Process for purifying bio-based propylene glycol

Abstract

A method for purifying bio-based propylene glycol, comprising separating impurities having boiling points close to that of propylene glycol. 20 Lipophilic alcohol compounds, C5-C 20 Alkanes and / or C4-C 20 A lipophilic ketone compound is used as an azeotropic agent to azeotropically distill bio-based propylene glycol to obtain an azeotropic mixture containing propylene glycol; the azeotropic agent in the azeotropic mixture is then separated and removed to obtain crude propylene glycol; and a pure propylene glycol substance is further obtained from the crude propylene glycol.

Description

[Technical field]

[0001] Technical Field The present invention relates to a process for purifying propylene glycol, and in particular to a process for purifying bio-based propylene glycol containing impurities such as butanediol and pentanediol having boiling points close to that of propylene glycol. [Background technology]

[0002] Background technology In recent years, due to the instability of crude oil prices and the growing attention of people to sustainable development, the technology for producing propylene glycol using biomass as a raw material has developed rapidly. However, when producing propylene glycol via the biomass route, due to the difference in the synthesis route, by-products different from those produced when producing propylene glycol via the petroleum route are produced, such as impurities such as butanediol, pentanediol, hexanediol, and propylene carbonate, whose boiling points are very close to that of propylene glycol. The conventional method for obtaining liquid compounds as pure substances is the rectification process, which separates substances with different boiling points. However, the boiling points of these impurities are close to that of propylene glycol, and impurities including butanediol, pentanediol, hexanediol, and propylene carbonate have physical properties similar to those of propylene glycol and their boiling points are also very close to that of propylene glycol. Therefore, separation of propylene glycol from these very close boiling impurities using neat rectification would result in low distillation yields of propylene glycol and high energy consumption.

[0003] US Patent No. 4,935,102 and US Patent No. 5,423,955 each describe a technique for separating propylene glycol from butanediol by using different azeotropic solvents. The azeotropic solvent has an azeotropic point with propylene glycol. In general, the temperature of the azeotropic point is clearly lower than the boiling point of propylene glycol. Therefore, there is a clear temperature difference between the boiling point of the azeotropic mixture of propylene glycol and the azeotropic solvent and the boiling point of impurities such as butanediol. By using rectification, the separation of propylene glycol and butanediol can be achieved economically.

[0004] The process of producing propylene glycol via biomass will produce impurities other than butanediol, such as pentanediol, hexanediol, propylene carbonate, etc. These impurities have boiling points very close to that of propylene glycol. However, the above-mentioned documents only describe the effect of using an azeotropic solvent in separating propylene glycol from butanediol, but do not describe the effect of separating propylene glycol from other impurities such as pentanediol, hexanediol, propylene carbonate, etc., which have boiling points close to that of propylene glycol, using an azeotropic solvent. Summary of the Invention [Problem to be solved by the invention]

[0005] Contents of the invention The present invention provides a process for purifying bio-based propylene glycol, which separates impurities having boiling points close to that of propylene glycol, and can increase the purity of the propylene glycol to 99.50% or more, with a recovery rate of propylene glycol of 80% or more, preferably 85% or more.

[0006] The bio-based propylene glycol refers to propylene glycol produced from biomass feedstocks, including but not limited to propylene glycol, butanediol, pentanediol, hexanediol, and optionally propylene carbonate, where the propylene glycol is preferably 1,2-propylene glycol; the butanediol is preferably 1,2-butanediol, the pentanediol is preferably 1,2-pentanediol, and the hexanediol is preferably 1,2-hexanediol. [Means for solving the problem]

[0007] In the process of the present invention, one, two or more types of C5-C 20 Lipophilic alcohol compounds, C5-C 20 Alkanes and C4-C 20 A lipophilic ketone compound is used as an azeotropic solvent to undergo azeotropism with bio-based propylene glycol to obtain an azeotropic mixture containing propylene glycol, and then water is added to dissolve the propylene glycol in the azeotropic mixture, and the water-insoluble azeotropic solvent is separated from the aqueous propylene glycol solution, and the resulting aqueous propylene glycol solution is dehydrated and purified to obtain propylene glycol.

