Method for producing 1,4-butanediol and tetrahydrofuran, and method for purifying crude 1,4-butanediol

Abstract

This invention provides a method for producing 1,4-butanediol that efficiently co-produces tetrahydrofuran while simultaneously producing high-purity 1,4-butanediol. [Solution] A method for producing 1,4-butanediol and tetrahydrofuran, comprising separating crude 1,4-butanediol containing impurities into 1,4-butanediol and mother liquor by melt crystallization, hydrogenating the mother liquor and then carrying out a cyclization reaction, or separating tetrahydrofuran obtained by carrying out a cyclization reaction together with the hydrogenation treatment.

Description

Technical Field

[0001] The present invention relates to a method for producing 1,4-butanediol and tetrahydrofuran, and a method for purifying crude 1,4-butanediol. Background Art

[0002] Known methods for producing 1,4-butanediol (hereinafter sometimes abbreviated as "14BG") include: the butadiene method, in which butadiene is acetoxylated with acetic acid and oxygen, the resulting diacetoxybutane is then hydrogenated and hydrolyzed to obtain 14BG (see, for example, Patent Document 1, etc.); the maleic anhydride method, in which maleic anhydride is hydrogenated to co-produce 14BG and γ-butyrolactone (see, for example, Patent Document 2, etc.); the maleic acid method, in which maleic acid is hydrogenated to obtain 14BG and γ-butyrolactone (see, for example, Patent Document 3, etc.); and the acetylene method, in which 1,4-butenediol obtained by reacting acetylene with formaldehyde is hydrogenated to produce 14BG (see, for example, Patent Document 4, etc.).

[0003] In these production methods, crude 14BG is usually purified by distillation. However, since crude 14BG contains impurities having a boiling point extremely close to that of 14BG and impurities that azeotrope with 14BG, it is difficult to achieve high-purity purification by simple distillation purification. In order to increase the purity, there have been problems such as requiring large-scale purification equipment and consuming large amounts of energy.

[0004] Among the impurities contained in crude 14BG, 1,2-diacetoxybutane (hereinafter sometimes abbreviated as "12DAB"), 1,2-hydroxyacetoxybutane (hereinafter sometimes abbreviated as "12HAB"), 1,4-diacetoxybutane (hereinafter sometimes abbreviated as "14DAB"), 1,4-hydroxyacetoxybutane (hereinafter sometimes abbreviated as "14HAB"), dibutylene glycol (hereinafter sometimes abbreviated as "DBG"), 2-(4′-hydroxybutoxy)tetrahydrafran (hereinafter sometimes abbreviated as "BGTF"), 2-(4′-oxobutoxy)tetrahydrofuran (hereinafter sometimes abbreviated as "BDTF"), and 1,4-di-(2′-tetrahydrofloxy)butane (hereinafter sometimes abbreviated as "BGDTF") cause discoloration and thread breakage when 14BG is processed into resins, fibers, etc.

[0005] To remove these impurities, for example, Patent Document 5 proposes a method of hydrogenating crude 14BG, and Patent Document 6 proposes a method of hydrogenating crude 14BG after distillation separation of high-boiling-point components. However, in these methods, in order to separate the impurities, distillation must be performed again after the hydrogenation treatment, which presents problems such as requiring large-scale purification equipment and a large amount of energy.

[0006] While the structure and formation mechanisms of all impurities in crude 14BG obtained by various manufacturing methods such as the butadiene method, maleic anhydride method, and acetylene method have not been elucidated, it has been found that BGTF, BDTF, BGDTF, and especially BGTF are regenerated during the distillation process. Therefore, as long as distillation is applied as the purification method for crude 14BG, there are limitations to the removal of impurities, particularly BGTF, and the removal of impurities becomes even more difficult during continuous operation.

[0007] To address these problems, Patent Document 7 proposes a method for efficiently purifying crude 14BG by separating impurities with a freezing point lower than 14BG using a melt crystallization method. The melt crystallization method is used to further purify high-purity organic compounds (e.g., 97% by mass) to an even higher purity (e.g., 99.9% by mass).

[0008] Incidentally, 14BG can be converted to tetrahydrafran (hereinafter sometimes abbreviated as "THF") by a cyclization reaction (for example, Patent Document 8). Conventionally, THF has been used as a solvent for various organic compounds and is also known as a useful compound as a raw material monomer for polyether polyols such as polytetramethylene ether glycol. Furthermore, Patent Document 9 discloses that THF can be co-produced by deacetating and cyclizing 14HAB, which is produced in the process of manufacturing 14BG by the butadiene method. Moreover, Patent Document 10 describes partially hydrolyzing the acetate ester of 14BG to obtain 14BG, and then deacetating and cyclizing the acetate ester of the remaining 14BG to obtain THF. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 52-133912 [Patent Document 2] Japanese Patent Application Publication No. 2-233627 [Patent Document 3] Japanese Patent Application Publication No. 11-12207 [Patent Document 4] Japanese Patent Application Publication No. 52-91813 [Patent Document 5] Japanese Patent Publication No. 197534 / 1983 [Patent Document 6] Japanese Patent Application Publication No. 6-17235 [Patent Document 7] Japanese Patent Application Publication No. 11-71310 [Patent Document 8] Japanese Patent Publication No. 2017-141301 [Patent Document 9] Japanese Patent Publication No. 2003-48854 [Patent Document 10] Japanese Patent Application Publication No. 7-53424 [Overview of the project] [Problems that the invention aims to solve]

[0010] When producing 14BG and THF together, there is room for improvement in production costs and operational efficiency. For example, the method in Patent Document 9 yields only a small amount of THF compared to the amount of 14BG. Furthermore, the method in Patent Document 10 requires further removal of acetic acid contained in the THF. In this invention, we focused on the melt crystallization method and investigated the problem of providing a method for producing 1,4-butanediol and tetrahydrofuran that efficiently co-produces tetrahydrofuran while producing high-purity 1,4-butanediol. [Means for solving the problem]

[0011] As a result of their investigations, the present inventors have found that high-purity 1,4-butanediol and tetrahydrofuran can be efficiently produced together by a purification method in which crude 1,4-butanediol is separated into 1,4-butanediol and mother liquor by melt crystallization, and the mother liquor is hydrogenated and then subjected to a cyclization reaction, or hydrogenation is performed together with the cyclization reaction to obtain tetrahydrofuran, thereby separating the tetrahydrofuran obtained, and thus the present invention has been completed. In other words, the gist of the present invention is as follows.

