WO2021174487A1 - 制备对苯二甲酸酯的方法 - Google Patents

制备对苯二甲酸酯的方法 Download PDF

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WO2021174487A1
WO2021174487A1 PCT/CN2020/077996 CN2020077996W WO2021174487A1 WO 2021174487 A1 WO2021174487 A1 WO 2021174487A1 CN 2020077996 W CN2020077996 W CN 2020077996W WO 2021174487 A1 WO2021174487 A1 WO 2021174487A1
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crude ester
titanate
ester
crude
weight
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PCT/CN2020/077996
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English (en)
French (fr)
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王群朋
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王群朋
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Priority to PCT/CN2020/077996 priority Critical patent/WO2021174487A1/zh
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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C67/00—Preparation of carboxylic acid esters
    • C07C67/08—Preparation of carboxylic acid esters by reacting carboxylic acids or symmetrical anhydrides with the hydroxy or O-metal group of organic compounds
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C69/00—Esters of carboxylic acids; Esters of carbonic or haloformic acids
    • C07C69/76—Esters of carboxylic acids having a carboxyl group bound to a carbon atom of a six-membered aromatic ring
    • C07C69/80—Phthalic acid esters
    • C07C69/82—Terephthalic acid esters

Definitions

  • the present invention relates to a preparation method of terephthalate, especially dioctyl terephthalate (English abbreviation: DOTP).
  • Existing terephthalate production methods generally include first preparing crude esters, and then purifying the crude esters, including dealcoholization, neutralization, water washing, steam stripping, and filtration.
  • dioctyl terephthalate make terephthalic acid and octanol (2-ethylhexanol, the octanol mentioned below refers to this substance) in the titanate catalyst at 180-230°C (Usually 0.05-0.15% of the product, 0.117-0.353% of the PTA calculated as PTA) is reacted in an esterification reactor to prepare dioctyl terephthalate.
  • the esterification is completed and the crude ester is obtained.
  • This step generates 9wt% (based on the finished product) by-product water; because of the presence of dissolved organic matter, the COD (chemical oxygen demand) of the by-product water is about 9000-10000 mg/L.
  • the crude ester is dealcoholized in an esterification reactor or in a dealcoholization tower under reduced pressure, and most of the octanol is evaporated and removed and condensed by a condenser for recycling.
  • the crude ester after dealcoholization contains about 0.5 to 5% by weight of octanol.
  • the neutralization step neutralizes the monoester acid in the crude ester to reduce the acid value of the crude ester (for example, to ⁇ 0.02 mgKOH/g) and hydrolyze the catalyst to generate hydrated titanium dioxide.
  • the crude ester after dealcoholization is cooled to 80-95°C, and then an alkali solution of about 20-30% (wt) of the crude ester is added under stirring for neutralization, and then the oil phase and the water phase are separated. Most of the ester salt and titanium dioxide hydrate enter the water phase. Separate the water phase and use it as spent alkali water.
  • Monoester salt has both lipophilic and hydrophilic properties, and it carries part of dioctyl terephthalate into the water phase; titanium dioxide hydrate is flocculent, and also carries part of dioctyl terephthalate into the water phase, causing the
  • the COD value of the waste alkali water produced in the step is about 40,000-50000 mg/L.
  • the neutralized crude ester is washed with water.
  • water with an amount of about 20-30% by weight of the crude ester and stir.
  • Alkali, monoester and titanium dioxide hydrate enter the water phase. Separate the oil phase and the water phase and separate the water phase as waste water.
  • the COD value of the wastewater produced in this step is about 15000-20000 mg/L.
  • the octanol and water can be further removed from the crude ester after being washed with neutralization water, for example, by steam stripping treatment.
  • the stripped alcohol and water are condensed in the condenser, and then the alcohol and water are separated.
  • the separated octanol can be recycled and the separated water is used as waste water.
  • the COD of the wastewater produced in this step is about 2000-3000 mg/L.
  • the stripped crude ester can be dried to further remove water.
  • the crude ester can optionally be further filtered to obtain the final terephthalate product.
  • CN101184721A discloses a method for purifying crude esters, which includes treating the crude esters with an alkaline aqueous solution of alkali metal salts at a temperature of 100-140°C, and the amount of water present in the treatment process is 0.7-1.4 wt% of the weight of the crude esters.
  • the method disclosed in this document overcomes the problem of large amounts of waste water by using low-level water in the neutralization treatment, it also causes additional problems.
  • the method of the reference document uses an alkali metal lower than the stoichiometric amount relative to the acidity of the crude ester, which easily leads to insufficient neutralization, and makes the acid value of the final product too high.
  • the method of this document requires the use of a low-level titanium catalyst, and the amount of titanium used is at most 0.07% by weight based on the amount of acid or anhydride reagent used in the esterification reaction. It is believed that the method of the reference document limits the amount of alkali and catalyst used because the sodium bicarbonate crystals and titanium dioxide crystals formed by neutralization tend to form small crystals, which can easily cause filter clogging problems. The use of low levels of alkali and catalyst can reduce the burden of filtration and enable the method of this reference document.
  • the titanate catalyst is deactivated to form flocs, which are difficult to filter out, and filter aids must be added to perform filtration, resulting in increased consumption and increased costs.
  • the CN101184721A method uses a low level of catalyst, its method is not suitable for the production of terephthalate.
  • terephthalic acid and octanol since terephthalic acid is insoluble in octanol, the reaction is a solid-liquid reaction, and the reaction speed is relatively slow, and more catalysts need to be added to promote the reaction.
  • the amount of titanate is 0.117 wt% to 0.353 wt% of the amount of terephthalic acid.
  • This high level of catalyst results in high levels of titanium dioxide crystals in the purification process, which exceeds the filtration processing capacity of the CN101184721A method.
  • Dibasic terephthalate (mainly dioctyl terephthalate) with high catalyst usage (0.117-0.353wt%, based on the amount of terephthalic acid)
  • this method forms a dense filter layer in the filtration process, the production cannot be carried out.
  • This application provides an improved method for preparing terephthalate, which can reduce the amount of waste water, is not troubled by filtration problems (excellent filtration ability), and the resulting terephthalate final product has favorable properties , Including acid value, chroma, purity, moisture, flash point, volume resistivity, etc.
  • This application provides a method for preparing terephthalic acid dibasic ester, especially a method for purifying the crude ester obtained after the esterification is completed.
  • this application provides a method for purifying crude dibasic ester prepared by reacting terephthalic acid and alcohol in the presence of an esterification catalyst, the method comprising the following steps:
  • the crude ester is treated with an aqueous alkali solution to obtain a crude ester after alkali treatment, wherein the relative The amount of the aqueous alkali solution used in the weight of the crude ester is 0.5wt%-2wt%, preferably 0.6wt%-1.5wt%, more preferably 0.8wt%-1.2wt%, most preferably 1wt%;
  • the dehydrated crude ester is filtered to obtain the filtered crude ester.
  • the above filtered crude ester can also be subjected to further processing, including subjecting the filtered crude ester to a steam stripping treatment to obtain the stripped crude ester, and drying the stripped crude ester to provide Ester products.
  • the ester product can also be filtered to ensure that the ester product does not contain any solid particles.
  • the process of the present application uses an aqueous alkali solution to treat the crude ester under an elevated pressure sufficient to prevent water from evaporating.
  • the pressure should be greater than or equal to the saturated vapor pressure of water at the treatment temperature to maintain the aqueous alkali solution in a liquid state.
  • the pressure is 0.3 MPa to 3 MPa, more preferably the pressure is 0.4 to 1.0 MPa.
  • the crude ester before the crude ester is treated with an aqueous alkali solution, the crude ester may be dealcoholized.
  • This dealcoholization treatment is an operation known in the art.
  • the alcohol content of the crude ester is reduced to not more than 5% by weight of the crude ester, preferably not more than 3% by weight of the crude ester, and more preferably not more than 1% by weight of the crude ester.
  • the base is selected from hydroxides, carbonates and bicarbonates.
  • the base is alkali metal and calcium hydroxide, carbonate and bicarbonate. More preferably, the base is selected from alkali metal carbonates and bicarbonates, such as sodium carbonate, sodium bicarbonate, potassium carbonate and potassium bicarbonate. Most preferably, the base is selected from sodium carbonate or potassium carbonate.
