Process for purifying a stream comprising 1,4-butanediol

Abstract

A crude product stream of 1,4-butandiol and one or more of -butyrolactone, 2-(4-hydroxybutoxy)-tetrahydrofuran, 4-hydroxybutyl(4-hydroxybutyrate), and 3-(4-hydroxybutoxy)-tetrahydrofuran is supplied to a first distillation column. A side-draw of 1,4-butanediol and light components is removed, with the light components including at least some of those produced by reaction in the first distillation column. The stream is passed to a hydrogenation zone and subjected to hydrogenation in the presence of a hydrogenation catalyst. A 1,4-butanediol product stream having a reduced content of 2-(4-hydroxybutoxy)-tetrahydrofuran is recovered and passed to a second distillation column operated such that (4-hyroxybutyl)-4-hydroxybutyrate is removed as a bottom stream and a 1,4-butanediol stream is removed as overhead. The overhead stream removed is passed to a third distillation column and a purified 1,4-butanediol stream is recovered.

Claims

1. A process for purifying a stream comprising 1,4-butanediol comprising the steps of: (a) supplying a crude product stream comprising (i) 1,4-butandiol, (ii) -butyrolactone, and (iii) one or more of 2-(4-hydroxybutoxy)-tetrahydrofuran,4-hydroxybutyl(4-hydroxybutyrate), and 3-(4-hydroxybutoxy)-tetrahydrofuran to a first distillation column; (b) removing a side-draw comprising 1,4-butanediol, and light components, said light components including at least some of those produced by reaction in the first distillation column; (c) passing the side-draw to a hydrogenation zone; (d) subjecting the stream from step (c) to hydrogenation in the hydrogenation zone in the presence of a hydrogenation catalyst, and recovering from the hydrogenation zone a 1,4-butanediol product stream having a reduced content of 2-(4-hydroxybutoxy)tetrahydrofuran; (e) passing the 1,4-butaendiol product stream from step (d) to a second distillation column operated such that (4-hydroxybutyl)-4-hydroxybutyrate is removed as a bottom stream and removing a 1,4-butanediol stream as overhead; and f) passing the overhead stream removed in (e) to a third distillation column to remove -butyrolactone formed in the sump of the column in step (e) and recovering therefrom a purified 1,4-butanediol.

2. The process according to claim 1 wherein the side draw from the first distillation column is taken from a point above the point at which the feed is added to the column.

3. The process according to claim 1 wherein the process additionally includes the step of: (b1) passing the side draw to the hydrogenation zone via a further distillation column in which at least some of the light components are stripped from the stream before it is passed to the hydrogenation zone.

4. The process according to claim 3, wherein the first and further distillation columns are combined into a single vessel.

5. The process according to claim 4, wherein the vessel includes a separating baffle.

6. The process according to claim 1, wherein the second and third distillation columns are combined into a single vessel.

7. The process according to claim 6, wherein the vessel includes a separating baffle.

8. The process according to claim 1, wherein a recycle from the second and/or third distillation column is fed to the first distillation column.

9. The process according to claim 1, wherein the hydrogenation is carried out at a temperature of from about 30 C. to about 170 C.

10. The process according to claim 1, wherein the hydrogenation is carried out at a pressure of from about 3.45 bar (about 50 psia) to about 137.90 bar (about 2000 psia).

11. The process according to claim 1, wherein the feed to the hydrogenation zone is supplied at a liquid hourly space velocity of from about 0.1 h.sup.1 to about 4.0 h.sup.1.

12. The process according to claim 1, wherein the distillation columns are operated at pressures of from about 0.1 to about 1 bar abs.

13. The process according to claim 1, wherein the distillation columns are operated at temperatures of from about 100 C. to about 250 C.

14. The process according to claim 1, wherein the distillation columns contain from about 10 to about 100 theoretical stages.

15. The process according to claim 1, wherein the 1,4-butanediol product stream having a reduced content of 2-(4-hydroxybutoxy)-tetrahydrofuran further includes (4-hydroxybutyl)-4-hydroxybutyrate formed by reaction of -butyrolactone.

