CN109852987B - Method for preparing sodium glyoxylate by coupling reverse osmosis technology - Google Patents
Method for preparing sodium glyoxylate by coupling reverse osmosis technology Download PDFInfo
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Abstract
The invention relates to a method for preparing sodium glyoxylate by coupling a reverse osmosis technology, in particular to a process flow for preparing sodium glyoxylate by electrolysis, and relates to a process for concentrating the sodium glyoxylate generated after reverse osmosis is introduced into electrolysis reaction and neutralization reaction and a process for recycling oxalic acid after electrodialysis is introduced into electrolysis. The low-concentration reaction solution is concentrated by a reverse osmosis process, so that the sodium glyoxylate electrosynthesis process with high electrolyte concentration is realized. The high electrolyte concentration is beneficial to reducing the operation voltage of the electrolytic cell, improving the current efficiency and the stability of the lead electrode in the reaction process, reducing the comprehensive cost of the product and having good industrialization prospect.
Description
Technical Field
The invention relates to a process flow for preparing sodium glyoxylate by electrolysis, belonging to the field of organic electrochemical synthesis.
Background
Glyoxylic acid and sodium glyoxylate thereof have important application in the fields of essences and flavors, such as the synthesis of vanillin and ethyl vanillin, and medical intermediates, such as the synthesis of allantoin. Patent US4146731 reports a process for preparing glyoxylic acid by oxidizing glyoxal with nitric acid, which has harsh reaction conditions, difficult inhibition of side reactions, poor selectivity of the target product, large amount of nitric acid, and difficult removal of much residual nitric acid in the product. Moreover, the nitric acid has serious corrosion to equipment, and NOx generated in the reaction process is a main source of acid rain, so that environmental pollution is easily caused. Patent CN106431885A reports a method for synthesizing glyoxylic acid by ozonization of maleic anhydride mixed solvent, but because ozone is used as oxidant in the reaction process, the method has large investment, high energy consumption and harsh reaction conditions, and the method for preparing C2 glyoxylic acid from C4 maleic anhydride produces by-products of formic acid and carbon dioxide, and has low atom economy, which is not in line with the development direction of green chemical industry. US3779875 describes a process for the preparation of glyoxylic acid by the electrolytic reduction of oxalic acid. As a synthetic route, the electrolytic preparation of glyoxylic acid has the advantages of mild operating conditions, cleanness, no pollution, less side reactions and good atom economy. However, the adoption of the electrolysis method to prepare the glyoxylic acid solution also has the problems of large energy consumption, poor stability of the catalytic performance of the lead electrode, difficult continuous operation and the like. Patent CN01105991.5 reports a method for preparing glyoxylic acid by electrolytic reduction using oxalic acid as raw material in an electrolytic cell with a fixed bed cathode, which maintains high current efficiency and glyoxylic acid chemical selectivity and greatly improves the production capacity of the electrolytic cell. However, the cathode solution of the glyoxylic acid is still separated and purified by adopting the conventional reduced pressure evaporation and low-temperature filtration method, and the mass concentration of the glyoxylic acid in the reaction solution needs to be ensured to be higher than 5 percent, otherwise, the energy consumption of the reduced pressure evaporation cannot be borne. However, the concentration of oxalic acid in the reaction solution in the latter half of the reaction is low, and a sufficient reactant cannot be supplied to the electrode, resulting in a decrease in current efficiency. Meanwhile, oxalic acid is also an electrolyte in the cathode reaction solution. As oxalic acid is consumed, electrolyte is reduced and the cell voltage rises in the latter half of the batch reaction. This is also a significant cause of lead electrode deactivation. Therefore, the process for preparing glyoxylic acid by electrolyzing oxalic acid still faces the challenges of high energy consumption and lead electrode inactivation.
Disclosure of Invention
Aiming at the problems of high energy consumption and lead electrode inactivation in the existing process for preparing glyoxylic acid by oxalic acid electrolysis, the invention provides a process for preparing sodium glyoxylate by oxalic acid electrolysis, which has low electrolysis energy consumption and better lead electrode stability.
