Anhydrous lactitol and preparation method thereof

Abstract

The invention discloses anhydrous lactitol and a preparation method thereof, and belongs to the technical field of sugar alcohol preparation. The preparation method of the anhydrous lactitol comprises the following steps: S1, adjusting the pH value of a lactose solution, adding sodium citrate, and carrying out a hydrogenation reaction to obtain a hydrogenation reaction solution; s2, sequentially carrying out decoloration, ion exchange and vacuum concentration on the hydrogenation reaction solution to obtain a concentrated solution; s3, sequentially carrying out heating crystallization, cooling crystallization, centrifugation and drying on the concentrated solution to obtain anhydrous lactitol; through specific control of the crystallization process, the anhydrous lactitol is uniform in form, is in an orthorhombic shape, is high in melting point and narrow in melting range, the melting range is 145-150 DEG C, and the product stability is higher. The temperature in the crystallization process is controlled to be 70-80 DEG C, the crystallization yield is ensured through heating crystallization and cooling crystallization, the primary crystallization yield is 60-65%, the energy consumption is lower, and the crystal morphology can be kept not to change by controlling separation and drying.

Description

Technical Field

[0001] The invention belongs to the technical field of sugar alcohol preparation, and particularly relates to anhydrous lactitol and a preparation method thereof. Background Art

[0002] Lactitol, with the chemical name 4-O-β-D-galactopyranosyl-D-sorbitol, is a low-calorie sweetener with mild sweetness, no aftertaste, and only half the calories of sucrose, making it a good substitute for sucrose. The physiological effects of lactitol include: 1. It has prebiotic effects, can regulate intestinal flora, and improve the body's immunity; 2. Lactitol can effectively treat constipation; 3. Lactitol can prevent dental caries; 4. The GI value of lactitol is only 2~3, and its metabolism does not depend on insulin, so it can be used as a sweetener for diabetic patients. Due to its significant physiological effects, lactitol is widely used in the fields of food, medicine and health products.

[0003] Anhydrous lactitol is a type of lactitol that does not contain water of crystallization and is a crystalline powder. Due to its low water activity, high stability and excellent performance, it is more suitable for use in low water activity foods, instant foods, pharmaceutical excipients or fillers. At present, anhydrous lactitol is mostly obtained by high-temperature crystallization. Because the solubility of lactitol increases under high temperature conditions, in order to improve the production yield, the temperature range is generally controlled in the range of 98°C to 70°C, and a large temperature difference is used to stimulate crystallization and improve the yield of the product. The maximum temperature of this type of method reaches above 95°C, consuming a large amount of steam or other energy, and the lactitol concentration also reaches more than 90%. The viscosity of the lactitol solution is extremely high, which affects the molecular movement in the solution, resulting in non-uniform product morphology, both regular octahedral and rhombohedral, with a low melting point and a large melting range. Patent CN 119143817 A discloses a method for preparing anhydrous lactitol crystals with controllable particle size, which utilizes gradient temperature drying of monohydrate or dihydrate lactitol to obtain anhydrous lactitol. However, this method cannot achieve continuous discharging and is not suitable for large-scale production.

[0004] Therefore, there is an urgent need for an anhydrous lactitol with uniform morphology, low energy consumption, high yield and continuous production. Summary of the invention

[0005] In view of this, the object of the present invention is to provide anhydrous lactitol and a preparation method thereof. The present invention specifically controls the crystallization process so that the obtained anhydrous lactitol product has a uniform morphology, a rhombohedral shape, a high melting point, and a narrow melting range. The obtained product has a melting range of 145-150°C, and the product stability is stronger.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] In a first aspect, the present invention provides a method for preparing anhydrous lactitol, comprising the following steps:

[0008] S1. adjusting the pH of the lactose solution and adding sodium citrate to carry out a hydrogenation reaction to obtain a hydrogenation reaction solution;

[0009] S2. The hydrogenation reaction liquid is sequentially subjected to decolorization, ion exchange, and vacuum concentration to obtain a concentrated solution;

[0010] S3. The concentrated solution is subjected to sequential heating crystallization, cooling crystallization, centrifugation and drying to obtain anhydrous lactitol.

