Method for preparing gluconic acid by bipolar membrane electrodialysis

Abstract

The invention belongs to the field of organic acid manufacturing, and particularly provides a method for preparing gluconic acid through bipolar membrane electrodialysis. The method specifically comprises the following steps: treating a gluconate solution by using bipolar membrane electrodialysis, introducing CO2 into an alkali chamber of the bipolar membrane electrodialysis, finally obtaining carbonate or bicarbonate in the alkali chamber, and obtaining a gluconic acid solution in an acid chamber of the bipolar membrane electrodialysis; or obtaining carbonate or bicarbonate in an alkali chamber, and obtaining a mixed solution of gluconic acid and residual gluconate in a salt chamber combined with acid and salt of bipolar membrane electrodialysis. According to the method, the process of treating the gluconate through CO2 reinforced bipolar membrane electrodialysis is utilized, the alkali concentration of bipolar membrane electrodialysis is improved, the energy consumption is reduced, the current efficiency is improved, meanwhile, carbonate or bicarbonate co-produced in the bipolar membrane electrodialysis process can be selected to be used for producing the gluconate, and circulation of CO2 is achieved.

Description

Technical Field

[0001] The present invention belongs to the field of organic acid manufacturing, and specifically, the present invention provides a method for preparing gluconic acid by bipolar membrane electrodialysis. It mainly relates to a process of using CO2 to strengthen bipolar membrane electrodialysis to treat gluconate (sodium / potassium / ammonium gluconate), increase the alkali concentration of bipolar membrane electrodialysis and reduce energy consumption, improve current efficiency, and at the same time, the carbonate or bicarbonate (sodium carbonate / potassium / ammonium or sodium bicarbonate / potassium hydrogen / ammonium hydrogen) co-produced in the bipolar membrane electrodialysis process can be selected for the production of gluconate (sodium / potassium / ammonium gluconate), and a method for realizing CO2 circulation. Background Art

[0002] Gluconic acid (scientific name 1,2,3,4,5-pentahydroxyhexanoic acid, soluble in water, weakly acidic, ionization constant K a 2.5×10 -4 ) is an important industrial raw material. Gluconic acid and its salts have been widely used in the fields of medicine, food and chemical industry.

[0003] At present, the industrial production methods of gluconic acid mainly include fermentation method and dual enzyme method. The fermentation method (patent application CN201310610412; China Brewing, 2015 (1): 5) is to use Aspergillus niger to ferment sodium gluconate. The process is to add inorganic salts, nitrogen sources and other nutrients to a 300-350g / L glucose solution, sterilize it, add Aspergillus niger seed liquid, and ferment it with ventilation. During the fermentation process, sodium hydroxide (generally 32% NaOH) is added to control the pH of the fermentation liquid to about 5.2 and the temperature to about 38°C. After the fermentation liquid is filtered and sterilized, it is evaporated, concentrated and crystallized to obtain sodium gluconate crystals; the dual enzyme method (China Food Additives, 2019, 30 (8): 6; China Food Additives, 2019, 30 (11): 5) is to add glucose oxidase and catalase to a 380-400g / L glucose solution, ventilate it, and add 32% NaOH to adjust the pH during the enzyme conversion process, and the temperature is about 40°C. The enzyme conversion liquid can be filtered, decolorized, evaporated, concentrated and crystallized to obtain sodium gluconate crystals. Since alkali needs to be added to control the pH value during the process, the fermentation liquid / conversion liquid obtained by the fermentation method / double enzyme method is a sodium gluconate solution.

[0004] The industrial method of further using sodium gluconate to produce gluconic acid (gluconolactone) is: dissolving sodium gluconate crystals, converting sodium gluconate into gluconic acid by cation exchange, and then concentrating and crystallizing to obtain the gluconolactone product (one molecule of water is removed to form lactone when gluconic acid crystallizes); the cation exchange column is regenerated into hydrogen form with sulfuric acid, and at the same time, ion exchange wastewater containing sodium sulfate is generated.

[0005] The common point of the fermentation method / dual enzyme method for producing sodium gluconate is that they are all aerobic processes, and the fermentation or enzyme conversion process requires the addition of NaOH (generally 32% NaOH is used in industry) to control the pH of the fermentation liquid / enzyme conversion liquid. The main disadvantages of the process of producing gluconic acid (gluconolactone) from sodium gluconate are: high sulfuric acid consumption per unit product, and a large amount of wastewater containing sodium sulfate (10-12 tons of wastewater per ton of gluconic acid), while the market value of sodium sulfate is very low, and the wastewater containing sodium sulfate has no treatment value.

[0006] Therefore, people proposed to use bipolar membrane electrodialysis to replace the cation exchange method (patent application CN 102002725A) to convert sodium gluconate into gluconic acid and NaOH, and reuse the regenerated NaOH in the fermentation step. Figure 1 As shown, 70-75% of the sodium gluconate is converted into gluconic acid and NaOH in the bipolar membrane electrodialysis step, and the remaining sodium gluconate is still converted into gluconic acid by cation exchange. Compared with the traditional cation exchange process, the load and wastewater generation of the cation exchange step are significantly reduced, but about 3 tons of sodium sulfate-containing wastewater are still generated per ton of gluconic acid.

[0007] Bipolar membrane electrodialysis can regenerate salt into corresponding acid and base. Bipolar membrane is an ion exchange membrane with special functions. It can dissociate water molecules in the membrane into H under the action of electric field. + and OH - and released outside the membrane.

[0008] Figure 2 The diagram shows the membrane stack structure (taking sodium sulfate as an example) and ion migration diagram of conventional "acid-salt-base" three-chamber bipolar membrane electrodialysis. AM is an anion exchange membrane (hereinafter referred to as anion membrane), CM is a cation exchange membrane (hereinafter referred to as cation membrane), and BM is a bipolar membrane; the compartment between AM and CM is called the salt chamber, and a salt-containing feed solution (aqueous solution of sodium sulfate) is initially added to the salt chamber; the compartment between AM and BM is called the acid chamber, and the compartment between CM and BM is called the base chamber. Under the action of the electric field, the water molecules in the bipolar membrane dissociate into H + and OH - , move toward the cathode and anode into the acid chamber and alkaline chamber respectively, H + With the anions (SO4 2- ) combine in the acid chamber to obtain acid (H2SO4); OH - The cations (Na + ) to obtain a base (NaOH) in the base chamber.

[0009] Will Figure 2The anionic membrane in the "acid-salt-base" three-chamber bipolar membrane electrodialysis stack shown in the figure is removed, that is, the salt chamber and the acid chamber are combined to obtain a "salt-base" two-chamber structure membrane stack. The conventional "salt-base" two-chamber bipolar membrane electrodialysis stack structure (taking sodium gluconate as an example) and the schematic diagram of ion migration are shown in FIG. Figure 3 As shown. CM is a cation exchange membrane, BM is a bipolar membrane; the compartment between BM and CM is a salt chamber, and a salt-containing feed solution (aqueous solution of sodium gluconate) is initially added to the salt chamber; the compartment between BM and CM is an alkali chamber, and under the action of the electric field, the water molecules in the bipolar membrane dissociate into OH - and H + , respectively migrate into the base chamber and the salt chamber, and the cations in the salt chamber (Na + ) migrates into the alkali chamber, obtains alkali (NaOH) in the alkali chamber, and obtains a mixture of acid and salt (a mixture of gluconic acid and remaining sodium gluconate) in the salt chamber.

[0010] The above two membrane stack structures can be used to prepare gluconic acid from sodium gluconate by bipolar membrane electrodialysis. Among them, the "salt-alkali" two-chamber bipolar membrane electrodialysis can realize the conversion of sodium gluconate into gluconic acid and NaOH, while the "acid-salt-alkali" three-chamber bipolar membrane electrodialysis can also realize the separation of gluconic acid and residual sodium gluconate.

