JP2010235452A - Process for producing high purity tetrahydrofuran - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide process for efficiently producing constant high purity tetrahydrofuran from a tetrahydrofuran-containing substance secondarily produced in the production of polyester. <P>SOLUTION: The process for producing the high purity tetrahydrofuran comprises purifying a tetrahydrofuran-containing substance water (B) and a 3-10C alcohol by steps comprising a step (a) of distilling the tetrahydrofuran-containing substance containing the water, the 3-10C alcohol, and tetrahydrofuran to concentrate the tetrahydrofuran, a supplying step (b) having a concentration detecting means to continuously detect the concentration of the tetrahydrofuran-containing substance to be supplied to the concentration step, a flow rate controlling means to control the flow rate of the tetrahydrofuran-containing substance to be supplied to the concentration step according to the result of detection, and a means to supply the controlled amount of the tetrahydrofuran to the concentration step, a step (c) of dehydrating the concentrated solution of the tetrahydrofuran-containing substance by adsorption with the use of an adsorbent, and a step (d) of distilling the tetrahydrofuran-containing substance dehydrated by adsorption to remove impurities. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing high purity tetrahydrofuran. The present invention particularly relates to a method for producing high-purity tetrahydrofuran, in which tetrahydrofuran by-produced in an esterification reaction using 1,4-butanediol as a raw material is easily recovered as high-purity tetrahydrofuran.

  Since polybutylene terephthalate (hereinafter referred to as PBT) has excellent physical and chemical properties, it is widely used in various applications such as fibers, films, and other molded articles. In addition, since it is excellent in mechanical properties such as strength and elastic modulus, heat resistance and the like, it is widely used particularly as an engineering plastic.

  As one of the methods for producing such PBT, an esterification step for obtaining bishydroxybutyl terephthalate and its low polymer by an esterification reaction of terephthalic acid and 1,4-butanediol, and bishydroxybutyl terephthalate and its low polymer In general, the reaction is carried out in two stages: a reaction for obtaining a high degree of polymerization PBT while distilling excess 1,4-butanediol under high temperature and high vacuum, a so-called polycondensation process. When PBT is obtained by this method, tetrahydrofuran is by-produced and distilled by dehydration cyclization reaction of 1,4-butanediol used as a raw material in the esterification step. The main components of the distillate from the esterification step are water generated during the esterification reaction and when 1,4-butanediol is converted to tetrahydrofuran by dehydration cyclization reaction and the aforementioned tetrahydrofuran, and the tetrahydrofuran concentration is the ester concentration. The tetrahydrofuran content is usually 50% by weight or less, although it is affected by the crystallization conditions.

  Tetrahydrofuran is widely used as a reaction solvent, an extraction solvent, and a general solvent because it has a high solubility in polymer compounds such as vinyl chloride resin, polyurethane resin, and vinylidene chloride resin and has a low boiling point. In recent years, tetrahydrofuran has been used as a raw material for producing polyoxytetramethylene glycol (hereinafter referred to as PTMG) obtained by ring-opening polymerization using a Lewis acid or a protonic acid as a catalyst, and is an extremely useful substance. In addition to water and tetrahydrane, the distillate contains alcohol compounds, aldehyde compounds, dihydrofuran compounds, and the like. As a method for removing these water, alcohol compounds and aldehyde compounds, Patent Document 1 discloses. There has been proposed a method in which a mixture of tetrahydrofuran and water is distilled, and then water is removed from the distillate mixture by a molecular sieve adsorption / desorption method, and further, tetrahydrofuran content is distilled to remove impurities. Patent Document 2 proposes a method of supplying a moisture content and a steam supply amount of a raw material steam to be supplied to a dehydration process using a molecular sieve.

  However, in the above method, when the raw material supply amount supplied to the primary concentration step is constantly supplied, the amount of tetrahydrofuran varies when the tetrahydrofuran concentration varies depending on the esterification conditions. There arises a problem that the amount of steam supplied to the dewatering process by the sieve fluctuates accordingly. To solve this problem, supply the raw material vapor supplied to the dehydration process using molecular sieves after condensing the primary concentrated tetrahydrofuran and water mixed vapor, storing the condensed distillate in a tank, and evaporating it with an evaporator. Although the amount can be adjusted to be constant, such a method has a problem that it consumes a lot of energy and is not economical because it requires a storage tank for distillate. Also, if the tetrahydrofuran concentration of the tetrahydrofuran and water collected by distillation from the esterification process varies depending on the esterification conditions, the tetrahydrofuran concentration is sampled manually in a tank where the distillate is temporarily stored and the tetrahydrofuran concentration is manually analyzed. The amount of tetrahydrofuran supplied to the primary concentration step can be adjusted according to the result, but such a method is complicated and cannot be continuously analyzed, resulting in an unstable problem.

