Method for preparing lactulose and co-producing lactitol

Abstract

The invention provides a method for preparing lactulose and co-producing lactitol, and belongs to the field of functional sugar. The method comprises the following steps: sequentially carrying out first high-temperature isomerization, concentration and second high-temperature isomerization on a decolored lactose solution to obtain a mixed solution; sequentially carrying out refining and chromatographic separation extraction on the mixed solution to obtain a lactulose solution and raffinate; refining, crystallizing and drying the lactulose solution to obtain crystalline lactulose; refining the raffinate, adjusting the pH value, and carrying out hydrogenation reaction to obtain a lactitol crude liquid; the lactitol crude liquid is subjected to refining and nanofiltration membrane filtration in sequence, and a lactitol solution is obtained; and refining, crystallizing and drying the lactitol solution in sequence to obtain crystallized lactitol. According to the method, the lactose is subjected to two times of high-temperature conversion under the alkaline condition, the conversion rate of the lactulose can reach 55% or above and is far higher than that of an existing lactulose preparation method, the content of the lactose in the converted feed liquid is reduced, and the problem that unreacted lactose is easy to separate out and crystallize in the lactulose preparation process is solved.

Description

Technical Field

[0001] The invention relates to the field of functional sugar technology, and in particular to a method for preparing lactulose and co-producing lactitol. Background Art

[0002] Lactulose (C12H22O11,4-O-β-D-galactopyranosyl-D-fructose), also known as isomerized lactose, is a low-calorie functional disaccharide with multiple functional properties. Lactulose can promote intestinal peristalsis in patients with constipation, increase intestinal osmotic fluid pressure, absorb intestinal bacteria, soften feces, and help promote defecation in patients with constipation. Lactulose can treat hepatic encephalopathy caused by hyperammonemia.

[0003] Lactitol, also known as lactosorbitol, has a chemical name of 4-O-β-D-galactopyranose-D-sorbitol. Lactitol is often used as an incremental sweetener and is a health-care sweetener. Lactitol does not cause insulin to rise, does not promote the accumulation of neutral fat, does not participate in metabolism in the human body, prevents tooth decay, inhibits diarrhea, and regulates the balance of intestinal flora.

[0004] At present, the industrial production of lactulose is rare, mainly because lactose isomerizes into lactulose under alkaline conditions, and the side reaction is violent, with more by-products such as fructose, galactose, and glucose. In addition, most chemical methods for preparing lactulose add boric acid, which makes subsequent desalination difficult. The isomerization yield is low under high temperature alkaline conditions without adding boric acid, and the general conversion rate is 25%-30%. The unreacted lactose is very easy to crystallize and precipitate, resulting in serious lactose loss and low utilization rate. In addition, the color of the feed liquid is dark, making subsequent decolorization difficult.

[0005] Chinese patent CN108191923A discloses a method for preparing lactulose, wherein the lactose isomerization reaction liquid is decolorized with granular carbon, the decolorized lactulose solution is separated by a nanofiltration membrane to remove salt and boric acid, the nanofiltrate is nanofiltered and concentrated again, and then ion exchange and concentration are performed to obtain a concentrated lactulose solution.

[0006] Chinese patent CN111138501A discloses a method for preparing high-purity lactulose, which adopts a two-phase system and selectively combines lactulose with phenylboronic acid compounds and extracts it into an organic phase, thereby promoting the isomerization reaction of lactose to form lactulose and improving the yield of lactulose; and the lactulose extracted into the organic phase can be released into an acidic aqueous solution by reverse desorption to obtain a high-purity lactulose solution.

[0007] At present, the industrial production of lactulose mainly adopts the chemical isomerization method, using lactose as raw material and boric acid as catalyst to prepare lactulose under alkaline conditions. The similarity of solubility properties and the limited limit level increase the difficulty of desalination (boric acid). Industrial desalination technologies include ion exchange desalination and membrane separation desalination. Ion exchange desalination requires a large amount of resin, severe sugar adsorption, and requires a large amount of regenerated acid and alkali; membrane separation technology has a high desalination cost and is difficult to apply to industrial production. In addition, it is difficult to obtain high-purity lactulose using only ion exchange technology.

