3 is selected from hydrogen and C.sub.1-C.sub.4-alkyl, R.sub.4, R.sub.5 and R.sub.6 are independently selected from hydrogen and 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, to obtain a treated fluid stream and a laden absorbent. The process allows for a high cyclic capacity while the compounds of the absorbent have a reduced tendency to foaming and low volatility.

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Claims

1.-13. (canceled)

14. A process for removing acid gases from a fluid stream, comprising contacting the fluid stream with an absorbent comprising a solution of a compound of the general formula (I) ##STR00006## wherein R.sub.1 and R.sub.2 are independently C.sub.1-C.sub.4-alkyl; R.sub.3 is selected from hydrogen and C.sub.1-C.sub.4-alkyl, R.sub.4, R.sub.5 and R.sub.6 are independently selected from hydrogen and C.sub.1-C.sub.4-alkyl; x and y are independently integers from 2 to 4 and z is an integer from 1 to 3; to obtain a treated fluid stream and a laden absorbent.

15. The process according to claim 14, wherein the compound of the general formula (I) is selected from the group consisting of N-[2-(2-tert-butylaminoethoxy)ethyl]-morpholine and N-[2-(3-tert-butylaminopropoxy)ethyl]-morpholine, and combinations thereof.

16. The process according to claim 14, wherein the absorbent is an aqueous solution.

17. The process according to claim 16, wherein the absorbent comprises an acid.

18. The process according to claim 14, wherein the absorbent comprises an organic solvent.

19. The process according to claim 18, wherein the organic solvent is selected from the group consisting of C.sub.4-10 alcohols, ketones, esters, lactones, amides, lactams, sulfones, sulfoxides, glycols, polyalkylene glycols, di- or mono(C.sub.1-4-alkyl ether) glycols, di- or mono(C.sub.1-4-alkyl ether) polyalkylene glycols, cyclic ureas, thioalkanols and mixtures thereof.

20. The process according to claim 19, wherein the organic solvent is selected from the group consisting of sulfones, glycols and polyalkylene glycols.

21. The process according to claim 14, wherein the absorbent comprises a tertiary amine or severely sterically hindered amine other than a compound of the general formula (I).

22. The process according to claim 21, wherein the tertiary amine is methyldiethanolamine and the severely sterically hindered amine is tert-butylamine ethoxyethanol.

23. The process according to claim 14 for selective removal of hydrogen sulfide from a fluid stream comprising carbon dioxide and hydrogen sulfide.

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

25. (canceled)

26. (canceled)

Description

[0108] The invention is illustrated in detail by the appended drawings and the examples which follow.

[0109] FIG. 1 is a schematic diagram of a plant suitable for performing the process of the invention.

[0110] FIG. 2 is a plot of the selectivity of H.sub.2S over CO.sub.2 as a function of acid gas loading with different amine aqueous solutions an amine concentration of 36 wt.-%.

[0111] FIG. 3 is a plot of the CO.sub.2 and H.sub.2S uptake as a function of treatment time by aqueous amine solutions.

[0112] FIG. 4 is a plot of the selectivity of H.sub.2S over CO.sub.2 as a function of acid gas loading with different amine aqueous solutions an amine concentration of 2.17 M.

[0113] FIG. 5 is a plot of the CO.sub.2 and H.sub.2S uptake as a function of treatment time by aqueous amine solutions.

[0114] According to FIG. 1, via the inlet Z, a suitably pre-treated gas comprising hydrogen sulfide and carbon dioxide is contacted in counter-current, 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.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] 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.

[0119] The invention is illustrated in detail by the examples which follow.

[0120] The following abbreviations were used:

[0121] MDEA: methyldiethanolamine

[0122] TBAEE: tert-butylamine ethoxyethanol

[0123] M3ETB: methoxyethoxyethoxyethyl-tert-butylamine

[0124] TBAEEM: tert-butylaminoethoxyethylmorpholine

[0125] TBAEM: tert-butylaminoethylmorpholine

[0126] Bis-MOE: bis-(2-morpholinoethyl)ether

PRODUCTION EXAMPLE 1: PREPARATION OF TERT-BUTYLAMINOETHOXYETHYLMORPHOLINE

[0127] Two oil-heated metal reactors having a length of 100 cm each and an internal diameter of 12 mm were connected in series. Each of the reactors was charged with 90 ml (122 g) of an amination catalyst (containing Ni, Co, Cu, Sn on Al.sub.2O.sub.3 obtained according to WPO 2011/067199, example 5). Subsequently, the catalyst was activated by passing 10 NL/h H.sub.2 at 260 C. and ambient pressure.

[0128] A mixture of morpholine and 2-(2-tert-butylaminoethoxy)ethanol (molar ratio 2:1) was passed over the catalyst at 170 to 195 C. and a pressure of 70 bar together with hydrogen (10 NL/h). The 2-(2-tert-butylaminoethoxy)ethanol weight hourly space velocity was set to 0.2 kg/(l.Math.h). The reaction output was 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.

