Abstract
A process for refining a crude ethylene glycol stream comprising monoethylene glycol and at least one acid contaminant is disclosed. The process comprises reacting the acid contaminant with the monoethylene glycol in at least one reaction zone to form an ester and removing the ester in a separation step.
Claims
1. A process for refining a crude ethylene glycol stream comprising monoethylene glycol and at least one acid contaminant, the process comprising reacting the acid contaminant with the monoethylene glycol in at least one reaction zone to form an ester and removing the ester in a separation step.
2. A process according to claim 1, wherein the crude ethylene glycol further comprises diethylene glycol, and the process comprises reacting the acid contaminant with at least one of the monoethylene glycol or the diethylene glycol.
3. A process according to claim 1 or claim 2, wherein the crude ethylene glycol stream further comprises water and the process includes a water removal step before the reaction zone.
4. A process according to claim 3, wherein the monoethylene glycol, and diethylene glycol if present, are produced by hydrogenation of alkyl glycolate, which is in turn produced by esterification of glycolic acid with an alkanol.
5. A process according to claim 4, wherein the crude ethylene glycol stream further comprises the alkanol and the alkanol and water are removed in the water removal step.
6. A process according to claim 1, wherein water is removed from the reaction zone.
7. A process according to claim 1 wherein the process comprises reacting the acid contaminant with the monoethylene glycol, or with the at least one of the monoethylene glycol or the diethylene glycol if diethylene glycol is present, to form the ester in two reaction zones, with water removal between the two reaction zones.
8. A process according to claim 7, wherein the crude ethylene glycol stream further comprises a light ester having a boiling point lower than monoethylene glycol and the water removal also removes the light ester.
9. A process according to claim 1 wherein the at least one reaction zone comprises a catalyst selected from silica, resin, zeolites and silica-alumina.
10. A process according to claim 9 wherein the catalyst is a resin and the temperature in the reaction zone is from 50° C. to 90° C.
11. A process according to claim 9 wherein the catalyst is a silica or silica-alumina catalyst and the temperature in the reaction zone is from 140° C. to 170° C.
12. A process according to claim 1 wherein the crude ethylene glycol stream is produced by hydrogenating a stream comprising methyl glycolate.
13. A process according to claim 12, wherein the stream comprising methyl glycolate is produced by esterification of glycolic acid and methanol.
14. A process according to claim 13, wherein the stream comprising methyl glycolate further comprises glycolic acid and the hydrogenating is operated so as to convert not more than 99% of the glycolic acid to monoethylene glycol.
15. A process according to claim 13, wherein the glycolic acid used in the production of methyl glycolate by esterification of glycolic acid and methanol is produced by a hydrocarboxylation reaction between formaldehyde and carbon monoxide.
16. A process according to claim 1, wherein the acid contaminant comprises one or more of methoxyacetic acid or glycolic acid.
17. A process according to claim 1, wherein the acid contaminant is methoxyacetic acid.
18. A process according to claim 1, wherein the process further comprises collecting a low-acid stream from the at least one reaction zone and passing it to at least one further separation which separates the low-acid stream into at least a monoethylene glycol product stream comprising monoethylene glycol and a recycle stream comprising the ester.
19. A process according to claim 18, wherein the monoethylene glycol product stream comprises at least 99.9% (m/m) monoethylene glycol.
20. A process according to claim 18, wherein the at least one further separation separates the low-acid stream into at least the monoethylene glycol product stream comprising monoethylene glycol, a diethylene glycol product stream comprising diethylene glycol and the recycle stream comprising the ester.
21. A process according to claim 20, wherein the diethylene glycol product stream comprises at least 99.9% (m/m) diethylene glycol.
22. A process for producing monoethylene glycol, the process comprising hydrogenating a stream comprising methyl glycolate to produce a crude ethylene glycol stream comprising monoethylene glycol and an acid contaminant and passing the crude ethylene glycol stream to a process according to claim 1.
23. A process for producing monoethylene glycol and diethylene glycol, the process comprising hydrogenating a stream comprising methyl glycolate to produce a crude ethylene glycol stream comprising monoethylene glycol, diethylene glycol and an acid contaminant and passing the crude ethylene glycol stream to a process according to claim 1.