[0011] Preferably, the specific method of the temperature-raising crystallization in step S3 is: adding 3-8 wt‰ of seed crystals on a dry basis to the concentrated solution at 68-72°C, stabilizing for 30-90 minutes, and then performing temperature-raising crystallization;

[0012] Further preferably, the temperature-raising crystallization procedure is: controlling the vacuum degree to -0.07~-0.1Mpa, controlling the solid content to 84.5~87.0% at 70~72°C; controlling the solid content to 87.0~88.5% at 72~74°C; controlling the solid content to 88.5~89.5% at 74~76°C; controlling the solid content to 89.5~91.0% at 76~78°C; controlling the solid content to 91.0~92.5% at 78~80°C, and stabilizing at 80°C for 3h;

[0013] The heating frequency is 0.5~1.0℃ / h;

[0014] Preferably, the specific method of the cooling crystallization is: cooling from 80°C to 70°C, with a cooling frequency of 0.3-0.6°C / h, and after cooling to 70°C, stabilizing at 70°C for 3h.

[0015] By adopting the above technical scheme, the crystallization method of the present invention adopts two crystallizations, namely, heating crystallization and cooling crystallization. First, by reducing the crystallization rate, the phenomenon of inconsistency of crystal morphology and crystal agglomeration caused by excessive crystallization is avoided. Second, the two crystallizations fully consume the supersaturation and improve the crystallization yield.

[0016] Preferably, the solid content of the lactose solution in S1 is 45-50%.

[0017] Preferably, the amount of sodium citrate added in S1 is 5wt‰~2wt% of the lactose solution. By adopting the above technical solution, the present invention adds sodium citrate during hydrogenation to play a role of pH buffering, which can buffer the decrease of pH during hydrogenation, promote hydrogenation reaction, and obtain lactitol with higher purity.

[0018] Preferably, the conditions for the hydrogenation reaction in S1 are:

[0019] pH is 7.0-8.0;

[0020] The hydrogenation temperature is 130~150℃;

[0021] Hydrogen pressure is 6~12MPa;

[0022] The reaction time is 3.5~5h;

[0023] The catalyst is Raney nickel;

[0024] The amount of catalyst added is 2~5wt% of the lactose solution.

[0025] Preferably, the lactitol purity of the hydrogenation reaction liquid in S1 is ≥95%, and the reducing sugar content is ≤0.1%.

[0026] Preferably, the specific method for decolorization in S2 is: adding 5‰~1% of activated carbon powder on a dry basis to the hydrogenation reaction liquid, keeping warm at 75~85°C for 30~60min, filtering through a plate and frame filter press to obtain a lactitol solution with a transmittance ≥95%, and a filtration pressure of 0.2~0.35Mpa.

[0027] Preferably, the specific method of ion exchange in S2 is: after the decolorization is completed, the solution is sequentially passed through a weakly acidic cation exchange resin, a strongly basic ion exchange resin, and a weakly basic cation exchange resin at a flow rate of 2.0-3.0 BV / h and a temperature of 30-45°C; a lactitol solution with a transmittance of ≥98%, a reducing sugar content of ≤0.1%, and a pH of 4.5-7.0 is obtained. By adopting the above-mentioned technical solution, the present invention can prevent decomposition caused by ion exchange and increase of reducing sugar content by arranging and combining the resins in the described order through the set ion exchange procedure.

[0028] Preferably, the specific method of vacuum concentration in S2 is: entering into a vacuum evaporator for concentration after the ion exchange is completed, the pressure during concentration is -0.06~-0.1Mpa, the temperature is 65~75°C, and a lactitol solution with a solid content of 84.5~86.5% is obtained.

[0029] Preferably, the solid content of the concentrated liquid in S2 is 84.5-86.5%.

[0030] Preferably, the seed crystals used for the temperature-raising crystallization in S3 are lactitol powders with a purity of more than 99%, a moisture content of less than 1%, and a particle size of 0.075-0.09 mm.

[0031] Preferably, the centrifugal process in S3 is controlled at a temperature of 70-73° C. and a centrifugal speed of 400-900 rpm.

[0032] Preferably, the drying process in S3 uses fluidized bed drying, and the air inlet temperature is controlled at 95-105°C and the relative humidity RH is 20-30%. By adopting the above technical solution, the present invention reduces the transformation of lactitol morphology during the centrifugation process by setting the centrifugation temperature, the drying process temperature and the relative humidity.

[0033] In a second aspect, the present invention provides anhydrous lactitol prepared by the above-mentioned preparation method.

[0034] Preferably, the moisture content of the anhydrous lactitol is ≤1%, and the lactitol content is ≥99.0%;

[0035] The melting range of the anhydrous lactitol is 145-150° C., and the melting point is 145-146° C.

