Environment-friendly method for preparing micron crystal cellulose and nano crystal cellulose through multi-stage co-production

Abstract

The invention discloses an environment-friendly method for preparing micron crystal cellulose and nano crystal cellulose through multi-stage co-production, and belongs to the technical field of preparation of cellulose products. The method comprises the following steps: hydrolyzing a plant fiber raw material or micron crystal cellulose by using high-concentration inorganic acid to obtain white colloidal nano crystal cellulose, and separating the obtained medium-concentration inorganic acid to hydrolyze the plant fiber raw material to obtain white colloidal micron crystal cellulose. The separated medium-concentration inorganic acid can be used for cyclically hydrolyzing plant fiber raw materials or high-concentration inorganic acid obtained in an evaporation and concentration mode is used for preparing nanocrystal cellulose, and low-concentration acid for washing white colloidal micron crystal cellulose or nanocrystal cellulose is neutralized by insoluble carbonate to obtain a neutral solution. According to the method, the multi-stage efficient utilization of the inorganic acid solution is realized, the negative influence of the discharge of the inorganic acid waste liquid is eliminated, the environment-friendly production is realized, and the co-production preparation of the micron crystal cellulose and the nano crystal cellulose is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of environmentally friendly preparation of cellulose products, and in particular relates to an environmentally friendly multi-stage co-production method for preparing micron-crystalline cellulose and nano-crystalline cellulose. Background Art

[0002] Cellulose is the most abundant natural polymer in nature, and is widely found in plants such as sugarcane, bamboo, wood, and straw. Cellulose exists in aggregated forms of different dimensions from macroscopic to microscopic. In plants, cellulose is an important scaffold component of plants. Millimeter cellulose obtained by industrial dissociation through pulping (fiber separation) and other technical methods is the main raw material for the papermaking industry. Using millimeter cellulose fibers as raw materials, micron crystalline cellulose can be prepared through dilute acid hydrolysis, and millimeter or micron cellulose fibers can be prepared through strong acid hydrolysis to obtain nanocrystalline cellulose.

[0003] The main laboratory-scale preparation process of microcrystalline cellulose is to hydrolyze it with inorganic acids such as hydrochloric acid, sulfuric acid or phosphoric acid at low concentrations (such as 2N HCl) at a certain temperature (such as 90°C) for 0.5 hours, and its particle size is in the range of 20-80μm. Its industrial-scale preparation is mainly carried out by 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 that has emerged in recent years. Its laboratory-scale preparation process is to hydrolyze it with inorganic acids such as hydrochloric acid, sulfuric acid or phosphoric acid at high concentrations (such as 64% sulfuric acid) at a certain temperature (such as 60°C) for 1.5 hours. Its particle size is 5-20nm wide and 80-200nm long. Currently, industrial-scale preparation has not yet been achieved in the world. The preparation of nanocrystalline cellulose produces a large amount of inorganic acid waste liquid, which is high in concentration and highly corrosive, and has a harmful impact on the environment.

[0005] Therefore, a method for preparing nanocrystalline cellulose with a high-concentration inorganic acid solution, and then using a medium-concentration inorganic acid solution to separate the nanocrystalline cellulose with a diluted concentrated inorganic acid to prepare micron-crystalline cellulose is developed, so as to realize multi-stage efficient utilization of inorganic acids and reduce their toxic side effects on the biosphere. At the same time, an environmentally friendly preparation method for preparing micron-cellulose and nanocellulose in multi-stage co-production will significantly improve the utilization efficiency of inorganic acids, reduce the amount of acid used, and reduce the degree of pollution to the environment. Summary of the invention

[0006] The technical problem solved by the present invention is to provide an environmentally friendly multi-stage co-production method for preparing micron-crystalline cellulose and nano-crystalline cellulose.

[0007] Technical solution: In order to solve the above technical problems, the technical solution adopted by the present invention 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 micron-crystalline cellulose with a high-concentration inorganic acid solution, and obtaining white colloidal nanocrystalline cellulose and a medium-concentration inorganic acid solution through post-treatment;

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

[0011] (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-crystalline cellulose, or a high-concentration inorganic acid solution is obtained by evaporation and concentration to prepare nanocrystalline cellulose.