[0008] In one embodiment of the present invention, C5 to C 20 The lipophilic alcohol compound is preferably a C6-C 15 Lipophilic alcohol compounds, preferably C7-C 12 Lipophilic alcohol compounds, particularly preferably C7-C 10Lipophilic alcohol compounds. Lipophilic alcohol compounds can be aliphatic alcohols and heterocyclic alcohols. For example, examples of lipophilic alcohol compounds include pentanol and its isomers, hexanol and its isomers, heptanol and its isomers, octanol and its isomers, nonanol and its isomers, decanol and its isomers, undecanol and its isomers, lauryl alcohol and its isomers, and benzyl alcohol. Particularly preferably, the lipophilic alcohol compounds are heptanol, n-heptanol, 2-heptanol, octanol, n-octanol, isooctanol, sec-octanol, nonanol, n-nonanol, isononanol, decanol, n-decanol, and isodecanol.

[0009] In another embodiment of the present invention, C5 to C 20 The alkane is preferably C5-C 15 Alkanes, preferably C5-C 12 Alkanes are preferred, particularly C5-C9 alkanes. The alkanes may be linear alkanes, branched alkanes, cycloalkanes, or alkanes containing a benzene ring. Examples of alkanes include pentane and its isomers, hexane and its isomers, heptane and its isomers, octane and its isomers, nonane and its isomers, decane and its isomers, undecane and its isomers, dodecane and its isomers, cyclopentane and cyclohexane, and ethylbenzene and its isomers. Particularly preferred alkanes are hexane, heptane, octane, nonane, decane, undecane, dodecane, cyclopentane, cyclohexane, and ethylbenzene.

[0010] In another embodiment of the present invention, C4 to C 20 The lipophilic ketone compound is preferably a C5-C 15 Lipophilic ketone compounds, preferably C6-C 12 Lipophilic ketone compounds, particularly preferably C6-C 10It is a lipophilic ketone compound. The ketone can be an aliphatic ketone or an alicyclic ketone. Particularly preferred ketones are cyclohexanone, heptanone, 4-heptanone, diisobutyl ketone, isophorone, nonanone, and 2-nonanone.

[0011] Biomass according to the present invention preferably refers to edible first generation biomass such as corn and sugarcane, and inedible second generation biomass such as straw, wood, bagasse, and agricultural and forestry waste. Preferably, the bio-based propylene glycol of the present invention includes, but is not limited to, propylene glycol (preferably 1,2-propylene glycol), butanediol (preferably 1,2-butanediol), pentanediol (preferably 1,2-pentanediol), hexanediol (preferably 1,2-hexanediol), and propylene carbonate. The bio-based propylene glycol of the present invention optionally includes propylene glycol. More preferably, the bio-based propylene glycol includes, but is not limited to, 1 to 100% by weight of propylene glycol (excluding the boundary value of 100% by weight), preferably 1 to 99% by weight of propylene glycol, more preferably 5 to 99% by weight of propylene glycol, particularly preferably 10 to 95% by weight of propylene glycol (the propylene glycol is preferably 1,2-propylene glycol); 0 to 95% by weight, preferably 0 to 70% by weight, more preferably 0 to 50% by weight, particularly preferably 0 to 30% by weight (excluding the boundary value 0) of butanediol (preferably 1,2-butanediol); 0 to 95% by weight, preferably 0 to 50% by weight, more preferably 0 to 10% by weight, particularly preferably 0 to 1% by weight (excluding the boundary value 0) of a pentanediol (preferably 1,2-pentanediol); 0 to 95% by weight, preferably 0 to 50% by weight, more preferably 0 to 10% by weight, particularly preferably 0 to 1% by weight (excluding the boundary value 0) of hexanediol (preferably 1,2-hexanediol); propylene carbonate at 0 to 95% by weight, preferably 0 to 50% by weight, more preferably 0 to 10% by weight, and particularly preferably 0 to 1% by weight; Includes.

[0012] The bio-based propylene glycol optionally comprises: 0 to 95% by weight, preferably 0 to 50% by weight, of ethylene glycol, and / or 0 to 50% by weight, preferably 0 to 10% by weight, of 2,3-butanediol; Further includes.

