Sulfonated lignin modified environment-friendly adhesive based on straw biogas residue and preparation process of sulfonated lignin modified environment-friendly adhesive

Abstract

The invention provides a sulfonated lignin modified environment-friendly adhesive based on straw biogas residues and a preparation process thereof, and belongs to the technical field of adhesives. A preparation process of a sulfonated lignin modified environment-friendly adhesive based on straw biogas residues comprises the following steps: stirring and washing straw biogas residues obtained after biogas fermentation with clear water for multiple times to obtain washed biogas residues; dehydrating the washed biogas residues to obtain clean biogas residues of which the water content is less than or equal to 70%; mixing the clean biogas residues with the modified liquid, performing heating reaction, and performing centrifugal separation to obtain a sodium lignin sulfonate crude liquid; carrying out concentration treatment on the sodium lignin sulfonate crude liquid until the solid content is greater than or equal to 20% to obtain a concentrated liquid; adding a sulfamic acid composite catalyst into the concentrated solution, then slowly dropwise adding epoxy chloropropane, and reacting to obtain an epoxy-sulfonated lignin copolymer; and adding a surfactant, and adjusting the pH value to obtain the environment-friendly adhesive. Through efficient separation and purification and directional modification, the utilization rate of straw biogas residues is increased, and the performance of the adhesive is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of adhesives, and particularly relates to a sulfonated lignin modified environmental protection adhesive based on straw biogas residue and its preparation process. Background Art

[0002] Traditional adhesives, such as urea-formaldehyde resin and phenolic resin, mainly rely on petrochemical raw materials and have problems such as high pollution and non-renewability. In order to reduce the dependence on fossil raw materials, researchers have tried to use lignin in biomass resources to prepare adhesives. However, existing lignin-based adhesives mostly use lignin extracted from paper-making black liquor, but this method has problems such as high raw material cost and insufficient purity.

[0003] In addition, although straw biogas residue is rich in lignin and is currently mainly used to manufacture organic fertilizers, its nutritional value is not high and it hardly generates economic benefits. More importantly, when straw biogas residue is directly used to prepare lignin adhesives, there are many impurities and it is difficult to separate, resulting in unstable adhesive performance. At the same time, due to its complex chemical structure and tight binding with other components, it is difficult to directly extract and utilize lignin in straw biogas residue.

[0004] Therefore, how to use straw biogas residue to produce lignin adhesives with stable performance is still a technical problem to be solved urgently.

[0005] In view of this, the present invention is specifically proposed. Summary of the Invention

[0006] Aiming at the deficiencies of the prior art, the technical problem to be solved by the present invention is to provide a preparation process for a sulfonated lignin modified environmental protection adhesive based on straw biogas residue, which improves the utilization rate of straw biogas residue and the performance of the adhesive through efficient separation, purification and directional modification.

[0007] To solve the above technical problem, the technical solution adopted by the present invention is: a preparation process for a sulfonated lignin modified environmental protection adhesive based on straw biogas residue, comprising the following steps: Step 1: Stir and wash the straw biogas residue after biogas fermentation with clear water for multiple times to remove sediment and soluble impurities, and obtain the washed biogas residue; Step 2: Dehydrate the washed biogas residue to obtain clean biogas residue with a moisture content ≤ 70% by mass percentage; Step 3: Mix the clean biogas residue with a modification liquid, heat at 85 - 95 °C for 1.5 - 2.5 hours, and perform centrifugal separation to obtain a crude sodium lignosulfonate liquid; Step 4: Concentrate the crude sodium lignosulfonate liquid to make the solid content ≥ 20% to obtain a concentrated liquid; Step 5: Add an amino sulfonic acid composite catalyst to the concentrated solution, then slowly dropwise add epichlorohydrin. Under nitrogen protection, react at pH = 8.8 - 9.2 and 50°C - 90°C for 2.5 - 3.5 hours to obtain an epoxy-sulfonated lignin copolymer; Step 6: Add a surfactant and adjust the pH to obtain an environment-friendly adhesive.

[0008] Optionally, the number of times of stirring and washing is more than 3 times.

[0009] Optionally, the mass ratio of the straw biogas residue to the clear water is 1:(4 - 6).

[0010] Optionally, the dehydration is carried out by a screw extrusion separator with a filter screen aperture of 0.1 - 0.3 mm and a pressure of 4.5 - 5.5 MPa.

[0011] Optionally, the modification liquid contains 4 - 10% by mass of sodium sulfite and 1 - 10% by mass of sodium hydroxide, and the balance is water. The mass ratio of the clean biogas residue to the modification liquid is 1:(8 - 12).

[0012] Optionally, the concentration treatment is to concentrate the crude sodium lignin sulfonate solution through a vacuum spray concentration tower. The process parameters include: atomization particle size ≤ 50 μm, inlet air temperature 100 - 130°C, the flow direction of the hot air inlet is opposite to that of the material, and cool down to below 50°C for standby after concentration.

[0013] Optionally, the dosage of the amino sulfonic acid composite catalyst is 0.5% - 1.5% of the dry basis mass of the concentrated solution, and the amino sulfonic acid composite catalyst is compounded from amino sulfonic acid and triethylamine according to a mass ratio of 1:(0.2 - 0.5).

[0014] Optionally, the epichlorohydrin is 10 - 30% of the dry basis mass of the concentrated solution.

[0015] Optionally, the surfactant is polystyrene sulfonic acid, and the added mass of the surfactant is 1% - 3% of the solid content of the epoxy-sulfonated lignin copolymer.

