CN111039918A - Method for preparing D-lactide by one-step gas phase reaction - Google Patents
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Abstract
The invention belongs to the technical field of organic synthesis, and particularly discloses a method for preparing D-lactide by one-step gas phase reaction. The preparation method provided by the invention adopts a fixed bed reactor or a fluidized bed reactor, solid catalyst is fixedly carried in the reactor, D-lactate is gasified to obtain D-lactate gas, then the D-lactate gas is mixed with protective gas to form mixed gas flow, the mixed gas flow is continuously introduced into the reactor, and D-lactide is generated through heating and catalytic reaction. The method takes the D-lactate as a raw material, and the D-lactate is subjected to ester exchange reaction under the action of protective gas and a catalyst through gas phase reaction, so that the D-lactide can be obtained through one-step reaction, and the method has the advantages of simple reaction process, short reaction time, low energy consumption and high production efficiency; the D-lactide can be continuously prepared by catalytic synthesis by adopting a fixed bed reactor or a fluidized bed reactor, and is suitable for industrial production; the prepared product has simple system, easy product separation and high yield.
Description
Technical Field
The invention relates to the technical field of organic synthesis, in particular to a method for preparing D-lactide by one-step gas phase reaction.
Background
Polylactic acid is also called polylactide, is a polymer with excellent performance and biocompatibility and biodegradability, and is mainly used in the aspects of degradable packaging materials, drug microsphere carriers, anti-adhesion films, biological catheters, orthopedic fixtures, orthopedic surgery devices, artificial bones and the like.
Polylactic acid can be synthesized through two ways, one is direct polycondensation of lactic acid monomers, and the method is generally difficult to prepare polymers with high relative molecular mass; secondly, a two-step method is adopted, namely lactic acid is dehydrated and polycondensed to obtain lactic acid oligomer, the lactic acid oligomer is subjected to cyclization reaction of the oligomer to synthesize intermediate product lactide, and the lactide is subjected to ring-opening polymerization to generate polylactic acid. Lactide becomes an important intermediate for synthesizing the polylactic acid which is a degradable material.
At present, lactic acid is mostly adopted as a raw material in the synthesis method of lactide, although lactic acid monomers on the market are relatively cheap, the steps for directly preparing lactide from the lactic acid monomers are relatively complicated, and the problems of too long dehydration time, too high depolymerization temperature of lactic acid oligomers, large system viscosity, serious oxidation of reactants and the like in the reaction process also exist, so that the yield of the lactide is not high, the energy consumption is high, the production efficiency is low, and the production cost of polylactic acid is further overhigh, thereby seriously limiting the production scale and the wide application of the polylactic acid.
Disclosure of Invention
The invention mainly solves the technical problem of providing a method for preparing D-lactide by one-step gas phase reaction.
In order to solve the technical problems, the invention adopts a technical scheme that: a method for preparing D-lactide by one-step gas phase reaction is characterized in that mixed gas flow of D-lactate gas and protective gas is introduced into a fixed bed reactor or a fluidized bed reactor which is immobilized with a catalyst, and D-lactide is generated by catalytic reaction.
As a preferred embodiment, the catalyst is any one or a compound of more of aluminum oxide, germanium oxide, antimony oxide, zinc oxide, magnesium oxide, titanium dioxide, silicon dioxide, H-beta molecular sieve, calcium oxide, tin oxide and stannous oxide. Further preferably, the catalyst is a nano-scale or micro-scale catalyst. The nano-scale or micro-scale catalyst is adopted, the specific surface area of the catalyst is large, the catalyst is easier to contact with reactants, and the catalytic efficiency is higher. The catalyst selected by the invention is a nano-scale or micron-scale solid catalyst, can be immobilized on a fixed bed or in a fluidized bed, and can be directly catalyzed to generate D-lactide in one step.
Preferably, the protective gas is rare gas, nitrogen and CO2Any one or more of the gases. The protective gas plays a role in pressurizing in the reaction process, so that the reaction is carried out under certain pressure.
Preferably, the D-lactate gas is obtained by heating and gasifying D-lactate, and the purity of the D-lactate is more than or equal to 98%. The purity of the raw material D-alkyl lactate is controlled to be not less than 98% in the preparation process, and if the concentration is low, excessive impurities are easily generated, so that the purity of the synthesized D-lactide product is not high, the product is not easy to separate, and the purification difficulty of the D-lactide is increased.
Preferably, in the mixed gas flow of the D-lactate gas and the protective gas, the mass ratio of the D-lactate gas to the protective gas is (80-1): 20-99); preferably (40-2) and (60-98). The protective gas and the D-alkyl lactate gas are mixed in a proper proportion and enter a reaction system, which is beneficial to improving the conversion rate of reactants. By setting the proper ratio of the raw material gas to the protective gas, the raw material can be more effectively contacted with the catalyst when flowing through the fixed bed, the efficiency of the catalyst is improved, and the conversion rate is improved.