[0013] In the process of the present invention, the azeotropic solvent forms an azeotrope with propylene glycol by azeotroping. There is a clear temperature difference between the boiling point of the azeotrope and the boiling points of impurities such as butanediol, pentanediol, hexanediol, and propylene carbonate, as well as other impurities whose boiling points are close to those of propylene glycol. Therefore, for example, a rectification process can be used to economically obtain pure propylene glycol.

[0014] The azeotropic solvent can be separated from the aqueous solution containing propylene glycol by mixing the azeotropic mixture with water and then subjecting it to an extraction process, which is followed by dehydration and purification to obtain propylene glycol. [Brief description of the drawings]

[0015] Description of the drawings [Figure 1] FIG. 1 is a flow diagram of the process for azeotropic purification of bio-based propylene glycol of the present invention. [Diagram 2] FIG. 2 is a flow diagram of a conventional rectification process for bio-based propylene glycol. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] MODE FOR CARRYING OUT THE DISCLOSURE The purification process of the present invention will be described below with reference to FIG. The mixed polyol feed and the azeotropic solvent feed are mixed before entering the azeotropic tower (here, the fractionator). The weight ratio of the azeotropic solvent feed to the propylene glycol of the mixed polyol feed is 0.1:1 to 20:1, preferably 0.2:1 to 20:1, more preferably 0.5:1 to 20:1. The operating pressure of the azeotropic tower is 1 kPa (absolute) to 101 kPa (absolute), and the weight ratio of the reflux liquid to the distillate (extracted material) of the azeotropic tower (i.e., reflux ratio) is 0.1:1 to 15:1. Here, most of the propylene glycol in the mixed polyol feed and a small amount of other impurities are withdrawn together with the azeotropic solvent from the top of the azeotropic tower (i.e., stream 1) and flow into the distillate decanter. Heavy impurities, including but not limited to butanediol, pentanediol, hexanediol, and optionally propylene carbonate, and a small amount of azeotropic solvent are withdrawn from the bottom of the azeotropic column (i.e., stream 8) and enter the evaporator.

[0017] Steam 1 is mixed with fresh water and optional recycle water (i.e., stream 4) and the layers separate in the distillate decanter. The azeotropic solvent layer (i.e., stream 2) is recycled to the azeotropic column, while the water layer (i.e., stream 3) enters the Water removal column for azeotropic column distillate.

[0018] The water in stream 3 is withdrawn from the top of the azeotropic distillate dehydration column (i.e., stream 4) and recycled to the distillate decanter, while the crude propylene glycol withdrawn from the bottom of the column (i.e., stream 5) flows into the MPG light removal column.

[0019] After most of the light impurities of the crude propylene glycol (i.e., stream 5) are separated in the MPG lights removal column, crude propylene glycol (i.e., stream 6) is withdrawn from the bottom of the MPG lights removal column and flows into the MPG purification column, with most of the light impurities being withdrawn from the top of the MPG lights removal column.

[0020] The heavy and remaining light components in the crude propylene glycol (i.e., Stream 6) after removal of the light components are separated in the MPG purification column: propylene glycol is withdrawn as a side stream; the remaining light components are withdrawn from the top of the MPG purification column; and the heavy components (i.e., Stream 14) are recycled and mixed with the mixed polyol feed before entering the azeotropic column.

[0021] The material in the azeotropic column bottoms (i.e., Stream 8) flows into an evaporator where very heavy boiling impurities are separated from the bottom of the evaporator and discharged out of the system (i.e., Stream 9).

[0022] The azeotropic solvent, stream 10, containing but not limited to, butanediol, pentanediol, hexanediol, and optional propylene carbonate, enters the bottoms decanter. It is then mixed with fresh water and optional recycle water (i.e., stream 13) and the layers are separated, where the azeotropic solvent layer (i.e., stream 11) is recycled to the azeotropic tower, while the water layer (i.e., stream 12), containing but not limited to, water, butanediol, pentanediol, hexanediol, and optional propylene carbonate, is sent to the azeotropic tower bottoms dehydration tower for dehydration.

[0023] Water in the water layer of the bottoms decanter (i.e., stream 12) is separated in the water removal column for azeotropic column bottom and withdrawn from the top of the column (i.e., stream 13) and returned to the bottoms decanter. Impurities including, but not limited to, butanediol, pentanediol, and hexanediol, and optionally propylene carbonate, are withdrawn from the bottom of the azeotropic column bottoms and discharged outside the system.

