PROCESS FOR PREPARING ALKANOLAMINES USEFUL IN REMOVAL OF ACID-GAS FROM A GASEOUS STREAM

Abstract

The invention relates to a process for preparing alkanolamines, useful in the removal of CO.sub.2 and/or H.sub.2S from a CO.sub.2 and/or H.sub.2S containing gaseous stream, wherein the preparation of the alkanolamines is conducted using specifically selected ionic liquids under specifically selected reaction conditions.

Claims

1. A process for preparing an alkanolamine compound of formula I and/or an alkanolamine compound of formula II, or salts thereof: ##STR00022## wherein: R.sub.1 and R.sub.2 are independently selected from hydrogen, a C.sub.1 to C.sub.8, straight chain or branched alkyl group, a C.sub.2 to C.sub.8 straight chain or branched alkenyl group, a C.sub.3 to C.sub.8 cycloalkyl group, a C.sub.6 to C.sub.10 aryl group, a 3 to 10 membered heterocyclic group, a polysaccharide group, a polyethylene oxide group, or R.sub.1 and R.sub.2 together with the nitrogen atom to which they are attached form a heterocyclic group, wherein said alkyl, alkenyl, cycloalkyl, aryl and heterocyclic groups are unsubstituted or may be substituted by one to three groups selected from: C.sub.1 to C.sub.6 alkoxy, C.sub.2 to C.sub.8 alkoxyalkoxy, C.sub.3 to C.sub.8 cycloalkyl, C.sub.6 to C.sub.10 aryl, 3 to 10 membered heterocyclic, C.sub.7 to C.sub.10 aralkyl, 3 to 10 membered heterocyclic-C.sub.1 to C.sub.4 alkyl, OH, CH.sub.2CH(OH)CH.sub.2(OH), CH(CH.sub.2OH).sub.2, or NR.sub.3R.sub.4, wherein R.sub.3 and R.sub.4 are independently selected from hydrogen or C.sub.1 to C.sub.6 straight chain or branched alkyl group; said process comprising the following steps: i) preparing glycidol in a one-pot reaction of glycerol with dimethylcarbonate, at a temperature of from 100 C. to 160 C. and a molar ratio of glycerol to dimethylcarbonate of from 1:4 to 1:10, in the presence of an ionic liquid catalyst having the formula:
[Cat.sup.+][X.sup.] wherein: [Cat.sup.+] represents one or more cationic species, and [X.sup.] represents one or more anionic species; ii) reacting the product of step i) with an amine of formula III, ##STR00023## wherein: R.sub.1 and R.sub.2 are as defined for formula I and II.

2. A process according to claim 1, wherein the molar ratio of glycerol to dimethylcarbonate in step i) is from 1:5 to 1:8.

3. A process according to claim 1 or claim 2, wherein the reaction in step i) is conducted at a temperature of from 110 C. to 140 C.

4. A process according to any of claims 1 to 3, wherein the reaction in step i) is conducted at a temperature of from 115 C. to 130 C.

5. A process according to any of claims 1 to 4, wherein the reaction in step i) is conducted at a temperature of from 115 C. to 125 C.

6. A process according to any of claims 1 to 5, wherein the amount of ionic liquid catalyst in step i) is at least 5 mol % based on glycerol.

7. A process according to any of claims 1 to 6, wherein the glycidol formed in step i) is reacted with the amine of formula III in step ii) without prior separating from the reaction mixture.

8. A process according to any of claims 1 to 6, wherein the glycidol formed in step i) is isolated from the reaction mixture before being reacted with the amine of formula III in step ii).

9. A process according to claim 8, wherein glycidol is isolated from the reaction mixture using liquid-liquid extraction and glycidol is preferentially extracted into an organic phase.

10. A process according to claim 9, wherein the liquid extraction is with ethyl acetate and glycidol is preferentially extracted into an ethyl acetate organic phase.

11. A process according to claim 8, wherein glycidol is isolated from the reaction mixture using azeotropic distillation.

12. A process according to claim 11, wherein azeotropic distillation is performed using cumene.

13. A process according to claim 12, wherein the glycidol-cumeme mixture obtained from azeoptropic distillation is used directly for reaction with the amine of formula III in step ii).

14. A process according to any of claims 1 to 13 wherein glycidol is added portion-wise to the amine of formula III for reaction in step ii).

15. A process according to claim 14 wherein glycidol is added drop-wise to the amine of formula III for reaction in step ii).

16. A process according to any of claims 1 to 15, wherein the reaction in step ii) is conducted at a temperature of from 10 C. to 100 C.

17. A process according to any of claims 1 to 16, wherein the reaction in step ii) is conducted at a temperature of from 30 C. to 70 C.

18. A process according to any of claims 1 to 17, wherein the reaction in step ii) is conducted at a temperature of from 40 C. to 60 C., for example 50 C.

19. A process according to any of claims 1 to 18, further comprising isolating the alkanolamine compound of formula I and/or II from the product mixture of step ii).

20. A process according to claim 19, wherein the alkanolamine compound of formula I and/or II is isolated by distillation.

