Process for the production of xylose and xylitol

Abstract

The application provides a method for producing xylose and xylitol, and the method for producing xylose comprises the following steps: preparing a decolorized sugar solution by sequentially performing impurity removal, hydrolysis, neutralization and filtration, first ion exchange, first concentration and activated carbon decolorization on corn cob to obtain the decolorized sugar solution; preparing an ion exchange liquid by performing second ion exchange on the decolorized sugar solution to obtain the ion exchange liquid; preparing an effluent by performing particle carbon adsorption on the ion exchange liquid at a certain flow rate to obtain the effluent; preparing a concentrated sugar solution by performing second concentration on the effluent to obtain the concentrated sugar solution; and preparing a crystallization raw material by performing filtration and third concentration on the concentrated sugar solution to obtain the crystallization raw material. The application improves the xylose production process, reduces crystallization inhibitors and adhesive substances, improves the cleanliness of the feed liquid before crystallization, and reduces the replacement frequency of filter cartridges during precision filtration. The application also provides a method for preparing xylitol from xylose.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for producing xylose and xylitol. BACKGROUND

[0002] Xylose from corn cob is affected by the place of origin of corn cob, weather during the growth period, and storage time. Changes in impurities such as gum in the corn cob will affect the filtration at each stage in the production process of xylose, and the light transmittance of the xylose ion exchange liquid, especially the precise filtration step before crystallization (which requires frequent replacement of the filter element). In addition, the centrifugation time of the crystallized xylose is long, the crystal particles are small, and the 100-mesh sieve passing rate is >70%. The small particles cause the product to cake after about 30 days of storage.

[0003] Xylose that is prone to caking also causes long filter membrane filtration time, poor flowability, high water activity, and easy caking of xylitol products when used to produce xylitol, thereby shortening the shelf life and affecting use. SUMMARY

[0004] To solve the above problems, the technical solution of the present application is as follows:

[0005] The present application provides a method for producing xylose, comprising the following steps:

[0006] Preparation of decolorized sugar liquid: corn cob is sequentially subjected to impurity removal, hydrolysis, neutralization filtration, first ion exchange, first concentration, and activated carbon decolorization to obtain a decolorized sugar liquid;

[0007] Preparation of ion exchange liquid: the decolorized sugar liquid is subjected to second ion exchange to obtain an ion exchange liquid, the xylose content of the ion exchange liquid is greater than or equal to 70%, the conductivity is less than or equal to 100 us / cm, and the light transmittance is greater than or equal to 70%;

[0008] Preparation of effluent: the ion exchange liquid is subjected to granular carbon adsorption at a certain flow rate to obtain an effluent, and the light transmittance of the effluent is 90% to 99%;

[0009] Preparation of concentrated sugar liquid: the effluent is subjected to second concentration to obtain a concentrated sugar liquid, and the colority of the concentrated sugar liquid is ≤50;

[0010] Preparation of crystallization raw material: the concentrated sugar liquid is subjected to filtration and third concentration to obtain a crystallization raw material.

[0011] In some modes of the present application, the light transmittance of the effluent is 90% to 95%.

[0012] In some modes of the present application, the method for producing xylose further comprises the following steps:

[0013] Temperature reduction and cooling crystallization: xylose powder is added to the crystallization raw material as a seed crystal, and three-stage temperature reduction and cooling crystallization is sequentially performed;

[0014] Preparation of wet xylose: the crystallized raw material after cooling crystallization is aged at 25-30°C for 5-24h, and the wet xylose is obtained after centrifugation;

[0015] Preparation of xylose: the wet xylose is dried to obtain xylose.

[0016] In some embodiments of the present application, the moisture content of the wet xylose is less than 1.5%; and / or,

[0017] The moisture content of the xylose is less than 0.3%.

[0018] In some embodiments of the present application, the sugar concentration of the concentrated sugar solution is 60%-65%; and / or,

[0019] The sugar concentration of the crystallized raw material is 80%-85%; and / or,

[0020] In the preparation of the decolorized sugar solution, the sugar concentration of the decolorized sugar solution is 20%-30%.

[0021] In some embodiments of the present application, in the preparation of the effluent, the flow rate is 0.5-4BV / h.

[0022] In some embodiments of the present application, in the preparation of the effluent, the flow rate is 1-3BV / h.

[0023] In some embodiments of the present application, in the preparation of the crystallized raw material, the temperature of the third concentration is lower than 75°C.

