Method for continuously producing 1, 4-cyclohexanedimethanol by using waste polyester as raw material

Abstract

The invention relates to the field of polyester, and discloses a method for continuously producing 1, 4-cyclohexanedimethanol by taking waste polyester as a raw material. Comprising the following steps: 1) mixing waste polyester with ethylene glycol, and performing alcoholysis under the action of an alcoholysis catalyst to obtain alcoholysis liquid containing diethylene glycol terephthalate; 2) performing primary hydrogenation on the alcoholysis solution under the catalysis of a hydrogenation catalyst A to obtain a reaction solution containing 1, 4-cyclohexane dioctyl phthalate diglycol ester; 3) performing secondary hydrogenation on the reaction liquid under the catalysis of a hydrogenation catalyst B to obtain a reaction liquid containing 1, 4-cyclohexanedimethanol; and 4) carrying out gas-liquid separation and rectification on the reaction liquid to obtain ethylene glycol and 1, 4-cyclohexanedimethanol. According to the method, the CHDM is produced by taking the waste polyester as the raw material, the method is simple in production process flow, and continuous production can be realized; through optimization of the catalyst and the process, high PET conversion rate, high CHDM selectivity, high CHDM yield and low production cost can be realized under relatively mild reaction conditions.

Description

Technical Field

[0001] The invention relates to the field of polyester, in particular to a method for continuously producing 1,4-cyclohexanedimethanol by taking waste polyester as raw material. Background Art

[0002] At present, the accumulated stock of waste textiles in my country exceeds hundreds of millions of tons, but the recycled spinning capacity is less than 10 million tons, and the recycling rate is only 10%, resulting in a large amount of polyester waste being buried and incinerated as garbage, which not only wastes a lot of resources, but also puts great pressure on the social ecological environment. Therefore, the development of polyester recycling technology is of great significance to reducing environmental pollution and recycling waste gas and garbage.

[0003] At present, the recycling methods of waste polyester mainly include mechanical recycling, chemical recycling and energy recovery. Mechanical recycling is to crush and clean the waste polyester by physical methods for recycling; chemical recycling is to process the waste polyester into monomer compounds by chemical methods, and then manufacture new polyester products; energy recovery is to use the waste polyester that is difficult to chemically recycle and utilize as fuel, and recover and utilize energy through combustion. At present, chemical recycling methods mainly include hydrolysis, alcoholysis and aminolysis. PET can obtain dimethyl terephthalate (DMT) through methanol alcoholysis, DMT can be hydrogenated to produce dimethyl 1,4-cyclohexanedicarboxylate (DMCD), and DMCD can be further hydrogenated to produce 1,4-cyclohexanedimethanol (CHDM), a chemical with higher added value.

[0004] 1,4-Cyclohexanedimethanol is an important diol monomer, widely used in the polyester industry. It is one of the raw materials for the development of new polyester products. It is often used in industry to replace ethylene glycol or other alcohols to synthesize high-performance polyesters with high thermal stability, high strength and chemical resistance. Polyethylene terephthalate (PETG and PCTG) prepared by using CHDM to partially replace ethylene glycol has excellent properties such as low density, high melting point, good physical processability and stability. For example, poly(cyclobutylene terephthalate) (PCCT) copolymerized with CHDM, CBDO and PTA has excellent properties such as high glass transition temperature, good transparency and green environmental protection. In addition, CHDM can also be used as a modified monomer to improve the thermal stability and other properties of polyester fibers for the production of differentiated fibers.

[0005] At present, the main production methods of CHDM are DMT hydrogenation method, PTA hydrogenation method and BHET method. DMT method is the currently industrialized CHDM production method. The first step of DMT hydrogenation to produce DMCD uses Pd-based or Ru-based catalysts. The second step of hydrogenation is the hydrogenation of DMCD to produce CHDM, usually using Cu-based catalysts. The two-step hydrogenation of DMT is similar to the two-step hydrogenation catalyst of BHET, but the hydrogenation of BHET is more difficult, the hydrogenation reaction network of BHET is more complex, and there are many side reactions. At the same time, the structure of the hydroxyl groups at both ends of BHET makes it easier to esterify, transesterify or dehydrate into ethers to produce macromolecular substances during the hydrogenation process of BHET, resulting in catalyst adhesion poisoning and a significant reduction in catalytic activity. The patent with publication number CN1398841 A discloses a Cu-ZnO-Al2O3 catalyst, which achieves a DMCD conversion rate of 97.2% and a CHDM selectivity of 91.4% under the reaction conditions of 6MPa and 240°C; the patent with publication number CN107188782B discloses a method for preparing a Cu-Zn-A1 catalyst by a sedimentation method, which conducts a DMCD hydrogenation reaction through a two-stage reactor, and obtains a DMCD conversion rate of 99.9% and a CHDM selectivity of 98.4% under the reaction conditions of 8.5MPa and the reaction temperatures of the first and second stage reactors being 175-180°C and 205-210°C, respectively. However, the reaction has the disadvantages of high hydrogen pressure and complex reaction process, which increases the production cost; although the DMT method has been industrialized, due to the high cost of DMT and heavy reliance on imports, it is impossible to effectively reduce the production cost of CHDM, limiting the production capacity of downstream PETG.

