Preparation method of microcrystalline cellulose and microcrystalline cellulose

Abstract

The invention provides a preparation method of microcrystalline cellulose. The preparation method comprises the following steps: providing fine bamboo material components; screening the fine bamboo material components to obtain bamboo hybrid cells; inorganic acid is added into the bamboo hybrid cells to obtain pulp, the concentration of the inorganic acid in the pulp is 0.5%-2%, and the pulp concentration is 3%-5%; heating to enable the temperature of the slurry to rise to 95-130 DEG C, and reacting for 2-4 hours under a dynamic mixing condition; cooling the slurry after the reaction to below 80 DEG C, and carrying out solid-liquid separation to obtain a solid matter; washing the solid matter to be neutral, drying and crushing to obtain the microcrystalline cellulose. According to the preparation method of the microcrystalline cellulose, the production excess material, namely bamboo hybrid cells, of the bamboo fluff pulp is taken as a raw material, so that the utilization efficiency of the production excess material is improved, the procedure of shortening fibers in advance is omitted, relatively high economic value and environmental protection benefits are achieved, and the microcrystalline cellulose with stable quality and relatively high yield can be obtained only by adopting low-concentration inorganic acid for hydrolysis. The invention also provides the microcrystalline cellulose prepared by the preparation method of the microcrystalline cellulose.

Description

Technical Field

[0001] The present application relates to a preparation method of microcrystalline cellulose and microcrystalline cellulose prepared by the preparation method. Background Art

[0002] Microcrystalline cellulose (MCC for short) is an ultrafine powder product produced by hydrolysis of natural cellulose. MCC has functions such as viscosity regulation, gel promotion, fat substitution, and anti-caking. It is a green additive with extremely strong biocompatibility, high added value, and is widely used in industries such as medicine, food, and cosmetics.

[0003] At present, most of the microcrystalline cellulose on the market is prepared by acid hydrolysis and degradation using cotton fiber as the raw material. This method has a simple process, is stable and reliable, but high-concentration acid (acid concentration above 5%) corrodes the equipment greatly, and the equipment maintenance and treatment cost is relatively high; in addition, there is also a method of preparing MCC using biological enzymatic hydrolysis technology. Compared with the former, this method has low requirements for equipment, and environmental protection and energy conservation are its remarkable features, but the reaction time is long and it is greatly affected by the quality fluctuation of raw materials.

[0004] Therefore, it is necessary to develop a new preparation method of microcrystalline cellulose. Summary of the Invention

[0005] The purpose of the present application is to provide a preparation method of microcrystalline cellulose, which uses the miscellaneous cells separated from bamboo fluff pulp production as raw materials and adopts low-concentration inorganic acid hydrolysis to reduce costs and be low-carbon and environmentally friendly. The present application also provides a microcrystalline cellulose prepared by the preparation method.

[0006] The present application provides a preparation method of microcrystalline cellulose, including the following steps: (1) Provide fine bamboo material components; (2) Screen the fine bamboo material components to obtain bamboo miscellaneous cells; (3) Add inorganic acid to the bamboo miscellaneous cells to obtain a slurry, so that the concentration of inorganic acid in the slurry is 0.5%-2%, and the pulp concentration is 3%-5%; (4) Heat the slurry to 95-130°C and react for 2-4 hours under dynamic mixing conditions; (5) Cool the reacted slurry to below 80°C, and then perform solid-liquid separation to obtain a solid and waste acid; (6) Wash the solid to neutral; (7) Dry the solid obtained in step (6), and pulverize it to obtain microcrystalline cellulose.

[0007] As a further improvement of the above solution, the fine bamboo material components are the fine components obtained in the screening process of bleached bamboo fluff pulp production.

[0008] As a further improvement to the above solution, the screening process includes: pumping bleached bamboo pulp into a bamboo pulp screening system for screening and grading to separate long fiber pulp and the fine fraction.

[0009] As a further improvement to the above solution, in the fine bamboo material fraction, the content of bamboo miscellaneous cells is not less than 80%.

[0010] As a further improvement to the above solution, in step (2), the fine bamboo material fraction is screened using a curved screen, the aperture of the screen holes of the curved screen is 0.5 - 1.0 mm, and the bamboo miscellaneous cells are the part passing through the screen holes after screening.

[0011] As a further improvement to the above solution, the inorganic acid is any one of sulfuric acid or hydrochloric acid.

