WO2018103361A1

WO2018103361A1 - Method for preparing high-purity lactulose by efficient removal of sodium meta-aluminate

Info

Publication number: WO2018103361A1
Application number: PCT/CN2017/096543
Authority: WO
Inventors: 杨瑞金; 汪明明; 华霄; 赵伟; 张文斌; 冯英慧
Original assignee: 江南大学
Priority date: 2016-12-05
Filing date: 2017-08-09
Publication date: 2018-06-14
Also published as: CN108148099B; CN108148099A

Abstract

A method for preparing high-purity lactulose by efficient removal of sodium meta-aluminate, pertaining to the technical field of oligosaccharide preparation. The method comprises preparing a high-purity lactulose syrup and a product thereof by pretreatment of a syrup, removal of a catalyst, removal of a monosaccharide and a salt, and posttreatment of the syrup. The efficient removal and recycling of the catalyst sodium meta-aluminate is realized. In the final product, Al residue is < 10 ppm (with respect to lactulose) and the purity of lactulose is > 95%. The preparation process meets resource-saving and environmentally-friendly production requirements, and facilitates clean, efficient, and environmentally-friendly industrial production of high-purity lactulose.

Description

Method for efficiently removing sodium metaaluminate to prepare high-purity lactulose

Technical field

The invention relates to a method for efficiently removing sodium metaaluminate to prepare high-purity lactulose, and belongs to the technical field of oligosaccharide preparation.

Background technique

Lactulose (also known as lactulose or isomerized lactose, molecular formula: C ₁₂ H ₂₂ O ₁₁ ; molecular weight: 342.30 Da; chemical name: 4-O-β-D-galactopyranosyl-D-fructose) A bifidobacteria promoting factor has the advantages of low calorie, high safety, good stability and wide application. In 1996, Japan approved lactulose as a food for specified health uses (FOSHU: food for specified health uses), and more than 100 countries around the world have approved it to enter the pharmacopoeia. Lactulose is widely used in addition to medicines, health products, food additives and animal feeds, and can also be used as a functional factor in infant formula. In recent years, with the sharp increase in people's demand, the world's total output of lactulose has also increased significantly, and the current annual output has exceeded 60,000 tons. As a functional prebiotic, lactulose has huge market demand and broad development prospects.

The industrial preparation of lactulose is mainly by isomerization of lactose under alkaline conditions. Conventional alkaline catalysts include sodium hydroxide, calcium hydroxide, potassium hydroxide, etc., and strongly basic organic amines, but under such a single basic catalyst, not only long reaction time, but also many by-products, conversion The rate is low, and the subsequent separation and purification process is complicated, and it is difficult to truly realize industrial production. In addition, there are patents for the isomerization production using strong alkaline ion exchange resins abroad (for example, Russian Patent Application No. 2101358, 1994). Although the separation and purification of the method is relatively simple, the conversion rate is low, and the production cost is high, and it is also unsuitable for industrial continuous production. Basic alkaline complex catalysts such as borate and metaaluminate, because of the ability to form stable complexes with lactulose, allow the reaction to proceed in a direction favoring lactulose production, thereby achieving higher lactulose conversion. (about 70%). At present, borate is used as a catalyst to prepare lactulose, but boric acid is difficult to completely remove from the final reaction system, and expensive deboron resin is required. In addition, a large amount of boron is produced during the nanofiltration purification process. Ionized wastewater can cause great pollution to the environment. Whether it is from an economic point of view or an environmental point of view, there are certain problems.

In foreign countries, there is a report on the preparation of lactulose by isomerization of metaaluminate as a catalyst. The conversion rate of lactulose is higher than that of using boric acid as a catalyst, and can reach more than 75%. At the same time, the lactose in the final system of the method is transformed as much as possible. Therefore, the ratio of lactulose in the disaccharide is high, and the purity of the lactulose can be high after separation and purification. However, this method still has deficiencies in the separation and purification of the catalyst and lactulose. On the one hand, the metaaluminate is converted into aluminum hydroxide precipitate, and then removed by centrifugation and membrane separation, which not only causes a large loss of lactulose encapsulated in the precipitation of aluminum hydroxide, but also has a limited effect of removing aluminum hydroxide. Moreover, the subsequent removal of the catalyst by ultrafiltration membrane separation will inevitably produce aluminum-containing wastewater, and the subsequent treatment of the aluminum-containing wastewater is complicated and costly. On the other hand, using a resin desalting method for lactulose The slurry is purified, it is difficult to effectively remove the generated monosaccharide, and a large amount of resin is consumed, and it is difficult to obtain a high-purity lactulose syrup while increasing the cost. At present, there is no patent for the preparation of lactulose by isomerization of lactose with a complex catalyst such as sodium metaaluminate, and there are only a few companies producing lactulose in China, and the products are mostly low-purity lactulose syrup. Almost all of the high-purity lactulose is imported. Therefore, the development of an efficient and environmentally friendly preparation method of lactulose is urgently needed in the development of China's lactulose industry. In addition, how to realize the continuous use of catalysts is also a new challenge for the industrialization of China's lactulose.

