CN111484395A - Method for recovering bisphenol A by catalyzing polycarbonate to carry out methanol alcoholysis by composite metal oxide - Google Patents

Abstract

The invention discloses a method for recycling bisphenol A (BPA for short) by using composite metal oxide as a catalyst to depolymerize a carbonate material (PC for short) with methanol and alcohol, belonging to the technical field of high-value conversion of waste resources. The method uses composite metal oxide Mg_xAl-L DO (x is 2,3,4) is used as catalyst, methanol alcoholysis PC, after the reaction is finished, BPA product is recovered through operations of filtering, centrifuging, distilling and the like, the conversion rate of PC can reach 100%, and the yield of BPA product can reach more than 98.3%The BPA recovery process is simple; the catalyst has the advantages of simple preparation method, cheap and easily obtained raw materials, little dosage, easy separation and repeated use, is an economic and effective method, and is worthy of popularization.

Description

Method for recovering bisphenol A by compound metal oxide catalyzed methanol alcoholysis of polycarbonate

technical field

The invention belongs to the technical field of high-value conversion of waste resources, and mainly relates to a method for efficiently catalyzing methanol alcoholysis of polycarbonate (PC) to recover bisphenol A (BPA) by using composite metal oxide Mg ₃ Al-LDO as a catalyst.

Background technique

Polycarbonate (PC) is a thermoplastic material with excellent comprehensive properties and is widely used in various fields. With the rapid increase in the production and sales of PC materials, more and more PC waste is generated. Although the toxicity of PC waste itself is not large, it is difficult to degrade under natural conditions, and its accumulation is large, occupying space, and causing serious waste of resources. Therefore, the recycling of PC waste is more and more people's attention. At present, the chemical recovery methods of PC waste are mainly thermal cracking and chemical depolymerization. Most of the thermal cracking methods are carried out in the molten state, the reaction temperature is high, and the energy consumption is large. The cracking mechanism of PC is usually random chain cleavage, so the resulting product is complex, and it is difficult to obtain a high-purity target product. Compared with the thermal cracking method, the chemical depolymerization method has more advantages, and the alcoholysis method can be used as one of the effective methods. The alcoholysis of PC is mainly carried out with traditional strong bases as catalysts, such as Nikje et al (Polimery, 2011, 56(5): 381-384), Liu et al (Journal of Polymer Environment, 2009, (17): 7208-211 ) reported that using sodium hydroxide as a catalyst to catalyze the methanol alcoholysis of PC to recover BPA, although this process can effectively degrade PC, a large amount of strong base needs to be used as a catalyst, the catalyst is difficult to reuse, and the equipment is easily corroded and the amount of waste water is large. . Pan Zhiyan et al. (Journal of Chemical Engineering in Universities, 2008, 22(4): 597-603), Huang et al. (Polymer Degradation and Stability, 2006, 91(10): 2307-2314) investigated PC methanol alcohol under supercritical conditions respectively. Although the supercritical technology can greatly speed up the reaction, and there are no problems such as equipment corrosion and environmental pollution, there are still some shortcomings, such as: harsh reaction conditions, high equipment material requirements, difficult to achieve industrialized operation, etc. . Li et al. (Fibers and Polymers, 2013, 14(3): 365-368), Liu et al. (Journal of hazardous Materials, 2010, 174(1-3): 872-875) reported the use of ionic liquids as catalysts and reactions However, the synthesis steps of ionic liquids (ILs) are complicated, the cost is high, and the separation and recovery are difficult. Patents (CN2018106067111, CN2018106073911) reported that deep eutectic solvents (DESs) with urea (urea) as hydrogen bond acceptor can effectively catalyze the alcoholysis of PC to recover BPA. Similarly, they are all liquid, and the separation and recovery of the catalyst is still complicated. Patent (CN2016110933413) reported that solid catalyst CaO-SBA-15 molecular sieve is used for methanol alcoholysis reaction of PC. This method can also efficiently recover BPA, and catalyst separation is easy, but there are also complicated catalyst preparation process, high cost and tetrahydrofuran. It is a solvent, which leads to the disadvantages of cumbersome product separation steps. Therefore, it is of great significance to adopt new ideas and methods to improve the disadvantages of the existing process and realize the chemical recycling of waste polycarbonate materials.

