A method for recycling waste mother liquor after erythritol crystallization

Abstract

The present invention belongs to the technical field of erythritol recovery, and particularly relates to a method for recycling the waste mother liquor after erythritol crystallization. The method comprises the following steps: filtering the waste mother liquor after erythritol crystallization with a ceramic membrane, decolorizing and desalting, and performing chromatographic separation to obtain an erythritol solution; the chromatographic separation uses a hydrogen-type chromatographic resin column. The present invention filters the waste mother liquor to remove macromolecular substances, then performs chromatographic separation after decolorizing and desalting. The obtained erythritol solution has an erythritol mass content of more than 95% based on dry matter. By concentrating and crystallizing or combining the erythritol solution with the original solution for treatment, an erythritol product with a purity of more than 99.9% can be obtained. The present invention enables the total recovery rate of erythritol to exceed 95%, and has a high product recovery rate. The present invention effectively reduces sewage discharge, improves the recovery rate of erythritol, reduces production costs, can not only relieve the environmental protection pressure, but also increase benefits, and has a huge promoting effect on the development of the erythritol industry.

Description

Technical Field

[0001] The present invention belongs to the technical field of erythritol recovery, and particularly relates to a method for recycling waste mother liquor after erythritol crystallization. Background Art

[0002] Erythritol is a four-carbon sugar alcohol that widely exists in nature. Erythritol is a white crystalline powder with a refreshing sweet taste, high temperature resistance, and insensitivity to pH changes. Due to the advantages of high temperature stability, non-participation in human metabolism, anti-cariogenicity, antioxidant property, and moisture retention of erythritol, it has currently been widely used in the fields of beverages, baked foods, candies, desserts, and pharmaceuticals and cosmetics.

[0003] Currently, erythritol is mainly obtained by fermentation. The fermentation broth is obtained as a stock solution through multi-stage membrane filtration and ion exchange desalination, and then the stock solution is concentrated and crystallized multiple times to obtain a qualified erythritol product. The waste mother liquor generated after multiple crystallizations of erythritol has undergone repeated concentration and crystallization to recover erythritol, and impurities have continuously accumulated in the waste mother liquor. Eventually, due to the interference of high-concentration impurities, part of the erythritol cannot be recovered by crystallization again, resulting in a decrease in the yield. In this part of the waste mother liquor, there are pigments, 5wt% - 10wt% protein, more than 10wt% sugars, and more than 35wt% erythritol. Direct discharge will greatly increase the environmental protection pressure, and more than 5% of the total erythritol production is lost with the waste mother liquor. If this waste mother liquor is not recycled, the erythritol yield is only between 90% and 93%, and the production capacity is low.

[0004] Currently, for the waste mother liquor after multiple crystallizations of erythritol, membrane filtration, ion exchange desalination, activated carbon decolorization and other means are used to remove impurities and recover erythritol again. However, since the vast majority of the impurities in the waste mother liquor are substances that cannot be well removed by the above means during the production of the stock solution, separating the waste mother liquor again according to the stock solution means has poor separation effect and low erythritol yield. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a method for recycling waste mother liquor after erythritol crystallization. The recycling method of the present invention can separate erythritol from impurities and improve the erythritol yield.

[0006] The present invention provides a method for recycling waste mother liquor after erythritol crystallization, comprising the following steps:

[0007] Filter the waste mother liquor after erythritol crystallization with a ceramic membrane to obtain a first filtrate;

[0008] Decolorize and desalt the first filtrate to obtain a decolorized and desalted feed liquid;

[0009] Perform chromatographic separation on the decolorized and desalted feed liquid to obtain an erythritol solution; use a hydrogen-type chromatographic resin column for the chromatographic separation; in the erythritol solution, the mass content of erythritol based on dry matter is ≥95%.

[0010] Preferably, 6 hydrogen-type chromatographic resin columns are used for the chromatographic separation, which are sequentially denoted as column 1# to column 6#. The height-diameter ratio of each hydrogen-type chromatographic resin column is 1.5:1. The chromatographic separation includes the following steps:

[0011] First step: Connect column 1# to column 5# in series, feed the decolorized and desalted feed liquid into column 1# at a rate of 1.7 BV / h for 0.23 BV, and the material at the outlet of column 5# is denoted as the first material;

[0012] Second step: Connect column 1# to column 6# in series to form a closed loop, and operate at a rate of 1.56 BV / h for 0.5 h;

[0013] Third step: Connect column 2# to column 4# in series, feed water into column 2# at a rate of 1.7 BV / h for 0.28 BV, and the material at the outlet of column 4# is denoted as the second material; feed water into column 5# at a rate of 1.6 BV / h for 0.22 BV, and the material at the outlet of column 5# is denoted as the third material;

[0014] Repeat the three steps in a cycle. Each time a cycle is completed, the series-connected column numbers and the inlet and outlet column numbers are postponed by one column and cycle among column 1# to column 6#; the second material is the erythritol solution.