[0129] The GC analysis showed a conversion of 73-98% based on 2-(2-tert-butylaminoethoxy)ethanol used, and tert-butylaminoethoxyethylmorpholine (TBAEEM) was obtained in a selectivity of 17-21%. The crude product was purified by distillation. After the removal of excess morpholine at 80 C. and 1 mbar, the target product was isolated at a distillation temperature of 64 C. at 1 mbar in a purity of >97%.

REFERENCE PRODUCTION EXAMPLE 2: PREPARATION OF TERT-BUTYLAMINOETHYLMORPHOLINE

[0130] An oil-heated glass reactor having a length of 0.9 m and an internal diameter of 28 mm was charged with 250 mL of V2A mesh rings (diameter 5 mm), above that 200 mL of a copper catalyst (support: alumina) and finally 550 mL of V2A mesh rings (diameter 5 mm).

[0131] 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.

[0132] The oil bath temperature was set to 180 to 200 C. 65-130 g/h of a mixture of tert-butylamine (TBA) and N-(2-hydroxyethyl)-morpholine (molar ratio of 4:1) was passed over the catalyst at 200 C. together with hydrogen (80 L/h). The reaction output was condensed by means of a jacketed coil condenser and analyzed by means of gas chromatography (column: 30 m DB1 from Agilent, internal diameter: 0.25 mm, d.sub.f: 1.0 m, temperature program 80 C. to 280 C. in steps of 10 C./min). The following analysis values are reported in GC area percent.

[0133] The GC analysis showed a conversion of 80% based on N-(2-hydroxyethyl)-morpholine used, and 2-methyl-N-(2-morpholinoethyl)-propane-2-amine was obtained in a selectivity of 90%. 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 115 C. and a distillation temperature of 104 C. at 10 mbar in a purity of >99.7%.

EXAMPLE 1SELECTIVITY STUDIES

[0134] The following experimental and analytical methods were used in the selectivity studies. The process absorption unit (PAU) is a semi-batch system, comprising a water saturator, a stirred autoclave to which gas can be fed in up-flow mode, and a condenser. The autoclave is equipped with a pressure gauge and a type J thermocouple. A safety rupture disc is attached to the autoclave head. A high wattage ceramic fiber heater is used to supply heat to the autoclave. The gas flows are regulated by Brooks mass flow controllers and the temperature of the condenser is maintained by a chiller.

[0135] A custom LabVIEW program is used to control the PAU operation and to acquire experimental data (temperature, pressure, stirrer speed, pH, gas flow rate, and off-gas concentration).

[0136] The experiments described hereinbelow were performed by flowing the test acid gas mixture through the autoclave in which the amine solution was previously loaded. The acid gas mixture was fed to the bottom of the reactor by-passing the water saturator. The gases leaving the autoclave were transferred through the condenser (maintained at 10 C.) in order to remove any entrained liquids. A slip-stream of the off-gas leaving the condenser was piped to a micron-GC (Inficon) for analysis while the main gas flow passed through a scrubber. After reaching breakthrough, nitrogen was used to purge the system.

[0137] The off-gas composition was measured using a custom-built micro GC. The micro GC is configured as a refinery Gas Analyzer and includes four columns (Mole Sieve, PLOT U, OV-1, PLOT Q) and four TCD detectors. A slip stream of the off-gas was injected into the micro GC approximately every 2 minutes. A small internal vacuum pump was used to transfer the sample into the micro GC. The nominal pump rate was 20 mL/min in order to achieve 10 the volume of line flushes between the sample tee and the micro GC. The actual gas injected into the micro GC was 1 L. The PLOT U column was used to separate and identify H.sub.2S and CO.sub.2, and the micro TCD was used to quantify H.sub.2S and CO.sub.2.

[0138] In Example 1, amine aqueous solutions at a concentration of 36 wt.-% amine were tested. Test conditions for Example 1 were as follows: gas feed composition: 10 mol % CO.sub.2, 1 mol % H.sub.2S, balance N.sub.2; gas flow rate: 154 sccm; temperature: 40.8 C., pressure: 1 bar; volume: 15 mL; stirring rate: 200 rpm.

[0139] FIG. 2 is a plot of the selectivity of H.sub.2S over CO.sub.2 as a function of acid gas loading with different amine aqueous solutions. FIG. 3 is a plot of the CO.sub.2 and H.sub.2S uptake as a function of treatment time by aqueous amine solutions.

[0140] The following conclusions are readily apparent from the plotted data of FIGS. 2 and 3. The capability of TBAEEM to selectively remove H.sub.2S is higher than MDEA, TBAEE and M3ETB. Higher H.sub.2S selectivity obtained by TBAEEM is due to higher H.sub.2S absorption when compared with the other sterically hindered amines, TBAEE and M3ETB. M3ETB and TBAEEM have similar CO.sub.2 pickup.

