RECOVERY OF MONO-PROPYLENE GLYCOL USING A DISTILLATION SOLVENT

Abstract

RECOVERY OF MONO-PROPYLENE GLYCOL USING A DISTILLATION SOLVENT A method for recovering mono-propylene glycol from a mixture feed comprising bio-derived diols and an organic impurity is disclosed. The method comprises: - supplying the mixture feed to a first distillation column comprising 20 to 200 theoretical stages, in which first distillation column a first distillation process is carried out; - supplying a distillation solvent to the first distillation column, wherein the distillation solvent is a diol or a sugar alcohol having a boiling point at least 80°C higher than the boiling point of mono-propylene glycol at atmospheric pressure, and wherein the weight ratio of the distillation solvent to the total mixture feed is between 2.5:1 and 10:1;- the separation of the organic impurity from the mono-propylene glycol using the distillation solvent by carrying out the first distillation process at a head temperature of between 70 and 140°C and a head pressure of between 0.01 and 0.2 bar, and with a reflux ratio of between 2 and 50; and – the recovery of the mono-propylene glycol. (FIG. 1);

Description

Title of the invention: RECOVERY OF MONO-PROPYLENE GLYCOL USING A DISTILLATION SOLVENT Technical field

[0001] The present disclosure relates to a process for recovering mono-propylene glycol from a mixed feed comprising bio-derived diols. BACKGROUND

[0002] Mono-propylene glycol (MPG, also known as 1,2-propanediol), is an important raw material that finds use, for example, in the manufacture of polymers. Mono-propylene glycol is a compound that is generally recognized as safe and can be further used, for example, for food applications as well as as a vehicle for topical, oral and certain intravenous pharmaceutical preparations. Mono-propylene glycol can be produced from propylene oxide, for example, by a high-temperature non-catalytic process at a temperature between 200°C and 220°C, or by a catalytic process, which takes place at a temperature between 150°C and 180°C in the presence of an ion exchange resin or a small amount of sulfuric acid or alkali. Mono-propylene glycol can also be obtained from glycerol, a by-product of biodiesel production.

[0003] In addition, mono-propylene glycol can be produced from sugars together with mono-ethylene glycol. However, when producing such polyols as mono-ethylene glycol and mono-propylene glycol from sugars, other diols, alcohols and other substances are also formed as by-products. Typically, when mono-ethylene glycol is distilled from such a composition, mono-propylene glycol may be obtained as a by-product together with other lighter impurities and requires further purification. Purification of mono-propylene glycol has, however, been difficult. The inventor thus recognized the need to provide a means of recovering purified mono-propylene glycol, for example, from the by-product during the production of monoethylene glycol. SUMMARY

[0004] A process for recovering mono-propylene glycol from a mixed feed comprising bio-derived diols and an organic impurity is disclosed. The mixed feed comprises mono-propylene glycol in an amount of at least 40% by weight of the total weight of the mixed feed. The process comprises:

[0005] - supplying the mixed feed to a first distillation column comprising 20 to 200 theoretical stages, in this first distillation column a first distillation process is carried out;

[0006] - supplying a distillation solvent to the first distillation column, where the distillation solvent is a diol or sugar alcohol having a boiling point which is at least 80°C higher than the boiling point of mono-propylene glycol at atmospheric pressure, and where the weight ratio of distillation solvent to total mixed feed is between 2.5:1 and 10:1;

[0007] - separation of organic impurity from mono-propylene glycol using the solvent distillation by carrying out the first distillation process at a head temperature of between 70 and 140°C and a head pressure of between 0.01 and 0.2 bar, and with a reflux ratio of between 2 and 50; and

[0008] - the recovery of mono-propylene glycol. Brief description of the drawings

[0009] The accompanying drawing, which is included to provide a better understanding of the embodiments and is part of this description, illustrates one embodiment. In the drawing:

[0010] [Fig.l] discloses an embodiment of the distillation method disclosed in the current description; and

[0011] [Fig.2] discloses an embodiment of the distillation method disclosed in the current description. DETAILED DESCRIPTION

[0012] A process for recovering mono-propylene glycol from a mixed feed comprising bio-derived diols and an organic impurity is disclosed. The mixed feed comprises mono-propylene glycol in an amount of at least 40% by weight of the total weight of the mixed feed. The process comprises:

[0013] - supplying the mixed feed to a first distillation column comprising 20 to 200 theoretical stages, in this first distillation column a first distillation process is carried out;

[0014] - supplying a distillation solvent to the first distillation column, where the distillation solvent is a diol or sugar alcohol having a boiling point which is at least 80°C higher than the boiling point of mono-propylene glycol at atmospheric pressure, and where the weight ratio of distillation solvent to total mixed feed is between 2.5:1 and 10:1;

[0015] - separation of organic impurity from mono-propylene glycol using the solvent distillation by carrying out the first distillation process at a head temperature between 70 and 140°C and a head pressure between 0.01 and 0.2 bar, and with a reflux ratio between 2 and 50; and

[0016] - the recovery of mono-propylene glycol.

[0017] Distillation can generally be viewed as a process for separating components or substances from a mixture using selective boiling and condensation. Distillation may result in essentially complete separation into nearly pure components, or it may be a partial separation that increases the concentration of selected components in the mixture. The distillation process exploits differences in the relative volatility of the different components in the mixture.

[0018] A "theoretical stage", "theoretical plate" or "distillation stage" as it may also be called, which may be used in many separation processes, may be considered as a hypothetical zone or stage where two phases, such as the liquid and vapor phases of a substance, establish an equilibrium with each other. Such equilibrium stages may also be referred to as an equilibrium stage, ideal stage or theoretical plate. The performance of many separation processes depends on the presence of a series of equilibrium stages and can be improved by providing a greater number of such stages. In other words, having more theoretical plates increases the efficiency of the separation process, whether it is distillation, absorption, chromatography, adsorption or a similar process.

[0019] When designing the distillation of a certain medium, the number of theoretical stages is usually first designed or considered and the theoretical stages then define the physical height of the distillation column. In the distillation column, the theoretical stages or distillation stages may be formed by trays or packings, also called packed beds. A packed bed may be a structured packed bed or a random packed bed.

[0020] The inventor surprisingly discovered that the combination of using the specified number of theoretical stages and the specified reflux ratio together with the distillation solvent in the specified amount allowed for efficient separation of mono-propylene from the mixed feed comprising, in addition to other bio-derived diols, the organic impurity.

