A process for the preparation of mannitol

Abstract

The application discloses a preparation method of mannitol, and is characterized by comprising the following steps: S1, preparing a hydrolysis substrate into an aqueous solution, wherein the hydrolysis substrate is hemicellulose or maltose; S2, adding a solid acid catalyst into the aqueous solution in step S1, and hydrolyzing for 2-6 hours; S3, adding ammonium molybdate into the hydrolyzed aqueous solution in step S2, and performing isomerization reaction for 1-4 hours; S4, filtering the solution after the isomerization reaction in step S3, and removing the solid acid catalyst; S5, adding a hydrogenation catalyst into the filtered solution in step S4, performing hydrogenation, filtering, and obtaining a hydrogenated solution; and S6, purifying mannitol from the hydrogenated solution in step S5 to obtain the mannitol. The process provided by the application is simple, the product is convenient to purify, the purity is high, and the application value is good.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of mannitol synthesis, and particularly relates to a preparation method of mannitol. BACKGROUND

[0002] Mannitol (D-mannitol) is also known as D-mannitol, wood honey alcohol, and its molecular formula is C6H 14 O6, and its molecular weight is 182.1. D-mannitol is a white needle-like or rhombic prism crystal, has a cool sweet taste, and its sweetness is 57% to 72% of that of sucrose. D-mannitol is slightly soluble in methanol and ethanol, insoluble in ethers, and has no hygroscopicity. D-mannitol has the chemical properties of polyols, and can be esterified, etherified, oxidized, and dehydrated. Therefore, D-mannitol is widely used in medicine, food, textiles, and chemical industry.

[0003] There are many production methods of mannitol, but the main methods include kelp extraction method, sugar hydrolysis catalytic hydrogenation method, glucose electrolytic reduction method, and biological enzyme chemical catalyst combined action to prepare mannitol. The kelp extraction method is the main method for producing mannitol in China, and it is a method of extracting mannitol from the wastewater after extracting iodine and sodium alginate from kelp. The sugar hydrolysis catalytic hydrogenation method is to reduce 50% sucrose aqueous solution under the condition of nickel catalyst at 500 Mpa and high temperature to obtain the product, and the total yield is 100%. The product is obtained by catalytic hydrogenation reduction in a suspension reactor or a tubular reactor under the condition of nickel catalyst, and then the reaction liquid is filtered, decolorized, refined, concentrated, cooled, and crystallized to separate the product. The glucose electrolytic reduction method uses starch hydrolysis glucose as raw material to electrolyze glucose in an electrode tank to obtain mannitol, and the conversion rate is 99.8%. Then, the product is obtained by neutralization, evaporation, desalination, crystallization, refinement, and drying. This method consumes too much energy, and is generally not adopted. The biological enzyme method uses a special biological catalyst, enzyme, to convert glucose in the raw material into fructose, and then converts it into the final product by chemical catalyst hydrogenation.

[0004] CN115364856 A discloses a catalyst for hydrogenation of fructose to prepare mannitol and a preparation method thereof. The preparation method comprises the following steps: (1) dissolving an active component precursor and urea in water to obtain a mixed solution, then adding an alkaline silica sol, stirring and mixing, and then adjusting the pH to 8.5-9.5 by using ammonia water to obtain a precipitate suspension; (2) transferring the precipitate suspension to a reaction kettle and placing it in a dynamic homogeneous reactor, and then performing hydrothermal reaction at 200-250 DEG C for 10-15 hours, and then performing subsequent conventional operations. However, this process has high reaction temperature and long reaction time, and the reaction conditions are relatively harsh. SUMMARY

[0005] The present application provides a preparation method of mannitol, which has the advantages of simple process, convenient product purification, high purity and good popularization and application value.

[0006] The present application provides a preparation method of mannitol, which has the advantages of simple process, convenient product purification, high purity and good popularization and application value.