  • the amount of alkali used in the treatment is 100%-200% of the theoretical amount calculated based on the acid value of the crude ester before treatment, preferably 105%-180%, more preferably 110%-150%, most Preferably 110%-120%.
  • the water content of the dehydrated crude ester does not exceed 0.2% by weight, preferably does not exceed 0.1% by weight, and more preferably does not exceed 0.08% by weight.
  • a filter aid can be used to facilitate the filtration of the dehydrated crude ester.
  • the filter aid is added to the crude ester before, during or after the treatment of the crude ester with the aqueous solution of the base.
  • the filter aid is selected from attapulgite, diatomaceous earth, calcium carbonate, activated carbon, kaolin and activated clay.
  • the added amount of the filter aid is 0.01-0.15% of the weight of the crude ester, more preferably 0.02-0.05%.
  • the esterification catalyst is a titanium catalyst.
  • the titanium catalyst is a titanate catalyst, more preferably the titanium catalyst is selected from the group consisting of tetramethyl titanate, tetraethyl titanate, tetra-n-propyl titanate, tetraisopropyl titanate, titanic acid Tetra-n-butyl, tetraisobutyl titanate, tetrapentyl titanate, tetrahexyl titanate, tetraheptyl titanate, tetraoctyl titanate, tetranonyl titanate, tetradecyl titanate, titanic acid Tetra-(2-propylheptyl) ester, tetra(dodecyl) titanate, tetra(hexadecyl) titanate, tetra(octadec
  • the alcohol used to prepare the ester various alcohols generally used in the art can be used.
  • the alcohol is an alcohol having 4-15 carbon atoms, preferably octanol, ie 2-ethylhexanol.
  • the terephthalate product obtained by the method of the present invention has advantageous properties and can be used in various applications, including as a plasticizer for polymer materials such as PVC, as an additive, and so on.
  • the present application provides an improved method for preparing terephthalic acid esters, and more specifically, the present application provides a method for purifying the crude ester obtained after the esterification reaction is completed.
  • the method of the present application includes the following steps: providing a crude ester; treating the crude ester with an aqueous alkali solution at a temperature of 145° C. to 165° C.
  • the amount of the aqueous alkali solution is 0.5 wt% to 2 wt%; the crude ester after the alkali treatment is dehydrated to obtain a dehydrated crude ester; and the dehydrated crude ester is filtered to obtain a filtered crude ester.
  • the crude ester in the method of the present application refers to the esterification reaction product containing impurities obtained after the esterification reaction, including the terephthalic acid dibasic ester product as the main component, and unreacted raw materials such as terephthalic acid.
  • the esterification reaction product containing impurities obtained after the esterification reaction including the terephthalic acid dibasic ester product as the main component, and unreacted raw materials such as terephthalic acid.
  • Formic acid mono-alcohol ester and alcohol, by-product water, and esterification catalyst formic acid mono-alcohol ester and alcohol, by-product water, and esterification catalyst.
  • the crude ester can be prepared by in-situ reaction of terephthalic acid and octanol (2-ethylhexanol), or the crude ester can be from other sources, such as from other factories and the like.
  • the preparation of the crude ester is known in the art and various methods known in the art can be used to prepare the crude ester.
  • terephthalic acid and excess 2-ethylhexanol can be used as raw materials, and reacted in an esterification reactor in the presence of a catalyst such as titanate at an elevated temperature, for example, 180-230°C.
  • the esterification reaction can be carried out under the protection of an inert gas.
  • an inert gas for example, nitrogen can be used as the protective gas. It is believed that the use of inert gas can improve the color properties of terephthalate products, and even make it possible to omit the use of activated carbon to decolorize.
  • the alcohol used in the method of the present invention is a linear or branched primary or secondary alcohol having 1 to 18 carbon atoms, preferably a primary or secondary alkanol.
  • the alcohol is an alcohol having 4-15 carbon atoms.
  • alcohols that may be mentioned include methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, hexanol, heptanol, 2-ethylhexanol, nonanol, decanol, etc., And their mixtures.
  • the alcohol is 2-ethylhexanol.
  • the crude ester is preferably prepared using a titanium catalyst.
  • the titanium catalyst is a titanate catalyst, more preferably the titanium catalyst is selected from the group consisting of tetramethyl titanate, tetraethyl titanate, tetra-n-propyl titanate, tetraisopropyl titanate, titanic acid Tetra-n-butyl, tetraisobutyl titanate, tetrapentyl titanate, tetrahexyl titanate, tetraheptyl titanate, tetraoctyl titanate, tetranonyl titanate, tetradecyl titanate, titanic acid Tetra-(2-propylheptyl) ester, tetra(dodecyl) titanate, tetra(hexadecyl) titanate, tetra(octa
  • the titanate catalyst is selected to be used, and the amount of the titanate catalyst relative to the weight of terephthalic acid is 0.117-0.353%, preferably 0.235-0.353% by weight.
  • esterification reaction proceeds to the required extent in the esterification reactor, it can be considered that the esterification reaction has been completed.
  • the terephthalic acid solids in the esterification reactor are all dissolved and the acid value of the material reaches ⁇ 0.2 mgKOH/g, it is considered that the esterification has been completed and subsequent treatment can be carried out.
  • the crude ester Before treating the crude ester with an aqueous alkali solution, optionally, the crude ester may be dealcoholized to remove the alcohol remaining in the crude ester.
  • the dealcoholization treatment can be carried out in the esterification reactor or in the dealcoholization tower.
  • the crude ester is distilled to remove alcohol under reduced pressure, for example, at 1-5 kPa absolute pressure.
  • the alcohol content of the crude ester is reduced to no more than 5% by weight of the crude ester, preferably no more than 3% by weight of the crude ester, more preferably no more than 1% by weight of the crude ester.
  • the treatment of the crude ester (after dealcoholization or without dealcoholization) with an aqueous alkali solution is carried out at a higher temperature, such as 145°C to 165°C.
  • This treatment can neutralize the monoester acid in the crude ester and reduce the acid value of the crude ester.
  • the acid value of the crude ester is reduced to no more than 0.02 mgKOH/g.
  • this treatment can hydrolyze the titanate catalyst to produce hydrated titanium dioxide.
  • the crude ester is treated with an aqueous alkali solution at a temperature of 145°C to 165°C, preferably at a temperature of 145°C to 160°C, more preferably at a temperature of 150°C to 155°C.
  • the applicant unexpectedly found that when a temperature exceeding 165°C was used, the acid value of the treated crude ester increased abnormally. It is believed that this abnormal increase in acid value is because when the temperature exceeds 165°C, the activity of titanate increases and the dibasic terephthalate undergoes a reverse reaction in the presence of water. This reverse reaction causes the hydrolysis of the terephthalic acid dibasic ester into monoester acid and alcohol, causing the acid value of the crude ester to increase. By using the temperature required in this application, the reverse reaction can be reduced or eliminated, maintaining rapid hydrolysis of titanate and at the same time reducing heat energy loss.
  • the process of the present application uses an aqueous alkali solution to treat the crude ester under an elevated pressure sufficient to prevent water from evaporating.
  • the pressure should be greater than or equal to the saturated vapor pressure of water at the treatment temperature to maintain the aqueous alkali solution in a liquid state.
  • the pressure is 0.3 MPa to 3 MPa, preferably the pressure is 0.4 to 1.8 MPa, and more preferably the pressure is 0.4 to 1.0 MPa.
  • the amount of the aqueous alkali solution is important because water is a reactant for the hydrolysis of titanate to form titanium dioxide hydrate.
  • the amount of the aqueous solution used cannot be too small, because too little water will make the titanate incompletely hydrolyzed and cause the filter screen to be blocked in the subsequent filtration operation.
  • water is also an impurity in crude esters and should be removed in subsequent operations. Therefore, too much aqueous solution cannot be added.
  • the amount of the aqueous alkali solution used is 0.5wt%-2wt%, preferably 0.6wt%-1.5wt%, more preferably 0.8-1.2%, most preferably about 1wt% .
  • the aqueous alkali solution of the present application has a relatively low alkali concentration.
  • the concentration of the aqueous alkali solution of the present application is 0.2wt%-5wt%, preferably 0.5wt%-3wt%, more preferably 1wt%-2wt%.
