A method for controlling the high-particle size process of semi-fiber xylose refining

Abstract

The present invention relates to the technical field of xylose production, and in particular to a method for controlling a high-particle size process of refining xylose from semi-fiber, comprising the following steps: hemicellulose extraction, hemicellulose acid hydrolysis, decolorization, electrodialysis, ion exchange, evaporation and concentration, cooling crystallization, centrifugation, drying and xylose packaging; the evaporation and concentration specifically refers to controlling the purity and refraction of xylose by evaporation and concentration, controlling the corresponding refraction of 78-79% of xylose with a purity of 75-78%, or controlling the corresponding refraction of 79-80% of xylose with a purity of 72-75%; the cooling and crystallization specifically refers to: optimizing the initial crystallization particle generation temperature reduction rate of xylose crystallization by temperature optimization, when 70 degrees are reduced to 55 degrees, 0.1-0.35 degrees / hour are used for cooling, and the rapid cooling method is used for cooling at 55 degrees-32 degrees. Through this control method, the particle size of more than 80 meshes can be effectively accounted for, effectively solving the problem that the particle size of the finished product does not meet the requirements.

Description

Technical Field

[0001] The invention relates to the technical field of xylose production, in particular to a process control method for refining high-granularity semi-fiber xylose. Background Art

[0002] At present, the international xylose market is highly competitive. In the international market, xylose is generally dissolved to make xylitol, so the smaller the particles, the better. However, it needs to be transported overseas by sea. Particles that are too small will be compacted and agglomerated if squeezed for a long time, making subsequent operations difficult. In order to ensure transportation, the exported xylose needs to have a certain particle size. Internationally, many requirements for xylose particles are above 80 mesh, and above 80 mesh specifically refers to particles with a particle size greater than 80 mesh. If the particle size of most of the particles in the current xylose process is increased to above 80 mesh, the quality of the finished product will be greatly improved, meeting the standard requirements of export xylose customers, improving customer recognition, and smoothly expanding the market for refined xylose for export.

[0003] At present, we have tested the particle size of finished products of 407 batches from two xylose factories that are among the top three in China in terms of production. There were 14 batches in which the particle size above 80 mesh accounted for more than 20%, and there were 2 batches in which the particle size above 80 mesh accounted for more than 30%, which could not meet the export demand.

[0004] In the prior art, a Chinese invention patent document with publication number CN1805969 and publication date July 19, 2006 is proposed. The technical solution disclosed in the patent document is as follows: a method for producing crystalline xylose from sugarcane bagasse, the xylose consisting of microcrystals with a defined structure and a narrow particle size range, the method in question comprising an initial step of producing xylose by acid hydrolysis of sugarcane bagasse; a second step of purifying the xylose solution thus formed; a third step of achieving xylose crystallization by controlled cooling of the aqueous solution, thereby producing crystals with a xylose content of more than 99.0 wt %, based on dry solids; a fourth step of hydrogenating xylose and its subsequent conversion to xylitol; a fifth step of treating and evaporating the xylitol solution; and a final step of xylitol crystallization, which is also achieved by controlled cooling, thereby resulting in the xylitol content of the prepared crystals never being less than 99.5 wt %, based on dry solids.

[0005] In actual use, the ultimate goal of the above technical solution is to increase the yield of the crystallized product, rather than to control the particle size of the crystal. In the crystallization process, the crystallization yield is promoted by adding seed crystals, and it is necessary to screen part of the finished product as seeds, and separate xylose crystals equal to at most 5% of the total mass, thereby promoting the next crystallization process and crystallization yield. This technical solution only requires more product crystallization, which promotes the crystallization yield by adding seed crystals, and screens part of the finished product as seeds, with a ratio of 0.5-3%, thereby accelerating the crystallization process and improving the crystallization yield. Its ultimate goal is to increase the crystallization yield, and the controlled seeds are only a small part screened out by physical methods, and the seed crystals screened in this part are 20-40um as seeds, which is not in the same research direction as the purpose of this patent to produce sugar granules with a particle size of more than 178um (more than 80 mesh) that meet the export.

[0006] Although the average diameter of the xylose particles obtained by the above technical solution is approximately equal to 200 microns, from the detailed distribution of particle size, the proportion of xylose particles with a particle size greater than 250 microns is only 31.5%, which cannot meet export demand. Summary of the invention

[0007] In order to solve the above technical problems, the present invention proposes a high-particle size process control method for refining semi-fiber xylose, which can effectively increase the proportion of particle sizes above 80 meshes and effectively solve the problem that the particle size of the finished product does not meet the requirements.