Summary of the invention

In view of the problems that the catalyst existing in the preparation process of the existing lactulose is difficult to remove, the product separation and purification is complicated, and it is difficult to realize industrial production, the object of the present invention is to provide an efficient and environmentally friendly method for removing the sodium metaaluminate catalyst. It is removed by converting sodium metaaluminate into aluminum hydroxide precipitate, which does not produce aluminum-containing wastewater, and compensates for and overcomes the shortcomings in the current preparation of lactulose by using sodium metaaluminate as a catalyst.

A method for efficiently removing sodium metaaluminate from the present invention for preparing high-purity lactulose, the method comprising the steps of:

(1) Pretreatment of syrup:

Adjusting the syrup solution to a lactulose concentration of 10 to 500 g/L, and then adding an acidic substance to adjust the pH of the system to 3.5 to 8.0 to obtain a mixed solution containing an aluminum hydroxide flocculation precipitation system; wherein the syrup solution refers to partial Sodium aluminate is a catalyst for catalyzing lactose or lactose-containing material to prepare a lactulose syrup solution;

(2) Separation of slag liquid:

Adding 1 to 10 volumes of water to the mixed solution containing the aluminum hydroxide flocculation and precipitation system obtained in the step (1), dispersing the aluminum hydroxide flocculation precipitation system into aluminum hydroxide particles by stirring, and releasing the aluminum hydroxide flocculation The lactulose encapsulated in the precipitation system is separated by a slag liquid to obtain a lactulose clear liquid and a precipitate of aluminum hydroxide;

(3) Purification of lactulose supernatant:

The lactulose supernatant obtained in the step (2) is subjected to nanofiltration treatment to remove salts and monosaccharides to obtain a high-purity lactulose syrup solution.

In one embodiment, the syrup solution in the step (1) is a lactulose-containing syrup solution prepared by isomerizing lactose under suitable conditions using sodium metaaluminate/sodium hydroxide as a basic complex catalyst. .

In one embodiment, the addition of the acidic material in step (1) is added with stirring.

In one embodiment, step (1) is to adjust the pH to 4.5 to 8.0, or to 3.5 to 7.0.

In one embodiment, after adjusting the pH to 3.5-7.0 in step (1), the sodium meta-aluminate in the syrup is converted into colloidal aluminum hydroxide under stirring to obtain flocculation of aluminum hydroxide. A mixture of precipitation systems.

In one embodiment, the preparation of the syrup solution of step (1), specifically: adding the lactose substrate to the water, stirring The mixture is dissolved to obtain a lactose solution having a mass concentration of 10 to 500 g/L; according to the weight ratio of sodium metaaluminate: lactose substrate = 0.02 to 1:1, sodium metaaluminate is added to the lactose solution, and the mixture is stirred. Dissolve, add sodium hydroxide, adjust the pH of the reaction system to 9.0 ~ 13.0, then stir the reaction at 40 ~ 80 ° C for 20 ~ 240 minutes; after the reaction is completed, the reaction system is cooled to room temperature to obtain isomerized milk Fructose syrup, a syrup solution containing lactulose.

In one embodiment, the lactose or lactose-containing material in step (1) includes, but is not limited to, food grade lactose, whey, and cow's milk.

In one embodiment, the acidic substance in the step (1) includes not only, but not limited to, inorganic acids such as hydrochloric acid and sulfuric acid, and organic acids such as lactic acid and citric acid, and any of the above inorganic or organic acids. Aqueous solution of concentration.