Japanese Patent Application Laid-Open No. 2004-277412 JP 2000-334257 A

  An object of the present invention is to provide a method for purifying tetrahydrofuran capable of stably producing tetrahydrofuran having a certain high purity without changing the purity of tetrahydrofuran in the step of purifying a tetrahydrofuran-containing product by an adsorption method using molecular sieves. Is to provide.

  As a result of intensive studies to solve the above problems, the present inventors measured the tetrahydrofuran concentration in the tetrahydrofuran-containing material in the transfer line when feeding the tetrahydrofuran-containing material to the concentration step, and fed back to the transfer line. As a result, the amount of tetrahydrofuran supplied to the concentration step can be adjusted arbitrarily, and the amount of tetrahydrofuran content supplied to the adsorption and dehydration step using molecular sieves can be adjusted without changing the amount of tetrahydrofuran contained in the product. It has been found that this can be done, and has led to the present invention.

That is, the gist of the present invention is as follows.
(1) A method for producing high-purity tetrahydrofuran, in which a tetrahydrofuran-containing product containing water and an alcohol having 3 to 10 carbon atoms is purified by a process including the following (a) to (d).
(A) A step of distilling a tetrahydrofuran-containing material containing water, an alcohol having 3 to 10 carbon atoms and tetrahydrofuran to primarily concentrate the tetrahydrofuran.
(B) Concentration detection means for continuously detecting the concentration of the tetrahydrofuran-containing material supplied to the concentration step, a flow rate control means for controlling the flow rate of the tetrahydrofuran-containing material supplied to the primary concentration step based on the detection result, and a controlled amount A supply step having means for supplying the tetrahydrofuran of the product to the concentration step.
(C) A step of adsorbing and dehydrating a concentrated solution containing tetrahydrofuran using an adsorbent.
(D) A step of distilling the adsorbed and dehydrated tetrahydrofuran-containing material to remove impurities.

The present invention also provides:
(2) The method for producing high-purity tetrahydrofuran according to (1), wherein the concentration detection means and the flow rate control means are simultaneously performed,
(3) The above-mentioned tetrahydrofuran-containing material is esterified with a dicarboxylic acid containing terephthalic acid as a main component and a diol containing 1,4-butanediol as a main component, and then subjected to a polycondensation reaction to produce a polyester. This is a process for producing high-purity tetrahydrofuran according to (1) or (2), which is a distillate produced during the esterification reaction.

  According to the present invention, it is possible to provide a method for efficiently purifying tetrahydrofuran without changing the purity of the purified tetrahydrofuran. In addition, the process capability can be maximized and high-purity tetrahydrofuran can be produced with the optimum supply amount.

An example of the schematic of the tetrahydrofuran manufacturing apparatus in this invention.

  Hereinafter, the present invention will be described in detail.

  In the method for producing high purity tetrahydrofuran of the present invention, the tetrahydrofuran-containing material contains tetrahydrofuran, water, and an alcohol having 3 to 10 carbon atoms. In the method for producing high-purity tetrahydrofuran of the present invention, the tetrahydrofuran-containing product may further contain an aldehyde composed of at least one selected from isobutyraldehyde or n-butyraldehyde.

  In the present invention, the usual composition ratio in the tetrahydrofuran-containing material is preferably 2 to 50% by weight, more preferably 5 to 45% by weight, still more preferably 10 to 10% by weight of tetrahydrofuran (A) in the entire tetrahydrofuran-containing material. 40% by weight, preferably water (B) is 98-50% by weight, more preferably 55-95% by weight, even more preferably 60-90% by weight, preferably (A) + (B ) Is 90 to 99.7% by weight, more preferably 92 to 99.5% by weight.

  In the present invention, the tetrahydrofuran-containing material is preferably 0.3 to 5.0 parts by weight, more preferably 0.5 to 4.0 parts by weight, of an alcohol having 3 to 10 carbon atoms with respect to 100 parts by weight of tetrahydrofuran. Part. Moreover, when it contains an aldehyde, Preferably it is 0.005-0.1 weight part with respect to 100 weight part of tetrahydrofuran, More preferably, 0.007-0.08 weight part is contained.

  The tetrahydrofuran-containing material preferably used in the present invention is obtained by esterifying a dicarboxylic acid containing terephthalic acid as a main component and a diol containing 1,4-butanediol as a main component, and then subjecting it to a polycondensation reaction. In the production of the product, a distillate containing tetrahydrofuran produced during the esterification reaction is included.

  The raw material for polybutylene terephthalate is preferably a dicarboxylic acid mainly composed of terephthalic acid and a diol component mainly composed of 1,4-butanediol. The terephthalic acid preferably accounts for 50 mol% or more of the total dicarboxylic acid component, more preferably 60 mol% or more, and even more preferably 70% or more. The 1,4-butanediol preferably accounts for 50 mol% or more of the total diol component, more preferably 60 mol% or more, and even more preferably 70% or more.

