阅读说明：本技术 一种大粒径对苯二甲酸双羟乙酯的制备方法 (Preparation method of large-particle-size dihydroxy ethyl terephthalate ) 是由 刘宝树 袁培权 孙华 于 2020-12-31 设计创作，主要内容包括：本发明提供一种大粒径对苯二甲酸双羟乙酯的制备方法,包括以下步骤：将对苯二甲酸双羟乙酯粗品加入乙二醇中,加热至68-75℃溶解,然后缓慢降温至50-52℃,加入对苯二甲酸双羟乙酯晶种养晶10-30min,然后持续缓慢降温至0-15℃,并在降温至45-49℃时,滴加媒晶剂水溶液,滴加结束后于0-15℃养晶60-150min,得对苯二甲酸双羟乙酯产品；其中,媒晶剂为吐温80、司盘80或烷基糖苷中至少一种。通过本发明提供的制备方法,得到了大粒径且粒径分布集中的高纯度对苯二甲酸双羟乙酯产品,产品纯度可达99％以上,产品中值粒径可达1200μm以上,且产品流动性好,存贮不易结块,具有极高的推广应用价值。(The invention provides a preparation method of dihydroxy ethyl terephthalate with large particle size, which comprises the following steps: adding the crude product of the dihydroxyethyl terephthalate into ethylene glycol, heating to 68-75 ℃ for dissolution, then slowly cooling to 50-52 ℃, adding a dihydroxyethyl terephthalate seed crystal for growing crystals for 10-30min, then continuously and slowly cooling to 0-15 ℃, dropwise adding a crystallization agent aqueous solution when cooling to 45-49 ℃, and growing crystals for 60-150min at 0-15 ℃ after dropwise adding to obtain a dihydroxyethyl terephthalate product; wherein the mordant is at least one of Tween 80, span 80 or alkyl glycoside. The preparation method provided by the invention can be used for obtaining the high-purity hydroxyethyl terephthalate product with large particle size and concentrated particle size distribution, the product purity can reach more than 99%, the median particle size of the product can reach more than 1200 mu m, the product has good fluidity, is not easy to agglomerate when stored, and has extremely high popularization and application values.)

1. A preparation method of large-particle-size dihydroxy ethyl terephthalate is characterized by comprising the following steps of:

step one, adding a crude product of dihydroxy ethyl terephthalate into ethylene glycol, heating to 68-75 ℃ to dissolve to obtain a crude product solution of dihydroxy ethyl terephthalate;

step two, slowly cooling the crude bis-hydroxyethyl terephthalate solution to 50-52 ℃ under the stirring condition, adding bis-hydroxyethyl terephthalate seed crystals, and growing the crystals for 10-30min to obtain a crystal suspension;

step three, continuously and slowly cooling the crystallization suspension to 0-15 ℃, starting to dropwise add a water solution of a habit modifier when the temperature is reduced to 45-49 ℃, growing crystals at 0-15 ℃ for 60-150min after dropwise adding is finished, filtering, washing and drying to obtain a dihydroxy ethyl terephthalate product; wherein the mordant is at least one of tween 80, span 80 or alkyl glycoside.

2. The method for preparing big-particle-size dihydroxy ethyl terephthalate according to claim 1, wherein in step one, the mass ratio of the crude dihydroxy ethyl terephthalate to ethylene glycol is 1-3: 10.

3. The method of claim 1, wherein in step two, the temperature is decreased to 50-52 ℃ at a rate of 0.1-0.4 ℃/min.

4. The method for preparing big-particle-size dihydroxy ethyl terephthalate according to claim 1, wherein in step two, the particle size of the dihydroxy ethyl terephthalate seed crystal is 150-200 μm.

5. The method for preparing big-particle-size dihydroxy ethyl terephthalate according to claim 4, wherein in step two, the amount of the dihydroxy ethyl terephthalate seed crystals added is 1% -5% of the mass of the crude dihydroxy ethyl terephthalate.

6. The method of claim 1, wherein the temperature of the dihydroxy ethyl terephthalate with a large particle size is continuously and slowly decreased to 0-15 ℃ at a rate of 0.1-0.2 ℃/min in the third step.

7. The method of claim 1, wherein in step three, the medium crystal is tween 80.

8. The method for preparing big-particle-size dihydroxy ethyl terephthalate according to claim 1, wherein in step three, the amount of the habit modifier added is 0.6% -1% of the mass of the crude dihydroxy ethyl terephthalate.