[0007] S1: the hydrolysis substrate is prepared into an aqueous solution, and is fully mixed by stirring, and the concentration of the hydrolysis substrate is 45-60wt%, and the hydrolysis substrate is hemicellulose or maltose, and the product obtained when the hydrolysis substrate is hemicellulose has higher purity;

[0008] S2: the solid acid catalyst is added into the aqueous solution in step S1, and is heated to 90-130 DEG C, and is hydrolyzed for 2-6h;

[0009] S3: the aqueous solution after hydrolysis in step S2 is added with ammonium molybdate, and is subjected to isomerization reaction at a temperature of 90-130 DEG C for 1-4h, and the isomerization reaction in the presence of the solid acid has better selectivity, and the finally prepared mannitol has higher purity;

[0010] S4: the solution after isomerization reaction in step S3 is filtered to remove the solid acid catalyst, and then is subjected to decolorization with activated carbon

[0011] and adsorption of the micro solid therein, and is filtered again;

[0012] S5: the solution after filtration in step S4 is added with a hydrogenation catalyst, and is subjected to hydrogenation, and the reaction temperature is controlled to be 90-130 DEG C, the reaction pressure is 0.5-2MPa, and the reaction time is 4-6h, and then is filtered to obtain a solution after hydrogenation;

[0013] S6: the mannitol in the solution after hydrogenation in step S5 is purified to obtain mannitol.

[0014] Further, the hemicellulose in step S1 is polyglucose mannose hemicellulose. Because there are many types of hemicellulose, and most of the types have low conversion rate and low product purity, only the polyglucose mannose hemicellulose can be converted into mannitol at high yield through screening.

[0015] Further, the hemicellulose in step S1 is hemicellulose prepared from coniferous wood, and the hemicellulose prepared from coniferous wood is hemicellulose prepared from Chinese fir or cypress. The preparation method of the above hemicellulose is as follows: the Chinese fir or cypress powder, alkali and water are mixed, and are rapidly stirred, and are heated to 50-80 DEG C, and are stirred for 15 min, and are centrifuged, and the obtained filtrate is a hemicellulose extraction solution; ethanol is added into the hemicellulose extraction solution to precipitate the hemicellulose, and the hemicellulose is filtered and dried. The polyglucose mannose content in the Chinese fir or cypress hemicellulose is high, and the hemicellulose has good effect as a raw material for synthesizing mannitol.

[0016] Further, the solid acid catalyst in step S2 is at least one of Hβ molecular sieve catalyst, carbon-based sulfonic acid catalyst, and natural zeolite catalyst. Hydrolysis is carried out using the solid acid catalyst instead of inorganic acid, which is more environmentally friendly. When natural zeolite is used as the catalyst, good experimental results can also be obtained after prolonging the reaction time.

[0017] Further, the solid acid catalyst in step S2 is at least one of Hβ molecular sieve catalyst, carbon-based sulfonic acid catalyst, and natural zeolite catalyst. Hydrolysis is carried out using the solid acid catalyst instead of inorganic acid, which is more environmentally friendly. When natural zeolite is used as the catalyst, good experimental results can also be obtained after prolonging the reaction time.

[0018] Further, the amount of ammonium molybdate added in step S3 is 0.1-0.5wt% of the mass of hemicellulose. When the hydrolysis substrate is maltose, more ammonium molybdate is needed to have a better isomerization reaction. When the hydrolysis substrate is hemicellulose, the content of mannose in the hydrolysis product is higher, and the isomerization reaction is prone to occur, so less ammonium molybdate is needed.

[0019] Further, the hydrogenation catalyst in step S5 is Raney nickel, and the amount of Raney nickel added is 3-8wt% of the mass of hemicellulose.

[0020] Further, the hydrogenation catalyst in step S5 is metal powder and 37% hydrochloric acid. The amount of metal powder added is 5-10wt% of the mass of hemicellulose, and the amount of 37% hydrochloric acid added is 15-30wt% of the mass of hemicellulose. The composition of the metal powder is 45wt% tin powder and 55wt% palladium powder. When metal powder and 37% hydrochloric acid are used as catalysts, on the one hand, palladium can be used as a catalyst for hydrogenation, and on the other hand, the hydrogen atoms generated by the reaction of hydrochloric acid and tin powder have good hydrogenation activity. Under the synergistic action of the two, the hydrogenation effect is very good, and the conversion rate of mannitol is very high.