[0006] Due to the poor solubility of PTA in water, the reaction needs to be carried out under high temperature and high pressure conditions. The preferred reaction conditions in CN 114685241 A are 160-260°C and 6-15MPa. In the embodiment, the inventors used 5% Ru-4% Sn-0.5% Pd / carbon nanotube catalyst, reacted at 230°C, 8MPa for 10 hours, and hydrogenated PTA into CHDM in one step. The PTA conversion rate is 100%, and the highest yield of CHDM is 95%. However, the low hydrogenation activity and slow reaction rate of the PTA method, and the need for high temperature and high pressure to carry out the PTA method have hindered the industrialization process of this route.

[0007] The diethylene glycol terephthalate (BHET) method is currently the most likely method to further reduce the cost of CHDM. Waste polyester can be depolymerized with ethylene glycol at room temperature to obtain BHET, and the raw material cost of BHET will be significantly lower than that of DMT. Unfortunately, the BHET method has been less studied. In the CN105294393A patent, Ru-Pt-Sn is selected as the active component, and alumina, silica or molecular sieve is used as the carrier to prepare a ternary component catalyst for hydrogenation of diethylene glycol terephthalate as the raw material. The first step reaction temperature of this method is 150-200°C, the second step reactant temperature is 220-280°C, the BHET conversion rate is 100%, and the CHDM selectivity is as high as 87.1%. It can be seen that the yield of CHDM produced by the BHET method is still larger than that of the DMT method.

[0008] Therefore, it is urgent to develop a CHDM production process suitable for waste polyester as raw material and an efficient polyester hydrogenation catalyst to achieve efficient conversion of waste polyester to CHDM under milder reaction conditions, improve the quality of CHDM products and reduce production costs. Summary of the invention

[0009] In order to solve the above technical problems, the present invention provides a method for continuously producing 1,4-cyclohexanedimethanol using waste polyester as raw material. The present invention innovatively proposes to produce CHDM using waste polyester as raw material. The production process of the method is simple, and no separation and purification is required during the process, and continuous production can be achieved. The present invention can achieve high PET conversion rate, high CHDM selectivity, high CHDM yield and low production cost under relatively mild reaction conditions through the optimization of catalysts and processes.

[0010] The specific technical scheme of the present invention is as follows: The present invention provides a method for continuously producing 1,4-cyclohexanedimethanol using waste polyester as raw material, comprising the following steps: 1) Mixing waste polyester (PET) with ethylene glycol, and performing alcoholysis under the action of an alcoholysis catalyst to obtain an alcoholysis solution containing diethylene glycol terephthalate (BHET).

[0011] 2) The alcoholysis liquid is directly introduced into a primary hydrogenation reactor containing a hydrogenation catalyst A for hydrogenation without separation to obtain a reaction liquid containing 1,4-cyclohexanedicarboxylic acid diethylene glycol ester (BHCD); the hydrogenation catalyst A is selected from Ru / C, Ru / Al2O3, Ru / SBA-15, Pd / C, Pd / Al2O3 and Pd / SBA-15.

[0012] 3) The reaction liquid is directly introduced into a secondary hydrogenation reactor containing a hydrogenation catalyst B for hydrogenation without separation to obtain a reaction liquid containing 1,4-cyclohexanedimethanol (CHDM); the hydrogenation catalyst B contains Cu or CuO as an active metal and contains at least one of Mn, Zn, Mg, Ce and Al or its oxide as a promoter metal.

[0013] 4) The reaction liquid is subjected to gas-liquid separation, and the resulting liquid is distilled to obtain ethylene glycol and 1,4-cyclohexanedimethanol, respectively, and a small amount of residue is discharged from the bottom of the distillation tower.

[0014] In the above steps, the present invention mainly involves three-step reactions. The first step is to produce diethylene glycol terephthalate (BHET) by alcoholysis of ethylene glycol from waste polyester (PET), the second step is to hydrogenate the benzene ring of BHET to produce diethylene glycol 1,4-cyclohexanedicarboxylate (BHCD), and the third step is to hydrogenate BHCD to produce 1,4-cyclohexanedimethanol (CHDM). The present invention innovatively proposes to produce CHDM using waste polyester as raw material. The production process of this method is simple, and waste PET is directly used as raw material. The BHET produced by alcoholysis does not need to be separated and purified, and can be directly used for hydrogenation to produce CHDM (the existing process first produces DMT by alcoholysis, and DMT can be used for hydrogenation after being purified by distillation. The main reason is that the homogeneous catalyst used in alcoholysis is mostly acidic, which leads to catalyst poisoning in the DMT hydrogenation process, and is more prone to product side reactions, etc., which greatly reduces the stability of the catalyst).

[0015] In the alcoholysis reaction, the conventional alcoholysis catalyst is mostly a homogeneous catalyst, which is difficult to separate, while the alcoholysis catalyst used in the present invention is a heterogeneous catalyst, which is easy to separate. In the first and second hydrogenation reactions, the present invention uses a self-developed hydrogenation catalyst, which has the advantages of high PET conversion rate, high CHDM selectivity and good stability.

[0016] The present invention can achieve high PET conversion rate, high CHDM selectivity, high CHDM yield and low production cost under relatively mild reaction conditions through optimization of catalysts and processes.

[0017] Preferably, in 1), the mass ratio of the waste polyester to ethylene glycol is 1:2 to 1:10; and the mass of the alcoholysis catalyst is 0.25 to 1 wt % of the waste polyester.