9. The method of claim 8, wherein in step three, the mass of water in the aqueous solution of the habit modifier is 2-4 times that of the glycol.

10. The method of claim 1, wherein in step three, the aqueous solution of the habit modifier is added dropwise at a rate of 5-10 mL/min.

Technical Field

The invention relates to the technical field of fine chemical production, in particular to a preparation method of large-particle-size dihydroxy ethyl terephthalate.

Background

BHET (CAS No. 959-26-2) is white powder with low purity, and its crystal is white after recrystallizationThe color scale or needle shape is easy to be damped and agglomerated into a block shape after being exposed in the air for a long time, and the density is 1.368g/cm³The melting point is 110 ℃, and the molecular formula structure is shown as follows.

The dihydroxy ethyl terephthalate is a main raw material for producing the ethylene terephthalate (PET), the polyester produced by the PET has excellent performance, and the PET can also be used for producing plastic products such as films or bottles and the like and has important application in engineering plastics and other industrial fields. Currently, methods for producing BHET mainly include an ester exchange method (DMT method), a direct esterification method (PTA method), an ethylene oxide addition method, and a PET depolymerization method. In the prior art, a PET depolymerization method mainly uses PET as a raw material, dihydric alcohol as a depolymerizing agent and magnesium hydroxide as a catalyst to depolymerize the PET to generate a BHET crude product, and then the BHET crude product is subjected to processes of cooling crystallization, separation, drying and the like in water to obtain the BHET product. The obtained BHET product can be reused for synthesizing PET, thereby realizing green recycling of PET. However, the crude BHET prepared by the depolymerization method contains more impurities, the purity of the product is still low after subsequent recrystallization, and the prepared BHET product has small grain size and wide grain size distribution, is difficult to filter, wash and dry, and is inconvenient for subsequent processing and use. Therefore, it is very important to find a method for preparing high-content and high-purity dihydroxy ethyl terephthalate with large particle size.

Disclosure of Invention

Aiming at the problems of low purity, small grain size, wide grain size distribution and inconvenience in subsequent processing and use of the dihydroxy ethyl terephthalate product prepared by the existing PET depolymerization method, the invention provides a preparation method of dihydroxy ethyl terephthalate with large grain size.

In order to solve the technical problems, the technical scheme provided by the invention is as follows:

a preparation method of large-particle-size dihydroxy ethyl terephthalate comprises the following steps:

step one, adding a crude product of dihydroxy ethyl terephthalate into ethylene glycol, heating to 68-75 ℃ to dissolve to obtain a crude product solution of dihydroxy ethyl terephthalate;

step two, slowly cooling the crude bis-hydroxyethyl terephthalate solution to 50-52 ℃ under the stirring condition, adding bis-hydroxyethyl terephthalate seed crystals, and growing the crystals for 10-30min to obtain a crystal suspension;

step three, continuously and slowly cooling the crystallization suspension to 0-15 ℃, starting to dropwise add a habit modifier aqueous solution when the crystallization suspension is cooled to 45-49 ℃, growing crystals at 0-15 ℃ for 60-150min after dropwise adding, filtering, washing and drying to obtain a dihydroxy ethyl terephthalate product; wherein the mordant is at least one of tween 80, span 80 or alkyl glycoside.

Because the solubility of the dihydroxyethyl terephthalate in water is low, the traditional dihydroxyethyl terephthalate crystallization process usually adopts water as a crystallization solvent to improve the yield of the dihydroxyethyl terephthalate. However, since the solubility of the dihydroxyethyl terephthalate in water is low, the crude dihydroxyethyl terephthalate needs to be dissolved at high temperature when being dissolved in water, and the energy consumption is high. And the prepared dihydroxy ethyl terephthalate product is generally fine needle-shaped crystals with small grain diameter and uneven grain size distribution by taking water as a crystallization solvent.

Compared with the prior art, the preparation method of the dihydroxyethyl terephthalate provided by the invention adopts ethylene glycol as a crystallization solvent, adds the Tween 80, span 80 or alkyl glycoside mordant at a specific stage, and obtains the long rod-shaped large-particle-size dihydroxyethyl terephthalate crystal with complete crystal form and without coalescence by controlling the conditions of the crystallization process, such as the adding temperature of the seed crystal, the adding temperature of the mordant and the like. The crystallization method of the dihydroxyethyl terephthalate can prepare the dihydroxyethyl terephthalate product with higher purity and yield by one-time crystallization, has complete crystal form, large granularity, easy filtration, washing and drying of crystal slurry, low labor intensity of process operation, good product fluidity and difficult dust raising and caking, and can greatly improve the production efficiency and the product quality of the dihydroxyethyl terephthalate by taking the dihydroxyethyl terephthalate obtained by the preparation process as a raw material for preparing the ethylene terephthalate.

