Process for reducing the amount of 1,2-pentanediol from ethylene glycol

Abstract

A process for removing 1,2-pentanediol from a mixture rich in ethylene glycol, which process comprises extractive distillation using an entrainer in said extractive distillation having a Hansen solubility parameter δH of between 5 and 15 and the entrainer having a boiling point at atmospheric pressure of at least 200°C.

Description

[0001] PROCESS FOR REDUCING THE AMOUNT OF 1,2-PENTANEDIOL FROM ETHYLENE GLYCOL

[0002] Introduction

[0003] The present invention relates to a process for reducing the amount of 1,2-pentanediol from a mixture rich in ethylene glycol, and which mixture comprises a small amount of 1,2-pentanediol. The process comprises extractive distillation using an entrainer in said extractive distillation having a Hansen solubility parameter 6H of between 5 and 15 and the entrainer having a boiling point at atmospheric pressure of at least 200°C.

[0004] Background of the invention

[0005] Since about a decade, there is ongoing research in developing processes for manufacturing chemical building blocks from renewable sources. One such process of interest is obtaining monoethylene glycol (in short: ethylene glycol, MEG, or EG) from a (renewable) carbohydrate source such as sugar.

[0006] WO 2016 / 114661 discloses a continuous process for preparation of ethylene glycol from a carbohydrate source. Said process is carried out in a stirred tank reactor (CSTR) in which a catalyst system is present. Said catalyst system comprises a tungsten compound and at least one hydrogenolysis metal. The hydrogenolysis metal is preferably present in the form of a catalyst supported on a carrier. Such heterogeneous catalyst particles can fairly easily be separated from the effluent stream and added back.

[0007] The liquid effluent obtained is usually subjected to a series of separation steps, e.g. to separate the tungsten compound used as co-catalyst (or a tungsten compound that is formed by the process), but also to separate the various (volatile) alcohols, polyols and glycols produced. Generally, the target product in the processes like the reference above and similar processes is ethylene glycol. Whilst such processes may have a selectivity for ethylene glycol of about 40 to 70%, considerable amounts of other components are also produced, mainly monopropylene glycol (MPG), but also polyols like glycerol, sorbitol and erythritol. The mixture produced usually contains also other glycols and diols next to MEG and MPG, such as 1,2- butanediol and 1,4-butanediol. Although the typical way to separate miscible liquids on an industrial scale would be fractional distillation, such method has its limits in separating these glycols and diols, as boiling points are often close together, and some of the glycols or polyols to be separated form azeotropes, which makes separation by distillation even more difficult.

[0008] Whilst the separation of e.g. 1,2-butanediol from ethylene glycol in the context of the conversion of carbohydrates to ethylene glycol has been widely researched, less work seems to have been done on removing 1,2-pentanediol from mixtures which are rich in ethylene glycol. In the processes such as in WO 2016 / 114661 and similar 1,2-pentanediol is formed in amounts up to 1 to 2% (by weight, based on ethylene glycol produced). The problem with removing 1,2-pentanediol from ethylene glycol to a high degree, preferably such that the ethylene glycol has sufficient purity for use in the manufacturing of polyester (in short: polyester-grade EG) is that 1,2-pentanediol forms an azeotrope with ethylene glycol. Hence, removal of 1,2-pentanediol from EG to obtain EG with a limited amount of 1,2-pentanediol by conventional fractional distillation is difficult or leads to loss of large amounts of EG.

