Method for synthesizing lactide from L-lactic acid by adopting fixed bed reactor

A fixed-bed reactor and lactide technology, applied in the direction of organic chemistry, can solve problems such as easy coking, unfavorable industrial production, long process flow, etc., achieve high-temperature resistant catalytic performance, easy industrial implementation, and reduce free acid content Effect

Active Publication Date: 2022-07-01
CHINA PETROLEUM & CHEM CORP +1
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Problems solved by technology

For example, Chinese patent CN108610323A discloses the use of lactic acid in the presence of H-beta molecular sieves under reduced pressure and heating conditions to directly complete the synthesis of lactic acid to lactide. The yield of lactide is low, which is not conducive to industrial production
Chinese patents CN108424408A, CN110105324A, etc. use tin or zinc catalysts in the reactor to catalyze the synthesis of lactide from lactic acid under high temperature and high vacuum conditions. Although the problem of lactide yield has been solved, the catalyst is easy to coke and block the pipeline under high temperature conditions. And the problem of low optical purity of lactide still exists
The current lactide preparation process mainly has the following main problems: (1) During the dehydration polycondensation stage of lactic acid, water molecules cannot be completely evaporated, and the degree of polymerization of the generated lactic acid oligomers is small, which cannot meet the requirements of further depolymerization Require
(2) Crude lactide contains more lactic acid, lactoyl lactic acid and lactic acid linear polymers, the content of free acid is high, and the purification process is cumbersome
(3) The tin (or zinc) catalyst used is easy to coke under high temperature, and it is easy to cause pipeline blockage. At the same time, the catalyst is highly toxic, has a short service life, and is expensive

Method used

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  • Method for synthesizing lactide from L-lactic acid by adopting fixed bed reactor

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Effect test

Embodiment 1

[0027] Preparation of silicon-substituted aluminum phosphate molecular sieve catalyst: mix phosphoric acid solution with deionized water, then add inorganic aluminum salt, white carbon black and tetraethylammonium hydroxide to the mixed solution in turn, stir evenly; heat the above mixed solution at 55°C Heating in a water bath for 4 hours while continuing to stir, the obtained gel was poured into a polytetrafluoroethylene-lined reaction kettle, and then put into a dynamic crystallization box for crystallization at a heating rate of 4.5 °C / h, and heated to 220 °C. ℃ constant temperature reaction for 50h, cooling, washing, drying and roasting after crystallization is completed to obtain silicon-substituted aluminum phosphate molecular sieve. Si in the catalyst is SiO 2 meter, Al to Al 2 O3 Count, P to P 2 O 5 Gauge, SiO 2 :Al 2 O 3 1:2, SiO 2 :P 2 O 5 is 1:2, and the average particle size of the catalyst is 0.5 μm.

[0028] The liquid hourly volume space velocity of L...

Embodiment 2

[0032] Preparation of silicon-substituted aluminum phosphate molecular sieve catalyst: mix phosphoric acid solution with deionized water, then add inorganic aluminum salt, white carbon black and tetraethylammonium hydroxide to the mixed solution in turn, stir evenly; heat the above mixed solution at 55°C Heating in a water bath for 5 hours, while continuing to stir, the obtained gel was poured into a PTFE-lined reaction kettle, and then put into a dynamic crystallization box for crystallization at a heating rate of 5 °C / h, and heated to 220 °C. ℃ constant temperature reaction for 55h, after crystallization is completed, cooling, washing, drying and roasting, to obtain silicon-substituted aluminum phosphate molecular sieve. Si in the catalyst is SiO 2 meter, Al to Al 2 O 3 Count, P to P 2 O 5 Gauge, SiO 2 :Al 2 O 3 1:2, SiO 2 :P 2 O 5 is 1:2.4, and the average particle size of the catalyst is 0.6 μm.

[0033] The liquid hourly volume space velocity of L-lactic acid r...

Embodiment 3

[0037] Preparation of silicon-substituted aluminum phosphate molecular sieve catalyst: mix phosphoric acid solution with deionized water, then add inorganic aluminum salt, white carbon black and tetraethylammonium hydroxide to the mixed solution in turn, stir evenly; heat the above mixed solution at 50°C Heating in a water bath for 4 hours while continuing to stir, the obtained gel was poured into a polytetrafluoroethylene-lined reaction kettle, and then put into a dynamic crystallization box for crystallization at a heating rate of 4.5 °C / h, and heated to 210 °C. ℃ constant temperature reaction 50h, after crystallization is completed, cooling, washing, drying and roasting, to obtain silicon-substituted aluminum phosphate molecular sieve. Si in the catalyst is SiO 2 meter, Al to Al 2 O 3 Count, P to P 2 O 5 Gauge, SiO 2 :Al 2 O 3 1:2.5, SiO 2 :P 2 O 5 is 1:2, and the average particle size of the catalyst is 0.7 μm.

[0038] The liquid hourly volume space velocity of...

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Abstract

The invention relates to a method for synthesizing lactide from L-lactic acid by using fixed bed reactors, which comprises the following steps: L-lactic acid is sequentially introduced into two fixed bed reactors connected in series, the two fixed bed reactors are filled with a silicon-substituted aluminophosphate molecular sieve catalyst, and nitrogen which continuously flows in and out is also introduced into the first fixed bed reactor; and sequentially carrying out an L-lactic acid condensation polymerization reaction and an L-lactic acid oligomer depolymerization reaction in two fixed bed reactors to obtain the crude L-lactide. According to the method, the reaction of synthesizing lactide from L-lactic acid is realized by adopting two fixed bed reactors connected in series, continuous reaction is realized, and the selected catalyst is high in carbon deposition resistance and adsorption performance, resistant to high temperature, stable in catalytic performance, not prone to coking to block a pipeline and long in service life; water molecules generated by polycondensation and evaporated L-lactic acid molecules are taken away in time by utilizing nitrogen flow, so that the polymerization degree of the L-lactic acid oligomer is improved, the content of free acid in the L-lactide is reduced, and the optical purity of the L-lactide is improved.

Description

technical field [0001] The invention relates to a method for synthesizing lactide from L-lactic acid, in particular to a method for synthesizing lactide from L-lactic acid by using a fixed bed reactor, and belongs to the technical field of material synthesis. Background technique [0002] With the continuous development of economy and society, people's production and life are more and more dependent on petrochemical energy, but at present, oil, coal and other difficult-to-renewable energy sources are in short supply, and the consumption of fossil energy also pollutes the environment very seriously. Materials are non-degradable, so it is necessary to find green resources that can replace oil to relieve the pressure of resource shortage. In recent years, the research on biodegradable materials has become a hot topic in academia and industrial production, aiming to reduce the harm of fossil energy consumption to the natural environment. As one of the biodegradable materials, p...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C07D319/12
CPCC07D319/12
Inventor 张雷孙启梅白富栋李澜鹏张通
Owner CHINA PETROLEUM & CHEM CORP
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