[0015] Preferably, before the ceramic membrane filtration, it also includes: adjusting the pH value of the waste mother liquor to 3.5 - 6.5 and heating; the heating temperature is 75 - 85 °C.

[0016] Preferably, the pore size of the ceramic membrane is 20 - 200 nm.

[0017] Preferably, the decolorization is carried out with activated carbon, and the mass of the activated carbon in the activated carbon decolorization is 0.2% - 5% of the dry matter mass in the first filtrate.

[0018] Preferably, the desalting is carried out with ion exchange resin. The ion exchange resin desalting uses cation exchange resin and anion exchange resin, and the cation exchange resin is a strong acid type cation exchange resin.

[0019] Preferably, the recycling method further includes:

[0020] Concentrate, crystallize for the first time, centrifuge, dissolve the crystal, decolorize, crystallize for the second time, and dry the erythritol solution to obtain the first erythritol;

[0021] Alternatively, the erythritol solution is mixed with the original solution and then further processed to obtain secondary erythritol; the original solution is the material solution obtained by subjecting the fermentation broth to ceramic membrane filtration, nanofiltration membrane filtration, and ion exchange desalination treatment in sequence.

[0022] Preferably, the mass concentration of the material obtained by concentration is 45% - 70%.

[0023] Preferably, both the primary crystallization and the secondary crystallization are cooling crystallization, the cooling rate of the cooling crystallization is 1 - 5 °C / h, and the end temperature of the cooling crystallization is 20 - 25 °C.

[0024] Preferably, the further processing includes: concentration, primary crystallization, centrifugation, crystal dissolution, decolorization, secondary crystallization, and drying.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention provides a method for recycling waste mother liquor after erythritol crystallization, including the following steps: subjecting the waste mother liquor after erythritol crystallization to ceramic membrane filtration to obtain a first filtrate; decolorizing and desalting the first filtrate to obtain a decolorized and desalted material solution; subjecting the decolorized and desalted material solution to chromatographic separation to obtain an erythritol solution; using a hydrogen-type chromatographic resin column for the chromatographic separation; the erythritol solution has an erythritol mass content of ≥95% based on dry matter.

[0027] The present invention filters the waste mother liquor to be treated to remove macromolecular substances in the waste mother liquor, then performs decolorization and desalting, and then performs chromatographic separation to extract and separate erythritol in the waste mother liquor in one step. The obtained erythritol solution has an erythritol mass content of more than 95% based on dry matter. Concentrating and crystallizing the erythritol solution, or combining and processing the erythritol solution with the original solution, can obtain an erythritol product with a purity of more than 99.9%. The present invention can make the total recovery rate of erythritol exceed 95%, and the product recovery rate is high. Moreover, the erythritol product obtained by the present invention has a high purity.

[0028] Through chromatographic separation, the present invention can effectively extract erythritol in the waste mother liquor at a relatively low extraction cost. The present invention can increase the yield of erythritol, reduce costs, increase profits, and reduce environmental protection pressure. The popularization of the present invention can greatly promote the development of the erythritol industry. Detailed Embodiments

[0029] The present invention provides a method for recycling waste mother liquor after erythritol crystallization, including the following steps:

[0030] Subjecting the waste mother liquor after erythritol crystallization to ceramic membrane filtration to obtain a first filtrate;

[0031] Decolorizing and desalting the first filtrate to obtain a decolorized and desalted material solution;

[0032] Perform chromatographic separation on the decolorized and desalted feed liquid to obtain an erythritol solution; the chromatographic separation uses a hydrogen-form chromatographic resin column; in the erythritol solution, the mass content of erythritol based on dry matter is ≥95%.

[0033] In the present invention, unless otherwise specified, the materials and equipment used are commercially available products in the art.

[0034] In the present invention, the waste mother liquor after erythritol crystallization is filtered by a ceramic membrane to obtain a first filtrate.

[0035] In the present invention, the waste mother liquor after erythritol crystallization is the feed liquid after multiple crystallizations of the original liquid. The original liquid is the feed liquid obtained by successively subjecting the fermentation broth to ceramic membrane filtration, nanofiltration membrane filtration, and ion exchange desalination treatment. The number of times of the multiple crystallizations is preferably 3 - 5 times, and specifically can be 4 times.