[0036] Contains at least the following beneficial technical effects:

[0037] The present invention provides an anhydrous lactitol production process, through specific control of the crystallization process, the obtained anhydrous lactitol product has a uniform morphology, a rhombohedral shape, a high melting point, a narrow melting range, a melting range of 145-150° C., and a stronger product stability. The crystallization process of the present invention controls the temperature within 70° C.-80° C., and the crystallization yield is ensured by one temperature increase crystallization and one temperature decrease crystallization, the one crystallization yield is 60-65%, and the temperature is controlled within the range of 70-80° C., which is lower in energy consumption than within the range of 70-95° C. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a morphology diagram of anhydrous lactitol crystals obtained in Example 1;

[0039] Figure 2 This is a morphology diagram of anhydrous lactitol crystals obtained in Example 2;

[0040] Figure 3 This is a morphology diagram of anhydrous lactitol crystals obtained in Example 3;

[0041] Figure 4 This is a crystal morphology of anhydrous lactitol prepared in Comparative Example 6;

[0042] Figure 5 This is a morphology diagram of anhydrous lactitol crystals obtained in Comparative Example 7;

[0043] Figure 6 This is the crystal morphology of anhydrous lactitol prepared in Comparative Example 8. DETAILED DESCRIPTION

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0049] The "room temperature" and "normal temperature" mentioned in the present invention are all calculated as 25±2°C unless otherwise specified.

[0050] The raw materials and instruments used in the following examples of the present invention are commercially available unless otherwise specified.

[0051] Example 1

[0052] S1. Prepare a solution of lactose with a solid content of 48% and then adjust the pH to 7.5, add 1wt% sodium citrate of the lactose solution to carry out a hydrogenation reaction; obtain a hydrogenation reaction solution with a lactitol purity of ≥98.1% and a reducing sugar content of 0.04%.

[0053] The conditions of the hydrogenation reaction are: hydrogenation temperature is controlled at 140° C., hydrogen pressure is 9 MPa, reaction time is 4 h, and the amount of Raney nickel is 3 wt % of the lactose solution.

[0054] S2. Add 8‰ of activated carbon powder on a dry basis to the hydrogenation reaction liquid, keep warm at 80°C for 45 minutes, filter through a plate and frame filter press to obtain a lactitol solution with a transmittance of 99.1% and a filtration pressure of 0.3Mpa; then pass through a weakly acidic cation exchange resin, a strongly basic ion exchange resin, and a weakly basic cation exchange resin in sequence at a flow rate of 2.5BV / h and a temperature of 38°C to obtain lactitol with a transmittance of ≥99.6%, a reducing sugar content of 0.02%, and a pH of 6.0; finally enter a vacuum evaporator for concentration at a pressure of -0.08Mpa and a temperature of 70°C to obtain a concentrated solution with a solid content of 85.5%.

[0055] S3. Add 5‰ of seed crystals of dry basis weight to the concentrated solution at 70℃, stabilize for 60min, and then heat up for crystallization; the temperature crystallization procedure is: vacuum degree control -0.08Mpa, at 70~72℃, control the solid content to 86.0%; at 72~74℃, control the solid content to 88%; at 74~76℃, control the solid content to 89%; at 76~78℃, control the solid content to 90.0%; at 78~80℃, control the solid content to 92%. Stable at 80℃ for 3h. The heating frequency is 0.5~1.0℃ / h; the seed crystal is lactitol powder with a purity of more than 99.6%, a moisture content of 0.4%, and a particle size of 0.08mm.

[0056] After the heating is completed, the temperature is lowered from 80°C to 70°C with a cooling frequency of 0.5°C / h. After dropping to 70°C, it is stabilized at 70°C for 3h.

[0057] After the cooling crystallization is completed, the temperature is controlled at 72°C, and centrifugal separation is carried out at a centrifugal speed of 500 rpm. Then, a fluidized bed is used for drying, and the inlet air temperature is controlled at 100°C and the relative humidity RH is 25%. After drying, an anhydrous lactitol product with a moisture content of 0.02% and a lactitol content of 99.8% is obtained, and the primary crystallization yield is 65.2%.

[0058] After testing, the product's melting range is 146~150℃ and its melting point is 146℃.

[0059] The crystal morphology of anhydrous lactitol is shown in Figure 1 , it can be seen that its morphology is rhombohedral.

[0060] Example 2

[0061] S1. Prepare a solution of lactose with a solid content of 50% and then adjust the pH to 8.0, add 2wt% sodium citrate of the lactose solution to carry out a hydrogenation reaction; obtain a hydrogenation reaction solution with a lactitol purity of ≥97.6% and a reducing sugar content of 0.06%.