[0008] At the same time, during the isomerization reaction, lactulose and lactitol will undergo degradation reactions to generate monosaccharides such as galactose, fructose, etc., and organic acids and pigments will also be produced. Currently, there is a lack of processes for producing lactulose and lactitol at the same time, and in order to obtain high-purity lactulose solids or crystals, other miscellaneous sugars must be removed. In industry, sugar separation mostly uses simulated moving bed chromatography, but this technology has high equipment investment, large land occupation, and high water consumption. In addition, due to the requirements for feed solid content, it needs to be concentrated, and the energy consumption is relatively large. Summary of the invention

[0009] In view of this, the object of the present invention is to provide a method for preparing lactulose and co-producing lactitol. In the present invention, the lactose is converted twice at high temperature under alkaline conditions, and the lactulose conversion rate can reach more than 55%, which is much higher than the conversion rate of the existing preparation of lactulose, reduces the content of lactose in the converted feed liquid, and overcomes the problem that unreacted lactose is easy to precipitate and crystallize in the lactulose preparation process.

[0010] In order to achieve the above object, the present invention provides the following technical solutions:

[0011] The present invention provides a method for preparing lactulose and co-producing lactitol, comprising the following steps:

[0012] S1. The decolorized lactose solution is subjected to a first high temperature isomerization and a second high temperature isomerization in sequence to obtain a mixed solution; wherein the sugar concentration of the concentrated lactose solution is 45-55%;

[0013] By adopting the above technical scheme, the purpose of decolorizing the lactose solution is to remove the protein and color in the lactose. After decolorization, the transmittance and chromaticity are detected by a spectrophotometer, and the protein content in the lactose is detected by Coomassie Brilliant Blue staining. After decolorization, the transmittance of lactose is 96%-98%, the chromaticity is almost 0, and the decolorization is considered to be complete when the protein content is not detected.

[0014] S2. The mixed solution is sequentially subjected to decolorization, desalination, concentration, and chromatographic separation to obtain a lactulose solution and a raffinate;

[0015] The sugar concentration of the concentrated mixed solution is 50-55%; the purity of lactulose is ≥96% and the yield is above 90%;

[0016] S3. The lactulose solution is decolorized, desalted, concentrated, crystallized, and dried to obtain crystalline lactulose;

[0017] The sugar concentration of the concentrated lactulose solution is 80-85%;

[0018] S4. The raffinate is sequentially decolorized, desalted, concentrated, pH adjusted, and hydrogenated to obtain a crude lactitol solution;

[0019] S5. The lactitol crude solution is sequentially decolorized, desalted, and filtered through a nanofiltration membrane to obtain a lactitol solution;

[0020] S6. The lactitol solution is sequentially decolorized, desalted, concentrated, crystallized, and dried to obtain crystalline lactitol;

[0021] The sugar concentration of the concentrated lactitol solution is 80-85%.

[0022] Preferably, the sugar concentration of the lactose solution in S1 is 35-45%.

[0023] Preferably, the temperature of the first high temperature isomerization in S1 is 110-120°C and the time is 20-30 min; and the pH of the lactose solution is maintained at 9.0 during the first high temperature isomerization.

[0024] Preferably, the temperature of the second high temperature isomerization in S1 is 120-130°C and the time is 20-30 min; and the pH of the lactose solution is maintained at 9.0 during the second high temperature isomerization.

[0025] More preferably, the first high-temperature isomerization and the second high-temperature isomerization are heated by an ejector.

[0026] Preferably, calcium type chromatographic resin is used for chromatographic separation in S2; the chromatographic separation temperature is 55-60°C, the feed concentration is 50%-60%, the feed amount is 0.02-0.05kg / L resin / h, and the water-to-material ratio is 2.5:1.

[0027] Furthermore, the simulated moving bed chromatography used is composed of 6 chromatography columns, and the 6 chromatography columns are connected end to end in series to form a simulated moving bed chromatography separation device.

[0028] Preferably, the mixture in S1 comprises 55-60% lactulose, 30-35% lactose, 5-10% galactose and 2-6% fructose.

[0029] Preferably, the catalyst for the hydrogenation reaction in S4 is Raney nickel, and the amount of Raney nickel added is 0.2-0.8% of the dry basis mass of lactose.

[0030] Preferably, the reaction temperature in S4 is 100-120° C., the reaction time is 2-3 h, and the reaction pressure is 10-12 MPa.

