CN112521264A - Method and device for recovering lactic acid from polylactic acid synthetic substrate - Google Patents
Method and device for recovering lactic acid from polylactic acid synthetic substrate Download PDFInfo
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- C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
- C07C51/09—Preparation of carboxylic acids or their salts, halides or anhydrides from carboxylic acid esters or lactones
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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
- C07C67/08—Preparation of carboxylic acid esters by reacting carboxylic acids or symmetrical anhydrides with the hydroxy or O-metal group of organic compounds
Abstract
The invention belongs to the technical field of polylactic acid production, and particularly discloses a method for recovering lactic acid from a polylactic acid synthetic substrate, and also relates to a recovery device. Aiming at the problems that synthetic substrate components formed in the synthesis of polylactic acid are complex and have high viscosity, and valuable components such as lactic acid and the like in the synthetic substrate cannot be recovered by a direct distillation method, the synthetic substrate of the polylactic acid is firstly subjected to esterification reaction with alcohol, lactic acid-containing components in the synthetic substrate of the polylactic acid are converted into lactate, then the lactate is extracted from an esterified product, and then the lactate is hydrolyzed to obtain a lactic acid product, so that the aim of recovering the lactic acid from the synthetic substrate of the polylactic acid is fulfilled.
Description
Technical Field
The invention relates to the technical field of polylactic acid production, in particular to a method for resource recovery of a substrate generated by polylactic acid synthesis, specifically to a method for recovering lactic acid from a substrate generated by polylactic acid synthesis, and also relates to a recovery device.
Background
Polylactic acid (PLA) is a high molecular polymer obtained by polymerizing lactic acid, has the characteristics of environmental protection, no toxicity, bacteria resistance, flame retardance, good biocompatibility, biodegradability and the like, and is considered as a new material which has the greatest prospect of impacting the traditional status of petroleum-based plastics and chemical fibers in the future. However, compared with the traditional petroleum-based polymer material, the polylactic acid is expensive and has no price advantage in the market competition process. The production cost of the polylactic acid is reduced, the polylactic acid breaks through the price barrier and is more widely applied to the product market, which is an important problem to be solved in the polylactic acid industry at present.
In the production process of polylactic acid, some synthetic substrates containing lactic acid components are inevitably produced, and the substrates are dark in color and high in viscosity, and valuable components such as lactic acid cannot be recovered by a direct distillation method. A method for efficiently recovering a lactic acid component from a substrate for polylactic acid synthesis has not been disclosed. For the production of polylactic acid, how to effectively treat substrates generated in the production process of the polylactic acid is very important for reducing the cost of the polylactic acid.
In order to improve the utilization rate of raw materials in the synthetic process of polylactic acid, improve the comprehensive yield of the synthetic polylactic acid and effectively reduce the synthetic cost of the polylactic acid, the problem of recycling of substrates generated in the synthetic process of the polylactic acid needs to be researched, and an effective recycling method is provided.
Disclosure of Invention
The invention mainly solves the technical problem of providing a method for recovering lactic acid from a polylactic acid synthetic substrate, which can recover and obtain high-purity lactic acid from the polylactic acid synthetic substrate for utilization.
The invention also provides a device for recovering lactic acid from the polylactic acid synthetic substrate.
In order to solve the above technical problems, in a first aspect, the present invention provides a method for recovering lactic acid from a substrate for polylactic acid synthesis, comprising the steps of:
carrying out esterification reaction on a polylactic acid synthetic substrate and alcohol, and converting lactic acid-containing components in the polylactic acid synthetic substrate into lactate; and the number of the first and second groups,
and extracting lactate from the esterified product, and hydrolyzing the extracted lactate to obtain a lactic acid product.
As a preferred embodiment of the present invention, the method for recovering lactic acid further comprises the steps of:
hydrolyzing the lactate to obtain an alcohol-containing aqueous solution, and purifying the alcohol-containing aqueous solution to obtain an alcohol product.
