CN111905828B - Naphthyl ligand MOF activated carbon composite catalyst and preparation method and application thereof - Google Patents
Naphthyl ligand MOF activated carbon composite catalyst and preparation method and application thereof Download PDFInfo
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Abstract
The invention provides a naphthyl ligand MOF composite activated carbon catalyst and a method for preparing high-purity lactide by using the same, wherein the MOF organic metal framework activated carbon composite catalyst is used for catalyzing the polymerization reaction of L-lactic acid, metal elements are used as active components, 2,3,6, 7-tetraacylimidazolyl-alpha-naphthoic acid is used as an MOF catalyst ligand, and activated carbon is used as a carrier. The catalyst has the advantages of low price of raw materials, high thermal stability, certain acid resistance, difficult decomposition under low pressure, simple preparation method, easy industrialization and good catalytic activity.
Description
Technical Field
The invention relates to a naphthyl ligand MOF activated carbon composite catalyst, a preparation method thereof and application of the catalyst in preparation of lactide from L-lactic acid.
Background
Lactide is an important raw material for the synthesis of polylactic acid. The polylactic acid material has good biodegradability, biocompatibility and mechanical strength, is an ideal biodegradable material, and has wide application prospect in the aspects of human tissue repair, wound suture, medicine and pesticide controlled release; in other application fields, polylactic acid replaces the traditional polymer material, and can reduce the pollution and the harm to the environment. The dominant method for the industrial synthesis of polylactic acid is the lactide ring-opening polymerization method, and this technique is described in many patent documents, for example: US5053522A, US5247058A, US5357035A, US6005067A, US6277951B1, US6326458B1, US5274127A, US20050222379a1, US20120302724a1, US20110155557a1, CN1951933A, CN1594313A, CN1488628A, WO2010105143a2, and the like. At present, the industrial production mainly adopts a method of generating polylactic acid through four steps of dehydration, prepolymerization, depolymerization, and ring-opening polymerization by heating at a high temperature and using a tin-based chemical substance as a catalyst (for example, stannous 2-ethylhexanoate (1I), stannic chloride, etc.) in a vacuum environment. In order to avoid oxidation of the reactants at high temperatures (. gtoreq.180 ℃), the chemical reaction is usually carried out under an inert gas atmosphere (e.g.nitrogen).
In the prepolymerization process, the conventional catalyst needs to react lactic acid under a higher vacuum degree (5-25 hpa), so that the energy consumption and the cost investment in industrial amplification are greatly increased, and in the depolymerization process, part of oligomers can be depolymerized under the high-temperature and low-pressure reaction conditions (200-250 ℃) and the other part of oligomers can be further polymerized into a polymer with higher molecular weight. The conventional tin-based catalyst is a homogeneous catalyst, so that the separation and the reuse of the lactide catalyst in the kettle residue after the synthesis of the lactide are difficult; meanwhile, the conventional catalyst does not significantly promote the prepolymerization process, so that the energy consumption of the prepolymerization process in the amplification process is high, and the yield of lactide synthesized by the conventional method is only 50-70%. For example, U.S. patent application No. US5053522A mentions that a process for the synthesis of lactide using a tin-based catalyst requires high temperature 200-260 ℃ to separate the lactide product in 69% yield. In a single batch production, the yield of lactide was 56.8% in US patent application US 5274127A. While the low catalytic efficiency of other metal compounds for the prepolymerization and depolymerization reactions results in a decrease (< 70%) in the production yield of lactide. For example, zinc oxide particles are used in US201203027A1, where the lactide product is separated by distillation at 230-240 deg.C, and the yield is less than 72%. Meanwhile, according to experiments and literature experiences, a large amount of byproducts can be generated in the process of ring-opening polymerization of polylactic acid by using a low-purity lactide raw material, and a polylactic acid product which can be applied on a large scale cannot be prepared, so that a high-yield and high-purity lactide process generated in the steps of prepolymerization and depolymerization synthesis is a crucial core step of a process for synthesizing a large-scale polylactic acid product which can be applied on an industrial scale.
Disclosure of Invention
The invention aims to provide a naphthyl ligand MOF activated carbon composite catalyst and a preparation method thereof, and on one hand, the ligand structure of the invention has larger molecular space to obtain larger steric hindrance, thereby obviously enhancing the catalytic stability of the catalyst under the system; on the other hand, the active metal is taken as a central atom, so that the reaction activity of the catalyst is enhanced, the activity of polymerization reaction is improved, the bonding process of lactic acid prepolymerization reaction is promoted, the selectivity of L-lactide in the depolymerization process is increased, the regularity of the space structure of a polymerization product is obviously improved, and the energy consumption in the amplification process of prepolymerization depolymerization reaction can be obviously reduced.
The catalyst prepared by the method has obvious promotion effect on the prepolymerization and depolymerization processes of the lactic acid, and the catalyst has the advantages of relatively simple synthetic route, easily obtained raw materials, high thermal stability, good stability in a reaction system and easy industrialized large-scale production.
