CN113527093A - System and method for preparing high-purity methyl lactate by direct esterification method - Google Patents
System and method for preparing high-purity methyl lactate by direct esterification method Download PDFInfo
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- ODQWQRRAPPTVAG-GZTJUZNOSA-N doxepin Chemical compound C1OC2=CC=CC=C2C(=C/CCN(C)C)/C2=CC=CC=C21 ODQWQRRAPPTVAG-GZTJUZNOSA-N 0.000 title claims abstract description 55
- LPEKGGXMPWTOCB-UHFFFAOYSA-N 8beta-(2,3-epoxy-2-methylbutyryloxy)-14-acetoxytithifolin Natural products COC(=O)C(C)O LPEKGGXMPWTOCB-UHFFFAOYSA-N 0.000 title claims abstract description 53
- 229940057867 methyl lactate Drugs 0.000 title claims abstract description 53
- 238000000034 method Methods 0.000 title claims abstract description 40
- 238000005886 esterification reaction Methods 0.000 title claims abstract description 30
- 230000032050 esterification Effects 0.000 title claims abstract description 20
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 claims abstract description 147
- JVTAAEKCZFNVCJ-UHFFFAOYSA-N lactic acid Chemical compound CC(O)C(O)=O JVTAAEKCZFNVCJ-UHFFFAOYSA-N 0.000 claims abstract description 103
- 239000004310 lactic acid Substances 0.000 claims abstract description 47
- 235000014655 lactic acid Nutrition 0.000 claims abstract description 47
- 239000000047 product Substances 0.000 claims abstract description 44
- 239000012043 crude product Substances 0.000 claims abstract description 35
- 238000011084 recovery Methods 0.000 claims abstract description 28
- 238000007670 refining Methods 0.000 claims abstract description 26
- 230000018044 dehydration Effects 0.000 claims abstract description 24
- 238000006297 dehydration reaction Methods 0.000 claims abstract description 24
- 238000002156 mixing Methods 0.000 claims abstract description 19
- 238000006386 neutralization reaction Methods 0.000 claims abstract description 18
- NWUYHJFMYQTDRP-UHFFFAOYSA-N 1,2-bis(ethenyl)benzene;1-ethenyl-2-ethylbenzene;styrene Chemical compound C=CC1=CC=CC=C1.CCC1=CC=CC=C1C=C.C=CC1=CC=CC=C1C=C NWUYHJFMYQTDRP-UHFFFAOYSA-N 0.000 claims abstract description 5
- 239000003456 ion exchange resin Substances 0.000 claims abstract description 5
- 229920003303 ion-exchange polymer Polymers 0.000 claims abstract description 5
- 238000000746 purification Methods 0.000 claims abstract description 5
- 238000010992 reflux Methods 0.000 claims description 31
- 239000000463 material Substances 0.000 claims description 24
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 17
- 238000000605 extraction Methods 0.000 claims description 15
- 239000012535 impurity Substances 0.000 claims description 14
- 238000005086 pumping Methods 0.000 claims description 10
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims description 9
- 239000000203 mixture Substances 0.000 claims description 8
- 239000002994 raw material Substances 0.000 claims description 8
- 230000002378 acidificating effect Effects 0.000 claims description 4
- 238000004821 distillation Methods 0.000 claims description 4
- 239000007787 solid Substances 0.000 claims description 4
- 238000002360 preparation method Methods 0.000 claims description 3
- 239000003513 alkali Substances 0.000 claims description 2
- 239000007809 chemical reaction catalyst Substances 0.000 claims description 2
- 239000007788 liquid Substances 0.000 claims description 2
- 230000003472 neutralizing effect Effects 0.000 claims description 2
- 238000003756 stirring Methods 0.000 claims description 2
- 230000015572 biosynthetic process Effects 0.000 abstract description 5
- 239000003054 catalyst Substances 0.000 abstract description 5
- 238000003786 synthesis reaction Methods 0.000 abstract description 5
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 abstract description 4
- 238000005516 engineering process Methods 0.000 abstract description 3
- JVTAAEKCZFNVCJ-UHFFFAOYSA-M Lactate Chemical compound CC(O)C([O-])=O JVTAAEKCZFNVCJ-UHFFFAOYSA-M 0.000 abstract 1
- 238000006243 chemical reaction Methods 0.000 description 6
- 230000000630 rising effect Effects 0.000 description 5
- 239000002904 solvent Substances 0.000 description 4
- 239000012459 cleaning agent Substances 0.000 description 3
- 230000003287 optical effect Effects 0.000 description 3
- 238000004140 cleaning Methods 0.000 description 2
- JJTUDXZGHPGLLC-UHFFFAOYSA-N lactide Chemical compound CC1OC(=O)C(C)OC1=O JJTUDXZGHPGLLC-UHFFFAOYSA-N 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 238000006068 polycondensation reaction Methods 0.000 description 2
- 238000007639 printing Methods 0.000 description 2