[0012] As a further improvement to the above solution, this preparation method further includes a step of adding lime to the waste acid produced in step (5), and gypsum is obtained after the waste acid and lime undergo a neutralization reaction.

[0013] As a further improvement to the above solution, the degree of polymerization of the microcrystalline cellulose is not higher than 375.

[0014] As a further improvement to the above solution, in step (7), the solid obtained in step (6) is dried until its dryness is higher than 93%.

[0015] This application also provides a kind of microcrystalline cellulose, which is prepared by the preparation method of microcrystalline cellulose described in any one of the above, the yield of the microcrystalline cellulose is not less than 50%, and its carbohydrate content is not less than 97%.

[0016] The preparation method of microcrystalline cellulose provided by this application uses the processing residue in bamboo fluff pulp production - bamboo miscellaneous cells as raw materials, improves the utilization efficiency of production residues, has high economic value and environmental benefits. The bamboo miscellaneous cells are the fine fraction obtained in the screening process during the production of bleached bamboo fluff pulp, and can meet the requirements of the carrier for microcrystalline cellulose preparation from a macroscopic dimension, saving the process of pre-shortening fibers required in the existing microcrystalline cellulose preparation. And the bamboo miscellaneous cells have been through the bleaching process to remove impurities such as lignin, resin and gum in them, and their internal structure is loose and porous, the reaction reagents are more likely to penetrate, accelerating the reaction process. Only low-concentration inorganic acid hydrolysis is used to obtain microcrystalline cellulose with stable quality and a high yield. Detailed implementation manners

[0017] Currently, there are the following problems in the process of using bamboo fibers to make fluff pulp. Since bamboo fibers are slender, with an average fiber length of about 2.0 mm, a small wall thickness and lumen, a large density, and a large number of miscellaneous cells and fine components, screening treatment is usually required before making bamboo fluff pulp to remove fine components such as miscellaneous cells in the bamboo pulp. In some scenarios, the dry weight of fine components such as miscellaneous cells in the bamboo pulp reaches more than 30% of the dry weight of the pulp before screening. If these fine components cannot be utilized, it will cause a large waste of fiber resources.

[0018] In the process of producing bleached bamboo fluff pulp, the content of bamboo miscellaneous cells in a large number of fine components generated by the screening process is high. These cells are in the shape of stones or waist drums. In a large number of exploratory application studies, it is found that bamboo miscellaneous cells do not have advantages when used in household paper, cultural paper and other industrial papers. Therefore, it is necessary to develop its application scenarios in other fields, such as the food, medicine, and coating industries. The inventors of this application have found through long-term research that bamboo miscellaneous cells have the characteristics of small macroscopic size, loose and porous structure, good reagent permeability, and high whiteness, and have a good basis for the preparation of microcrystalline cellulose.

[0019] In view of the above, the inventors of this application have developed a method for preparing microcrystalline cellulose, which includes the following steps: (1) Provide fine bamboo material components; (2) Screen the fine bamboo material components to obtain bamboo miscellaneous cells; (3) Add inorganic acid to the bamboo miscellaneous cells to obtain a slurry, so that the concentration of inorganic acid in the slurry is 0.5%-2%, and the pulp concentration is 3%-5%; (4) Heat the slurry to 95-130°C and react for 2-4 hours under dynamic mixing conditions; (5) Cool the reacted slurry to below 80°C, and then perform solid-liquid separation to obtain a solid and waste acid; (6) Wash the solid to neutral; (7) Dry the solid obtained in step (6), and crush it to obtain microcrystalline cellulose.

[0020] This method for preparing microcrystalline cellulose uses bamboo miscellaneous cells, which are production leftovers in the production of bamboo fluff pulp, as raw materials, improves the utilization efficiency of industrial production leftovers, and has high economic value and environmental benefits. The bamboo miscellaneous cells are the main components of the fine components obtained in the screening process of bleached bamboo fluff pulp production, and can meet the requirements of the carrier for microcrystalline cellulose preparation in terms of macroscopic size, saving the process of pre-shortening fibers required for the existing preparation of microcrystalline cellulose.

[0021] Among them, in the step (1), the fine bamboo material components are the fine components obtained in the screening process of bleached bamboo fluff pulp production.

[0022] Further, the screening process includes: pumping the bleached bamboo pulp into a bamboo pulp screening system for screening and grading to separate long fiber pulp and the fines component.

[0023] Further, in the fines bamboo material component, the content of bamboo miscellaneous cells is not less than 80%.