[0031] Preferably, the nanofiltration membrane used in the nanofiltration in S5 is a CO300 nanofiltration membrane; and the filtration pressure is 1-2 MPa.

[0032] Preferably, the decolorization is independently performed by activated carbon decolorization, and more preferably, the amount of activated carbon added is 0.5% of the dry basis mass; the desalination is independently performed by ion exchange resin desalination, and more preferably, the ion exchange resin is strong acid cation resin D001 and strong base anion resin D201; and the concentration is concentrated by a four-effect evaporator.

[0033] Beneficial technical effects:

[0034] 1. The present invention aims at the defects of the existing process. Lactose is converted twice at high temperature under alkaline conditions, and the lactulose conversion rate can reach more than 55%, which is much higher than the conversion rate of the existing chemical method for preparing lactulose without adding boric acid. The lactose content in the converted feed liquid is reduced, and the problem that unreacted lactose is easy to precipitate and crystallize in the lactulose preparation process is overcome.

[0035] 2. In the present invention, the lactulose raffinate is hydrogenated to prepare lactitol from the lactose in the raffinate, thereby improving the utilization rate of lactose in the production of lactulose, reducing the production cost, and facilitating industrial production.

[0036] 3. In the present invention, the lactose is decolorized and refined before lactose isomerization to remove the protein, impurities and color in the lactose, thereby reducing the chromaticity of the lactose after isomerization, reducing the difficulty of subsequent liquid refining, and improving the product quality. DETAILED DESCRIPTION

[0037] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0038] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0039] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0040] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present application description and examples are exemplary only.

[0041] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0042] The "room temperature" and "normal temperature" mentioned in the present invention are all calculated as 25±2°C unless otherwise specified.

[0043] Unless otherwise specified, the equipment or raw materials used in the following examples can be commercially available.

[0044] Example 1

[0045] A method for preparing lactulose and co-producing lactitol, comprising the following steps:

[0046] S1. Prepare lactose into a 30% lactose solution, heat it to 80°C, add powdered activated carbon at 0.5% on a dry basis, and keep warm for 30 minutes; filter it through a plate filter press. Use a spectrophotometer to detect transmittance and color, and the transmittance is 97% and the color is 0. Use Coomassie Brilliant Blue staining to determine the protein content, and the protein content is from 0.5% before decolorization to undetectable;

[0047] The decolorized lactose solution was then concentrated to 35%, the pH was adjusted to 9.0, the temperature was instantly raised to 110°C using an ejector, the temperature was kept for 20 minutes, and the first high-temperature isomerization was performed; it was then concentrated to a sugar concentration of 45%, the pH was adjusted to 9.0, the temperature was instantly raised to 120°C using an ejector, the temperature was kept for 20 minutes, and the second high-temperature isomerization was performed; a mixed solution of lactulose, lactose, galactose and fructose was obtained, wherein lactulose was 55%, lactose was 32%, galactose was 8% and fructose was 5%, all in mass percentage.

[0048] S2. The chromaticity of the mixed solution was measured by spectrophotometer (A420-A720) / 0.61478 to be 865. Activated carbon was added at 1% dry basis for decolorization, and after decolorization, it was desalted by strong acid cation resin and strong base anion resin, and concentrated to 50% sugar concentration by four-effect evaporator after desalination; then simulated moving bed chromatography was used to separate the components of the mixed solution, and calcium type chromatographic resin was selected for chromatographic resin, six columns were selected for chromatographic columns, water was used as mobile phase, the feed liquid operating temperature was 60°C, the water-to-material ratio was 2.5:1, and the feed amount was 0.03kg / L resin / h. After the feed liquid was purified by calcium type chromatographic resin, the extract was lactulose, the purity of lactulose was 96%, and the yield was 90.5%; the raffinate was a mixed solution including lactose, galactose, fructose, etc.

[0049] S3. The lactulose solution is decolorized by activated carbon, desalted by ion exchange resin, concentrated to a sugar concentration of 85% by a four-effect evaporator, and crystallized and dried to obtain the target product, crystalline lactulose.