  • the base is selected from hydroxides, carbonates, bicarbonates or mixtures thereof.
  • the base is alkali metal and calcium hydroxide, carbonate and bicarbonate.
  • the base is selected from alkali metal carbonates and bicarbonates, such as sodium carbonate, sodium bicarbonate, potassium carbonate and potassium bicarbonate.
  • the base is selected from sodium carbonate or potassium carbonate.
  • the amount of alkali used in the treatment is 100%-200% of the theoretical amount calculated based on the acid value of the crude ester before treatment, preferably 105%-180%, more preferably 110%-150%, most Preferably 110%-120%.
  • the aqueous solution of the alkali used can be adjusted according to the type and concentration of the catalyst used and the alkali used, including the amount of the aqueous solution and the concentration of the alkali in the aqueous solution. These adjustments can be easily determined and implemented by those skilled in the art. Preferably, it is adjusted within the concentration and dosage range disclosed in this application, although it can also deviate from the range disclosed in this application when necessary.
  • stirring may be performed.
  • Those skilled in the art can choose a suitable stirring method as long as it can promote the processing process.
  • the treated crude ester is dehydrated to obtain a dehydrated crude ester.
  • the purpose of dehydrating the crude ester after treatment with the aqueous alkali solution is to reduce the water content in the crude ester.
  • the water content of the dehydrated crude ester does not exceed 0.2% by weight, preferably does not exceed 0.1% by weight, preferably does not exceed 0.08% by weight, and more preferably does not exceed 0.05% by weight.
  • Dehydration can be carried out by means generally known in the art, including but not limited to distillation, flash evaporation, vacuum distillation, and the like.
  • a dehydration operation is performed immediately after treating the crude ester with an aqueous alkali solution. Therefore, the temperature of the crude ester during the dehydration operation is slightly lower than the temperature when the crude ester is treated with an aqueous alkali solution (because of the addition of water and natural heat dissipation and cooling, not special cooling).
  • the temperature at which the dehydration operation is performed is therefore a temperature of 120°C to 155°C, preferably a temperature of 125°C to 155°C, more preferably 130°C to 150°C.
  • the crude ester is sent to a distillation column (dehydration column) at a temperature of 130° C.-150° C.; the distillation column is at a reduced pressure, for example, an absolute pressure of 10-30 KPa Run down to distill out the water, thereby reducing the water content in the crude ester to the required level.
  • a distillation column dehydration column
  • the distillation column is at a reduced pressure, for example, an absolute pressure of 10-30 KPa Run down to distill out the water, thereby reducing the water content in the crude ester to the required level.
  • the process of crystal formation of titanium dioxide can adsorb polar substances in crude esters, such as colored substances, and adsorb monoesters. Because these crystals are removed by subsequent filtration, this is also advantageous for removing polar substances, which is advantageous for reducing the chromaticity of the product and improving the volume resistance of the product.
  • the product color number can reach 10-15 (platinum-cobalt color number).
  • the COD of the water removed in this dehydration step is about 2000-3000 mg/L and contains no salt.
  • the water removed from the dehydration step is used to prepare the alkali solution used above, thereby further reducing waste water discharge, which is particularly advantageous.
  • the dehydrated crude ester is filtered. Through filtration, the crystals in the dehydrated crude ester are filtered out.
  • Filtering methods generally known in the art for plasticizers can be used for filtering.
  • a plate-type hermetic filter can be used for filtering.
  • the filter residue obtained by filtration contains titanium dioxide, monoester and dibasic terephthalate.
  • the filter residue contains 30-35% by weight of dibasic terephthalate, about 30% by weight of titanium dioxide and 35-40% by weight of monoester.
  • the crystals formed in the crude ester have better properties (size and morphology), so that the filtration can proceed smoothly.
  • a dense and low-porosity filter cake will not be formed during the filtration process.
  • the dehydrated crude ester has a temperature of 110-130° C. (the temperature is reduced due to the heat absorption of water evaporation and natural heat dissipation, without special cooling), and is filtered with a plate-type airtight filter to obtain a clarified crude ester.
  • a filter aid may also be used to further facilitate the filtration of the dehydrated crude ester.
  • the filter aid has the function of preventing crystals from forming a dense and low-porosity filter layer on the filter cloth and thus quickly clogging the filter.
  • the filter aid may be added to the crude ester before, during or after the treatment of the crude ester with the aqueous solution of the base.
  • the filter aid is added after the crude ester is treated with the aqueous solution of the alkali, it is preferable to add the filter aid immediately after the treatment with the aqueous solution of the alkali. This application uses filter aids commonly used in this field.
  • the filter aid is selected from attapulgite, diatomaceous earth, calcium carbonate, activated carbon, kaolin and activated clay.
  • the filter aid is used in an amount commonly used in the art.
  • the added amount of the filter aid is 0.01-0.15% by weight of the crude ester, more preferably 0.02-0.05%.
  • an adsorbent such as activated carbon can also be added to the crude ester before, during or after the treatment of the crude ester with the aqueous alkali solution.
  • the adsorbent is added together with the filter aid.
  • the adsorbent provides a product with a lighter color and/or a lower metal content.
  • This application uses adsorbents commonly used in this field.
  • alumina, activated clay, activated carbon, magnesia, activated alumina, and silica can be mentioned.
  • activated carbon is used as the adsorbent.
  • the filter aid and/or adsorbent may be added together while being treated with an aqueous alkali solution or immediately afterwards.
  • the crude ester after the above filtration may be further processed.
  • the further treatment may include subjecting the filtered crude ester to a steam stripping treatment to obtain the stripped crude ester, and drying the stripped crude ester to provide an ester product.
  • the ester product can also be precision filtered to ensure that the ester product does not contain any solid particles.
  • the filtered crude ester is stripped to further remove alcohol and water.
  • the steam stripping may use water vapor or an inert gas, such as nitrogen.
  • steam stripping is performed using steam.
  • the filtered crude ester is heated to 145-165°C, and then stripped with steam, for example in a stripper, to further remove light components such as octanol and moisture.
  • the stripper works under reduced pressure, for example, an absolute pressure of 5-15 KPa.
  • Direct steam is introduced into the stripping tower, and the direct steam can reduce the gas phase partial pressure of octanol, which is beneficial to the removal of octanol.
  • the added amount of the direct steam is 5-10% by weight of the crude ester.
  • an evaporator such as a falling film evaporator, is provided to heat the crude ester to keep the temperature of the crude ester at 145-165°C.
  • the evaporated alcohol and water are condensed in the condenser, and then enter the alcohol-water separation tank.
  • the separated octanol can be recycled as a raw material, and the water is sent to the wastewater treatment system.
  • the COD of the wastewater separated in this step is 2000-3000mg/L.
  • the crude ester after stripping contains a small amount of water. Therefore, the stripped material can be dried to remove water.
  • the drying treatment generally used in the field of ester plasticizers can be used.
  • a drying tower at an absolute pressure of 1-3 KPa can be used to treat the stripped crude ester to further remove moisture.
  • the obtained ester product can be used as the final product.
  • the ester product can be further filtered. According to one embodiment, this further filtration is precision filtration to ensure that the final ester product does not contain solid particles.
  • the method of the present application can be carried out in batch, semi-continuous or continuous mode. According to one embodiment, at least part of the method of the application is performed in a continuous manner.
  • the esterification reaction may be performed in a batch mode to prepare and provide the crude ester, but the steps of treating the crude ester with an aqueous alkali solution, dehydrating the crude ester, and filtering the dehydrated crude ester are performed in a continuous manner.
  • the subsequent steps of steam stripping, drying and precision filtration again are also carried out in a continuous manner.
  • the entire process of the method of the present application is performed in a continuous manner.
  • the method of the present application can be implemented in the following manner: After the terephthalic acid esterification reaction is completed, the crude ester, optionally after dealcoholization, is directly exposed to pressure (0.4-1.5 MPa) The pressure is neutralized with an aqueous alkali solution in the neutralization reactor; an aqueous alkali solution with a crude ester amount of about 1% is added during neutralization; the alkali is Na 2 CO 3 or NaHCO 3 , preferably Na 2 CO 3 ; Na 2
  • the CO 3 concentration is 110-150% of the theoretical value calculated based on the acid value of the crude ester; then the water in the crude ester is removed (the COD of the removed water is 2000-3000mg/l, without salt, it can be used to prepare alkaline solutions, Recycling); then filter to remove the monoester sodium salt in the crude ester and the titanium dioxide formed by catalyst deactivation; then use steam for steam stripping and drying; finally, perform precision filtration to obtain the final product.