[0008] The present invention is achieved by adopting the following technical solutions:

[0009] A method for controlling the high-particle-size refined process of hemicellulose xylose is characterized in that it comprises the following steps: hemicellulose extraction, hemicellulose acid hydrolysis, decolorization, electrodialysis, ion exchange, evaporation and concentration, cooling crystallization, centrifugation, drying and xylose packaging; the evaporation and concentration specifically refers to controlling the purity and refractive index of xylose by evaporation and concentration, controlling the refractive index of xylose with a purity of 75-78% to 78-79%, or controlling the refractive index of xylose with a purity of 72-75% to 79-80%; the cooling crystallization specifically refers to optimizing the temperature reduction rate of the initial crystallization particle formation of xylose crystallization by temperature optimization, adopting 0.1-0.35 degrees / hour to cool down when the temperature drops from 70 degrees to 55 degrees, and adopting a rapid cooling method to cool down when the temperature drops from 55 degrees to 32 degrees.

[0010] The centrifugal treatment specifically refers to centrifugation using an upward-spinning centrifuge or a tripod centrifuge.

[0011] During the evaporation and concentration, the purity of xylose during evaporation and concentration is controlled by redistributing 99% pure xylose.

[0012] During the evaporation concentration process, the final refraction of the evaporation concentration is controlled by water mist injection.

[0013] During the evaporation and concentration process, the refractive index fluctuation is controlled within ±0.1 by water mist injection.

[0014] During the cooling crystallization process, cooling water with a lower temperature is used to achieve rapid cooling.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] 1. The conventional xylose crystallization process only obtains 10%-20% of particles with a diameter of more than 80 meshes, while the comparative document 1 achieves a high yield by adding a large amount of seed crystals and controlling the temperature, but the proportion of xylose particles with a diameter greater than 250 microns is only 31.5%. On the contrary, the present invention improves the conventional xylose crystallization process, does not need to add seed crystals, and controls the key factors affecting the particle size of the finished xylose product through two processing steps of evaporation concentration and cooling crystallization. By controlling the concentration, refraction and temperature, the particle size is controlled, and the proportion of particles with a diameter of more than 80 meshes is effectively increased. The proportion of xylose crystals with a diameter of more than 80 meshes obtained by the process of the present invention can reach more than 80%.

[0017] In the present invention, the xylose with a purity of 75-78% is controlled to correspond to a refractive index of 78-79%, or the xylose with a purity of 72-75% is controlled to correspond to a refractive index of 79-80%. Under this correspondence between purity and crystallization, the maximum yield can be achieved, and crystallization can be avoided before entering the crystallization tank. In the crystal generation stage, when the temperature drops from 70 degrees to 55 degrees, 0.1-0.35 degrees / hour are used for cooling to avoid excessive cooling to cause a large number of crystal nuclei to be generated, thereby reducing the final crystal particles. In the stage of forming crystal nuclei, the slower the temperature, the more effectively the probability of forming large-particle crystals can be improved.

[0018] Regarding the cooling crystallization, Comparative Document 1 used 60 hours to achieve the highest balance between equipment utilization and crystallization yield. The process purpose of the present invention is not to achieve the highest crystallization yield, but to significantly extend the crystal appearance and growth cycle by adopting a slow crystallization process of 80-190 hours, which significantly extends the crystal growth process, so that the final xylose crystal particle size of 80 mesh or above can reach more than 80%, which meets the acceptance standards of some international manufacturers.

[0019] 2. In the prior art, there is no technical solution that discloses the effect of different centrifuges on crystal particle size. In order to achieve the control requirement of crystal particle size, the present invention makes a special selection of centrifuges, that is, the centrifugal treatment specifically refers to centrifugation using an upward-spinning centrifuge or a tripod centrifuge. The above two centrifuges have a significant effect on improving the particle size of 20-80 mesh, and the percentage of particles of 20-80 mesh is increased by 5-6 percentage points compared with the downward-spinning centrifuge.

[0020] 3. In the present invention, the technical solution of controlling the purity of xylose during evaporation and concentration by redeeming 99% pure xylose is contrary to the conventional technology in the field and is not easy to think of. Because 99% pure xylose is already a finished product, in the conventional xylose crystallization process, there will be no redemption of 99% pure xylose that is already a finished product to control the purity of xylose, because the redemption process is useless and will consume the company's equipment and energy resources. However, the present invention adopts this technical solution in order to cooperate with the evaporation and concentration steps, dissolve the xylose in the raw materials, ensure the purity control effect, and finally achieve the goal of obtaining a finished product that meets the specific particle size requirements, even if a certain xylose yield is lost.