[0024] In some embodiments of the present application, in the cooling crystallization, the three-stage cooling crystallization is as follows: the first stage is cooled to 70-60°C at a cooling rate of 0.3-0.6°C / h, the second stage is cooled to 55-45°C at a cooling rate of 0.75-1.2°C / h, and the third stage is cooled to 25-35°C at a cooling rate of 1.2-1.7°C / h; or,

[0025] The mesh number of the xylose powder is 80-100 mesh.

[0026] In some embodiments of the present application, in the preparation of the crystallized raw material, a filter membrane with a pore size of 0.45um is used.

[0027] The present application provides the use of the xylose prepared by the above method in the preparation of xylitol.

[0028] The present application provides a xylitol prepared by using the xylose prepared by the above method.

[0029] The present application provides a method for preparing xylitol by using the xylose prepared by the above method, which comprises the following steps:

[0030] The xylose is prepared by saccharifying, hydrogenation, filtration, decolorization, ion exchange, concentration, crystallization and centrifugal drying.

[0031] Compared with the prior art, the application has the following beneficial effects:

[0032] The xylose production process is improved, a granular carbon adsorption step is added after ion exchange and before crystallization, trace impurities remaining in the solution are adsorbed by the granular carbon, colored impurities eluted during the operation of the ion exchange resin are adsorbed, crystallization inhibitors are reduced, adhesive substances are reduced, the cleanliness of the solution before crystallization is improved, and the frequency of replacing the filter core during precision filtration is reduced.

[0033] After the granular carbon adsorption, the light transmittance of the sugar solution is 90% to 95%, and the chroma is less than or equal to 50. The xylose particles obtained after the sugar solution in the index range is crystallized are large (100 mesh screen passing rate < 30%), the mother liquor is quickly secreted during centrifugation, the centrifugation time is shortened by more than half, the moisture content of the centrifuged xylose is reduced to less than or equal to 1%, the energy consumption for drying is reduced, and the product caking period is extended from about 30 days to more than 12 months.

[0034] In the technical solution of the application, the sugar solution with a light transmittance of 90.0% to 95.0% and a chroma of the crystallization raw material of less than or equal to 50 is used, the time for passing through a 0.45 um filter membrane is shortened from the original 20 min to less than or equal to 5 min, the centrifugation time of the xylose is shortened by more than half, the number of centrifugal washing times is shortened from 2 to 3 times to 1 time, and the production efficiency is greatly improved. The moisture content of the xylose after centrifugation is greatly reduced, the moisture content of the dried xylose is reduced to less than 0.1%, the 100 mesh screen passing rate is less than 30%, and caking has not occurred for 392 days (13 months). In the light transmittance range, the product quality is obviously improved, the data fluctuation is small, and stable production is beneficial.

[0035] When the xylose prepared by the method is used to produce xylitol, the filter membrane filtration time of the xylitol product is greatly shortened, the water activity is obviously reduced, and the anti-caking performance is also significantly improved. DETAILED DESCRIPTION

[0036] The application will be further described below in conjunction with examples. It should be understood that the examples are only used to further illustrate and explain the application, and are not used to limit the application.

[0037] Unless otherwise defined, technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, the preferred materials and methods are described below. In case of conflict, the present specification, including that set forth in the following detailed description, controls. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be practiced without some or all of these specific details. In other instances, well known methods have not been described in detail, in order not to unnecessarily obscure the present application.

[0038] In the present application, the sugar concentration is the total sugar content in the sugar solution, and the total sugar includes other small amounts of heterosides except xylose; wherein the sugar concentration is measured by a handheld saccharimeter.

[0039] In the present application, the mesh number refers to the particle size or fineness of the material, which is generally defined as the number of mesh in an area of 1 inch x 1 inch, i.e. the mesh number of the screen, and the material can pass through the mesh is defined as the mesh number.

[0040] The present application provides a method for producing xylose, comprising the following steps: preparation of decolorized sugar solution: corn cob is sequentially subjected to impurity removal, hydrolysis, neutralization and filtration, first ion exchange, first concentration, and activated carbon decolorization to obtain a decolorized sugar solution; preparation of ion exchange liquid: the decolorized sugar solution is subjected to second ion exchange to obtain an ion exchange liquid, the xylose content of the ion exchange liquid is greater than or equal to 70%, the conductivity is less than or equal to 100 us / cm, and the light transmittance is greater than or equal to 70%; preparation of effluent: the ion exchange liquid is subjected to granular carbon adsorption at a certain flow rate to obtain an effluent, the light transmittance of the effluent is 90%-99%, preferably 90%-95%; preparation of concentrated sugar solution: the effluent is subjected to second concentration to obtain a concentrated sugar solution, the colority of the concentrated sugar solution is ≤50; preparation of crystallization raw material: the concentrated sugar solution is subjected to filtration and third concentration to obtain a crystallization raw material.