[0062] The conditions of the hydrogenation reaction are: hydrogenation temperature is controlled at 150° C., hydrogen pressure is 6 MPa, reaction time is 5 h, and the amount of Raney nickel used is 5 wt % of the lactose solution.

[0063] S2. Add 8‰ of activated carbon powder on a dry basis to the hydrogenation reaction liquid, keep warm at 85°C for 45 minutes, filter through a plate and frame filter press to obtain a lactitol solution with a transmittance of 98.9% and a filtration pressure of 0.35Mpa; then pass through a weakly acidic cation exchange resin, a strongly basic ion exchange resin, and a weakly basic cation exchange resin in sequence at a flow rate of 3.0BV / h and a temperature of 45°C to obtain lactitol with a transmittance of ≥99.4%, a reducing sugar content of 0.04%, and a pH of 7.0; finally, enter a vacuum evaporator for concentration at a pressure of -0.1Mpa and a temperature of 65°C to obtain a concentrated solution with a solid content of 86.5%.

[0064] S3. Add 8‰ of seed crystals of dry basis weight to the concentrated solution at 65℃, stabilize for 90min, and then heat up for crystallization; the temperature-raising crystallization procedure is: vacuum degree control -0.1Mpa, at 70~72℃, control the solid content to 87.0%; at 72~74℃, control the solid content to 88.5%; at 74~76℃, control the solid content to 89.5%; at 76~78℃, control the solid content to 91.0%; at 78~80℃, control the solid content to 92.5%. Stable at 80℃ for 3h. The heating frequency is 1.0℃ / h; the seed crystal is lactitol powder with a purity of more than 99.3%, a moisture content of 0.6%, and a particle size of 0.09mm.

[0065] After the heating is completed, the temperature is lowered from 80°C to 70°C with a cooling frequency of 0.6°C / h. After dropping to 70°C, it is stabilized at 70°C for 3h.

[0066] After the cooling crystallization is completed, the temperature is controlled at 73°C, and centrifugal separation is carried out at a centrifugal speed of 400 rpm. Then, a fluidized bed is used for drying, and the inlet air temperature is controlled at 105°C and the relative humidity RH30% for drying. After drying, an anhydrous lactitol product with a moisture content of 0.03% and a lactitol content of 99.7% is obtained, and the primary crystallization yield is 64.3%.

[0067] After testing, the product's melting range is 145~150℃ and its melting point is 145℃.

[0068] The crystal morphology of anhydrous lactitol is shown in Figure 2 , it can be seen that its morphology is rhombohedral.

[0069] Example 3

[0070] S1. Prepare a solution of lactose with a solid content of 55% and then adjust the pH to 7.0, add 2wt‰ of sodium citrate to the lactose solution for hydrogenation reaction; obtain a hydrogenation reaction solution with a lactitol purity of ≥97.3% and a reducing sugar content of 0.08%.

[0071] The conditions of the hydrogenation reaction are: hydrogenation temperature is controlled at 130° C., hydrogen pressure is 12 MPa, reaction time is 3.5 h, and the amount of Raney nickel is 2 wt % of the lactose solution.

[0072] S2. Add 5‰ of activated carbon powder on a dry basis to the hydrogenation reaction liquid, keep warm at 75°C for 60 minutes, filter through a plate and frame filter press to obtain a lactitol solution with a transmittance of 98.4% and a filtration pressure of 0.2Mpa; then pass through a weakly acidic cation exchange resin, a strongly basic ion exchange resin, and a weakly basic cation exchange resin in sequence at a flow rate of 2.0BV / h and a temperature of 30°C to obtain lactitol with a transmittance of ≥99.1%, a reducing sugar content of 0.06%, and a pH of 4.5; finally enter a vacuum evaporator for concentration at a pressure of -0.06Mpa and a temperature of 75°C to obtain a concentrated solution with a solid content of 84.5%.

[0073] S3. Add 3‰ of seed crystals of dry basis weight to the concentrated solution at 68℃, stabilize for 30min, and then heat up for crystallization; the temperature-raising crystallization procedure is: vacuum degree control -0.07Mpa, at 70~72℃, control the solid content to 84.5%; at 72~74℃, control the solid content to 87.0%; at 74~76℃, control the solid content to 88.5%; at 76~78℃, control the solid content to 89.5%; at 78~80℃, control the solid content to 91%. Stable at 80℃ for 3h. The heating frequency is 0.5℃ / h; the seed crystal is lactitol powder with a purity of more than 99.3%, a moisture content of 0.7%, and a particle size of 0.075mm.

