Method and apparatus for preparing glyoxylic acid from methyl glycolate

Abstract

The present invention relates to a method and apparatus for preparing glyoxylic acid from methyl glycolate. The method comprises the following steps: S1 oxidation reaction: introducing methyl glycolate and an oxidant into a reactor filled with an oxidation reaction catalyst, and performing an oxidation reaction to obtain a methyl glyoxylate product solution; S2 reduced-pressure hydrolysis: performing reduced-pressure hydrolysis on the methyl glyoxylate product solution, analyzing components of the resulting hydrolysate after online sampling, and entering the next process after reaching a preset value; S3 concentration and rectification: concentrating and rectifying the hydrolysate that reaches the preset value, analyzing components of the resulting glyoxylic acid solution after online sampling, and entering the next process after reaching a preset value; and S4 decarboxylation reaction: introducing the glyoxylic acid solution that reaches the preset value into a reactor filled with a decarboxylation catalyst for a catalytic decarboxylation reaction to obtain a glyoxylic acid solution of target quality. Compared with the prior art, the present invention has the advantages of low environmental pollution, low energy consumption, high product purity, excellent color, and the like. The content of oxalic acid in the product is less than 400 ppm, and the product is colorless or pale yellow.

Description

Method and device for preparing glyoxylic acid from methyl glycolate TECHNICAL FIELD

[0001] The present application relates to the technical field of glyoxylic acid production, and in particular to a method and device for preparing glyoxylic acid from methyl glycolate. BACKGROUND

[0002] Glyoxylic acid is composed of an aldehyde group (-CHO) and a carboxyl group (-COOH), and is the simplest aldehyde acid. As an important organic synthesis intermediate raw material, glyoxylic acid is active in chemical properties and plays a significant role in the fields of cosmetics, medicine, food, etc. For example, glyoxylic acid is often used as a raw material to produce mandelic acid, vanillin, acetophenone, allantoin, etc.

[0003] Currently, the main methods for producing glyoxylic acid in industry include glyoxal nitric acid oxidation method, oxalic acid electrolysis method, and maleic anhydride ozonation reduction method. The glyoxal nitric acid oxidation method can synthesize glyoxylic acid in one step, but this reaction has the following shortcomings: the reaction is prone to over-oxidation, the raw materials used are expensive, the content of by-products is high, and the equipment is prone to corrosion, etc.; the oxalic acid electrolysis method is easy to operate and has little pollution, but the quality of the product produced is poor and the energy consumption is high; the maleic anhydride ozonation reduction method produces products with good quality and high yield, but the reaction conditions are harsh and the operation is not convenient. Therefore, it is of great significance to develop a new method for synthesizing glyoxylic acid.

[0004] Compared with the industrialized process, the oxidation of methyl glycolate to prepare methyl glyoxylate and then hydrolysis to glyoxylic acid has broader development prospects. Methyl glycolate is a by-product derived from the process of synthesizing glycol from dimethyl oxalate, and its use to prepare glyoxylic acid improves the utilization rate of the by-product and solves the problem of the supply of raw materials for the production of glyoxylic acid. This process has the advantages of simple operation, easy control of reaction, and little pollution. The use of this route to produce glyoxylic acid has more economic benefits.

[0005] Previous studies have shown that the selection of catalyst and oxidant has a great influence on the reaction in the process of preparing methyl glyoxylate from methyl glycolate, and in the subsequent synthesis of glyoxylic acid, because the glyoxylic acid solution contains many heat-sensitive substances, if the reaction temperature is too high or the reaction time is too long during the synthesis, the product solution color will be too dark, which does not meet the industrialized solution color standard, and affects the development of downstream products. In the existing technology, the production of glyoxylic acid includes the synthesis of crude product and the refining and purification of the crude product. The synthesis of the crude product is usually carried out at normal pressure, and the refining and purification of the crude product includes concentrating to the target product solution under reduced pressure or cooling crystallization to monohydrate after concentration in a batch kettle. The whole process is relatively cumbersome, and the batch reaction has the disadvantages of high equipment operation cost, low production efficiency, long reaction time, and high energy consumption. In view of the above shortcomings, relevant technical personnel have carried out relevant research on the synthesis process of glyoxylic acid.

[0006] Chinese patent CN112778118 A discloses a method for preparing glyoxylic acid from methyl glycolate, in which methyl glycolate is contacted with a mixture of solvents and an oxidation catalyst and a hydrolysis catalyst, and glyoxylic acid is obtained by reaction. The conversion rate of reactants and the selectivity of products are high in the whole process, but the polar solvent used is trifluoroacetic acid and / or fluorinated alcohol compounds, which are highly toxic and not suitable for mass production.

[0007] Chinese patent CN107445830 A synthesizes a catalyst with molybdenum and vanadium as active components, alumina, zirconia and titania as carriers, and palladium, manganese, nickel, cerium and potassium as additives. Nitrogen oxides are added to the oxygen-containing gas to prevent the excessive oxidation of methyl glyoxalate, but the post-reaction tail gas treatment is difficult and the energy consumption is high. SUMMARY

[0008] The purpose of the present application is to provide a method and device for preparing glyoxylic acid from methyl glycolate, which has low environmental pollution, low energy consumption, high product purity and excellent color, and the content of oxalic acid in the product is less than 400 ppm, which is colorless or light yellow.

[0009] The purpose of the present application can be achieved by the following technical solution: a method for preparing glyoxylic acid from methyl glycolate, comprising the following steps:

[0010] S1 oxidation reaction: methyl glycolate and an oxidizing agent are introduced into a reactor filled with an oxidation reaction catalyst, and methyl glycolate product liquid is obtained by oxidation reaction;

[0011] S2 pressure reduction hydrolysis: the methyl glycolate product liquid is subjected to pressure reduction hydrolysis, and the composition of the obtained hydrolysis liquid is analyzed after online sampling. When the preset value is reached, the next process is entered;

[0012] S3 concentration and rectification: the hydrolysis liquid reaching the preset value is subjected to concentration and rectification, and the composition of the obtained glyoxylic acid solution is analyzed after online sampling. When the preset value is reached, the next process is entered;

[0013] S4 decarboxylation reaction: the glyoxylic acid solution reaching the preset value is introduced into a reactor filled with a decarboxylation catalyst to perform catalytic decarboxylation reaction, and a target quality glyoxylic acid solution is obtained.

[0014] Preferably, the oxidizing agent of step S1 includes oxygen, and the oxidation reaction catalyst includes a metal-modified VPO-based catalyst.

[0015] Further preferably, step S1 introduces a mixed gas containing 5-20% oxygen by volume into the reactor filled with the oxidation reaction catalyst.

[0016] More preferably, the mixed gas is air and nitrogen mixed gas.

[0017] Further preferably, the temperature of the oxidation reaction in step S1 is 100-300℃, the pressure is 0.05-1.0 MPa, the molar ratio of the oxygen alcohol is (0.5:1)-(16:1), and the liquid hourly space velocity is 0.1-1 h -1 .

[0018] Further preferably, the metal-modified VPO-based catalyst is a metal M1 and / or M2 modified VPO-based catalyst, M1 includes one or more of Mo, W, Mn, Nb, Zr, and M2 is one or more of alkaline earth metals.

