A method for co-production of myo-inositol and potassium dihydrogen phosphate crystals from corn steep liquor

Abstract

The present application relates to wastewater treatment technical field, provide a kind of method for producing inositol and potassium dihydrogen phosphate crystal of corn soaking water.The corn soaking water is carried out ultrafiltration, evaporation concentration, cooling crystallization, filtration, anion resin adsorption and analysis, and the potassium phytate analysis solution is obtained;The potassium phytate analysis solution is first nanofiltrated, and then enzymolysis, and then the enzymatic hydrolysate is sequentially subjected to activated carbon decolorization, second nanofiltration and chromatography desalination, and inositol solution and potassium dihydrogen phosphate solution are obtained respectively;The inositol solution is subjected to ion exchange, third nanofiltration, evaporation concentration, crystallization and centrifugation, and inositol crystal is obtained;The potassium dihydrogen phosphate solution is subjected to resin decolorization, evaporation concentration, crystallization and centrifugation, and potassium dihydrogen phosphate crystal is obtained.The method provided by the present application can realize efficient treatment of corn soaking water, and is simple to operate, mild conditions, can obtain high-purity inositol and potassium dihydrogen phosphate, realize high value-added utilization of corn soaking water, and has significant economic benefits.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to a method for co-producing inositol and potassium dihydrogen phosphate crystals by soaking corn in water. Background Technology

[0002] Corn soaking water is wastewater generated during the wet milling process of corn starch production. In the wet milling process, corn kernels need to be soaked in a soaking agent (sulfurous acid solution) to soften the kernels and separate the outer skin from the endosperm. During this process, a large amount of water-soluble components in the corn kernels (such as proteins, phytic acid, sugars, inorganic salts, etc.) dissolve into the soaking solution, which is the corn soaking water.

[0003] Corn soaking water contains phytic acid, water-soluble protein, lactic acid, amino acids, and inorganic salts, making it a natural resource with great development potential. Currently, the traditional method for treating corn soaking water is to convert it into corn steep liquor through evaporation and concentration, which is then sold at a low price as a feed additive. However, this method is energy-intensive and has low economic efficiency.

[0004] In conclusion, how to effectively treat and utilize corn soaking water to achieve high added value is a problem that urgently needs to be solved in this field. Summary of the Invention

[0005] In view of this, the present invention provides a method for co-producing inositol and potassium dihydrogen phosphate crystals from corn soaking water. The method provided by the present invention enables efficient treatment of corn soaking water, simultaneously yielding high-purity inositol and potassium dihydrogen phosphate, thus realizing high-value-added utilization of corn soaking water.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: A method for co-producing inositol and potassium dihydrogen phosphate crystals by soaking corn in water includes the following steps: (1) Soak corn in water and then perform ultrafiltration to obtain ultrafiltrate and ultrafiltrate concentrate; (2) The ultrafiltrate is evaporated and concentrated to obtain a first concentrate; the first concentrate is cooled and crystallized and then filtered to obtain a first filtrate and a first filter residue; (3) The first filtrate is adsorbed by an anion exchange resin and then desorbed to obtain potassium phytate solution; the desorbing agent used is potassium salt solution, potassium hydroxide solution or potassium salt-hydrochloric acid mixture. (4) The potassium phytate solution is subjected to a first nanofiltration to obtain a first nanofiltration concentrate and a first nanofiltration permeate; (5) Mix the first nanofiltration concentrate with phytase and perform enzymatic hydrolysis to obtain the hydrolysate; (6) The enzymatic hydrolysate was subjected to activated carbon decolorization, second nanofiltration and chromatographic desalting in sequence to obtain inositol solution and potassium dihydrogen phosphate solution, respectively; (7) The inositol solution was subjected to ion exchange, third nanofiltration, evaporation and concentration and crystallization in sequence to obtain inositol crystals; (8) The potassium dihydrogen phosphate solution was subjected to resin decolorization, evaporation and concentration and crystallization in sequence to obtain potassium dihydrogen phosphate crystals; There is no time order restriction for steps (7) and (8).

[0007] Preferably, the ultrafiltration conditions include: the ultrafiltration membrane is a silicon carbide membrane, the pore size of the ultrafiltration membrane is 20~200nm, and the pressure is 0.5~1MPa; After obtaining the ultrafiltration concentrate, the process further includes: adjusting the pH value of the ultrafiltration concentrate to 6-8 using a calcium-containing alkaline compound and then filtering it to obtain a second filtrate and a second filter residue; the second filtrate is liquid organic fertilizer.

[0008] Preferably, the solid content of the first concentrate is 35-45 wt%; the endpoint temperature of the cooling crystallization is below 30°C; the solid content of the first filtrate is 32-33 wt%; and the moisture content of the first filter residue is less than 40 wt%.

[0009] Preferably, the anion exchange resin used for adsorption is HA-213; the anion exchange resin adsorption is a three-stage intermittent adsorption, with each stage having an adsorption time of 0.5-2 hours; the potassium salt solution is a potassium chloride solution, potassium sulfate solution, or potassium nitrate solution; the concentration of the potassium salt solution is 10-25 wt%; the concentration of the potassium hydroxide solution is 10-25 wt%; the concentration of potassium salt in the potassium salt-hydrochloric acid mixture is 10-25 wt%, and the hydrochloric acid content is less than 0.5 wt%.

[0010] Preferably, the molecular weight cutoff of the nanofiltration membrane used in the first nanofiltration is 200~500 Da; the first nanofiltration permeate is returned to step (3) for the preparation of the desorption agent.