21. A process according to any of claims 1 to 20, wherein R.sub.1 and R.sub.2 are independently selected from hydrogen, a C.sub.1 to C.sub.8, straight chain or branched alkyl group, a C.sub.2 to C.sub.8 straight chain or branched alkenyl group, a C.sub.3 to C.sub.8 cycloalkyl group, a C.sub.6 to C.sub.10 aryl group, a 3 to 10 membered heterocyclic group, or R.sub.1 and R.sub.2 together with the nitrogen atom to which they are attached form a heterocyclic group, wherein said alkyl, alkenyl, cycloalkyl, aryl and heterocyclic groups are unsubstituted or may be substituted by one to three groups selected from: C.sub.1 to C.sub.6 alkoxy, C.sub.2 to C.sub.8 alkoxyalkoxy, C.sub.3 to C.sub.8 cycloalkyl, C.sub.6 to C.sub.10 aryl, 3 to 10 membered heterocyclic, C.sub.7 to C.sub.10 aralkyl, 3 to 10 membered heterocyclic-C.sub.1 to C.sub.4 alkyl, OH, CH.sub.2CH(OH)CH.sub.2(OH), CH(CH.sub.2OH).sub.2, or NR.sub.yR.sup.z, wherein R.sub.y and R.sub.z are independently selected from hydrogen or C.sub.1 to C.sub.6 straight chain or branched alkyl group.

22. A process according to any of claims 1 to 21, wherein R.sub.1 and R.sub.2 are independently selected from hydrogen, a C.sub.1 to C.sub.6, straight chain or branched alkyl group, a C.sub.3 to C.sub.6 cycloalkyl group, a C.sub.6 to C.sub.10 aryl group, a 3 to 8 membered heterocyclic group, or R.sub.1 and R.sub.2 together with the nitrogen atom to which they are attached form a heterocyclic group, wherein said alkyl, cycloalkyl, aryl, heterocyclic groups are unsubstituted or may be substituted by one to three groups selected from: C.sub.1 to C.sub.6 alkoxy, C.sub.2 to C.sub.8 alkoxyalkoxy, C.sub.3 to C.sub.6 cycloalkyl, C.sub.6 to C.sub.10 aryl, 3 to 8 membered heterocyclic, C.sub.7 to C.sub.10 aralkyl, 3 to 10 membered heterocyclic-C.sub.1 to C.sub.4 alkyl, OH, CH.sub.2CH(OH)CH.sub.2(OH), CH(CH.sub.2OH).sub.2, or NR.sub.yR.sup.z, wherein R.sub.y and R.sup.z are independently selected from hydrogen or C.sub.1 to C.sub.6 straight chain or branched alkyl group.

23. A process according to any of claims 1 to 22, wherein R.sub.1 and R.sub.2 are independently selected from hydrogen, a C.sub.1 to C.sub.6, straight chain or branched alkyl group, a C.sub.3 to C.sub.6 cycloalkyl group, a C.sub.6 to C.sub.10 aryl group, a 3 to 8 membered heterocyclic group, or R.sub.1 and R.sub.2 together with the nitrogen atom to which they are attached form a heterocyclic group, wherein said alkyl, cycloalkyl, aryl, heterocylic groups are unsubstituted or may be substituted by one to three groups selected from: C.sub.1 to C.sub.6 alkoxy, C.sub.2 to C.sub.8 alkoxyalkoxy, C.sub.3 to C.sub.6 cycloalkyl, C.sub.6 to C.sub.10 aryl, 3 to 8 membered heterocyclic, OH, CH.sub.2CH(OH)CH.sub.2(OH), CH(CH.sub.2OH).sub.2, or NR.sub.yR.sup.z, wherein R.sub.y and R.sub.z are independently selected from hydrogen or C.sub.1 to C.sub.6 straight chain or branched alkyl group.

24. A process according to any of claims 1 to 23, wherein R.sub.1 and R.sub.2 are independently selected from hydrogen and a C.sub.1 to C.sub.6, straight chain or branched alkyl group, or R.sub.1 and R.sub.2 together with the nitrogen atom to which they are attached form a heterocyclic group, wherein said alkyl group or said heterocyclic group are unsubstituted or may be substituted by one to three groups selected from: C.sub.1 to C.sub.6 alkoxy, C.sub.2 to C.sub.8 alkoxyalkoxy, C.sub.3 to C.sub.6 cycloalkyl, C.sub.6 to C.sub.8 aryl, 3 to 8 membered heterocyclic, OH, CH.sub.2CH(OH)CH.sub.2(OH), CH(CH.sub.2OH).sub.2, or NR.sub.yR.sup.z, wherein R.sub.y and R.sub.z are independently selected from hydrogen or C.sub.1 to C.sub.6 straight chain or branched alkyl group.

25. A process according to any of claims 1 to 24, wherein R.sub.1 and R.sub.2 are independently selected from hydrogen and a C.sub.1 to C.sub.6, straight chain or branched alkyl group wherein said alkyl group is unsubstituted or may be substituted by one to three groups selected from: C.sub.3 to C.sub.6 cycloalkyl, C.sub.6 to C.sub.8 aryl, OH and NR.sub.yR.sup.z, wherein R.sub.y and R.sup.z are independently selected from hydrogen or C.sub.1 to C.sub.6 straight chain or branched alkyl group.

