Separation process and reactor system for glycol-water mixtures

Abstract

The separation process separates polyol compounds from water to obtain a purified product stream comprising polyol compounds at an output concentration of at least 90 wt%. To this end, a mixture of polyol compounds and water is provided, the mixture having a polyol concentration. The polyol concentration of the mixture is increased in an evaporation stage. Subsequently, the mixture is processed in a distillation stage to obtain a purified product stream comprising polyol compounds at an output concentration of at least 90 wt%. Herein, the distillation stage is operated to produce a vapor output, which is optionally compressed to a vapor pressure, and coupled to the evaporation stage. The maximum distillation pressure and / or the compressed vapor pressure is not less than the maximum evaporation pressure. A reactor system is configured to perform the separation process.

Description

Technical Field

[0001] The present invention relates to a method for separating a polyol compound from water at least partially to obtain a purified product stream comprising an output concentration of at least 90% by weight of the polyol compound, the method comprising the steps of: providing a mixture of the polyol compound and water, and treating the mixture in a distillation stage to increase the concentration of the polyol compound.

[0002] The present invention also relates to a reactor system for carrying out the method. Background Technology

[0003] Polyols, such as diols, are used in a variety of chemical processes, including natural gas purification, the preparation of ethylene oxide, polyethylene glycol, and polypropylene glycol, as well as the polymerization and depolymerization of polyesters such as polyethylene terephthalate (PET), typically as a step in waste recycling. One of the most commonly used diols is ethylene glycol.

[0004] Typically, the use of these diols results in a mixture containing water. It is known in the art that regenerating pure or nearly pure diols or other polyol compounds using distillation and other treatments requires significant energy. Furthermore, there is a risk that additional compounds present in the mixture may evaporate, potentially causing environmental pollution. Additionally, there is a risk that additional compounds present in the mixture may decompose or form reaction products, potentially contaminating another downstream chemical process, such as when the resulting polyol product stream is reused as a solvent for depolymerization processes. Therefore, several methods have been envisioned for purifying diols from water, including reverse osmosis, membrane distillation, total evaporation, distillation, ozonation, absorption using activated carbon, aldehyde separation by stripping and ion exchange. Many of these methods focus on reducing the concentration of diols in aqueous waste streams.

[0005] A specific method is known from US2,218,234. This patent discloses a method for separating isopropanol (50-75%), ethylene glycol (10-30%), water, dyes, and salts (5-15% total). In a first step, the mixture is treated by distillation to remove isopropanol and some water. The residue is transferred to a feed tank and supplied from there to another distillation column. Hydrocarbons with boiling points below 140°C, such as toluene, are then added as vapor to the second distillation column. Due to the presence of toluene, there is no specific dehydration of the glycols, but toluene carries out the glycols and water at a temperature of approximately 109°C. Therefore, it does not provide an efficient method for removing water from glycols.

[0006] Another method is known from US4,332,643. The aim of this method is to provide a glycol, such as triethylene glycol, with a concentration of at least 99.9% starting from a “dilute” mixture of water and glycol. This dilute mixture is used as a reflux condenser coolant, in which it is heated to 140-150°F (60-65°C) and directed to a three-phase separator, where any gases are separated. It then has a concentration of approximately 94.5% by weight and is directed to a distillation column, where it is concentrated to 98.5-99.0% by weight. The concentrated glycol enters a reboiler operating at 198°C, and then a water exhauster operating at 198-221°C. This is an expensive process for achieving anhydrous glycols while the initial concentration is already above 90% by weight.

[0007] Another method and system are also known from US 5,234,552. The purpose of this disclosure is to prevent the emission of aromatic compounds into the atmosphere during glycol dehydration. Such emissions include liquid water and hydrocarbons in vapor form. The disclosed system includes a cryogenic separation system to separate usable gases and hydrocarbons from a distillate well. In this system, a drying agent such as diethylene glycol or triethylene glycol is injected, which exits the separator as a mixed stream of glycols and water with some hydrocarbons. This stream is then transferred to a glycol reboiler operating at a temperature of 350–400°F (177–204°C). However, this temperature is far above the atmospheric boiling point of water. In other words, it is not an energy-efficient method, and improvements are desired. Summary of the Invention

[0008] Therefore, there remains a need for an energy-efficient method for dehydrating polyol compounds such as glycols, in which the reuse of the resulting polyol product stream is enhanced. A reactor system in which such a method can be implemented is also needed.

[0009] Therefore, according to a first aspect, the present invention provides a method for separating a polyol compound from water at least partially according to claim 1 to obtain a purified product stream comprising an output concentration of at least 90% by weight of the polyol compound. The method of the present invention comprises the steps of: (1) providing a mixture of a polyol compound and water, the mixture having a polyol concentration; (2) increasing the polyol concentration of the mixture in an evaporation stage, wherein the evaporation stage operates at an evaporation pressure range including a maximum maximum evaporation pressure; and (3) treating the mixture in a distillation stage to obtain a purified product stream comprising an output concentration of at least 90% by weight of the polyol compound, the distillation stage operating at a maximum maximum distillation pressure. According to the invention, the distillation stage is operated to produce a vapor output, which is optionally compressed to a vapor pressure and coupled to the evaporation stage by means of a heat exchange, wherein the maximum distillation pressure and / or the optionally compressed vapor pressure is not less than the maximum evaporation pressure, and wherein the maximum distillation pressure is at least 0.2 bar and less than 1.0 bar.

[0010] According to a second aspect, the present invention provides a reactor system for separating a polyol compound from water to obtain a purified product stream comprising an output concentration of at least 90% by weight of the polyol compound. The reactor system of the present invention includes an evaporation stage comprising an inlet for a mixture of the polyol compound in water and an outlet for enriching the polyol compound stream, said evaporation stage being configured to operate at an evaporation pressure range including a maximum maximum evaporation pressure. The reactor system further includes a distillation stage comprising an inlet for the enriched polyol compound stream from the evaporation stage, an outlet for the purified product stream, and an outlet for a vapor output, said distillation stage being configured to operate at a maximum maximum distillation pressure, wherein the vapor output is coupled to the evaporation stage by means of a heat exchange, and wherein the vapor output is optionally compressed to a vapor pressure such that the maximum distillation pressure and / or said optionally compressed vapor pressure is not less than the maximum evaporation pressure; and wherein the maximum distillation pressure is at least 0.2 bar and less than 1.0 bar.

[0011] The inventors have discovered that the boiling point of water-glycol mixtures tends to increase rapidly with the concentration of ethylene glycol, particularly when the glycol concentration is above 50% by weight rather than approximately 20% by weight as in US 5,269,933. However, such an increase can be prevented or at least strongly suppressed by arranging the evaporation and distillation stages in series, wherein the pressure increases from the first stage to the last stage rather than the other (as is typical in apparatuses with multiple distillation stages or effects).