[0041] In the present application, the concentration is not limited in any way, as long as the purpose is achieved, and the concentration can be selected from one or more of negative pressure concentration, vacuum concentration, atmospheric pressure concentration, three-effect concentration, centrifugal concentration, thin film concentration, electrodialysis, and MVR.

[0042] In the present application, the first concentration is MVR concentration.

[0043] In the present application, the second concentration is three-effect concentration.

[0044] In the present application, the third concentration is negative pressure concentration.

[0045] In some embodiments of the present application, the xylose content of the ion exchange liquid is greater than or equal to 70%, for example, the xylose content of the ion exchange liquid can be 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, or more, or any range therebetween.

[0046] In some embodiments of the application, the conductivity of the eluent is less than or equal to 100 us / cm, for example, the conductivity of the eluent can be 100 us / cm, 98 us / cm, 96 us / cm, 94 us / cm, 92 us / cm, 90 us / cm, 88 us / cm, 86 us / cm, 84 us / cm, 82 us / cm, 80 us / cm, 78 us / cm, 76 us / cm, 74 us / cm, 72 us / cm, 70 us / cm, 68 us / cm, 66 us / cm, 64 us / cm, 62 us / cm, 60 us / cm, 58 us / cm, 56 us / cm, 54 us / cm, 52 us / cm, 50 us / cm, 48 us / cm, 46 us / cm, 44 us / cm, 42 us / cm, 40 us / cm, 38 us / cm, 36 us / cm, 34 us / cm, 32 us / cm, 30 us / cm, 28 us / cm, 26 us / cm, 24 us / cm, 22 us / cm, 20 us / cm, 18 us / cm, 16 us / cm, 14 us / cm, 12 us / cm, 10 us / cm or less, or any range therebetween.

[0047] In some embodiments of the application, the transmittance of the eluent is greater than or equal to 70%, for example, the transmittance of the eluent can be 70%, 68%, 66%, 64%, 62%, 60%, 58%, 56%, 54%, 52%, 50%, 48%, 46%, 44%, 42%, 40%, 38%, 36%, 34%, 32%, 30%, 28%, 26%, 24%, 22%, 20%, 18%, 16%, 14%, 12%, 10% or less, or any range therebetween.

[0048] In some embodiments of the application, the transmittance of the effluent can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or any range therebetween.

[0049] In some embodiments of the application, the color of the concentrated sugar solution can be 50, 45, 40, 35, 30, 25, 20, 15, 10, 5 or any range therebetween.

[0050] In some embodiments of the application, the method for producing xylose further comprises the following steps: cooling crystallization: adding xylose powder as a crystal seed to the crystallization raw material, and sequentially performing three-stage cooling crystallization; preparation of wet xylose: incubating the crystallization raw material after cooling crystallization at 25-30°C for 5-24h, and obtaining wet xylose after centrifugation; preparation of xylose: obtaining xylose after drying the wet xylose.

[0051] In some embodiments of the present application, the temperature for the crystallization can be 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, or any range therebetween.

[0052] In some embodiments of the present application, the time for the crystallization can be 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h, 24h, or any range therebetween.

[0053] In some embodiments of the present application, in the cooling crystallization, the three-stage cooling crystallization is as follows: the first stage is cooled to 70-60°C at a cooling rate of 0.3-0.6°C / h, the second stage is cooled to 55-45°C at a cooling rate of 0.75-1.2°C / h, and the third stage is cooled to 25-35°C at a cooling rate of 1.2-1.7°C / h; for example, the cooling rate of the first stage can be 0.3°C / h, 0.4°C / h, 0.5°C / h, 0.6°C / h, or any range therebetween, and the first stage can be cooled to 70°C, 69°C, 68°C, 67°C, 66°C, 65°C, 64°C, 63°C, 62°C, 61°C, 60°C, or any range therebetween; the cooling rate of the second stage can be 0.75°C / h, 0.8°C / h, 0.9°C / h, 1.0°C / h, 1.1°C / h, 1.2°C / h, or any range therebetween, and the second stage can be cooled to 55°C, 54°C, 53°C, 52°C, 51°C, 50°C, 49°C, 48°C, 47°C, 46°C, 45°C, or any range therebetween; the cooling rate of the third stage can be 1.2°C / h, 1.3°C / h, 1.4°C / h, 1.5°C / h, 1.6°C / h, 1.7°C / h, or any range therebetween, and the third stage can be cooled to 35°C, 34°C, 33°C, 32°C, 31°C, 30°C, 29°C, 28°C, 27°C, 26°C, 25°C, or any range therebetween.

