JP5902985B2 - Process for producing ethylene glycols - Google Patents

Description

  The present invention relates to a method for producing ethylene glycols. More specifically, the present invention relates to a method for producing triethylene glycol and tetraethylene glycol.

  Ethylene glycols (for example, mono, di, tri, and tetraethylene glycol) are used as synthetic raw materials for solvents, antifreeze solutions, lubricants, polyesters, and the like, and are highly useful compounds. When used in these applications, ethylene glycols with high purity and low color are desired. However, ethylene glycols often contain aldehyde as a by-product in the production process, and are easily colored. was there.

  Therefore, for example, in Patent Document 1, as a method for reducing aldehydes contained in ethylene glycols, an apparatus used for obtaining ethylene glycols is partially or entirely surface-treated with a reducing phosphorus compound. A method is disclosed.

  Further, Patent Document 2 discloses a method of distilling after treating an organic solvent with sulfuric acid as a method of removing the colored substance.

JP 2000-503978 Gazette JP-A-10-218798

  However, the method described in Patent Document 1 has a problem in that the manufacturing cost increases in that the phosphorus compound is expensive and the step of adding the phosphorus compound is added separately to the manufacturing step. Further, in the method described in Patent Document 2, a step of adding sulfuric acid and distilling is added to the manufacturing process separately, a yield is generated after distillation, and a yield is reduced, and a processing cost for discarding the residue is required. In that respect, there is a problem that the manufacturing cost increases. Furthermore, the methods described in Patent Document 1 and Patent Document 2 also have a problem that high-purity and high-quality ethylene glycols cannot be obtained in the long term from the viewpoints of both aldehyde content and coloring.

  Then, this invention is made | formed in view of the said situation, and it aims at providing the method of manufacturing ethylene glycol with low aldehyde content and little coloring by an inexpensive method.

  As a result of intensive studies, the present inventors have found that the amount of precipitate deposited on the inner surface of the tube of the multi-tubular reboiler used in producing ethylene glycol is the aldehyde content and coloration of the resulting ethylene glycols. It was found to correlate with the degree. Based on such knowledge, when producing ethylene glycols using a rectifier equipped with a multi-tubular reboiler, when a predetermined amount of deposits are deposited on the inner surface of the reboiler, It was found that the above object was achieved by removing precipitates from the inner surface of the tube by physical treatment, and the present invention was completed. That is, the above object is a method for producing tri- or tetraethylene glycol using a rectifying column, a multi-tubular reboiler, and a rectifying apparatus comprising a pipe connecting them, wherein a predetermined amount of precipitates is the reboiler. This is achieved by a method for producing tri- or tetraethylene glycol, which includes a removal step of removing the precipitate by physically treating the inner surface of the reboiler tube when it is deposited on the inner surface of the tube.

  According to the present invention, a method for producing ethylene glycols (tri or tetraethylene glycol) having a low aldehyde content and little coloration is provided by an inexpensive method.

It is the schematic of the manufacturing apparatus used for manufacture of ethylene oxide. It is process schematic of the apparatus structure of ethylene glycol used for the manufacturing method which is one Embodiment of this invention.

  The present invention relates to a method for producing tri- or tetraethylene glycol using a rectifying column, a multi-tubular reboiler, and a rectifying apparatus provided with a pipe for connecting them, wherein a predetermined amount of precipitate is a pipe of the reboiler. The present invention relates to a method for producing tri- or tetraethylene glycol, which includes a removing step of removing the precipitate by physically treating the inner surface of the reboiler tube when it is deposited on the inner surface.

  According to the production method of the present invention, the precipitates are removed by physically treating the inner surface of a tube of a multi-tubular reboiler (hereinafter sometimes simply referred to as “reboiler”), whereby the aldehyde content is reduced. A low or less colored tri or tetraethylene glycol is obtained.

  In the present specification, di, tri and / or tetraethylene glycol may be referred to as “ethylene glycols”.