[0012] Furthermore, the inventors have discovered that a maximum distillation pressure below 1.0 bar can significantly reduce or prevent the formation of contaminants in the product stream. In addition, the inventors have discovered that when the polyol product stream is reused as a solvent for a depolymerization process, the contaminants formed may interfere with the depolymerization process and / or may interfere with the recovery or separation processes used to obtain any desired products from the depolymerization process. For example, it has been found that contaminants formed during the distillation process may interfere with the crystallization process of desired products from the depolymerization process of polyesters. Therefore, a distillation pressure below 1.0 bar enhances the availability of the polyol product stream as a solvent for chemical processes such as depolymerization and improves the solvent efficiency of said chemical processes.

[0013] Any contaminant in the context of this invention can be a dissolved component formed from the reaction products of a chemical reaction process, such as a reaction product component formed from the depolymerization process of a condensation polymer. In one example, the contaminant may include dissolved reaction derivatives from monomers and / or oligomers and / or solvents (which are obtained in the stream from the depolymerization process of the condensation polymer). In a particular example, an evaporation stage and a distillation stage may be used to process a mixture containing monomers, oligomers, water, and a glycol solvent to recover the glycol solvent, wherein dissolved contaminants are formed during these stages. The contaminant may include at least one of diethylene glycol and condensation products based on any combination of monomers, oligomers, and glycols.

[0014] Furthermore, energy efficiency is maintained because the steam from the distillation stage is used to heat at least a portion of the evaporation stage. For this purpose, the steam outlet is connected to the tower or effector in the evaporation stage.

[0015] In the implementation scheme, the maximum distillation pressure is at least 0.4 bar, preferably at least 0.6 bar, and more preferably at least 0.7 bar.

[0016] In other embodiments, the maximum distillation pressure is at most 0.95 bar, preferably at most 0.9 bar.

[0017] Furthermore, in other embodiments, the distillation stage is operated such that the distillation temperature within the distillation stage is at most 200°C. It may also be at most 190°C, at most 180°C, at most 170°C, at most 160°C, or at most 150°C. In one embodiment, the distillation stage is operated such that the distillation temperature within the distillation stage is at least 130°C.

[0018] The maximum distillation pressure can be adjusted to control the maximum distillation temperature. It has been found that by lowering the maximum distillation temperature, the formation of unwanted contaminants can be reduced or prevented.

[0019] In the implementation scheme, the steam output is compressed to a steam pressure higher than the maximum distillation pressure. This further enhances the energy-saving integration of the evaporation and distillation stages.

[0020] In one embodiment, at least a portion of the mixture is treated in a reboiler stage after an evaporation stage and / or after an optional concentration stage and / or after a distillation stage to remove contaminant portions from the mixture. Here, the contaminant portion is the portion of the mixture with a higher boiling temperature. Optionally, the contaminant portion includes components resulting from the depolymerization of condensation polymers such as polyesters. Removing the contaminant portion from the mixture before supplying it to the distillation stage enhances the reduction or prevention of the formation of other undesirable contaminants during the distillation stage.

[0021] In embodiments where the evaporation stage includes a distillation column and / or flash vessel, the connection at the steam outlet occurs via a heat exchanger. Suitably, the heat exchanger exchanges heat between the steam stream and a portion of the mixture's outlet stream, which is returned to the distillation column or flash vessel. When the evaporation stage includes apparatus for multi-effect distillation, the steam stream can be applied to its heating passages. Preferably, the system is configured such that the evaporation temperature (as defined at atmospheric pressure) within this stage is at least 30°C higher than the boiling point of pure water at atmospheric pressure, more preferably at least 20°C. The evaporation temperature (as defined at atmospheric pressure) within this stage is at least 30°C.

[0022] In a suitable embodiment of the invention, the evaporation stage includes at least one flash vessel. Such flash vessels are well-known robust devices in the process industry. Their advantage lies in their ability to absorb temporary, such as intermittent, additional energy supplied when heat becomes available, such as when another reactor operating at a high temperature is emptied. To transfer such intermittently available energy, a buffer tank can be used. Alternatively, material from said other reactor can be added directly to the distillation stage. The increased heat is then transferred to the evaporation stage via a heat exchanger. It is preferable to use multiple flash vessels in series. Such a series of reactors (or vessels) allows for a gradual increase in pressure, and each of the reactors can be configured such that the amount of water evaporated is similar or equal in each of them. The term "similar" here means a variation of up to 25%.

[0023] Preferably, at least one flash vessel is provided with a reboiler. This is an effective device for generating steam at the bottom side of the flash vessel. As those skilled in the art know, the reboiler can be located outside or inside the flash vessel. Preferably, the heat required to operate the reboiler is supplied by a vessel located further downstream. In particular, the steam flow leaving such a downstream vessel is considered suitable for this purpose. It has been observed that, according to the invention, the further downstream vessel operates at a higher pressure. Therefore, the temperature of the steam from such a downstream vessel is higher than the temperature of the vessel connected to the reboiler. Thus, heat exchange will be very efficient.

[0024] In another embodiment, at least one flash vessel includes at least one distillation tray between the feed inlet and the inlet for the recirculated flow from the reboiler. In one embodiment where the evaporation stage includes multiple vessels, such as a first, second, and third vessel in series, it is highly preferred that the third and second vessels are provided with at least one such distillation tray. It has been found that the presence of distillation trays allows for a significant reduction in energy consumption. Preferably, each vessel has at least two distillation trays, for example, up to 10, more preferably up to 6, such as in the range of 2-5. Nevertheless, this vessel is not a distillation column, as it does not contain any means for reflux. Therefore, although the temperature in a distillation column is between the boiling points of the first component (i.e., the polyol) and the second component (i.e., water), this is not necessary in a flash vessel with distillation trays. Needless to say, the number of distillation trays does not need to be the same for all available vessels.

[0025] Optionally, at least one flash vessel includes structured packing. The advantage of such structured packing is a reduced pressure drop across the vessel. This is particularly suitable for evaporation stages involving lower pressures, thus limiting the width of the required evaporation pressure range.