The invention provides the following technical scheme according to the conception:
specifically, the invention provides a process for preparing sodium glyoxylate by electrolyzing oxalic acid, which comprises the following steps:
(1) an electrolysis process: continuously adding oxalic acid solution with mass concentration of 6-12% into the catholyte head tank, adding sulfuric acid solution into the anolyte head tank, enabling reaction liquid in the two head tanks to flow into the electrolytic bath for electrolysis, respectively pumping the anolyte head tank and the catholyte head tank back, and supplementing deionized water into the anolyte head tank;
(2) a separation process: when the content of glyoxylic acid in the catholyte head tank reaches 0.75-2.5%, pumping catholyte in the catholyte head tank into a first crystallization kettle to condense and crystallize oxalic acid contained in the catholyte head tank, and filtering;
(3) introducing the solution filtered in the step (2) into a neutralization device for neutralization, so that glyoxylic acid contained in the solution and residual oxalic acid are converted into sodium glyoxylate and sodium oxalate respectively, and heating;
(4) concentrating the solution neutralized in the step (3) by a reverse osmosis device to obtain a concentrated sodium glyoxylate solution, putting the concentrated sodium glyoxylate solution in a second crystallization kettle to crystallize and condense sodium oxalate contained in the sodium glyoxylate solution, and filtering to obtain a sodium glyoxylate solution;
(5) and (4) dissolving sodium oxalate crystals obtained by condensing the crystals in the crystallization kettle II in the step (4), and then feeding the dissolved sodium oxalate crystals into an electrodialysis device to prepare oxalic acid and a sodium hydroxide solution.
The electrolytic reduction device used by the invention consists of a cathode-anode liquid head tank and an electrolytic tank, and the storage tank is divided into a cathode liquid head tank and an anode liquid head tank, and is a continuous production device.
The electrolytic reduction device operates as follows: continuously adding 6-12% oxalic acid solution into the catholyte head tank, and pumping the solution in the catholyte head tank into the cathode chamber of the electrolytic tank at a certain flow rate by a circulating pump. The reaction condition is that the oxalic acid solution is controlled at 15-25 ℃. The current density is controlled to be 1000-2000A/m2. The reaction formula is COOHCOOH +2H++2e→COOHCHO+H2O
The reaction liquid containing the glyoxylic acid is sent back to the catholyte head tank, and the discharging amount of the reaction liquid is the same as the feeding amount by adjusting the feeding amount of the oxalic acid to be 750-2000g/h, so that the reaction residence time of about 1-2h is obtained (namely, the reaction residence time of the reaction liquid is 1-2h according to batch electrolysis for obtaining the same glyoxylic acid chemical selectivity). The concentration of the glyoxylic acid discharged from the cell is controlled to be 0.75-2.5%, the content of oxalic acid is 4-12%, the current efficiency is improved, and the cell voltage is reduced; part of glyoxylic acid is oxidized into glyoxal or glycolic acid in one step in the reaction process, the selectivity of the process is more than 84 percent, and the selectivity calculation formula is as follows.
The method for separating glyoxylic acid comprises the following steps: because the concentration of the glyoxylic acid discharged from the tank is controlled to be 0.75-2.5 percent, if the traditional low-temperature filtration and reduced-pressure evaporation separation process is adopted, the energy consumption cost is greatly increased. Therefore, the process comprises the steps of introducing the reaction liquid into a crystallization kettle, crystallizing and separating out oxalic acid solid in the reaction liquid at the temperature of-5-0 ℃ until the concentration of oxalic acid is reduced to 0.1-0.5%, and stopping crystallization to prepare 8-10% oxalic acid solution for recycling. In order to continuously process the reaction liquid, the crystallization process adopts a continuous mode of two crystallization kettles in which intermittent operation is simulated, the crystallization kettle filled with the reaction liquid is replaced by an empty kettle every 24 hours, then cooling crystallization and filtering operation are carried out, and the emptied crystallization kettle is connected back to the production line for switching.
In order to improve the rejection rate of products in the reverse osmosis process, the crystallized solution containing glyoxylic acid and oxalic acid is pumped into a neutralization device to react with NaOH to generate sodium oxalate and sodium glyoxylate, and the pH value in the neutralization reaction is adjusted to 6.5-7.5. Then enters a heat exchanger, and the temperature is raised to 40-50 ℃. Introducing the solution which is subjected to heat exchange and consists of 1.8-4% of sodium glyoxylate and 0.1-1% of sodium oxalate into a raw water tank of the reverse osmosis device. Under the pressure of 30-100 kg, water molecules in the reaction liquid pass through a reverse osmosis membrane and are discharged through a fresh water chamber, the content of sodium glyoxylate discharged from a concentration chamber is 12-15%, and the content of sodium oxalate is 0.3-2.5%. Removing sodium oxalate in the solution at-5-0 ℃ by using a cooling crystallization filtration mode until the concentration of the sodium oxalate is reduced to 0.1% -0.5%, and dissolving the filtered sodium oxalate crystals into 8-10% sodium oxalate water solution. The sodium oxalate solution is prepared into sodium hydroxide solution and oxalic acid solution again by an electrodialysis device, the electrodialysis temperature is 40 ℃, and the current density is 1000A/m2And the solvent ratio (the mass ratio of the sodium oxalate solution to the pure water on the two sides of the electrodialysis membrane) is 1:1, 10% of oxalic acid and 10% of sodium hydroxide are prepared and respectively recycled to the neutralization device and the electrolytic cell. Dissolving sodium glyoxylate after removing sodium oxalateThe solution is evaporated in vacuum until the content of sodium glyoxylate is 40-50%.