[0011] However, due to OH - The migration activity of cation exchange membranes in aqueous solution is significantly higher than that of other anions. - The blocking effect is limited. With the increase of the concentration of the regenerated alkali solution in the alkali chamber, the OH - The concentration difference increases, and the OH in the alkali chamber - It is easy to "leak" into the salt chamber through the cation exchange membrane. Moreover, the higher the NaOH concentration in the alkali chamber, the - The more serious the leakage, the more difficult it is to obtain a high NaOH concentration by bipolar membrane electrodialysis.

[0012] For this reason, the concentration of NaOH obtained by preparing gluconic acid from sodium gluconate using bipolar membrane electrodialysis in industry is low, and the mass percentage concentration is generally 5-6% (1.25-1.5 mol / L NaOH). The NaOH added to adjust the pH in the existing fermentation / enzyme conversion process is as high as possible (32%), and the volume of the reaction solution will still be expanded to 1.2-1.25 times the volume of the initial reaction solution at the end of the fermentation / enzyme conversion. If the dilute NaOH obtained by bipolar membrane electrodialysis is used to adjust the pH, it will not only further dilute the reaction liquid and lose the volume capacity of the reactor, but also increase the load of evaporation, concentration and crystallization of the sodium gluconate solution; of course, the dilute NaOH obtained by bipolar membrane electrodialysis can also be evaporated and concentrated first and then reused in the fermentation / enzyme conversion step. In short, the extra water added by the dilute NaOH obtained by bipolar membrane electrodialysis compared to 32% NaOH will always evaporate, increasing the load and cost of evaporation.

[0013] Regenerated OH - Leakage into the salt chamber will also cause the loss of alkali, and part of the current will be OH - The leakage consumption reduces the current efficiency of bipolar membrane electrodialysis, resulting in increased energy consumption. In addition, the above-mentioned OH- leakage problem also leads to a low one-way conversion rate of sodium gluconate in bipolar membrane electrodialysis. The remaining sodium gluconate needs to be converted into acid by cation exchange. The one-way conversion rate of sodium gluconate in the bipolar membrane electrodialysis link in current industrial production is only 70-75%. Summary of the invention

[0014] In order to solve the above-mentioned problems that only dilute NaOH (5-6%, NaOH 1.25-1.5 mol / L) can be obtained when preparing gluconic acid and NaOH from sodium gluconate by bipolar membrane electrodialysis, the dilute NaOH is difficult to recycle, the evaporation load is increased, and the power consumption is extremely high and the current efficiency is low when forcibly preparing high-concentration NaOH with a large current density, the present invention provides a method for preparing gluconic acid by bipolar membrane electrodialysis characterized by CO2 circulation.

[0015] The main technical route and principle of the present invention are as follows: In the existing production process, the sodium gluconate fermentation / enzyme conversion step does not produce CO2 (Note: sodium gluconate fermentation will produce a small amount of CO2 during the bacterial growth stage, while the conversion of glucose to gluconic acid does not produce CO2; the enzymatic conversion process of glucose to gluconic acid does not produce CO2). As an option, the present invention replaces the NaOH added in the sodium gluconate fermentation / enzyme conversion step with sodium carbonate, and the sodium carbonate is neutralized with gluconic acid to produce CO2; the CO2 produced by the neutralization of sodium carbonate and gluconic acid is passed into the alkaline chamber of bipolar membrane electrodialysis to alleviate OH -Leakage, improve current efficiency, reduce power consumption of bipolar membrane electrodialysis, increase alkali concentration in alkali chamber, avoid concentration of dilute alkali solution or reduce the load of concentration of dilute alkali solution, and then use the high concentration sodium carbonate solution obtained in alkali chamber for sodium gluconate fermentation / enzyme conversion step to adjust pH value and produce CO2, thus realizing closed-loop circulation of CO2. Further, the high-concentration sodium carbonate solution can be expanded into a high-concentration solution or crystal of sodium carbonate / potassium / ammonium or sodium bicarbonate / potassium hydrogen / ammonium hydrogen, which has the advantages that: when the potassium gluconate / ammonium remaining after bipolar membrane electrodialysis treatment is converted into gluconic acid by subsequent cation exchange, the cation exchange column (regenerated into hydrogen type with sulfuric acid or hydrochloric acid) produces ion exchange wastewater containing potassium sulfate / ammonium or potassium chloride / ammonium, which can be concentrated and crystallized to obtain potassium sulfate / ammonium or potassium chloride / ammonium, and potassium sulfate / ammonium or potassium chloride / ammonium itself has market value (for example, used as fertilizer); when expanded into sodium bicarbonate, due to the low solubility of sodium bicarbonate, it can be naturally crystallized from the alkali chamber during the bipolar membrane electrodialysis process, and can be used in the form of solid powder or high-concentration slurry for sodium gluconate fermentation / enzyme conversion step, and also plays the role of high-concentration alkali (instead of high-concentration NaOH solution).

[0016] The method for preparing gluconic acid by bipolar membrane electrodialysis of the present invention is as follows: Figure 4 As shown, the following steps are included:

[0017] 1) Bipolar membrane electrodialysis: When treating a gluconate solution by bipolar membrane electrodialysis, CO2 is introduced into the alkali chamber of the bipolar membrane electrodialysis to finally obtain carbonate or bicarbonate in the alkali chamber, obtain a gluconic acid solution in the acid chamber of the bipolar membrane electrodialysis, or obtain a mixed solution of gluconic acid and remaining gluconate in the salt chamber where the acid salt is combined.

[0018] Preferably, the CO2 is the CO2 released during the fermentation / enzymatic conversion process to prepare gluconate (ie, the fermentation / enzymatic conversion step of gluconate).

[0019] The fermentation / enzyme conversion step involved in the present invention comprises the following steps: preparing gluconate by fermentation (Aspergillus niger) / enzyme conversion (glucose oxidase and catalase) according to a conventional method; wherein the carbonate (high concentration) or bicarbonate obtained in the alkali chamber of step 1) is used as a pH regulator (i.e., a neutralizer) for the fermentation / enzyme conversion of gluconate to control the pH value of the reaction solution, while releasing CO2; the released CO2 is introduced into the alkali chamber of the bipolar membrane electrodialysis in step 1); and the gluconate prepared by fermentation / enzyme conversion is used as a feed solution for the salt chamber of the bipolar membrane electrodialysis in step 1).

[0020] According to the method of the present invention, as a preferred embodiment, the gluconate solution comprises one or more of sodium gluconate, potassium gluconate and ammonium gluconate solutions;

[0021] The carbonate includes one or more of sodium carbonate, potassium carbonate and ammonium carbonate, and the bicarbonate includes one or more of sodium bicarbonate, potassium bicarbonate and ammonium bicarbonate.

[0022] The "released CO2" is the tail gas containing CO2 released during the fermentation / enzymatic conversion process to prepare gluconate (such as but not limited to sodium / potassium / ammonium gluconate); the tail gas can be directly introduced into the alkali chamber of the bipolar membrane electrodialysis in step 1), or the CO2 in the tail gas can be enriched, captured or purified and then introduced into the alkali chamber of the bipolar membrane electrodialysis in step 1).

[0023] The bipolar membrane electrodialysis described in step 1) includes three-chamber bipolar membrane electrodialysis or two-chamber bipolar membrane electrodialysis. Preferably, the three-chamber bipolar membrane electrodialysis is "acid-salt-alkali" three-chamber bipolar membrane electrodialysis, or the two-chamber bipolar membrane electrodialysis is "salt-alkali" two-chamber bipolar membrane electrodialysis.

[0024] The step 1) of “introducing CO2 into the alkali chamber of bipolar membrane electrodialysis” means introducing CO2 into the alkali chamber material cylinder of bipolar membrane electrodialysis.

[0025] The carbonate (such as but not limited to sodium carbonate / potassium / ammonium) (high concentration) or bicarbonate (such as but not limited to sodium bicarbonate / potassium hydrogen / ammonium hydrogen) obtained in the alkali chamber in step 1) can be an aqueous solution or crystal; the crystal is naturally crystallized and precipitated in the alkali chamber (because it exceeds its saturation concentration) during the bipolar membrane electrodialysis process; the crystal can be separated in situ or ex situ in the alkali chamber material cylinder, and conventional methods such as sedimentation, filtration, and centrifugation can be used.