SUMMARY OF THE INVENTION

In order to solve the shortcomings of the prior art, such as catalyst corrosion equipment, environmental pollution, poor reusability or complex synthesis steps, high cost, large dosage and harsh reaction conditions, the present invention provides a composite metal oxide Mg _x Al -LDO (x=2,3,4) is a method for catalyzing the methanol alcoholysis of PC materials to recover BPA. Without adding any solvent, the product obtained by this method has high purity, the catalyst synthesis method is simple, the cost is low, and it is easy to separate and recover , can be reused after calcination.

The technical scheme of the present invention is realized as follows: PC, methanol and catalyst of a certain quality are added into the reaction kettle, and the alcoholysis reaction of PC is carried out under a certain temperature and pressure. After the reaction is completed, the catalyst is recovered by filtration, centrifugation and calcination. , the filtrate is distilled to recover unreacted methanol to obtain product BPA, and the catalyst can be reused.

The catalyst used in the present invention is a self-made product, and the concrete steps are as follows:

(1) Preparation of Mg _x Al-LDH: Mg(NO ₃ ) ₂ ·6H ₂ O and Al(NO ₃ ) ₃ ·9H ₂ O with molar ratios of 2:1, 3:1 and 4:1 were weighed respectively , dissolved in 100mL of deionized water to prepare a mixed salt solution; another 0.12mol of sodium hydroxide and 0.04mol of anhydrous sodium carbonate were taken and dissolved in 100mL of deionized water to prepare a mixed alkali solution. Under the condition of constant stirring, add the alkaline solution dropwise to the salt solution, dropwise to pH=10, continue stirring for 30 minutes, heat up to 90 ° C for crystallization for 5 hours, cool and stand, filter, wash, dry, grind to obtain Precursor Mg _x Al-LDH, x=2,3,4.

(2) Preparation of Mg _x Al-LDO: The precursor Mg _x Al-LDH was placed in a muffle furnace and heated to 500 °C at 5 °C/min for 3 h. After natural cooling, Mg _x Al-LDO, x =2,3,4.

The catalyst composite metal oxide Mg _x Al-LDO, where x = 2, 3, 4, has a good effect on PC methanol alcoholysis reaction, and the PC alcoholysis rate can reach 100%. As a preference, when x = 3 , that is, when Mg ₃ Al-LDO is used as the catalyst, the degradation effect of PC is better, and the yield of BPA is the highest.

At first, the inventors tested a variety of composite metal oxides as catalysts for the alcoholysis of PC, but many of them had no catalytic effect. The inventors even gave up the initial efforts to find a suitable catalyst for the alcoholysis of PC. We were pleasantly surprised to find that the composite metal oxides formed by alkaline earth metals have catalytic effects on PC alcoholysis. The reason may be that PC alcoholysis is a transesterification reaction, and alkaline catalysts are beneficial to the reaction.

Preferably, the alcoholysis reaction temperature is 100-135°C, the mass ratio of PC to catalyst is 100:1-5, the molar ratio of PC to methanol is 1:3-10, and the reaction time is 0.5-3h.

More preferably, the alcoholysis reaction temperature is 110°C, the mass ratio of PC to the catalyst is 100:3, the molar ratio of PC to methanol is 1:5, the reaction time is 1h, and the BET of the catalyst Mg ₃ Al-LDO is Specific surface area≥62.455m ² /g, pore volume≥0.327cm ³ /g, pore size≥7.452nm.