- 239000000376 reactant Substances 0.000 description 2
- 238000005299 abrasion Methods 0.000 description 1
- 239000002585 base Substances 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000006065 biodegradation reaction Methods 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 238000010924 continuous production Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000004973 liquid crystal related substance Substances 0.000 description 1
- 230000014759 maintenance of location Effects 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 231100000989 no adverse effect Toxicity 0.000 description 1
- 231100000252 nontoxic Toxicity 0.000 description 1
- 230000003000 nontoxic effect Effects 0.000 description 1
- 231100000956 nontoxicity Toxicity 0.000 description 1
- 238000006116 polymerization reaction Methods 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C67/00—Preparation of carboxylic acid esters
- C07C67/08—Preparation of carboxylic acid esters by reacting carboxylic acids or symmetrical anhydrides with the hydroxy or O-metal group of organic compounds
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
- C07C51/42—Separation; Purification; Stabilisation; Use of additives
- C07C51/43—Separation; Purification; Stabilisation; Use of additives by change of the physical state, e.g. crystallisation
- C07C51/44—Separation; Purification; Stabilisation; Use of additives by change of the physical state, e.g. crystallisation by distillation
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C67/00—Preparation of carboxylic acid esters
- C07C67/48—Separation; Purification; Stabilisation; Use of additives
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C67/00—Preparation of carboxylic acid esters
- C07C67/48—Separation; Purification; Stabilisation; Use of additives
- C07C67/52—Separation; Purification; Stabilisation; Use of additives by change in the physical state, e.g. crystallisation
- C07C67/54—Separation; Purification; Stabilisation; Use of additives by change in the physical state, e.g. crystallisation by distillation
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C67/00—Preparation of carboxylic acid esters
- C07C67/48—Separation; Purification; Stabilisation; Use of additives
- C07C67/60—Separation; Purification; Stabilisation; Use of additives by treatment giving rise to chemical modification
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Abstract
The invention belongs to the technical field of methyl lactate, and particularly relates to a system and a method for preparing high-purity methyl lactate by a direct esterification method. The system comprises a lactic acid pretreatment tower, a mixing tank, a fixed bed reactor, a neutralization tank, a methanol recovery tower, a dehydration tower, a crude product tower and a product refining tower which are sequentially connected in series; the specific working steps of the system comprise the steps of dehydration, esterification, neutralization and purification, wherein the esterification reaction process is realized by using a fixed bed technology, and the esterification step adopts the catalyst of ion exchange resin HND-8, so that compared with the traditional sulfuric acid catalyst, the system is friendly to equipment and is not easy to corrode. Therefore, the continuous synthesis process directly prepares the methyl lactate product with the purity of over 99.95 percent, and compared with the prior method for preparing the lactate product by an intermittent process and a two-step method, the continuous synthesis process has the advantages of simple process flow, easy operation, higher purity of the obtained product and higher market value.
Description
Technical Field
The invention belongs to the technical field of methyl lactate, and particularly relates to a system and a method for preparing high-purity methyl lactate by a direct esterification method.
Background
Methyl lactate is a biodegradable and non-toxic solvent, and has the capacity of replacing some traditional solvents. Methyl lactate as a cleaning agent has the advantages of low loss, good economy, no adverse effect on cleaned objects, no toxicity, easy biodegradation and the like, is a novel substitute cleaning agent of an ODS solvent type cleaning agent, and is widely applied to the electronic industry. The methyl lactate can be used for cleaning various optical disks, liquid crystal displays, magnetic heads, chips, circuit board bases and modules, can also be used for cleaning optical lenses, printing screens, printing ink and metals, and is a 'green solvent' with development value and application prospect.
