An environmentally friendly multistage co-production method for preparing microcrystalline cellulose and nanocrystalline cellulose

Abstract

The application discloses an environment-friendly multistage co-production method for preparing microcrystal cellulose and nanocrystal cellulose, and belongs to the technical field of cellulose product preparation. White colloidal nanocrystal cellulose is obtained by hydrolyzing plant fiber raw materials or microcrystal cellulose with high-concentration inorganic acid; white colloidal microcrystal cellulose is obtained by separating and obtaining medium-concentration inorganic acid hydrolyzed plant fiber raw materials; medium-concentration inorganic acid can be recycled to hydrolyze plant fiber raw materials or high-concentration inorganic acid is obtained by evaporation concentration and used for preparing nanocrystal cellulose; and low-concentration acid for washing white colloidal microcrystal cellulose or nanocrystal cellulose is neutralized by insoluble carbonate to obtain a neutral solution. The application realizes multistage efficient utilization of inorganic acid solution, eliminates negative effects of inorganic acid waste liquid discharge, realizes environment-friendly production, and realizes co-production preparation of microcrystal cellulose and nanocrystal cellulose.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of environment-friendly preparation of cellulose products, and particularly relates to an environment-friendly method for preparing microcrystalline cellulose and nanocrystalline cellulose through multi-stage and multi-production. BACKGROUND

[0002] Cellulose is the most abundant natural polymer in nature, and exists widely in plants such as sugarcane, bamboo, wood and straw. Cellulose exists in different dimensional aggregation states from macro to micro. In plants, cellulose is an important support component of plants. Millimeter cellulose obtained by industrial dissociation through pulping (fiber separation) and other technologies is the main raw material of the papermaking industry. Microcrystalline cellulose can be prepared by dilute acid hydrolysis of millimeter cellulose fibers. Millimeter or micro cellulose fibers can be hydrolyzed by strong acid to prepare nanocrystalline cellulose.

[0003] The main laboratory-scale preparation process of microcrystalline cellulose is to use hydrochloric acid, sulfuric acid or phosphoric acid and other inorganic acids to hydrolyze at a low concentration (such as 2N HCl) and a certain temperature (such as 90℃) for 0.5 hours to obtain a particle size in the range of 20-80μm. The main industrial-scale preparation of microcrystalline cellulose is to use hydrochloric acid hydrolysis. The preparation of microcrystalline cellulose produces a large amount of inorganic acid waste liquid, which has a harmful impact on the environment.

[0004] Nanocrystalline cellulose is a new type of cellulose-based nanomaterial in recent years. The laboratory-scale preparation process is to use hydrochloric acid, sulfuric acid or phosphoric acid and other inorganic acids to hydrolyze at a high concentration (such as 64% sulfuric acid) and a certain temperature (such as 60℃) for 1.5 hours to obtain a particle size width in the range of 5-20nm and a length in the range of 80-200nm. The industrial-scale preparation of nanocrystalline cellulose has not been realized in the world. The preparation of nanocrystalline cellulose produces a large amount of inorganic acid waste liquid, which has a harmful impact on the environment due to its high concentration and strong corrosion.

[0005] Therefore, it is necessary to develop an environment-friendly method for preparing microcrystalline cellulose and nanocrystalline cellulose through multi-stage and multi-production, which uses high-concentration inorganic acid solution to prepare nanocrystalline cellulose, then uses the inorganic acid solution with medium concentration obtained by diluting the concentrated inorganic acid to separate nanocrystalline cellulose as a hydrolysis liquid to prepare microcrystalline cellulose, realizes multi-stage and efficient utilization of inorganic acid, reduces its toxic and side effects on the biosphere, and realizes the environment-friendly preparation of microcrystalline cellulose and nanocrystalline cellulose through multi-stage and multi-production. SUMMARY

[0006] The present application solves the technical problem of providing an environment-friendly method for preparing microcrystalline cellulose and nanocrystalline cellulose through multi-stage and multi-production.