[0012] [1] A method for producing 1,4-butanediol and tetrahydrofuran, comprising separating crude 1,4-butanediol containing impurities into 1,4-butanediol and a mother liquor by melt crystallization, hydrogenating the mother liquor and then carrying out a cyclization reaction, or separating tetrahydrofuran obtained by carrying out a cyclization reaction together with the hydrogenation treatment. [2] The method for producing 1,4-butanediol and tetrahydrofuran according to [1], wherein the crude 1,4-butanediol comprises 2-(4′-hydroxybutoxy)tetrahydrafran and / or 1,4-hydroxyacetoxybutane. [3] The method for producing 1,4-butanediol and tetrahydrofuran according to [1] above, wherein the crude 1,4-butanediol comprises methanol and / or n-propanol. [4] The method for producing 1,4-butanediol and tetrahydrofuran according to [1] above, wherein the crude 1,4-butanediol comprises 2-methylpropanediol and / or n-propanol. [5] The method for producing 1,4-butanediol and tetrahydrofuran according to [1] above, wherein the crude 1,4-butanediol comprises ethanol and / or n-butanol. [6] A method for producing 1,4-butanediol and tetrahydrofuran according to any one of [1] to [5] above, wherein the melt crystallization is carried out by a melt crystallization method comprising a crystallization step of obtaining 1,4-butanediol crystals by cooling the crude 1,4-butanediol to below the freezing point of 1,4-butanediol, and a recovery step of recovering the 1,4-butanediol crystals as a crystalline melt by heating above the freezing point of 1,4-butanediol. [7] The method for producing 1,4-butanediol and tetrahydrofuran according to [6], wherein the melt crystallization method includes a sweating step in which impurities are removed from the 1,4-butanediol crystals as a sweat liquid. [8] A method for producing 1,4-butanediol and tetrahydrofuran according to any one of [1] to [7] above, wherein the melt crystallization is performed by a wall melt crystallization method comprising a crystallization step of obtaining 1,4-butanediol crystals by flowing a molten crude 1,4-butanediol onto a wall cooled to below the freezing point of 1,4-butanediol, and a recovery step of recovering the 1,4-butanediol crystals as a crystalline melt by heating the wall above the freezing point of 1,4-butanediol. [9] The method for producing 1,4-butanediol and tetrahydrofuran according to [8] above, wherein the crystal thickness of the 1,4-butanediol crystal is 1 to 20 mm.

[10] A method for producing 1,4-butanediol and tetrahydrofuran according to any one of [1] to [9] above, wherein the crude 1,4-butanediol contains impurities in a total amount of 1% by mass or more.

[11] The method for producing 1,4-butanediol and tetrahydrofuran according to any one of [1] to

[10] above, wherein the impurities in the crude 1,4-butanediol are impurities that do not crystallize together with the crude 1,4-butanediol.

[12] A method for producing 1,4-butanediol and tetrahydrofuran according to any one of [1] to

[11] above, wherein the impurity of the crude 1,4-butanediol is one or more compounds selected from the group consisting of 1,2-diacetoxybutane, 1,2-hydroxyacetoxybutane, 1,4-diacetoxybutane, 1,4-hydroxyacetoxybutane, dibutylene glycol, 2-(4′-hydroxybutoxy)tetrahydrafuran, 2-(4′-oxobutoxy)tetrahydrofuran, 1,4-di-(2′-tetrahydrofloxy)butane, 2-methyl-1,4-butanediol, γ-butyrolactone, 2-hydroxytetrahydrofuran, methanol, ethanol, n-propanol, n-butanol, acetal, 2-methylpropanediol, 2-methylpentanediol, and acetic acid.

[13] A method for purifying crude 1,4-butanediol, comprising separating crude 1,4-butanediol containing impurities into 1,4-butanediol and a mother liquor by melt crystallization, hydrogenating the mother liquor and then carrying out a cyclization reaction, or separating tetrahydrofuran obtained by carrying out a cyclization reaction together with the hydrogenation.

[14] The method for purifying crude 1,4-butanediol according to

[13] above, wherein the crude 1,4-butanediol comprises 2-(4′-hydroxybutoxy)tetrahydrafuran and / or 1,4-hydroxyacetoxybutane.

[15] The method for purifying crude 1,4-butanediol according to

[13] above, wherein the crude 1,4-butanediol comprises methanol and / or n-propanol.

[16] The method for purifying crude 1,4-butanediol according to the above

[13] , wherein the crude 1,4-butanediol comprises 2-methylpropanediol and / or n-propanol.

[17] The method for purifying crude 1,4-butanediol according to the above

[13] , wherein the crude 1,4-butanediol comprises ethanol and / or n-butanol. Effects of the Invention

[0013] According to the present invention, there can be provided a method for producing 1,4-butanediol and tetrahydrofuran, which efficiently co-produces tetrahydrofuran while producing high-purity 1,4-butanediol. Mode for Carrying Out the Invention

[0014] The present invention is described in detail below. The following description is an example of an embodiment of the present invention, and the present invention is not limited to the following description as long as it does not exceed the gist of the present invention, and can be implemented with any modifications within a range that does not deviate from the gist of the present invention.

[0015] [Method for Producing 1,4-Butanediol and Tetrahydrofuran] The method for producing 1,4-butanediol and tetrahydrofuran of the present invention comprises separating crude 1,4-butanediol containing impurities into 1,4-butanediol and a mother liquor by melt crystallization, subjecting the mother liquor to hydrogenation treatment, then carrying out a cyclization reaction, or separating tetrahydrofuran obtained by carrying out a cyclization reaction together with the hydrogenation treatment. By using the method for producing 1,4-butanediol and tetrahydrofuran of the present invention, high-purity 1,4-butanediol can be produced, and at the same time, tetrahydrofuran can also be efficiently co-produced.

[0016] The crude 1,4-butanediol used in the present invention contains 1,4-butanediol and impurities (hereinafter referred to as "impurity A"). Crude 14BG can be obtained by known methods such as butadiene method, Reppe method, allyl alcohol method, maleic anhydride method, acetylene method, etc.

