CN111484395B - Method for recovering bisphenol A by catalyzing polycarbonate to carry out methanol alcoholysis by composite metal oxide - Google Patents
Method for recovering bisphenol A by catalyzing polycarbonate to carry out methanol alcoholysis by composite metal oxide Download PDFInfo
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- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 title claims abstract description 117
- IISBACLAFKSPIT-UHFFFAOYSA-N bisphenol A Chemical compound C=1C=C(O)C=CC=1C(C)(C)C1=CC=C(O)C=C1 IISBACLAFKSPIT-UHFFFAOYSA-N 0.000 title claims abstract description 85
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- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C37/00—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom of a six-membered aromatic ring
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/02—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the alkali- or alkaline earth metals or beryllium
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- B01J23/02—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the alkali- or alkaline earth metals or beryllium
- B01J23/04—Alkali metals
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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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 x Al-LDO (x is 2,3,4) is used as a catalyst, methanol is used for alcoholysis of PC, after the reaction is finished, BPA products are recovered through operations such as filtration, centrifugation and distillation, the conversion rate of PC can reach 100%, and the yield of BPA products can reach more than 98.3%. The catalyst and the method provided by the invention can obviously improve the PC conversion rate and the BPA yield, and meanwhile, the reaction condition is mild, and 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
Technical Field
The invention belongs to the technical field of high-value conversion of waste resources, and mainly relates to a composite metal oxide Mg 3 The Al-LDO is a catalyst for efficiently catalyzing the alcoholysis of Polycarbonate (PC) methanol to recover bisphenol A (BPA).
Background
Polycarbonate (PC) is a thermoplastic material with excellent overall properties and is widely used in various fields. With the rapid increase of the production and sales of PC materials, more and more PC waste materials are generated. Although PC waste is not toxic, it is difficult to degrade under natural conditions, and the amount of PC waste accumulated is large, occupying space and causing serious waste of resources. Therefore, the recycling of PC waste is receiving more and more attention. At present, the chemical recovery method of PC waste is mainly a thermal cracking method and a chemical depolymerization method. The thermal cracking process is mostly carried out in a molten state, the reaction temperature is high, and the energy consumption is large. The cleavage mechanism of PC is usually random chain cleavage, so the resulting product is complex and it is difficult to obtain a target product with high purity. The chemical depolymerization method is more advantageous than the thermal decomposition method, in which the alcoholysis method can be one of the effective means. Alcoholysis of PC is mainly carried out by using traditional strong base as a catalyst, for example, Nikje et al (Polimery,2011,56(5):381- & lt384), Liu et al (Journal of Polymer environmental, 2009, (17):7208- & lt211) report that BPA is recovered by catalyzing alcoholysis of PC methanol by using sodium hydroxide as a catalyst. The panyan et al (journal of chemical engineering in colleges and universities, 2008,22(4): 597-: the reaction conditions are harsh, the requirement on equipment materials is high, and the industrial operation is difficult to realize. Li et al (Fibers and Polymers,2013,14(3): 365-. Patents (CN2018106067111, CN2018106073911) report that eutectic solvents (DESs) with urea (urea) as a hydrogen bond acceptor can effectively catalyze alcoholysis of PC to recover BPA, although the steps for synthesizing DESs are simple and low in cost, the DESs is similar to ILs and is liquid, and the separation and recovery of the catalyst are still complicated. The patent (CN2016110933413) reports that a solid catalyst CaO-SBA-15 molecular sieve is used for a methanol alcoholysis reaction of PC, BPA can be efficiently recovered by the method, the catalyst is easy to separate, but the method also has the defects of complicated catalyst preparation process, high cost, complicated product separation steps caused by taking tetrahydrofuran as a solvent and the like. Therefore, the new thought and method are adopted to overcome the defects of the prior art, and the chemical recycling of the waste polycarbonate material is of great significance.
Disclosure of Invention
In order to solve the defects of corrosion of equipment, environmental pollution, poor reusability or complex synthesis steps, high cost, large using amount, harsh reaction conditions and the like of catalysts in the prior art, the invention provides a composite metal oxide Mg x The method for recovering BPA by catalyzing the alcoholysis of methanol by using the PC material with Al-LDO (x ═ 2,3,4) as the catalyst has the advantages of high purity of the obtained product, simple synthesis method of the catalyst, low cost, easy separation and recovery and reusability after calcination.