[0009] As mentioned, there are processes developed for removing 1,2-butanediol from a mixture rich in ethylene glycol, yet the separation of 1,2, -pentanediol seems less well researched. Only CN104370696 and CN104230658 refer to separation of EG and 1,2-pentanediol. In these references removal of 1,2- pentanediol from a mixture rich in ethylene glycol using azeotropic distillation is disclosed. These references do not give details as to the entrainer used in these references. For the azeotropic distillation of these references, an entrainer is added and the ethylene glycol / entrainer azeotrope is obtained at the top. This azeotropic mixture is then separated by the addition of an extractant and by filtration. The filtrate is a mixed solution of ethylene glycol and an extractant, and the filter cake is an azeotropic agent. The entrainer can be recycled after it has been recovered. The separated ethylene glycol and extractant mixture is subjected to atmospheric or vacuum distillation in a rectification column to enable efficient separation of ethylene glycol from the extractant, to obtain an ethylene glycol product, and to circulate the extractant. This requires both an entrainer and an extractant, and several unit operations (and associated equipment) to operate this process. Also, this requires that all of the ethylene glycol is processed through the entrainer recovery column, which is undesired as it is a large volume and as it risks thermal damage to the ethylene glycol.

[0010] WO 2017 / 050847 discloses a process for extractive distillation to remove 1,2-butanediol from ethylene glycol, using as extractant C3-C6 sugar alcohols, e.g. glycerol. In the process of this reference, the extractive distillation is such that the ethylene glycol is extracted by the extractant: 1,2-butanediol and propylene glycol (and side products 2,3 butanediol, 1,2 pentanediol, 2,3-pentanediol, 1,2-hexanol and 1,2 heptanol) are removed at the top of the extraction distillation column, and at the bottom the mixture of ethylene glycol and extractant are obtained. Said bottom mixture is then subjected to a separation to yield ethylene glycol without 1,2-butanediol and extractant. It should be noted that this is exemplified in this reference by modelling only, not by experiments actually carried out. The description and figure 2 suggest that the top stream may be separated by (fractional) distillation in a stream of purified propylene glycol and a stream of the mentioned side products. The examples do not give any evidence, and given the closeness of the boiling points of 2,3-pentanediol (that is, the mixture of (2R,3S) 2,3-pentanediol and (2S,3R) 2,3-pentanediol) and propylene glycol (187-189.5°C and 188.2°C, respectively) this is not possible in practice. Another disadvantage of the method of WO 2017 / 050847 is that the extractant is to be separated from the main product (ethylene glycol) which means that the stream that is processed in the extractant recovery column has to handle a big volume: all extractant and all ethylene glycol. This has consequences from an investment point of view (larger equipment) and operational-cost point of view (large volumes which have to be heated and cooled) and hence is undesired.

[0011] Similar to WO 2017 / 050847 referred to above, also WO 2022 / 073923 discloses extractive distillation to remove 1,2-butanediol from MEG, using extractive distillation using a C3-C6 sugar alcohol or C4-C6 polyol as extractant. Similar to the previous reference W02017 / 050847, the desired diol (MEG) is obtained at the bottom stream together with the extractant. The diol to be removed (1,2-butanediol) is removed at the top. This case suffers from the same disadvantages as WO 2017 / 050847. Both WO 2017 / 050847 and WO 2022 / 073923 deal with removing 1,2-butanediol from MEG. However, there is no evidence of the methods of these two references being able to remove 1,2-pentanediol from MEG.

[0012] Hence, there is a desire for a purification process that allows reducing the amount of 1,2-pentanediol present in a mixture comprising at least 80% (preferably at least 90%) by weight of ethylene glycol and from 0.2 to 5% by weight of 1,2-pentanediol. In such process, it is preferred that the amount of ethylene glycol that is lost in such purification process is minimized, e.g. less than 10% of the ethylene glycol of the mixture. It is furthermore desired that the number of unit operations required is as low as possible and that the process preferably does not have the disadvantages of the prior art.

[0013] Summary of the invention

[0014] It has now been found that the above objective(s) may be achieved, at least in part, by a process for reducing the content of 1,2-pentanediol in a mixture comprising 90-99.9% by weight ethylene glycol and 0.05-5% by weight 1,2-pentanediol by extractive distillation, using an entrainer in said extractive distillation having a Hansen solubility parameter 6H of between 5 and 15 and the entrainer having a boiling point at atmospheric pressure of at least 200°C. Preferably, the entrainer further has a Hansen solubility parameter 6P of between 2 and 13, preferably of between 3 and 11, more preferably between 3.7 and 10, and most preferably between 3.8 and 9. Even more preferably, said entrainer further has a Hansen solubility parameter 6D of between 15 and 20, preferably of between 15 and 18. As to a Hansen solubility parameter 6H, it is preferred that said entrainer has a Hansen solubility parameter 6H of between 5 and 15, and more preferably of between 7 and 13.