26. A process according to any of claims 1 to 25, wherein R.sub.1 and R.sub.2 are independently selected from hydrogen and a C.sub.1 to C.sub.6, straight chain or branched alkyl group wherein said alkyl group is unsubstituted or may be substituted by one to three groups selected from: OH and NR.sub.yR.sup.z, wherein R.sub.y and R.sup.z are independently selected from hydrogen or C.sub.1 to C.sub.6 straight chain or branched alkyl group.

27. A process according to any of claims 1 to 20, wherein R.sub.1 is selected from a polysaccharide group or a polyethylene oxide group.

28. A process according to claim 27, wherein R.sub.1 is derived from chitosan polysaccharide.

29. A process according to any of claims 1 to 28, wherein [Cat.sup.+] comprises a cationic species selected from: ammonium, benzimidazolium, benzofuranium, benzothiophenium, benzotriazolium, borolium, cinnolinium, diazabicyclodecenium, diazabicyclononenium, 1,4-diazabicyclo[2.2.2]octanium, diazabicyclo-undecenium, dithiazolium, furanium, guanidinium, imidazolium, indazolium, indolinium, indolium, morpholinium, oxaborolium, oxaphospholium, oxazinium, oxazolium, iso-oxazolium, oxothiazolium, phospholium, phosphonium, phthalazinium, piperazinium, piperidinium, pyranium, pyrazinium, pyrazolium, pyridazinium, pyridinium, pyrimidinium, pyrrolidinium, pyrrolium, quinazolinium, quinolinium, iso-quinolinium, quinoxalinium, quinuclidinium, selenazolium, sulfonium, tetrazolium, thiadiazolium, iso-thiadiazolium, thiazinium, thiazolium, iso-thiazolium, thiophenium, thiuronium, triazinium, triazolium, iso-triazolium, and uronium.

30. A process according to any of claims 1 to 29 wherein [Cat.sup.+] comprises an acyclic cation selected from:
[N(R.sup.a)(R.sup.b)(R.sup.c)(R.sup.d)].sup.+, [P(R.sup.a)(R.sup.b)(R.sup.c)(R.sup.d)].sup.+, and [S(R.sup.a)(R.sup.b)(R.sup.c)].sup.+, wherein: R.sup.a, R.sup.b, R.sup.c, and R.sup.d are each independently selected from a C.sub.1 to C.sub.30, straight chain or branched alkyl group, a C.sub.3 to C.sub.8 cycloalkyl group, or a C.sub.6 to C.sub.10 aryl group; and wherein said alkyl, cycloalkyl or aryl groups are unsubstituted or may be substituted by one to three groups selected from: C.sub.1 to C.sub.6 alkoxy, C.sub.2 to C.sub.12 alkoxyalkoxy, C.sub.3 to C.sub.8 cycloalkyl, C.sub.6 to C.sub.10 aryl, C.sub.7 to C.sub.10 alkaryl, C.sub.7 to C.sub.10 aralkyl, CN, OH, SH, NO.sub.2, CO.sub.2R.sup.x, OC(O)R.sup.x, C(O)R.sup.x, C(S)R.sup.x, CS.sub.2R.sup.x, SC(S)R.sup.x, S(O)(C.sub.1 to C.sub.6)alkyl, S(O)O(C.sub.1 to C.sub.6)alkyl, OS(O)(C.sub.1 to C.sub.6)alkyl, S(C.sub.1 to C.sub.6)alkyl, SS(C.sub.1 to C.sub.6alkyl), NR.sup.xC(O)NR.sup.yR.sup.z, NR.sup.xC(O)OR.sup.y, OC(O)NR.sup.yR.sup.z, NR.sup.xC(S)OR.sup.y, OC(S)NR.sup.yR.sup.z, NR.sup.xC(S)SR.sup.y, SC(S)NR.sup.yR.sup.z, NR.sup.xC(S)NR.sup.yR.sup.z, C(O)NR.sup.yR.sup.z, C(S)NR.sup.yR.sup.z, NR.sup.yR.sup.z, or a heterocyclic group, wherein R.sup.x, R.sup.y and R.sup.z are independently selected from hydrogen or C.sub.1 to C.sub.6 alkyl.

31. A process according to any of claims 1 to 30 wherein [Cat.sup.+] comprises an aromatic heterocyclic cationic species selected from: benzimidazolium, benzofuranium, benzothiophenium, benzotriazolium, cinnolinium, diazabicyclodecenium, diazabicyclononenium, diazabicyclo-undecenium, dithiazolium, imidazolium, indazolium, indolinium, indolium, oxazinium, oxazolium, iso-oxazolium, oxathiazolium, phthalazinium, pyrazinium, pyrazolium, pyridazinium, pyridinium, pyrimidinium, quinazolinium, quinolinium, iso-quinolinium, quinoxalinium, tetrazolium, thiadiazolium, iso-thiadiazolium, thiazinium, thiazolium, iso-thiazolium, triazinium, triazolium, and iso-triazolium.

32. A process according to any of claims 1 to 31, wherein [Cat.sup.+] comprises a saturated heterocyclic cation selected from cyclic ammonium, 1,4-diazabicyclo[2.2.2]octanium, morpholinium, cyclic phosphonium, piperazinium, piperidinium, quinuclidinium, and cyclic sulfonium.