[0007] Technical solution: In order to solve the above technical problems, the technical scheme adopted by the present application is as follows:

[0008] An environmentally friendly multi-stage co-production method for preparing microcrystalline cellulose and nanocrystalline cellulose, characterized by comprising the following steps:

[0009] (1) Hydrolyzing plant fiber raw material powder or directly hydrolyzing microcrystalline cellulose in a high-concentration inorganic acid solution, and obtaining white colloidal nanocrystalline cellulose and a medium-concentration inorganic acid solution after post-processing;

[0010] (2) Using the medium-concentration inorganic acid solution obtained in step (1) as a hydrolysis solution to hydrolyze plant fiber raw material powder, and obtaining white colloidal microcrystalline cellulose and a medium-concentration inorganic acid solution after separation;

[0011] (3) Using the medium-concentration inorganic acid solution obtained in step (2) to hydrolyze plant fiber raw material powder multiple times to prepare white colloidal microcrystalline cellulose, or using evaporation concentration to obtain a high-concentration inorganic acid solution for preparing nanocrystalline cellulose.

[0012] (4) Using an insoluble carbonate to neutralize the low-concentration inorganic acid solution obtained by washing the white colloidal microcrystalline cellulose and nanocrystalline cellulose in steps (1)-(3) to obtain a neutral solution.

[0013] The high-concentration inorganic acid solution of step (1) includes 50-70wt% sulfuric acid, 8-10mol / L phosphoric acid, and 8-10N hydrochloric acid.

[0014] The preheating temperature of steps (1)-(3) is 40-110℃, and the reaction time is 50-180 minutes.

[0015] The plant fiber of steps (1)-(3) includes bamboo fiber, wood fiber, straw fiber, and sugarcane residue fiber.

[0016] The medium-concentration inorganic acid solution of steps (1)-(3) includes 10-20wt% sulfuric acid, 2-5mol / L phosphoric acid, and 1-3N hydrochloric acid.

[0017] The inorganic acid solution of step (1) is used for the production and preparation of microcrystalline cellulose or nanocrystalline cellulose of different scale cellulose products.

[0018] In step (2), the high-concentration inorganic acid solution of step (1) is diluted to a medium-concentration inorganic acid solution for preparing microcrystalline cellulose after hydrolyzing plant fiber to prepare nanocrystalline cellulose, and the low-concentration inorganic acid solution obtained by washing the microcrystalline cellulose and nanocrystalline cellulose is neutralized by insoluble salt.

[0019] The low-concentration inorganic acid solution of the step (4) includes <1wt% sulfuric acid, <0.2mol / L phosphoric acid, <0.2N hydrochloric acid.

[0020] The insoluble carbonate of the step (4) includes barium carbonate, calcium carbonate, silver carbonate.

[0021] Compared with the prior art, the present application has the following advantages:

[0022] (1) The present application directly hydrolyzes plant fiber raw materials or microcrystal cellulose with high-concentration inorganic acid solution, then hydrolyzes plant fiber raw material powder with the medium-concentration inorganic acid solution obtained by separating and purifying nanocrystal cellulose, repeatedly uses the medium-concentration inorganic acid solution to hydrolyze plant fiber raw material powder to prepare white colloidal microcrystal cellulose, or uses evaporation concentration to obtain high-concentration inorganic acid solution for preparing nanocrystal cellulose. The low-concentration inorganic acid solution obtained by washing microcrystal cellulose and nanocrystal cellulose is neutralized, the whole process realizes multi-stage efficient use of inorganic acid solution, and realizes environment-friendly production.

[0023] (2) The present application hydrolyzes to prepare microcrystal cellulose with medium-concentration inorganic acid solution, and hydrolyzes to prepare nanocrystal cellulose with high-concentration inorganic acid solution, realizing combined preparation of cellulose products (microcrystal cellulose and nanocrystal cellulose) of different sizes. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 It is a process flow chart for preparing microcrystal cellulose and nanocrystal cellulose based on environment-friendly multi-stage combined production. DETAILED DESCRIPTION

[0025] The present application will be further illustrated by specific examples, the examples are implemented on the premise of the technical scheme of the present application, and it should be understood that the examples are only used for illustrating the present application and are not used for limiting the scope of the present application.