EXAMPLE 2

[0141] In this example, amine aqueous solutions at a molar concentration of 2.17 M amine were tested. Test conditions for Example 2 were as follows: gas feed composition: 10 mol % CO.sub.2, 1 mol % H.sub.2S, balance N.sub.2; gas flow rate: 154 sccm; temperature: 40.8 C., pressure: 1 bar; volume: 15 mL; stirring rate: 200 rpm.

[0142] FIG. 4 is a plot of the selectivity of H.sub.2S over CO.sub.2 as a function of acid gas loading with different amine aqueous solutions. FIG. 5 is a plot of the CO.sub.2 and H.sub.2S uptake as a function of treatment time by aqueous amine solutions.

[0143] The following conclusions are readily apparent from the plotted data of FIGS. 4 and 5. TBAEEM gives even higher selectivity towards H.sub.2S when compared with TBAEE, MDEA and M3ETB up to 0.34 mol/mol amine. Similarly to M3ETB selectivity and capacity decline as loading increases when this more concentrated solution is used: 2.17M vs. 1.50M.

EXAMPLE 3RELATIVE VOLATILITY

[0144] The volatility of M3ETB, TBAEEM and TBAEE was measured for 30 wt.-% aqueous solutions.

[0145] A glass condenser, which was operated at 5 C., was attached to a glass cylinder with a thermostated jacket. The glass cylinder was thermostated to 50 C., and 200 mL of the absorbent were introduced in each case. Over an experimental duration of 8 h, 30 NL/h of N.sub.2 were passed through the absorbent at ambient pressure. Thereafter, the condensate obtained in the glass condenser was separated and analyzed for its composition by GC analysis and Karl-Fischer titration.

[0146] The results are shown in the following table:

TABLE-US-00001 Amount of condensate Water Amine Solution [g] [g/100 g] [g/100 g] 30% M3ETB* 30.1 99.2 0.7 30% TBAEE* 30 99.3 0.7 30% MDEA* 27.1 99.4 0.7 30% TBAEEM 30.5 99.6 0.2 *comparative example

[0147] From the data above, it is readily apparent that volatility of TBAEEM is significantly lower compared to TBAEE and M3ETB.

EXAMPLE 4FOAM TEST

[0148] All foam tests are carried out at 25 C. 150 ml of 30 wt.-% aqueous amine solution was poured into a 500 ml graduated glass cylinder. Next, a spherical diffusor stone with a defined pore size was inserted into the solution. A constant nitrogen flow of 60 Nl/h was bubbled through the diffusor stone into the solution. After 5 minutes the diffusor stone was removed out of the cylinder. The total breakdown time (collapse time) of the foam was recorded. The experiments were performed in triplicate, the corresponding average collapse times are given in the table below.

TABLE-US-00002 TBAEE TBAEEM TBAEM collapse time [sec] 32 23 23

[0149] Solutions having a collapse smaller than 30 sec can be considered as solutions having a low foaming tendency. Solutions with collapse time >30 sec have a strong foaming tendency. It can be seen that TBAEEM and TBAEM have a significant smaller foaming tendency compared to the reference example.

EXAMPLE 5SOUR GAS LOADING CAPACITY

[0150] Sour loading capacities of M3ETB, TBAEEM, TBAEM, TBAEE, MDEA, and Bis-MOE were measured for 30 wt.-% aqueous solutions.

[0151] 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 NL/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:

[0152] 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).

[0153] 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 NL/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.

[0154] 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.

[0155] The experimental results are summarized in the Table below:

TABLE-US-00003 CO.sub.2 loading CO.sub.2 loading Cyclic after loading after stripping Capacity (mol.sub.CO2/ (mol.sub.CO2/ (mol.sub.CO2/ Run Absorbent mol.sub.amine) mol.sub.amine) mol.sub.amine) 1 30 wt.-% MDEA 0.77 0.05 0.72 2 30 wt.-% TBAEE 0.97 0.24 0.73 3 30 wt.-% M3ETB 0.97 0.17 0.80 4 30 wt.-% TBAEEM 1.04 0.01 1.03 5 30 wt.-% TBAEM 0.93 0.03 0.90 6 30 wt.-% Bis-MOE 0.25 0.02 0.23 H.sub.2S loading H.sub.2S loading after after Cyclic loading stripping Capacity (mol.sub.H2S/ (mol.sub.H2S/ (mol.sub.H2S/ Run Absorbent mol.sub.amine) mol.sub.amine) mol.sub.amine) 7 30 wt.-% TBAEEM 1.04 0.03 1.01 8 30 wt.-% Bis-MOE 0.26 0.01 0.25

[0156] It can be seen that TBAEEM has a higher cyclic capacity for CO.sub.2 compared to the reference amines MDEA, TBAEE, TBAEM, M3ETB and Bis-MOE. Further, it can be seen that TBAEEM has a higher cyclic capacity for H.sub.2S compared to Bis-MOE.