33. A process according to claim 32, wherein [Cat.sup.+] comprises a saturated heterocyclic cation having the formula: ##STR00024##

34. A process according to any of claims 1 to 33, wherein [X.sup.] comprises one or more anions selected from hydroxides, halides, perhalides, pseudohalides, sulphates, sulphites, sulfonates, sulfonimides, phosphates, phosphites, phosphonates, methides, borates, carboxylates, azolates, carbonates, carbamates, thiophosphates, thiocarboxylates, thiocarbamates, thiocarbonates, xanthates, thiosulfonates, thiosulfates, nitrate, nitrite, perchlorate, halometallates, amino acids and borates.

35. A process according to any of claims 1 to 34, wherein [X.sup.] comprises an anion selected from [CO.sub.3].sup.2, [HCO.sub.3].sup., [MeCO.sub.3].sup., [OH].sup., and [SH].sup..

36. A process according to any of claims 1 to 28, wherein the ionic liquid is tributylmethylammonium methylcarbonate.

37. A process according to any of claims 1 to 28, wherein the ionic liquid is 1-butyl-1-methylpyrrolidinium methylcarbonate.

38. A process according to any of claims 1 to 28, wherein the ionic liquid is tetramethylammonium hydroxide.

39. A process according to any of claims 1 to 38, further comprising the steps of: iii) contacting a CO.sub.2 and/or H.sub.2S containing gaseous stream with an alkanolamine compound of formula I and/or an alkanolamine compound of formula II, or salts thereof, prepared in step ii); and iv) obtaining a treated gaseous stream having a reduced content of CO.sub.2 and/or H.sub.2S compared with the CO.sub.2 and/or H.sub.2S containing gaseous stream of step iii).

40. A process according to claim 39, wherein the alkanolamine compound of formula I and/or II is provided in the form of a solution.

41. A process according to claim 40, wherein the total amount of alkanolamine compound of formula I and/or II in the solution is from 20% to 70% by weight.

42. A process according to claim 40 or claim 41, wherein the total amount of alkanolamine compound in the solution is from 30% to 60% by weight, for example 40% by weight.

43. A process according to any of claims 40 to 42, wherein the solution is aqueous.

44. A process according to claim 39, wherein the alkanolamine compound is provided in supported form.

45. A process according to claim 44, wherein the support is a membrane based support.

46. A process according to claim 45, wherein the support is a polyethersulfone based support.

47. A process according to any of claims 39 to 46, wherein contacting step iii) is performed at a temperature of from 10 to 80 C.

48. A process according to any of claims 39 to 47, wherein contacting step iii) is performed at a temperature of from 20 to 60 C.

49. A process according to any of claims 39 to 48, wherein contacting step iii) is performed at a temperature of from 30 to 50 C.

50. A process according to any of claims 39 to 49, wherein contacting step iii) is performed at a pressure of from 100 to 2000 kPa.

51. A process according to any of claims 39 to 50, wherein contacting step iii) is performed at a pressure of from 200 to 1000 kPa.

52. A process according to any of claims 39 to 51, wherein contacting step iii) is performed at a pressure of 500 kPa.

53. A process according to any of claims 39 to 52, further comprising separating CO.sub.2 and/or H.sub.2S absorbed by the alkanolamine compound of formula I and/or II in contacting step iii) by subjecting to a reduced pressure.

54. A process according to any of claims 39 to 53, further comprising separating CO.sub.2 and/or H.sub.2S absorbed by the alkanolamine compound of formula I and/or II in contacting step iii) by stripping with steam.

55. Use of an alkanolamine compound of formula I and/or formula II prepared by the process defined in any of the preceding claims for removing CO.sub.2 and/or H.sub.2S from a CO.sub.2 and/or H.sub.2S containing gaseous stream.

56. Use according to claim 55, wherein the gaseous stream is a methane-containing gaseous stream.

57. Use according to claim 55 or claim 56, wherein the gaseous stream is a natural gas stream.

58. Use according to claim 55, wherein the gaseous stream is a biogas-derived stream.

59. Use according to claim 55, wherein the gaseous stream is a flue gas stream.

60. Use according to claim 55, wherein the gaseous stream is a breathing gas stream for a life support system.

Description

[0181] The present invention will now be illustrated by way of the following examples and with reference to the following figures:

[0182] FIG. 1: Graphical representation of effect of temperature on conversion and selectivity as reported in Gade et al;

[0183] FIG. 2: Graphical representation of effect of GL:DMC ratio on conversion and selectivity as reported in Gade et al;

[0184] FIG. 3: Graphical representation of the effect of temperature (microwave heating with 15 minutes hold time) on glycidol selectivity for a glycidol synthesis wherein GL:DMC ratio is 1:5 using tributylmethylammonium methylcarbonate, 1-butyl-1-methylpyrrolidium methylcarbonate or tetramethylammonium hydroxide as ionic liquid catalyst;

[0185] FIG. 4: Graphical representation showing the vapour pressure-temperature profiles for industry standards MEA, DEA and MDEA;

[0186] FIG. 5: Graphical representation showing the vapour pressure-temperature profiles for industry standards DEA and MDEA against alkanolamines A and B prepared in accordance with the process of the present invention;

[0187] FIG. 6: Graphical representation comparing the CO.sub.2 absorption capacities of alkanolamines A and B prepared in accordance with the process of the invention and industry standards MEA, DEA and MDEA;

[0188] FIG. 7: Graphical representation illustrating reproducibility of results for repeated CO.sub.2 uptake experiments for alkanolamines A and B prepared in accordance with the process of the invention, as well as for industry standards MEA, DEA and MDEA; and

[0189] FIG. 8: Graphical representation illustrating how an alkanolamine prepared in accordance with the process of the present invention exhibits both chemical and physical absorption characteristics.