[0054] In some embodiments of the present application, the mesh number of the xylose powder is 80-100 mesh. For example, the mesh number of the xylose powder can be 80 mesh, 82 mesh, 84 mesh, 86 mesh, 88 mesh, 90 mesh, 92 mesh, 94 mesh, 96 mesh, 98 mesh, 100 mesh, or any range therebetween.

[0055] In some embodiments of the present application, the sugar concentration of the concentrated sugar solution is 60%-65%; for example, the sugar concentration of the concentrated sugar solution can be 60%, 61%, 62%, 63%, 64%, 65%, or any range therebetween.

[0056] In some embodiments of the application, the concentration of the crystallization raw material sugar is 80% to 85%; for example, the concentration of the crystallization raw material sugar can be 80%, 81%, 82%, 83%, 84%, 85%, or any range between them.

[0057] In some embodiments of the application, the concentration of the decolorized sugar solution is 20% to 30%; for example, the concentration of the decolorized sugar solution can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, or any range between them.

[0058] In some embodiments of the application, in the preparation of the effluent, the flow rate is 0.5 to 4 BV / h, preferably 1 to 3 BV / h; further adsorbing residual colorants, lignin, adhesives and other trace amounts of difficult-to-detect crystallization inhibitors; for example, the flow rate can be 0.5 BV / h, 1 BV / h, 1.5 BV / h, 2 BV / h, 2.5 BV / h, 3 BV / h, 3.5 BV / h, 4 BV / h, or any range between them. Applicants found that if the flow rate is adjusted to 0.5 BV / h, the requirements of 90% to 95% light transmittance and ≤50 colority can also be met, but the flow rate is too slow, the production efficiency and capacity decrease; when the flow rate is >3 BV / h, the light transmittance can also reach 93.0%, but the colority is >50, indicating that the adsorption is not thorough, and the final product 161 days of caking. From the perspective of production and benefit, the flow rate of the effluent is 1 to 3 BV / h.

[0059] In some embodiments of the application, in the preparation of the crystallization raw material, the temperature of the third concentration is lower than 75℃.

[0060] In some embodiments of the application, in the preparation of the crystallization raw material, a filter membrane of 0.45 um is used for filtration.

[0061] In some embodiments of the application, the moisture content in the wet xylose is lower than 1.5%; for example, the moisture content in the wet xylose can be 1.5%, 1.4%, 1.3%, 1.2%, 1.1%, 1.0%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3% and below, or any range between them.

[0062] In some embodiments of the application, the moisture content in the xylose is lower than 0.3%; for example, the moisture content in the xylose can be 0.3%, 0.28%, 0.26%, 0.24%, 0.22%, 0.20%, 0.18%, 0.16%, 0.14%, 0.12%, 0.10%, 0.08%, 0.06%, 0.04%, 0.02% and below, or any range between them.

[0063] In some embodiments of the present application, the xylose content in the obtained xylose product is above 99.1%, meeting the requirements of the national standard GB / T 23532-2009 for xylose.

[0064] In some embodiments of the present application, the method for producing xylose comprises the following steps:

[0065] (1) The corn cob is screened to remove impurities, washed, and then hydrolyzed. The hydrolysis liquid is neutralized and filtered to obtain a sugar liquid rich in xylose. The hydrolyzed sugar liquid is subjected to primary ion exchange to remove most of the salt and lignin. The sugar liquid after primary ion exchange is concentrated to a sugar concentration of 20%-30% by MVR, and then decolorized by adding powdered activated carbon to obtain a decolorized sugar liquid;

[0066] (2) The decolorized sugar liquid is subjected to secondary ion exchange in an ion exchange system to further remove residual salt, to obtain an ion exchange liquid with a xylose content of >70%, a conductivity of <100 us / cm, and a light transmittance of >70%;

[0067] (3) The ion exchange liquid is passed through a granular carbon column at a flow rate of 0.5-4 BV / h to further adsorb residual pigment, lignin, gum, and other trace amounts of crystallization inhibitors that are difficult to detect. The effluent has a light transmittance of 90%-99%. The sugar liquid is concentrated to a sugar concentration of 60%-65% by three-effect concentration, with the sugar liquid temperature controlled below 75°C during concentration. The concentrated sugar liquid with a colority of ≤50 is used as the raw material for crystallization;

[0068] (4) The concentrated sugar liquid is subjected to precision filtration through a 0.45 um filter membrane, and then subjected to negative pressure concentration in a sugar boiling tank at a concentration temperature of 65°C-75°C, to obtain a sugar concentration of 80%-85%;