Invention effect

Compared with the catalysts commonly used in the prior art, the composite metal oxide catalyst adopted in the present invention has the advantages of low cost, less consumption, simple preparation, stable catalytic performance, easy separation and recovery, and can make up for the traditional catalyst when catalyzing PC methanol alcoholysis. of insufficiency. The experimental results show that, with the catalyst and method provided by the invention, the PC alcoholysis rate can reach 100%, and the product BPA yield can reach more than 98%. At the same time, the catalyst recovery process is simple and the reuse performance is good.

Description of drawings

Fig.1 XRD patterns of Mg ₂ Al-LDO, Mg ₃ Al-LDO and Mg ₄ Al-LDO;

The influence of Fig. 2 reaction temperature on PC alcoholysis reaction;

The influence of Fig. 3 reaction time on PC alcoholysis reaction;

The influence of Fig. 4 catalyst dosage on PC alcoholysis reaction;

The influence of the amount of methanol in Fig. 5 on PC alcoholysis reaction;

Figure 6 is the IR and ¹ H NMR spectra of the product of Example 4 and BPA standard;

Fig. 7 is the IR spectrogram of Mg ₃ Al-LDO before and after the reuse of Example 8;

8 is the SEM spectrogram of the Mg ₃ Al-LDO before and after the reuse of Example 8;

Detailed ways

The invention discloses a method for recovering bisphenol A (BPA) by using a composite metal oxide as a catalyst for methanol alcoholysis of polycarbonate (PC). Those skilled in the art can learn from the content of this document and appropriately improve the process parameters to achieve. It should be particularly pointed out that all similar substitutions and modifications are obvious to those skilled in the art, and they are deemed to be included in the present invention. The method and application of the present invention have been described through the preferred embodiments, and it is obvious that relevant persons can make changes or appropriate changes and combinations of the methods and applications described herein without departing from the content, spirit and scope of the present invention to achieve and Apply the technology of the present invention.

In order to enable those skilled in the art to better understand the present invention, the present invention is further described in detail below with reference to specific embodiments.

Example 1: Preparation of Composite Metal Oxide Mg ₂ Al-LDO

(1) Preparation of Mg ₂ Al-LDH: Weigh 0.02 mol of Mg(NO ₃ ) ₂ ·6H ₂ O and 0.01 mol of Al(NO ₃ ) ₃ ·9H ₂ O, dissolve in 100 mL of deionized water, and prepare Mixed salt solution; take another 0.12mol of sodium hydroxide and 0.04mol of anhydrous sodium carbonate, dissolve in 100mL of deionized water, and prepare a mixed alkali solution. Under the condition of constant stirring, add the alkaline solution dropwise to the salt solution, dropwise to pH=10, continue stirring for 30 minutes, heat up to 90 °C for crystallization for 5 hours, cool and stand, filter, wash, dry, grind, This precursor is denoted as Mg ₂ Al-LDH.

(2) Preparation of Mg ₂ Al-LDO: The precursor Mg ₃ Al-LDH was placed in a muffle furnace and heated to 500° C. at 5°C/min for 3 hours, and then the composite metal oxide Mg ₂ Al was prepared after natural cooling. -LDO.

Example 2: Preparation of Composite Metal Oxide Mg ₃ Al-LDO

(1) Preparation of Mg ₃ Al-LDH: Weigh 0.03 mol of Mg(NO ₃ ) ₂ ·6H ₂ O and 0.01 mol of Al(NO ₃ ) ₃ ·9H ₂ O, dissolve in 100 mL of deionized water, and prepare Mixed salt solution; take another 0.12mol of sodium hydroxide and 0.04mol of anhydrous sodium carbonate, dissolve in 100mL of deionized water, and prepare a mixed alkali solution. Under the condition of constant stirring, add the alkaline solution dropwise to the salt solution, dropwise to pH=10, continue stirring for 30 minutes, heat up to 90 ° C for crystallization for 5 hours, cool and stand, filter, wash, dry, grind, This precursor is denoted as Mg ₃ Al-LDH.