[0026] The method provided in the present application uses plant fiber powder as raw material, and prepares microcrystal cellulose and nanocrystal cellulose through multi-stage combined production by acid solution treatment, and includes the following steps:

[0027] (1) configuring high-concentration inorganic acid solution (including 50-70wt% sulfuric acid, 8-10mol / L phosphoric acid, 8-10N hydrochloric acid), preheating to 40-110℃, hydrolyzing plant fiber raw material powder or directly hydrolyzing microcrystal cellulose for 50-180 minutes, obtaining white colloidal nanocrystal cellulose through post-treatment, and medium-concentration inorganic acid solution (including 10-20wt% sulfuric acid, 2-5mol / L phosphoric acid, 1-3N hydrochloric acid);

[0028] (2) The medium concentration inorganic acid solution obtained in step (1) is used as a hydrolysis solution to hydrolyze the plant fiber raw material powder multiple times, and after separation, white colloidal micrometer crystal cellulose and a medium-low concentration inorganic acid solution are obtained; wherein the medium concentration inorganic acid solution can be concentrated by evaporation to obtain a high concentration inorganic acid solution for preparing nanocrystal cellulose in step (1).

[0029] (3) The white colloidal micrometer crystal cellulose and the white colloidal nanocrystal cellulose obtained in steps (1)-(2) are washed respectively to obtain neutral white colloidal micrometer crystal cellulose, neutral white colloidal nanocrystal cellulose and a low concentration acid solution (including <1wt% sulfuric acid, <0.2mol / L phosphoric acid, <0.2N hydrochloric acid), wherein the low concentration inorganic acid solution is neutralized by insoluble carbonate to obtain a neutral solution.

[0030] The following specific embodiments are carried out according to the above method:

[0031] Example 1

[0032] (1) Bamboo fiber is crushed and passed through a 200-mesh screen to obtain bamboo fiber powder, and a 64wt% sulfuric acid solution is prepared, which is preheated to 50°C, and 20g of bamboo fiber powder is added to 175mL of the preheated 64wt% sulfuric acid solution, and the reaction is carried out under mechanical stirring for 75 minutes;

[0033] (2) The reaction solution is poured into a separating funnel containing distilled water and left to stand until the solid and liquid are separated, and the white colloidal nanocrystal cellulose is taken out from the lower layer, and its size is characterized by AFM, with a diameter of 3-6nm and a length of 80-120nm, and a yield of 30%, and the upper layer clear transparent sulfuric acid solution is diluted to 15wt%;

[0034] (3) The white colloidal nanocrystal cellulose obtained in step (2) is washed to obtain neutral white colloidal nanocrystal cellulose and a low concentration acid solution (<1wt%), wherein the low concentration sulfuric acid solution is neutralized with calcium carbonate to obtain a neutral solution;

[0035] (4) The 700mL of the upper layer clear transparent acid solution diluted to 15wt% in step (2) is preheated to 50°C, and then 70g of bamboo fiber powder is added, and the reaction is carried out under mechanical stirring for 90 minutes;

[0036] (5) The reaction solution is poured into a separating funnel and left to stand until the solid and liquid are separated, and the white colloidal micrometer crystal cellulose is taken out from the lower layer, and its size is characterized by optical microscope, with a size of 40-80μm and a yield of 75%, and the upper layer clear transparent medium concentration sulfuric acid solution (15wt%);

[0037] (6) The white colloidal microcrystalline cellulose obtained in step (5) is washed to obtain neutral white colloidal nanocrystalline cellulose and a low-concentration sulfuric acid solution (<1 wt%), wherein the low-concentration sulfuric acid solution is neutralized with calcium carbonate to obtain a neutral solution;

[0038] (7) Wherein, the medium-concentration sulfuric acid solution obtained in step (2) or step (5) is used to hydrolyze microcrystalline cellulose to prepare white colloidal nanocrystalline cellulose and a medium-concentration sulfuric acid solution by concentrating; or the medium-concentration sulfuric acid solution obtained in step (5) can be recycled to hydrolyze plant fiber raw materials to prepare white colloidal microcrystalline cellulose and a medium-concentration sulfuric acid solution.

[0039] Example 2

[0040] (1) Bamboo fibers are crushed and passed through a 200-mesh screen to obtain bamboo fiber powder. A 10 mol / L phosphoric acid solution is prepared and preheated to 100°C. 20 g of bamboo fiber powder is added to the preheated 175 mL 10 mol / L phosphoric acid solution, and the reaction is carried out under mechanical stirring for 180 minutes;

[0041] (2) The reaction solution is poured into a separating funnel containing distilled water and allowed to stand until the solid and liquid are separated. The white colloidal nanocrystalline cellulose is taken from the lower layer, and its size is characterized by AFM, with a diameter of 6-12 nm and a length of 100-140 nm. The upper layer of clear transparent phosphoric acid solution is diluted to 3 mol / L;