[0015] Suitable entrainers are preferably selected from a C6-C10 glycol ether, or a C9-C18 primary or secondary aliphatic unbranched alcohol, and mixtures thereof.

[0016] Detailed description of the invention

[0017] The word "entrainer" herein encompasses pure compounds but also mixtures of compounds having the Hansen solubility parameters and boiling point claimed.

[0018] Inventors of the present case found that entrainers suitable for the purpose have in common that they have a Hansen solubility parameter 6H of between 5 and 15 (and preferably a Hansen solubility parameter 6P of between 2 and 13, and a Hansen solubility parameter 6D of between 15 and 20). Reducing the amount of 1,2-pentanediol in ethylene glycol was problematic, in particular when present in small amounts of e.g. 0.5-2%, due to formation of an azeotrope between 1,2-pentanediol and ethylene glycol. With the present method, it was found that the amount of 1,2-pentanediol present in a composition mainly comprising monoethylene glycol can be reduced to a substantial degree. For practical reasons (in view of the temperatures involved), the entrainer used in the present method has a boiling point of at least 200°C, at atmospheric pressure.

[0019] In order to identify suitable entrainers, numerous chemical components were subjected to laboratory screening of the relative volatility of ethylene glycol and 1,2-pentanediol, and how such is modified by the presence of an entrainer. This provides a prediction of the suitability of an entrainer for the purpose. The details are set out in example 1. Compounds that came out promising in this test were several glycol ethers, and some aliphatic alcohols, and all were found to fit the Hansen solubility parameters now claimed. Hence, it is preferred that the entrainer for the present invention is selected from a C6-C10 glycol ether, or a C9-C18, preferably C10-C12, primary or secondary aliphatic unbranched alcohol, and mixtures thereof. A "C6-C10 glycol ether" herein means a glycol ether having from 6 to 10 (including 6 and 10) carbon atoms in its formula. Similarly, a "C9-C18 primary or secondary aliphatic unbranched alcohol" herein means a primary or secondary aliphatic unbranched alcohol containing from 9 to 18 carbon atoms.

[0020] Following this (and the requirement that the boiling point at atmospheric conditions should be at least 200°C), it is preferred that in the process of the present invention, the entrainer, when such is a glycol ether, such is selected from the group consisting of as appears in table 1, and mixtures thereof. Table 1 also gives the Hansen solubility parameters of the individual compounds.

[0021] Table 1

[0022] Hence, these are preferred glycol ethers in the present invention. Depending e.g. on cost, availability and safety, impurities, thermal stability, in case a glycol ether is used as entrainer, said glycol ether is preferably selected from the group consisting of triethylene glycol monoethyl ether, triethyleneglycol monobutyl ether, and mixtures thereof.

[0023] As alternative to glycols, the entrainers may also be a C9-C18, preferably C10-C12, primary or secondary aliphatic unbranched alcohol. Following this (and the requirement that the boiling point at atmospheric conditions should be at least 200°C), it is preferred that in the process of the present invention, the entrainer, when such is a alcohol such is selected from the group consisting of as appears in table 2, and mixtures thereof.

[0024] Table 2

[0025] Yet a further suitable entrainer for the purpose of the invention is triethylphosphate. This compound has a 6D of 16.7, a 6P of 11.4, and a 6H of 9.2.