[0018] Preferably, in 1), the alcoholysis temperature is 170-240° C., and the time is 0.5-4 h.

[0019] Preferably, in 1), the alcoholysis catalyst is a solid acid catalyst; More preferably, the alcoholysis catalyst is selected from Al / SBA-15, TiO2-SiO2 or Al2O3-SiO2, and the particle size of the alcoholysis catalyst is 10-300 μm.

[0020] Preferably, the waste polyester includes but is not limited to leftover powder and granules from PET production enterprises or waste silk fibers or waste plastic bottles or waste plastic packaging boxes from polyester enterprises.

[0021] Preferably, in 2), the loading amount of Ru or Pd in ​​the hydrogenation catalyst A is 1-5 wt%.

[0022] Preferably, in 2), the hydrogenation catalyst A is selected from Ru / C, Ru / Al2O3 and Ru / SBA-15.

[0023] Preferably, in 2), the particle size of the hydrogenation catalyst A is 0.5-3 mm.

[0024] Preferably, in 2), the hydrogenation temperature is 100-130°C, the pressure is 1-4 MPa, the hydrogen-oil molar ratio is 50-300:1, and the liquid hourly space velocity is 1-5 h -1 .

[0025] Preferably, in 2), a solvent is introduced into the primary hydrogenation reactor to control the content of diethylene glycol terephthalate to be 5 to 20 wt%.

[0026] Preferably, in 2), the solvent is selected from one or more of 1,4-dioxane, cyclohexane, methanol, ethyl acetate and 1,4-butanediol.

[0027] Preferably, in 2), the alcoholysis liquid is filtered before being introduced into the hydrogenation reactor, and the obtained alcoholysis catalyst is returned to 1) for recycling.

[0028] Preferably, in 3), the hydrogenation catalyst B is selected from CuMnAl, CuZnAl, CuZnSi, CuCe-Al, Cu-CeO-MgO and CuZn-Mg, and the loading amount of Cu is 10-50wt%.

[0029] Preferably, in 3), the hydrogenation temperature is 180-220°C, the pressure is 1-4 MPa, the hydrogen-oil molar ratio is 50-300:1, and the liquid hourly space velocity is 1-5 h -1 .

[0030] Preferably, in 3), the particle size of the hydrogenation catalyst B is 0.5-3 mm.

[0031] Preferably, in 4), the distillation pressure is 1-50 kPa, the reflux ratio is 1-4:1; the primary distillation temperature is 50-130°C, the secondary distillation temperature is 160-200°C; and the tertiary distillation temperature is 180-240°C.

[0032] The distillation tower used in the present invention is divided into three stages of distillation, and ethylene glycol and solvent are separated in sequence according to different boiling points. For example, pure ethylene glycol can be obtained in the first stage and recycled to the alcoholysis reactor, and a high-purity solvent can be obtained by distillation in the second stage and recycled to the first stage hydrogenation reactor. A qualified CHDM product is discharged from the top of the third distillation tower, and the bottom of the tower is a partial alcoholysis / hydrogenation residue.

[0033] Compared with the prior art, the beneficial effects of the present invention are: (1) The present invention innovatively proposes to produce CHDM using waste polyester as raw material. The production process of this method is simple. Waste PET is directly used as raw material. BHET produced by alcoholysis does not need to be separated and purified, and can be directly used for hydrogenation to produce CHDM. The reaction conditions are mild, the production cost of CHDM produced is low, and the CHDM yield is high.

[0034] (2) The present invention adopts self-developed alcoholysis catalyst and hydrogenation catalyst, which has the advantages of high PET conversion rate, high CHDM selectivity and good stability. Traditional alcoholysis catalysts are mostly homogeneous catalysts, which are difficult to separate, while the alcoholysis catalyst used in the present invention is a heterogeneous catalyst, which is easy to separate.

[0035] (3) The present invention directly uses waste polyester as raw material to produce high value-added CHDM, which not only solves the problems of low resource utilization rate of waste polyester and environmental pollution, but also solves the problems of high price of high-end polyester monomer CHDM. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a transmission scanning electron microscope image of the primary hydrogenation catalyst and the secondary hydrogenation catalyst in Example 1.

[0037] Figure 2 The high performance liquid chromatography and gas chromatography diagrams of the products at each stage in the production process of Example 1 are shown. DETAILED DESCRIPTION

[0038] The present invention will be further described below in conjunction with the embodiments.

[0039] Overall embodiment A method for continuously producing 1,4-cyclohexanedimethanol using waste polyester as raw material comprises the following steps: 1) Mixing waste polyester (PET) with ethylene glycol, and performing alcoholysis under the action of an alcoholysis catalyst to obtain an alcoholysis solution containing diethylene glycol terephthalate (BHET).

[0040] In some specific implementation cases, the waste polyester includes but is not limited to leftover powder and granules from PET production enterprises or waste silk fibers or waste plastic bottles or waste plastic packaging boxes from polyester enterprises.

[0041] In some specific implementation cases, the mass ratio of the waste polyester to ethylene glycol is 1:2 to 1:10; the mass of the alcoholysis catalyst is 0.25 to 1 wt % of the waste polyester.

[0042] In some specific implementation cases, the alcoholysis temperature is 170-240° C., and the time is 0.5 to 4 hours.