[0069] (5) 0.5‰-1‰ of 80-100 mesh xylose powder is added as a seed crystal, and then cooling crystallization is started. In the first stage, the temperature is decreased from 75°C to 65°C at a rate of 0.5°C / h. In the second stage, the temperature is decreased from 65°C to 50°C at a rate of 1.0°C / h. In the third stage, the temperature is decreased from 50°C to 30°C at a rate of 1.4-1.7°C / h. After the cooling is completed, the crystals are grown at 30°C for 5-24 h. During this stage, the yield is slowly increased;

[0070] (6) After the crystallization is completed, the centrifugation time is 1-10 min. When no mother liquor is exuded, the crystal condition is observed. If there is no yellow sugar in the crystals, the crystals are dried. If the crystals are yellow, the centrifugation is continued, and the crystals are washed by spraying ionized water for 5 s. Each washing is continued until no liquid is exuded. When there is no yellow sugar in the crystals, the centrifugation is stopped. If there is yellow sugar, the centrifugation and washing are continued;

[0071] (7) The centrifuged crystals are dried and packaged.

[0072] The light transmittance of the sugar solution after granular carbon adsorption in the present application is 90.0% to 95.0%, and the colority of the crystallization raw material is ≤50, the time for passing through a 0.45 um filter membrane is shortened from the original 20 min to within 5 min, the centrifugation time of xylose is shortened by more than half, the centrifugal washing times are shortened from 2 to 3 times to 1 time, and the production efficiency is greatly improved. After centrifugation, the moisture of the xylose is greatly reduced, the moisture of the dried xylose is reduced to <0.1%, the 100 mesh sieve passing rate is <30%, and clumping has not occurred for 392 days (13 months). Within the light transmittance range, the product quality is significantly improved, the data fluctuation is small, and it is conducive to stable production.

[0073] The present application improves the xylose production process, and a granular carbon adsorption step is added after ion exchange and before crystallization. The trace amount of pigment remaining is adsorbed, the colored impurities released during the operation of the ion exchange resin are adsorbed, the crystallization inhibitors are reduced, the adhesives are reduced, the cleanliness of the feed liquid before crystallization is improved, and the replacement frequency of the filter core during precision filtration is reduced.

[0074] Embodiment

[0075] The corn cob is screened to remove impurities, washed with water, and then hydrolyzed. The hydrolyzate is neutralized and filtered to obtain a sugar solution rich in xylose. The hydrolyzed sugar solution is subjected to first ion exchange to remove most of the salt and lignin. The ion-exchanged sugar solution is concentrated to a sugar concentration of 20% to 30%, and then powdered activated carbon is added for decolorization to obtain a decolorized sugar solution.

[0076] The decolorized sugar solution is subjected to second ion exchange to further remove residual salt to obtain an ion-exchanged solution. The ion-exchanged solution has a xylose content of 71.57%, a conductivity of 75.2 us / cm, and a light transmittance of 74.1%.

[0077] The same batch of ion-exchanged solution is used as the feed liquid for the granular carbon column in Examples 1-17 and Comparative Examples 1-4. The ion-exchanged solution has a xylose content of 71.57%, a conductivity of 75.2 us / cm, and a light transmittance of 74.1%.

[0078] Example 1

[0079] Granular carbon adsorption: After the granular carbon column is flushed, the ion-exchanged solution is passed through the granular carbon column at a flow rate of 2 BV / h, and the light transmittance of the effluent is detected. The light transmittance of the effluent is 98.3%.

[0080] Sugar solutions with different light transmittances are collected and concentrated to be used as crystallization raw materials. When the light transmittance of the effluent of the granular carbon column is consistent (i.e., the light transmittance of the effluent is 74.1%), the feeding is stopped. Ionized water is fed to flush out the residual sugar solution in the column until the sugar concentration of the effluent is <0.1%. After the regeneration of the granular carbon, it is recycled for use.

[0081] Preparation of concentrated sugar solution: the effluent with a transmittance of 98.3% is subjected to three-effect concentration to obtain a concentrated sugar solution, the sugar concentration of the concentrated sugar solution is 61.5%, and the colority of the concentrated sugar solution is 35;

[0082] Preparation of crystallization raw material: 1000 mL of the concentrated sugar solution is subjected to 0.45 um filter membrane filtration and further negative pressure concentration, the filtration time is 3'54", and the concentration temperature is 65-70 DEG C, to obtain a crystallization raw material, the sugar concentration of the crystallization raw material is 83%. 1‰ of 80-100 mesh xylose powder is added as a crystal seed, and then cooling crystallization is started, the first stage is cooled from 75 DEG C to 65 DEG C at a cooling rate of 0.5 DEG C / h, the second stage is cooled from 65 DEG C to 50 DEG C at a rate of 1.0 DEG C / h, and the third stage is cooled from 50 DEG C to 30 DEG C at a rate of 1.5 DEG C / h. 30 DEG C is kept for crystallization, and after 24 h of crystallization, centrifugation is carried out.

