Method for synthesizing lactic acid through carbonylation, production system and industrial production method

Abstract

The invention discloses a method for synthesizing lactic acid through carbonylation, a production system and an industrial production method, and belongs to the technical field of chemical engineering. According to the method for synthesizing lactic acid through carbonylation, vinyl acetate and CO are used as raw materials, and lactic acid is synthesized through carbonylation reaction under the action of a palladium / nickel catalyst. The production system disclosed by the invention comprises a lactic acid reactor, a high-low pressure separator, a groove type distillation kettle, a vacuum tower, a hydrolysis tower, a refining tower, a lactate rectifying tower and a lactate hydrolysis tower which are connected in sequence. The invention further discloses an industrial production method adopting the production system. The lactic acid is synthesized from traditional chemical raw materials (the initial raw material is natural gas), closed-loop production can be achieved through a whole-process industrial chain, raw material sources are stable, the method is environmentally friendly, the scale is economical and reasonable, and the rate of return on investment is high.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical industry, and specifically relates to a method for synthesizing lactic acid by carbonylation, a production system and an industrial production method. Background Art

[0002] Lactic acid, with the chemical formula C3H6O3 and the chemical name α-hydroxypropionic acid, is widely used in pharmaceutical, brewing, food, beverage, health care products, papermaking, leather making, cigarette, paint, ink, electroplating and plastic industries, as well as oil pipeline corrosion protection.

[0003] In the prior art, the industrial production of lactic acid is mainly done by fermentation and synthesis. The main principle of the fermentation method is that carbohydrates (such as sucrose or starch sugar) are anaerobicly fermented to produce acid under the action of lactic acid bacteria. The pH value of the fermentation process is adjusted to about 5, and maintained at about 50-60dm; crude lactic acid is obtained after fermentation for 3-5 days. The raw materials of the fermentation method are generally starchy raw materials such as corn, rice, and sweet potatoes (alfalfa, cellulose, etc. are also used as raw materials, and some studies have proposed the recycling of kitchen waste and fish waste to produce lactic acid). There are many lactic acid bacteria that can produce acid in the lactic acid fermentation stage, but there are not many with high acid production quality, mainly Rhizopus and Lactobacillus strains. Different strains have different fermentation pathways, which can be divided into homotypic fermentation and heterotypic fermentation. In fact, due to the presence of other physiological activities of microorganisms, it may not be a single fermentation pathway.

[0004] The fermentation process generally includes: raw material preparation, fermentation process, lactic acid separation, and refined lactic acid. Fermentation has become a relatively mature lactic acid production method due to its simple process, sufficient raw materials, and early development, accounting for more than 70% of lactic acid production, but the cycle is long and can only be produced intermittently or semi-continuously. In addition, the quality of domestic fermented lactic acid is poor and it is difficult to meet international standards.

[0005] In addition, during the anaerobic fermentation process, the pH value of the fermentation liquid will decrease with the generation of lactic acid, and calcium hydroxide or calcium carbonate must be added to neutralize the lactic acid to maintain the pH fermentation conditions. After fermentation, the bacteria and impurities are separated by filtration and centrifugation, and can be used as a feed additive. After the fermentation liquid is cooled, the calcium lactate precipitate generated by the neutralization of calcium hydroxide and lactic acid must be dissolved with sulfuric acid to extract lactic acid. This process will generate a calcium sulfate precipitate by-product. After filtration and separation, the solid waste generated can be used as gypsum in the construction field. The crude lactic acid liquid extracted in this way still contains a large amount of soluble protein, sugar, salt, miscellaneous acids, etc., which must be purified and removed.

[0006] The methods for synthesizing lactic acid used in industrial production include the lactonitrile method, the acrylonitrile method, the propionic acid method, and the like.

[0007] (1) Lactic nitrile method: The lactonitrile method is to continuously feed acetaldehyde and cold hydrocyanic acid into a reactor to generate lactonitrile (or directly use lactonitrile as raw material), pump the lactonitrile into a hydrolysis kettle, inject sulfuric acid and water to hydrolyze the lactonitrile to obtain crude lactic acid. Then the crude lactic acid is fed into an esterification kettle, ethanol is added for esterification, and refined lactic acid is obtained through distillation, concentration, and decomposition. Sterling Chemical Company in the United States and Musashino Chemical Company in Japan both use this method to synthesize lactic acid.

[0008] (2) Acrylonitrile method: The acrylonitrile method is to send acrylonitrile and sulfuric acid into a reactor for hydrolysis, and then send the hydrolyzate into an esterification reactor to react with methanol; then after the ammonium bisulfate is separated, the crude ester is sent to a distillation tower, and the refined ester is obtained at the bottom of the tower; the refined ester is then sent to a second distillation tower, heated and decomposed, and dilute lactic acid is obtained at the bottom of the tower, which is then concentrated in vacuum to obtain the product.

[0009] (3) Propionic acid method: The propionic acid method uses propionic acid as raw material, and undergoes chlorination and hydrolysis to obtain crude lactic acid; then esterification, distillation, and hydrolysis are performed to obtain the product. The raw material price of this method is relatively expensive, and only a few manufacturers such as Japan Daisiro Company use it.

[0010] In summary, the existing technology of lactic acid using biological raw material fermentation technology has problems such as high energy consumption, high cost, poor product quality and insufficient purity. With the expansion of market application and production scale, the biological raw material fermentation-lactic acid technology route may compete with food for land. The synthetic method uses petroleum-based chemicals as raw materials, so it is easily affected by crude oil supply and sharp price fluctuations.

[0011] Therefore, providing a method for synthesizing lactic acid with a stable raw material source, low production cost, environmental friendliness, and scale advantage has become an urgent problem to be solved by those skilled in the art. Summary of the invention

[0012] One of the purposes of the present invention is to provide a method for synthesizing lactic acid by carbonylation, wherein acetic acid is produced by using the byproduct tail gas of acetylene produced by oxidation of natural gas, and then vinyl acetate is produced by using acetylene and acetic acid as raw materials, while CO is extracted by using acetylene byproduct tail gas PSA, and then lactic acid is synthesized by carbonylation of vinyl acetate and CO. The whole process industrial chain can realize closed-loop production, and the process technology except for lactic acid synthesis is highly mature, with reasonable economies of scale and high return on investment.

[0013] A second object of the present invention is to provide a production system for synthesizing lactic acid by carbonylation.

[0014] The third object of the present invention is to provide an industrial production method for synthesizing lactic acid by carbonylation.

[0015] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0016] The present invention discloses a method for synthesizing lactic acid by carbonylation, which uses vinyl acetate and CO as raw materials, and synthesizes lactic acid by carbonylation reaction under the action of palladium / nickel catalysts; the synthesis route is as follows:

[0017] CH2=CHOCOCH3+CO+H2O→HOOCCH(OCOCH3)CH3

[0018] HOOCCH(OCOCH3)CH3+H20→CH3CH(OH)COOH+CH3COOH

[0019] In some embodiments of the present invention, the reaction pressure is 2.0 to 3.0 MPaG and the reaction temperature is 150° C. to 300° C.;

[0020] Preferably, the raw material vinyl acetate is synthesized from acetylene and acetic acid, wherein acetylene is produced by oxidation of natural gas, and acetic acid is produced from by-product tail gas of acetylene produced by oxidation of natural gas.