[0026] Preferably, the carbonate (for example but not limited to sodium carbonate / potassium / ammonium) obtained in the alkali chamber of the bipolar membrane electrodialysis in step 1) is an aqueous solution; further preferably, the concentration of the aqueous solution is ≥2.5 mol / L (i.e., 5 equivalents / L); wherein, further preferably, the concentration of the aqueous solution of sodium carbonate (note: saturated concentration of about 4.5 mol / L) is ≥3.0 mol / L, or, the concentration of the aqueous solution of potassium carbonate (saturated concentration of about 8 mol / L) is ≥4.5 mol / L, and the concentration of the aqueous solution of ammonium carbonate (saturated concentration of about 6.9 mol / L) is ≥4.0 mol / L.

[0027] Preferably, the bicarbonate (for example but not limited to sodium bicarbonate / potassium bicarbonate / ammonium bicarbonate) obtained in the alkali chamber of the bipolar membrane electrodialysis in step 1) is crystalline; further preferably, sodium bicarbonate (saturated concentration of about 1.32 mol / L), potassium bicarbonate (saturated concentration of about 4 mol / L), and ammonium bicarbonate (saturated concentration of about 3.4 mol / L) are continuously crystallized and precipitated when CO2 is introduced into the alkali chamber cylinder as their concentration accumulates to exceed their saturated concentration, and settle to the bottom of the alkali chamber cylinder for in-situ separation.

[0028] After step 1), a concentration step of the alkali chamber feed solution can be added. The carbonate (such as but not limited to sodium carbonate / potassium / ammonium) aqueous solution or bicarbonate (such as but not limited to sodium bicarbonate / potassium hydrogen / ammonium hydrogen) aqueous solution obtained in the alkali chamber can be further concentrated into a (higher concentration) aqueous solution, or concentrated and crystallized to obtain crystals; conventional methods can be used. The concentrated aqueous solution and the crystals obtained by concentrated crystallization are used for fermentation / enzymatic conversion to prepare gluconate (such as but not limited to sodium / potassium / ammonium gluconate).

[0029] During the operation of the bipolar membrane electrodialysis described in step 1), the addition flow rate of CO2 is adjusted by measuring the pH of the alkali chamber liquid, and the pH of the alkali chamber liquid is controlled to be near the normal pH of carbonate or bicarbonate by adjusting the flow rate of CO2 added to the alkali chamber. For example, the pH of the alkali chamber liquid of the bipolar membrane electrodialysis is controlled at 11.5-12.5 to obtain sodium carbonate, or the pH of the alkali chamber liquid is controlled at 7.8-8.8 to obtain sodium bicarbonate. Conventional feedback control methods can be used, that is, the addition flow rate of CO2 is adjusted by pH value feedback.

[0030] As a selection, after fermentation / enzyme conversion, the steps of filtering, decolorizing, concentrating, and crystallizing of the gluconate fermentation liquid / enzyme conversion liquid can be added to obtain the crystals of gluconate. Conventional filtering, decolorizing, concentrating, and crystallization methods can be adopted. Further, the step of dissolving the gluconate crystals can be added to obtain the gluconate solution used for step 1).

[0031] Before step 1), a step of decolorizing the gluconate solution and / or removing calcium and magnesium ions may be added, using conventional methods, such as activated carbon decolorization and chelating resin decalcification and magnesium removal.

[0032] After step 1), conventional cation exchange can be carried out to convert the remaining gluconate into gluconic acid, and then all the gluconic acid obtained is concentrated and crystallized to obtain the gluconolactone product.

[0033] The method for preparing gluconic acid by bipolar membrane electrodialysis of the present invention has the advantages that:

[0034] 1. The present invention introduces CO2 generated by the neutralization of carbonate and gluconic acid into the alkali chamber of bipolar membrane electrodialysis, which can effectively inhibit the "hydroxyl leakage" of the alkali chamber of conventional bipolar membrane electrodialysis, thereby significantly improving the current efficiency of bipolar membrane electrodialysis, reducing energy consumption, increasing the ion migration membrane flux and alkali concentration, and improving the single-pass conversion rate of sodium gluconate / potassium / ammonium;

[0035] 2. The problem that the dilute NaOH alkali obtained by conventional bipolar membrane electrodialysis is difficult to utilize is overcome. High-concentration sodium carbonate / potassium / ammonium or sodium bicarbonate / potassium hydrogen / ammonium hydrogen can be obtained in the alkali chamber, so that it can be conveniently used (in the form of a high-concentration aqueous solution, or in the form of a solid powder or a high-concentration slurry) for the fermentation / enzyme conversion process of preparing sodium / potassium / ammonium gluconate.

[0036] 3. Using CO2 as the medium, the performance of bipolar membrane electrodialysis was comprehensively enhanced and improved, the evaporation load of sodium gluconate obtained by neutralization with dilute NaOH was reduced, and the closed-loop circulation of CO2 was realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Process flow chart of preparing gluconic acid by bipolar membrane method in the prior art.

[0038] Figure 2 It is a schematic diagram of the conventional "acid-salt-alkali" three-chamber bipolar membrane electrodialysis membrane stack structure and ion migration (taking sodium sulfate regeneration of sulfuric acid and sodium hydroxide as an example);

[0039] Among them: AM is anion exchange membrane, CM is cation exchange membrane, BM is bipolar membrane; "salt" represents salt chamber liquid, "acid" represents acid chamber liquid, "base" represents base chamber liquid, and "polar liquid" represents polar chamber liquid.

[0040] Figure 3 This is a schematic diagram of the conventional "salt-alkali" two-chamber bipolar membrane electrodialysis membrane stack structure and ion migration (taking sodium gluconate to regenerate gluconic acid and NaOH as an example);

[0041] Among them: CM is a cation exchange membrane, BM is a bipolar membrane; "salt" refers to the salt chamber liquid, "alkali" refers to the alkali chamber liquid, "polar liquid" refers to the polar chamber liquid, C6H 11 O7 - represents the gluconate ion, C6H 12 O7 represents a gluconic acid molecule.

[0042] Figure 4 The process flow chart of preparing gluconic acid by the bipolar membrane method of the present invention.

[0043] Figure 5 The "acid-salt-alkali" three-chamber bipolar membrane electrodialysis membrane stack structure and ion migration schematic diagram of the present invention (taking the alkali chamber co-production of sodium carbonate as an example);

[0044] Among them: AM is an anion exchange membrane, CM is a cation exchange membrane, BM is a bipolar membrane; "salt" refers to the salt chamber liquid, "acid" refers to the acid chamber liquid, "base" refers to the base chamber liquid, "polar liquid" refers to the polar chamber liquid, C6H 11 O7 - represents the gluconate ion, C6H 12 O7 represents a gluconic acid molecule.

[0045] Figure 6 The diagram of the "salt-alkali" two-chamber bipolar membrane electrodialysis membrane stack structure and ion migration of the present invention (taking the alkali chamber co-production of sodium carbonate as an example);

[0046] Among them: CM is a cation exchange membrane, BM is a bipolar membrane; "salt" refers to the salt chamber liquid, "alkali" refers to the alkali chamber liquid, "polar liquid" refers to the polar chamber liquid, C6H 11 O7 - represents the gluconate ion, C6H 12 O7 represents a gluconic acid molecule.

[0047] Figure 7 This is the multi-stage countercurrent organization mode of the "acid-salt-alkali" three-chamber bipolar membrane electrodialysis of the present invention (taking the alkali chamber co-production of sodium carbonate as an example).