[0021] Further, the purification method in step S6 is as follows. The solution after hydrogenation in step S5 is added with inorganic salt to precipitate mannitol, and then the first filtration, washing, and drying are carried out to obtain the mannitol product. The filtrate is further cooled to 5-10℃ to further precipitate mannitol, and then the second filtration, washing, and drying are carried out to obtain the mannitol product. The inorganic salt is one of sodium chloride and sodium acetate. When sodium acetate is used as the salting-out reagent, the purity of the product is higher.

[0022] Further, the purification method in step S6 is as follows. The solution after hydrogenation in step S5 is added with inorganic salt to precipitate mannitol, and then the first filtration, washing, and drying are carried out to obtain the mannitol product. The filtrate is further cooled to 5-10℃ to further precipitate mannitol, and then the second filtration, washing, and drying are carried out to obtain the mannitol product. The inorganic salt is one of sodium chloride and sodium acetate. When sodium acetate is used as the salting-out reagent, the purity of the product is higher. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0025] Example 1

[0026] A method for preparing mannitol, characterized by comprising the following steps:

[0027] S1: Prepare an aqueous solution of maltose and stir thoroughly. The concentration of maltose is 45 wt%.

[0028] S2: Add a carbon-based sulfonic acid catalyst, with a mass of 5 wt% of the maltose mass, to the aqueous solution from step S1, and then...

[0029] Hydrolyze at 90–110℃ for 2 hours;

[0030] S3: Add ammonium molybdate (0.5 wt% of the maltose mass) to the aqueous solution after hydrolysis in step S2 and carry out the isomerization reaction for 2 hours at a temperature between 90 and 110°C.

[0031] S4: Filter the solution after the isomerization reaction in step S3 to remove the carbon-based sulfonic acid catalyst, and then use activated carbon to remove the catalyst.

[0032] It absorbs and adsorbs the tiny solids within, and then filters them again;

[0033] S5: Add the Raney nickel hydrogenation catalyst (4 wt% of maltose mass) to the filtered solution from step S4 for hydrogenation. Control the reaction temperature at 90–110°C, the reaction pressure at 1–2 MPa, and the reaction time at 4 h. Filter.

[0034] The hydrogenated solution is obtained;

[0035] S6: Add sodium chloride to the hydrogenated solution from step S5 to precipitate mannitol. Filter the solution for the first time, wash and dry to obtain the mannitol product. Continue to cool the filtrate to 5-10°C to further precipitate mannitol. Filter the solution for the second time, wash and dry to obtain the mannitol product with a purity of 99.0%.

[0036] Example 2

[0037] A method for preparing mannitol, characterized by comprising the following steps:

[0038] S1: hemicellulose is prepared into an aqueous solution, and is fully mixed by stirring, and the concentration of the hemicellulose is 45wt%, and the hemicellulose is a polyglucamannan hemicellulose, and the preparation method is that cedar powder, alkali and water are mixed, and then fast stirring is performed, and the temperature is raised to 50-80℃, and stirring is performed for 15min, and centrifugation is performed, and the obtained filtrate is a hemicellulose extraction solution; ethanol is added into the hemicellulose extraction solution, so that the hemicellulose is precipitated, and filtration and drying are performed, and the hemicellulose is obtained;

[0039] S2: the aqueous solution in step S1 is added with an Hβ molecular sieve catalyst, the mass of the Hβ molecular sieve catalyst is 12wt% of the mass of the hemicellulose, and the temperature is raised to 110-130℃, and hydrolysis is performed for 4h;

[0040] S3: the aqueous solution after hydrolysis in step S2 is added with ammonium molybdate, the mass of the ammonium molybdate is 0.1wt% of the mass of the hemicellulose, the temperature is between 90-110℃, and isomerization reaction is performed for 4h;

[0041] S4: the solution after isomerization reaction in step S3 is filtered, the Hβ molecular sieve catalyst is removed, and then activated carbon is used for decolorization and adsorption of small solid substances, and filtration is performed again;