  Tri or tetraethylene glycol can be obtained by reacting diethylene glycol with ethylene oxide in the presence of a catalyst. At this time, an alkali metal or an alkaline earth metal is preferably used as the catalyst. Diethylene glycol, triethylene glycol, and triethylene glycol are fractionated by repeating the distillation operation on the reaction solution containing the mono- or diethylene glycol, ethylene oxide, and the catalyst. Under the present circumstances, distillation operation is performed with the rectification apparatus provided with the rectification column, the multitubular reboiler, and the piping which connects these. It was observed that precipitates derived from alkali metals or alkaline earth metals were produced in a multitubular reboiler that performs the heating operation of the reaction solution. The inventors of the present invention obtained ethylene glycols having excellent quality by causing the precipitate to cause a high aldehyde content and a high degree of coloring, and removing the precipitate by physical treatment. It has been found that. That is, the present invention is based on the first finding that precipitates adhering to the inner surface of the reboiler tube have an influence on the problems of aldehyde content and coloring, which have been problems.

  Moreover, according to the production method of the present invention, it is not necessary to perform physical treatment for at least 4 years after continuous operation only by performing physical treatment on the deposits adhering to the inner surface of the reboiler tube. For example, even in the case of continuous production, continuous production is possible for more than 4 years. During that time, physical treatment to the reboiler is not required, and excellent quality ethylene glycols continue. Obtained. Therefore, according to the manufacturing method of the present invention, it is only necessary to perform physical treatment when a predetermined amount of precipitate is deposited on the inner surface of the reboiler tube, and it is necessary to add a physical treatment process to the manufacturing process. Absent. That is, according to the production method of the present invention, it is possible to obtain ethylene glycols of excellent quality by a simple method with reduced production costs.

  Hereinafter, the manufacturing method of ethylene glycol of this embodiment is demonstrated in order.

  Monoethylene glycol, which is a raw material for tri- and tetraethylene glycol, is produced by a hydrolysis reaction of ethylene oxide. In general, an ethylene oxide production plant and an ethylene glycol (mono, di, tri, and tetraethylene glycol) production plant are provided side by side. Regarding these processes, for example, “Chemical Process” edited by Chemical Engineering Society, pages 121 to 128, 9. It is described in ethylene oxide and ethylene glycol (Tokyo Kagaku Dojin, published on March 25, 1998).

  An example of an ethylene oxide / ethylene glycol production process is shown in FIG. As shown in FIG. 1, a product gas obtained by vapor-phase oxidation of ethylene with molecular oxygen in the presence of a silver-based catalyst is led to an ethylene oxide absorption tower and contacted with an aqueous medium absorption liquid (for example, water). Absorption treatment is performed to obtain an aqueous ethylene oxide solution as the bottom liquid. In the ethylene oxide aqueous solution, a low molecular weight polymer of ethylene oxide, ethylene glycol which is a reaction product of ethylene oxide and water (in this case, a small amount of diethylene glycol and triethylene glycol are also generated in addition to monoethylene glycol), and Reaction products of ethylene oxide and impurities are included. The ethylene oxide aqueous solution is guided to an ethylene oxide stripping tower, and the bottom of the ethylene oxide stripping tower is heated with heated steam to dissipate ethylene oxide from the aqueous solution. From the top of the stripping tower, stripped steam containing ethylene oxide is obtained. The stripped steam contains low boiling point impurities such as formaldehyde and high boiling point impurities such as acetaldehyde and acetic acid in addition to ethylene oxide, water, carbon dioxide, inert gas (nitrogen, argon, methane, ethane, etc.). However, purified ethylene oxide is obtained through each of the dehydration step, the light component separation step, and the heavy component separation step. And the aqueous solution substantially free of ethylene oxide obtained from the bottom of the ethylene oxide diffusion tower is circulated and used as an absorption liquid supplied to the ethylene oxide absorption tower.

  Ethylene glycol is obtained by concentrating and dehydrating the aqueous solution after separating ethylene oxide (that is, an aqueous solution substantially free of ethylene oxide). Hereinafter, the aqueous solution after separation of ethylene oxide is referred to as “crude glycol (1)”. The crude glycol (1) is a composition containing monoethylene glycol as a main component and containing diethylene glycol and triethylene glycol. The crude glycol (1) also contains impurities contained in the aqueous ethylene oxide solution.