[0011] Preferably, the phytase has an enzyme activity of 50,000 to 100,000 u / mL; the amount of phytase used is 0.2 to 1‰ of the volume of the first sodium filtrate concentrate; and the enzymatic hydrolysis temperature is 50 to 60°C, and the time is 6 to 12 h.

[0012] Preferably, the nanofiltration membrane used in the second nanofiltration has a molecular weight cutoff of 1000~2000 Da; the second nanofiltration yields a second nanofiltration concentrate and a second nanofiltration permeate; the second nanofiltration concentrate is returned to step (5) for enzymatic hydrolysis; the second nanofiltration permeate is subjected to chromatographic desalting; The conditions for chromatographic desalting include: the chromatographic column packing material is strong acid ion exchange resin HA-10, the feed temperature is 55~60℃, the mobile phase is water, and the volume ratio of the mobile phase to the second nanofiltration permeate is 2.5~3:1. The inositol solution has an inositol purity ≥92wt%, conductivity ≤2000μs / cm, solid content of 4~7wt%, and pH value of 3.5~4.5; the potassium dihydrogen phosphate solution has a potassium dihydrogen phosphate purity ≥92wt%, solid content of 10~13wt%, and pH value of 3.5~4.5.

[0013] Preferably, the ion exchange in step (7) includes: passing the inositol solution into a cation exchange resin for cation exchange, and then passing the effluent from the cation exchange into an anion exchange resin for anion exchange to obtain an ion exchange solution; the packing material in the cation exchange resin column is a 001×7 type cation exchange resin, and the packing material in the anion exchange resin column is a D201 and / or D301 type anion exchange resin; the conductivity of the ion exchange solution is ≤50μs / cm, the pH value is 5~8, and the transmittance is ≥99%.

[0014] Preferably, the molecular weight cutoff of the nanofiltration membrane used in the third nanofiltration is 100~200 Da; The discharge temperature of the evaporation and concentration in step (7) is ≥90℃, and the solid content of the discharge is ≥40wt%; The crystallization in step (7) includes sequential vacuum crystallization and atmospheric pressure assisted crystallization; the conditions for vacuum crystallization include: vacuum degree of -0.06~-0.095MPa, time of 6~12h, and discharge temperature ≤50℃; the conditions for atmospheric pressure assisted crystallization include: time of 6~10h, and discharge temperature of 25~30℃.

[0015] Preferably, the resin used for resin decolorization in step (8) is reverse polymer resin HA-9; the transmittance of the decolorized liquid obtained by resin decolorization is greater than or equal to 95%; The discharge temperature of the evaporation and concentration in step (8) is ≥90℃, and the solid content of the discharge is ≥40wt%; The crystallization in step (8) includes sequential vacuum crystallization and atmospheric pressure assisted crystallization; the conditions for vacuum crystallization include: vacuum degree of -0.06~-0.095MPa, time of 6~12h, and discharge temperature ≤50℃; the conditions for atmospheric pressure assisted crystallization include: time of 6~10h, and discharge temperature of 25~30℃.

[0016] This invention provides a method for co-producing inositol and potassium dihydrogen phosphate crystals from corn soaking water, comprising the following steps: (1) ultrafiltration of corn soaking water to obtain ultrafiltrate and ultrafiltrate concentrate; (2) evaporation and concentration of the ultrafiltrate to obtain a first concentrate; cooling and crystallizing the first concentrate and then filtering to obtain a first filtrate and a first filter residue; (3) adsorption of the first filtrate onto an anion exchange resin and then leaching to obtain potassium phytate leaching solution; wherein the leaching agent used is a potassium salt solution or a potassium hydroxide solution; (4) first nanofiltration of the potassium phytate leaching solution. (5) The nanofiltration concentrate and the first nanofiltration permeate are mixed with phytase and enzymatically hydrolyzed to obtain an enzymatic hydrolysate; (6) The enzymatic hydrolysate is subjected to activated carbon decolorization, second nanofiltration and chromatographic desalting in sequence to obtain an inositol solution and a potassium dihydrogen phosphate solution, respectively; (7) The inositol solution is subjected to ion exchange, third nanofiltration, evaporation concentration and crystallization in sequence to obtain inositol crystals; (8) The potassium dihydrogen phosphate solution is subjected to resin decolorization, evaporation concentration and crystallization in sequence to obtain potassium dihydrogen phosphate crystals; Steps (7) and (8) are not subject to any time order restrictions. This invention first removes solid particles and suspended impurities from corn soaking water using ultrafiltration to obtain ultrafiltrate. Then, magnesium lactate in the ultrafiltrate is removed through evaporation, concentration, crystallization, and filtration, improving the efficiency of adsorption and desorption in subsequent processes. After obtaining potassium phytate eluent, the anion content in the feed solution is reduced by a first nanofiltration process, and the eluent is recovered, improving the purity of potassium phytate and increasing the efficiency of subsequent enzymatic hydrolysis. This invention decomposes potassium phytate through enzymatic hydrolysis under mild reaction conditions, avoiding high temperature and high pressure. After obtaining the enzymatic hydrolysate, impurities in the hydrolysate are removed by decolorization and a second nanofiltration process, separating unhydrolyzed potassium phytate, which helps improve product yield and ensures the purity of the inositol and potassium dihydrogen phosphate solutions obtained in subsequent chromatographic desalting processes. This invention purifies the inositol solution through ion exchange and a third nanofiltration process, allowing for the acquisition of inositol crystals with a purity of over 99% with only one evaporation, concentration, and crystallization step. Similarly, the potassium dihydrogen phosphate solution is purified by resin decolorization, requiring only one evaporation, concentration, and crystallization step to obtain potassium dihydrogen phosphate crystals with a purity of over 98%.