[0019] More preferably, the alkaline earth metal includes Mg, Ca, and Ba.

[0020] Further preferably, the metal-modified VPO-based catalyst is supported on SiO2, Al2O3, ZSM-5, or mordenite.

[0021] Further preferably, in the metal-modified VPO-based catalyst, the atomic ratio of M1, M2, and V is 0.06-0.8:1, and the mass of M1 and M2 accounts for 10%-40% of the total mass of the catalyst.

[0022] Further preferably, the preparation method of the metal-modified VPO-based catalyst comprises the following steps:

[0023] (1) Ammonium metavanadate is added to deionized water and stirred until completely dissolved, 85wt% phosphoric acid is quickly added dropwise to the solution, and then oxalic acid dihydrate is added, after dissolution, the solution is allowed to stand, and soluble salts of M1 and / or M2 are sequentially added;

[0024] (2) The solution obtained in step (1) is used to impregnate the carrier, and the carrier is allowed to stand for 8-12 h, then dried at 80-150℃ for 6-12 h, and then calcined at 500-700℃ for 3-6 h to obtain the metal-modified VPO-based catalyst.

[0025] The catalyst used in the oxidation reaction process has good activity, high product selectivity, and can be recycled, and the process is simple to operate. The oxidizing agent used is stable in nature, low in price, and non-polluting. The reaction product has relatively low impurity content, which reduces the difficulty of impurity separation in the subsequent hydrolysis process, thereby reducing the production cost of the entire process. The conversion rate of methyl glycolate in the oxidation reaction is more than 99%, and the selectivity of methyl glyoxylate is more than 98%.

[0026] Preferably, the liquid product obtained by the oxidation reaction in step S1 is subjected to gas-liquid separation in a gas-liquid separation tank, and the liquid product obtained is subjected to vacuum hydrolysis.

[0027] Further preferably, the condensation temperature of the gas-liquid separation tank is -40 to -10℃.

[0028] In the present application, the content of methyl glyoxylate in the liquid product and the stability can be further improved by gas-liquid separation, and the content of organic phase in the gas phase is reduced.

[0029] In the present application, the composition of the liquid product comprises 82-89 wt% of methyl glyoxylate, 0.10-0.20 wt% of methyl glycolate, 0.5-1.2 wt% of oxalic acid, 0.1-0.4 wt% of methanol, and 14-18 wt% of water.

[0030] Preferably, the pressure-reduced hydrolysis in step S2 is carried out in a pressure-reduced hydrolysis rectifying column, and the absolute pressure in the pressure-reduced hydrolysis rectifying column is 0-100 kPa.

[0031] In the present application, the reaction temperature can be reduced by designing the pressure-reduced condition, which is beneficial to solve the problem of deepening of the color of the solution due to decomposition of heat-sensitive substances at high temperatures.

[0032] Further preferably, the pressure-reduced hydrolysis in step S2 specifically comprises the following steps: first, adding a raw solution to the pressure-reduced hydrolysis rectifying column to 30-50% of the maximum volume capacity, and then, after the temperature of the column bottom and the column top is stabilized, introducing the methyl glyoxylate product liquid obtained by the oxidation reaction.

[0033] In the present application, by first introducing the raw solution to 30-50% of the maximum volume capacity, the pressure-reduced hydrolysis rectifying column can be quickly started and quickly reach a stable state.

[0034] More preferably, the raw solution is one of a 40-60 wt% aqueous glyoxylic acid solution and deionized water.

[0035] More preferably, after the raw solution is added to the pressure-reduced hydrolysis rectifying column, the column top circulating condenser is opened, the temperature of the column bottom heater is set, the reflux ratio is set, the reaction is started, and after the temperature of the column bottom and the column top is stabilized, the methyl glyoxylate product liquid and water are introduced into the pressure-reduced hydrolysis rectifying column for pressure-reduced hydrolysis.

[0036] Preferably, the temperature of the column bottom heater of the pressure-reduced hydrolysis rectifying column is 40-110°C, the temperature of the column top is 30-110°C, and the reflux ratio is 1-30.

[0037] Further preferably, the temperature of the column top of the pressure-reduced hydrolysis rectifying column is 30-80°C.

[0038] Further preferably, the reflux ratio is 1-20.

[0039] Preferably, the molar ratio or mass ratio of water to methyl glyoxylate in the methyl glyoxylate product liquid introduced into the pressure-reduced hydrolysis rectifying column is 1-20.

[0040] Further preferably, the water fed into the decompression hydrolysis rectification tower includes water fed into the decompression hydrolysis rectification tower through the process water pipeline and water contained in the methyl glyoxylate product liquid.

[0041] Further preferably, the device used for online sampling in step S2 includes a liquid taking circuit arranged at the outlet of the decompression hydrolysis rectification tower, and a vacuum valve is arranged on the liquid taking circuit. After the temperature of the tower bottom and the tower top is stable, the vacuum valve is opened to collect the tower bottom effluent for online sampling. After sampling is completed, the vacuum valve is closed, and the collected tower bottom effluent is detected and analyzed.

[0042] Alternatively, the online sampling and analysis in step S2 includes detection by connecting a mass spectrometer or other instrument to the tower bottom of the decompression hydrolysis rectification tower.

[0043] Further preferably, the sampling amount of each online sampling in step S2 is 3-5 mL.

[0044] Preferably, after online sampling in step S2, the conversion rate of methyl glyoxylate and the concentration of glyoxylic acid in the hydrolysis liquid are analyzed. When the values of the two reach preset values, concentration rectification is performed. The preset value of the conversion rate of methyl glyoxylate is 99-100%, and the preset value of the concentration of glyoxylic acid is 20-70 wt%. The yield of glyoxylic acid after hydrolysis is above 98%.

[0045] Preferably, the concentration rectification in step S3 is performed in a concentration rectification tower, and the absolute pressure in the concentration rectification tower is 0-100 kPa.

[0046] Further preferably, the concentration rectification in step S3 specifically includes the following steps: the hydrolysis liquid is fed into the concentration rectification tower, and after the amount of the hydrolysis liquid reaches 30-50% of the maximum volume of the concentration rectification tower, the hydrolysis liquid is heated for concentration. After the temperature of the tower bottom and the tower top is stable, the feeding is continued.

[0047] Further preferably, a feeding flow meter is arranged at the feeding inlet of the concentration rectification tower for detecting the feeding flow rate, and a tower bottom effluent flow meter is arranged at the tower bottom for detecting the amount of the tower bottom effluent.

[0048] Further preferably, the device used for online sampling in step S3 includes a liquid taking circuit arranged at the outlet of the concentration rectification tower, and a vacuum valve is arranged on the liquid taking circuit. After the temperature of the tower bottom and the tower top is stable, the vacuum valve is opened to collect the tower bottom effluent for online sampling. After sampling is completed, the vacuum valve is closed, and the collected tower bottom effluent is detected.

[0049] Alternatively, the online sampling and analysis in step S3 includes detection by connecting a mass spectrometer or other instrument to the tower bottom of the concentration rectification tower.

[0050] Further preferably, the sampling amount of each online sampling in step S3 is 3-5 mL.