[0026] Potential entrainers that are used in industry for similar purposes have been tested for the purpose of the invention, and these appeared to be unsatisfactory in the context of the invention. These are listed in table 3. Table 3

[0027] For reasons of e.g. cost, availability and safety, impurities, thermal stability, in case the entrainer is a primary or secondary aliphatic unbranched alcohol, preferred alcohols for such are 1-dodecanol and 2- decanol. Preferred glycol ethers in this invention are: triethyleneglycol monoethyl ether, triethyleneglycol monobutyl ether. Hence, it is preferred that in the present invention the entrainer is selected from triethyleneglycol monoethyl ether, triethyleneglycol monobutyl ether, 1-dodecanol and 2-decanol, and mixtures thereof.

[0028] In the present invention, in a process for reducing the content of 1,2-pentanediol in a mixture comprising 90-99.9% by weight ethylene glycol and 0.05-5% by weight 1,2-pentanediol by extractive distillation, using an entrainer in said extractive distillation having a Hansen solubility parameter 6H of between 5 and 15 and the entrainer having a boiling point at atmospheric pressure of at least 200°C, the actual extractive distillation can be carried out by a process, wherein said process comprises: a) feeding said mixture to a distillation column 1, b) feeding to said distillation column 1 said entrainer, c) removing ethylene glycol from the top section of the column, d) removing from the bottom section of the distillation column 1 a mixture comprising entrainer and 1,2-pentanediol. By employing said process, the ethylene glycol obtained in c) preferably has an amount of 1,2-pentanediol which is 2 to 20% by weight of the amount of 1,2-pentanediol of the mixture fed to distillation column 1 in a).

[0029] The above process has the advantage, compared to the prior art processes, that the ethylene glycol is obtained as a relatively pure component (containing less 1,2, -pentanediol that the feed) without being mixed with the entrainer. Rather, the entrainer contains the component to be removed: 1,2-pentanediol.

[0030] Clearly, the entrainer will need to be freed of the 1,2-pentanediol in order to be reused again. Such process is a regeneration process of the entrainer. Hence, the invention further relates to a process comprising: feeding the mixture comprising entrainer and 1,2-pentanediol obtained in step d) to a column 2 yielding regenerated entrainer at the bottom section of column 2 and a mixture comprising entrainer and 1,2-pentanediol at the top section of column 2, combining said regenerated entrainer with feeding of the entrainer of b) to column 1.

[0031] The distillation in column 1, to which is fed the (crude) ethylene glycol to be purified (which thus contains some 1,2-pentanediol, e.g. between 0.05-5%, preferably between 0.1 and 3% by weight on the crude ethylene glycol) can be carried out in a distillation column as known in the art.

[0032] Regarding this extractive distillation column 1 it is generally preferred for effective extractive distillation that the feed of the stream to be purified is neither added near the top, nor near the bottom section of column 1. Preferably, the feed is added in the middle half of the column (between the top quarter and the bottom quarter). This is to be understood as: if column 1 has 100 theoretical stages, the feed to be purified is preferably added between stages 25 and 75 of this column. Also, it is generally preferred that the entrainer is added above the feed. Hence, in the process according to the present invention, it is preferred that feeding the mixture comprising ethylene glycol and 1,2-pentanediol to column 1 in a) is at a stage N of the column and wherein the feeding of the entrainer to column 1 in b) is at a stage M of the column, wherein stage M is above stage N. As the entrainer is preferably to be fed at a point in the column above that of the feed of the crude ethylene glycol, said distillation column 1 preferably has two inlets. The distillation column 1 is connected to a reboiler at the bottoms section and a condenser at the top section.

[0033] In the process according to the present invention the weight ratio of entrainer fed to column 1 : mixture fed to column 1 is preferably from 15 : 1 to 1: 1 for a good operation, such e.g. depending on the amount of 1,2-pentanediol to be removed, and the entrainer used. More preferably, such ratio is between 12 : 1 and 2 : 1.