[0042] S5: the solution after filtration in step S4 is added with a metal powder and a 37% hydrochloric acid hydrogenation catalyst, the mass of the metal powder is 6wt% of the mass of the hemicellulose, the mass of the 37% hydrochloric acid is 20wt% of the mass of the hemicellulose, the composition of the metal powder is 45wt% tin powder and 55wt% palladium powder, hydrogenation is performed, the reaction temperature is controlled to be 110-130℃, the reaction pressure is 0.5-1MPa, the reaction time is 6h, and filtration is performed, and the solution after hydrogenation is obtained;

[0043] S6: the solution after hydrogenation in step S5 is added with sodium acetate, and mannitol is precipitated, first filtration is performed, washing and drying are performed, and the mannitol product is obtained, the filtrate is further cooled to 5-10℃, and mannitol is further precipitated, second filtration, washing and drying are performed, and the mannitol product is obtained, and the purity is 99.4%.

[0044] Example 3

[0045] A preparation method of mannitol, characterized in that the method comprises the following steps:

[0046] S1: hemicellulose is prepared into an aqueous solution, and is fully mixed by stirring, and the concentration of the hemicellulose is 45wt%, and the hemicellulose is a polyglucamannan hemicellulose, and the preparation method is that cedar powder, alkali and water are mixed, and then fast stirring is performed, and the temperature is raised to 50-80℃, and stirring is performed for 15min, and centrifugation is performed, and the obtained filtrate is a hemicellulose extraction solution; ethanol is added into the hemicellulose extraction solution, so that the hemicellulose is precipitated, and filtration and drying are performed, and the hemicellulose is obtained;

[0047] S2: adding natural zeolite to the aqueous solution in step S1, the mass of the natural zeolite being 12% of the mass of the hemicellulose, and heating to 110-130°C, and hydrolyzing for 6 hours;

[0048] S3: adding ammonium molybdate to the aqueous solution after hydrolysis in step S2, the mass of the ammonium molybdate being 0.2% of the mass of the hemicellulose, and isomerizing at a temperature of 90-110°C for 4 hours;

[0049] S4: filtering the solution after isomerization in step S3, removing the natural zeolite, and then decolorizing with activated carbon and adsorbing the fine solids, and filtering again;

[0050] S5: adding metal powder and 37% hydrochloric acid to the filtered solution in step S4, the mass of the metal powder being 10% of the mass of the hemicellulose, and the mass of the 37% hydrochloric acid being 30% of the mass of the hemicellulose, the metal powder comprising 45% tin powder and 55% palladium powder, and hydrogenating, the reaction temperature being controlled at 110-130°C, the reaction pressure being 0.5-1 MPa, and the reaction time being 6 hours, and filtering to obtain a hydrogenated solution;

[0051] S6: directly cooling the hydrogenated solution in step S5 to 5-10°C to precipitate mannitol, and filtering, washing, and drying to obtain a mannitol product with a purity of 99.1%.

[0052] Comparative Example 1

[0053] A method for preparing mannitol, comprising the following steps:

[0054] S1: preparing an aqueous solution of maltose, and stirring to mix thoroughly, the concentration of the maltose being 45% by mass;

[0055] S2: adding a carbon-based sulfonic acid catalyst to the aqueous solution in step S1, the mass of the carbon-based sulfonic acid catalyst being 5% of the mass of the maltose, and heating to 90-110°C, and hydrolyzing for 2 hours;

[0056] S3: adding ammonium molybdate to the aqueous solution after hydrolysis in step S2, the mass of the ammonium molybdate being 0.5% of the mass of the maltose, and isomerizing at a temperature of 90-110°C for 2 hours;

[0057] S4: filtering the solution after isomerization in step S3, removing the carbon-based sulfonic acid catalyst, and then decolorizing with activated carbon and adsorbing the fine solids, and filtering again;

[0058] S5: adding Raney nickel to the filtered solution in step S4, the mass of the Raney nickel being 4% of the mass of the maltose, and hydrogenating, the reaction temperature being controlled at 90-110°C, the reaction pressure being 1-2 MPa, and the reaction time being 4 hours, and filtering to obtain a hydrogenated solution.