[0017] In summary, the method provided by this invention can achieve efficient treatment of corn soaking water, and is simple to operate under mild conditions. It can obtain high-purity inositol and potassium dihydrogen phosphate, realizing high-value-added utilization of corn soaking water and having significant economic benefits. Detailed Implementation

[0018] This invention provides a method for co-producing inositol and potassium dihydrogen phosphate crystals by soaking corn in water, comprising the following steps: (1) Soak corn in water and then perform ultrafiltration to obtain ultrafiltrate and ultrafiltrate concentrate; (2) The ultrafiltrate is evaporated and concentrated to obtain a first concentrate; the first concentrate is cooled and crystallized and then filtered to obtain a first filtrate and a first filter residue; (3) The first filtrate is adsorbed by an anion exchange resin and then desorbed to obtain potassium phytate solution; the desorbing agent used is a potassium salt solution or a potassium hydroxide solution. (4) The potassium phytate solution is subjected to a first nanofiltration to obtain a first nanofiltration concentrate and a first nanofiltration permeate; (5) Mix the first nanofiltration concentrate with phytase and perform enzymatic hydrolysis to obtain the hydrolysate; (6) The enzymatic hydrolysate was subjected to activated carbon decolorization, second nanofiltration and chromatographic desalting in sequence to obtain inositol solution and potassium dihydrogen phosphate solution, respectively; (7) The inositol solution is subjected to ion exchange, third nanofiltration, evaporation concentration and crystallization in sequence; (8) The potassium dihydrogen phosphate solution was subjected to resin decolorization, evaporation and concentration and crystallization in sequence to obtain potassium dihydrogen phosphate crystals; There is no time order restriction for steps (7) and (8).

[0019] This invention involves ultrafiltration of corn soaking water to obtain ultrafiltrate and ultrafiltrate concentrate. In this invention, the solid content of the corn soaking water is preferably 10-12 wt%, and the pH value is preferably 3.5-4.5. The corn soaking water preferably includes 1-1.5 wt% phytic acid, 5-6 wt% water-soluble protein, 2-3 wt% lactic acid, 1-2 wt% amino acids, 0.5-2 wt% inorganic salts, and 5000-7000 ppm potassium ions. The ultrafiltration conditions preferably include: the ultrafiltration membrane is a silicon carbide membrane with a pore size of 20-200 nm. The wavelength can be 20nm, 40nm, 100nm, or 200nm, and the pressure is 0.2~1MPa, specifically 0.2MPa, 0.6MPa, 0.8MPa, or 1MPa; the volume of the ultrafiltration solution is preferably 90~95% of the volume of the corn soaking water sedimentation solution; this invention removes solid particles and suspended impurities from corn soaking water through ultrafiltration, and the invention uses a silicon carbide membrane as the ultrafiltration membrane, which can improve the ultrafiltration efficiency and ensure that the turbidity of the ultrafiltration solution is less than 10 NTU. After obtaining the ultrafiltration concentrate, the present invention preferably further includes: adjusting the pH value of the ultrafiltration concentrate to 6-8 using a calcium-containing alkaline compound and then filtering it to obtain a second filtrate and a second filter residue; the calcium-containing alkaline compound is preferably calcium hydroxide and / or lime; the filtration is preferably plate and frame filtration, and the mesh size of the filter cloth used in the plate and frame filtration is preferably 500-1000 mesh; the present invention adjusts the pH value of the ultrafiltration concentrate to 6-8 (specifically 7 or 7.5), which enables the phytic acid in the ultrafiltration concentrate to precipitate out, and the main components of the second filter residue obtained by filtration are calcium phytate, magnesium phytate and solid impurities, and the second filter residue can be sold as an additional product; the main components of the second filtrate are protein, lactic acid and potassium salt, and it can be sold as liquid organic fertilizer.

[0020] After obtaining the ultrafiltrate, the present invention evaporates and concentrates the ultrafiltrate to obtain a first concentrate; the first concentrate is cooled and crystallized and then filtered to obtain a first filtrate and a first filter residue. In the present invention, the discharge temperature of the evaporation and concentration in step (2) is preferably 55~60℃, and the discharge solid content is preferably 35~45wt%; the solid content of the first concentrate is preferably 35~45wt%, specifically 40wt%; the endpoint temperature of the cooling crystallization is preferably below 30℃, specifically 20℃ or 25℃; the cooling time of the cooling crystallization is preferably 6~12h, and the discharge temperature is preferably 25~30℃; during the cooling crystallization process, it is preferred to stir for 20~30min every 2~3h, and the stirring speed is preferably 1~3r / min; the cooling crystallization is preferably carried out in a horizontal crystallizer. The filtration in step (2) is preferably plate and frame filtration, and the mesh size of the filter cloth used in the plate and frame filtration is preferably 300-1000 mesh, specifically 500 mesh or 800 mesh; the solid content of the first filtrate is preferably 32-33 wt%; the moisture content of the first filter residue is less than 40%; the main component of the first filter residue is magnesium lactate, which can be sold as an by-product; the main components of the first filtrate include water-soluble protein, phytic acid, lactic acid, miscellaneous sugars and water-soluble inorganic salts (potassium chloride, magnesium chloride, etc.). In this invention, before the anion exchange resin adsorption and desorption, the ultrafiltrate is first evaporated, concentrated, cooled, crystallized, and filtered, which can improve the desorption efficiency of subsequent processes.