[0026] Optionally, the evaporation stage is at least partially embodied as a multi-effect distillation unit. Its use is cost-effective. Furthermore, if desired or required, the pressure can be set at a low minimum pressure within the multi-effect distillation unit without the need for specific construction or safety measures. In other words, the minimum pressure in multi-effect distillation can be lower than the minimum pressure when using flash vessels and columns without requiring large volumes or additional safety measures. The ability to use lower minimum pressures (e.g., as low as 0.1 bar) has the advantage that the distillation stage can operate at near atmospheric pressure and without requiring compression of the vapor output of the distillation stage. The number of effectors in such a multi-effect distillation unit is preferably at least three. For clarity, it is observed that multi-effect distillation can, of course, be combined with the presence of one flash vessel or even more vessels. However, choosing multi-effect distillation or a flash vessel as the technical implementation of the evaporation stage appears to be more advantageous.

[0027] In another embodiment, a concentration stage is located downstream of the evaporation stage and upstream of the distillation stage. While it is preferred that the heat in the evaporation stage is ultimately provided by the distillation stage, the heat supplied to the concentration stage can originate from a source outside the reactor system used to separate the polyol compound from water. For example, the heat can come from the reactor, such as waste heat from the reactor supplying the feed to the evaporation stage. The heat is supplied to the mixture in the concentration stage by means of a heat exchange. This can be a conventional heat exchanger or an evaporation device equipped with a circulation system for the waste heat (in the form of steam or liquid). A most preferred embodiment of such a concentration stage is an evaporator designed as a multi-effect unit, and more preferably, structurally similar to a multi-effect distillation unit used for the evaporation stage.

[0028] In another embodiment, the reactor further includes a reboiler stage arranged downstream of the evaporation stage, and / or optionally downstream of the concentration stage, and / or downstream of the distillation stage, wherein the reboiler stage is configured to process at least a portion of the mixture from the respective stage to remove contaminant portions from the mixture, wherein optionally the contaminant portions include components arising from the depolymerization of condensation polymers such as polyesters.

[0029] As mentioned above, one option according to the invention is to compress the steam output from the distillation stage in a steam compressor. The use of a steam compressor allows the distillation stage to operate at near atmospheric pressure, while the evaporation stage can operate at higher pressures than the distillation stage.

[0030] In another embodiment, a steam compressor is arranged at the steam output end of the evaporation stage to compress the steam output of the evaporation stage. The resulting compressed steam flow from the steam output of the evaporation stage can be combined with any other steam output, such as steam exiting the steam outlet from a sub-stage of the evaporation stage arranged further downstream.

[0031] Typically, when using multiple containers, preferably a flash evaporator comprising at least one distillation tray in the area between the feed inlet and the steam inlet, the compressed steam is directed to the container located at the very downstream end of the evaporation stage—in other words, directly upstream of the distillation stage. The advantage is that such a downstream container can operate at near atmospheric pressure.

[0032] Optionally or additionally, it is feasible to apply vapor compression to the vapor output from the first vessel or effector in the evaporation stage. The compressed vapor output is then directed to the vapor output of another vessel or effector. Here, the first vessel or effector operates at a reduced pressure relative to the other vessel or effector. In this embodiment, no vapor compression is applied to the vapor stream returning from the distillation stage to the evaporation stage to maintain the pressure difference. Instead, vapor compression is applied to the vapor output from the low-pressure vessel or effector to ensure that such vapor is boosted to the higher pressure of the other vessel or effector.

[0033] In cases where a concentration stage exists between the evaporation and distillation stages, the steam output from the distillation stage is reused in the evaporation stage, thereby passing through any container or effector in the concentration stage.

[0034] While the reactor system and method are feasible for any type of polyol compound, diol compounds are considered advantageous. A preferred diol compound is ethylene glycol. Suitably, the initial concentration of the mixture of the polyol compound and water is at least 40% by weight of the polyol compound. Preferably, this initial concentration is even higher, such as at least 45% by weight or even at least 50% by weight. More preferably, the method is used for the regeneration of ethylene glycol, such as that used in the depolymerization of polyesters like polyethylene terephthalate. Attached Figure Description

[0035] These and other aspects of the invention will be further explained with reference to the accompanying drawings, in which:

[0036] Figure 1 A first embodiment of the reactor system of the present invention is schematically shown, which includes an evaporation stage having a flash vessel and two distillation columns connected in series;

[0037] Figure 2 A second embodiment of the reactor system of the present invention is schematically shown, which includes an evaporation stage having a flash vessel;

[0038] Figure 3 A third embodiment of the reactor system of the present invention is illustrated schematically, which includes an evaporation stage embodied in a multi-effect distillation apparatus;

[0039] Figure 4 , Figure 5 and Figure 6 A variant of the first embodiment is illustrated schematically, in which a steam compressor is used.

[0040] Figure 7 and Figure 8 A variant of the second implementation scheme is illustrated schematically.

[0041] Figure 9-11A variant of the third implementation scheme is illustrated schematically.

[0042] Figure 12 An embodiment of the reboiler stage that can be used in the embodiments of the present invention is illustrated schematically. Detailed Implementation

[0043] These diagrams are not drawn to scale. Identical reference numerals in different diagrams refer to the same or corresponding elements. When referring to bar, this refers to absolute pressure. Therefore, 1 bar equals 10... 5 Pa. Each figure illustrates the reactor system of the present invention, which includes a distillation stage 100 and an evaporation stage 200. The distillation stage is in Figure 1-10 The implementation plan is embodied in a distillation column. Figure 11 In this implementation, the distillation stage is an effector in a multi-effect distillation unit. Distillation stage 100 may correspond to distillation columns 220, 230 or an effector in evaporation stage 200, but this is not required. In any case, distillation stage 100 is driven by power from outside the reactor system, such as high-pressure steam (not shown in the figure).

[0044] For clarity, the reactor system of the present invention is suitably preceded by other reactor systems in which a mixture of polyol compounds (preferably glycols, such as ethylene glycol) and water is produced. Typically, the mixture contains any other compounds removed from the mixture in one or more pretreatments. For example, glycols such as ethylene glycol are used for the catalytic depolymerization of polyesters or polyamides, etc. A specific example is the catalytic depolymerization of polyethylene terephthalate in ethylene glycol, wherein water is added for cooling and separation purposes in order to remove the catalyst and oligomers by means of centrifugation. The resulting mixture will contain particulate contaminants to be filtered out and monomers and / or oligomers for polyesters such as BHET (dihydroxyethyl terephthalate), which will be separated by crystallization and solid-liquid separation.

[0045] As will be detailed below, catalytic depolymerization can be carried out in batch mode and at temperatures close to the boiling point of the glycol (typically ethylene glycol), and thus, for example, in the range of 160-200°C, preferably 180-200°C. The venting of the depolymerization reactor results in the release of heat. In specific embodiments of the method and reactor system of the present invention, this heat is reused in the dehydration of the glycol.