Preferably, the crude dihydroxy ethyl terephthalate product in the invention is prepared by a PET depolymerization method, and the content of dihydroxy ethyl terephthalate in the crude dihydroxy ethyl terephthalate product is 94%.

Preferably, in the first step, the mass ratio of the crude dihydroxy ethyl terephthalate product to the ethylene glycol is 1-3: 10.

The mass ratio of the crude product of the dihydroxyethyl terephthalate to the ethylene glycol is too low, so that the yield of the product is reduced; the mass ratio is too high, and although the yield of the product can be improved, the supersaturation degree in the system is not easy to control in a range favorable for good growth of crystals, and impurities are easy to be occluded in the bis-hydroxyethyl terephthalate crystals, which is not favorable for improving the purity of the product. And the too high mass ratio also can cause the crystallization nucleation rate to be too fast, the magma suspension density to be too high, and the fine microcrystals are easy to adhere to the crystal surface, so that the particle size distribution of the product is not uniform, and the coalescence phenomenon is caused.

The preferable mass ratio can also reduce impurity occlusion in the crystal, improve the purity of the product and facilitate the grain size distribution of the prepared dihydroxy ethyl terephthalate crystal to be more uniform on the premise of ensuring the product yield.

Preferably, in the second step, the temperature is reduced to 50-52 ℃ at the speed of 0.1-0.4 ℃/min.

Preferably, in the second step, the particle size of the bis-hydroxyethyl terephthalate seed crystal is 150-200 μm.

Preferably, in the second step, the adding amount of the bis-hydroxyethyl terephthalate seed crystals is 1-5% of the mass of the crude bis-hydroxyethyl terephthalate product.

The preferable grain size and the addition amount of the seed crystal are matched with the addition temperature of the seed crystal, so that explosive nucleation can be avoided, the supersaturation degree of a system can be consumed, and the generation of new nuclei is inhibited, thereby being beneficial to preparing the large-grain-size dihydroxyethyl terephthalate crystal with uniform grain size distribution; meanwhile, the purity of the bis-hydroxyethyl terephthalate product is improved.

Preferably, in the third step, the temperature is continuously and slowly reduced to 0-15 ℃ at the speed of 0.1-0.2 ℃/min.

If the temperature of the system is not reduced to 0-15 ℃ after the aqueous solution of the mordant is dripped, the temperature is required to be reduced to 0-15 ℃ at the same cooling rate, and then crystal growth is started, wherein the crystal growth time is 60-150 min.

By controlling the cooling rate of each step, the crystallization system can be in proper supersaturation, the nucleation and growth of the crystal are controlled, the explosive nucleation is avoided, the impurity occlusion in the crystal is reduced, the generation of new nuclei is inhibited, and the acquisition of the dihydroxyethyl terephthalate crystal with large grain diameter and uniform grain diameter distribution is facilitated.

Preferably, in the third step, the mordant is tween 80.

Preferably, in the third step, the addition amount of the habit modifier is 0.6-1% of the mass of the crude dihydroxy ethyl terephthalate product.

Preferably, in the third step, the mass of water in the aqueous solution of the mordant is 2-4 times of that of the ethylene glycol.

Preferably, in the third step, the dropping rate of the aqueous solution of the mordant is 5-10 mL/min.

By controlling the acceleration rate of the aqueous solution drops of the mordant, the supersaturation of a system can be effectively controlled, and the continuous growth of crystals can be prevented from being further promoted under the condition that fine crystals are generated, so that the purity, yield and particle size of the product are improved.

Optionally, in the second step and the third step, the stirring speed is 100-.

Optionally, in the third step, the drying mode is vacuum drying at 60-70 ℃ for 6-10 h.

