Method for preparing 1, 4-cyclohexanedimethanol from PET plastic

Abstract

The invention provides a method for preparing 1, 4-cyclohexanedimethanol by efficiently degrading PET (polyethylene terephthalate) waste plastics through a three-step method. In the method, the first step is that PET waste plastics are subjected to alcoholysis degradation to obtain dimethyl terephthalate, the second step is that the supported Ru-based catalyst catalyzes dimethyl terephthalate hydrogenation to prepare 1, 4-cyclohexanedicarboxylic acid dimethyl ester, and the third step is that the Cu-based catalyst catalyzes the 1, 4-cyclohexanedicarboxylic acid dimethyl ester to prepare the 1, 4-cyclohexanedimethanol. The catalyst is simple and convenient to prepare, low in cost and easy to recover, the product is easy to separate, the reaction process is green and environment-friendly, and conditions are mild. According to the technical scheme, the novel method for preparing the important polyester monomer 1, 4-cyclohexanedimethanol through efficient catalysis of the PET waste plastics is provided, waste is turned into wealth, and the method has excellent application prospects.

Description

Technical Field

[0001] The invention provides a method for preparing a catalyst for efficiently catalyzing PET waste plastics to prepare 1,4-cyclohexanedimethanol and application thereof. Background Art

[0002] 1,4-cyclohexanedimethanol (CHDM) is a raw material monomer for the production of polyester materials with excellent thermal stability and insulation, with a price of up to 30,000-40,000 yuan / ton. 1,4-cyclohexanedimethanol is mainly used to produce polyethylene terephthalate (PETG). PETG has excellent transparency, processing performance and heat resistance, and is widely used in packaging, electronics, automobiles and other fields. In addition, CHDM can also be used to produce other high-performance polymers, such as polyurethane elastomers, thermoplastic elastomers, polyether carbonates, etc. As the core raw material for the production of high-end polyester, the production technology of 1,4-cyclohexanedimethanol has been mastered by companies in Japan, the United States, South Korea and other countries, including Japan Co., Ltd., Eastman Company of the United States, and SK Chemicals of South Korea. At present, the main industrial route for the production of 1,4-cyclohexanedimethanol is to use dimethyl terephthalate (DMT) as a raw material to prepare 1,4-cyclohexanedimethanol through benzene ring hydrogenation and ester group hydrogenation using two catalysts. Its disadvantages are that the process route is complicated, the raw material dimethyl terephthalate is expensive, the reaction conditions are harsh, and it is not conducive to reducing the consumption of energy resources. For example, Eastman Company in the United States uses Pd / Al2O3 and CuCrOx catalysts to realize DMT hydrogenation to prepare CHDM, with a reaction pressure of 20-41MPa and a reaction temperature of 180-250°C (Tianjin Chemical Industry, 2023, Vol. 37, No. 6). The CHDM production process of Mitsubishi Corporation and Co., Ltd. in Japan is to use 5% Pd (Rh) catalyst and CuCrOx catalyst to catalyze DMT hydrogenation to prepare CHDM in two steps, with a reaction pressure of 5MPa and a reaction temperature of 150°C. Li Xiaohong's research group at East China Normal University also developed a method for preparing CHDM from DMT in one pot using 5Pd / CMK and Cu-based catalysts (Applied Catalysis A, General 632 (2022) 118510). In addition, patent CN102580732B also discloses the one-step method of RuSnPt / Al2O3 to catalyze low-concentration DMT (2.5-6.6wt%) to prepare CHDM. Although this method only requires one step, the raw material concentration is low, and the maximum precious metal loading reaches 16wt%, which is not suitable for industrial production. Patent CN115301248B reports a path to obtain 1,4-cyclohexanedimethanol by esterification and hydrogenation using 1,4-cyclohexanedicarboxylic acid as raw material. In summary, there is currently a lack of technical routes for directly preparing 1,4-cyclohexanedimethanol using waste plastic PET as raw material. The present invention will focus on developing high-performance catalysts to achieve efficient preparation of high-end polyester monomer CHDM from PET waste plastics. Summary of the invention

[0003] The present invention proposes a technical route for preparing 1,4-cyclohexanedimethanol by a three-step production process using PET waste plastics, and proposes a preparation method for preparing dimethyl terephthalate by degrading PET with a catalyst-free solvent, and a preparation method for a catalyst for preparing 1,4-cyclohexanedimethanol by catalytic hydrogenation of dimethyl terephthalate. Compared with the prior art, the invention technology directly uses PET as a raw material, effectively improves the yield of the target product 1,4-cyclohexanedimethanol, has mild reaction conditions, and a simple catalyst preparation method with low cost.