As a preferred embodiment of the invention, the alcohol is a lower alcohol, preferably methanol and/or ethanol.
Preferably, the mass ratio of the polylactic acid synthetic substrate to the alcohol is as follows: the substrate for polylactic acid synthesis is 100 (200-300) of alcohol.
In a preferred embodiment of the present invention, a catalyst is used during the esterification reaction, and the catalyst is an acidic catalyst, preferably sulfuric acid, hydrochloric acid, nitric acid and/or an organic sulfonic acid.
Preferably, the mass ratio of the polylactic acid synthetic substrate to the catalyst is as follows: and (3) a polylactic acid synthesis substrate, namely a catalyst of 100 (0.5-2).
In a preferred embodiment of the present invention, the temperature of the esterification reaction is 100 to 140 ℃. The pressure of the esterification reaction is 0.3-0.8 Mpa.
In a preferred embodiment of the invention, the extraction of lactate from the esterified product is performed in a lactate purification tower, wherein the temperature of the top of the purification tower is 50-80 ℃, and the temperature of the bottom of the purification tower is 150-220 ℃. The pressure in the purification tower is 1-3 KPa.
In a preferred embodiment of the present invention, the lactate hydrolysis is performed in a hydrolysis tower, wherein the top temperature of the hydrolysis tower is 110 to 150 ℃, and the bottom temperature of the hydrolysis tower is 150 to 190 ℃. The pressure in the hydrolysis tower is 0.3-0.8 MPa.
In a preferred embodiment of the present invention, the alcohol-containing aqueous solution is purified in an alcohol recovery tower, wherein the temperature of the top of the alcohol recovery tower is 40 to 60 ℃, and the temperature of the bottom of the alcohol recovery tower is 60 to 80 ℃. The pressure in the alcohol recovery tower is 10-30 KPa.
The synthetic substrate formed in the synthesis of polylactic acid has complex components, dark color and high viscosity, and the main components of the synthetic substrate comprise lactic acid oligomer, lactide, lactic acid, glucose, sorbitol, water, inorganic salt and the like. The invention provides an effective recovery method aiming at the problem that valuable components such as lactic acid and the like in a synthetic substrate containing lactic acid components generated in the production of polylactic acid cannot be recovered by a direct distillation method due to the dark color and high viscosity of the substrate.
The method comprises the steps of firstly carrying out esterification reaction on a polylactic acid synthetic substrate and alcohol, converting lactic acid-containing components (such as lactic acid, lactic acid oligomer, lactide and the like) in the polylactic acid synthetic substrate into lactate, then extracting the lactate from the esterified product, and then hydrolyzing the lactate to obtain a lactic acid product, thereby achieving the purpose of recovering the lactic acid from the polylactic acid synthetic substrate.
Specifically, after a lactic acid-containing component in a synthetic substrate is converted into lactate, by utilizing the characteristic that the boiling point of the lactate is lower than that of other components (such as incompletely esterified lactic acid oligomer, sorbitol, inorganic salt and the like) in the lactate-containing substrate, a heavy phase, a light phase and a lactate product can be respectively obtained through rectification, purification and separation in a lactate purification tower, wherein the heavy phase is discharged from a reboiler, the light phase (mainly excessive ethanol added during esterification) is discharged from the top of the tower, and the lactate product is discharged from the middle of the purification tower, so that the purification and separation of the lactate are realized.
The lactic acid recovered by the method can be used as a raw material to be reused for synthesizing the polylactic acid, so that the utilization rate of the lactic acid is improved, and the production cost of the polylactic acid is effectively reduced. The purity of the lactic acid recovered by the method is more than 85 percent, and the lactic acid meets the feed-grade lactic acid standard (GB/T22142-2008).