The technical scheme of the invention is realized as follows: adding PC, methanol and a catalyst with certain mass into a reaction kettle, carrying out alcoholysis reaction on the PC at a certain temperature and under a certain pressure, filtering, centrifuging and calcining the mixture after the reaction is finished to recover the catalyst, distilling the filtrate to recover the unreacted methanol to obtain a product BPA, wherein the catalyst can be repeatedly used.
The catalyst used in the invention is a self-prepared product, and comprises the following specific steps:
(1)Mg x preparation of Al-LDH: mg (NO) is weighed according to the molar ratio of 2:1, 3:1 and 4:1 respectively 3 ) 2 ·6H 2 O and Al (NO) 3 ) 3 ·9H 2 Dissolving O in 100mL of deionized water to prepare a mixed salt solution; 0.12mol of sodium hydroxide and 0.04mol of anhydrous sodium carbonate are dissolved in 100mL of deionized water to prepare a mixed alkali solution. Under the condition of continuous stirring, dropwise adding an alkali solution into a salt solution 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 a precursor Mg x Al-LDH，x＝2,3,4。
(2)Mg x Preparing Al-LDO: adding precursor Mg x Placing Al-LDH in a muffle furnace, heating to 500 ℃ at a speed of 5 ℃/min, keeping for 3h, and naturally cooling to obtain Mg x Al-LDO，x＝2,3,4。
Catalyst composite metal oxide Mg x Al-LDO, wherein x is 2,3,4, has good effect on PC methanol alcoholysis reaction, and PC alcoholysisThe ratio can reach 100%, preferably, when x is 3, namely Mg 3 When Al-LDO is used as a catalyst, the PC degradation effect is better, and the yield of BPA is highest.
At the beginning, the inventor has tested various composite metal oxides as catalysts for PC alcoholysis, but many of them have no catalytic effect, and even the inventor has abandoned the initial efforts for searching suitable catalysts for PC alcoholysis once, however, as the tests are carried out, we have surprisingly found that the composite metal oxide formed by alkaline earth metal has catalytic effect on PC alcoholysis, and the reason for this is probably because the PC alcoholysis reaction is a transesterification reaction, and the alkaline catalyst is favorable for the reaction.
Preferably, the alcoholysis reaction temperature is 100-135 ℃, the mass ratio of the PC to the catalyst is 100: 1-5, the molar ratio of the PC to the methanol is 1: 3-10, and the reaction time is 0.5-3 h.
More preferably, the alcoholysis reaction temperature is 110 ℃, 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 catalyst is Mg 3 The BET specific surface area of the Al-LDO is more than or equal to 62.455m 2 G, pore volume is more than or equal to 0.327cm 3 The pore diameter is more than or equal to 7.452 nm.
Effects of the invention
Compared with the catalyst commonly used in the prior art, the composite metal oxide catalyst adopted by the invention has the advantages of low cost, small dosage, simple preparation, stable catalytic performance, easy separation and recovery, and can make up the defects of the traditional catalyst when catalyzing the alcoholysis of PC methanol. Experimental results show that the catalyst and the method provided by the invention have the advantages that the alcoholysis rate of PC can reach 100%, and the yield of BPA (bisphenol A) products can reach more than 98%. Meanwhile, the catalyst is simple in recovery process and good in reusability.
Drawings
FIG. 1Mg 2 Al-LDO、Mg 3 Al-LDO、Mg 4 XRD spectrogram of Al-LDO;
FIG. 2 influence of reaction temperature on alcoholysis reaction of PC;
FIG. 3 effect of reaction time on alcoholysis reaction of PC;
FIG. 4 effect of catalyst dosage on the alcoholysis reaction of PC;
FIG. 5 effect of methanol dosage on alcoholysis of PC;
FIG. 6 is an IR sum of the product of example 4 with BPA standards 1 H NMR spectrum;
FIG. 7 Mg before and after recycle for example 8 3 IR spectrum of Al-LDO;
FIG. 8 depicts Mg before and after recycling in example 8 3 SEM spectrogram of Al-LDO;
Detailed Description
The invention discloses a method for recovering bisphenol A (BPA) by using composite metal oxide as a catalyst to depolymerize carbonic ester (PC) by methanol and alcohol. Those skilled in the art can modify the process parameters appropriately to achieve the desired results with reference to the disclosure herein. It is expressly intended that all such similar substitutes and modifications which would be obvious to those skilled in the art are deemed to be included in the invention. While the methods and applications of this invention have been described in terms of preferred embodiments, it will be apparent to those of ordinary skill in the art that variations and modifications in the methods and applications described herein, as well as other suitable variations and combinations, may be made to implement and use the techniques of this invention without departing from the spirit and scope of the invention.