[0048] Figure 8 This is the multi-stage countercurrent organization mode of the "salt-alkali" two-chamber bipolar membrane electrodialysis of the present invention (taking the alkali chamber co-production of sodium carbonate as an example). DETAILED DESCRIPTION

[0049] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; the materials, reagents, etc. used in the following examples, unless otherwise specified, can be obtained from commercial channels.

[0050] The method for preparing gluconic acid by bipolar membrane electrodialysis of the present invention comprises the following steps:

[0051] 1) Bipolar membrane electrodialysis: When treating a gluconate solution by bipolar membrane electrodialysis, CO2 is introduced into the alkali chamber of the bipolar membrane electrodialysis to finally obtain carbonate or bicarbonate in the alkali chamber, obtain a gluconic acid solution in the acid chamber of the bipolar membrane electrodialysis, or obtain a mixed solution of gluconic acid and remaining gluconate in the salt chamber where the acid salt is combined.

[0052] The membrane stack structure of the bipolar membrane electrodialysis of the present invention needs to include a salt chamber (a compartment into which the sodium gluconate / potassium / ammonium feed solution is initially introduced) and an independent alkali chamber (in which OH is continuously introduced). - Produced), that is, a "acid-salt-base" three-chamber structure or a "salt-base" two-chamber structure can be adopted.

[0053] The "acid-salt-base" three-chamber bipolar membrane electrodialysis membrane stack structure and ion migration schematic diagram of the present invention are shown in FIG. Figure 5 The present invention and Figure 2 The difference between the conventional "acid-salt-alkali" three-chamber bipolar membrane electrodialysis membrane stack structure and the ion migration schematic diagram is that when sodium gluconate / potassium / ammonium is treated by three-chamber bipolar membrane electrodialysis (i.e., the sodium gluconate / potassium / ammonium aqueous solution to be treated is added to the salt chamber of the three-chamber bipolar membrane electrodialysis membrane stack), CO2 is added to the alkali chamber of the three-chamber bipolar membrane electrodialysis, and finally a high concentration of sodium carbonate / potassium / ammonium or sodium bicarbonate / potassium hydrogen / ammonium hydrogen is obtained in the alkali chamber, and gluconic acid is obtained in the acid chamber. Therefore, the present invention can effectively inhibit the "hydroxyl leakage" of the alkali chamber of the conventional three-chamber bipolar membrane electrodialysis, thereby significantly improving the current efficiency of the conventional three-chamber bipolar membrane electrodialysis, reducing the energy consumption of regenerating acid and alkali, and increasing the ion migration membrane flux, and overcoming the problem that the dilute NaOH obtained by the conventional three-chamber bipolar membrane electrodialysis is difficult to utilize.

[0054] The schematic diagram of the "salt-alkali" two-chamber bipolar membrane electrodialysis membrane stack structure and ion migration of the present invention is shown in FIG. Figure 6 The present invention and Figure 3 The difference between the conventional "salt-alkali" two-chamber bipolar membrane electrodialysis membrane stack structure and the ion migration schematic diagram shown is that when sodium gluconate / potassium / ammonium is treated with "salt-alkali" two-chamber bipolar membrane electrodialysis (i.e., the sodium gluconate / potassium / ammonium aqueous solution to be treated is added to the salt chamber of the "salt-alkali" two-chamber bipolar membrane electrodialysis membrane stack), CO2 is added to the alkali chamber of the "salt-alkali" two-chamber bipolar membrane electrodialysis, and finally a high concentration of sodium carbonate / potassium / ammonium or sodium bicarbonate / potassium hydrogen / ammonium hydrogen is obtained in the alkali chamber, and gluconic acid is obtained in the salt chamber. Therefore, the present invention can effectively inhibit the "hydroxyl leakage" of the alkali chamber of the conventional "salt-alkali" two-chamber bipolar membrane electrodialysis, thereby significantly improving the current efficiency of the conventional "salt-alkali" two-chamber bipolar membrane electrodialysis, reducing the energy consumption of regenerating acid and alkali, and improving the ion migration membrane flux, and overcoming the problem that the dilute NaOH obtained by the conventional "salt-alkali" two-chamber bipolar membrane electrodialysis is difficult to utilize.

[0055] The CO2 in the "introducing CO2 into the alkali chamber of the bipolar membrane electrodialysis" in step 1) of the present invention comes from the tail gas released during the fermentation / enzyme conversion process to prepare sodium / potassium / ammonium gluconate, which contains the remaining components after the oxygen in the air introduced into the fermentation / enzyme conversion reactor is consumed by the fermentation / enzyme conversion reaction of sodium / potassium / ammonium gluconate and the CO2 generated by the neutralization of the added sodium carbonate / potassium / ammonium or sodium bicarbonate / potassium hydrogen / ammonium hydrogen with gluconic acid. The tail gas can be directly introduced into the alkali chamber of the bipolar membrane electrodialysis described in step 1), or the CO2 in the tail gas can be enriched, captured or purified before being introduced into the alkali chamber of the bipolar membrane electrodialysis described in step 1).

[0056] The "introducing into the alkali chamber of the bipolar membrane electrodialysis described in step 1)" means that the tail gas containing CO2 or the CO2 enriched, captured or purified from the tail gas is directly introduced into the alkali chamber material cylinder (Note: the alkali chamber liquid circulates between the alkali chamber material cylinder and the alkali chamber of the bipolar membrane electrodialysis), and gas-liquid exchange and mass transfer occur with the alkali chamber feed liquid, and CO2 dissolves into the alkali chamber feed liquid. Preferably, the gas-liquid two-phase countercurrent is in the alkali chamber material cylinder.

[0057] During the operation of bipolar membrane electrodialysis, the pH of the alkaline chamber liquid is measured to feedback and control the amount of CO2 added to the tail gas containing CO2 or CO2 enriched, captured or purified from the tail gas, so as to control the pH of the alkaline chamber liquid at the desired pH.

[0058] The bipolar membrane electrodialyzer in the present invention is a conventional bipolar membrane electrodialyzer device, and can adopt conventional operation methods, including constant pressure, constant current or variable pressure, variable current mode.

[0059] The organizational modes of the bipolar membrane electrodialyzer in the present invention include a single-stage mode and a multi-stage mode, wherein preferably, the organizational mode of the bipolar membrane electrodialyzer is a multi-stage countercurrent organizational mode.

[0060] The multi-stage countercurrent organization method described in the present invention is to configure the bipolar membrane electrodialyzer into multiple bipolar membrane electrodialysis membrane stacks, each bipolar membrane electrodialysis membrane stack is a stage, and CO2 is added to the alkali chamber of at least one stage of bipolar membrane electrodialysis.

[0061] The number of stages of the multi-stage countercurrent organization method of the present invention is greater than or equal to two, preferably two or three.

[0062] The multi-stage countercurrent organization method of the present invention can adopt an "acid-salt-alkali" three-chamber bipolar membrane electrodialyzer (such as Figure 7 as shown) or a "salt-alkali" two-chamber bipolar membrane electrodialyser (as Figure 8 Specifically, taking the "acid-salt-alkali" three-chamber bipolar membrane electrodialyzer as an example, the process includes: injecting sodium gluconate / potassium / ammonium aqueous solution into the salt chamber of the first stage, injecting acid chamber initial solution into the acid chamber of the last stage (Nth stage), and injecting alkali chamber initial solution into the alkali chamber of the last stage (Nth stage); finally, obtaining the residual solution of sodium gluconate / potassium / ammonium aqueous solution in the salt chamber of the last stage, obtaining gluconic acid in the acid chamber of the first stage, and obtaining high-concentration sodium carbonate / potassium / ammonium or sodium bicarbonate / potassium hydrogen / ammonium hydrogen in the alkali chamber of the first stage.

[0063] The electrode chamber liquid composition of the bipolar membrane electrodialyzer described in the present invention is the electrode chamber liquid composition commonly used in conventional industrial bipolar membrane electrodialyzers, such as 0.1-0.5 mol / L aqueous solution of sodium sulfate or other inert electrolytes; the volume of the electrode chamber is a conventional volume, usually sufficient for the electrode chamber liquid to circulate normally in the membrane stack.