The invention also provides the application of the catalyst in preparing lactide from L-lactic acid, so that the lactide synthesis process conditions are mild (the temperature is low, the prepolymerization temperature can be 120-160 ℃, the depolymerization temperature can be 180-200 ℃, the vacuum degree is low, the prepolymerization absolute pressure can be 80-120 hpa, the depolymerization absolute pressure can be 25-50 hpa, the reaction time is short, the molecular weight of lactic acid oligomer in the prepolymerization process can stably reach 1000-3500, the molecular weight distribution of the oligomer is narrow PD (1.1-2.8), the lactide yield in the depolymerization process is high (the lactide yield can reach 80.0-95.0%, the optical purity is more than 99.9%, and the total yield of the lactide can reach 90.0-95.0% after separation and reuse).
In order to achieve the above purpose, the technical scheme provided by the invention is as follows:
a naphthyl ligand MOF composite activated carbon catalyst is prepared by taking metal as an active component, wherein the active metal is active metal In periods 4, 5 and 6 In the periodic table of elements and metal elements In main groups II to VIA, preferably one or more of Sn, Zn, Ga, Ge, In, Sb, Tl, Pb, Bi, Po, Ti, Al, Ba, Rh, Ru, Ni, Cu, Fe, Cr, Co, Pd, Mn, V, Sc, Cd, Ag, Tc, Mo, Nb, Zr and Y, and more preferably one or more of Sn, Zn, Al, Pd and Ni; 2,3,6, 7-tetracarboxyl imidazolyl-alpha-naphthoic acid is taken as a ligand, activated carbon is taken as a carrier, and the molar ratio of the active component, the ligand and the activated carbon is preferably (0.005-0.02): (0.01-0.015): 1.3-2.5); the structural formula of the 2,3,6, 7-tetracarboxyl imidazolyl-alpha-naphthoic acid is as follows:
the preparation method of the catalyst comprises the following steps: comprises the following steps: (1) preparation of organic ligand: dissolving N, N' -carbonyl diimidazole and alpha-naphthoic acid in a solvent, preferably anhydrous dichloromethane, slowly dropwise adding trifluoromethanesulfonic acid, heating and stirring the reaction mixture, adding cold water, stirring overnight, and performing aftertreatment to obtain ligand 2,3,6, 7-tetraacylimidazolyl-alpha-naphthoic acid; (2) the obtained ligand, soluble salt of active metal component and active carbon are made into hydrothermal reaction in solvent (water, methanol, ethanol, etc.), and the catalyst is obtained after the post-treatment.
In the ligand preparation method of the catalyst of the present invention, as a preferable scheme, the molar ratio of the α -naphthoic acid, the trifluoromethanesulfonic acid, the N, N' -carbonyldiimidazole and the dichloromethane is: (0.2-0.4), (0.2-0.45), (0.1-0.2): (3-7), heating and stirring for 1-5 h at the temperature of 40-90 ℃, adding cold water, and continuing to stir overnight (12 h).
In the method for preparing the ligand of the catalyst, the molar ratio of the alpha-naphthoic acid, the trifluoromethanesulfonic acid, the N, N' -carbonyldiimidazole, the dichloromethane and the cold water in the step (1) is as follows: (0.2-0.4), (0.2-0.45), (0.1-0.2): (3-7): (2-5).
In the ligand preparation method of the catalyst, the post-treatment in the step (1) is to use a sodium hydroxide solution (1mol/L) with the volume ratio of 1: 1-1: 4 to the material to alkalize the mixture and extract the mixture twice with chloroform to complete the separation of the extract; then, the organic layer is washed with a dilute sulfuric acid solution (pH 4-6) and brine respectively until the pH is 6-7. After distillation, 2,3,6, 7-tetracarboxyl imidazolyl-alpha-naphthoic acid is obtained as pasty liquid; with anhydrous MgSO4And (3) drying: the crude product can be further purified by silica gel column chromatography (hexane: ethyl acetate ═ 1:3) to afford the desired ligand:
in the preparation method of the catalyst of the present invention, as a preferable scheme, in the step (2), the obtained active metal component, ligand, activated carbon and optionally other ligands (including terephthalic acid, 4-dicarboxydiphenyl ether, imidazole, dimethylimidazole, etc., and trimesic acid is preferably used as a complex ligand in the present invention) are mixed at room temperature in a molar ratio of (0.01 to 0.02): (0.01-0.015): (1.3-2.5): (0.01-0.016) adding ultrapure water or/and methanol (the dosage is 10-20 times of the mass of the activated carbon), stirring, placing in a high-temperature oven at 110-180 ℃ for reacting for 40-60 h, and filtering the obtained mixture to obtain the target catalyst. Preferably, the obtained product is boiled in 50-80 ℃ ultrapure water for 4-6 hours, then boiled in 40-55 ℃ ethanol or methanol solution for 5-8 hours, filtered, dried at 80-110 ℃, recovered with a catalyst, and dried in air overnight for later use.