[0036] In the present invention, the mass content of dry matter in the waste mother liquor after erythritol crystallization is about 60%, including 35% - 45% erythritol, 10% - 15% reducing sugar, 5% - 10% protein, 3% - 5% ribitol and mannitol, 2% inorganic salts, and also contains pigments and unknown components.

[0037] In the present invention, before the ceramic membrane filtration, it also includes: adjusting the pH value of the waste mother liquor to 3.5 - 6.5 and heating. The pH value is preferably 5 - 5.5; the heating temperature is preferably 75 - 85°C, specifically can be 80°C. The function of heating is to denature the protein in the waste mother liquor.

[0038] In the present invention, the inlet membrane pressure for the ceramic membrane filtration is preferably 2 - 15 bar, specifically can be 10 bar or 15 bar, and the transmembrane pressure difference is preferably 0 - 6 bar, specifically can be 5 bar. The temperature of the waste mother liquor during filtration is preferably 50 - 55°C.

[0039] In the present invention, the pore size of the ceramic membrane is preferably 20 - 200 nm, specifically can be 50 nm. The function of the ceramic membrane filtration is to remove macromolecular substances, including protein.

[0040] After obtaining the first filtrate, the present invention decolorizes and desalts the first filtrate to obtain a decolorized and desalted feed liquid.

[0041] In the present invention, the decolorization is preferably activated carbon decolorization. The mass of the activated carbon in the activated carbon decolorization is preferably 0.2% - 5% of the mass of the dry matter in the first filtrate, specifically can be 2% or 3%; the temperature of the activated carbon decolorization is preferably 55 - 85°C, specifically can be 60°C, and the time is preferably 0.5 - 2 h, specifically can be 1 h.

[0042] In the present invention, solid-liquid separation is further included after decolorization, and the solid-liquid separation method is preferably plate-and-frame filtration to remove activated carbon.

[0043] In the present invention, the desalting is preferably carried out by ion exchange resin desalting. The ion exchange resin desalting preferably uses cation exchange resin and anion exchange resin. The cation exchange resin is preferably a strong acid type cation exchange resin, specifically it can be Wandong 001×7 (732) or Zhengguang ZGD001-FD; the anion exchange resin is preferably a strong base or weak base type anion exchange resin. The strong base type anion exchange resin can be Wandong D201, and the weak base type anion exchange resin can be Zhengguang ZGD354-FD.

[0044] In the present invention, the desalting process preferably controls the conductivity of the feed liquid to be below 200 μm / cm, specifically it can be below 50 μm / cm, and the chromaticity to be below 100.

[0045] After obtaining the decolorized and desalted feed liquid, the present invention performs chromatographic separation on the obtained decolorized and desalted feed liquid to obtain an erythritol solution; the chromatographic separation uses a hydrogen form chromatographic resin column; in the erythritol solution, calculated on a dry matter basis, the mass content of erythritol is ≥95%.

[0046] In the present invention, the hydrogen form chromatographic resin column is preferably obtained by acidifying a sodium form chromatographic separation resin with hydrochloric acid and then packing it.

[0047] In the present invention, the chromatographic separation preferably uses 6 hydrogen form chromatographic resin columns, which are sequentially denoted as column 1# to column 6#. The height-to-diameter ratio of each hydrogen form chromatographic resin column is preferably 1.5:1. The chromatographic separation preferably includes the following steps:

[0048] The first step: Connect column 1# to column 5# in series, feed the decolorized and desalted feed liquid into column 1# at a rate of 1.7 BV / h for 0.23 BV, and the material at the outlet of column 5# is denoted as the first material;

[0049] The second step: Connect column 1# to column 6# in series to form a closed loop, and run at a rate of 1.56 BV / h for 0.5 h;

[0050] The third step: Connect column 2# to column 4# in series, feed water into column 2# at a rate of 1.7 BV / h for 0.28 BV, and the material at the outlet of column 4# is denoted as the second material; feed water into column 5# at a rate of 1.6 BV / h for 0.22 BV, and the material at the outlet of column 5# is denoted as the third material;

[0051] The three steps are cycled. Each time it is cycled, the series column numbers and the inlet and outlet column numbers are extended by one, and the cycle is carried out among column 1# to column 6#; the second material is the erythritol solution;

[0052] The first material and the third material are waste liquids containing impurities.

