METHOD FOR SYNTHESIS OF DIMETHYL TEREPHTHALATE

Abstract

The present invention provides a method for the synthesis of dimethyl terephthalate, which includes: carrying out a primary esterification reaction by adding a sulfonic acid catalyst to methanol and terephthalic acid; carrying out a secondary esterification reaction by adding methanol; and crystallizing and distilling the secondary esterification product to obtain dimethyl terephthalate; where the catalyst includes hexylbenzenesulfonic acid, dodecyl sulfonic acid, pentadecyl sulfonic acid, or dodecylbenzenesulfonic acid. The catalyst used in the present invention significantly reduces equipment wear and exhibits excellent reusability.

Description

METHOD FOR SYNTHESIS OF DIMETHYL TEREPHTHALATE TECHNICAL FIELD The present invention relates to the technical field of preparation of dimethyl terephthalate and, specifically, It relates to a method for synthesizing dimethyl terephthalate. PREVIOUS TECHNIQUE Dimethyl terephthalate (abbreviated as DMT) is a white, needle-shaped crystal under normal conditions; It sublimes readily, is insoluble in water, and is soluble in methanol, diethyl ether, chloroform, and ethyl acetate. It dissolves in organic solvents such as those mentioned. DMT is primarily used in polyester resins and polyesters. It is used in the synthesis of films, fibers, engineering plastics and similar materials. For example, DMT can undergo a transesterification reaction with ethylene glycol. then, through polycondensation, it has excellent toughness, wear resistance and mechanical properties. Polyethylene terephthalate (PET), the most important engineering plastic, is produced from DMT. DMT also... Poly(butylenedipate-co-terephthalate) has good heat resistance, plasticity and biodegradability. It can also be used to synthesize (PBAT) via a transesterification method. Additional PTT material formed by polymerization of DMT and 1,3-propanediol (1,3-PDO). is a polymer material widely used worldwide, this material is good It has processability, high strength and good flexibility. Synthetic fibers and engineering. Plastics offer a wide range of application potential in the fields of carpets and nonwovens. It can be used in the production of fabrics, staple fibers, etc. Currently, the production of dimethyl terephthalate from terephthalic acid is mainly done using concentrated sulfuric acid. This is carried out through a catalyzed process. Document CN104072374A describes a catalyst. It describes a method using concentrated sulfuric acid, in which terephthalic acid and excess Methanol is reacted at 170-180°C for 10-18 hours, followed by filtration. 1. Removal of alcohol, washing with water, removal of impurities, and gas stripping processes. This method achieves a purity of 99.8-99.9%. This process involves the esterification reaction. excess alcohol as a water carrier agent to ensure gradual completion It is used, which simplifies the process while achieving high-quality products. However, the use of concentrated sulfuric acid as a catalyst, This causes significant wear and tear on the equipment. Furthermore, the production process generates a substantial amount of waste acid. and produces a large volume of washing wastewater, which presents significant challenges in terms of treatment. It produces and causes serious environmental pollution. Therefore, this type of process It is relatively outdated and not suitable for long-term study. Document CN115353453A describes the formation of double long carbon chain terephthalates under the influence of a catalyst. production of dimethyl terephthalate via a transesterification reaction between methanol It describes a method aimed at using C6-C10 long-chain raw materials. Terephthalates and methanol are used, with organic titanium as a catalyst. The reaction, At a temperature ranging from 140 to 270 °C and a pressure of 1.0-4.0 MPa, bis-long carbon chain molar ratio of terephthalates to methanol feed is 1:(4-30) and bis-long- The mass ratio of carbon-chain terephthalates to titanate-based catalyst shall be 1:(0.001-0.2) This method is performed and the yield is between 86-94%. This method is direct esterification. It avoids reactions and all raw materials used are liquid at normal temperature. This is the case. This prevents solid raw material handling and associated equipment clogging, as well as subsequent problems. Cleaning problems are eliminated, which allows for better control of the reaction process. It simplifies things and increases production efficiency. It reduces equipment investment and energy consumption. It effectively reduces the amount of C6-C10 raw material. However, this method requires the use of long-lasting C6-C10 materials. It uses chain terephthalates, which are difficult to obtain and relatively expensive. The process is complex and introduces impurities such as long-chain alcohol esters, which This does not make it suitable for large-scale industrial production. Document CN1048542A describes oxidation and extraction using p-xylene as a raw material. dimethyl terephthalate via esterification, distillation, rectification and refrigerated flaking. It describes a method for its production. In this method, p-xylene is first produced from a Terephthalic acid and its derivatives were produced using cobalt acetate and manganese acetate in 2 oxidation columns. The mixture is then catalyzed. Subsequently, oxidized terephthalic acid and the mixture are combined. It is fed into an extraction column, where it is in counterflow contact with an extractant. found and under conditions of 0.1-0.3 MPa pressure and 94°C-105°C temperature, terephthalic acid and Meta-, ortho-, and non-para derivatives are removed from the mixture. After this, the mixture... It is fed into an esterification column for esterification with methanol, and the resulting product is ultimately... A mixture of dimethyl terephthalate and monoester is further distilled to remove impurities. It undergoes rectification, resulting in dimethyl terephthalate with 99.9% purity. This method provides high-quality and stable products, but the process flow... It is a long process and requires three crystallizations to achieve a product purity of 99.9%, and then... This requires distillation. This necessitates extensive equipment and is relatively expensive. This leads to