[0034] The separation process according to the present invention is preferably carried out downstream of a hydrogenolysis reactor in which carbohydrates are converted with hydrogen, in the presence of catalysts, to ethylene glycol. Propylene glycol is usually a by-product, next to 1,2-pentanediol, but in larger quantities than 1,2-pentanediol. Preferably, in the process according to the present invention, prior to the now claimed separation process there are one or more other separation processes. Downstream of the reactor and prior to the now claimed separation process there is preferably first a removal of volatiles and water. Furthermore, there is preferably also a separation of high boiling side products (higher boiling than ethylene glycol and propylene glycol) such as glycerol and erythritol. Also, it is preferred that there is already a separation of ethylene glycol and propylene glycol preceding the now claimed purification process. All above means that the stream of EG to be purified is smaller. Hence, it is preferred in the present invention that the mixture fed to column 1 in a) comprises less than 1 % by weight of propylene glycol.

[0035] As to the operating conditions for this column 1 that produces ethylene glycol with a reduced amount of 1,2-pentanediol at the top and entrainer with 1,2-pentanediol at the bottom, these are: the pressure of the reboiler of this column 1 is preferably between 20 and 500 mbara, more preferably at a pressure of between 40 and 250 mbara. This means that the bottom of the first column preferably has a pressure of between 20 and 500 mbara, more preferably at a pressure of between 40 and 250 mbara. the condenser of this column 1 preferably operates at a temperature of between 80 and 160°C, more preferably between 100 and 140°C. This means that the top of the first column preferably has a temperature of between 80 and 160°C, more preferably between 100 and 140°C. the reboiler of column 1 preferably operates at a temperature of between 160 and 220°, and more preferably between 165 and 210°C. This means that the bottom of the first column preferably has a temperature of between 160 and 220°, and more preferably between 165 and 210°C. this column 1 preferably operates with a reflux ratio of between 0.5 and 3, and preferably between 0.7 and 2.4, the number of theoretical stages of this column, including condenser and reboiler, is preferably between 30 and 150, and more preferably between 40 and 120, even more preferably between 40 and 100.

[0036] Other features of the first column such as the interior can be conventional for extractive distillation, as is known to the skilled person.

[0037] The separation by column 1 produces ethylene glycol with a reduced amount of 1,2-pentanediol, next to a stream of entrainer which contains, amongst others, 1,2-pentanediol. Apart from pentanediol, it was found that surprisingly other minor products from the hydrogenolysis of sugar (e.g. 1,2-hexanediol) are also removed with the entrainers in the process of the present invention. This is an added benefit of the present invention.

[0038] Additionally, it was found that when treating the ethylene glycol with the extractive distillation according to the present invention, some other diol components may be removed as well from the ethylene glycol. For example, it was found that the use of the entrainer according to the present invention also removes part of the 1,2-butanediol and / or 1,2-hexanediol from ethylene glycol. This is an added benefit of the process of the present invention.

[0039] The entrainer loaded with 1,2-pentanediol (and optionally other diols like 1,2-hexanediol or 1,2- butanediol) will need to be regenerated for re-use. This regeneration can be done in a way as known in the art for regenerating entrainers in extractive distillation using a regeneration column (column 2 in the process set out herein). The operating conditions for such are preferably: the reboiler of this column 2 preferably operates at a pressure of between 20 and 400 mbara, preferably being between 30 and 200 mbara, the condenser is preferably operating at a temperature of between 90 and 180°C, more preferably between 100 and 160°C, the reboiler of column 2 operating at a temperature of between 150 and 220°, preferably between 165 and 210°C, the a reflux ratio is preferably between 10 and 100, more preferably between 15 and 70, the number of theoretical stages of such column is preferably between 20 and 60, more preferably between 30 and 60.

[0040] Other features of the regeneration column such as the interior can be conventional for a column for regenerating an entrainer in extractive distillation, as is known to the skilled person.

[0041] EXAMPLES

[0042] Example 1

[0043] Example 1 is a laboratory screening of the relative volatility of ethylene glycol and 1,2-pentanediol, and how such is modified by the presence of an entrainer. This provides a prediction of the suitability of an entrainer for the purpose. The relative volatility is determined by gas chromatography of the headspace.