The crystallization method of the dihydroxyethyl terephthalate of the invention realizes the control of the grain diameter and the crystal form of the dihydroxyethyl terephthalate product in the crystallization process by strictly controlling the adding temperature, the grain diameter and the adding amount of the seed crystal, strictly controlling the adding temperature of the habit modifier and matching with the specific slow cooling rate through a combined strategy of adding the seed crystal to control the nucleation, adding the habit modifier at a specific speed in a specific stage and slowly cooling and growing the crystal by stages within the preferable parameter range, obtains the high-purity dihydroxyethyl terephthalate product with large grain diameter and concentrated grain diameter distribution, has the purity of the product of more than 99 percent and the yield of more than 75 percent, can prepare the dihydroxyethyl terephthalate crystal with the median grain diameter of more than 1200 mu m, has good product fluidity, is not easy to agglomerate during storage, has low process, high production efficiency and is convenient for post-treatment, saves the post-treatment cost and has extremely high popularization and application values.

Drawings

FIG. 1 is a photograph of a macro camera of a bishydroxyethyl terephthalate product prepared in example 1;

FIG. 2 is an optical micrograph of a bishydroxyethyl terephthalate product prepared in comparative example 1;

FIG. 3 is a photograph of a macro camera of a bishydroxyethyl terephthalate product prepared in comparative example 1;

FIG. 4 is a graph comparing the particle size distribution of the bishydroxyethyl terephthalate products prepared in comparative example 1 and example 1.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The crude bishydroxyethyl terephthalate used in the following examples and comparative examples was the crude bishydroxyethyl terephthalate prepared by the PET depolymerization method, and the content of bishydroxyethyl terephthalate in the crude bishydroxyethyl terephthalate was 94%.

Example 1

A preparation method of large-particle-size dihydroxy ethyl terephthalate comprises the following steps:

step one, weighing 3.0g of fully dried dihydroxy ethyl terephthalate crude product and 30g of ethylene glycol, adding into a crystallizer, starting the crystallizer to stir at the stirring speed of 150r/min, heating to 68 ℃, and stirring for 10min to obtain a dihydroxy ethyl terephthalate crude product solution;

step two, under the stirring condition of 150r/min, cooling the crude dihydroxy ethyl terephthalate solution to 50 ℃ at the cooling rate of 0.1 ℃/min, then adding 0.15g of dihydroxy ethyl terephthalate seed crystal, and carrying out heat preservation and crystal growth for 30min to obtain a crystal suspension; wherein the granularity of the dihydroxy ethyl terephthalate seed crystal is 200 mu m;

step three, adding 21mg of tween 80 into 60g of water, and uniformly mixing to obtain a tween 80 aqueous solution;

step four, under the stirring condition of 150r/min, cooling the crystallizer suspension to 45 ℃ at the cooling rate of 0.1 ℃/min, dropwise adding the prepared Tween 80 aqueous solution at the dropping rate of 8mL/min, keeping the cooling rate of 0.1 ℃/min for cooling while dropwise adding until the Tween 80 aqueous solution is completely dropwise added, and growing the crystal for 120min when the temperature is up to 4 ℃;

and step five, filtering the suspension obtained in the step four, washing a filter cake for 3 times by using water, and then drying for 6 hours in vacuum at the temperature of 60 ℃ to obtain 2.16g of white dihydroxy ethyl terephthalate product, wherein the yield of the product is 76%, and the purity of HPLC is 99.39%.

The photograph of the bishydroxyethyl terephthalate product prepared in this example with a macro camera is shown in fig. 1, and it can be seen from the photograph that the bishydroxyethyl terephthalate product prepared in this example is a white long rod-like crystal with large particle size, complete crystal form and no agglomeration.

The particle size distribution of the product obtained in this example is unimodal, the median particle diameter is 1380 μm and the diameter spacing is 1.710.

Example 2

This example provides a method for preparing dihydroxy ethyl terephthalate with large particle size, which is exactly the same as example 1 except that the habit modifier is span 80. The final product was 2.10g of white rod crystals, the product yield was 74%, the HPLC purity was 99.19%, the median particle diameter was 1350 μm, the diameter distance was 1.750, and the particle size distribution was unimodal.

Example 3

This example provides a method for preparing dihydroxy ethyl terephthalate with large particle size, which is exactly the same as example 1 except that the habit modifier is alkyl glycoside. The final product was prepared as white rod crystals 2.13g, product yield 75%, HPLC purity 99.16%, median particle size 1370 μm, diameter spacing 1.780, and particle size distribution as a single peak.