operating costs. Document CN107151208A describes a method for synthesizing dimethyl terephthalate crystals. This method explains that 0.4085 g (0.002 mol) of 7,7,8,8-tetracyanoquinodimethane and 0.1225 g (0.0005 mol) of manganese acetate tetrahydrate was weighed, and anhydrous manganese was used as a solvent. It is placed in a round-bottomed bottle along with methanol (approximately 40 ml). For 48 hours. After being heated under reflux, hot filtration and natural processes are used to obtain the crystals. Evaporation is carried out. This method is simple to implement, but dimethyl terephthalate Its efficiency is low. Document CN1320593A describes a study in which sulfate is used as a catalyst, mixed with methanol and terephthalic acid. This describes a method for producing dimethyl terephthalate by catalyzing its reaction. First, terephthalic acid, methanol, and sulfate are fed into a reactor and heated at a temperature of 90°C-130°C. The reaction takes place over a period of 2-4 hours. Excess methanol and water are removed under reduced pressure. It is evaporated. Then, for a second reaction, a group with the same properties as the first is used. A second batch of methanol and sulfate is added. After the second reaction is complete, the mixture It is drained, filtered, dried, and used for the preparation of dimethyl terephthalate. It undergoes vacuum rectification. The catalyst is calcined at high temperatures. It is selected from at least one of the following substances: ferric sulfate, titanium sulfate, manganese. 3 sulfates: barium sulfate and cobalt sulfate. This method uses concentrated sulfuric acid as a catalyst. It reduces equipment wear compared to its use. However, during DMT synthesis... Due to the low solubility of monomethyl terephthalate and terephthalic acid in DMT, Secondary esterification is necessary to increase the conversion rate. Typically, secondary esterification This is carried out in a tower reactor. A sulfate catalyst (e.g., iron(II) sulfate) When used, its solubility in methanol is low. Reagents for secondary esterification When it enters the tower reactor, the problem of clogging of the layers and the reactor base arises. This results in problems, which makes this method unsuitable for continuous industrial production. Therefore, the significant equipment wear and process complexity experienced in dimethyl terephthalate synthesis... Given existing problems such as low efficiency, the steps are simple and minimize wear. It reduces heat loss, provides high efficiency, has excellent thermal and chemical stability, and is environmentally friendly. And the development of a method for preparing dimethyl terephthalate in accordance with green chemistry principles is urgent. It has become a priority. A BRIEF DESCRIPTION OF THE INVENTION Considering the problems in the current dimethyl terephthalate production processes, the existing The invention involves the production of methanol and terephthalic acid as raw materials in the presence of a sulfonic acid catalyst. It is subjected to esterification and crystallization, and high-purity dimethyl terephthalate is obtained. It aims to provide a method for synthesizing dimethyl terephthalate. To achieve the above objective, the present invention is a dimethyl grouping that includes the following steps: It provides a method for synthesizing terephthalate: S1: methanol and terephthalic acid are mixed with sulfonic acid to obtain a primary esterification product. Performing a primary esterification reaction by adding a catalyst based on a catalyst; S2: methanol is added to the primary esterification product to obtain a secondary esterification product. carrying out a secondary esterification reaction by adding; 4 S3: Adding methanol to the secondary esterification product to obtain a crystalline product. crystallization is carried out; S4: Distillation of the crystallized product to obtain dimethyl terephthalate; Here, the catalyst is hexylbenzenesulfonic acid, dodecyl sulfonic acid, pentadecyl sulfonic acid, and It contains one or more dodecylbenzenesulfonic acids. The process flow of the present invention uses raw materials and catalysts that are readily available on the market. It uses commercial chemicals. The catalyst used has high catalytic efficiency as well. It exhibits improved thermal and chemical stability. Especially with the addition of additives, compared to conventional catalysts such as concentrated sulfuric acid and p-toluene sulfonic acid, the equipment Its abrasive effect is significantly reduced. Furthermore, the process flow and production... The procedures are simple and high-purity products are obtained. The entire process is green chemistry. and complies with economic feasibility requirements. According to a specific configuration of the present invention, preferably the catalyst mass is terephthalic. The concentration of the acid should be 0.5-3% by mass, preferably 1.5-2.5%. According to a specific configuration of the present invention, preferably in S1, with the addition of a catalyst. Simultaneously, an additive is added, and this additive is N-methylpyrrolidone. benzotriazole, dicyclohexylamine nitrite, and 2-mercaptobenzothiazole, one or more of the following: It contains, more preferably, N-methylpyrrolidone. According to the specific configuration of the present invention, the additive is preferentially placed in the catalyst. Depending on its mass, it is added in amounts ranging from 500-1,000 ppm, more preferably 500-800 ppm. According to a specific configuration of the present invention, preferably in S1, methanol to terephthalic acid The molar ratio is 10-15:1, preferably 12-14:1. According to a specific configuration of the present invention, preferably in S2, methanol, terephthalic acid It is added in an amount 5-12 times, preferably 5-10 times, the molar amount. According to a specific configuration of the present invention, primary esterification preferably in S1. reaction and / or secondary esterification reaction in S2, 140-180 °C, more preferably 150 °C- The process is carried out at a temperature of 170 °C for 1-2 hours. Primary esterification, preferably in S1, according to a specific configuration of the present invention. The reaction is carried out at a temperature of 140-180 °C, preferably 150 °C-170 °C, for 1-2 hours. is being carried