24. A process for producing monoethylene glycol, the process comprising esterifying glycolic acid with methanol to produce a stream comprising methyl glycolate and passing the stream comprising methyl glycolate to a process according to claim 22.
25. A process for producing monoethylene glycol and diethylene glycol, the process comprising esterifying glycolic acid with methanol to produce a stream comprising methyl glycolate and passing the stream comprising methyl glycolate to a process according to claim 23.
26. A process for producing monoethylene glycol, the process comprising reacting formaldehyde with carbon monoxide to produce a stream comprising glycolic acid and passing the stream comprising glycolic acid to a process according to claim 24.
27. A process for producing monoethylene glycol and diethylene glycol, the process comprising reacting formaldehyde with carbon monoxide to produce a stream comprising glycolic acid and passing the stream comprising glycolic acid to a process according to claim 25.
Description
DESCRIPTION OF THE DRAWINGS
[0039] Embodiments of the present invention will now be described, by way of example, and not in any limitative sense, with reference to the accompanying drawings, of which:
[0040] FIG. 1 is a schematic of a process according to the invention;
[0041] FIG. 2 is a schematic of a process according to the invention;
[0042] FIG. 3 is a schematic of a process according to the invention;
[0043] FIG. 4 is a schematic of a process according to the invention; and
[0044] FIG. 5 is a schematic of a process according to the invention comprising the process from FIG. 4 with additional separations.
DETAILED DESCRIPTION
[0045] In FIG. 1 carbon monoxide and formaldehyde are fed 5 either separately or together to a carbonylation reaction 1 in which the carbon monoxide and formaldehyde react to form glycolic acid. The resulting glycolic acid is fed 6 to an esterification 2 with methanol in which the glycolic acid is esterified to methyl glycolate. The methyl glycolate is fed 7 to a hydrogenation 3 in which the methyl glycolate is reacted with hydrogen to form MEG. DEG may also be formed. Acid contaminants, including MAA and glycolic acid are also produced. The product from the hydrogenation 3 is fed 8 to a purification step 4 in which the acid contaminants are esterified with one or both of the MEG and DEG and separated therefrom. Product stream 9 is produced containing purified MEG. A further product stream containing purified DEG may also be produced.
[0046] In FIG. 2 a purification system is shown. Crude ethylene glycol stream 10 comprises MEG and acid contaminants, including MAA and glycolic acid. Crude ethylene glycol stream 10 may also comprise DEG. In this embodiment, crude ethylene glycol stream 10 comprises 900 ppm MAA and 6500 ppm glycolic acid. The crude ethylene glycol stream 10 is fed to an esterification reactor 16 in which the acid contaminants are esterified by reaction with the MEG. In this embodiment the esterification reactor 16 operates at 60-80° C. with a resin catalyst. The crude ethylene glycol stream 10 may be passed through a cooler upstream of the esterification reactor 16 in order to lower the temperature of the crude ethylene glycol stream 10 to a suitable inlet temperature for the esterification reactor 16. To maximise the energy efficiency of the process, the cooler may comprise two stages. In the first stage the crude ethylene glycol stream 10 may be passed through an interchanger, where it is cooled by heat exchange with the cold stream 11 leaving the esterification reactor. In the second stage, the partially cooled stream leaving the interchanger is further cooled to the suitable inlet temperature for the esterification reactor by heat transfer to a cooling medium (e.g. water or air). Stream 11 leaving the esterification reactor is reheated as it passes through the interchanger.
[0047] The resin catalyst and conditions are chosen so as to limit the formation of DEG. Water may be removed from the esterification reactor 16 so as to increase the conversion of the acid contaminants. The outlet stream 11 from the esterification reactor 16 is fed to a distillation column 17. An MEG product stream 14 is taken as a side draw from the distillation column 17. In this embodiment, the level of acid contaminants in the MEG product stream 14 is less than 10 ppm. An overhead stream 15 from the distillation column 17 comprises components lighter than MEG. In order to obtain high MEG purity in the MEG product stream 14, some MEG may be allowed to slip into the overhead stream 15. The overhead stream 15 is therefore preferably recycled, optionally with a purge, and fed back into the crude ethylene glycol stream 10. In that way, the MEG in the overhead stream 15 is not lost. Bottoms stream 12 comprises components heavier than MEG, including the esters produced from the esterification of the acid contaminants. Bottoms stream 12 may be sent for further processing to recover valuable components, such as DEG for example, or may be recycled to an upstream hydrogenation, or otherwise removed from the process. The recycled stream may optionally be passed through a sulphur-removal system, for example if the resin catalyst is sulphonated and leaches sulphur.