In the preparation method of the catalyst of the present invention, further, the active metal component contained in the step (2) is soluble salts of the following metal elements and their metal clusters: the prepolymerization and depolymerization reaction process preferably uses one or more metal elements selected from Sn, Zn, Ga, Ge, In, Sb, Tl, Pb, Bi, Po, Ti, Al, Ba, Rh, Ru, Ni, Cu, Fe, Cr, Co, Pd, Mn, V, Sc, Cd, Ag, Tc, Mo, Nb, Zr and Y, and more preferably one or more metal elements selected from Sn, Zn, Al, Pd and Ni.
The application of the catalyst in the preparation of lactide specifically comprises the following steps:
(1) introducing liquid nitrogen into the L-lactic acid solution;
(2) adding the catalyst into the lactic acid solution into which the liquid nitrogen is introduced to obtain a raw material solution;
(3) heating the raw material liquid under the protection of nitrogen, and introducing the raw material liquid into a prepolymerization reactor for reaction to obtain a lactic acid prepolymer reaction liquid with a specific molecular weight range (preferably the molecular weight is 1000-3500);
(4) and (3) directly feeding the prepolymer reaction liquid into a depolymerization reactor, carrying out high-temperature negative-pressure depolymerization reaction to obtain crude lactide, and carrying out rectification, melting and crystallization to obtain a high-purity lactide product.
In the preparation of lactide, preferably, liquid nitrogen is introduced in the step (1) to ensure that the oxygen content in the L-lactic acid is less than 10ppm, preferably 3-7ppm, and more preferably 4-6 ppm.
Further, the amount of the catalyst used in the step (2) is 0.1-5 wt%, preferably 0.5-2 wt% of the mass of the lactic acid.
Further, the reaction temperature in the step (3) is 50-200 ℃, preferably 80-190 ℃, and more preferably 120-160 ℃. The absolute reaction pressure in the step (3) is 30-1009 hPa, preferably 35-200 hPa, and more preferably 80-120 hPa. The reaction time in the step (3) is 5-150 min, preferably 10-120 min, and more preferably 60-100 min.
Further, the reaction temperature in the step (4) is 50-240 ℃, preferably 80-210 ℃, and more preferably 180-200 ℃. The absolute reaction pressure in the step (4) is 20-1009 hPa, preferably 22-200 hPa, and more preferably 25-50 hPa. The reaction time in the step (4) is 5-150 min, preferably 10-40 min, and more preferably 15-30 min.
Further, after the step (4), the reaction product is purified by rectification, the number of theoretical plates in the rectification separation process mentioned in the step (4) is 40-60, and the main operation conditions are as follows: the pressure is 0.5-1 kPa, the wall temperature is 140-160 ℃, the reflux ratio is 2: 1-9: 1, and the kettle bottom temperature is 150-170 ℃. The initial temperature of melt crystallization is 100-105 ℃, and the final temperature of crystallization is 70-90 ℃; and (3) sweating the final temperature of 94-98 ℃, sweating time of 0.5-1 h, and finally obtaining the purified lactide product on the wall surface of the crystallizer.
The principle that the catalyst system in the prepolymerization and depolymerization processes can greatly improve the synthesis process conditions of the lactide is as follows: according to the characteristics of the metal framework material, the MOF material has ultrahigh specific surface area, adjustable pore diameter, unsaturated metal coordination and various structures, and the metal framework catalyst can effectively utilize abundant metal sites to open pi bonds among carbon-oxygen bonds in esterification reaction, promote the high-efficiency formation of tetrahedral intermediate products, reduce the reaction activation energy and accelerate the reaction; meanwhile, the naphthyl ligand has high stability, the formed metal framework has high porosity, and the naphthyl ligand is favorable for locking water generated in the esterification reaction process in a formed unique pore channel structure, promoting the esterification reaction balance to be carried out rightwards and increasing the yield of reaction products.
The invention has the positive effects that:
(1) the temperature condition in the prepolymerization stage can be reduced to 120-160 ℃; reducing the vacuum degree of the prepolymerization reaction to 80-120 hpa under the absolute pressure condition; the reaction time is shortened to 60-100 min;
(2) reducing the temperature condition of the depolymerization section to 180-200 ℃; reducing the vacuum degree of depolymerization reaction to 25-50 hpa absolute pressure; the reaction time is shortened to 15-30 min;
(3) the catalyst can control the molecular weight of the lactic acid prepolymer and can stably reach 1000-3500, the catalyst has high and stable catalytic reaction activity at high temperature, is easy to recover and reuse, the preparation route is simple, the industrial scale production and use are easy, and the yield of the lactide can be improved to 90.0-95.0%.