[0083] Centrifugation: after the sugar paste enters the centrifuge, centrifugation is started, and no mother liquor is observed to be excreted after 7 min of visual observation, the crystals in the centrifuge are slightly yellow, deionized water is sprayed for washing, the washing time is 5 s, and after 5 min of continuous centrifugation, no washing liquid is excreted, the crystals are white, the centrifugation is stopped, the total centrifugation time is 12 min, and the crystals are washed once with deionized water. The moisture of the centrifuged xylose (referred to as wet xylose) is 1.08%

[0084] After the centrifuged xylose is dried in a fluidized bed, xylose products are obtained, the moisture of the sample is 0.15%, the 100 mesh sieve passing rate is 39.56%, the xylose content in the obtained xylose products is more than 99.1%, and the requirements of the xylose national standard GB / T 23532-2009 are met. 1000 g of the packaged product is placed in a sample cabinet for storage, and the caking condition is observed at intervals of 7 days.

[0085] Example 2-17 is only different from example 1 in table 1, and the rest is the same as example 1.

[0086] Comparative examples 1-3

[0087] Comparative examples 1-3 are only different from example 1 in that the granular carbon adsorption is replaced by powder activated carbon adsorption, and the rest is the same as example 1. The amount of powder activated carbon added accounts for 0.1%, 0.5% and 1% of the mass of the sugar solution respectively, and the mixture is stirred at 50-60 DEG C for 30 min and then filtered.

[0088] After the granular carbon adsorption in comparative examples 1-3 is replaced by powder activated carbon decolorization adsorption, the applicant finds that when the amount of powder activated carbon is 0.1%, caking occurs at 77 days, and when the amount of powder activated carbon is increased to 1%, the caking time is obviously improved, but caking still occurs at 161 days. The whole process is time-consuming, and the powder activated carbon is harmful to the working environment. Increasing the amount of powder activated carbon will produce a large amount of waste activated carbon which will eventually become solid waste, and the post-treatment is difficult.

[0089] Comparative Example 4

[0090] Comparative Example 4 differs from Example 1 only in that the step of adsorption on granular carbon is omitted.

[0091] Transmittance: According to the method of GB / T 23532-2009, a spectrophotometer with a wavelength of 380-850 nm was used. The sample was placed in a 0.5 cm cuvette, and water was used as a blank to set the zero point. The transmittance was measured at a wavelength of 420 nm. The spectrophotometer was set to zero with water as a blank, and the measurement was taken at a wavelength of 420 nm with a 0.5 cm cuvette.

[0092] Sugar concentration: A handheld refractometer was used for detection. The specific method is as follows: open the cover, drop the sample on the prism, close the cover, and make sure the liquid covers the entire surface without bubbles. Align the prism with the light source, and the reading can be taken from the eyepiece. Use distilled water as a blank to set the zero point.

[0093] Xylose content: HPLC detection, according to the provisions of GB / T 23532-2009.

[0094] Flow rate: the volume of the granular carbon column per hour is expressed in BV / h.

[0095] Xylose moisture: 1 g of sample was taken and tested using a rapid moisture meter at 105°C.

[0096] 100 mesh sieve passing rate: the dried xylose was sieved with a 100 mesh standard sieve. The mass percentage of the undersize xylose to the total sample mass was calculated. The larger the 100 mesh sieve passing rate, the more fine particles there are.

[0097] Xylitol product filter membrane filtration time: 200 g of xylitol product was dissolved in 1000 ml of water, and then filtered with a 0.45 um microporous filter membrane. The time taken to completely filter 1000 ml of xylitol solution was recorded. The shorter the filtration time, the higher the cleanliness of the xylitol, and the less likely it is to form lumps.

[0098] Water activity: an HD-3A intelligent water activity meter was used. The detection method was as follows: 5 g of sample was weighed and placed on the sample plate, and then placed in the sensor. The detection time was set to 15 min. After clicking the confirmation key, the instrument automatically detected, and the reading was automatically taken after the time ended. Each sample was measured three times and the average value was taken.

[0099] Table 1

[0100] ;

[0101] .