  In order to fractionate monoethylene glycol from the crude glycol (1), the crude glycol (1) is sent to a monoethyl glycol (MEG) fractionator. The crude glycol (1) sent to the rectifying tower is distilled under reduced pressure and fractionated into monoethylene glycol having a low boiling point and diethylene glycol having a high boiling point. The monoethylene glycol vapor distilled from the top of the rectifying column is converted into monoethylene glycol that has been condensed and liquefied by a condenser provided on the pipe path. A part of this monoethylene glycol is returned to the rectifying column through a pipe as a reflux liquid, and the remaining monoethylene glycol is recovered through a pipe into a MEG product storage tank (not shown). On the other hand, the crude glycol at the bottom of the MEG rectification column (hereinafter referred to as “crude glycol (2)”) includes mono-, di-, and triethylene glycol. The crude glycol (2) is sent to a diethylene glycol (DEG) rectification tower through a pipe, and a diethylene glycol, triethylene glycol, and tetraethylene glycol fractionation and recovery step (hereinafter, this step is referred to as an “ethylene glycol rectification step”). Is also referred to as). The present invention is characterized by a rectification process of the ethylene glycol.

  In the rectification process of ethylene glycols, crude glycol (2) is reacted with ethylene oxide in the presence of a catalyst to produce tri- or tetraethylene glycol, and these are fractionated to produce di, tri, and tetraethylene. Each of the glycols is obtained.

  FIG. 2 shows a schematic diagram of the rectification process of di-, tri- and tetraethylene glycol from crude glycol (2). As shown in FIG. 2, a monoethylene glycol (MEG) rectification column 51, a first diethylene glycol (DEG) rectification column 52, a second DEG rectification column 54, and a triethylene glycol (TEG) rectification column. A distillation column 56 and a tetraethylene glycol (TRAEG) rectification column 58 are connected. These rectifying columns 52, 54, 56, 58 are respectively provided with multi-tubular reboilers 53, 55, 57, 59, and pipes 72, 73, 74, 75, 76, 77, 78, connecting them. 79. The first DEG rectification column 52 is connected to a triethylene glycol (TEG) synthesis reactor 60 by a pipe 60, and the reaction liquid discharged from the TEG synthesis reactor 60 is sent from the pipe 63 and from the MEG rectification tower 51 to the DEG. It passes through a pipe 61 connected to the rectifying column 52 and is guided to the first DEG rectifying column 52.

  Crude glycol (2) is led to first DEG rectification column 52 and heated by multi-tubular reboiler 53 to generate steam, which is led to TEG synthesis reactor 60 and ethylene oxide and alkali. Contact with a metal catalyst to produce triethylene glycol and tetraethylene glycol. The reaction solution obtained from the reaction is led from the pipe 63 to the first DEG rectification column 52 through the pipe 61. The reaction solution obtained in the first DEG rectification column 52 (hereinafter referred to as “crude glycol (3)”) is sent to the second DEG rectification column 54 in order to fractionate diethylene glycol. The crude glycol (3) sent to the second DEG rectification column 54 is distilled under reduced pressure and fractionated into low-boiling component diethylene glycol, high-boiling component tri- and tetraethylene glycol, and the like. The diethylene glycol vapor distilled from the top of the second DEG rectifying column 54 is diethylene glycol (DEG product) that has been fully condensed and liquefied by a condenser provided on the piping path.

  The crude glycol at the bottom of the second DEG rectifying column 54 (hereinafter referred to as “crude glycol (4)”) includes tri- and tetraethylene glycol. The crude glycol (4) is sent to the TEG rectification column 56 through a pipe and distilled under reduced pressure to be fractionated into a low-boiling component triethylene glycol, a high-boiling component tetraethylene glycol, and the like. The triethylene glycol vapor distilled from the top of the TEG rectification column 56 is triethylene glycol (TEG product) that has been condensed and liquefied by a condenser provided on the pipe path.

  The crude glycol (hereinafter, crude glycol (5)) at the bottom of the TEG rectification column 56 includes tri- and tetraethylene glycol. The crude glycol (5) is sent to the TRAEG rectification column 58 through a pipe and distilled under reduced pressure to be fractionated into a low-boiling component tetraethylene glycol, a high-boiling component, impurities, and the like. The tetraethylene glycol vapor distilled from the top of the TRAEG rectification column 58 is converted into tetraethylene glycol (TRAEG product) that has been condensed and liquefied by a condenser provided on the pipe path.

  As described above, the rectifying apparatus used in the present invention includes a rectifying column, a multi-tubular reboiler, and a pipe connecting them. In the present invention, when a predetermined amount of precipitates are deposited on the inner surface of the reboiler tube, physical treatment is performed on the inner surface of the reboiler tube to obtain ethylene glycols having a low aldehyde content and less color. It has been found that. That is, when ethylene glycols are continuously produced, the obtained ethylene glycols are found to have a tendency to increase the aldehyde content and the degree of coloration over time in proportion to the production amount. The present inventors have found a relationship between the precipitate deposited on the inner surface of the tube and the aldehyde content and coloration degree of ethylene glycols.