[0051] Preferably, the step S3 is to analyze the concentration of glyoxylic acid in the glyoxylic acid solution after sampling in line, and the decarboxylation reaction of the glyoxylic acid solution is carried out when the preset value of the concentration of glyoxylic acid is reached, and the preset value of the concentration of glyoxylic acid is 30-90wt%.

[0052] Preferably, the decarboxylation catalyst in the step S4 is a Pd (palladium) -based catalyst with inorganic material as the carrier and transition metal elements, post-transition metal elements or rare earth elements as the adjuvants.

[0053] Further preferably, the content of Pd in the decarboxylation catalyst is 0.1wt%-10wt%, and the content of the adjuvant is 0.1wt%-5wt%.

[0054] Further preferably, the inorganic material includes Al2O3, SiO2, TiO2, MCM-41, SAPO-34.

[0055] Further preferably, the transition metal elements include Cu, Ag, Co.

[0056] Further preferably, the post-transition metal elements include Bi.

[0057] Further preferably, the rare earth elements include Ce, La.

[0058] Further preferably, the carrier of the decarboxylation catalyst has a pore volume of 0.1cm 3 / g-1cm 3 / g, and a specific surface area of 200-600m 2 / g.

[0059] Further preferably, the decarboxylation catalyst is prepared by impregnation method, and the preparation method includes the following steps: dissolving PdCl2 and soluble salt of the adjuvant in 60-80mL aqueous solution, adjusting the pH value of the solution to 2-5 with hydrochloric acid solution, stirring the solution until complete dissolution, adding 2-5g of the carrier, continuing to stir at room temperature to dissolve, evaporating water at 60-80℃, and then drying at 80-120℃ and calcining at 500-700℃ to obtain the catalyst.

[0060] Further preferably, the decarboxylation catalyst is a Pd-based catalyst with Al2O3 as the carrier and Cu or Ag as the adjuvant, and the preparation method includes the following steps: dissolving PdCl2, Ag salt or Cu salt in 60-80mL aqueous solution, adjusting the pH value of the solution to 2-5 with hydrochloric acid solution, stirring the solution until complete dissolution, adding 2-5g of solid Al2O3, continuing to stir at room temperature to dissolve, evaporating water at 60-80℃, and then drying at 80-120℃ and calcining at 500-700℃ to obtain the catalyst.

[0061] Preferably, the Ag salt and Cu salt are one of nitrate and carbonate.

[0062] Preferably, the precursor salt used for synthesizing the carrier Al2O3 is Al(NO3)9H2O or C9H 21 AlO3.

[0063] Further preferably, the method for preparing the carrier Al2O3 comprises the following steps: dissolving the precursor salt of aluminum in 100-120 mL of aqueous solution, stirring until completely dissolved, adding concentrated ammonia water dropwise to the solution, adjusting the pH value to 8-10, and continuing to stir for 1-2 h, performing suction filtration on the obtained solid and washing with deionized water until the pH value is 7, drying the obtained filter cake at 110-120°C, and calcining at 500-600°C to obtain the carrier Al2O3.

[0064] Preferably, the decarboxylation reaction conditions in step S4 include: a reaction temperature of 40-90°C, a reaction pressure of normal pressure, a nitrogen atmosphere, a nitrogen flow rate of 100-800 mL / min, and an acetaldehyde acid solution feed liquid hourly space velocity of 0.5-3.0 h -1 .

[0065] The decarboxylation reaction catalyst has good activity, a low reaction temperature, and high product selectivity, and can effectively convert oxalic acid in the acetaldehyde acid solution into carbon monoxide, carbon dioxide, and water.

[0066] In the present application, the decarboxylation reaction product comprises acetaldehyde acid, glycolic acid (ppm level), oxalic acid (ppm level), carbon monoxide, carbon dioxide, and water. After decarboxylation, the acetaldehyde acid content in the acetaldehyde acid solution is 20-60 wt%, and the oxalic acid content is less than 400 ppm. The final product acetaldehyde acid solution is colorless or light yellow, and the solution colority is 20-200 Hazen (platinum-cobalt color number).

[0067] A device for realizing the above-mentioned method for preparing acetaldehyde acid from methyl glycolate comprises an oxidation fixed-bed reactor R101, a hydrolysis rectification tower T101, a concentration rectification tower T102, and a decarboxylation fixed-bed reactor R102 arranged in sequence.

[0068] Preferably, a first storage tank D102 is arranged between the hydrolysis rectification tower T101 and the concentration rectification tower T102.

[0069] Preferably, a second storage tank D103 is arranged between the concentration rectification tower T102 and the decarboxylation fixed-bed reactor R102.

[0070] Preferably, the decarboxylation fixed-bed reactor R102 is connected with an acetaldehyde acid product storage tank D104.

[0071] Preferably, a gas-liquid separation tank D101 is arranged between the oxidation reactor R101 and the hydrolysis rectification tower T101.

[0072] Further preferably, the condensation temperature of the gas-liquid separation tank D101 is -40 to -10°C.

[0073] Further preferably, the condensation temperature of the gas-liquid separation tank D101 is -30 to -20°C.

[0074] Preferably, the device further comprises a methanol separation column T103, and the top of the hydrolysis rectification column T101 and the top of the concentration rectification column T102 are connected to the methanol separation column T103.

[0075] In the present application, the purity of the methanol separated by the methanol separation column T103 can reach more than 99.5%.

[0076] Preferably, the device further comprises a tail gas absorption column T104, and the top of the oxidation fixed bed reactor R101 is connected to the tail gas absorption column T104, and the top of the decarboxylation fixed bed reactor R102 is connected to the tail gas absorption column T104.

[0077] Preferably, the bottom of the gas-liquid separation tank D101 is connected to the feed line of the hydrolysis rectification column T101, the feed inlet of the hydrolysis rectification column T101 is connected to the raw material liquid line and the water line, the top of the hydrolysis rectification column T101 is connected with a first top condenser E101, and the top outlet is connected to a first light phase receiving bottle D105, and the column kettle is connected with a first column kettle heater E102 and a first storage tank D102.

[0078] Preferably, the feed inlet of the hydrolysis rectification column T101 is provided with a first feed pump P101AB, and the control feed amount is 0 to 20 mL / min.

[0079] Preferably, the feed inlet of the concentration rectification column T102 is connected to the column kettle of the hydrolysis rectification column T101, and the column kettle and the top of the concentration rectification column T102 are also connected with a second column kettle heater E104 and a second top condenser E103, and a second light phase receiving bottle D106.

[0080] In the present application, the first light phase receiving bottle D105 and the second light phase receiving bottle D106 can store light phase, and the light phase is introduced into the methanol separation column T103 for methanol separation.

[0081] Preferably, the top condenser outlets of the hydrolysis rectification column T101 and the concentration rectification column T102 are respectively connected to a first high vacuum unit P101 and a second high vacuum unit P102.

[0082] Preferably, the hydrolysis rectification column T101 and the concentration rectification column T102 are both provided with a stirrer.

[0083] Preferably, the hydrolysis rectifying column T101 and the concentration rectifying column T102 are both provided with packing. In order to increase the mass transfer effect, the hydrolysis rectifying column T101 and the concentration rectifying column T102 are provided with packing, which is one of Rasching ring, Pall ring, stepped ring and Ket ring.