The electrodialysis device is a three-compartment bipolar membrane structure, adopts a titanium-coated ruthenium iridium electrode, and has an operating current density of 500-2The running temperature is 20-45 ℃.
Scraper area of scraper film evaporator is 1m2The main body of the device is made of titanium. The operation vacuum degree is 0.01-1Mpa, and the operation temperature is 40-100 ℃.
It should be noted that, unless otherwise specified, references to "content" and "concentration" in the present invention refer to the mass percentage concentration in an aqueous solution.
The technical scheme of the invention has the following characteristics and beneficial effects:
(1) the process adopts a mode of continuous feeding and continuous discharging, improves the production efficiency, improves the concentration of oxalic acid in the electrolytic cell, controls the discharging concentration of glyoxylic acid to be 1.5-2.5%, ensures the current efficiency and lower voltage of electrolytic reaction due to the oxalic acid serving as a raw material and an electrolyte in the reaction process, and further solves the problem of energy consumption in the oxalic acid electrolytic process.
(2) The reverse osmosis technology and the electrodialysis are introduced in the product separation process, so that the restriction of the separation process on the discharge concentration of the electrolysis process flow is removed at the cost of low energy consumption, and the concentration of oxalic acid in the electrolysis process is increased.
Drawings
FIG. 1 shows a process for producing glyoxylic acid by electrolyzing oxalic acid coupled with a reverse osmosis process, wherein the related devices are as follows: 1 anolyte head tank; 2, an electrolytic bath; 3 a catholyte head tank; 4, crystallizing the first kettle; 5a neutralization device; 6, a reverse osmosis device; 7, a second crystallization kettle; 8 an electrodialysis unit; 9 an evaporation device.
Wherein, the first crystallization kettle connected with the electrolytic bath is an intermittent replacement device, namely, an empty kettle is used for replacement at intervals.
Detailed Description
In the embodiment of the invention, all the mass fractions are mass percentages, all the current densities are electrode apparent current densities, and the connection relationship among the devices is shown in fig. 1. Wherein the content of the first and second substances,
an electrodialysis device: GCM-E-10, national science and technology (Xiamen) Inc.;
a reverse osmosis device: GCM-F-04, national science and technology (Xiamen) Co.
Example 1
An electrolysis process: the cathode of the electrolytic cell is pure lead electrode (lead content is 0.9999), the anode is DSA electrode, the electrode spacing is 1cm, the catholyte feed is 6% oxalic acid solution, the cathode solution enters the electrolytic cell from the catholyte head tank, the feed speed is 1300g/h, and the current density is 1000A/m2The surface flow rate of the electrode is 0.2m/s, the temperature of the electrolyte is controlled at 20 ℃, and the residence time of the reaction solution is 0.77 h. The sulfuric acid concentration in the anode electrode tank was kept at 10%. And pumping the electrolyzed anode and cathode reaction liquid back to the anode liquid head tank and the cathode liquid head tank respectively, and supplementing deionized water in the anode liquid head tank. The discharging speed of the catholyte after electrolysis is the same as the feeding speed, the content of glyoxylic acid in the discharged catholyte is 1.1 percent, and the concentration of oxalic acid is 4.6 percent. The process has current efficiency of 85%, chemical selectivity of 95% for glyoxylic acid and cell voltage of 3V.
A separation process: pumping the glyoxylic acid discharge liquid into a crystallization kettle I, cooling the reaction liquid to-5 ℃ for crystallization, stopping crystallization when the concentration of oxalic acid in the solution is controlled to be 0.1 percent, filtering oxalic acid crystals to dissolve the oxalic acid crystals into 8 percent oxalic acid solution for recycling. The filtrate was passed into a neutralization apparatus and adjusted to pH 7 by the addition of sodium hydroxide. Then the solution is introduced into a heat exchanger, the temperature is raised to 40 ℃, the composition of the solution is 0.15 percent of sodium oxalate and 2.2 percent of sodium glyoxylate, the heated solution is introduced into a reverse osmosis device, and the solution is concentrated until the content of the sodium glyoxylate is 12 percent and the content of the sodium oxalate is 1.6 percent. And (3) introducing the concentrated solution into a second crystallization kettle, cooling to 0 ℃ for crystallization, and filtering and separating the precipitated sodium oxalate crystals to obtain a solution containing 12% of sodium glyoxylate and 0.1% of sodium oxalate. Dissolving the filtered sodium oxalate crystals into 10 percent sodium oxalate solution, and passing the solution through an electrodialysis device at the temperature of 40 ℃ and the current density of 1000A/m2And the solvent ratio is 1:1, and solutions of 10% oxalic acid and 10% sodium hydroxide are prepared and prepared to be respectively recycled in the oxalic acid electrolysis step and the sodium hydroxide neutralization step. The sodium glyoxylate solution was evaporated at 4Kpa at 29 ℃ to give a 50% aqueous solution of sodium glyoxylate.