[0074] After the heating is completed, the temperature is lowered from 80°C to 70°C with a cooling frequency of 0.3°C / h. After dropping to 70°C, it is stabilized at 70°C for 3h.

[0075] After the cooling crystallization is completed, the temperature is controlled at 70°C, and centrifugal separation is carried out at a centrifugal speed of 900 rpm. Then, a fluidized bed is used for drying, and the inlet air temperature is controlled at 95°C and the relative humidity RH is 20% for drying. After drying, an anhydrous lactitol product with a moisture content of 0.05% and a lactitol content of 99.7% is obtained, and the primary crystallization yield is 63.4%.

[0076] After testing, the product's melting range is 145~149℃ and its melting point is 145℃.

[0077] The crystal morphology of anhydrous lactitol is shown in Figure 3 , it can be seen that its morphology is rhombohedral.

[0078] Comparative Example 1

[0079] The preparation method of this comparative example is the same as that of Example 1, except that sodium citrate is not added in S1.

[0080] The lactitol purity of the obtained hydrogenation reaction liquid was 86.3%, and the reducing sugar content was 5.3%.

[0081] Finally, an anhydrous lactitol product with a moisture content of 0.05% and a lactitol content of 95.7% was obtained; the primary crystallization yield was 39.6%; after testing, the melting range of the product was 144~149°C and the melting point was 144°C.

[0082] Comparative Example 1 did not add citric acid, resulting in low purity of the lactitol product.

[0083] Comparative Example 2

[0084] The preparation method of this comparative example is the same as that of Example 1, except that the ion exchange in S2 sequentially uses a strong alkaline ion exchange resin, a weakly acidic cation exchange resin, and a weakly alkaline cation exchange resin, and the rest is the same as Example 1. After the ion exchange, a lactitol solution with a transmittance of ≥98% and a reducing sugar content of 2.8% is obtained.

[0085] Comparative Document 2 did not follow the ion exchange sequence of weakly acidic cation exchange resin, strongly basic ion exchange resin, and weakly basic cation exchange resin, resulting in a high reducing sugar content in the lactitol solution after ion exchange.

[0086] Comparative Example 3

[0087] The preparation method of this comparative example is the same as that of Example 1, except that S3 does not have a cooling crystallization step.

[0088] Finally, an anhydrous lactitol product with a moisture content of 0.06% and a lactitol content of 98.5% was obtained; the primary crystallization yield was 42.7%; after testing, the melting range of the product was 145~150°C, and the melting point was 145°C.

[0089] Comparative Example 3 did not undergo cooling crystallization, and the product yield was reduced.

[0090] Comparative Example 4

[0091] The preparation method of this comparative example is the same as that of Example 1, except that only cooling crystallization is performed in S3.

[0092] Finally, an anhydrous lactitol product with a moisture content of 0.06% and a lactitol content of 98.4% was obtained; the primary crystallization yield was 40.8%; after testing, the melting range of the product was 144-149°C and the melting point was 144°C.

[0093] Comparative Example 4 did not heat up for evaporation and crystallization, and the product yield was reduced.

[0094] Comparative Example 5

[0095] The preparation method of this comparative example is the same as that of Example 1, except that the temperature of the S3 centrifugal process is controlled at 65°C, fluidized bed drying is used, and the inlet air temperature is controlled at 94°C.

[0096] Finally, a lactitol product with a moisture content of 1.82% and a lactitol content of 98.7% was obtained; the primary crystallization yield was 64.9%; after testing, the melting range of the product was 120~149°C and the melting point was 120°C.

[0097] Comparative Example 5 shows that the centrifugation temperature is too low, the structure of lactitol changes during the centrifugation process, and lactitol containing crystal water is produced.

[0098] Comparative Example 6

[0099] The preparation method of this comparative example is the same as that of Example 1, except that the heating frequency of S3 heating crystallization is 1.3°C / h.

[0100] Finally, anhydrous lactitol product with a moisture content of 0.09% and a lactitol content of 98.4% was obtained. The primary crystallization yield was 54.8%; after testing, the melting range of the product was 144-151°C and the melting point was 144°C.

[0101] Due to the high heating frequency, the crystal morphology of the product is not uniform, and the crystals are agglomerated and adhered. Figure 4 .

[0102] Comparative Example 7

[0103] The preparation method of this comparative example is the same as that of Example 1, except that the relative humidity RH is controlled at 35% during the S3 drying process.