In order that those skilled in the art will be better able to understand the present invention, the following detailed description of the invention refers to specific embodiments.
Example 1: composite metal oxide Mg 2 Preparation of Al-LDO
(1)Mg 2 Preparation of Al-LDH: weighing 0.02mol of Mg (NO) 3 ) 2 ·6H 2 O and 0.01mol of Al (NO) 3 ) 3 ·9H 2 Dissolving O in 100mL of deionized water to prepare a mixed salt solution; 0.12mol of sodium hydroxide and 0.04mol of anhydrous sodium carbonate are dissolved in 100mL of deionized water to prepare a mixed alkali solution. Under the condition of continuous stirring, dropwise adding an alkali solution into a salt solution 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 a precursor Mg 2 Al-LDH。
(2)Mg 2 Preparing Al-LDO: adding precursor Mg 3 Al-LDH was placed in a muffle furnace at 5 deg.CHeating to 500 deg.C for 3 hr, and naturally cooling to obtain composite metal oxide Mg 2 Al-LDO。
Example 2: composite metal oxide Mg 3 Preparation of Al-LDO
(1)Mg 3 Preparation of Al-LDH: weighing 0.03mol of Mg (NO) 3 ) 2 ·6H 2 O and 0.01mol of Al (NO) 3 ) 3 ·9H 2 Dissolving O in 100mL of deionized water to prepare a mixed salt solution; 0.12mol of sodium hydroxide and 0.04mol of anhydrous sodium carbonate are dissolved in 100mL of deionized water to prepare a mixed alkali solution. Under the condition of continuously stirring, dropwise adding an alkali solution into a salt solution 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 a precursor Mg 3 Al-LDH。
(2)Mg 3 Preparation of Al-LDO: adding precursor Mg 3 Heating Al-LDH in a muffle furnace at 5 deg.C/min to 500 deg.C, maintaining for 3 hr, and naturally cooling to obtain composite metal oxide Mg 3 Al-LDO。
Example 3: composite metal oxide Mg 4 Preparation of Al-LDO
(1)Mg 4 Preparation of Al-LDH: 0.04mol of Mg (NO) is weighed out 3 ) 2 ·6H 2 O and 0.01mol of Al (NO) 3 ) 3 ·9H 2 Dissolving O in 100mL of deionized water to prepare a mixed salt solution; 0.12mol of sodium hydroxide and 0.04mol of anhydrous sodium carbonate are dissolved in 100mL of deionized water to prepare a mixed alkali solution. Under the condition of continuous stirring, dropwise adding an alkali solution into a salt solution 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 a precursor Mg 4 Al-LDH。
(2)Mg 4 Preparation of Al-LDO: adding precursor Mg 4 Placing Al-LDH in a muffle furnace, heating to 500 ℃ at a speed of 5 ℃/min, keeping for 3h, and naturally cooling to obtain the composite metal oxide Mg 4 Al-LDO。
The XRD spectrum of the composite metal oxide is shown in figure 1, and curves a, b and c are sequentially Mg 2 Al-LDO、Mg 3 Al-LDO、Mg 4 XRD pattern of Al-LDO. As can be seen from figure 1, two obvious characteristic peaks appear in all three curves, namely the characteristic peak of MgO, the peak shape is relatively sharp, and the curves are proved to have good crystal forms.
Example 4: influence of the type of catalyst on alcoholysis reaction of PC
4g of PC, 0.2g of the catalyst shown in Table 1 and 2.53g of methanol were sequentially charged into a high-pressure reaction vessel equipped with a thermometer, and the mixture was stirred at 130 ℃ for 2 hours. Naturally cooling to room temperature, opening the kettle to separate unreacted PC residues, centrifuging the mixture, separating out the catalyst, transferring the mixture into an oven to dry at 80 ℃, calcining at 500 ℃ for 3 hours to recover the catalyst, and distilling the filtrate under reduced pressure to recover unreacted methanol to obtain the product, wherein the yield of the BPA and the conversion rate of the PC are shown in Table 1.