The methyl lactate synthesis process in the market is characterized in that methyl lactate is synthesized by esterification of methanol and lactic acid in an intermittent reaction kettle, and methyl lactate with higher purity (the purity is more than 99%) is obtained through a series of rectification operations.
Chinese patent CN101914022 discloses a two-step method for producing methyl lactate with high content and high optical purity, wherein lactic acid is first depolymerized by polycondensation to obtain lactide, and then the lactide and anhydrous methanol are subjected to total reflux reaction to obtain methyl lactate. The content of methyl lactate obtained by the method is more than 99.5 percent. In the process, lactic acid is subjected to polycondensation in advance and then is depolymerized, so that the process flow is complex. In view of this, there is a need for a simple and direct process for the synthesis of methyl lactate.
Disclosure of Invention
The invention aims to provide a system and a method for preparing high-purity methyl lactate by a direct esterification method aiming at the problems of complex process and low product purity of a production process of methyl lactate in the prior art.
In order to achieve the purpose, the invention provides the following technical scheme:
a system for preparing high-purity methyl lactate by a direct esterification method comprises a lactic acid pretreatment tower 11, a mixing tank 21, a fixed bed reactor 71, a neutralization tank 22, a methanol recovery tower 12, a dehydration tower 13, a crude product tower 14 and a product refining tower 15 which are sequentially connected in series;
the bottom outlet of the lactic acid pretreatment tower 11 is communicated with the lower inlet of a mixing tank 21 through a first pump 32, the outlet of the mixing tank 21 is communicated with the bottom inlet of a fixed bed reactor 71 through a second pump 33 and a preheater 51 in sequence, the top outlet of the fixed bed reactor 71 is communicated with the lower inlet of a neutralization tank 22 through a third pump 34, the middle outlet of the neutralization tank 22 is communicated with the middle inlet of a methanol recovery tower 12 through a pipeline, the bottom outlet of the methanol recovery tower 12 is communicated with the middle inlet of a dehydration tower 13 through a fourth pump 35, and the bottom outlet of the dehydration tower 13 is communicated with the middle inlet of a crude product tower 14 through a fifth pump 36;
the lower parts and the bottoms of the lactic acid pretreatment tower 11, the methanol recovery tower 12, the dehydration tower 13, the crude product tower 14 and the product refining tower 15 are respectively communicated through pipelines of a tower kettle reboiler 52, so that a lower reflux loop is formed between the bottoms and the lower parts;
the upper parts and the tops of the lactic acid pretreatment tower 11, the methanol recovery tower 12, the dehydration tower 13, the crude product tower 14 and the product refining tower 15 are respectively communicated through pipelines of a condenser 53, a reflux tank 23 and a reflux pump 31, so that an upper reflux loop is formed between the upper parts and the tops, and each upper reflux loop is connected with an upper extraction pipeline;
an upper extraction pipeline of the crude product tower 14 is communicated with an upper inlet of a product refining tower 15, an upper extraction pipeline of the methanol recovery tower 12 is communicated with a fresh methanol inlet, and the fresh methanol inlet is communicated with an upper inlet of a mixing tank 21 through a pipeline;
the bottom tower kettle of the crude product tower 14 is communicated with a lower extraction pipeline through a sixth pump 37, and the bottom tower kettle of the product refining tower 15 is communicated with a lower extraction pipeline through a seventh pump 38, so that heavy impurities are extracted; a product extraction pipeline is communicated with a side line of the product refining tower 15;
when the system works, the lactic acid pretreatment tower 11 is communicated with a raw material lactic acid inlet, the raw material lactic acid is rectified by the lactic acid pretreatment tower 11 firstly, then is mixed with fresh methanol, is neutralized by the neutralization tank 22 and solid alkali, and finally is purified by the methanol recovery tower 12, the dehydration tower 13, the crude product tower 14 and the product refining tower 15, so that the content of the obtained product methyl lactate is more than 99.95 percent.
The invention also discloses a preparation method of the system for preparing high-purity methyl lactate by the direct esterification method, which comprises the following steps:
step (1): dewatering
Introducing 15-18% of the water content of raw material lactic acid into the lactic acid pretreatment tower 11, carrying out reduced pressure distillation on the lactic acid to obtain dehydrated lactic acid with the water content of 1-3%, and extracting the dehydrated water through an overhead extraction pipeline of the lactic acid pretreatment tower 11; the number of theoretical plates of the lactic acid pretreatment tower 11 is 15-30, the working pressure is 3-8 kPa, and the temperature is 100-120 ℃.