[0043] In some specific implementation cases, the alcoholysis catalyst is a solid acid catalyst; further preferably, the alcoholysis catalyst is selected from A1 / SBA-15, TiO2-SiO2 or Al2O3-SiO2, and the particle size of the alcoholysis catalyst is 10-300 μm.

[0044] In some specific implementation cases, the preparation method of the alcoholysis catalyst is a crystallization method, in which the Al / Si / Ti precursor is prepared into an aqueous solution, and then a template (preferably P123\CTAB, polyethylene glycol, etc.) is added, and the sol generation is controlled by stirring, and then the sol is placed in a crystallization kettle for crystallization, dried, and calcined to obtain an alcoholysis catalyst.

[0045] 2) The alcoholysis liquid is introduced into a primary hydrogenation reactor containing a hydrogenation catalyst A for hydrogenation without separation to obtain a reaction liquid containing 1,4-cyclohexanedicarboxylic acid diethylene glycol ester (BHCD); the hydrogenation catalyst A is selected from Ru / C, Ru / Al2O3, Ru / SBA-15, Pd / C, Pd / Al2O3 and Pd / SBA-15.

[0046] In some specific implementation cases, the carrier C, Al2O3 and SBA-15 of the hydrogenation catalyst A are purchased from Aladdin Reagent Company. The loading method of metal Ru adopts impregnation method, colloid method and precipitation method, preferably precipitation method. Specifically, the RuCl3 precursor is prepared into a solution, the carrier is placed in the solution and stirred for adsorption, and then a precipitant is added to precipitate Ru in the pores or surface of the carrier, and the reaction is washed, dried and calcined to obtain the hydrogenation catalyst A. In some specific implementation cases, the loading amount of Ru or Pd in ​​the hydrogenation catalyst A is 1-5wt%.

[0047] In some preferred implementation cases, the hydrogenation catalyst A is selected from Ru / C, Ru / Al2O3 and Ru / SBA-15.

[0048] In some specific implementation cases, the particle size of the hydrogenation catalyst A is 0.5-3 mm.

[0049] In some specific implementation cases, the hydrogenation temperature is 100-130°C, the pressure is 1-4 MPa, the hydrogen-to-oil molar ratio is 50-300:1, and the liquid hourly space velocity is 1-5h -1 .

[0050] In some specific implementation cases, a solvent is introduced into the primary hydrogenation reactor to control the content of diethylene glycol terephthalate to be 5-20 wt %.

[0051] In some specific implementation cases, the solvent is selected from one or more of 1,4-dioxane, cyclohexane, methanol, ethyl acetate and 1,4-butanediol.

[0052] In some specific implementation cases, the alcoholysis liquid is filtered before being introduced into the hydrogenation reactor, and the obtained alcoholysis catalyst is returned to 1) for recycling.

[0053] 3) The reaction liquid is introduced into a secondary hydrogenation reactor containing a hydrogenation catalyst B for hydrogenation without separation to obtain a reaction liquid containing 1,4-cyclohexanedimethanol (CHDM); the hydrogenation catalyst B contains Cu or CuO as an active metal and contains at least one of Mn, Zn, Mg, Ce and Al or its oxide as a promoter metal.

[0054] In some preferred implementation cases, the hydrogenation catalyst B is selected from CuMnAl, CuZnAl, CuZnSi, CuCe-Al, Cu-CeO-MgO and CuZn-Mg, and the loading amount of Cu is 10-50wt%.

[0055] In some specific implementation cases, the hydrogenation catalyst B is prepared by a co-precipitation method, wherein the precursors of catalysts such as CuMnAl or Cu\Zn\Al or CuZnSi are prepared into an aqueous solution, and a precipitant such as an aqueous NaOH solution, a NaHCO3 solution, urea, ammonia water, etc. is added. After precipitation reaction, the catalyst B is obtained by filtering, washing, drying, and calcining.

[0056] In some specific implementation cases, the particle size of the hydrogenation catalyst B is 0.5-3 mm.

[0057] In some specific implementation cases, the hydrogenation temperature is 180-220°C, the pressure is 1-4 MPa, the hydrogen-to-oil molar ratio is 50-300:1, and the liquid hourly space velocity is 1-5h -1 .

[0058] 4) The reaction liquid is subjected to gas-liquid separation, and the resulting liquid is distilled to obtain ethylene glycol and 1,4-cyclohexanedimethanol, respectively, and a small amount of residue is discharged from the bottom of the distillation tower.

[0059] In some specific implementation cases, the distillation pressure is 1-50 kPa, the reflux ratio is 1-4:1; the primary distillation temperature is 50-130°C, the secondary distillation temperature is 160-200°C; and the tertiary distillation temperature is 180-240°C.

[0060] Specific Examples and Comparative Examples PET conversion rate = (W0-W1) / W0×100%; wherein W0 is the initial mass of PET and W1 is the mass of undegraded PET; BHET selectivity = (amount of substance generating BHET) / (amount of substance degraded PET theoretically); BHET conversion rate = (amount of generated BHET substance - amount of remaining BHET substance) / amount of generated BHET substance × 100%; BHCD selectivity = (the amount of substance generated BHCD) / (the amount of substance converted BHET theoretically); BHCD conversion rate = (amount of BHCD-generated substance - amount of remaining BHCD substance) / amount of BHCD-generated substance × 100%; CHDM selectivity = (the amount of CHDM produced) / (the amount of BHCD theoretically converted); Total molar yield of CHDM = (mass of CHDM produced by reaction) / (amount of substance converted into PET) × 100%; Mass yield of CHDM = (mass of CHDM obtained by distillation) / (amount of substance added to PET) × 100%; The above PET and BHET were analyzed by high performance liquid chromatography, and the BHCD and CHDM components were analyzed by gas chromatography.

