CN112028869A - Method for synthesizing lactide in one step - Google Patents
Method for synthesizing lactide in one step Download PDFInfo
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- CN112028869A CN112028869A CN202011005818.4A CN202011005818A CN112028869A CN 112028869 A CN112028869 A CN 112028869A CN 202011005818 A CN202011005818 A CN 202011005818A CN 112028869 A CN112028869 A CN 112028869A
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- C07D319/00—Heterocyclic compounds containing six-membered rings having two oxygen atoms as the only ring hetero atoms
- C07D319/10—1,4-Dioxanes; Hydrogenated 1,4-dioxanes
- C07D319/12—1,4-Dioxanes; Hydrogenated 1,4-dioxanes not condensed with other rings
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- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
- C08G63/02—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds
- C08G63/06—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds derived from hydroxycarboxylic acids
- C08G63/08—Lactones or lactides
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
- C08G63/78—Preparation processes
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Abstract
The invention discloses a method for synthesizing lactide in one step, which is characterized in that lactate ester is taken as a raw material, a tin-containing molecular sieve is taken as a catalyst, the lactide is synthesized by a gas-phase normal-pressure one-step method, the conversion rate of the lactate ester in the reaction can reach more than 98 percent, and the selectivity of the lactide is more than 92 percent. Compared with the traditional synthesis method which takes lactic acid as a raw material and carries out condensation polymerization and depolymerization after dehydration, the method has mild reaction conditions, simple process and continuous operation, does not need high vacuum and high boiling point solvent, and compared with the conventional metal compound catalyst, the tin-containing molecular sieve used in the method is safe, environment-friendly and recyclable, and is more suitable for the industrial production of lactide.
Description
Technical Field
The invention relates to a method for synthesizing lactide in one step, belonging to the field of catalytic reaction.
Background
Polylactic acid (PLA) has excellent biocompatibility and biodegradability. Polylactic acid and its copolymer are widely used in the field of biological materials, especially as tissue engineering scaffold materials, drug release materials and fracture internal fixation members, and are receiving attention from people. At present, the synthesis method of PLA mainly comprises a one-step method and a two-step method: the one-step method is to directly synthesize PLA by taking lactic acid, lactate and derivatives thereof as raw materials, but the synthesized PLA has low molecular weight, poor strength and low practical application value; the two-step method is to carry out polycondensation-depolymerization on the raw materials to obtain lactide, and carry out ring-opening polymerization on the refined and purified monomer to obtain PLA.
Lactide, which is an intermediate in the synthesis of polylactic acid and copolymers thereof, is also gaining attention as a biomedical material. Therefore, an important approach is to solve the problem of large-scale synthesis of lactide. The most common methods for preparing lactide are: firstly, lactic acid is directly polycondensed at low temperature under the action of catalyst to obtain oligolactic acid, then the lactic acid oligomer is depolymerized at higher temperature to produce lactide, and according to the mode of removing small molecular by-product water, the method can be divided into reduced pressure method and normal pressure gas flow method, and the patents CN100417652C, CN101585827A, CN101747314B, CN1951933A and CN104710401A, etc. all adopt said method, but because of the property of lactic acid, the raw material lactic acid must be dewatered before reaction. In order to simplify the reaction steps, the reaction may be carried out by using a lactic acid ester as a starting material.
The lactide synthesis method needs two steps, and in order to further simplify the process steps, the one-step lactide synthesis method has become a research hotspot in recent years. In the patent CN108610323A, lactic acid is used as a raw material, an H-beta molecular sieve is used as a catalyst, and lactide is synthesized by a one-step method under a reduced pressure condition; patents CN111039918A and CN101891733B disclose a one-step method for synthesizing lactide by using lactate as raw material and metal oxide as carrier for co-catalysis, but both use a large flow of nitrogen to vaporize the raw material and perform the reaction under reduced pressure.
In conclusion, the one-step synthesis of lactide by using a catalyst with excellent performance and a relatively simple and easy synthesis process is the target of the large-scale industrial production of lactide.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a method for synthesizing lactide, which takes a tin-containing molecular sieve as a catalyst and continuously synthesizes the lactide by a gas-phase normal-pressure one-step method, thereby simplifying the lactide synthesis process.