[0084] Preferably, the feeding position of the hydrolysis rectifying column T101 and the concentration rectifying column T102 is column feeding or tank feeding.

[0085] Preferably, the hydrolysis rectifying column T101 and the concentration rectifying column T102 are both provided with vacuum valves for on-line sampling.

[0086] Preferably, the concentration rectifying column T102 is connected with a second storage tank D103 and connected with the feeding line of the decarboxylation fixed bed reactor R102.

[0087] Preferably, the temperature of the first tank heater E102 and the second tank heater E104 is 40-110℃.

[0088] Preferably, the temperature of the first overhead condenser E101 and the second overhead condenser E103 is 30-80℃.

[0089] Preferably, the absolute pressure of the hydrolysis rectifying column T101 and the concentration rectifying column T102 is controlled at 0-100kPa.

[0090] Further preferably, the absolute pressure of the hydrolysis rectifying column T101 and the concentration rectifying column T102 is controlled at 2-98kPa.

[0091] Preferably, the vacuum degree of the hydrolysis rectifying column T101 and the concentration rectifying column T102 is controlled at 0.010MPa-0.098MPa by a high vacuum unit, so as to reduce the boiling point of the reaction solution and make the reaction at a lower temperature.

[0092] Preferably, the device is connected with a control system. Preferably, the method for preparing glyoxylic acid from methyl glycolate comprises the following steps:

[0093] S1 oxidation reaction: methyl glycolate and an oxidant are fed into an oxidation fixed bed reactor R101 filled with an oxidation reaction catalyst, and an oxidation reaction is carried out in the presence of the catalyst and the oxidant to obtain a methyl glyoxylate product liquid.

[0094] S2: Reducing pressure hydrolysis: The methyl glyoxylate product liquid is separated by gas-liquid separation tank D101, and then the separated product liquid is pumped into the reducing pressure hydrolysis rectifying tower T101 for reducing pressure hydrolysis. The first high vacuum unit P101 is opened, and the absolute pressure of the reducing pressure hydrolysis rectifying tower T101 is adjusted to 0-100 kPa. After the pressure of the reducing pressure hydrolysis rectifying tower T101 is stabilized, the original liquid is added to the hydrolysis rectifying tower T101 to 30%-50% of the maximum volume capacity, and then the first overhead condenser E101 is opened, the temperature of the first column heater E102 is set, and the reflux ratio is set to start the reaction. After the column bottom and overhead temperatures are stabilized, the separated product liquid and water are introduced into the reducing pressure hydrolysis rectifying tower for reducing pressure hydrolysis. The overhead light phase distillate is collected by the first light phase receiving bottle D105. After the column bottom and overhead temperatures are stabilized, the conversion rate of methyl glyoxylate and the concentration of glyoxylic acid in the hydrolysis liquid are analyzed by online sampling. When the values of the two reach the preset values, the next process is prepared.

[0095] S3: Concentration rectification: The second high vacuum unit P102 is opened to adjust the pressure of the concentration rectification tower T102 to 0-100 kPa. When the hydrolysis process is stable and the conversion rate of methyl glyoxylate and the concentration of glyoxylic acid reach the preset values, the hydrolysis liquid is introduced into the concentration rectification tower T102, and heating is performed after the concentration liquid reaches 30%-50% of the maximum volume capacity of the concentration rectification tower T102. At this time, the feed valve of the concentration rectification tower T102 is closed, the second overhead condenser E103 is opened, the temperature of the second column heater E104 is set, and the column bottom and overhead temperatures are stabilized. If the amount of hydrolysis liquid is large, it can be stored in the first storage tank D102, and the light phase is collected at the top of the tower by the second light phase receiving bottle D106. After the column bottom and overhead temperatures are stabilized, the concentration of glyoxylic acid is analyzed by online sampling, and when the preset value is reached, the product liquid is collected in the second storage tank D103.

[0096] S4: Decarboxylation reaction: The glyoxylic acid solution in the second storage tank D103 is introduced into the decarboxylation fixed bed reactor R102 for catalytic decarboxylation reaction to reduce the content of oxalic acid in the product and obtain a high-purity glyoxylic acid solution.

[0097] Compared with the prior art, the present application has the following beneficial effects:

[0098] 1. The present application refines methyl glycolate into a high-purity and high-color ethanedioic acid solution through the design of four processes of oxidation reaction, reducing pressure hydrolysis, concentration rectification, and decarboxylation reaction.

[0099] 2. The present application optimizes the process route of methyl glycolate to glyoxalic acid, which comprises four stages of oxidation, hydrolysis, concentration and refining. By selecting the catalyst for the oxidation stage, optimizing the conditions of the hydrolysis and concentration stage, and designing the online monitoring system for the hydrolysis and concentration steps, a high-quality glyoxalic acid solution with different concentrations can be obtained. The selected process has the characteristics of small environmental pollution, simple operation, low energy consumption, high product purity and excellent color.

[0100] 3. The oxidation stage of the present application uses a VPO-based catalyst modified with metal M1 and / or M2, and air as the oxidant under the condition of a fixed bed reactor. The catalyst has good activity, high product selectivity, and can be recycled. The process is simple to operate. The oxidant is stable in nature, low in price, and pollution-free. The reaction product has relatively low impurity content, which reduces the difficulty of impurity separation in the subsequent hydrolysis process, thereby reducing the production cost of the entire process.

[0101] 4. The hydrolysis and concentration of the present application are carried out under reduced pressure, and the reaction temperature is relatively low, which solves the problem of deepening of the color of the glyoxalic acid solution due to the decomposition of heat-sensitive substances in the solution at high temperature. The color of the final product, glyoxalic acid solution, is within the standard range.

[0102] 5. The hydrolysis and concentration of the present application can be carried out continuously, and real-time online sampling analysis can be used to avoid the vacuum adjustment process and temperature rising and falling process of batch reactions, so that the temperature and pressure of the reaction system are stable, the entire production cycle is short, and the energy consumption is reduced while reducing manual operation.

[0103] 6. The present application adds a process to remove oxalic acid, and obtains a glyoxalic acid solution with high purity and excellent color.

[0104] 7. The oxidation catalyst and decarboxylation catalyst of the present application are both heterogeneous catalysts, and the product and catalyst are easy to separate, which ensures the quality of the product.

[0105] 8. The entire process of the present application has small corrosion and pollution, less waste, and high safety. BRIEF DESCRIPTION OF DRAWINGS

[0106] Figure 1 is a process flow diagram of the present application;

[0107] Figure 2 is a process flow diagram of the present application;

[0108] In the figure:

[0109] R101-oxidation fixed bed reactor, R102-decarboxylation fixed bed reactor;

[0110] D101-gas-liquid separation tank, D102-first storage tank, D103-second storage tank, D104-glyoxalic acid product storage tank, D105-first light phase receiving bottle, D106-second light phase receiving bottle;

[0111] T101 - hydrolysis rectification column, T102 - concentration rectification column, T103 - methanol separation column, T104 - tail gas absorption column;

[0112] E101 - first column top condenser, E102 - first column bottom heater, E103 - second column top condenser, E104 - second column bottom heater;

[0113] P101 - first high vacuum set, P102 - second high vacuum set;

[0114] P101AB - first feed pump, P102AB - second feed pump, P103AB - third feed pump. DETAILED DESCRIPTION

[0115] The present application will be described in detail below with reference to the drawings and specific examples. The present embodiment is implemented on the premise of the technical solution of the present application, and gives a detailed implementation and specific operation process, but the protection scope of the present application is not limited to the following examples.