[0064] The temperature of the feed solution in each chamber (including the acid chamber, salt chamber, alkali chamber, and electrode chamber) of the present invention adopts the temperature of conventional electrodialysis operation, usually in the range of 5 to 50°C; the flow rate of each chamber (including the acid chamber, salt chamber, alkali chamber, and electrode chamber) adopts a conventional flow rate, usually in the range of 0.1 to 10 cm / s; the current density adopts a conventional current density, usually in the range of 1 to 200 mA / cm 2 range.

[0065] The bipolar membrane, anion exchange membrane and cation exchange membrane used in the bipolar membrane electrodialyser of the present invention are not particularly limited, and ion exchange membranes well known to those skilled in the art can be used, which can be purchased from the market. For example, conventional electrodialysis anion exchange membranes, cation exchange membranes and bipolar membranes, anion and cation exchange membranes commonly used in diffusion dialysis processes and monovalent anion and cation selective membranes (i.e., ion exchange membranes that allow monovalent anions or cations to pass preferentially and block divalent and higher valence ions from passing through) can also be used.

[0066] The present invention will be further described below in conjunction with the embodiments.

[0067] Example 1

[0068] Step 1) Bipolar membrane electrodialysis: Preparation of gluconic acid and co-production of potassium bicarbonate from potassium gluconate. Use a bipolar membrane electrodialysis stack containing a three-chamber structure of "acid-salt-base" (the stack structure is as follows Figure 5 The electrodialysis equipment (shown in Figure 1) treats aqueous solution containing potassium gluconate. The acid chamber regenerates gluconic acid, and the alkali chamber adds CO2 to co-produce potassium bicarbonate. The bipolar membrane electrodialyzer is a plate type, and the outer size of the membrane stack is 100mm×200mm. It uses 5 BP-1 bipolar membranes (ASTOM, Japan), 4 RXAM anion membranes (Hebei Yadeshi Environmental Protection Equipment Co., Ltd.) and 4 SHCM cation membranes (Shanghai Xiangfeng Water Treatment Equipment Co., Ltd.). Titanium-coated ruthenium is used as the anode plate, and stainless steel is used as the cathode plate. The partitions and meshes are all made of polypropylene, the partitions are non-loop partitions, and the meshes are woven meshes.

[0069] The salt chamber of the bipolar membrane electrodialysis was initially charged with 0.3 L of an aqueous solution containing 1.15 mol / L potassium gluconate, the acid chamber was initially charged with 0.6 L of deionized water, the alkali chamber was initially charged with 0.3 L of deionized water and CO2 gas was passed in. The two chambers shared a liquid storage tank, and the chamber liquid was 0.3 L of a 0.25 mol / L potassium sulfate aqueous solution.

[0070] Start the bipolar membrane electrodialyzer, keep the operating voltage at 12V, control the liquid flow velocity in each compartment to 3cm / s, and the feed liquid temperature in each compartment to 30℃. During the operation of the bipolar membrane electrodialysis, the pH of the alkali chamber liquid is monitored in real time, and the pH of the alkali chamber liquid is controlled to be around 8.3 by controlling the amount of CO2 added to the alkali chamber. Samples are taken every 10 minutes to measure the conductivity value of the solution in the salt chamber. When the conductivity value drops below 5mS / cm, the bipolar membrane electrodialysis operation is stopped and the feed liquid in the salt chamber is discharged. After 60 minutes of bipolar membrane electrodialysis operation, 0.25L of desalted solution (wherein the potassium gluconate concentration is less than 5g / L and the pH is 6.7) is recovered in the salt chamber, 0.64L of gluconic acid aqueous solution with a concentration of 0.532mol / L is obtained in the acid chamber, and 0.32L of potassium bicarbonate aqueous solution with a concentration of 1.06mol / L is obtained in the alkali chamber. According to calculation, the energy consumption of bipolar membrane electrodialysis is 154.4kWh / kmol potassium gluconate), and the membrane flux is 9.48mol potassium gluconate / m 2 / h, average current efficiency 76.1%.

[0071] At this time, the gluconic acid aqueous solution in the acid chamber and the potassium bicarbonate aqueous solution in the alkali chamber are respectively continued to remain in the acid chamber or the alkali chamber, and a new aqueous solution containing 1.15mol / L potassium gluconate is added to the salt chamber of the bipolar membrane electrodialysis, and the bipolar membrane electrodialysis operation of the next batch is started. After multiple batches of the above-mentioned operations, when the cumulative volume of the potassium gluconate aqueous solution treated in the salt chamber reaches 2.1L, 1.7L of desalted liquid with a potassium gluconate concentration of less than 5g / L and a pH value of 6.7 can be recovered in the salt chamber; 0.80L of gluconic acid aqueous solution with a concentration of 2.91mol / L can be recovered in the acid chamber; and 0.60L of potassium bicarbonate aqueous solution with a concentration of 3.91mol / L can be recovered in the alkali chamber.

[0072] Comparative Example 1

[0073] Preparation of Gluconic Acid and KOH from Potassium Gluconate The "acid-salt-base" three-chamber bipolar membrane electrodialyzer in Example 1 was used to treat an aqueous solution containing potassium gluconate in a conventional manner, i.e., the acid chamber regenerated gluconic acid and the base chamber regenerated KOH.

[0074] 0.3 L of an aqueous solution containing 1.15 mol / L potassium gluconate was passed into the salt chamber of the bipolar membrane electrodialysis, 0.6 L of deionized water was initially added to the acid chamber, and 0.3 L of deionized water was initially added to the alkali chamber. The two chambers shared a liquid storage tank, and the chamber liquid was 0.3 L of a 0.25 mol / L potassium sulfate aqueous solution.

[0075] Start the bipolar membrane electrodialyzer, keep the operating voltage constant at 12V, control the liquid flow linear velocity in each compartment to 3cm / s, and the feed liquid temperature in each compartment to 30°C. Take samples every 10 minutes to measure the conductivity of the solution in the salt chamber. When the conductivity value drops below 15mS / cm, stop the bipolar membrane electrodialysis operation and discharge the feed liquid in the salt chamber. After 80 minutes of bipolar membrane electrodialysis operation, 0.23L of desalted liquid (wherein the potassium gluconate concentration is less than 7g / L and the pH is 8.8) was recovered in the salt chamber, 0.63L of gluconic acid aqueous solution with a concentration of 0.502mol / L was obtained in the acid chamber, and 0.36L of KOH aqueous solution with a concentration of 0.81mol / L was obtained in the alkali chamber. It is calculated that the energy consumption of bipolar membrane electrodialysis is 175.1kWh / kmol potassium gluconate, and the membrane flux is 6.9mol potassium gluconate / m 2 / h, average current efficiency 59.6%.

[0076] After the first batch of operations were completed, 0.3L of a new aqueous solution containing 1.15mol / L potassium gluconate was added to the salt chamber of the bipolar membrane electrodialysis to perform the next batch of bipolar membrane electrodialysis operations. When this batch operation was repeated to the fifth batch (the total volume of the potassium gluconate aqueous solution put into the salt chamber reached 1.5L at this time), it was found that the conductivity of the salt chamber feed liquid did not decrease when it dropped to 50mS / cm, and it was difficult to reduce the conductivity of the salt chamber liquid by extending the operation time. At this time, the gluconic acid concentration in the acid chamber was 1.298mol / L, and the volume of the acid chamber liquid was 0.72L; the KOH concentration in the alkali chamber was 2.01mol / L, and the volume of the alkali chamber liquid was 0.57L.