Example 2
An electrolysis process: the cathode of the electrolytic cell is pure lead electrode (pure lead content is 0.9999), the anode is DSA electrode, the distance between electrodes is 1cm, the catholyte feed is 12% oxalic acid solution, the cathode solution enters the electrolytic cell from the catholyte head tank, the feed speed is 750g/h, and the current density is 1000A/m2The surface flow rate of the electrode is 0.2m/s, the temperature of the electrolyte is controlled at 25 ℃, and the residence time of the reaction solution is 1 h. The sulfuric acid concentration in the anode electrode tank was kept at 10%. And pumping the electrolyzed anode and cathode reaction liquid back to the anode liquid head tank and the cathode liquid head tank respectively, and supplementing deionized water in the anode liquid head tank. The discharging speed of the catholyte after electrolysis is the same as the feeding speed, the content of glyoxylic acid in the discharged catholyte is 2 percent, and the concentration of oxalic acid is 9.3 percent. The process has current efficiency of 80%, chemical selectivity of glyoxylic acid of 84% and cell voltage of 1V.
A separation process: pumping the glyoxylic acid discharge liquid into a crystallization kettle I, cooling the reaction liquid to-5 ℃ for crystallization, stopping crystallization when the concentration of oxalic acid in the solution is controlled to be 0.1 percent, filtering oxalic acid crystals and dissolving the oxalic acid crystals into an oxalic acid solution with the concentration of 8 percent for recycling. The filtrate was passed into a neutralization apparatus and adjusted to pH 7 by the addition of sodium hydroxide. Then the solution is introduced into a heat exchanger, the temperature is raised to 40 ℃, the composition of the solution is 0.15 percent of sodium oxalate and 3.1 percent of sodium glyoxylate, and the heated solution is introduced into a reverse osmosis device and concentrated until the content of the sodium glyoxylate is 12 percent and the content of the sodium oxalate is 0.4 percent. And (3) introducing the concentrated solution into a second crystallization kettle, cooling to 0 ℃ for crystallization, and filtering and separating the separated sodium oxalate crystals to obtain a solution containing 12% of sodium glyoxylate and 0.1% of sodium oxalate. Dissolving the filtered sodium oxalate crystals into 10 percent sodium oxalate solution, and passing the solution through an electrodialysis device at the temperature of 40 ℃ and the current density of 1000A/m2And the solvent ratio is 1:1, and solutions of 10% oxalic acid and 10% sodium hydroxide are prepared and prepared to be respectively recycled in the oxalic acid electrolysis step and the sodium hydroxide neutralization step. The sodium glyoxylate solution was evaporated at 4Kpa at 29 ℃ to give a 50% aqueous solution of sodium glyoxylate.
Example 3
An electrolysis process: the cathode of the electrolytic cell is pure lead electrode (pure lead content is 0.9999), the anode is DSA electrode, the electrode distance is 1cm, and the catholyte feed is 8%Oxalic acid solution enters the electrolytic cell from a catholyte head tank, the feeding speed is 1000g/h, and the current density is 1000A/m2The surface flow rate of the electrode is 0.2m/s, the temperature of the electrolyte is controlled at 20 ℃, and the residence time of the reaction solution is 1 h. The sulfuric acid concentration in the anode electrode tank was kept at 10%. And pumping the electrolyzed anode and cathode reaction liquid back to the anode liquid head tank and the cathode liquid head tank respectively, and supplementing deionized water in the anode liquid head tank. The discharging speed of the catholyte after electrolysis is the same as the feeding speed, the content of glyoxylic acid in the discharged catholyte is 1.5 percent, and the concentration of oxalic acid is 6.2 percent. The current efficiency of the process is 90%, the chemical selectivity of the glyoxylic acid is 95%, and the cell voltage is 1.5V.