  • the inventor of the present application has found that the method of the present application can provide ester products with particularly advantageous properties, including acid value, chroma, purity, moisture, flash point, volume resistivity, Ti content, etc. .
  • the quality of the ester product prepared by the method of the present application can reach or even be higher than the product quality of the prior art using the continuous neutralization and water washing process.
  • the quality of the ester product prepared by the method of the present application can meet or even exceed the standard of HG/T 2423-2008 superior grade.
  • the method of the present application can significantly reduce waste water discharge.
  • the COD emission of the method of the present application is reduced by about 90% by weight, and the amount of sewage is reduced by about 57% by weight. The reduction in sewage and COD emissions is calculated as follows:
  • the neutralization and water washing steps in the prior art produce 40-50wt% wastewater, and the COD of the mixed wastewater is about 30,000 mg/L.
  • the neutralization and water washing process uses the by-product water of the esterification reaction and the stripping condensate as the water source for the neutralization and water washing.
  • the COD of the by-product water of the esterification reaction is about 9000-10000 mg/L, and the amount is about 9% of the crude ester;
  • the waste water discharged by the method of the present application does not contain salt and does not contain suspended solids, so that the waste water can be directly subjected to biochemical treatment. Moreover, the amount of sludge generated in the wastewater treatment process of the present application is greatly reduced.
  • PTA terephthalic acid
  • octanol 1:3 (molar ratio)
  • titanate tetraisopropyl titanate or tetra-n-butyl titanate
  • the water produced by the reaction is condensed by the condenser, it is separated from the alcohol in the alcohol-water separation tank, and the alcohol is refluxed into the esterification tank to continue the reaction, and the separated water is discharged as waste water.
  • the amount of water in this part is about 9% of the crude ester, and the COD is about 9000-10000 mg/l.
  • This water is condensed water, does not contain salt and solid impurities, and the pH is about neutral.
  • the crude ester is dealcoholized in a dealcoholization tower at an absolute pressure of 1-5KPa; most of the 2-ethylhexanol is evaporated and then condensed by a condenser for use as a raw material.
  • the crude ester after dealcoholization contains less than 1% by weight of 2-ethylhexanol.
  • the temperature of the crude ester at this time is about 180-210°C.
  • the crude ester after dealcoholization is cooled to 140-160°C, and Na 2 CO 3 (or NaHCO 3 ) solution is added to the neutralization kettle for neutralization.
  • the amount of alkaline aqueous solution is about 1% of the crude ester, and the amount of alkali is 100-150% of the theoretical value calculated based on the acid value of the crude ester (the concentration of the alkaline aqueous solution is 1-2%), usually 110-120% of the theoretical value .
  • the pressure of the neutralization tank is 0.4-1.0MPa ( ⁇ the saturated vapor pressure of water at this temperature); under this condition, the lye remains liquid, and the monoester acid in the crude ester reacts with sodium carbonate to form monoester sodium salt, titanium The acid ester is hydrolyzed to titanium dioxide hydrate.
  • the neutralized crude ester enters the dehydration tower at a temperature of 130-150°C.
  • the dehydration tower operates under an absolute pressure of 10-30KPa, where the water evaporates, and the water content in the crude ester is reduced to below 0.08wt%.