The water of lactate ester is released to obtain a lactic acid product, and an aqueous solution containing alcohol is also generated. The obtained alcohol-containing aqueous solution is separated by an alcohol recovery tower to obtain alcohol, and the obtained alcohol product can be sold as a product and also can be returned to carry out esterification reaction with a polylactic acid synthetic substrate so as to be recycled.
By adopting the recovery method, the closed circulation of resources can be realized, and the production cost is effectively reduced.
In a second aspect, the invention also provides a device for recovering lactic acid from a polylactic acid synthetic substrate, which comprises an esterification reaction kettle, a lactate purification tower and a hydrolysis tower which are connected in sequence, wherein a feed inlet of the esterification reaction kettle is provided with a material mixer, the bottoms of the lactate purification tower and the hydrolysis tower are both provided with reboilers, a liquid phase outlet of the reboiler of the lactate purification tower is connected with a residual liquid tank, and a liquid phase outlet of the reboiler of the hydrolysis tower is connected with a lactic acid product tank.
As a preferred embodiment of the present invention, a lactate buffer tank is provided between the lactate purification column and the hydrolysis column for stable operation of the lactate purification column and the hydrolysis column.
Further, a condenser is arranged between the lactate buffer tank and the lactate purification tower. And condensing the gas-phase lactate from the top of the lactate purification tower by a condenser and then feeding the gas-phase lactate into a lactate cache tank.
In a preferred embodiment of the present invention, an alcohol recovery tower is further disposed after the hydrolysis tower to treat the alcohol-containing aqueous solution obtained by hydrolysis, a reboiler is disposed at the bottom of the alcohol recovery tower, a liquid phase outlet of the reboiler of the alcohol recovery tower is connected to the wastewater tank, and a top of the alcohol recovery tower is connected to the alcohol product tank through a condenser. And condensing the alcohol from the top of the alcohol recovery tower through a condenser and then feeding the alcohol into an alcohol product tank.
Preferably, for stable operation of the hydrolysis tower and the alcohol recovery tower, an aqueous alcohol buffer tank is provided between the hydrolysis tower and the alcohol recovery tower.
Further, a condenser is arranged between the water-containing alcohol buffer tank and the hydrolysis tower.
The aqueous alcohol buffer tank is also connected with the top of the lactate purification tower through a pipeline. The light phase (mainly the excessive ethanol added during esterification) from the top of the lactate purification tower is condensed and then enters a water-containing alcohol buffer tank, and then enters an alcohol recovery tower for treatment.
By adopting the device, the lactic acid product can be stably and safely separated from the polylactic acid synthetic substrate, and the recycling of alcohol is realized. The device has the advantages of safety, stable operation and easy operation and control.
The method for recovering lactic acid from the polylactic acid synthetic substrate makes up the technical blank that the lactic acid-containing substrate generated in the production process of the polylactic acid cannot effectively recover the lactic acid component in the substrate. According to the invention, lactic acid is recovered from a polylactic acid synthetic substrate, and through three steps of esterification, hydrolysis and alcohol recovery, the lactic acid-containing component in the lactic acid-containing substrate generated in the polylactic acid synthetic process can be effectively recovered, the comprehensive utilization rate of raw material lactic acid in the polylactic acid synthesis is improved, and the raw material cost of the polylactic acid synthesis is reduced. The method of the invention does not use toxic and harmful substances in the production process and does not relate to dangerous processes. Alcohols in the recovery process are treated by the alcohol recovery device, so that the utilization rate of alcohol substances is improved, and the running cost in the production process is reduced.
Drawings
FIG. 1 is a schematic diagram showing the connection relationship of an apparatus for recovering lactic acid from a substrate for polylactic acid synthesis according to the present invention.
Detailed Description
The technical solution of the present invention will be described in detail by specific examples.
The invention provides a method for recovering lactic acid from a polylactic acid synthetic substrate, which comprises the following steps:
carrying out esterification reaction on a polylactic acid synthetic substrate and alcohol, and converting lactic acid-containing components in the polylactic acid synthetic substrate into lactate; and the number of the first and second groups,
and extracting lactate from the esterified product, and hydrolyzing the extracted lactate to obtain a lactic acid product.