[0017] Furthermore, crude 1,4-butanediol may include embodiments derived from biomass. "Biomass" refers to living or dead biomaterials that can be directly or indirectly converted into useful chemical substances, usually derived from non-renewable hydrocarbon sources. Biomass includes cellulosic materials, grains, starches derived from grains, fatty acids, vegetable oils, and derivatives from these biomass materials. Examples of useful chemical substances, though not limited to these, include diols; diacides; monomers used in the production of acids such as diols and succinic acid; and monomers used in the production of polymers. Biomass-based crude 1,4-butanediol can be obtained from several resources. For example, the following processes can be used to produce biomass-based crude 1,4-butanediol. Agricultural biomass such as corn, grains, or sugar-derived grains can be converted to succinic acid by simple processes such as fermentation in the presence of microorganisms. This succinic acid can be readily converted to crude 1,4-butanediol by methods described in several publications, including U.S. Patent No. 4,096,156. Another method for converting succinic acid to crude 1,4-butanediol is also described in Smith et al.'s "Life Cycles Engineering Guidelines" (EPA publication, EPA / 600 / R-1 / 101 (2001)).

[0018] Before melt crystallization, it is preferable to remove low-boiling-point components from crude 1,4-butanediol by distillation. For example, crude 14BG obtained by the butadiene method may contain low-boiling-point components such as acetic acid, water, 12HAB, and 14HAB as impurities A, and it is preferable to remove these low-boiling-point components from crude 14BG by distillation. Distillation is preferably carried out in two stages, with water, acetic acid, etc. being removed in the first stage and 12HAB, 14HAB, etc. being removed in the second stage. Furthermore, the crude 14BG from which the low-boiling-point components have been removed by distillation can be withdrawn from the bottom or side flow of the distillation column.

[0019] Crude 1,4-butanediol preferably contains impurities of 1% by mass or more in total amount, and may contain 5% by mass or more. In the present invention, even if the impurities in crude 14BG are 1% by mass or more in total amount, high-purity 14BG can be purified and separated by melt crystallization, thereby reducing raw material costs. Furthermore, even if impurity A is removed by distillation before melt crystallization, the number of stages in the distillation column and the reflux ratio can be reduced, and the operating conditions can be relaxed. In addition, the amount of impurity A contained in crude 1,4-butanediol is acceptable as long as it is an amount that can be treated by hydrogenation. The impurity A is preferably 5% by mass or less in total amount, and may contain 1% by mass or less. If the impurities in crude 14BG are 5% by mass or less in total amount, the number of melt crystallization steps can be reduced, and even if impurities are removed by distillation before melt crystallization, the operating conditions can be relaxed.

[0020] The freezing point of crude 1,4-butanediol is approximately 19-20°C, but it is preferable that the impurities in crude 1,4-butanediol are impurities that do not crystallize together with the crude 1,4-butanediol. If impurity A is a compound that does not crystallize together with 1,4-butanediol, impurity A can be efficiently separated by melt crystallization.

[0021] The impurities in crude 1,4-butanediol are preferably one or more compounds selected from the group consisting of 1,2-diacetoxybutane, 1,2-hydroxyacetoxybutane, 1,4-diacetoxybutane, 1,4-hydroxyacetoxybutane, dibutylene glycol, 2-(4′-hydroxybutoxy)tetrahydrafran, 2-(4′-oxobutoxy)tetrahydrofuran, 1,4-di-(2′-tetrahydrofloxy)butane, 2-methyl-1,4-butanediol, γ-butyrolactone, 2-hydroxytetrahydrofuran, methanol, ethanol, n-propanol, n-butanol, acetal, 2-methylpropanediol, 2-methylpentanediol, and acetic acid. The above compound is impurity A contained in crude 14BG when crude 14BG is obtained by the butadiene process, etc. If the impurity in crude 14BG is the above compound, it can be efficiently separated as a mother liquor by melt crystallization, and the production efficiency of THF can be increased.

[0022] Embodiments of crude 1,4-butanediol containing the above-mentioned impurity A include embodiments containing 2-(4′-hydroxybutoxy)tetrahydrafuran and / or 1,4-hydroxyacetoxybutane obtained by the butadiene process, embodiments containing methanol and / or n-propanol obtained by the Reppe process, embodiments containing 2-methylpropanediol and / or n-propanol obtained by the allyl alcohol process, and embodiments containing ethanol and / or n-butanol obtained by the maleic acid process.

[0023] The melt crystallization of the present invention is preferably carried out by a melt crystallization method that includes a crystallization step of obtaining 1,4-butanediol crystals by cooling crude 1,4-butanediol to below the freezing point of 1,4-butanediol, and a recovery step of recovering the 1,4-butanediol crystals as a crystalline melt by heating above the freezing point of 1,4-butanediol. Furthermore, it is more preferable to carry out the melt crystallization method that includes a sweating step of removing impurities from the 1,4-butanediol crystals as a sweating liquid.

[0024] The melt crystallization method used in the present invention is not particularly limited, but may be any of the following: a method of growing purified crystals on a cooled wall surface (wall melt crystallization method), a method of cooling the molten liquid and growing purified crystals in the liquid to separate the mother liquor, etc. However, it is preferable to use the wall melt crystallization method. Specifically, it is preferable to carry out melt crystallization by a wall melt crystallization method that includes a crystallization step of obtaining 1,4-butanediol crystals by flowing a molten crude 1,4-butanediol onto a wall surface cooled to below the freezing point of 1,4-butanediol, and a recovery step of recovering the 1,4-butanediol crystals as crystalline melt by heating the wall surface to above the freezing point of 1,4-butanediol.

[0025] In wall-melt crystallization, a crystallization apparatus is typically used in which a liquid raw material is flowed onto one side of a smooth plate or tube, and the crystals are cooled from the other side to precipitate on the surface of that side. Preferably, a multi-stage crystallization method is used in which multiple tanks are used, and the mother liquor (uncrystallized residual liquid) and crystalline melt, and optionally the efflorescence, obtained when crystallization is performed on the liquid raw material in one tank are sent to separate tanks, and further crystallization is performed on the crystalline melt.

