Method for co-producing fibers and fulvic acid from straws at normal temperature

Abstract

The invention relates to the technical field of resource utilization of agricultural wastes, provides a method for co-producing fibers and fulvic acid from straws at normal temperature, and solves the problems of high energy consumption, heavy pollution and single product in the traditional process. According to the method, multi-stage enzymolysis and stepped mechanical pulping are combined through unique process arrangement, a synergistic effect is achieved, and efficient conversion and near-zero emission of straw resources at the normal temperature are achieved. The method comprises the following specific steps: after straw is crushed and dedusted, carrying out multi-stage enzymolysis and pulping treatment, sequentially degrading lignin and hemicellulose by using a compound enzyme A (laccase / xylanase), a compound enzyme C (compound enzyme A / compound enzyme B) and a compound enzyme B (lignin peroxidase / manganese peroxidase) in stages, refining fibers by combining high, medium and low gradient pulping, and then refining and screening the fibers, so as to obtain the lignin-hemicellulose composite fiber. The fulvic acid solution is recycled, and unqualified fibers are subjected to closed-loop circulation treatment. The method is suitable for various raw materials such as corn straws, cotton stalks and poplar chips, and has the advantages of low energy consumption, environmental protection and economy.

Description

Technical Field

[0001] The present invention relates to the technical field of agricultural waste resource utilization, and in particular to a method for efficiently co-producing fiber and fulvic acid from straw by combining multi-stage enzymatic hydrolysis and mechanical refining at room temperature. Background Art

[0002] As one of the main components of agricultural waste, straw is rich in organic matter such as cellulose, hemicellulose and lignin, and is an important renewable resource. Traditional treatment methods such as incineration or simple composting not only waste resources, but may also cause environmental pollution. In the existing technology, straw fiber extraction usually relies on chemical cooking, which requires high temperature and high pressure conditions, has the characteristics of high energy consumption and difficult wastewater treatment. In addition, the highly corrosive reagents destroy the fiber structure, resulting in a low cellulose yield. At the same time, the single product cannot simultaneously extract fiber and high value-added components, and the comprehensive resource utilization rate is low.

[0003] In recent years, laccase-assisted pretreatment technology has attracted much attention due to its ability to degrade lignin in a targeted manner. However, problems such as low reaction efficiency at room temperature, poor connection with subsequent processes, and long enzymatic hydrolysis cycle have not yet been overcome, making it difficult to meet the needs of industrial continuous production.

[0004] In response to the above bottlenecks, the present invention proposes an industrialized continuous production method for co-producing straw fiber and fulvic acid at room temperature, which realizes efficient resource conversion through technical innovations of multi-stage pulping and enzymatic hydrolysis synergistic system, enzyme and mechanical coupling treatment, and closed-loop resource utilization system design. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for co-producing fiber and fulvic acid from straw at room temperature. Through continuous feeding, step-by-step pulping and enzymatic hydrolysis, enzyme and acetic acid synergistic pretreatment, enzyme and mechanical pulping and cyclic screening processes, efficient and synchronous extraction of fiber and fulvic acid from straw is achieved. No high temperature and high pressure conditions are required, and there is no need to wait for a long enzymatic hydrolysis process. Industrial continuous production is achieved, and the method has the characteristics of low energy consumption, improved resource utilization, and strong adaptability to raw materials.

[0006] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0007] The present invention provides a method for co-producing fiber and fulvic acid from straw at room temperature, the method comprising the following steps:

[0008] (1) Straw pretreatment and enzyme reaction raw material preparation:

[0009] Crushing: The straw is crushed into 3-5 cm fragments by a disc crusher.

[0010] Dust removal: Use a dust collector to remove surface dust.

[0011] Screening: Remove impurities and straw fragments through a drum screen.

[0012] Cleaning: The cleaning machine cleans the remaining dust from the material.

[0013] Pre-treatment waste utilization: Collect dust and straw fragments, add organic material composting agent that meets the standards of "NY 609-2002" at a ratio of 1000:1.5, and stir to form nutrient-rich seedling soil.