The involved reactions include:
-[-OCH(CH3)COO-]n-+n R-OH→n CH3CH(OH)COOR
CH3CH(OH)COOR+H2O→CH3CH(OH)COOH+ROH。
the alcohol used in the esterification reaction is preferably a lower alcohol, and more preferably methanol and/or ethanol. More preferably methanol or ethanol.
The material ratio during the esterification reaction is that the mass ratio of the polylactic acid synthetic substrate to the alcohol is as follows: the substrate for polylactic acid synthesis is 100 (200-300) of alcohol. An excess of alcohol is employed to effect sufficient conversion of the lactic acid containing component of the polylactic acid synthesis substrate to lactate. The excess alcohol can be recovered in a subsequent step.
Preferably, a catalyst, preferably an acidic catalyst, is also added during the esterification reaction. Further preferred are sulfuric acid, hydrochloric acid, nitric acid and/or organic sulfonic acids.
Wherein the mass ratio of the polylactic acid synthetic substrate to the catalyst is as follows: and (3) a polylactic acid synthesis substrate, namely a catalyst of 100 (0.5-2). The organic sulfonic acid is preferably p-toluenesulfonic acid.
The reaction conditions during the esterification reaction are that the temperature of the esterification reaction is 100-140 ℃, and the pressure of the esterification reaction is 0.3-0.8 Mpa.
Under the conditions, the lactic acid-containing component in the substrate for polylactic acid synthesis can be converted into lactate, and the effective recovery of the lactic acid component in the substrate for polylactic acid synthesis can be realized.
And then extracting lactate from the esterified product in a lactate purification tower, wherein the temperature of the top of the tower is controlled to be 50-80 ℃, the temperature of the bottom of the tower is controlled to be 150-220 ℃, and the pressure in the purification tower is 1-3 KPa. Under the condition, the lactate can be effectively separated from other impurity components, so that the lactate with high purity is obtained, and the guarantee is provided for obtaining a lactic acid product with high purity in the next step.
And hydrolyzing the separated lactate, wherein the hydrolysis step is carried out in a hydrolysis tower, the temperature at the top of the tower is controlled to be 110-150 ℃, the temperature at the bottom of the tower is controlled to be 150-190 ℃, and the pressure in the hydrolysis tower is 0.3-0.8 MPa. Under the condition, the hydrolysis efficiency of the lactate is high, the lactic acid product is obtained by basically realizing complete hydrolysis, and the purity of the obtained lactic acid product is high.
Further, the hydrolysis step can not only obtain the lactic acid product, the alcohol generated by hydrolysis and water vapor are mixed and come out from the top of the hydrolysis tower in a gas phase form, and then the alcohol-containing water solution is obtained by condensation, and the obtained alcohol-containing water solution is separated and purified, so that the alcohol product can be recovered.
Preferably, the alcohol-containing water solution is purified in an alcohol recovery tower, the temperature of the top of the tower is controlled to be 40-60 ℃, the temperature of the bottom of the tower is controlled to be 60-80 ℃, and the pressure in the alcohol recovery tower is 10-30 KPa. Under the condition, the alcohol and the water are effectively separated, and the alcohol product with high purity is obtained at the top of the tower and can be returned to be used in the esterification reaction step.
The recovery method of the invention is adopted to carry out industrial tests, and the details are shown in example 1-example 3.
The composition of the polylactic acid synthesis substrate treated in examples 1 to 3 is specifically shown in Table 1.
TABLE 1
Polylactic acid synthesis substrates having the compositions shown in table 1 were treated separately.
The alcohol and the catalyst used in the esterification reaction are specifically shown in table 2. Wherein there is no particular requirement for the concentration of the catalyst.