(2) Preparation of Mg ₃ Al-LDO: The precursor Mg ₃ Al-LDH was placed in a muffle furnace at 5°C/min and heated to 500°C for 3 h, and then the composite metal oxide Mg ₃ Al was prepared after natural cooling. -LDO.

Example 3: Preparation of Composite Metal Oxide Mg ₄ Al-LDO

(1) Preparation of Mg ₄ Al-LDH: Weigh 0.04 mol of Mg(NO ₃ ) ₂ ·6H ₂ O and 0.01 mol of Al(NO ₃ ) ₃ ·9H ₂ O, dissolve them in 100 mL of deionized water, and prepare Mixed salt solution; take another 0.12mol of sodium hydroxide and 0.04mol of anhydrous sodium carbonate, dissolve in 100mL of deionized water, and prepare a mixed alkali solution. Under the condition of constant stirring, add the alkaline solution dropwise to the salt solution, dropwise to pH=10, continue stirring for 30 minutes, heat up to 90 °C for crystallization for 5 hours, cool and stand, filter, wash, dry, grind, This precursor is denoted as Mg ₄ Al-LDH.

(2) Preparation of Mg ₄ Al-LDO: The precursor Mg ₄ Al-LDH was placed in a muffle furnace at 5°C/min and heated to 500°C for 3 hours, and the composite metal oxide Mg ₄ Al could be prepared after natural cooling -LDO.

The XRD patterns of the composite metal oxides are shown in Figure 1, and the curves a, b, and c are the XRD patterns of Mg ₂ Al-LDO, Mg ₃ Al-LDO, and Mg ₄ Al-LDO in turn. It can be seen from Figure 1 that there are two obvious characteristic peaks in the three curves, which are characteristic peaks of MgO, and the peak shape is relatively sharp, indicating that it has a good crystal form.

Example 4: Influence of catalyst type on PC alcoholysis reaction

In an autoclave equipped with a thermometer, 4 g of PC, 0.2 g of the catalyst in Table 1, and 2.53 g of methanol were sequentially added, and the reaction was stirred at 130° C. for 2 h. After naturally cooling to room temperature, the unreacted PC residue was separated by opening the kettle, the mixture was centrifuged to separate the catalyst, and the catalyst was transferred to an oven for drying at 80 °C, and then calcined at 500 °C for 3 hours to recover the catalyst. The filtrate was distilled under reduced pressure to recover the unreacted catalyst The product is obtained after the reacted methanol, and the yield of BPA and the conversion rate of PC are shown in Table 1.

Table 1 Results of PC alcoholysis catalyzed by composite metal oxides

The data in Table 1 show that the alkaline earth composite metal oxides have a good catalytic effect on the methanolysis reaction of PC. Especially the catalytic effect of Mg/Al series is obviously better than that of Ca/Al series. Generally, the alcoholysis reaction of PC has a certain linear relationship with the alkalinity of the catalyst. The stronger the alkalinity, the better the catalytic effect. It shows that the alkalinity of Mg/Al series is stronger. This is consistent with the test results of XRD (Fig. 1), but the catalytic effect of Mg ₃ Al-LDO is better and the yield of BPA is higher.

Example 5: Optimization of PC alcoholysis reaction conditions

5.1 Influence of reaction temperature on PC alcoholysis

Under the conditions of t=2h, m(Mg ₃ Al-LDO):m(PC)=0.05:1, n(PC):n(CH ₃ OH)=1:5, PC(4g), different The effect of the reaction temperature on the PC alcoholysis reaction, the results are shown in Figure 2. It can be seen from the figure that the temperature has a significant effect on the PC alcoholysis reaction. When the reaction temperature is 100°C, the conversion rate of PC is only 62%, and when the temperature rises to 105°C, it can be increased to about 95%, and when the temperature continues to rise to 110°C, the PC conversion rate is 100%, The yield of BPA is over 98%. Continue to increase the reaction temperature, the conversion rate of PC and the yield of BPA remain basically unchanged, indicating that the alcoholysis reaction has reached equilibrium, but increasing the reaction temperature too much will increase energy consumption and waste data, so 110 ° C is better temperature.