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

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

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

[0015] The plant fibers in steps (1) to (3) include bamboo fibers, wood fibers, straw fibers, and bagasse fibers.

[0016] The medium concentration inorganic acid solution in steps (1) to (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 cellulose products of different sizes such as micron crystalline cellulose or nano crystalline cellulose.

[0018] The step (2) of preparing micron-crystalline cellulose comprises: using the high-concentration inorganic acid solution in the step (1) to hydrolyze the plant fibers to prepare nano-crystalline cellulose, and then diluting it to a medium-concentration inorganic acid solution for preparing micron-crystalline cellulose; and the low-concentration inorganic acid solution obtained by washing the micron-crystalline cellulose and the nano-crystalline cellulose is neutralized with an insoluble salt.

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

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

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

[0022] (1) The present invention directly hydrolyzes plant fiber raw materials or micron crystalline cellulose with a high-concentration inorganic acid solution, and then separates and purifies the nanocrystalline cellulose to obtain a medium-concentration inorganic acid solution to hydrolyze the plant fiber raw material powder, and recycles the medium-concentration inorganic acid solution to hydrolyze the plant fiber raw material powder multiple times to prepare white colloidal micron crystalline cellulose, or uses an evaporation concentration method to obtain a high-concentration inorganic acid solution for preparing nanocrystalline cellulose. The low-concentration inorganic acid solution that cannot be used for hydrolysis obtained by washing the microcrystalline cellulose and nanocrystalline cellulose is neutralized, and the whole process realizes multi-stage efficient utilization of the inorganic acid solution and realizes environmentally friendly production.

[0023] (2) The present invention prepares micron-crystalline cellulose by hydrolysis with a medium-concentration inorganic acid solution and prepares nano-crystalline cellulose by hydrolysis with a high-concentration inorganic acid solution, thereby achieving the combined preparation of cellulose products of different sizes (micron-crystalline cellulose and nano-crystalline cellulose). BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a process flow chart for preparing microcrystalline cellulose and nanocrystalline cellulose based on environmentally friendly multi-stage co-production. DETAILED DESCRIPTION

[0025] The present invention is further illustrated below in conjunction with specific examples. The examples are implemented based on the technical solutions of the present invention. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0026] The method provided in the present application uses plant fiber powder as raw material, and prepares micron crystalline cellulose and nanocrystalline cellulose by multi-stage co-production through acid solution treatment, comprising the following steps:

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

[0028] (2) using the medium-concentration inorganic acid solution obtained in step (1) as a hydrolyzing solution, and hydrolyzing the plant fiber raw material powder in multiple cycles to obtain white colloidal microcrystalline cellulose and medium- and low-concentration inorganic acid solutions after separation; wherein the medium-concentration inorganic acid solution can be concentrated by evaporation to obtain a high-concentration inorganic acid solution for preparing nanocrystalline cellulose in step (1).

[0029] (3) Washing the white colloidal microcrystalline cellulose and the white colloidal nanocrystalline cellulose in steps (1)-(2) respectively to obtain neutral white colloidal microcrystalline cellulose, neutral white colloidal nanocrystalline 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 with an insoluble carbonate to obtain a neutral solution.

[0030] According to the above method, the following specific implementation is carried out:

[0031] Example 1

[0032] (1) crushing bamboo fiber and passing it through a 200-mesh sieve to obtain bamboo fiber powder, preparing a 64 wt % sulfuric acid solution, preheating the sulfuric acid solution to 50° C., adding 20 g of bamboo fiber powder to 175 mL of preheated 64 wt % sulfuric acid, and reacting for 75 minutes under mechanical stirring;

[0033] (2) pouring the reaction solution into a separation funnel filled with distilled water and letting it stand until the solid and liquid layers are separated, taking out white colloidal nanocrystalline cellulose from the lower layer, and characterizing its size by AFM, with a diameter of 3-6 nm, a length of 80-120 nm, and a yield of 30%, and diluting the upper clear and transparent sulfuric acid solution to 15 wt %;