[0021] The present invention discloses a production system for synthesizing lactic acid by carbonylation, comprising a lactic acid reactor, a high-pressure and low-pressure separator, a tank distillation kettle, a vacuum tower, a hydrolysis tower, a refining tower, a lactate distillation tower, and a lactate hydrolysis tower connected in sequence;

[0022] The lactic acid reactor is connected to the CO raw material delivery line, the acid raw material delivery line and the vinyl acetate raw material delivery line; the hydrolysis tower is connected to the process water delivery line; the refining tower is connected to the methanol raw material delivery line; the lactate hydrolysis tower is connected to the second process water delivery line, and is connected to the lactic acid solution output line;

[0023] Preferably, a carbon monoxide output line is connected to the high-low pressure separator; preferably, the carbon monoxide output line is connected to the lactic acid reactor;

[0024] Preferably, a methanol output line is connected to the top of the lactate distillation tower, and more preferably, the methanol output line is connected to the refining tower;

[0025] Preferably, a lactic acid concentration tower connected to the lactate hydrolysis tower is also included. The lactate hydrolysis tower is connected to the lactic acid concentration tower via a lactic acid solution output line. The bottom of the lactic acid concentration tower is connected to a finished lactic acid delivery line.

[0026] In some embodiments of the present invention, the production system further comprises a propionic acid separation tank, a lactic acid recovery tower, an acetic acid recovery tower and a light component refining tower connected in sequence;

[0027] The propionic acid separation tank is connected to the tank distillation kettle; the propionic acid separation tank is connected to a β-hydroxypropionic acid output line;

[0028] Preferably, the lactic acid recovery tower is connected to the tank still via a lactic acid circulation line, so as to return the recovered lactic acid to the tank still;

[0029] Preferably, the acetic acid recovery tower is connected to an acetic acid output line;

[0030] Preferably, the top of the light component refining tower is connected to an acetaldehyde output line, and the bottom of the tower is connected to a vinyl acetate output line.

[0031] In some embodiments of the present invention, the production system further comprises a dehydration tower, a stripping tower and an acetic acid tower connected in sequence;

[0032] The dehydration tower is connected to the refining tower;

[0033] The bottom of the acetic acid tower is connected to a refined acetic acid circulation line, and the top of the tower is connected to an extractant circulation line;

[0034] Preferably, the refined acetic acid circulation line is connected to the lactic acid reactor, and the extractant circulation line is connected to the dehydration tower;

[0035] Preferably, a circulating water output line is connected to the top of the dehydration tower, and more preferably, the circulating water output line is connected to the hydrolysis tower.

[0036] In some embodiments of the present invention, the lactic acid reactor is a fixed bed reactor provided with a palladium / nickel catalyst bed;

[0037] The or / and refining tower is divided into two sections, the upper section is a packed tower, and the lower section is a tubular fixed bed, in which a modified cationic resin catalyst is installed.

[0038] The invention discloses an industrial production method for synthesizing lactic acid by carbonylation, which is carried out by adopting the above production system.

[0039] In some embodiments of the present invention, the industrial production method comprises the following steps:

[0040] S1. Continuous carbonylation of vinyl acetate: vinyl acetate, acetic acid and CO gas are fed into a lactic acid reactor and react with the catalyst bed in the lactic acid reactor to generate α-acetylpropionic acid and β-acetylpropionic acid. At the same time, part of the vinyl acetate is hydrolyzed to generate acetic acid and acetaldehyde.

[0041] In step S1 of the present invention, by adding acetic acid, the reaction rate of the side reaction of hydrolysis of vinyl acetate to generate acetic acid and acetaldehyde can be reduced. S2. Separation of α-acetyl propionic acid: The mixed material from the lactic acid reactor is sent to a high-low pressure separator for separation to separate CO gas and liquid mixed material; CO gas is discharged from the top of the high-low pressure separator, and the liquid mixed material is sent to a tank distillation kettle;

[0042] Preferably, the CO gas is discharged from the top of the high-low pressure separator and then circulated back to the lactic acid reactor to participate in the reaction again;

[0043] S3. Hydrolysis and separation: The β-acetyl propionic acid in the liquid mixture is hydrolyzed in a tank distillation kettle to generate β-hydroxypropionic acid and acetic acid, and part of the α-acetyl propionic acid in the liquid mixture is hydrolyzed to generate lactic acid and acetic acid;

[0044] α-Hydroxypropionic acid, part of vinyl acetate, part of acetic acid and part of lactic acid are discharged from the bottom of the tank distillation kettle and sent to a vacuum tower; unreacted vinyl acetate and acetic acid are recovered in the vacuum tower and returned to the lactic acid reactor through the bottom of the vacuum tower; the mixed liquid of α-hydroxypropionic acid and lactic acid is sent from the vacuum tower to a hydrolysis tower;

[0045] β-Hydroxypropionic acid is discharged from the upper part of the tank still together with acetaldehyde, part of vinyl acetate, part of acetic acid and part of lactic acid;

[0046] Preferably, the mixed material discharged from the upper part of the tank still is first sent to a propionic acid separation tank to separate β-hydroxypropionic acid, which is extracted as a by-product; the material from which β-hydroxypropionic acid is separated is successively recovered by a lactic acid recovery tower and an acetic acid recovery tower to recover acetic acid; the recovered lactic acid is returned to the tank still, and the recovered acetic acid is sent to an acetic acid tank, and then refined in the acetic acid tower and returned to the lactic acid reactor to continue to participate in the reaction or be extracted as a by-product; the top material of the acetic acid recovery tower is sent to a light component refining tower to separate formaldehyde as a by-product, and vinyl acetate is sold as a by-product, or is sent to the reactor as a raw material after being refined to a qualified level;

[0047] S4. Continuous hydrolysis of α-acetylpropionic acid: water is introduced into the hydrolysis tower, and the mixed solution of α-hydroxypropionic acid and lactic acid is continuously hydrolyzed in the hydrolysis tower to generate lactic acid; the hydrolyzed material is sent to the refining tower; the hydrolyzed material contains lactic acid, acetic acid and water;

[0048] S5. Esterification of lactic acid: The hydrolyzed material is stripped and separated in a refining tower, and is separated into crude lactic acid and acetic acid aqueous solution in the upper section. The crude lactic acid and methanol undergo esterification reaction in the lower section to produce methyl lactate; the bottom liquid is a methyl lactate mixed liquid containing methanol, which is sent to a lactate distillation tower for treatment;

[0049] Preferably, the acetic acid aqueous solution distilled from the top of the refining tower is sent to a dehydration tower for treatment;

[0050] More preferably, the dehydration tower uses an extractive distillation process to separate acetic acid and water, sulfolane is selected as the extraction solvent, the obtained water is circulated back to the hydrolysis tower to continue to participate in the hydrolysis reaction, the crude acetic acid enters the stripping tower, the heavy components are removed and sent to incineration treatment, and then enters the acetate tower to remove the sulfolane solvent, and the refined acetic acid is sent back to the reactor to continue to participate in the reaction, or sold as a by-product;

[0051] S6. Purification and hydrolysis of lactate: The methyl lactate mixed solution containing methanol enters the lactate distillation tower from the refining tower, and methanol is distilled from the top of the lactate distillation tower by using the boiling point pressure difference, and methyl lactate enters the lactate hydrolysis tower; water is introduced into the lactate hydrolysis tower, and methyl lactate is hydrolyzed in the lactate hydrolysis tower to produce lactic acid and methanol, and methanol is continuously distilled from the top of the lactate hydrolysis tower, so that the reaction continues, and methyl lactate is completely hydrolyzed in the hydrolysis tower to obtain lactic acid;

[0052] Preferably, methanol is distilled from the top of the distillation tower, cooled by circulating water, and then returned to the refining tower to continue the esterification reaction with lactic acid;

[0053] Preferably, the aqueous solution containing lactic acid obtained by hydrolysis is sent to a concentration tower to remove moisture to obtain finished high-purity lactic acid;

[0054] Preferably, the methanol is returned to the refining tower for recycling.