The invention aims to provide a method for preparing lactide with high conversion rate and high selectivity.
The invention discloses a method for synthesizing lactide in one step, which takes lactate as a raw material and a tin-containing molecular sieve as a catalyst, synthesizes the lactide in a gas phase and normal pressure one-step method, and comprises the following specific processes: firstly, heating and vaporizing lactate, and introducing the gaseous lactate into a reactor filled with a tin-containing molecular sieve catalyst for cyclization reaction to obtain the product lactide.
Further, in the technical scheme, the tin-containing molecular sieve is one or a mixture of more of Sn-Beta, Sn-MOR, Sn-ZSM-22, Sn-ZSM-35 and Sn-ZSM-5.
Further, in the above technical solution, the crystallinity of the tin-containing molecular sieve is greater than 95%, and the silica-alumina ratio is 2000-.
Further, in the above technical solution, the grain size of the tin-containing molecular sieve is 3000nm, preferably 1000nm and 100 nm.
Further, in the above technical solution, the content of tin in the tin-containing molecular sieve is 0.2-4%, preferably 1-2%.
Further, in the above embodiment, the lactate ester is methyl lactate, ethyl lactate, propyl lactate, or butyl lactate, and methyl lactate and ethyl lactate are preferable.
Further, in the above technical solution, the lactate may be L-lactate, D-lactate, or D, L-lactate.
Further, in the technical scheme, the vaporization temperature of the lactate is 150-.
Further, in the above technical scheme, the cyclization reaction temperature is 180-.
Further, in the above technical means, the catalyst and the raw material are subjected to a gas phase contact reaction, and a fixed bed, a fluidized bed, a moving bed, a boiling bed or an expanded bed may be used.
The invention provides a method for synthesizing polylactic acid, which takes lactate as a raw material and a tin-containing molecular sieve as a catalyst to synthesize lactide by a gas-phase normal-pressure one-step method, and comprises the following specific processes: firstly heating and vaporizing lactate, feeding the gaseous lactate into a reactor filled with a tin-containing molecular sieve catalyst for cyclization reaction to obtain lactide product, purifying the lactide, and polymerizing the lactide into a product with a relative weight average molecular weight of more than 2 x 10 under the action of a ring-opening polymerization catalyst5The polylactic acid has the polymerization catalyst of stannous octoate, stannous acetate or alkyl aluminum, the polymerization reaction temperature is 130-180 ℃, the reaction pressure is 100-300KPa, the reaction time is 2-6h, and the catalyst dosage is 250-600 mu g/g.
Further, in the technical scheme, the tin-containing molecular sieve is one or a mixture of more of Sn-Beta, Sn-MOR, Sn-ZSM-22, Sn-ZSM-35 and Sn-ZSM-5.
Further, in the above technical solution, the crystallinity of the tin-containing molecular sieve is greater than 95%, and the silica-alumina ratio is 2000-.
Further, in the above technical solution, the grain size of the tin-containing molecular sieve is 3000nm, preferably 1000nm and 100 nm.
Further, in the above technical solution, the content of tin in the tin-containing molecular sieve is 0.2-4%, preferably 1-2%.
Further, in the above embodiment, the lactate ester is methyl lactate, ethyl lactate, propyl lactate, or butyl lactate, and methyl lactate and ethyl lactate are preferable.
Further, in the above technical solution, the lactate may be L-lactate, D-lactate, or D, L-lactate.
Further, in the technical scheme, the vaporization temperature of the lactate is 150-.
Further, in the above technical scheme, the cyclization reaction temperature is 180-.
Further, in the above technical means, the catalyst and the raw material are subjected to a gas phase contact reaction, and a fixed bed, a fluidized bed, a moving bed, a boiling bed or an expanded bed may be used.
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The invention is further described with reference to the following figures and examples.
FIG. 1 is a mass spectrum of lactide synthesized in example 7.