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

[0035] (4) preheating 700 mL of the upper clear and transparent acid solution diluted to 15 wt% in step (2) to 50° C., then adding 70 g of bamboo fiber powder, and reacting for 90 minutes under mechanical stirring;

[0036] (5) The reaction solution was poured into a separation funnel and allowed to stand until solid-liquid separation. White colloidal microcrystalline cellulose was taken out from the lower layer. The size of the cellulose was 40-80 μm and the yield was 75% under an optical microscope. The upper layer was a clear and transparent medium-concentration sulfuric acid solution (15 wt%).

[0037] (6) washing the white colloidal microcrystalline cellulose obtained in step (5) 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 concentrated to obtain a high-concentration sulfuric acid solution to hydrolyze micron-crystalline cellulose to prepare white colloidal nano-crystalline cellulose and a medium-concentration sulfuric acid solution; or the medium-concentration sulfuric acid solution obtained in step (5) can be circulated multiple times to hydrolyze plant fiber raw materials to prepare white colloidal micron-crystalline cellulose and a medium-concentration sulfuric acid solution.

[0039] Example 2

[0040] (1) crushing bamboo fiber and passing it through a 200-mesh sieve to obtain bamboo fiber powder, preparing a 10 mol / L phosphoric acid solution, preheating the phosphoric acid solution to 100° C., adding 20 g of bamboo fiber powder to 175 mL of the preheated 10 mol / L phosphoric acid solution, and reacting for 180 minutes under mechanical stirring;

[0041] (2) The reaction solution was poured into a separation funnel filled with distilled water and allowed to stand until the solid and liquid layers were separated. White colloidal nanocrystalline cellulose was taken out from the lower layer and its size was characterized by AFM. The diameter was 6-12 nm and the length was 100-140 nm. The clear and transparent phosphoric acid solution in the upper layer was diluted to 3 mol / L.

[0042] (3) washing the white colloidal nanocrystalline cellulose obtained in step (2) 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) preheating 500 mL of the upper clear and transparent acid solution diluted to 3 mol / L in step (2) to 70° C., then adding 50 g of bamboo fiber powder and reacting for 90 minutes under mechanical stirring;

[0044] (5) The reaction solution was poured into a separation funnel and allowed to stand until solid-liquid separation. White colloidal microcrystalline cellulose was taken out from the lower layer. The size of the cellulose was 60-100 μm and the yield was 80% under an optical microscope. The upper layer was a clear and transparent medium-concentration phosphoric acid solution (3 mol / L).

[0045] (6) washing the white colloidal microcrystalline cellulose obtained in step (5) 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 concentrated to obtain a high-concentration phosphoric acid solution to hydrolyze micron-crystalline cellulose to prepare white colloidal nanocrystalline cellulose and a medium-concentration phosphoric acid solution; or the medium-concentration phosphoric acid solution obtained in step (5) can be circulated multiple times to hydrolyze plant fiber raw materials to prepare white colloidal micron-crystalline cellulose and a medium-concentration phosphoric acid solution.

[0047] Example 3

[0048] (1) crushing bamboo fiber and passing it through a 200-mesh sieve to obtain bamboo fiber powder, preparing an 8N hydrochloric acid solution, preheating the hydrochloric acid solution to 110° C., adding 20 g of bamboo fiber powder to 175 mL of the preheated 8N hydrochloric acid solution, and reacting for 120 minutes under mechanical stirring;

[0049] (2) The reaction solution was poured into a separation funnel filled with distilled water and allowed to stand until the solid and liquid layers were separated. White colloidal nanocrystalline cellulose was taken out from the lower layer and its size was characterized by AFM. The diameter was 14-20 nm and the length was 200-250 nm. The clear and transparent hydrochloric acid solution in the upper layer was diluted to 2N.