[0024] The technology of the present invention can separate propylene glycol in bio-based propylene glycol from impurities including but not limited to butanediol, pentanediol, hexanediol, and optional propylene carbonate under high recovery conditions, with the recovery rate of propylene glycol being 80% or more, preferably 85% or more. At the same time, the purity of propylene glycol is improved to 99.50% or more. Therefore, the problem that the existing technology for obtaining pure substances from bio-based propylene glycol cannot simultaneously achieve separation from butanediol, pentanediol, hexanediol, and optional propylene carbonate is solved.

[0025] Working Example The present invention will be further described by the following examples, but the present invention is not limited thereto. EXAMPLES

[0026] Example 1 The mixed polyol feed according to the flow diagram illustrated in Figure 1 was made from a material obtained by dehydrating and removing light components from a mixture of biomass-based products, and consisted of the following weight percentages: 55.65% 1,2-propylene glycol, 24.32% ethylene glycol, 15.24% 1,2-butanediol, 3.07% 2,3-butanediol, 0.2% 1,2-pentanediol, 0.2% 1,2-hexanediol, 0.1% propylene carbonate, and 1.22% other light and heavy components.

[0027] The mixed polyol feed and new azeotropic solvent isooctanol were mixed and flowed into the azeotropic tower at the 45th theoretical plate. The weight ratio of the azeotropic solvent (including the new azeotropic solvent and the recycled azeotropic solvent streams 2 and 11) to the propylene glycol in the mixed polyol feed was 3.6:1. The total number of theoretical plates in the azeotropic tower was 90. The azeotropic solvent stream 2 recycled from the overhead liquid and the azeotropic solvent stream 11 recycled from the bottom liquid were each flowed into the 40th theoretical plate of the azeotropic tower. The operating pressure of the azeotropic tower was 50 kPa (absolute) and the reflux ratio was 2:1. Stream 1 from the top of the column separated by the azeotropic column consisted of the azeotropic solvent, 1,2-propylene glycol, ethylene glycol, 1,2-butanediol, 2,3-butanediol, 1,2-pentanediol, 1,2-hexanediol, propylene carbonate, and other light components in weight percentages of 69.56%, 19.75%, 8.63%, 0.02%, 0.93%, 0%, 0%, 0%, and 1.11%, respectively.

[0028] A high boiling point heavy component stream 9 was separated from stream 8 by an evaporator.

[0029] Stream 10 and stream 13 from the top of the azeotropic column bottoms dehydrator were fed into the bottoms decanter. The separated azeotropic solvent layer was returned to the azeotropic distillation column as the circulating azeotropic solvent (i.e., stream 11); the water layer, which was a mixture of alcohol and water (i.e., stream 12), was fed into the azeotropic column bottoms dehydrator for dehydration, and the water (i.e., stream 13) was returned to the bottoms decanter.

[0030] Stream 1 from the top of the azeotropic tower was fed into the distillate decanter together with stream 4 from the top of the azeotropic tower distillate dehydrator. After separation in a phase separator, the aqueous layer stream (i.e., stream 3) was fed into the azeotropic tower distillate dehydrator for dehydration. After dehydration, stream 5 from the bottom of the tower was fed into the MPG light components removal tower at theoretical plate 60. The MPG light components removal tower had a total theoretical number of plates of 90, a reflux ratio of 80:1, and an operating pressure of 10 kPa (absolute). Crude propylene glycol (stream 6) was withdrawn from the MPG light components removal tower at theoretical plate 50 and fed into the MPG purification tower. The MPG purification tower had a total theoretical number of plates of 90, a reflux ratio of 10:1, and an operating pressure of 10 kPa (absolute). The propylene glycol product was withdrawn from the MPG purification tower at theoretical plate 10. According to the methods of the Chinese national standard GB29216-2012 and the US ASTM E202, the purity of the refined propylene glycol was 99.61% by weight, and the total yield of propylene glycol rectification was 89.2%.

[0031] Example 2 The mixed polyol feed according to the flow diagram illustrated in FIG. 1 was a material obtained by dehydrating and removing light components from the mixture of products produced using biomass as a raw material used in Example 1.