[0042] (3) The white colloidal nanocrystalline cellulose obtained in step (2) is washed to obtain neutral white colloidal nanocrystalline cellulose and a low-concentration acid solution (<0.2 mol / L), wherein the low-concentration phosphoric acid solution is neutralized with calcium carbonate to obtain a neutral solution;

[0043] (4) The upper layer of clear transparent acid solution of 500 mL diluted to 3 mol / L in step (2) is preheated to 70°C, and then 50 g of bamboo fiber powder is added. The reaction is carried out under mechanical stirring for 90 minutes;

[0044] (5) The reaction solution is poured into a separating funnel and allowed to stand until the solid and liquid are separated. The white colloidal microcrystalline cellulose is taken from the lower layer, and its size is characterized by optical microscopy, with a size of 60-100 μm and a yield of 80%. The upper layer is a clear transparent medium-concentration phosphoric acid solution (3 mol / L);

[0045] (6) The white colloidal microcrystalline cellulose obtained in step (5) is washed to obtain neutral white colloidal nanocrystalline cellulose and a low-concentration phosphoric acid solution (<0.2 mol / L), wherein the low-concentration phosphoric acid solution is neutralized with calcium carbonate to obtain a neutral solution;

[0046] (7) wherein the medium concentration phosphoric acid solution obtained in step (2) or step (5) is used to obtain a high concentration phosphoric acid solution by concentration to hydrolyze microcrystal cellulose to prepare white colloidal nanocrystal cellulose and medium concentration phosphoric acid solution; or the medium concentration phosphoric acid solution obtained in step (5) can be recycled to hydrolyze plant fiber raw material to prepare white colloidal microcrystal cellulose and medium concentration phosphoric acid solution.

[0047] Example 3

[0048] (1) Bamboo fiber is crushed and passed through a 200 mesh screen to obtain bamboo fiber powder. An 8N hydrochloric acid solution is prepared and preheated to 110°C. 20g of the bamboo fiber powder is added to 175mL of the preheated 8N hydrochloric acid solution and reacted for 120 minutes under mechanical stirring;

[0049] (2) The reaction solution is poured into a separating funnel containing distilled water and allowed to stand until the solid and liquid are separated. The white colloidal nanocrystal cellulose is taken from the lower layer and characterized by AFM. The diameter is 14-20nm and the length is 200-250nm. The upper layer clear transparent hydrochloric acid solution is diluted to 2N;

[0050] (3) The white colloidal nanocrystal cellulose obtained in step (2) is washed to obtain neutral white colloidal nanocrystal cellulose and low concentration acid solution (<0.2N). The low concentration hydrochloric acid solution is neutralized with silver carbonate to obtain a neutral solution;

[0051] (4) 700mL of the upper layer clear transparent acid solution diluted to 2N in step (2) is preheated to 70°C and then 70g of bamboo fiber powder is added. The reaction is carried out for 50 minutes under mechanical stirring;

[0052] (5) The reaction solution is poured into a separating funnel and allowed to stand until the solid and liquid are separated. The white colloidal microcrystal cellulose is taken from the lower layer and characterized by optical microscope. The size is 80-120μm and the yield is 85%. The upper layer clear transparent medium concentration hydrochloric acid solution (2N);

[0053] (6) The white colloidal microcrystal cellulose obtained in step (5) is washed to obtain neutral white colloidal nanocrystal cellulose and low concentration hydrochloric acid solution (<0.2N). The low concentration hydrochloric acid solution is neutralized with silver carbonate to obtain a neutral solution;

[0054] (7) wherein the medium concentration hydrochloric acid solution obtained in step (2) or step (5) is used to obtain a high concentration hydrochloric acid solution by concentration to hydrolyze microcrystal cellulose to prepare white colloidal nanocrystal cellulose and medium concentration hydrochloric acid solution; or the medium concentration hydrochloric acid solution obtained in step (5) can be recycled to hydrolyze plant fiber raw material to prepare white colloidal microcrystal cellulose and medium concentration hydrochloric acid solution.