Preferably, the flow velocity of the mixed gas flow is 0.5-100 h of weight hourly space velocity-1Preferably 1 to 50 hours-1. The mixed gas flow formed by the protective gas and the D-alkyl lactate gas enters a reaction system at a constant flow rate, if the flow rate is too high, the retention time of reactants on the surface of the catalyst is short, and the conversion rate is reduced; if the flow rate is too low, the treatment efficiency of the whole system is highThe productivity is affected. The weight hourly space velocity is the weight of feed per hour (liquid or gas)/weight of catalyst loading.
Preferably, the catalytic reaction temperature is 180-320 ℃, and preferably 200-280 ℃. The reaction temperature is controlled within the temperature range, so that the reaction rate can be ensured, the occurrence of side reactions can be reduced, and the yield of the product is improved. The reaction pressure is positive pressure, and the pressure range is 0.1-1.0 MPa.
Preferably, the D-lactate is D-lactic acid and alcohol CnH2n+1And (3) OH is prepared through esterification reaction, wherein n is an integer of 1-8.
Further preferably, the D-lactic acid ester is D-methyl lactate or D-ethyl lactate.
The catalyst is any one or more of aluminum oxide, germanium oxide, zinc oxide, magnesium oxide, titanium dioxide, silicon dioxide, tin oxide and stannous oxide.
More preferably, the catalyst is any two of aluminum oxide, germanium oxide, zinc oxide, magnesium oxide, titanium dioxide, silicon dioxide, tin oxide and stannous oxide.
Preferably, the mass concentration of the D-lactate gas in the mixed gas flow is 3-10%, more preferably 3-6%, and even more preferably 3-4%.
Preferably, the weight hourly space velocity of the mixed gas flow is 2-8 h-1。
Preferably, the catalyst is a germanium dioxide and zinc oxide compound catalyst (GeO)2-ZnO) or titanium dioxide and silicon dioxide complex catalyst (TiO)2-SiO2)。
The method for preparing D-lactide by one-step gas phase reaction adopts a fixed bed reactor or a fluidized bed reactor, solid catalyst is fixedly carried in the fixed bed reactor or the fluidized bed reactor, D-lactate is gasified to obtain D-lactate gas, the D-lactate gas is mixed with protective gas to form mixed gas flow, the mixed gas flow is continuously introduced into the reactor, and D-lactide is generated by heating catalytic reaction under the action of the catalyst.
The D-lactide obtained by the reaction contains alkyl alcohol, and pure D-lactide can be obtained by separation and purification. For example, the separation and purification method may be: firstly gasifying alkyl alcohol by a distillation or rectification mode, obtaining a gas phase which is a mixed gas of alkyl alcohol and protective gas, obtaining a liquid phase containing D-lactide and unreacted D-lactate, and then gasifying the unreacted D-alkyl lactate in the liquid phase by further distillation, wherein the remaining liquid phase is a pure D-lactide product.
The method of the invention has the following advantages:
(1) d-lactate is taken as a raw material, and through gas phase reaction, the D-lactate is subjected to ester exchange reaction under the action of protective gas and a catalyst, so that D-lactide can be obtained through one-step reaction, the reaction process is simple, the reaction time is short, the energy consumption is low, and the production efficiency is high;
(2) the D-lactide can be continuously prepared by catalytic synthesis by adopting a fixed bed reactor or a fluidized bed reactor, and is suitable for industrial production;
(3) the prepared product system is simple, the product is easy to separate, and the yield is high;
(4) the D-lactide prepared by the method can reduce the production cost, thereby further reducing the production cost of polylactic acid in industrial production and being beneficial to the expansion of the production scale of the polylactic acid.
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.
Example 1
The catalyst used in this example was Al2O3-SiO2Built-up catalysts, in which Al2O3The mass percentage of (B) is 8%. The catalyst is supported on a fluidized bed, and the catalyst can be supported by a method known in the artThe solid loading of the catalyst was 10.2 g. And loading the fluidized bed after the catalyst is immobilized into a reaction system. Firstly introducing nitrogen into the reaction system for purging for 20min, and then heating the fluidized bed reactor to the reaction temperature of 225 ℃.
D-methyl lactate with the purity of 99 percent is selected as the D-lactate and heated to the gasification temperature. Then, the mass ratio of the D-methyl lactate gas to the nitrogen gas is adjusted to ensure that the mass percentage of the D-methyl lactate in the formed mixed gas flow is 6%. Continuously introducing the mixed gas flow into the reaction system, wherein the temperature of the fluidized bed reactor is set at 225 ℃, and the weight hourly space velocity of the mixed gas flow is 2h-1And D-lactide is prepared under the action of a catalyst.