  The tetrahydrofuran-containing material preferably used in the present invention is a dicarboxylic acid component other than terephthalic acid, specifically, an aromatic dicarboxylic acid such as isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, sodium sulfoisophthalic acid, etc. Alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid and decalin dicarboxylic acid, and aliphatic dicarboxylic acids such as malonic acid, succinic acid, sebacic acid, adipic acid, and dodecanedioic acid.

  Further, the tetrahydrofuran-containing material preferably used in the present invention is, as a diol component other than 1,4-butanediol, specifically, for example, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, neopentyl. Aliphatic diols such as glycol, 1,6-hexanediol, polypropylene glycol and polytetramethylene glycol, alicyclic diols such as 1,4-cyclohexanediol and 1,4-cyclohexanedimethanol, 2,2-bis (4 And aromatic diols such as' -hydroxyphenyl) propane.

  Further, the tetrahydrofuran-containing material preferably used in the present invention includes, for example, glycolic acid, m-hydroxybenzoic acid, p-hydroxybenzoic acid, hydroxycarboxylic acid such as 6-hydroxy-2-naphthalenedicarboxylic acid, and benzyl alcohol. 1, monofunctional components such as benzoic acid and t-butylbenzoic acid, trifunctional or higher polyfunctional components such as glycerin, trimethylolpropane, pentaerythritol, trimellitic acid, trimesic acid, pyromellitic acid, tricarbalic acid, etc. Two or more species may be used as copolymerization components.

  As for the ratio of these raw materials, it is preferable to use an excess amount of butanediol relative to terephthalic acid, and specifically, it is preferable to use 1.1 to 3.0 times mol of terephthalic acid. It is particularly preferred to use 1 to 2.5 moles of 1,4 butanediol.

The method for producing high-purity tetrahydrofuran of the present invention is to obtain high-purity tetrahydrofuran by sequentially subjecting the tetrahydrofuran-containing material to the following steps (a), (b), (c), and (d).
(A) A step of distilling a tetrahydrofuran-containing material containing water, an alcohol having 3 to 10 carbon atoms and tetrahydrofuran to primarily concentrate the tetrahydrofuran.
(B) Concentration detection means for continuously detecting the concentration of the tetrahydrofuran-containing material supplied to the concentration step, a flow rate control means for controlling the flow rate of the tetrahydrofuran-containing material supplied to the concentration step according to the detection result, and a controlled amount A supply step having means for supplying tetrahydrofuran to the concentration step.
(C) A step of adsorbing and dehydrating a concentrated solution containing tetrahydrofuran using an adsorbent.
(D) A step of distilling the adsorbed and dehydrated tetrahydrofuran-containing material to remove impurities.

  In the present invention, the tetrahydrofuran-containing product refers to a product before purification, and purified tetrahydrofuran refers to tetrahydrofuran after purification.

  In the method for producing high-purity tetrahydrofuran of the present invention, first, in the step (a), a tetrahydrofuran-containing material containing water, an alcohol having 3 to 10 carbon atoms and tetrahydrofuran is distilled to concentrate the tetrahydrofuran.

  In the step (a), preferably, a mixture of tetrahydrofuran and water is distilled by distillation to remove most of the water (B) and alcohol having 3 to 10 carbon atoms. The distillation can preferably be performed at room temperature. The distillation pressure is preferably 53 kPa to 304 kPa, more preferably 67 kPa to 203 kPa. If the pressure is 53 kPa or less, low-temperature cooling water is required to condense the distillate mixture, and the equipment becomes complicated, and if it exceeds 304 kPa, the water in the distillate increases and the load on the next step Is unfavorable because of the increase. The reflux ratio is preferably 0.1 to 5, and more preferably 0.2 to 2. If it is less than 0.1, the alcohol having 3 to 1 carbon atoms in the distillate may not be 0.3 weight or less with respect to 100 parts by weight of tetrahydrofuran, and if it exceeds 5, it requires a lot of energy. Therefore, it is not preferable.

  The distillation method may be a distillation batch type or a continuous type, but a continuous type is preferably used from the viewpoint of efficiency.

  As a specific example in the case of using continuous distillation, a tetrahydrofuran-containing material is continuously supplied to a distillation column, and most of water and a part of tetrahydrofuran and alcohol having 3 to 10 carbon atoms are continuously supplied from the bottom of the column. The method of taking out and continuously distilling a tetrahydrofuran-water mixture from the tower top is mentioned.

  The number of theoretical plates of the distillation column is preferably 3 to 30, and more preferably 5 to 20. When the number of theoretical plates is 3 to 30, purification is sufficient, impurities in the tetrahydrofuran-containing material can be sufficiently separated, and it is efficient. The reason for this is presumed to be that bubbles are formed in the distillation column because the tetrahydrofuran-containing material contains a large amount of water and an alcohol component having 3 to 10 carbon atoms.