  Although the process of the manufacturing method of this invention can take any of a continuous process or a batch process, the continuous process is more efficient and preferable. The composition of the crude glycols (1) to (5) can be adjusted as appropriate by setting the production conditions. In the case of a continuous process, the supply of the crude glycol to the next continuous rectification process is carried out by continuously introducing part of the crude glycol to the next rectification column through a pipe while the reaction or distillation proceeds. Therefore, the continuous rectification step is a production process in which the crude glycol in the rectification column is continuously fed into the rectification column of the next rectification step while distilling off the glycol distilled in the rectification step. It is. Moreover, when performing by a batch process, the crude glycol which is a column bottom liquid of a rectification column is supplied through piping to the rectification column of the following distillation process after completion | finish of reaction or distillation.

  The structure of the rectifying column used in the present invention is not particularly limited, and examples thereof include a plate type rectifying column and a packed rectifying column. The number of theoretical plates of the rectifying column is not particularly limited, but is preferably 1 to 50 plates, more preferably 10 to 20 plates.

  In the present invention, the distillation of the crude glycol (2) in the first DEG rectification column 52 is preferably 10 to 550 hPa, more preferably 15 to 70 hPa, and the distillation temperature is preferably 125 to 225 ° C., more preferably. Is carried out at 135-195 ° C. In this step, the crude glycol (2) is led to the TEG synthesis reactor, but the TEG synthesis reaction temperature is not particularly limited, and is preferably 100 to 200 ° C, more preferably 140 to 150 ° C.

  The amount of ethylene oxide that reacts with the crude glycol (2) can be appropriately adjusted in consideration of the composition of the crude glycol (2) and the desired production amount of di, tri, or tetraethylene glycol.

  Moreover, the alkali metal catalyst used when the vapor | steam of crude glycol (2) reacts with ethylene oxide is not restrict | limited, A conventionally well-known thing can be used. For example, alkali metals such as lithium, sodium and potassium; alkali metal hydrides such as lithium hydride, sodium hydride and potassium hydride; alkoxy alkali metal salts such as sodium ethoxide and sodium butoxide; organics such as n-butyllithium Examples thereof include lithium compounds; sodium amides; metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide. These alkali metal catalysts may be used alone or in combination of two or more. Among these, sodium hydride, sodium hydroxide, potassium hydroxide, sodium ethoxide, and sodium butoxide are preferable from the viewpoint of ease of handling and economy, and sodium hydride, sodium hydroxide, and potassium hydroxide are more preferable. Sodium hydroxide and potassium hydroxide are more preferable. The amount of the alkali metal catalyst is not particularly limited, but is preferably 0.01 to 0.1% by weight, more preferably 0.05 to 0.06% by weight with respect to ethylene oxide used in the step.

  In the present invention, the distillation of the crude glycol (3) in the second DEG rectification column 54 is preferably 5 to 640 hPa, more preferably 6 to 50 hPa, and the distillation temperature is preferably 100 to 230 ° C., more preferably. Is carried out at 110 to 157 ° C.

  In the present invention, the distillation of the crude glycol (4) in the TEG rectification column 56 is preferably 10 to 220 hPa, more preferably 10 to 22 hPa, and the distillation temperature is preferably 159 to 230 ° C., more preferably 159 to Performed at 170 ° C.

  In the present invention, the distillation of the crude glycol (5) in the TRAEG rectification column 58 is preferably 4 to 57 kPa, more preferably 4 to 10 hPa, and the distillation temperature is preferably 150 to 230 ° C., more preferably 150 to Performed at 177 ° C.

  In the production method of the present invention, when ethylene glycols are produced, in the first DEG rectifying column 52, the second DEG rectifying column 54, the TEG rectifying column 56, or the TRAEG rectifying column 58, respectively. The deposits deposited on the pipe inner surface of the multi-tubular reboiler 53, 55, 57 or 59 connected through the pipe are removed by physical treatment. At that time, as the multi-tubular reboiler for performing physical treatment, the effect of the present invention is achieved as long as it is at least one selected from the multi-tubular reboilers 53, 55, 57, and 59. Of these, it is preferable to perform physical treatment on the multi-tubular reboiler 53. More preferably, the multi-tubular reboiler 53 and at least one selected from the multi-tubular reboilers 55, 57, and 59 are subjected to physical treatment, and more preferably the multi-tubular reboiler 53, 55. , 57, and 59 are all subjected to physical treatment.