[0026] The crystallization apparatus can be of any shape, such as a flat plate type, a tubular type, or other shapes, but a flat plate type is preferred for efficiently obtaining a thin film. The crystallization apparatus consists of a crystallizer, a storage tank, and a liquid transfer pump. The crystallizer has a crystal attachment plate (hereinafter sometimes abbreviated as "crystallization plate") made of stainless steel, for example, a flat plate measuring 2m in length, 1m in width, and 1mm in thickness. This crystallization plate is positioned vertically, and its upper end is bent to form an inclined surface. A raw material supply machine is provided, which serves as a raw material supply means for flowing liquid raw material in a thin film down one side of the crystallization plate via the inclined surface, or a vertical surface continuous with the upper end of the inclined surface. When scaling up, the processing capacity is increased by increasing the number of these flat plate crystallization units.

[0027] On the other side of the crystallization plate, a refrigerant supply pipe is provided for supplying a refrigerant that flows in a thin film at a temperature below the freezing point of the liquid raw material. This refrigerant supply pipe also serves as a heat medium supply pipe, which supplies a heat medium at a temperature near the freezing point of the liquid raw material to the other side of the crystallization plate. The liquid raw material is circulated by a liquid pump and supplied to one side of the crystallization plate, while the refrigerant is circulated and supplied to the other side of the crystallization plate via another liquid pump and cooler to the refrigerant supply pipe, and the heat medium is circulated and supplied to the heat medium supply pipe (which also serves as the refrigerant supply pipe) via yet another liquid pump and heater.

[0028] Any solvent capable of controlling the temperature of a crystallization apparatus, such as a heat transfer medium or refrigerant, can be used as the temperature control medium. Specifically, this includes commonly used and known solvents such as ethylene glycol; lower alcohols such as methyl alcohol and ethyl alcohol; water; and mixtures thereof.

[0029] In one embodiment of the present invention, the wall melt crystallization method involves circulating and supplying crude 14BG molten liquid to one side of the crystallization plate, allowing it to flow down in a thin film, and flowing a refrigerant at a temperature below the freezing point of 14BG (19-20°C) down in a thin film to the other side of the crystallization plate. Since crystals will not precipitate unless there is a certain degree of supercooling, it is necessary to keep the wall temperature of the crystallization plate below the nucleation start temperature (the temperature at which 14BG begins to solidify). The nucleation start temperature varies depending on the purity of the crude 14BG molten liquid, the supply rate, etc., and the lower the purity and the faster the supply rate, the lower the nucleation start temperature.

[0030] Crystal growth is faster at lower wall temperatures, but it is preferable to slow down the crystal growth rate to minimize the incorporation of impurities into the crystal during crystal growth. The crystal growth rate can be slowed by using a refrigerant to cool the wall temperature to a temperature at most about 8°C lower than the freezing point of 14BG (about 11°C) to start crystallization, and then gradually lowering the refrigerant temperature as the crystal grows, until the wall temperature is about 15°C lower than the freezing point of 14BG. When melt crystallization is performed in multiple stages, the crystal growth rate can be slowed by lowering the refrigerant temperature more slowly in the second stage than in the first stage, i.e., by slowing down the rate of refrigerant temperature decrease in the later crystallization steps, thereby obtaining crystals with fewer impurities.

[0031] By flowing a crude 14BG molten liquid down one side of the crystallization plate and a refrigerant down the other side, 14BG crystals are deposited on one side of the crystallization plate. The supply temperature of the crude 14BG molten liquid is preferably within a range of about 5°C higher than the freezing point of 14BG, and more preferably within a range of about 1°C higher. Since the crystal surface has difficulty maintaining its initial temperature due to the heat of crystallization and the decrease in heat transfer efficiency due to the crystal thickness, the refrigerant temperature is gradually lowered, taking into account the rise in crystal surface temperature. There is no particular upper limit to the flow rate of the crude 14BG molten liquid as long as a thin film flow can be obtained, but it is preferable to have as high a flow rate as possible because a higher flow rate prevents the liquid film from breaking, improves the heat transfer coefficient, and increases the processing speed.

[0032] After the crystal film thickness of 14BG reaches a predetermined value, the mother liquor is withdrawn from the circulation supply system. The crystal film thickness is preferably 1 to 20 mm, more preferably 3 to 15 mm, and even more preferably 5 to 10 mm. When the crystal film thickness is within the above range, it is easier to prevent the incorporation of impurities into the crystal, and the thermal conductivity is good, making it easier to shorten the crystallization time. Also, when combined with a sweating process, if the crystal film thickness is within the above range, the sweating time can be shortened and the separation of the crystal layer and the sweat liquid can be improved.

[0033] The 14BG crystals obtained in the crystallization step are preferably subjected to a sweating step as needed. The sweating step is a step in which liquid with a high concentration of impurities incorporated into the precipitated crystals or adhering to the surface of the crystals is melted and removed, and is performed in order to further reduce the impurity concentration of the crystals. Specifically, before the recovery step, the temperature is controlled to be close to the freezing point of the target pure substance, that is, by flowing a heat transfer medium in a thin film down the other side of the crystallization plate, thereby controlling the wall temperature of the crystallization plate to within ±5°C, preferably within ±3°C, of ​​the freezing point of the target pure substance, and partially melting the crystals. This sweating step can further reduce the impurity concentration of the crystals. In addition, the sweat liquid produced in the sweating step can be recovered and subjected to the crystallization step again.

[0034] There are no particular restrictions on the sweating time, and it is usually around 30 minutes, but 60 to 600 minutes is preferable. Although 14BG has a relatively high viscosity of 77 mPa·s (25℃), the concentration of impurities in the crystals can be further reduced within the above time frame.

[0035] The 14BG crystals obtained through the crystallization process, and optionally the subsequent sweating process, can be recovered as crystalline melt by flowing a heat transfer medium, heated to a temperature above the freezing point of 14BG, down to the other side of the crystallization plate. Alternatively, by heating the already obtained 14BG crystalline melt and flowing it down to one side of the crystallization plate, i.e., the crystal surface, along with the flow of the heat transfer medium, the 14BG crystals are heated from both sides and can be melted in a short time.