A separation process: pumping the glyoxylic acid discharge liquid into a crystallization kettle I, cooling the reaction liquid to-5 ℃ for crystallization, stopping crystallization when the concentration of oxalic acid in the solution is controlled to be 0.1 percent, filtering oxalic acid crystals and dissolving the oxalic acid crystals into an oxalic acid solution with the concentration of 8 percent for recycling. The filtrate was passed into a neutralization apparatus and adjusted to pH 7 by the addition of sodium hydroxide. Then the solution is introduced into a heat exchanger, the temperature is raised to 40 ℃, the composition of the solution is 0.15 percent of sodium oxalate and 2.3 percent of sodium glyoxylate, the heated solution is introduced into a reverse osmosis device, and the solution is concentrated until the content of the sodium glyoxylate is 12 percent and the content of the sodium oxalate is 0.8 percent. And (3) introducing the concentrated solution into a second crystallization kettle, cooling to 0 ℃ for crystallization, and filtering and separating the separated sodium oxalate crystals to obtain a solution containing 12% of sodium glyoxylate and 0.1% of sodium oxalate. Dissolving the filtered sodium oxalate crystals into 10 percent sodium oxalate solution, and passing the solution through an electrodialysis device at the temperature of 40 ℃ and the current density of 1000A/m2And the solvent ratio is 1:1, and solutions of 10% oxalic acid and 10% sodium hydroxide are prepared and prepared to be respectively recycled in the oxalic acid electrolysis step and the sodium hydroxide neutralization step. The sodium glyoxylate solution was evaporated at 4Kpa at 29 ℃ to give a 50% aqueous solution of sodium glyoxylate.
Example 4
An electrolysis process: the same cell apparatus as in example 1 was used, the catholyte feed was an 8% oxalic acid solution, and the feed rate was 660g/h, and the current density was 1000A/m2The surface flow rate of the electrode is 0.2m/s, the temperature of the electrolyte is controlled at 20 ℃, and the residence time of the reaction solution is controlled for 1.5 h. The concentration of sulfuric acid in the anode electrode tank is kept at 10 percent. And pumping the electrolyzed anode and cathode reaction liquid back to the anode liquid head tank and the cathode liquid head tank respectively, and supplementing deionized water in the anode liquid head tank. The discharging speed of the catholyte after electrolysis is the same as the feeding speed, the discharging liquid is 2 percent of glyoxylic acid, and the concentration of oxalic acid is 5.5 percent. The process has current efficiency of 85%, chemical selectivity of glyoxylic acid of 92% and cell voltage of 2.5V.
A separation process: pumping the glyoxylic acid discharge liquid into a first crystallization kettle, cooling the reaction liquid to 0 ℃ for crystallization, stopping crystallization when the concentration of oxalic acid in the solution is controlled to be 0.5 percent, filtering oxalic acid crystals to dissolve the oxalic acid crystals into 8 percent oxalic acid solution for reuse, wherein the concentration of the glyoxylic acid in the solution is 2.6 percent. The filtrate was passed into a neutralization apparatus and adjusted to pH 6.5 by the addition of sodium hydroxide. Then the solution is introduced into a heat exchanger, the temperature is raised to 40 ℃, the solution with the composition of 0.7 percent of sodium oxalate and 3.3 percent of sodium glyoxylate after temperature rise is introduced into a reverse osmosis device, and the solution is concentrated until the content of the sodium glyoxylate is 12 percent and the content of the sodium oxalate is 2.5 percent. And (3) introducing the concentrated solution into a second crystallization kettle, cooling to 0 ℃ for crystallization, and filtering and separating the separated sodium oxalate crystals to obtain a solution containing 12% of sodium glyoxylate and 0.1% of sodium oxalate. Dissolving the filtered sodium oxalate crystals into 10 percent sodium oxalate solution, and passing the solution through an electrodialysis device at the temperature of 40 ℃ and the current density of 1000A/m2And the solvent ratio is 1:1, and solutions of 10% oxalic acid and 10% sodium hydroxide are prepared and prepared to be respectively recycled in the oxalic acid electrolysis step and the sodium hydroxide neutralization step. The sodium glyoxylate solution was evaporated at 4Kpa at 29 ℃ to give a 50% aqueous solution of sodium glyoxylate.
Example 5
An electrolysis process: the same apparatus as in example 1 was used, and the catholyte feed was an 8% oxalic acid solution, which was fed from the catholyte head tank into the electrolytic bath at a feed rate of 500g/h and a current density of 1000A/m2The surface flow rate of the electrode is 0.2m/s, the temperature of the electrolyte is controlled at 20 ℃, and the residence time of the reaction solution is controlled for 2 hours. The sulfuric acid concentration in the anode electrode tank was kept at 10%. And pumping the electrolyzed anode and cathode reaction liquid back to the anode liquid head tank and the cathode liquid head tank respectively, and supplementing deionized water in the anode liquid head tank. The discharging speed of the catholyte after electrolysis is the same as the feeding speed, the discharging liquid glyoxylic acid is 2.5 percent, and the concentration of oxalic acid is 4.8 percent. The current efficiency of the process is 85 percentThe chemical selectivity of the glyoxylate is 90 percent, and the cell voltage is 3.5V.