[0102] From Table 1, the sugar solution after adsorption by granular carbon, the light transmittance at different values have the following characteristics:

[0103] From Examples 3-5, 7-9, the sugar solution with light transmittance of 90.0%~95.0%, and the colority of crystallization raw material ≤50, the time of passing through 0.45um filter membrane is shortened from 20min to within 5min, the centrifugation time of xylose is shortened by more than half, the washing times of centrifugation is shortened from 2~3 times to 1 time, which greatly improves the production efficiency. The moisture of xylose after centrifugation is greatly reduced, the moisture of dried xylose is reduced to <0.1%, the passing rate of 100 mesh screen is <30%, and the caking phenomenon does not appear for 392 days (13 months). Within the light transmittance range, the product quality is obviously improved, the data fluctuation is small, and it is conducive to stable production.

[0104] From Examples 1-2, when the colority of crystallization raw material is <50 and the light transmittance is >95%, the filter membrane time and the centrifugation time are obviously shortened, but the passing rate of 100 mesh screen is >30%, and the caking phenomenon appears at 175 days.

[0105] From Example 13, when the light transmittance is >95% and the colority of crystallization raw material is >50, the filter membrane time and the centrifugation time are shortened, and the passing rate of 100 mesh screen is >30%, but the caking phenomenon appears at 70 days.

[0106] From Example 6, the sugar solution with light transmittance <90% and the colority of crystallization raw material <50, the filter membrane time and the centrifugation time are shortened compared with those without granular carbon adsorption, but the passing rate of 100 mesh screen is >30%, the particles are fine, and the caking phenomenon appears within 77 days. And with the decrease of light transmittance, the increase of colority, the extension of centrifugation time, the increase of washing times, the increase of the passing rate of 100 mesh screen, and the shortening of the time of caking phenomenon.

[0107] From Example 12, the sugar solution with light transmittance <90% and the colority of crystallization raw material >50, the filter membrane time and the centrifugation time are shortened compared with those without granular carbon adsorption, but the passing rate of 100 mesh screen is >30%, the particles are fine, and the caking phenomenon appears within 42 days. And with the decrease of light transmittance, the increase of colority, the extension of centrifugation time, the increase of washing times, the gradual increase of the passing rate of 100 mesh screen, and the shortening of the time of caking phenomenon.

[0108] From Comparative Example 4, the sugar solution without granular carbon adsorption, the light transmittance is 74.1%, the colority of crystallization raw material is 150, the filter membrane time is long, the sugar paste is difficult to centrifuge, which is manifested as long centrifugation time, many washing times, high moisture of centrifuged xylose, large drying energy consumption; the particles are fine, which is manifested as the passing rate of 100 mesh screen >70%. The final product starts to appear caking phenomenon after 35 days.

[0109] From Examples 14-17, if the flow rate is adjusted to 0.5 BV / h, the requirements of 90%-95% light transmittance and ≤50 colority can also be achieved, but the flow rate is too slow, the production efficiency and capacity are reduced; when the flow rate is >3 BV / h, the light transmittance can also reach 93.0%, but the colority is >50, indicating that the adsorption is not thorough, and the final product 161 days appears to be caked.

[0110] In summary, after secondary ion exchange and before crystallization, the particle carbon adsorption step is increased, the light transmittance is controlled to 90%-95%, and the colority of the concentrated crystallization raw material is ≤50, which can make the final product have larger particles, the 100 mesh sieve passing rate is <30%, and the anti-caking period is more than 13 months.

[0111] Preparation of xylitol

[0112] Examples 18-21 and Comparative Examples 5-7 only differ in the source of xylose, as shown in Table 2.

[0113] The specific method for using xylose to produce xylitol is as follows:

[0114] Sugar: Dissolve xylose to a sugar concentration of 50%, transfer into a reaction kettle, and add 10% of catalyst Raney nickel.

[0115] Hydrogenation: Maintain hydrogen pressure in the reaction kettle at 5.5-6.0 MPa, temperature at 100°C-120°C, and react for 2 h.

[0116] Settling and filtration: After the reaction stops, fully settle to separate the catalyst from the hydrogenation liquid, discharge the hydrogenation liquid from above the catalyst, and filter the hydrogenation liquid for the next process.

[0117] Decolorization: Add 1‰ activated carbon to the hydrogenation liquid, stir at 50°C-60°C for 30 min for decolorization, and filter to obtain xylitol decolorization liquid.

[0118] Ion exchange: The decolorization liquid passes through a cation exchange column and an anion exchange column in sequence to remove residual metal ions to obtain xylitol ion exchange liquid.