out. Secondary esterification, preferably in S1, according to a specific configuration of the present invention. The reaction is carried out at a temperature of 140-180 °C, preferably 150 °C-170 °C, for 1-2 hours. is being carried out. Depending on the specific configuration of the present invention, preferably S1 and / or S2 may also include the following: includes: primary esterification reaction and / or secondary esterification reaction After completion, the primary esterification product and / or secondary esterification product is obtained. To achieve this, the residual methanol and water formed in the reaction system must be removed by distillation. According to a specific configuration of the present invention, preferably in S3, the secondary methanol The mass ratio of the esterification product to the ester is 1-4:1, preferably 1.5-3:1. According to a specific configuration of the present invention, preferably in S3, dimethyl terephthalate When crystallization is used for purification, the starting temperature of crystallization is 80- 120 °C, preferably 90-110 °C. According to a specific configuration of the present invention, preferably in S4, distillation at 180-210 °C, then This is preferably done at a temperature of 190 °C. According to a specific configuration of the present invention, distillation takes place under reduced pressure. is being carried out. 6 The technical solution offered by the present invention has the following beneficial effects: (1) Compared with conventional concentrated sulfuric acid catalysts, the present invention sulfonic acid-based catalyst used (especially if it contains additives), equipment It can significantly reduce wear and tear and offers excellent reusability. It can demonstrate this, thus better meeting the requirements of green chemistry. (2) The catalyst used in the present invention is low cost and has high catalytic efficiency. It exhibits good thermal and chemical stability. It shows low losses, for equipment. It does not clog and is less likely to contaminate the product. (3) The method for synthesizing dimethyl terephthalate according to the present invention is a simple production It has a flow rate, this method allows for the production of a high purity product exceeding 99.9%, and This ensures a high raw material utilization rate. DETAILED EXPLANATION OF THE CONFIGURATIONS To gain a clearer understanding of the technical specifications, purposes, and benefits of the present invention. For this purpose, the technical solution of the present invention will be described in detail below, however, This statement should not be interpreted as limiting the scope to which the present invention can be applied. Example 1 The example provides a method for synthesizing dimethyl terephthalate, as follows: It includes the following steps: (1) The molar ratio of methanol to terephthalic acid was chosen as 12:1. 33.23 g (0.2 77.90 g (2.4 mol) terephthalic acid, 77.90 g (2.4 mol) methanol and 0.50 g hexylbenzenesulfonic acid (catalyst; (1.5% of the mass of terephthalic acid) was added. The mixture was prepared for esterification. It was reacted at 160 °C for 2 hours. After the reaction was complete... After 7, we obtained a primary esterification product with a yield of 88.43% dimethyl terephthalate. Methanol and water were removed through rotary evaporation. (2) The resulting primary esterification product was placed in a reactor, 51.26 g (1.6 mol) Methanol was added and the mixture was heated at 150°C for 1 hour to allow a secondary esterification to occur. It was subjected to a reaction throughout. After the reaction was complete, 97.90% dimethyl To obtain a secondary esterification product with terephthalate yield, methanol and water are rotated. It was removed by evaporation. (3) 30 g of secondary esterification product was placed in a reactor, 60 g of methanol was added and The mixture was stirred at 100 °C for 15 minutes. Then the temperature was adjusted for crystallization. The temperature was lowered to 30 °C, yielding crystallized crude dimethyl terephthalate with a yield of 93.79%. (4) 10 g of crystallized crude dimethyl terephthalate was distilled with 99.14% yield and 99.91% purity. To obtain high-purity dimethyl terephthalate, it was placed in a vial and heated at 190 °C. Distilled under reduced pressure. The acidity of the product conforms to GB / T 264-83 “Petroleum When measured according to the "products - Determination of acid value" standard, it was determined to be 0.20. Example 2 The example provides a method for synthesizing dimethyl terephthalate, as follows: It includes the following steps: (1) The molar ratio of methanol to terephthalic acid was chosen as 14:1. 33.23 g (0.2 mol) was added to a reactor. terephthalic acid, 89.71 g (2.8 mol) methanol and 0.50 g dodecylbenzenesulfonic acid (catalyst; mass Terephthalic acid (1.5% by mass) was added to the mixture. The mixture was then prepared for esterification to occur. It was reacted at 160 °C for 2 hours. After the reaction was complete... then, to obtain a primary esterification product with a 90.15% dimethyl terephthalate yield. Methanol and water were removed through rotary evaporation. (2) The resulting primary esterification product was placed in a reactor, 51.26 g (1.6 mol) Methanol was added and the mixture was heated at 150°C for 1 hour to allow a secondary esterification to occur. It was subjected to a reaction throughout. After the reaction was complete, 98.25% dimethyl Methanol and water are rotated to obtain a secondary esterification product with a terephthalate yield of 8. It was removed by evaporation. (3) 30 g of secondary esterification product was placed in a reactor, 60 g of methanol was added and The mixture was stirred at 90 °C for 15 minutes. Then, for crystallization, 93.86% To obtain crystallized crude dimethyl terephthalate with a satisfactory yield, the temperature was lowered to 30 °C. (4) 10 g of crystallized crude dimethyl terephthalate was distilled to have 99.16% yield and 99.92% purity. To obtain a high-purity dimethyl terephthalate, it was placed in a vial and heated at 190 °C. Distilled under reduced pressure. GB / T 264-83 “Petroleum products - Determination When measured according to the "acid value" scale, the product's acid value was determined to be 0.20. Example 3 The example provides a method for synthesizing dimethyl terephthalate, as follows: It includes the following steps: (1) The molar ratio of methanol to terephthalic acid was chosen as 12:1. 