[0116] Unless otherwise specified, the reagents, methods, instruments and equipment used in the present application are conventional reagents, methods, instruments and equipment in the art. Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0117] Among them, the oxidation reaction catalyst used in the following examples is a VPO-based catalyst (oxidation reaction catalyst) modified with SiO2 as the carrier, Mo, Nb and Ba, and the preparation method comprises the following steps:

[0118] 1.86 g of ammonium metavanadate was added to 20 g of deionized water to prepare a solution with a vanadium concentration of 0.73 mol / kg, 10 g of 85 wt% phosphoric acid was added quickly, then 2 times the molar amount of oxalic acid dihydrate was slowly added, after dissolution, it was left to stand, then 4.2 g of ammonium heptamolybdate tetrahydrate, 0.60 g of ammonium niobium oxalate and 0.47 g of barium hydrogen phosphate were weighed and added to the solution in turn until completely dissolved, the resulting impregnation solution was impregnated with an equal volume of silica carrier, left to stand for 12 h, dried at 110°C for 8 h, and calcined at 600°C for 3 h to obtain the oxidation reaction catalyst.

[0119] The decarboxylation catalyst used in the following examples is a Pd-based catalyst with Al2O3 as the carrier and Cu or Ag as the additive, 0.5 wt% Pd / 1 wt% Cu-Al2O3 or 0.5 wt% Pd / 1 wt% Ag-Al2O3, which is prepared by impregnation method.

[0120] The preparation method of 0.5wt%Pd / 1wt%Cu-Al2O3 includes the following steps: dissolving PdCl2 and CuCO3 in 60mL aqueous solution, adjusting the pH value of the solution to 2 with hydrochloric acid solution, stirring the solution until completely dissolved, adding 3g of solid Al2O3, continuing to stir at room temperature to dissolve, evaporating water at 60°C, and then drying at 120°C and calcining at 500°C to obtain the decarboxylation catalyst.

[0121] The preparation method of 0.5wt%Pd / 1wt%Ag-Al2O3 includes the following steps: dissolving PdCl2 and Ag2CO3 in 80mL aqueous solution, adjusting the pH value of the solution to 3 with hydrochloric acid solution, stirring the solution until completely dissolved, adding 5g of solid Al2O3, continuing to stir at room temperature to dissolve, evaporating water at 70°C, and then drying at 100°C and calcining at 700°C to obtain the catalyst.

[0122] The following example raw material methyl glycolate is a derivative by-product in the process of synthesizing gas from dimethyl oxalate to ethylene glycol, and the composition includes 70-99wt% of methyl glycolate, and the rest is methanol and water.

[0123] A method and device for preparing glyoxylic acid from methyl glycolate, as shown in Figure 1, wherein the process method includes four stages of oxidation, hydrolysis, concentration and refining, and the process device includes the devices used for oxidation, hydrolysis, concentration and refining. The process method includes the following contents:

[0124] (1) Oxidation: The oxidation of methyl glycolate to methyl glyoxylate is carried out in a heterogeneous system of oxidation fixed bed reactor R101, and the oxidation reaction is carried out in the presence of catalyst and oxidant to obtain high selectivity of methyl glyoxylate product liquid;

[0125] (2) Hydrolysis distillation: The oxidation product is subjected to gas-liquid separation in a gas-liquid separation tank D101, and then the separated product liquid is pumped into a reduced-pressure hydrolysis distillation column T101 for hydrolysis reaction. A first high-vacuum unit P101 is opened, and the absolute pressure of the reduced-pressure hydrolysis distillation column T101 is adjusted to 0-100 kPa; after the pressure of the reduced-pressure hydrolysis distillation column T101 stabilizes, the original liquid is added to the hydrolysis distillation column T101 through a first feed pump P101AB to 30%-50% of the maximum volume capacity, and then heating is performed, a column top circulating condenser (first column top condenser E101) is opened, the load of a first column bottom heater E102 and the reflux ratio are adjusted, after the column bottom and column top temperatures stabilize, the feed liquid is introduced, and the hydrolysis distillation column T101 column bottom is stabilized to produce acetic acid aqueous solution. The feed liquid is a mixed liquid of two lines, including an ethylene glycol methyl ester oxidation product liquid (i.e., methyl glyoxylate product liquid) pipeline and a water pipeline. The column top light phase distillate is collected by a first light phase receiving bottle D105. The column bottom is sampled in real time to analyze the conversion rate of methyl glyoxylate and the concentration of glyoxylic acid in the hydrolysis liquid, and the values of the two are controlled to reach the preset values, wherein the hydrolysis liquid is stored in a first storage tank D102.

[0126] (3) Concentration distillation: a second high-vacuum unit P102 is opened to adjust the pressure of the concentration distillation column T102 to 0-100 kPa, when the hydrolysis process stabilizes and the conversion rate of methyl glyoxylate and the concentration of glyoxylic acid reach the preset values, the hydrolysis liquid is introduced into the concentration distillation column T102, and after the concentration liquid reaches 30%-50% of the maximum volume capacity of the concentration distillation column T102, heating is performed for distillation concentration, a second column top condenser E103 is opened, the load of a second column bottom heater E104 and the reflux ratio are adjusted, after the column bottom and column top temperatures stabilize, the hydrolysis liquid is continuously introduced, and the column bottom of the concentration distillation column is stabilized to produce glyoxylic acid product. The light phase of T102 is collected at the column top by a second light phase storage tank D106. The column bottom is sampled in real time to analyze and control the concentration of glyoxylic acid to be 30-90 wt%. The column top light phase liquid of the hydrolysis distillation column T101 and the concentration distillation column T102 is subjected to methanol separation by a methanol separation column T103, wherein methanol is collected at the column top, and the column bottom is connected to the feed pipeline of the hydrolysis distillation column T101 to make the aqueous solution containing a small amount of methyl glyoxylate undergo secondary hydrolysis.

[0127] (4) Glyoxylic acid solution refining: the glyoxylic acid solution in the second storage tank D103 is pumped into a decarboxylation fixed bed reactor R102 through a third feed pump P103AB, and catalytic decarboxylation reaction is performed under the set reaction conditions to reduce the oxalic acid content in the product and obtain a high-purity glyoxylic acid solution, wherein the tail gas is treated in a tail gas absorption column T104.

[0128] The following will be described in detail with reference to specific examples.