Example 2
The catalyst adopted in the embodiment is SnO-TiO2The compound catalyst comprises 6 percent of SnO by mass percent. The catalyst was supported on a fluidized bed at a catalyst loading of 10.4 g. And loading the fluidized bed after the catalyst is immobilized into a reaction system. Firstly introducing nitrogen into the reaction system for purging for 20min, and then heating the fluidized bed reactor to the reaction temperature of 225 ℃.
D-methyl lactate with the purity of 99 percent is selected as the D-lactate and heated to the gasification temperature. Then, the mass ratio of the D-methyl lactate gas to the nitrogen gas is adjusted to ensure that the mass percentage of the D-methyl lactate in the formed mixed gas flow is 6%. Continuously introducing the mixed gas flow into the reaction system, wherein the temperature of the fluidized bed reactor is set at 225 ℃, and the weight hourly space velocity of the mixed gas flow is 2h-1And D-lactide is prepared under the action of a catalyst.
Example 3
The catalyst used in this example was GeO2-ZnO built catalyst, wherein GeO2The mass percentage of (B) is 10%. The catalyst was supported on a fluidized bed at a catalyst loading of 10.8 g. And loading the fluidized bed after the catalyst is immobilized into a reaction system. Firstly introducing nitrogen into the reaction system for purging for 20min, and then heating the fluidized bed reactor to the reaction temperature of 250 ℃.
D-methyl lactate with the purity of 99 percent is selected as the D-lactate and heated to the gasification temperature. However, the device is not suitable for use in a kitchenAnd then adjusting the mass ratio of the D-methyl lactate gas to the nitrogen gas to ensure that the mass percentage of the D-methyl lactate in the formed mixed gas flow is 6 percent. Continuously introducing the mixed gas flow into the reaction system, wherein the temperature of the fluidized bed reactor is set at 250 ℃, and the weight hourly space velocity of the mixed gas flow is 5h-1And D-lactide is prepared under the action of a catalyst.
Example 4
The catalyst used in this example was TiO2-SiO2Built-up catalysts, in which TiO2The mass percentage of (B) is 6%. The catalyst was supported on a fluidized bed at an amount of 9.8 g. And loading the fluidized bed after the catalyst is immobilized into a reaction system. Firstly introducing nitrogen into the reaction system for purging for 20min, and then heating the fluidized bed reactor to the reaction temperature of 225 ℃.
D-methyl lactate with the purity of 99 percent is selected as the D-lactate and heated to the gasification temperature. Then, the mass ratio of the D-methyl lactate gas to the nitrogen gas is adjusted to ensure that the mass percentage of the D-methyl lactate in the formed mixed gas flow is 10 percent. Continuously introducing the mixed gas flow into the reaction system, wherein the temperature of the fluidized bed reactor is set at 225 ℃, and the weight hourly space velocity of the mixed gas flow is 8h-1And D-lactide is prepared under the action of a catalyst.
Example 5
The catalyst used in this example was TiO2-SiO2Built-up catalysts, in which TiO2The mass percentage of (B) is 6%. The catalyst was supported on a fluidized bed at an amount of 9.8 g. And loading the fluidized bed after the catalyst is immobilized into a reaction system. Firstly introducing nitrogen into the reaction system for purging for 20min, and then heating the fluidized bed reactor to the reaction temperature of 225 ℃.
D-methyl lactate with the purity of 99 percent is selected as the D-lactate and heated to the gasification temperature. Then, the mass ratio of the D-methyl lactate gas to the nitrogen gas is adjusted to ensure that the mass percentage of the D-methyl lactate in the formed mixed gas flow is 3 percent. Continuously introducing the mixed gas flow into the reaction system, wherein the temperature of the fluidized bed reactor is set at 225 ℃, and the weight hourly space velocity of the mixed gas flow is 2h-1And D-lactide is prepared under the action of a catalyst.
Example 6
The catalyst used in this example was TiO2-SiO2Built-up catalysts, in which TiO2The mass percentage of (B) is 6%. The catalyst was supported on a fluidized bed at an amount of 9.8 g. And loading the fluidized bed after the catalyst is immobilized into a reaction system. Introducing CO into the reaction system2The gas purge was carried out for 20min, after which the fluidized bed reactor was heated to a reaction temperature of 280 ℃.
D-ethyl lactate with the purity of 99 percent is selected as the D-lactate, and the D-ethyl lactate is heated to the gasification temperature. Then adjusting the D-ethyl lactate gas and CO2The mass ratio of the gas is that the mass percentage of the D-ethyl lactate in the formed mixed gas flow is 6 percent. Continuously introducing the mixed gas flow into the reaction system, wherein the temperature of the fluidized bed reactor is set at 280 ℃, and the weight hourly space velocity of the mixed gas flow is 2h-1And D-lactide is prepared under the action of a catalyst.
