Decolorization and purification method for BHET material

Abstract

To provide a decolorization and purification method for BHET material with improved hue of a finished product.SOLUTION: A first dose of activated carbon is added to preliminarily treat the BHET material. After the preliminary treatment, a first cooling crystallization process and filtration are performed to obtain BHET crystals. Afterwards, an oxidant is used to chemically react with the BHET crystals to destroy a dye or impurities, and then a second dose of activated carbon is added to adsorb a chemically reacted oxide. Next, a second cooling crystallization process, filtration, and drying are performed to obtain a finished product of BHET.SELECTED DRAWING: None

Description

【Technical Field】 【0001】 The present disclosure relates to a decolorization and purification method, and more particularly, to a decolorization and purification method of a BHET material. 【Background Art】 【0002】 Regarding a chemical recycling method of waste PET (polyethylene terephthalate) fabric, ethylene glycol (EG) is usually used to depolymerize PET into crude BHET (bis(2-hydroxyethyl) terephthalate), and then the crude BHET is decolorized and purified in order to obtain a pure white final product of BHET. However, waste PET fabric often contains impurities such as fiber auxiliaries and dyes. In particular, after the depolymerization of PET, the dye is usually compatible with BHET and difficult to separate, and as a result, the hue of the final product of BHET becomes relatively poor. 【0003】 Based on the above, in order to improve the hue of the final product of BHET, developing a decolorization and purification method of a BHET material is an important issue for current research. 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0004】 The present disclosure provides a decolorization and purification method of a BHET material that can decolorize and purify BHET formed by the depolymerization of various waste PET fabrics in order to obtain a pure white final product of BHET. 【Means for Solving the Problems】 【0005】 The decolorization and purification method for BHET material in this disclosure includes the following steps: Adding a first dose of activated carbon to pre-treat the BHET material. After pre-treatment, a first cooling crystallization process and filtration are carried out to obtain BHET crystals. Subsequently, an oxidizing agent is used to chemically react with the BHET to destroy dyes or impurities, and then a second dose of activated carbon is added to adsorb the chemically reacted oxides. Next, a second cooling crystallization process, filtration and drying are carried out to obtain the final BHET product. 【0006】 In one embodiment of this disclosure, the CIELAB color of the final product of BHET is defined as having an L value of 95 or higher, an a value of -1.0 to 1.0, and a b value of 4.0 or lower. 【0007】 In one embodiment of this disclosure, the first dose is 0.5% to 8% by weight, based on the total weight of the BHET material. 【0008】 In one embodiment of this disclosure, the processing temperature for the preliminary treatment is 80°C to 90°C. 【0009】 In one embodiment of this disclosure, the oxidizing agent includes hydrogen peroxide, calcium hypochlorite, or sodium hyposulfite. 【0010】 In one embodiment of this disclosure, the amount of oxidizing agent added is 0.1% to 1% by weight, based on the total weight of the BHET material. 【0011】 In one embodiment of this disclosure, the reaction temperature of the chemical reaction is 80°C to 90°C. 【0012】 In one embodiment of this disclosure, the second dose is 0.1% to 3% by weight, based on the total weight of the BHET material. 【0013】 In one embodiment of this disclosure, the processing temperature for adding the second dose of activated carbon is 80°C to 90°C. 【0014】 In one embodiment of the present disclosure, the process temperatures of the first cooling crystallization process and the second cooling crystallization process are 20°C. [Effects of the Invention] 【0015】 Based on the above, the decolorization and purification method for BHET material in this disclosure is optimized in a specific order of steps. It comprises a total of four steps in sequence, which can decolorize and purify BHET formed by the depolymerization of various waste PET fabrics in order to obtain pure white BHET. In particular, for dark-colored BHET material having impurities such as fiber additives and dyes, dyes and impurities that are difficult to remove are completely destroyed and removed in order to effectively improve the hue of the final BHET product. [Modes for carrying out the invention] 【0016】 The embodiments of this disclosure are described in detail below. However, these embodiments are exemplary and the disclosure is not limited thereto. 【0017】 In this specification, the range expressed as "from one number to another" is a simplified expression to avoid listing all the numbers within the range in the specification. Therefore, the description of a particular numerical range covers any number within that range and any smaller numerical range defined by any number within that range, just as the description of any number and its smaller numerical range in the specification. 【0018】 This disclosure provides a method for decolorizing and purifying a BHET material, comprising the following four steps in sequence: The first step is to add a first dose of activated carbon to pre-treat the BHET material. The second step is to perform a first cooling crystallization process and filtration after the pre-treatment to obtain BHET crystals. The third step is to chemically react the BHET crystals with an oxidizing agent to break down dyes or impurities, and then add a second dose of activated carbon to adsorb the chemically reacted oxides. The fourth step is to perform a second cooling crystallization process, filtration and drying to obtain the final BHET product. 【0019】 In the first procedural step, solvent extraction is used to determine the content of impurities in the BHET material, and based on this, the amount of activated carbon to be added for pretreatment (first dose of activated carbon) is determined. In this embodiment, the BHET material is, for example, a dark-colored BHET material, and the CIELAB color is defined as, for example, an L value of 30 to 45, an a value of -1 to -3, and a b value of -2 to -4. Solvent extraction is, for example, extracting the PET material with an alcohol ether solvent. The weight ratio of the alcohol ether solvent to the PET material is, for example, 20:1, and the reaction conditions are, for example, 2 hours at a temperature of 140°C. Based on the total weight of the PET material, the minimum content of extracted impurities is, for example, 0.2% to 1% by weight. In this embodiment, based on the total weight of the BHET material, the first dose of activated carbon is, for example, 0.5% to 8% by weight, and the pretreatment temperature and time are, for example, 3 hours at 80°C to 90°C. For example, the initial treatment of activated carbon is carried out after adding water. Then, filtration is performed to remove the activated carbon. 【0020】 In the second procedural step, the process temperature of the first cooling crystallization process is, for example, 20°C, and the first cooling crystallization process and filtration are carried out for 6 hours to obtain BHET crystals, during which time trace amounts of impurities are transferred to the aqueous phase. 【0021】 In the third step of the procedure, the oxidizing agent may include hydrogen peroxide, calcium hypochlorite, or sodium hyposulfite. Based on the total weight of the BHET material, the amount of oxidizing agent added is, for example, 0.1% to 1% by weight, and the reaction temperature and time for the chemical reaction of the BHET crystals using the oxidizing agent is, for example, 80°C to 90°C for 1 hour. For example, the oxidizing agent is used to break down dyes or impurities that are difficult to remove by chemical reaction after the addition of water. In this embodiment, based on the total weight of the BHET material, the second dose of activated carbon is, for example, 0.1% to 3% by weight, and the treatment temperature and time for adding the second dose of activated carbon to adsorb the chemically reacted oxides is, for example, 80°C to 90°C for 3 hours, after which the impurities are completely removed. Subsequently, filtration is carried out to remove the activated carbon. 【0022】 In the fourth procedural step, the process temperature of the second cooling crystallization process is, for example, 20°C, and the second cooling crystallization process, filtration, and drying are carried out for 6 hours to obtain BHET crystals, during which time trace amounts of impurities are transferred to the aqueous phase. The CIELAB color of the final BHET product obtained is defined, for example, as having an L value of 95 or higher, an a value of -1.0 to 1.0, and a b value of 4.0 or lower. Therefore, according to the decolorization and purification method of BHET material in this disclosure, dark-colored BHET material can be decolorized and purified to obtain pure white BHET. 【0023】 Based on the above, the decolorization and purification method for BHET material in this disclosure is optimized in a specific order of steps. It comprises a total of four steps in sequence, which can decolorize and purify BHET formed by the depolymerization of various waste PET fabrics in order to obtain pure white BHET. In particular, for dark-colored BHET materials containing impurities such as fiber additives and dyes, the dyes and impurities that are difficult to remove are completely destroyed and removed, thus effectively improving the hue of the final BHET product. The CIELAB color of the final BHET product is defined as having an L value of 95 or higher, an a value between -1.0 and 1.0, and a b value of 4.0 or lower. [Industrial applicability] 【0024】 The decolorization and purification method for BHET material described herein can be applied to BHET material.