[0032] The mixed polyol feed and n-nonanol, a new azeotropic solvent, were mixed and flowed into the azeotropic tower at the 45th theoretical plate. The weight ratio of the azeotropic solvent (including the new azeotropic solvent and the recycled azeotropic solvent streams 2 and 11) to the propylene glycol in the mixed polyol feed was 0.8:1. The total number of theoretical plates in the azeotropic tower was 90. The azeotropic solvent stream 2 recycled from the overhead liquid and the azeotropic solvent stream 11 recycled from the bottom liquid were each flowed into the 40th theoretical plate of the azeotropic distillation tower. The operating pressure of the azeotropic tower was 5 kPa (absolute) and the reflux ratio was 2:1. Stream 1 from the top of the column separated by the azeotropic column consisted of the azeotropic solvent, 1,2-propylene glycol, ethylene glycol, 1,2-butanediol, 2,3-butanediol, 1,2-pentanediol, 1,2-hexanediol, propylene carbonate, and other light components in weight percentages of 33.20%, 49.66%, 13.76%, 0.54%, 1.52%, 0%, 0%, 0%, and 1.32%, respectively.

[0033] A high boiling point heavy component stream 9 was separated from stream 8 by an evaporator.

[0034] Stream 10 and stream 13 from the top of the azeotropic column bottoms dehydrator were fed into the bottoms decanter. The separated azeotropic solvent layer was returned to the azeotropic column as circulating azeotropic solvent (i.e., stream 11); the water layer, which was a mixture of alcohol and water (i.e., stream 12), was fed into the azeotropic column bottoms dehydrator for dehydration, and the water (i.e., stream 13) was returned to the bottoms decanter.

[0035] Stream 1 from the top of the azeotropic tower was fed into the distillate decanter together with stream 4 from the top of the azeotropic tower distillate dehydrator. After separation in a phase separator, the aqueous layer stream (i.e., stream 3) was fed into the azeotropic tower distillate dehydrator for dehydration. After dehydration, stream 5 from the bottom of the tower was fed into the MPG light components removal tower at theoretical plate 60. The MPG light components removal tower had a total theoretical number of plates of 90, a reflux ratio of 80:1, and an operating pressure of 10 kPa (absolute). Crude propylene glycol (stream 6) was withdrawn from the MPG light components removal tower at theoretical plate 50 and fed into the MPG purification tower. The MPG purification tower had a total theoretical number of plates of 90, a reflux ratio of 10:1, and an operating pressure of 10 kPa (absolute). The propylene glycol product was withdrawn from the MPG purification tower at theoretical plate 10. According to the methods of the Chinese national standard GB29216-2012 and the US ASTM E202, the purity of the refined propylene glycol was 99.64% by weight, and the total yield of propylene glycol rectification was 85.5%.

[0036] Example 3 The mixed polyol feed according to the flow diagram illustrated in FIG. 1 was a material obtained by dehydrating and removing light components from the mixture of products produced using biomass as a raw material used in Example 1.

[0037] The mixed polyol feed and new azeotropic solvent 2-nonanone were mixed and flowed into the azeotropic tower at the 45th theoretical plate. The weight ratio of azeotropic solvent (including new azeotropic solvent and recycled azeotropic solvent streams 2 and 11) to propylene glycol in the mixed polyol feed was 3.5:1. The total number of theoretical plates in the azeotropic distillation tower was 90. Azeotropic solvent stream 2 recycled from the overhead liquid and azeotropic solvent stream 11 recycled from the bottom liquid each flowed into the 40th theoretical plate of the azeotropic distillation tower. The operating pressure of the azeotropic tower was 70 kPa (absolute) and the reflux ratio was 2.5:1. Stream 1 from the top of the column separated by the azeotropic column consisted of the azeotropic solvent, 1,2-propylene glycol, ethylene glycol, 1,2-butanediol, 2,3-butanediol, 1,2-pentanediol, 1,2-hexanediol, propylene carbonate, and other light components in weight percentages of 70.62%, 20.74%, 8.10%, 0.04%, 0.26%, 0%, 0%, 0%, and 0.24%, respectively.

[0038] A high boiling point heavy component stream 9 was separated from stream 8 by an evaporator.