5.2 Influence of reaction time on PC alcoholysis reaction

Under the conditions of reaction temperature of 110°C, m(Mg ₃ Al-LDO):m(PC)=0.05:1, n(PC):n(CH ₃ OH)=1:5, PC(4g), the The effect of reaction time on the alcoholysis reaction of PC was investigated, and the results are shown in Figure 3. As can be seen from the figure, the conversion rate of PC can reach more than 90% after 15min of reaction, and when the reaction time increases to 1h, the conversion rate of PC is 100%, and the yield of BPA is more than 98%. Continue to increase the reaction time, the PC conversion and BPA yield are basically unchanged, indicating that the alcoholysis reaction has reached equilibrium. Therefore, the preferred reaction time is 1 h.

5.3 Effect of catalyst dosage on PC alcoholysis reaction

Under the conditions of T=110℃, t=1h, m(PC)=4g, n(PC):n(CH ₃ OH)=1:5, the effect of catalyst dosage on PC alcoholysis was investigated. The results are as follows shown in Figure 3. It can be seen from Figure 4 that with the increase of the catalyst dosage, the PC conversion rate and the BPA yield both show an increasing trend. When m(Mg ₃ Al-LDO):m(PC)=0.01:1, the conversion rate of PC is only 59.6%, and the yield of BPA is 52.3%. When the amount of catalyst was increased to m(Mg ₃ Al-LDO):m(PC)=0.03:1, the PC conversion rate was 100%, and the BPA yield was 98.3%. Continue to increase the amount of catalyst, PC conversion and BPA yield remained basically unchanged, indicating that the alcoholysis reaction has reached equilibrium. Therefore, the preferred catalyst dosage is m(Mg ₃ Al-LDO):m(PC)=0.03:1.

5.4 Influence of methanol dosage on PC alcoholysis effect

Under the conditions of T=110℃, t=1h, m(Mg ₃ Al-LDO):m(PC)=0.03:1, m(PC)=4g, the amount of methanol was investigated, and the results are shown in Figure 5 shown. With the increase of methanol consumption, PC conversion and BPA yield first increased and then decreased. When n(PC):n(CH ₃ OH)=1:3, the conversion rate of PC reached 96.6%, and the yield of BPA reached 94.2%. When the amount of methanol was increased to n(PC):n(CH ₃ OH)=1:5, the PC conversion rate was 100%, and the BPA yield was 98.8%. The increase of catalyst did not have a great influence on the improvement of PC conversion rate and BPA yield, indicating that within this dosage range, the change of methanol dosage has little effect on PC alcoholysis reaction. Continuing to increase the amount of methanol, the conversion rate of PC and the yield of BPA decreased a little, which may be caused by the decrease of the concentration of the system due to the increase of the amount of methanol. Therefore, the preferred amount of methanol is n(PC):n(CH ₃ OH)=1:5.

Example 6: PC methanol alcoholysis reaction

In an autoclave equipped with a thermometer, 4 g of PC, 0.12 g of Mg ₃ Al-LDO, and 2.53 g of methanol were sequentially added, and the reaction was stirred at 110° C. for 1 h. After naturally cooling to room temperature, the mixture was centrifuged to separate out the catalyst, transferred to an oven for drying at 80°C, and then calcined at 500°C for 3 hours to recover the catalyst. The filtrate was distilled under reduced pressure to obtain 3.53 g of product BPA, and the PC alcoholysis rate was 100%. , the yield is 98.3%.