[0004] The present invention converts PET into 1,4-cyclohexanedimethanol through a three-step process. In the first step, PET is degraded into dimethyl terephthalate (DMT) by alcoholysis, in the second step, DMT is hydrogenated to prepare dimethyl 1,4-cyclohexanedicarboxylate (DMCD), and in the third step, DMCD is hydrogenated to prepare 1,4-cyclohexanedimethanol (CHDM). Methanol, a product of the third step reaction, can be used as a solvent to participate in the first step reaction, forming a cycle and reducing costs.

[0005] In the first step of PET alcoholysis, the preferred solvent is anhydrous methanol. The reaction is carried out in a reactor, and the PET mass content (PET mass / (PET+solvent) mass) is 5-50wt%, preferably 20-30wt.%. The reaction temperature is 140-240°C, preferably 160-220°C. The reaction time is 4-16h, preferably 8-12h. After the reaction is completed, it is filtered and separated, and dissolved in 1,4-dioxane, and then further distilled and separated (the boiling point of 1,4-dioxane at normal pressure is only 101°C) to obtain 1,4-cyclohexanedicarboxylic acid dimethyl ester (DMCD).

[0006] In the second step of preparing dimethyl 1,4-cyclohexanedicarboxylate (DMCD) by hydrogenation of DMT, the catalyst is an Al2O3-loaded noble metal catalyst. The noble metals are one or two or more of Pt, Pd, Rh and Ru, preferably Ru. The Ru content is 1wt%-5wt% of the catalyst mass, preferably 1-3wt.%, and the Ru / Al2O3 catalyst preparation method is:

[0007] By means of an equal volume impregnation method, the metal Ru precursor is dissolved in water, then added to the Al2O3 carrier, fully impregnated and stirred, dried at 120°C for 12h, and then roasted at 200-500°C for 1-4h, preferably at 250-350°C for 2-3h. The catalyst is reduced at 200-400°C for 0.5-4h before use, preferably at 200-350°C for 1-2h. The precursors of metal Ru correspond to one or more of Ru chloride, acetylacetonate and acetate, preferably acetate. The reaction is carried out in a reactor, and the solvent is one or more of ethylene glycol, 1,4-dioxane, ethyl acetate, and tetrahydrofuran, preferably 1,4-dioxane as the solvent. The DMT concentration is 1-50wt.%, and the mass ratio of the catalyst to DMT is 0.1-0.5, preferably 0.2-0.3. The reaction hydrogen pressure is 2-10MPa, the reaction temperature is 100-200°C, preferably the hydrogen pressure is 4-6MPa, and the reaction temperature is 140-160°C. The reaction time is 2-12h, preferably 6-10h. n-Dodecane is used as the internal standard. After the reaction, the solid catalyst, the liquid product and the solvent are separated by filtration, and the liquid product is separated by rectification (the boiling point of the solvent 1,4-dioxane is only 101°C under normal pressure) to obtain dimethyl 1,4-cyclohexanedicarboxylate (DMCD, boiling point: 132°C / 1.463kPa).

[0008] In the third step of hydrogenating dimethyl 1,4-cyclohexanedicarboxylate (DMCD) to prepare 1,4-cyclohexanedimethanol (CHDM), the catalyst is a Cu-based catalyst. The Cu-based catalyst is composed of active metal Cu, auxiliary agent A and oxide carrier B. The auxiliary agent A is one or two or more of iron oxide, zinc oxide, cerium oxide and molybdenum oxide. The oxide carrier B is one or two or more of aluminum oxide, magnesium oxide and titanium oxide. The preparation method of the catalyst is as follows:

[0009] The bulk composite metal oxide catalyst is prepared by the sol-gel method. The preparation method is as follows: the active component Cu, the auxiliary agent A (iron oxide, zinc oxide, cerium oxide, molybdenum oxide) and the oxide carrier B (aluminum oxide, magnesium oxide, titanium oxide) precursor salt are fully stirred and dissolved in water, preferably the auxiliary agent is zinc oxide, and the oxide carrier is preferably aluminum oxide. The Cu-based composite metal oxide catalyst is prepared by the sol-gel method. First, the active metal Cu, the auxiliary agent A and the carrier precursor salt are dissolved in 200-400mL of water, and after fully stirring and dissolving, 200-400mL of mixed alkaline solution is added to adjust the pH to 9-11, preferably pH = 9.5-10.5. After stirring at room temperature for 0.5-1.5h, age in a water bath at 50-80℃ for 4-12h, and preferably the aging temperature and time are 60-70℃ for 8-12h. The NaOH concentration in the mixed alkali solution is between 1.7-2.9 mol / L, and the NaOH concentration is preferably 2.0-2.7 mol / L, respectively. The NaOH / Na2CO3 molar ratio in the mixed alkali solution is between 1-3.4, and more preferably 2-3.4. The blue jelly-like colloid is then filtered and washed until the pH of the filtrate is 7-7.5, and the catalyst is dried at 80-120°C for 6-12h. The dried and ground catalyst is calcined at 300-600°C in an air atmosphere for 0.5-6h, preferably 400-500°C for 3-5h. The resulting catalyst is then reduced at 150-400°C in a hydrogen atmosphere for 1-4h, preferably at a reduction temperature of 200-300°C, and preferably for a reduction time of 1-2h, to finally obtain a bulk catalyst Cu-based catalyst. The mass of active metal Cu is 10-50wt% relative to the mass of the oxide carrier, preferably 20-30wt%. The mass of the auxiliary agent A is 5-20 wt.%, preferably 5-10 wt.%, relative to the mass of the oxide support.