TABLE 2
| Example 1 | Example 2 | Example 3 | |
| Alcohol(s) | Methanol | Ethanol | Ethanol |
| Catalyst and process for preparing same | Sulfuric acid | Nitric acid | P-toluenesulfonic acid |
The mass ratio of the polylactic acid synthetic substrate, the alcohol and the catalyst during the esterification reaction is shown in table 3.
TABLE 3
| Example 1 | Example 2 | Example 3 | |
| Synthesizing a substrate: alcohol: catalyst and process for preparing same | 100:280:1.8 | 100:250:1.2 | 100:200:0.6 |
The control conditions of examples 1 to 3 during the esterification reaction are shown in Table 4.
TABLE 4
| Example 1 | Example 2 | Example 3 | |
| Temperature/. degree.C | 136 | 126 | 120 |
| pressure/MPa | 0.75 | 0.60 | 0.50 |
And (3) feeding the esterified product obtained by the esterification reaction into a lactate purification tower to extract lactate, and feeding the extracted lactate into a hydrolysis tower to hydrolyze to obtain a lactic acid product and alcohol. Mixing alcohol generated by hydrolysis with water vapor, taking out from the top of the hydrolysis tower in a gas phase form, condensing to obtain an alcohol-containing aqueous solution, and separating and purifying the obtained alcohol-containing aqueous solution by an alcohol recovery tower to obtain an alcohol product.
Wherein, the control parameters of the lactate purification column, the hydrolysis column and the alcohol recovery column are respectively shown in tables 5 to 7 below.
TABLE 5 lactate purification column control parameters
| Example 1 | Example 2 | Example 3 | |
| Overhead temperature/. degree.C | 58 | 56 | 53 |
| Temperature of the bottom of the column/. degree.C | 216 | 208 | 191 |
| pressure/KPa | 2.5 | 1.9 | 1.3 |
TABLE 6 hydrolysis column control parameters
| Example 1 | Example 2 | Example 3 | |
| Overhead temperature/. degree.C | 131 | 128 | 121 |
| Temperature of the bottom of the column/. degree.C | 178 | 172 | 163 |
| pressure/MPa | 0.60 | 0.66 | 0.70 |
TABLE 7 alcohol recovery column control parameters
| Example 1 | Example 2 | Example 3 | |
| Overhead temperature/. degree.C | 41 | 47 | 45 |
| Temperature of the bottom of the column/. degree.C | 68 | 76 | 77 |
| pressure/KPa | 18 | 11 | 14 |
The quality of the lactic acid products obtained in examples 1 to 3 are shown in Table 8.
TABLE 8
| Example 1 | Example 2 | Example 3 | |
| Lactic acid content/%, wt | 88 | 86 | 93 |
| Moisture content/%, wt | 12 | 14 | 7 |
The lactic acid product obtained by the method has good quality and high purity which is over 85 percent and even over 90 percent. The yield of lactic acid in actual operation is about 86% by calculation.
Example 4
The embodiment provides a device for recovering lactic acid from a polylactic acid synthetic substrate, which comprises an esterification reaction kettle TK1, a lactate purification tower CO1 and a hydrolysis tower CO2 which are sequentially connected, wherein a feed inlet of the esterification reaction kettle TK1 is provided with a material mixer SM1, the bottoms of the lactate purification tower CO1 and the hydrolysis tower CO2 are respectively provided with a reboiler, a liquid phase outlet of the reboiler FF1 of the lactate purification tower CO1 is connected with a residual liquid tank, and a liquid phase outlet of the reboiler FF2 of the hydrolysis tower CO2 is connected with a lactic acid product tank, as shown in FIG. 1.
A lactate buffer tank TK2 is arranged between the lactate purification tower CO1 and the hydrolysis tower CO2, and a condenser CD2 is arranged between the lactate buffer tank TK2 and the lactate purification tower CO 1.