The reaction products of examples 1 to 6 above were subjected to gas chromatography analysis, and the composition thereof is shown in Table 1.
TABLE 1
As can be seen from the data in Table 1, the D-lactide content in the products obtained by the reactions of examples 1-6 is greater than 50%, and it can be seen that the reactions of the above examples all have high selectivity. The content of D-lactide in the products obtained by the reactions of the examples 3 to 6 reaches 80 percent, the selectivity is better, and the unexpected technical effect is achieved. In particular, the preparation method of example 5 can achieve 53% of D-lactide single-pass conversion rate and 91% of D-lactide purity obtained by reaction.
The above examples illustrate that the method of the present invention directly uses D-lactate as a raw material, and performs a gas phase reaction to perform an ester exchange reaction of D-lactate under the action of a protective gas and a catalyst, and then performs a one-step reaction to obtain D-lactide.
Compared with the method for preparing lactide by lactic acid in the prior art, the method reduces complex reaction links such as lactic acid oligomerization dehydration and cracking, has simpler reaction process, shorter reaction time and lower energy consumption, can obtain pure D-lactide by simply separating and purifying the D-lactide and alkyl alcohol, and has high yield; in addition, the raw materials of the lactate are easy to obtain, so that the method for preparing the D-lactide can improve the production efficiency of the lactide and reduce the production cost, thereby further reducing the production cost of the polylactic acid in industrial production and being beneficial to the expansion of the production scale of the polylactic acid.
The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.
Claims (10)
1. A method for preparing D-lactide by one-step gas phase reaction is characterized in that mixed gas flow of D-lactate gas and protective gas is introduced into a fixed bed reactor or a fluidized bed reactor which is immobilized with a catalyst, and D-lactide is generated by catalytic reaction.
2. The preparation method of claim 1, wherein the catalyst is any one or more of aluminum oxide, germanium oxide, antimony oxide, zinc oxide, magnesium oxide, titanium dioxide, silicon dioxide, H-beta molecular sieve, calcium oxide, tin oxide and stannous oxide; preferably, the catalyst is a nano-scale or micro-scale catalyst.
3. The method of claim 2, wherein the shielding gas is diluteWith gas, nitrogen, CO2Any one or more of the gases.
4. The production method according to claim 3, wherein the D-lactate gas is a gas obtained by heating and gasifying D-lactate, and the purity of D-lactate is not less than 98%.
5. The production method according to any one of claims 1 to 4, wherein the mass ratio of the D-lactate gas to the shielding gas in the mixed gas stream of the D-lactate gas and the shielding gas is (80-1): 20-99, preferably (40-2): 60-98.
6. The preparation method of claim 5, wherein the flow rate of the mixed gas flow is 0.5-100 h at weight hourly space velocity-1Preferably 1 to 50 hours-1。
7. The method of claim 6, wherein the catalytic reaction temperature is 180 to 320 ℃, preferably 200 to 280 ℃; the reaction pressure is 0.1-1.0 MPa.
8. The method according to claim 7, wherein the D-lactate is D-lactic acid and alcohol CnH2n+1And (3) OH is prepared through esterification reaction, wherein n is an integer of 1-8.
9. The method according to any one of claims 6 to 8, wherein the D-lactate is D-methyl lactate or D-ethyl lactate; and/or the catalyst is any one or more of aluminum oxide, germanium oxide, zinc oxide, magnesium oxide, titanium dioxide, silicon dioxide, tin oxide and stannous oxide.
10. The preparation method according to claim 9, wherein the mass concentration of the D-lactate gas in the mixed gas stream is 3-10%, preferably 3-6%, and more preferably 3-4%; the mixed gas flowThe weight hourly space velocity of the reactor is 2-8 h-1The catalyst is a compound catalyst of germanium oxide and zinc oxide or a compound catalyst of titanium dioxide and silicon dioxide.
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| CN202010429236.2A CN111533727B (en) | 2019-12-24 | 2020-05-20 | Method for preparing lactide by one-step gas phase reaction |
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| US5138074A (en) * | 1990-06-28 | 1992-08-11 | E. I. Du Pont De Nemours And Company | Continuous catalyzed vapor phase dimeric cyclic ester process |
| US5332839A (en) * | 1990-09-18 | 1994-07-26 | Biopak Technology, Ltd. | Catalytic production of lactide directly from lactic acid |
| CN112442006A (en) * | 2019-08-28 | 2021-03-05 | 上海东庚化工技术有限公司 | Method for continuously synthesizing L-lactide |
| CN111039918A (en) * | 2019-12-24 | 2020-04-21 | 安徽丰原发酵技术工程研究有限公司 | Method for preparing D-lactide by one-step gas phase reaction |
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