In one embodiment, the slag liquid separation in the step (2) refers to any one of a sedimentation, filtration, and centrifugation, or a combination of several operations, including a sedimentation-centrifugal combination, a sedimentation-filtration combination, and a filtration-centrifugation combination. The centrifugal-centrifugal combination and the sedimentation-filtration-centrifugation combination are completed.

In one embodiment, the method further comprises adding an ion exchange resin treatment step to the lactulose clear solution between step (2) and step (3); the ion exchange resin obtained in step (2) The supernatant is subjected to adsorption treatment to remove residual aluminum ions. The residual of Al in the syrup solution treated by the ion exchange resin was <10 ppm (to the weight of lactulose).

In one embodiment, the ion exchange resin includes, but is not limited to, a strongly acidic cation exchange resin and a weakly acidic cation exchange resin, and the like.

In one embodiment, the nanofiltration of step (3) is a nanofiltration membrane.

In one embodiment, the molecular weight cut-off of the nanofiltration membrane in the step (3) is between 200 and 300 Da.

In one embodiment, the step (3) is treatment until the electrical conductivity is less than 1000 [mu]s/cm, such as less than 100 [mu]s/cm.

In one embodiment, the method further comprises subjecting the high-purity lactulose syrup solution obtained in the step (3) to a subsequent treatment to prepare a high-purity lactulose product.

In one embodiment, the subsequent treatment comprises concentration, crystallization, spray drying, or a combination of the above, including a concentration-crystallization combination, a concentration-spray drying combination, and the like.

In one embodiment, the high-purity lactulose product comprises the high-purity lactulose syrup solution obtained by the above step (3) being concentrated to obtain a high-purity lactulose syrup product, which is subjected to crystallization treatment to obtain high-purity crystallization. The lactulose product is spray-dried to obtain a high-purity lactulose powder product.

In one embodiment, the method further comprises adding an alkaline solution to the aluminum hydroxide precipitate obtained in the step (2) to convert the aluminum hydroxide precipitate into a metaaluminate solution for a new round. Preparation of a syrup solution.

The invention has the following beneficial effects:

(1) The invention discloses acidity adjustment, dilution, dispersion and slag separation of lactulose syrup prepared by isomerization of lactose The operation results in the precipitation of lactulose clear liquid and aluminum hydroxide, and the sodium metaaluminate is converted into aluminum hydroxide to be removed, thereby effectively avoiding the use of a large amount of aluminum-containing wastewater generated by membrane separation means such as ultrafiltration;

(2) The invention realizes high-efficiency separation of aluminum hydroxide and slag liquid of lactulose syrup by physical sedimentation, centrifugation and filtration or a combination thereof, and recovers aluminum hydroxide to the utmost extent; the recovered aluminum hydroxide precipitate is treated by lye After being directly converted into metaaluminate, the catalyst can be repeatedly recycled, and the aluminum hydroxide flocculation and precipitation is wrapped with a large amount of lactulose, thereby causing the defect of low lactulose yield, and the production efficiency is effectively improved;

(3) The present invention performs an ion exchange resin adsorption treatment on the syrup before the membrane separation, and effectively removes residual aluminum ions, and finally the lactulose syrup contains no or only a very low amount (Al ³⁺ <10 ppm, the quality of the lactulose The aluminum ion meets the requirements of edible and pharmaceutical grade lactulose standards, and the subsequent purification operation does not require an additional dealumination step, which simplifies the production process while avoiding the influence of aluminum ions on membrane separation performance;

(4) The present invention prepares lactulose by high-isomerization of lactose by using sodium metaaluminate/sodium hydroxide as a basic complex catalyst, and the conversion rate reaches 85%, and the lactulose concentration reaches 360 g/L, which is much higher than At present, the conversion rate of lactulose and lactulose concentration are prepared by using boric acid/sodium hydroxide system; the lactulose clear solution is treated with desalting and monosaccharide to obtain high-purity lactulose solution, which can be used to prepare high-purity lactulose syrup and crystal lactulose And high-purity lactulose powder and other products.

(5) The preparation method of the invention meets the resource-saving and environment-friendly production requirements, and provides a useful reference and reference for promoting the industrial production of clean, high-efficiency and environmentally-friendly lactulose.

DRAWINGS

1 is a process flow diagram of a continuous cycle preparation method of a high-purity lactulose solution and a subsequent product of the present invention.