TABLE 1 results of composite metal oxide catalyzed PC alcoholysis reaction
The data in Table 1 show that the alkaline earth composite metal oxide has better catalytic effect on the alcoholysis reaction of PC methanol. Particularly, the catalytic effect of the Mg/Al series is remarkably better than that of the Ca/Al series. Generally, the alcoholysis reaction of PC has a certain linear relationship with the alkalinity of the catalyst, and the stronger the alkalinity, the better the catalytic effect. Indicating that the Mg/Al series is more basic. This is consistent with XRD (FIG. 1) test results, but Mg 3 The Al-LDO has better catalytic effect and higher yield of BPA.
Example 5: optimization of PC alcoholysis reaction conditions
5.1 Effect of reaction temperature on the alcoholysis reaction of PC
When t is 2h, m (Mg) 3 Al-LDO):m(PC)＝0.05:1，n(PC):n(CH 3 The effect of different reaction temperatures on the alcoholysis reaction of PC (4g) was examined under the conditions of 1:5 OH) and PC (4g), and the results are shown in fig. 2. As can be seen from the figure, temperature has a significant effect on the PC alcoholysis reaction. The PC conversion was only 62% when the reaction temperature was 100 ℃ and increased to 9 when the temperature was increased to 105 ℃About 5 percent, when the temperature is continuously increased to 110 ℃, the conversion rate of PC is 100 percent, and the yield of BPA reaches more than 98 percent. The PC conversion and BPA yield remained substantially unchanged by further increasing the reaction temperature, indicating that the alcoholysis reaction has reached equilibrium, but increasing the reaction temperature too much increases energy consumption and wastes data, so 110 ℃ is the preferred temperature.
5.2 Effect of reaction time on alcoholysis of PC
At a reaction temperature of 110 ℃ and m (Mg) 3 Al-LDO):m(PC)＝0.05:1，n(PC):n(CH 3 The effect of reaction time on the alcoholysis reaction of PC was examined under the conditions of 1:5 OH and 4g PC, and the results are shown in FIG. 3. As can be seen from the figure, the conversion rate of PC can reach more than 90% after the reaction is carried out for 15min, and when the reaction time is increased to 1h, the conversion rate of PC is 100% and the yield of BPA reaches more than 98%. Continuing to increase the reaction time, the PC conversion and BPA yield remained essentially unchanged, indicating that the alcoholysis reaction had reached equilibrium. Therefore, the preferred reaction time is 1 h.
5.3 Effect of catalyst dosage on the alcoholysis reaction of PC
At 110 deg.C, T1 h, m (PC) 4g, n (PC) n (CH) 3 The effect of the amount of catalyst on the alcoholysis of PC was examined under the condition of 1:5 OH), and the results are shown in FIG. 3. As can be seen from fig. 4, both PC conversion and BPA yield showed increasing trends with increasing catalyst usage. When m (Mg) 3 Al-LDO) m (PC) 0.01:1, the conversion of PC was only 59.6%, and the yield of BPA was 52.3%. And when the amount of catalyst is increased to m (Mg) 3 Al-LDO) m (PC) 0.03:1, PC conversion was 100%, BPA yield was 98.3%. The PC conversion and BPA yield remained essentially unchanged with continued increase in catalyst usage, indicating that the alcoholysis reaction had reached equilibrium. Therefore, the preferred amount of catalyst is m (Mg) 3 Al-LDO):m(PC)＝0.03:1。
5.4 Effect of methanol dosage on alcoholysis Effect of PC
At T110 deg.C, T1 h, m (Mg) 3 Al-LDO), m (pc) 0.03:1, and m (pc) 4g, the amounts of methanol used were examined, and the results are shown in fig. 5. As the amount of methanol was increased, the PC conversion and BPA yield increased first and then decreased. When the temperature is higher than the set temperaturen(PC):n(CH 3 When OH) ═ 1:3, the conversion of PC reached 96.6% and the yield of BPA reached 94.2%. When the amount of methanol is increased to n (PC) n (CH) 3 When OH) ═ 1:5, the PC conversion was 100% and the BPA yield was 98.8%. The increase of the catalyst has no great influence on the improvement of the PC conversion rate and the BPA yield, which shows that the change of the methanol dosage has little influence on the PC alcoholysis reaction within the dosage range. With increasing methanol usage, the PC conversion and BPA yield decreased a little, probably due to the decreased concentration of the system caused by the increased methanol usage. Therefore, the preferred amount of methanol is n (PC) n (CH) 3 OH)＝1:5。
Example 6: alcoholysis reaction of PC (polycarbonate) methanol
4g of PC and 0.12g of Mg were sequentially added into a high-pressure reaction kettle equipped with a thermometer 3 Al-LDO and 2.53g of methanol were reacted at 110 ℃ for 1 hour with stirring. Naturally cooling to room temperature, centrifuging the mixture, separating out the catalyst, drying the catalyst in an oven at 80 ℃, calcining the catalyst for 3 hours at 500 ℃ to recover the catalyst, and distilling the filtrate under reduced pressure to obtain 3.53g of BPA, wherein the alcoholysis rate of PC is 100% and the yield is 98.3%.