The IR of the obtained product and the standard sample is shown in Figure 6(A), the curve a is the ^IR of the BPA standard sample, and the curve b is the IR of the obtained product. It can be seen from the figure that around 3370cm ^-1 is the stretching vibration of -OH on BPA; around 3020cm ^-1 is the stretching vibration of CH on the benzene ring; around 2963cm ^-1 is the stretching vibration of -CH ₃ ; 1643cm ^-1 , 1611cm ^-1 , 1509cm ^-1 is the skeleton vibration of the benzene ring; 1445cm ^-1 and 1383cm ^-1 are the bending vibrations of -CH ₃ ; 1237cm ^-1 and 1176cm ^-1 are the stretching vibrations of CO; around 826cm ^-1 is the para-substitution absorption peak of the benzene ring . By comparing with the spectrum of BPA standard sample, it is found that the two curves are basically identical, which proves that the product of PC alcoholysis is BPA.

The ¹ H NMR of the obtained product and the standard sample is shown in Figure 6(B), it can be seen from the figure that the curve a is the ¹ H NMR of the BPA standard sample, and the curve b is the ¹ H NMR of the obtained product. The singlet with δ=9.15ppm is attributed to the 2 Hs in the OH on the benzene ring, the doublet at about δ=6.99ppm is attributed to the 4 Hs in the CH near OH on the benzene ring, and the doublet at about δ=6.64ppm The doublet is assigned to the 4 Hs of CH close to CH ₃ on the benzene ring, and the singlet appeared at about δ=1.52 ppm is assigned to the 6 H of -CH ₃ . Comparing the two spectral lines, it can be seen that the peak positions of each peak are consistent, which proves that the product obtained from the reaction is BPA.

Example 7: Repeatability investigation of PC methanol alcoholysis experiment

The experimental conditions and steps are the same as those in Example 6. Under this condition, the repeatability of the experiment was investigated, and the results are shown in Table 2. As can be seen from Table 2, at T=110°C, t=1h, m(cat):m(PC)=0.03:1, n(PC):n(CH ₃ OH)=1:5, the experiment was repeated The performance of the catalyst is good, and the catalytic effect has no obvious difference, indicating that the catalyst performance is stable.

Table 2 Investigation of the repeatability experiment of PC alcoholysis

Example 8: Reuse experiment of Mg ₃ Al-LDO catalyzed PC methanol alcoholysis reaction

The experimental conditions and steps were the same as those of Example 6, and the catalyst in Example 6 was reused for 5 times and then subjected to a catalytic effect experiment on its catalytic effect. The experimental results obtained are shown in Table 3.

Table 3 The repeated use experimental results of Mg ₃ Al-LDO catalyzed methanol alcoholysis of PC

It can be seen from Table 3 that the conversion of PC and the yield of bisphenol A did not decrease significantly after 5 cycles of the catalyst Mg ₃ Al-LDO. It shows that the catalytic activity of the catalyst remains basically unchanged during the recycling process, and the recycling performance is good.

Before and after recycling, the catalytic activity _of Mg ₃ Al _- LDO remained basically unchanged _. The LDO was characterized by IR and SEM. FIG. 7 is the IR spectrum before and after the catalyst is recycled, the curve a is the IR spectrum before the catalyst is used, and the curve b is the IR spectrum after the catalyst is recycled for 5 times. The absorption peak near 3480.23 cm ^-1 is the -OH stretching vibration, and the absorption peak below 1000 cm ^-1 is the MO skeleton vibration peak. Comparing the two curves, it can be found that the positions of the absorption peaks before and after Mg ₃ Al-LDO catalysis are basically the same, indicating that there is no obvious change in the structure and composition of the catalyst before and after catalysis. Figure 8 is the SEM spectrum of Mg ₃ Al-LDO, the left side is the SEM spectrum of the catalyst before use, and the right side is the SEM spectrum after use. It can be seen from the figure that the Mg ₃ Al-LDO is all agglomerated structure, and after 5 cycles of use, the catalyst has no obvious morphology change.

Comparative Example 1 Effects of catalyst types on PC methanol alcoholysis

Identical to the operation steps of Example 6, the temperature of reaction, the reaction time, catalyst type and consumption in Example 6 are modified to the respective parameters in Table 4, wherein CaO-SBA-15 also needs to add 6g tetrahydrofuran when it is a catalyzer. solvent, and the experimental results obtained are shown in Table 4.