EXAMPLES

[0190] Preparation of Ionic Liquids

[0191] Tetramethylammonium hydroxide was prepared from a commercially available 25% solution of aqueous tetramethylammonium solution. Water was removed from the solution using a rotary evaporator.

[0192] Tributylmethylammonium methylcarbonate and 1-butyl-1-methylpyrrolidinium methylcarbonate were prepared according to the microwave-assisted synthesis of methylcarbonate salts reported in Holbrey et al., Green Chem., 2010, 12, pp 407 to 413.

[0193] Tributylamine (1.854 g, 10 mmol), DMC (0.90 g, 10 mmol) and methanol (2 ml) were added to 10 ml glass microwave process vial together with a magnetic stirring bar before the vial was sealed and placed inside a CEM Explorer microwave reactor. The solution was heated at 160 C. for 1 hour hold time with magnetic stirring. Tributylmethylammonium methylcarbonate was isolated after removal of the volatile solvent and excess DMC under reduced pressure.

[0194] 1-butylpyrrolidine (1.272 g, 10 mmol), DMC (0.90 g, 10 mmol) and methanol (2 ml) were added to 10 ml glass microwave process vial together with a magnetic stirring bar before the vial was sealed and placed inside a CEM Explorer microwave reactor. The solution was heated at 140 C. for 1 hour hold time with magnetic stirring. 1-butyl-1-methylpyrrolidinium methylcarbonate was isolated after removal of the volatile solvent and excess DMC under reduced pressure.

[0195] Microwave Reactions

[0196] A CEM Explorer microwave reactor was used for performing microwave reactions, operating at a frequency of 2450 MHz with a maximum power output of 80 W. The ingredients were added to a 10 ml glass microwave process vial together with a magnetic stirrer bar before the vial was sealed and placed inside the reactor. Samples were then run for a predetermined time at a specified hold temperature. Run times referred to below, unless otherwise indicated, refer to the time a sample is held at a particular temperature, and not the total irradiation time.

[0197] Analysis of Product Samples

[0198] Following the reaction, samples were analysed by gas chromatography (GC) using an Agilent 6890N gas chromatograph with a HP-Innowax capillary column employing a He carrier gas operated according to the following: i) flow rate of 0.7 cm.sup.3 min.sup.1 at 50 C. for one minute; ii) linear gradient of 25 C. min.sup.1 to 200 C.; iii) linear gradient of 3 C. min.sup.1 from 200 C. 10 to 230 C.; and iv) 18 minutes hold at 230 C.

[0199] One-Pot Preparation of Glycidol from Dimethyl Carbonate and Glycerol

Example 1

[0200] 1-butyl-1-methylpyrrolidinium methylcarbonate (0.02173 g, 0.1 mmol) was combined with glycerol (0.093 g, 1 mmol) and dimethylcarbonate (0.45 g, 5 mmol) in a 20 ml sealed glass tube with a pressure rating of 1000 kPa (10 bar), along with a magnetic stirrer bar. The sealed glass tube was placed in an oil bath pre-heated to 120 C. and stirred for 15 minutes with vigorous magnetic stirring. The glass tube was then removed from the oil bath and allowed to cool to room temperature before a sample extracted for gas chromatography (GC) analysis.

Example 2

[0201] The process of Example 1 was repeated, except that the reaction was heated for 30 minutes at 120 C. Catalyst loading was kept constant at 10 mol % based on glycerol and the same molar ratio of glycerol:dimethyl carbonate was employed (1:5).

Example 3

[0202] 1-butyl-1-methylpyrrolidinium methylcarbonate (0.02173 g, 0.1 mmol) was combined with glycerol (0.093 g, 1 mmol) and dimethylcarbonate (0.45 g, 5 mmol) in a 10 ml glass microwave process vial, along with a magnetic stirrer bar, before the vial was sealed. The sample was placed inside a CEM Explorer microwave reactor heated with magnetic stirring for a hold time of 15 minutes at 120 C. and a pressure of 550 kPa (5.5 bar), before the reaction mixture was analysed directly by gas chromatography (GC).

Example 4

[0203] The process of Example 3 was repeated, except that tributylmethylammonium methyl carbonate was used in place of 1-butyl-1-methylpyrrolidinium methylcarbonate. Catalyst loading was kept constant at 10 mol % based on glycerol and the same molar ratio of glycerol:dimethyl carbonate was employed (1:5).