[0059] S6: The hydrogenated solution in step S5 is directly cooled to 5-10°C to precipitate mannitol, which is filtered, washed, and dried to obtain a mannitol product with a purity of 89.2%.

[0060] Compared with Example 1, the purity of the product is reduced after the purification method is changed, indicating that when maltose is used as the hydrolysis substrate, there are more impurities in the final hydrogenated solution, mainly because there is still a large amount of glucose after the isomerization reaction, which affects the final purity. Only by using the optimal purification scheme in Example 1 can the purity of the product be higher.

[0061] Comparative Example 2

[0062] A method for preparing mannitol, characterized in that it comprises the following steps:

[0063] S1: Hemicellulose is prepared into an aqueous solution, and is fully mixed by stirring. The concentration of the hemicellulose is 45 wt%. The hemicellulose is polyglucomannan hemicellulose, and the preparation method is to mix cedar powder, alkali, and water, then quickly stir, heat to 50-80°C, stir for 15 min, and centrifuge to obtain a hemicellulose extract. Ethanol is added to the hemicellulose extract to precipitate the hemicellulose, which is filtered and dried to obtain the hemicellulose.

[0064] S2: Natural zeolite is added to the aqueous solution in step S1, and the mass of the natural zeolite is 12 wt% of the mass of the hemicellulose. The aqueous solution is heated to 110-130°C, and hydrolysis is performed for 6 h.

[0065] S3: The aqueous solution after hydrolysis in step S2 is added with ammonium molybdate, and the mass of the ammonium molybdate is 0.2 wt% of the mass of the hemicellulose. The temperature is controlled between 90-110°C, and isomerization is performed for 4 h.

[0066] S4: The solution after isomerization in step S3 is filtered to remove the natural zeolite, then decolorized with activated carbon and adsorbed to remove small solid particles, and then filtered again.

[0067] S5: The filtered solution in step S4 is added with a metal powder and 37% hydrochloric acid hydrogenation catalyst. The mass of the metal powder is 10 wt% of the mass of the hemicellulose, and the mass of the 37% hydrochloric acid is 30 wt% of the mass of the hemicellulose. The metal powder is 100 wt% palladium powder. Hydrogenation is performed with the reaction temperature controlled at 110-130°C, the reaction pressure controlled at 0.5-1 MPa, and the reaction time controlled at 6 h. The solution is filtered to obtain a hydrogenated solution.

[0068] S6: The hydrogenated solution in step S5 is directly cooled to 5-10°C to precipitate mannitol, which is filtered, washed, and dried to obtain a mannitol product with a purity of 89.2%. The purity of the product is reduced because tin powder is not added in step S5, indicating that the presence of tin powder has a very large impact on the hydrogenation reaction.

[0069] Comparative Example 3

[0070] A method for preparing mannitol, characterized in that it comprises the following steps:

[0071] S1: hemicellulose is prepared into an aqueous solution, and is fully mixed by stirring, the concentration of the hemicellulose is 45 wt%, the hemicellulose is polyglucorannan hemicellulose, and the preparation method is as follows: cedar powder, alkali and water are mixed, rapid stirring is performed after the temperature is raised to 50-80 DEG C, stirring is performed for 15 min, and the obtained filtrate is a hemicellulose extraction solution; ethanol is added to the hemicellulose extraction solution to precipitate the hemicellulose, filtration and drying are performed, and the hemicellulose is obtained;

[0072] S2: natural zeolite is added to the aqueous solution in step S1, the mass of the natural zeolite is 12 wt% of the mass of the hemicellulose, and the temperature is raised to 110-130 DEG C, hydrolysis is performed for 6 h, and the natural zeolite is removed by filtration;

[0073] S3: the aqueous solution after hydrolysis in step S2 is added with ammonium molybdate, the mass of the ammonium molybdate is 0.2 wt% of the mass of the hemicellulose, the temperature is between 90-110 DEG C, and isomerization is performed for 4 h;