Example 4

A preparation method of large-particle-size dihydroxy ethyl terephthalate comprises the following steps:

step one, weighing 5.0g of fully dried dihydroxy ethyl terephthalate crude product and 30g of ethylene glycol, adding the weighed materials into a crystallizer, starting the crystallizer to stir at the stirring speed of 200r/min, heating to 72 ℃, and stirring for 20min to obtain a dihydroxy ethyl terephthalate crude product solution;

step two, under the stirring condition of 200r/min, cooling the crude dihydroxy ethyl terephthalate solution to 51 ℃ at the cooling rate of 0.3 ℃/min, then adding 0.15g of dihydroxy ethyl terephthalate seed crystal, and carrying out heat preservation and crystal growth for 20min to obtain a crystal suspension; wherein the granularity of the dihydroxy ethyl terephthalate seed crystal is 150 mu m;

step three, adding 31.5mg of span 80 into 120g of water, and uniformly mixing to obtain a span 80 aqueous solution;

step four, under the stirring condition of 200r/min, cooling the crystallizer suspension to 47 ℃ at the cooling rate of 0.1 ℃/min, dropwise adding the prepared span 80 aqueous solution at the dropping rate of 5mL/min, and keeping the cooling rate of 0.1 ℃/min for cooling while dropwise adding until the span 80 aqueous solution is completely dropwise added, and growing the crystal for 60min when the temperature is up to 10 ℃;

and step five, filtering the suspension obtained in the step four, washing a filter cake for 3 times by using water, and then carrying out vacuum drying for 8 hours at the temperature of 65 ℃ to obtain 3.75g of white dihydroxy ethyl terephthalate product, wherein the yield of the product is 79 percent, and the HPLC purity is 99.08 percent.

The particle size distribution of the product obtained in this example is unimodal, with a median particle size of 1250 μm and a diameter spacing of 2.015.

Example 5

A preparation method of large-particle-size dihydroxy ethyl terephthalate comprises the following steps:

step one, weighing 9.0g of fully dried dihydroxy ethyl terephthalate crude product and 30g of ethylene glycol, adding into a crystallizer, starting the crystallizer to stir at a stirring speed of 270r/min, heating to 75 ℃, and stirring for 20min to obtain a dihydroxy ethyl terephthalate crude product solution;

step two, under the condition of stirring at 270r/min, cooling the crude dihydroxy ethyl terephthalate solution to 52 ℃ at the cooling rate of 0.4 ℃/min, then adding 0.09g of dihydroxy ethyl terephthalate seed crystal, and carrying out heat preservation and crystal growth for 10min to obtain a crystal suspension; wherein the granularity of the dihydroxy ethyl terephthalate seed crystal is 150 mu m;

step three, adding 0.09g of Tween 80 into 90g of water, and uniformly mixing to obtain a Tween 80 aqueous solution;

step four, under the condition of stirring at 270r/min, cooling the crystallizer suspension to 49 ℃ at a cooling rate of 0.2 ℃/min, dropwise adding the prepared Tween 80 aqueous solution at a dropping rate of 5mL/min, and keeping the cooling rate of 0.2 ℃/min for cooling while dropwise adding until the Tween 80 aqueous solution is completely dropwise added, and growing the crystal for 150min at the temperature of 15 ℃;

and step five, filtering the suspension obtained in the step four, washing a filter cake for 3 times by using water, and then carrying out vacuum drying for 10 hours at the temperature of 70 ℃ to obtain 7.18g of white dihydroxy ethyl terephthalate product, wherein the product yield is 84%, and the HPLC purity is 99.02%.

The particle size distribution of the product obtained in this example is unimodal, with a median particle size of 1310 μm and a diameter distance of 1.930.

Example 6

A preparation method of large-particle-size dihydroxy ethyl terephthalate comprises the following steps:

step one, weighing 3.0g of fully dried dihydroxy ethyl terephthalate crude product and 30g of ethylene glycol, adding into a crystallizer, starting the crystallizer to stir at the stirring speed of 230r/min, heating to 70 ℃, and stirring for 10min to obtain a dihydroxy ethyl terephthalate crude product solution;

step two, under the stirring condition of 230r/min, cooling the crude dihydroxy ethyl terephthalate solution to 50 ℃ at the cooling rate of 0.1 ℃/min, then adding 0.09g of dihydroxy ethyl terephthalate seed crystal, and carrying out heat preservation and crystal growth for 30min to obtain a crystal suspension; wherein the granularity of the dihydroxy ethyl terephthalate seed crystal is 150 mu m;