[0048] In FIG. 3 a purification system is shown. Crude ethylene glycol stream 20 comprises MEG and acid contaminants, including MAA and glycolic acid. Crude ethylene glycol stream 20 may also comprise DEG. In this embodiment, crude ethylene glycol stream 20 comprises 900 ppm MAA and 6500 ppm glycolic acid. The crude ethylene glycol stream 20 is fed to an esterification reactor 26 in which the acid contaminants are esterified by reaction with the MEG. In this embodiment the esterification reactor 26 operates at 60-80° C. with a resin catalyst. Around 95% (m/m) of the MAA is converted in the esterification reactor 26. The crude ethylene glycol stream 20 may be passed through a cooler upstream of the esterification reactor 26 in order to lower the temperature of the crude ethylene glycol stream 20 to a suitable inlet temperature for the esterification reactor 26. The resin catalyst and conditions are chosen so as to limit the formation of DEG. The outlet stream 32 from esterification reactor 26 is fed to a distillation column 28. In the distillation column 28 water and other light components are removed in an overhead stream 29. The bottom stream 30 from the distillation column 28 is fed to a further esterification reactor 31 in which remaining acid contaminants are esterified by reaction with the MEG. The further esterification reactor 31 comprises a resin catalyst and operates at around 60-80° C. Around 95% of the remaining MAA is converted in the further esterification reactor 31. The resin catalyst and temperature range are again chosen to reduce the production of DEG. DEG production involves the production of water, which is detrimental to the conversion level of the acid contaminants. The provision of two esterification reactors 26 and 31, with intermediate water removal in distillation column 28, preferably means that water removal from the esterification reactors 26 and 31 is not required. That simplifies the design, and cost, of the esterification reactors 26 and 31 and the distillation column 28 can serve other useful purposes in the separation by removing other light components along with the water. Prior art separation processes may already include a column suitable to function as distillation column 28 and the process of the invention may therefore be implemented by inserting the esterification reactor 26 upstream of that column and the further esterification reactor 31 downstream of that column. The outlet stream 21 from the further esterification reactor 31 is fed to a distillation column 27. An MEG product stream 24 is taken as a side draw from the distillation column 27. In this embodiment, the level of acid contaminants in the MEG product stream 24 is less than 10 ppm. An overhead stream 25 from the distillation column 27 comprises components lighter than MEG. In order to obtain high MEG purity in the MEG product stream 24, some MEG may be allowed to slip into the overhead stream 25. The overhead stream 25 is therefore preferably recycled, optionally with a purge, and fed back into the crude ethylene glycol stream 20. In that way, the MEG in the overhead stream 25 is not lost. Bottoms stream 22 comprises components heavier than MEG, including the esters produced from the esterification of the acid contaminants. Bottoms stream 22 may be sent for further processing to recover valuable components, such as DEG for example, or may be recycled to an upstream hydrogenation or otherwise removed from the process.