[0050] (3) washing the white colloidal nanocrystalline cellulose obtained in step (2) to obtain neutral white colloidal nanocrystalline cellulose and a low concentration acid solution (<0.2N), wherein the low concentration hydrochloric acid solution is neutralized with silver carbonate to obtain a neutral solution;

[0051] (4) preheating 700 mL of the upper clear and transparent acid solution diluted to 2N in step (2) to 70° C., then adding 70 g of bamboo fiber powder and reacting for 50 minutes under mechanical stirring;

[0052] (5) The reaction solution was poured into a separation funnel and allowed to stand until solid-liquid separation. White colloidal microcrystalline cellulose was taken out from the lower layer. The size of the cellulose was 80-120 μm under an optical microscope. The yield was 85%. The upper layer was a clear and transparent medium-concentration hydrochloric acid solution (2N);

[0053] (6) washing the white colloidal microcrystalline cellulose obtained in step (5) to obtain neutral white colloidal nanocrystalline cellulose and a low concentration hydrochloric acid solution (<0.2N), wherein the low concentration hydrochloric acid solution is neutralized with silver carbonate to obtain a neutral solution;

[0054] (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 micron-crystalline cellulose to prepare white colloidal nano-crystalline cellulose and a medium-concentration hydrochloric acid solution; or the medium-concentration hydrochloric acid solution obtained in step (5) can be circulated multiple times to hydrolyze plant fiber raw materials to prepare white colloidal micron-crystalline cellulose and a medium-concentration hydrochloric acid solution.

[0055] Example 4

[0056] (1) crushing wood fiber and passing it through a 200-mesh sieve to obtain wood fiber powder, preparing a 64 wt % sulfuric acid solution, preheating the sulfuric acid solution to 65° C., adding 20 g of the wood fiber powder to 175 mL of the preheated 64 wt % sulfuric acid solution, and reacting for 90 minutes under mechanical stirring;

[0057] (2) pouring the reaction solution into a separation funnel filled with distilled water and letting it stand until the solid and liquid layers are separated, taking out white colloidal nanocrystalline cellulose from the lower layer, and characterizing its size by AFM, with a diameter of 3-6 nm, a length of 80-120 nm, and a yield of 25%. The clear and transparent sulfuric acid solution in the upper layer is diluted to 15 wt %;

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

[0059] (4) preheating 800 mL of the upper clear and transparent acid solution diluted to 15 wt% in step (2) to 50° C., then adding 80 g of wood fiber powder, and reacting for 90 minutes under mechanical stirring;

[0060] (5) The reaction solution was poured into a separation funnel and allowed to stand until solid-liquid separation. White colloidal microcrystalline cellulose was taken out from the lower layer. The size of the cellulose was 60-100 μm and the yield was 60% under an optical microscope. The upper layer was a clear and transparent medium-concentration sulfuric acid solution (15 wt%).

[0061] (6) washing the white colloidal microcrystalline cellulose obtained in step (5) 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;

[0062] (7) wherein the medium-concentration sulfuric acid solution obtained in step (2) or step (5) is concentrated to obtain a high-concentration sulfuric acid solution to hydrolyze micron-crystalline cellulose to prepare white colloidal nano-crystalline cellulose and a medium-concentration sulfuric acid solution; or the medium-concentration sulfuric acid solution obtained in step (5) can be circulated multiple times to hydrolyze plant fiber raw materials to prepare white colloidal micron-crystalline cellulose and a medium-concentration sulfuric acid solution.

[0063] Example 5

[0064] (1) crushing wood fiber and passing it through a 200-mesh sieve to obtain wood fiber powder, preparing a 10 mol / L phosphoric acid solution, preheating the phosphoric acid solution to 100° C., adding 20 g of the wood fiber powder to 175 mL of the preheated 10 mol / L phosphoric acid solution, and reacting for 180 minutes under mechanical stirring;

[0065] (2) The reaction solution was poured into a separation funnel filled with distilled water and allowed to stand until the solid and liquid layers were separated. White colloidal nanocrystalline cellulose was taken out from the lower layer and its size was characterized by AFM. The diameter was 4-10 nm and the length was 80-120 nm. The clear and transparent phosphoric acid solution in the upper layer was diluted to 3 mol / L.

