Method for graded utilization of all components of bagasse based on lactic acid

Abstract

The invention discloses a method for graded utilization of all components of bagasse based on lactic acid, and belongs to the technical field of bio-refinery. The method comprises the following steps: hydrolyzing bagasse in a dilute lactic acid solution to obtain a filter residue I and a filtrate I, and concentrating and drying the filtrate I to obtain xylooligosaccharide; then the filter residues I are pretreated with a high-concentration lactic acid solution, filtrate II and filter residues II are obtained, and lignin nanoparticles are recycled from the obtained filtrate II through an anti-solvent precipitation method; and finally, the filter residue II is subjected to a bleaching pulping process to obtain the dissolving pulp. The lactic acid grading method is simple in operation process, has high economic feasibility and environmental friendliness, can recycle lactic acid, and is suitable for green grading and efficient conversion of large-scale biomass.

Description

Technical Field

[0001] The invention belongs to the technical field of biorefining, and in particular relates to a method for utilizing all components of bagasse based on lactic acid classification. Background Art

[0002] Lignocellulosic biomass (e.g., bagasse) contains hemicellulose, cellulose, and lignin, all of which have important conversion potential and can be used to produce a variety of high-value-added products. However, traditional biomass fractionation methods usually rely on harmful chemical reagents or multiple solvents, which increases the complexity, cost, and environmental risks of the process. Therefore, a more efficient, green, and economically viable biomass fractionation process is urgently needed to effectively utilize all components in biomass.

[0003] As an organic acid, lactic acid has gradually become a research hotspot in the field of biomass fractionation due to its non-toxicity, recyclability and selective catalytic ability for biomass components. At present, there have been studies on the preparation of oligoxylose by lactic acid hydrolysis, but the residual lignin and cellulose have not been fully utilized. Therefore, the existing lactic acid-based fractionation method still needs to be further developed to improve the fractionation and conversion efficiency of all biomass components. Summary of the invention

[0004] The technical problem solved by the present invention is to provide a method for utilizing all components of bagasse based on lactic acid classification. The method is simple and efficient, improves the comprehensive utilization rate of resources, and is more conducive to realizing industrial production.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0006] A method for utilizing all components of bagasse based on lactic acid fractionation, comprising the following steps:

[0007] 1) hydrolyzing bagasse in a dilute lactic acid solution to obtain a filter residue I and a filtrate I, and concentrating and drying the filtrate I to obtain xylo-oligosaccharides;

[0008] 2) pre-treating the filter residue I obtained in step 1) with a high concentration lactic acid solution to obtain a filtrate II and a filter residue II, and recovering lignin nanoparticles from the obtained filtrate II by an anti-solvent precipitation method;

[0009] 3) The filter residue II obtained in step 2) is subjected to a bleaching pulping process to obtain a dissolving pulp.

[0010] The concentration of the dilute lactic acid solution in step 1) is 0.1% to 1%.

[0011] In the step 1), the dilute lactic acid hydrolysis temperature is 150-170° C., and the reaction time is 30-60 min.

[0012] In the step 1), the filtrate I is concentrated and spray-dried to obtain xylo-oligosaccharides.

[0013] The concentration of the high-concentration lactic acid solution in step 2) is 50% to 100%.

[0014] In the step 2), the high concentration pretreatment temperature is 160-180° C., and the reaction time is 30-90 min.

[0015] In the anti-solvent precipitation method in step 2), deionized water is gradually added to the filtrate II and stirred, and the resulting precipitate is lignin nanoparticles.

[0016] In the step 2), the lactic acid is recovered by rotary evaporation and recycled.

[0017] In the step 2), the filtrate II is precipitated with an anti-solvent, filtered, washed, and freeze-dried to obtain lignin nanoparticles.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] (1) The present invention adopts a single catalyst, lactic acid, for the first time, as a catalyst for preparing xylo-oligosaccharides from sugarcane bagasse and as a catalyst for separating lignin from sugarcane bagasse. By combining pretreatment with lactic acid of different concentrations with anti-solvent precipitation and bleaching pulping processes, xylo-oligosaccharides, lignin nanoparticles and dissolving pulp are co-produced, which not only has a high yield, but also has excellent performance indicators of lignin nanoparticles and dissolving pulp, thereby increasing the utilization rate of sugarcane bagasse components and the added value of products.