Example 5

[0204] The process of Example 3 was repeated, except that tetramethylammonium hydroxide was used in place of 1-butyl-1-methylpyrrolidinium methylcarbonate. Catalyst loading was kept constant at 10 mol % based on glycerol and the same molar ratio of glycerol:dimethyl carbonate was employed (1:5).

Example 6

[0205] The process of Example 3 was repeated, except that a molar ratio of glycerol:dimethyl carbonate of 1:8 was used. Catalyst loading was kept constant at 10 mol % based on glycerol.

Example 7

[0206] The processes of Examples 3 to 5 were repeated for a range of different hold temperatures (100 C., 140 C. and 160 C.). Catalyst loading was kept constant at 10 mol % based on glycerol and the same molar ratio of glycerol:dimethyl carbonate was employed (1:5) in each case.

Example 8

[0207] The process of Example 3 was repeated, except that a molar ratio of glycerol:dimethyl carbonate of 1:15 was used. Catalyst loading was kept constant at 10 mol % based on glycerol.

[0208] Table 1 below shows the results of Examples 1 to 8. The results in Table 1 (corresponding to Entries 3, 4 and 7 to 16) have also been used for generating a graphical representation (FIG. 3).

TABLE-US-00001 TABLE 1 GD GC Temp. GL:DMC Conversion selectivity selectivity Entry Catalyst ( C.) ratio of GL (%) (%) (%) 1.sup.1 1-butyl-1- 120 C. 1:5 100 85 15 methylpyrrolidinium methylcarbonate 2.sup.2 1-butyl-1- 120 C. 1:5 100 86 12 methylpyrrolidinium methylcarbonate 3.sup.3 1-butyl-1- 100 C. 1:5 100 79 21 methylpyrrolidinium methylcarbonate 4.sup.3 1-butyl-1- 120 C. 1:5 100 90 8 methylpyrrolidinium methylcarbonate 5.sup.3 1-butyl-1- 120 C. 1:8 100 89 methylpyrrolidinium methylcarbonate 6.sup.3 1-butyl-1- 120 C. 1:15 100 41 30 methylpyrrolidinium methylcarbonate 7.sup.3 1-butyl-1- 140 C. 1:5 100 79 1 methylpyrrolidinium methylcarbonate 8.sup.3 1-butyl-1- 160 C. 1:5 100 76 0 methylpyrrolidinium methylcarbonate 9.sup.3 tetramethylammonium 100 C. 1:5 100 79 0 hydroxide 10.sup.3 tetramethylammonium 120 C. 1:5 97 82 15 hydroxide 11.sup.3 tetramethylammonium 140 C. 1:5 100 65 21 hydroxide 12.sup.3 tetramethylammonium 160 C. 1:5 100 58 0 hydroxide 13.sup.3 tributylmethylammonium 100 C. 1:5 78 45 32 methylcarbonate 14.sup.3 tributylmethylammonium 120 C. 1:5 96 83 13 methylcarbonate 15.sup.3 tributylmethylammonium 140 C. 1:5 100 69 21 methylcarbonate 16.sup.3 tributylmethylammonium 160 C. 1:5 100 39 0 methylcarbonate .sup.1Reaction time = 15 minutes; Heating = oil bath .sup.2Reaction time = 30 minutes; Heating = oil bath .sup.3Microwave heating GL = Glycerol; DMC = Dimethylcarbonate, GD = Glycidol, GC = Glycerol carbonate

[0209] The results of Table 1 show a surprisingly high rate of conversion and selectivity for glycidol achieved in step i) of the process according to the present invention and obtainable within a short reaction time. For instance, a GL conversion of 100% and a GD selectivity of 85% is obtained when GL and DMC, in a GL:DMC molar ratio of 1:5, are reacted in the presence of 1-butyl-1-methylpyrrolidinium methylcarbonate catalyst for 15 minutes at 120 C. using heat from an oil bath (Entry 1).

[0210] A GL conversion of 100% and a GD selectivity of 90% is obtained when GL and DMC, in a GL:DMC molar ratio of 1:5, are reacted in the presence of a 1-butyl-1-methylpyrrolidinium methylcarbonate catalyst at 120 C. in a microwave for a hold time of 15 minutes (Entry 4). A GL conversion of 97% and a GD selectivity of 82% is obtained when GL and DMC, in a GL:DMC molar ratio of 1:5, are reacted in the presence of a tetramethylammonium hydroxide catalyst at 120 C. in a microwave for a hold time of 15 minutes (Entry 10).

[0211] Isolation of Glycidol

[0212] The general procedure for isolating glycidol formed in the ionic liquid catalysed reactions was by liquid-liquid extraction. Specifically, two volume equivalents of ethyl acetate based on the volume of the reaction mixture and a single equivalent of water based on the volume of the reaction mixture were added to reaction vessel following completion of the reaction. Glycidol preferentially partitioned into the organic phase, which was then separated by decanting, before the organic solvent was removed under reduced pressure leaving a crude glycidol product.