[0077] Example 2

[0078] Step 1) Bipolar membrane electrodialysis: Preparation of gluconic acid and co-production of sodium carbonate from sodium gluconate. The three-chamber bipolar membrane electrodialysis equipment in Example 1 is used to treat an aqueous solution containing sodium gluconate, the acid chamber regenerates gluconic acid, and the alkali chamber adds CO2 to co-produce sodium carbonate. The salt chamber of the bipolar membrane electrodialysis is fed with 0.3L of an aqueous solution containing 1.15mol / L sodium gluconate, the acid chamber is initially charged with 0.6L of deionized water, the alkali chamber is initially charged with 0.3L of deionized water, the alkali chamber is fed with tail gas containing about 10% CO2 released during the preparation of sodium gluconate by fermentation (with sodium carbonate aqueous solution to adjust the pH value) in an air bag, and the two polar chambers share a liquid storage tank, and the polar chamber liquid is 0.3L of 0.25mol / L sodium sulfate aqueous solution.

[0079] Start the bipolar membrane electrodialyzer, keep the operating voltage at 12V, control the liquid flow linear velocity in each compartment to 3cm / s, and the feed liquid temperature in each compartment to 30℃. During the operation of bipolar membrane electrodialysis, the pH value of the alkali chamber liquid is monitored in real time, and the pH of the alkali chamber liquid is controlled to be around 12 by controlling the amount of CO2 added to the alkali chamber. Samples are taken every 10 minutes to measure the conductivity value of the solution in the salt chamber. When the conductivity value drops below 6mS / cm, the bipolar membrane electrodialysis operation is stopped and the feed liquid in the salt chamber is discharged. After 60 minutes of bipolar membrane electrodialysis operation, 0.26L of desalted solution (wherein the sodium gluconate concentration is less than 4g / L and the pH is 6.9) is recovered in the salt chamber, 0.63L of gluconic acid aqueous solution with a concentration of 0.53mol / L is obtained in the acid chamber, and 0.32L of sodium carbonate aqueous solution with a concentration of 0.54mol / L is obtained in the alkali chamber. According to calculation, the energy consumption of bipolar membrane electrodialysis is 136.9 kWh / kmol sodium gluconate, and the membrane flux is 9.46 mol sodium gluconate / m 2 / h, average current efficiency 78.6%.

[0080] At this time, the gluconic acid aqueous solution in the acid chamber and the sodium carbonate aqueous solution in the alkali chamber are continued to remain in the acid chamber and the alkali chamber, and a new aqueous solution containing 1.15 mol / L sodium gluconate is added to the salt chamber of the bipolar membrane electrodialysis, and the bipolar membrane electrodialysis operation of the next batch is started. After multiple batches of the above operations, when the total volume of the sodium gluconate aqueous solution treated in the salt chamber reaches 1.8L, 1.52L of desalted liquid with a sodium gluconate concentration of less than 5g / L and a pH value of 6.9 can be recovered in the salt chamber; 0.9L of gluconic acid aqueous solution with a concentration of 2.24mol / L can be recovered in the acid chamber; 0.43L of sodium carbonate aqueous solution with a concentration of 2.36mol / L can be recovered in the alkali chamber, which is used for pH adjustment of the step of preparing sodium gluconate by fermentation.

[0081] Preparation of sodium gluconate by fermentation: Different from the conventional method of using NaOH as a pH regulator, this embodiment uses a sodium carbonate aqueous solution as a pH regulator to control the pH value of the fermentation liquid. The sodium gluconate production strain is Aspergillus niger, a 1.0L fermentation tank is used, the culture medium is composed of 340g / L glucose, 3.5g / L corn steep liquor, 2.0g / L yeast extract, and 1.5g / L magnesium sulfate. The fermentation process temperature is controlled at 38°C and the dissolved oxygen is 20%. The 2.36mol / L sodium carbonate aqueous solution obtained in the above-mentioned bipolar membrane electrodialysis step is used to control the pH value of the fermentation liquid at 5.6±0.2. The fermentation cycle is 24h, and the sodium gluconate output is 348g / L. The released tail gas is collected in an air bag during the process. The obtained fermentation liquid is filtered to remove the bacterial body, 1% activated carbon is decolorized and filtered to remove the activated carbon, and the rotary evaporator is concentrated and crystallized to obtain sodium gluconate crystals. The obtained crystals are used for the preparation of gluconic acid by bipolar membrane electrodialysis in step 1).

[0082] Comparative Example 2

[0083] Preparation of gluconic acid and NaOH from sodium gluconate The "acid-salt-base" three-chamber bipolar membrane electrodialyzer in Example 1 was used to treat an aqueous solution containing sodium gluconate in a conventional manner, i.e., the acid chamber regenerated gluconic acid and the base chamber regenerated NaOH.

[0084] The salt chamber of the bipolar membrane electrodialysis was introduced with 0.3 L of an aqueous solution containing 1.15 mol / L sodium gluconate, the acid chamber was initially added with 0.6 L of deionized water, and the alkali chamber was initially added with 0.3 L of deionized water. The two chambers shared a liquid storage tank, and the chamber liquid was 0.3 L of a 0.25 mol / L sodium sulfate aqueous solution.

[0085] Start the bipolar membrane electrodialyzer, keep the operating voltage constant at 12V, control the liquid flow linear velocity in each compartment to 3cm / s, and the feed liquid temperature in each compartment to 30℃. Take samples every 10 minutes to measure the conductivity of the solution in the salt chamber. When the conductivity value drops below 9.5mS / cm, stop the bipolar membrane electrodialysis operation and discharge the feed liquid in the salt chamber. After 80 minutes of bipolar membrane electrodialysis operation, 0.27L of desalted solution (wherein the sodium gluconate concentration is less than 6g / L and the pH is 8.0) was recovered in the salt chamber, 0.62L of gluconic acid aqueous solution with a concentration of 0.49mol / L was obtained in the acid chamber, and 0.34L of NaOH aqueous solution with a concentration of 0.97mol / L was obtained in the alkali chamber. It is calculated that the energy consumption of bipolar membrane electrodialysis is 167.6kWh / kmol sodium gluconate, and the membrane flux is 6.98mol sodium gluconate / m 2 / h, average current efficiency 63.6%.

[0086] After the first batch of operations were completed, a new aqueous solution containing 1.15 mol / L sodium gluconate was added to the salt chamber of the bipolar membrane electrodialysis to carry out the next batch of bipolar membrane electrodialysis operations. When this batch operation was repeated to the fifth batch (the total volume of the sodium gluconate aqueous solution put into the salt chamber reached 1.5 L at this time), it was found that the conductivity of the salt chamber feed liquid would no longer decrease when it dropped to 63 mS / cm, and it was difficult to reduce the conductivity of the salt chamber liquid by extending the operation time. At this time, the gluconic acid concentration in the acid chamber was 1.49 mol / L, and the volume of the acid chamber liquid was 0.68 L; the NaOH concentration in the alkali chamber was 2.1 mol / L, and the volume of the alkali chamber liquid was 0.50 L.

[0087] Example 3

[0088] Step 1) Bipolar membrane electrodialysis: Preparation of gluconic acid and sodium carbonate from sodium gluconate. Use a bipolar membrane electrodialysis stack containing a "salt-alkali" two-chamber structure (the stack structure is as follows Figure 6The electrodialysis equipment (shown in Figure 1) treats aqueous solution containing sodium gluconate, and CO2 is added to the alkali chamber to co-produce sodium carbonate. The bipolar membrane electrodialyzer is a plate type, and the outer size of the membrane stack is 100mm×200mm. It uses 5 RXBM bipolar membranes (Hebei Yadeshi Environmental Protection Equipment Co., Ltd.) and 4 SHCM cation membranes (Shanghai Xiangfeng Water Treatment Equipment Co., Ltd.). Titanium-coated ruthenium is used as the anode plate, and stainless steel is used as the cathode plate. The partition and the mesh are all made of polypropylene, the partition is a non-loop partition, and the mesh is a woven mesh type.

[0089] 0.3 L of an aqueous solution containing 1.35 mol / L sodium gluconate was introduced into the salt chamber of the bipolar membrane electrodialysis, 0.3 L of deionized water was initially added to the alkali chamber, and the tail gas containing about 10% CO2 released during the preparation of sodium gluconate by an enzyme conversion method (the pH value was adjusted with an aqueous sodium carbonate solution) contained in an air bag was introduced into the alkali chamber feed cylinder. The two polar chambers shared a liquid storage tank, and the polar chamber liquid was 0.3 L of a 0.25 mol / L sodium sulfate aqueous solution.