[0039] Stream 10 and stream 13 from the top of the azeotropic column bottoms dehydrator were fed into the bottoms decanter. The separated azeotropic solvent layer was returned to the azeotropic column as circulating azeotropic solvent (i.e., stream 11); the water layer, which was a mixture of alcohol and water (i.e., stream 12), was fed into the azeotropic column bottoms dehydrator for dehydration, and the water (i.e., stream 13) was returned to the bottoms decanter.

[0040] Stream 1 from the top of the azeotropic tower was fed into the distillate decanter together with stream 4 from the top of the azeotropic tower distillate dehydrator. After separation in a phase separator, the aqueous layer stream (i.e., stream 3) was fed into the azeotropic tower distillate dehydrator for dehydration. After dehydration, stream 5 from the bottom of the tower was fed into the MPG light components removal tower at theoretical plate 60. The MPG light components removal tower had a total theoretical number of plates of 90, a reflux ratio of 80:1, and an operating pressure of 10 kPa (absolute). Crude propylene glycol (stream 6) was withdrawn from the MPG light components removal tower at theoretical plate 50 and fed into the MPG purification tower. The MPG purification tower had a total theoretical number of plates of 90, a reflux ratio of 10:1, and an operating pressure of 10 kPa (absolute). The propylene glycol product was withdrawn from the MPG purification tower at theoretical plate 10. According to the methods of the Chinese national standard GB29216-2012 and the US ASTM E202, the purity of the refined propylene glycol was 99.55% by weight, and the total yield of propylene glycol rectification was 88.3%.

[0041] Example 4 The mixed polyol feed according to the flow diagram illustrated in FIG. 1 was a material obtained by dehydrating and removing light components from the mixture of products produced using biomass as a raw material used in Example 1.

[0042] The mixed polyol feed and the new azeotropic solvent, 4-nonanone, were mixed and flowed into the azeotropic tower at the 45th theoretical plate. The weight ratio of the azeotropic solvent (including the new azeotropic solvent and the recycled azeotropic solvent streams 2 and 11) to the propylene glycol in the mixed polyol feed was 12.5:1. The total number of theoretical plates in the azeotropic tower was 90. The azeotropic solvent stream 2 recycled from the overhead liquid and the azeotropic solvent stream 11 recycled from the bottom liquid were each flowed into the azeotropic tower at the 40th theoretical plate. The operating pressure of the azeotropic tower was 70 kPa (absolute) and the reflux ratio was 2.5:1. Stream 1 from the top of the column separated by the azeotropic column consisted of the azeotropic solvent, 1,2-propylene glycol, ethylene glycol, 1,2-butanediol, 2,3-butanediol, 1,2-pentanediol, 1,2-hexanediol, propylene carbonate, and other light components in weight percentages of 89.98%, 7.30%, 2.17%, 0.14%, 0.35%, 0%, 0%, 0%, and 0.06%, respectively.

[0043] A high boiling point heavy component stream 9 was separated from stream 8 by an evaporator.

[0044] Stream 10 and stream 13 from the top of the azeotropic column bottoms dehydrator were fed into the bottoms decanter. The separated azeotropic solvent layer was returned to the azeotropic distillation column as the circulating azeotropic solvent (i.e., stream 11); the water layer, which was a mixture of alcohol and water (i.e., stream 12), was fed into the azeotropic column bottoms dehydrator for dehydration, and the water (i.e., stream 13) was returned to the bottoms decanter.

[0045] Stream 1 from the top of the azeotropic tower was fed into the distillate decanter together with stream 4 from the top of the azeotropic tower distillate dehydrator. After separation in a phase separator, the aqueous layer stream (i.e., stream 3) was fed into the azeotropic tower distillate dehydrator for dehydration. After dehydration, stream 5 from the bottom of the tower was fed into the MPG light components removal tower at theoretical plate 60. The MPG light components removal tower had a total theoretical number of plates of 90, a reflux ratio of 80:1, and an operating pressure of 10 kPa (absolute). Crude propylene glycol (stream 6) was withdrawn from the MPG light components removal tower at theoretical plate 50 and fed into the MPG purification tower. The MPG purification tower had a total theoretical number of plates of 90, a reflux ratio of 20:1, and an operating pressure of 10 kPa (absolute). The propylene glycol product was withdrawn from the MPG purification tower at theoretical plate 10. According to the methods of the Chinese national standard GB29216-2012 and the US ASTM E202, the purity of the propylene glycol after impurity removal was 99.58% by weight, and the total yield of propylene glycol through rectification was 85.1%.