Description

(1) The present invention will now be described by way of example with reference to the accompanying drawings in which:

(2) FIG. 1 is a simplified schematic representation of one arrangement for the process of the present invention;

(3) FIG. 2 is a simplified schematic representation of a second arrangement for the process of the present invention;

(4) FIG. 3 is a simplified schematic representation of a third arrangement for the process of the present invention;

(5) FIG. 4 is a simplified schematic representation of a fourth arrangement for the process of the present invention;

(6) FIG. 5 is a graph referred to in Example 1; and

(7) FIG. 6 is a graph referred to in Example 2.

(8) It will be understood that the drawings are diagrammatic and that further items of equipment such as reflux drums, pumps, compressors, vacuum pumps, temperature sensors, pressure sensors, pressure relief valves, control valves, flow controllers, level controllers, holding tanks, storage tanks and the like may be required in a commercial plant. The provision of such ancillary items of equipment forms no part of the present invention and is in accordance with conventional chemical engineering practice.

(9) As illustrated in FIG. 1, a feed stream is fed in line 1. In one arrangement this feed stream will comprise butanediol, -butyrolactone, dialkyl alkoxysuccinate, transesters such as 4 hydroxybutyl methyl succinate, heavy ethers such as bis(4-hydroxy)dibutyl ether, 4-hydroxybutyl (4-hydroxybutyrate), 2-(4 hydroxybutoxy)-tetrahydrofuran, 3-(4 hydroxybutoxy)-tetrahydrofuran, other minor impurities and residual alkanols, tetrahydrofuran and water. This stream is fed to distillation column A. A recycle stream 9 containing heavy components from downstream units can also be fed to first distillation column A. This recycle stream may be fed to first distillation column A at the same point as feed stream 1 and/or it may be supplied to the column at a different point, which will generally be lower than the point at which stream 1 is fed to first distillation column A.

(10) The heavy components in the feed 1 and recycle stream 9 will concentrate in section A1 of the first distillation column and are removed in purge stream 2. The heavy components concentrating in section A1 will include 4-hydroxybutyl (4-hydroxybutyrate) which will react in the sump to reform to 1,4-butanediol, and -butyrolactone. The -butyrolactone, being lighter, will then travel back up the column.

(11) The concentration of heavy components, including 4-hydroxybutyl (4-hydroxybutyrate) will reduce in section A2 of the column thereby reducing the heavy component content in the product side draw 3. The stream removed in side draw will include the -butyrolactone formed in the sump by the reaction of 4-hydroxybutyl (4-hydroxybutyrate).

(12) In one arrangement, the side draw 3 is taken from above the feed stream 1. At least some of the light components from the feed stream will also be present in the stream removed by the side draw 3. This stream is passed to the further distillation column B where they are at least partially removed and returned to distillation column A via stream 4.

(13) Reflux for the further distillation column B is provided by a partial condenser H3. By this combination of distillation columns, the light and heavy components in the feed and the light components produced by reaction in the sump of the first distillation column A are removed and therefore the stream 6 removed from the bottom of the further distillation column B has a reduced content of these components.

(14) In an alternative arrangement the side draw can be taken at a point below the point of entry of feed stream 1. This lower side draw is illustrated in FIG. 1 as line 3a. This stream is then partially condensed in the condenser H3, without being passed through further distillation column B. This will reduce the light component content of the stream 6a, but only partially reduce the heavy component content of the stream 6a. Whether or not the further distillation column B is present the remaining light components, including -butyrolactone, dialkyl alkoxysuccinate, and residual alkanols, tetrahydrofuran and water are concentrated in section A3 of distillation column A and removed in the overhead stream 5.

(15) The stream 6 or 6a will contain the majority of the 2-(4 hydroxybutoxy)-tetrahydrofuran and 3-(4 hydroxybutoxy)-tetrahydrofuran from the feed stream 1. The 2-(4 hydroxybutoxy)-tetrahydrofuran is removed in the hydrogenation zone C as described in U.S. Pat. No. 6,137,016. Residual -butyrolactone in stream 6 or 6a will react to 4-hydroxybutyl (4-hydroxybutyrate) in the hydrogenation zone C. However the -butyrolactone content of stream 6 and hence the amount of 4-hydroxybutyl (4-hydroxybutyrate) made in hydrogenation zone (C) will be considerably less where the further distillation column B is present to reduce the lights content of stream 6 without taking into account the reaction of heavy components to light components in the sump of distillation column A.