[0066] (3) washing the white colloidal nanocrystalline cellulose obtained in step (2) 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;

[0067] (4) preheating 500 mL of the upper clear and transparent acid solution diluted to 3 mol / L in step (2) to 70° C., then adding 50 g of wood fiber powder and reacting for 90 minutes under mechanical stirring;

[0068] (5) The reaction solution was poured into a separation funnel and allowed to stand until solid-liquid separation. White colloidal microcrystalline cellulose was taken out from the lower layer. The size of the cellulose was 50-90 μm and the yield was 75% under an optical microscope. The upper layer was a clear and transparent medium-concentration phosphoric acid solution (3 mol / L).

[0069] (6) washing the white colloidal microcrystalline cellulose obtained in step (5) 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;

[0070] (7) wherein the medium-concentration phosphoric acid solution obtained in step (2) or step (5) is concentrated to obtain a high-concentration phosphoric acid solution to hydrolyze micron-crystalline cellulose to prepare white colloidal nanocrystalline cellulose and a medium-concentration phosphoric acid solution; or the medium-concentration phosphoric acid solution obtained in step (5) can be circulated multiple times to hydrolyze plant fiber raw materials to prepare white colloidal micron-crystalline cellulose and a medium-concentration phosphoric acid solution.

[0071] Example 6

[0072] (1) Crush wood fiber and pass it through a 200-mesh sieve to obtain wood fiber powder, prepare 8N hydrochloric acid solution, preheat the hydrochloric acid solution to 110° C., add 20 g of wood fiber powder to 175 mL of the preheated 8N hydrochloric acid solution, and react for 120 minutes under mechanical stirring;

[0073] (2) The reaction solution was poured into a separation funnel filled with distilled water and allowed to stand until the solid and liquid layers were separated. White colloidal nanocrystalline cellulose was taken out from the lower layer and its size was characterized by AFM. The diameter was 10-16 nm and the length was 180-250 nm. The clear and transparent hydrochloric acid solution in the upper layer was diluted to 2N.

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

[0075] (4) preheating 700 mL of the upper clear and transparent acid solution diluted to 2N in step (2) to 70° C., then adding 70 g of bamboo fiber powder and reacting for 50 minutes under mechanical stirring;

[0076] (5) The reaction solution was poured into a separation funnel and allowed to stand until solid-liquid separation. White colloidal microcrystalline cellulose was taken out from the lower layer. The size of the cellulose was 50-110 μm and the yield was 85% under an optical microscope. The upper layer was a clear and transparent medium-concentration hydrochloric acid solution (2N);

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

[0078] (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 micron-crystalline cellulose to prepare white colloidal nano-crystalline cellulose and a medium-concentration hydrochloric acid solution; or the medium-concentration hydrochloric acid solution obtained in step (5) can be circulated multiple times to hydrolyze plant fiber raw materials to prepare white colloidal micron-crystalline cellulose and a medium-concentration hydrochloric acid solution.

[0079] Example 7

[0080] (1) crushing bamboo fiber and passing it through a 200-mesh sieve to obtain bamboo fiber powder, preparing a 58 wt % sulfuric acid solution, preheating the sulfuric acid solution to 60° C., adding 20 g of bamboo fiber powder to 175 mL of preheated 58 wt % sulfuric acid, and reacting for 75 minutes under mechanical stirring;

[0081] (2) pouring the reaction solution into a separation funnel filled with distilled water and letting it stand until the solid and liquid layers are separated, taking out white colloidal nanocrystalline cellulose from the lower layer, and characterizing its size by AFM, with a diameter of 5-8 nm, a length of 100-160 nm, and a yield of 40%. The clear and transparent sulfuric acid solution in the upper layer is diluted to 10 wt %;

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

[0083] (4) preheating 1000 mL of the upper clear and transparent acid solution diluted to 10 wt% in step (2) to 40° C., then adding 100 g of bamboo fiber powder, and reacting for 120 minutes under mechanical stirring;

[0084] (5) The reaction solution was poured into a separation funnel and allowed to stand until solid-liquid separation. White colloidal microcrystalline cellulose was taken out from the lower layer. The size of the cellulose was 60-120 μm and the yield was 80% under an optical microscope. The upper layer was a clear and transparent medium-concentration sulfuric acid solution (10 wt%).