[0021] The mixed feed comprising bio-derived diols may comprise, for example, mono-ethylene glycol (MEG, also referred to as ethylene glycol or 1,2-ethanediol), mono-propylene glycol (MPG, also referred to as 1,2-propanediol) and butylene glycols (1,2-BDO, also referred to as 1,2-butanediol and 2,3-BDO also referred to as 2,3-butanediol) as well as an organic impurity. Such a mixed feed of bio-derived diols may be derived, for example, from a process for producing glycols, such as a method for producing mono-ethylene glycol. In one embodiment, the mixture feed comprising bioderived diols comprises mono-ethylene glycol, mono-propylene glycol, butylene glycols and the organic impurity. The butylene glycols may appear in structures different from each other with respect to the location of the OH units. Such structures are, for example, 1,2-butanediol and 2,3-butanediol. These have different boiling points. 1,2-butanediol has a higher boiling point and 2,3-butanediol has a lower boiling point than mono-propylene glycol as shown below:

[0022] [Tables 1] Boiling point (at atmospheric pressure) °C 1,2-butanediol 196.5 2,3-butanediol 182.0 mono-propylene glycol 187.0 mono-ethylene glycol 197.1

[0023] The mixed feed may comprise mono-ethylene glycol, mono-propylene glycol, butylene glycols and the organic impurity in an amount of at least 80% by weight, or at least 85% by weight, or at least 90% by weight, of the total weight of the mixed feed. The mixed feed may comprise mono-propylene glycol in an amount of at least 45% by weight, or at least 50% by weight, or at least 55% by weight, of the total weight of the mixed feed.

[0024] The mixed feed comprising bio-derived diols may further comprise water. In one embodiment, the mixed feed comprises water in an amount of between 0 and 8% by weight, or between 0.5 and 6% by weight, or between 1 and 5% by weight, or between 1.5 and 4% by weight, or between 2 and 3% by weight, based on the total weight of the mixed feed. In one embodiment, the mixed feed comprises essentially no water.

[0025] The mixed feed may be introduced into the first distillation column in the form of a liquid or in the form of water vapor or steam, or in the form of any mixture thereof.

[0026] Mono-ethylene glycol as well as mono-propylene glycol can be produced from a process for preparing a liquid glycol composition comprising, for example, mono-ethylene glycol. Such a liquid glycol composition can be prepared from a raw material of plant origin. The raw material of plant origin may be a wood-based raw material, such as hardwood or softwood. The wood-based raw material may come from, for example, pine, poplar, beech, aspen, spruce, eucalyptus, ash, oak, maple, chestnut, willow, or birch. The wood-based raw material may also be any combination or mixture of these.

[0027] Such a method of producing a liquid glycol composition may comprise:

[0028] - providing a wood-based feedstock from a material wood-based feedstock comprising wood chips, and subjecting the wood-based feedstock to at least one pretreatment to form a liquid fraction and a fraction comprising solid cellulose particles;

[0029] - subjecting the fraction comprising solid cellulose particles to a enzymatic hydrolysis to form a lignin fraction and a carbohydrate fraction;

[0030] - subjecting the carbohydrate fraction to a catalytic conversion to form a liquid composition of glycols.

[0031] Providing the wood-based feedstock may include subjecting the wood-based raw material to a mechanical treatment selected from debarking, chipping, splitting, cutting, refining, grinding, crushing, splitting, screening and / or washing the wood-based raw material to form the wood-based feedstock. Providing the wood-based feedstock may include purchasing the wood-based feedstock.

[0032] Pretreating the wood-based feedstock may include at least one of the following: pre-steaming the wood-based feedstock, subjecting the wood-based feedstock to an impregnation treatment, and subjecting the wood-based feedstock to a steam explosion.

[0033] The pretreatment may comprise subjecting the wood-based feedstock to pre-steaming. The pretreatment may comprise an impregnation treatment and / or a steam explosion and may comprise, prior to subjecting the wood-based feedstock to an impregnation treatment and / or a steam explosion, subjecting the wood-based feedstock to pre-steaming. The pre-steaming of the wood-based feedstock may be carried out with steam having a temperature between 100 and 130°C at atmospheric pressure. During the pre-steaming, the wood-based feedstock is treated with low-pressure steam. The pre-steaming may also be carried out with steam having a temperature below 100°C, or below 98°C, or below 95°C.

[0034] Further, the pretreatment may include subjecting the feedstock wood-based feedstock to at least one impregnation treatment with an impregnation liquid. The impregnation treatment may be performed on the wood-based feedstock received from the mechanical treatment and / or pre-steaming. The pretreatment may comprise, prior to subjecting to steam explosion, subjecting the wood-based feedstock to at least one impregnation treatment with an impregnation liquid selected from water, at least one acid, at least one alkali, at least one alcohol, or any combination or mixture thereof. The impregnation liquid may comprise water, at least one acid, at least one alkali, at least one alcohol, or any combination or mixture thereof.

[0035] The pretreatment may comprise subjecting the wood-based feedstock to a steam explosion. The wood-based feedstock from the mechanical treatment, the pre-steaming step and / or the impregnation treatment may be subjected to a steam explosion.

[0036] The pretreatment may include at least one of mechanically treating a wood-based material to form a wood-based feedstock, pre-steaming the wood-based feedstock, impregnating the wood-based feedstock, and steam exploding the wood-based feedstock. The pretreatment may include mechanically treating a wood-based material to form a wood-based feedstock, pre-steaming the wood-based feedstock, impregnating the pre-steamed wood-based feedstock, and steam exploding the impregnated wood-based feedstock. The pretreatment may include pre-steaming the wood-based feedstock, impregnating the pre-steamed wood-based feedstock, and steam exploding the impregnated wood-based feedstock.The pretreatment may include an impregnation treatment of the wood-based feedstock and a steam explosion of the impregnated wood-based feedstock. That is, the wood-based feedstock having undergone the impregnation treatment may then be subjected to the steam explosion. In addition, the wood-based feedstock having been subjected to pre-steaming may then be subjected to the impregnation treatment and then the wood-based feedstock having been subjected to the impregnation treatment may then be subjected to a steam explosion.

[0037] In this specification, the term "steam explosion" may refer to a hemihydrolysis process in which the wood-based feedstock is treated in a reactor with steam having a temperature between 130 and 240°C under a pressure between 0.17 and 3.25 MPaG and then the steam-treated wood-based feedstock undergoes a sudden explosive decompression which results in the rupture of the fibrous structure. The output of the steam explosion may be mixed with a suitable liquid, for example, water, to form a slurry comprising solid cellulose particles. The fraction comprising solid cellulose particles may be separated from the liquid fraction by a suitable separation method, for example, by solid-liquid separation.