The IR of the resulting product versus standard is shown in FIG. 6(A), curve a is that of the BPA standard IR And curve b is the IR of the resulting product. It can be seen that 3370cm -1 The left and the right are stretching vibration of-OH on BPA; 3020cm -1 C-H stretching vibration on benzene rings is performed on the left and the right; 2963cm -1 Left and right is-CH 3 The stretching vibration of (2); 1643cm -1 、1611cm -1 、1509cm -1 A skeleton of a benzene ring vibrates; 1445cm -1 And 1383cm -1 is-CH 3 Bending vibration of (2); 1237cm -1 And 1176cm -1 C-O stretching vibration; 826cm -1 The left and right are para-substituted absorption peaks of benzene ring. By comparing with a BPA standard sample spectrogram, the two curves are basically completely consistent, and the PC alcoholysis product is proved to be BPA.
Of the obtained products and standards 1 H NMR is shown in FIG. 6(B), from which it can be seen that curve a is for BPA standards 1 H NMR, curve b of the product obtained 1 H NMR. The single peak with delta being 9.15ppm is attributed to 2H in O-H on benzene ring, and delta being 6The doublet at about 99ppm is attributed to 4H of C-H near OH on the benzene ring, and the doublet at about 6.64ppm is attributed to CH on the benzene ring 3 The single peak of about 1.52ppm of 4H, delta of C-H in (A) is assigned to-CH 3 6H of (a). Comparing the two spectral lines, the peak positions of the peaks are consistent, and the product obtained by the reaction is proved to be BPA.
Example 7: repeatability investigation of PC methanolysis experiment
The experimental conditions and procedures were the same as those in example 6, and the results obtained by examining the reproducibility of the experiment under these conditions are shown in Table 2. As can be seen from Table 2, at T110 deg.C, T1 h, m (cat): m (PC): 0.03:1, n (PC): n (CH) 3 OH) is 1:5, the repeatability of the experiment is good, and the catalytic effect has no obvious difference, which indicates that the catalyst has stable performance.
TABLE 2 PC alcoholysis repeatability Experimental investigation
Example 8: mg (Mg) 3 Recycling experiment for alcoholysis reaction of PC methanol catalyzed by Al-LDO
The experimental conditions and procedures were the same as in example 6, and the catalyst in example 6 was recycled for 5 times and then subjected to a catalytic effect experiment, and the experimental results are shown in table 3.
TABLE 3 Mg 3 Repeated use experiment result of alcoholysis reaction of PC methanol catalyzed by Al-LDO
As can be seen from Table 3, the catalyst Mg 3 The Al-LDO is recycled by 5 times, and the conversion rate of PC and the yield of bisphenol A are not obviously reduced. The catalyst has basically unchanged catalytic activity and good recycling performance in the recycling process.