  Thus, in the step (a), the distilled tetrahydrofuran-containing material is mixed with an alcohol having 3 to 10 carbon atoms in the tetrahydrofuran-water mixture, and the amount of the mixture is preferably 100 parts by weight of tetrahydrofuran (A). 0.3 parts by weight or less. The mixing amount of the alcohol having 3 to 10 carbon atoms is more preferably 0.2 parts by weight or less, and even more preferably 0.15 parts by weight or less, thereby further reducing the impurity concentration in the purified product finally obtained. can do.

  Examples of the alcohol having 3 to 10 carbon atoms include alkyl alcohol and aralkyl alcohol. Specific examples include n-propanol, isopropanol, n-butanol, octyl alcohol, and benzyl alcohol.

  In the step (a), the amount of water present in the distilled tetrahydrofuran-containing product is usually 3 to 15% by weight based on the entire distillate mixture, although it varies depending on the distillation conditions. The amount of water present in the distilled tetrahydrofuran-containing material is preferably 4 to 12% by weight.

  In the method for producing high-purity tetrahydrofuran of the present invention, the step (b) includes concentration detecting means for continuously detecting the concentration of the tetrahydrofuran-containing material supplied to the concentration step, and the tetrahydrofuran-containing material supplied to the concentration step based on the detection result. A flow rate control means for controlling the flow rate of the liquid and a means for supplying a controlled amount of tetrahydrofuran to the concentration step.

  The step (b) of the present invention is preferably a concentration detection means for continuously detecting the concentration of the tetrahydrofuran-containing material obtained in the polyester production process, and the flow rate of the tetrahydrofuran-containing material supplied to the concentration step based on the detection result. A supply step having a flow rate control means for controlling and a means for supplying a controlled amount of tetrahydrofuran to the concentration step. More preferably, the tetrahydrofuran-containing material obtained in the production process of the polyester is once stored in a tank, and the liquid of the tetrahydrofuran-containing material is circulated by a pump, and a part thereof is supplied to the step (a). Circulation by the pump is not particularly limited and may be only supplied to the process (a), but is preferably circulated.

  The concentration detection means used in the present invention is preferably an on-line type analyzer that does not inhibit the flow of the tetrahydrofuran-containing material. Commonly known analyzers include gas chromatography, ultrasonic analyzers, density meters, and Coriolis mass flow meters, but as online analyzers installed in plants, density and flow can be measured simultaneously. A Coriolis mass flow meter is particularly preferred. Such concentration detecting means is preferably installed in the transfer line of the tetrahydrofuran-containing material, but a side pipe branched into the transfer line is provided, a detector is installed in this side pipe, and the tetrahydrofuran flowing through the side pipe The content of may be analyzed. Note that the object can be achieved even if a sample collected from the transfer line is analyzed with a detection tube at another location.

  As the flow rate control means for controlling the flow rate of the tetrahydrofuran-containing material supplied to the concentration step, a valve is preferable, and as the valve for controlling the flow rate, a globe, a butterfly valve, and a ball valve are more preferable. In order to control the flow rate with high accuracy, a globe valve is particularly preferable. The flow rate control means includes manual control and automatic control, but automatic control is preferably used from the viewpoint of efficiency.

  As a means for supplying a controlled amount of tetrahydrofuran to the concentration step, a pump is preferable, and a liquid containing tetrahydrofuran may be circulated by the pump and a part thereof may be supplied to step (a).

  In the step (b) of the present invention, it is preferable that the concentration detection means and the flow rate control means are simultaneously performed. In the present invention, the simultaneous execution of the concentration detection means and the flow rate control means means that the information detected by the concentration detection means is transmitted to the flow rate control means, and the concentration detection and the flow rate control are mutually controlled.

  In the method for producing high-purity tetrahydrofuran of the present invention, as a step (c), a concentrated solution containing tetrahydrofuran is adsorbed and dehydrated using an adsorbent.

  In the method for producing high purity tetrahydrofuran of the present invention, as the adsorbent used in step (c), specifically, for example, silica gel, activated alumina, molecular sieve (synthetic and natural zeolite, carbon molecular sieve, etc.), ion, etc. Examples thereof include exchange resins, sulfate anhydrides, carbonate anhydrides, activated carbon, and starch. In the present invention, it is preferable to use a molecular sieve as the adsorbent, and any commercially available granular molecular sieve such as naturally produced zeolite, synthetic zeolite, carbon molecular sieve or the like can be suitably used. The shape of the granular molecular sieve may be any of a spherical shape, a cylindrical shape, a pellet shape, a crushed shape, a granular shape, and the like, and any one having a size in the range of 30 to 3 mesh can be used. Among these, it is particularly preferable to use a granular molecular sieve having an average pore diameter of 0.2 to 0.5 nm, and in particular, a granular zeolite 3A, zeolite 4A, zeolite 5A or NSC-4 carbon molecular sieve. Is preferably used.

  In the present invention, these adsorbents may be used alone or in admixture of two or more.

  A more preferred adsorption method using molecular sieves used in the present invention is described below.