[0050] S4. The raffinate is decolorized with activated carbon and desalted with ion exchange resin, concentrated to 30% sugar concentration by a four-effect evaporator, adjusted to pH 7.8, and after 2 / 3 volume of sugar solution is injected into the reactor, the air is expelled 3 times with nitrogen, and then the nitrogen is expelled with hydrogen to make the hydrogen concentration reach more than 99%. 0.5% (Raney nickel to mixed syrup dry basis mass ratio) of Raney nickel catalyst is added, the temperature is controlled at 110°C, the hydrogen pressure is 10MPa, high pressure sealed stirring is started, the speed is 220r / min, hydrogen is continuously added, hydrogenation is promoted, the reaction is carried out for 2.5 hours, when the hydrogen introduced is no longer absorbed, the reducing sugar content is determined by 3.5-dinitrosalicylic acid colorimetry, and the reaction is terminated when the reducing sugar reaches 0.3%, and a lactitol crude liquid containing 74% galactitol, 13% mannitol, 10% galactitol, and 3% lactose is prepared.

[0051] S5. The lactitol crude liquid is decolorized with activated carbon, desalted with ion exchange resin, and then concentrated and purified by a CO300 nanofiltration membrane with a pressure controlled at 1.2 MPa, and the monosaccharide alcohol is filtered out to obtain a lactitol solution with a purity of 95% and a yield of 85%.

[0052] S6. The lactitol solution is decolorized by activated carbon, desalted by ion exchange resin, concentrated by a four-effect evaporator to a sugar concentration of 85%, and then crystallized and dried to obtain the target product, crystalline lactitol.

[0053] Example 2

[0054] A method for preparing lactulose and co-producing lactitol, comprising the following steps:

[0055] S1. Prepare lactose into a 30% lactose solution, heat it to 80°C, add powdered activated carbon at 0.5% on a dry basis, and keep warm for 30 minutes; filter it through a plate filter press. Use a spectrophotometer to detect transmittance and color, and the transmittance is 97% and the color is 0. Use Coomassie Brilliant Blue staining to determine the protein content, and the protein content is from 0.5% before decolorization to undetectable;

[0056] The decolorized lactose solution was then concentrated to 40%, the pH was adjusted to 9.0, the temperature was instantly raised to 115°C using an ejector, and the temperature was kept for 25 minutes for the first high-temperature isomerization; it was then concentrated to a sugar concentration of 50%, the pH was adjusted to 9.0, the temperature was instantly raised to 125°C using an ejector, and the temperature was kept for 20 minutes for the second high-temperature isomerization; a mixed solution of lactulose, lactose, galactose and fructose was obtained, of which 56.5% of lactulose, 30.5% of lactose, 7.5% of galactose and 5.5% of fructose were in percentage by mass.

[0057] S2. The chromaticity of the mixed solution was measured to be 975 by a spectrophotometer (A420-A720) / 0.61478. Activated carbon was added at 1% on a dry basis for decolorization. After decolorization, it was desalted by a strong acid cation resin and a strong base anion resin. After desalting, it was concentrated to a sugar concentration of 50% by a four-effect evaporator. Then, simulated moving bed chromatography was used to separate the components of the mixed solution. The chromatographic resin was a calcium-type chromatographic resin, and a six-column chromatographic column was selected. Water was used as the mobile phase. The feed liquid operating temperature was 60°C, the water-to-feed ratio was 2.6:1, and the feed amount was 0.04kg / L resin / h. After the feed liquid was purified by the calcium-type chromatographic resin, the extract was lactulose with a purity of 96.5% and a yield of 90%. The raffinate was a mixed solution including lactose, galactose, fructose, etc.

[0058] S3. The lactulose solution is decolorized by activated carbon, desalted by ion exchange resin, concentrated to a sugar concentration of 85% by a four-effect evaporator, and crystallized and dried to obtain the target product, crystalline lactulose.

[0059] S4. The raffinate is decolorized with activated carbon and desalted with ion exchange resin, concentrated to 30% sugar concentration by four-effect evaporator, adjusted to pH 7.8, and after 2 / 3 volume of sugar solution is injected into the reactor, air is expelled 3 times with nitrogen, and then nitrogen is expelled with hydrogen to make the hydrogen concentration reach more than 99%. 0.6% (Raney nickel to mixed syrup dry basis mass ratio) of Raney nickel catalyst is added, the temperature is controlled at 110°C, the hydrogen pressure is 11MPa, high pressure sealed stirring is started, the speed is 220r / min, hydrogen is continuously added, hydrogenation is promoted, the reaction is carried out for 3 hours, when the hydrogen introduced is no longer absorbed, the reducing sugar content is determined by 3.5-dinitrosalicylic acid colorimetry, and the reaction is terminated when the reducing sugar reaches 0.3%, and a lactitol crude liquid containing 76% galactitol, 12% mannitol, 10% galactitol, and 2% lactose is prepared.