[0046] Typically, the mixture of polyol compound and water has a concentration of at least 40% by weight, preferably at least 45% by weight, and more preferably at least 50% by weight of the polyol compound. If the concentration of the polyol compound is low, it can be increased in a suitable manner. This can be done by means of flash evaporation vessels, membrane distillation, or any other known technique. This is not critical because the boiling point of mixtures in which the polyol compound is less than 40% by weight is not very sensitive to concentration.

[0047] According to the invention, the purified mixture has a concentration of at least 90% by weight of polyol compounds. This concentration is likely to be higher, such as at least 95% by weight or at least 99% by weight. In the case of regeneration of the mixture derived from depolymerization, the mixture will also contain some dissolved compounds generated by depolymerization, such as monomers, dimers, and other oligomers. A concentration of 100% polyol compounds would be impractical. It is not excluded that the regenerated polyol composition contains some other additives, such as salts.

[0048] Turn Figure 1 The reactor system shown has a distillation stage 100 (embodied as a distillation column) and an evaporation stage 200 (embodied as having three sub-stages: a flash vessel 210 and two additional columns or vessels 220, 230). Feed stream 199 (a mixture of polyol compound, water, and any other additives, wherein the initial concentration of the polyol compound is, for example, between 40% and 50% by weight) enters the evaporation stage 200 at feed inlet 201. It then enters the first sub-stage 210, which in the illustrated embodiment is a flash vessel. The flash vessel boils at reduced pressure and temperature, in the current embodiment, for example, at 0.2 bar and 60°C. Steam exits vessel 210 via steam outlet 213 and is directed to condenser 240 after passing through heat exchanger 241. Stream 219, enriched with polyol compound, exits the flash vessel at the bottom.

[0049] A portion 214 returns to vessel 210 after passing through heat exchanger 215. This heat exchanger 215 is also called a reboiler. Such a reboiler can be implemented as part of flash vessel 210 (or any distillation column) or as a separate unit. A pump can be present as part of return branch 215, but this is not considered strictly necessary. The mixture in return branch 214 is heated in reboiler / heat exchanger 214 using steam 228 originating from second sub-stage 220. Therefore, the temperature at the bottom of first sub-stage 210 will be equal to or nearly equal to the temperature of steam 228. The term "nearly equal to" as used herein refers to any deviation caused by heat losses in transport and heat exchange. In another embodiment, distillation trays exist in flash vessel 210 between feed inlet 199 and the inlet from reboiler 214. The distillation trays below feed inlet 199 result in some distillation without requiring reflux flow. This confirms a positive effect on efficient evaporation, which is beneficial for overall operation. In addition, it contributes to the operational stability of flash evaporators at relatively low pressures (such as below 0.5 bar).

[0050] The operation of the second sub-stage 220 and the third sub-stage 230 is essentially a repetition of the operation of the first sub-stage 210. However, even though the first sub-stage 210 does not include any distillation trays, it is preferable that the second sub-stage 220 and the third sub-stage 230 include such distillation trays. These trays will be located between the feed inlets (from streams 219, 229) and the reboiling streams 224, 234. Compared to using distillation columns in the second sub-stage 220 and the third sub-stage 230 during the evaporation stage, there is no reflux. This is cost-effective and allows operation of sub-stages 220 and 230 using top and bottom temperatures deviating from the effective boiling point. Furthermore, and even more importantly, the presence of distillation trays provides the advantage that any polyols, such as ethylene glycol, evaporated with water in the reboiler will be washed out of the vapor and flow back with the feed towards the outlet at the bottom. Therefore, the steam exiting these sub-stages at steam outlets 213, 223, and 233 of sub-stages 210, 220, and 230 will contain less contaminants and polyols, i.e., have a higher level of purity.

[0051] Furthermore, as will be understood, the pressure, temperature, and concentration of the polyol compounds in the second sub-stage 220 and the third sub-stage 230 are higher than in the first sub-stage 210. The most downstream sub-stage 230 receives heat from the vapor 192 of distillation stage 100, which exits distillation stage 100 at vapor outlet 103. For efficiency, [the following is omitted as it is not directly related to the preceding text]. Figure 1 The implementation shown in the figure and other implementations shown in the figures are designed to reduce the water content of the feed at input 101.

[0052] Distillation stage 100 also includes an inlet 101 for the enriched stream 239 originating from evaporation stage 200, a product outlet 102 for the purified stream 191, and a heat exchanger 105 in the return branch 104. Although in Figure 1 Not specified, but this heat exchanger 105 is suitably used as the feed for high-pressure steam into distillation stage 100. The remaining low-pressure steam can be used as stream 193 (see...). Figure 2 The remaining heat is further directed to transfer to the evaporation stage 200. Although not shown, the distillation stage 100 is also provided with a reflux device known to those skilled in the art. Here, the steam 192 leaving the distillation stage 100 at the steam outlet 103 is divided toward the reboiler 235 (or optionally as shown) of the previous stage. Figure 2 The reflux section (215) includes a portion from the distillation stage 100 and a portion from the reflux. This reflux includes condensed vapor, which is directed to the reflux tank and the liquid is pumped from the reflux tank back to the top of the distillation stage 100. As those skilled in the art will understand, the exact implementation of the reflux apparatus can be modified.

[0053] With the aid of this sequence, where the pressure gradually increases, the mixture can be progressively enriched with polyol compounds, wherein the water released in each step is approximately equal (approximately equal means within a range of up to 50%, suitably up to 30%). Furthermore, this achieves a boiling temperature that does not increase significantly. As can be seen from Table 1, the steam 228 exiting distillation stage 100 at steam outlet 103 has a temperature of only 92°C, and the highest distillation temperature is 150°C.

[0054]

[0055] Table 1– Figure 1 The operation of the multi-stage reactor system shown.

[0056] Figure 2A reactor system of the invention according to a second embodiment is schematically illustrated. In this second embodiment, the evaporation stage 200 comprises only a flash vessel 210. Such a system benefits less from gradually reducing the pressure to achieve equilibrium evaporation at each stage. However, the system is feasible and energy-efficient in terms of heat reuse. The principles illustrated can also be applied to reactor systems comprising an evaporation stage 200 with multiple distillation columns. In the illustrated system, high-pressure steam is used to heat the distillation stage 100 via a heat exchanger 105 to a return branch 104. Thereafter, steam 193 can still be used to preheat the enriched stream 219 that will enter the distillation stage at inlet 101. Still, the remaining steam is useful because it can be used to heat the feed 199 that will enter the flash vessel 210 at inlet 201. The increased temperature of the feed 199 will result in evaporation under reduced pressure in the evaporation stage 200 (as in the flash vessel 210). This is particularly effective in the method of the present invention, wherein the flash vessel operates at a lower pressure than the distillation stage, because the lower pressure results in a lower boiling temperature in the flash vessel 210. Therefore, it becomes feasible to evaporate most of the water in the water-alcohol mixture in the flash vessel, which is clearly advantageous in achieving the desired result of having at most a small amount of water as the alcohol solvent within it.