33.23 g (0.2 mol) was added to a reactor. terephthalic acid, 77.90 g (2.4 mol) methanol and 0.83 g dodecyl sulfonic acid (catalyst, mass 2.5% by mass of terephthalic acid was added to the mixture. The mixture was then prepared for esterification to occur. It was reacted at 170°C for 2 hours. After the reaction was complete... then, to obtain a primary esterification product with a dimethyl terephthalate yield of 88.22%. Methanol and water were removed through rotary evaporation. (2) The resulting primary esterification product was placed in a reactor, 51.26 g (1.6 mol) Methanol was added and the mixture was heated at 150°C for 1 hour to allow a secondary esterification to occur. It was subjected to a reaction throughout. After the reaction was complete, 97.75% dimethyl To obtain a secondary esterification product with terephthalate yield, methanol and water are rotated. It was removed by evaporation. (3) 30 g of secondary esterification product was placed in a reactor, 60 g of methanol was added and The mixture was stirred at 100 °C for 15 minutes. Then, for crystallization, 93.71% To obtain a crystallized crude dimethyl terephthalate with a yield, the temperature is raised to 30 °C. It has been dropped. 9 (4) 10 g of crystallized crude dimethyl terephthalate, distilled with 99.26% yield and 99.91% purity To obtain high-purity dimethyl terephthalate, it was placed in a vial and heated at 190 °C. Distilled under reduced pressure. GB / T 264-83 “Petroleum products - Determination When measured according to the "acid value" scale, the product's acid value was determined to be 0.21. Example 4 The example provides a method for synthesizing dimethyl terephthalate, as follows: It includes the following steps: (1) The molar ratio of methanol to terephthalic acid was chosen as 14:1. 33.23 g (0.2 mol) terephthalic acid, 89.71 g (2.8 mol) methanol, 0.30 g pentadecyl sulfonic acid and 0.20 g dodecylbenzene sulfonic acid Acid (catalysts; their mass is 1.5% of the mass of terephthalic acid) was added to a reactor. The mixture was reacted at 170°C for 2 hours to allow esterification to occur. After the reaction is complete, a primary molecule with a yield of 89.52% dimethyl terephthalate is obtained. Methanol and water are esterified by rotary evaporation to obtain the esterification product. has been removed. (2) The resulting primary esterification product was placed in a reactor, 51.26 g (1.6 mol) Methanol was added and the mixture was heated at 150 °C for 1 hour to allow secondary esterification to occur. It was subjected to a reaction throughout. After the reaction was complete, 97.72% dimethyl To obtain a secondary esterification product with terephthalate yield, methanol and water are rotated. It was removed by evaporation. (3) 30 g of secondary esterification product was placed in a reactor, 60 g of methanol was added and The mixture was stirred at 110 °C for 15 minutes. Then, for crystallization, 93.65% To obtain a crystallized crude dimethyl terephthalate with a yield, the temperature is raised to 30 °C. It has been dropped. (4) 10 g of crystallized crude dimethyl terephthalate was distilled with 99.08% yield and 99.90% purity. The processed high-purity dimethyl terephthalate is placed in a vial and Distilled at 190 °C under reduced pressure. The acidity of the product conforms to GB / T 264-83. According to "Petroleum products - Determination of acid value", it is measured as 0.20. It has been determined. As can be seen from Examples 1-4, increasing the amount of methanol used increases the reaction rate. It facilitates the process, increases esterification efficiency, and consequently, acid obtaining dimethyl terephthalate with a purity exceeding 99.9% while meeting the value requirements. This provides that, according to the present invention, DMT can be processed using the process method. This demonstrates that its preparation is possible. Furthermore, the sulfonic compounds used in the present invention... The acid-based catalyst exhibits high catalytic efficiency, leading to suitable product yields. This leads to... Comparative Example 1 This comparative example provides a method for the synthesis of dimethyl terephthalate. and includes the following steps: (1) The molar ratio of methanol to terephthalic acid was chosen as 12:1. 33.23 g (0.2 mol) was added to a reactor. terephthalic acid, 77.90 g (2.4 mol) methanol and 0.50 g p-toluenesulfonic acid (catalyst; mass Terephthalic acid (1.5% by mass) was added to the mixture. The mixture was then prepared for esterification to occur. It was reacted at 160 °C for 2 hours. After the reaction was complete... Then, to obtain a primary esterification product with a dimethyl terephthalate yield of 86.98%, Methanol and water were removed through rotary evaporation. (2) The resulting primary esterification product was placed in a reactor, 51.26 g (1.6 mol) Methanol was added and the mixture was heated at 150°C for 1 hour to allow a secondary esterification to occur. It was subjected to a reaction throughout. After the reaction was complete, 96.74% dimethyl To obtain a secondary esterification product with terephthalate yield, methanol and water are rotated. It was removed by evaporation. (3) 30 g of secondary esterification product was placed in a reactor, 60 g of methanol was added and The mixture was stirred at 100 °C for 15 minutes. Then, for crystallization, the primary After 11 crystallizations, we obtained crude dimethyl terephthalate with a yield of 93.11% at the given temperature. It has been reduced to °C. (4) After primary crystallization, 10 g of crude dimethyl terephthalate yielded 99.18% and 99.84%. to obtain distilled high-purity dimethyl terephthalate with a purity level in a bottle It was placed and distilled at 190 °C under reduced pressure. The acid value of the product is, According to GB / T 264-83 “Petroleum products - Determination of acid value”, the measurement is 3.16. It has been determined as follows. Comparative Example 2 This comparative example provides a method for the synthesis of dimethyl terephthalate. and includes the following steps: (1) The molar ratio of methanol to terephthalic acid was chosen as 12:1. 