Detailed Description
In order to better understand the present invention, the following examples are further provided to illustrate the present invention, but the present invention is not limited to the illustrated examples.
The lactate is selected from any commercially available reagent, requiring a purity of no less than 98%; the tin-containing molecular sieve of the catalyst is self-made or commercially available, and the relative crystallinity of the tin-containing molecular sieve is required to be more than 95 percent.
For the purpose of better illustrating the present invention, the preparation of the tin-containing molecular sieve is set forth, but is not limited to the tin-containing molecular sieve prepared by the following method.
The synthesis method of the tin-containing molecular sieve comprises the following steps: taking a tin-free molecular sieve as a raw material, performing acid treatment and dealumination, taking anhydrous stannic chloride as a tin source, performing gas phase treatment for 6-24h at the temperature of 450-plus-material and 700 ℃, washing, drying and roasting to obtain raw powder of the tin-containing molecular sieve, uniformly mixing the raw powder and sesbania powder, adding a binder, further uniformly mixing, extruding into strips by a strip extruding machine for molding, drying the molded sample at the temperature of 100 ℃ for 12h, and roasting to obtain the strip-shaped tin-containing molecular sieve.
Example 1
The tin-containing molecular sieve Sn-Beta (tin content: 1.7%, silica-alumina ratio: 3000) catalyst is sieved into 20-40 mesh particles, 4g of the catalyst is filled into the middle section of a fixed bed reaction tube, inert quartz sand is filled at two ends of the reaction tube, the vaporization temperature of L-methyl lactate is 220 ℃, the reaction temperature is 240 ℃, the feeding amount of L-methyl lactate is 12g/h, the reaction is carried out under normal pressure, and the reaction result is shown in Table 1.
Example 2
The tin-containing molecular sieve Sn-Beta (tin content: 1.7%, silica-alumina ratio: 3000) catalyst is sieved into 20-40 mesh particles, 4g of the catalyst is filled into the middle section of a fixed bed reaction tube, inert quartz sand is filled at two ends of the reaction tube, the vaporization temperature of L-methyl lactate is 260 ℃, the reaction temperature is 240 ℃, the feeding amount of L-methyl lactate is 12g/h, the reaction is carried out under normal pressure, and the reaction result is shown in Table 1.
Example 3
The tin-containing molecular sieve Sn-Beta (tin content: 1.7%, silica-alumina ratio: 3000) catalyst is sieved into 20-40 mesh particles, 4g of the catalyst is filled into the middle section of a fixed bed reaction tube, inert quartz sand is filled at two ends of the reaction tube, the vaporization temperature of L-methyl lactate is 220 ℃, the reaction temperature is 220 ℃, the feeding amount of L-methyl lactate is 12g/h, the reaction is carried out under normal pressure, and the reaction result is shown in Table 1.
Example 4
The tin-containing molecular sieve Sn-Beta (tin content: 1.7%, silica-alumina ratio: 3000) catalyst is sieved into 20-40 mesh particles, 4g of the catalyst is filled into the middle section of a fixed bed reaction tube, inert quartz sand is filled at two ends of the reaction tube, the vaporization temperature of L-methyl lactate is 220 ℃, the reaction temperature is 280 ℃, the feeding amount of L-methyl lactate is 12g/h, the reaction is carried out under normal pressure, and the reaction result is shown in Table 1.
Example 5
The tin-containing molecular sieve Sn-Beta (tin content: 1.7%, silica-alumina ratio: 3000) catalyst is sieved into 20-40 mesh particles, 4g of the catalyst is filled into the middle section of a fixed bed reaction tube, inert quartz sand is filled at two ends of the reaction tube, the vaporization temperature of L-methyl lactate is 220 ℃, the reaction temperature is 240 ℃, the feeding amount of L-methyl lactate is 6g/h, the reaction is carried out under normal pressure, and the reaction result is shown in Table 1.