[0055] In some embodiments of the present invention, in step S1, the raw materials are mixed uniformly in a mixer and then fed into a lactic acid reactor;

[0056] Preferably, the process operating conditions of the lactic acid reactor include: a volume space velocity of 2 to 6 h -1 ; Reaction pressure is 2.0~3.0MPaG; Reactor inlet temperature is 150~300℃; Reactor temperature rise is 15~45℃; Reactor pressure drop is 0.1~0.5MPa;

[0057] Preferably, the volume ratio of vinyl acetate to acetic acid is 4:1 to 5:1;

[0058] Or / and in step S3, the process operating conditions of the tank distillation kettle include: operating pressure of 20-60KPaA; top temperature of 100-150°C; bottom temperature of the kettle of 200-250°C;

[0059] Or / and in step S4, the process operating conditions of the hydrolysis tower include: the operating pressure is normal pressure, the feed temperature of the α-hydroxypropionic acid and lactic acid mixture is ≤250°C, the feed temperature of the process water is ≤100°C; the feed mass ratio of the α-hydroxypropionic acid and lactic acid mixture to water is 1 to 3:1;

[0060] Or / and in step S5, the process operating conditions of the refining tower include: the tower top pressure is 10-60KPaG, the tower bottom pressure is 10-60KPaG, the tower top temperature is 60-100°C, the tower bottom temperature is 80-120°C, and the reflux ratio is 2-30;

[0061] Or / and in step S6, the process operating conditions of the lactate hydrolysis tower include: the operating pressure is normal pressure,

[0062] The methyl lactate feed temperature is ≤120°C, the water feed temperature is ≤60°C, and the water / methyl lactate feed ratio is 10 to 30:1.

[0063] In some embodiments of the present invention, the raw material vinyl acetate is synthesized from acetylene and acetic acid, wherein acetylene is produced by oxidation of natural gas, and acetic acid is produced from the by-product tail gas of acetylene produced by oxidation of natural gas.

[0064] Compared with the prior art, the present invention has the following beneficial effects:

[0065] The present invention uses natural gas as the initial raw material, produces acetic acid with the byproduct tail gas of acetylene produced by oxidation of natural gas, and then produces vinyl acetate with acetylene and acetic acid as raw materials, and simultaneously uses acetylene byproduct tail gas PSA to extract CO, and then uses vinyl acetate and CO to carbonylate and synthesize lactic acid. The whole process industrial chain can realize closed-loop production, and the process technology maturity except for lactic acid synthesis is high, the scale economy is reasonable, and the investment return rate is high. According to the reaction production of 1 ton of lactic acid (100%), about 1.33 tons of raw material vinyl acetate, 0.42 tons of carbon monoxide gas, 0.67 tons of byproduct acetic acid, 0.19 tons of β-hydroxypropionic acid, and 0.06 tons of acetaldehyde are required.

[0066] The invention adopts traditional chemical raw materials (natural gas is used as the initial raw material) to synthesize and prepare lactic acid. There is no fermentation process in the production process, and it is not necessary to use acid or alkali to adjust the pH. No by-products such as bacterial residues and calcium sulfate and other highly polluting solid wastes are produced, and no large amount of high-concentration nitrogen oxide waste gas is generated or discharged. Compared with microbial fermentation product-lactic acid as raw material and other chemical synthesis process routes, the raw material source is stable, the impurities are less, the production cost is low, the by-product value is high, the three wastes are discharged in a small amount, the treatment difficulty is low, and it is environmentally friendly.

[0067] The present invention uses natural gas as the initial raw material, produces acetic acid with the byproduct tail gas of acetylene produced by oxidation of natural gas, and then produces vinyl acetate with acetylene and acetic acid as raw materials. At the same time, CO is extracted by using the byproduct tail gas PSA of acetylene, and then vinyl acetate and CO are carbonylated to synthesize lactic acid. The whole process industrial chain can realize closed-loop production. The process technology except lactic acid synthesis is highly mature, with reasonable economies of scale and high return on investment. According to the reaction production of 1 ton of lactic acid (100%), about 1.33 tons of raw vinyl acetate, 0.42 tons of carbon monoxide gas, 0.67 tons of byproduct acetic acid, 0.19 tons of β-hydroxypropionic acid, and 0.06 tons of acetaldehyde are required.

[0068] The present invention has scale advantages in the selection of raw materials and technical routes, can further reduce production costs, and has good social and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Attached Figure 1 It is a schematic diagram of the structure of the production system of the present invention.

[0070] The names corresponding to the reference numerals are:

[0071] 1-lactic acid reactor, 2-high and low pressure separator, 3-tank still, 4-vacuum tower, 5-hydrolysis tower, 6-refining tower, 7-lactate distillation tower, 8-lactate hydrolysis tower, 9-lactic acid concentration tower, 10-propionic acid separation tank, 11-lactic acid recovery tower, 12-acetic acid recovery tower, 13-light component refining tower, 14-dehydration tower, 15-stripping tower, 16-acetic acid tower;

[0072] 101-CO raw material conveying line, 102-acid raw material conveying line, 103-vinyl acetate raw material conveying line, 104-carbon monoxide output line, 105-liquid mixed material conveying line, 106-β-hydroxypropionic acid mixed material conveying line, 107-α-hydroxypropionic acid mixed conveying line, 108-circulating vinyl acetate conveying line, 109-α-hydroxypropionic acid and lactic acid mixed liquid conveying line, 110-process water conveying line, 111-first hydrolysis material conveying line, 112-methanol raw material conveying line, 113-acetic acid aqueous solution conveying line, 114-methanol-methyl lactate mixed liquid conveying line, 115-methanol output line, 116-methyl lactate conveying line, 11 7-second process water conveying line, 118-lactic acid solution output line, 120-finished lactic acid conveying line, 121-wastewater discharge line, 122-dehydrated material conveying line, 123-acetic acid-extractant mixed material conveying line, 124-refined acetic acid circulation line, 125-refined acetic acid external transmission line, 126-β-hydroxypropionic acid output line, 127-first recovered mixed material conveying line, 128-lactic acid circulation line, 129-second recovered mixed material conveying line, 130-light component mixed material conveying line, 131-acetic acid output line, 132-acetaldehyde output line, 133-vinyl acetate output line, 134-extractant circulation line, 135-circulating water output line. DETAILED DESCRIPTION

[0073] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0074] Example 1

[0075] This embodiment discloses a production system for carbonylation synthesis of lactic acid, comprising a lactic acid reactor 1, a high-pressure and low-pressure separator 2, a tank distillation kettle 3, a vacuum tower 4, a hydrolysis tower 5, a refining tower 6, a lactate distillation tower 7, and a lactate hydrolysis tower 8 connected in sequence;

[0076] The lactic acid reactor 1 is connected to a CO raw material delivery line 101, a acetic acid raw material delivery line 102 and a vinyl acetate raw material delivery line 103; the hydrolysis tower 5 is connected to a process water delivery line 110; the refining tower 6 is connected to a methanol raw material delivery line 112; the lactate hydrolysis tower 8 is connected to a second process water delivery line 117, and is connected to a lactic acid solution output line 118.