  As a specific example of the adsorption method using molecular sieves, the distillation mixture obtained in the step (b) is used in an apparatus equipped with at least two adsorption towers, and (I) one of the organic compounds containing water is used as a vapor. An adsorption step in which water is adsorbed to the adsorption / desorption tower and adsorbed by the adsorbent; (II) in the other adsorption tower in which the adsorbent absorbs the moisture; A part of the organic vapor is supplied as a purge gas, desorbs moisture adsorbed on the adsorbent, and then performs a desorption / pressurization step in which the inside of the adsorption / desorption tower is pressurized to the adsorption step pressure with the purge gas, Pressure swing adsorption method that operates by switching between adsorption process and desorption / pressurization process. (A) Continuously supply to the adsorption / desorption column depressurized from the step, and continuously remove 0.05 parts by weight or less of water (B) from 100 parts by weight of tetrahydrofuran (A) from the top of the tower. (D) The mixture is supplied to the step, and a tetrahydrofuran-water mixture is continuously distilled from the bottom of the column, and returned to the step (b) again.

  In the method for producing high-purity tetrahydrofuran of the present invention, a pressure swing adsorption method is preferably used as step (c). The pressure swing adsorption method can be either a batch method or a continuous method, but a continuous method is preferably used from the viewpoint of efficiency.

  In the method for producing high purity tetrahydrofuran of the present invention, as the step (c), the adsorption pressure is preferably 100 to 300 kPa, and the desorption pressure is preferably 1 to 50 kPa. Further, the temperature of the steam introduced into the adsorption step is preferably 40 to 200 ° C., and the water content is desirably 20% by weight or less, particularly preferably 10% by weight or less. The amount of purge gas is preferably 5 to 50%, more preferably 25 to 40%, of the amount of tetrahydrofuran supplied to the step (a). In the dehydration method, an inert gas may be supplied as the purge gas instead of supplying a part of the vapor obtained in the adsorption process. The inert gas is preferably at least one selected from the group consisting of nitrogen, carbon dioxide, hydrogen, methane, argon, and helium, and the purge gas is an inert gas and a part of the vapor obtained in the adsorption step. It is preferable to consist of.

  In the present invention, in the step (c), preferably, the distillate mixture obtained in the step (a) is subjected to the step (c), and then the water of the distillate mixture obtained is reduced to 100 parts by weight of tetrahydrofuran. 0.05 parts by weight or less, more preferably 0.03 parts by weight or less, and even more preferably 0.01 parts by weight or less of water with respect to 100 parts by weight of tetrahydrofuran (A).

  In the method for producing high-purity tetrahydrofuran according to the present invention, as the step (d), the tetrahydrofuran-containing material that has been adsorbed and dehydrated is distilled to remove impurities.

  Impurities are generally organic impurities, and more specifically, alcohols having 3 to 10 carbon atoms, aldehydes, propionaldehyde, dihydrofuran, methacrolein, methyltetrahydrofuran and the like of the present invention can be mentioned.

  In the step (d), the distillation method can be either a batch method or a continuous method, but a continuous method is preferably used from the viewpoint of efficiency.

  In the step (d), the distillation apparatus is preferably a distillation column. One or more distillation towers can be used, but when using a plurality of towers, it is preferable to use two towers in terms of equipment cost. In this case, the first tower removes low boiling impurities from the top of the tower. In the second column, it is more preferable to remove high boiling impurities from the bottom of the column and obtain the desired distillate from the top of the column. In the case of carrying out in one column, a method of removing low boiling and high boiling impurities in one column is preferred. Low boiling impurities are extracted from the column top and high boiling impurities are extracted from the column bottom, and the target distillate is removed from the middle column of the distillation column. It is preferable to obtain.

  In the step (d), the number of theoretical plates of the distillation column is preferably 20 to 60, more preferably 30 to 50. When the number of theoretical plates is 20 to 60, the organic impurities can be sufficiently separated and the purified tetrahydrofuran targeted by the present invention can be obtained, and the equipment is not expensive.

  In the step (d), the pressure of the distillation tower is preferably 53 kPa to 304 kPa, more preferably 67 kPa to 203 kPa. If the pressure is 53 kPa to 304 kPa, low-temperature cooling water is not required to condense the distillate containing the tetrahydrofuran as a main component, so that the facility is not complicated and the temperature during distillation is not increased. No new impurities are generated due to the reaction. About the reflux ratio of a distillation column, 5-100 are used preferably and 10-60 are more preferable.

  In the method for producing high-purity tetrahydrofuran of the present invention, after passing through step (d), the distillate obtained is preferably 0.01 parts by weight or less of water and aldehyde (D) with respect to 100 parts by weight of tetrahydrofuran. Is 0.005 part by weight or less.