[0053] After the decolorized and desalted feed liquid enters the chromatographic column, pure erythritol is separated by the different migration rates of different substances in the chromatographic resin column. The chromatographic separation conditions described in the present invention can separate erythritol from other impurities to obtain an erythritol solution with an erythritol mass content of more than 95% in the dry matter. Moreover, the chromatographic separation method described in the present invention has a small water consumption ratio, and the water consumption per unit volume of the material is only about 2.2.

[0054] In the present invention, the recycling method preferably further includes:

[0055] Concentrating, first crystallizing, centrifuging, dissolving crystals, decolorizing, second crystallizing, and drying the erythritol solution to obtain the first erythritol;

[0056] Or mixing the erythritol solution with the stock solution and continuing the treatment to obtain the second erythritol; the stock solution is the feed liquid obtained by subjecting the fermentation broth to ceramic membrane filtration, nanofiltration membrane filtration, and ion exchange desalination treatment in sequence.

[0057] In the present invention, mixing the erythritol solution with the stock solution and continuing the treatment preferably includes: concentrating, first crystallizing, centrifuging, dissolving crystals, decolorizing, second crystallizing, and drying.

[0058] In the present invention, the concentration is preferably carried out by an evaporator, and the evaporator preferably includes a multi-effect plate evaporator, a multi-effect rising film evaporator, or a multi-effect falling film evaporator.

[0059] In the present invention, the temperature of the concentration is preferably 73-80°C, and the pressure is preferably -0.095 MPa.

[0060] In the present invention, the mass concentration of the material obtained by the concentration is preferably 45%-70%, specifically it can be 60%, and the density is preferably 1.185-1.19 g / cm 3 .

[0061] In the present invention, both the first crystallization and the second crystallization are preferably cooling crystallization. The cooling rate of the cooling crystallization is preferably 1-5°C / h, specifically it can be 1-2°C / h or 2-5°C / h; the cooling crystallization process is preferably accompanied by stirring, and the rotation speed of the stirring is preferably 30 rpm or 50 rpm; the end temperature of the cooling crystallization is preferably 20-25°C.

[0062] In the present invention, the centrifugation preferably adopts a horizontal spiral centrifuge or a flat scraper bottom discharge centrifuge. The crystal dissolution preferably adopts 4°C pure water, and the mass concentration of erythritol in the solution obtained by the crystal dissolution is preferably 55%~60% (W / V), specifically 55% or 58%. The decolorization is preferably activated carbon decolorization, and the mass of activated carbon in the activated carbon decolorization is preferably 0.5%~1% of the dry matter mass, the temperature of the activated carbon decolorization is preferably 70°C, and the processing time is preferably 60min. The drying is preferably 105°C hot air drying, and the drying is preferably carried out using a boiling fluidized bed.

[0063] In the present invention, the purity of the first erythritol and the second erythritol is independently above 99.9%.

[0064] In order to further illustrate the present invention, the method for recycling the waste mother liquor after erythritol crystallization provided by the present invention is described in detail below in conjunction with the examples, but they should not be understood as limiting the scope of protection of the present invention.

[0065] In the embodiment of the present invention, the erythritol waste mother liquor used is the effluent mother liquor after four crystallizations in the erythritol industrial production workshop, containing about 60% dry matter, including about 37% erythritol, 11% reducing sugar, 7% protein, 4% ribitol and mannitol, 2% inorganic salts, and a large amount of pigments and other unknown components.

[0066] Example 1

[0067] The pH value of the erythritol waste liquor was adjusted to 5.0 and heated to 75°C to denature the protein therein. After the temperature dropped to 50°C, the filtrate was filtered using a 50nm ceramic membrane at an inlet pressure of 10 bar and a transmembrane pressure difference of 5 bar, and the filtrate was collected.

[0068] To the obtained filtrate, 3% of the total dry matter weight of the material was added with activated carbon powder, and the mixture was decolorized at 60°C for 1 hour. After the decolorization was completed, the material was filtered using a plate and frame filter, and the filtrate was collected.

[0069] The filtrate obtained after decolorization is desalted by using Wandong 001×7 (732) strong acid cation exchange resin and Wandong D201 strong basic anion exchange resin in sequence, and further decolorized at the same time. The conductivity of the material after desalination is controlled to be below 50μm / cm and the chromaticity is below 100 to obtain a decolorized and desalted feed solution.

[0070] The sodium type chromatographic separation resin ZGSPC106Na was converted into hydrogen type chromatographic separation resin with hydrochloric acid and filled into 6 chromatographic columns in the chromatographic separation system. The height-to-diameter ratio of the chromatographic columns was 1.5:1. The columns were connected by pipeline valves, and the material, water and column temperature were maintained at 60±1°C.