[0038] The enzymatic hydrolysis of the fraction comprising solid cellulose particles may be carried out at a temperature of between 30 and 70°C, or between 35 and 65°C, or between 40 and 60°C, or between 45 and 55°C, or between 48 and 53°C while maintaining the pH of the fraction comprising solid cellulose particles at a pH value of between 3.5 and 6.5, or between 4.0 and 6.0, or between 4.5 and 5.5, and wherein the enzymatic hydrolysis is allowed to continue for 20 to 120 h, or 30 to 90 h, or 40 to 80 h. The enzymatic hydrolysis may result in the formation of a lignin fraction and a carbohydrate fraction. Enzymes are catalysts for the enzymatic hydrolysis. The enzymatic reaction lowers the pH and by shortening the length of the cellulose fibers, it can also decrease the viscosity.Subjecting the fraction comprising solid cellulose particles to enzymatic hydrolysis can lead to the transformation of cellulose into glucose monomers with enzymes. The lignin present in the fraction comprising solid cellulose particles may remain essentially in solid form.

[0039] At least one enzyme may be used to carry out the enzymatic hydrolysis. The at least one enzyme may be selected from a group consisting of cellulases, hemicellulases, laccases and lignolytic peroxidases. Cellulases are multi-protein complexes consisting of synergistic enzymes with different specific activities which may be divided into exo- and endo-cellulases (glucanase) and [3-glucosidase (cellobiose). The enzymes may be either commercially available cellulase mixtures or manufactured on site.

[0040] The catalytic conversion of the carbohydrate fraction may comprise subjecting the carbohydrate fraction to catalytic hydrogenolysis. That is, the carbohydrate fraction may be subjected to catalysts in the presence of hydrogen. The catalytic conversion may be carried out in the presence of water. In one embodiment, the catalytic conversion of the carbohydrate fraction comprises subjecting the carbohydrate fraction to catalytic hydrogenation in the presence of a solvent, preferably water, and a catalyst system. The catalytic conversion may be carried out in the presence of a catalyst system comprising one or more catalysts. The catalytic conversion may alternatively be carried out on a carbohydrate feed derived from sugar cane, sugar beet, corn, and / or wheat.

[0041] Subjecting the carbohydrate fraction to a catalytic conversion can lead to a liquid composition of glycols. The catalytic conversion accomplishes at least hydrogenation and hydrocracking reactions to obtain the hydrogenation and hydrocracking of the carbohydrate fraction so that a liquid glycol composition is formed. The liquid glycol composition may comprise or consist of mono-ethylene glycol, mono-propylene glycol and butylene glycol. These glycols may be present at a concentration of between 0.1 and 40% by weight relative to the total weight of the liquid glycol composition. The liquid glycol composition may also comprise other by-products. The liquid composition may also comprise water.

[0042] For example, mono-ethylene glycol may be recovered from the liquid glycol composition, for example, by a separation technique selected from adsorption, evaporation, distillation, extractive distillation, azeotropic distillation, vacuum distillation, atmospheric distillation, membrane separation, filtration, reactive purification, or a combination thereof.

[0043] The feed of mixture comprising bio-derived diols applied in the current description may however also come from any other process for producing glycols. The process as described in the current description should not be understood as being related to the process described above for producing a liquid glycol composition.

[0044] Prior to the distillation process described in the current disclosure, one or more separation or purification processes may take place. For example, water, alcohols such as methanol and ethanol, organic acids, sugar alcohols such as glycerol, catalysts, and residual sugars may be removed in separate steps in a desired order. Typically, water and alcohols with the lowest boiling point may be removed first, and then components with a boiling point higher than that of mono-ethylene glycol are removed. The remaining components may comprise primarily diols with boiling points close to that of mono-propylene glycol, which may then be separated in additional purification steps.

[0045] By the expression "mixed feed comprising bio-derived diols" is meant in this description, unless otherwise indicated, a mixed feed of one or more diols, which are derived from a bio-sourced origin or raw material. In one embodiment, the bio-derived diols are diols derived from plants, for example diols derived from wood. The diols may thus be derived, for example, from hardwood, softwood or a combination thereof. The diols may also be derived from hardwood. The diols may be derived, for example, from pine, poplar, beech, aspen, spruce, eucalyptus, ash or birch, or from any combination or mixture thereof. The diols may further be derived from sugarcane, sugar beet, corn, wheat, or any combination or mixture thereof.

[0046] The inventor has discovered that the mixture feed comprising bioderived diols may also comprise an organic impurity. In one embodiment, the organic impurity is characterized by a retention time of between 6.5 and 6.7 minutes when determined by gas chromatography-flame ionization detector (GC-FID). In one embodiment, the organic impurity is characterized by a retention time of between 6.5 and 6.7 minutes when determined by gas chromatography-flame ionization detector (GC-FID) with the following parameters: The column is DB-HeavyWax (30 mx 0.32 mm, 0.5 µm); the carrier gas is helium at a flow rate of 1.9 ml / min; the injection temperature is 250°C. The samples are injected without dilution for identification or qualitative analysis. The starting temperature is 140°C and the oven is kept at this temperature for 10 minutes.Then the temperature is raised to 270°C at a heating rate of 15°C per minute. Then the sample is kept at this temperature for 10 minutes. The total operating time is 28.67 min.

[0047] In one embodiment, the organic impurity is characterized by the highest peak value at 59 m / z when determined by gas chromatography-mass spectrometer (GC-MS). In one embodiment, the organic impurity is characterized by the highest peak value at 59 m / z when determined by gas chromatography-mass spectrometer (GC-MS) with the aforementioned column. The organic impurity may further be characterized by an additional peak value at 45 m / z when determined by gas chromatography-mass spectrometer (GC-MS).

[0048] The organic impurity may form an azeotrope with the mono-propylene glycol, whereby its separation from the mono-propylene glycol in order to obtain a high yield of pure mono-propylene glycol may be difficult. The inventor surprisingly discovered that by using a specified amount of distillation solvent in the first distillation process, the azeotrope may disappear or it may be broken, so that the organic impurity and the mono-propylene glycol can be at least partially separated by distillation.

[0049] An azeotrope can be considered a mixture that has the same concentration in both the vapor and liquid phases. This contrasts with ideal solutions with one component generally more volatile than the other. If the mixture forms an azeotrope, the vapor and liquid concentrations are the same, which can prevent separation in conventional fractional distillation.

[0050] The first distillation process is carried out in a first distillation column, into which a distillation solvent is introduced to assist or facilitate the separation of mono-propylene glycol from the organic impurity present in the bio-based blend feed. The distillation solvent can further improve the separation of 1,2-butanediol and mono-ethylene glycol from mono-propylene glycol.

