CN111533727A - Method for preparing 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 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, lactate is gasified to obtain lactate gas, then the lactate gas is mixed with inert gas to form mixed gas flow, the mixed gas flow is continuously introduced into the reactor, and the lactide is generated through heating and catalytic reaction. According to the method, the lactate is taken as a raw material, and through a gas phase reaction, the lactate is subjected to an ester exchange reaction in an inert gas environment under the action of a catalyst, so that the 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; the fixed bed reactor or the fluidized bed reactor is adopted, the lactide can be continuously prepared by catalytic synthesis, and the method 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 chemical production, in particular to a method for preparing 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 lactide by one-step gas phase reaction.
In order to solve the technical problems, the invention adopts a technical scheme that: a process for preparing lactide by one-step gas-phase reaction features that the mixed gas flow prepared from lactate gas and inertial gas is introduced to the fixed-bed reactor or fluidized-bed reactor where catalyst is carried, and the 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 used for directly catalyzing and generating lactide in one step.
Preferably, the inert gas is a gas that does not react with the reactant lactate gas. The inert gas is preferably helium, neon, argon, krypton, xenon, radon, nitrogen, CO2Any one or a mixture of gases. The inert gas is used as protective gas to play a role in pressurizing in the reaction process, so that the reaction is carried out under certain pressure.
Preferably, the lactate gas is any one of D-lactate gas, DL-lactate gas, and L-lactate gas. The D-lactate gas, the DL-lactate gas or the L-lactate gas is obtained by heating and gasifying corresponding lactate, the purity of the lactate is more than or equal to 90 percent, and preferably the purity of the lactate is more than or equal to 98 percent. Accordingly, the lactide obtained may be D-lactide, DL-lactide or L-lactide. The purity of the raw material lactate is controlled to be not less than 90% in the preparation process, and if the concentration is low, excessive impurities are easily generated, so that the purity of the synthesized lactide product is not high, the product is not easy to separate, and the purification difficulty of the lactide is increased.
Preferably, in the mixed gas flow formed by the lactate gas and the inert gas, the mass ratio of the lactate gas to the inert gas is (50-0.1): 50-99.9); preferably (40-2) and (60-98). Inert gas and alkyl lactate gas are mixed into the reaction system in a proper proportion, which is beneficial to improving the conversion rate of reactants. By setting the proper ratio of the raw material gas to the inert 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-1More preferably 1 to 10 hours-1. The mixed gas flow formed by inert gas and 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 a catalyst is short, and the conversion rate is reduced; if the flow rate is too low, the processing efficiency of the whole system will be reduced, which affects the productivity. 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 120-350 ℃, 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.
Preferably, the reaction pressure is positive pressure, and the pressure range is 0.1-1.0 MPa.
Preferably, the lactate is lactic acid and alcohol CnH2n+1And (3) OH is prepared through esterification reaction, wherein n is an integer of 1-8.
Further preferably, the lactate is methyl lactate, ethyl lactate, propyl lactate or butyl 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.
Preferably, the mass concentration of the lactate gas in the mixed gas flow is 5-20%, and more preferably 3-10%.
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 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, lactate is gasified to obtain lactate gas, and then the lactate gas is mixed with inert gas to form mixed gas flow, the mixed gas flow is continuously introduced into the reactor, and the lactide is generated by one-step heating catalytic reaction under the action of the catalyst.
The lactide obtained by the reaction contains alkyl alcohol, and pure 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 of a mixed gas of alkyl alcohol and inert gas, obtaining a liquid phase containing lactide and unreacted lactate, and then gasifying the unreacted alkyl lactate in the liquid phase by further distillation, wherein the remaining liquid phase is a pure lactide product.
The method of the invention has the following advantages:
(1) the lactide is obtained by one-step reaction by taking lactate as a raw material and carrying out ester exchange reaction on the lactate in an inert gas environment under the action of a catalyst through gas phase reaction, and the reaction process is simple, short in reaction time, low in energy consumption and high in production efficiency;
(2) the fixed bed reactor or the fluidized bed reactor is adopted, the lactide can be continuously prepared by catalytic synthesis, and the method 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 raw materials of the lactate are easy to obtain, and the lactide prepared by the method can 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;
(5) through the proper proportion of lactate gas and inert gas and under proper catalyst, reaction temperature, reaction pressure and catalyst dosage, the conversion rate of the reaction and the content of lactide in the product are obviously improved.