[0085] (6) washing the white colloidal microcrystalline cellulose obtained in step (5) 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 barium carbonate to obtain a neutral solution;

[0086] (7) wherein the medium-concentration sulfuric acid solution obtained in step (2) or step (5) is concentrated to obtain a high-concentration sulfuric acid solution to hydrolyze micron-crystalline cellulose to prepare white colloidal nano-crystalline cellulose and a medium-concentration sulfuric acid solution; or the medium-concentration sulfuric acid solution obtained in step (5) can be circulated multiple times to hydrolyze plant fiber raw materials to prepare white colloidal micron-crystalline cellulose and a medium-concentration sulfuric acid solution.

[0087] Example 8

[0088] (1) crushing bamboo fiber and passing it through a 200-mesh sieve to obtain bamboo fiber powder, preparing an 8 mol / L phosphoric acid solution, preheating the phosphoric acid solution to 90° C., adding 20 g of bamboo fiber powder to 175 mL of the preheated 8 mol / L phosphoric acid solution, and reacting for 120 minutes under mechanical stirring;

[0089] (2) The reaction solution was poured into a separation funnel filled with distilled water and allowed to stand until the solid and liquid layers were separated. White colloidal nanocrystalline cellulose was taken out from the lower layer and its size was characterized by AFM. The diameter was 14-20 nm and the length was 140-180 nm. The clear and transparent phosphoric acid solution in the upper layer was diluted to 5 mol / L.

[0090] (3) washing the white colloidal nanocrystalline cellulose obtained in step (2) 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 barium carbonate to obtain a neutral solution;

[0091] (4) preheating 400 mL of the upper clear and transparent acid solution diluted to 5 mol / L in step (2) to 50° C., then adding 40 g of bamboo fiber powder and reacting for 90 minutes under mechanical stirring;

[0092] (5) The reaction solution was poured into a separation funnel and allowed to stand until solid-liquid separation. White colloidal microcrystalline cellulose was taken out from the lower layer. The size of the cellulose was 40-80 μm and the yield was 75% under an optical microscope. The upper layer was a clear and transparent medium-concentration phosphoric acid solution (5 mol / L).

[0093] (6) washing the white colloidal microcrystalline cellulose obtained in step (5) 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 barium carbonate to obtain a neutral solution;

[0094] (7) wherein the medium-concentration phosphoric acid solution obtained in step (2) or step (5) is concentrated to obtain a high-concentration phosphoric acid solution to hydrolyze micron-crystalline cellulose to prepare white colloidal nanocrystalline cellulose and a medium-concentration phosphoric acid solution; or the medium-concentration phosphoric acid solution obtained in step (5) can be circulated multiple times to hydrolyze plant fiber raw materials to prepare white colloidal micron-crystalline cellulose and a medium-concentration phosphoric acid solution.

[0095] Example 9

[0096] (1) crushing bamboo fiber and passing it through a 200-mesh sieve to obtain bamboo fiber powder, preparing a 10N hydrochloric acid solution, preheating the hydrochloric acid solution to 90° C., adding 20 g of bamboo fiber powder to 175 mL of the preheated 10N hydrochloric acid solution, and reacting for 120 minutes under mechanical stirring;

[0097] (2) The reaction solution was poured into a separation funnel filled with distilled water and allowed to stand until the solid and liquid layers were separated. White colloidal nanocrystalline cellulose was taken out from the lower layer and its size was characterized by AFM. The diameter was 12-20 nm and the length was 160-200 nm. The clear and transparent hydrochloric acid solution in the upper layer was diluted to 3N.