[0036] The melt crystallization is preferably a multi-stage crystallization method in which the obtained crystalline melt is further crystallized one or more times. High-purity 14BG can be obtained through melt crystallization consisting of a crystallization step, a sweating step if necessary, and a recovery step. However, even higher-purity 14BG can be obtained by using the molten 14BG crystal in the crystallization step instead of the molten crude 14BG. Therefore, extremely high-purity 14BG can be obtained by performing melt crystallization in multiple stages.

[0037] The mother liquor obtained by melt crystallization can be subjected to hydrogenation treatment and then a cyclization reaction to obtain THF, or the cyclization reaction may be carried out together with the hydrogenation treatment. The mother liquor obtained by melt crystallization may contain impurities such as 14DAB, 14HAB, 14BG, DBG, BGTF, BDTF, BGDTF, γ-butyrolactone, 2-methyl-propanol (hereinafter referred to as "impurity B"), but by performing a cyclization reaction after hydrogenation treatment of the mother liquor, or by performing a cyclization reaction together with the hydrogenation treatment, impurity B can also be converted into THF, and high-purity THF can be efficiently obtained from the mother liquor. If only the cyclization reaction is carried out without hydrogenation treatment, the yield of separated THF may be low, or the purity of THF may be low.

[0038] The hydrogenation treatment is preferably carried out so that the BGTF concentration is 1.0% or less, more preferably 0.5% or less, even more preferably 0.1% or less, and most preferably 0.01% or less. When the BGTF concentration is within the above range, the viscosity of the THF raw material after hydrogenation treatment can be reduced, and the precipitation of solids can be suppressed. The BGTF concentration can be controlled by appropriately analyzing the outlet of the hydrogenation reactor.

[0039] Hydrogenation is carried out by continuously supplying mother liquor and hydrogen to a reactor packed with a catalyst. The catalyst is preferably a silica catalyst supported with a noble metal, preferably ruthenium. The reactor pressure can be either atmospheric pressure or pressurized, but a pressurized pressure of 0.4 to 2 MPa is preferred. The reactor temperature is preferably 40 to 250°C, and more preferably 50 to 120°C.

[0040] The cyclization reaction is preferably carried out using an acid catalyst, more preferably using a solid acid catalyst, and even more preferably using a solid acid catalyst with a pKa value of 4 or less. Examples of acid catalysts include heterogeneous catalysts such as cation exchange resins, sulfated zirconia, and fluorosulfonic acid-containing resins, and homogeneous catalysts such as sulfuric acid, nitric acid, phosphoric acid, heteropoly acids (phosphotungstic acid, phosphomolybdic acid, silicatungstic acid), and sulfonic acid compounds. In continuous processes, the use of solid catalysts is preferred, while in batch reactions, homogeneous acid catalysts such as p-toluenesulfonic acid can also be used. The cyclization reaction is preferably carried out under atmospheric pressure or a pressure of 1.2 MPa or less, and the temperature is preferably 50 to 120°C.

[0041] Crude THF obtained through hydrogenation and cyclization reactions can be separated from light-boiling components such as THF and water by distillation, and from high-boiling components. The number of stages in the distillation column is not particularly limited, but typically, the theoretical number of stages is 1 to 100, preferably 1 to 10, more preferably 1 to 5, and even more preferably 1 to 4. Keeping the theoretical number of stages within the above range can reduce equipment costs. The distillate containing THF and light-boiling components separated by distillation can be further subjected to precision distillation to obtain high-purity THF. The high-boiling components separated by distillation can be incinerated, but from the viewpoint of operating costs, it is preferable to distill them again and use a portion as raw material for crude 14BG.

[0042] The distillate obtained by distillation, which contains THF and light-boiling components, is preferably subjected to dihydrofuran (hereinafter sometimes abbreviated as "DHF") hydration treatment. Although DHF is contained in the light-boiling components of the distillate, it can be separated by distillation after hydration treatment. The DHF hydration treatment is preferably carried out until the DHF concentration is 100 ppb or less.

[0043] DHF hydration is carried out by continuously supplying distillates containing THF and light-boiling components to a reactor packed with a catalyst. It is preferable to use an ion exchange resin as the catalyst. The reactor pressure is preferably atmospheric pressure, and the reactor temperature is preferably 30-50°C. The THF purity of the treated liquid can be further increased by distillation.

[0044] Furthermore, it is preferable to treat the distillate containing THF and light-boiling components obtained by distillation with n-butyraldehyde (hereinafter sometimes abbreviated as "NBD"). Although NBD is contained in the light-boiling components of the distillate, it can be separated by distillation after hydrogenation. It is preferable to continue the NBD hydrogenation treatment until the NBD concentration falls below the detection limit.

[0045] NBD hydrogenation is carried out by continuously supplying distillates containing THF and light-boiling components to a reactor packed with a catalyst. A ruthenium-supported catalyst is preferably used. The reactor pressure is preferably 0.3 to 1.0 MPa, and the reactor temperature is preferably 30 to 80°C. The THF purity of the liquid treated with NBD hydrogenation can be further increased by distillation.

[0046] Furthermore, it is preferable to dehydrate the liquid that has undergone DHF hydration treatment and / or NBD hydrogenation treatment. The dehydration treatment is preferably carried out until the water content is 0.3% by mass or less.

[0047] Dehydration is performed by adding 15 to 45 parts by mass of a commonly used desiccant such as MgSO4 to 100 parts by mass of the treatment liquid, shaking, and then pressure filtering using a membrane filter or the like.

[0048] [Method for purifying crude 1,4-butanediol] The present invention provides a method for purifying 1,4-butanediol, comprising separating crude 1,4-butanediol containing impurities into 1,4-butanediol and mother liquor by melt crystallization, hydrogenating the mother liquor and then carrying out a cyclization reaction, or separating tetrahydrofuran obtained by carrying out a cyclization reaction together with the hydrogenating treatment. As the crude 1,4-butanediol, the previously described method can be used, and the purification method is preferably carried out by the melt crystallization method described above.