Before and after recycling, Mg 3 The catalytic activity of Al-LDO was substantially unchanged, in order to further verify Mg 3 Al-LDO has good performanceGood reusability of Mg after 5 times of reuse 3 Al-LDO and fresh Mg 3 The Al-LDO is structurally characterized by adopting IR and SEM. Fig. 7 is an IR spectrum before and after the catalyst cycle, curve a is an IR spectrum before the catalyst is used, and curve b is an IR spectrum after the catalyst is recycled 5 times. 3480.23cm -1 The vicinity is an absorption peak of-OH stretching vibration, 1000cm -1 The following absorption peaks are M-O skeleton vibration peaks. Comparing the two curves, Mg can be found 3 The positions of absorption peaks before and after the catalysis of the Al-LDO are basically consistent, which shows that the structure and the composition before and after the catalysis of the catalyst have no obvious change. FIG. 8 is Mg 3 And the SEM spectrogram of the Al-LDO is shown in the left side before the catalyst is used, and the SEM spectrogram after the catalyst is used in the right side. As can be seen from the figure, Mg 3 The Al-LDO is an agglomerated structure, and the catalyst has no obvious shape change after 5 times of recycling.
Comparative example 1 Effect of catalyst type on the alcoholysis reaction of PC methanol
The same procedure as in example 6 was followed, except that the reaction temperature, reaction time, catalyst type and amount used in example 6 were changed to those shown in Table 4, in which 6g of tetrahydrofuran was added as a solvent when CaO-SBA-15 was used as a catalyst, and the results of the experiment are shown in Table 4.
TABLE 4 influence of catalyst type on the alcoholysis reaction of PC with methanol
As shown in Table 4, the catalyst was mixed with molecular sieve CaO-SBA-15, eutectic solvent ChCl-2Urea, and ionic liquid [ Amim ]]Cl、[Amim]Br、[Bmim]OAc and [ Bmim ]]Cl compared with Mg 3 Al-LDO showed better catalytic activity. Although the conversion rate of PC is 100% and the yield of BPA is 98.8% when the eutectic solvent ChCl-2Urea is used as the catalyst, the reaction temperature is 130 ℃, the reaction time needs to be prolonged to 2.5h, the use amount of the catalyst and methanol is relatively large, and the ChCl-2Urea is liquid and is difficult to separate after the reaction. And a composite metal oxide Mg 3 The Al-LDO has unexpected catalytic effect on the alcoholysis of PC methanol, thereby not only reducingThe reaction temperature and the reaction time are also shortened, and the dosage of the catalyst and the dosage of the methanol are less. More importantly, the Mg used in the invention 3 The Al-LDO catalyst has the advantages of simple preparation method, low cost, stable performance, simple recovery process and better reusability.
The foregoing is only an embodiment of the invention, and it should be noted that, for those skilled in the art, various modifications and improvements can be made without departing from the principle of the invention, and these modifications and improvements should also be considered as the protection scope of the invention.
Claims (3)
1. A method for reclaiming bisphenol A by using composite metal oxide as a catalyst to carry out methanol-alcohol depolymerization on carbonic ester is characterized by comprising the following steps: according to mass ratio m PC :m Catalyst and process for producing the same 100: 1-5, molar ratio n PC :n Methanol Adding 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 a product BPA, wherein the catalyst can be repeatedly used; the catalyst is Mg x Al-LDO, wherein x =2,3, 4; the PC is polycarbonate, and the BPA is bisphenol A;
catalyst Mg used x The Al-LDO is a self-prepared product and is prepared by the following steps:
（1）Mg x preparation of Al-LDH: mg (NO) is weighed according to the molar ratio of 2:1, 3:1 and 4:1 respectively 3 ) 2 •6H 2 O and Al (NO) 3 ) 3 •9H 2 Dissolving O in 100mL of deionized water to prepare a mixed salt solution; dissolving 0.12mol of sodium hydroxide and 0.04mol of anhydrous sodium carbonate in 100mL of deionized water to prepare a mixed alkali solution; under the condition of continuous stirring, dropwise adding an alkali solution into a salt solution 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 a precursor Mg x Al-LDH, wherein x =2,3, 4;
（2）Mg x preparation of Al-LDO: adding precursor Mg x Placing Al-LDH in a muffle furnace, heating to 500 ℃ at a speed of 5 ℃/min, keeping for 3h, and naturally cooling to obtain Mg x Al-LDO, wherein x =2,3, 4.
2. 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 catalyst 3 The mass ratio of Al-LDO is 100:3, and the molar ratio of PC to methanol is 1: 5.
3. The process as claimed in claim 2, wherein the catalyst Mg is used 3 The BET specific surface area of the Al-LDO is more than or equal to 62.455m 2 G, pore volume is more than or equal to 0.327cm 3 The pore diameter is not less than 7.452 nm.
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