[0044] Mixtures of components (ethylene glycol, 1,2-pentanediol and entrainer) were prepared in ratios presented in table 4 below. A 5 mL volume of the mixture was inserted into a 10 mL vial. The vial was purposefully left half empty to ensure proper volume of headspace available for achieving liquid-vapor equilibrium. The entrainers tested were: Triethylene glycol monobutyl ether, Propylene glycol monophenyl ether (l-Phenoxy-2-propanol), Dodecanol, Triethylphosphate, Diethylene Glycol Monoethyl Ether Acetate, 2-Decanol, diethylene glycol monobutyl ether, Di(ethylene glycol) hexyl ether, Tripropylene glycol methyl ether, Dipropylene glycol methyl ether, Di(ethylene glycol) divinyl ether, Ethylene glycol monobenzyl ether.

[0045] As comparative entrainers: Dipropylene glycol, Glycerol, Triethylene glycol, Diethylene glycol, Octadecane, Decane, Dodecane.

[0046] Table 4

[0047] After preparing the vial, the content of the vial was thoroughly mixed to ensure homogeneous distribution of content in the liquid phase. Subsequently, the vials were placed in a Headspace-Gas chromatography (HS-GC) autosampler where the vials were heated to 130°C. After 60 minutes, the vial's headspace which contains the gas content was sampled and analyzed by the machine. This injection resulted in a chromatogram where the separated peaks each represent one of the mixtures' components, and the area under the peak indicates their respective concentration in the gas phase.

[0048] The obtained areas are proportional to the components partial pressure and the relative volatility (a) was calculated as: wherein:

[0049] Anis HS-GCMS area of component n with entrainer addition

[0050] An,o is HS-GCMS area of component n in reference sample (no entrainer addition)

[0051] Pn,sat is saturation pressure of component n xnis molar fraction of component n in liquid phase

[0052] 1 is index for component 1 (here: ethylene glycol)

[0053] 2 is index for component 2 (here: 1,2-pentanediol)

[0054] The relative volatility in distillation is an indication of feasible separation of the components in a mixture. Higher relative volatility shows that the relative concentration of component 1 to 2 is higher in the gas phase than in liquid phase. Hence, in a single stage separation such as in this test for triethylene glycol monobutyl ether, the ethylene glycol is shown to be more volatile than the 1,2-pentanediol in the presence of triethylene glycol monobutyl ether. And so on for other entrainers.

[0055] As a point of reference, the relative volatility of the mixture without the entrainer present shows that almost no separation of the two components is possible (relative volatility =~1). The results of the relative volatility a are set out in figure 1 (EG means ethylene glycol) for the compounds according to the invention and figure 2 for comparatives.

[0056] The higher the relative volatility of a given compound in this test the better the suitability of this compound as entrainer in extractive distillation. There is no hard cut-off, but the lower the relative volatility in this test the more entrainer (in relation to the ethylene glycol) would be needed to remove 1,2-pentanediol from ethylene glycol, or the 1,2-pentanediol is not removed to the same extent. A lower amount of entrainer is desired for operational and economic reasons.

[0057] Example 2

[0058] For this experiment, a trial was conducted in a distillation column having maximum 100 theoretical stages, with triethylene glycol monobutyl ether (BTEG) as entrainer, on a model feed.

[0059] The composition of the model feed was: a mixture of 97.72 wt% ethylene glycol, 1.68 wt% 1,2-pentanediol and 0.54 wt% 1,2-hexanediol and some minor components (other impurities).

[0060] In continuous operation mode, the ethylene glycol-containing feed mixture (at 78-85°C and ambient pressure) and triethylene glycol monobutyl ether entrainer (at 111-112°C and ambient pressure) were introduced (the entrainer higher than the ethylene glycol feed mixture) into a maximum 100 theoretical stage column where the purified propylene glycol is separated in the distillate and the impurities of the feed leave the column with the entrainer as bottom stream.