Specific implementation

Lactulose purity test method:

The specific procedure for determining the purity of lactulose by HPLC is as follows: after sampling, centrifugation (8000-12000 rpm, 15-20 min), the supernatant is filtered through a 0.22 μm microporous membrane, and the filtrate is loaded for HPLC analysis.

The specific detection conditions for determining the purity of lactulose by HPLC were as follows: chromatograph: Waters 209; column: Lichrosorb 3.9 x 150 mm NH ₂ column; mobile phase: 75% (v/v) acetonitrile/water solution; mobile phase flow rate: 1 mL/ Min; temperature: 25 ° C; detector: R401 differential refractive index detector; injection volume: 10 μL.

The following is a detailed description of the invention.

Example 1

The lactulose syrup prepared by catalytically isomerizing lactose by sodium metaaluminate is adjusted to a lactulose concentration of 100 g/L, and a hydrochloric acid solution is added dropwise to the above lactulose syrup under stirring to adjust the pH of the system to 5.5. Forming a mixed system of lactulose-aluminum hydroxide flocculation precipitation.

Adding 2 times volume of water to the above mixed system, stirring uniformly, then naturally sedimenting, then taking out the upper layer liquid, and then centrifuging the upper layer liquid to obtain lactulose syrup serum, and 2 g of dry resin in the lactulose syrup serum solution The ratio of /100mL syrup solution was added to the ion exchange resin. After static adsorption for 1 hour, the supernatant was taken out, and then subjected to nanofiltration desalting and demonosaccharide treatment to obtain a high-purity lactulose syrup solution. The purity of lactulose was 95%, and the residual of Al ion was 20 ppm. (For the quality of lactulose), the final yield of lactulose was 82% (w/w, for the quality of the produced lactulose), and the above solution was concentrated to finally obtain a high-purity lactulose syrup product having a solid content of 70%.

Example 2:

The lactulose syrup prepared by catalytically isomerizing lactose by sodium metaaluminate is adjusted to a lactulose concentration of 150 g/L, and a sulfuric acid solution is added to the above lactulose syrup under stirring to adjust the pH of the system to 6.5. Forming a mixed system of lactulose-aluminum hydroxide flocculation precipitation.

Adding 4 times volume of water to the above mixed system, stirring uniformly, the mixture is first centrifuged through a decanter centrifuge, and the liquid phase obtained by snail centrifugation is further centrifuged through a tube centrifuge to obtain a lactulose syrup solution. The clear liquid can be directly subjected to nanofiltration desalting and monosaccharide treatment to obtain a high-purity lactulose syrup solution. The purity of lactulose is 95%, the residual of Al ion is 10 ppm (the quality of lactulose), and the final yield of lactulose is 87% (w). /w, for the quality of the produced lactulose), the above solution was subjected to crystallization treatment to finally obtain lactulose crystals having a purity of 98%.

Example 3:

The lactulose syrup prepared by catalytically isomerizing lactose by sodium metaaluminate is adjusted to a lactulose concentration of 250 g/L, and a hydrochloric acid solution is added dropwise to the above lactulose syrup under stirring to adjust the pH of the system to 7.5. Forming a mixed system of lactulose-aluminum hydroxide flocculation precipitation.

After 7 times the volume of water in the above mixed system is stirred uniformly, the upper layer liquid is first obtained by natural sedimentation, and the upper layer liquid is filtered through a plate frame to obtain a filtrate, and the obtained filtrate is further centrifuged continuously through a tube centrifuge. The lactulose syrup clear solution is obtained, and the obtained clear liquid is passed through a resin column pre-charged into the ion exchange resin, and the effluent liquid is collected, and subjected to nanofiltration desalting and demonosaccharide treatment to obtain a high-purity lactulose syrup solution, and the lactulose purity is 98. %, Al ion residue is 5ppm (for lactulose mass), lactulose final yield is 90% (w/w, for the produced lactulose mass), the above solution is spray-dried to finally obtain 98% pure milk Fructose powder product.

Example 4:

Compared with Example 1, the lactulose syrup solution was directly subjected to nanofiltration desalting and demonosaccharide treatment, and the ion exchange resin treatment step was absent; other parameters or steps were consistent with Example 1.

The results showed that the obtained high-purity lactulose syrup solution had a purity of about 95%, but the Al ion residue was 86 ppm (for the lactulose mass).