An alcohol recovery tower CO3 is arranged behind the hydrolysis tower CO2, a reboiler FF3 is arranged at the bottom of the alcohol recovery tower CO3, a liquid phase outlet of the reboiler FF3 of the alcohol recovery tower is connected with a wastewater tank, and the top of the alcohol recovery tower CO3 is connected with an alcohol product tank TK4 through a condenser CD 4.
An aqueous alcohol buffer tank TK3 is arranged between the hydrolysis tower CO2 and the alcohol recovery tower CO3, and a condenser CD3 is arranged between the aqueous alcohol buffer tank TK3 and the hydrolysis tower CO 2.
The aqueous alcohol buffer tank TK3 is also connected via a pipeline to the top of the lactate purification column CO 1. The light phase (mainly the excessive ethanol added during esterification) from the top of the lactate purification tower CO1 is condensed by a condenser CD1 and then enters an aqueous alcohol buffer tank TK3, and then enters an alcohol recovery tower CO3 for treatment.
Wherein, the lactate purification tower CO1 and the alcohol recovery tower CO3 are packed towers, and the towers are filled with reticular packing. The hydrolysis column CO2 is a tray column.
The operation of recovering lactic acid from a substrate for polylactic acid synthesis by using the recovery apparatus of this example is specifically as follows.
Referring to fig. 1, a polylactic acid synthetic substrate, alcohol and a catalyst are mixed by a material mixer SM1 according to a certain proportion and then enter an esterification reaction kettle TK1, and a lactic acid-containing component in the polylactic acid synthetic substrate and the alcohol undergo an esterification reaction under the action of the catalyst to generate lactate. The mixture after esterification reaction enters a lactate purification tower CO1 from an esterification reaction kettle TK1 in a liquid form under the action of a material transfer pump GP1, the material entering the lactate purification tower CO1 moves from top to bottom from the top of the lactate purification tower CO1 under the action of gravity, and enters a reboiler FF1 from the bottom of the lactate purification tower CO1 under the action of a material circulation pump GP 2. The material entering the reboiler FF1 is heated, the lactate component in the material is vaporized and enters the lactate purification tower CO1 from the bottom of the lactate purification tower CO1 in a gas form, the lactate gas runs from bottom to top in the lactate purification tower CO1, and the material exchanges with the liquid material entering from the top of the lactate purification tower CO1 under the action of the filler inside the lactate purification tower CO 1. Materials in an esterification reaction kettle TK1 are subjected to the action of a lactate purification tower CO1, non-lactate components are discharged out of a system from the bottom of a reboiler FF1 through a raffinate delivery pump GP3 in the form of raffinate, the lactate components are liquefied in the form of gas under the action of a condenser CD2 and then enter a lactate buffer tank TK2, and a separated light phase passes through a condenser CD1 from the top of a lactate purification tower CO1 and then enters an aqueous alcohol buffer tank TK3, so that the purification and separation of lactate are completed, and the lactate is obtained through purification.
The lactate enters the hydrolysis tower CO2 from a lactate buffer tank TK2 through the top of the hydrolysis tower CO2 under the action of a material transfer pump GP4, and the lactate liquid entering the hydrolysis tower CO2 moves downwards from top to bottom inside the hydrolysis tower CO2 under the action of gravity. Water vapor enters a hydrolysis tower CO2 from the bottom of the hydrolysis tower CO2, the hydrolysis reaction is carried out while the water vapor is contacted with lactate liquid, and the generated alcohol moves upwards in the hydrolysis tower CO2 together with the water vapor in a gas form, and enters an aqueous alcohol buffer tank TK3 in a liquid form after being treated by a condenser CD 3. Lactic acid components generated by hydrolysis and lactic acid ester which is not completely hydrolyzed enter a reboiler FF2 under the action of a material conveying pump GP5, the lactic acid ester is heated and vaporized by a reboiler FF2, the lactic acid ester enters a hydrolysis tower CO2 for hydrolysis reaction again, the lactic acid components are discharged from the bottom of the reboiler FF2 through a material conveying pump GP6, and the recovery of the lactic acid is completed.