33.23 g (0.2 mol) was added to a reactor. terephthalic acid, 77.90 g (2.4 mol) methanol and 0.50 g concentrated sulfuric acid (catalyst, mass Terephthalic acid (1.5% by mass) was added to the mixture. The mixture was then prepared for esterification to occur. It was reacted at 150 °C for 2 hours. After the reaction was complete... Then, to obtain a primary esterification product with a yield of 65.44% dimethyl terephthalate, Methanol and water were removed through rotary evaporation. (2) The resulting primary esterification product was placed in a reactor, 51.26 g (1.6 mol) Methanol was added and the mixture was heated at 150 °C for 1 hour to allow a secondary esterification to occur. It was subjected to a reaction throughout. After the reaction was complete, 79.94% dimethyl To obtain a secondary esterification product with terephthalate yield, methanol and water are rotated. It was removed by evaporation. As can be seen in Example 1, as well as in Comparative Examples 1 and 2, Benzenesulfonic acid and p-toluenesulfonic acid catalysts to concentrated sulfuric acid catalyst It has a higher esterification efficiency compared to p-toluene sulfonic. Since the boiling point of the acid is close to the boiling point of DMT products, distillation During this process, catalyst loss occurs, which causes the acidity of the product to become excessively high. This leads to a rise in 12% and negatively impacts the product's applications in subsequent stages. It has an effect. Example 5 The example provides a method for synthesizing dimethyl terephthalate, as follows: It includes the following steps: (1) The molar ratio of methanol to terephthalic acid was chosen as 12:1. An additive to a reactor 33.23 g (0.2 mol) terephthalic acid, 77.90 g (2.4 mol) methanol, 0.50 g hexylbenzenesulfonic acid acid (catalyst, 1.5% by mass of terephthalic acid) and additive at 500 ppm N-methylpyrrolidone was added (relative to the mass of the catalyst). The mixture was then subjected to esterification. It was reacted at 150°C for 2 hours. After the reaction was complete... Then, to obtain a primary esterification product with a dimethyl terephthalate yield of 88.47%, Methanol and water were removed through rotary evaporation. (2) The resulting primary esterification product was placed in a reactor, 51.26 g (1.6 mol) Methanol was added and the mixture was heated at 150°C for 1 hour to allow a secondary esterification to occur. It was subjected to a reaction throughout. After the reaction was complete, 97.83% dimethyl To obtain a secondary esterification product with terephthalate yield, methanol and water are rotated. It was removed by evaporation. (3) 30 g of secondary esterification product was placed in a reactor, 60 g of methanol was added and The mixture was stirred at 100 °C for 15 minutes. Then, the primary crystallization... To obtain crude dimethyl terephthalate with a yield of 93.49%, crystallization was performed. The temperature has been lowered by 30°C. (4) 10 g of crystallized crude dimethyl terephthalate was distilled to have 99.13% yield and 99.90% purity. To obtain high-purity dimethyl terephthalate, it was placed in a vial and heated at 190 °C for 2 It was distilled for hours. GB / T 264-83 “Petroleum products - Determination of acid According to the "value" scale, the acidity of the product was determined to be 0.20. Example 6 13 The example provides a method for synthesizing dimethyl terephthalate, as follows: It includes the following steps: (1) 33.23 g (0.2 mol) terephthalic acid, 77.90 g (2.4 mol) as an additive to a reactor. methanol, 0.50 g dodecylbenzenesulfonic acid (catalyst, 1.5% by mass of terephthalic acid) Up to 800 ppm (based on the mass of the catalyst) of N-methylpyrrolidone was added to the mixture. To achieve esterification, the mixture was reacted at 150°C for 2 hours. After the reaction is complete, a primary molecule with a yield of 88.44% dimethyl terephthalate is obtained. Methanol and water are esterified by rotary evaporation to obtain the esterification product. has been removed. (2) The resulting primary esterification product was placed in a reactor, 51.26 g (1.6 mol) Methanol was added and the mixture was heated at 150°C for 1 hour to allow secondary esterification to occur. It was subjected to a reaction throughout. After the reaction was complete, 97.80% dimethyl To obtain a secondary esterification product with terephthalate yield, methanol and water are rotated. It was removed by evaporation. (3) 30 g of secondary esterification product was placed in a reactor, 60 g of methanol was added and The mixture was stirred at 100 °C for 15 minutes. Then, for crystallization, the primary To obtain crude dimethyl terephthalate with a yield of 93.55% as a result of crystallization. The temperature has been lowered by 30°C. (4) 10 g of crystallized crude dimethyl terephthalate was distilled to have 99.11% yield and 99.91% purity. To obtain high-purity dimethyl terephthalate, it was placed in a vial and heated at 190 °C for 2 It was distilled for hours. GB / T 264-83 “Petroleum products - Determination of acid According to the "value" scale, the acidity of the product was determined to be 0.20. Experimental Example 1 Thermal stability of benzenesulfonic acid catalyst: 14 (1) The molar ratio of methanol to terephthalic acid was chosen as 12:1. 33.23 g (0.2 mol) was added to a reactor. terephthalic acid, 77.90 g (2.4 mol) methanol and 0.50 g benzenesulfonic acid (catalyst, mass Terephthalic acid (1.5% by mass) was added to the mixture. The mixture was then prepared for esterification to occur. It was reacted at 150 °C for 2 hours. After the reaction was complete... Then, to obtain a primary esterification product with a dimethyl terephthalate yield of 88.48%, Methanol and water were removed through rotary evaporation. (2) The resulting primary esterification product was placed in a reactor, 51.26 g (1.6 mol) Methanol was added and the mixture was heated at 150°C for 1 hour to allow secondary esterification to occur. It was subjected to a reaction throughout. After the reaction was complete, 97.86% dimethyl To obtain a secondary esterification product with terephthalate yield, methanol and water are rotated. It was removed by evaporation. (3) The secondary esterification product is placed in a bottle and kept at 190 °C for 2 hours. distilled under