[0049] In the present invention's method for purifying crude 1,4-butanediol, the purity of the 1,4-butanediol is preferably 97.5% by mass or higher, more preferably 98.0% by mass or higher, even more preferably 98.5% by mass or higher, even more preferably 99.0% by mass or higher, and most preferably 99.5% by mass or higher. Furthermore, the total content of BGTF, BDTF, and BGDTF in the produced 1,4-butanediol is preferably less than 0.5% by mass, more preferably less than 0.3% by mass, and even more preferably less than 0.1% by mass. [Examples]

[0050] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the essence of the invention.

[0051] (Example 1) Butadiene and acetic acid were subjected to acetoxylation in the presence of an acetoxylation catalyst (3% palladium and 0.6% tellurium supported on activated carbon) under conditions of 8 MPa pressure and 70-85°C, with nitrogen-diluted air (oxygen concentration 5.8 vol%) supplied to obtain an acetoxylation product solution. This solution was distilled in a distillation column to remove acetic acid and high-boiling substances, and then supplied to a pre-hydrogenation reactor packed with a palladium catalyst and a post-hydrogenation reactor packed with a ruthenium catalyst. The pre-hydrogenation reaction was carried out under a pressure of 5 MPa and a temperature of 40-70°C, and the post-hydrogenation reaction was carried out under a pressure of 5 MPa and a temperature of 70-100°C. The resulting reaction solution was separated into gas and liquid and then distilled to obtain a diacetoxybutane mixture containing 1,4-diacetoxybutane.

[0052] The above diacetoxybutane mixture was passed through a hydrolysis reactor filled with Diaion SK1BH (a product of Mitsubishi Chemical Corporation, a sulfonic acid type cation exchange resin; Diaion is a registered trademark of the company) at 40-60°C to carry out the hydrolysis reaction. The resulting hydrolysis reaction solution was continuously distilled at a column bottom temperature of 158°C and a column top pressure of 15 kPa to distill off water and acetic acid from the top of the column, and the bottom liquid with the following composition was obtained from the bottom of the column.

[0053] The (composition of the bottom liquid)% is all expressed in mass%. 1,4-Diacetoxybutane 10.6% 1,4-Hydroxyacetoxybutane 43.0% 1,4-Butanediol 36.8% 1,2-Diacetoxybutane 0.9% 1,2-Hydroxyacetoxybutane 2.4% 1,2-Butanediol 6.2%

[0054] The bottom liquid described above was continuously distilled using a distillation column with 100 theoretical plates at a bottom temperature of 194°C, a top pressure of 21 kPa, and a reflux ratio of 30, and was separated into a top fraction, a side flow fraction, and a bottom fraction. Of these, the composition of the bottom fraction used for crystallization below was 14BG: 94.0%, BGTF: 0.48%, 14HAB: 0.02%, and other unknown components: 5.5%.

[0055] The bottom fraction described above was used as crude 1,4-butanediol, and two-stage melt crystallization was performed using a plate-type crystallizer. The crystallizer had a stainless steel crystallization plate measuring 200 mm wide x 600 mm high, and a 30-40% aqueous solution of ethylene glycol was used as the refrigerant and heat transfer medium.

[0056] The above crude 14BG 500g was sent to a circulation tank, and then circulated from the circulation tank to a crystallization apparatus to perform the crystallization process. The wall temperature of the crystallization apparatus was cooled to approximately 11°C with a refrigerant before crystallization began, and was gradually lowered to approximately 4°C. When the thickness of the crystal layer reached 3.3 mm, crystallization was stopped, and 50g of mother liquor was sent from the circulation supply system to the mother liquor storage tank to obtain 450g of 14BG crystals. The obtained 14BG crystals were subjected to a sweating process to remove impurities. The wall temperature of the crystallization apparatus was heated to 19°C using a heat transfer medium, and 200g of 14BG crystals were subjected to sweating for approximately 2 hours. The resulting sweat liquid was then transferred to a sweat liquid storage tank. The 14BG crystals after the sweating process were recovered as crystalline melt in the recovery process. The wall temperature of the crystallization apparatus was heated to 25°C to obtain 250g of the first stage crystalline melt of 14BG. Furthermore, the composition of the first stage crystalline melt was approximately 97.7% purity of 1,4-butanediol and 0.19% BGTF content.

[0057] The second stage of melt crystallization was performed using the first stage crystalline melt of 14BG obtained. The crystallization process, sweating process, and recovery process were carried out in the same manner as in the first stage, yielding 10 g of mother liquor, 165 g of sweated liquid, and 75 g of second stage crystalline melt of 14BG. The composition of the obtained second stage crystalline melt was as follows.

[0058] (Composition of the second stage crystalline melt of 14BG) Purity of 1,4-butanediol: approximately 99.7%. BGTF content: 0.08%

[0059] The above procedure was repeated until the mother liquor obtained in the crystallization process reached 700g, at which point the following steps were performed: a.) to i.).

[0060] a.) Hydrogenation treatment of mother liquor 700 g of the mother liquor obtained in the crystallization process was subjected to hydrogenation. The hydrogenation was carried out in a 1 L autoclave under conditions of 0.9 MPa pressure and 140 °C in the presence of 28 g of palladium-supported catalyst. After the reaction was complete, the catalyst was removed by filtration, and the resulting hydrogenated solution was 623.5 g. The conversion rate of BGTF was 99.9%.

[0061] b.) Cyclization reaction A cyclization reaction was carried out using the hydrogenated liquid obtained from the hydrogenation treatment. The cyclization reaction was carried out by filling a reaction vessel with 200 ml of ion exchange resin (Diaion SK1BH) and continuously supplying it under the conditions of a pressure of 0.5 MPa, a temperature of 85°C, and a raw material supply rate of 20 ml / hr. The conversion rate of 14BG by the cyclization reaction was 45.6-47.1%.

[0062] c.) Crude THF purification distillation After the cyclization reaction, 800g of crude THF was obtained and then purified by distillation. 800g of crude THF was subjected to atmospheric distillation at a column bottom temperature of 80°C and a column top temperature of 63°C, yielding 255g of a mixture of THF and water (80% THF purity) from the top of the column.

[0063] d.) Dihydrofuran (DHF) hydration treatment A mixture of THF and water obtained by distillation was subjected to DHF hydration treatment. For the hydration treatment, 100 ml of ion exchange resin (Diaion SK1BH) was filled into a reaction vessel, and the raw materials at a reaction temperature of 40°C were continuously circulated into the reaction vessel until the DHF concentration reached 100 ppb.