  • the evaporated water is condensed in the condenser.
  • the dehydration process is also the process of dehydration and recrystallization of monoester sodium salt and dehydration of hydrated titanium dioxide to form titanium dioxide recrystallization.
  • the process of crystallization of titanium dioxide can adsorb polar substances in crude esters, thereby removing some of the color-forming substances and monoester sodium salt, which is beneficial to reduce the color and volume resistance of the product.
  • the temperature of the crude ester is 110-130°C (the temperature is lowered by the evaporation of water and natural heat dissipation, no special cooling is required), and the plate-type airtight filter is used to filter to obtain the clarified crude ester, which is used as the raw material for steam stripping.
  • the filter residue contains 30-35% DOTP, about 30% titanium dioxide and 35-40% monoester sodium salt.
  • the filtered crude ester is heated to 145-165°C, and light components such as octanol and moisture are removed in the stripper.
  • the stripping tower is under 5-15KPa absolute pressure, and direct steam is introduced into the tower. Direct steam can reduce the gas phase partial pressure of octanol, which is beneficial to the removal of octanol; the amount of direct steam added is 5 to the amount of crude ester. 10wt%.
  • the evaporated alcohol and water are condensed in the condenser, and then enter the alcohol-water separation tank, and the separated octanol is recycled as a raw material.
  • Water enters the wastewater treatment system.
  • the COD of the wastewater separated in this step is about 2000-3000 mg/L. Because steam is introduced into the stripping tower, the crude ester contains a small amount of water.
  • the crude ester after steam stripping is dried by a drying tower, and the drying tower further removes the moisture in the drying tower at an absolute pressure of 1-3KPa.
  • the crude ester after steam stripping and drying is filtered through a precision filter to obtain the final product.
  • the precision filter is used as a safety device to prevent incomplete filtration in the early stage, which can ensure that the product does not contain solid particles.

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Abstract

一种制备对苯二甲酸酯的方法，具体而言，提供了一种通过对苯二甲酸与醇在酯化催化剂的存在下反应制备的二元酯粗酯的纯化方法，所述方法包括以下步骤：提供所述粗酯；在145℃-165℃的温度、优选在145℃-160℃的温度、更优选在150℃-155℃的温度，用碱的水溶液处理所述粗酯以得到碱处理后的粗酯，其中相对于粗酯的重量使用的所述碱的水溶液的量为0.5wt％-2wt％，优选0.6wt％-1.5wt％，更优选0.8wt％-1.2wt％，最优选1wt％；将所述碱处理后的粗酯脱水以得到脱水粗酯；和过滤所述脱水粗酯以得到过滤后粗酯。

Description

制备对苯二甲酸酯的方法 技术领域
本发明涉及对苯二甲酸酯、特别是对苯二甲酸二辛酯(英文缩写：DOTP)的制备方法。
背景技术
现有对苯二甲酸酯生产方法一般地包括首先制备粗酯，然后对粗酯纯化处理，包括脱醇、中和、水洗、汽提和过滤。
以对苯二甲酸二辛酯为例，使对苯二甲酸和辛醇(即2-乙基己醇，本文以下提到的辛醇即指此物质)在180-230℃在钛酸酯催化剂(通常产品的0.05-0.15％，以PTA计为PTA的0.117-0.353％)的存在下在酯化反应器中反应以制备对苯二甲酸二辛酯。当对苯二甲酸固体全部溶解且酸值(以氢氧化钾溶液滴定粗酯到终点，每克物料消耗的KOH的毫克数)达到小于等于0.2mgKOH/g时，酯化完成，得到粗酯。这一步骤生成9wt％(以成品计)的副产物水；因为存在溶解的有机物，该副产物水的COD(化学需氧量)为约9000-10000mg/L。
得到粗酯后，将粗酯在酯化反应器中或在脱醇塔中在减压条件下脱醇，其中绝大部分的辛醇蒸发除去并经冷凝器冷凝以循环使用。一般地，脱醇后的粗酯含有约0.5-5wt％的辛醇。
然后对脱醇后的粗酯进行中和。该中和步骤中和粗酯中的单酯酸从而降低粗酯的酸值(例如降至≤0.02mgKOH/g)并且使催化剂水解，生成水合二氧化钛。将脱醇后的粗酯降温至80-95℃，然后在搅拌下加入粗酯量的约20-30％(wt)的碱溶液进行中和，然后使得油相和水相分层，其中单酯酸盐和二氧化钛水合物大部分进入水相。将水相分离，作为废碱水。单酯酸盐同时具有亲油和亲水性，其携带部分对苯二甲酸二辛酯进入水相；二氧化钛水合物呈絮状，也携带部分对苯二甲酸二辛酯进入水相，导致该步骤产生的废碱水的COD值为约40000-50000mg/L。
然后对经中和的粗酯进行水洗。向经中和的粗酯中加入粗酯量约20-30wt％的水并进行搅拌。碱、单酯酸盐和二氧化钛水合物进入水相。使油相和水相分层并将水相分离， 作为废水。该步骤产生的废水的COD值为约15000-20000mg/L。
经中和水洗后的粗酯可以进一步脱除其中的辛醇和水，例如通过汽提处理。汽提出的醇和水在冷凝器中冷凝，然后进行醇水分离，分离出的辛醇可以循环使用，而分离的水作为废水。此步骤产生的废水的COD为约2000-3000mg/L。在汽提步骤后，可以对汽提后的粗酯进行干燥以进一步除去水。在汽提和干燥后，可以任选对粗酯进行进一步过滤以得到最终的对苯二甲酸酯产品。
从以上过程可以看出，对苯二甲酸酯生产过程中产生大量废水。中和及水洗步骤产生产量40-50％重量的废水，其中混合后的废水COD高达约30000mg/L。这样的废水呈碱性、具有高COD并且包含二氧化钛水合物，导致废水处理复杂，费用高。