[0055] Example 4

[0056] (1) Wood fibers were pulverized through a 200-mesh screen to obtain wood fiber powder, a 64wt% sulfuric acid solution was prepared, the sulfuric acid solution was preheated to 65°C, and 20 g of wood fiber powder was added to 175 mL of the preheated 64wt% sulfuric acid solution, and the reaction was carried out under mechanical stirring for 90 minutes;

[0057] (2) The reaction solution was poured into a separating funnel containing distilled water and allowed to stand until the solid and liquid were separated, and then the white colloidal nanocrystalline cellulose was taken from the lower layer, and its size was characterized by AFM, with a diameter of 3-6 nm and a length of 80-120 nm, and a yield of 25%, and the upper layer of clear transparent sulfuric acid solution was diluted to 15wt%;

[0058] (3) The white colloidal nanocrystalline cellulose obtained in step (2) was washed to obtain neutral white colloidal nanocrystalline cellulose and a low-concentration acid solution (<1wt%), and the low-concentration sulfuric acid solution was neutralized with calcium carbonate to obtain a neutral solution;

[0059] (4) 800 mL of the upper layer of clear transparent acid solution diluted to 15wt% in step (2) was preheated to 50°C, and then 80 g of wood fiber powder was added, and the reaction was carried out under mechanical stirring for 90 minutes;

[0060] (5) The reaction solution was poured into a separating funnel and allowed to stand until the solid and liquid were separated, and then the white colloidal microcrystalline cellulose was taken from the lower layer, and its size was characterized by optical microscopy, with a size of 60-100 μm and a yield of 60%, and the upper layer of clear transparent medium-concentration sulfuric acid solution (15wt%);

[0061] (6) The white colloidal microcrystalline cellulose obtained in step (5) was washed to obtain neutral white colloidal nanocrystalline cellulose and a low-concentration sulfuric acid solution (<1wt%), and the low-concentration sulfuric acid solution was neutralized with calcium carbonate to obtain a neutral solution;

[0062] (7) The medium-concentration sulfuric acid solution obtained in step (2) or step (5) was used to prepare white colloidal nanocrystalline cellulose and a medium-concentration sulfuric acid solution by hydrolyzing microcrystalline cellulose using a concentration method, or the medium-concentration sulfuric acid solution obtained in step (5) could be recycled to hydrolyze plant fiber raw materials to prepare white colloidal microcrystalline cellulose and a medium-concentration sulfuric acid solution.

[0063] Example 5

[0064] (1) Wood fiber is crushed and passed through a 200-mesh screen to obtain wood fiber powder. A 10 mol / L phosphoric acid solution is prepared and preheated to 100°C. 20 g of the wood fiber powder is added to 175 mL of the preheated 10 mol / L phosphoric acid solution, and the mixture is stirred for 180 minutes under mechanical stirring;

[0065] (2) The reaction solution is poured into a separating funnel containing distilled water and allowed to stand until the solid and liquid are separated. The white colloidal nanocrystalline cellulose is taken from the lower layer, and its size is characterized by AFM. The diameter is 4-10 nm, and the length is 80-120 nm. The clear and transparent phosphoric acid solution in the upper layer is diluted to 3 mol / L;

[0066] (3) The white colloidal nanocrystalline cellulose obtained in step (2) is washed to obtain neutral white colloidal nanocrystalline cellulose and a low-concentration acid solution (<0.2 mol / L). The low-concentration phosphoric acid solution is neutralized with calcium carbonate to obtain a neutral solution;

[0067] (4) 500 mL of the clear and transparent acid solution in the upper layer obtained in step (2) is preheated to 70°C, and then 50 g of wood fiber powder is added. The mixture is stirred for 90 minutes under mechanical stirring;

[0068] (5) The reaction solution is poured into a separating funnel and allowed to stand until the solid and liquid are separated. The white colloidal microcrystalline cellulose is taken from the lower layer, and its size is characterized by optical microscopy. The yield is 75%, and the size is 50-90 μm. The clear and transparent medium-concentration phosphoric acid solution (3 mol / L) is in the upper layer;

[0069] (6) The white colloidal microcrystalline cellulose obtained in step (5) is washed to obtain neutral white colloidal nanocrystalline cellulose and a low-concentration phosphoric acid solution (<0.2 mol / L). The low-concentration phosphoric acid solution is neutralized with calcium carbonate to obtain a neutral solution;

[0070] (7) The medium-concentration phosphoric acid solution obtained in step (2) or step (5) is concentrated to obtain a high-concentration phosphoric acid solution, which is used to hydrolyze microcrystalline cellulose to prepare white colloidal nanocrystalline cellulose and a medium-concentration phosphoric acid solution. The medium-concentration phosphoric acid solution obtained in step (5) can be recycled to hydrolyze plant fiber raw materials to prepare white colloidal microcrystalline cellulose and a medium-concentration phosphoric acid solution.