A separation process: pumping the glyoxylic acid discharge liquid into a first crystallization kettle, cooling the reaction liquid to 0 ℃ for crystallization, stopping crystallization when the concentration of oxalic acid in the solution is controlled to be 0.25 percent, filtering oxalic acid crystals to dissolve the oxalic acid crystals into 8 percent oxalic acid solution for reuse, wherein the concentration of the glyoxylic acid in the solution is 2.6 percent. The filtrate was passed into a neutralization apparatus and adjusted to pH 7 by the addition of sodium hydroxide. Then the solution is introduced into a heat exchanger, the temperature is raised to 40 ℃, the solution with the composition of 0.4 percent of sodium oxalate and 3.3 percent of sodium glyoxylate after temperature rise is introduced into a reverse osmosis device, and the solution is concentrated until the content of the sodium glyoxylate is 12 percent and the content of the sodium oxalate is 1.5 percent. And (3) introducing the concentrated solution into a second crystallization kettle, cooling to-5 ℃ for crystallization, and filtering and separating the separated sodium oxalate crystals to obtain a solution containing 12% of sodium glyoxylate and 0.1% of sodium oxalate. Dissolving the filtered sodium oxalate crystals into 10 percent sodium oxalate solution, and passing the solution through an electrodialysis device at the temperature of 40 ℃ and the current density of 1000A/m2And the solvent ratio is 1:1, and solutions of 10% oxalic acid and 10% sodium hydroxide are prepared and prepared to be respectively recycled in the oxalic acid electrolysis step and the sodium hydroxide neutralization step. The sodium glyoxylate solution was evaporated at 4Kpa at 29 ℃ to give a 50% aqueous solution of sodium glyoxylate.
Example 6
An electrolysis process: the same apparatus as in example 1 was used, and the catholyte feed was an 8% oxalic acid solution, which was fed from the catholyte head tank into the electrolytic bath at a feed rate of 500g/h and a current density of 1000A/m2The surface flow rate of the electrode is 0.2m/s, the temperature of the electrolyte is controlled at 20 ℃, and the residence time of the reaction solution is controlled for 2 h. The sulfuric acid concentration in the anode electrode tank was kept at 10%. And pumping the electrolyzed anode and cathode reaction liquid back to the anode liquid head tank and the cathode liquid head tank respectively, and supplementing deionized water in the anode liquid head tank. The discharging speed of the catholyte after electrolysis is the same as the feeding speed, the discharging liquid glyoxylic acid is 2.5 percent, and the concentration of oxalic acid is 4.6 percent. The current efficiency of the process is 85 percent, the chemical selectivity of the glyoxylic acid is 90 percent, and the cell voltage is 3.5V.
A separation process: pumping the discharged glyoxylic acid solution into a first crystallization kettle, cooling the reaction solution to-5 ℃ for crystallization, stopping crystallization when the concentration of oxalic acid in the solution is controlled at 0.1 percent, controlling the concentration of glyoxylic acid in the solution to be 2.6 percent,and filtering the oxalic acid crystal and dissolving the oxalic acid crystal into 8 percent oxalic acid solution for recycling. The filtrate was passed into a neutralization apparatus and adjusted to pH 7 by the addition of sodium hydroxide. Then the solution is introduced into a heat exchanger, the temperature is raised to 50 ℃, the solution consists of 0.15 percent of sodium oxalate and 3.3 percent of sodium glyoxylate, and the heated solution is introduced into a reverse osmosis device and concentrated until the content of the sodium glyoxylate is 15 percent and the content of the sodium oxalate is 0.7 percent. And (3) introducing the concentrated solution into a second crystallization kettle, cooling to-5 ℃ for crystallization, and filtering and separating the separated sodium oxalate crystals to obtain a solution containing 15% of sodium glyoxylate and 0.1% of sodium oxalate. Dissolving the filtered sodium oxalate crystals into 10 percent sodium oxalate solution, and passing the solution through an electrodialysis device at the temperature of 40 ℃ and the current density of 1000A/m2And the solvent ratio is 1:1, and solutions of 10% oxalic acid and 10% sodium hydroxide are prepared and prepared to be respectively recycled in the oxalic acid electrolysis step and the sodium hydroxide neutralization step. The sodium glyoxylate solution was evaporated at 4Kpa at 29 ℃ to give a 50% aqueous solution of sodium glyoxylate.