[0024] In the step (2), an arc sieve is used to screen the fines bamboo material component to separate a small amount of longer fibrous components therein, and the bamboo miscellaneous cells are the part passing through the sieve holes after screening.

[0025] Further, the aperture of the sieve holes of the arc sieve is 0.5 - 1.0 mm, that is, the bamboo miscellaneous cells are fines bamboo material components with two-dimensional dimensions not greater than 0.5 mm - 1.0 mm.

[0026] In the step (3), inorganic acid is added to the bamboo miscellaneous cells to obtain a slurry, so that the concentration of the inorganic acid in the slurry is 0.5% - 2%, and the pulp consistency is 3% - 5%.

[0027] Among them, the inorganic acid is any one of sulfuric acid or hydrochloric acid.

[0028] In this application, since the bamboo miscellaneous cells have been through a bleaching process to remove impurities such as lignin, resin, and gum, their internal structure is loose and porous, the reaction reagent is more likely to penetrate, accelerating the reaction process. Therefore, only low-concentration acid hydrolysis with an inorganic acid concentration of 0.5% - 2% can obtain microcrystalline cellulose with stable quality and high yield. Compared with the existing high-concentration acid degradation of cotton fiber preparation process, the reaction conditions of the preparation method in this application are milder, reducing the corrosion of equipment and lowering equipment loss.

[0029] Further, in the step (4), the slurry is heated to raise its temperature to 105 - 120 °C and reacted for 2 - 4 hours under continuous stirring.

[0030] Further, this preparation method also includes the step of adding lime (calcium hydroxide) to the waste acid produced in the step (5). After the waste acid and lime are neutralized, gypsum (calcium sulfate crystal salt) is obtained. This gypsum can be reused as a by-product or sold externally, reducing equipment corrosion and acid recovery costs.

[0031] In the step (6), the solid matter is washed with water until the pH is 6.8 - 7.5 and it does not contain chloride ions.

[0032] In the step (7), the solid matter obtained in the step (6) is dried until its dryness is higher than 93%, and then pulverized to obtain white powdery microcrystalline cellulose.

[0033] The yield of the microcrystalline cellulose is not less than 50%, and its carbohydrate content is not less than 97%.

[0034] The degree of polymerization of microcrystalline cellulose is one of the important factors affecting its properties and applications. It refers to the number of glucose units in the microcrystalline cellulose molecule, that is, the length of the cellulose molecular chain. The higher the degree of polymerization, the longer the cellulose molecular chain, and the physical and chemical properties of microcrystalline cellulose will also change accordingly.

[0035] In this application, the degree of polymerization of the microcrystalline cellulose is controlled not to exceed 375. To ensure that the microcrystalline cellulose has good fluidity, water absorption, and higher reaction performance during chemical modification processes such as carboxymethylation, acetylation, and esterification. The microcrystalline cellulose is suitable for preparing emulsifying stabilizers, suspending agents, etc.

[0036] This application also provides a microcrystalline cellulose prepared by the above-mentioned preparation method of microcrystalline cellulose, and its yield is not less than 60%.

[0037] The microcrystalline cellulose is in the form of a white powder, with a carbohydrate content of not less than 97% and a degree of polymerization not exceeding 375.

[0038] The following elaborates on this application in conjunction with examples, so that the advantages and features of this application can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of this application.

[0039] Example 1: This example provides a preparation method of microcrystalline cellulose, including the following steps: S1. Provide fine bamboo material components. The preparation process of the fine bamboo material components is as follows: ① Feed the bleached bamboo pulp diluted to a concentration of 0.6%-1.0% into the pulp tank before screening.

[0040] Among them, the pulp tank before screening is a storage container for the pulp to be screened. Its bottom is equipped with a propeller to facilitate the mixing of the pulp and prevent fluctuations in the concentration of the pulp to be screened caused by the precipitation of solids.

[0041] ② Pump the bleached bamboo pulp to the bamboo pulp screening system through a non-clogging pulp pump for screening and grading.

[0042] Among them, the non-clogging pulp pump controls the stability of the feeding flow rate of the pulp to be screened through frequency conversion, and controls the screening pressure of the bamboo pulp screening system to be 0.1-0.5 MPa.

[0043] Furthermore, the bamboo pulp screening system includes two stages of grading screens arranged in parallel. The bamboo pulp to be screened is fed into the grading screens in two stages, and the two stages of grading screens are connected in parallel; each stage of the grading screen is connected in series with three levels, and the grading screens at the same level are connected in series.