[0119] Concentration: Concentrate the xylitol ion exchange liquid to the crystallization point, supplement the material while concentrating, and stop supplementing when the total material mass reaches the crystallization kettle capacity.

[0120] Crystallization: Put the concentrated sugar paste into a crystallization kettle, reduce the temperature at a rate of 1°C / h, and when the sugar paste is viscous and the stirring current suddenly increases, discharge and centrifuge.

[0121] Centrifugal drying: the crystalline sugar paste was put into the centrifuge to start centrifugation, and when no mother liquor was observed to be excreted, deionized water was sprayed to wash, and when the crystals turned white, the centrifugation was stopped. After the centrifuged xylitol was dried by the fluidized bed, the xylitol product was obtained, and the indicators met the requirements of GB 1886.234-2016. 500 g of the product was packaged and stored in the sample cabinet, and the caking condition was observed every 7 days.

[0122] Table 2

[0123]

[0124] As can be seen from Table 2, when the xylitol produced by the method of the present application is used to produce xylitol, the water activity of the xylitol product is significantly reduced, and the filter membrane filtration time is shortened to less than 4 min, indicating that the cleanliness of the xylitol crystals is very good. The reduction of water activity and the improvement of cleanliness are beneficial to improve the flowability of xylitol product and prolong the caking period of the product. Compared with Comparative Examples 5-7, the caking period of xylitol is increased from 28 days to 420 days, greatly prolonging the shelf life of the product, which is beneficial to the use of customers.

[0125] Although the present case has been disclosed as above, it is not intended to limit the present case, and anyone with ordinary knowledge in the art can make some changes and modifications without departing from the spirit and scope of the present case. Therefore, the protection scope of the present case shall be subject to the scope defined in the following patent application.

Claims

1.A method for producing xylose, comprising the following steps: preparing a decolorized sugar solution by sequentially subjecting corncob to impurity removal, hydrolysis, neutralization and filtration, first ion exchange, first concentration, and activated carbon decolorization; preparing an ion exchange effluent by subjecting the decolorized sugar solution to second ion exchange, wherein the ion exchange effluent has a xylose content of 70% or more, a conductivity of 100 μs / cm or less, and a light transmittance of 70% or more; preparing an effluent by subjecting the ion exchange effluent to granular carbon adsorption at a flow rate, wherein the effluent has a light transmittance of 90%-95%, and the flow rate is 1-3 BV / h; preparing a concentrated sugar solution by subjecting the effluent to second concentration, wherein the concentrated sugar solution has a colority of 50 or less; preparing a crystallization raw material by subjecting the concentrated sugar solution to filtration and third concentration; cooling crystallization by sequentially subjecting the crystallization raw material to three-stage cooling crystallization, wherein xylose powder is added to the crystallization raw material as a seed crystal; preparing wet xylose by subjecting the crystallization raw material after cooling crystallization to crystal aging at 25-30°C for 5-24 h, and then centrifuging; preparing xylose by drying the wet xylose. 2.The method according to claim 1, wherein the moisture content of the wet xylose is less than 1.5%; and / or the moisture content of the xylose is less than 0.3%. 3.The method according to claim 1 or 2, wherein the sugar concentration of the concentrated sugar solution is 60%-65%; and / or the sugar concentration of the crystallization raw material is 80%-85%; and / or the sugar concentration of the decolorized sugar solution is 20%-30% in the preparation of the decolorized sugar solution. 4.The method according to claim 1, wherein the temperature of the third concentration is less than 75°C in the preparation of the crystallization raw material. 5.The method according to claim 2, wherein the three-stage cooling crystallization in the cooling crystallization is as follows: the first stage is cooling to 60-70°C at a cooling rate of 0.3-0.6°C / h, the second stage is cooling to 45-55°C at a cooling rate of 0.75-1.2°C / h, and the third stage is cooling to 25-35°C at a cooling rate of 1.2-1.7°C / h; or the mesh number of the xylose powder is 80-100. 6.The method according to claim 1, wherein a filter membrane with a pore size of 0.45 μm is used for filtration in the preparation of the crystallization raw material. 7.The use of xylose prepared by the method of any one of claims 1-6 in the preparation of xylitol. 8.Xylitol prepared by using xylose prepared by the method of any one of claims 1-6. 9.A method for preparing xylitol by using xylose prepared by the method of any one of claims 1-6, comprising the following steps: subjecting the xylose to sugar conversion, hydrogenation reaction, filtration, decolorization, ion exchange, concentration, crystallization, and centrifugal drying. ​ ​ ​ ​ ​ ​ ​ ​ ​

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