[0061] The column was operated at 116°C and 50 mbara condenser conditions, with a column pressure drop of 13.5-15 mbara. A reflux ratio of 2 was used throughout the experiment.

[0062] Three experiments were performed where the entrainer to feed ratio was varied, according to the data in table 5 below. The table also lists the results. The amount of 1,2-pentanediol in the top stream was below the detection limit of 0.001 wt%.

[0063] Table 5

[0064] Note: "sep mass % in bottom stream" refers the percentage of the stated component that is present in the bottom stream, based on the amount of said component in the EG feed stream.

Claims

CLAIMS1. Process for reducing the content of 1,2-pentanediol in a mixture comprising 90-99.9% by weight ethylene glycol and 0.05-5% by weight 1,2-pentanediol by extractive distillation, using an entrainer in said extractive distillation having a Hansen solubility parameter 6H of between 5 and 15 and the entrainer having a boiling point at atmospheric pressure of at least 200°C.

2. Process according to claim 1, wherein said entrainer further has a Hansen solubility parameter 6P of between 2 and 12, preferably of between 3 and 11, more preferably between 3.7 and 10, most preferably between 3.8 and 9.

3. Process according to claim 1 or 2, wherein said entrainer further has a Hansen solubility parameter 6D of between 15 and 20, preferably of between 15 and 18.

4. Process according to any of the preceding claims, wherein said entrainer has a Hansen solubility parameter 6H of between 6 and 14, preferably of between 7 and 13.

5. Process according to any of the preceding claims, wherein the entrainer is selected from a C6-C10 glycol ether, or a C9-C18 primary or secondary aliphatic unbranched alcohol, and mixtures thereof.

6. Process according to claim 5, wherein the entrainer is selected from triethyleneglycol monoethyl ether, triethyleneglycol monobutyl ether, 1-dodecanol and 2-decanol, and mixtures thereof.

7. Process according to any of the preceding claims, wherein said process comprises: a) feeding said mixture to a distillation column 1, b) feeding to said distillation column 1 said entrainer, c) removing ethylene glycol from the top section of the column, d) removing from the bottom section of the distillation column 1 a mixture comprising entrainer and 1,2-pentanediol.

8. Process according to claim 7,feeding the mixture comprising entrainer and 1,2-pentanediol obtained in step d) to a column 2 yielding regenerated entrainer at the bottom section of column 2 and a mixture comprising entrainer and 1,2-pentanediol at the top section of column 2, combining said regenerated entrainer with feeding of the entrainer of b) to column 1.

9. Process according to claim 7 or 8, wherein the ethylene glycol obtained in c) has an amount of 1,2- pentanediol which is 2 to 20% by weight of the amount of 1,2-pentanediol of the mixture fed to distillation column 1 in a).

10. Process according to any of claims 7 to 9, wherein feeding the mixture comprising ethylene glycol and 1,2-pentanediol to column 1 in a) is at a stage N of the column and wherein the feeding of the entrainer to column 1 in b) is at a stage M of the column, wherein stage M is above stage N.

11. Process according to any of claims 7 to 10, wherein the weight ratio of entrainer in b) to the mixture in a) is from 15 : 1 to 1: 1, preferably between 12 : 1 and 2 : 1.

12. Process according to any of claims 7 to 11, wherein the reboiler of column 1 operates at a pressure of between 20 and 500 mbara, preferably at a pressure of between 40 and 250 mbara.

13. Process according to any of claims 7 to 12, wherein the condenser of column 1 operates at a temperature of between 80 and 160°C, preferably between 100 and 140°C.

14. Process according to any of claims 7 to 13, wherein the reboiler of column 1 operates at a temperature of between 160 and 220°, preferably between 165 and 210°C.

15. Process according to any of claims 7 to 14, wherein column 1 operates with a reflux ratio of between 0.5 and 3, preferably between 0.7 and 2.4.

Images