[0077] Example 2

[0078] This embodiment discloses a production system for synthesizing lactic acid by carbonylation, comprising a lactic acid reactor 1, a high-pressure and low-pressure separator 2, a tank still 3, a vacuum tower 4, a hydrolysis tower 5, a refining tower 6, a lactate distillation tower 7, a lactate hydrolysis tower 8 and a lactic acid concentration tower 9 connected in sequence;

[0079] The lactic acid reactor 1 is connected to a CO raw material delivery line 101, an acid raw material delivery line 102 and a vinyl acetate raw material delivery line 103; the lactic acid reactor 1 is connected to a high-low pressure separator 2 via a pipeline;

[0080] A carbon monoxide output line 104 is connected to the high-low pressure separator 2; the carbon monoxide output line 104 is connected to the lactic acid reactor 1; and a carbon monoxide circulation compressor and a cooler are arranged on the carbon monoxide output line 104 in sequence according to the flow direction of carbon monoxide; the high-low pressure separator 2 is connected to the tank still 3 via a liquid mixture material conveying line 105;

[0081] The upper part of the tank still 3 is connected to a β-hydroxypropionic acid mixed material conveying line 106, and the lower part is connected to the vacuum tower 4 through an α-hydroxypropionic acid mixed material conveying line 107;

[0082] The upper part of the vacuum tower 4 is connected to the hydrolysis tower 5 via the α-hydroxypropionic acid and lactic acid mixed liquid conveying line 109, and the lower part is connected to the lactic acid reactor 1 via the circulating vinyl acetate conveying line 108;

[0083] The hydrolysis tower 5 is connected to a process water delivery line 110, and the lower part is connected to the refining tower 6 through a first hydrolysis material delivery line 111;

[0084] The refining tower 6 is connected to a methanol raw material delivery line 112; an acetic acid aqueous solution delivery line 113 is connected thereto; the refining tower 6 is connected to the lactate distillation tower 7 via a methanol-methyl lactate mixed liquid delivery line 114;

[0085] A methanol output line 115 is connected to the top of the lactate distillation tower 7, and the methanol output line 115 is connected to the refining tower 6; the lactate distillation tower 7 is connected to the lactate hydrolysis tower 8 via a methyl lactate delivery line 116, and a cooler is provided on the methanol output line 115;

[0086] The lactate hydrolysis tower 8 is connected to a second process water delivery line 117, and the lactate hydrolysis tower 8 is connected to the lactic acid concentration tower 9 via a lactic acid solution output line 118.

[0087] The top of the lactate hydrolysis tower 8 is connected to a methanol-water mixture material circulation line 119, on which a cooler is provided, and the methanol-water mixture material circulation line 119 is connected to the upper part of the lactate hydrolysis tower 8. The methanol and water mixture is evaporated from the top of the lactate hydrolysis tower, and after cooling, it is returned to the tower to continue the reaction. The lactic acid concentration tower 9 is connected to a finished lactic acid delivery line 120 and a wastewater discharge line 121.

[0088] This embodiment 2 provides a more preferred technical solution based on embodiment 1. Specifically, the production system includes a lactic acid concentration tower 9, and provides a specific connection relationship between the lactic acid reactor 1, the high and low pressure separator 2, the tank still 3, the vacuum tower 4, the hydrolysis tower 5, the refining tower 6, the lactate distillation tower 7, the lactate hydrolysis tower 8 and the lactic acid concentration tower 9.

[0089] Example 3

[0090] This embodiment discloses a production system for synthesizing lactic acid by carbonylation, comprising a lactic acid reactor 1, a high-pressure and low-pressure separator 2, a tank still 3, a vacuum tower 4, a hydrolysis tower 5, a refining tower 6, a lactate distillation tower 7, a lactate hydrolysis tower 8 and a lactic acid concentration tower 9 connected in sequence;

[0091] The lactic acid reactor 1 is connected to a CO raw material delivery line 101, an acid raw material delivery line 102 and a vinyl acetate raw material delivery line 103; the lactic acid reactor 1 is connected to a high-low pressure separator 2 via a pipeline;

[0092] A carbon monoxide output line 104 is connected to the high-low pressure separator 2; the carbon monoxide output line 104 is connected to the lactic acid reactor 1; and a carbon monoxide circulation compressor and a cooler are arranged on the carbon monoxide output line 104 in sequence according to the flow direction of carbon monoxide; the high-low pressure separator 2 is connected to the tank still 3 via a liquid mixture material conveying line 105;

[0093] The upper part of the tank still 3 is connected to a β-hydroxypropionic acid mixed material conveying line 106, and the lower part is connected to the vacuum tower 4 through an α-hydroxypropionic acid mixed material conveying line 107;

[0094] The upper part of the vacuum tower 4 is connected to the hydrolysis tower 5 via the α-hydroxypropionic acid and lactic acid mixed liquid conveying line 109, and the lower part is connected to the lactic acid reactor 1 via the circulating vinyl acetate conveying line 108;

[0095] The hydrolysis tower 5 is connected to a process water delivery line 110, and the lower part is connected to the refining tower 6 through a first hydrolysis material delivery line 111;

[0096] The refining tower 6 is connected to a methanol raw material delivery line 112; an acetic acid aqueous solution delivery line 113 is connected thereto; the refining tower 6 is connected to the lactate distillation tower 7 via a methanol-methyl lactate mixed liquid delivery line 114;

[0097] A methanol output line 115 is connected to the top of the lactate distillation tower 7, and the methanol output line 115 is connected to the refining tower 6; the lactate distillation tower 7 is connected to the lactate hydrolysis tower 8 via a methyl lactate delivery line 116, and a cooler is provided on the methanol output line 115;

[0098] The lactate hydrolysis tower 8 is connected to a second process water delivery line 117, and the lactate hydrolysis tower 8 is connected to the lactic acid concentration tower 9 via a lactic acid solution output line 118.

[0099] The top of the lactate hydrolysis tower 8 is connected to a methanol-water mixture material circulation line 119, on which a cooler is provided, and the methanol-water mixture material circulation line 119 is connected to the upper part of the lactate hydrolysis tower 8. The mixture of methanol and water is evaporated from the top of the lactate hydrolysis tower, and after cooling, it returns to the tower to continue the reaction.

[0100] The lactic acid concentration tower 9 is connected to a finished lactic acid delivery line 120 and a wastewater discharge line 121 .