  The precipitate generated in the rectification apparatus in the present invention is an impurity such as a by-product due to the reaction, and its component is not particularly limited. However, as one of the components of the precipitate, an alkali used in producing tri and tetraethylene glycol is used. It is presumed to be derived from a metal salt.

  The time when the physical treatment of the inner surface of the multitubular reboiler is performed is the time when a predetermined amount of deposits are deposited on the inner surface of the multitubular reboiler. This may be set in consideration of the timing at which ethylene glycols having a predetermined aldehyde content and coloring degree are obtained. As the predetermined aldehyde content and coloring degree, for example, as triethylene glycol, the aldehyde content is preferably 0 to 50 ppm, more preferably 0 to less than 40 ppm, further preferably 0 to 30 ppm, and sulfuric acid coloring is preferably APHA. No. 0 to 1000, more preferably APHA No. 0-850, more preferably APHA No. 0-700. Tetraethylene glycol has an aldehyde content of preferably 0 to 120 ppm, more preferably 0 to less than 70 ppm, and more preferably 0 to 50 ppm. 0-15, more preferably Gardner No. 0 to 13, more preferably Gardner No. 0-10. When this value is exceeded, it is better to carry out physical treatment on the inner surface of the tube of the multitubular reboiler. Further, the aldehyde content of triethylene glycol is 50 ppm or less, and the sulfuric acid coloration is APHA No. 1000 or less and tetraethylene glycol aldehyde content of 120 ppm or less, Gardner No. In order to continuously obtain 15 or less ethylene glycols, it may be carried out preferably 1 to 8 years / once, more preferably 3 to 4 years / once.

  In addition, about distillation amount, it changes with the desired range of the aldehyde content and coloring degree of ethylene glycol to manufacture.

  The amount of the precipitate removed by the physical treatment is not particularly limited, as long as it is ethylene glycols having a desired aldehyde content and coloring degree as described above. In addition, the aldehyde content of tri and tetraethylene glycol is a value measured according to the “MBTH method” (E. Savicky et al, (1961) Analyt. Chem., 33, 92-96).

  Examples of the physical treatment in the present invention include polishing treatment (brushing and the like). When performing the polishing process (brushing), it is more preferable to perform brushing using various brushes such as a wire brush, a channel brush, and a torsion brush (also referred to as a tube brush or a condenser brush). The hair of the brush is not particularly limited, and examples thereof include materials such as brass, steel, SUS, polyester, and nylon. Of these, brass and SUS are preferred. The size of the brush is not particularly limited, and is appropriately adjusted according to the size of the portion to be cleaned and the amount of precipitates.

  As a guideline for carrying out the polishing treatment (brushing), for example, it is preferable to carry out to the extent that a lump of 1 to 100 mm is removed. In the case of continuous operation, for example, the amount of deposits in the reboiler tube removed in the 10-year production is about 3 to 4 kg.

  In this preferred embodiment of the present invention, the inside of the reboiler tube is treated by chemical treatment. That is, the manufacturing method of the present invention preferably further includes a step of treating the inside of the reboiler tube by chemical treatment after the removing step. At that time, as the multi-tubular reboiler for performing chemical treatment, it is preferable to perform chemical treatment on the multi-tubular reboiler subjected to physical treatment.

  Examples of the chemical treatment include acid washing, alkali washing, and rust prevention treatment. Of these, acid washing and rust prevention treatment are preferred, acid washing and rust prevention treatment are more preferred, and rust prevention treatment is more preferred after acid washing. In the production of the ethylene glycols of the present invention, an alkali metal catalyst is used, so it is considered that salts such as alkali metal salts are included as precipitates. Therefore, acid cleaning is preferable as the chemical treatment, and the inside of the system (such as the inside of a reboiler tube or a rectifying tower) is acidified by acid cleaning. Deterioration such as rust can be suppressed.

  The acid cleaning is performed using an acidic aqueous solution under conditions such that the inside of the reboiler tube is immersed in the acidic aqueous solution. Specifically, the acidic aqueous solution is circulated in the rectification column and the reboiler at preferably 25 to 65 ° C, more preferably 60 to 65 ° C. Therefore, in a preferred embodiment of the present invention, the acid cleaning is performed inside the rectification column and inside the reboiler tube. Therefore, acid cleaning is also performed on the pipe connecting the rectification column and the reboiler.