reduced pressure and distilled dodecylbenzenesulfonic acid The catalyst has been recovered. (4) Recovered benzenesulfonic acid catalyst in a reactor, 33.23 g (0.2 mol) terephthalic acid and 77.90 g (2.4 mol) of methanol was added. The mixture was heated at 150°C for esterification to occur. The reaction was carried out for 2 hours. After the reaction was complete, 88.53% dimethyl was obtained. Rotary evaporation to obtain the primary esterification product with terephthalate yield. methanol and water were removed through this process. (5) The resulting primary esterification product was placed in a reactor, 51.26 g (1.6 mol) Methanol was added and the mixture was heated at 150°C for 1 hour to allow a secondary esterification to occur. It was subjected to a reaction throughout. After the reaction was complete, 97.84% dimethyl To obtain a secondary esterification product with terephthalate yield, methanol and water are rotated. It was removed by evaporation. As seen in Experimental Example 1, the benzenesulfonic acid catalyst, under reduced pressure while maintaining suitable thermal stability even after distillation, at high temperatures. It maintains its catalytic efficiency. This is due to the high temperatures in the distillation column. This shows that the isolated benzenesulfonic acid still possesses good catalytic activity. Experimental Example 2 Corrosiveness of benzenesulfonic acid after the addition of the additive: (1) Test, GB / T4334.6-2015 “Test Method for Stainless Steels Corrosion in Sulfuric Acid” This was carried out accordingly. Three parallel 316L stainless steel test specimens were taken and The samples were sanded with sandpaper, avoiding overheating. The dimensions of the samples are... The total surface area of ​​the samples was measured using a vernier caliper to calculate it. Then, The samples were placed in clean water for ultrasonic cleaning and then in an oven for 30 minutes. They were dried throughout. After cooling to room temperature, the samples were measured with an accuracy of 0.0001 g. It was weighed on an analytical balance. (2) The samples were placed in a vertical connection piece with a conical stone and providing sufficient cooling effect. It is housed in a flask equipped with a reflux glass condenser. Made of stainless steel. Dodecylbenzenesulfonic acid as an additive to completely coat the samples. N-methylpyrrolidone was added at a concentration of 500 ppm (based on catalyst mass). The temperature was raised to 150 °C and held at that level for 12 hours. (3) When the predetermined wear time is reached, stainless steel wear test specimens They were removed and placed under running water to clean the abrasion products on the surface of the samples. They were scrubbed with a soft brush. After drying in the oven, the weathered samples were weighed. (4) 316L stainless steel caused by dodecylbenzenesulfonic acid containing additives The wear and tear weight loss rate has been calculated. Experimental Sample 3 Corrosiveness of dodecyl sulfonic acid after addition of the additive: (1) Test, GB / T4334.6-2015 “Test Method for Stainless Steels Corrosion in Sulfuric Acid” This was carried out accordingly. Three parallel 316L stainless steel test specimens were taken and The samples were sanded with sandpaper, avoiding overheating. The dimensions of the samples are... The total surface area of ​​the samples was measured using a vernier caliper. Next, the samples were placed in clean water for ultrasonic cleaning and then in an oven for 30 minutes. They were dried for 16 minutes. After cooling to room temperature, the samples weighed 0.0001 g. It was weighed on an analytical balance with a certain degree of precision. (2) Samples are placed in a vertical container with a conical overflow fitting that provides sufficient cooling effect. It is housed in a flask equipped with a reflux glass condenser. Made of stainless steel. Dodecyl sulfonic acid was added to completely coat the samples, and an additive was used. 800 ppm N-methylpyrrolidone was added (based on catalyst mass). Temperature It was heated to 150 °C and held at that level for 12 hours. (3) When the predetermined wear time is reached, stainless steel wear test specimens They were removed and placed under running water to clean the abrasion products on the surface of the samples. They were scrubbed with a soft brush. After drying in the oven, the weathered samples were weighed. (4) 316L stainless steel caused by dodecylbenzenesulfonic acid containing additives The wear and tear weight loss rate has been calculated. Comparative Experimental Example 1 Corrosiveness of dodecylbenzenesulfonic acid catalyst: (1) Test, GB / T4334.6-2015 “Test Method for Stainless Steels Corrosion in Sulfuric Acid” This was carried out accordingly. Three parallel 316L stainless steel test specimens were taken and The samples were sanded with sandpaper, taking care to avoid overheating. The dimensions of the samples are: The total surface area of ​​the samples was measured using a vernier caliper. Next, the samples were placed in clean water for ultrasonic cleaning and then in an oven for 30 minutes. They were dried for minutes. After cooling to room temperature, the samples weighed 0.0001 g. It was weighed on an analytical balance with a certain degree of precision. (2) The samples were placed in a vertical connection piece with a conical stone and providing sufficient cooling effect. It is housed in a flask equipped with a reflux glass condenser. Made of stainless steel. Dodecylbenzenesulfonic acid was added to completely coat the samples. Temperature It was heated to 150 °C and held at that level for 12 hours. (3) When the predetermined wear time is reached, stainless steel wear test specimens They were removed and placed under running water to clean the abrasion products on the surface of the samples. 