Step (2): esterification
Introducing fresh methanol into the mixing tank 21, pumping the dehydrated lactic acid into the mixing tank 21, fully mixing the dehydrated lactic acid and the methanol to obtain a mixture, wherein the molar ratio of the methanol to the dehydrated lactic acid is 2-8,
preheating the mixture to 40-70 ℃ through a preheater 51, pumping the mixture into the fixed bed reactor 71 for esterification reaction, wherein the esterification reaction temperature is 40-70 ℃, the esterification reaction residence time is 15-60 min, and the esterification reaction catalyst is acidic ion exchange resin; and obtaining a crude product of methyl lactate, wherein the content of methyl lactate is 30-40%.
And (3): neutralization
Pumping the methyl lactate crude product into a neutralization tank 22, introducing sodium hydroxide solid into the neutralization tank 22, fully stirring, neutralizing lactic acid in the methyl lactate crude product, and adjusting the pH value to 7-8.
And (4): purification of
Introducing the neutralized material into a methanol recovery tower 12, carrying out reduced pressure distillation on the neutralized material,
and (3) methanol extracted from the tower top enters a mixing tank 21 through a methanol recovery pipeline, wherein the number of theoretical plates of the methanol recovery tower 12 is 15-30, and the tower pressure is 25-35 kPa.
The material in the tower kettle of the methanol recovery tower 12 is sent to a dehydrating tower 13 by a fourth pump 35 for dehydration, the water content of the dehydrated kettle liquid is 1-2%, and water is extracted from the tower top; the number of theoretical plates of the dehydration tower 13 is 15-30, and the tower pressure is 3-7 kPa;
pumping dehydrated methyl lactate from the tower kettle of the dehydrating tower 13 into a crude product tower 14 for continuous purification, extracting a crude methyl lactate product from the tower top, extracting heavy impurities from the tower kettle, wherein the theoretical plate number of the crude product tower 14 is 45-60, and the tower pressure is 3-7 kPa;
pumping a methyl lactate crude product extracted from the top of the crude product tower 14 into a product refining tower 15, extracting a product methyl lactate from a side line, extracting light impurities from the top of the tower, and extracting heavy impurities from a tower kettle; the number of theoretical plates of a product refining tower 15 is 45-60, the tower pressure is 3-7 kPa, and the content of the methyl lactate product is over 99.95 percent.
Further, the reflux ratio of the lactic acid pretreatment tower 11, the methanol recovery tower 12 and the dehydration tower 13 is 0.1-1, the reflux ratio of the crude product tower 14 is 1-10, the reflux ratio of the product refining tower 15 is 5-30, and the reflux temperature is 5-20 ℃.
The invention has the following beneficial technical effects:
the core technology of the system and the method for preparing high-purity methyl lactate by the direct esterification method is a continuous synthesis process. The purity of the methyl lactate product obtained by the device after operation is up to more than 99.95 percent, and the device also has the following advantages:
1. compared with a kettle type reactor, the fixed bed reactor adopted by the invention has the advantages of simple operation, small reactor, high single-pass conversion rate of lactic acid which can reach more than 90 percent and the like, and realizes the continuous production of the methyl lactate.
2. The method for preparing high-purity methyl lactate by the direct esterification method adopts the vacuum rectification method to carry out dehydration pretreatment on the lactic acid, not only improves the one-way conversion rate of the lactic acid in the esterification process, but also adopts H in the prior patent2SO4Compared with the dehydration technology, the polymerization degree of the lactic acid is lower, and the utilization rate of the lactic acid is high.
3. According to the method for preparing high-purity methyl lactate by the direct esterification method, the adopted catalyst is acidic ion exchange resin, and compared with the traditional sulfuric acid catalyst, the method is friendly to equipment and is not easy to corrode; and the acidic ion exchange resin is filled in the fixed bed reactor, so that the abrasion is not easy to occur, and the service life of the catalyst is long.
Drawings
FIG. 1 is a schematic diagram of the system of the present invention.