Detailed Description
The following examples are not intended to limit the scope of the present invention, and modifications and equivalents may be made thereto without departing from the spirit and scope of the present invention, which is defined in the appended claims.
Analytical methods instrumentation and conditions:
1. the instrument model of nuclear magnetic resonance spectrum nuclear magnetic resonance is as follows: bruker DMX-500 (H: 500MHz, 13C: 125 MHz). Hydrogen spectrum sample configuration: 5-10 mg, carbon spectrum sample preparation: about 20mg, adding 0.5-0.6mL of deuterated reagent, and testing at room temperature.
GPC measurement
GPC measurements were performed on a set of LC-20AD solvent delivery pumps, a combination of Wyatt OPTILAB rEX refractive index detector and Styragel P8512-10E3A10, P8512-10E4A10 and P8512-10E5A10, with effective molar mass ranges of 100-40000, 400-500000 and 10000-2000000, respectively. THF was used as eluent (flow rate 1mLmin1, T ═ 40C).
GC test
Agilent6820 gas chromatograph, column: OV-1 capillary chromatography column (50m 0.25 mm); column temperature: (temperature programming) initial temperature is 129 ℃, the temperature is kept for 4min, the temperature rising rate is 0.5 ℃/min, the termination temperature is 132 ℃, and the temperature is kept for 35 min; vaporization temperature: 280 ℃; detector temperature: 250 ℃; the split ratio is as follows: 80: 1; carrier gas: high-purity hydrogen with the pressure of 0.1 MPa; tail blowing: 29 ml/min; and (3) sample introduction mode: shunting and sampling; sample introduction amount: 0.2 uL.
Example 1
(1) Preparation of organic ligands and synthesis of MOF materials: 11.2g of α -naphthoic acid and 5.52g of N, N' -carbonyldiimidazole were added to 117.162g of a methylene chloride solution and stirred uniformly, and 13.12g of trifluoromethanesulfonic acid was added dropwise to the solution and stirred at 60 ℃ for reaction for 2 hours, then 16.69g of cold water was added to the solution and the mixture was stirred overnight. The product was isolated by basifying the mixture with 1:2 by volume sodium hydroxide to the feed for 30min, and then extracting the mixture twice with chloroform. The organic extract was washed with dilute sulfuric acid solution having a pH of 5 and then water. Distilling the organic phase to obtainTo the target ligand with anhydrous MgSO4Drying and purification through silica gel column chromatography (hexane: ethyl acetate ═ 1:3) multiple times afforded the desired ligand in 56.3% yield. And (3) performing nuclear magnetic analysis and qualitative analysis:1H NMR(D2O,400MHz):δ9.94(s,1H),8.93(s,1H),8.75(s,1H)，8.71(s,4H),8.03(d,J＝7.5Hz,4H),7.32(d,J＝7.5Hz,4H).
13C NMR(D2O,100MHz):δ169.3,167.7,138.6,136.8,136.5,135.6,135.5,134.1,132.6,131.6,131.5,130.8,129.6,129.0,117.6.
adding 80g of ultrapure water into 5.48g of ligand, 4.5g of active metal component stannous chloride, 2.1g of trimesic acid, 15.6g of activated carbon and 80g of methanol at room temperature, stirring, placing in a high-temperature oven at 130 ℃ for reaction for 48h, and filtering the obtained mixture to obtain the MOF (Sn). And (3) boiling the obtained product in ultrapure water at 80 ℃ for 6 hours, then boiling the product in ethanol at 50 ℃ for 6 hours, carrying out suction filtration, drying the product at 90 ℃, recovering the catalyst, and drying the product in the air overnight for later use.
In the synthesis operation of lactide, firstly, 300g L-lactic acid aqueous solution (87 wt%) is added into a 1L prepolymerization reactor, a certain amount of liquid nitrogen is introduced to ensure that the oxygen content in a liquid phase is lower than 10ppm, the temperature of the system is raised to 100 ℃, the pressure is 100kpa, dehydration is carried out for 30min, and the water content is detected to be lower than 1%; then, 2.86g of prepared catalyst MOF (Sn) is added, the reaction system is heated to 120 ℃, the system pressure is 80hpa, the reaction is carried out for 60min, the molecular weight of the lactic acid oligomer obtained by the prepolymerization reaction is distributed at about 1500, and the distribution coefficient is 1.23-1.35; finally, taking out the pre-polymerization reaction liquid, placing the pre-polymerization reaction liquid in a depolymerization reaction kettle, heating to 180 ℃, the system pressure is 25hpa, reacting for 90min, then separating by a rectifying column (the number of plates is 45 theoretical plates, the operation pressure is 0.5kpa, the wall temperature is 146 ℃, the reflux ratio is 4:1, the kettle temperature is 160 ℃) to obtain the lactide yield of 98.6%, then melting crude lactide at 105 ℃ and crystallizing, wherein the final temperature of crystallization is 70 ℃ (the cooling rate is 5 ℃/h); the final sweating temperature is 97 ℃, the sweating time is 0.5h, the yield of the lactide is 93.2 percent, and the optical purity is 99.5 percent.