[0044] Further, the grading sieve is a perforated sieve, and sieve holes with a diameter of φ0.2 - 0.8 mm are provided on the sieve frame of the grading sieve, and the aperture ratio of the sieve frame is set to 14% - 25%.

[0045] ③ Collect the tail pulp of each grading sieve in the two-stage grading sieve to obtain the fine bamboo material component.

[0046] In the fine bamboo material component, the content of bamboo miscellaneous cells is not less than 80%; the fine bamboo material component contains fine components with a weighted average length of 0.45 - 1.2 mm, a width of 13.0 - 16.5 um, a length-width ratio of 65% - 90%, and an area ratio of 40% - 70%.

[0047] S2. Screen the fine bamboo material component to obtain bamboo miscellaneous cells; Use a curved sieve to screen the fine bamboo material component to separate a small amount of longer fibrous components therein, and collect the sieved part as the bamboo miscellaneous cells.

[0048] Among them, the pulp concentration is controlled at 0.5%, the aperture of the sieve holes of the curved sieve is selected to be 1.0 mm, and two-stage screening is adopted.

[0049] S3. Add sulfuric acid to the bamboo miscellaneous cells to obtain a slurry, so that the concentration of sulfuric acid in the slurry is 1.5% and the pulp concentration is 5%.

[0050] Among them, the pulp concentration refers to the weight percentage of bamboo miscellaneous cells in the slurry.

[0051] S4. Heat the slurry to 120°C and react for 3 hours under dynamic mixing conditions.

[0052] S5. Cool the reacted slurry to 60°C, and then perform solid-liquid separation to obtain a solid and waste acid.

[0053] The waste acid is neutralized with lime to produce gypsum.

[0054] S6. Wash the solid to a pH of 6.8 - 7.2 and free of chloride ions.

[0055] The chloride ion content is determined by silver nitrate titration. The standard for being free of chloride ions is that there is no white precipitate after silver nitrate titration (chloride ions react with silver ions to form a white precipitate).

[0056] S7. Dry the solid obtained in step S6 to a dryness of 95%, and crush it to obtain microcrystalline cellulose.

[0057] After measurement, the yield of this microcrystalline cellulose is 65%, the degree of polymerization (DP) is 298, and the carbohydrate content is 99.2%.

[0058] Among them, the yield of microcrystalline cellulose = (absolute dry weight of microcrystalline cellulose / absolute dry weight of bamboo miscellaneous cells) * 100%.

[0059] Example 2: This example provides a method for preparing microcrystalline cellulose. The difference from Example 1 is that in S2, the screening pulp concentration is controlled at 0.2%, and the aperture of the sieve holes of the arc sieve is selected to be 0.5 mm; in S3, sulfuric acid is added to the bamboo miscellaneous cells to obtain a slurry, so that the concentration of sulfuric acid in the slurry is 2%, and the pulp concentration is 3%; in S4, the slurry is heated to 120 °C and reacted for 4 hours under dynamic mixing conditions.

[0060] The microcrystalline cellulose prepared by the method for preparing microcrystalline cellulose in this example has a yield of 60%, a degree of polymerization (DP) of 220, and a carbohydrate content of 98.7%.

[0061] Example 3: This example provides a method for preparing microcrystalline cellulose. The difference from Example 1 is that in S3, sulfuric acid is added to the bamboo miscellaneous cells to obtain a slurry, so that the concentration of sulfuric acid in the slurry is 1.2%, and the pulp concentration is 4%; in S4, the slurry is heated to 115 °C and reacted for 4 hours under dynamic mixing conditions.

[0062] The microcrystalline cellulose prepared by the method for preparing microcrystalline cellulose in this example has a yield of 70%, a degree of polymerization (DP) of 350, and a carbohydrate content of 97.0%.

[0063] Comparative Example 1: This comparative example provides a method for preparing microcrystalline cellulose. The difference from Example 1 is that in S3, the concentration of sulfuric acid in the slurry is 0.6%, and the pulp concentration is 7%; in S4, the slurry is heated to 100 °C and reacted for 4 hours under dynamic mixing conditions.

[0064] The microcrystalline cellulose prepared by the method for preparing microcrystalline cellulose in this comparative example has a yield of 80%, a degree of polymerization (DP) of 400, and a carbohydrate content of 99.9%.