Wherein: 11 lactic acid pretreatment tower, 12 methanol recovery tower, 13 dehydration tower, 14 crude product tower, 15 product refining tower, 23 reflux tank, 21 mixing tank, 22 neutralization tank, 31 reflux pump, 32 first pump, 33 second pump, 34 third pump, 35 fourth pump, 36 fifth pump, 37 sixth pump, 38 seventh pump, 53 condenser, 52 tower kettle reboiler, 51 preheater and 71 fixed bed reactor.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the detailed description and specific examples, while indicating the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
Example 1
Referring to FIG. 1, the lactic acid content of the raw material from the tank field is 72.03%, the water content is 17.07%, the raw material is fed into a lactic acid pretreatment tower 11 for vacuum rectification, the total number of plates of the lactic acid pretreatment tower 11 is 20, the tower pressure is set to 5kPa, the reflux ratio is 0.5, and the temperature of the tower bottom is set to 110 ℃. The steam rising from the tower top is condensed by a condenser 51 and enters a reflux tank 23, one part of the material flows back to the tower, the other part of the material is extracted, the content of the treated lactic acid is increased to 85.12 percent, and the water content is reduced to 2.00 percent.
The materials extracted from the tower bottom are pumped into a reactant mixing tank 21 through a first pump 32 to be mixed with methanol, the molar ratio of the methanol to dehydrated lactic acid is 4:1, the mixture enters a fixed bed reactor 71 to undergo esterification reaction after being preheated to 65 ℃ by a preheater 51, and the esterification retention time is set as 27.5 min. The esterified methyl lactate product is generated, the content of methyl lactate is 38.45 percent, the content of water is 7.56 percent, the content of methanol is 42.92 percent, the content of lactic acid is 5.24 percent, the material flow after reaction is sent into a neutralization tank 22 to be neutralized with sodium hydroxide to remove the unreacted lactic acid, and the pH value is 7.16.
The neutralized material flow enters a methanol recovery tower 12, the total number of the tower plates of the methanol recovery tower 12 is 20, the tower pressure is set to be 30kPa, and the reflux ratio is 0.5. The steam rising from the tower top is condensed by a condenser 54 and enters a reflux tank 24, one part of the material flows back into the tower, the other part of the material is extracted and circulated to a reactant mixing tank 21 to participate in the reaction, and the content of methyl lactate, water, methanol and lactic acid in the material at the tower bottom is 67.36%, 12.58%, 0.70% and 0.00%.
The tower bottom material flow enters a dehydrating tower 13, the total number of tower plates of the dehydrating tower 13 is 20, the tower pressure is set to be 5kPa, and the reflux ratio is 0.5. The steam rising from the tower top is condensed by a condenser 56 and enters a reflux tank 25, one part of the material flows back to the tower, the other part is extracted, and the content of methyl lactate, the content of water, the content of methanol and the content of heavy impurities in the material in the tower bottom are 76.07 percent, 1.58 percent and 0.00 percent respectively.
The material extracted from the tower bottom enters a crude product tower 14, the total number of tower plates of the crude product tower 14 is 50, the tower pressure is set to be 5kPa, and the reflux ratio is 5. The steam rising from the tower top is condensed by a condenser 58 and enters a reflux tank 26, one part of the material flows back into the tower, the other part of the material is extracted and enters a product refining tower 15, and heavy impurities are extracted from the tower bottom. The material fed into the product refining tower 15 contains methyl lactate 97.96%, water 2.04% and heavy impurities 0.00%.
The material flow extracted from the top of the crude product tower 14 is further purified in a product refining tower 15, the total number of tower plates of the product refining tower 15 is 50, the tower pressure is set to be 5kPa, and the reflux ratio is 8. The product is extracted from the side line, similarly, the steam rising from the top of the tower is condensed by a condenser 60 and enters a reflux tank 27, one part of the material flows back into the tower, the other part of the material is extracted from light impurities, and the heavy impurities are extracted from the bottom of the tower. The content of methyl lactate in the obtained product is 99.98%, the content of water is 0.02%, and the content of heavy impurities is 0.00%.