[0213] Reaction of Glycidol with Amine of Formula III

[0214] Glycidol prepared from the reaction of dimethyl carbonate and glycerol in the presence of an ionic liquid was added to a vessel containing an amine and the resulting mixture stirred at elevated temperature in order to form the corresponding alkanolamine. In the following examples glycidol was used in pure form. However, it is possible to transfer the product mixture of step ii) of the process comprising glycidol and the ionic liquid catalyst directly to the amine without having to first isolate glycidol. Although less preferred, it is also possible to transfer amine to the product mixture of step ii) comprising glycidol and ionic liquid catalyst. However, this approach may increase the possibility of side undesired side reactions, such as glycidol polymerisation, and therefore reduce alkanolamine yield.

Example 9

[0215] Alkanolamine Mixture A

##STR00019##

[0216] Glycidol (4.96 g, 64 mmol) was added dropwise to n-propylamine (39.9 g, 675 mmol, 10.5 equiv) at 5 C. and the mixture stirred for 16 h. After this time, the excess n-propylamine was removed under vacuum. 7.49 g|.sub.[MJS1](88.1% yield) of a colourless, slightly viscous liquid was recovered. From .sup.1H NMR, the products formed were a mixture of the ring-opened structural isomers, as illustrated above and conversion was complete with respect to glycidol. The amounts of each structural isomers formed could not be determined from the .sup.1H NMR as a result of signal overlap.

Example 10

[0217] Alkanolamine Mixture B

##STR00020##

[0218] Glycidol (5.143 g, 69 mmol) was added dropwise to diethylamine (5.608 g, 77 mmol, 1.12 equiv) at 50 C. and the mixture stirred for 16 h. After this time, the excess diethylamine was removed under vacuum. 7.61 g (89.7% yield) of a colourless, slightly viscous liquid was recovered. From .sup.1H NMR, the products formed were a mixture of the ring-opened structural isomers, as illustrated above, and conversion was complete with respect to glycidol. The amounts of each structural isomer formed could not be determined from .sup.1H NMR as a result of signal overlap.

[0219] Assessing Physical Properties of Alkanolamines

Example 11

[0220] Boiling points for alkanolamine mixtures A and B, as well as industry standards MEA, DEA and MDEA were measured at reduced pressure. Atmospheric pressure boiling points were subsequently determined by extrapolation using a nomograph. The results are presented in Table 2 below. The results show that alkanolamine mixtures A and B both have boiling points which are significantly greater than MEA, and which are comparable to the boiling points of DEA and MDEA. As discussed hereinbefore, high boiling point is advantageous for reducing losses in acid-gas desorption processes during alkanolamine recycling. Alkanolamine mixture A has a boiling point which is 30 C. higher than that of Alkanolamine mixture B. This is believed to be due to increased hydrogen bonding of the secondary alkanolamine relative to the tertiary alkanolamine.

TABLE-US-00002 TABLE 2 Compound Boiling Point ( C.) MEA 170.8 DEA 268.8 MDEA 246-248 Alkanolamine A 262-263 Alkanolamine B 232-233

Example 12

[0221] Vapour pressures for alkaolamine mixtures A and B, as well as for MEA, DEA and MDEA were determined using an isoteniscope equipped with an Edwards pressure sensor. FIG. 4 shows the vapour pressure-temperature profiles for industry standards MEA, DEA and MDEA, from which it is clear that MEA has a significantly higher vapour pressure than DEA and MDEA. FIG. 5 shows the vapour pressure-temperature profiles for industry standards DEA and MDEA against alkanolamines A and B. FIG. 5 demonstrates that the alkanolamines A and B have comparable vapour pressure to DEA and MDEA.

[0222] CO.sub.2 Uptake StudyExperimental Procedure

[0223] In a typical experiment, the volume of a pressure vessel [Parr pressure system] was first determined by evacuating it under reduced pressure and subsequently pumping a known amount of gas at a certain temperature and pressure into the vessel. Measurement of the amount of gas was read as the volume of gas at standard conditions from the mass flow controller [BROOKS Smart Massflow]. The ideal gas law was used to calculate the actual volume of the pressure vessel.

[0224] A known mass and volume of alkanolamine-water mixture was placed in a pressure vessel and the vessel evacuated to 10 kPa. Carbon dioxide was then pumped into the stirred pressure vessel (500 rpm) through the mass flow controller up to 500 kPa and at 20.0 C. The system is allowed to equilibrate for 1 hour, or until no more gas was being added according to the mass flow controller.

[0225] Calculation of the total amount of gas introduced into the pressure vessel is made using the reading in the mass flow controller. The actual amount of gas in the gas phase was calculated by the ideal gas law, where the volume of the gas phase was equal to the volume of the pressure vessel minus the volume of the liquid phase. The amount of gas dissolved in the liquid phase was calculated by subtracting the actual amount of gas in the gas phase from the total amount of gas introduced into the pressure vessel.

Example 13

[0226] A 40 wt % aqueous solution of alkanolamine mixture A was prepared. 4.858 ml of the mixture was transferred to the autoclave (500 rpm), and subsequently equilibrated to 20 C. A momentary vacuum was applied, followed by the introduction of CO.sub.2 via a mass flow controller. The reactor was pressurised to 500 kPa and the total volume of CO.sub.2 added was recorded. The results are presented in Error! Reference source not found., as moles of CO.sub.2 absorbed per litre, moles absorbed per kg of absorbent and moles CO.sub.2 absorbed per mol alkanolamine.