[0071] Example 6

[0072] (1) Wood fiber is crushed and passed through a 200-mesh screen to obtain wood fiber powder. An 8N hydrochloric acid solution is prepared and preheated to 110°C. 20 g of the wood fiber powder is added to 175 mL of the preheated 8N hydrochloric acid solution, and the mixture is stirred for 120 minutes under mechanical stirring;

[0073] (2) The reaction solution is poured into a separating funnel containing distilled water and left to stand until the solid and liquid are separated, then the white colloidal nanocrystalline cellulose is taken from the lower layer, and its size is characterized by AFM, with a diameter of 10-16 nm and a length of 180-250 nm, and the clear and transparent acid solution in the upper layer is diluted to 2N;

[0074] (3) The white colloidal nanocrystalline cellulose obtained in step (2) is washed to obtain neutral white colloidal nanocrystalline cellulose and a low-concentration acid solution (<0.2N), and the low-concentration acid solution is neutralized with silver carbonate to obtain a neutral solution;

[0075] (4) 700 mL of the clear and transparent acid solution in the upper layer diluted to 2N in step (2) is preheated to 70°C, and then 70 g of bamboo fiber powder is added, and the reaction is carried out for 50 minutes under mechanical stirring;

[0076] (5) The reaction solution is poured into a separating funnel and left to stand until the solid and liquid are separated, then the white colloidal microcrystalline cellulose is taken from the lower layer, and its size is characterized by optical microscopy, with a size of 50-110 μm, and the yield is 85%, and the clear and transparent acid solution in the upper layer is diluted to 2N;

[0077] (6) The white colloidal microcrystalline cellulose obtained in step (5) is washed to obtain neutral white colloidal nanocrystalline cellulose and a low-concentration acid solution (<0.2N), and the low-concentration acid solution is neutralized with silver carbonate to obtain a neutral solution;

[0078] (7) The medium-concentration acid solution obtained in step (2) or step (5) is used to prepare white colloidal nanocrystalline cellulose and a high-concentration acid solution by concentrating the medium-concentration acid solution; or the medium-concentration acid solution obtained in step (5) can be recycled to hydrolyze plant fiber raw materials to prepare white colloidal microcrystalline cellulose and a medium-concentration acid solution.

[0079] Example 7

[0080] (1) Bamboo fibers are crushed and passed through a 200-mesh sieve to obtain bamboo fiber powder, and a 58wt% sulfuric acid solution is prepared, and the sulfuric acid solution is preheated to 60°C, and 20 g of bamboo fiber powder is added to 175 mL of preheated 58wt% sulfuric acid, and the reaction is carried out for 75 minutes under mechanical stirring;

[0081] (2) The reaction solution is poured into a separating funnel containing distilled water and left to stand until the solid and liquid are separated, then the white colloidal nanocrystalline cellulose is taken from the lower layer, and its size is characterized by AFM, with a diameter of 5-8 nm and a length of 100-160 nm, and the yield is 40%, and the clear and transparent acid solution in the upper layer is diluted to 10wt%;

[0082] (3) The white gelatinous nanocrystalline cellulose obtained in step (2) is washed to obtain neutral white gelatinous nanocrystalline cellulose and a low-concentration sulfuric acid solution (<1 wt%), wherein the low-concentration sulfuric acid solution is neutralized with barium carbonate to obtain a neutral solution;

[0083] (4) The upper layer clear transparent acid solution of 10 wt% obtained in step (2) is diluted to 1000 mL and preheated to 40°C, and then 100 g of bamboo fiber powder is added, and the reaction is carried out for 120 minutes under mechanical stirring;

[0084] (5) The reaction liquid is poured into a separating funnel and left to stand until the solid-liquid separation is completed, and then the white gelatinous microcrystalline cellulose is taken out from the lower layer, and the size thereof is characterized by an optical microscope to be 60-120 μm, and the yield thereof is 80%, and the upper layer clear transparent medium-concentration sulfuric acid solution (10 wt%);

[0085] (6) The white gelatinous microcrystalline cellulose obtained in step (5) is washed to obtain neutral white gelatinous nanocrystalline cellulose and a low-concentration sulfuric acid solution (<1 wt%), wherein the low-concentration sulfuric acid solution is neutralized with barium carbonate to obtain a neutral solution;

[0086] (7) The medium-concentration sulfuric acid solution obtained in step (2) or step (5) is used to hydrolyze microcrystalline cellulose to prepare white gelatinous nanocrystalline cellulose and a medium-concentration sulfuric acid solution by means of concentration; or the medium-concentration sulfuric acid solution obtained in step (5) can be recycled to hydrolyze plant fiber raw materials to prepare white gelatinous microcrystalline cellulose and a medium-concentration sulfuric acid solution.