[0061] Preparation of alcoholysis catalyst 30g deionized water and 70g HCl (0.28mol / L) were mixed evenly and then moved to a 40℃ water bath; 4.0g P123 was added and stirred until the solution was clear; 9.0g TEOS was mixed with aluminum isopropoxide solution and slowly dripped into the above solution with a microinjection pump, and gently stirred for 24h at 40℃; the obtained suspension was added to a polytetrafluoroethylene liner, placed in a crystallization kettle, and moved to a blast oven for crystallization at 110℃ for 24h; the crystallized suspension was washed with water and ethanol several times, respectively, and moved to a blast drying oven, and dried at 80℃ for 10h; the obtained sample powder was poured into a crucible and moved to a muffle furnace, heated to 550℃ at 1℃ / min, and calcined at a constant temperature for 6h. The obtained alcoholysis catalyst was recorded as Al / SBA-15.

[0062] Preparation of hydrogenation catalyst A Add 250ml of deionized water to a three-necked flask, add 0.388g of RuCl3H2O and stir evenly, and observe to ensure that no precipitation is produced; add 5g of alumina powder, stir for 4h, add 5g of ammonia water, and react for 10h; wash the resulting suspension with deionized water several times, move it to a blast oven, dry it at 110℃ for 10h, calcine it at 350℃ for 3h, and the heating rate is 2℃ / min. It should be noted that hydrogenation catalyst A needs to be reduced before use. The catalyst is placed in a tubular furnace at 400℃ for reduction for 3h (20% H2 / N2), recorded as 3% Ru / Al2O3, and the particle size of the catalyst is 1mm.

[0063] Preparation of hydrogenation catalyst B Dissolve 12.97g AlCl3·6H2O, 5.08g Cu(NO3)2·3H2O, and 20.51g Mg(NO3)2·6H2O in 500mL deionized water, and stir to dissolve evenly to obtain a solution; dissolve 22.68g NaHCO3 in 400mL deionized water, and stir to dissolve evenly to obtain a solution. Under room temperature stirring, use a syringe to quantitatively inject the two solutions into a beaker at the same time. During the titration process, the pH of the mixed solution is controlled at about 9.5. After the titration is completed, the obtained suspension is transferred to a hydrothermal kettle and hydrothermally crystallized at 100℃ for 14h; then the obtained solid is filtered and washed with deionized water until the filtrate is neutral; then put it in an 80℃ oven and dry it for 12h; finally, the obtained sample is calcined at 400℃ in air atmosphere for 4h, and the heating rate is 5℃ / min. The hydrogenation catalyst B prepared by this method needs to be reduced in a tube furnace at 400°C for 3h (20% H2 / N2) before use, and is denoted as CuMgAl. The catalyst has a particle size of 1.5mm after tableting. The remaining hydrogenation catalysts B are prepared by this method, such as the CuMnAl catalyst, where Mg is replaced by a precursor of Mn. The contents of Cu and Mg can be calculated and quantitatively controlled.

[0064] Example 1 500g of waste polyester (waste plastic bottles) recycled from the waste spinning recycling center was used as the raw material, and 2kg of ethylene glycol and 2.5g of heterogeneous catalyst Al / SBA-15 were added to the raw material preparation kettle. After the raw material preparation kettle was heated to 170℃ by heat transfer oil and mixed evenly, a slurry pump was used to pump it into the alcoholysis reactor. The alcoholysis reactor temperature was 200℃ and the residence time was 120min. The residence time of the slurry bed reactor was controlled by controlling the solid-liquid flow rate and the reactor size. After analysis, the alcoholysis PET conversion rate was 100%, and the BHET and oligomer yields were greater than 99%.

[0065] After the alcoholysis reaction is completed, the alcoholysis catalyst is separated through a metal sintered filter. The alcoholysis catalyst returns to the alcoholysis reactor, and the alcoholysis liquid flows into the hydrogenation reactor. There is no need to separate and purify BHET. A high-pressure horizontal flow pump is used to pump the alcoholysis liquid and the solvent 1,4 two-ring six-ring into the primary hydrogenation reactor respectively. After the solvent is introduced, the content of BHET is controlled at 10%. The primary hydrogenation reactor is filled with a 2mm hydrogenation catalyst 3% Ru / Al2O3. The temperature of the hydrogenation reaction is 110℃, the pressure is 2MPa, the hydrogen-to-oil ratio is 50:1, and the liquid hourly space velocity is 4h -1 After analysis, the conversion rates of BHET and oligomers were greater than 99.5%, and the yield of 1,4-cyclohexanedicarboxylic acid diethylene glycol ester (BHCD) was greater than 98.2%.

[0066] The first-stage hydrogenation reaction liquid flows into the second-stage hydrogenation reactor without separation, with a reaction temperature of 220°C, a pressure of 2MPa, a hydrogen-to-oil ratio of 100:1, and a liquid hourly space velocity of 4h -1 The reactor is filled with 1.5 mm CuMnAl hydrogenation catalyst. After analysis, the conversion rate of BHCD is greater than 99.1%, and the selectivity of CHDM is greater than 97.3%.