Example 6
The tin-containing molecular sieve Sn-Beta (tin content: 1.7%, silica-alumina ratio: 3000) catalyst is sieved into 20-40 mesh particles, 4g of the catalyst is filled into the middle section of a fixed bed reaction tube, inert quartz sand is filled at two ends of the reaction tube, the vaporization temperature of L-methyl lactate is 220 ℃, the reaction temperature is 240 ℃, the feeding amount of L-methyl lactate is 12g/h, the reaction is carried out under normal pressure, and the reaction result is shown in Table 1.
Example 7
The tin-containing molecular sieve Sn-Beta (tin content: 1.7%, silica-alumina ratio: 3000) catalyst is sieved into particles of 20-40 meshes, 4g of the catalyst is filled into the middle section of a fixed bed reaction tube, inert quartz sand is filled at two ends of the reaction tube, the vaporization temperature of D, L-methyl lactate is 220 ℃, the reaction temperature is 240 ℃, the feeding amount of D, L-methyl lactate is 12g/h, the reaction is carried out under normal pressure, and the reaction result is shown in table 1. And (3) separating and purifying the material obtained by the reaction to obtain a product D, L-lactide, wherein the mass spectrum of the product is shown in the attached figure.
Example 8
The tin-containing molecular sieve Sn-Beta (tin content: 1.7%, silica-alumina ratio: 3000) catalyst is sieved into 20-40 mesh particles, 4g of the catalyst is filled into the middle section of a fixed bed reaction tube, inert quartz sand is filled at two ends of the reaction tube, the vaporization temperature of L-ethyl lactate is 220 ℃, the reaction temperature is 240 ℃, the feeding amount of L-ethyl lactate is 12g/h, the reaction is carried out under normal pressure, and the reaction result is shown in Table 1.
Example 9
The tin-containing molecular sieve Sn-Beta (tin content: 2.0%, silica-alumina ratio: 5000) catalyst is sieved into 20-40 mesh particles, 4g of the catalyst is filled into the middle section of a fixed bed reaction tube, inert quartz sand is filled at two ends of the reaction tube, the vaporization temperature of L-methyl lactate is 220 ℃, the reaction temperature is 240 ℃, the feeding amount of L-methyl lactate is 12g/h, the reaction is carried out under normal pressure, and the reaction result is shown in table 1.
Example 10
The tin-containing molecular sieve Sn-MOR (tin content: 1.8%, silica-alumina ratio: 3200) catalyst is sieved into 20-40 mesh particles, 4g of the catalyst is filled into the middle section of a fixed bed reaction tube, inert quartz sand is filled at two ends of the reaction tube, the vaporization temperature of L-methyl lactate is 220 ℃, the reaction temperature is 240 ℃, the feeding amount of L-methyl lactate is 12g/h, the reaction is carried out under normal pressure, and the reaction result is shown in Table 1.
Example 11
The tin-containing molecular sieve Sn-ZSM-35 (tin content: 1.7%, silica alumina ratio: 3000) catalyst was sieved into 20-40 mesh particles, 4g of the catalyst was loaded into the middle section of a fixed bed reaction tube, inert quartz sand was loaded into both ends of the reaction tube, the L-methyl lactate vaporization temperature was 220 ℃, the reaction temperature was 240 ℃, the L-methyl lactate feed amount was 12g/h, the reaction was carried out at normal pressure, and the reaction results are shown in Table 1.
Example 12
Screening Sn-ZSM-5 (with tin content of 2.0% and silica-alumina ratio of 4000) catalyst containing tin molecular sieve into 20-40 mesh particles, filling 4g of catalyst into the middle section of a fixed bed reaction tube, filling inert quartz sand into two ends of the reaction tube, carrying out reaction at normal pressure, wherein the vaporization temperature of L-methyl lactate is 220 ℃, the reaction temperature is 240 ℃, the feeding amount of L-methyl lactate is 12g/h, and the reaction result is shown in Table 1
Example 13
Preparing polylactic acid: dissolving 0.012g stannous octoate in petroleum ether, adding the dissolved stannous octoate and 30g lactide prepared in the embodiment into a stainless steel reaction kettle, evacuating the kettle for at least three times by using nitrogen, vacuumizing for 0.5h under stirring to remove the petroleum ether, raising the temperature to 160 ℃, timing, keeping the reaction pressure at 200KPa, stopping the reaction after 5h to obtain polylactic acid, and measuring the relative weight-average molecular weight of the polylactic acid by a Gel Permeation Chromatograph (GPC) to be 2.77 multiplied by 105。
The above-mentioned embodiments are only for illustrating the technical idea and features of the present invention, and the purpose of the present invention is to enable those skilled in the art to understand the content of the present invention and implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.