Comparative Example 1:

Compared with Example 1, the mixed system of lactulose-aluminum hydroxide flocculation precipitation was directly subjected to subsequent treatment without dilution with water, and other parameters or steps were completely in accordance with Example 1.

The results showed that the obtained high-purity lactulose syrup solution had a purity of 95% lactulose and a residual of 20 ppm of Al ion (the quality of lactulose), but the final yield of lactulose was only 70-74% (w/w, for generation The lactulose mass was around, which was lower than the yield of 82% (w/w, for the added lactose mass) of Example 1.

Comparative Example 2:

In the patent, Carobbi et al. first used sodium metaaluminate to catalyze the preparation of lactulose from lactose, followed by Carobbi et al., Process for preparaing lactulose from lactose by epimerization with sodium aluminate. H ₂ SO ₄ (3N ~ 5N) is added in a continuous manner, in which part of the sodium metaaluminate is converted into aluminum hydroxide, then removed by centrifugation, and the resulting supernatant is removed by ultrafiltration/microfiltration. Residual aluminum hydroxide, and then the supernatant is then subjected to salt removal by ion exchange resin to prepare a lactulose syrup solution, and the centrifuged aluminum hydroxide precipitate is adjusted to pH by 48% (w/w) sodium hydroxide solution. It is 11-12, and after calcination at 700-800 ° C, sodium metaaluminate is obtained for recycling.

In this patent, (1) the sodium metaaluminate is converted to aluminum hydroxide by continuous acidification and centrifuged, which will inevitably lead to a large amount of lactulose loss in the precipitation of aluminum hydroxide. In this method, only the lactose loss caused by the step of removing aluminum hydroxide by centrifugation reaches 30% (accounting for the total amount of lactulose); (2) the method directly removes the acidified syrup to remove aluminum hydroxide by centrifugation. The single centrifugal operation has a limited effect of dealuminization. The residual aluminum hydroxide content after centrifugation in the patent is about 6000-8000ppm (for lactulose mass); (3) as described in the patent, the residual aluminum hydroxide is ultrafiltered. Or the microfiltration membrane separation method is removed. On the one hand, a large amount of waste water containing heavy metal aluminum is involved, which causes harm to the environment, and on the other hand, the removal effect of aluminum is limited (>500 ppm, the quality of lactulose); (4) As stated in the patent, the syrup solution after removal of aluminum hydroxide by ultrafiltration or microfiltration is directly subjected to desalting treatment through an ion exchange resin, which consumes a large amount of ion exchange resin and is difficult to treat small molecular sugars in the syrup. ( The sugar is effectively removed, the result will inevitably lead to high production cost, and the final purity of lactulose is low. As stated in the patent, the purity of the final syrup is only 88.80% (w/w), and the lactose content reaches 3.02% (w/ w), and up to 8.17% (w/w) of monosaccharide (galactose) is still present in the final syrup solution, difficult to remove by means of ion exchange resin; (5) as described in the patent After the aluminum hydroxide precipitation is treated with alkali solution and calcined and converted into sodium metaaluminate, the repeated use, the energy consumption is large and the lactulose encapsulated in the precipitate is completely lost during the calcination process, which inevitably leads to the yield of lactulose in the whole production process. Low and long process time.

Completely according to the steps described in the patent, the final lactulose yield is only 50%-60% (w/w, for the produced lactulose mass), aluminum ion residue >500ppm (for lactulose mass), and the final product Purity can only reach 88-90%, the product It contains a large amount of monosaccharide components (8.17% in terms of galactose) which is difficult to remove effectively.

Example 5: Preparation of high purity lactulose syrup

Under mechanical agitation, 20 kg of food grade lactose and 3 kg of sodium metaaluminate as lactose substrate were added to 100 L of deionized water and dissolved, then sodium hydroxide was added, and the pH of the system was adjusted to 11.5, then at 50 ° C. The reaction was stirred for 2 h. After completion of the reaction, the system was cooled to room temperature to obtain an isomerized lactulose syrup. The conversion of lactulose was 66% at this time, and the mass concentration of lactulose was 135 g/L. In this process, the present embodiment adjusts the reaction system, reacts under high concentration of lactose, weakens the hydrolysis of lactose, effectively increases the production rate of lactulose, and effectively avoids the hydrolysis of a large amount of lactose, which not only transforms the product. The rate is greatly improved and the purity of the product is also effectively improved.