[0067] The secondary hydrogenation liquid flows through the distillation tower for refining treatment. The distillation tower is divided into three stages of distillation. The first stage can be distilled to obtain high-purity solvent dioxane, which can be returned to the primary hydrogenation reactor with a purity of more than 99.5%; the secondary distillation tower, operating conditions are vacuum degree 10kpa, tower bottom temperature 190℃, can obtain pure ethylene glycol for return to the alcoholysis reactor, used as alcoholysis solvent, with a purity of 99.5%. The third stage distillation tower top out qualified CHDM products, operating conditions are vacuum degree 5kpa, operating temperature 220℃, tower bottom is partial alcoholysis / hydrogenation residue, CHDM purity is about 99.5%.

[0068] According to calculation, 340.5 g of CHDM can be recovered from 500 g of waste polyester (the theoretical mass yield is 75%), the total molar yield of CHDM is about 94.62%, the CHDM mass yield is 68.1%, and the distillation mass loss is 3.9% (experimental value, the loss rate of industrial distillation tower will be lower).

[0069] Figure 1 1 is a transmission scanning electron microscope image of the primary hydrogenation catalyst and the secondary hydrogenation catalyst in Example 1; Figure 2 The high performance liquid chromatography and gas chromatography diagrams of the products at each stage in the production process of Example 1 are shown.

[0070] Example 2 The same process as in Example 1, as well as the same alcoholysis catalyst, primary hydrogenation catalyst and secondary hydrogenation catalyst, the same process conditions and the same distillation operation conditions were used. By changing different waste polyester raw materials, it was verified that the method of the present invention has a broad spectrum of polyester raw materials.

[0071] Table 1: Different types of waste polyester raw materials Types of waste polyester raw materials Waste polyester scraps Waste Silk Waste PET bottles Second-hand polyester clothing Waste polyester conversion rate (%) 99.15 99.98 99.87 98.65 Total molar yield of CHDM (%) 94.22 95.23 94.62 91.23 As shown in the table above, waste polyester materials, whether PET scraps, industrial waste silk, waste PET bottles or second-hand polyester clothing, can all be used as raw materials for CHDM production. The conversion rate of second-hand polyester clothing is slightly lower than that of other polyester products. This may be because in addition to PET, there are a small amount of other components in the dimerized polyester clothing fabric that affect the PET conversion rate and CHDM yield. From the experiment, it can be seen that the process route of using cheap waste polyester products as raw materials to produce high-purity CHDM products is feasible, which is conducive to significantly reducing the production cost of CHDM.

[0072] Example 3 The same waste polyester raw material and process as in Example 1, as well as the same alcoholysis temperature, residence time and alcoholysis process conditions, primary hydrogenation catalyst and secondary hydrogenation catalyst, and two-stage hydrogenation conditions were used to explore the effect of the alcoholysis catalyst on this process.

[0073] Table 2: Effects of different waste polyester alcoholysis catalysts Alcoholysis Catalyst Al / SBA-15 <![CDATA[TiO2-SiO2]]> <![CDATA[Al2O3-SiO2]]> Zinc acetate Waste polyester conversion rate (%) 99.15 99.98 99.87 98.65 BHET component selectivity (%) 99.22 99.71 98.97 99.31 BHCD selectivity (%) 98.65 98.72 97.72 94.64 CHDM selectivity (%) 97.51 97.23 97.33 93.21 Total molar yield of CHDM 94.62 95.69 94.01 86.42 Note: TiO2-SiO2 and Al2O3-SiO2 catalysts are physical combinations of aluminum oxide and silicon oxide in a mass ratio of 1:1 to 1:5, and this embodiment uses 1:2. Zinc acetate catalyst was purchased from Aladdin Chemical Reagent Company.

[0074] From the data in Table 2, it can be seen that when using waste PET bottles as raw materials, using different alcoholysis catalysts such as Al / SBA-15, TiO2-SiO2 and Al2O3-SiO2, the waste polyester conversion rate and CHDM yield are both greater than 94%. When zinc acetate is used as a catalyst, the PET alcoholysis efficiency is higher, but because zinc acetate is a homogeneous catalyst, it cannot be effectively separated from the alcoholysis solution, resulting in Zn2 + It flows into the primary hydrogenation reactor and deposits on the hydrogenation catalyst, resulting in reduced activity of the two-stage hydrogenation catalyst and a decrease in the total molar yield of CHDM.

[0075] Comparative Example 1 The same waste polyester raw material waste PET bottles, alcoholysis catalyst Al / SBA-15, primary hydrogenation catalyst and secondary hydrogenation catalyst and two-stage hydrogenation conditions as in Example 1 were used to explore the influence of alcoholysis process on this process. This comparative example mainly explores the influence of alcoholysis temperature, residence time and alcoholysis catalyst dosage on the total molar yield of CHDM.