Example 7
An electrolysis process: the same apparatus as in example 1 was used, and the catholyte feed was an 8% oxalic acid solution, which was fed from the catholyte head tank into the electrolytic bath at a feed rate of 500g/h and a current density of 1000A/m2The surface flow rate of the electrode is 0.2m/s, the temperature of the electrolyte is controlled at 20 ℃, and the residence time of the reaction solution is controlled for 2 hours. The sulfuric acid concentration in the anode electrode tank was kept at 10%. And pumping the electrolyzed anode and cathode reaction liquid back to the anode liquid head tank and the cathode liquid head tank respectively, and supplementing deionized water in the anode liquid head tank. The discharging speed of the catholyte after electrolysis is the same as the feeding speed, the discharging liquid glyoxylic acid is 2.5 percent, and the concentration of oxalic acid is 4.6 percent. The current efficiency of the process is 85 percent, the chemical selectivity of the glyoxylic acid is 90 percent, and the cell voltage is 3.5V.
A separation process: pumping the glyoxylic acid discharge liquid into a crystallization kettle I, cooling the reaction liquid to-5 ℃ for crystallization, stopping crystallization when the concentration of oxalic acid in the solution is controlled to be 0.1 percent, filtering oxalic acid crystals to dissolve the oxalic acid solution to 8 percent for recycling, wherein the concentration of the glyoxylic acid in the solution is 2.6 percent. The filtrate was passed into a neutralization apparatus and adjusted to pH 7 by the addition of sodium hydroxide. Then introducing into a heat exchanger, wherein the solution comprises sodium oxalate 0.15% and sodium glyoxylate 3.3%, heating to 45 deg.C, and introducing into reverse osmosisAnd concentrating the mixture by a device until the content of sodium glyoxylate is 13 percent and the content of sodium oxalate is 0.6 percent. And (3) introducing the concentrated solution into a second crystallization kettle, cooling to-5 ℃ for crystallization, and filtering and separating the separated sodium oxalate crystals to obtain a solution containing 13% of sodium glyoxylate and 0.1% of sodium oxalate. Dissolving the filtered sodium oxalate crystals into 10 percent sodium oxalate solution, and passing the solution through an electrodialysis device at the temperature of 40 ℃ and the current density of 1000A/m2And the solvent ratio is 1:1, and solutions of 10% oxalic acid and 10% sodium hydroxide are prepared and prepared to be respectively recycled in the oxalic acid electrolysis step and the sodium hydroxide neutralization step. The sodium glyoxylate solution was evaporated at 4Kpa at 29 ℃ to give a 50% aqueous solution of sodium glyoxylate.
Example 8
An electrolysis process: the same apparatus as in example 1 was used, and the catholyte feed was an 8% oxalic acid solution, which was fed from the catholyte head tank into the electrolytic bath at a feed rate of 1000g/h and a current density of 2000A/m2The surface flow rate of the electrode is 0.2m/s, the temperature of the electrolyte is controlled at 20 ℃, and the residence time of the reaction solution is controlled for 1 h. The sulfuric acid concentration in the anode electrode tank was kept at 10%. And pumping the electrolyzed anode and cathode reaction liquid back to the anode liquid head tank and the cathode liquid head tank respectively, and supplementing deionized water in the anode liquid head tank. The discharging speed of the catholyte after electrolysis is the same as the feeding speed, the discharging liquid glyoxylic acid is 2.3 percent, and the concentration of oxalic acid is 4.9 percent. The current efficiency of the process is 85 percent, the chemical selectivity of the glyoxylic acid is 85 percent, and the cell voltage is 3.5V.
A separation process: pumping the glyoxylic acid discharge liquid into a crystallization kettle I, cooling the reaction liquid to-5 ℃ for crystallization, stopping crystallization when the concentration of oxalic acid in the solution is controlled to be 0.1 percent, filtering oxalic acid crystals and dissolving the oxalic acid crystals into an oxalic acid solution with the concentration of 8 percent for recycling. The filtrate was passed into a neutralization apparatus and adjusted to pH 7 by the addition of sodium hydroxide. Then the solution is introduced into a heat exchanger, the solution consists of 0.15 percent of sodium oxalate and 3.1 percent of sodium glyoxylate, the temperature is raised to 45 ℃, and the heated solution is introduced into a reverse osmosis device and concentrated until the content of the sodium glyoxylate is 13 percent and the content of the sodium oxalate is 0.6 percent. And (3) introducing the concentrated solution into a second crystallization kettle, cooling to-5 ℃ for crystallization, and filtering and separating the separated sodium oxalate crystals to obtain a solution containing 13% of sodium glyoxylate and 0.1% of sodium oxalate. The sodium oxalate crystals obtained by filtration are dissolved intoPassing 10% sodium oxalate solution through electrodialysis device at electrodialysis temperature of 40 deg.C and current density of 1000A/m2And the solvent ratio is 1:1, and solutions of 10% oxalic acid and 10% sodium hydroxide are prepared and prepared to be respectively recycled in the oxalic acid electrolysis step and the sodium hydroxide neutralization step. The sodium glyoxylate solution was evaporated at 4Kpa at 29 ℃ to give a 50% aqueous solution of sodium glyoxylate.