[0021] After obtaining the first filtrate, the present invention performs anion exchange resin adsorption and subsequent leaching to obtain potassium phytate eluent. In this invention, the preferred type of anion exchange resin used for adsorption is HA-213; the anion exchange resin adsorption is preferably carried out under stirring conditions, with a stirring speed preferably of 5-10 r / min, and 2-3 m³ of the first filtrate adsorbed per cubic meter of resin. 3The anion exchange resin adsorption is preferably an intermittent three-stage adsorption, with each stage preferably having an adsorption time of 0.5 to 2 hours. Specifically, the first stage adsorption time is preferably 1 to 2 hours, the second stage adsorption time is preferably 0.5 to 1 hour, and the third stage adsorption time is preferably 0.5 to 1 hour. In a specific embodiment of the present invention, it is preferable to first pump the first filtrate into a first-stage adsorption tank for first-stage adsorption, then sieve it, and return the sieved resin to the first-stage adsorption tank for continued use. The filtrate (referred to as the first-stage filtrate) enters a second-stage adsorption tank for second-stage adsorption, then sieves it, and return the sieved resin to the second-stage adsorption tank for continued use. The filtrate (referred to as the second-stage filtrate) is concentrated and can be used as protein feed. The primary, secondary, and tertiary adsorption tanks are all intermittent adsorption tanks with stirring. The sieving after the first, second, and third adsorption stages all uses a 60-80 mesh vibrating screen. This invention performs intermittent desorption under stirring conditions, which can increase the solid content of the feed. The solid content of the feed in traditional resin adsorption tanks is no higher than 15 wt%. This invention performs adsorption under intermittent and stirring conditions, which can increase the solid content of the feed to more than 35 wt%, thereby improving the adsorption efficiency.

[0022] After the anion exchange resin has completed adsorption, the present invention preferably rinses the saturated resin with pure water and then performs elution. The elution agent is preferably a potassium salt solution, potassium hydroxide solution, or a potassium salt-acid mixture. The potassium salt solution is preferably one or more of potassium chloride solution, potassium nitrate solution, and potassium sulfate solution. The concentration of the potassium salt solution is preferably 10-25 wt%, specifically 15 wt% or 20 wt%. The concentration of the potassium hydroxide solution is preferably 10-25 wt%. The concentration of potassium salt in the potassium salt-hydrochloric acid mixture is preferably 10-25 wt%, and the hydrochloric acid content is preferably less than 0.5 wt%. The elution solution obtained is a potassium phytate elution solution. The concentration of potassium phytate in the potassium phytate elution solution is preferably 10-20 wt%. In a specific embodiment of the present invention, the rinsing is preferably a three-stage rinsing process. The first stage uses secondary water, and the rinse water is discharged. The second stage uses primary water, and the rinse water is recycled as secondary water. The third stage uses pure water, and the rinse water is recycled as primary water. The amount of water used in each stage of rinsing is preferably 2 to 5 times the volume of the resin. In the present invention, the analysis is preferably a two-stage analysis. The first stage analysis uses secondary analysis solution to enter the column for analysis, producing analysis solution. The second stage analysis uses a newly prepared analysis agent to enter the column for analysis, and the resulting analysis solution is used as secondary analysis solution in the next batch of first-stage analysis. In a specific embodiment of the present invention, after the corn soaking water is adsorbed by the anion exchange resin column, the phytic acid content in the effluent is preferably ≤0.2wt%. The present invention uses pure water to rinse the adsorbed resin, resulting in good cleaning effect and no resin column clogging. The quality of the obtained potassium phytate analysis solution is better, with a protein content of less than 0.1wt%, while the protein content in the feed solution after adsorption and analysis by the resin column in the traditional method is greater than 0.3wt%.

[0023] After obtaining the potassium phytate eluent, the present invention performs a first nanofiltration on the potassium phytate eluent to obtain a first nanofiltration concentrate and a first nanofiltration permeate. In the present invention, the molecular weight cutoff of the nanofiltration membrane used for the first nanofiltration is preferably 200~500 Da, specifically 300 Da or 400 Da; pure water is preferably added during the first nanofiltration process, and the amount of pure water added is preferably 10~20% of the volume of the potassium phytate eluent; the solid content of the first nanofiltration concentrate is preferably 20~25 wt%; the potassium phytate content in the first nanofiltration concentrate is preferably 20~25 wt%, and the chloride ion content is preferably less than 100 ppm; the first nanofiltration permeate is returned to step (3) for preparing the eluent. The present invention performs nanofiltration on the potassium phytate eluent before enzymatic hydrolysis, which can reduce the chloride ion content in the feed solution, recover potassium chloride, and improve the purity of potassium phytate.

[0024] After obtaining the first nanofiltration solution, the present invention mixes the first nanofiltration concentrate with phytase for enzymatic hydrolysis to obtain an enzymatic hydrolysate. In the present invention, the phytase activity is preferably 50,000 to 100,000 u / mL, specifically 60,000 u / mL, 80,000 u / mL, or 90,000 u / mL; the amount of phytase is preferably 0.2 to 1‰ of the volume of the first nanofiltration concentrate, specifically 2‰, 5‰, 6‰, or 8‰; the enzymatic hydrolysis temperature is preferably 50 to 60°C, specifically 55°C; the time is preferably 6 to 12 hours, specifically 6 hours, 8 hours, or 12 hours; the pH value of the enzymatic hydrolysis is preferably 4 to 5, specifically 4.5; the pressure of the enzymatic hydrolysis is preferably atmospheric pressure; the enzymatic hydrolysis is preferably carried out under stirring conditions, and the stirring speed is preferably 30 to 60 r / min; the enzymatic hydrolysis is preferably carried out in an enzymatic hydrolysis tank; in a specific embodiment of the present invention, after mixing the first nanofiltration concentrate and phytase, the pH value of the solution is preferably adjusted to 4 to 5 using lime or calcium hydroxide before enzymatic hydrolysis. The phytic acid content in the enzymatic hydrolysate is preferably less than 0.2 wt%. This invention decomposes potassium phytate into inositol and potassium dihydrogen phosphate via enzymatic hydrolysis, and the resulting enzymatic hydrolysate is a mixed solution of inositol and potassium dihydrogen phosphate. Furthermore, this invention decomposes potassium phytate using enzymatic hydrolysis, with mild reaction conditions, avoiding high temperature and high pressure.