step three, adding 25.5mg of alkyl glycoside into 60g of water, and uniformly mixing to obtain an alkyl glycoside aqueous solution;

step four, under the stirring condition of 230r/min, cooling the crystallizer suspension to 47 ℃ at the cooling rate of 0.1 ℃/min, dropwise adding the prepared alkyl glycoside aqueous solution at the dropping rate of 10mL/min, and keeping the cooling rate of 0.1 ℃/min for cooling while dropwise adding until the dropping of the alkyl glycoside aqueous solution is finished, and growing the crystals for 90min when the temperature is up to 0 ℃;

and step five, filtering the suspension obtained in the step four, washing a filter cake for 3 times by using water, and then carrying out vacuum drying for 10 hours at the temperature of 70 ℃ to obtain 2.16g of white dihydroxy ethyl terephthalate product, wherein the product yield is 76%, and the HPLC purity is 99.21%.

The product obtained in this example had a monomodal particle size distribution with a median particle diameter of 1260 μm and a diameter spacing of 1.908.

Example 7

This example provides a method for preparing dihydroxy ethyl terephthalate, which is the same as example 1 except that the cooling rate in the fourth step is 0.3 ℃/min. The obtained product was 2.11g of white rod-shaped crystals, the product yield was 74%, the HPLC purity was 99.02%, the median particle diameter was 750 μm, and the diameter distance was 2.81.

Example 8

This example provides a method for preparing dihydroxy ethyl terephthalate, which is the same as example 1 except that Tween 80 was added in an amount of 12mg in step four. The obtained product was 2.08g of white rod-shaped crystals, the product yield was 73%, the HPLC purity was 99.04%, the median particle diameter was 560 μm, and the diameter spacing was 3.61.

Comparative example 1

A method for preparing dihydroxy ethyl terephthalate comprises the following steps:

step one, weighing 3.0g of fully dried dihydroxy ethyl terephthalate and 50g of water, adding the weighed materials into a crystallizer, and heating the materials to 80 ℃ to obtain a crude dihydroxy ethyl terephthalate solution;

and step two, rapidly cooling the crude dihydroxyethyl terephthalate solution to 65 ℃, uniformly cooling the crude dihydroxyethyl terephthalate solution to 40 ℃ from 65 ℃ for 5 hours, uniformly cooling the crude dihydroxyethyl terephthalate solution to 20 ℃ for 2 hours, keeping the temperature for 2 hours, separating out dihydroxyethyl terephthalate crystals, and then centrifuging, washing and drying the crystals to obtain the dihydroxyethyl terephthalate crystals with the average length of 80-120 mu m.

The optical micrograph of the crystals of bishydroxyethyl terephthalate obtained in this comparative example is shown in FIG. 2, and it can be seen that the bishydroxyethyl terephthalate product obtained by the above-mentioned method has a small and uneven particle size and is agglomerated.

The photograph of the bishydroxyethyl terephthalate product prepared in this comparative example with a macro camera is shown in fig. 3, and it can be seen from the photograph that the bishydroxyethyl terephthalate product prepared in this comparative example is white powder and is easily agglomerated.

The particle size distribution of the bishydroxyethyl terephthalate product prepared in this comparative example and example 1 is shown in FIG. 4, from which it can be seen that the bishydroxyethyl terephthalate crystal prepared in comparative example 1 is not a monomodal distribution, the particle size distribution is not uniform, and the median particle size is 9.56. mu.m. The crystalline product of bishydroxyethyl terephthalate prepared in example 1 had a monomodal distribution and a median particle diameter of 1380 μm.

Comparative example 2

This comparative example provides a method for preparing dihydroxy ethyl terephthalate, which is exactly the same as example 1 except that the habit modifier is polyoxyethylene ether. The obtained product was 2.13g of white rod-shaped crystals, the product yield was 74%, the HPLC purity was 98.08%, the median particle diameter was 120 μm, and the diameter distance was 4.390.

Comparative example 3

This comparative example provides a method of making bishydroxyethyl terephthalate exactly the same as in example 1, except that the habit modifier was alkylolamide. The obtained product was 2.06g of white rod-shaped crystals, the product yield was 72%, the HPLC purity was 98.53%, the median particle diameter was 130 μm, and the diameter distance was 4.612.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents or improvements made within the spirit and principle of the present invention should be included in the scope of the present invention.