[0071] The chromatographic separation process cycles through three steps:

[0072] First step: Connect Column 1 to Column 5 in series in sequence. Feed the decolorized and desalted feed liquid into Column 1 at a rate of 1.7 BV / h for 0.23 BV. The material at the outlet of Column 5 is recorded as the first material.

[0073] Second step: Connect 6 chromatographic columns from Column 1 to Column 6 in series to form a closed loop and operate at a rate of 1.56 BV / h for 0.5 h.

[0074] Third step: Connect Column 2 to Column 4 in series. Feed water into Column 2 at a rate of 1.7 BV / h for 0.28 BV. The material at the outlet of Column 4 is recorded as the second material. Feed water into Column 5 at a rate of 1.6 BV / h for 0.22 BV. The material at the outlet of Column 5 is recorded as the third material.

[0075] After each cycle of the three steps, the series column numbers and the inlet and outlet column numbers are extended by one column and cycle among Column 1 to Column 6.

[0076] Utilize the different migration rates of different substances in the chromatographic resin to separate erythritol from other impurities. When the chromatographic column starts to operate, the materials discharged from the outlets of the three materials are all water. Repeat the above process, and the concentrations of the materials discharged from the outlets of the three materials gradually increase until they reach stability. Among them, the first material and the third material are waste liquids containing impurities, and the second material is an erythritol solution. Calculated by dry matter, the mass content of erythritol is ≥95%.

[0077] Utilize a triple-effect MVR evaporator to concentrate the collected erythritol solution. The outlet temperature of the concentrated material is 75 °C, and the outlet concentration is 60%.

[0078] Utilize a 10m 3 crystallizer to cool and crystallize the material discharged from the evaporator: The stirring frequency is 50 rpm, the cooling rate is 2 - 5 °C / h, and the outlet temperature of the crystallized material is 25 °C.

[0079] Utilize a horizontal spiral centrifuge to centrifuge the crystallized crystal slurry to obtain a liquid and wet crystals:

[0080] Concentrate and recrystallize the liquid. The liquid obtained from the recrystallization is mixed into the filtrate obtained by ceramic membrane filtration for reuse. The wet crystals obtained from the recrystallization are mixed into the erythritol solution after chromatographic separation for reuse;

[0081] Dissolve the wet crystals in pure water to a mass concentration of 60%, add activated carbon powder accounting for 1% of the dry matter mass for decolorization, and filter off the carbon using an Amma filter after the decolorization is completed. The decolorized material is again utilized with a 10m 3The crystallizer is cooled for crystallization, and a flat blade bottom discharge centrifuge is used to separate the crystals. The centrifuged liquid is mixed into the decolorized and desalted feed liquid before chromatographic separation for recycling. The wet crystals are dried in a fluidized bed, screened by a vibrating screen, deironed, and packaged to obtain erythritol products.

[0082] Detection was carried out according to the national standard detection method for erythritol (GB 26404-2011 National Food Safety Standard Food Additive Erythritol). The detection results of each index of the erythritol product obtained in Example 1 are shown in Table 1 below:

[0083] Table 1 Detection results of each index of the erythritol product obtained in Example 1

[0084]

[0085] It can be seen that the purity of the erythritol product exceeds 99.9%. The recovery rate is calculated as: (total mass of recovered erythritol ÷ total mass of erythritol in the initial waste mother liquor) * 100%. The recovery rate of erythritol in the waste mother liquor of this example reaches 91.3%.

[0086] Example 2

[0087] The pH value of the waste mother liquor was adjusted to 5.5 and heated to 80 °C to denature the protein therein. After the temperature of the material was lowered to 55 °C using a plate heat exchanger, the material was filtered using a 50 nm ceramic membrane at an inlet membrane pressure of 15 bar and a transmembrane pressure difference of 5 bar, and the filtrate was collected.

[0088] To the obtained filtrate, activated carbon powder accounting for 2% of the total dry matter mass of the material was added, and decolorization was carried out at 60 °C for 1 h. After the decolorization was completed, the material was filtered using a plate and frame, and the filtrate was collected.

[0089] The decolorized filtrate was desalted successively using Zheng Guang ZGD001-FD strongly acidic cation exchange resin and Zheng Guang ZGD354-FD weakly basic anion exchange resin, and further decolorization would be carried out simultaneously. The conductivity of the material after desalting was controlled below 50 μm / cm and the chromaticity was below 100 to obtain a decolorized and desalted feed liquid.