[0129] Example 1

[0130] Example 1 provides a method and device for preparing glyoxylic acid from methyl glycolate. The process method comprises: using a VPO-based catalyst modified with Mo, Nb and Ba as the oxidation catalyst, using air-nitrogen mixed gas with 15% O2volume fraction as the oxidant, and allowing methyl glycolate to undergo oxidation reaction in an oxidation fixed-bed reactor R101. The oxidation reaction temperature is 200°C, the pressure is 0.5 MPa, the molar ratio of oxygen to alcohol is 8:1, the liquid hourly space velocity is 0.5 h -1 -1 The oxidation reaction product is subjected to gas-liquid separation in a gas-liquid separation tank D101 with a condensation temperature of -20°C, and the typical composition of the obtained liquid phase product is as follows:

[0131] The separated product liquid is then introduced into the hydrolysis distillation column T101 to perform the hydrolysis reaction. The first high vacuum unit P101 is opened to adjust the absolute pressure of the hydrolysis distillation column T101 to 25 kPa; after the pressure is stabilized, the 40 wt% glyoxylic acid solution is added to the hydrolysis distillation column T101 through the first feed pump P101AB to 50% of the maximum volume capacity, and then the circulating condenser (the first overhead condenser E101) is opened, the first column heater E102 is set to 50°C, and the reflux ratio is 10 to start the reaction. After the column and overhead temperatures are stabilized, the first feed pump P101AB is opened to start feeding at a feed rate of 3 mL / min, wherein the feed liquid is a mixture of the two lines, including the methyl glycolate oxidation product liquid line and the water line, and the water ester ratio is 2. The overhead light phase distillate is collected by the first light phase receiving bottle D105. After the column and overhead temperatures are stabilized, the vacuum valve is opened for online sampling to analyze the conversion rate of methyl glyoxylate and the concentration of glyoxylic acid in the hydrolysis liquid. When the conversion rate of methyl glyoxylate is more than 99% and the concentration of glyoxylic acid is 20 wt%, the hydrolysis liquid is introduced into the concentration distillation column T102. After the amount of the concentrated liquid reaches 30% of the maximum volume capacity of the concentration distillation column, heating is performed for concentration. At this time, the feed valve of the concentration distillation column T102 is closed. The concentration distillation column T102 has been adjusted to a pressure of 3 kPa by the second high vacuum unit P102. The second overhead condenser E103 is opened, the second column heater E104 is set to a temperature of 40°C, and the reflux ratio is 10. After the column and overhead temperatures are stabilized, the feed valve is opened for continuous feeding by observing the feed rate of the hydrolysis distillation column T101 and the column discharge rate. If the amount of the hydrolysis liquid is large, it can be stored in the first storage tank D102, wherein the light phase is collected at the top by the second light phase receiving bottle D106. The stability of the concentration distillation column T102 is controlled by the feed flow meter and the column discharge flow meter to maintain the continuity of the entire process and to keep the volume capacity of the hydrolysis and concentration distillation columns within a small range of fluctuations. After the column and overhead temperatures are stabilized, the vacuum valve is opened for online sampling to analyze the concentration of glyoxylic acid. When the concentration of glyoxylic acid reaches 50 wt%, the product liquid is collected in the second storage tank D103 by opening the discharge pump.

[0132] The glyoxylic acid solution in the second storage tank D103 is pumped into the decarboxylation fixed bed reactor R102 packed with a decarboxylation catalyst 0.5 wt% Pd / 1 wt% Cu-Al203 by the third feed pump P103AB to perform the decarboxylation reaction. The decarboxylation reaction is performed under the conditions of normal pressure, nitrogen atmosphere, nitrogen flow rate of 500 mL / min, liquid hourly space velocity of 0.5 h -1 -1, reaction temperature of 80°C.

[0133] The oxalate-removed glyoxylic acid solution is nearly colorless, with a colority of 30 Hazen (platinum-cobalt color number), a mass fraction of glyoxylic acid of 50 wt% in the solution, an oxalic acid content of 300 ppm, and a glycolic acid content of 200 ppm.

[0134] The process device for preparing glyoxylic acid from methyl glycolate mainly comprises an oxidation fixed-bed reactor R101, a gas-liquid separation tank D101, a hydrolysis rectifying tower T101, a concentration rectifying tower T102, a decarboxylation fixed-bed reactor R102, a methanol separation tower T103, a tail gas absorption tower T104, light phase connection bottles (D105, D106), glyoxylic acid product storage tanks (D102, D103, D104), feed pumps (P101AB, P102AB, P103AB), and other devices, and pipelines connecting the devices.

[0135] The oxidation fixed-bed reactor R101 is connected to the tail gas absorption tower T104 at the top, and the product pipeline is connected to the gas-liquid separation tank D101. The bottom of the gas-liquid separation tank D101 is connected to the feed pipeline of the hydrolysis rectifying tower T101. The feed inlet of the hydrolysis rectifying tower T101 is connected to the raw material liquid pipeline and the water pipeline. The top of the hydrolysis rectifying tower T101 is connected to the first tower top condenser E101, and the top outlet is connected to the first light phase connection bottle D105. The tower kettle is connected to the first kettle heater E102 and the first storage tank D102. The feed inlet of the concentration rectifying tower T102 is connected to the tower kettle of the hydrolysis rectifying tower T101. The tower kettle and the tower top of the concentration rectifying tower T102 are also connected to the second kettle heater E104 and the second tower top condenser E103, and the second light phase connection bottle D106. The condenser outlets of the tower tops of the hydrolysis rectifying tower T101 and the concentration rectifying tower T102 are respectively connected to the first high vacuum unit P101 and the second high vacuum unit P102. Stirrers are installed in the towers. The tower bottom of the concentration rectifying tower T102 is connected to the second storage tank D103 and connected to the feed pipeline of the decarboxylation fixed-bed reactor R102. The tower tops of the hydrolysis rectifying tower T101 and the concentration rectifying tower T102 are connected to the methanol separation tower T103. The top of the decarboxylation fixed-bed reactor R102 is connected to the tail gas absorption tower T104.

[0136] The feed positions of the hydrolysis rectifying tower T101 and the concentration rectifying tower T102 are both in the middle of the towers (as shown in FIG. 2). The hydrolysis rectifying tower T101 and the concentration rectifying tower T102 are both filled with packing rings. In order to make the reaction proceed for a long time, the light phase connection bottles and the product storage tanks of the hydrolysis rectifying tower T101 and the concentration rectifying tower T102 are all provided with 6 bottles. Flow meters are installed at the feed inlets and the tower kettles of the hydrolysis rectifying tower T101 and the concentration rectifying tower T102, which facilitates real-time control of the material in-out flow.