The mixture of liquid alcohol and water obtained by condensation after hydrolysis in the hydrolysis tower CO2 and the liquid obtained by condensation of the light phase component separated from the top of the lactate purification tower CO1 enter the alcohol recovery tower CO3 from the aqueous alcohol buffer tank TK3 under the action of the material transfer pump GP 7. The liquid alcohol moves from top to bottom in the alcohol recovery column CO3 under the action of gravity and enters the reboiler FF3 under the action of the feed transfer pump GP 8. The material entering the reboiler FF3 is heated, alcohol components in the material are vaporized and enter the alcohol recovery tower CO3 from the bottom of the alcohol recovery tower CO3 in a gas form, and the alcohol gas moves from bottom to top in the alcohol recovery tower CO3 and exchanges substances with the liquid material entering from the top of the alcohol recovery tower CO3 under the action of internals of the alcohol recovery tower CO 3. The alcohol substances move upward in the alcohol recovery column CO3 in a gaseous form, and the non-alcohol substances such as water move downward in the alcohol recovery column CO3 in a liquid form, thereby completing the separation of the alcohol substances from the non-alcohol substances. Non-alcohol substances such as water and the like are discharged out of the system from the bottom of a reboiler FF3 under the action of a material delivery pump GP9, and the alcohol substances are condensed by a condenser CD4 and then enter an alcohol product tank TK 4.
The liquefied alcohol substances enter the esterification reaction kettle TK1 from the alcohol product tank TK4 through the material mixer SM1 under the action of the material delivery pump GP10, so that the recycling of the alcohol substances is realized.
Through industrial tests, the recovery system is safe and stable to operate and simple and convenient to operate.
Although the invention has been described in detail hereinabove by way of general description, specific embodiments and experiments, it will be apparent to those skilled in the art that many modifications and improvements can be made thereto based on the invention. Accordingly, such modifications and improvements are intended to be within the scope of the invention as claimed.
Claims (10)
1. A method for recovering lactic acid from a polylactic acid synthesis substrate, comprising the steps of:
carrying out esterification reaction on a polylactic acid synthetic substrate and alcohol, and converting lactic acid-containing components in the polylactic acid synthetic substrate into lactate; and the number of the first and second groups,
and extracting lactate from the esterified product, and hydrolyzing the extracted lactate to obtain a lactic acid product.
2. The method for recovering lactic acid according to claim 1, further comprising the steps of:
hydrolyzing the lactate to obtain an alcohol-containing aqueous solution, and purifying the alcohol-containing aqueous solution to obtain an alcohol product.
3. The method for recovering lactic acid according to claim 1 or 2, characterized in that the alcohol is a lower alcohol, preferably methanol and/or ethanol; and/or the mass ratio of the polylactic acid synthetic substrate to the alcohol is as follows: the substrate for polylactic acid synthesis is 100 (200-300) of alcohol.
4. The method for recovering lactic acid according to any one of claims 1 to 3, wherein a catalyst is used during the esterification reaction, and the catalyst is an acidic catalyst, preferably sulfuric acid, hydrochloric acid, nitric acid and/or an organic sulfonic acid; and/or the mass ratio of the polylactic acid synthetic substrate to the catalyst is as follows: a substrate for synthesizing polylactic acid, namely a catalyst of 100 (0.5-2); and/or the presence of a gas in the gas,
the temperature of the esterification reaction is 100-140 ℃; and/or the pressure of the esterification reaction is 0.3-0.8 Mpa.
5. The method for recovering lactic acid according to claim 1, wherein the extraction of lactic acid ester from the esterified product is performed in a lactic acid ester purification tower, wherein the temperature at the top of the tower is 50 to 80 ℃, and the temperature at the bottom of the tower is 150 to 220 ℃; and/or the pressure in the purification tower is 1-3 KPa.