(16) The product 7 from the hydrogenation zone C is fed to the second distillation column D. The residual 4-hydroxybutyl (4-hydroxybutyrate) formed in the hydrogenation zone C is concentrated in section D1 of distillation column D, and purged from the bottom of the column via stream 8. Other impurities which may be present will also be concentrated in section D1. Stream 8 can be recycled to the first distillation column A via stream 9 to further recover 1,4-butanediol and further react the 4-hydroxybutyl (4-hydroxybutyrate) to reduce the loss of heavy material. Reflux for the second distillation column D is provided by partial condenser H5. The heavy components, including 4-hydroxybutyl (4-hydroxybutyrate) are removed in section D2 of column D. This significantly reduces the quantity of 4-hydroxybutyl (4-hydroxybutyrate) being fed to the third distillation column E in stream 10. The advantage of this is there will be less 4-hydroxybutyl (4-hydroxybutyrate) in the sump of the third distillation column E to react to -butyrolactone, and hence this will reduce the -butyrolactone content in the third distillation column E. This will assist in the separation of 3-(4 hydroxybutoxy)-tetrahydrofuran in the third distillation column E, which would otherwise be difficult to separate in the presence of significant quantities of -butyrolactone.

(17) The 3-(4 hydroxybutoxy)-tetrahydrofuran, any residual -butyrolactone and other residual light components are removed in section E1 of the third distillation column E. The light components are concentrated in section E2 of the third distillation column E and removed overhead in stream 11. The overhead stream 11 can be recycled via stream 12 to the first distillation column A or via separation columns upstream of first distillation column A to recover 1,4-butanediol and -butyrolactone in stream 12. A purge stream 13 can be used to remove the light impurities including 3-(4 hydroxybutoxy)-tetrahydrofuran from this recycle. The product 1,4-butanediol is removed as a bottom stream 14 or preferably as a sidestream close to, or at, the bottom of third distillation column E.

(18) An alternative arrangement of the second and third distillation columns D and E is illustrated in FIG. 2. The scheme is the same as that of FIG. 1 up to the hydrogenation zone C. The product stream 7 from the hydrogenation zone C is fed to the second distillation column D. The residual 4-hydroxybutyl (4-hydroxybutyrate) formed in the hydrogenation zone C is concentrated in section D1 of the second distillation column D, and purged from the bottom of the column via stream 8. Other impurities which may be present will also be concentrated in section D1. Reflux for column D is provided by a condenser H5. The heavy components, including 4-hydroxybutyl (4-hydroxybutyrate) are removed in section D2 of the second distillation column D. A side draw 13 is taken from the second distillation column D above the feed stream 7 and fed to the third distillation column E. The 3-(4 hydroxybutoxy)-tetrahydrofuran, any residual -butyrolactone and other residual light components are removed in section E1 of the third distillation column E. Reflux for the third distillation column E is provided by a partial condenser H7 and the light components removed are fed to the second distillation column D via stream 14. The light components are concentrated in section D3 of the second distillation column D and removed overhead in stream 10. The product 1,4-butanediol 15 is removed as a bottom stream or preferably as a sidestream close to, or at, the bottom of the third distillation column E.

(19) Alternative arrangements of distillation columns A, B, D and E can be used. One alternative arrangement is illustrated in FIG. 3. In this arrangement the duties of condensers H1 and H3 can be combined, and condensers H5 and H7 can be combined, saving on the number of installed equipment items. This is applicable to both schemes illustrated in FIGS. 1 and 2.

(20) A further alternative arrangement of distillation columns A, B, D and E can be used and is illustrated in FIG. 4. In this arrangement the operations of first and further distillation columns A and B are combined into a single vessel by use of a sealed, separating baffle 20 which extends completely to the bottom of the vessel. The single vessel will require two reboilers, H2 and H4. Similarly second distillation column D and third distillation column E can be combined into a single vessel by use of a sealed, separating baffle 21 which extends completely to the bottom of the vessel. The single vessel has two reboilers H6 and H8. In terms of separation the schemes in FIGS. 3 and 4 are equivalent and hence the description and line numbers for FIG. 3 is the same for FIG. 4. Both schemes will achieve the removal of the light and heavy impurities in the feed stream 1 in conjunction with the light components produced as a product of reaction in the sumps of distillation columns A and C, to produce high purity 1,4-butanediol.