[0020] (2) The lactic acid used in the present invention can be recycled during the production process, and the lactic acid consumption per unit product is low.

[0021] (3) The preparation method of the present invention is simple and efficient, has a simple process, low cost, is green and friendly, and has little environmental impact. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The present invention is a flow chart of a process for co-producing xylooligosaccharides, lignin nanoparticles and dissolving pulp by using lactic acid-graded bagasse. DETAILED DESCRIPTION

[0023] 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.

[0024] The detection method of the xylooligosaccharide content in the hydrolyzate in the following embodiments is as follows:

[0025] The contents of xylose, xylose, xylose, xylopentaose and xylohexose in the hydrolyzate were determined by high performance liquid ion chromatography. Chromatographic conditions: American Dionex ICS-3000 ion chromatography system, equipped with CarboPacM PA200 (3mm×250mm) chromatographic column and retaining column (3×50mm), ED electrochemical detector, column temperature 30℃, injection volume 10μL; binary gradient elution was performed with 500mmol / L sodium acetate solution (A) and 100mmol / L sodium hydroxide solution (B) as eluents, and the flow rate was 0.3mL / min (elution program: 0min, 100% A; 30min, 75% A, 25% B; 38-45min, 100% A). The detection mode of the electrochemical detector was a gold working electrode and a pH-Ag / AgCl composite reference electrode, and the content of the sugar components was determined by the integrated pulse amperometric detection method and the chromatographic peak area integration method.

[0026] Lignin nanoparticles and particle size determination method: The particle size and Zeta potential of lignin nanoparticles are measured based on the principle of dynamic light scattering. The sample is suspended in deionized water and ultrasonically treated to fully disperse it. The suspension is then placed in a quartz cuvette and analyzed using a Zetasizer Nano ZS instrument, which determines the particle size by analyzing the intensity of reflected light. To ensure accurate results, each sample is measured 3 times. The sample is placed in a cuvette equipped with a charged electrode, and the Zeta potential is calculated by measuring the movement speed of the charged lignin nanoparticles in the electric field. The measurement process is repeated 3 times and the average value is taken.

[0027] Fock reactivity determination of dissolving pulp samples: Place the dissolving pulp sample in a NaOH solution for oscillation reaction. Then add carbon disulfide for sulfonation reaction. After the sulfonation reaction is completed, add deionized water for centrifugation. Then take a certain amount of supernatant and mix it with sulfuric acid to completely remove carbon disulfide. Then add sulfuric acid, potassium dichromate and potassium iodide solution, and then titrate and analyze with sodium thiosulfate.

[0028] Lignin and lactic acid recovery method: The lactic acid pretreatment liquid containing lignin is dripped into 10 times the volume of deionized water drop by drop to precipitate lignin, which is then dialyzed, centrifuged and freeze-dried to obtain lignin nanoparticles. The liquid part is rotary evaporated to recover lactic acid.

[0029] The method of the anti-solvent precipitation process is as follows: the lactic acid pretreatment solution containing lignin is dripped into deionized water at a rate of 1 mL / min, and the obtained lignin suspension is dialyzed in deionized water for 72 hours, and the water is changed every 12 hours; after dialysis, the suspension is centrifuged at 8000 rpm for 15 minutes, and then freeze-dried to obtain lignin nanoparticles.

[0030] The bleaching pulping process is as follows: the bagasse residue is treated with 2% sodium hydroxide at 80°C for 2 hours, 2% ethylenediaminetetraacetic acid at 60°C for 2 hours, and 3% hydrogen peroxide combined with 0.5% sodium hydroxide and 0.1% magnesium sulfate at 80°C for 1 hour. After the reaction is completed, the solid part is washed with deionized water to neutrality and then dried at 105°C overnight to obtain a dissolving pulp.

[0031] Determination of whiteness of dissolving pulp samples: Press the dissolving pulp sample into a uniform thin layer, making sure that its surface is flat and free of impurities. Then, place the sample in the measurement window of the whiteness meter, making sure that the instrument light source shines on the sample surface. The instrument emits light and measures the intensity of the reflected light, and calculates its whiteness value based on the chromaticity and brightness characteristics of the sample's reflected light.