  The purified tetrahydrofuran obtained by the method for producing high-purity tetrahydrofuran of the present invention preferably has 0.01 parts by weight or less of water and 0.005 parts by weight or less of aldehyde with respect to 100 parts by weight of tetrahydrofuran. As for the form, water is 0.005 part by weight or less, aldehyde is 0.003 part by weight or less with respect to 100 parts by weight of tetrahydrofuran, and as a still more preferred form, water is 0.003 part by weight or less with respect to 100 parts by weight of tetrahydrofuran. The aldehyde is 0.002 parts by weight or less.

  When water exceeds 0.01 part by weight or aldehyde exceeds 0.005 part by weight with respect to 100 parts by weight of tetrahydrofuran, it is not preferable because it is colored when used as a raw material for PTMG (polytetramethylene ether glycol). Further, impurities other than the above, specifically, propionaldehyde, dihydrofuran, and methacrolein are also preferably 0.003 parts by weight or less, and 0.002 parts by weight or less with respect to 100 parts by weight of tetrahydrofuran. Is more preferable.

  In the present invention, the amount of water can be determined by measuring the amount of water using a Karl Fischer moisture meter and determining the content ratio relative to the sample.

For each organic substance including tetrahydrofuran, a capillary gas chromatograph is used to determine the content ratio of each component from the peak area corresponding to each component (X%), and the water concentration determined in (1) (W%). Based on the above, the content is obtained by correcting with the following formula (Y%). The content with respect to tetrahydrofuran is obtained by dividing the target organic content by the content of tetrahydrofuran.
Y (%) = (100−W) / 100 × X (%)

  In the method for producing high purity tetrahydrofuran of the present invention, high purity tetrahydrofuran can be produced. The composition of the obtained purified tetrahydrofuran is, for example, 0.05 parts by weight or less of water with respect to 100 parts by weight of tetrahydrofuran, 0.003 parts by weight or less of alcohol having 3 to 10 carbon atoms, 0.002 parts by weight or less of purified tetrahydrofuran can be obtained.

  Next, an esterification reaction and a polycondensation reaction method for producing polybutylene terephthalate will be described.

In the present invention, in order to effectively advance the esterification reaction and polycondensation reaction for producing polybutylene terephthalate, it is preferable to add a catalyst during these reactions, and the catalyst preferably used is an organic titanium compound. And a compound represented by the following formula is preferably used.
(R ₁ -O) ₄ Ti
Here, R ₁ represents a hydrocarbon group having 3 to 10 carbon atoms.

  Specific examples of catalysts preferably used include tetra-n-propyl ester, tetraisopropyl ester, tetra-n-butyl ester, tetraisobutyl ester, tetra-tert-butyl ester, tetra-2ethylhexyl ester, tetraoctyl of titanic acid. Examples include esters, tetrastearyl esters, and mixed esters thereof. Among these, tetra-n-propyl ester, tetraisopropyl ester, and tetra-n-butyl ester of titanic acid are preferable, and tetra-n-butyl titanate is preferable. Esters are particularly preferably used.

  These organic titanium compounds may use only 1 type and can use 2 or more types together. Further, the same species may be used during the esterification reaction and polycondensation, or different organic titanium compounds may be used. Further, this organic titanium compound may be added together with a suitable organic solvent. Examples of the organic solvent in this case include isopropanol, n-butanol, isobutanol, ethylene glycol, propylene glycol, and 1,4-butanediol. In consideration of the influence on quality, etc., 1,4-butanediol is preferable. Used.

  The amount of the organic titanium compound added is preferably 0.005 parts by weight or more and 0.5 parts by weight or less, particularly in the range of 0.01 parts by weight or more and 0.2 parts by weight or less with respect to 100 parts by weight of the produced polyester. Is preferred.

  There is no particular limitation on the timing of addition of the organic titanium compound as long as at least a part of the organic titanium compound is present at the time of esterification. Even if it is added all at once before the esterification reaction, it is partially added before the esterification reaction. , The remainder may be added in divided steps at any stage until the end of the polycondensation reaction.

  In the esterification and polycondensation reaction, a catalyst other than the organic titanium compound can be used separately to effectively advance the reaction. For example, antimony compounds such as antimony trioxide and antimony acetate, zirconium tetra n- Zirconia compounds such as butoxy and tin compounds may be used, and the use of tin compounds is particularly preferable.

  Specific examples include dibutyltin oxide, methylphenyltin oxide, tetraethyltin, hexaethylditin oxide, cyclohexahexylditin oxide, didodecyltin oxide, triethyltin hydroxide, triphenyltin hydroxide, triisobutyltin acetate. , Dibutyltin diacetate, diphenyltin dilaurate, monobutyltin trichloride, dibutyltin dichloride, tributyltin chloride, dibutyltin sulfide, butylhydroxytin oxide, and the like. Of these, a monoalkyltin oxide compound is particularly preferably used. Only 1 type may be used for catalysts other than said organic titanium compound, and 2 or more types can also be used together. Moreover, it is preferable to add the addition amount of catalysts other than the said organic titanium compound in 0.01 to 0.2 weight part with respect to 100 weight part of polyester to produce | generate.