Useful comparative tables for the method of the invention.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (3)
1. A system for preparing high-purity methyl lactate by a direct esterification method is characterized in that:
comprises a lactic acid pretreatment tower (11), a mixing tank (21), a fixed bed reactor (71), a neutralization tank (22), a methanol recovery tower (12), a dehydration tower (13), a crude product tower (14) and a product refining tower (15) which are connected in series in sequence;
the bottom outlet of the lactic acid pretreatment tower (11) is communicated with the lower inlet of a mixing tank (21) through a first pump (32), the outlet of the mixing tank (21) is communicated with the bottom inlet of a fixed bed reactor (71) through a second pump (33) and a preheater (51) in sequence, the top outlet of the fixed bed reactor (71) is communicated with the lower inlet of a neutralization tank (22) through a third pump (34), the middle outlet of the neutralization tank (22) is communicated with the middle inlet of a methanol recovery tower (12) through a pipeline, the bottom outlet of the methanol recovery tower (12) is communicated with the middle inlet of a dehydration tower (13) through a fourth pump (35), and the bottom outlet of the dehydration tower (13) is communicated with the middle inlet of a crude product tower (14) through a fifth pump (36);
the lower parts and the bottoms of the lactic acid pretreatment tower (11), the methanol recovery tower (12), the dehydration tower (13), the crude product tower (14) and the product refining tower (15) are communicated through pipelines of a tower kettle reboiler (52), so that a lower reflux loop is formed between the bottom and the lower part;
the upper parts and the tops of the lactic acid pretreatment tower (11), the methanol recovery tower (12), the dehydration tower (13), the crude product tower (14) and the product refining tower (15) are communicated through a condenser (53), a reflux tank (23) and a reflux pump (31) by pipelines, so that an upper reflux loop is formed between the upper part and the top, and each upper reflux loop is connected with an upper extraction pipeline;
an upper extraction pipeline of the crude product tower (14) is communicated with an upper inlet of a product refining tower (15), an upper extraction pipeline of the methanol recovery tower (12) is communicated with a fresh methanol inlet, and the fresh methanol inlet is communicated with an upper inlet of a mixing tank (21) through a pipeline;
the bottom tower kettle of the crude product tower (14) is communicated with a lower extraction pipeline through a sixth pump (37), and the bottom tower kettle of the product refining tower (15) is communicated with a lower extraction pipeline through a seventh pump (38), so that heavy impurities are extracted; a product extraction pipeline is communicated with the side line of the product refining tower (15);
when the system works, the lactic acid pretreatment tower (11) is communicated with a raw material lactic acid inlet, the raw material lactic acid is rectified by the lactic acid pretreatment tower (11), then is mixed with fresh methanol, is neutralized by a neutralization tank (22) and solid alkali, and finally is purified by a methanol recovery tower (12), a dehydration tower (13), a crude product tower (14) and a product refining tower (15), so that the content of the obtained product methyl lactate is more than 99.95 percent.
2. The preparation method of the system for preparing the high-purity methyl lactate by the direct esterification method according to claim 1, which is characterized by comprising the following steps: the method comprises the following steps:
step (1): dewatering
Introducing raw material lactic acid (with the water content of 15-18%) into a lactic acid pretreatment tower (11), carrying out reduced pressure distillation on the lactic acid to obtain dehydrated lactic acid (with the water content of 1-3%), and extracting the dehydrated water through a tower top extraction pipeline extraction system of the lactic acid pretreatment tower (11); the number of theoretical plates of the lactic acid pretreatment tower (11) is 15-30, the working pressure is 3-8 kPa, and the temperature is 100-120 ℃;
step (2): esterification
Introducing fresh methanol into the mixing tank (21), pumping the dehydrated lactic acid into the mixing tank (21) to fully mix the dehydrated lactic acid and the methanol to obtain a mixture, wherein the molar ratio of the methanol to the dehydrated lactic acid is 2-8,