[0032] The calculation formulas for calculating the yield of xylo-oligosaccharides, the removal rate of lignin and the yield of dissolving pulp in the following examples are as follows:

[0033] The yield of oligoxylose in the hydrolyzate (%) = the mass of oligoxylose produced by hydrolysis (g) / the mass of xylan in the untreated bagasse (g) × 100%;

[0034] Lignin removal rate (%) = lignin content in solid residue after pretreatment (g) / lignin content in untreated bagasse (g) × 100%;

[0035] Dissolving pulp yield (%) = absolute dry mass of dissolving pulp sample (g) / absolute dry mass of solid residue after continuous lactic acid pretreatment (g) × 100%.

[0036] Example 1

[0037] A method for utilizing all components of bagasse based on lactic acid fractionation, the specific steps are as follows:

[0038] (1) The bagasse is naturally air-dried and then crushed by a pulverizer, sieved through 40 meshes, and the moisture content is ≤8%. The bagasse is pre-hydrolyzed at 170° C. for 60 minutes using a 0.1% lactic acid aqueous solution with a solid-liquid ratio of 1:10. After the reaction is completed, the bagasse is cooled to room temperature and filtered. The filtrate is vacuum concentrated and spray-dried to obtain xylo-oligosaccharides, and the yield of xylo-oligosaccharides (degree of polymerization 2-6) is 65.0%.

[0039] (2) The obtained filter residue was dried and treated with 80% lactic acid aqueous solution at 170°C for 60 minutes, with a solid-liquid ratio of 1:10; after the reaction was completed, the filter was filtered, and the lignin extraction rate was 96.6%; the filtrate was subjected to an anti-solvent precipitation process to obtain lignin nanoparticles, and the diameter of the obtained lignin nanoparticles was 122.3nm and the Zeta potential was -30.8mV

[0040] (3) The obtained cellulose-rich filter residue was subjected to a bleaching pulping process to obtain a dissolving pulp with a yield of 92.2%, a cellulose content of 93.9%, a whiteness of 86.2%, and a Fock reaction activity of 92.5%.

[0041] Example 2

[0042] Based on the method of Example 1 above, the lactic acid concentration, hydrolysis temperature and hydrolysis time of the low-concentration lactic acid hydrolysis process for preparing xylo-oligosaccharides were changed respectively. The xylo-oligosaccharides in the final hydrolyzate were measured and calculated, and the changes in the xylo-oligosaccharides yield with reaction conditions were compared, as shown in Table 1 below.

[0043] Table 1 Comparative table of the effects of changing the conditions for preparing xylo-oligosaccharides in Example 1 on the yield of xylo-oligosaccharides

[0044]

[0045]

[0046] From the comparison of the treatment conditions and the final product yields in Table 1, it can be seen that at a lower hydrolysis temperature (150°C), 1% lactic acid hydrolysis obtained a higher yield of xylo-oligosaccharides; when the hydrolysis temperature was increased to 170°C, 0.1% lactic acid hydrolysis obtained the highest yield of xylo-oligosaccharides. Within the hydrolysis parameter range of 0.1% to 2% lactic acid concentration, 150°C to 170°C hydrolysis temperature, and 30min to 75min hydrolysis time, the highest yield of xylo-oligosaccharides was 65.0% when 0.1% lactic acid was used to hydrolyze sugarcane bagasse at 170°C for 60min.

[0047] Example 3

[0048] A method for utilizing all components of bagasse based on lactic acid fractionation, the specific steps are as follows:

[0049] (1) The bagasse is naturally air-dried and then crushed by a pulverizer, sieved through 40 meshes, and the moisture content is ≤8%. The bagasse is pre-hydrolyzed at 170° C. for 60 minutes using a 0.1% lactic acid aqueous solution, with a solid-liquid ratio of 1:10. After the reaction is completed, the bagasse is cooled to room temperature and filtered. The filtrate is vacuum concentrated and spray-dried to obtain xylo-oligosaccharides, and the yield of xylo-oligosaccharides (degree of polymerization 2-6) is 65.0%.

[0050] (2) The obtained filter residue was dried and treated with 50% lactic acid aqueous solution at 170°C for 60 minutes, with a solid-liquid ratio of 1:10; after the reaction was completed, it was filtered, and the lignin extraction rate was 69.4%; the filtrate was subjected to an anti-solvent precipitation process to obtain lignin nanoparticles, and the diameter of the obtained lignin nanoparticles was 171.5nm and the Zeta potential was -26.1mV.