[0049] In FIG. 4 a purification system is shown. Crude ethylene glycol stream 50 comprises MEG and acid contaminants, including MAA and glycolic acid. Crude ethylene glycol stream 50 may also comprise DEG. In this embodiment, crude ethylene glycol stream 50 comprises 900 ppm MAA and 6500 ppm glycolic acid. The crude ethylene glycol stream 50 is fed to a water removal distillation column 63. An overhead stream 64 from the water removal distillation column 64 comprises water and, if methanol is present in the crude ethylene glycol stream, for example from methyl glycolate production, methanol. Bottoms stream 65 from the water removal distillation column 63 comprises the MEG, DEG if present, and the acid contaminants. Bottoms stream 65 is fed to an esterification reactor 56 in which the acid contaminants are esterified by reaction with the MEG. In this embodiment the esterification reactor 56 operates at 150-160° C. with a silica catalyst. Around 95% (m/m) of the MAA is converted in the esterification reactor 56. The bottoms stream 65 may be passed through a cooler upstream of the esterification reactor 56 in order to lower the temperature of the bottoms stream 65 to a suitable inlet temperature for the esterification reactor 56. The silica catalyst and conditions are chosen so as to limit the formation of DEG. The silica catalyst also does not leach any sulphur. The outlet stream 62 from esterification reactor 56 is fed to a distillation column 58. In the distillation column 58 water and other light components are removed in an overhead stream 59. The bottom stream 60 from the distillation column 58 is fed to a further esterification reactor 61 in which remaining acid contaminants are esterified by reaction with the MEG. The further esterification reactor 61 comprises a silica catalyst and operates at around 150-160° C. Around 95% of the remaining MAA is converted in the further esterification reactor 61. The resin catalyst and temperature range are again chosen to reduce the production of DEG. DEG production involves the production of water, which is detrimental to the conversion level of the acid contaminants. The provision of two esterification reactors 56 and 61, with intermediate water removal in distillation column 58, preferably means that water removal from the esterification reactors 56 and 61 is not required. That simplifies the design, and cost, of the esterification reactors 56 and 61 and the distillation column 58 can serve other useful purposes in the separation by removing other light components along with the water. Prior art separation processes may already include a column suitable to function as distillation column 58 and the process of the invention may therefore be implemented by inserting the esterification reactor 56 upstream of that column and the further esterification reactor 61 downstream of that column. The outlet stream 51 from the further esterification reactor 61 is fed to a distillation column 57. An MEG product stream 54 is taken as a side draw from the distillation column 57. In this embodiment, the level of acid contaminants in the MEG product stream 54 is less than 10 ppm. An overhead stream 55 from the distillation column 57 comprises components lighter than MEG. In order to obtain high MEG purity in the MEG product stream 54, some MEG may be allowed to slip into the overhead stream 55. The overhead stream 25 is therefore recycled, optionally with a purge, and fed back into the crude ethylene glycol stream 50. In that way, the MEG in the overhead stream 55 is not lost. Bottoms stream 52 comprises components heavier than MEG, including the esters produced from the esterification of the acid contaminants. Bottoms stream 52 may be sent for further processing to recover valuable components, such as DEG for example, or may be recycled to an upstream hydrogenation or otherwise removed from the process.
[0050] In FIG. 5, the process of FIG. 4 is repeated, with like numbered items having like meaning, which is not reproduced here. In this embodiment the crude ethylene glycol stream 50 comprises DEG as well as MEG, and the DEG is thus comprised in the bottoms stream 52 from the distillation column 57, along with the esters from the esterification of the acid contaminants, some slipped MEG and other heavy contaminants.
[0051] The bottoms stream 52 from the distillation column 57 is passed to a distillation column 66. An overhead stream 67 from distillation column 66 is recycled to be fed into outlet stream 51 from the further esterification reactor 61. The overhead stream 67 comprises MEG and any MEG that was slipped into the bottoms stream 52 is thus recycled to the distillation column 57 and not lost from the process. Bottoms stream 68 from distillation column 66 comprises DEG, the esters from the esterification of the acid contaminants and other heavy contaminants. The bottoms stream 68 is fed to distillation column 71, from which DEG product stream 70 comprising DEG is taken overhead. The DEG product stream 70 may additionally or alternatively be taken as a side draw. A bottoms stream 69 comprising the esters from the esterification of the acid contaminants, some slipped DEG to ensure high purity of DEG in the DEG product stream 70 and other heavy contaminants is removed from the bottom of the distillation column 71. The bottoms stream 69 may be recycled to an upstream hydrogenation or otherwise removed from the process.
[0052] It will be appreciated by persons skilled in the art that the above embodiments have been described by way of example only, and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims. For example, embodiments described as using a resin catalyst could alternatively be operated using a silica catalyst or vice versa. Other catalysts, such as silica-alumina or zeolites, could also be used. The process of FIG. 5 could be rearranged so that the esters from the esterification of the acid contaminants are removed as a bottoms stream in a first distillation column, with a stream comprising the MEG and DEG being taken overhead and sent to a second column in which the MEG and DEG are separated. The columns could also potentially be combined, for example as a split wall column.