[0046] Comparative Example 1 As the mixed polyol raw material, a material obtained by dehydrating and removing light components from the mixture of products produced using biomass as a raw material, as used in Example 1, was used. Separation was carried out using a conventional rectification method as illustrated in FIG. 2. Since no azeotropic solvent is added in the conventional rectification process, no azeotropic section or extraction section is required, and therefore no azeotropic tower, distillate decanter, bottom liquid decanter, azeotropic tower distillate dehydration tower, azeotropic tower bottom liquid dehydration tower, or evaporator is required. Compared to Example 1, the total theoretical plate numbers and operating conditions of the MPG light component removal tower and MPG purification tower in the two processes were the same. The propylene glycol product consisted of 1,2-propylene glycol, ethylene glycol, 1,2-butanediol, 2,3-butanediol, 1,2-pentanediol, 1,2-hexanediol, propylene carbonate, and other light and heavy components at weight percentages of 97.86%, 0.192%, 0.23%, 0%, 0.01%, 0.01%, 0.01%, and 1.688%, respectively. The overall yield from fractionation of the less pure propylene glycol was 29.0%.

[0047] The experimental results show that the conventional rectification without using an azeotropic solvent cannot effectively separate 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, propylene carbonate, and other light and heavy components in propylene glycol. In order to reach a purity of 99.5%, it is necessary to increase the column height, reflux ratio, and energy consumption. The process of the present invention can effectively improve the purity of the propylene glycol to 99.50% or more under the condition of high yield of propylene glycol.

Claims

1. 1. A process for purifying propylene glycol from a mixture comprising: (i) mixing one or more azeotropic solvents with a bio-based propylene glycol mixture to obtain a propylene glycol feed containing an azeotrope; (ii) refluxing the propylene glycol feed containing the azeotrope in an azeotropic or fractionating column at a pressure of 1 to 101 kPa (absolute); (iii) obtaining a distillate from the top of the azeotropic column or fractionator; (iv) dissolving the propylene glycol in the azeotrope by adding water to the distillate; (v) separating the water-insoluble azeotropic solvent from the aqueous propylene glycol solution; and (vi) obtaining propylene glycol by dehydrating and purifying the obtained aqueous propylene glycol solution, the one or more azeotropic solvents are selected from cyclohexanone, heptanone, 4-heptanone, diisobutyl ketone, isophorone, nonanone, 2-nonanone, and C5 to C20 lipophilic alcohol compounds; The mixture includes propylene glycol and one or more of butanediol, pentanediol, and hexanediol. process.

2. Said C ５ ~C ２０ The lipophilic alcohol compound is C ６ ~C １５ The process of claim 1 , wherein the compound is a lipophilic alcohol.

3. Said C ５ ~C ２０ 3. The process of claim 2, wherein the lipophilic alcohol compounds are heptanol, n-heptanol, 2-heptanol, octanol, n-octanol, isooctanol, sec-octanol, nonanol, n-nonanol, isononanol, decanol, n-decanol, and isodecanol.

4. 2. The process of claim 1, wherein the bio-based propylene glycol mixture is produced from biomass.

5. 2. The process of claim 1, wherein the bio-based propylene glycol mixture comprises propylene glycol, butanediol, pentanediol, hexanediol, and optionally propylene carbonate.

6. 5. The process of claim 4, wherein the biomass comprises edible first generation biomass.

7. The process of claim 6 , wherein the edible first generation biomass comprises corn.

8. 7. The process of claim 6, wherein the edible first generation biomass comprises sugarcane.

9. 7. The process of claim 6, wherein the edible first generation biomass comprises inedible second generation biomass of agricultural and / or forestry waste.

10. 10. The process of claim 9, wherein the inedible second generation biomass of agricultural and / or forestry waste comprises straw.

11. 10. The process of claim 9, wherein the inedible second generation biomass of agricultural and / or forestry waste comprises wood.

12. 10. The process of claim 9, wherein the inedible second generation biomass of agricultural and / or forestry waste comprises bagasse.

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