TABLE 1 results of the reaction
Claims (11)
1. A method for synthesizing lactide in one step is characterized in that lactate is taken as a raw material, a tin-containing molecular sieve is taken as a catalyst, and the lactide is synthesized in a gas phase normal pressure one-step method, which comprises the following specific steps: firstly, heating and vaporizing lactate, and introducing the gaseous lactate into a reactor filled with a tin-containing molecular sieve catalyst for cyclization reaction to obtain the product lactide.
2. The one-step lactide synthesis process of claim 1, wherein the tin-containing molecular sieve is one or more of Sn-Beta, Sn-MOR, Sn-ZSM-22, Sn-ZSM-35, Sn-ZSM-5.
3. The method as claimed in claim 2, wherein the tin-containing molecular sieve has a crystallinity of greater than 95% and a silica to alumina ratio of 2000-.
4. The method as claimed in claim 2, wherein the tin-containing molecular sieve has a grain size of 100-3000nm, preferably 200-1000 nm.
5. The process of claim 1, wherein the tin content of the tin-containing molecular sieve is from 0.2 to 4%, preferably from 1 to 2%.
6. The method according to claim 1, characterized in that the lactate ester is methyl lactate, ethyl lactate, propyl lactate, butyl lactate, preferably methyl lactate and ethyl lactate.
7. The method according to claim 7, wherein the lactate ester is L-lactate, D-lactate, or D, L-lactate.
8. The method according to claim 1, characterized in that the lactate vaporization temperature is 150-600 ℃, preferably 180-350 ℃.
9. The process as claimed in claim 1, wherein the cyclization reaction temperature is 180-300 ℃, the reaction pressure is normal pressure, and the feed mass space velocity is 1-8g lactate per gram catalyst per hour.
10. The method of claim 1, wherein the catalyst and the raw material are subjected to gas phase contact reaction, and a fixed bed, a fluidized bed, a moving bed, an ebullating bed or an expanded bed can be used.
11. The method of claim 1, wherein the synthesized lactide can be used for synthesizing polylactic acid, and the specific process for synthesizing the polylactic acid is as follows: the method is characterized in that lactide is synthesized by taking lactate as a raw material and a tin-containing molecular sieve as a catalyst through a gas-phase normal-pressure one-step method, and the specific process is as follows: firstly heating and vaporizing lactate, feeding the gaseous lactate into a reactor filled with a tin-containing molecular sieve catalyst for cyclization reaction to obtain lactide product, purifying the lactide, and polymerizing the lactide into a product with a relative weight average molecular weight of more than 2 x 10 under the action of a ring-opening polymerization catalyst5The polylactic acid has the polymerization catalyst of stannous octoate, stannous acetate or alkyl aluminum, the polymerization reaction temperature is 130-180 ℃, the reaction pressure is 100-300KPa, the reaction time is 2-6h, and the catalyst dosage is 250-600 mu g/g.
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CN114377720A (en) * | 2022-01-25 | 2022-04-22 | 浙江省林业科学研究院 | Tin-based catalyst and preparation method and application thereof |
CN114377720B (en) * | 2022-01-25 | 2024-04-19 | 浙江省林业科学研究院 | Tin-based catalyst and preparation method and application thereof |
CN115382570A (en) * | 2022-08-02 | 2022-11-25 | 马鞍山同杰良生物材料有限公司 | Nanometer Beta molecular sieve for preparing lactide and preparation method thereof |
CN115417851A (en) * | 2022-08-30 | 2022-12-02 | 中国科学院长春应用化学研究所 | Method for directly preparing lactide from lactic acid |
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