[0010] The hydrogenation of dimethyl 1,4-cyclohexanedicarboxylate (DMCD) to prepare 1,4-cyclohexanedimethanol is carried out in a reactor, and the solvent is one or two or more of methanol, ethylene glycol, 1,4-dioxane, and tetrahydrofuran, preferably 1,4-dioxane as the solvent. The concentration of DMCD is 1-50wt.%, the mass ratio of catalyst to DMT is 0.1-0.5, and the preferred ratio is 0.2-0.3. The reaction hydrogen pressure is 2-10MPa, the reaction temperature is 160-240°C, preferably the hydrogen pressure is 4-6MPa, and the preferred reaction temperature is 180-220°C. The reaction time is 4-48h, preferably 12-24h. n-Dodecane is used as the internal standard. After the reaction, the solid catalyst, liquid solvent and product are separated by centrifugation or filtration, and methanol (methanol boiling point 64.7°C at normal pressure) can be obtained by distillation separation.

[0011] The catalyst of the present invention is easy to prepare, low in cost, easy to recycle, the product is easy to separate, the reaction process is green and environmentally friendly, and the conditions are mild. The technical solution of the present invention provides a new method for efficiently catalyzing PET waste plastic to prepare the important polyester monomer 1,4-cyclohexanedimethanol, which realizes the transformation of waste into treasure and has excellent application prospects.

[0012] Advantages of the present invention:

[0013] (1) Compared with existing literature and patents, the present invention proposes a method for preparing 1,4-cyclohexanedimethanol in three steps directly from PET waste plastics.

[0014] (2) The reaction conditions required for the second and third steps are milder, and the second step DMT hydrogenation catalyst is a Ru-based catalyst, which has a significantly lower cost than the mainstream Pd-based catalyst. In addition, the prepared Cu-based catalyst exhibits excellent stability in the third step hydrogenation reaction.

[0015] (3) The methanol product from the third step can be used as the solvent for the first step reaction after distillation separation. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 (a) is the raw material of PET plastic bottle, (b) is the product after PET depolymerization, and (c) is the product DMT dissolved in 1,4-dioxane;

[0017] Figure 2 This is the stability test result of preparing 1,4-cyclohexanedimethanol by hydrogenation of dimethyl 1,4-cyclohexanedicarboxylate catalyzed by 20Cu5ZnAl; reaction conditions: 5g dimethyl 1,4-cyclohexanedicarboxylate, 5g 1,4-dioxane, 1g 20Cu5ZnAl catalyst, reaction temperature 200℃, reaction pressure 5MPa, reaction time 12h. DETAILED DESCRIPTION

[0018] The specific implementation of the present invention is described in detail below in conjunction with the technical scheme and the accompanying drawings.

[0019] Example 1

[0020] In the first step, PET is depolymerized to prepare DMT. 20g PET plastic and 80g methanol are added to the reactor, replaced with nitrogen three times, and then heated to 200°C for 12h. After the reaction is completed, the white crystals are dissolved in 1,4-dioxane. The undissolved part is the unconverted PET, and the dissolved part is DMT. The 1,4-dioxane solution (mass ratio of solvent to DMT is 1:1) is collected. Figure 1 shown. Figure 1 (a) PET plastic bottle raw material, (b) PET depolymerization product, (c) product DMT dissolved in 1,4-dioxane

[0021] The process and conditions are the same as those in Example 1, except that the reaction is carried out at 200°C, the reaction temperature of the above process is changed (see Table 1 for details), and the first step reaction is carried out. The results are shown in Table 1;

[0022] Table 1 Effect of reaction temperature on PET depolymerization

[0023]

[0024] Reaction conditions: 20wt% PET, methanol solvent, 12h. Note: The other product ethylene glycol is not considered when calculating DMT selectivity.