  The acidic aqueous solution used in the acid cleaning is not particularly limited, and examples thereof include aqueous solutions of hydrochloric acid, nitric acid, perchloric acid, sulfuric acid, oxalic acid, acetic acid, formic acid, carbonic acid, phosphoric acid, citric acid, sulfamic acid and the like. These acids may be used alone or in combination of two or more. As the acidic aqueous solution, hydrochloric acid, nitric acid, sulfuric acid, oxalic acid and sulfamic acid are preferable, hydrochloric acid, sulfuric acid, oxalic acid and sulfamic acid are more preferable, hydrochloric acid, sulfuric acid, oxalic acid and sulfamic acid are more preferable, and oxalic acid and sulfamic acid are preferable. It is particularly preferable to use in combination. The amount of the acidic substance in these acidic aqueous solutions is not particularly limited. For example, it is preferable that 3 to 5% by mass of acidic substances are contained in the solution (acidic aqueous solution) in the system when performing acid cleaning.

  The acid washing may be prepared by dissolving an acidic substance in water or the like, or a commercially available product can be used as it is or after being appropriately diluted.

As a guideline for acid cleaning, an acidic aqueous solution of preferably 1 kg to 100 kg, more preferably 5 kg to 15 kg is preferably used with respect to the volume (1 m ³ ) of the object to be cleaned (for example, inside the reboiler tube and inside the rectifying column). Can be used.

  The rust prevention treatment is performed under the condition that the inside of the reboiler tube is immersed in an aqueous solution containing the rust prevention treatment agent using a rust prevention treatment agent. Specifically, the aqueous solution containing a rust preventive is preferably refluxed in a rectifying column and a reboiler at 40 to 65 ° C, more preferably 60 to 65 ° C. Therefore, as a preferred embodiment of the present invention, the rust prevention treatment is carried out inside the rectifying column and inside the reboiler tube. Therefore, the anticorrosion treatment is also performed on the pipe connecting the rectification tower and the reboiler.

  As the rust preventive agent used in the rust preventive treatment, a known rust preventive agent can be used. For example, a vaporizable rust preventive agent, a water-soluble rust preventive agent, etc. can be used. Is preferred.

  Examples of the vaporizable rust preventive include nitrites of organic amines such as dicyclohexylammonium nitrite and diisopropylammonium nitrite; cyclohexylammonium caprylate, dicyclohexylammonium salicylate, dicyclohexylammonium benzoate, diisopropylammonium benzoate, monoethanolamine benzoate, Examples thereof include carboxylates or carbonates of organic amines such as cyclohexylammonium carbonate; hydroxyamines such as butylmonoethanolamine; nitro compounds such as nitronaphthaleneammonium nitrite and nitrophenol; benzotriazole.

  Examples of water-soluble rust preventives include, for example, inorganic compounds using borate, phosphate, citrate, nitrite, etc., and both water and oil such as alkanolamines, fatty acids, carboxylic acids or their salts. Examples include soluble organic compound systems, and combinations of the above-mentioned inorganic compound systems and organic compound systems. Specifically, inorganic compounds such as ammonium citrate, sodium nitrite and citric acid; alkanolamines such as triethanolamine, ethylenediamine, morpholine and cyclohexylamine; fats such as caproic acid, caprylic acid, lauric acid and myristic acid Aliphatic carboxylic acids or amine salts thereof; aliphatic dicarboxylic acids such as suberic acid, azelaic acid and sebacic acid or amine salts thereof; nitrobenzoic acid, dinitrobenzoic acid, aminobenzoic acid, cinnamic acid, nitrocinnamic acid, toluic acid, Examples thereof include aromatic carboxylic acids such as cumic acid and butylbenzoic acid or amine salts thereof; aromatic dicarboxylic acids such as phthalic acid and nitrophthalic acid or amine salts thereof;

  The amount of the antirust treatment agent used is not particularly limited, and is preferably 1 to 10% by mass, more preferably 1 to 5% by mass, and further preferably 1 to 2% by mass with respect to the total amount of the aqueous solution used for the antirust treatment. It is.