[0090] Start the bipolar membrane electrodialyzer, keep the operating voltage constant at 12V, control the liquid flow linear velocity in each compartment to 3cm / s, and the feed liquid temperature in each compartment to 30℃. During the operation of bipolar membrane electrodialysis, the pH value of the alkali chamber liquid is monitored in real time, and the pH of the alkali chamber liquid is controlled to be around 12 by controlling the amount of CO2 added to the alkali chamber. Samples are taken every 10 minutes to measure the pH value of the solution in the salt chamber. When the pH value of the salt chamber liquid is lower than 2, the bipolar membrane electrodialysis operation is stopped and the feed liquid in the salt chamber is discharged. After 60 minutes of bipolar membrane electrodialysis operation, 0.29L of desalted liquid (with a sodium ion concentration of less than 2g / L and a pH of 1.94) was recovered in the salt chamber, and 0.31L of a sodium carbonate aqueous solution with a concentration of 0.61mol / L was obtained in the alkali chamber. It is calculated that the energy consumption of bipolar membrane electrodialysis is 52.3kWh / kmol sodium ion, and the membrane flux is 10.8mol sodium ion / m 2 / h, average current efficiency 84.5%.

[0091] At this time, the sodium carbonate aqueous solution in the alkali chamber is left in the alkali chamber, and a new aqueous solution containing 1.35 mol / L sodium gluconate is added to the salt chamber of the bipolar membrane electrodialysis to start the next batch of bipolar membrane electrodialysis operation. After multiple batches of the above operations, when the total volume of the sodium gluconate aqueous solution treated in the salt chamber reaches 2.4 L, 2.30 L of desalted liquid with a sodium ion concentration of less than 2 g / L and a pH value of 1.9 can be recovered in the salt chamber; 0.42 L of sodium carbonate aqueous solution with a concentration of 3.60 mol / L can be recovered in the alkali chamber for pH adjustment in the step of preparing sodium gluconate by enzymatic conversion.

[0092] Preparation of sodium gluconate by enzyme conversion: Different from the conventional method of using NaOH as a pH regulator, this embodiment uses sodium carbonate aqueous solution as a pH regulator to control the pH value of the reaction solution. A 2L fermenter is used, the initial feed is 380g / L glucose, the addition amount of glucose oxidase is 30U / g sugar, glucose oxidase: catalase = 1:85, the temperature of the conversion process is controlled at 42°C, the dissolved oxygen is 20%, and the 3.60mol / L sodium carbonate aqueous solution obtained in the above-mentioned bipolar membrane electrodialysis step is added to control the pH of the reaction solution to 5.9±0.2. During the process, the released tail gas is collected with an air bag. After 21 hours of reaction, the sodium gluconate yield is 370g / L. The obtained enzyme conversion solution is filtered and clarified, decolorized with 1% activated carbon, filtered to remove the activated carbon, concentrated and crystallized by a rotary evaporator to obtain sodium gluconate crystals. The obtained crystals are used for the preparation of gluconic acid by bipolar membrane electrodialysis in step 1).

[0093] Comparative Example 3: Simple preparation of gluconic acid and NaOH, two compartments, no co-production, no CO2 circulation

[0094] Preparation of gluconic acid and NaOH from sodium gluconate The "salt-alkali" two-chamber bipolar membrane electrodialysis device in Example 3 was used to treat the aqueous solution containing sodium gluconate, and the conventional "salt-alkali" two-chamber bipolar membrane electrodialysis operation mode was adopted to regenerate NaOH in the alkali chamber.

[0095] 0.3 L of an aqueous solution containing 1.35 mol / L sodium gluconate was passed into the salt chamber of the bipolar membrane electrodialysis, and 0.3 L of deionized water was initially added to the alkali chamber. The two chambers shared a liquid storage tank, and the chamber liquid was 0.3 L of a 0.25 mol / L sodium sulfate aqueous solution.

[0096] Start the bipolar membrane electrodialyzer, keep the operating voltage constant at 12V, control the liquid flow linear velocity in each compartment to 3cm / s, and the feed liquid temperature in each compartment to 30℃. Take samples every 10 minutes to measure the pH value of the salt chamber liquid. When the pH value is lower than 2 or the pH value no longer increases, stop the bipolar membrane electrodialysis operation and discharge the feed liquid in the salt chamber. After 80 minutes of bipolar membrane electrodialysis operation, the pH value of the salt chamber liquid drops to 1.97 and no longer decreases, so stop the bipolar membrane electrodialysis operation. 0.30L of desalted solution with a sodium ion concentration of 3g / L is obtained in the salt chamber, and 0.31L of NaOH aqueous solution with a concentration of 1.15mol / L is obtained in the alkali chamber. It is difficult for the aqueous solution in the salt chamber to achieve a high desalination rate under these conditions.

[0097] According to calculations, the energy consumption of bipolar membrane electrodialysis is 63.7 kWh / kmol sodium ion, and the membrane flux is 7.88 mol sodium ion / m 2 / h, average current efficiency 72.5%.

[0098] Example 4

[0099] Step 1) Bipolar membrane electrodialysis: Preparation of gluconic acid from sodium gluconate to co-produce sodium bicarbonate. The "salt-alkali" two-chamber bipolar membrane electrodialysis equipment in Example 3 is used to treat the enzyme conversion solution (purified solution) containing sodium gluconate, and CO2 is added to the alkali chamber to co-produce sodium bicarbonate.

[0100] 0.3 L of enzyme conversion solution (purified solution) containing 1.575 mol / L sodium gluconate was introduced into the salt chamber of the bipolar membrane electrodialysis, 0.35 L of deionized water was initially added to the alkali chamber, and the tail gas containing about 18% CO2 released during the preparation of sodium gluconate by enzyme conversion (pH value was adjusted with sodium bicarbonate slurry) contained in an air bag was introduced into the alkali chamber cylinder. The two polar chambers shared a liquid storage tank, and the polar chamber liquid was 0.3 L of 0.25 mol / L sodium sulfate aqueous solution.

[0101] Start the bipolar membrane electrodialyzer, keep the operating voltage constant at 12V, control the liquid flow linear velocity in each compartment to 3cm / s, and the feed liquid temperature in each compartment to 30℃. During the operation of the bipolar membrane electrodialysis, the pH value of the alkali chamber liquid is monitored in real time, and the pH of the alkali chamber liquid is controlled to be around 8.3 by controlling the amount of CO2 added to the alkali chamber. Samples are taken every 10 minutes to measure the pH value of the solution in the salt chamber. When the pH value of the salt chamber liquid is lower than 2, the bipolar membrane electrodialysis operation is stopped and the feed liquid in the salt chamber is discharged. After 70 minutes of bipolar membrane electrodialysis operation, 0.29L of desalted liquid (with a sodium ion concentration of less than 2g / L and a pH of 1.9) was recovered in the salt chamber, and 0.36L of a sodium bicarbonate aqueous solution with a concentration of 1.23mol / L was obtained in the alkali chamber. It is calculated that the energy consumption of bipolar membrane electrodialysis is 56.5kWh / kmol sodium ion, and the membrane flux is 9.33mol sodium ion / m 2 / h, average current efficiency 88.4%.