[0025] The reaction conditions of Examples 2-6 and Comparative Examples 1-2 in Table 1 are different from those of Example 1 in that the reaction temperature is different, and the other conditions are the same. When the reaction temperature is lower than 140°C, the PET conversion rate is low, and when the reaction temperature is higher than 240°C, although PET is fully converted, excessive hydrogenolysis and cleavage of the CO bond in some of the product DMT occurs, resulting in a selectivity of the target product of only 54.3%. Therefore, in the preferred temperature range of 160-220°C, the DMT selectivity and conversion rate are both 100%;

[0026] The process and conditions are the same as those of Example 1, except that the reaction is carried out at 200°C, the reaction time of the above process is changed (see Table 2 for details), and the first step reaction is carried out. The results are shown in Table 2;

[0027] Table 2 Effect of reaction time on PET depolymerization

[0028]

[0029]

[0030] Reaction conditions: 20wt% PET, methanol solvent, 200°C. Note: The other product ethylene glycol is not considered when calculating the DMT selectivity.

[0031] The reaction conditions in Examples 7-9 and Comparative Examples 3-4 in Table 2 are different from those in Example 1 in terms of reaction time, and the rest are the same. Obviously, as the reaction time increases, the PET conversion rate gradually increases, and when the reaction time exceeds 16 hours, the DMT selectivity decreases. Within 4-16 hours, the DMT yield is not less than 64%, and within the preferred time range, that is, the reaction time is 8-12 hours, the DMT yield is ≥95.6%.

[0032] The DMT obtained from the degradation of PET in the first step reaction is the raw material for the second step reaction. The specific implementation method of the second step reaction is described in detail below in combination with the technical scheme and examples.

[0033] Example 10

[0034] Preparation of Ru / Al2O3 catalyst: Add 1.5mL 10wt% Ru precursor (RuCl3·3H2O) aqueous solution to 4.85g Al2O3 carrier, fully impregnate and stir, dry at 120℃ for 12h, and then calcine in air at 300℃ for 2h. Before using the catalyst, reduce it in hydrogen at 300℃ for 1h to obtain 3Ru / Al2O3 catalyst. The numbers before metal in the following examples and comparative examples have the same meaning, which are the mass percentage of the metal in the catalyst.

[0035] The reaction was carried out in a reactor, with 5 g of solvent 1,4-dioxane, 5 g of raw material DMT, 1 g of 3Ru / Al2O3 catalyst, and 0.02 g of n-dodecane as an internal standard. The reaction hydrogen pressure was 5 MPa, the reaction temperature was 140°C, and the reaction time was 8 h. After the reaction, the solid catalyst was separated by centrifugation, and the liquid product was qualitatively analyzed by GC-MS and quantitatively analyzed by GC (the following examples and comparative examples were analyzed by this method after the reaction, which will not be repeated).

[0036] The liquid product is separated by distillation (the boiling point of the solvent 1,4-dioxane is only 101°C under normal pressure) to obtain dimethyl 1,4-cyclohexanedicarboxylate (DMCD, boiling point: 132°C / 1.463kPa).

[0037] The process and conditions are the same as in Example 10, except that the catalyst in the above process is changed (see Table 3 for details) to carry out the second step reaction. The results are shown in Table 3:

[0038] Table 3 Preparation of dimethyl 1,4-cyclohexanedicarboxylate (DMCD) by hydrogenation of DMT catalyzed by different catalysts

[0039]

[0040]

[0041] Reaction conditions: 5g DMT, 5g solvent 1,4-dioxane, 1g catalyst, 140℃ for 8h, hydrogen pressure 5MPa

[0042] The reaction conditions of Examples 11-16 and Comparative Examples 5-12 in Table 3 are different from those of Example 10 in that the catalysts used are different, and the other reaction conditions are the same. Among them, the difference between Examples 11-13 and Example 10 is that the selected metal salt precursors are chloroplatinic acid, palladium chloride and rhodium chloride, respectively. The process and conditions are the same as the preparation of Ru / Al2O3 catalyst, except that the type of metal salt precursor and the amount of solution used are different, and / or the type of carrier is different).

[0043] Obviously, the alumina-supported noble metal catalysts all have good catalytic performance and realize 100% conversion of DMT into DMCD. Considering the catalyst preparation cost, Ru is one of the cheapest noble metals, and its price is only 8%-30% of other noble metals, which has excellent cost advantages and is conducive to industrial promotion. Comparative Examples 5-6 use non-noble metal catalysts Co / Al2O3 and Ni / Al2O3, and the metal salt precursors used are cobalt nitrate and nickel nitrate, respectively. The remaining catalyst preparation conditions are the same as those in Example 10 (ensuring that the Co and Ni loadings are 10wt%). The main products on the non-noble metal catalysts are by-products such as p-xylene. The catalyst preparation methods of Comparative Examples 7-8 and Examples 14-16 differ from those of Example 10 in that the amount of Ru metal salt precursors used is different, and the remaining preparation and reaction conditions are the same. It can be seen that the effect of different Ru contents on the hydrogenation performance of DMT, with the increase of Ru content, the DMT conversion rate gradually increases. Taking into account the catalyst preparation cost and reaction performance, the preferred Ru content is 1-3wt%, at which time the DMT conversion rate is greater than 79%, and the DMCD selectivity is 100%. The difference between Comparative Examples 9-12 and Example 10 is only that the carriers are different, and the other preparation conditions and reaction conditions are the same. Different carriers have a greater impact on the performance of DMT hydrogenation reaction. Obviously, compared with magnesium oxide, titanium oxide, zirconium oxide and silicon oxide, aluminum oxide has more advantages. This is mainly due to the fact that aluminum oxide not only has a large relative area, which is conducive to Ru dispersion and improves metal utilization, but also has a low cost, is easy to shape, and is convenient for industrial large-scale production.