[0014] Preparation of complex enzymes: The enzyme dosage unit for this invention is U / g, which is the total amount of enzyme activity required per gram of absolute dry straw. Based on the activity unit ratio, laccase (Lac) and xylanase (Xylanase) are combined in a ratio of 1:6 to 1:8 to form complex enzyme A. Lignin peroxidase (LiP) and manganese peroxidase (MnP) are combined in a ratio of 1:1 to 1:1.2 to form complex enzyme B. Complex enzyme C is prepared by combining complex enzymes A and B in a ratio of 1:2 to 1:3.

[0015] Preparation of acidic enzyme reaction buffer: Use citric acid, lactic acid or acetic acid and water to prepare acidic enzyme reaction buffer.

[0016] (2) Primary enzymatic hydrolysis:

[0017] Pretreatment of rubbing and grinding the silk: spray the acidic enzyme reaction buffer at the feed port of screw conveyor No. 1, and adjust the material feed concentration to 30% to 35% and the pH to 3 to 3.5.

[0018] Rubbing and separating: The material is sent to the extrusion and kneading machine through the No. 1 screw conveyor, and is squeezed, separated and kneaded to destroy the epidermis and wax layer and increase the contact area with the acetic acid solution.

[0019] Primary enzymatic hydrolysis pretreatment: the kneaded material is fed into the No. 1 enzymatic hydrolysis tank via the No. 2 screw conveyor, and the compound enzyme A (6-9 U / g) is sprayed at the feed port of the No. 2 screw conveyor.

[0020] Primary enzymatic hydrolysis: The material enters the No. 1 enzymatic hydrolysis tank, and the enzymatic hydrolysis time is 240 to 600 minutes to achieve the initial separation of some lignin, hemicellulose and cellulose.

[0021] (3) Secondary enzymatic hydrolysis:

[0022] Refining pretreatment: The material after primary enzymatic hydrolysis continuously enters the feed port of No. 3 screw conveyor from the discharge port of No. 1 enzymatic hydrolysis tank. Acidic enzyme reaction buffer is sprayed at the feed port of No. 3 screw conveyor to adjust the material feed concentration to 25%-30% and pH 3.5-4 before being fed into the high-consistency refiner.

[0023] Refining treatment: After being processed by high-concentration refiner, the material wire diameter is 0.5-1.2mm. After refining, the material enters the feed port of No. 4 screw conveyor.

[0024] Secondary enzymatic hydrolysis pretreatment: spray compound enzyme C (8-12 U / g) at the feed inlet of No. 4 screw conveyor.

[0025] Secondary enzymatic hydrolysis: enters the No. 2 enzymatic hydrolysis tank through the No. 4 screw conveyor, and the enzymatic hydrolysis time is 240 to 600 minutes to achieve partial dissociation of lignin, hemicellulose and cellulose.

[0026] (4) Tertiary enzymatic hydrolysis:

[0027] Fine refining pretreatment: The material after secondary enzymatic hydrolysis continuously enters the feed port of screw conveyor No. 5 from the discharge port of enzymatic hydrolysis tank No. 2. Acidic enzyme reaction buffer is sprayed at the feed port of screw conveyor No. 5 to adjust the material feed concentration to 25%-30% and pH 4-4.5 before being fed into the medium-consistency refiner.

[0028] Refining treatment: After being processed by medium-consistency refiner, the material wire diameter is reduced to 0.25-0.7mm. After refining, the material enters the feed port of No. 6 screw conveyor;

[0029] Three-stage enzymatic pretreatment: After refining, the material is sprayed with complex enzyme B (10-14 U / g) through the feed port of No. 6 screw conveyor.

[0030] Three-stage enzymatic hydrolysis: After refining, the material enters the No. 3 enzymatic hydrolysis tank through the No. 6 screw conveyor for enzymatic hydrolysis for 240 to 600 minutes. The undecomposed lignin, hemicellulose and cellulose in the material are deeply enzymatically hydrolyzed again to promote the production of fulvic acid.