[0074] S4: the solution after isomerization in step S3 is subjected to decolorization and adsorption of small solid particles in the solution by using activated carbon, and is filtered again;

[0075] S5: the filtered solution in step S4 is added with a metal powder and a 37% hydrochloric acid hydrogenation catalyst, the mass of the metal powder is 10 wt% of the mass of the hemicellulose, the mass of the 37% hydrochloric acid is 30 wt% of the mass of the hemicellulose, the metal powder comprises 45 wt% tin powder and 55 wt% palladium powder, hydrogenation is performed, the reaction temperature is controlled to be 110-130 DEG C, the reaction pressure is 0.5-1 MPa, the reaction time is 6 h, and filtration is performed, and the hydrogenated solution is obtained;

[0076] S6: the hydrogenated solution in step S5 is directly cooled to 5-10 DEG C, mannitol is precipitated, filtration, washing and drying are performed, and the mannitol product is obtained, and the purity is 93.1%.

[0077] The "filtration and removal of the natural zeolite" in step S4 is moved to step S2, there is no solid acid in the isomerization reaction, and the purity of the final product is reduced, which indicates that the presence of the solid acid is beneficial to the isomerization reaction and affects the final purity of the product.

Claims

1. A process for the preparation of mannitol, characterized in that, The method comprises the following steps: S1: preparing a hydrolysis substrate into an aqueous solution, stirring and mixing thoroughly, the concentration of the hydrolysis substrate is 45-60wt%, the hydrolysis substrate is hemicellulose or maltose; S2: adding a solid acid catalyst into the aqueous solution in step S1, and heating to 90-130℃, hydrolyzing for 2-6h; S3: adding ammonium molybdate into the hydrolyzed aqueous solution in step S2, and isomerizing at a temperature of 90-130℃ for 1-4h; S4: filtering the solution after isomerization in step S3 to remove the solid acid catalyst, then decolorizing and adsorbing small solid particles in the solution by using activated carbon, and filtering again; S5: adding a hydrogenation catalyst into the filtered solution in step S4, and hydrogenating, the reaction temperature is controlled to be 90-130℃, the reaction pressure is 0.5-2MPa, the reaction time is 4-6h, filtering to obtain a hydrogenated solution; S6: purifying mannitol from the hydrogenated solution in step S5 to obtain mannitol; The solid acid catalyst in step S2 is Hβ molecular sieve catalyst; The hydrogenation catalyst in step S5 is metal powder and 37% hydrochloric acid, the addition amount of the metal powder is 5-10wt% of the mass of the hemicellulose, the addition amount of the 37% hydrochloric acid is 15-30wt% of the mass of the hemicellulose, the composition of the metal powder is 45wt% tin powder and 55wt% palladium powder; The purification method in step S6 is that, after the hydrogenated solution in step S5, an inorganic salt is added to precipitate mannitol, the first filtration, washing and drying obtain the mannitol product, the filtrate is further cooled to 5-10℃ to further precipitate mannitol, the second filtration, washing and drying obtain the mannitol product, the inorganic salt is one of sodium chloride and sodium acetate.

2. The process for the preparation of mannitol according to claim 1, characterized in that, The hemicellulose in step S1 is polyglucuronoxylan hemicellulose.

3. The process for the preparation of mannitol according to claim 2, characterized in that, The hemicellulose in step S1 is coniferous wood hemicellulose, the coniferous wood hemicellulose is hemicellulose prepared from Chinese fir or cypress.

4. The method of claim 1, wherein the mannitol is prepared by a process comprising: The addition amount of the solid acid catalyst in step S2 is 3-15wt% of the mass of the hemicellulose.

5. The method for preparing mannitol according to claim 1, characterized in that, The addition amount of the ammonium molybdate in step S3 is 0.1-0.5wt% of the mass of the hemicellulose.

6. The method for preparing mannitol according to claim 1, characterized in that, The hydrogenation catalyst in step S5 is Raney nickel, and the addition amount is 3-8wt% of the mass of the hemicellulose.