[0101] The production system also includes a propionic acid separation tank 10, a lactic acid recovery tower 11, an acetic acid recovery tower 12 and a light component refining tower 13 which are connected in sequence;

[0102] The propionic acid separation tank 10 is connected to the tank distillation kettle 3 via the β-hydroxypropionic acid mixed material conveying line 106, and is connected to the lactic acid recovery tower 11 via the first recovered mixed material conveying line 127; the propionic acid separation tank 10 is connected to a β-hydroxypropionic acid output line 126;

[0103] The lactic acid recovery tower 11 is connected to the tank still 3 via a lactic acid circulation line 128, for returning the recovered lactic acid to the tank still 3; and is connected to the acetic acid recovery tower 12 via a second recovery mixed material conveying line 129, on which a cooler is provided;

[0104] The acetic acid recovery tower 12 is connected to a first acetic acid output line 131; the acetic acid recovery tower 12 is connected to the light component refining tower 13 via a light component mixed material conveying line 130;

[0105] The light component refining tower 13 has an acetaldehyde output line 132 connected to the top and a vinyl acetate output line 133 connected to the bottom.

[0106] This embodiment 3 provides a more preferred technical solution based on embodiment 2. Specifically, the production system also includes a propionic acid separation tank 10, a lactic acid recovery tower 11, an acetic acid recovery tower 12 and a light component refining tower 13 connected in sequence; and provides a specific connection relationship between the propionic acid separation tank 10, the lactic acid recovery tower 11, the acetic acid recovery tower 12 and the light component refining tower 13, as well as a specific connection relationship between the tank still 3 and the propionic acid separation tank 10 and the lactic acid recovery tower 11.

[0107] Example 4

[0108] This embodiment discloses a production system for synthesizing lactic acid by carbonylation, comprising a lactic acid reactor 1, a high-pressure and low-pressure separator 2, a tank still 3, a vacuum tower 4, a hydrolysis tower 5, a refining tower 6, a lactate distillation tower 7, a lactate hydrolysis tower 8 and a lactic acid concentration tower 9 connected in sequence;

[0109] The lactic acid reactor 1 is connected to a CO raw material delivery line 101, an acid raw material delivery line 102 and a vinyl acetate raw material delivery line 103; the lactic acid reactor 1 is connected to a high-low pressure separator 2 via a pipeline;

[0110] A carbon monoxide output line 104 is connected to the high-low pressure separator 2; the carbon monoxide output line 104 is connected to the lactic acid reactor 1; and a carbon monoxide circulation compressor and a cooler are arranged on the carbon monoxide output line 104 in sequence according to the flow direction of carbon monoxide; the high-low pressure separator 2 is connected to the tank still 3 via a liquid mixture material conveying line 105;

[0111] The upper part of the tank still 3 is connected to a β-hydroxypropionic acid mixed material conveying line 106, and the lower part is connected to the vacuum tower 4 through an α-hydroxypropionic acid mixed material conveying line 107;

[0112] The upper part of the vacuum tower 4 is connected to the hydrolysis tower 5 via the α-hydroxypropionic acid and lactic acid mixed liquid conveying line 109, and the lower part is connected to the lactic acid reactor 1 via the circulating vinyl acetate conveying line 108;

[0113] The hydrolysis tower 5 is connected to a process water delivery line 110, and the lower part is connected to the refining tower 6 through a first hydrolysis material delivery line 111;

[0114] The refining tower 6 is connected to a methanol raw material delivery line 112; an acetic acid aqueous solution delivery line 113 is connected thereto; the refining tower 6 is connected to the lactate distillation tower 7 via a methanol-methyl lactate mixed liquid delivery line 114;

[0115] A methanol output line 115 is connected to the top of the lactate distillation tower 7, and the methanol output line 115 is connected to the refining tower 6; the lactate distillation tower 7 is connected to the lactate hydrolysis tower 8 via a methyl lactate delivery line 116, and a cooler is provided on the methanol output line 115;

[0116] The lactate hydrolysis tower 8 is connected to a second process water delivery line 117, and the lactate hydrolysis tower 8 is connected to the lactic acid concentration tower 9 via a lactic acid solution output line 118.

[0117] The top of the lactate hydrolysis tower 8 is connected to a methanol-water mixture material circulation line 119, on which a cooler is provided, and the methanol-water mixture material circulation line 119 is connected to the upper part of the lactate hydrolysis tower 8. The mixture of methanol and water is evaporated from the top of the lactate hydrolysis tower, and after cooling, it returns to the tower to continue the reaction.

[0118] The lactic acid concentration tower 9 is connected to a finished lactic acid delivery line 120 and a wastewater discharge line 121 .

[0119] The production system also includes a propionic acid separation tank 10, a lactic acid recovery tower 11, an acetic acid recovery tower 12 and a light component refining tower 13 which are connected in sequence;

[0120] The propionic acid separation tank 10 is connected to the tank distillation kettle 3 via the β-hydroxypropionic acid mixed material conveying line 106, and is connected to the lactic acid recovery tower 11 via the first recovered mixed material conveying line 127; the propionic acid separation tank 10 is connected to a β-hydroxypropionic acid output line 126;

[0121] The lactic acid recovery tower 11 is connected to the tank still 3 via a lactic acid circulation line 128, for returning the recovered lactic acid to the tank still 3; and is connected to the acetic acid recovery tower 12 via a second recovery mixed material conveying line 129, on which a cooler is provided;

[0122] The acetic acid recovery tower 12 is connected to a first acetic acid output line 131; the acetic acid recovery tower 12 is connected to the light component refining tower 13 via a light component mixed material conveying line 130;

[0123] The light component refining tower 13 has an acetaldehyde output line 132 connected to the top and a vinyl acetate output line 133 connected to the bottom.

[0124] The production system also includes a dehydration tower 14, a stripping tower 15 and an acetic acid tower 16 connected in sequence;

[0125] The dehydration tower 14 is connected to the refining tower 6 via the acetic acid aqueous solution conveying line 113, the dehydration tower 14 is connected to a circulating water output line 135, the circulating water output line 135 is connected to the hydrolysis tower 5, the dehydration tower 14 is connected to the stripping tower 15 via the dehydration material conveying line 122, the stripping tower 15 is connected to a heavy component discharge line 136, the stripping tower 15 is connected to the acetic acid tower 16 via the acetic acid-extractant mixed material conveying line 123, the top of the acetic acid tower 16 is connected to an extractant circulation line 134, and the bottom of the tower is connected to a refined acetic acid circulation line 124. The extractant circulation line 134 is connected to the dehydration tower 14, and a cooler is provided on the extractant circulation line 134. The refined acetic acid circulation line 124 is connected to the lactic acid reactor 1. The refined acetic acid circulation line 124 is also connected to a refined acetic acid output line 125.

[0126] This embodiment 4 provides a more preferred technical solution based on embodiment 3. Specifically, the production system further includes a dehydration tower 14, a stripping tower 15 and an acetic acid tower 16 connected in sequence; and provides a specific connection relationship between the dehydration tower 14, the stripping tower 15 and the acetic acid tower 16, as well as a specific connection relationship between the dehydration tower 14 and the hydrolysis tower 5 and the refining tower 6, and a specific connection relationship between the acetic acid tower 16 and the lactic acid reactor 1.