[0090] The Zheng Guang ZGSPC106Na sodium-type chromatographic separation resin was converted into a hydrogen-type chromatographic separation resin using hydrochloric acid and filled into 6 chromatographic columns in the chromatographic separation system. The height-to-diameter ratio of the chromatographic columns was 1.5:1, and the columns were connected by pipeline valves. The material, water, and column temperature were maintained at 60 ± 1 °C.

[0091] The chromatographic separation process was carried out by cycling three steps:

[0092] First step: Columns 1# to 5# were connected in series in sequence, and the decolorized and desalted feed liquid was fed into Column 1# at a rate of 1.7 BV / h for 0.23 BV. The material at the outlet of Column 5# was recorded as the first material;

[0093] Step 2: Connect six chromatographic columns numbered from Column 1# to Column 6# in series to form a closed loop, and operate at a rate of 1.56 BV / h for 0.5 h.

[0094] Step 3: Connect Column 2# to Column 4# in series. Feed water into Column 2# at a rate of 1.7 BV / h for 0.28 BV, and the material at the outlet of Column 4# is recorded as the second material. Feed water into Column 5# at a rate of 1.6 BV / h for 0.22 BV, and the material at the outlet of Column 5# is recorded as the third material.

[0095] After each cycle of the three steps, the serial column numbers and the inlet and outlet column numbers are postponed by one column and cycle among Column 1# to Column 6#.

[0096] Utilize the different migration rates of different substances in the chromatographic resin to separate erythritol from other impurities. When the chromatographic column starts to operate, the materials discharged from the outlets of the three materials are all water. Repeat the above process, and the concentrations of the materials discharged from the outlets of the three materials gradually increase until they reach stability. Among them, the first material and the third material are waste liquids containing impurities, and the second material is an erythritol solution. Calculated on a dry matter basis, the mass content of erythritol is ≥95%.

[0097] Mix the obtained erythritol solution into the original liquid production line (the original erythritol production line). The original liquid is the material obtained by treating the fermentation broth through ceramic membrane, nanofiltration membrane, and ion exchange desalination processes. The obtained erythritol solution and the original liquid are jointly concentrated, crystallized for the first time, centrifuged, redissolved, decolorized, crystallized for the second time, centrifuged, dried, screened, de-ironed, and packaged to obtain erythritol products.

[0098] The detection indexes of the obtained erythritol products are shown in Table 2 below:

[0099] Table 2 Detection results of various indexes of the erythritol products obtained in Example 2

[0100]

[0101] In this example, the extraction yield of the erythritol original liquid production line is increased from 91.5% to 95.2%. Without a significant change in cost, the production capacity is increased by 4%, and the product quality remains stable.

[0102] Comparative Example 1

[0103] Refer to the method of Patent Invention CN 102603478 A to treat the erythritol mother liquor:

[0104] 1. Pretreatment: Take the erythritol mother liquor after multiple crystallizations and dilute it with pure water to a 20% (W / W) solution.

[0105] 2. Ceramic membrane filtration: Filter the above diluted solution with a 50 nm ceramic membrane.

[0106] 3. Nanofiltration membrane filtration: Filter the above-diluted solution using a 500 Da nanofiltration membrane;

[0107] 4. Activated carbon decolorization: Add activated carbon accounting for 2% of the dry matter mass, keep it at 70 °C for 60 min, and filter the activated carbon.

[0108] 5. Ion exchange: Use anion and cation exchange desalination resins to remove salts and some pigments in the solution, and control the conductivity of the discharged material below 500 μs / cm.

[0109] 6. Evaporation and concentration: Concentrate the above ion-exchanged solution to a concentration of 60% (W / W) at a temperature of 75 °C and a pressure of -0.095 MPa;

[0110] 7. Cooling crystallization: Cool down at a rate of 2 °C to 5 °C per hour to 30 °C. Centrifuge the obtained crystal slurry using a centrifuge to collect the wet crystals;

[0111] 8. Drying: Dry the wet crystals using an oven.

[0112] The erythritol product obtained in Comparative Example 1 has the following indicators in Table 3:

[0113] Table 3 Detection results of various indicators of the erythritol product obtained in Comparative Example 1

[0114]

[0115] Due to the large amount of impurities such as ribitol and mannitol in the material, the crystallization rate is low, and there are a large number of tiny crystals in the obtained crystals that are not easy to recover due to the influence of impurities. A large amount of flushing water is also required during the crystal centrifugation process, resulting in a total yield of erythritol in Comparative Example 1 of only about 44%. Moreover, due to the inability to completely remove impurities such as pigments and reducing sugars, the obtained product has a low light transmittance, a yellow color, and a caramel odor.