Comparative example
An electrolysis process: the same cell apparatus as in example 1 was used, the catholyte feed was an 8% oxalic acid solution, and the feed rate was 300g/h, and the current density was 1000A/m2The surface flow rate of the electrode is 0.2m/s, the temperature of the electrolyte is controlled at 20 ℃, the anode is 10 percent sulfuric acid solution, the residence time of the reaction solution is controlled for 3.3 hours, and the concentration of the sulfuric acid in the anode electrode tank is kept at 10 percent. And pumping the electrolyzed anode and cathode reaction liquid back to the anode liquid head tank and the cathode liquid head tank respectively, and supplementing deionized water in the anode liquid head tank. The discharge liquid of the cathode high-level tank contains 4 percent of glyoxylic acid and 3 percent of oxalic acid. The process has current efficiency of 80%, chemical selectivity of glyoxylic acid of 92% and cell voltage of 4.5V. The electrolytic bath voltage of the comparative example is 50% higher than that of the examples in the patent, and the corresponding energy consumption of electrolysis is also 50% higher.
Claims (8)
1. A method for preparing sodium glyoxylate by coupling a reverse osmosis process is characterized by comprising the following steps:
(1) an electrolysis process: continuously adding oxalic acid solution with mass concentration of 6-12% into the catholyte head tank, adding sulfuric acid solution into the anolyte head tank, enabling reaction liquid in the two head tanks to flow into the electrolytic bath for electrolysis, respectively pumping the anolyte head tank and the catholyte head tank back, and supplementing deionized water into the anolyte head tank;
(2) a separation process: controlling the content of glyoxylic acid in the catholyte head tank to be 0.75-2.5%, pumping the catholyte of the catholyte head tank into a first crystallization kettle to cool and crystallize oxalic acid contained in the catholyte head tank, and filtering;
(3) introducing the solution filtered in the step (2) into a neutralization device for neutralization, so that glyoxylic acid contained in the solution and residual oxalic acid are converted into sodium glyoxylate and sodium oxalate respectively, and heating;
(4) concentrating the solution neutralized in the step (3) by a reverse osmosis device to obtain a concentrated sodium glyoxylate solution, putting the concentrated sodium glyoxylate solution in a crystallization kettle II to crystallize and condense sodium oxalate contained in the solution, and filtering to obtain a sodium glyoxylate solution; concentrating by reverse osmosis until the content of sodium glyoxylate is 12-15%;
(5) dissolving sodium oxalate crystals obtained by condensing the crystals in the crystallization kettle II in the step (4), and then feeding the dissolved sodium oxalate crystals into an electrodialysis device to prepare oxalic acid and a sodium hydroxide solution;
the feeding speed of the oxalic acid solution and the discharging speed of the glyoxylic acid solution are both 750-2000 g/h.
2. The method of claim 1, wherein: in the reaction process, the components of the reaction solution in the electrolytic cell are 6-12% by mass of oxalic acid and 0.75-2.5% by mass of glyoxylic acid, the feeding speed of the oxalic acid solution is the same as the discharging speed of the glyoxylic acid solution, the temperature of the electrolytic cell is 15-25 ℃, and the current density is 1000-2。
3. The method according to any one of claims 1-2, wherein: in the step (2), when the first crystallization kettle is used for condensation crystallization, the temperature of the reaction liquid is controlled to be-5-0 ℃ to obtain oxalic acid crystals, the crystallization is stopped until the concentration of oxalic acid is reduced to 0.1-0.5%, and the oxalic acid crystals are dissolved into 8-10% oxalic acid solution to be reused in the step (1).
4. The method according to any one of claims 1-2, wherein: in the step (3), the solution obtained after neutralization is heated to 40-50 ℃ by using a heat exchanger.
5. The method according to any one of claims 1-2, wherein: in the step (3), the pH value is adjusted to 6.5-7.5 during the neutralization reaction.
6. The method according to any one of claims 1-2, wherein: and (4) introducing the solution which is heated in the step (3) and consists of 1.8-4% of sodium glyoxylate and 0.1-1% of sodium oxalate into a reverse osmosis device, and performing reverse osmosis concentration until the content of the sodium oxalate is 0.3-2.5%.
7. The method according to any one of claims 1-2, wherein: and dissolving the sodium oxalate crystals obtained in the second crystallization kettle into 8-10% sodium oxalate solution before entering the electrodialysis device.
8. The method according to any one of claims 1-2, wherein: and preparing the sodium oxalate solution into a sodium hydroxide solution and an oxalic acid solution again after electrodialysis, and respectively recycling the sodium hydroxide solution and the oxalic acid solution to the neutralization device and the electrolytic cell.
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