[0060] S5. The lactitol crude liquid is subjected to activated carbon decolorization, ion exchange resin desalination, and then through a CO300 nanofiltration membrane with the pressure controlled at 1.4 MPa for concentration and purification, and the monosaccharide alcohol is filtered out to obtain a lactitol solution with a purity of 95.5% and a yield of 86%.

[0061] S6. The lactitol solution is decolorized by activated carbon, desalted by ion exchange resin, concentrated by a four-effect evaporator to a sugar concentration of 85%, and then crystallized and dried to obtain the target product, crystalline lactitol.

[0062] Example 3

[0063] A method for preparing lactulose and co-producing lactitol, comprising the following steps:

[0064] S1. Prepare lactose into a 30% lactose solution, heat it to 80°C, add powdered activated carbon at 0.5% on a dry basis, and keep warm for 30 minutes; filter it through a plate filter press. Use a spectrophotometer to detect transmittance and color, and the transmittance is 97% and the color is 0. Use Coomassie Brilliant Blue staining to determine the protein content, and the protein content is from 0.5% before decolorization to undetectable;

[0065] The decolorized lactose solution was then concentrated to 45%, the pH was adjusted to 9.5, the temperature was instantly raised to 120°C using an ejector, the temperature was kept for 30 minutes, and the first high-temperature isomerization was performed; it was then concentrated to a sugar concentration of 55%, the pH was adjusted to 9.5, the temperature was instantly raised to 130°C using an ejector, the temperature was kept for 30 minutes, and the second high-temperature isomerization was performed; a mixed solution of lactulose, lactose, galactose and fructose was obtained, wherein lactulose was 58%, lactose was 30%, galactose was 8% and fructose was 4%, all in mass percentage.

[0066] S2. The chromaticity of the mixed solution was measured to be 975 by a spectrophotometer (A420-A720) / 0.61478. Activated carbon was added at 1% on a dry basis for decolorization. After decolorization, it was desalted by a strong acid cation resin and a strong base anion resin. After desalting, it was concentrated to a sugar concentration of 55% by a four-effect evaporator. Then, simulated moving bed chromatography was used to separate the components of the mixed solution. The chromatographic resin was a calcium-type chromatographic resin, and a six-column chromatographic column was selected. Water was used as the mobile phase. The feed liquid operating temperature was 65°C, the water-to-feed ratio was 2.8:1, and the feed amount was 0.05kg / L resin / h. After the feed liquid was purified by the calcium-type chromatographic resin, the extract was lactulose with a purity of 97% and a yield of 90%. The raffinate was a mixed solution including lactose, galactose, fructose, etc.

[0067] S3. The lactulose solution is decolorized by activated carbon, desalted by ion exchange resin, concentrated to a sugar concentration of 85% by a four-effect evaporator, and crystallized and dried to obtain the target product, crystalline lactulose.

[0068] S4. The raffinate is decolorized with activated carbon and desalted with ion exchange resin, concentrated to 30% sugar concentration by a four-effect evaporator, adjusted to pH 7.8, and after 2 / 3 volume of sugar solution is injected into the reactor, the air is removed 3 times with nitrogen, and then the nitrogen is removed with hydrogen to make the hydrogen concentration reach more than 99%. 0.8% (Raney nickel to mixed syrup dry basis mass ratio) of Raney nickel catalyst is added, the temperature is controlled at 120°C, the hydrogen pressure is 11MPa, high pressure sealed stirring is started, the speed is 220r / min, hydrogen is continuously added, hydrogenation is promoted, the reaction is carried out for 3 hours, when the hydrogen introduced is no longer absorbed, the reducing sugar content is determined by 3.5-dinitrosalicylic acid colorimetry, and the reaction is terminated when the reducing sugar reaches 0.3%, and a lactitol crude liquid containing 76.5% galactitol, 10.5% mannitol, 11% galactitol, and 2% lactose is prepared.