[0087] Example 8

[0088] (1) Bamboo fiber is crushed and passed through a 200-mesh screen to obtain bamboo fiber powder, and a phosphoric acid solution of 8 mol / L is prepared, and the phosphoric acid solution is preheated to 90°C, and 20 g of bamboo fiber powder is added to 175 mL of the preheated 8 mol / L phosphoric acid solution, and the reaction is carried out for 120 minutes under mechanical stirring;

[0089] (2) The reaction liquid is poured into a separating funnel containing distilled water and left to stand until the solid-liquid separation is completed, and then the white gelatinous nanocrystalline cellulose is taken out from the lower layer, and the size thereof is characterized by AFM to be 14-20 nm in diameter and 140-180 nm in length, and the upper layer clear transparent phosphoric acid solution is diluted to 5 mol / L;

[0090] (3) The white gelatinous nanocrystalline cellulose obtained in step (2) is washed to obtain neutral white gelatinous nanocrystalline cellulose and a low-concentration acid solution (<0.2 mol / L), wherein the low-concentration phosphoric acid solution is neutralized with barium carbonate to obtain a neutral solution;

[0091] (4) The step (2) is diluted to 5 mol / L of the upper clear transparent acid solution 400 mL preheated to 50°C, then 40 g of bamboo fiber powder is added, and the reaction is carried out for 90 minutes under mechanical stirring;

[0092] (5) The reaction liquid is poured into a separating funnel and left to stand, and when the solid-liquid separation is completed, the white colloidal micron crystalline cellulose is taken out from the lower layer, and the size thereof is characterized by an optical microscope, which is 40-80 μm, and the yield is 75%, and the upper clear transparent medium concentration phosphoric acid solution (5 mol / L);

[0093] (6) The white colloidal micron crystalline cellulose obtained in step (5) is washed to obtain neutral white colloidal nanocrystalline cellulose and low concentration phosphoric acid solution (<0.2 mol / L), wherein the low concentration phosphoric acid solution is neutralized with barium carbonate to obtain a neutral solution;

[0094] (7) Among them, the medium concentration phosphoric acid solution obtained in step (2) or step (5) is used to hydrolyze micron crystalline cellulose to prepare white colloidal nanocrystalline cellulose and medium concentration phosphoric acid solution by concentrating; or the medium concentration phosphoric acid solution obtained in step (5) can be recycled to hydrolyze plant fiber raw materials to prepare white colloidal micron crystalline cellulose and medium concentration phosphoric acid solution.

[0095] Example 9

[0096] (1) The bamboo fiber is crushed and passed through a 200 mesh screen to obtain bamboo fiber powder, a 10N hydrochloric acid solution is prepared, the hydrochloric acid solution is preheated to 90°C, 20 g of bamboo fiber powder is added to the preheated 175 mL 10N hydrochloric acid solution, and the reaction is carried out for 120 minutes under mechanical stirring;

[0097] (2) The reaction liquid is poured into a separating funnel containing distilled water and left to stand, and when the solid-liquid separation is completed, the white colloidal nanocrystalline cellulose is taken out from the lower layer, and the size thereof is characterized by AFM, which is 12-20 nm in diameter and 160-200 nm in length, and the upper clear transparent hydrochloric acid solution is diluted to 3N;

[0098] (3) The white colloidal nanocrystalline cellulose obtained in step (2) is washed to obtain neutral white colloidal nanocrystalline cellulose and low concentration acid solution (<0.2N), wherein the low concentration hydrochloric acid solution is neutralized with silver carbonate to obtain a neutral solution;

[0099] (4) The step (2) is diluted to 3N of the upper clear transparent acid solution 600 mL preheated to 80°C, then 60 g of bamboo fiber powder is added, and the reaction is carried out for 50 minutes under mechanical stirring;

[0100] (5) The reaction solution is poured into a separating funnel and left to stand until the solid-liquid separation is achieved. The white gelatinous microcrystalline cellulose is taken out from the lower layer, and its size is characterized by an optical microscope to be 60-100 μm, and the yield is 80%. The upper layer is a clear and transparent medium-concentration hydrochloric acid solution (3N);

[0101] (6) The white gelatinous microcrystalline cellulose obtained in step (5) is washed to obtain neutral white gelatinous nanocrystalline cellulose and low-concentration hydrochloric acid solution (<0.2N). The low-concentration hydrochloric acid solution is neutralized by silver carbonate to obtain a neutral solution.