[0137] Comparative Example 1

[0138] The process device for preparing glyoxylic acid from methyl glycolate of Comparative Example 1 is the same as that of Example 1. The process for preparing glyoxylic acid from methyl glycolate is as follows: the Mo, Nb and Ba modified VPO based catalyst is used as the oxidation reaction catalyst, the air-nitrogen mixed gas with 15% of O2 volume fraction is used as the oxidant, the oxidation reaction of methyl glycolate is carried out in the oxidation fixed bed reactor R101, the gas-liquid separation of the oxidation reaction product is carried out in the gas-liquid separation tank D101 with the condensation temperature of -20℃, and then the separated product liquid is introduced into the normal pressure hydrolysis rectification tower T101 to carry out the hydrolysis reaction. The 40wt% glyoxylic acid solution is added into the hydrolysis rectification tower T101 through the feed pump to 50% of the maximum volume loading, and then the circulating condenser (the first tower top condenser E101) is opened, the first tower bottom heater E102 is set to 140℃, and the reflux ratio is 10 to start the reaction. After the tower bottom and tower top temperatures are stable, the feed pump is opened to start the feeding at the feeding amount of 3mL / min, wherein the feeding liquid is the mixed liquid of two lines, including the methyl glycolate oxidation product liquid line and the water line, and the water ester ratio is 2. The tower top light phase distillate is collected by the first light phase receiving bottle D105. After the tower bottom and tower top temperatures are stable, the vacuum valve is opened to analyze the conversion rate of methyl glycolate and the concentration of glyoxylic acid in the hydrolysis liquid by online sampling. When the conversion rate of methyl glycolate is more than 99% and the concentration of glyoxylic acid is 20wt%, the hydrolysis liquid is introduced into the concentration rectification tower T102. After the concentration liquid amount reaches 30% of the maximum volume loading of the concentration rectification tower, heating is carried out for concentration. At this time, the concentration rectification tower T102 feeding valve is closed. The concentration rectification tower T102 has been adjusted to 3kPa by the second high vacuum unit P102 before this time. The second tower top condenser E103 is opened, the second tower bottom heater E104 is set to 40℃, and the reflux ratio is 10. After the tower bottom and tower top temperatures are stable, the feeding valve is opened for continuous feeding by observing the feeding amount of the hydrolysis rectification tower T101 and the tower bottom yield. If the hydrolysis liquid amount is large, it can be stored in the first storage tank D102, wherein the light phase is collected at the tower top by the second light phase receiving bottle D106. The stability of the concentration rectification tower T102 is controlled by the feeding flow meter and the tower bottom yield flow meter to maintain the continuity of the whole process and keep the volume loading of the hydrolysis and concentration rectification towers in a small range of fluctuation. After the tower bottom and tower top temperatures are stable, the vacuum valve is opened to analyze the concentration of glyoxylic acid by online sampling. When the concentration of glyoxylic acid reaches 50wt%, the product liquid is collected into the second storage tank D103 by opening the liquid discharge pump.

[0139] The obtained concentrated glyoxylic acid solution is orange-yellow in color, with a colority of 450 Hazen (Pt-Co color number), a mass fraction of glyoxylic acid of 50% by weight, an oxalic acid content of 0.70%, and a glycolic acid content of 300 ppm.

[0140] Example 2

[0141] The process device used in Example 2 is the same as that in Example 1, wherein the feed positions of the hydrolysis rectification tower T101 and the concentration rectification tower T102 are both column bottom feed; the hydrolysis rectification tower T101 and the concentration rectification tower T102 are both filled with Raschig rings. In order to allow the reaction to proceed for a long time, the light phase connection bottles and the product storage tanks of the hydrolysis rectification tower T101 and the concentration rectification tower T102 are both provided with 10. The hydrolysis rectification tower T101 and the concentration rectification tower T102 are both provided with flow meters at the feed inlet and the column bottom outlet, so as to facilitate real-time control of the material in and out flow.

[0142] A method for preparing glyoxylic acid from methyl glycolate. A VPO-based catalyst modified with Mo, Nb and Ca is used as the catalyst for the oxidation reaction, and air-nitrogen mixed gas with 15% O2 volume fraction is used as the oxidant. Methyl glycolate is subjected to oxidation reaction in an oxidation fixed bed reactor R101, and the oxidation reaction product is subjected to gas-liquid separation in a gas-liquid separation tank D101 with a condensation temperature of -25℃. Subsequently, the separated product liquid is introduced into a vacuum hydrolysis rectification tower T101 for hydrolysis reaction. A first high vacuum unit P101 is opened, and the absolute pressure of the vacuum hydrolysis rectification tower T101 is adjusted to 55 kPa. After the pressure is stabilized, 50wt% glyoxylic acid solution is added to the hydrolysis rectification tower T101 through a feed pump to 40% of the maximum volume capacity. Subsequently, a circulating condenser (first overhead condenser E101) is opened, the first column bottom heater E102 is set to 60℃, and the reflux ratio is set to 6 to start the reaction. After the column bottom and overhead temperatures are stabilized, the feed pump is opened to start feeding at a feed rate of 5 mL / min, wherein the feed liquid is a mixture of two lines, including a methyl glycolate oxidation product liquid line and a water line, and the water ester ratio is 2.5. The overhead light phase distillate is collected by a first light phase receiving bottle D105. After the column bottom and overhead temperatures are stabilized, a vacuum valve is opened for online sampling analysis of the conversion rate of methyl glycolate and the concentration of glyoxylic acid in the hydrolysis liquid. When the conversion rate of methyl glycolate is above 99% and the concentration of glyoxylic acid is 30wt%, the hydrolysis liquid is introduced into a concentration rectification tower T102. After the amount of the concentrated liquid reaches 40% of the maximum volume capacity of the concentration rectification tower, heating is performed for concentration. At this time, the feed valve of the concentration rectification tower T102 is closed. The concentration rectification tower T102 has been adjusted to a pressure of 10 kPa through a second high vacuum unit P102. A second overhead condenser E103 is opened, the second column bottom heater E104 is set to a temperature of 50℃, and the reflux ratio is set to 6. After the column bottom and overhead temperatures are stabilized, continuous feeding is performed by observing the feed rate of the hydrolysis rectification tower T101 and the column bottom take-off rate, and opening the feed valve. If the amount of the hydrolysis liquid is large, it can be stored in a first storage tank D102, wherein the light phase is collected at the top by a second light phase receiving bottle D106. The stability of the concentration rectification tower T102 is controlled by a feed flow meter and a column bottom take-off flow meter to maintain the continuity of the entire process and keep the filling amount of the hydrolysis and concentration rectification towers within a small range of fluctuations. After the column bottom and overhead temperatures are stabilized, a vacuum valve is opened for online sampling analysis of the concentration of glyoxylic acid. When the concentration of glyoxylic acid reaches 50wt%, a discharge pump is opened to collect the product liquid into a second storage tank D103. The overhead light phase liquid of the hydrolysis rectification tower T101 and the concentration rectification tower T102 is subjected to methanol separation in a methanol separation tower T103, wherein the methanol is taken off from the top, and the column bottom is connected to the feed line of the hydrolysis rectification tower T101 to allow the aqueous solution containing a small amount of methyl glycolate to be subjected to secondary hydrolysis.

[0143] The glyoxylic acid solution in the second storage tank D103 is pumped into a decarboxylation fixed bed reactor R102 filled with decarboxylation catalyst 0.5wt% Pd / 1wt% Ag-Al203 by a third feed pump P103AB to carry out decarboxylation reaction. The decarboxylation reaction is carried out under normal pressure, nitrogen atmosphere, nitrogen flow rate of 400 mL / min, liquid hourly space velocity of 0.3 h -1 -1, reaction temperature of 70°C, to obtain oxalic acid-removed glyoxylic acid solution, the color of which is light yellow, the colority of which is 70 Hazen (platinum-cobalt color number), the mass fraction of glyoxylic acid in the solution is 40%, the oxalic acid content is 350 ppm, and the glycolic acid content is 250 ppm.