Example 2
(1) Preparation of organic ligands and synthesis of MOF materials: 23.14g of alpha-naphthoic acid and 8.72g of N, N' -carbonyldiimidazole are takenThe mixture was added to 187.62g of a methylene chloride solution and stirred uniformly, 21g of trifluoromethanesulfonic acid was added dropwise to the solution, the reaction was stirred at 60 ℃ for 2 hours, then 26.8g of cold water was added to the solution, and the mixture was stirred overnight. The product was isolated by basifying the mixture for 30min with 1:1 by volume sodium hydroxide to the feed and extracting the mixture twice with chloroform. The organic extract was washed three times with dilute sulfuric acid solution having a pH of 6 and then with water. Distilling the organic phase to obtain target ligand, and adding anhydrous MgSO4Drying, purifying by silica gel column chromatography (hexane: ethyl acetate ═ 1:3) many times to give the target ligand in 57.2% yield; taking 5.48g of ligand, 3.6g of active metal component nickel nitrate, 2.1g of trimesic acid, 15.6g of activated carbon and 160g of methanol, stirring, placing in a high-temperature oven at 130 ℃ for reaction for 48h, and filtering the obtained mixture to obtain the MOF (Ni). And (3) boiling the obtained product in ultrapure water at 80 ℃ for 6 hours, then boiling the product in ethanol at 50 ℃ for 6 hours, carrying out suction filtration, drying the product at 80-100 ℃, recovering the catalyst, and drying the product in the air overnight for later use.
In the lactide synthesis operation, firstly, 300g L-lactic acid aqueous solution (87 wt%) is put into a 1L prepolymerization reactor, a certain amount of liquid nitrogen is introduced to ensure that the oxygen content in a liquid phase is lower than 10ppm, the temperature of the system is raised to 100 ℃, the pressure is 100kpa, dehydration is carried out for 30min, and the water content is detected to be lower than 1%; then adding 3.12g of prepared catalyst MOF (Sn), heating the reaction system to 160 ℃, controlling the system pressure to 80hpa, reacting for 100min, and obtaining lactic acid oligomer by prepolymerization with the molecular weight distribution of 3500 and the distribution coefficient of 2.6-2.8; finally, heating the prepolymerization reaction liquid to 210 ℃, enabling the system pressure to be 40hpa, reacting for 30min, then separating by a rectifying column (the number of plates is 45 theoretical plates, the operating pressure is 0.5kpa, the wall temperature is 146 ℃, the reflux ratio is 4:1, the kettle temperature is 160 ℃), the lactide yield is 95.3%, then melting crude lactide at 105 ℃, and crystallizing, wherein the final temperature of crystallization is 70 ℃ (the cooling rate is 5 ℃/h); the final sweating temperature is 97 ℃, the sweating time is 1h, and the lactide yield is 90.4 percent (the optical purity is 99.7 percent)
Example 3
(1) Preparation of organic ligands and synthesis of MOF materials: 18.217g of alpha-naphthoic acid and 7.657g of N, N' -carbonyldiimidazole are added to 133.84g of dichloroThe methane solution was stirred well and 16.057g of trifluoromethanesulfonic acid was added dropwise to the solution and the reaction was stirred for 2h at 60 ℃ and then 22.257g of cold water was added to the solution and the mixture was stirred overnight. The product was isolated by basifying the mixture for 30min with 1:1 by volume sodium hydroxide to the feed and extracting the mixture twice with chloroform. The organic extract was washed three times with dilute sulfuric acid solution having a pH of 6 and then with water. Distilling the organic phase to obtain target ligand, and adding anhydrous MgSO4Drying and multiple purifications by silica gel column chromatography (hexane: ethyl acetate ═ 1:3) gave the desired ligand in 56.2% yield. Taking 5.48g of ligand, 3.19g of active metal component aluminum nitrate, 2.1g of trimesic acid, 15.6g of activated carbon and 160g of methanol, stirring, placing in a high-temperature oven at 130 ℃ for reaction for 48 hours, and filtering the obtained mixture to obtain the MOF (Al). And (3) boiling the obtained product in ultrapure water at 80 ℃ for 6 hours, then boiling the product in ethanol at 50 ℃ for 6 hours, carrying out suction filtration, drying the product at 80-100 ℃, recovering the catalyst, and drying the product in the air overnight for later use.