[0102] (7) The medium-concentration hydrochloric acid solution obtained in step (2) or step (5) is concentrated to obtain a high-concentration hydrochloric acid solution to hydrolyze microcrystalline cellulose and prepare white gelatinous nanocrystalline cellulose and medium-concentration hydrochloric acid solution. The medium-concentration hydrochloric acid solution obtained in step (5) can be recycled to hydrolyze plant fiber raw materials to prepare white gelatinous microcrystalline cellulose and medium-concentration hydrochloric acid solution.

[0103] The above only describes the preferred embodiments of the present application. It should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. An environmentally friendly, multi-stage co-production method for preparing micron-crystalline cellulose and nanocrystalline cellulose, characterized in that, Includes the following steps: (1) Plant fiber raw material powder is hydrolyzed with a high-concentration inorganic acid solution or micron-sized crystalline cellulose is directly hydrolyzed, and then post-processed to obtain white colloidal nanocrystalline cellulose and a medium-concentration inorganic acid solution; the high-concentration inorganic acid solution includes 50-70 wt% sulfuric acid or 8-10 mol / L phosphoric acid or 8-10 N hydrochloric acid; the inorganic acid solution is used for the production and preparation of cellulose products of different scales, such as micron-sized crystalline cellulose or nanocrystalline cellulose; (2) The medium-concentration inorganic acid solution obtained in step (1) is used as the hydrolysis solution to hydrolyze the plant fiber raw material powder. After separation, white colloidal micron-sized crystalline cellulose and medium-concentration inorganic acid solution are obtained. In step (2), micron-sized crystalline cellulose is prepared by hydrolyzing plant fiber with the high-concentration inorganic acid solution in step (1) to prepare nano-crystalline cellulose. The solution is then diluted to a medium-concentration inorganic acid solution for preparing micron-sized crystalline cellulose. The low-concentration inorganic acid solution obtained by washing micron-sized crystalline cellulose and nano-crystalline cellulose is neutralized with insoluble salt. (3) The medium-concentration inorganic acid solution obtained in step (2) is recycled multiple times to hydrolyze the plant fiber raw material powder to prepare white colloidal micron-sized crystalline cellulose, or a high-concentration inorganic acid solution is obtained by evaporation and concentration to prepare nanocrystalline cellulose. (4) The low-concentration inorganic acid solution obtained by washing the white colloidal micron-sized crystalline cellulose and nano-crystalline cellulose in steps (1)-(3) is neutralized with insoluble carbonate to obtain a neutral solution; the low-concentration inorganic acid solution includes <1 wt% sulfuric acid or <0.2 mol / L phosphoric acid or <0.2 N hydrochloric acid; The medium-concentration inorganic acid solutions in steps (1) to (3) include 10-20 wt% sulfuric acid, 2-5 mol / L phosphoric acid, or 1-3 N hydrochloric acid.

2. The method for preparing micron-crystalline cellulose and nanocrystalline cellulose through environmentally friendly multi-stage co-production according to claim 1, characterized in that: The preheating temperature of the high-concentration inorganic acid solution in steps (1) to (3) is 40 to 110 ℃, and the reaction time for hydrolyzing plant fiber raw material powder or directly hydrolyzing micron-sized crystalline cellulose is 50 to 180 minutes.

3. The method for preparing micron-crystalline cellulose and nanocrystalline cellulose through environmentally friendly multi-stage co-production according to claim 1, characterized in that: The plant fibers used in steps (1) to (3) include bamboo fiber, wood fiber, straw fiber, or bagasse fiber.

4. The method for preparing micron-crystalline cellulose and nanocrystalline cellulose through environmentally friendly multi-stage co-production according to claim 1, characterized in that: The insoluble carbonate in step (4) includes barium carbonate, calcium carbonate, or silver carbonate.

Images