Under a mechanical stirring condition, a 6 mol/L hydrochloric acid solution was added dropwise to the above isomerized lactulose syrup, and the pH of the system was adjusted to 6.5 to form a mixed solution containing an aluminum hydroxide flocculation precipitation system.

100L of deionized water was added to the above mixture, and the aluminum hydroxide flocculation and precipitation system was fully dispersed into fine aluminum hydroxide particles by mechanical stirring, and then the fructose clear liquid and hydrogen were obtained by plate and frame filtration through a plate and frame filter. Alumina precipitated.

The aluminum hydroxide precipitate was redissolved with a 5 mol/L sodium hydroxide solution and converted to sodium metaaluminate, which was then added to the new lactose substrate for the next round of lactose isomerization.

The above-mentioned lactulose clear solution was subjected to desalting and demonosaccharide treatment using a nanofiltration membrane (molecular weight cutoff of 250 Da) until the conductivity of the lactulose solution reached 50 μs/cm, thereby obtaining a high-purity lactulose solution, and finally the Al in the lactulose clear liquid. The residue was 268 ppm (for lactulose mass) and the purity of lactulose was 95% as determined by HPLC. The above solution was concentrated to finally obtain 10.8 kg of high-purity lactulose syrup, and the yield of lactulose was 82% (w/w, for the quality of the produced lactulose).

Example 6: Preparation of crystallized lactulose

Under mechanical agitation, 35 kg of food grade lactose and 8 kg of sodium metaaluminate as lactose substrate were added to 100 L of deionized water and dissolved, then sodium hydroxide was added, and the pH of the system was adjusted to 12.0, then at 60 ° C. The reaction was stirred for 1 h, and after completion of the reaction, the system was cooled to room temperature to obtain an isomerized lactulose syrup. The conversion of lactulose was 85% and the concentration of lactulose was 298 g/L as determined by HPLC. In this process, the present embodiment adjusts the reaction system, reacts under high concentration of lactose, weakens the hydrolysis of lactose, effectively increases the production rate of lactulose, and effectively avoids the hydrolysis of a large amount of lactose, which not only transforms the product. The rate is greatly improved and the purity of the product is also effectively improved.

Under mechanical stirring, 10 mol/L of sulfuric acid was added dropwise to the above isomerized lactulose syrup, and the pH of the system was adjusted to 5.0 to form a mixed solution containing an aluminum hydroxide flocculation precipitation system.

200L of deionized water was added to the above mixture, and the aluminum hydroxide flocculation and precipitation system was fully dispersed into fine aluminum hydroxide particles by mechanical stirring, and then centrifuged by a centrifuge (decanter centrifuge-tubular centrifuge) ) Precipitate to lactulose clear solution and aluminum hydroxide.

The aluminum hydroxide precipitate was redissolved using a 6 mol/L sodium hydroxide solution and converted to sodium metaaluminate, which was then added to the new lactose substrate for the next round of lactose isomerization.

The above-mentioned lactulose clear solution was subjected to desalting and demonosaccharide treatment using a nanofiltration membrane (molecular weight cutoff of 250 Da) until the conductivity of the lactulose solution reached 50 μs/cm, thereby obtaining a high-purity lactulose solution, and finally the Al in the lactulose clear liquid. The residue was 50 ppm (for lactulose mass) and the purity of lactulose was 96% as determined by HPLC. The above solution was subjected to crystallization treatment to finally obtain 25 kg of crystallized lactulose, and the yield of lactulose was 84% (w/w, for the quality of the produced lactulose).

Example 7: Preparation of high purity lactulose powder

Under mechanical agitation, 50 kg of food grade lactose and 24 kg of sodium metaaluminate as lactose substrate were added to 100 L of deionized water and dissolved, then sodium hydroxide was added, and the pH of the system was adjusted to 12.5, then at 65 ° C. The reaction was stirred for 45 min. After completion of the reaction, the system was cooled to room temperature to obtain an isomerized lactulose syrup. The conversion of lactulose was 72% and the concentration of lactulose was 360 g/L as determined by HPLC.

Under mechanical stirring, 10 mol/L hydrochloric acid was added dropwise to the above isomerized lactulose syrup, and the pH of the system was adjusted to 5.5 to form a mixed solution containing an aluminum hydroxide flocculation precipitation system.