[0051] (3) The obtained cellulose-rich filter residue was subjected to a bleaching pulping process to obtain a dissolving pulp with a yield of 89.2%, a cellulose content of 97.9%, a whiteness of 63.1%, and a Fock reaction activity of 86.2%.

[0052] Example 4

[0053] A method for utilizing all components of bagasse based on lactic acid fractionation, the specific steps are as follows:

[0054] (1) The bagasse is naturally air-dried and then crushed by a pulverizer, sieved through 40 meshes, and the moisture content is ≤8%. The bagasse is hydrolyzed at 170° C. for 60 minutes using a 0.1% lactic acid aqueous solution with a solid-liquid ratio of 1:10. After the reaction is completed, the bagasse is cooled to room temperature and filtered. The filtrate is vacuum concentrated and spray-dried to obtain xylo-oligosaccharides, and the yield of xylo-oligosaccharides (degree of polymerization 2-6) is 65.0%.

[0055] (2) The obtained filter residue was dried and treated with 100% lactic acid aqueous solution at 170°C for 60 minutes, with a solid-liquid ratio of 1:10; after the reaction was completed, the residue was filtered, and the lignin extraction rate was 96.6%; the filtrate was subjected to an anti-solvent precipitation process to obtain lignin nanoparticles, and the diameter of the obtained lignin nanoparticles was 110.2nm and the Zeta potential was -32.2mV.

[0056] (3) The obtained cellulose-rich filter residue was subjected to a bleaching pulping process to obtain a dissolving pulp with a yield of 91.5%, a cellulose content of 98.1%, a whiteness of 87.1%, and a Fock reaction activity of 92.1%.

[0057] Example 5

[0058] Based on the method of Example 1 above, the lactic acid concentration, treatment temperature and treatment time of the high-concentration lactic acid pretreatment process for removing lignin were changed respectively. By measuring and calculating the final lignin removal rate, the changes in lignin removal rate with changes in high-concentration lactic acid pretreatment conditions were compared, as shown in Table 1 below.

[0059] Table 2 Comparison of the effects of changing the lactic acid pretreatment conditions in Example 1 on the lignin removal rate

[0060] Lactate concentration Hydrolysis temperature℃ Hydrolysis time min Lignin extraction rate % Process 1 80％ 160 30 79.3 Process 2 80％ 160 60 83.6 Process 3 80％ 160 90 90.6 Process 4 80％ 170 30 88.3 Process 5 80％ 170 60 96.6 Process 6 80％ 170 90 97.7 Process 7 80％ 180 30 91.0 Process 8 80％ 180 60 96.2 Process 9 80％ 180 90 98.6 Processing 10 30％ 170 90 43.1 Process 11 30％ 180 90 58.3 Processing 12 40％ 170 90 50.1 Process 13 40％ 180 90 65.3

[0061] From the comparison of the treatment conditions and the final lignin extraction rate of each group in Table 2, it can be seen that the lignin extraction rate increases with the increase of lactic acid treatment temperature and time. However, when the lactic acid concentration is 30% or 40%, even if it is treated at 180℃ for 90min, the lignin extraction rate only reaches 58.3% to 65.3%. When the lactic acid concentration is 80%, the lignin extraction rate is 90.6% when it is treated at 160℃ for 90min; and a higher lignin extraction rate of 96.6% is obtained when the temperature is further increased to 180℃ for 90min, and the lignin extraction rate is only increased to 98.6%.

[0062] Comparative Example 1

[0063] A method for producing xylo-oligosaccharides by pre-hydrolyzing bagasse with lactic acid, the specific steps are as follows:

[0064] The bagasse is naturally air-dried and then crushed by a grinder, sieved through 40 meshes, with a moisture content of ≤8%, and pre-hydrolyzed at 170°C for 60 minutes with a 0.1% lactic acid aqueous solution, with a solid-liquid ratio of 1:10. After the reaction is completed, the bagasse is cooled to room temperature and filtered. The filtrate is vacuum concentrated and spray-dried to obtain xylo-oligosaccharides, with a yield of xylo-oligosaccharides (degree of polymerization 2-6) of 65.0%.