[0025] After obtaining the enzymatic hydrolysate, the present invention sequentially performs activated carbon decolorization, second nanofiltration, and chromatographic desalting on the enzymatic hydrolysate to obtain inositol solution and potassium dihydrogen phosphate solution, respectively. In the present invention, the decolorizing agent used in step (6) is preferably powdered activated carbon; the amount of powdered activated carbon is preferably 3~5 kg / m³. 3 The preferred temperature for activated carbon decolorization is 50-70℃, and the preferred time is 30-40 min. After decolorization, the activated carbon is filtered through a plate and frame filter to obtain a decolorized solution. The mesh size of the filter cloth used for plate and frame filtration is preferably 300-500 mesh. The transmittance of the decolorized solution is preferably greater than 60%. The molecular weight cutoff of the nanofiltration membrane used in the second nanofiltration is preferably 1000-2000 Da, specifically 1500 Da or 1800 Da. The second nanofiltration yields a second nanofiltration concentrate and a second nanofiltration permeate. The second nanofiltration concentrate is returned to step (5) for enzymatic hydrolysis. The second nanofiltration permeate is preferably evaporated and concentrated to a solid content of 35-50 wt% before chromatographic desalting. The preferred temperature for evaporation and concentration is 55-60℃. In this invention, the decolorized solution is subjected to a second nanofiltration, which can separate the unhydrolyzed potassium phytate and return it to the pre-hydrolysis stage for further enzymatic hydrolysis, which is beneficial to improving the product yield and ensuring the purity of the solution after chromatographic desalting in the subsequent process.

[0026] In this invention, the preferred conditions for chromatographic desalting include: the chromatographic column packing material is a strong acid ion exchange resin HA-10, the feed temperature is 55~60℃, the mobile phase is water, and the volume ratio of the mobile phase to the second nanofiltration permeate is 2.5~3:1.

[0027] In this invention, the purity of inositol in the inositol solution is preferably ≥92wt%, the conductivity is preferably ≤2000μs / cm, the solid content is preferably 4~7wt%, and the pH value is preferably 3.5~4.5; the purity of potassium dihydrogen phosphate in the potassium dihydrogen phosphate solution is ≥92wt%, the solid content is preferably 10~13wt%, and the pH value is preferably 3.5~4.5.

[0028] After obtaining the inositol solution, this invention sequentially performs ion exchange, a third nanofiltration, evaporation concentration, and crystallization to obtain inositol crystals. In this invention, the ion exchange preferably includes: passing the inositol solution through a cation exchange resin for cation exchange, and then passing the effluent from the cation exchange through an anion exchange resin for anion exchange to obtain an ion exchange solution; the packing material in the cation exchange resin column is preferably a 001×7 type cation exchange resin, and the packing material in the anion exchange resin column is preferably a D201 and / or D301 type anion exchange resin; the conductivity of the ion exchange solution is preferably ≤50 μs / cm, the pH value is preferably 5~8, and the transmittance is preferably ≥99%. This invention, by performing ion exchange on the inositol solution before subsequent nanofiltration and evaporation concentration, can reduce steam consumption and remove small-molecule inorganic salts.

[0029] In this invention, the molecular weight cutoff of the nanofiltration membrane used in the third nanofiltration is preferably 100-200 Da; the third nanofiltration yields a third nanofiltration concentrate and a third nanofiltration permeate; the solid content of the third nanofiltration concentrate is preferably 10-12 wt%; the third nanofiltration permeate is returned to the chromatographic desalting step, and the third nanofiltration concentrate is subjected to subsequent evaporation and concentration. This invention uses ion exchange and nanofiltration to purify the inositol solution, and subsequently, inositol crystals with a purity of over 99% can be produced through a single concentration and crystallization, whereas traditional methods require recrystallization to obtain inositol crystals with a purity of over 99%.

[0030] In this invention, the discharge temperature of the evaporation and concentration in step (7) is preferably ≥90℃, specifically 90℃ or 95℃, and the solid content of the discharge is preferably ≥40wt%, specifically 40wt% or 50wt%; the condensate generated by the evaporation and concentration is recycled in the chromatographic desalting step.

[0031] In this invention, the crystallization in step (7) preferably includes vacuum crystallization and atmospheric pressure assisted crystallization in sequence; the conditions for vacuum crystallization preferably include: vacuum degree of -0.06~-0.095MPa, specifically -0.08MPa or -0.09MPa, time of 6~12h, specifically 8h or 10h, and discharge temperature ≤50℃, specifically 30℃ or 40℃; the conditions for atmospheric pressure assisted crystallization preferably include: time of 6~10h, specifically 7h or 8h, discharge temperature of 25~30℃, and stirring speed of 1~3r / min; the atmospheric pressure assisted crystallization is preferably carried out in a horizontal crystallizer.