  The production method of polybutylene terephthalate may be a batch method or a continuous method, and the esterification conditions used for normal polyester production can be applied as they are. The esterification reaction is preferably performed at a reaction temperature of 180 to 250 ° C, more preferably 200 to 240 ° C, and the pressure is preferably 6.7 kPa to 101.3 kPa, and 13.3 kPa to 93.3 kPa. More preferably, it is carried out under reduced pressure. Further, the reaction rate of the PBT oligomer after the total esterification reaction is preferably 97% or more, and more preferably 98% or more. Moreover, a known apparatus can be used as the esterification reaction apparatus. As the esterification reaction tank, for example, a stirring type vertical complete mixing tank, a heat convection type vertical mixing tank, a tower type continuous reaction tank, etc. Alternatively, two or more of the same type or different types of tanks can be used in series. Further, a tetrahydrofuran-containing product mainly composed of water and by-product tetrahydrofuran generated by the esterification reaction can be distilled from the top of a rectification column connected to the esterification reaction tank.

The PBT oligomer produced by the esterification reaction is transferred to a polycondensation reaction tank, and preferably polycondensed at a reduced pressure of 230 to 260 ° C., more preferably 240 to 255 ° C., preferably 13.3 Pa to 13.3 kPa. Reaction takes place. In addition, as the polycondensation reaction tank, for example, one stirring type vertical polymerization tank, stirring type horizontal polymerization tank, thin film evaporation type polymerization tank or the like is used, or two or more of the same or different types are used in series. be able to. Further, the finally obtained PBT polymer is pelletized in a granulation step or the like, and further increased in molecular weight by solid phase polymerization as necessary.

  In the method for producing high-purity tetrahydrofuran according to the present invention, the tetrahydrofuran-containing material is preferably obtained by subjecting a dicarboxylic acid containing terephthalic acid as a main component and a diol containing 1,4-butanediol as a main component to an esterification reaction. Next, it is a distillate produced during the esterification reaction when a polyester is produced by a polycondensation reaction.

  The present invention will be described more specifically with reference to the following examples. In addition, the analysis in an Example was performed in accordance with the following method.

(1) Amount of water in tetrahydrofuran-containing material For a tetrahydrofuran-containing material containing 1% or more of water, about 10 to 100 μl of the sample (depending on the water content in the sample) is precisely weighed, and then a volumetric titration type Karl Fischer moisture meter The amount (μg) of water was measured using (manufactured by Hiranuma Sangyo Co., Ltd.), and was calculated as a weight percentage with respect to the sample. For tetrahydrofuran-containing products or purified tetrahydrofuran containing less than 1% by weight of water, weigh about 0.1 to 1 ml of the sample (depending on the water content in the sample), and then use a coulometric titration Karl Fischer moisture meter (Mitsubishi Chemical). The amount of water (μg) was measured using a product manufactured by (Co., Ltd.), and the weight% relative to the sample was calculated. In addition, when calculating | requiring the weight part with respect to 100 weight part of tetrahydrofuran (A), it calculated | required based on the quantity of tetrahydrofuran (A) calculated | required by the following term.

(2) Organic content of tetrahydrofuran-containing material Using a capillary type gas chromatograph (manufactured by Shimadzu Corporation) with Ultra-1 (cross-linked methylsiloxane type) as a column, each component has a peak area corresponding to each component. The content ratio was determined (X%), and the content was determined (Y%) by correcting with the following formula based on the water concentration (W%) determined in (1). In addition, when calculating | requiring the weight part with respect to 100 weight part of tetrahydrofuran, it calculated | required based on the quantity of tetrahydrofuran.
Y (%) = (100−W) / 100 × X (%)

Example 1
754 parts by weight of terephthalic acid / hour and 692 parts by weight of 1,4-butanediol as raw materials and 0.05 part by weight of tetrabutyl titanate as a catalyst are continuously fed to an esterification reaction tank equipped with a rectifying column and a stirrer. After esterification, polybutylene terephthalate was obtained for the polycondensation reaction step. Water and tetrahydrofuran generated in the esterification reaction tank were distilled off through a rectifying column to obtain a tetrahydrofuran-containing material.

  FIG. 1 shows a schematic diagram of the apparatus used in Example 1.

  The above-mentioned tetrahydrofuran-containing material is supplied from a conduit 3 to a distillation column 5 (first distillation column) having 10 theoretical plates, and the density is measured using a micro motion flow meter ELITE (manufactured by Emerson) as an analyzer 4. Was reflected in the tetrahydrofuran concentration, and the tetrahydrofuran concentration was continuously and automatically calculated. From the measurement results, the supply amount was automatically controlled online with a globe valve so that the amount of tetrahydrofuran supplied to the first distillation column was 1200 parts by weight / hour, and distilled at normal pressure, at a column bottom temperature of 110 ° C., and at a reflux ratio of 1. Then, water, some tetrahydrofuran and a part of n-butanol were distilled from the tower bottom 6. Distilled mixed steam was obtained from the top of the column.