[0057] In the context of the second embodiment, the pressure during the distillation stage is preferably in the range of at least 0.4 bar and less than 1.0 bar, and the pressure at the flash vessel is suitably 20-60% of that, for example, at most less than 1.0 bar and preferably 0.1-0.6 bar.

[0058] In addition, such as Figure 2 As shown, the vapor 192 generated in distillation stage 100 is directed to condenser 140 via heat exchanger 205. In this way, the heat of distillation stage 100 is effectively transferred to evaporation stage 200. Furthermore, distillation stage 100 can be fed with an additional predominantly liquid stream via an additional inlet 109. Such an additional stream suitably originates from another part of the process, such as a centrifuge. It is typically the heat flow entering distillation stage 100, so that its temperature does not interfere with the operation of distillation stage 100. It is considered preferable to add such a predominantly liquid stream 109 only in distillation stage 100 to prevent contamination of preceding stages. While various liquid streams with different purities can be used, it is not excluded that such a predominantly liquid stream may contain specific contaminants in the form of particulate matter or solutes. An example of particulate contaminants is, for example, a heterogeneous catalyst.

[0059] Figure 3The reactor system of the present invention according to a third embodiment is schematically illustrated. Here, the evaporation stage 200 is embodied as a multi-effect distillation (MED) device 280. Although the first effector 280A of the multi-effect distillation device can operate at the same low pressure (or even lower) as the first sub-stage 210 of the evaporation stage 200 according to the first embodiment, the volume of the first effector 280A does not need to be as large as the volume of the flash vessel of the first sub-stage 210 in the first embodiment. In fact, it is feasible to add additional effectors or additional MED devices 280 if the capacity of a single first effector 280A is insufficient.

[0060] Figure 3 The MED device 280 shown includes three effectors 280A, 280B, and 280C. Feed 199 enters the evaporation stage 200 at inlet 201 and thus into the MED device 280. It then passes through a feed distributor 282, which divides the feed into multiple droplets to spray the feed onto the respective horizontal surfaces of the first effector 280A. Heat is supplied to this first stage 280A via a heating channel 281. Additionally, vapor 912 from the distillation stage is directed to the MED device 280. Effectors 280A, B, and C cause water vapor to separate from the remaining liquid through membranes. The water vapor condenses against the walls. The released heat is transferred through the walls to adjacent effectors. The resulting condensate is removed via condensate outlet 288. The remaining concentrated liquid exits effectors 280A, 280B, and 280C via a second outlet 286 and is subsequently pumped to the corresponding inlet 287 of the next effector, or, for the most downstream effector 280C, to distillation stage 100. Pumps are required between each stage to allow the liquid mixture to flow from low pressure to high pressure. Vapor remaining in the most upstream effector 280A is directed to condenser 240.

[0061] Figure 4-6 A variation of the first embodiment is shown, in which steam condensers 160 and 260 are used. The use of steam condensers 160 and 260 is considered advantageous in the context of this invention because it allows for limiting the effective range between the minimum and maximum pressures in the reactor system when the method is applied. Nevertheless, the number of sub-stages in the evaporation stage can be sufficiently large or even optimal.

[0062] exist Figure 4In the schematically illustrated embodiment, a steam condenser 160 (also indicated by SC) is arranged between the steam outlet 103 of distillation stage 100 and the heat exchanger of evaporation stage 200 (and more specifically, the heat exchanger 235 of sub-stage 230, which is arranged at the downstream end within evaporation stage 200 and thus at the highest pressure). It would not be impossible to direct the compressed steam stream 192 to the heat exchanger of another sub-stage 210, 220. This is particularly feasible if heat exchanger 235 can be supplied with heat from another heat source. Although not shown in this figure, it is feasible that the steam applied to heat exchanger 105 of distillation stage 100 could subsequently be reused to heat the enriched mixture 239 fed into distillation stage 100 and / or to heat (or preheat) a mixture of polyol compounds and water at another location within the reactor system.

[0063] The effect of the steam compressor can be understood from Table 2 and a comparison with Table 1. Although the water flow rate and evaporation rate differ in implementations with and without a steam compressor (respectively...), the overall effect is different. Figure 1 and Figure 4 The requirements are the same throughout, but in the embodiment with a steam compressor, the pressure in the first sub-stage is 50% higher (0.22-0.23 bar vs. 0.15-0.16 bar). Therefore, the volume of the first sub-stage (suitably a flash vessel) can be significantly reduced. Correspondingly, the temperature in the evaporation sub-stage is higher, between 63°C and 112°C, instead of between 54°C and 92°C. When looking at the required steam pressure, the minimum pressure is 0.37 bar instead of 0.22 bar.

[0064] This simplifies the management and construction of the reactor system.

[0065]

[0066] Table 2– Figure 4 The operating setup of the reactor system shown

[0067] It was observed that this example used a vapor compression of 0.75 to 1.5 bar, which is known to provide sufficient power to allow the temperature in the third sub-stage to reach 92°C at 0.75 bar. It is not excluded that the vapor compressor will compress the vapor less forcefully, for example, increasing the pressure by 50% (or 0.37 bar) relative to the distillation stage pressure instead of 100% (0.75 bar). A smaller pressure increase favors a simpler vapor compressor, the effect of which is that the pressure in the first sub-stage will decrease accordingly. It is evident that it is possible to alternatively increase the pressure in distillation stage 100 and decrease the vapor compression ratio (= output pressure to input pressure) relative to the ratio of 2 shown in Table 2.

[0068] exist Figure 5 and Figure 6 In the illustrated embodiment, a steam compressor 260 is arranged in a steam line 218 at the steam outlet 213 of the first sub-stage 210 of the evaporation stage 200. The sub-stage is embodied as a flash vessel equipped with reboilers 215, 225, 235 and preferably some distillation trays between the feed inlet 199 and the inlet from the reboiler 215. The resulting compressed steam stream 217 is combined with steam exiting the steam outlet from a further downstream sub-stage. Although not strictly necessary, it appears preferable that the sub-stage is a second sub-stage 220, which, as... Figure 5 and Figure 6 Instructions. The resulting steam stream 228 will be more or less at the outlet pressure of the second sub-stage 220. This steam will then be strong enough to maintain the first sub-stage 210 at the appropriate pressure and temperature, which... Figure 5 and Figure 6 In the example, the temperature is 0.16 bar and 63°C for the steam at outlet 103 and 73°C and 0.23 bar for the enriched liquid mixture 219.