6. The method for recovering lactic acid according to claim 1 or 5, wherein the hydrolysis of the lactic acid ester is carried out in a hydrolysis tower, wherein the temperature at the top of the tower is 110 to 150 ℃, and the temperature at the bottom of the tower is 150 to 190 ℃; and/or the pressure in the hydrolysis tower is 0.3-0.8 MPa.
7. The method for recovering lactic acid according to claim 2, wherein the alcohol-containing aqueous solution is purified in an alcohol recovery tower, the temperature at the top of the tower is 40 to 60 ℃, and the temperature at the bottom of the tower is 60 to 80 ℃; and/or the pressure in the alcohol recovery tower is 10-30 KPa.
8. The device for recovering lactic acid from the polylactic acid synthetic substrate is characterized by comprising an esterification reaction kettle, a lactate purification tower and a hydrolysis tower which are sequentially connected, wherein a material mixer is arranged at a feed inlet of the esterification reaction kettle, reboilers are arranged at the bottoms of the lactate purification tower and the hydrolysis tower, a liquid phase outlet of the reboiler of the lactate purification tower is connected with a residual liquid tank, and a liquid phase outlet of the reboiler of the hydrolysis tower is connected with a lactic acid product tank; preferably, a lactate buffer tank is arranged between the lactate purification tower and the hydrolysis tower, and a condenser is arranged between the lactate buffer tank and the lactate purification tower.
9. The device for recovering the lactic acid is characterized in that an alcohol recovery tower is arranged after the hydrolysis tower, a reboiler is arranged at the bottom of the alcohol recovery tower, a liquid phase outlet of the reboiler of the alcohol recovery tower is connected with a wastewater tank, and the top of the alcohol recovery tower is connected with an alcohol product tank through a condenser; preferably, an aqueous alcohol buffer tank is arranged between the hydrolysis tower and the alcohol recovery tower, and a condenser is arranged between the aqueous alcohol buffer tank and the hydrolysis tower; the aqueous alcohol buffer tank is also connected with the top of the lactate purification tower through a pipeline.
10. The method for recovering lactic acid according to any one of claims 1 to 7, wherein the apparatus according to claim 8 or 9 is used for recovering lactic acid.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114805058A (en) * | 2022-04-21 | 2022-07-29 | 济宁市技师学院 | Method and device for recovering lactic acid from polylactic acid synthetic substrate |
| CN115073280A (en) * | 2022-08-02 | 2022-09-20 | 马鞍山同杰良生物材料有限公司 | Method for recovering high-optical-purity lactic acid from polylactic acid synthetic substrate |
| CN115504958A (en) * | 2022-10-20 | 2022-12-23 | 山东寿光巨能金玉米开发有限公司 | Method for joint production of lactide and lactate |
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| CN111620771A (en) * | 2020-06-29 | 2020-09-04 | 华东理工大学 | Esterification-hydrolysis method lactic acid purification process flow based on catalytic reaction rectification coupling technology |
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| CN101456812A (en) * | 2009-01-07 | 2009-06-17 | 南京中狮化学品有限公司 | Purification method of lactic acid ester |
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114805058A (en) * | 2022-04-21 | 2022-07-29 | 济宁市技师学院 | Method and device for recovering lactic acid from polylactic acid synthetic substrate |
| CN115073280A (en) * | 2022-08-02 | 2022-09-20 | 马鞍山同杰良生物材料有限公司 | Method for recovering high-optical-purity lactic acid from polylactic acid synthetic substrate |
| CN115504958A (en) * | 2022-10-20 | 2022-12-23 | 山东寿光巨能金玉米开发有限公司 | Method for joint production of lactide and lactate |
| CN115504958B (en) * | 2022-10-20 | 2023-12-19 | 山东寿光巨能金玉米开发有限公司 | Method for joint production of lactide and lactate |
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