[0069] S5. The lactitol crude liquid is subjected to activated carbon decolorization, ion exchange resin desalination, and then through a CO300 nanofiltration membrane with the pressure controlled at 1.8 MPa for concentration and purification, and the monosaccharide alcohol is filtered out to obtain a lactitol solution with a purity of 96% and a yield of 85%.

[0070] S6. The lactitol solution is decolorized by activated carbon, desalted by ion exchange resin, concentrated by a four-effect evaporator to a sugar concentration of 85%, and then crystallized and dried to obtain the target product, crystalline lactitol.

[0071] Comparative Example 1

[0072] A method for preparing lactulose comprises the following steps:

[0073] (1) Isomerization reaction: prepare a 40% lactose solution, add boric acid in a molar mass ratio of 1:1 to lactose, adjust the pH to 10.0, and keep it at 80°C for 2 h. The reaction produces a reaction solution containing 70% lactulose, 10% lactose, 8% galactose, 8% epiratose, and 4% fructose; the light transmittance is 6%, the color is very dark and exceeds the range, and the conductivity exceeds the range of the laboratory conductivity meter and cannot be measured.

[0074] (2) Decolorization: Add powdered activated carbon at 10% of the dry basis, decolorize 3 times, transmittance 68%, chromaticity 2858, and filtering is difficult during decolorization, with a material loss of 20%.

[0075] (3) Ion exchange: The feed solution obtained in step (2) is sequentially passed through 1# cation exchange resin, 2# boric acid adsorption resin, 3# boric acid adsorption resin, 4# boric acid adsorption resin, 5# cation exchange resin, and 6# boron selective adsorption resin, and eluted with water, and the conductivity is still 2ms / cm. In the chromatographic separation process, not only the components are separated, but also chromatographic desalination is performed, the water-to-material ratio is 5:1, the feed amount is 0.02kg / L resin / h, and the qualified lactulose solution is collected, with a lactulose content of 92% and a yield of 70%. The target product, crystalline lactulose, is obtained by concentration and crystallization.

[0076] Comparative Example 2

[0077] A method for preparing lactulose comprises the following steps:

[0078] (1) The decolorized lactose was prepared into a 40% lactose solution, the pH was adjusted to 9.5, and the temperature was instantly raised to 120°C by an ejector, and the temperature was kept for 30 minutes to obtain an aqueous solution with a lactulose content of 27%. The solution was decolorized by activated carbon, desalted by strong acid cation resin and strong base anion resin, and concentrated to a sugar concentration of 45% by a four-effect evaporator.

[0079] (2) The simulated moving bed chromatography was used to separate the components of the feed solution in step (2). The extract was lactulose with a purity of 69% and a yield of 70%. The lactulose had a low purity and could not be crystallized.

[0080] Compared with the embodiment, only one isomerization is performed, the lactulose conversion rate is low, the feed liquid concentration cannot be higher than 45% in the later refining process, lactose is easy to precipitate and block the pipeline, the production efficiency is reduced due to the low feed liquid concentration, and the lactulose purity is low after chromatographic separation, and the yield is low.

[0081] Comparative Example 3

[0082] A method for preparing lactulose and co-producing lactitol, comprising the following steps:

[0083] (1) Prepare a 40% lactose solution, adjust the pH to 9.5, use an ejector to instantly heat it to 115°C, keep it warm for 25 minutes, and then concentrate it to a sugar concentration of 50%. Adjust the pH to 9.5, use an ejector to instantly heat it to 125°C, and keep it warm for 20 minutes. Get a mixture of lactulose, lactose, galactose, and fructose, of which lactulose is 55%, lactose is 32%, galactose is 7%, and fructose is 6%, all by mass percentage. The chromaticity is 2652 measured by a spectrophotometer (A420-A720) / 0.61478. Add activated carbon at 5% dry basis for two decolorizations. During the decolorization process, filtration is difficult and the liquid loss is 5%. After decolorization, it is desalted by strong acid cation resin and strong base anion resin, and concentrated to a sugar concentration of 50% by a four-effect evaporator.