[0044] The process and conditions are the same as those of Example 10, except that the solvent in the above process is changed (see Table 4 for details), and the second step reaction is carried out. The results are shown in Table 4;

[0045] Table 4 Effect of different solvents on DMT hydrogenation performance

[0046]

[0047]

[0048] Reaction conditions: 5g DMT, 5g solvent, 1g 3Ru / Al2O3 catalyst, 140℃ for 8h, hydrogen pressure 5MPa

[0049] Since DMT is solid at room temperature, the solvent is crucial for the conversion of DMT. Table 4 examines the effects of different solvents on the conversion of DMT. The reaction conditions of Examples 17-19 and Comparative Examples 13-14 are different from those of Example 10 in that the selected solvents are different, and the rest are the same. Among the various solvents, 1,4-dioxane has the best effect, which is mainly due to the excellent DMT solubility of 1,4-dioxane, so 1,4-dioxane is preferably used as a solvent. For Comparative Examples 13-14, when water and methanol are used as solvents, DMT is difficult to dissolve and convert.

[0050] The process and conditions are the same as in Example 10, except that the reaction temperature of the above process is changed (see Table 5 for details), and the second step reaction is carried out. The results are shown in Table 5;

[0051] Table 5 Effect of reaction temperature on DMT hydrogenation performance

[0052]

[0053] Reaction conditions: 5g DMT, 5g solvent 1,4-dioxane, 1g 3Ru / Al2O3 catalyst, reaction time 8h, hydrogen pressure 5MPa

[0054] Table 5 examines the effect of reaction temperature on DMT hydrogenation performance. The reaction conditions of Examples 20-24 and Comparative Examples 15-16 are different from those of Example 10 only in the reaction temperature, and the rest are the same. At a lower reaction temperature, the DMT conversion rate is lower, and when the reaction temperature is ≥180°C, although DMT is completely converted, byproducts such as methyl cyclohexanecarboxylate begin to appear, and the DMCD selectivity decreases. Preferably, within the range of 140-160°C, the DMCD yield reaches 100%.

[0055] The process and conditions are the same as in Example 10, except that the reaction time of the above process is changed (see Table 6 for details), and the second step reaction is carried out. The results are shown in Table 6;

[0056] Table 6 Effect of reaction time on DMT hydrogenation performance

[0057]

[0058]

[0059] Reaction conditions: 5g DMT, 5g solvent 1,4-dioxane, 1g 3Ru / Al2O3 catalyst, reaction temperature 140°C, hydrogen pressure 5MPa

[0060] Table 6 shows the effect of reaction time on DMT hydrogenation performance. The reaction conditions of Examples 25-29 and Comparative Examples 17-18 are different from those of Example 10 only in the reaction time. The rest is the same. Obviously, as the reaction time is prolonged, the conversion rate gradually increases. When the reaction time reaches 12h, the by-product methyl cyclohexanecarboxylate begins to gradually appear. Within the preferred reaction time range, i.e., within 6-10h, the DMT conversion rate is greater than 94%, and the DMCD selectivity reaches 100%.

[0061] The process and conditions are the same as in Example 10, except that the hydrogen pressure in the above process is changed (see Table 7 for details), and the second step reaction is carried out. The results are shown in Table 7;

[0062] Table 7 Effect of reaction pressure on DMT hydrogenation performance

[0063]

[0064] Reaction conditions: 5g DMT, 5g solvent 1,4-dioxane, 1g 3Ru / Al2O3 catalyst, reaction temperature 140℃, reaction time 8h

[0065] Table 7 shows the effect of reaction pressure on DMT hydrogenation performance. The reaction conditions of Examples 30-34 and Comparative Examples 19-20 are different from those of Example 10 only in the hydrogen pressure, and the rest are the same. Obviously, as the hydrogen pressure increases, the conversion rate gradually increases. When the hydrogen pressure exceeds 8MPa, excessive hydrogenolysis products such as methyl cyclohexanecarboxylate and cyclohexane begin to gradually appear. In the preferred hydrogen pressure range, i.e., within 4-6MPa, the DMT conversion rate is greater than 89%, and the DMCD selectivity reaches 100%.