In the lactide synthesis operation, firstly, 300g L-lactic acid aqueous solution (87 wt%) is put into a 1L prepolymerization reactor, a certain amount of liquid nitrogen is introduced to ensure that the oxygen content in a liquid phase is lower than 10ppm, the temperature of the system is raised to 120 ℃, the pressure is 100kpa, dehydration is carried out for 30min, and the water content is detected to be lower than 1%; then adding 3.12g of prepared catalyst MOF (Al), heating the reaction system to 160 ℃, controlling the system pressure to be 50hpa, reacting for 60min, and distributing the molecular weight of lactic acid oligomer obtained by prepolymerization to about 2600, wherein the distribution coefficient is 1.9-2.3; finally, heating the prepolymerization reaction liquid to 210 ℃, enabling the system pressure to be 50hpa, reacting for 40min, then separating by a rectifying column (the number of plates is 45 theoretical plates, the operating pressure is 0.5kpa, the wall temperature is 146 ℃, the reflux ratio is 4:1, the kettle temperature is 160 ℃), the lactide yield is 95.6%, then melting crude lactide at 105 ℃, and crystallizing, wherein the final temperature of crystallization is 80 ℃ (the cooling rate is 5 ℃/h); the final sweating temperature is 97 ℃, the sweating time is 1h, and the lactide yield is 92.4 percent (the optical purity is 99.6 percent)
Example 4
(1) Preparation of organic ligands and synthesis of MOF materials: 18.217g of alpha-naphthoic acid and 8.1g of N, N' -carbonyldiimidazole are added to 187.6g of methylene chloride solution and stirredAfter stirring, 21g of trifluoromethanesulfonic acid was added dropwise to the solution, the reaction was stirred at 60 ℃ for 2 hours, then 27.2g of cold water was added to the solution, and the mixture was stirred overnight. The product was isolated by basifying the mixture for 30min with 1:1 by volume sodium hydroxide to the feed and extracting the mixture twice with chloroform. The organic extract was washed three times with dilute sulfuric acid solution having a pH of 6 and then with water. Distilling the organic phase to obtain target ligand, and adding anhydrous MgSO4Drying and multiple purifications by silica gel column chromatography (hexane: ethyl acetate ═ 1:3) gave the desired ligand in 56.2% yield. Adding 185g of ultrapure water into 5.48g of ligand and 2.413g of active metal component zinc chloride, 3.032g of trimesic acid, 20.4g of activated carbon and 20g of methanol at room temperature, stirring, placing in a high-temperature oven at 130 ℃ for reaction for 48h, and filtering the obtained mixture to obtain the MOF (Zn). And (3) boiling the obtained product in ultrapure water at 80 ℃ for 6 hours, then boiling the product in ethanol at 50 ℃ for 6 hours, carrying out suction filtration, drying the product at 80-100 ℃, recovering the catalyst, and drying the product in the air overnight for later use.
In the lactide synthesis operation, firstly, 300g L-lactic acid aqueous solution (87 wt%) is put into a 1L prepolymerization reactor, a certain amount of liquid nitrogen is introduced to ensure that the oxygen content in a liquid phase is lower than 10ppm, the temperature of the system is raised to 120 ℃, the pressure is 100kpa, dehydration is carried out for 30min, and the water content is detected to be lower than 1%; then adding 3.12g of prepared catalyst MOF (Zn), heating the reaction system to 160 ℃, controlling the system pressure to 80hpa, reacting for 60min, and obtaining lactic acid oligomer through prepolymerization, wherein the molecular weight of the lactic acid oligomer is distributed at about 1900-2100, and the distribution coefficient is 1.8-2.0; finally, transferring the pre-polymerization reaction liquid to a depolymerization reactor, heating to 200 ℃, reacting for 40min under the system pressure of 50hpa, separating by a rectifying column (the number of plates is 45 theoretical plates, the operating pressure is 0.5kpa, the wall temperature is 146 ℃, the reflux ratio is 4:1, the kettle temperature is 160 ℃), the lactide yield is 94.3%, melting crude lactide at 105 ℃, and crystallizing at the final temperature of 70 ℃ (the cooling rate is 5 ℃/h); the final sweating temperature is 97 ℃, the sweating time is 0.5h, and the yield of the lactide is 90.7 percent (the optical purity is 99.1 percent)
Comparative example 1
In the lactide synthesis operation, firstly, 300g L-lactic acid solution (87 wt%) is put into a 1L prepolymerization reactor, a certain amount of liquid nitrogen is introduced to ensure that the oxygen content in a liquid phase is lower than 10ppm, the temperature of the system is raised to 120 ℃, the pressure is 100kpa, dehydration is carried out for 30min, and the water content is detected to be lower than 1%; then adding 3.12g of zinc oxide powder catalyst to heat the reaction system to 180 ℃, controlling the system pressure to be 25hpa, reacting for 180min, wherein the molecular weight distribution of lactic acid oligomer obtained by prepolymerization is about 1800, and the distribution coefficient is 1.9; finally, transferring the prepolymerization reaction liquid into a depolymerization kettle, heating to 240 ℃, reacting for 90min under the system pressure of 10hpa, separating by a rectification column (operating plate number is 45 theoretical plates, operating pressure is 0.5kpa, wall temperature is 146 ℃, reflux ratio is 4:1, kettle temperature is 160 ℃) to obtain lactide 87.2%, melting crude lactide at 105 ℃ and crystallizing, wherein the final temperature of crystallization is 70 ℃ (cooling rate is 5 ℃/h); the final sweating temperature is 97 ℃, the sweating time is 0.5h, and the yield of the lactide after crystallization is 74.5 percent (the optical purity is 97.3 percent).