CN101184721A公开了一种粗酯的提纯方法，该方法包括在100-140℃的温度用碱金属盐的碱性水溶液处理粗酯，处理过程中存在的水量是粗酯重量的0.7-1.4wt％。该文件公开的方法虽然通过在中和处理中使用低水平的水克服了废水量大的问题，但也导致另外的问题。该对比文件的方法使用低于相对于粗酯酸度的化学计算量的碱金属，这容易导致中和不充分，使得最终产品的酸值过高。该文件的方法要求使用低水平的钛催化剂，以酯化反应中使用的酸或酸酐试剂的量为基准计，钛的用量是至多0.07wt％。据信该对比文件的方法限制碱和催化剂的用量是因为中和形成的碳酸氢钠晶体和二氧化钛晶体容易形成小晶体，容易造成过滤堵塞问题。使用低水平的碱和催化剂可以减轻过滤负担，使得该对比文件的方法能够进行。
在CN101184721A的方法中，在该条件下，钛酸酯催化剂失活后形成絮状物，难以滤除，须要添加助滤剂才能进行过滤，导致消耗的升高和成本的增加。
由于CN101184721A的方法使用低水平的催化剂，使得其方法不适合用于对苯二甲酸酯的生产。对于对苯二甲酸和辛醇的反应，由于对苯二甲酸不溶于辛醇，反应为固液反应，反应的速度比较慢，需要添加较多催化剂来促进反应。一般地，钛酸酯的量为对苯二甲酸量的0.117wt％-0.353wt％。这种高水平的催化剂导致纯化过程中存在高水平二氧化钛晶体，这超出了CN101184721A方法的过滤处理能力。
这样导致该方法在实际中不能使用在催化剂使用量高(0.117-0.353wt％，以对苯二甲酸的量为基准计)的对苯二甲酸二元酯(主要为对苯二甲酸二辛酯)的生产中，因为该方法在过滤工序形成致密的滤层导致生产无法进行。
因此，仍然需要提供制备对苯二甲酸酯的方法，其能够克服现有技术方法中的一个或多个缺点。
发明内容
本申请提供了改进的制备对苯二甲酸酯的方法，其能够降低废水量，不受过滤问题的困扰(出色的过滤能力)，并且得到的对苯二甲酸酯最终产品具有有利的性质，包括酸值、色度、纯度、水分、闪点、体积电阻率等等。
本申请提供了对苯二甲酸二元酯的制备方法，特别是酯化完成后得到的粗酯的纯化方法。根据一个实施方案，本申请提供了一种通过对苯二甲酸与醇在酯化催化剂的存在下反应制备的二元酯粗酯的纯化方法，所述方法包括以下步骤：
提供所述粗酯；
在145℃-165℃的温度、优选在145℃-160℃的温度、更优选在150℃-155℃的温度，用碱的水溶液处理所述粗酯以得到碱处理后的粗酯，其中相对于粗酯的重量使用的所述碱的水溶液的量为0.5wt％-2wt％，优选0.6wt％-1.5wt％，更优选0.8wt％-1.2wt％，最优选1wt％；
将所述碱处理后的粗酯脱水以得到脱水粗酯；和
过滤所述脱水粗酯以得到过滤后粗酯。
根据本申请的一个实施方案，还可以将以上过滤后粗酯进行进一步的处理，包括将过滤后粗酯进行汽提处理以得到汽提后粗酯，和干燥所述汽提后粗酯以提供酯产品。任选地，还可以对该酯产品进行过滤以确保该酯产品不包含任何固体颗粒。
根据本申请的一个实施方案，本申请方法中使用碱的水溶液处理粗酯在足以防止水蒸发的升高的压力下进行。所述压力应该大于或等于处理温度下水的饱和蒸汽压以将碱的水溶液保持为液态。优选地，所述压力为0.3MPa-3MPa，更优选所述压力为0.4-1.0MPa。
根据本申请的一个实施方案，本申请方法中在使用碱的水溶液处理粗酯之前，可以对所述粗酯进行脱醇处理。该脱醇处理是本领域已知的操作。优选将粗酯的醇含量降低到不超过粗酯重量的5％，优选不超过粗酯重量的3％，更优选不超过粗酯重量的1％。
对于本申请方法中使用的所述碱，本申请的方法没有特别要求，可以使用本领域中通常使用的碱。根据一个实施方案，所述碱选自氢氧化物、碳酸盐和碳酸氢盐。优选地，所述碱是碱金属和钙的氢氧化物、碳酸盐和碳酸氢盐。更优选地，所述碱选自碱金属的碳酸盐和碳酸氢盐，例如碳酸钠、碳酸氢钠、碳酸钾和碳酸氢钾。最优选所述碱选自碳酸钠或碳酸钾。根据一个实施方案，所述处理中使用的碱的量为根据处理前粗酯的酸值计算的理论量的100％-200％，优选105％-180％，更优选110％-150％，最优选110％-120％。
根据一个实施方案，所述脱水粗酯的水含量不超过0.2wt％，优选不超过0.1wt％，更优选不超过0.08wt％。
可以使用助滤剂来促进对所述脱水粗酯的过滤。根据一个实施方案，在用所述碱的水溶液处理所述粗酯之前、期间或之后将助滤剂加入粗酯。优选地，所述助滤剂选自凹凸棒土、硅藻土、碳酸钙、活性炭、高岭土和活性白土。所述助滤剂的加入量为粗酯重量的0.01-0.15％，更优选0.02-0.05％。
对于酯化催化剂，可以使用本领域中已知的各种催化剂。根据一个实施方案，所述酯化催化剂是钛催化剂。优选地，所述钛催化剂是钛酸酯催化剂，更优选地所述钛催化剂选自钛酸四甲酯、钛酸四乙酯、钛酸四正丙酯、钛酸四异丙酯、钛酸四正丁酯、钛酸四异丁酯、钛酸四戊酯、钛酸四己酯、钛酸四庚酯、钛酸四辛酯、钛酸四壬酯、钛酸四癸酯、钛酸四-(2-丙基庚基)酯、钛酸四(十二烷基)酯、钛酸四(十六烷基)酯、钛酸四(十八烷基)酯和钛酸四苯酯。所述钛酸酯催化剂的用量相对于所述对苯二甲酸的重量计为0.117-0.353％，优选0.235-0.353wt％。
对于用于制备酯的所述醇，可以使用本领域通常使用的各种醇。优选地，所述醇是具有4-15个碳原子的醇，优选辛醇，即2-乙基己醇。
本发明的方法得到的对苯二甲酸酯产品具有有利的性质，可以用于各种用途，包括作为聚合物材料例如PVC的增塑剂，作为添加剂等等。
具体实施方式
本申请提供了改进的制备对苯二甲酸酯的方法，更具体地本申请提供了纯化酯化反应完成后得到的粗酯的方法。本申请的方法包括以下步骤：提供粗酯；在145℃-165℃的温度，用碱的水溶液处理所述粗酯以得到碱处理后的粗酯，其中相对于粗酯的重量使用的所述碱水溶液的量为0.5wt％-2wt％；将所述碱处理后的粗酯脱水以得到脱水粗酯；和过滤所述脱水粗酯以得到过滤后粗酯。
对于本申请方法中的粗酯，其是指酯化反应后得到的含有杂质的酯化反应产物，包含作为主要组分的对苯二甲酸二元酯产物，和未反应的原料例如对苯二甲酸单醇酯和醇、副产物水、和酯化催化剂。
所述粗酯可以由对苯二甲酸与辛醇(2-乙基己醇)原位反应制备，或者所述粗酯可以来自其他来源例如来自其他工厂等等。所述粗酯的制备是本领域中已知的并且可以使用本领域中已知的各种方法制备所述粗酯。例如可以使用对苯二甲酸和过量的2-乙基己 醇作为原料，在催化剂例如钛酸酯存在下在酯化反应器中在升高的温度例如180-230℃反应。
根据一个实施方案，可以在惰性气体的保护下进行所述酯化反应。例如可以使用氮气作为保护气体。据信惰性气体的采用可以改进对苯二甲酸酯产品的颜色性质，甚至可以使得省略使用活性炭脱色的程序。
对于用于制备对苯二甲酸酯的醇，可以使用本领域通常使用的各种醇。根据一个实施方案，本发明方法中使用的醇为具有1至18个碳原子的直链或支链伯或仲醇，优选伯或仲烷醇。根据一个实施方案，所述醇是具有4-15个碳原子的醇。作为例子，可提及的醇包括甲醇、乙醇、正丙醇、异丙醇、正丁醇、异丁醇、己醇、庚醇、2-乙基己醇、壬醇、癸醇等等，以及它们的混合物。根据一个实施方案所述醇是2-乙基己醇。
虽然可以使用各种已知的催化剂来制备所述对苯二甲酸酯，但是根据一个实施方案，所述粗酯优选地使用钛催化剂制备。优选地，所述钛催化剂是钛酸酯催化剂，更优选地所述钛催化剂选自钛酸四甲酯、钛酸四乙酯、钛酸四正丙酯、钛酸四异丙酯、钛酸四正丁酯、钛酸四异丁酯、钛酸四戊酯、钛酸四己酯、钛酸四庚酯、钛酸四辛酯、钛酸四壬酯、钛酸四癸酯、钛酸四-(2-丙基庚基)酯、钛酸四(十二烷基)酯、钛酸四(十六烷基)酯、钛酸四(十八烷基)酯和钛酸四苯酯。
对于所述酯化反应，本领域技术人员可以选择催化剂和所选催化剂的用量。根据一个实施方案，选择使用钛酸酯催化剂，并且钛酸酯催化剂的用量相对于对苯二甲酸的重量计为0.117-0.353％，优选0.235-0.353wt％。
当酯化反应在酯化反应器中进行到要求的程度时，可以认为酯化反应已经完成。根据一个实施方案，当酯化反应器中对苯二甲酸固体全部溶解、物料酸值达到≤0.2mgKOH/g时，认为酯化已经完成，可以进行后续处理。
在使用碱的水溶液处理粗酯之前，任选地，可以对所述粗酯进行脱醇处理，以除去粗酯中剩余的醇。该脱醇处理可以在酯化反应器中或者在脱醇塔中进行。一般地，在降低的压力下例如在1-5KPa绝对压力下对粗酯进行蒸馏以除去醇。通过脱醇处理，粗酯中大部分的醇被蒸发出来。蒸发出来的醇被冷凝并且冷凝的醇可以循环使用。根据一个实施方案，将粗酯的醇含量降低到不超过粗酯重量的5％，优选不超过粗酯重量的3％，更优选不超过粗酯重量的1％。
用碱的水溶液处理粗酯(脱醇后或未脱醇)是在较高的温度例如145℃-165℃进行。该处理可以中和粗酯中的单酯酸，降低粗酯的酸值。根据一个实施方案，将粗酯的 酸值降低到不超过0.02mgKOH/g。另外，该处理可以使钛酸酯催化剂水解，生成水合二氧化钛。