17. They were rubbed with a soft brush. After being dried in an oven, the weathered samples It has been weighed. (4) Weight loss of 316L stainless steel due to dodecylbenzenesulfonic acid wear. The rate has been calculated. Comparative Experimental Example 2 Corrosiveness of p-toluenesulfonic acid catalyst: (1) Test, GB / T4334.6-2015 “Test Method for Stainless Steels Corrosion in Sulfuric Acid” This was carried out accordingly. Three parallel 316L stainless steel test specimens were taken and The samples were sanded with sandpaper, avoiding overheating. The dimensions of the samples are... The total surface area of ​​the samples was measured using a vernier caliper. Next, the samples were placed in clean water for ultrasonic cleaning and then in an oven for 30 minutes. They were dried for minutes. After cooling to room temperature, the samples weighed 0.0001 g. It was weighed on an analytical balance with a certain degree of precision. (2) The samples were placed in a vertical connection piece with a conical stone and providing sufficient cooling effect. It is housed in a flask equipped with a reflux glass condenser. Made of stainless steel. p-toluenesulfonic acid was added to completely coat the samples. The temperature was raised to 150 °C. It was raised and held at that level for 12 hours. (3) When the predetermined wear time is reached, stainless steel wear test specimens They were removed and placed under running water to clean the abrasion products on the surface of the samples. It was rubbed with a soft brush. After drying in an oven, the weathered samples... It has been weighed. (4) Weight loss rate of 316L stainless steel caused by p-toluenesulfonic acid It has been calculated. Comparative Experimental Example 3 Corrosiveness of sulfuric acid: 18 (1) Test, GB / T4334.6-2015 “Test Method for Stainless Steels Corrosion in Sulfuric Acid” This was carried out accordingly. Three parallel 316L stainless steel test specimens were taken and The samples were sanded with sandpaper, taking care to avoid overheating. The dimensions of the samples are: The total surface area of ​​the samples was measured using a vernier caliper. Next, the samples were placed in clean water for ultrasonic cleaning and then in an oven for 30 minutes. They were dried for minutes. After cooling to room temperature, the samples weighed 0.0001 g. It was weighed on an analytical balance with a certain degree of precision. (2) The samples were placed in a vertical connection piece with a conical stone and providing sufficient cooling effect. It is housed in a flask equipped with a reflux glass condenser. Made of stainless steel. DMT containing 5% sulfuric acid was added to completely coat the samples. Temperature It was heated to 150 °C and held at that level for 12 hours. (3) When the predetermined wear time is reached, stainless steel wear test specimens They were removed and placed under running water to clean the abrasion products on the surface of the samples. It was rubbed with a soft brush. After drying in an oven, the weathered samples... It has been weighed. (4) Wear weight loss of 316L stainless steel caused by DMT containing 5% sulfuric acid. The rate has been calculated. Table 1. Weight loss rate in stainless steel wear test. Stainless steel sheet Average Wear from Original Wear Features: Weight, Wear Sample No. Mass Subsequent Ratio loss / g ratio Length Width Thickness 2 / g mass / g / g / (m ·h) 2 / cm / cm / cm / g / (m ·h) 2.54 1.06 0.17 3.7600 3.7478 0.0028 0.3530 Experimental 2.50 1.02 0.17 3.5920 3.5808 0.0025 0.3309 0.3304 Example 2 2.50 1.06 0.17 3.7944 3.7816 0.0024 0.3072 Experimental 2.48 1.01 0.17 3.5003 3.4988 0.0015 0.2017 0.2084 Example 3 2.51 1.00 0.17 3.5485 3.5471 0.0014 0.1878 19 2.55 1.01 0.17 3.5824 3.5806 0.0018 0.2358 2.56 1.04 0.17 3.7478 3.7433 0.0045 0.5726 Comparative Experimental 2.52 1.01 0.17 3.6161 3.6113 0.0048 0.6359 0.6182 Example 1 2.51 1.02 0.17 3.6055 3.6006 0.0049 0.6460 Comparative 2.60 1.09 0.17 3.9531 3.7622 0.0075 0.9028 Experimental 2.50 0.96 0.17 3.3559 3.1838 0.0066 0.9203 0.9164 Example 2 2.50 0.99 0.17 3.4947 3.3242 0.0070 0.9261 Comparative 2.57 1.03 0.17 3.7988 3.7067 0.0921 11.7747 Experimental 2.46 1.01 0.17 3.4542 3.3632 0.0910 12.3326 12.0666 Example 3 2.49 1.04 0.17 3.5668 3.4742 0.0926 12.0962 As shown in the table above for Comparative Experimental Examples 1-3, the present invention The wear rate of stainless steel when using a sulfonic acid-based catalyst is reduced with p-toluene sulfonic. significantly higher than the rate of corrosion caused by DMT containing acid and 5% sulfuric acid. is low. Therefore, with p-toluene sulfonic acid and concentrated sulfuric acid catalysts In comparison, the use of benzenesulfonic acid catalyst increases esterification efficiency. It can reduce equipment wear while increasing efficiency. As shown in the table above for Experimental Samples 1-2 and Comparative Experimental Sample 1. Accordingly, after the addition of the additive, the sulfonic acid-based catalyst of the present invention It significantly reduces the wear rate of stainless steel as the amount of additives increases. It has been observed that the abrasiveness to steel is reduced. Therefore, the addition of the additive... This further reduces equipment wear and tear and lowers environmental pollution, thus promoting green practices. It meets the chemical requirements. The difference between Example 1 and Examples 5-6 lies in the addition of the additive to the reaction system. It lies there. As can be seen from the results, the addition of the additive leads to esterification. It reduces equipment wear without compromising efficiency or the acid value of the product. Experimental Sample 4 Thermal stability of benzenesulfonic acid catalyst after addition of additive: (1) The molar ratio of methanol to terephthalic acid was chosen as 12:1. One reactor, one additive The ingredients include 33.23 g (0.2 mol) terephthalic acid, 77.90 g (2.4 mol) methanol, and 0.50 g benzenesulfonic acid (catalyst, mass of which is 1.5% of the mass of terephthalic acid) and 500 ppm N-methylpyrrolidone (based on the mass of the catalyst) was added to a reactor. The mixture, To achieve esterification, the mixture was reacted at 150°C for 2 hours. After the reaction is complete, a primary molecule with a yield of 88.41% dimethyl terephthalate is obtained. Methanol and water are esterified by rotary evaporation to obtain the esterification product. has been removed. (2) The resulting primary esterification product was placed in a reactor, 51.26 g (1.6 mol) methanol added and the mixture was heated at 150°C for 1 hour to allow a secondary esterification to occur. It was subjected to a reaction. After the reaction was complete, 97.89% dimethyl terephthalate was obtained. To obtain a secondary esterification