[0031] (5) Solid-liquid separation:

[0032] Dehydration: The material discharged from the No. 3 enzymatic hydrolysis tank is processed by a screw squeezer to a concentration of ≥60%, and the aqueous solution containing fulvic acid is pumped to the fulvic acid water-soluble fertilizer production workshop.

[0033] Fiber coarse material: The material processed by the screw squeezer enters the No. 1 slurry mixing tank, and water is added to adjust the material concentration to 2% to 3%.

[0034] (6) Fiber refining:

[0035] Pressure screening: After slurry adjustment, the material is pumped into a pressure screen with a screen gap of 0.35-0.8 mm. The fibers that pass through the pressure screen are qualified fibers with a fiber beating degree of 35-40°SR.

[0036] Fiber collection: Qualified fibers are directly collected after being processed by a double-wire pulping machine.

[0037] (7) Loop processing:

[0038] Circular treatment of waste liquid: The liquid separated by the double-net slurry press is separated into residual fulvic acid and clean water through a 50kDa membrane ultrafiltration system. The residual fulvic acid enters the fulvic acid water-soluble fertilizer production workshop, and the clean water is circulated back to the No. 1 slurry mixing tank.

[0039] Circular fiber processing: The crude fiber that fails to pass the screening enters the No. 2 pulping tank, and the concentration is adjusted to 2% to 3%. After being processed by the low-concentration refiner to 0.25 to 0.6 mm, it returns to the No. 1 pulping tank for circular screening.

[0040] Key technical features

[0041] Room-temperature enzymatic hydrolysis: The process flow of the present invention is to carry out multi-stage enzymatic hydrolysis and gradient refining at room temperature without the need for additional heating.

[0042] Multi-stage enzymatic hydrolysis: The first-stage enzymatic hydrolysis tank, the second-stage enzymatic hydrolysis tank, and the third-stage enzymatic hydrolysis tank respectively carry out enzymatic hydrolysis reactions at different stages. The enzymatic hydrolysis at different stages can be used independently or in combination according to the characteristics of the processed raw materials. The synergistic effect of multi-stage enzymatic hydrolysis improves the fiber separation efficiency and fulvic acid conversion rate.

[0043] Enzymatic-mechanical synergistic system: Achieve efficient lignin dissociation at room temperature. Pretreatment with complex enzymes and acidic enzyme reaction buffer reduces refining energy consumption, achieving energy savings compared to traditional pulping methods.

[0044] Cascade refining: high-consistency refining dissociates fiber bundles and refines fibers, medium-consistency refining optimizes fiber morphology, and low-consistency refining increases fiber beating degree.

[0045] Closed-loop screening: Materials that fail the pressure screen are recycled to increase fiber yield. A closed-loop water-enzyme-fiber system is constructed to achieve near-zero emissions.

[0046] Preferably, the cascade enzymatic hydrolysis described in the present invention can select a combination of primary and secondary enzymatic hydrolysis, or a combination of primary, secondary and tertiary enzymatic hydrolysis according to the type of straw being processed. For example, a combination of primary and secondary enzymatic hydrolysis is selected to process corn straw, and a combination of primary, secondary and tertiary enzymatic hydrolysis is selected to process poplar wood chips. Preferably, a combination of primary, secondary and tertiary enzymatic hydrolysis is selected.

[0047] Preferably, the ratio of laccase (Lac) and xylanase (Xylanase) to the compound enzyme A in step (1) is 1:6 to 1:8, such as 1:6, 1:7 or 1:8, preferably 1:6.

[0048] Preferably, the ratio of the lignin peroxidase (LiP) and manganese peroxidase (MnP) to the complex enzyme B in step (1) is 1:1 to 1:1.2, such as 1:1, 1:1.1 or 1:1.2, preferably 1:1.