[0065] Comparative Example 2

[0066] A method for producing lignin nanoparticles and dissolving pulp by pretreating bagasse with lactic acid, the specific steps are as follows:

[0067] (1) The bagasse was naturally air-dried and then crushed by a crusher, sieved through 40 meshes, and the moisture content was ≤8%. The bagasse was treated with 80% lactic acid aqueous solution at 170°C for 60 minutes, with a solid-liquid ratio of 1:10. After the reaction was completed, the bagasse was filtered, and the lignin extraction rate was 83.2%. The filtrate was subjected to an anti-solvent precipitation process to obtain lignin nanoparticles, and the diameter of the obtained lignin nanoparticles was 160.2nm and the Zeta potential was -29.2mV.

[0068] (2) The obtained cellulose-rich filter residue was subjected to a bleaching pulping process to obtain a dissolving pulp with a yield of 88.6%, a cellulose content of 92.3%, a whiteness of 76.8%, and a Fock reaction activity of 89.2%.

[0069] Comparative Example 3

[0070] A method for producing lignin nanoparticles and dissolving pulp by pretreating bagasse with lactic acid, the specific steps are as follows:

[0071] (1) The bagasse was naturally air-dried and then crushed by a pulverizer, sieved through 40 meshes, and the moisture content was ≤8%. The bagasse was treated with a 100% lactic acid aqueous solution at 170°C for 60 minutes, with a solid-liquid ratio of 1:10. After the reaction was completed, the bagasse was filtered, and the lignin extraction rate was 77.2%. The filtrate was subjected to an anti-solvent precipitation process to obtain lignin nanoparticles, and the diameter of the obtained lignin nanoparticles was 154.2 nm and the Zeta potential was -30.3 mV.

[0072] (2) The obtained cellulose-rich filter residue was subjected to a bleaching pulping process to obtain a dissolving pulp with a yield of 85.6%, a cellulose content of 91.9%, a whiteness of 80.1%, and a Fock reaction activity of 88.2%.

[0073] 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. A method for utilizing all components of bagasse based on lactic acid fractionation, characterized in that: The following steps are involved: 1) hydrolyzing bagasse in a dilute lactic acid solution to obtain a filter residue I and a filtrate I, and concentrating and drying the filtrate I to obtain xylo-oligosaccharides; 2) pre-treating the filter residue I obtained in step 1) with a high concentration lactic acid solution to obtain a filtrate II and a filter residue II, and recovering lignin nanoparticles from the obtained filtrate II by an anti-solvent precipitation method; 3) The filter residue II obtained in step 2) is subjected to a bleaching pulping process to obtain a dissolving pulp.

2. A method for utilizing all components of bagasse based on lactic acid classification according to claim 1, characterized in that: The concentration of the dilute lactic acid solution in step 1) is 0.1% to 1%.

3. The method for utilizing all components of bagasse based on lactic acid classification according to claim 1, characterized in that: In the step 1), the dilute lactic acid hydrolysis temperature is 150-170° C., and the reaction time is 30-60 min.

4. The method for utilizing all components of bagasse based on lactic acid classification according to claim 1, characterized in that: In the step 1), the filtrate I is concentrated and spray-dried to obtain xylo-oligosaccharides.

5. The method for utilizing all components of bagasse based on lactic acid classification according to claim 1, characterized in that: The concentration of the high-concentration lactic acid solution in step 2) is 50% to 100%.

6. The method for utilizing all components of bagasse based on lactic acid classification according to claim 1, characterized in that: In the step 2), the high concentration pretreatment temperature is 160-180° C., and the reaction time is 30-90 min.

7. The method for utilizing all components of bagasse based on lactic acid fractionation according to claim 1, characterized in that: In the anti-solvent precipitation method in step 2), deionized water is gradually added to the filtrate II and stirred, and the resulting precipitate is lignin nanoparticles.

8. The method for utilizing all components of bagasse based on lactic acid fractionation according to claim 1, characterized in that: In the step 2), the lactic acid is recovered by rotary evaporation and recycled.

9. The method for utilizing all components of bagasse based on lactic acid fractionation according to claim 1, characterized in that: In the step 2), the filtrate II is precipitated with an anti-solvent, filtered, washed, and freeze-dried to obtain lignin nanoparticles.

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