[0021] 4. In the prior art, conventional processes are all aimed at achieving a higher refractive index as much as possible, and generally no water is added to it. This operation not only wastes energy, but also reduces the final xylose yield, so general xylose manufacturers will not do this. On the contrary, the present application adds water to the concentrated solution during the evaporation and concentration process, and the particle size control of the crystallization can be achieved through this process. During the water addition process, because the high-concentration sugar solution is not miscible with water, the evaporation refractive index of xylose is not easy to be accurate, and the refractive index fluctuates at ±0.5. The raw material can be evaporated excessively by water mist spraying, and then the refractive index fluctuation can be accurately controlled at ±0.1 by water mist spraying. Since the liquid refractive index is between 78-80%, it is very difficult to control the refractive index fluctuation due to its high viscosity. Only by excessive evaporation and then dilution and regulation with more precise spray equipment can its refractive index range be controlled. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, wherein:

[0023] Figure 1 It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0024] Example 1

[0025] The present invention includes a high-particle-size process control method for refining hemicellulose xylose, which includes the following steps: hemicellulose extraction, hemicellulose acid hydrolysis, decolorization, electrodialysis, ion exchange, evaporation concentration, cooling crystallization, centrifugation, drying and xylose packaging. Among them, hemicellulose extraction includes obtaining wood pulp from felling residues, lumbering residues and processing residues, extracting cellulose by alkali solution, obtaining hemicellulose liquid containing alkali solution, and then performing dealkalization.

[0026] In the evaporation and concentration stage, the purity of xylose during evaporation and concentration is controlled by redeeming 99% pure xylose, so that the purity is at 75%. The final refractive index of evaporation and concentration is controlled by water mist spraying, and the refractive index is controlled to be 79%, and the refractive index fluctuation is controlled to be ±0.1. In the cooling crystallization, cooling water with a lower temperature is used to achieve rapid cooling. When the temperature drops from 70 degrees to 55 degrees, the temperature is cooled by 0.1 degrees / hour, and the temperature is cooled by a rapid cooling method of 0.5 degrees / hour between 55 degrees and 32 degrees. In the centrifugal treatment stage, an upward-spinning centrifuge is used for centrifugation.

[0027] Example 2

[0028] The remaining steps are the same as step 1. In the evaporation and concentration stage, the purity is controlled at 78% and the refractive index is controlled at 78%. In the cooling crystallization, when the temperature drops from 70 degrees to 55 degrees, the temperature is lowered by 0.2 degrees / hour, and when the temperature drops from 55 degrees to 32 degrees, the temperature is lowered by 0.5 degrees / hour. In the centrifugal treatment stage, an upward centrifuge is used for centrifugation.

[0029] Example 3

[0030] The remaining steps are the same as step 1. In the evaporation and concentration stage, the purity is controlled at 72% and the refractive index is controlled at 80%. In the cooling crystallization, when the temperature drops from 70 degrees to 55 degrees, the temperature is lowered by 0.25 degrees / hour, and when the temperature drops from 55 degrees to 32 degrees, the temperature is lowered by 0.5 degrees / hour. In the centrifugal treatment stage, an upward centrifuge is used for centrifugation.

[0031] Example 4

[0032] The remaining steps are the same as step 1. In the evaporation and concentration stage, the purity is controlled at 74% and the refractive index is controlled at 79.5%. In the cooling crystallization, when the temperature drops from 70 degrees to 55 degrees, the temperature is lowered by 0.28 degrees / hour, and when the temperature drops from 55 degrees to 32 degrees, the temperature is lowered by 0.5 degrees / hour. In the centrifugal treatment stage, a three-legged centrifuge is used for centrifugation.

[0033] Example 5

[0034] The remaining steps are the same as step 1. In the evaporation and concentration stage, the purity is controlled at 76% and the refractive index is controlled at 78.5%. In the cooling crystallization, when the temperature drops from 70 degrees to 55 degrees, the temperature is lowered by 0.35 degrees / hour, and when the temperature drops from 55 degrees to 32 degrees, the temperature is lowered by 0.5 degrees / hour. In the centrifugal treatment stage, a three-legged centrifuge is used for centrifugation.