[0049] Preferably, in step (1), the ratio of the compound enzyme A and compound enzyme B to the compound enzyme C is 1:2 to 1:3, for example, 1:2 or 1:3, preferably 1:3.

[0050] Preferably, the acidic enzyme reaction buffer in step (1) can be prepared with citric acid, lactic acid or acetic acid, preferably acetic acid.

[0051] Preferably, the added amount of the complex enzyme A in step (2) is (6-9 U / g) straw, such as 6 U / g, 7 U / g, 8 U / g or 9 U / g, preferably 7 U / g.

[0052] Preferably, the added amount of the complex enzyme C in step (3) is (8-12 U / g) straw, such as 8 U / g, 9 U / g, 10 U / g, 11 U / g or 12 U / g, preferably 10 U / g.

[0053] Preferably, the addition amount of the complex enzyme B in step (4) is (10-14 U / g) straw, such as 10 U / g, 11 U / g, 12 U / g, 13 U / g or 14 U / g, preferably 12 U / g.

[0054] Preferably, the pH of the material is adjusted in step (1) to 3-3.5, such as 3, 3.2 or 3.5, preferably 3.2.

[0055] Preferably, the pH of the material adjusted in step (1) is 3.5-4, such as 3.5, 3.8 or 4, preferably 3.8.

[0056] Preferably, the pH of the material adjusted in step (1) is 4 to 4.5, such as 4, 4.3 or 3.5, preferably 4.3.

[0057] Preferably, the enzymatic hydrolysis time in steps (3) to (5) is 240 to 600 minutes, for example, 240 minutes, 300 minutes, 360 minutes, 420 minutes, 480 minutes, 540 minutes or 600 minutes, preferably 600 minutes.

[0058] Beneficial effects

[0059] The present invention uses an innovative process arrangement to construct a three-stage enzymatic hydrolysis and cascade refining synergistic system, achieving efficient co-production of straw fiber and fulvic acid under normal temperature conditions. The use of compound enzymes for phased addition to achieve sequential enzymatic hydrolysis, combined with gradient pH adjustment of pretreatment and multi-stage gradient refining, effectively improves the fulvic acid conversion rate and fiber yield. Through a closed-loop circulation system integrating a 50kDa ultrafiltration membrane and reverse osmosis technology, wastewater reuse and fulvic acid recovery are achieved, building a near-zero emission production system. Compared with traditional processes, this technology does not require high temperature and high pressure conditions, reduces overall energy consumption, reduces water consumption, and has a wide adaptability to raw materials, such as corn straw, cotton stalks, and wood chips. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] The accompanying drawing is a process flow chart of the present invention, showing multi-stage enzymatic hydrolysis, cascade refining, material circulation path and waste material conversion path. DETAILED DESCRIPTION

[0061] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0062] Example 1

[0063] Raw material: corn stalks

[0064] Pretreatment and enzyme reaction raw material preparation: crush to 3-5 cm, remove dust, screen and wash; add composting agent to the crushed powder and dust at a ratio of 1000:1.5 to make seedling soil; complex enzyme A (laccase:xylanase = 1:6), complex enzyme B (lignin peroxidase:manganese peroxidase = 1:1), complex enzyme C (complex enzyme A:complex enzyme B = 1:3); acetic acid solution.

[0065] Primary enzymatic hydrolysis: The material is sprayed with acidic buffer by screw conveyor No. 1 to adjust the pH of the material to 3.2, kneaded by extrusion and kneading machine to separate into threads, and sprayed with complex enzyme A (7U / g) by screw conveyor No. 2 to adjust the concentration to 35%; and then enters the enzymatic hydrolysis tank No. 1 for enzymatic hydrolysis for 600 minutes.

[0066] Secondary enzymatic hydrolysis: The material was sprayed with acidic buffer by screw conveyor No. 3 to adjust the pH of the material to 3.8, processed by high-concentration refiner, sprayed with complex enzyme C (10U / g) by screw conveyor No. 4 to adjust the concentration to 25%, and then entered into enzymatic hydrolysis tank No. 2 for enzymatic hydrolysis for 480 minutes.