[0144] From the above examples and comparative examples, it can be seen that the method of the present application can significantly reduce the colority and oxalic acid content of the product, and can obtain glyoxylic acid solution with high purity and excellent color.

[0145] The above description of the examples is for the purpose of facilitating the understanding and use of the present application by those skilled in the art. Those skilled in the art can obviously make various modifications to the examples and apply the general principles described herein to other examples without having to go through creative labor. Therefore, the present application is not limited to the above examples, and the improvements and modifications made by those skilled in the art according to the disclosure of the present application without departing from the scope of the present application should be within the scope of protection of the present application.

Claims

1. A process for the preparation of glyoxylic acid from methyl glycolate, characterized in that, The method comprises the following steps: S1 oxidation reaction: introducing methyl glycolate and an oxidant into a reactor loaded with an oxidation reaction catalyst to obtain a methyl glyoxylate product liquid through oxidation reaction; S2 vacuum hydrolysis: performing vacuum hydrolysis on the methyl glyoxylate product liquid, analyzing the composition of the obtained hydrolysis liquid after online sampling, and entering the next process after reaching the preset value; S3 concentration rectification: performing concentration rectification on the hydrolysis liquid reaching the preset value, analyzing the composition of the obtained glyoxylic acid solution after online sampling, and entering the next process after reaching the preset value; S4 decarboxylation reaction: introducing the glyoxylic acid solution reaching the preset value into a reactor loaded with a decarboxylation catalyst to perform catalytic decarboxylation reaction, and obtaining a glyoxylic acid solution of target quality.

2. The process for the preparation of glyoxalic acid from methyl glycolate according to claim 1, characterized in that, The oxidizing agent in step S1 includes oxygen, the oxidation reaction catalyst includes a metal-modified VPO-based catalyst, the oxidation reaction temperature is 100-300°C, the pressure is 0.05-1.0 MPa, the oxygen-alcohol molar ratio is (0.5:1) - (16:1), the liquid hourly space velocity is 0.1-1 h -1 .

3. The process for the preparation of glyoxalic acid from methyl glycolate according to claim 1, characterized in that, The methyl glyoxylate product liquid obtained in step S1 oxidation reaction is subjected to gas-liquid separation in a gas-liquid separation tank, and the obtained liquid product is subjected to vacuum hydrolysis; The condensation temperature of the gas-liquid separation tank is -40 to -10 ℃.

4. The process for the preparation of glyoxalic acid from methyl glycolate according to claim 1, characterized in that, The vacuum hydrolysis in step S2 is performed in a vacuum hydrolysis rectification column, and the absolute pressure in the vacuum hydrolysis rectification column is 0 to 100 kPa.

5. The process for the preparation of glyoxalic acid from methyl glycolate according to claim 4, characterized in that, The vacuum hydrolysis in step S2 specifically comprises the following steps: First, add a raw liquid to the vacuum hydrolysis rectification column to 30 to 50% of the maximum volume capacity, and then introduce the methyl glyoxylate product liquid obtained by oxidation reaction after the temperature of the column bottom and the column top stabilizes; The raw liquid is one of 40 to 60 wt% glyoxylic acid aqueous solution and deionized water.

6. The process for the preparation of glyoxalic acid from methyl glycolate according to claim 5, characterized in that, The temperature of the column bottom heater of the vacuum hydrolysis rectification column is 40 to 110 ℃, the column top temperature is 30 to 110 ℃, and the reflux ratio is 1 to 30.

7. The method of claim 1, wherein the glycollic acid methyl ester is prepared by the reaction of glycollic acid and methanol in the presence of a catalyst. After online sampling in step S2, the conversion rate of methyl glyoxylate and the concentration of glyoxylic acid in the hydrolysis liquid are analyzed, and when the values of the two reach the preset value, concentration rectification is performed, the preset value of the conversion rate of methyl glyoxylate is 99 to 100%, and the preset value of the concentration of glyoxylic acid is 20 to 70 wt%.

8. The method of claim 1, wherein the glycollic acid methyl ester is prepared by the method comprising: reacting glycollic acid with methanol in the presence of a catalyst to produce the glycollic acid methyl ester. The concentration rectification in step S3 is performed in a concentration rectification column, and the absolute pressure in the concentration rectification column is 0 to 100 kPa. The hydrolysis liquid is introduced into the concentration rectification column, heated for rectification concentration after the amount of the hydrolysis liquid reaches 30 to 50% of the maximum volume capacity of the concentration rectification column, and the feeding is continued after the temperature of the column bottom and the column top stabilizes.

9. The process for the preparation of glyoxalic acid from methyl glycolate according to claim 8, characterized in that, The feeding inlet of the concentration rectification column is provided with a feeding flow meter for detecting the feeding flow, and the column bottom is provided with a column bottom production flow meter for detecting the column bottom production.

10. The process for the preparation of glyoxalic acid from methyl glycolate according to claim 1, characterized in that, After online sampling in step S3, the concentration of glyoxylic acid in the glyoxylic acid solution is analyzed, and when the preset value is reached, the decarboxylation reaction of the glyoxylic acid solution is performed, and the preset value of the concentration of glyoxylic acid is 30 to 90 wt%.

11. The process for the preparation of glyoxalic acid from methyl glycolate according to claim 1, characterized in that, The decarboxylation catalyst in step S4 is a Pd-based catalyst with inorganic material as the carrier and transition metal elements, post-transition metal elements or rare earth elements as the additives. The content of Pd in the decarboxylation catalyst is 0.1 to 10 wt%, and the content of the additives is 0.1 to 5 wt%.

12. The process for the preparation of glyoxalic acid from methyl glycolate according to claim 11, characterized in that, The inorganic material includes Al2O3, SiO2, TiO2, MCM-41 and SAPO-34; The transition metal elements include Cu and Ag; The post-transition metal elements include Bi; The rare earth elements include Ce and La.

13. The method for preparing glyoxylic acid from methyl glycolate according to claim 11, characterized in that, The support pore volume of the decarboxylation catalyst is 0.1 cm 3 / g~1 cm 3 / g, and the specific surface area is 200~600 m 2 / g.

14. The method of claim 1, wherein the glycollic acid methyl ester is prepared by the method comprising: reacting glycollic acid with methanol in the presence of a catalyst to form the glycollic acid methyl ester. The decarboxylation reaction condition of step S4 includes: reaction temperature is 40-90℃, reaction pressure is normal pressure, nitrogen atmosphere, nitrogen flow is 100-800 mL / min, acetic acid solution feed liquid space velocity is 0.5-3.0 h -1 .

15. An apparatus for carrying out the process of any one of claims 1 to 14 for the preparation of glyoxalic acid from methyl glycolate, characterized in that The hydrolysis rectifying tower T101 and the concentration rectifying tower T102 are connected through a first storage tank D102, and the concentration rectifying tower T102 and the decarboxylation fixed bed reactor R102 are connected through a second storage tank D103. The hydrolysis rectifying tower T101 and the concentration rectifying tower T102 are connected through a first storage tank D102, and the concentration rectifying tower T102 and the decarboxylation fixed bed reactor R102 are connected through a second storage tank D103.

Images