温度的选择对于本申请的方法是重要的。根据一个实施方案，在145℃-165℃的温度、优选在145℃-160℃的温度、更优选在150℃-155℃的温度，用碱的水溶液处理所述粗酯。
一般地，采用较高的温度是有利的，因为这可以减少热能损失并且可以加快钛酸酯的水解。但是，申请人出人意料地发现，当采用超过165℃的温度时，处理后的粗酯的酸值异常升高。据信这种酸值的异常升高是因为当温度超过165℃时，钛酸酯活性升高导致对苯二甲酸二元酯在水存在下发生逆反应。这种逆反应导致对苯二甲酸二元酯水解为单酯酸和醇，引起粗酯的酸值升高。通过使用本申请中要求的温度，可以减少或消除所述逆反应，保持钛酸酯的快速水解并且同时减少热能损失。
根据本申请的一个实施方案，本申请方法中使用碱的水溶液处理粗酯在足以防止水蒸发的升高的压力下进行。所述压力应该大于或等于处理温度下水的饱和蒸汽压以将碱的水溶液保持为液态。优选地，所述压力为0.3MPa-3MPa，优选所述压力为0.4-1.8MPa，更优选所述压力为0.4-1.0MPa。
用碱的水溶液处理粗酯时，该碱的水溶液的量是重要的，因为水是钛酸酯水解生成二氧化钛水合物的反应物。使用的水溶液的量不能过少，因为过少的水会使得钛酸酯水解不彻底，导致后续过滤操作出中滤网堵塞。但是，水也是粗酯中的杂质，应该在后续操作中除去。因此，也不能加入过多的水溶液。根据一个实施方案，相对于粗酯的重量，使用的所述碱的水溶液的量为0.5wt％-2wt％，优选0.6wt％-1.5wt％，更优选0.8-1.2％，最优选约1wt％。
一般地，本申请的碱水溶液具有较低的碱浓度。根据一个实施方案，本申请的碱水溶液的浓度为0.2wt％-5wt％，优选0.5wt％-3wt％，更优选1wt％-2wt％。
对于碱的水溶液中使用的碱，可以使用本领域中通常使用的碱。根据一个实施方案，所述碱选自氢氧化物、碳酸盐、碳酸氢盐或它们的混合物。优选地，所述碱是碱金属和钙的氢氧化物、碳酸盐和碳酸氢盐。更优选地，所述碱选自碱金属的碳酸盐和碳酸氢盐，例如碳酸钠、碳酸氢钠、碳酸钾和碳酸氢钾。最优选，所述碱选自碳酸钠或碳酸钾。对应使用碱的水溶液处理粗酯时碱的量，本领域技术人员可以使用本领域中通常使用的量。根据一个实施方案，所述处理中使用的碱的量为根据处理前粗酯的酸值计算的理论量的100％-200％，优选105％-180％，更优选110％-150％，最优选110％-120％。
本领域技术人员知晓，可以根据使用的催化剂的类型和浓度和使用的碱调节使用的碱的水溶液，包括该水溶液的用量和水溶液中碱的浓度。这些调节本领域技术人员可以容易地确定和实现。优选地，在本申请公开的浓度和用量范围进行调节，虽然也可以在必要时偏离本申请中公开的范围。
在使用碱的水溶液处理粗酯时，可以进行搅拌。本领域技术人员可以选择合适的搅拌方式，只要能够促进处理过程的进行。
在使用碱的水溶液处理粗酯之后，对所述处理后的粗酯进行脱水以得到脱水粗酯。对经碱的水溶液处理后的粗酯进行脱水的目的是降低粗酯中的水含量。根据一个实施方案，脱水粗酯的水含量不超过0.2wt％，优选不超过0.1wt％，优选不超过0.08wt％，更优选不超过0.05wt％。脱水可以通过本领域中通常已知的方式进行，包括但不限于蒸馏、闪蒸、减压蒸馏等等。
根据一个实施方案，在使用碱的水溶液处理粗酯之后紧接着进行脱水操作。因此，进行脱水操作时粗酯的温度略低于用碱的水溶液处理所述粗酯时的温度(因为水的加入和自然散热降温，非专门降温)。进行脱水操作的温度因此是120℃-155℃的温度、优选125℃-155℃的温度、更优选130℃-150℃。根据一个实施方案，在使用碱的水溶液处理粗酯之后，将粗酯在130℃-150℃的温度送入蒸馏塔(脱水塔)；该蒸馏塔在降低的压力下例如10-30KPa的绝对压力下运行以蒸馏出水，从而将粗酯中的水含量降低到要求的水平。
在该脱水过程中，由于水的减少，单酯酸盐例如单酯酸钠盐发生结晶形成晶体并且水合二氧化钛失水形成二氧化钛晶体。据信，本申请方法采用的条件，包括碱的水溶液的用量、碱水浓度、碱的水溶液处理粗酯的温度、脱水操作等等，使得脱水过程中形成的晶体具有更大的晶体尺寸，使得有利于后续的过滤操作。本申请的方法甚至可以使得不使用助滤剂而仍然能够实现良好的过滤操作。另外，据信二氧化钛结晶形成晶体的过程可以吸附粗酯中的极性物质例如有色物质以及吸附单酯酸盐。因为这些晶体被后续过滤除去，所以这另外有利于除去极性物质，这对降低产品的色度以及改进产品的体积电阻是有利的。在工业化生产中，在有氮气保护的条件下，不用添加活性炭和助滤剂，产品色号可以达到10-15号(铂-钴色号)。
该脱水步骤除去的水的COD为约2000-3000mg/L，并且不含盐。根据一个实施方案，将该脱水步骤除去的水用于配置以上所使用的碱的溶液，从而进一步降低废水排放，这是特别有利的。
在对粗酯进行脱水得到脱水粗酯后，对脱水粗酯进行过滤。通过过滤，将脱水粗酯中的晶体滤除。
可以采用增塑剂本领域中通常已知的过滤方式进行过滤。例如可以采用板式密闭过滤机进行过滤。过滤得到的滤渣包含二氧化钛、单酯酸盐和对苯二甲酸二元酯。根据一个实施方案，所述滤渣含有30-35wt％对苯二甲酸二元酯、约30wt％的二氧化钛和35-40wt％的单酯酸盐。
据信，本申请的方法中，粗酯中形成的晶体具有更好的性质(尺寸和形态)，使得过滤能够平稳顺畅的进行。本申请的方法中，过滤过程中不会形成致密且低孔隙率的滤饼。在现有技术的方法中，容易形成致密且低孔隙率的滤饼，导致不能继续进行过滤。
根据一个实施方案，脱水后的粗酯，温度在110-130℃(水蒸发吸热及自然散热导致的温度降低，不用专门降温)，用板式密闭过滤机过滤，得到澄清的粗酯。
虽然本申请的方法实现了有利的过滤，但是，根据一个实施方案，也可以使用助滤剂来进一步促进对脱水粗酯的过滤。通常，助滤剂具有防止晶体在滤布上形成致密且低孔隙率的滤层并因此快速堵塞过滤器的功能。根据一个实施方案，可以在用所述碱的水溶液处理所述粗酯之前、期间或之后将助滤剂加入粗酯。当在用所述碱的水溶液处理所述粗酯之后加入助滤剂时，优选在用碱的水溶液处理之后立即添加助滤剂。本申请使用本领域中通常使用的助滤剂。优选的，所述助滤剂选自凹凸棒土、硅藻土、碳酸钙、活性炭、高岭土和活性白土。以本领域中通常使用的量使用所述助滤剂。根据一个实施方案，所述助滤剂的加入量为粗酯重量的0.01-0.15％，更优选0.02-0.05％。
在一个进一步的实施方案中，还可以在用碱的水溶液处理粗酯之前、期间或之后，将吸附剂如活性炭加入到粗酯中。优选地，将吸附剂与助滤剂一起加入。通常吸附剂提供了具有较浅颜色和/或较低金属含量的产物。本申请使用本领域中通常使用的吸附剂。作为吸附剂的例子，可以提及氧化铝、活性陶土、活性炭、氧化镁、活性氧化铝和氧化硅。优选地，使用活性炭作为吸附剂。
在一个实施方案中，所述助滤剂和/或吸附剂可以在用碱的水溶液处理的同时一起添加或者之后立即添加。
根据本申请的一个实施方案，为了进一步提升酯产品的品质，还可以将以上过滤后的粗酯进行进一步的处理。所述进一步的处理可以包括将过滤后粗酯进行汽提处理以得到汽提后粗酯，和干燥所述汽提后粗酯以提供酯产品。任选地，还可以对该酯产品进行精密过滤以确保该酯产品不包含任何固体颗粒。
对于汽提处理，这是酯增塑剂制备领域的一种常见处理。根据一个实施方案，对过滤后的粗酯进行汽提以进一步除去其中的醇和水。所述汽提可以使用水蒸气或惰性气体，例如氮气。根据一个实施方案，使用水蒸气进行汽提。
根据一个实施方案，将过滤后的粗酯加热到145-165℃，然后使用水蒸汽进行汽提，例如在汽提塔中，以进一步除去其中的辛醇、水分等轻组分。汽提塔在减压例如5-15KPa的绝对压力下工作。在汽提塔中通入直接水蒸汽，该直接水蒸汽可以降低辛醇的气相分压，有利于辛醇的脱除。一般地，所述直接水蒸汽的加入量为粗酯量的5-10wt％。在汽提塔的下部，设置有蒸发器，例如降膜蒸发器，以加热粗酯将粗酯的温度保持在145-165℃。蒸发的醇和水在冷凝器中冷凝，然后进入醇水分离罐。分离的辛醇可以作为原料循环使用，水送入废水处理系统。这一步骤分离的废水的COD在2000-3000mg/L。
在使用水蒸汽进行汽提的情况下，汽提后的粗酯含有微量的水。因此，可以对汽提后的物料进行干燥处理以除去水。可以采用酯增塑剂领域通常使用的干燥处理。例如，可以使用处于1-3KPa绝对压力下的干燥塔处理汽提后的粗酯，以将水分进一步除去。
通常，在对汽提后的粗酯进行干燥处理后，可以将得到酯产品作为最终产品使用。然而，任选地，在所述干燥后，还可以对酯产品进行进一步过滤。根据一个实施方案，该进一步的过滤是精密过滤，以确保最终酯产品不包含固体颗粒。
本申请的方法可以以间歇、半连续或连续方式进行。根据一个实施方案，本申请方法的至少一部分以连续方式进行。例如，可以以间歇方式进行酯化反应以制备并提供粗酯，但是以连续方式进行用碱的水溶液处理粗酯、对粗酯脱水以及过滤脱水粗酯的步骤。任选地，之后的汽提、干燥和再次精密过滤步骤也以连续方式进行。作为另外的选择，本申请方法的全部过程以连续方式进行。