[0032] After the atmospheric pressure crystallization is completed, the present invention preferably centrifuges and dries the obtained inositol crystallization solution; the centrifugation is preferably carried out using a bag-type centrifuge; the mother liquor obtained after centrifugation is mainly composed of a mixture of inositol and potassium dihydrogen phosphate, which can be sold as an external by-product; the moisture content of the wet material obtained by centrifugation is preferably less than 3 wt%; the drying is preferably carried out using a vibrating fluidized bed; the moisture content of the dried inositol crystals is preferably less than 0.2 wt%.

[0033] After obtaining a potassium dihydrogen phosphate solution, this invention sequentially subjects the potassium dihydrogen phosphate solution to resin decolorization, evaporation concentration, and crystallization to obtain potassium dihydrogen phosphate crystals. In this invention, the resin used for resin decolorization is preferably the reverse-phase polymerization resin HA-9; the transmittance of the decolorized solution obtained from resin decolorization is preferably greater than or equal to 95%; after resin decolorization, the used resin is preferably regenerated, and the regenerating agent used is preferably hydrochloric acid and liquid alkali. This invention purifies potassium dihydrogen phosphate through resin decolorization, and subsequently, potassium dihydrogen phosphate crystals with a purity of over 98% can be produced through a single concentration and crystallization process.

[0034] In this invention, the discharge temperature of the evaporation and concentration in step (8) is preferably ≥90°C, specifically 90°C or 95°C, and the solid content of the discharge is preferably ≥40wt%, specifically 40wt% or 45wt%; the evaporation and concentration also yields condensate, which is preferably reused in the chromatographic desalting step as a mobile phase.

[0035] In this invention, the crystallization in step (8) preferably includes vacuum crystallization and atmospheric pressure assisted crystallization in sequence; the conditions for vacuum crystallization preferably include: vacuum degree of -0.06~-0.095MPa, specifically -0.08MPa or -0.09MPa, time of 6~12h, specifically 8h or 10h, and discharge temperature ≤50℃, specifically 30℃ or 40℃; the conditions for atmospheric pressure assisted crystallization preferably include: time of 6~10h, specifically 7h or 8h, discharge temperature of 25~30℃, and stirring speed of 1~3r / min; the atmospheric pressure assisted crystallization is preferably carried out in a horizontal crystallizer.

[0036] After the atmospheric pressure crystallization is completed, the obtained potassium dihydrogen phosphate crystal solution is preferably centrifuged and dried. The centrifugation is preferably carried out using a horizontal spiral concentrator centrifuge. The mother liquor obtained after centrifugation can be sold as an external by-product. The moisture content of the wet material obtained by centrifugation is preferably less than 8 wt%. The drying is preferably carried out using a vibrating fluidized bed. The moisture content of the dried potassium dihydrogen phosphate crystals is preferably less than 0.5 wt%.

[0037] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0038] Example 1 The corn soaking water used in this embodiment has a solid content of 10wt%, a pH value of 4, a phytic acid content of 1.5wt%, a water-soluble protein content of 5wt%, a lactic acid content of 3wt%, an amino acid content of 2wt%, an inorganic salt content of 2wt%, and a potassium ion content of 6000ppm.

[0039] Corn soaking water is subjected to ultrafiltration to obtain ultrafiltrate and ultrafiltrate concentrate. The ultrafiltration membrane used is a silicon carbide membrane with a pore size of 100 nm and an ultrafiltration pressure of 0.6 MPa. The volume of the ultrafiltrate is 90% of the volume of the corn soaking water sedimentation liquid. The ultrafiltrate is evaporated and concentrated to a solid content of 35 wt%, and then cooled for crystallization. The final temperature of cooling for crystallization is 25°C. The crystallized liquid is filtered through a plate and frame filter to obtain a first filter residue (moisture content less than 40 wt%) and a first filtrate. The first filter residue is sold as a by-product. The ultrafiltrate concentrate is adjusted to pH 7 with lime, and then filtered through a plate and frame filter (filter cloth with a mesh size of 500) to obtain a second filter residue and a second filtrate. The second filter residue is transported for processing, and the second filtrate is sold as organic fertilizer.

[0040] The first filtrate was subjected to anion exchange resin adsorption using HA-213. The adsorption process was as follows: the first filtrate was pumped into a primary adsorption tank for 2 hours, then passed through a 60-mesh vibrating screen. The sieved resin was returned to the primary adsorption tank for reuse. The primary filtrate then entered a secondary adsorption tank for 1 hour, followed by another 60-mesh vibrating screen. The sieved resin was returned to the secondary adsorption tank for reuse. The secondary filtrate then entered a tertiary adsorption tank for 1 hour, followed by another 60-mesh vibrating screen. The sieved resin was returned to the tertiary adsorption tank for reuse. The tertiary filtrate was concentrated and sold as protein feed. All three adsorption tanks were equipped with agitators at a speed of 30 rpm. After adsorption, a three-stage rinsing process is performed. The first stage uses secondary water, and the rinse water is discharged. The second stage uses primary water, and the rinse water is recycled as secondary water. The third stage uses pure water, and the rinse water is recycled as primary water. The amount of water used in each stage of rinsing is twice the volume of the resin. After rinsing, a 20wt% potassium chloride solution is used for desorption. The desorption process is performed in two stages. The first stage uses secondary desorption solution to enter the column for desorption, generating a desorption solution. The second stage uses a freshly prepared desorption reagent to enter the column for desorption, and the resulting desorption solution is used as the secondary desorption solution in the first stage of the next batch for further desorption.