[0127] In Examples 1 to 4 of the present invention, the lactic acid reactors are all fixed bed reactors provided with a palladium / nickel catalyst bed;

[0128] In Examples 1 to 4 of the present invention, β-acetylpropionic acid is preferentially hydrolyzed in a tank distillation kettle to generate β-hydroxypropionic acid and acetic acid, and a small portion of α-acetylpropionic acid is also hydrolyzed to generate lactic acid and acetic acid, and the reaction is a slightly exothermic reaction.

[0129] In the embodiments 1 to 4 of the present invention, the refining tower is divided into two sections, the upper section adopts a packed tower, the lower section is a tubular fixed bed, a modified cationic resin catalyst is installed inside, the top cooler is cooled by circulating cooling water, the tower bottom reboiler is a kettle type, and steam is used as a heat source. The mixed solution containing lactic acid, acetic acid, water, etc. from the hydrolysis tower is separated into crude lactic acid and acetic acid aqueous solution in the upper section, and the crude lactic acid and methanol undergo esterification reaction in the lower section to generate methyl lactate.

[0130] In the embodiment of the present invention, the lactic acid recovery tower, the acetic acid recovery tower and the acetic acid tower are all distillation towers.

[0131] In the embodiment of the present invention, the propionic acid separation tank is provided with a silica gel adsorbent to separate the β-hydroxypropionic acid through adsorption separation.

[0132] Example 5

[0133] This example discloses a method for synthesizing lactic acid by carbonylation using the system of Example 4, and the specific steps are as follows:

[0134] S1. Continuous carbonylation of vinyl acetate: vinyl acetate, acetic acid and CO gas are mixed uniformly in a mixer and then fed into a lactic acid reactor, where a reaction occurs on a palladium / nickel catalyst bed to generate α-acetoxypropionic acid and β-acetoxypropionic acid. At the same time, part of the vinyl acetate is hydrolyzed to generate acetic acid and acetaldehyde.

[0135] The raw material vinyl acetate is synthesized from acetylene and acetic acid, wherein acetylene is produced by oxidation of natural gas, and acetic acid is produced from the by-product tail gas of acetylene produced by oxidation of natural gas.

[0136] The process operating conditions of the lactic acid reactor include: volume space velocity of 2 to 6 h -1 ; Reaction pressure is

[0137] 2.0~3.0MPaG; reactor inlet temperature is 150~300℃; reactor temperature rise is 15~45℃; reactor pressure drop is 0.1~0.5MPa;

[0138] The volume ratio of vinyl acetate to acetic acid is 4:1 to 5:1; the molar ratio of CO to vinyl acetate is 2:1 to 3:1;

[0139] The reaction formula is:

[0140] CH2=CHOCOCH3(vinyl acetate)+CO+H2O→HOOCCH(OCOCH3)CH3(α-acetoxypropionic acid)

[0141] The side reaction equation is as follows:

[0142] CH2=CHOCOCH3(vinyl acetate)+CO+H2O→HOOCCH2CH2OCOCH3(β-acetylpropionic acid)

[0143] CH2=CHOCOCH3(vinyl acetate)+H2O→CH3COOH(acetic acid)+CH3CHO(acetaldehyde);

[0144] S2. Separation of α-acetylpropionic acid: The mixed material coming out of the lactic acid reactor is sent to a high-low pressure separator for separation to separate CO gas and liquid mixed material; the CO gas is discharged from the top of the high-low pressure separator, cooled, and recycled back to the lactic acid reactor to participate in the reaction again; the liquid mixed material is sent to a tank distillation kettle.

[0145] S3. Hydrolysis and separation: β-acetyl propionic acid in the liquid mixture is preferentially hydrolyzed in the tank still to generate β-hydroxypropionic acid and acetic acid, and part of α-acetyl propionic acid in the liquid mixture is hydrolyzed to generate lactic acid and acetic acid; the process operating conditions of the tank still include: operating pressure of 20-60KPaA; top temperature of

[0146] 100~150℃; the bottom temperature of the kettle is 200~250℃; the reaction formula is as follows:

[0147] HOOCCH2CH2OCOCH3(β-acetylpropionic acid)+H2O→CH2(OH)CH2COOH(β-hydroxypropionic acid)+

[0148] CH3COOH(acetic acid)

[0149] CH3 CH(OCOCH3)COOH(α-acetoxypropionic acid)+H2O→CH3CH(OH)COOH(lactic acid)+CH3COOH

[0150] (acetic acid)

[0151] α-acetyl propionic acid, part of vinyl acetate, part of acetic acid and part of lactic acid are discharged from the bottom of the tank distillation kettle and sent to a vacuum tower; unreacted vinyl acetate and acetic acid are recovered in the vacuum tower and returned to the lactic acid reactor through the bottom of the vacuum tower; the mixed liquid of α-acetyl propionic acid and lactic acid is sent from the vacuum tower to a hydrolysis tower;

[0152] β-Hydroxypropionic acid is distilled from the top of the tank still together with acetaldehyde, part of vinyl acetate, part of acetic acid and part of lactic acid;

[0153] The mixed material distilled from the top of the tank still is first sent to the propionic acid separation tank, where it is separated by adsorption through a silica gel adsorbent to separate β-hydroxypropionic acid and extracted as a by-product; the material from which β-hydroxypropionic acid has been separated is distilled in a lactic acid recovery tower to recover lactic acid and in an acetic acid recovery tower to recover acetic acid, according to the different boiling points of lactic acid (220°C) and acetic acid (110°C). The recovered lactic acid is returned to the tank still, and the recovered acetic acid is sent to the acetic acid tank, and then refined in the acetic acid tower and returned to the lactic acid reactor to continue to participate in the reaction or be extracted as a by-product; the top material of the acetic acid recovery tower is sent to a light component refining tower, where it is separated by a distillation tower using the different boiling points of vinyl acetate (70°C) and acetaldehyde (20°C); acetaldehyde is separated as a by-product; vinyl acetate is sold as a by-product, or sent to the reactor as a raw material after being refined to a qualified standard;

[0154] S4. Continuous hydrolysis of α-acetylpropionic acid: water is introduced into the hydrolysis tower, and the α-acetylpropionic acid in the mixed solution of α-acetylpropionic acid and lactic acid is continuously hydrolyzed in the hydrolysis tower to generate lactic acid; the reaction formula is:

[0155] CH3 CH(OCOCH3)COOH(α-acetoxypropionic acid)+H2O→CH3CH(OH)COOH(lactic acid)+CH3COOH(acetic acid);

[0156] The process operating conditions of the hydrolysis tower include: the operating pressure is normal pressure, the feed temperature of the α-acetylpropionic acid and lactic acid mixture is ≤250°C, the feed temperature of the process water is ≤100°C; the feed mass ratio of the α-hydroxypropionic acid and lactic acid mixture to water is 1 to 3:1;

[0157] The hydrolyzed material is sent to the refining tower; the hydrolyzed material contains lactic acid, acetic acid and water.