Table 4 Effects of catalyst types on PC methanol alcoholysis

It can be seen from Table 4 that compared with molecular sieve CaO-SBA-15, deep eutectic solvent ChCl-2Urea, ionic liquids [Amim]Cl, [Amim]Br, [Bmim]OAc and [Bmim]Cl, Mg ₃ Al-LDO showed better catalytic activity. Although the PC conversion rate was 100% and the BPA yield was 98.8% when the deep eutectic solvent ChCl-2Urea was used as the catalyst, the reaction temperature was 130 °C, the reaction time needed to be extended to 2.5 h, and the amount of catalyst and methanol was relatively large. Furthermore, ChCl-2Urea is a liquid, and it is difficult to separate after the reaction. The composite metal oxide Mg ₃ Al-LDO has an unexpected catalytic effect on the methanolysis of PC, which not only reduces the reaction temperature, but also shortens the reaction time, and the amount of catalyst and methanol is relatively small. More importantly, the Mg ₃ Al-LDO catalyst used in the present invention has a simple preparation method, low cost, stable performance, and at the same time, the catalyst has a simple recovery process and good reusability.

The above are only the advantageous embodiments of the present invention. It should be pointed out that for those skilled in the art, without departing from the principles of the present invention, several improvements and modifications can be made. It should be regarded as the protection scope of the present invention.

Claims (5)

1. A method for recovering bisphenol A (BPA) by methanol alcohol depolymerization of Polycarbonate (PC) by taking composite metal oxide as a catalyst comprises the following steps: according to mass ratio m_PC:m_{Catalyst and process for preparing same}100: 1-5, molar ratio n_PC:n_MethanolAdding PC, methanol and a catalyst into a reaction kettle, carrying out alcoholysis reaction for 0.5-3 h at 100-135 ℃, filtering, centrifuging, calcining and recovering the catalyst after the reaction is finished, and simply distilling the filtrate to recover unreacted methanol to obtain the product BPA, wherein the catalyst can be repeatedly used.

2. The catalyst of claim 1 being Mg_xAl-L DO, where x is 2,3, 4.

3. The catalyst of claim 1, wherein the catalyst used is Mg_xAl-L DO is a self-made product prepared by the following steps:

(1)Mg_xpreparation of Al-L DH Mg (NO) was weighed in a molar ratio of 2:1, 3:1, 4:1, respectively₃)₂·6H₂O and Al (NO)₃)₃·9H₂Dissolving O in 100m L deionized water to obtain mixed salt solution, dissolving 0.12mol of sodium hydroxide and 0.04mol of anhydrous sodium carbonate in 100m L deionized water to obtain mixed alkali solution, dripping the alkali solution into the salt solution under the condition of continuous stirring until the pH value is 10, continuously stirring for 30min, heating to 90 ℃, crystallizing for 5h, cooling, standing, filtering, washing, drying and grinding to obtain precursor Mg_xAl-L DH, where x is 2,3, 4.

(2)Mg_xPreparing Al-L DO by adding precursor Mg_xPlacing Al-L DH in a muffle furnace, heating to 500 deg.C at a rate of 5 deg.C/min, maintaining for 3h, and naturally cooling to obtain Mg_xAl-L DO, where x is 2,3, 4.

4. The process of claim 1, wherein the alcoholysis reaction is carried out at a temperature of 110 ℃ for a period of 1h and comprises PC and Mg as a catalyst₃The mass ratio of Al-L DO was 100:3 and the molar ratio of PC to methanol was 1: 5.

5. The process as claimed in claim 4, wherein the catalyst Mg is used₃The BET specific surface area of Al-L DO is more than or equal to 62.455m²The pore volume is more than or equal to 0.327cm³The pore diameter is not less than 7.452 nm.

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