[0065] Comparative Example 2: This comparative example provides a method for preparing microcrystalline cellulose. The difference from Example 1 is that in S3, sulfuric acid is added to the bamboo miscellaneous cells to obtain a slurry, so that the concentration of sulfuric acid in the slurry is 1.0%, and the pulp concentration is 8%; in S4, the slurry is heated to 120 °C and reacted for 3 hours under dynamic mixing conditions.

[0066] The microcrystalline cellulose prepared by the method for preparing microcrystalline cellulose in this comparative example has a yield of 75%, a degree of polymerization (DP) of 390, and a carbohydrate content of 98.1%.

[0067] Comparative Example 3: This comparative example provides a method for preparing microcrystalline cellulose. The difference from Example 1 is that in S3, sulfuric acid is added to the bamboo miscellaneous cells to obtain a slurry, so that the concentration of sulfuric acid in the slurry is 1.5% and the pulp consistency is 9%; in S4, the slurry is heated to 90 °C and reacted for 4 hours under dynamic mixing conditions.

[0068] The microcrystalline cellulose prepared by the method for preparing microcrystalline cellulose in this comparative example has a yield of 82%, a degree of polymerization (DP) of 480, and a carbohydrate content of 99.2%.

[0069] As can be seen from the above examples and comparative examples, in Comparative Examples 1-3, the reaction pulp consistency is greater than 5%, and the yield of the prepared microcrystalline cellulose is slightly higher than that in Examples 1-3. However, its degree of polymerization (DP) cannot meet the requirement that the degree of polymerization of microcrystalline cellulose is not higher than 375.

[0070] In this application, the degree of polymerization (DP) of the microcrystalline cellulose is measured by a viscosity method or an infrared spectroscopy method; the carbohydrate content of the microcrystalline cellulose is measured by a spectrophotometry method, a chromatography method or a titration method.

[0071] The above are only the embodiments of this application, and do not limit the patent scope of this application. Any equivalent structure or equivalent process transformation made by using the content of this application's specification, or directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of this application.

Claims

1. A method for preparing microcrystalline cellulose, characterized in that, It includes the following steps: (1) Provide fine bamboo material components; (2) Screen the fine bamboo material components to obtain bamboo miscellaneous cells; (3) Add inorganic acid to the bamboo miscellaneous cells to obtain a slurry, such that the concentration of the inorganic acid in the slurry is 0.5% - 2%, and the pulp consistency is 3% - 5%; (4) Heat to raise the temperature of the slurry to 95 - 130 °C, and react for 2 - 4 hours under dynamic mixing conditions; (5) Cool the reacted slurry to below 80 °C, and then perform solid - liquid separation to obtain a solid and waste acid; (6) Wash the solid to neutral; (7) Dry the solid obtained in step (6), and pulverize it to obtain microcrystalline cellulose.

2. The preparation method of microcrystalline cellulose according to claim 1, characterized in that, The fine bamboo material components are the fine components obtained in the screening process of bleached bamboo fluff pulp production.

3. The preparation method of microcrystalline cellulose according to claim 2, characterized in that, The screening process includes: pumping bleached bamboo pulp into a bamboo pulp screening system for screening and grading, and separating out long - fiber pulp and the fine components.

4. The preparation method of microcrystalline cellulose according to claim 1, characterized in that, In the fine bamboo material components, the content of bamboo miscellaneous cells is not less than 80%.

5. The preparation method of microcrystalline cellulose according to claim 1, characterized in that, In step (2), an arc - shaped screen is used to screen the fine bamboo material components. The aperture of the screen holes of the arc - shaped screen is 0.5 - 1.0 mm, and the bamboo miscellaneous cells are the part passing through the screen holes after screening.

6. The preparation method of microcrystalline cellulose according to claim 1, wherein, The inorganic acid is any one of sulfuric acid or hydrochloric acid.

7. The method for preparing microcrystalline cellulose according to claim 1, characterized in that, This preparation method further includes a step of adding lime to the waste acid produced in step (5). After the waste acid and lime undergo a neutralization reaction, gypsum is obtained.

8. The preparation method of microcrystalline cellulose according to claim 1, characterized in that, The degree of polymerization of the microcrystalline cellulose is not higher than 375.

9. The preparation method of microcrystalline cellulose according to claim 1, characterized in that, In step (7), dry the solid obtained in step (6) until its dryness is higher than 93%.

10. A kind of microcrystalline cellulose is prepared by the method for preparing microcrystalline cellulose according to any one of claims 1 - 9. The yield of the microcrystalline cellulose is not less than 50%, and its carbohydrate content is not less than 97%.