[0051] The distillation solvent is a diol or sugar alcohol having a boiling point that is at least 80°C higher than the boiling point of mono-propylene glycol at atmospheric pressure. The distillation solvent may have a boiling point that is at least 85°C or at least 90°C higher than the boiling point of mono-propylene glycol at atmospheric pressure. The distillation solvent may have a boiling point that is 80 to 100°C, or 82 to 98°C, or 95 to 95°C, higher than the boiling point of mono-propylene glycol at atmospheric pressure. The distillation solvent may have a boiling point between 265 and 350°C, or between 265 and 300°C, or between 275 and 300°C. In one embodiment, the distillation solvent is a diol having a boiling point that is at least 80°C higher than the boiling point of mono-propylene glycol at atmospheric pressure.In one embodiment, the distillation solvent is a sugar alcohol having a boiling point that is at least 80°C higher than the boiling point of mono-propylene glycol at atmospheric pressure.

[0052] In one embodiment, the weight ratio of distillation solvent to total mixed feed is between 4:1 and 9:1 or between 5:1 and 8:1. The inventor has surprisingly discovered that the specified amount of distillation solvent used in the distillation process effectively helps to separate the organic impurity from mono-propylene glycol.

[0053] In one embodiment, the distillation solvent is tri-ethylene glycol or tri-propylene glycol. In one embodiment, the distillation solvent is tri-ethylene glycol or tri-propylene glycol. In one embodiment, the distillation solvent is tri-ethylene glycol.

[0054] The distillation solvent used has the additional utility of having a boiling point higher than that of mono-propylene glycol and also those of the other diols in the mixed feed. Thus, the distillation solvent used may not boil in the first distillation column and the vapor flux in the first distillation column may not increase even if a high amount of the distillation solvent is used. Thus, the size of the column does not necessarily have to be increased considerably due to the amount of the distillation solvent used.

[0055] The distillation process as disclosed in the current description is carried out in a first distillation column. The first distillation column may comprise 20 to 200, or 40 to 120, or 40 to 80, or 60 to 120 theoretical stages. The number of theoretical stages being 20 to 200 has the additional utility of allowing the separation to take place with a rather high efficiency so that separation rates reasonable reflux can be used.

[0056] The mixed feed may be introduced into the first distillation column at a point, which is below the point, where the distillation solvent is introduced into the first distillation column.

[0057] The mixed feed may be introduced into the first distillation column at a point, which is located between two theoretical stages. The distillation column may comprise packings or packed beds, where a packed bed comprises two or more theoretical stages. In such a situation, the mixed feed may be introduced into the distillation column at a point located between two of these packed beds. The mixed feed may be introduced into the first distillation column at a point, which is located below, above or at least on a theoretical stage. When using trays as theoretical stages, the mixed feed may be introduced on a theoretical stage or above a theoretical stage.

[0058] In one embodiment, the distillation solvent is introduced into the first distillation column at any point between the 1st and 10th, or 2nd and 9th, or 3rd and 7th, theoretical stages as calculated from the top of the first distillation column. The distillation solvent may be introduced into the first distillation column above the highest theoretical stage as calculated from the top of the first distillation column.

[0059] In one embodiment, the first distillation process is carried out with a reflux ratio of between 3 and 40, or between 4 and 30, or between 5 and 20, or between 6 and 10. The reflux ratio can generally be defined as the ratio of the overhead liquid returned to the distillation column divided by the liquid removed or recovered from the distillation column as product.

[0060] The inventor has surprisingly discovered that, in particular, the combination of the use of the distillation solvent in the specified amount together with the other process conditions in the first distillation column has the additional utility of allowing the separation of the mono-propylene glycol from the organic impurity present in the mixed feed and thus allowing the recovery of the mono-propylene glycol with high purity and yield.

[0061] In one embodiment, the process comprises recovering mono-propylene glycol with a purity of at least 80% by weight, or at least 85% by weight, or at least 90% by weight, or at least 93% by weight. In one embodiment, the mono-propylene glycol is recovered with a purity of between 99.0 and 99.99% by weight, or between 99.3 and 99.95% by weight, or between 99.5 and 99.9% by weight, or between 99.6 and 99.8% by weight. Such purity can be achieved when a second distillation process is used after the first distillation process. The purity is calculated as the percentage of the amount of mono-propylene glycol in the recovered product versus total recovered product flow quantity.

[0062] In one embodiment, the yield of recovered mono-propylene glycol is between 93 and 100%, or between 95 and 98%. The yield is calculated as the percentage of the amount of recovered mono-propylene glycol relative to the amount of mono-propylene glycol in the mixed feed.

[0063] In one embodiment, the first distillation process is carried out at a head temperature of between 75 and 135°C, or between 90 and 130°C, or between 100 and 120°C.

[0064] In one embodiment, the first distillation process is carried out at a bottom temperature of between 150 and 230°C, or between 160 and 200°C or between 170 and 190°C.

[0065] In one embodiment, the first distillation process is carried out at a head pressure of between 0.01 and 0.2 bar, or between 0.015 and 0.1 bar, or between 0.02 and 0.1 bar.

[0066] In one embodiment, the pressure drop on the distillation column is between 0.05 and 0.2 bar, or between 0.07 and 0.15 bar, or between 0.08 and 0.1 bar.

[0067] In one embodiment, the residence time of the mixed feed and the distillation solvent in the first distillation column is between 1 and 10 minutes, or between 1.2 and 7 minutes, or between 1.5 and 6 minutes, or between 1.8 and 5.4 minutes.

[0068] The bottom temperature of the first distillation column may be maintained at a temperature of at most 230°C. Maintaining the bottom temperature of the distillation column at a temperature of at most 230°C has the additional utility of preventing or reducing degradation of the compound.

[0069] In this description, the term "head temperature" is used to refer to the temperature in the vapor space in the distillation column which is above the packed bed or the highest stage and below the vapor pipe of the distillation column. It will be clear to those skilled in the art that the temperature in the distillation column as such may differ from the temperature, for example, in the condenser or reboiler which may be operatively connected to the distillation column. In this description, the term "bottom temperature" is used to refer to the temperature of the liquid in the reboiler.

[0070] In this specification, the term "head pressure" is used to refer to the pressure in the vapor space in the distillation column that is above the packed bed or topmost stage and below the vapor pipe of the distillation column.

[0071] In one embodiment, at least one condenser is used in the distillation process. In one embodiment, the distillation arrangement comprises at least least one condenser. The condenser(s) used may be (a) partial condenser(s), (a) total condenser(s) or a combination of these may be used. The condenser(s) may be thermally integrated or it may use a cooling medium, such as cooling water, or it may operate with air cooling.

[0072] In one embodiment, a reboiler is used in the distillation process. In one embodiment, the distillation arrangement comprises a reboiler. The reboiler may operate at a vapor pressure of between 0.06 and 0.4 bar or between 0.1 and 0.2 bar.