Claims

[Claim 1] A method for decolorizing and purifying BHET (bis(2-hydroxyethyl) terephthalate) material, To pre-treat the BHET material, a first dose of activated carbon is added, After the aforementioned preliminary treatment, a first cooling crystallization process and filtration are performed to obtain BHET crystals. An oxidizing agent is used to chemically react with the BHET crystal to destroy the dye or impurities, and then a second dose of activated carbon is added to adsorb the chemically reacted oxide. A method for decolorizing and purifying a BHET material, comprising carrying out a second cooling crystallization process, filtration, and drying in order to obtain a final BHET product. [Claim 2] The method for decolorizing and purifying a BHET material according to claim 1, wherein the CIELAB color of the final BHET product is defined as having an L value of 95 or more, an a value of -1.0 to 1.0, and a b value of 4.0 or less. [Claim 3] The method for decolorizing and purifying a BHET material according to claim 1, wherein the first dose is 0.5% to 8% by weight, based on the total weight of the BHET material. [Claim 4] The decolorization and purification method for BHET material according to claim 1, wherein the processing temperature for the pretreatment is 80°C to 90°C. [Claim 5] The decolorization and purification method for BHET material according to claim 1, wherein the oxidizing agent comprises hydrogen peroxide, calcium hypochlorite, or sodium hyposulfite. [Claim 6] The method for decolorizing and purifying a BHET material according to claim 1, wherein the amount of oxidizing agent added is 0.1% to 1% by weight, based on the total weight of the BHET material. [Claim 7] The method for decolorizing and purifying a BHET material according to claim 1, wherein the reaction temperature of the chemical reaction is 80°C to 90°C. [Claim 8] The method for decolorizing and purifying a BHET material according to claim 1, wherein the second dose is 0.1% to 3% by weight, based on the total weight of the BHET material. [Claim 9] The method for decolorizing and purifying a BHET material according to claim 1, wherein the processing temperature for adding the second dose of activated carbon is 80°C to 90°C. [Claim 10] The method for decolorizing and purifying a BHET material according to claim 1, wherein the process temperature of the first cooling crystallization process and the second cooling crystallization process is 20°C.