[0069] exist Figure 5 In this embodiment, the distillation stage is operated at a pressure of 0.75 bar. Those skilled in the art will understand that this distillation stage can optionally be operated at a lower pressure (as low as 0.2 bar), and then another steam compressor can be applied to steam 192, such as... Figure 4 As shown in the image.

[0070] exist Figure 6 In this embodiment, the concentration stage 500 exists upstream of the distillation stage 100 and downstream of the evaporation stage 200. This concentration stage is heated by a heat flow 534 (typically steam) originating from an external heat source (more particularly waste heat, such as waste heat from an emptied reactor). Therefore, the steam 192 from the distillation stage 100 is directly directed through the concentration stage 500 to the downstream vessel 220 in the evaporation stage 200.

[0071] In this embodiment, the concentration stage 500 comprises two sub-stages 510 and 520, each of which, in the illustrated embodiment, is embodied as sub-stages 210 and 220 corresponding to the evaporation stage 200. Therefore, containers 510 and 520 are each provided with a feed inlet, a steam outlet 513 and 523, and reboilers 515 and 525. The mixture flows from the second sub-stage 220 as a stream 229 enriched with polyols to the inlet of the third sub-stage 510. The further enriched mixture 519 flows or is flowed (if necessary, by means of a pump) to the fourth sub-stage 520. The further enriched mixture 529 flows to the inlet 101 of the distillation stage 100. In the illustrated embodiment, the heat stream 534 has a temperature exceeding 190°C and its volume is set to allow heating of the fourth sub-stage 520 to a temperature of 120°C at its steam outlet 523 at a pressure of 2 bar. In the third sub-stage 510, the temperature at the steam outlet 513 is 97°C at a pressure of 0.9 bar. The temperature of mixture 519 is approximately 120°C, and the temperature of mixture 529 is even 160°C. Given the chosen pressure, it is not necessary to apply vapor compression to the steam 192 originating from distillation stage 100.

[0072] Instead of choosing an evaporation rate that is equal in all sub-stages 210 and 220 of evaporation stage 200, 510 and 520 of concentration stages, and 100 of distillation stage, it is feasible and potentially useful to set the evaporation rate in a manner that minimizes the overall reactor size. For example, the evaporation rate in the first sub-stage 210 could be reduced while the evaporation rate in another sub-stage could be increased. For example, the second sub-stage 220 could be larger and / or could be represented as two parallel vessels.

[0073] Figure 7-8 As shown Figure 2 The illustration shows a variant of the second embodiment of the invention. Figure 7 An option for further heat reuse is shown. This is accomplished by means of heat exchange on stream 409. Alternatively, a predominantly liquid stream 109 can be added to distillation stage 100. Stream 409 and liquid stream 109 originate, for example, from a reactor, such as a depolymerization reactor operating at a higher temperature than that used in the operation of the method of the present invention. Stream 409 originates from buffer tank 400, which is designed to convert temporary batch 401 from a batch reactor into continuous stream 409. Heat exchange occurs in heat exchanger 410. Receiver stream 411 is, for example, water and / or steam, but can be any type of heat transfer medium (including oil). Receiver stream 411 can then exchange heat with feed 199, but can optionally be used to directly heat flash vessel 210, for example, as a jacket around vessel 210.

[0074] exist Figure 8In the illustrated embodiment, vapor compression is applied to the steam output 218 of the first (and only) sub-stage 210 of evaporation stage 200. This is done by means of a steam compressor 260. The compressed stream 217 is then combined with a steam stream originating from a downstream stage (in this example, steam 192 originating from distillation stage 100).

[0075] Furthermore, in Figure 8 As shown, stream 409 (originating from the reactor) exchanges heat with feed 199 in heat exchanger 399. To match the available heat in stream 409 with the heat required by feed 199, the feed is split into a first feed line 199A that bypasses heat exchanger 399 and a second feed line 199B that does pass through heat exchanger 399. Thus, the first feed line 199A constitutes a bypass. By controlling the flow rates in the first and second feed lines 199A and 199B, feed heating can be regulated to be effective while avoiding excessive boiling in flash vessel 210. A kettle boiler can be used instead of heat exchanger 399. Such a kettle boiler will operate under vacuum in distillation stage 100. The addition of some glycol, such as ethylene glycol, is not excluded to ensure that the viscosity of the enriched mixture remains correct.

[0076] Figure 9-11 Three variations of the third embodiment using a multi-effect distillation (MED) apparatus 280 are shown. Figure 9 In the schematically illustrated embodiment, the MED device 280 includes four effectors 280A-280D. Figure 10 In the implementation scheme, the MED device 280 includes five effectors 280A-280E. Figure 11 In one embodiment, the MED device 280 includes six effectors 280A-280F. Although integrated into a single MED device 280, there is a conceptual distinction between the first three stages 280A-C and the remaining stages 280D, 280E, and 280F. The first three stages 280A-C constitute the evaporation stage as discussed above. This evaporation stage 200 is heated by steam 192 originating from the distillation stage 100. As in embodiments utilizing separate containers and columns 210, 220, and 230, each effector operates at a separate pressure, with the pressure increasing from the first effector 280A toward the third effector 280C.

[0077] The remaining effectors 280D, 280E, and 280F are part of the concentration stage 500. No steam evaporation is used here. Instead, these effectors function as heat exchangers, where another liquid or gas flows through channels or pipes without contacting the feed stream of the effector. This liquid or gas typically originates from an external heat source. This could be the feed stream from the reactor, or optionally based on waste heat. More specifically, heat flow 534 is supplied and circulated via pipe 541 through effector 280D (…). Figure 9 (in the middle) or effectors 280D and 280E ( Figure 10 and Figure 11 It leaves the stage as stream 535 and is then discarded as waste (although the possibility of reusing stream 535 is not excluded). The tube can be embodied in any suitable shape, including perforated trays. The resulting concentrated mixture 519 is directed to the inlet of distillation stage 100.

[0078] exist Figure 10 and 11 In this configuration, heat flow 534 is directed from the fifth effector 280E to the fourth effector 280D via the extension 536. It is observed that only heat exchange occurs in these effectors 280D and 280E. Therefore, the pressures in the two effectors 280D and 280E are equal, and no separation barrier 281 is required between the two effectors 280D and 280E.

[0079] exist Figure 11 In the concentration stage 500, a sixth effector 280F is included, which is supplied with heat flow 537, which extends through the effector via a circulation system 543. The sixth effector 280F is maintained at the same pressure as the preceding effectors 280D and 280E in the concentration stage 500. Figure 11 In the illustrated embodiment, another vapor recirculation 289 is provided. This is the recirculation from the second sub-stage or effector 280B back to distillation stage 100. Thus, vapor 192 is supplied from distillation stage 100 to the top of the second effector 280B, and after passing through the second effector 280B, returns to distillation stage 100 via recirculation 289. As will be understood, this recirculation can be vapor or liquid, or a mixture of both.