[0073] In one embodiment, the method comprises:

[0074] - the removal of the organic impurity together with the distillation solvent in a first bottom stream from the first distillation process; and

[0075] - the elimination of mono-propylene glycol in a first overhead stream coming from of the first distillation process.

[0076] With the aid of the distillation solvent, the organic impurity will separate from the mono-propylene glycol during the first distillation process and the mono-propylene glycol will, as a lower boiling component, be distilled into the first overhead stream. The organic impurity separated from the mono-propylene glycol, having a higher boiling point than that of the mono-propylene glycol, can then be removed together with the distillation solvent with the first bottom stream.

[0077] In one embodiment, the method comprises recycling the distillation solvent removed in the first bottoms stream from the first distillation process by reinjecting it into the first distillation column. From the first distillation column, the distillation solvent may be fed into a recovery column. In the recovery column, the lighter components may be removed in a second overhead stream of the recovery column and the distillation solvent may be removed in a second bottoms stream of the recovery column. The second bottoms stream, comprising predominantly the distillation solvent, may then be fed back into the first distillation column and thus reused.If necessary, a portion of the recycled distillation solvent stream can be continuously purged to reduce or limit the accumulation of heavier degradation compounds if these occur.

[0078] In one embodiment, the method comprises providing the mono-propylene glycol removed in a first overhead stream from the first distillation process to a second distillation column, in which a second distillation process is carried out. In one embodiment, the method comprises providing the mono-propylene glycol removed in a first overhead stream from the first distillation process to a second distillation column, wherein a second distillation process is carried out to recover mono-propylene glycol at a concentration of at least 98% by weight, or at least 98.5% by weight, or at least 99% by weight.

[0079] In one embodiment, the second distillation process is carried out at a head temperature of between 104 and 140°C, or between 90 and 130°C or between 100 and 120°C.

[0080] In one embodiment, the second distillation process is carried out at a bottom temperature of between 134 and 170°C, or between 145 and 165°C, or between 150 and 160°C.

[0081] In one embodiment, the second distillation process is carried out at a head pressure of between 0.1 and 0.5 bar.

[0082] In one embodiment, the second distillation process is carried out at a bottom pressure of between 0.15 and 0.6 bar.

[0083] The process as described in the current specification has the additional utility of enabling separation of the organic impurity present from the mono-propylene glycol. The use of the distillation solvent in a specified amount in the first distillation process has the additional utility of enabling the use of distillation conditions such that the possible azeotrope between the organic impurity and the mono-propylene glycol can disappear and separation of the organic impurity and the mono-propylene glycol is possible. EXAMPLES

[0084] Reference will now be made in detail to various embodiments.

[0085] The description below discloses certain embodiments in such detail that a person skilled in the art is able to use the embodiments based on the disclosure. Not all steps or features of the embodiments are described in detail, as many steps or features will be obvious to those skilled in the art based on this specification.

[0086] For simplicity, the item numbers will be retained in the following exemplary embodiments in the case of repeating components.

[0087] The attached [Fig.l] discloses an example of an embodiment for the recovery of mono-propylene glycol from a mixed feed comprising bio-derived diols and an organic impurity. The mixed feed 2b comprises mono-propylene glycol in an amount of at least 40% by weight of the total weight of the mixed feed. The mixed feed is supplied to a first distillation column 1, in which a first distillation process is carried out. The first distillation column comprises an inlet 2b for introducing the mixture feed into the first distillation column 1. The first distillation column 1 comprises packed beds comprising 20 to 200 theoretical stages 4a, 4b,... 4n. The mixture feed 2b is introduced into the first distillation column 1 at a point, which is below the point where the distillation solvent 2a is introduced into the first distillation column 1 as calculated from the head of the distillation column. The total height of the distillation column is determined based on the number of theoretical stages 4a, 4b, .. .4n. The first distillation column is configured to operate with a reflux ratio between 2 and 50 and at a head temperature between 70 and 140°C and a head pressure between 0.01 and 0.2 bar. The mono-propylene glycol is recovered from the first distillation column 1 in a first head stream 3a.The distillation solvent and the organic impurity are removed from the first distillation column 1 in a first bottom stream 3b. [Fig.l] further shows the presence of a condenser 5 and a reboiler 6.

[0088] The attached [Fig.2] discloses an example of an embodiment for the recovery of mono-propylene glycol from a mixed feed comprising bio-derived diols and an organic impurity. The process begins in a manner similar to that shown above in [Fig.l] by carrying out the first distillation process in the first distillation column 1. From the first distillation column 1, the mono-propylene glycol recovered in a first overhead stream 3a is fed to a second distillation column 7, in which a second distillation process is carried out. Following the second distillation process, the mono-propylene glycol can be recovered at a concentration of at least 98% by weight from the second bottom stream 7b. 2,3-butanediol is recovered, with the second overhead stream 7a from the second distillation column 7, together with water and a mixture of light components.The distillation solvent removed from the first distillation column 1 in a first bottom stream 3b is introduced into a recovery column 8. The distillation solvent may be purified in the recovery column 8 for further recycling into the bottom recovery stream 8b for addition with the feed 2a to the first distillation column 1. Any waste formed may be recovered from the recovery column 8 in an overhead waste stream 8a.

[0089] The distillation process will be described in more detail in the examples below. The calculations in the examples below were performed with a simulation performed with Aspen Plus VI1, using the NRTL property method with properties from the Aspen database or an estimate if the values were not available. The properties of the organic impurity were generated so that there is an azeotrope with mono-propylene glycol (MPG), the azeotropic ratio being within the range that is the ratio of organic impurity to MPG in the feed. This means an azeotropic mass ratio between 98% and 99% by weight of MPG and between 1% and 2% by weight of the organic impurity. As a model compound in the simulation, 2-methyl-2,3-pentanediol was used as the organic impurity because it has a boiling point very close to that of MPG and forms an azeotrope with it. In this way, the observed non-performance of simple fractional distillation was reproduced. A RadFrac block was used for the distillation column with a total condenser.

[0090] Example 1 - Distillation of a mixture comprising bio-derived diols

[0091] In this example, a mixed feed comprising bio-sourced diols and the organic impurity was subjected to the first distillation process. The following parameters were used in this example:

[0092] [Tables2] Number of Theoretical Stages 50 Mix Feed Mix Feed Feed Stage 30 MPG 52.82% TEG Feed Stage 5 MEG 20.57% Reflux Ratio 5.0 1.2-BDO 17.60% Head Pressure (bar) 0.08 2.3-BDO 3.62% Column Pressure Drop (bar) 0.04 Organic Impurity 0.61% Mix Feed Flow Rate (kg / h) 100 Water 4.78% Distillate Flow Rate (kg / h) 58

[0093] In the table above as well as in the following examples, the following abbreviations are used:

[0094] MPG = mono-propylene glycol

[0095] MEG = mono-ethylene glycol

[0096] BDO = butylene glycol

[0097] TEG = triethylene glycol

[0098] The feed stages are counted from the head of the distillation column.