[0041] The potassium phytate eluent was subjected to nanofiltration. The nanofiltration membrane had a molecular weight cutoff of 200 Da, yielding a concentrated nanofiltration solution (potassium phytate content of 20 wt%) and a nanofiltration permeate. The permeate was reused for the preparation of the eluent. The concentrated nanofiltration solution was pumped into an enzymatic hydrolysis vessel, phytase was added, and the pH was adjusted to 4 with lime. Enzymatic hydrolysis was initiated at a phytase activity of 100,000 u / mL, an addition rate of 0.5‰ (volume fraction), a hydrolysis temperature of 50℃, and a hydrolysis time of 6 hours. The hydrolysis endpoint was defined as a phytate content in the liquid being less than 0.2 wt%, yielding the hydrolysate. Powdered activated carbon was added to the hydrolysate for decolorization, with a dosage of 3 kg / m³. 3 The decolorization temperature was 50℃ for 30 minutes. After decolorization, the solution was filtered through a plate and frame filter (300 mesh filter cloth) to obtain a decolorized solution. The decolorized solution was then subjected to nanofiltration (nanofiltration membrane with a molecular weight cutoff of 1000 Da). The concentrated nanofiltration solution was returned to the enzymatic hydrolysis tank for enzymatic hydrolysis, and the nanofiltration permeate was subjected to chromatographic desalting. The chromatographic desalting conditions were as follows: the chromatographic column packing was strong acid ion exchange resin HA-10, the feed temperature was 55℃, the mobile phase was water, and the volume ratio of the mobile phase to the nanofiltration permeate was 3:1. Chromatographic desalting yielded an inositol solution and a potassium dihydrogen phosphate solution. The inositol solution had a purity of 95 wt%, an electrical conductivity of 1000 μS / cm, a solid content of 7 wt%, and a pH of 4. The potassium dihydrogen phosphate solution had a purity of 92 wt%, an electrical conductivity of 50000 μS / cm, a solid content of 12 wt%, and a pH of 3.5.

[0042] Inositol solution is passed through a cation exchange resin for cation exchange, and the effluent from the cation exchange is then passed through an anion exchange resin for anion exchange to obtain an ion exchange solution. The packing material in the cation exchange resin column is preferably a 001×7 type cation exchange resin, and the packing material in the anion exchange resin column is a D201 type anion exchange resin. The conductivity of the ion exchange solution is 50 μS / cm, the pH is 5, and the transmittance is ≥99%. The ion exchange solution is then subjected to nanofiltration. The nanofiltration membrane has a molecular weight cutoff of 100 Da. Nanofiltration yields a nanofiltration concentrate and a nanofiltration permeate. The nanofiltration permeate is returned to the chromatographic desalting step. The nanofiltration concentrate is evaporated and concentrated to a solid content of 45 wt%, and then subjected to vacuum crystallization and atmospheric pressure assisted crystallization sequentially. The conditions for vacuum crystallization are: vacuum degree -0.06 MPa, time 6 h, and outlet temperature 40 °C. The conditions for atmospheric pressure assisted crystallization are: time 6 h, outlet temperature 25 °C, and stirring speed 3 r / min. The atmospheric pressure assisted crystallization is carried out in a horizontal crystallizer. The crystallization solution obtained by atmospheric pressure crystallization was centrifuged using a bag-type centrifuge, and the resulting mother liquor was sold as a by-product. The wet material obtained by centrifugation was dried using a vibrating fluidized bed to obtain inositol crystals with a purity of 99.5 wt%, a moisture content of 0.18 wt%, and a yield of 90%.

[0043] A potassium dihydrogen phosphate solution was decolorized using a resin, specifically the inverse polymer HA-9. The resulting decolorized solution had a transmittance of 95%. The decolorized solution was concentrated to a solid content of 40 wt%, followed by vacuum crystallization and atmospheric pressure assisted crystallization. The vacuum crystallization conditions were: vacuum degree -0.06 MPa, time 6 h, and discharge temperature 30 °C. The atmospheric pressure assisted crystallization conditions were: time 6 h, discharge temperature 25 °C, and stirring speed 3 r / min. The atmospheric pressure assisted crystallization was carried out in a horizontal crystallizer. The crystallized solution obtained from the atmospheric pressure assisted crystallization was centrifuged using a horizontal spiral concentrator centrifuge. The mother liquor obtained after centrifugation was sold as a by-product. The wet material obtained from centrifugation was dried using a vibrating fluidized bed to obtain potassium dihydrogen phosphate crystals with a purity of 99 wt%, a moisture content of 0.5 wt%, and a yield of 95%.

[0044] Example 2 Other conditions are the same as in Example 1, except that the enzymatic hydrolysis conditions are changed to: pH value of 5, phytase activity of 80,000 u / mL, addition amount of 0.2‰ (volume fraction), enzymatic hydrolysis temperature of 60℃, and time of 12h.

[0045] The final inositol crystals had a purity of 99 wt%, a moisture content of 0.2 wt%, and a yield of 90%. The potassium dihydrogen phosphate crystals had a purity of 99 wt%, a moisture content of 0.5 wt%, and a yield of 90%.