[0158] S5. Esterification of lactic acid: The hydrolyzed material is separated by steam stripping in a refining tower, and is separated into crude lactic acid and acetic acid aqueous solution in the upper section of the refining tower. The crude lactic acid and methanol undergo esterification reaction under the action of a modified cationic resin catalyst in the lower section of the refining tower to produce methyl lactate; the bottom liquid is a methyl lactate mixed liquid containing methanol, which is sent to a lactate distillation tower for treatment; the acetic acid aqueous solution distilled from the top of the refining tower is sent to a dehydration tower for treatment;

[0159] The process operating conditions of the refining tower include: tower top pressure of 10-60KPaG, tower bottom pressure of 10-60KPaG, tower top temperature of 60-100°C, tower bottom temperature of 80-120°C, and reflux ratio of 2-30;

[0160] The dehydration tower uses an extractive distillation process to separate acetic acid and water, and sulfolane is selected as the extraction solvent; the separated water is circulated back to the hydrolysis tower to continue to participate in the hydrolysis reaction; the separated crude acetic acid-extractant mixture enters the stripping tower. In the stripping tower, the crude acetic acid-extractant mixture is stripped to remove the heavy components (esterification waste liquid). The removed heavy components are sent to incineration. The acetic acid-extractant mixture with the heavy components removed enters the acetic acid tower, and is distilled and separated by using the boiling point difference between acetic acid (boiling point 110°C) and the extractant sulfolane (boiling point 285°C). The extractant sulfolane is removed, and the refined acetic acid obtained is sent back to the reactor to continue to participate in the reaction, or sold as a by-product; the extractant sulfolane is returned to the dehydration tower.

[0161] S6. Refining and hydrolysis of lactate: The methyl lactate mixed solution containing methanol enters the lactate distillation tower from the refining tower, and methanol and methyl lactate are separated by boiling point pressure difference. Methanol is distilled from the top of the lactate distillation tower, cooled by circulating water, and returns to the refining tower to continue esterification reaction with lactic acid; methyl lactate enters the lactate hydrolysis tower;

[0162] Water is introduced into the lactate hydrolysis tower, and methyl lactate is hydrolyzed in the lactate hydrolysis tower to generate lactic acid and methanol. Methanol is continuously distilled from the top of the lactate hydrolysis tower, so that the reaction continues. Methyl lactate is completely hydrolyzed in the hydrolysis tower to obtain lactic acid; the aqueous solution containing lactic acid obtained by hydrolysis is sent to the concentration tower to remove water, and the finished product of high-purity lactic acid is obtained. The methanol continuously distilled from the top of the lactate hydrolysis tower returns to the refining tower to continue to participate in the reaction;

[0163] The process operating conditions of the lactate hydrolysis tower include: the operating pressure is normal pressure, the methyl lactate feed temperature is ≤120°C, the water feed temperature is ≤60°C, and the water / methyl lactate feed ratio is 10 to 30:1.

[0164] In this embodiment, based on the reaction production of 1 ton of lactic acid (100%), approximately 1.33 tons of raw material vinyl acetate, 0.42 tons of carbon monoxide gas, 0.67 tons of by-product acetic acid, 0.19 tons of β-hydroxypropionic acid, and 0.06 tons of acetaldehyde are required.

[0165] The present invention uses natural gas as the initial raw material, uses the byproduct tail gas of acetylene produced by oxidizing natural gas to produce acetic acid, and then uses acetylene and acetic acid as raw materials to produce vinyl acetate. At the same time, acetylene byproduct tail gas PSA is used to extract CO, and then vinyl acetate and CO are carbonylated to synthesize lactic acid. The whole process industrial chain can realize closed-loop production. Except for the synthesis of lactic acid, the process technology is highly mature, the scale economy is reasonable, and the return on investment is high.

[0166] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for synthesizing lactic acid by carbonylation, characterized in that: Lactic acid is synthesized by carbonylation reaction with vinyl acetate and CO as raw materials in the presence of palladium / nickel catalysts. The synthesis route is as follows: CH2=CHOCOCH3+CO+H2o→HOOCCH(OCOCH3)CH3 HOOCCH(OCOCH3)CH3+H2O→CH3CH(OH)COOH+CH3COOH.

2. The method for synthesizing lactic acid by carbonylation according to claim 1, characterized in that: The reaction pressure is 2.0-3.0 MPaG, and the reaction temperature is 150°C-300°C; Preferably, the raw material vinyl acetate is synthesized from acetylene and acetic acid, wherein acetylene is produced by oxidation of natural gas, and acetic acid is produced from by-product tail gas of acetylene produced by oxidation of natural gas.

3. A production system for synthesizing lactic acid by carbonylation, characterized in that: It comprises a lactic acid reactor (1), a high-pressure and low-pressure separator (2), a tank distillation kettle (3), a vacuum tower (4), a hydrolysis tower (5), a refining tower (6), a lactate distillation tower (7), and a lactate hydrolysis tower (8) which are connected in sequence; The lactic acid reactor (1) is connected to a CO raw material conveying line (101), an acetic acid raw material conveying line (102) and a vinyl acetate raw material conveying line (103); the hydrolysis tower (5) is connected to a process water conveying line (110); the refining tower (6) is connected to a methanol raw material conveying line (112); the lactate hydrolysis tower (8) is connected to a second process water conveying line (117), and is connected to a lactic acid solution output line (118); Preferably, a carbon monoxide output line (104) is connected to the high-low pressure separator (2); preferably, the carbon monoxide output line (104) is connected to the lactic acid reactor (1); Preferably, a methanol output line (115) is connected to the top of the lactate distillation tower (7), and more preferably, the methanol output line (115) is connected to the refining tower (6); Preferably, the method further comprises a lactic acid concentration tower (9) connected to the lactate hydrolysis tower (8), wherein the lactate hydrolysis tower (8) is connected to the lactic acid concentration tower (9) via a lactic acid solution output line (118), and a finished lactic acid delivery line (120) is connected to the bottom of the lactic acid concentration tower (9).

4. The production system of carbonylation synthesis of lactic acid according to claim 3, characterized in that: It also includes a propionic acid separation tank (10), a lactic acid recovery tower (11), an acetic acid recovery tower (12) and a light component refining tower (13) which are connected in sequence; The propionic acid separation tank (10) is connected to the tank still (3); the propionic acid separation tank (10) is connected to a β-hydroxypropionic acid output line (126); Preferably, the lactic acid recovery tower (11) is connected to the tank still (3) via a lactic acid circulation line (128) for returning the recovered lactic acid to the tank still (3); Preferably, the acetic acid recovery tower (12) is connected to an acetic acid output line (131); Preferably, the light component refining tower (13) has an acetaldehyde output line (132) connected to the top and a vinyl acetate output line (133) connected to the bottom.

5. The production system of carbonylation synthesis of lactic acid according to claim 3, characterized in that: It also includes a dehydration tower (14), a stripping tower (15) and an acetic acid tower (16) which are connected in sequence; The dehydration tower (14) is connected to the refining tower (6); The bottom of the acetic acid tower (16) is connected to a refined acetic acid circulation line (124), and the top of the tower is connected to an extractant circulation line (134); Preferably, the refined acetic acid circulation line (124) is connected to the lactic acid reactor (1), and the extractant circulation line (134) is connected to the dehydration tower (14); Preferably, a circulating water output line (135) is connected to the top of the dehydration tower (14), and more preferably, the circulating water output line (135) is connected to the hydrolysis tower (5).