[0076] Table 3: Effects of different alcoholysis processes By comparing with Example 1, it can be seen that alcoholysis time, alcoholysis temperature and alcoholysis catalyst concentration have a greater impact on the total molar yield of CHDM. When the alcoholysis time is too short, the alcoholysis temperature is too low, the catalyst concentration is too low, and the ethylene glycol / PET ratio is too small, the alcoholysis of PET is insufficient, the PET conversion rate is not enough, and the BHET selectivity is not high, and PET is converted into the oligomer of BHET. When the BHET oligomer content is too high, the conversion rate of BHET hydrogenation and the selectivity of BHCD are affected, and then the total molar yield of CHDM is affected. On the other hand, when the alcoholysis time is too long, the alcoholysis temperature is too high, and the catalyst concentration is too high, the total yield of CHDM is not greatly affected, and BHET will be hydrolyzed in small amounts at high temperature or when the alcoholysis catalyst concentration is high and the residence time is long, resulting in a reduction in the CHDM yield. When the amount of ethylene glycol is too large, the alcoholysis of PET is beneficial, and the PET conversion rate and BHET yield are both higher, but the amount of ethylene glycol is large, resulting in a reduction in the subsequent BHET and BHCD hydrogenation reaction rates, and the total molar yield of CHDM is reduced. In addition, when the alcoholysis temperature is high, the alcoholysis catalyst concentration is high, the amount of ethylene glycol is large, and the residence time is long, the reaction throughput is low, the reactor size is large, and the cycle energy consumption is large and uneconomical. In summary, the preferred alcoholysis temperature is 170-240°C, the alcoholysis time is 0.5-4h, and the alcoholysis catalyst concentration is 0.25-1%.

[0077] Comparative Example 2 The same waste polyester raw materials and process as in Example 1, as well as the same alcoholysis temperature, ethylene glycol dosage, alcoholysis residence time, etc., were used to explore the effects of the primary hydrogenation catalyst and the secondary hydrogenation catalyst on the process, and the hydrogenation process conditions remained consistent. Changing the conditions is a controlled variable method, such as when the primary hydrogenation catalyst is changed, the secondary hydrogenation catalyst is the same as in Example 1.

[0078] Table 4: Effect of different hydrogenation catalysts It can be seen from the data in Table 4 that waste PET bottles are used as raw materials, and the same alcoholysis catalyst and alcoholysis process conditions are used. The alcoholysis liquid is filtered and the alcoholysis catalyst is directly flowed into the primary hydrogenation reactor. The catalysts in the primary hydrogenation reactor are respectively loaded with industrial Raney nickel catalyst, industrial catalyst Ni / Al2O3 (Ni loading 10%) and Pd / C catalyst, and the secondary catalyst is still selected from the Cu-based catalyst in Example 1. The experimental results show that when the primary hydrogenation catalyst is selected from Pd-based and Ni-based catalysts under the same experimental conditions as Example 1, the conversion rate of BHET is low.

[0079] By analyzing the experimental data of Comparative Examples 2-1 and 2-2 with Example 1, it can be seen that the reaction temperature required for the hydrogenation of benzene rings by Ni-based catalysts is relatively high. When the reaction temperature is adjusted to 200°C, the BHET conversion rate for Ni-based catalysts is significantly increased, but the selectivity of BHCD is not significantly improved. By comparing Examples 2-3 and 2-5 with Example 1, it can be seen that for Pd-based catalysts, the BHCD conversion rate and CHDM selectivity are significantly lower than those of Cu-based catalysts, but are comparable to Ru-based catalysts for the BHET hydrogenation stage.

[0080] In summary, combined with Example 1, it can be seen that the primary hydrogenation catalyst can be selected from Ru-based catalysts and Pd-based catalysts, but the applicable process temperatures of the two are different. The Ru-based catalyst has the best reaction results at 100-140°C, and the Pd-based catalyst has better reaction conditions at 180-220°C, while the Ni-based catalyst is not suitable for the benzene ring hydrogenation reaction of BHET.

[0081] Similarly, waste PET bottles were used as raw materials, and the same alcoholysis catalyst and alcoholysis process conditions were used. After the alcoholysis liquid was filtered and the alcoholysis catalyst was removed, it flowed directly into the primary hydrogenation reactor. The catalysts in the primary hydrogenation reactor were filled with Ru-based catalysts, while the secondary reactor was filled with 15% Cu / Al2O3 or 5% Pd / Al2O3 catalysts. The experimental results showed that when the secondary catalyst was a Cu-based catalyst, the total molar yield of CHDM decreased to 89.12%, but when the Pd-based catalyst was selected, the CHDM selectivity decreased significantly, indicating that the carbonyl hydrogenation catalyst should preferably be a Cu-based catalyst. When CuMgAl (Cu loading 15%, Mg loading 10%, the rest is Al, Mg and Al both exist in the form of oxides, self-developed catalyst) catalyst is selected, the total molar yield of CHDM is higher, about 96%, which indicates that the auxiliary agent Mg has a higher hydrogenation efficiency than the auxiliary agent Mn. This may be because the alkalinity of Mg is stronger than that of Mn. During the hydrogenation of BHCD, a small amount of ether or ester will be generated due to the presence of two hydroxyl groups. This by-product is an acid-catalyzed reaction. Appropriate conditions for the acidity and alkalinity of the catalyst auxiliary are conducive to reducing the by-product content and improving the total yield of CHDM.

[0082] Comparative Example 3 Using the same waste polyester raw material, waste PET bottles, alcoholysis catalyst Al / SBA-15 and the same alcoholysis process conditions as in Example 1, and the same primary hydrogenation catalyst 3% Ru / Al2O3 / and second-stage hydrogenation catalyst 15% CuMnAl, the effects of primary and secondary hydrogenation processes on the total molar yield of CHDM were investigated.