  A neutralizing agent may be used during the rust prevention treatment. Although it does not restrict | limit especially as a neutralizer, For example, hydroxides, such as sodium hydroxide, calcium hydroxide, barium hydroxide; Carbonates, such as sodium carbonate and potassium carbonate; Sodium hydrogencarbonate, potassium hydrogencarbonate, hydrogencarbonate Examples thereof include hydrogen carbonates such as ammonium; nitrates such as sodium nitrate, potassium nitrate, and ammonium nitrate; nitrites such as sodium nitrite (which is a rust inhibitor) and potassium nitrite; These neutralizing agents may be used alone or in combination of two or more. The amount of the neutralizing agent used is not particularly limited, and is appropriately adjusted so that the pH becomes neutral after the work is completed.

As a standard for performing the rust prevention treatment, the amount of rust prevention is preferably 1 kg to 100 kg, more preferably 5 kg to 15 kg with respect to the capacity (1 m ³ ) of the object to be cleaned (for example, inside the reboiler tube and inside the rectifying tower) It can be performed using an aqueous solution containing a treatment agent.

  These chemical treatments are preferably carried out until the desired range of aldehyde content and coloring degree of the resulting ethylene glycols is obtained. Specifically, as triethylene glycol, the aldehyde content is preferably 0 to 50 ppm, more preferably 0 to 30 ppm, and sulfuric acid coloring is preferably APHA No. 0 to 1000, more preferably APHA No. It is preferable to perform chemical treatment until it becomes 0-600. Tetraethylene glycol has an aldehyde content of preferably 0 to 300 ppm, more preferably 0 to 120 ppm. 0-20, more preferably Gardner No. Chemical treatment is preferably performed until 0-9.

  As described above, the chemical treatment in the production method of the present invention is preferably carried out inside the rectifying column and inside the reboiler tube. That is, it is preferable to further include a step of treating the inside of the rectification column by chemical treatment. By carrying out the chemical treatment also inside the rectification column, ethylene glycols having a low aldehyde content and a low color can be obtained, and the effect can be maintained for a long period of time.

  In this embodiment, even when only the physical treatment is performed on the inner surface of the reboiler tube, ethylene glycols having a low aldehyde content and a low degree of coloration can be obtained, but physical treatment and chemical treatment are used in combination. In addition, the effect is maintained for a long time. Further, it is preferable to perform the physical treatment and the chemical treatment in this order, that is, by performing the chemical treatment after the physical treatment, the effect of the present invention can be maintained for a longer period.

  The effects of the present invention will be described using the following examples and comparative examples. However, the technical scope of the present invention is not limited only to the following examples.

<Evaluation>
In the following examples, the obtained ethylene glycols were evaluated by the following measurement methods.

(Aldehyde content)
The aldehyde content is a value measured according to the “MBTH method”. E. Savicky et al, (1961) Analyt. Chem. , 33, 92-96.

(Sulfuric acid coloring)
(1) Triethylene glycol The sulfuric acid coloring of triethylene glycol was measured according to ASTM D5386-10.

(2) Tetraethylene glycol The sulfuric acid coloration of tetraethylene glycol was measured according to JIS K0071-2 (1998 edition).

(Example 1)
In the rectification apparatus shown in FIG. 2, the internal surface of the reboiler 53 of the DEG rectification column 52 of the rectification apparatus was washed by brushing with a brush to remove a 5 mm film-like precipitate. Similarly, the reboiler 55 of the DEG rectifying column 54, the reboiler 57 of the TEG rectifying column 56, and the reboiler 59 of the TRAEG rectifying column 58 were brushed to remove precipitates.

Then, for the DEG rectifying column 52 and its reboiler 53, the DEG rectifying column 54 and its reboiler 55, the TEG rectifying column 56 and its reboiler 57, the TRAG rectifying column 58 and its reboiler 59, the acidity of the composition shown in Table 1 An acidic aqueous solution was circulated at 60 ° C. using the aqueous solution, and acid washing was performed for 4 hours. Next, using the rust preventive agent having the composition shown in Table 1, the rust preventive agent was circulated at 60 ° C. to perform a rust preventive treatment. Moreover, after completion | finish of the work of a rust prevention process, the neutralizing agent of Table 1 was suitably added to the aqueous solution containing a rust prevention agent so that pH might become neutral. In addition, as an aqueous solution containing an acid aqueous solution at the time of acid cleaning and a rust preventive agent at the time of rust prevention, the capacity (1 m ³ ) of the object to be cleaned (inside the reboiler tube and inside the rectifying column) An amount of 10 kg was used. In addition, as for the chemical treatment, triethylene glycol has an aldehyde content of 20 ppm and sulfuric acid coloring is APHA No. 550, tetraethylene glycol has an aldehyde content of 43 ppm, and sulfuric acid coloring is Gardner No. It went until it became nine.