[0067] Solid-liquid separation: spiral squeezing is used to obtain coarse fiber material; pressure screening is used to obtain qualified fiber, and the aqueous solution containing fulvic acid is sent to the fulvic acid water-soluble fertilizer production workshop.

[0068] Circulation treatment: The unscreened crude fiber enters the No. 2 pulping tank, is processed by the low-consistency refiner and re-screened, and the fulvic acid residual liquid is fully recovered.

[0069] Effect data: fiber yield 84.2%, fiber beating degree 38°SR, ash content 0.7%, tensile index 48.5N·m / g, fulvic acid conversion rate 78%, comprehensive energy consumption per ton of straw ≤100kWh, raw material utilization rate 98.5%, and organic matter content in seedling soil reaches 47%.

[0070] Example 2

[0071] Raw materials: Poplar wood chips

[0072] Pretreatment and enzyme reaction raw material preparation: Poplar wood chips are crushed into 3-4 cm fragments by a crusher, and sawdust smaller than 0.3 cm is removed by a vibrating screen; a composting agent is added to the crushed wood and dust at a ratio of 1000:1.5 to prepare seedling soil; complex enzyme A (laccase:xylanase = 1:6), complex enzyme B (lignin peroxidase:manganese peroxidase = 1:1.2), and complex enzyme C (complex enzyme A:complex enzyme B = 1:3); the acidic buffer is acetic acid solution.

[0073] Primary enzymatic hydrolysis: The material is sprayed with acidic buffer by screw conveyor No. 1 to adjust the pH of the material to 3.5, kneaded by extrusion and kneading machine to separate into threads, and sprayed with complex enzyme A (9U / g) by screw conveyor No. 2 to adjust the concentration to 35%; and then enters the enzymatic hydrolysis tank No. 1 for enzymatic hydrolysis for 600 minutes.

[0074] Secondary enzymatic hydrolysis: The material is sprayed with acidic buffer by screw conveyor No. 3 to adjust the pH of the material to 4.2, treated in a high-concentration refiner, sprayed with complex enzyme C (10U / g) by screw conveyor No. 4 to adjust the concentration to 25%, and then enters the enzymatic hydrolysis tank No. 2 for enzymatic hydrolysis for 400 minutes.

[0075] The material was treated in a medium-consistency refiner after being sprayed with acidic buffer solution via No. 5 screw conveyor to adjust the pH value to 4.5. The material was then treated in a medium-consistency refiner after being sprayed with complex enzyme B (14 U / g) via No. 6 screw conveyor to adjust the concentration to 25%. The material was then subjected to enzymatic hydrolysis in No. 2 enzymatic hydrolysis tank for 600 minutes.

[0076] Solid-liquid separation: spiral squeezing is used to obtain coarse fiber material; pressure screening is used to obtain qualified fiber, and the aqueous solution containing fulvic acid is sent to the fulvic acid water-soluble fertilizer production workshop.

[0077] Circulation treatment: The unscreened crude fiber enters the No. 2 pulping tank, is processed by the low-consistency refiner and re-screened, and the fulvic acid residual liquid is fully recovered.

[0078] Performance data: Cellulose yield 78.4%, fiber decomposition 40°SR, ash content 0.4%, tensile index 34.3 N·m / g, fulvic acid conversion rate 70.7%, comprehensive energy consumption per ton of raw material ≤ 95 kWh, raw material utilization rate 97%, and organic matter content in seedling soil 43%.