[0104] Finally, a lactitol product with a moisture content of 0.08% and a lactitol content of 99.1% was obtained; the primary crystallization yield was 64.9%; after testing, the melting range of the product was 139~152°C, and the melting point was 139°C.

[0105] Comparative Example 7 shows that the relative humidity is too low and the morphology of lactitol changes during the drying process. The product crystal form is a mixed crystal form of regular octahedron and rhombus, see Figure 5 .

[0106] Comparative Example 8

[0107] Comparative Example 8 is prepared in the same manner as Example 1, except that S3. Heating crystallization is finally heated from 70° C. to 90° C. After the heating is completed, the temperature is lowered from 90° C. to 70° C. The frequency and steps of heating and cooling are the same as those in Example 1.

[0108] After drying, an anhydrous lactitol product with a moisture content of 0.06% and a lactitol content of 99.1% was obtained, and the primary crystallization yield was 58.3%.

[0109] After testing, the product's melting range is 137~150℃ and its melting point is 137℃.

[0110] The product of Comparative Example 8 has different shapes, including both regular octahedron and rhombohedron, with a low melting point and a large melting range. Figure 6 .

[0111] 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 anhydrous lactitol, characterized in that: The following steps are involved: S1. adjusting the pH of the lactose solution and adding sodium citrate to carry out a hydrogenation reaction to obtain a hydrogenation reaction solution; S2. The hydrogenation reaction liquid is sequentially subjected to decolorization, ion exchange, and vacuum concentration to obtain a concentrated solution; S3. The concentrated solution is sequentially subjected to heating crystallization, cooling crystallization, centrifugation, and drying to obtain anhydrous lactitol; The specific method of the heating crystallization in step S3 is: adding 3-8 wt‰ of seed crystals on a dry basis to the concentrated solution at 68-72°C, stabilizing for 30-90 minutes, and then heating the solution for crystallization; The temperature-raising crystallization procedure is as follows: the vacuum degree is controlled at -0.07~-0.1Mpa, the solid content is controlled at 84.5~87.0% at 70~72°C; the solid content is controlled at 87.0~88.5% at 72~74°C; the solid content is controlled at 88.5~89.5% at 74~76°C; the solid content is controlled at 89.5~91.0% at 76~78°C; the solid content is controlled at 91.0~92.5% at 78~80°C, and the mixture is stabilized at 80°C for 3h; The heating frequency is 0.5~1.0℃ / h; The specific method of the cooling crystallization is: cooling from 80°C to 70°C, with a cooling frequency of 0.3-0.6°C / h, and after cooling to 70°C, stabilizing at 70°C for 3h.

2. The preparation method according to claim 1, characterized in that: The solid content of the lactose solution in the S1 is 45-50%.

3. The preparation method according to claim 2, characterized in that: The amount of sodium citrate added in S1 is 5wt‰~2wt% of the lactose solution.

4. The preparation method according to claim 2, characterized in that: The conditions for the hydrogenation reaction in S1 are: pH is 7.0-8.0; The hydrogenation temperature is 130~150℃; Hydrogen pressure is 6~12MPa; The reaction time is 3.5~5h; The catalyst is Raney nickel; The amount of catalyst added is 2~5wt% of the lactose solution.

5. The preparation method according to claim 1, characterized in that: The lactitol purity of the hydrogenation reaction liquid in S1 is ≥95%, and the reducing sugar content is ≤0.1%.

6. The preparation method according to claim 1, characterized in that: The specific method of ion exchange in S2 is: after the decolorization is completed, the ion is passed through a weakly acidic cation exchange resin, a strongly basic ion exchange resin, and a weakly basic cation exchange resin in sequence at a flow rate of 2.0-3.0 BV / h and a temperature of 30-45°C.

7. The preparation method according to claim 1, characterized in that: The solid content of the concentrated liquid in S2 is 84.5-86.5%.

8. The preparation method according to claim 1, characterized in that: The seed crystals used for the temperature-raising crystallization in S3 are lactitol powders with a purity of more than 99%, a moisture content of less than 1%, and a particle size of 0.075-0.09 mm.

9. Anhydrous lactitol, characterized in that The invention is prepared by the preparation method according to any one of claims 1 to 8.

10. Anhydrous lactitol according to claim 9, characterized in that The moisture content of the anhydrous lactitol is ≤1%, and the lactitol content is ≥99.0%; The melting range of the anhydrous lactitol is 145-150° C., and the melting point is 145-146° C.

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