(21) The present invention will now be discussed with reference to the following examples.

EXAMPLE 1

(22) A fluid stream produced by the hydrogenation of dimethyl maleate containing approximately 15 wt % -butyrolactone and 4 wt % 4-hydroxybutyl(4-hydroxybutyrate) is fed to a distillation column with a side draw below the feed point. The graph set out in FIG. 5 illustrates the -butyrolactone content obtainable in the side draw, when the 4-hydroxybutyl(4-hydroxybutyrate) reacts in the sump of the column to produce 1,4-butanediol and -butyrolactone. There is a lower limit below which it is difficult to reduce this composition. This limit is dependent on the composition of 1,4-butanediol and -butyrolactone produced in the hydrogenation.

(23) By way of comparison, the graph of FIG. 5 also illustrates the 4-hydroxybutyl(4-hydroxybutyrate) in the side draw if the 4-hydroxybutyl(4-hydroxybutyrate) did not react in the sump of the column. In this case, where distillative effects alone would determine composition, the -butyrolactone content is almost zero.

(24) Also by way of comparison, the graph of FIG. 5 illustrates the -butyrolactone composition achievable in the product of the side draw from column A is taken above the feed and fed to a second column B. In this case the -butyrolactone is substantially reduced.

EXAMPLE 2

(25) A fluid stream from the hydrogenation zone C containing approximately 1-1.5 wt % -butyrolactone and 1-1.5 wt % 4-hydroxybutyl(4-hydroxybutyrate) is fed to a distillation column with a side draw below the feed point. The stream also contains other light and heavy impurities and a reduced content of 2-(4-hydroxybutoxy)-tetrahydrofuran as a result of the reaction in hydrogenation zone C. The graph of FIG. 6 illustrates the -butyrolactone content obtainable in the side draw, when the 4-hydroxybutyl(4-hydroxybutyrate) reacts in the sump of the column to produce 1,4-butanediol and -butyrolactone, and the achievable product purity.

(26) By way of comparison the graph also illustrates the -butyrolactone composition and product purity achievable if the side draw from column D is taken from above the feed and fed to a second column E. This illustrates that substantially higher purity can be achieved with this arrangement.

EXAMPLE 3

(27) A stream of fluid containing 0.14 wt % 3-(4-hydroxybutoxy)-tetrahydrofuran, 0.25 wt % -butyrolactone and the remainder 1,4 butanediol and other impurities, was heated to the boiling point of the mixture. The mixture was then allowed to partially flash in a glass vessel at a vacuum pressure of 175 mbar. The vapour from this flash was condensed in a glass condenser and the resultant liquid collected and analysed. The liquid from the flash was also collected and analysed. Analysis was by gas chromatography. The vapour from this flash contained 0.18 wt % of 3-(4-hydroxybutoxy)-tetrahydrofuran, and 97.12 wt % of 1,4 butanediol. The liquid contained 0.13 wt % 3-(4-hydroxybutoxy)-tetrahydrofuran and 92.52 wt % of 1,4 butanediol. The volatility of 3-(4-hydroxybutoxy)-tetrahydrofuran relative to 1,4 butanediol in this mixture was 1.32.

(28) A second similar stream of fluid containing 0.11 wt % 3-(4-hydroxybutoxy)-tetrahydrofuran, 15 wt % -butyrolactone and the remainder 1,4 butanediol and other impurities, was flashed in a similar manner. The vapour from this flash contained 0.076 wt % of 3-(4-hydroxybutoxy)-tetrahydrofuran and 52.6 wt % of 1,4 butanediol. The liquid contained 0.096 wt % 3-(4-hydroxybutoxy)-tetrahydrofuran and 77.98 wt % of 1,4 butanediol. The volatility of 3-(4-hydroxybutoxy)-tetrahydrofuran relative to 1,4 butanediol in this mixture was 1.17.

(29) The higher volatility of 3-(4-hydroxybutoxy)-tetrahydrofuran relative to 1,4 butanediol at the lower -butyrolactone concentration illustrates that the separation of 3-(4-hydroxybutoxy)-tetrahydrofuran from 1,4 butanediol is easier at lower -butyrolactone concentration in the feed.