[0035] Example 6

[0036] The remaining steps are the same as step 1. In the evaporation and concentration stage, the purity is controlled at 73% and the refractive index is controlled at 79.2%. In the cooling crystallization, when the temperature drops from 70 degrees to 55 degrees, the temperature is lowered by 0.35 degrees / hour, and when the temperature drops from 55 degrees to 32 degrees, the temperature is lowered by 0.5 degrees / hour. In the centrifugal treatment stage, a three-legged centrifuge is used for centrifugation.

[0037] The data obtained from each embodiment are shown in the following table:

[0038]

[0039] The experiment shows that by controlling the concentration, refraction and temperature, the crystallization state can be effectively improved and the proportion of particle sizes above 80 mesh can be effectively increased.

[0040] The most influential factor is the cooling method, followed by the purity and refractive index of the liquid. Through repeated regulation of these three factors, the crystal particles that meet the export standard can be controlled. The choice of centrifuge as a subsequent physical and chemical treatment method is a physical variable in which the crystal is destroyed by centrifugation, and as a process step that can change the particle size composition.

[0041] The present invention also conducted a separate test on the effect of different centrifuges on particle size. This test was conducted for 2 batches, and the particle size of the products was sampled and tested after separation by an upward-spinning centrifuge, a downward-spinning centrifuge, and a three-legged centrifuge. The comparison results are shown below:

[0042] Centrifuge Type Upward Spin Centrifuge Downspin centrifuge Three-column centrifuge Upward Spin Centrifuge Downspin centrifuge Three-column centrifuge 20-40 mesh 16.98 17.5 12.38 12.48 10.28 16.86 40-60 mesh 35.5 24.52 44.38 46.42 36.01 42.78 60-80 mesh 34.25 39.86 30.41 26.43 34.53 25.92 80-100 mesh 12.06 16.46 11.98 13.87 17.58 13.6 100 mesh 1.21 1.66 0.85 0.8 1.6 0.84

[0043] 20-80 mesh 86.73 81.88 87.17 85.33 80.82 85.56

[0044] The test shows that the downward-spinning centrifuge has a significant effect on reducing the particle size, and in terms of particle control, the use of upward-spinning or three-legged centrifuge has a significant effect on protecting the particle size of 20-80 mesh.

[0045] In the actual production process, the effect of the cooling gradient curve on the particle distribution was tested:

[0046]

[0047] The experiment shows that in the range of 70-55, slow cooling helps the slow formation of crystal nuclei, avoiding the rapid increase of supersaturation due to rapid cooling, thereby forming a large number of crystal nuclei. Excessive crystal nucleation does not allow subsequent crystals to have enough growth space.

[0048] In summary, after reading the present invention document, ordinary technicians in this field can make various other corresponding transformation schemes based on the technical scheme and technical concept of the present invention without creative mental labor, which all fall within the scope of protection of the present invention.

Claims

1. A process control method for refining high-particle size xylose from semi-fiber, characterized in that: The following steps are involved: Hemicellulose extraction, hemicellulose acid hydrolysis, decolorization, electrodialysis, ion exchange, evaporation and concentration, cooling crystallization, centrifugation, drying and xylose packaging; the evaporation and concentration specifically refers to controlling the purity and refractive index of xylose by evaporation and concentration, controlling the refractive index of xylose with a purity of 75% to 78% to 78% or controlling the refractive index of xylose with a purity of 72% to 75% to 79%; the cooling crystallization specifically refers to optimizing the temperature reduction rate of the initial crystallization of xylose crystallization by temperature optimization, when the temperature drops from 70 degrees to 55 degrees, the temperature is reduced by 0.25 to 0.35 degrees per hour; the temperature is reduced by a rapid cooling method of 0.5 degrees per hour at 55 degrees to 32 degrees; during the evaporation and concentration, the purity of xylose during evaporation and concentration is controlled by converting 99% pure xylose; during the evaporation and concentration process, the final refractive index of evaporation and concentration is controlled by spraying water mist.

2. The method for controlling the high-particle size process of semi-fiber xylose according to claim 1, characterized in that: The centrifugal treatment specifically refers to centrifugation using an upward-spinning centrifuge or a tripod centrifuge.

3. The method for controlling the high-particle size process of semi-fiber xylose according to claim 1, characterized in that: During the evaporation and concentration process, the refractive index fluctuation is controlled within ±0.1 by water mist injection.

4. The method for controlling the high-particle size process of semi-fiber xylose according to claim 1, characterized in that: During the cooling crystallization process, cooling water with a lower temperature is used to achieve rapid cooling.

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