[0066] The third step reaction uses dimethyl 1,4-cyclohexanedicarboxylate as raw material (DMCD), and the target product is 1,4-cyclohexanedimethanol (CHDM), accompanied by the production of methanol. The produced methanol can be used as the solvent for the first step reaction of DMT alcoholysis and depolymerization after distillation separation.

[0067] Embodiment 35

[0068] Preparation of 20Cu5ZnAl catalyst: Taking the preparation method of 20wt%Cu5wt%ZnO-Al2O3 as an example (abbreviated as 20Cu5ZnAl, the same below): 73.6g of aluminum nitrate nine hydrate (aluminum nitrate for short, equivalent to 10g of aluminum oxide), copper nitrate trihydrate (copper nitrate for short) with a Cu content of 20% of the mass of aluminum oxide, and zinc nitrate trihydrate with a zinc oxide content of 5wt% of the mass of aluminum oxide are dissolved in 200mL of water, and after stirring and dissolving, add alkaline solution (2mol / LNaOH+0.6mol / LNa2CO3) to adjust the pH to 10, then stir at room temperature for 1h, and age in a 70℃ water bath for 12h. Then filter and wash the blue jelly-like colloid until the filtrate is close to neutral (pH=7-7.5), and dry the catalyst at 120℃ for 12h. Then roast at 500℃ for 4h in an air atmosphere, and after cooling to room temperature, reduce the resulting solid powder at 250℃ for 2h in a hydrogen atmosphere. After the reduction was completed and the temperature dropped to room temperature, 1% O2 / N2 (volume fraction) was used for passivation for 1 hour. The obtained catalyst was recorded as 20Cu5ZnAl.

[0069] The reaction was carried out in a reactor, with 5 g of solvent 1,4-dioxane, 5 g of raw material DMCD, 1 g of catalyst, and 0.02 g of n-dodecane as an internal standard. The reaction hydrogen pressure was 5 MPa, the reaction temperature was 220°C, and the reaction time was 24 h. After the reaction, the solid catalyst was separated by centrifugation, and the liquid product was qualitatively analyzed by GC-MS and quantitatively analyzed by GC (the following examples and comparative examples were analyzed by this method after the reaction, which will not be repeated).

[0070] After the reaction, the solid catalyst, liquid solvent and product are separated by centrifugation or filtration, and methanol can be obtained by distillation (the boiling point of methanol is 64.7°C at normal pressure).

[0071] The process and conditions are the same as in Example 35, except that the catalyst in the above process is changed (see Table 8 for details) to carry out the third step reaction. The results are shown in Table 8;

[0072] Table 8 Preparation of 1,4-cyclohexanedimethanol (CHDM) by hydrogenation of DMCD catalyzed by different catalysts

[0073]

[0074]

[0075] Reaction conditions: 5g DMCD, 5g solvent 1,4-dioxane, 1g catalyst, 220℃ for 24h, hydrogen pressure 5MPa (Note: methanol is not considered when calculating selectivity)

[0076] Table 8 examines the effects of different active metals, additives and carriers on the preparation of CHDM by hydrogenation of DMCD. The only difference between Examples 36-38 and Example 35 is that the carrier precursors are selected differently (the precursors are weighed according to 10g of the corresponding oxide), namely aluminum nitrate, magnesium nitrate and titanium tetrachloride, and the remaining preparation conditions and reaction test conditions are the same as Example 35. Although the DMCD conversion rate on the catalysts with magnesium oxide and titanium oxide as carriers is greater than 84%, and the CHDM selectivity is greater than 78%, aluminum oxide has better performance as the carrier component, and the DMCD conversion rate and CHDM selectivity are both 100%, so Al2O3 is preferred. At the same time, Al2O3 as a carrier in the second step of DMT hydrogenation to DMCD reaction also has excellent performance, so it is beneficial to reduce the cost of catalyst preparation and promote industrial-scale production.

[0077] The difference between Examples 38-40 and Examples 38-40 is that the selected auxiliary agents are different (all ensuring that the auxiliary agent content is 5wt% of the mass of the oxide carrier), namely iron nitrate, ammonium molybdate, and cerium nitrate, respectively, and the other preparation conditions and reaction test conditions are the same. Obviously, different metal oxide auxiliary agents have good deoxidation performance and perform well in the 50wt% high-concentration ester hydrogenation process. The DMCD conversion rate is greater than 78%, and the CHDM selectivity is greater than 65%. Among them, zinc oxide has the best performance as an auxiliary agent, so zinc oxide auxiliary agent is preferred. At the same time, when iron oxide and molybdenum oxide are used as auxiliary agents, Fe and Mo will be lost to varying degrees after multiple cycles of reaction.