[0099] The results are presented below:

[0100] [Tables3] TEG Flow Rate kg / h TEG to Total Mix Feed Weight Ratio Organic Impurity in Distillate kg / h MPG Purity MPG Yield Top Temperature (°C) Bottom Temperature (°C) 0 0:1 0.52 64.6% 71.0% 114.5 137.9 250 2.5:1 0.47 84.7% 93.0% 113.1 178.9 350 3.5:1 0.42 84.7% 93.1% 113.1 184.1 500 5:1 0.38 84.8% 93.1% 113.1 188.3 750 7.5:1 0.33 84.9% 93.2% 113.1 191.8 1000 10:1 0.29 84.9% 93.3% 113.1 193.8

[0101] Example 2 - Distillation of a mixture comprising bio-derived diols

[0102] In this example, a mixed feed comprising bio-sourced diols and the organic impurity was subjected to the first distillation process. The following parameters were used in this example:

[0103] [Tables4] Number of Theoretical Stages 80 Mix Feed Mix Feed Feed Stage 40 MPG 52.82% TEG Feed Stage 5 MEG 20.57% Reflux Ratio 10.0 1.2-BDO 17.60% Head Pressure (bar) 0.04 2.3-BDO 3.62% Column Pressure Drop (bar) 0.08 Organic Impurity 1.02% Mix Feed Flow Rate (kg / h) 100 Water 4.37% Distillate Flow Rate (kg / h) 60

[0104] Compared to Example 1, the other parameters remained the same but the number of theoretical stages, the reflux ratio, the feed stage of the mixed feed, the head pressure and the pressure drop were modified. In addition, the composition of the mixed feed was different. The results are shown below. TEG Flow Rate kg / h TEG to Total Mix Feed Weight Ratio Organic Impurity in Distillate kg / h MPG Purity MPG Yield Top Temperature (°C) Bottom Temperature (°C) 0 0:1 0.87 63.6% 72.3% 101.2 138.1 250 2.5:1 0.82 85.3% 96.9% 99.7 181.2 350 3.5:1 0.74 85.5% 97.1% 99.7 186.1 500 5:1 0.65 85.6% 97.2% 99.7 190.0 750 7.5:1 0.56 85.8% 97.4% 99.7 193.2 1000 10:1 0.49 85.9% 97.5% 99.7 194.9

[0106] Example 3 - Distillation of a mixture comprising bio-derived diols

[0107] In this example, a mixed feed comprising bio-sourced diols and the organic impurity was subjected to the first distillation process. The following parameters were used in this example:

[0108] [Tableauxô] Number of Theoretical Stages 100 Mix Feed Mix Feed Feed Stage 50 MPG 52.82% TEG Feed Stage 5 MEG 20.57% Reflux Ratio 10.0 1.2-BDO 17.60% Head Pressure (bar) 0.08 2.3-BDO 3.62% Column Pressure Drop (bar) 0.06 Organic Impurity 1.02% Mix Feed Flow Rate (kg / h) 100 Water 4.37% Distillate Flow Rate (kg / h) 60

[0109] Compared to Example 2, the other parameters remained the same but the number of theoretical stages, the feed stage of the mixture feed, the head pressure and the pressure drop were modified. The results are presented below. TEG Flow Rate kg / h TEG Weight Ratio to Total Mixed Feed Organic Impurity in Distillate kg / h MPG Purity MPG Yield Top Temperature (°C) Bottom Temperature (°C) 0 0:1 0.84 63.8% 72.5% 115.3 141.7 250 2.5:1 0.70 85.5% 97.1% 113.8 185.4 350 3.5:1 0.60 85.7% 97.3% 113.8 190.4 500 5:1 0.51 85.8% 97.5% 113.9 194.3 750 7.5:1 0.42 86.0% 97.6% 113.9 197.5 1000 10:1 0.36 86.0% 97.7% 113.9 199.2 [YES] Example 4 - Distillation of a mixture comprising bio-derived diols

[0112] In this example, a mixed feed comprising bio-sourced diols and the organic impurity was subjected to the first distillation process. The following parameters were used in this example:

[0113] [Tables8] Number of Theoretical Stages 100 Mix Feed Mix Feed Feed Stage 50 MPG 52.82% TEG Feed Stage 5 MEG 20.57% Reflux Ratio 10.0 1.2-BDO 17.60% Head Pressure (bar) 0.08 2.3-BDO 3.62% Column Pressure Drop (bar) 0.06 Organic Impurity 0.61% Mix Feed Flow Rate (kg / h) 100 Water 4.78% Distillate Flow Rate (kg / h) 60

[0114] Compared to Example 3, the other parameters remained the same but the composition of the mixed feed was different. The results are shown below:

[0115] [Tables9] TEG Flow Rate kg / h TEG to Total Mix Feed Weight Ratio Organic Impurity in Distillate kg / h MPG Purity MPG Yield Top Temperature (°C) Bottom Temperature (°C) 0 0:1 0.49 63.8% 72.5% 114.7 141.7 250 2.5:1 0.45 85.3% 96.9% 113.3 185.3 350 3.5:1 0.38 85.4% 97.0% 113.3 190.3 500 5:1 0.32 85.5% 97.1% 113.3 194.2 750 7.5:1 0.26 85.6% 97.2% 113.3 197.4 1000 10:1 0.22 85.6% 97.3% 113.3 199.1

[0116] Example 5 - Distillation of a mixture comprising bio-derived diols

[0117] In this example, a mixed feed comprising bio-sourced diols and the organic impurity was subjected to the first distillation process. The following parameters were used in this example:

[0118] [TableauxlO] Number of Theoretical Stages 50 Mix Feed Mix Feed Feed Stage 30 MPG 52.82% TEG Feed Stage 5 MEG 20.57% Reflux Ratio 10.0 1.2-BDO 17.60% Head Pressure (bar) 0.08 2.3-BDO 3.62% Column Pressure Drop (bar) 0.04 Organic Impurity 0.61% Mix Feed Flow Rate (kg / h) 100 Water 4.78% Distillate Flow Rate (kg / h) 60

[0119] Compared to Example 1, the other parameters remained the same but the reflux rate was modified. The results are shown below:

[0120] [Tables] TEG Flow Rate kg / h TEG to Total Mix Feed Weight Ratio Organic Impurity in Distillate kg / h MPG Purity MPG Yield Top Temperature (°C) Bottom Temperature (°C) 0 0:1 0.51 64.8% 71.1% 114.4 137.9 250 2.5:1 0.48 84.6% 92.9% 113.1 178.9 350 3.5:1 0.45 84.7% 93.0% 113.1 184.0 500 5:1 0.42 84.8% 93.1% 113.1 188.3 750 7.5:1 0.37 84.9% 93.2% 113.1 191.8 1000 10:1 0.34 84.9% 93.2% 113.1 193.8

[0121] Example 6 - Distillation of a mixture comprising bio-derived diols

[0122] In this example, a mixed feed comprising bio-sourced diols and the organic impurity was subjected to the first distillation process. The following parameters were used in this example:

[0123] [Tablesl2] Number of Theoretical Stages 100 Mix Feed Mix Feed Feed Stage 50 MPG 52.82% TEG Feed Stage 5 MEG 20.57% Reflux Ratio 5.0 1.2-BDO 17.60% Head Pressure (bar) 0.08 2.3-BDO 3.62% Column Pressure Drop (bar) 0.06 Organic Impurity 1.02% Mix Feed Flow Rate (kg / h) 100 Water 4.37% Distillate Flow Rate (kg / h) 60

[0124] Compared to Example 3, the other parameters remained the same but the reflux rate was modified. The results are shown below:

[0125] [Tablesl3] TEG Flow Rate kg / h TEG to Total Mix Feed Weight Ratio Organic Impurity in Distillate kg / h MPG Purity MPG Yield Top Temperature (°C) Bottom Temperature (°C) 0 0:1 0.81 63.9% 72.6% 115.3 141.7 250 2.5:1 0.73 85.5% 97.1% 113.8 185.4 350 3.5:1 0.62 85.6% 97.3% 113.8 190.4 500 5:1 0.54 85.8% 97.4% 113.9 194.3 750 7.5:1 0.44 85.9% 97.6% 113.9 197.5 1000 10:1 0.37 86.1% 97.8% 113.9 199.2

[0126] Example 7 - Distillation of a mixture comprising bio-derived diols

[0127] In this example, a mixed feed comprising bio-sourced diols and the organic impurity was subjected to the first distillation process. The following parameters were used in this example:

[0128] [Tablesl4] Number of Theoretical Stages 100 Mix Feed Mix Feed Feed Stage 75 MPG 52.82% TEG Feed Stage 5 MEG 20.57% Reflux Ratio 10.0 1.2-BDO 17.60% Head Pressure (bar) 0.08 2.3-BDO 3.62% Column Pressure Drop (bar) 0.06 Organic Impurity 1.02% Mix Feed Flow Rate (kg / h) 100 Water 4.37% Distillate Flow Rate (kg / h) 60

[0129] Compared to Example 4, the other parameters remained the same but the number of theoretical stages, the feed stage of the mixture feed and the pressure drop were modified. The results are shown below:

[0130] [Tables 15] TEG Flow Rate kg / h TEG Weight Ratio to Total Mixed Feed Organic Impurity in Distillate kg / h MPG Purity MPG Yield Top Temperature (°C) Bottom Temperature (°C) 0 0:1 0.73 58.3% 66.3% 115.8 144.3 250 2.5:1 0.49 85.9% 97.5% 113.9 189.2 350 3.5:1 0.40 86.0% 97.7% 113.9 194.2 500 5:1 0.34 86.1% 97.8% 113.9 198.1 750 7.5:1 0.27 86.2% 97.9% 113.9 201.2 1000 10:1 0.23 86.3% 98.0% 113.9 203.0

[0131] Example 8 - Distillation of a mixture comprising bio-derived diols

[0132] In this example, a mixed feed comprising bio-sourced diols and the organic impurity was subjected to the first distillation process followed by the second distillation process. The mixed feed and the parameters of the first distillation process are the same as in Example 3, however, maintaining the TEG flow rate at 750 kg / h.

[0133] The following parameters were used in the second distillation process:

[0134] [Tables 16] Number of Theoretical Stages 70 First Head Stream Mixing First Head Stream Feed Stage 25 MPG 85.9% Reflux Ratio 50 MEG 0.00% Head Pressure (bar) 0.1 1.2-BDO 0.0% Column Pressure Drop (bar) 0.04 2.3-BDO 6.0% Distillate Flow Rate (kg / h) 8.5 TEG 0.0% Organic Impurity 0.7% Water 7.3% Mass Flow Rate (kg / h) 60.00

[0135] The results are presented below:

[0136] [Tables 17] Units Product MPG (stream 7b in Figure 2) Distillate MPG (stream 7a in Figure 2) Head Temperature °C 133.0 49.7 Head Pressure bar 0.14 0.1 Mass Flow Rates Kg / h 51.50 8.50 Mass Fractions MEG 0.002% 0.0% MPG 99.1% 6.0% 1,2-BDO 0.000% 0.0% 2,3-BDO 0.003% 42.6% TEG 0.0% 0.0% Organic Impurity 0.9% 0.0% Water 0.0% 51.4%

[0137] The yield of mono-propylene glycol in this example was 97%.

[0138] Example 9 - Distillation of a mixture comprising bio-derived diols

[0139] In this example, a mixed feed comprising bio-sourced diols and the organic impurity was subjected to the first distillation process followed by the second distillation process. The mixed feed and the parameters of the first distillation process are the same as in Example 4, however, maintaining the TEG flow rate at 750 kg / h.

[0140] The following parameters were used in the second distillation process:

[0141] [Tablesl8] Number of Theoretical Stages 70 First Head Stream Mixing First Head Stream Feed Stage 25 MPG 85.6% Reflux Ratio 50 MEG 0.00% Head Pressure (bar) 0.1 1.2-BDO 0.0% Column Pressure Drop (bar) 0.04 2.3-BDO 6.0% Distillate Flow Rate (kg / h) 8.5 TEG 0.0% Organic Impurity 0.4% Water 8.0% Mass Flow Rate (kg / h) 60.00

[0142] The results are presented below:

[0143] [Tablesl9] Units Product MPG (stream 7b in Figure 2) Distillate MPG (stream 7a in Figure 2) Head Temperature °C 133.0 48.6 Head Pressure bar 0.14 0.1 Mass Flow Rates Kg / h 51.50 8.50 Mass Fractions MEG 0.003% 0.0% MPG 99.5% 1.3% 1,2-BDO 0.000% 0.0% 2,3-BDO 0.028% 42.4% TEG 0.0% 0.0% Organic Impurity 0.9% 0.5% Water 0.0% 56.2%

[0144] The yield of mono-propylene glycol in this example was 97%.