6. The production system of carbonylation synthesis of lactic acid according to claim 3, characterized in that: The lactic acid reactor (1) is a fixed bed reactor provided with a palladium / nickel catalyst bed; Or / and the refining tower (6) is divided into two sections, the upper section is a packed tower, and the lower section is a tubular fixed bed, wherein the tubular fixed bed is filled with a modified cationic resin catalyst.

7. An industrial production method for synthesizing lactic acid by carbonylation, characterized in that: The method is carried out using the system described in any one of claims 3 to 6.

8. The industrial production method according to claim 7, characterized in that: The steps include: S1. Continuous carbonylation of vinyl acetate: vinyl acetate, acetic acid and CO gas are fed into a lactic acid reactor and react with the catalyst bed in the lactic acid reactor to generate α-acetylpropionic acid and β-acetylpropionic acid. At the same time, part of the vinyl acetate is hydrolyzed to generate acetic acid and acetaldehyde. S2. Separation of α-acetylpropionic acid: The mixed material from the lactic acid reactor is sent to a high-low pressure separator for separation to separate CO gas and liquid mixed material; CO gas is discharged from the top of the high-low pressure separator, and the liquid mixed material is sent to a tank distillation kettle; Preferably, the CO gas is discharged from the top of the high-low pressure separator and then circulated back to the lactic acid reactor to participate in the reaction again; S3. Hydrolysis and separation: The β-acetyl propionic acid in the liquid mixture is hydrolyzed in a tank distillation kettle to generate β-hydroxypropionic acid and acetic acid, and part of the α-acetyl propionic acid in the liquid mixture is hydrolyzed to generate lactic acid and acetic acid; α-Hydroxypropionic acid, part of vinyl acetate, part of acetic acid and part of lactic acid are discharged from the bottom of the tank distillation kettle and sent to a vacuum tower; unreacted vinyl acetate and acetic acid are recovered in the vacuum tower and returned to the lactic acid reactor through the bottom of the vacuum tower; the mixed liquid of α-hydroxypropionic acid and lactic acid is sent from the vacuum tower to a hydrolysis tower; β-Hydroxypropionic acid is discharged from the upper part of the tank still together with acetaldehyde, part of vinyl acetate, part of acetic acid and part of lactic acid; Preferably, the mixed material discharged from the upper part of the tank still is first sent to a propionic acid separation tank to separate β-hydroxypropionic acid, which is extracted as a by-product; the material from which β-hydroxypropionic acid is separated is successively recovered by a lactic acid recovery tower and an acetic acid recovery tower to recover acetic acid; the recovered lactic acid is returned to the tank still, and the recovered acetic acid is sent to an acetic acid tank, and then refined in the acetic acid tower and returned to the lactic acid reactor to continue to participate in the reaction or be extracted as a by-product; the top material of the acetic acid recovery tower is sent to a light component refining tower to separate formaldehyde as a by-product, and vinyl acetate is sold as a by-product, or is sent to the reactor as a raw material after being refined to a qualified level; S4. Continuous hydrolysis of α-acetylpropionic acid: water is introduced into the hydrolysis tower, and the mixed solution of α-hydroxypropionic acid and lactic acid is continuously hydrolyzed in the hydrolysis tower to generate lactic acid; the hydrolyzed material is sent to the refining tower; the hydrolyzed material contains lactic acid, acetic acid and water; S5. Esterification of lactic acid: The hydrolyzed material is stripped and separated in a refining tower, and is separated into crude lactic acid and acetic acid aqueous solution in the upper section. The crude lactic acid and methanol undergo esterification reaction in the lower section to produce methyl lactate; the bottom liquid is a methyl lactate mixed liquid containing methanol, which is sent to a lactate distillation tower for treatment; Preferably, the acetic acid aqueous solution distilled from the top of the refining tower is sent to a dehydration tower for treatment; More preferably, the dehydration tower uses an extractive distillation process to separate acetic acid and water, sulfolane is selected as the extraction solvent, the obtained water is circulated back to the hydrolysis tower to continue to participate in the hydrolysis reaction, the crude acetic acid enters the stripping tower, the heavy components are removed and sent to incineration treatment, and then enters the acetate tower to remove the sulfolane solvent, and the refined acetic acid is sent back to the reactor to continue to participate in the reaction, or sold as a by-product; S6. Purification and hydrolysis of lactate: The methyl lactate mixed solution containing methanol enters the lactate distillation tower from the refining tower, and methanol is distilled from the top of the lactate distillation tower by using the boiling point pressure difference, and methyl lactate enters the lactate hydrolysis tower; water is introduced into the lactate hydrolysis tower, and methyl lactate is hydrolyzed in the lactate hydrolysis tower to produce lactic acid and methanol, and methanol is continuously distilled from the top of the lactate hydrolysis tower, so that the reaction continues, and methyl lactate is completely hydrolyzed in the hydrolysis tower to obtain lactic acid; Preferably, methanol is distilled from the top of the distillation tower, cooled by circulating water, and then returned to the refining tower to continue the esterification reaction with lactic acid; Preferably, the aqueous solution containing lactic acid obtained by hydrolysis is sent to a concentration tower to remove moisture to obtain finished high-purity lactic acid; Preferably, the methanol is returned to the refining tower for recycling.

9. The industrial production method according to claim 8, characterized in that: In step S1, the raw materials are mixed evenly in a mixer and then fed into a lactic acid reactor; Preferably, the process operating conditions of the lactic acid reactor include: a volume space velocity of 2 to 6 h -1 ; Reaction pressure is 2.0~3.0MPaG; Reactor inlet temperature is 150~300℃; Reactor temperature rise is 15~45℃; Reactor pressure drop is 0.1~0.5MPa; Preferably, the volume ratio of vinyl acetate to acetic acid is 4:1 to 5:1; Or / and in step S3, the process operating conditions of the tank distillation kettle include: operating pressure of 20-60KPaA; top temperature of 100-150°C; bottom temperature of the kettle of 200-250°C; Or / and in step S4, the process operating conditions of the hydrolysis tower include: the operating pressure is normal pressure, the feed temperature of the α-hydroxypropionic acid and lactic acid mixture is ≤250°C, the feed temperature of the process water is ≤100°C; the feed mass ratio of the α-hydroxypropionic acid and lactic acid mixture to water is 1 to 3:1; Or / and in step S5, the process operating conditions of the refining tower include: the tower top pressure is 10-60KPaG, the tower bottom pressure is 10-60KPaG, the tower top temperature is 60-100°C, the tower bottom temperature is 80-120°C, and the reflux ratio is 2-30; Or / and in step S6, the process operating conditions of the lactate hydrolysis tower include: the operating pressure is normal pressure, The methyl lactate feed temperature is ≤120°C, the water feed temperature is ≤60°C, and the water / methyl lactate feed ratio is 10 to 30:

1.

10. The industrial production method according to claim 8 or 9, characterized in that: The raw material vinyl acetate is synthesized from acetylene and acetic acid, wherein acetylene is produced by oxidation of natural gas, and acetic acid is produced from the by-product tail gas of acetylene produced by oxidation of natural gas.

Images