  The distillate mixed vapor was supplied via a conduit 7 to an adsorption tower 8 (adsorption tower) filled with a molecular sieve that selectively adsorbs water. Although the adsorption tower 8 has two adsorption towers, one adsorption tower has a pressure of 0.15 MPa and a tower top temperature of 120 ° C., supplies distilled mixed vapor from the conduit 7, adsorbs water by molecular sieves, Tetrahydrofuran vapor dehydrated was obtained from the top of the column (adsorption process).

  A part of this vapor is returned to another adsorption tower having a pressure of 70 kPa to desorb water adsorbed on the molecular sieve (desorption process), and the desorbed liquid containing tetrahydrofuran, water and the like passes through the conduit 9 from the bottom of the adsorption tower through the conduit 9. It returned to the content storage tank 2. Vapor composed mainly of tetrohydrofuran that was dehydrated continuously was obtained by switching the adsorption column between the adsorption step and the desorption step between the two adsorption columns using front and rear valves.

  This steam is supplied to a distillation column 11 (second distillation column) having a theoretical plate number of 20 through a conduit 10, and distilled at normal pressure, a column bottom temperature of 70 ° C., and a reflux ratio of 50 to obtain isobutyraldehyde, propionaldehyde, dihydro Tetrahydrofuran-containing material containing a large amount of furan was extracted from the conduit 12 and supplied from the bottom of the column via the conduit 13 to the distillation column 14 (third distillation column). The distillation column 14 is distilled at a theoretical plate number of 35, normal pressure, a column bottom temperature of 70 ° C., and a reflux ratio of 10. A tetrahydrofuran-containing material containing a large amount of n-butyraldehyde and n-butanol is extracted from the column bottom through a conduit 16, 800 parts by weight of purified tetrahydrofuran / hour was obtained from the top via conduit 15. The amount of water in the purified tetrahydrofuran was 30 ± 3 ppm.

Examples 2-7
Tetrahydrofuran was purified in the same manner as in Example 1. Table 1 shows the operating conditions and the amount of purified tetrahydrofuran extracted and the amount of water.

Comparative Example 1
Example 1 except that the tetrahydrofuran-containing material to be supplied to the distillation column 5 (first distillation column) was withdrawn every 6 hours without performing online control, the tetrahydrofuran concentration was measured, and the amount of tetrahydrofuran supplied was manually controlled. The same conditions were used. The amount of water in the purified tetrahydrofuran was 60 ± 20 ppm.

Comparative Example 2
It performed on the same conditions as Example 1 except having performed constant supply amount of the tetrahydrofuran containing material supplied to the distillation column 5 (1st distillation column), without performing online control. The amount of water in the purified tetrahydrofuran was 120 ± 50 ppm.

  Tetrahydrofuran purified by this purification method has a certain high purity without changing its purity, and is excellent in quality, so it is useful as a raw material for reaction solvents, extraction solvents, general solvents and elastic fibers. Can do.

DESCRIPTION OF SYMBOLS 1 Tetrahydrofuran content receiving line 2 Tetrahydrofuran content storage tank 3 Tetrahydrofuran content supply pipe 4 Analyzer 5 First distillation tower 6 Tower bottom extraction line 7 Adsorption tower supply line 8 Adsorption tower 9 Desorption liquid extraction line 10 Second distillation tower supply Line 11 Second distillation column 12 Column top extraction line 13 Third distillation column supply line 14 Third distillation column 15 Purified tetrahydrofuran extraction line 16 Column bottom extraction line

Claims (3)

A method for producing high-purity tetrahydrofuran, comprising purifying a tetrahydrofuran-containing product containing water (B) and an alcohol having 3 to 10 carbon atoms by a process comprising the following (a) to (d).
(A) A step of distilling a tetrahydrofuran-containing material containing water, an alcohol having 3 to 10 carbon atoms and tetrahydrofuran to concentrate the tetrahydrofuran.
(B) Concentration detection means for continuously detecting the concentration of the tetrahydrofuran-containing material supplied to the concentration step, a flow rate control means for controlling the flow rate of the tetrahydrofuran-containing material supplied to the concentration step according to the detection result, and a controlled amount A supply step having means for supplying tetrahydrofuran to the concentration step.
(C) A step of adsorbing and dehydrating a concentrated solution containing tetrahydrofuran using an adsorbent.
(D) A step of distilling the adsorbed and dehydrated tetrahydrofuran-containing material to remove impurities.   The method for producing high-purity tetrahydrofuran according to claim 1, wherein the concentration detection means and the flow rate control means are simultaneously performed.   When the above-mentioned tetrahydrofuran-containing material esterifies the dicarboxylic acid mainly composed of terephthalic acid and the diol mainly composed of 1,4-butanediol, and then polycondensates to produce a polyester. The method for producing high-purity tetrahydrofuran according to claim 1 or 2, wherein the product is a distillate produced during the esterification reaction.

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