Claims

1. A method for co-producing fiber and fulvic acid from straw at room temperature, characterized in that: The following steps are involved: (1) Straw pretreatment and enzyme reaction raw material preparation: Straw pretreatment: Crush the straw into 3-5 cm fragments, sieve to remove impurities and debris, and then send it into an extrusion and kneading machine after cleaning to collect the debris and dust as raw materials for making seedling soil. Preparation of complex enzymes: Complex enzyme A is a mixture of laccase (Lac) and xylanase (Xylanase) in a ratio of 1:6 to 1:8; complex enzyme B is a mixture of lignin peroxidase (LiP) and manganese peroxidase (MnP) in a ratio of 1:1 to 1:1.2; complex enzyme C is a mixture of complex enzyme A and complex enzyme B in a ratio of 1:2 to 1:

3. Preparation of acidic enzyme reaction buffer: Use citric acid, lactic acid or acetic acid and water to prepare acidic enzyme reaction buffer. (2) Primary enzymatic hydrolysis: spray acidic buffer to adjust the material concentration to 30% to 35% and pH to 3 to 3.

5. After the epidermis is destroyed by an extrusion and kneading machine, spray compound enzyme A 6 to 9 U / g and perform enzymatic hydrolysis for 240 to 600 minutes. (3) Secondary enzymatic hydrolysis: spray acidic buffer to adjust the material concentration to 25% to 30% and pH to 3.5 to 4, process it in a high-consistency refiner to a fiber diameter of 0.5 to 1.2 mm, and then spray compound enzyme C 8 to 12 U / g for enzymatic hydrolysis for 240 to 600 minutes. (4) Tertiary enzymatic hydrolysis: spray acidic buffer to adjust the material concentration to 25% to 30% and pH 4 to 4.5, process it through a medium-consistency refiner to a fiber diameter of 0.25 to 0.7 mm, and then spray complex enzyme B 10 to 14 U / g for enzymatic hydrolysis for 240 to 600 minutes. (5) Solid-liquid separation: After dehydration, the fiber coarse material and the aqueous solution containing fulvic acid are separated. The coarse material is slurried to a concentration of 2% to 3%, and the aqueous solution containing fulvic acid is sent to the fulvic acid water-soluble fertilizer production workshop. (6) Fiber refining: Fibers with a beating degree of 35-40°SR are obtained by screening through a pressure screen with a screen gap of 0.35-0.8 mm. (7) Circulation treatment: The waste liquid is recovered by ultrafiltration to separate the aqueous solution containing fulvic acid and the purified water. The aqueous solution containing fulvic acid is sent to the fulvic acid water-soluble fertilizer production workshop, and the purified water is reused. The crude fiber that does not pass the screening is processed in a low-consistency refiner to a fiber diameter of 0.25-0.6 mm and then recycled for screening.

2. The method according to claim 1, characterized in that The ratio of laccase to xylanase in the complex enzyme A is 1:6-1:8, the ratio of lignin peroxidase to manganese peroxidase in the complex enzyme B is 1:1-1:1.2, and the ratio of complex enzyme A to complex enzyme B in the complex enzyme C is 1:2-1:

3.

3. The method according to claim 1, characterized in that The acidic enzyme reaction buffer is prepared by mixing citric acid, lactic acid or acetic acid with water.

4. The method according to claim 1, wherein The enzymatic hydrolysis time of steps (2) to (4) is 240 to 600 minutes, and the pH gradient of the tertiary enzymatic hydrolysis is 3 to 3.5 → 3.5 to 4 → 4 to 4.

5.

5. The method according to claim 1, wherein The refining process of steps (2) to (4) includes: a high-consistency refiner processes a material with a wire diameter of 0.5 to 1.2 mm, a medium-consistency refiner processes a material with a wire diameter of 0.25 to 0.7 mm, and a low-consistency refiner processes a material with a wire diameter of 0.25 to 0.6 mm. A cascade refining process with multiple refiners working together.

6. The method according to claim 1, characterized in that The recycling treatment in step (7) includes a 50 kDa ultrafiltration membrane system and a crude fiber path design that does not pass the screening, achieving a water reuse rate of ≥96% and a fulvic acid recovery rate of ≥95%.

7. The method according to claim 1, characterized in that The enzymatic hydrolysis stages are selected according to the type of raw materials: primary enzymatic hydrolysis and secondary enzymatic hydrolysis or primary, secondary and tertiary enzymatic hydrolysis.

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