[0084] (2) The feed liquid of step (2) was separated into components by simulated moving bed chromatography. The chromatographic resin was calcium-type chromatographic resin, the chromatographic column was six-column, water was used as the mobile phase, the feed liquid operating temperature was 60° C., the water-to-material ratio was 2.6:1, the feed amount was 0.04 kg / L resin / h, and after the feed liquid was purified by the calcium-type chromatographic resin, the extract was lactulose, the purity of lactulose was 95.5%, and the yield was 90%.

[0085] Compared with Example 2, the lactose before isomerization was not decolorized, resulting in a dark color of the liquid after isomerization, which caused difficulties in the subsequent refining. During refining, a large amount of activated carbon was used, filtration was difficult, and material loss was large, which was not conducive to industrial production.

[0086] By comparing Examples 1-3 of the present invention with Comparative Example 1, it can be seen that the method provided by the present invention does not require the addition of alkaline catalysts such as borates or aluminates, no borates or aluminates remain, the refining process is simple and easy, and high-purity lactitol is obtained while obtaining lactulose, which greatly reduces the production cost of lactulose and is conducive to its industrial production.

[0087] By comparing Examples 1-3 of the present invention with Comparative Example 2, it can be seen that the present invention addresses the defects of the existing process. Lactose is isomerized twice at high temperature under alkaline conditions, while the lactulose preparation process of Comparative Example 2 is isomerized once at high temperature and the conversion rate of lactulose is 27%, which is far inferior to the method of the present invention.

[0088] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing lactulose and co-producing lactitol, characterized in that: The following steps are involved: S1. The decolorized lactose solution is sequentially subjected to a first high temperature isomerization, concentration, and a second high temperature isomerization to obtain a mixed solution; S2. The mixed solution is sequentially subjected to decolorization, desalination, concentration, and chromatographic separation to obtain a lactulose solution and a raffinate; The sugar concentration of the concentrated mixed solution is 50-55%; S3. The lactulose solution is decolorized, desalted, concentrated, crystallized, and dried to obtain crystalline lactulose; The sugar concentration of the concentrated lactulose solution is 80-85%; S4. The raffinate is sequentially decolorized, desalted, concentrated, pH adjusted, and hydrogenated to obtain a crude lactitol solution; The concentration of the concentrated raffinate is 30%; S5. The lactitol crude solution is sequentially decolorized, desalted, and filtered through a nanofiltration membrane to obtain a lactitol solution; S6. The lactitol solution is sequentially decolorized, desalted, concentrated, crystallized, and dried to obtain crystalline lactitol; The sugar concentration of the concentrated lactitol solution is 80-85%.

2. The method according to claim 1, characterized in that The sugar concentration of the lactose solution in S1 is 35-45%.

3. The method according to claim 1, characterized in that The temperature of the first high temperature isomerization in S1 is 110-120° C. and the time is 20-30 min. The pH value of the lactose solution is maintained at 9.0 during the first high temperature isomerization.

4. The method according to claim 1, characterized in that: The temperature of the second high temperature isomerization in S1 is 120-130° C. and the time is 20-30 min. The pH value of the lactose solution is maintained at 9.0 during the second high temperature isomerization.

5. The method according to claim 1, characterized in that The chromatographic separation in S2 uses a calcium-type chromatographic resin; the chromatographic separation temperature is 55-60°C, the feed concentration is 50%-60%, the feed amount is 0.02-0.05kg / L resin / h, and the water-to-material ratio is 2.5:

1.

6. The method according to claim 1, characterized in that The composition of the mixed solution in S1 is 55-60% lactulose, 30-35% lactose, 5-10% galactose and 2-6% fructose.

7. The method according to claim 1, characterized in that The catalyst for the hydrogenation reaction in S4 is Raney nickel, and the amount of Raney nickel added is 0.2-0.8% of the dry basis mass of lactose.

8. The method according to claim 6, characterized in that In the S4, the reaction temperature is 100-120° C., the reaction time is 2-3 h, and the reaction pressure is 10-12 MPa.

9. The method according to claim 1, characterized in that: The nanofiltration membrane used for nanofiltration in S5 is a CO300 nanofiltration membrane; the filtration pressure is 1-2 MPa.

10. The method according to claim 1, characterized in that The decolorization is independently performed by activated carbon decolorization; and the desalination is independently performed by ion exchange resin desalination.