[0116] Comparative Examples 2 - 7

[0117] Adjust the pH value of the erythritol waste mother liquor to 5.0 and heat it to 75 °C to denature the protein in it. After the temperature drops to 50 °C, filter it using a 50 nm ceramic membrane at an inlet membrane pressure of 10 bar and a transmembrane pressure difference of 5 bar, and collect the filtrate.

[0118] Add activated carbon powder accounting for 3% of the total dry matter mass of the material to the obtained filtrate, and maintain it at 60 °C for 1 h for decolorization. After the decolorization is completed, filter the material using a plate and frame to collect the filtrate.

[0119] The filtrate obtained after decolorization is desalted by using Wandong 001×7 (732) strong acid cation exchange resin and Wandong D201 strong basic anion exchange resin in sequence, and further decolorized at the same time. The conductivity of the material after desalination is controlled to be below 50μm / cm and the chromaticity is below 100 to obtain a decolorized and desalted feed solution.

[0120] The sodium type chromatographic separation resin ZGSPC106Na was converted into hydrogen type chromatographic separation resin with hydrochloric acid and filled into 6 chromatographic columns in the chromatographic separation system. The height-to-diameter ratio of the chromatographic columns was 1.5:1. The columns were connected by pipeline valves, and the material, water and column temperature were maintained at 60±1°C.

[0121] The chromatographic separation process proceeds in a cycle of three steps:

[0122] Step 1: Connect columns 1# to 5# in series, feed (a) BV of decolorized and desalted liquid from column 1# at a rate of 1.7 BV / h, and the material at the outlet of column 5# is recorded as the first material;

[0123] Step 2: Connect the 6 chromatographic columns #1 to #6 in series to form a closed loop, and the material runs at a rate of 1.56 BV / h (b) h;

[0124] Step 3: Connect columns 2# to 4# in series, feed water (c) BV from column 2# at a rate of 1.7 BV / h, and the material at the outlet of column 4# is recorded as the second material; feed water 0.22 BV from column 5# at a rate of 1.6 BV / h, and the material at the outlet of column 5# is recorded as the third material;

[0125] Each time the three steps are repeated, the serial column number and the inlet and outlet column number are extended by one, and circulated between columns 1# to 6#. The first material and the third material are waste liquid containing impurities, and the second material is erythritol solution.

[0126] The collected erythritol solution was concentrated using a triple-effect MVR evaporator, with a concentrated discharge temperature of 75°C and a discharge concentration of 60%.

[0127] Using 10m 3 The crystallizer cools and crystallizes the material discharged from the evaporator: stirring frequency is 50 rpm, cooling rate is 2~5℃ / h, and the crystallization discharge temperature is 25℃.

[0128] The crystal slurry after crystallization is centrifuged using a horizontal spiral centrifuge to obtain liquid and wet crystals:

[0129] The liquid is concentrated and recrystallized, the liquid obtained by recrystallization is mixed into the filtrate obtained by ceramic membrane filtration for reuse, and the wet crystals obtained by recrystallization are mixed into the erythritol solution after chromatographic separation for reuse;

[0130] Dissolve the wet crystals in pure water to a mass concentration of 60%, add activated carbon powder accounting for 1% of the dry matter mass for decolorization, and filter out the carbon using an Amma filter after decolorization. Re-cool the decolorized material in a 3 3 crystallizer for crystallization, separate the crystals using a flat blade bottom discharge centrifuge, and recycle the centrifuged liquid into the decolorized and desalted feed liquid before chromatographic separation. The wet crystals are dried in a fluidized bed, screened by a vibrating screen, de-ironed, and packaged to obtain erythritol products.

[0131] The conditions of chromatographic separation processes a, b, and c in Comparative Examples 2 to 7 are shown in Table 4, and the purity and recovery rates of the obtained erythritol products are shown in Table 5.

[0132] Table 4 Specific chromatographic conditions of Comparative Examples 2 to 7

[0133]

[0134] Table 5 Purity and recovery rates of erythritol obtained in Comparative Examples 2 to 7

[0135]

[0136] It can be seen that in Comparative Example 2, the feed rate was increased, the volume occupied by the material in the chromatographic column increased, and the impurities and erythritol needed to migrate a longer distance in the chromatographic column to be separated. As a result, the purity of the erythritol obtained in Comparative Example 2 decreased, and the yield decreased significantly. In Comparative Example 3, the feed rate was decreased, and the material and impurities were more easily separated; the purity and yield of the product obtained in Comparative Example 3 increased slightly, but the water consumption increased significantly, and the water consumption per unit volume of the actual processed material reached 3.4.