根据一个实施方案，本申请的方法可以以下方式实施：在对苯二甲酸酯化反应完成后，粗酯，任选进行脱醇以后，在140-160℃，直接在承压(0.4-1.5MPa)压力在中和反应器中用碱的水溶液中和；中和时加入粗酯量约1％的碱水溶液；所述碱是Na 2CO 3或NaHCO 3，优选Na 2CO 3；Na 2CO 3浓度为依据粗酯酸值计算的理论值的110-150％；然后将粗酯中的水脱除(脱出的水COD为2000-3000mg/l，不含盐，可用于配置碱溶液，循环利用)；然后过滤将粗酯中的单酯酸钠盐及催化剂失活形成的二氧化钛滤除；然后使用水蒸汽进行汽提、干燥；最后进行精密过滤，得到最终产品。
本申请的发明人发现，采用本申请的方法，可以提供具有特别有利的性质的酯产品，这些有利的性质包括酸值、色度、纯度、水分、闪点、体积电阻率、Ti含量等等。一方面，采用本申请的方法制备的酯产品的品质可达到或甚至高于现有技术采用连续中和、 水洗工艺的产品品质。另一方面，采用本申请的方法制备的酯产品的品质可以达到或甚至超过HG/T 2423-2008优级品的标准。
同时，本申请的方法可以显著降低废水排放。采用本申请的方法，除酯化反应的副产物水和汽提冷凝水以外，过程中没有废水排放。与现有技术采用连续中和、水洗工艺的方法相比，本申请方法的COD排放减少约90wt％，污水量减少约57wt％。污水和COD排放减少的计算如下：
现有技术的中和及水洗步骤产生40-50wt％的废水，并且混合后的废水COD为约30000mg/L。现有技术方法中，中和及水洗处理使用酯化反应的副产物水和汽提冷凝水作为中和及水洗的水源。本申请的方法中，酯化反应的副产物水的COD为约9000-10000mg/L，量为粗酯量的约9％；汽提冷凝水的COD为约2000-3000mg/L，量为粗酯量的约8％；混合后总量为粗酯量的17％，COD为约6000-7000mg/L。因此，废水量相当于现有技术方法的约43％(0.17÷0.40＝42.5％，)，COD相当于现有技术方法的约9.2％[(0.17×6500)/(0.4×30000)]。
另外，值得注意的是，本申请的方法排放的废水不含盐、不含固体悬浮物，使得废水可直接进行生化处理。而且，本申请的废水处理过程中产生的污泥量大幅度减少。
最后，值得注意的是在对粗酯脱水后，对脱水粗酯进行过滤时，没有过滤问题的困扰。这说明本申请的方法制备的脱水粗酯具有出色的过滤能力。这相对于现有技术的方法而言，是显著进步。
下面，使用实施例进一步说明本申请的方法。
实施例
实施例1
对苯二甲酸二辛酯的合成
以对苯二甲酸(PTA)和辛醇(2-乙基己醇)为原料，原料配比PTA:辛醇＝1:3(摩尔比)，以0.117-0.353％，优选0.235-0.353wt％(基于PTA重量)的钛酸酯(钛酸四异丙酯或钛酸四正丁酯)为催化剂，在酯化釜中在180-230℃进行酯化反应。当PTA固体全部溶解且物料酸值达到≤0.2(mgKOH/g物料)时，酯化完成。反应生成的水经冷凝器冷凝后，在醇水分离罐中和醇分离，醇回流进酯化釜继续反应，分离出的水作为废水排放。该部分的水的量为粗酯量的约9％，COD为约9000-10000mg/l。此水为冷凝水，不含盐及固体杂质，pH为约中性。
粗酯脱醇
酯化完成后的粗酯，含有摩尔比对苯二甲酸二辛酯：2-乙基己醇＝1：1的2-乙基己醇。该粗酯在脱醇塔中，在绝压1-5KPa下脱醇；其中绝大部分的2-乙基己醇蒸发，然后经冷凝器冷凝，作为原料使用。脱醇后的粗酯含有小于1wt％的2-乙基己醇。此时粗酯的温度为约180-210℃。
中和
脱醇后的粗酯，降温至140-160℃，在中和釜中加入Na 2CO 3(或NaHCO 3)溶液中和。碱水溶液量为粗酯量的约1％，碱的量为依据粗酯酸值计算的理论值的100-150％(碱水溶液浓度为1-2％)，通常为理论值的110-120％。中和釜压力为0.4-1.0MPa(≥该温度下水的饱和蒸气压)；在该条件下，碱液保持液态，粗酯中的单酯酸和碳酸钠反应，生成单酯酸钠盐，钛酸酯水解为二氧化钛水合物。
脱水
中和后的粗酯，在130-150℃的温度，进入脱水塔。脱水塔在10-30KPa的绝压下运行，其中水分蒸发，粗酯中的水分含量降低到0.08wt％以下。蒸发的水分在冷凝器中冷凝。脱水的过程，同时也是单酯酸钠盐失水再结晶和水合二氧化钛失水形成二氧化钛再结晶的过程。而且二氧化钛形成结晶的过程可以吸附粗酯中的极性物质，从而除去部分形成颜色的物质及单酯酸钠盐，这对降低产品的色度及体积电阻有利。
过滤
脱水后的粗酯，温度在110-130℃(水蒸发吸收热量及自然散热导致的降温，不用专门降温)，使用板式密闭过滤机过滤，得到澄清的粗酯，作为汽提的原料。滤渣含有30-35％DOTP、约30％二氧化钛和35-40％的单酯酸钠盐。
汽提及干燥
过滤后的粗酯加热至145-165℃，在汽提塔中脱除掉其中的辛醇、水分等轻组分。汽提塔在5-15KPa绝压下，在塔中通入直接蒸汽，直接蒸汽可以降低辛醇的气相分压，有利于辛醇的脱除；直接蒸汽的加入量为粗酯量的5-10wt％。在汽提塔的下部，有降膜蒸发器，加热粗酯保持粗酯的温度在145-165℃。蒸发的醇和水在冷凝器中冷凝，然后进入醇水分离罐，分离的辛醇作为原料循环使用。水进入废水处理系统。该步骤分离的废水的COD为约2000-3000mg/L。因为汽提塔中通入蒸汽，粗酯中含有微量的水。汽提后的粗酯经过干燥塔进行干燥，干燥塔在1-3KPa绝压下，将其中的水分进一步脱除。
精密过滤
汽提并且干燥后的粗酯经过精密过滤器过滤，得到最终产品。精密过滤器作为预防前期过滤不彻底的保险装置，可以确保产品不含有固体颗粒。
在已工业化的10万吨/年DOTP(对苯二甲酸二辛酯)装置中，生产过程中不加入助滤剂及活性炭，最终产品以HG/T 2423-2008标准检验结果如下：
Figure PCTCN2020077996-appb-000001

Claims (9)

  1. 通过对苯二甲酸与醇在酯化催化剂的存在下反应制备的二元酯粗酯的纯化方法，所述方法包括以下步骤：
    提供所述粗酯；
    在145℃-165℃的温度、优选在145℃-160℃的温度、更优选在150℃-155℃的温度，用碱的水溶液处理所述粗酯以得到碱处理后的粗酯，其中相对于粗酯的重量使用的所述碱的水溶液的量为0.5wt％-2wt％，优选0.6wt％-1.5wt％，更优选0.8wt％-1.2wt％，最优选1wt％；
    将所述碱处理后的粗酯脱水以得到脱水粗酯；和
    过滤所述脱水粗酯以得到过滤后粗酯。
  2. 如权利要求1所述的方法，所述方法还包括：
    将过滤后粗酯进行汽提处理以得到汽提后粗酯，
    干燥所述汽提后粗酯以提供酯产品，和
    任选地，对酯产品进行过滤。
  3. 根据权利要求1或2所述的方法，其中所述使用碱的水溶液的处理在足以防止水蒸发的升高的压力下进行，优选地所述压力为0.3MPa-3MPa，更优选地所述压力为0.4-1.0MPa。
  4. 根据权利要求1或2所述的方法，其中在使用碱的水溶液处理粗酯之前，对所述粗酯进行脱醇处理，优选将粗酯的醇含量降低到不超过粗酯重量的5％，优选不超过粗酯重量的3％，更优选不超过粗酯重量的1％。
  5. 根据权利要求1或2所述的方法，其中所述碱选自氢氧化物、碳酸盐和碳酸氢盐，优选地所述碱选自碱金属和钙的氢氧化物、碳酸盐和碳酸氢盐，更优选选自碱金属的碳酸盐和碳酸氢盐，最优选选自碳酸钠或碳酸钾。
  6. 根据权利要求1或2所述的方法，其中所述碱的水溶液包含的碱的量为根据处理前粗酯的酸值计算的理论量的100％-200％，优选105％-180％，更优选110％-150％，最优选110％-120％。
  7. 根据权利要求1或2所述的方法，其中所述脱水粗酯的水含量不超过0.2wt％，优选不超过0.1wt％，更优选不超过0.08wt％。
  8. 如权利要求1或2所述的方法，其中所述酯化催化剂是钛催化剂，优选地所述钛催化剂是钛酸酯催化剂，更优选地所述钛催化剂选自钛酸四甲酯、钛酸四乙酯、钛酸四丙酯、钛酸四异丙酯、钛酸四正丁酯、钛酸四异丁酯、钛酸四戊酯、钛酸四己酯、钛酸四庚酯、钛酸四辛酯、钛酸四壬酯、钛酸四癸酯、钛酸四-(2-丙基庚基)酯、钛酸四(十二烷基)酯、钛酸四(十六烷基)酯、钛酸四(十八烷基)酯和钛酸四苯酯，更优选地所述钛酸酯催化剂的用量相对于所述对苯二甲酸酸的重量计为0.117-0.353％。
  9. 如权利要求1所述的方法，其中所述醇是具有4-15个碳原子的醇，优选辛醇,即2-乙基己醇，成品即对苯二甲酸二辛酯(英文缩写DOTP)。
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