[0083] Table 5: Effects of different hydrogenation processes It can be seen from Tables 4 and 5 that the hydrogenation reaction conditions and the hydrogenation catalyst should be closely coordinated to obtain a higher total molar yield of CHDM. When the reaction temperature and pressure are too low or too high, the hydrogenation conversion rate is too low or the hydrogenation selectivity is reduced, mainly because the temperature is too high or the reaction pressure is too high, resulting in an increase in over-hydrogenation by-products. Similar hydrogenation hydrogen-to-oil molar ratios and space velocity will have a certain impact on the total yield of CHDM. If the space velocity is too low and the residence time is too long, the over-hydrogenation product will increase; if the hydrogen-to-oil ratio is too small (greater than the theoretical molar ratio of 4:1), the heat released by the hydrogenation reaction cannot be removed in time, resulting in excessively high local temperatures, which increases the over-hydrogenation product. In summary, in order to ensure the total yield of CHDM, the catalyst and process conditions must be closely coordinated with each other.

[0084] The raw materials and equipment used in the present invention, unless otherwise specified, are all commonly used raw materials and equipment in the art; the methods used in the present invention, unless otherwise specified, are all conventional methods in the art.

[0085] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent transformation made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for continuously producing 1,4-cyclohexanedimethanol using waste polyester as raw material, characterized in that include: 1) alcoholyzing the waste polyester with ethylene glycol in the presence of an alcoholysis catalyst to obtain an alcoholysis solution containing diethylene glycol terephthalate; 2) the alcoholysis liquid is subjected to a first-stage hydrogenation under the action of a hydrogenation catalyst A to obtain a reaction liquid containing diethylene glycol 1,4-cyclohexanedicarboxylate; the hydrogenation catalyst A is selected from Ru / C, Ru / Al2O3, Ru / SBA-15, Pd / C, Pd / Al2O3 and Pd / SBA-15; 3) The reaction liquid is subjected to secondary hydrogenation under the action of a hydrogenation catalyst B to obtain a reaction liquid containing 1,4-cyclohexanedimethanol; the hydrogenation catalyst B has Cu or CuO as an active metal and at least one of Mn, Zn, Mg, Ce and Al or its oxide as a promoter metal; 4) The reaction liquid is subjected to gas-liquid separation and distillation to obtain ethylene glycol and 1,4-cyclohexanedimethanol.

2. The method according to claim 1, characterized in that: 1) In The mass ratio of the waste polyester to ethylene glycol is 1:2 to 1:10; The alcoholysis catalyst is a solid acid catalyst; The mass of the alcoholysis catalyst is 0.25-1wt% of the waste polyester; The alcoholysis temperature is 170-240° C., and the time is 0.5-4 h.

3. The method according to claim 1 or 2, characterized in that: 1), the alcoholysis catalyst is selected from Al / SBA-15, TiO2-SiO2 or Al2O3-SiO2, and the particle size of the alcoholysis catalyst is 10-300 μm.

4. The method according to claim 1, characterized in that: 2), the loading amount of Ru or Pd in ​​the hydrogenation catalyst A is 1-5wt%.

5. The method according to claim 1 or 4, characterized in that: 2), the hydrogenation catalyst A is selected from Ru / C, Ru / Al2O3 and Ru / SBA-15.

6. The method according to claim 1 or 4, characterized in that: 2), the particle size of the hydrogenation catalyst A is 0.5-3 mm.

7. The method according to claim 1 or 4, characterized in that: 2), the temperature of the first stage hydrogenation is 100-130°C, the pressure is 1-4MPa, the hydrogen-oil molar ratio is 50-300:1, and the liquid hourly space velocity is 1-5h -1 .

8. The method according to claim 1, characterized in that: 2), a solvent is introduced into the first-stage hydrogenation reactor to control the content of diethylene glycol terephthalate to be 5-20 wt%.

9. The method according to claim 8, characterized in that: 2), the solvent is selected from one or more of 1,4-dioxane, cyclohexane, methanol, ethyl acetate and 1,4-butanediol.

10. The method according to claim 1, characterized in that: In 2), the alcoholysis liquid is filtered before being introduced into the hydrogenation reactor, and the obtained alcoholysis catalyst is returned to 1) for recycling.

11. The method according to claim 1, characterized in that: 3), the hydrogenation catalyst B is selected from CuMnAl, CuZnAl, CuZnSi, CuCe-Al, Cu-CeO-MgO and CuZn-Mg, and the loading amount of Cu is 10-50wt%.

12. The method according to claim 1 or 11, characterized in that: 3), the temperature of the secondary hydrogenation is 180-220°C, the pressure is 1-4 MPa, the hydrogen-oil molar ratio is 50-300:1, and the liquid hourly space velocity is 1-5 h -1 .

13. The method according to claim 1 or 11, characterized in that: 3), the particle size of the hydrogenation catalyst B is 0.5-3 mm.

14. The method according to claim 1, characterized in that: 4), the distillation pressure is 1-50 kPa, the reflux ratio is 1-4:1; the primary distillation temperature is 50-130°C, the secondary distillation temperature is 160-200°C; and the tertiary distillation temperature is 180-240°C.

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