preheating the mixture to 40-70 ℃ through a preheater (51), pumping the mixture into the fixed bed reactor (71) for esterification reaction, wherein the esterification reaction temperature is 40-70 ℃, the esterification reaction residence time is 15-60 min, and the esterification reaction catalyst is acidic ion exchange resin; obtaining a crude product of methyl lactate, wherein the content of methyl lactate is 30-40%;
neutralization in step (3)
Pumping the methyl lactate crude product into a neutralization tank (22), introducing sodium hydroxide solid into the neutralization tank (22), fully stirring, neutralizing lactic acid in the methyl lactate crude product, and adjusting the pH to 7-8;
and (3): purification of
Introducing the neutralized material into a methanol recovery tower (12), carrying out reduced pressure distillation on the neutralized material,
methanol extracted from the tower top enters a mixing tank (21) through a methanol recovery pipeline, the number of theoretical plates of the methanol recovery tower (12) is 15-30, and the tower pressure is 25-35 kPa;
the material in the bottom of the methanol recovery tower (12) is sent to a dehydrating tower (13) by a fourth pump (35) for dehydration, the water content of the bottom liquid after dehydration is 1-2%, and water is extracted from the top of the tower; the number of theoretical plates of the dehydration tower (13) is 15-30, and the tower pressure is 3-7 kPa;
pumping dehydrated methyl lactate from the tower kettle of the dehydrating tower (13) into a crude product tower (14) for continuous purification, extracting a crude methyl lactate product from the tower top, extracting heavy impurities from the tower kettle, wherein the theoretical plate number of the crude product tower (14) is 45-60, and the tower pressure is 3-7 kPa;
pumping a methyl lactate crude product extracted from the top of the crude product tower (14) into a product refining tower (15), extracting a product methyl lactate from a side line, extracting light impurities from the top of the tower, and extracting heavy impurities from a tower kettle; the number of theoretical plates of the product refining tower (15) is 45-60, the tower pressure is 3-7 kPa, and the content of the methyl lactate product is more than 99.95%.
3. The preparation method of the system for preparing the high-purity methyl lactate by the direct esterification method according to claim 2, which is characterized by comprising the following steps: the reflux ratio of the lactic acid pretreatment tower (11), the methanol recovery tower (12) and the dehydration tower (13) is 0.1-1, the reflux ratio of the crude product tower (14) is 1-10, the reflux ratio of the product refining tower (15) is 5-30, and the reflux temperature is 5-20 ℃.
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| CN202110804978.3A CN113527093A (en) | 2021-07-16 | 2021-07-16 | System and method for preparing high-purity methyl lactate by direct esterification method |
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| JPS58189138A (en) * | 1982-04-21 | 1983-11-04 | エス・カ−・ヴエ−・トロ−ストベルク・アクチエンゲゼルシヤフト | Continuous purification of methyl lactate ester |
| WO2010012606A1 (en) * | 2008-07-30 | 2010-02-04 | Galactic Sa | Continuous process for obtaining a lactic ester |
| CN102381973A (en) * | 2011-09-19 | 2012-03-21 | 南京大学 | Production process of ultra-high purity (electronic grade) lactate product |
| CN102659578A (en) * | 2012-04-28 | 2012-09-12 | 孝感市易生新材料有限公司 | Method for synthesizing lactate through microwave irradiation |
| WO2013159347A1 (en) * | 2012-04-27 | 2013-10-31 | 孝感市易生新材料有限公司 | Method for continuously producing high-content high-optical-purity lactate |
| CN107033000A (en) * | 2016-02-03 | 2017-08-11 | 天津中福工程技术有限公司 | A kind of continuous liquid of fixed bed method that catalysis prepares lactate admittedly |
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| JPS58189138A (en) * | 1982-04-21 | 1983-11-04 | エス・カ−・ヴエ−・トロ−ストベルク・アクチエンゲゼルシヤフト | Continuous purification of methyl lactate ester |
| WO2010012606A1 (en) * | 2008-07-30 | 2010-02-04 | Galactic Sa | Continuous process for obtaining a lactic ester |
| CN102105430A (en) * | 2008-07-30 | 2011-06-22 | 银河股份公司 | Continuous process for obtaining a lactic ester |
| CN102381973A (en) * | 2011-09-19 | 2012-03-21 | 南京大学 | Production process of ultra-high purity (electronic grade) lactate product |
| WO2013159347A1 (en) * | 2012-04-27 | 2013-10-31 | 孝感市易生新材料有限公司 | Method for continuously producing high-content high-optical-purity lactate |
| CN102659578A (en) * | 2012-04-28 | 2012-09-12 | 孝感市易生新材料有限公司 | Method for synthesizing lactate through microwave irradiation |
| CN107033000A (en) * | 2016-02-03 | 2017-08-11 | 天津中福工程技术有限公司 | A kind of continuous liquid of fixed bed method that catalysis prepares lactate admittedly |
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