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 was supported on a fluidized bed, and the catalyst was supported by a method known in the art, and the catalyst supported by 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-1The reaction pressure is 0.2MPa, and 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. Introducing nitrogen into the reaction system for purging for 20min, and fluidizingThe bed reactor was heated to a 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-1The reaction pressure is 0.5MPa, and 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. 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 250 ℃, and the weight hourly space velocity of the mixed gas flow is 5h-1The reaction pressure is 0.5MPa, and 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 adjusting the mass ratio of the D-methyl lactate gas to the nitrogen gas to form D-milk in the mixed gas flowThe mass percentage content of the methyl ester 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-1The reaction pressure is 0.2MPa, and 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-1The reaction pressure is 0.2MPa, and 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 ℃.
L-ethyl lactate with the purity of 99 percent is selected as the L-lactate, and the L-ethyl lactate is heated to the gasification temperature. Then adjusting the L-ethyl lactate gas and CO2The mass ratio of the gas is that the mass percentage of the L-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-1Reaction pressureIs 0.8MPa, and is prepared under the action of a catalyst to obtain the L-lactide.
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 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 lactide content in the products obtained by the reactions of the examples 3-6 reaches 80%, 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 lactate as a raw material, and performs a gas phase reaction to perform an ester exchange reaction on the lactate under the action of an inert shielding gas and a catalyst, so as to obtain lactide through a one-step reaction.
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 lactide by simply separating and purifying the lactide and alkyl alcohol, and has high yield; in addition, the raw materials of the lactate are easy to obtain, so that the lactide prepared by the method 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 lactide by one-step gas phase reaction is characterized in that mixed gas flow of lactate gas and inert gas is introduced into a fixed bed reactor or a fluidized bed reactor which is fixedly loaded with a catalyst, and 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 production method according to claim 1 or 2, characterized in that the inert gas is a gas that does not react with a lactate gas; the inert gas is preferably helium, neon, argon, krypton, xenon, radon, nitrogen, or CO2Any one or a mixture of gases.
4. The production method according to any one of claims 1 to 3, characterized in that the lactate gas is any one of D-lactate gas, DL-lactate gas, and L-lactate gas; the D-lactate gas, the DL-lactate gas or the L-lactate gas are obtained by heating and gasifying corresponding lactate, and the purity of the lactate is more than or equal to 90 percent.
5. The production method according to any one of claims 1 to 4, wherein the mass ratio of the lactate gas to the inert gas in the mixed gas stream of the lactate gas and the inert gas is (50-0.1): (50-99.9), preferably (40-2): (60-98).
6. The method according to any one of claims 1 to 5, wherein the flow rate of the mixed gas stream is 0.5 to 100 hours at a weight hourly space velocity-1Preferably 1 to 50 hours-1More preferably 1 to 10 hours-1。
7. The method according to any one of claims 1 to 6, wherein the catalytic reaction temperature is 120 to 350 ℃, preferably 200 to 280 ℃; and/or the reaction pressure is 0.1-1.0 MPa.
8. The method according to claim 1 or 7, wherein the lactate is 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 lactate ester is methyl lactate, ethyl lactate, propyl lactate, or butyl 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 production method according to claim 1 or 9, wherein the mass concentration of the lactate gas in the mixed gas stream is 5 to 20%, more preferably 3 to 10%; and/or the weight hourly space velocity of the mixed gas flow is 2-8 h-1(ii) a And/or the catalyst is a germanium oxide and zinc oxide compound catalyst or a titanium dioxide and silicon dioxide compound catalyst.
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| CN112010834A (en) * | 2020-09-23 | 2020-12-01 | 中触媒新材料股份有限公司 | Method for synthesizing glycolide in one step |
| CN112028869A (en) * | 2020-09-23 | 2020-12-04 | 中触媒新材料股份有限公司 | Method for synthesizing lactide in one step |
| CN112266376A (en) * | 2020-10-16 | 2021-01-26 | 中触媒新材料股份有限公司 | Preparation method of lactide |
| CN114437017A (en) * | 2020-10-31 | 2022-05-06 | 中国石油化工股份有限公司 | Method for preparing lactide from lactic acid |
| CN114539207A (en) * | 2020-11-24 | 2022-05-27 | 万华化学(四川)有限公司 | Method and catalyst for preparing lactide |
| CN114805285A (en) * | 2022-06-07 | 2022-07-29 | 南昌大学 | Method for preparing lactide from L-lactic acid |
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| CN111039918A (en) | 2020-04-21 |
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