Example 5
(1) Preparation of organic ligands and synthesis of MOF materials: 18.217g of alpha-naphthoic acid and 7.657g of N, N' -carbonyldiimidazole are added to 133.84g of dichloromethane solution and stirred uniformly, 16.057g of trifluoromethanesulfonic acid is added dropwise to the solution, the solution is heated at 60 ℃ and stirred for reaction for 2 hours, 22.257g of cold water is then added to the solution, and the mixture is stirred overnight. The product was isolated by basifying the mixture for 30min with 1:1 by volume sodium hydroxide to the feed and extracting the mixture twice with chloroform. The organic extract was washed three times with dilute sulfuric acid solution having a pH of 6 and then with water. Distilling the organic phase to obtain target ligand, and adding anhydrous MgSO4Drying and multiple purifications by silica gel column chromatography (hexane: ethyl acetate ═ 1:3) gave the desired ligand in 56.2% yield. Taking 5.72g of ligand, 2.73g of palladium chloride serving as an active metal component, 2.52g of trimesic acid, 27.4g of activated carbon and 20g of methanol, adding 180g of ultrapure water at room temperature, stirring, placing in a high-temperature oven at 130 ℃ for reaction for 48h, and filtering the obtained mixture to obtain the MOF (Pd). And (3) boiling the obtained product in ultrapure water at 80 ℃ for 6 hours, then boiling the product in ethanol at 50 ℃ for 6 hours, carrying out suction filtration, drying the product at 80-100 ℃, recovering the catalyst, and drying the product in the air overnight for later use.
In the lactide synthesis operation, firstly, 300g L-lactic acid aqueous solution (87 wt%) is put into a 1L prepolymerization reactor, a certain amount of liquid nitrogen is introduced to ensure that the oxygen content in a liquid phase is lower than 10ppm, the temperature of the system is raised to 120 ℃, the pressure is 100kpa, dehydration is carried out for 30min, and the water content is detected to be lower than 1%; then adding 3.12g of prepared catalyst MOF (Pd), heating the reaction system to 160 ℃, controlling the system pressure to 80hpa, reacting for 60min, and obtaining lactic acid oligomer through prepolymerization, wherein the molecular weight of the lactic acid oligomer is about 1900-2300, and the distribution coefficient is 1.72-2.06; finally, heating the prepolymerization reaction liquid to 200 ℃, enabling the system pressure to be 50hpa, reacting for 40min, then separating by a rectifying column (the number of plates is 45 theoretical plates, the operating pressure is 0.5kpa, the wall temperature is 146 ℃, the reflux ratio is 4:1, the kettle temperature is 160 ℃), the lactide yield is 97.3%, then melting crude lactide at 105 ℃, and crystallizing, wherein the final temperature of crystallization is 70 ℃ (the cooling rate is 5 ℃/h); the final sweating temperature is 97 ℃, the sweating time is 0.5h, and the yield of the lactide is 92.3 percent (the optical purity is 99.4 percent)
It should be understood that the above-described specific embodiments are merely illustrative of the present invention and are not intended to limit the present invention. Obvious variations or modifications of the present invention are possible within the spirit of the present invention.
Claims (22)
1. The naphthyl ligand MOF composite activated carbon catalyst is characterized In that metal is used as an active component, the active metal is one or more of Sn, Zn, Ga, Ge, In, Sb, Tl, Pb, Bi, Po, Ti, Al, Ba, Rh, Ru, Ni, Cu, Fe, Cr, Co, Pd, Mn, V, Sc, Cd, Ag, Tc, Mo, Nb, Zr and Y, 2,3,6, 7-tetraacylimidazolyl-alpha-naphthoic acid is used as a ligand, activated carbon is used as a carrier, the molar ratio of the active component to the ligand to the activated carbon is (0.005-0.02), (0.01-0.015), (1.3-2.5), and the structural formula of the 2,3,6, 7-tetraacylimidazolyl-alpha-naphthoic acid is as follows:
2. the catalyst of claim 1, wherein the active component is one or more of Sn, Zn, Al, Pd, Ni.
3. The method for preparing a catalyst according to any one of claims 1-2, comprising the steps of: (1) preparation of organic ligand: dissolving N, N' -carbonyldiimidazole and alpha-naphthoic acid in a solvent in sequence, then adding trifluoromethanesulfonic acid, heating and stirring the reaction mixture, adding cold water, stirring overnight, and performing aftertreatment to obtain a ligand 2,3,6, 7-tetraacylimidazolyl-alpha-naphthoic acid; (2) and (2) carrying out hydrothermal reaction on the ligand obtained in the step (1), soluble salt of an active metal component and active carbon in a solvent, and carrying out post-treatment to obtain the catalyst.