[0137] In Comparative Example 4, the circulation time of the material in the chromatographic column was decreased, but due to insufficient migration of the material in the chromatographic column, the material and impurities were not completely separated, and a large amount of impurities were recovered into the material, resulting in low product purity and yield. In Comparative Example 5, the circulation time of the material in the chromatographic column was increased, the production efficiency decreased, and the yield also decreased.

[0138] In Comparative Example 6, the water inflow when collecting the erythritol solution was decreased, resulting in insufficient recovery and utilization of some erythritol, and a low yield. In Comparative Example 7, the water inflow when collecting the erythritol solution was increased, the purity of erythritol decreased, and the water consumption and energy consumption required for subsequent evaporation and concentration increased.

[0139] Although the above embodiments have described the present invention in detail, they are only a part of the embodiments of the present invention, not all of them. People can also obtain other embodiments according to the embodiments of the present invention without creative work, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for recycling waste mother liquor after erythritol crystallization, characterized in that: The following steps are involved: The waste mother liquor after the crystallization of erythritol is filtered through a ceramic membrane to obtain a first filtrate; Decolorizing and desalting the first filtrate to obtain a decolorized and desalted feed solution; The decolorized and desalted feed solution is subjected to chromatographic separation to obtain an erythritol solution; The chromatographic separation uses a hydrogen-type chromatographic resin column; the erythritol solution has an erythritol mass content of ≥95% based on dry matter; The chromatographic separation uses 6 hydrogen-type chromatographic resin columns, which are sequentially recorded as 1# column to 6# column, and the height-to-diameter ratio of each hydrogen-type chromatographic resin column is 1.5:

1. The chromatographic separation comprises the following steps: Step 1: Connect columns 1# to 5# in series, feed 0.23 BV of decolorized and desalted liquid from column 1# at a rate of 1.7 BV / h, and the material at the outlet of column 5# is recorded as the first material; Step 2: Connect columns 1# to 6# in series to form a closed loop, and run at a rate of 1.56 BV / h for 0.5h; Step 3: Connect columns 2# to 4# in series, add 0.28BV of water from column 2# at a rate of 1.7BV / h, and the material at the outlet of column 4# is recorded as the second material; add 0.22BV of water from column 5# at a rate of 1.6BV / h, and the material at the outlet of column 5# is recorded as the third material; The three steps are repeated in a cycle. Each time the series column number and the inlet and outlet column numbers are extended by one, the columns are repeated between the 1# column and the 6# column. The second material is erythritol solution.

2. The recycling method according to claim 1, characterized in that: Before the ceramic membrane filtration, the method also includes: adjusting the pH value of the waste mother liquor to 3.5-6.5 and heating; the heating temperature is 75-85°C.

3. The recycling method according to claim 1 or 2, characterized in that: The pore size of the ceramic membrane is 20-200 nm.

4. The recycling method according to claim 1, characterized in that: The decolorization is performed by activated carbon decolorization, and the mass of the activated carbon in the activated carbon decolorization is 0.2% to 5% of the mass of the dry matter in the first filtrate.

5. The recycling method according to claim 1, characterized in that: The desalination is ion exchange resin desalination, and the ion exchange resin desalination uses cation exchange resin and anion exchange resin, and the cation exchange resin is a strong acid cation exchange resin.

6. The recycling method according to claim 1, characterized in that: The recycling method further comprises: The erythritol solution is concentrated, crystallized once, centrifuged, dissolved, decolorized, crystallized twice, and dried to obtain the first erythritol; Alternatively, the erythritol solution is mixed with the stock solution and then further processed to obtain the second erythritol; the stock solution is the feed solution obtained after the fermentation liquid is filtered through a ceramic membrane, filtered through a nanofiltration membrane, and subjected to ion exchange desalination treatment in sequence.

7. The recycling method according to claim 6, characterized in that: The mass concentration of the concentrated material is 45% to 70%.

8. The recycling method according to claim 6, characterized in that: The primary crystallization and the secondary crystallization are both cooling crystallizations, the cooling rate of the cooling crystallization is 1-5°C / h, and the terminal temperature of the cooling crystallization is 20-25°C.

9. The recycling method according to claim 6, characterized in that: The further treatment includes: concentration, primary crystallization, centrifugation, crystal dissolution, decolorization, secondary crystallization and drying.

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