[0078] The difference between Examples 41-44 and Comparative Examples 21-22 and Example 35 is that the amount of copper nitrate precursor used is different, which is equivalent to 5wt%, 10wt%, 30wt%, 40wt%, 50wt% and 70wt% of the alumina carrier, respectively, and the other preparation conditions and reaction test conditions are the same. Obviously, as the Cu content increases, the DMCD conversion rate and CHDM selectivity gradually increase, and when the Cu content further increases, by-products such as excessive hydrogenolysis products such as methylcyclohexane methanol will be produced. It is preferred that within the Cu content range, that is, within 20-30wt.%, the DMCD conversion rate is 100% and the CHDM selectivity is greater than 95%.

[0079] The difference between Examples 45-46 and Comparative Examples 23-24 and Example 35 is that the amount of auxiliary agent precursor zinc nitrate is different, which is equivalent to 1wt%, 10wt%, 20wt% and 30wt% of the alumina carrier respectively, and the other preparation conditions and reaction test conditions are the same. The Zn content is preferably within the range. That is, 5-10wt%, the DMCD conversion rate reaches 100%, and the CHDM selectivity is greater than 98%. For Comparative Example 23, the Zn content is less, and the promoting effect on DMCD conversion is weak. For Comparative Example 24, when the Zn content is too high, the Cu active sites are covered, resulting in a significant decrease in DMCD conversion rate and CHDM selectivity.

[0080] Compared with Example 35, Comparative Examples 25-26 differ in that the selected active metal precursors are nickel nitrate and cobalt nitrate, respectively, and the remaining preparation conditions and reaction test conditions are the same. When the active metal is Ni or Co, excessive hydrogenolysis of DMCD leads to an increase in by-products, such as 4-methylcyclohexane methanol. In summary, Cu has suitable activation hydrogen and hydrogenolysis capabilities, and Cu is preferably used as an active metal. Example 47 is a stability test of the preparation of 1,4-cyclohexanedimethanol (CHDM) by hydrogenation of 1,4-cyclohexanedicarboxylic acid dimethyl ester (DMCD) catalyzed by the catalyst 20Cu5ZnAl used in Example 35. The specific operating steps are as follows: 5g DMCD, 5g solvent 1,4-dioxane, internal standard n-dodecane 0.02g, 1g 20Cu5ZnAl catalyst, reaction temperature 220°C, reaction pressure 5MPa (constant pressure), reaction time 24h. After each reaction, the catalyst was centrifuged and washed with solvent 5 times, then freeze-dried for 4 hours, and then added to the reactor, and 5g DMCD and 5g solvent 1,4-dioxane were added, 5MPa hydrogen was filled, and the temperature was raised to 220℃ for the next cycle reaction. The liquid product after each reaction was centrifuged and then qualitatively analyzed by mass spectrometry and quantitatively analyzed by gas chromatography. The reaction results are shown in Figure 2 It can be seen from the figure that the DMCD conversion rate and CHDM selectivity of the 20Cu5ZnAl catalyst prepared by the present invention remain basically unchanged in 5 cycles, both maintained at about 100%, indicating that the catalyst has excellent stability and good industrial application prospects.

Claims

1. A method for preparing 1,4-cyclohexanedimethanol using PET plastic, characterized in that: The reaction is divided into three steps. The first step is to degrade PET waste plastic to produce dimethyl terephthalate (DMT); the second step is to hydrogenate dimethyl terephthalate to produce dimethyl 1,4-cyclohexanedicarboxylate (DMCD); the third step is to hydrogenate dimethyl 1,4-cyclohexanedicarboxylate to produce 1,4-cyclohexanedimethanol (CHDM).

2. The method according to claim 1, characterized in that: The first step reaction, PET degradation reaction, does not require a catalyst, and the solvent is anhydrous methanol; the reaction is carried out in a reactor, the mass content of PET is 5-50wt%, preferably 20-30wt.%; the reaction temperature is 140-240°C, preferably 160-220°C; the reaction time is 4-16h, preferably 8-12h.

3. The method according to claim 1, characterized in that: In the second step reaction, the catalyst used is an Al2O3-loaded precious metal catalyst; the precious metals are one or two or more of Pt, Pd, Rh and Ru, preferably Ru; the precious metal content is 1wt%-5wt% of the catalyst mass, preferably 1-3wt.%.

4. The method according to claim 3, characterized in that: The preparation process of Al2O3 loaded noble metal catalyst is as follows: By means of equal volume impregnation method, the noble metal precursor is dissolved in water, then added to the Al2O3 carrier, fully impregnated and stirred, dried at 80-120°C for 8-12h, and then calcined at 200-500°C for 1-4h, preferably calcined at 250-350°C in air for 2-3h; before the catalyst is used, it is reduced with hydrogen at 200-400°C for 0.5-4h, preferably at 250-350°C for 1-2h; The noble metal (Pt, Pd, Rh and Ru) precursors correspond to one or two or more of the corresponding chlorides, acetylacetonates and acetates, respectively, preferably acetates.