[0098] (3) washing the white colloidal nanocrystalline cellulose obtained in step (2) to obtain neutral white colloidal nanocrystalline cellulose and a 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) preheating 600 mL of the upper clear and transparent acid solution diluted to 3N in step (2) to 80° C., then adding 60 g of bamboo fiber powder and reacting for 50 minutes under mechanical stirring;

[0100] (5) The reaction solution was poured into a separation funnel and allowed to stand until solid-liquid separation. White colloidal microcrystalline cellulose was taken out from the lower layer. The size of the cellulose was 60-100 μm and the yield was 80% under an optical microscope. The upper layer was a clear and transparent medium-concentration hydrochloric acid solution (3N);

[0101] (6) washing the white colloidal microcrystalline cellulose obtained in step (5) to obtain neutral white colloidal nanocrystalline cellulose and a low concentration hydrochloric acid solution (<0.2N), wherein the low concentration hydrochloric acid solution is neutralized with 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 micron-crystalline cellulose to prepare white colloidal nano-crystalline cellulose and a medium-concentration hydrochloric acid solution; or the medium-concentration hydrochloric acid solution obtained in step (5) can be circulated multiple times to hydrolyze plant fiber raw materials to prepare white colloidal micron-crystalline cellulose and a medium-concentration hydrochloric acid solution.

[0103] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An environmentally friendly multi-stage co-production method for preparing microcrystalline cellulose and nanocrystalline cellulose, characterized in that: The steps include: (1) hydrolyzing plant fiber raw material powder or directly hydrolyzing micron-crystalline cellulose with a high-concentration inorganic acid solution, and obtaining white colloidal nanocrystalline cellulose and a medium-concentration inorganic acid solution through post-treatment; (2) using the medium concentration inorganic acid solution obtained in step (1) as a hydrolyzing liquid to hydrolyze the plant fiber raw material powder, and obtaining white colloidal microcrystalline cellulose and the medium concentration inorganic acid solution after separation; (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-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 microcrystalline cellulose and nanocrystalline cellulose in steps (1) to (3) is neutralized with an insoluble carbonate to obtain a neutral solution.

2. The environmentally friendly multi-stage co-production method for preparing microcrystalline cellulose and nanocrystalline cellulose according to claim 1, characterized in that: The high concentration inorganic acid solution in step (1) comprises 50-70wt% sulfuric acid, 8-10mol / L phosphoric acid, and 8-10N hydrochloric acid.

3. The environmentally friendly multi-stage co-production method for preparing microcrystalline cellulose and nanocrystalline cellulose according to claim 1, characterized in that: The preheating temperature of steps (1) to (3) is 40 to 110° C., and the reaction time is 50 to 180 minutes.

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

5. The environmentally friendly multi-stage co-production method for preparing microcrystalline cellulose and nanocrystalline cellulose according to claim 1, characterized in that: The medium concentration inorganic acid solution in steps (1) to (3) includes 10-20wt% sulfuric acid, 2-5mol / L phosphoric acid, and 1-3N hydrochloric acid.

6. The environmentally friendly multi-stage co-production method for preparing microcrystalline cellulose and nanocrystalline cellulose according to claim 1, characterized in that: The inorganic acid solution of step (1) is used for the production and preparation of cellulose products of different sizes such as micron crystalline cellulose or nano crystalline cellulose.

7. The environmentally friendly multi-stage co-production method for preparing microcrystalline cellulose and nanocrystalline cellulose according to claim 1, characterized in that: The step (2) of preparing micron-crystalline cellulose comprises: using the high-concentration inorganic acid solution in the step (1) to hydrolyze the plant fibers to prepare nano-crystalline cellulose, and then diluting it to a medium-concentration inorganic acid solution for preparing micron-crystalline cellulose; and the low-concentration inorganic acid solution obtained by washing the micron-crystalline cellulose and the nano-crystalline cellulose is neutralized with an insoluble salt.

8. The environmentally friendly multi-stage co-production method for preparing microcrystalline cellulose and nanocrystalline cellulose according to claim 1, characterized in that: The low concentration inorganic acid solution in step (4) includes <1wt% sulfuric acid, <0.2mol / L phosphoric acid, and <0.2N hydrochloric acid.

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

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