[0064] e.) THF dehydration distillation Dehydration distillation was performed on the solution treated with DHF hydration. 747g of the DHF-treated solution was subjected to atmospheric distillation at a column bottom temperature of 68°C and a column top temperature of 66°C, yielding 722g of a mixture of THF and water (THF purity 95%) from the top of the column.

[0065] f.) Hydrogenation of n-butyraldehyde (NBD) Hydrogenation of NBD contained in the liquid obtained by THF dehydration distillation was performed. The hydrogenation treatment was carried out by treating 450g of the reaction mixture in a 1L autoclave under conditions of 0.69 MPa pressure and 50°C in the presence of 5g of ruthenium-supported catalyst. After the reaction was complete, the catalyst was removed by filtration, and the resulting hydrogenated NBD solution was 445g. The conversion rate of NBD was 99.9%.

[0066] h.) Dehydration of THF with MgSO4 677 g of NBD hydrogenation solution was mixed with 177 g of MgSO4, and dehydration was carried out until the water content was 0.3 wt% or less. MgSO4 was separated from the solution with the desired water content by pressure filtration using a membrane filter to obtain 496 g of dehydrated THF.

[0067] g.) Purification and distillation of THF Distillation purification of dehydrated THF was performed. 493g of dehydrated THF was subjected to atmospheric pressure distillation at a column bottom temperature of 68°C and a column top temperature of 66°C, yielding 435g of purified THF (a mixture of THF and water (99.97% THF)) from the top of the column.

[0068] i.) Polytetramethyl ether (PTME) conversion reaction Purified THF, acetic anhydride, and catalyst (ZrO2-SiO2) were supplied to flasks in the amounts shown in Table 1, stirred at 40°C for 6 hours, and the reaction was carried out under atmospheric pressure with a nitrogen seal in the flask. After the reaction was complete, the catalyst was separated using a PTFE filter cloth. GPC (gel permeation chromatography) analysis of the obtained liquid revealed a molecular weight of Mw / Mn = 1.87 and an APHA (Hasen unit color number) of 18. The results are also shown in Table 1. The GPC and APHA were performed as follows.

[0069] (GPC) Equipment: Tosoh HLC-8420GPC Column: This column TSKgel SuperHZM-N 4.6mm ID x 15cm Part Number 19660 Guard column TSKgel guardcolumn SuperHZ-L 4.6mm ID×2cm Part number 19314 Reference column TSKgel SuperH-RC 6.0mm ID×150cm Part number 18004 Injection volume: 1~500μL Injection method: Autosampler Inlet temperature: Column oven temperature 40°C, Pump oven temperature 40°C Carrier gas: None Detectors: RI and UV (2 types)

[0070] (APHA) Equipment: Nippon Denshoku Industries Co., Ltd. Colorimeter ZE6000 Measurement method: Direct reading of XYZ tristimulus values Measurement method: Davnore beam method Illumination and light reception conditions: transmission Optical path length of glass cell: 1cm

[0071] (Example 2) A mixture of 94.2% 1,4-butanediol, 0.04% γ-butyrolactone, 0.06% 2-methyl-1,4-butanediol, 1.6% methanol, 2.5% n-propanol, 1.2% n-butanol, and 0.04% acetal, as described in paragraph 0036 of Japanese Patent Publication No. 2010-518174, was prepared to obtain crude 1,4-butanediol.

[0072] Except for using the crude 14BG mentioned above, the crystalline melt and mother liquor were obtained in the same manner as in Example 1. The composition of the crystalline melt was as follows. (Composition of crystalline melt) Purity of 1,4-butanediol: 97.8% γ-Butyrolactone: 0.18% Propanol: 1.22% Butanol: 0.63% Acetal: 0.06%

[0073] 700 g of the mother liquor obtained in the crystallization process was subjected to the same procedures a) to g) as in Example 1 to obtain 630 g of purified THF (a mixture of THF and water (THF purity 99.70%)). Using the purified THF, the same procedure i) as in Example 1 was performed to carry out the polytetramethyl ether (PTME) conversion reaction. The results are shown in Table 1.

[0074] (Example 3) A mixture containing 1,4-butanediol, 2-methyl-1,3-propanediol, and propanol, having the same composition as the product after the reaction described in EXAMPLE 3 of US5,426,250, was prepared to obtain crude 1,4-butanediol.

[0075] Except for using the crude 14BG mentioned above, the crystalline melt and mother liquor were obtained in the same manner as in Example 1. The composition of the crystalline melt was as follows. (Composition of crystalline melt) Purity of 1,4-butanediol: 99.2% 2-Methyl-propanediol: 0.51% Propanol: 0.13%

[0076] 700 g of the mother liquor obtained in the crystallization process was subjected to the same procedures a) to g) as in Example 1 to obtain 595 g of purified THF (a mixture of THF and water (THF purity 99.95%)). Using the purified THF, the same procedure i) as in Example 1 was performed to carry out the polytetramethyl ether (PTME) conversion reaction. The results are shown in Table 1.

[0077] (Example 4) A mixture of 1.6% tetrahydrofuran, 0.3% γ-butyrolactone, 92.8% 1,4-butanediol, and 4.6% n-butanol, as described in paragraph 0055 of Japanese Patent Publication No. 11-12207, was prepared to obtain crude 1,4-butanediol.

[0078] Except for using the crude 14BG mentioned above, the crystalline melt and mother liquor were obtained in the same manner as in Example 1. The composition of the crystalline melt was as follows. (Composition of crystalline melt) Purity of 1,4-butanediol: 98.0% Tetrahydrofuran: 0.54% γ-Butyrolactone: 0.36% Butanol: 0.83%

[0079] 700 g of the mother liquor obtained in the crystallization process was subjected to the same procedures a) to g) as in Example 1 to obtain 616 g of purified THF (a mixture of THF and water (THF purity 99.97%)). Using the purified THF, the same procedure i) as in Example 1 was performed to carry out the polytetramethyl ether (PTME) conversion reaction. The results are shown in Table 1.