5. The method according to claim 3 or 4, characterized in that: The reaction is carried out in a reactor, the solvent is one or two or more of ethylene glycol, 1,4-dioxane, ethyl acetate, and tetrahydrofuran, preferably 1,4-dioxane is the solvent; the DMT concentration is 1-50wt.%, the mass ratio of the catalyst to DMT is 0.1-0.5, and the preferred ratio is 0.2-0.3; the reaction hydrogen pressure is 2-10MPa, the reaction temperature is 100-200°C, preferably the hydrogen pressure is 4-6MPa, and the preferred reaction temperature is 140-160°C; the reaction time is 2-12h, preferably 6-10h.

6. The method according to claim 1, characterized in that: In the third step reaction, the catalyst used is a Cu-based catalyst; the Cu-based catalyst is composed of active metal Cu, an additive A and an oxide carrier B; wherein the additive A is one or two or more of iron oxide, zinc oxide, cerium oxide and molybdenum oxide; the oxide carrier B is one or two or more of aluminum oxide, magnesium oxide and titanium oxide; The mass of active metal Cu is 10-50wt% relative to the mass of the oxide support, preferably 20-30wt%; the mass of additive A is 5-20wt.%, preferably 5-10wt.% relative to the mass of the oxide support.

7. The method according to claim 6, characterized in that: The preparation process of Cu-based catalyst is as follows: The bulk composite metal oxide catalyst is prepared by a sol-gel method, and the preparation method is as follows: the active component Cu, the auxiliary agent A and the oxide carrier B precursor salt are fully stirred and dissolved in water, the auxiliary agent is preferably zinc oxide, and the oxide carrier is preferably aluminum oxide; First, the active metal Cu, the additive A and the carrier precursor salt are dissolved in 200-400 mL of water, and after being fully stirred and dissolved, 200-400 mL of a mixed alkali solution is added to adjust the pH to 9-11, preferably pH = 9.5-10.5; after stirring at room temperature for 0.5-1.5 hours, the mixture is aged in a water bath at 50-80° C. for 4-12 hours, and preferably the aging temperature and time are 60-70° C. for 8-12 hours; The NaOH concentration in the mixed alkali (NaOH+Na2CO3) solution is between 1.7-2.9 mol / L, and more preferably the NaOH concentration is 2.0-2.7 mol / L, respectively, and the NaOH / Na2CO3 molar ratio in the mixed alkali solution is between 1-3.4, and more preferably 2-3.4; Then, the blue jelly-like colloid is filtered out and washed until the pH value of the filtrate is 7-7.5, and the catalyst is dried at 80-120° C. for 6-12 hours; the dried catalyst is calcined at 300-600° C. for 0.5-6 hours, preferably at 400-500° C. for 3-5 hours in an air atmosphere; then, the obtained catalyst is reduced at 150-400° C. for 1-4 hours in a hydrogen atmosphere, preferably at a reduction temperature of 200-300° C., and preferably at a reduction time of 1-2 hours, to finally obtain a bulk phase catalyst Cu-based catalyst; The active metal Cu salt precursor selected for the third step hydrogenation Cu-based catalyst is one or more of their corresponding acetates or nitrates; the precursor salts of iron oxide, zinc oxide and cerium oxide in the metal oxide additive A are one or more of their corresponding acetates or nitrates, and the precursor salt of molybdenum oxide is ammonium molybdate; the precursor salts of aluminum oxide and magnesium oxide in the oxide carrier B are corresponding nitrates or acetates, and the precursor salt of titanium oxide is titanium chloride.

8. The method according to claim 6 or 7, characterized in that: The reaction of hydrogenating 1,4-cyclohexanedicarboxylic acid dimethyl ester (DMCD) to prepare 1,4-cyclohexanedimethanol is carried out in a reactor, and the solvent is one or two or more of methanol, ethylene glycol, 1,4-dioxane, and tetrahydrofuran, preferably 1,4-dioxane is used as the solvent; the DMCD concentration is 1-50wt.%, the mass ratio of the catalyst to DMCD is 0.1-0.5, and the preferred ratio is 0.2-0.3; the reaction hydrogen pressure is 2-10MPa, the reaction temperature is 160-240°C, preferably the hydrogen pressure is 4-6MPa, and the preferred reaction temperature is 180-220°C; the reaction time is 4-48h, preferably 12-24h.

9. The method according to claim 8, characterized in that: The product methanol of the third step reaction can be used as the solvent for the first step PET degradation reaction after centrifugation or filtration and distillation separation steps; the raw material PET plastic of the first step reaction can be used PET waste plastic.

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