[0145] Example 10 - Distillation of a mixture comprising bio-derived diols

[0146] In this example, a mixed feed comprising bio-sourced diols and the organic impurity was subjected to the first distillation process followed by the second distillation process. The mixture feed and parameters of the first distillation process are the same as in Example 4, but with the TEG flow rate maintained at 750 kg / h and the distillate flow rate at 58 kg / h.

[0147] The following parameters were used in the second distillation process:

[0148] [Tables20] Number of Theoretical Stages 70 First Head Stream Mixing First Head Stream Feed Stage 25 MPG 85.2% Reflux Ratio 50 MEG 0.00% Head Pressure (bar) 0.1 1.2-BDO 0.0% Column Pressure Drop (bar) 0.04 2.3-BDO 6.2% Distillate Flow Rate (kg / h) 8.5 TEG 0.0% Organic Impurity 0.3% Water 8.2% Mass Flow Rate (kg / h) 58.00

[0149] The results are presented below:

[0150] [Tables21] Units Product MPG (stream 7b in Figure 2) Distillate MPG (stream 7a in Figure 2) Head Temperature °C 133.0 48.6 Head Pressure bar 0.14 0.1 Mass Flow Rates Kg / h 49.50 8.50 Mass Fractions MEG 0.003% 0.0% MPG 99.6% 1.3% 1,2-BDO 0.000% 0.0% 2,3-BDO 0.03% 42.4% TEG 0.0% 0.0% Organic Impurity 0.9% 0.4% Water 0.0% 56.2%

[0151] The yield of mono-propylene glycol in this example was 93%.

[0152] From the above examples and their results, it can be seen that the higher the TEG flow rate (= weight ratio of TEG to total mixture feed), the lower the amount of organic impurities in the distillate. At the same time, compared to the absence of TEG in the process, the yield and purity of mono-propylene glycol are always higher and, furthermore, the yield and purity of mono-propylene glycol are increased when the amount of TEG used in the process is increased. This trend is visible with all numbers of theoretical stages and reflux ratios. The more theoretical stages used, the better the removal of organic impurity.

[0153] It will be apparent to those skilled in the art that with advances in technology, the basic idea can be implemented in a variety of ways. The embodiments are therefore not limited to the examples described above; instead, they may vary within the scope of the claims.

[0154] The embodiments described above may be used in any combination with each other. Several of the embodiments may be combined together to form another embodiment. A method disclosed herein may include at least one of the embodiments described above. It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments. The embodiments are not limited to those that solve all or some of the stated problems or those that have all or some of the stated benefits and advantages. It will further be understood that a reference to "an" item refers to one or more of these items.The term "comprising" is used in this description to mean including the feature(s) or act(s) that follow thereafter, without excluding the presence of one or more additional features or acts.

Claims

Claims

1. A process for recovering mono-propylene glycol from a mixed feed comprising bio-derived diols and an organic impurity, wherein the mixed feed comprises mono-propylene glycol in an amount of at least 40% by weight of the total weight of the mixed feed, and wherein the process comprises: - supplying the mixed feed to a first distillation column comprising 20 to 200 theoretical stages, in which first distillation column a first distillation process is carried out; - supplying a distillation solvent to the first distillation column, wherein the distillation solvent is a diol or a sugar alcohol having a boiling point at least 80°C higher than the boiling point of mono-propylene glycol at atmospheric pressure, and wherein the weight ratio of the distillation solvent to the total mixed feed is between 2.5:1 and 10:1;- separating the organic impurity from the mono-propylene glycol using the distillation solvent by carrying out the first distillation process at a head temperature of between 70 and 140°C and a head pressure of between 0.01 and 0.2 bar, and with a reflux ratio of between 2 and 50; and - recovering the mono-propylene glycol, wherein the organic impurity is characterized: - by a retention time of between 6.5 and 6.7 minutes when determined by gas chromatography-flame ionization detector (GC-FID), and - by the highest peak value at 59 m / z when determined by gas chromatography-mass spectrometer (GC-MS).;

2. The method of claim 1, wherein the mixed feed comprises mono-propylene glycol in an amount of at least 45% by weight, at least 50% by weight or at least 55% by weight, of the total weight of the mixed feed.

3. The method of any preceding claim, wherein the mixed feed comprises mono-ethylene glycol, mono-propylene glycol, butylene glycol and the organic impurity in an amount of at least 80% by weight, or at least 85% by weight, or at least 90% by weight of the total weight of the mixed feed. blend.

4. The process of any preceding claim, wherein the process comprises recovering mono-propylene glycol at a concentration of at least 75% by weight, or at least 80% by weight, or at least 85% by weight, or at least 90% by weight, or at least 93% by weight, or at least 94% by weight, or at least 94.5% by weight.

5. The process of any preceding claim, wherein the weight ratio of distillation solvent to total mixed feed is between 4:1 and 9:1 or 5:1 and 8:

1.

6. The process of any preceding claim, wherein the distillation solvent is triethylene glycol or tripropylene glycol.

7. The process of any preceding claim, wherein the process comprises: - removing the organic impurity together with the distillation solvent in a first bottoms stream from the first distillation process; and - removing the mono-propylene glycol in a first overhead stream from the first distillation process.

8. The method of any preceding claim, wherein the first distillation column comprises 40 to 120, or 40 to 80, or 60 to 120 theoretical stages.

9. The method of any preceding claim, wherein the mixed feed is introduced into the first distillation column at a point, which is below the point, where the distillation solvent is introduced into the first distillation column.

10. The process of any preceding claim, wherein the first distillation process is carried out at a head temperature of between 75 and 135°C, or between 90 and 130°C or between 100 and 120°C.

11. The process of any preceding claim, wherein the first distillation process is carried out at a bottom temperature of between 150 and 230°C, or between 160 and 200°C or between 170 and 190°C.

12. The process of any preceding claim, wherein the first distillation process is carried out at a head pressure of between 0.01 and 0.2 bar, or between 0.015 and 0.1 bar, or between 0.02 and 0.1 bar.

13. The method of any preceding claim, wherein the pressure drop across the distillation column is between 0.05 and 0.2 bar, or between 0.07 and 0.15 bar, or between 0.08 and 0.1 bar.

14. The process of any preceding claim, wherein the first distillation process is carried out with a reflux ratio of between 3 and 40, or between 4 and 30, or between 5 and 20, or between 6 and 10.

15. The method of any preceding claim, wherein the method comprises recycling the distillation solvent removed in the first bottoms stream from the first distillation process by reinjecting it into the first distillation column.

16. The process of any preceding claim, wherein the process comprises providing the mono-propylene glycol removed in a first overhead stream from the first distillation process to a second distillation column, wherein a second distillation process is carried out to recover the mono-propylene glycol at a concentration of at least 98% by weight, or at least 98.5% by weight, or at least 99% by weight.

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