4. The method for preparing the catalyst according to claim 3, wherein the solvent in the step (1) is anhydrous dichloromethane.
5. The method according to claim 3, wherein the reaction temperature of the α -naphthoic acid and the N, N' -carbonyldiimidazole in the step (1) is 40 to 90 ℃ and the reaction time is 1 to 5 hours.
6. The method according to claim 3, wherein the molar ratio of α -naphthoic acid, trifluoromethanesulfonic acid, and N, N' -carbonyldiimidazole is: (0.2-0.4), (0.2-0.45), (0.1-0.2).
7. The preparation method according to any one of claims 3 to 6, wherein the hydrothermal reaction temperature in the step (2) is 110 ℃ to 180 ℃, and the reaction time is 40h to 60 h; and/or the post-treatment in the step (2) comprises washing with water at the temperature of 50-80 ℃ for 4-6 h and washing with alcohol at the temperature of 40-55 ℃ for 5-8 h, and then filtering and drying.
8. The method according to claim 7, wherein the drying temperature is 80 to 110 ℃.
9. Use of the catalyst according to any one of claims 1-2 or the catalyst prepared by the preparation method according to any one of claims 3-8 in the preparation of lactide from L-lactic acid.
10. The use of claim 9, wherein the method for preparing lactide comprises the step of adding a catalyst into L-lactic acid mother liquor to perform heating and negative pressure stirring reaction, and the content of the catalyst in the L-lactic acid mother liquor is 0.1-5 wt%.
11. Use according to claim 10, characterized in that the catalyst is present in the L-lactic acid mother liquor in an amount of 0.5-2 wt%.
12. Use according to any one of claims 9-11, characterized in that the preparation of lactide comprises the following steps:
(1) introducing liquid nitrogen into the L-lactic acid solution;
(2) adding a catalyst into the lactic acid solution into which the liquid nitrogen is introduced to obtain a raw material solution;
(3) heating the raw material liquid under the protection of nitrogen, and introducing the raw material liquid into a prepolymerization reactor for reaction to obtain a lactic acid prepolymer reaction liquid with the molecular weight of 1000-3500;
(4) and (3) directly feeding the prepolymer reaction liquid into a depolymerization decompression reactor, carrying out high-temperature negative-pressure depolymerization reaction to obtain crude lactide, and carrying out rectification, melting and crystallization to obtain a lactide product.
13. Use according to claim 12, wherein in step (1) the L-lactic acid is kept at an oxygen content of less than 10 ppm.
14. The use according to claim 13, wherein in step (1), the L-lactic acid has an oxygen content of 3 to 7 ppm.
15. The use according to claim 14, wherein in step (1), the L-lactic acid has an oxygen content of 4 to 6 ppm.
16. The use according to claim 12, wherein the reaction temperature of step (3) is 50-200 ℃; and/or the absolute reaction pressure in the step (3) is 80-120 hPa; and/or the reaction time in the step (3) is 60-100 min.
17. The use according to claim 16, wherein the reaction temperature of step (3) is 80-190 ℃; and/or the absolute reaction pressure in the step (3) is 35-200 hPa; and/or the reaction time in the step (3) is 10-120 min.
18. The use according to claim 17, wherein the reaction temperature of step (3) is 120-160 ℃; and/or the absolute reaction pressure in the step (3) is 80-120 hPa; and/or the reaction time in the step (3) is 60-100 min.
19. The use according to claim 12, wherein the depolymerization reaction temperature of step (4) is 50 to 240 ℃; and/or the absolute reaction pressure of the step (4) is 20-1009 hPa; and/or the reaction time in the step (4) is 5-150 min.
20. The use according to claim 19, wherein the depolymerization reaction temperature of step (4) is 80-210 ℃; and/or the absolute reaction pressure in the step (4) is 22-200 hPa; and/or the reaction time in the step (4) is 10-40 min.
21. The use according to claim 20, wherein the depolymerization reaction temperature of step (4) is 180-200 ℃; and/or the absolute reaction pressure in the step (4) is 25-50 hPa; and/or the reaction time in the step (4) is 15-30 min.
22. The use of claim 12, wherein the theoretical plate number of the rectification separation in the step (4) is 40-60, and the main operation conditions are as follows: the pressure is 0.5-1 kPa, the wall temperature is 140-160 ℃, the kettle bottom temperature is 150-170 ℃, and the reflux ratio is 2: 1-9: 1; and/or the initial temperature of melt crystallization is 100-105 ℃, and the final temperature of crystallization is 70-90 ℃; the final sweating temperature is 94-98 ℃, and the sweating time is 0.5-1 h.
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