To the above mixture, 300 L of deionized water was added, and the aluminum hydroxide flocculation and precipitation system was sufficiently dispersed into fine aluminum hydroxide particles by mechanical stirring, and then the lactulose clear liquid and the aluminum hydroxide precipitate were obtained by suction filtration.

The above-mentioned lactulose clear solution was subjected to desalting and demonosaccharide treatment using a nanofiltration membrane (molecular weight cutoff of 250 Da) until the conductivity of the lactulose solution was 50 μs/cm, thereby obtaining a high-purity lactulose solution, and finally the Al in the lactulose clear liquid. The residue was 190 ppm (for lactulose mass) and the purity of lactulose was 95% as determined by HPLC. The above solution was spray-dried to finally obtain 32.4 kg of high-purity lactulose powder, and the yield of lactulose was 90% (w/w, for the quality of the produced lactulose).

Although the present invention has been disclosed in the above preferred embodiments, the present invention is not limited thereto, and various modifications and changes can be made thereto without departing from the spirit and scope of the invention. The scope of the invention should be determined by the scope of the claims.

Claims

A method for efficiently removing sodium metaaluminate to prepare high-purity lactulose, characterized in that the method comprises the following steps:

(1) Pretreatment of syrup:

Adjusting the syrup solution to a lactulose concentration of 10 to 500 g/L, and then adding an acidic substance to adjust the pH of the system to 3.5 to 8.0 to obtain a mixed solution containing an aluminum hydroxide flocculation precipitation system; wherein the syrup solution refers to partial Sodium aluminate is a catalyst for catalyzing the preparation of a syrup solution of lactose or a substance containing lactose;

(2) Separation of slag liquid:

Adding 1 to 10 volumes of water to the mixed solution containing the aluminum hydroxide flocculation and precipitation system obtained in the step (1), dispersing the aluminum hydroxide flocculation precipitation system into aluminum hydroxide particles by stirring, and releasing the aluminum hydroxide flocculation The lactulose encapsulated in the precipitation system is separated by a slag liquid to obtain a lactulose clear liquid and a precipitate of aluminum hydroxide;

(3) Purification of lactulose supernatant:

The lactulose supernatant obtained in the step (2) is subjected to nanofiltration treatment to remove salts and monosaccharides to obtain a high-purity lactulose syrup solution.
The method according to claim 1, further comprising the step of adding an ion exchange resin treatment step to the lactulose clear liquid between the step (2) and the step (3); The supernatant obtained in the step (2) is subjected to adsorption treatment to remove residual aluminum ions.
The method of claim 2 wherein said ion exchange resin comprises, but is not limited to, a strongly acidic cation exchange resin, a weakly acidic cation exchange resin.
The method according to claim 1, wherein the slag liquid separation in the step (2) refers to any one of a sedimentation, filtration, and centrifugation or a combination of several operations.
The method according to claim 1, wherein the nanofiltration membrane used in the nanofiltration in the step (3) has a molecular weight cut off between 200 and 300 Da.
The method according to any one of claims 1 to 5, characterized in that the method further comprises subjecting the high-purity lactulose syrup solution obtained in the step (3) to a subsequent treatment to prepare a high-purity lactulose product.
The method according to any one of claims 1 to 6, characterized in that the method further comprises adding an alkaline solution to the precipitate of aluminum hydroxide obtained in the step (2) to convert the precipitate of aluminum hydroxide into metaaluminic acid. Salt solution for the preparation of a new round of syrup solution.
The method according to any one of claims 1 to 7, wherein the preparation of the syrup solution of the method step (1) is specifically: adding a lactose substrate to water, stirring to dissolve it, and obtaining a mass concentration of 10 ~ 500g / L of lactose solution; according to the weight ratio of sodium metaaluminate: lactose substrate = 0.02 ~ 1:1, add sodium metaaluminate to the lactose solution, stir to dissolve, then add sodium hydroxide, will The pH of the reaction system is adjusted to 9.0 to 13.0, and then the reaction is stirred at 40 to 80 ° C. After 20 to 240 minutes; after the reaction is completed, the reaction system is cooled to room temperature to obtain an isomerized lactulose syrup, that is, a syrup solution containing lactulose.
A lactulose syrup solution prepared by the method according to any one of claims 1 to 8.
The lactulose product obtained by the subsequent treatment of the lactulose syrup solution prepared by the method according to any one of claims 1 to 8.