product with a certain yield, methanol and water are rotated. It was removed by evaporation. (3) The secondary esterification product was placed in a bottle and reduced at 190 °C for 2 hours. distilled under pressure and DMT recovered through distillation. The liquid remaining at the bottom of the bottle (dodecylbenzenesulfonic acid catalyst) has been collected. (4) A reactor was filled with 33.23 g (0.2 mol) terephthalic acid, a catalyst recovered from benzenesulfonic acid. and 77.90 g (2.4 mol) of methanol was added. The mixture was heated at 150°C for esterification to occur. It was subjected to a reaction for 2 hours. After the reaction was complete, a primary Methanol and water are combined via rotary evaporation to obtain the esterification product. has been removed. (5) The resulting primary esterification product was placed in a reactor, 51.26 g (1.6 mol) methanol added and the mixture was heated at 150°C for 1 hour to allow a secondary esterification to occur. It was subjected to a reaction. After the reaction was complete, 97.86% dimethyl terephthalate was obtained. To obtain a secondary esterification product with a certain yield, methanol and water are mixed in a rotating motion. It was removed by evaporation. 21 From Experimental Sample 4, the additive-modified benzenesulfonic acid catalyst resulted in reduced... It has been observed that it maintains adequate thermal stability even after distillation under pressure. This The situation involves substances being separated at high temperatures in a distillation column and with added additives. This shows that benzenesulfonic acid still possesses good catalytic activity. The present invention uses methanol and terephthalic acid as raw materials and a high boiling point catalyst. Dimethyl sulfonic acid with a purity exceeding 99.9% was produced using a dotted sulfonic acid and an additive. It enables the production of terephthalate. This involves a primary esterification, a secondary esterification, a process that includes crystallization and distillation stages and has a simple process flow This is carried out through a conventional method catalyzed by concentrated sulfuric acid. Compared to the esterification process, this method ensures catalyst stability and It increases esterification efficiency while reducing equipment wear, thus promoting green chemistry. It meets the requirements. The above only applies to the preferred version of the present invention. their configurations and the aim is not to restrict the existing invention in any other way. It does not include any modifications based on the technical essence of the present invention. or an equivalent modification, will still fall within the scope claimed by the existing invention. 22

Claims

1. This is a method for synthesizing dimethyl terephthalate, involving the following steps: It includes: S1: To obtain a primary esterification product, methanol and terephthalic acid A primary esterification reaction by adding a sulfonic acid-based catalyst implementation; S2: primary esterification to obtain a secondary esterification product. by adding methanol to the product, a secondary esterification reaction implementation; S3: Crystallization by adding methanol to the secondary esterification product. carrying out and obtaining the crystallized product; S4: Distillation of the crystallized product to produce dimethyl terephthalate; here, catalyst, hexylbenzenesulfonic acid, dodecyl sulfonic acid, pentadecyl sulfonic acid and It contains one or more dodecylbenzenesulfonic acids.

2. The mass of the catalyst is 0.5–3% of the mass of terephthalic acid, according to Claim 1. A method for synthesizing dimethyl terephthalate.

3. The mass of the catalyst is 1.5-2.5% of the mass of terephthalic acid, according to Claim 2. A method for synthesizing dimethyl terephthalate. In section 4. S1, an additive is added simultaneously with the catalyst, and the following is stated: The additive in question is N-methylpyrrolidone, benzotriazole, dicyclohexylamine nitrite and 2- Containing one or more mercaptobenzothiazoles, dimethyl according to Claim 1. A method for synthesizing terephthalate.

5. The additive is added in an amount of 500-1,000 ppm depending on the mass of the catalyst. Method for the synthesis of dimethyl terephthalate according to claim 4. 23 In section 6. S1, the molar ratio of methanol to terephthalic acid is 10-15:1, according to claim 1, dimethyl A method for synthesizing terephthalate.

7. In S1, the molar ratio of methanol to terephthalic acid is 12-14:1, according to Claim 6. A method for synthesizing dimethyl terephthalate. In section 8. S1, the primary esterification reaction was carried out at a temperature of 140-180 °C for 1-2 hours. The method for synthesizing dimethyl terephthalate, as described in Claim 1.

9. In S2, methanol is present in an amount 5-12 times greater than the molar amount of terephthalic acid. The method for synthesizing dimethyl terephthalate, as specified in Claim 1, has been added.

10. In S2, the secondary esterification reaction is carried out at a temperature of 140-180 °C for 1-2 hours. The method for synthesizing dimethyl terephthalate, as described in Claim 1.

11. Method for the synthesis of dimethyl terephthalate according to claim 1, where S1 and / or S2 also includes: primary esterification reaction and / or After the secondary esterification reaction is complete, what forms in the reaction system methanol and water are then removed by distillation, thus completing the primary esterification. Obtaining the product and / or secondary esterification product. In section 12. S3, the mass ratio of methanol to the secondary esterification product is 1-4:1, according to Claim 1. According to the method for synthesizing dimethyl terephthalate. In section 13.S3, the mass ratio of methanol to the secondary esterification product is 1.5-3:1, Claim. Method for synthesizing dimethyl terephthalate according to 12. In section 24 14. S3, when crystallization is used for the purification of dimethyl terephthalate, According to Claim 1, the crystallization onset temperature is 80-120 °C for dimethyl. A method for synthesizing terephthalate. In section 15. S4, the distillation was carried out at a temperature of 180-210 °C, according to claim 1, using dimethyl A method for synthesizing terephthalate.