[0102] At this time, the sodium bicarbonate aqueous solution of the alkali chamber is continued to be retained in the alkali chamber, and a new enzyme conversion solution (purified solution) containing 1.575mol / L sodium gluconate is added to the salt chamber of the bipolar membrane electrodialysis, and the bipolar membrane electrodialysis operation of the next batch is started. From the second batch, as the alkali chamber liquid concentration increases, sodium bicarbonate is separated out from the alkali chamber material cylinder and settled at the bottom of the material cylinder, and partly adheres to the material cylinder wall. Through multiple batches of the above-mentioned operations, when the salt chamber processes the total volume of the enzyme conversion solution (purified solution) containing sodium gluconate to reach 2.4L, 2.32L of desalted solution with a sodium ion concentration less than 2g / L and a pH value of 1.9 can be recovered in the salt chamber; a saturated solution of 0.41L sodium bicarbonate and 203 grams of sodium bicarbonate solid powder can be recovered in the alkali chamber, and the two are mixed into a slurry for pH regulation of the step of preparing sodium gluconate by enzyme conversion.

[0103] Preparation of sodium gluconate by enzyme conversion: Different from the conventional method of using NaOH as a pH regulator, this embodiment uses sodium bicarbonate slurry as a pH regulator to control the pH value of the reaction solution. A 2L fermenter is used, the initial feed of glucose is 380g / L, the addition amount of glucose oxidase is 30U / g sugar, glucose oxidase: catalase = 1:85, the temperature of the conversion process is controlled at 42°C, the dissolved oxygen is 20%, and the sodium bicarbonate slurry obtained in the above-mentioned bipolar membrane electrodialysis step is added to control the pH of the reaction solution to 5.9±0.2. During the process, the released tail gas is collected with an air bag. After 21.5 hours of reaction, the sodium gluconate yield is 372g / L. The obtained enzyme conversion solution is filtered and clarified, decolorized with 1% activated carbon, and the activated carbon is filtered to remove the activated carbon to obtain a purified solution with a sodium gluconate concentration of 343g / L (=1,575mol / L). The purified solution of the obtained enzyme conversion solution is used for the preparation of gluconic acid by bipolar membrane electrodialysis in step 1).

[0104] Example 5

[0105] Step 1) Bipolar membrane electrodialysis: Preparation of gluconic acid and co-production of ammonium carbonate from ammonium gluconate. The "salt-alkali" two-chamber bipolar membrane electrodialysis equipment in Example 3 is used to treat the aqueous solution containing ammonium gluconate, and CO2 is added to the alkali chamber to co-produce ammonium carbonate.

[0106] In the salt chamber of the bipolar membrane electrodialysis, 0.3 L of an aqueous solution containing 1.35 mol / L ammonium gluconate was introduced. 0.3 L of deionized water was initially added to the alkali chamber and CO2 gas was introduced. The two chambers shared a liquid storage tank, and the chamber liquid was 0.3 L of a 0.25 mol / L ammonium sulfate aqueous solution.

[0107] Start the bipolar membrane electrodialyzer, keep the operating voltage constant at 12V, control the liquid flow linear velocity in each compartment to 3cm / s, and the feed liquid temperature in each compartment to 30℃. During the operation of the bipolar membrane electrodialysis, the pH value of the alkali chamber liquid is monitored in real time, and the pH of the alkali chamber liquid is controlled to be around 8.5 by controlling the amount of CO2 added to the alkali chamber. Samples are taken every 10 minutes to measure the pH value of the solution in the salt chamber. When the pH value of the salt chamber liquid is lower than 1.9, the bipolar membrane electrodialysis operation is stopped and the feed liquid in the salt chamber is discharged. After 60 minutes of bipolar membrane electrodialysis operation, 0.29L of desalted liquid (ammonium ion concentration is less than 1.5g / L, pH is 1.85) is recovered in the salt chamber, and 0.31L of ammonium carbonate aqueous solution with a concentration of 0.61mol / L is obtained in the alkali chamber. It is calculated that the energy consumption of bipolar membrane electrodialysis is 51.5kWh / kmol ammonium ion, and the membrane flux is 10.9mol ammonium ion / m 2 / h, average current efficiency 85.5%.

[0108] At this time, the ammonium carbonate aqueous solution in the alkali chamber is continued to remain in the alkali chamber, and a new aqueous solution containing 1.35 mol / L ammonium gluconate is added to the salt chamber of the bipolar membrane electrodialysis to start the next batch of bipolar membrane electrodialysis operations. After multiple batches of the above operations, when the total volume of the ammonium gluconate aqueous solution treated in the salt chamber reaches 2.4 L, 2.33 L of desalted solution with an ammonium ion concentration of less than 1.5 g / L and a pH value of 1.88 can be recovered in the salt chamber; 0.4 L of ammonium carbonate aqueous solution with a concentration of 3.69 mol / L can be recovered in the alkali chamber.

[0109] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention is described in detail with reference to the embodiments, it should be understood by those skilled in the art that any modification or equivalent replacement of the technical solutions of the present invention does not depart from the spirit and scope of the technical solutions of the present invention and should be included in the scope of the claims of the present invention.

Claims

1. A method for preparing gluconic acid by bipolar membrane electrodialysis, comprising the following steps: 1) treating the gluconate solution with bipolar membrane electrodialysis, introducing CO2 into the alkali chamber of the bipolar membrane electrodialysis, finally obtaining carbonate or bicarbonate in the alkali chamber, and obtaining gluconic acid solution in the acid chamber of the bipolar membrane electrodialysis; or, Carbonate or bicarbonate is obtained in the alkali chamber, and a mixed solution of gluconic acid and remaining gluconate is obtained in the salt chamber where the acid salt is combined by bipolar membrane electrodialysis.

2. The method according to claim 1, characterized in that The CO2 is CO2 released during the fermentation / enzyme conversion process to prepare gluconate, wherein the alkali added during the fermentation / enzyme conversion process to prepare gluconate is carbonate or bicarbonate.

3. The method according to claim 2, characterized in that The gluconate prepared by fermentation / enzyme conversion is used as the feed solution for the salt chamber of the bipolar membrane electrodialysis in step 1), and the carbonate or bicarbonate obtained in the alkali chamber in step 1) is used as a pH regulator in the process of preparing gluconate by fermentation / enzyme conversion.

4. The method according to claim 2, characterized in that: After the gluconate is prepared by fermentation / enzyme conversion, the steps of filtering, decolorizing, concentrating and crystallizing the fermentation broth or the enzyme conversion broth are added to obtain gluconate crystals.

5. The method according to claim 1, characterized in that The bipolar membrane electrodialysis described in step 1) includes three-chamber bipolar membrane electrodialysis or two-chamber bipolar membrane electrodialysis.

6. The method according to claim 5, characterized in that The three-chamber bipolar membrane electrodialysis is an "acid-salt-alkali" three-chamber bipolar membrane electrodialysis, and the two-chamber bipolar membrane electrodialysis is a "salt-alkali" two-chamber bipolar membrane electrodialysis.

7. The method according to any one of claims 1 to 6, characterized in that: The gluconate solution includes one or more of sodium gluconate, potassium gluconate and ammonium gluconate solutions; The carbonate includes one or more of sodium carbonate, potassium carbonate and ammonium carbonate, and the bicarbonate includes one or more of sodium bicarbonate, potassium bicarbonate and ammonium bicarbonate.

8. The method according to any one of claims 1 to 6, characterized in that: The carbonate or bicarbonate obtained in the alkali chamber is an aqueous solution or crystal.

9. The method according to claim 8, characterized in that The carbonate obtained in the alkali chamber of the bipolar membrane electrodialysis in step 1) is an aqueous solution; or, the bicarbonate obtained in the alkali chamber of the bipolar membrane electrodialysis in step 1) is a crystal.

10. The method according to any one of claims 1 to 6, characterized in that: During the operation of the bipolar membrane electrodialysis described in step 1), the addition flow rate of CO2 is adjusted by measuring the pH of the alkali chamber liquid, and the pH of the alkali chamber liquid is controlled to be near the normal pH of carbonate or bicarbonate by adjusting the flow rate of CO2 added to the alkali chamber.

11. The method according to any one of claims 1 to 6, characterized in that: Before step 1), a step of decolorizing the gluconate solution and / or removing calcium and magnesium ions is added.

12. The method according to any one of claims 1 to 6, characterized in that: After step 1), gluconic acid is concentrated and crystallized to obtain gluconolactone.

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