[0080] Although not shown, it is possible that a portion of the vapor 192 originating from distillation stage 100 is directed to the first effector 280A, or that vapor / liquid from the second effector 280B is further directed to the first effector 280A. Typically, in multi-effect distillation, heat is transferred via the partition wall or barrier 281 between the effectors. Although only in Figure 9-11The diagram is schematic, but each effector is preferably designed in a corresponding manner to allow for integration. The construction of a multi-effect distillation apparatus is known in itself and feasible for experts in multi-effect distillation apparatuses.

[0081] In operation Figure 9 In one example of the apparatus shown, the enriched stream exiting the first effector 280A at outlet 286 and heading towards the inlet 287 of the second effector 280B has a temperature of 70°C (containing approximately 57% by weight of diol). At the bottom of the second effector 280B, the temperature is 80°C (containing approximately 67% by weight of diol). At the bottom of the third effector, the temperature changes to 97°C (containing approximately 78% by weight of diol). Heating the fourth effector 280D using a separate heat flow 534 (e.g., entering the fourth effector at a temperature of 195-200°C) results in the enriched mixture 219 reaching a temperature of 135°C, and the diol concentration will reach 90% by weight.

[0082] Figure 9 It is also shown that a vapor compressor 260 is used, which compresses the vapor from the first effector 280A to a higher pressure (here, about 1 bar), instead of (or alternatively, in addition to) transferring the vapor to a condenser. The increased vapor flow rate into the third effector 280C effectively enhances evaporation. Therefore, it becomes feasible to reduce the size of the distillation column in distillation stage 100. For clarity, it is observed that the vapor 192 originating from distillation stage 100, along with the compressed stream 217, enters the heating passage 281 of the MED unit 280.

[0083] Figure 12 An embodiment of the reboiler stage is shown, which can be used in embodiments of the present invention. In this embodiment, a mixture stream 239 enriched with polyol compounds from evaporation stage 200 is divided into a mixture stream 239a and a mixture stream 601. The mixture stream 239a is supplied to distillation stage 100 at inlet 101 of the stream 239a from evaporation stage 200 for enriching polyol compounds, and the mixture stream 601 is supplied to reboiler stage 600. The volume ratio between the mixture stream 239a supplied to distillation stage 100 and the mixture stream 601 supplied to reboiler stage 600 can be suitably controlled. In one example, the mixture stream 601 supplied to reboiler stage 600 is selected within the range of 0-100 vol% (preferably 0-20 vol%) of the mixture stream 239 from evaporation stage 200.

[0084] The reboiler stage 600 is configured to process the mixture stream 601 by forming an evaporation stream 602 at the top outlet of the reboiler stage 600. In this embodiment, the evaporation stream 602 is supplied to the distillation stage 100. The distillation stage 100 includes an inlet 106 for the stream 602, which is arranged at any location in the distillation stage 100, for example, near the inlet 101 for the stream 239.

[0085] The reboiler stage 600 is also configured to remove a contaminant portion (as contaminant stream 603) from the mixture stream 601 from the evaporation stage 200. The contaminant portion, or contaminant stream 603, has a higher boiling temperature than the evaporation stream 602. The contaminant portion is enriched with dissolved reactive components resulting from the depolymerization of condensation polymers such as polyesters or polyamides. These reactive components typically include monomers and / or oligomers derived from the condensation polymers. The dissolved reactive components increase the boiling temperature of the polyol mixture.

[0086] The reboiler stage can be heated by any heat flow, such as heat from an external heat source, and more particularly waste heat, such as waste heat from an emptied reactor.

[0087] In optional or additional embodiments, the reboiler stage may be arranged downstream of the concentration stage 500 or the distillation stage 100 to process the mixture stream 602 from the concentration stage 500 or the distillation stage 100 by forming an evaporation stream at the top outlet of the reboiler stage 600 and to remove a portion of the contaminant stream (as a contaminant stream 603) from the mixture stream.

[0088] According to any of these implementation schemes, the reboiler stage can be combined with, for example... Figure 1-11 Any combination of the embodiments of the present invention shown is used.

[0089] Reference number list

[0090] 100 distillation stage

[0091] 101 is the inlet for enriching polyol compounds and from the streams (239, 219) of evaporation stage 200.

[0092] 102 Outlet for purified product stream 191

[0093] 103 Outlet for steam output 192

[0094] 104 Return to branch road

[0095] 105 Heat Exchanger

[0096] 106 Inlet for the evaporation stream 602 from reboiler stage 600

[0097] 109 Inlet for the residual flow that is mainly liquid

[0098] 125 Heat exchanger in the feed stream

[0099] 140 condenser

[0100] 160 Steam Compressor

[0101] 191 Purified Product Stream

[0102] 192 Steam output flow

[0103] 193. Heat flow (e.g., steam) from distillation stage 100 to evaporation stage 200.

[0104] 199 Feed Flow

[0105] 199A Feed Flow Shortcut

[0106] 199B Feed stream passing through heat exchanger 420 with heat outlet flow

[0107] 200 Evaporation Stage

[0108] 201 Feed Inlet

[0109] 210 Evaporation stage 200, the first sub-stage (e.g., represented by a flash evaporation vessel).

[0110] 213 Steam outlet of the first sub-stage 210

[0111] 214 Return branch (from enriched flow 219)

[0112] 215 Heat Exchanger

[0113] 218 Steam outlet flow

[0114] 217 Compressed Steam Flow

[0115] 219. Stream of mixtures enriched with polyol compounds

[0116] 220 Evaporation stage, the second sub-stage of 200 (e.g., represented by a distillation column).

[0117] 223 Steam outlet of sub-stage 220

[0118] 224 Return branch (from enriched flow 229)

[0119] 225 heat exchanger

[0120] 228 The steam output stream is directed to the heat exchangers 215 and 315 of the preceding sub-stages 210 and 310.

[0121] 229. Stream of mixtures enriched with polyol compounds

[0122] 230 Evaporation stage 200 is the third sub-stage (e.g., represented by a distillation column).

[0123] Steam outlet of sub-stage 230 (233)

[0124] 234 Return to branch (from enriched flow 239)

[0125] 235 heat exchanger

[0126] 238 The steam output stream is directed to the heat exchanger 225 of the preceding sub-stage 220.