[0080] (Reference example) The procedure was the same as in i.), except that purified THF was replaced with commercial THF (manufactured by Mitsubishi Chemical Corporation). The molecular weight of the obtained PTME was Mw / Mn = 1.95, and the APHA was 28. The molecular weights of PTME using purified THF and PTME using commercial THF were almost the same, but it was found that PTME using purified THF had a better APHA.

[0081] [Table 1]

[0082] (Comparative Example 1) Crude 14BG was prepared in the same manner as in Example 1, and the crystalline melt and mother liquor were obtained in the same manner as in Example 1.

[0083] For 700 g of mother liquor obtained in the crystallization process, operations b.) to g.) were carried out in the same manner as in Example 1, except that a.) the mother liquor was not subjected to hydrogenation treatment, to obtain 167 g of purified THF (a mixture of THF, water, and BGTF (THF purity 98.67%)).

[0084] In the examples, high-purity 14BG can be produced by melt crystallization of crude 14BG. Furthermore, by hydrogenating the separated mother liquor and then performing a cyclization reaction, or by performing a cyclization reaction in conjunction with the hydrogenating treatment, 62 to 90% by mass of THF relative to the weight of the mother liquor can be separated, and the separated THF is of high purity. Moreover, the polytetramethyl ether produced using the obtained THF has superior APHA, an indicator of color tone, compared to the polytetramethyl ether produced using the reference example product THF, and is therefore also useful in terms of practical performance. In a comparative example where the mother liquor was not hydrogenated and the cyclization reaction was carried out, the ratio of the weight of separated THF to the weight of the mother liquor was low at 24% by mass, and the purity was also low. Furthermore, the separated THF contained BGTF, which is highly likely to cause performance problems.

Claims

1. Crude 1,4-butanediol containing impurities is separated into 1,4-butanediol and mother liquor by melt crystallization. A method for producing 1,4-butanediol and tetrahydrofuran, comprising hydrogenating the mother liquor and then carrying out a cyclization reaction, or separating the tetrahydrofuran obtained by carrying out a cyclization reaction together with the hydrogenation treatment.

2. The method for producing 1,4-butanediol and tetrahydrofuran according to claim 1, wherein the crude 1,4-butanediol comprises 2-(4'-hydroxybutoxy)tetrahydrafuran and / or 1,4-hydroxyacetoxybutane.

3. The method for producing 1,4-butanediol and tetrahydrofuran according to claim 1, wherein the crude 1,4-butanediol comprises methanol and / or n-propanol.

4. The method for producing 1,4-butanediol and tetrahydrofuran according to claim 1, wherein the crude 1,4-butanediol comprises 2-methylpropanediol and / or n-propanol.

5. The method for producing 1,4-butanediol and tetrahydrofuran according to claim 1, wherein the crude 1,4-butanediol comprises ethanol and / or n-butanol.

6. A method for producing 1,4-butanediol and tetrahydrofuran according to any one of claims 1 to 5, wherein the melt crystallization is carried out by a melt crystallization method comprising a crystallization step of obtaining 1,4-butanediol crystals by cooling the crude 1,4-butanediol to below the freezing point of 1,4-butanediol, and a recovery step of recovering the 1,4-butanediol crystals as a crystalline melt by heating above the freezing point of 1,4-butanediol.

7. The method for producing 1,4-butanediol and tetrahydrofuran according to claim 6, wherein the melt crystallization method includes a sweating step in which impurities are removed from the 1,4-butanediol crystals as a sweat liquid.

8. A method for producing 1,4-butanediol and tetrahydrofuran according to any one of claims 1 to 5, wherein the melt crystallization is performed by a wall melt crystallization method comprising a crystallization step of obtaining 1,4-butanediol crystals by flowing a molten crude 1,4-butanediol onto a wall cooled to below the freezing point of 1,4-butanediol, and a recovery step of recovering the 1,4-butanediol crystals as a crystalline melt by heating the wall above the freezing point of 1,4-butanediol.

9. The method for producing 1,4-butanediol and tetrahydrofuran according to claim 8, wherein the crystal thickness of the 1,4-butanediol crystal is 1 to 20 mm.

10. The method for producing 1,4-butanediol and tetrahydrofuran according to any one of claims 1 to 5, wherein the crude 1,4-butanediol contains impurities in a total amount of 1% by mass or more.

11. A method for producing 1,4-butanediol and tetrahydrofuran according to any one of claims 1 to 5, wherein the impurities in the crude 1,4-butanediol are impurities that do not crystallize together with the crude 1,4-butanediol.

12. The method for producing 1,4-butanediol and tetrahydrofuran according to claim 1, wherein the impurities of the crude 1,4-butanediol are one or more compounds selected from the group consisting of 1,2-diacetoxybutane, 1,2-hydroxyacetoxybutane, 1,4-diacetoxybutane, 1,4-hydroxyacetoxybutane, dibutylene glycol, 2-(4'-hydroxybutoxy)tetrahydrafran, 2-(4'-oxobutoxy)tetrahydrofuran, 1,4-di-(2'-tetrahydrofloxy)butane, 2-methyl-1,4-butanediol, γ-butyrolactone, 2-hydroxytetrahydrofuran, methanol, ethanol, n-propanol, n-butanol, acetal, 2-methylpropanediol, 2-methylpentanediol, and acetic acid.

13. Crude 1,4-butanediol containing impurities is separated into 1,4-butanediol and mother liquor by melt crystallization. A method for purifying crude 1,4-butanediol, comprising hydrogenating the mother liquor and then carrying out a cyclization reaction, or separating the tetrahydrofuran obtained by carrying out a cyclization reaction together with the hydrogenation treatment.

14. The method for purifying crude 1,4-butanediol according to claim 13, wherein the crude 1,4-butanediol comprises 2-(4'-hydroxybutoxy)tetrahydrafuran and / or 1,4-hydroxyacetoxybutane.

15. The method for purifying crude 1,4-butanediol according to claim 13, wherein the crude 1,4-butanediol comprises methanol and / or n-propanol.

16. The method for purifying crude 1,4-butanediol according to claim 13, wherein the crude 1,4-butanediol comprises 2-methylpropanediol and / or n-propanol.

17. The method for purifying crude 1,4-butanediol according to claim 13, wherein the crude 1,4-butanediol comprises ethanol and / or n-butanol.

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