Example 14

[0227] A 40 wt % aqueous solution of alkanolamine mixture B was prepared. 4.923 ml of the mixture was transferred to the autoclave, and subsequently equilibrated to 20 C. A momentary vacuum was applied, followed by the introduction of CO.sub.2 via a mass flow controller. The reactor was pressurised to 500 kPa and the total volume of CO.sub.2 added was recorded. The results are presented in Error! Reference source not found., as moles of CO.sub.2 absorbed per litre, moles absorbed per kg of absorbent and moles CO.sub.2 absorbed per mol alkanolamine.

Comparative Example 1

[0228] A 40 wt % solution of diethanolamine (DEA) in water was prepared. 4.984 ml of the mixture was transferred to the autoclave, and subsequently equilibrated to 20 C. A momentary vacuum was applied, followed by the introduction of CO.sub.2 via a mass flow controller. The reactor was pressurised to 500 kPa and the total volume of CO.sub.2 added was recorded. The results are presented in Error! Reference source not found., as moles of CO.sub.2 absorbed per litre, moles absorbed per kg of absorbent and moles CO.sub.2 absorbed per mol alkanolamine.

Comparative Example 2

[0229] A 40 wt % solution of methyl diethanolamine (MDEA) in water was prepared. 4.887 ml of the mixture was transferred to the autoclave, and subsequently equilibrated to 20 C. A momentary vacuum was applied, followed by the introduction of CO.sub.2 via a mass flow controller. The reactor was pressurised to 500 kPa and the total volume of CO.sub.2 added was recorded. The results are presented in Error! Reference source not found., as moles of CO.sub.2 absorbed per litre, moles absorbed per kg of absorbent and moles CO.sub.2 absorbed per mol alkanolamine.

TABLE-US-00003 TABLE 3 Vol. CO.sub.2 CO.sub.2 CO.sub.2/ Alkanol- Alkanolamine/ added Absorbed Absorbed alkanolamine amine water (w/w) (ml) (mol/L) (mol/kg) (mol/mol) A 40/60 4.858 1.98 1.94 0.64 B 40/60 4.923 1.97 1.93 0.71 DEA 40/60 4.984 3.16 3.01 0.79 MDEA 40/60 4.887 2.91 3.47 0.84

[0230] The results presented in Table 3 demonstrate that alkanolamines according to Formula I and II of the present invention exhibit comparable CO.sub.2 absorption with industry standard alkanolamines, DEA and MDEA. A notable advantage of the alkanolamines according to the present invention (A and B) is that they are more cost effective to prepare from cheap and readily available glycerol precursor.

Example 15

[0231] The methods of Examples 13 and 14 were repeated using different reactor pressures (between 100 kPa and 700 kPa CO.sub.2 partial pressure). The same procedure was also adopted across the same range of CO.sub.2 partial pressure for 40 wt % aqueous solution of MEA. For each CO.sub.2 partial pressure tested, the corresponding absorption capacity, a (mol CO.sub.2/mol alkanolamine), of the alkanolamine absorbent was determined. The results of these experiments, together with those for Comparative Examples 1 and 2 (500 kPa CO.sub.2 partial pressure) are represented graphically in FIG. 6. The results show that alkanolamine mixtures A and B, preparable by the process of the invention, have CO.sub.2 absorption capacities which are comparable with industry standards MEA, DEA and MDEA.

[0232] The results of CO.sub.2 repeated uptake experiments, performed substantially as described in Examples 13 and 14, as well as Comparative Examples 1 and 2, and conducted at a CO.sub.2 partial pressure of 500 kPa (5 bar) for alkanolamine mixtures A and B, and industry standards MEA, DEA and MDEA, are shown in FIG. 7. FIG. 7 demonstrates a high level of reproducibility of results with alkanolamines prepared in accordance with the present invention, which is comparable to the reproducibility observed with industry standards MEA, DEA and MDEA.

[0233] Chemical and Physical Absorption

Example 16

[0234] To observe the chemical and physical absorption behaviour of alkanolamines prepared in accordance with the process of the invention, uptake of CO.sub.2 by a 40 wt. % aqueous mixture of Alkanolamine Mixture A was measured for varying CO.sub.2 partial pressure.

[0235] Alkanolamine Mixture A:

##STR00021##

[0236] The alkanolamine solution was added to a cleaned/dried vessel and the vessel evacuated to 10 kPa (0.1 bar). CO.sub.2 pressure was then adjusted to 100 kPa (1 bar) and CO.sub.2 was introduced via a mass flow controller. After 2 hours, pressure was equilibrated at 100 kPa (1 bar) and the volume of CO.sub.2 added recorded. Subsequently, pressure is increased to 150 kPa (1.5 bar) and equilibrated and increased thereafter in units of 50 kPa (0.5 bar). The results of the CO.sub.2 solubility in the alkanolamine mixture are presented in FIG. 8. FIG. 8 clearly shows absorption of CO.sub.2 beyond 0.5 mol CO.sub.2 per mol of alkanolamine, as CO.sub.2 partial pressure is increased, indicating physical absorption in addition to chemical absorption.