[0127] 239, 239a: Mixture streams enriched with polyol compounds

[0128] 240 Condenser (when manifested as a flash vessel, connected to the first sub-stage 210)

[0129] 241 Heat Exchanger

[0130] 260 Steam Compressor

[0131] 280 Multi-Effect Distillation Unit

[0132] The various effectors of the 280A, B, C, D, E, F multi-effect distillation unit 280.

[0133] 281 Heating channels between each effector 280A, B, and C

[0134] 282 Feed Distributor

[0135] 286 Export of logistics for enriching polyol compounds

[0136] 287 Inlet for the stream of polyol compounds for enrichment

[0137] 288 For condensate outlet

[0138] 289 The channel that guides the stream of enriched polyol compounds from effector inlet 287 to distributor 282.

[0139] 310 Evaporation stage 200 another sub-stage

[0140] 314 Return branch (from enriched flow 319)

[0141] 315 heat exchanger

[0142] 318 The steam output stream is directed to the heat exchanger 215 of the previous sub-stage 210.

[0143] 319. Stream of mixtures enriched with polyol compounds

[0144] 399 Heat exchanger between hot outlet flow 409 and feed flow 199B

[0145] 400 Buffer Tank

[0146] 401 Inlet for buffer tank

[0147] 409 Hot outlet flow

[0148] 410 Heat exchanger for effluent flow

[0149] 411 Heat flow between heat exchanger 410 and sub-stage (210) of evaporation stage

[0150] 416 For the outlet of the heat flow after heating the multi-effect distillation apparatus 280

[0151] 417 Connection for heat flow between effectors D and E in a multi-effect distillation apparatus 280

[0152] 418, 419, 420 are used to heat the effectors D, E, and F of the multi-effect distillation apparatus 280.

[0153] 434 Waste heat flow

[0154] 500 Concentration Stage

[0155] 600 Reboiler Stage

[0156] 601 The mixture stream supplied from evaporation stage 200 to reboiler stage 600

[0157] 602 Evaporation Flow

[0158] 603 Pollutant Flow

Claims

1. A method for at least partially separating a polyol compound from water to obtain a purified product stream comprising at least 90% by weight of said polyol compound, the method comprising the following steps: - A mixture of the polyol compound and water is provided, the mixture having a polyol concentration; - The concentration of the polyol in the mixture is increased during the evaporation phase, wherein the evaporation phase is operated at an evaporation pressure range including a maximum evaporation pressure; - The mixture is processed in a distillation stage to obtain the purified product stream containing at least 90% by weight of the polyol compound in the output concentration, the distillation stage being operated at at most maximum distillation pressure. The distillation stage is equipped with a reflux device and is operated to generate a steam output, the steam output being connected to the evaporation stage, wherein the maximum distillation pressure is not less than the maximum evaporation pressure; and wherein the maximum distillation pressure is at least 0.2 bar and less than 1.0 bar.

2. The method of claim 1, wherein the maximum distillation pressure is at least 0.4 bar, and / or wherein the maximum distillation pressure is at most 0.95 bar.

3. The method of claim 1, wherein the distillation stage is operated such that the distillation temperature within the distillation stage is at most 200°C.

4. The method according to any one of claims 1 to 3, wherein the steam output is compressed to a compressed steam pressure and coupled to the evaporation stage, wherein the compressed steam pressure is higher than the maximum distillation pressure.

5. The method according to any one of claims 1 to 3, wherein the evaporation stage and the distillation stage are operated such that the evaporation temperature in the evaporation stage, as defined at atmospheric pressure, is up to 30°C higher than the boiling point of pure water at atmospheric pressure.

6. The method according to any one of claims 1 to 3, wherein the evaporation stage comprises a plurality of containers connected in series, each container operating at a different pressure within the evaporation pressure range, wherein the steam output of the distillation stage is connected to the downstream container of the evaporation stage, wherein the downstream container of the evaporation stage has a steam output connected to the container directly preceding it by means of heat exchange, and wherein the downstream container operates at a higher pressure than the container directly preceding it.

7. The method according to any one of claims 1 to 3, wherein the polyol concentration of the provided mixture is at least 40 by weight.

8. The method according to any one of claims 1 to 3, wherein the polyol compound is a diol compound.

9. The method according to any one of claims 1 to 3, wherein the mixture of the polyol compound and water further comprises at least one of a monomer and an oligomer, each of which is generated from the depolymerization of the condensation polymer.

10. The method of claim 9, wherein the condensate comprises a polyester.

11. The method according to any one of claims 1 to 3, wherein the mixture is treated in a concentration stage after passing through the evaporation stage to further increase the concentration of the polyol, wherein the mixture is heated in the concentration stage by means of waste heat supplied from the reactor.

12. The method of claim 11, wherein at least a portion of the mixture is treated in a reboiler stage after the evaporation stage, and / or after the optional concentration stage, and / or after the distillation stage, to remove contaminant portions from the mixture.

13. A reactor system for separating a polyol compound from water to obtain a purified product stream comprising an output concentration of at least 90% by weight of the polyol compound, said reactor system comprising: - An evaporation stage, comprising an inlet for a mixture of the polyol compounds in water and an outlet for enriching a stream of the polyol compounds, the evaporation stage being configured to operate within an evaporation pressure range including a maximum evaporation pressure. - A distillation stage comprising an inlet for the stream enriched with the polyol compound from the evaporation stage, an outlet for the purified product stream, and an outlet for vapor output, the distillation stage being provided with a reflux device and further configured to operate at a maximum distillation pressure, wherein the vapor output is connected to the evaporation stage such that the maximum distillation pressure is not less than the maximum evaporation pressure; and wherein the maximum distillation pressure is at least 0.2 bar and less than 1.0 bar.

14. The reactor system of claim 13, further comprising a steam compressor for compressing the steam output of the distillation stage to a compressed steam pressure such that the compressed steam pressure is higher than the maximum evaporation pressure.

15. The reactor system of claim 13, wherein the steam output of the distillation stage is connected to the downstream vessel of the evaporation stage.

16. The reactor system of claim 15, wherein the downstream vessel of the evaporation stage has a steam outlet connected to the vessel directly preceding it by means of heat exchange, and wherein the downstream vessel operates at a higher pressure than the vessel directly preceding it.

17. The reactor system according to any one of claims 13 to 16, further comprising a concentration stage downstream of the evaporation stage and upstream of the distillation stage, the concentration stage being provided with a supply source for a heating stream derived from waste heat supplied from the reactor.

18. The reactor system of claim 17, further comprising a reboiler stage disposed downstream of the evaporation stage and / or optionally downstream of the concentration stage and / or downstream of the distillation stage, wherein the reboiler stage is configured to process at least a portion of the mixture from the respective stages to remove contaminant portions from the mixture.

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