[0046] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for co-producing inositol and potassium dihydrogen phosphate crystals by soaking corn in water, characterized in that, Includes the following steps: (1) The corn was soaked in water and then ultrafiltered to obtain ultrafiltrate and ultrafiltrate concentrate; the ultrafiltration membrane used was a silicon carbide membrane and the turbidity of the ultrafiltrate was less than 10 NTU. (2) The ultrafiltrate is evaporated and concentrated to obtain a first concentrate; the first concentrate is cooled and crystallized, then filtered to obtain a first filtrate and a first filter residue; the solid content of the first concentrate is 35~45wt%; the final temperature of the cooling and crystallization is below 30℃; the solid content of the first filtrate is 32~33wt%; the moisture content of the first filter residue is less than 40wt%. (3) The first filtrate is adsorbed by an anion exchange resin and then desorbed to obtain potassium phytate solution; the desorbing agent used is potassium salt solution, potassium hydroxide solution or potassium salt-hydrochloric acid mixture. (4) The potassium phytate solution is subjected to a first nanofiltration to obtain a first nanofiltration concentrate and a first nanofiltration permeate; (5) Mix the first nanofiltration concentrate with phytase and perform enzymatic hydrolysis to obtain the hydrolysate; (6) The enzymatic hydrolysate is subjected to activated carbon decolorization, second nanofiltration and chromatographic desalting in sequence to obtain inositol solution and potassium dihydrogen phosphate solution, respectively; the nanofiltration membrane used in the second nanofiltration has a molecular weight cutoff of 1000~2000 Da; (7) The inositol solution is subjected to ion exchange, third nanofiltration, evaporation concentration and crystallization in sequence to obtain inositol crystals; the molecular weight cutoff of the nanofiltration membrane used in the third nanofiltration is 100~200 Da; (8) The potassium dihydrogen phosphate solution was subjected to resin decolorization, evaporation and concentration and crystallization in sequence to obtain potassium dihydrogen phosphate crystals; There is no time order restriction for steps (7) and (8).

2. The method according to claim 1, characterized in that, The conditions for ultrafiltration include: the pore size of the ultrafiltration membrane is 20~200nm, and the pressure is 0.5~1MPa; After obtaining the ultrafiltration concentrate, the process further includes: adjusting the pH value of the ultrafiltration concentrate to 6-8 using a calcium-containing alkaline compound and then filtering it to obtain a second filtrate and a second filter residue; the second filtrate is liquid organic fertilizer.

3. The method according to claim 1, characterized in that, The anion exchange resin used for adsorption is HA-213; the anion exchange resin adsorption is a three-stage intermittent adsorption, with each stage having an adsorption time of 0.5-2 hours; the potassium salt solution is potassium chloride solution, potassium sulfate solution, or potassium nitrate solution; the concentration of the potassium salt solution is 10-25 wt%; the concentration of the potassium hydroxide solution is 10-25 wt%; the concentration of potassium salt in the potassium salt-hydrochloric acid mixture is 10-25 wt%, and the hydrochloric acid content is less than 0.5 wt%.

4. The method according to claim 1, characterized in that, The molecular weight cutoff of the nanofiltration membrane used in the first nanofiltration is 200~500 Da; the first nanofiltration permeate is returned to step (3) for the preparation of the desorption agent.

5. The method according to claim 1, characterized in that, The phytase activity is 50,000 to 100,000 u / mL; the amount of phytase used is 0.2 to 1‰ of the volume of the first nanofiltration concentrate; the enzymatic hydrolysis temperature is 50 to 60°C, and the time is 6 to 12 h.

6. The method according to claim 1, characterized in that, The second nanofiltration yields a second nanofiltration concentrate and a second nanofiltration permeate; the second nanofiltration concentrate is returned to step (5) for enzymatic hydrolysis; the second nanofiltration permeate is subjected to chromatographic desalting. The conditions for chromatographic desalting include: the chromatographic column packing material is strong acid ion exchange resin HA-10, the feed temperature is 55~60℃, the mobile phase is water, and the volume ratio of the mobile phase to the second nanofiltration permeate is 2.5~3:

1. The inositol solution has an inositol purity ≥92wt%, conductivity ≤2000μs / cm, solid content of 4~7wt%, and pH value of 3.5~4.5; the potassium dihydrogen phosphate solution has a potassium dihydrogen phosphate purity ≥92wt%, solid content of 10~13wt%, and pH value of 3.5~4.

5.

7. The method according to claim 1, characterized in that, The ion exchange in step (7) includes: passing the inositol solution into a cation exchange resin for cation exchange, and then passing the effluent from the cation exchange into an anion exchange resin for anion exchange to obtain an ion exchange solution; the packing material in the cation exchange resin column is a 001×7 type cation exchange resin, and the packing material in the anion exchange resin column is a D201 and / or D301 type anion exchange resin; the conductivity of the ion exchange solution is ≤50μs / cm, the pH value is 5~8, and the transmittance is ≥99%.

8. The method according to claim 1, characterized in that, The discharge temperature of the evaporation and concentration in step (7) is ≥90℃, and the solid content of the discharge is ≥40wt%; The crystallization in step (7) includes sequential vacuum crystallization and atmospheric pressure assisted crystallization; the conditions for vacuum crystallization include: vacuum degree of -0.06~-0.095MPa, time of 6~12h, and discharge temperature ≤50℃; the conditions for atmospheric pressure assisted crystallization include: time of 6~10h, and discharge temperature of 25~30℃.

9. The method according to claim 1, characterized in that, The resin used for decolorization in step (8) is reverse-phase polymer resin HA-9; the transmittance of the decolorized liquid obtained by the resin decolorization is greater than or equal to 95%; The discharge temperature of the evaporation and concentration in step (8) is ≥90℃, and the solid content of the discharge is ≥40wt%; The crystallization in step (8) includes sequential vacuum crystallization and atmospheric pressure assisted crystallization; the conditions for vacuum crystallization include: vacuum degree of -0.06~-0.095MPa, time of 6~12h, and discharge temperature ≤50℃; the conditions for atmospheric pressure assisted crystallization include: time of 6~10h, and discharge temperature of 25~30℃.