  After the rust prevention treatment, ethylene glycols were continuously operated under the following conditions.

<Ethylene glycol production conditions>
First DEG rectification column 52: distillation temperature 147 to 157 ° C., 20 to 50 hPa
Second DEG rectification column 54: distillation temperature 122-129 ° C., 7-15 hPa
TEG rectification column 56: distillation temperature 159 to 170 ° C., 10 to 22 hPa
TRAEG rectification column 58: distillation temperature 162 to 174 ° C., 4 to 10 hPa

Ethylene glycols were continuously distilled using the rectifying apparatus that had been treated in Example 1, and the aldehyde content and sulfuric acid coloration of the obtained ethylene glycols were measured and are shown in Table 2.

  After the treatment of Example 1, the quality of ethylene glycols improved dramatically, and the cleaning effect lasted for over 1 year, lasting up to 4 years.

(Comparative Example 1)
Using the rectifying apparatus shown in FIG. 2, ethylene glycols were continuously produced under the same conditions as in Example 1. After 10 years, the aldehyde content and sulfuric acid coloration were measured. Shown as “before washing” ethylene glycol.

  When washing treatment (physical treatment and chemical treatment) is not performed, aldehyde content and sulfuric acid coloration of ethylene glycols are poor, suggesting that high-purity ethylene glycols cannot be obtained by continuous operation in this state. ing.

(Comparative Example 2)
Diethylene glycols were distilled for 10 years by continuous operation using the rectifying apparatus shown in FIG. At that time, the aldehyde content and sulfuric acid coloring value of each ethylene glycol obtained before washing are shown as “before washing” ethylene glycol in Table 3.

About the DEG rectification column 52 and its reboiler 53, the DEG rectification column 54 and its reboiler 55, and the TEG rectification column 56 and its reboiler 57 of the rectification apparatus, an acidic aqueous solution having the composition shown in Table 1 is used. The acidic aqueous solution was circulated and acid cleaning was performed. Next, using the rust preventive agent having the composition shown in Table 1, the rust preventive agent was circulated at 60 ° C. to perform a rust preventive treatment. In addition, as an aqueous solution containing an acid aqueous solution at the time of acid cleaning and a rust preventive agent at the time of rust prevention, the capacity (1 m ³ ) of the object to be cleaned (inside the reboiler tube and inside the rectifying column) An amount of 10 kg was used.

  After the rust preventive treatment, the production of ethylene glycol was continuously operated under the same conditions as in Example 1, and the aldehyde content and sulfuric acid coloring of the obtained tri- and tetraethylene glycol were periodically evaluated. Table 3 shows the results. showed that.

  When only chemical treatment is performed, there is no change in aldehyde content and sulfuric acid coloring before and after washing, suggesting that high-purity ethylene glycols cannot be obtained by continuous operation in this state.

  As described above, when the rectifying apparatus is treated by the method of Example 1 as compared with the case of treating the rectifying apparatus by the methods of Comparative Examples 1 and 2, ethylene glycol has a low aldehyde content and a low degree of coloring. Can be produced over a long period of time.

51 MEG rectification tower,
52 First DEG rectification tower,
53, 55, 57, 59 Multitubular reboiler,
54 Second DEG rectification tower,
56 TEG rectification tower,
58 TRAEG rectification tower,
60 TEG synthesis reactor,
61, 62, 63, 64, 65, 66 piping,
67, 69, 71 piping,
72, 73, 74, 75, 76, 77, 78, 79 Piping.

Claims (4)

A method for producing tri- or tetraethylene glycol using a rectifying apparatus comprising a rectifying column, a multi-tubular reboiler, and a pipe connecting them,
When a predetermined amount of deposits are deposited on the inner surface of the reboiler tube, the inner surface of the reboiler tube is subjected to a polishing process to remove the deposit,
A method for producing tri- or tetraethylene glycol.   The manufacturing method according to claim 1, further comprising a cleaning step of processing the inside of the reboiler tube by chemical treatment after the removing step. The manufacturing method according to claim 2 , wherein the chemical treatment is acid cleaning and rust prevention treatment.   The manufacturing method of any one of Claims 1-3 which further includes the process of processing the inside of the said rectification tower | column by chemical processing.

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