[0016] Optionally, the viscosity of the environment-friendly adhesive ≥ 10 mPa·s, pH = 7 - 9, solid content ≥ 20%, storage stability ≥ 180 days, bonding strength ≥ 1.5 MPa, residual free epichlorohydrin ≤ 0.01%, and free formaldehyde content ≤ 0.01%.

[0017] The present invention also provides an environmentally friendly adhesive obtained by a preparation process of a sulfonated lignin-modified environmentally friendly adhesive based on straw biogas digested residue. The viscosity of the environmentally friendly adhesive is ≥10 mPa·s, the pH is 7-9, the solid content is ≥20%, the storage stability is ≥180 days, the bonding strength is ≥1.5 MPa, the residual free epichlorohydrin is ≤0.01%, and the free formaldehyde content is ≤0.01%.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention provides a preparation process of a sulfonated lignin-modified environmentally friendly adhesive based on straw biogas digested residue. Through efficient separation, purification and directional modification, the utilization rate of straw biogas digested residue is improved and the performance of the adhesive is improved.

[0019] First of all, the present invention uses waste straw biogas digested residue to replace the traditional lignin source, reducing the cost by more than 40%.

[0020] Secondly, in the preparation process of the present invention, the digested residue is pretreated first. Through more than 3 times of washing with clear water, the residual sediment and soluble impurities in the digested residue are effectively removed, avoiding the interference of impurities in the subsequent reaction on the sulfonation process; spiral extrusion dehydration controls the moisture content to ≤70%, which not only prevents excessive dissolution of lignin, but also ensures the effective penetration of the modification liquid in the subsequent sulfonation reaction. Example 2 shows that the utilization rate of the digested residue can reach 92.3% after 3 times of washing, while in Comparative Example 1, when only 1 time of washing is carried out, the utilization rate drops sharply to 72.1%, indicating that this step plays a key role in the decontamination and purification of raw materials and can improve the utilization rate of raw materials. Then, a composite modification liquid of 4-10% sodium sulfite and 1-10% sodium hydroxide is used to achieve deep sulfonation of lignin at 85-95°C; sodium hydroxide promotes the cleavage of ether bonds in lignin, and sodium sulfite introduces sulfonic acid groups, significantly improving the water solubility and reaction activity of lignin. When sodium sulfite was not added in Comparative Example 3, the bonding strength was only 0.62 MPa, less than 40% of that in Example 1, indicating that the sulfonation process has an obvious impact on the subsequent epoxy modification. Then, through a spray concentration process with an atomization particle size ≤50 μm and reverse hot air at 100-130°C, while avoiding high-temperature degradation, the solid content is increased to more than 20%, providing a stable precursor for the subsequent copolymerization reaction. Then, under the condition of pH 8.8-9.2, the amino sulfonic acid composite catalyst accurately controls the grafting reaction of epichlorohydrin and sulfonated lignin to form a stable copolymer. Nitrogen protection inhibits side reactions, making the residual free epichlorohydrin <0.01%. When the catalyst was in excess in Comparative Example 4, gelation occurred in the product, indicating that excessive use of the catalyst would have an adverse effect on the product performance; at the same time, when the pH was lower in Comparative Example 5, the storage stability and bonding strength of the product decreased. Finally, 1-3% of polystyrene sulfonic acid surfactant is added. Through electrostatic repulsion and steric hindrance effects, the adhesive forms a stable colloid at pH 7-9, and the storage stability at room temperature (25°C) >180 days.

[0021] Thirdly, the utilization rate of traditional straw biogas residue is less than 50%, and there are common problems with lignin-based adhesives such as low strength (<1.0 MPa) and formaldehyde residue. Through the double modification of "deep sulfonation-epoxy copolymerization", the utilization rate of biogas residue can be increased to more than 90% in this invention, the bonding strength reaches 1.85 MPa, and at the same time, the residues of formaldehyde and epichlorohydrin are both ≤0.01%, solving the long-term pain points in the industry.

[0022] It can be seen that through multi-step collaborative innovation and refined parameter control in this invention, the high-value utilization of straw biogas residue and the breakthrough of the performance of environmental protection adhesives are realized. The viscosity of the obtained environmental protection adhesive is ≥10 mPa·s, pH = 7-9, the solid content is ≥20%, the storage stability at room temperature (25°C) is ≥180 days, the bonding strength is ≥1.5 MPa, the residual free epichlorohydrin is ≤0.01%, and the free formaldehyde content is ≤0.01%, which can better meet the market application requirements. Detailed implementation manners

[0023] To better understand this invention, the content of this invention will be further clearly elaborated below in combination with embodiments. However, the protected content of this invention is not limited to the following embodiments only. In the following description, a large number of specific details are given to provide a more thorough understanding of this invention. However, it is obvious to those skilled in the art that this invention can be implemented without one or more of these details.

[0024] Based on the embodiments in this invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of this invention.

[0025] In all the examples shown and discussed here, any specific value should be interpreted as merely exemplary, rather than as a limitation. Therefore, other examples of the exemplary embodiments may have different values.

[0026] Unless otherwise specified, all raw materials are from commercially available products, and unless otherwise specified, they do not contain other components not explicitly mentioned except for inevitable impurities.

[0027] In the following tests, the test method for the bonding strength is as follows: The manufacture and strength test of plywood are carried out according to the provisions of Section 4.17 in GB / T17657-2022 "Test Methods for Physical and Chemical Properties of Wood-Based Panels and Decorative Wood-Based Panels". The specific preparation steps are as follows: Select fast-growing poplar veneers to prepare three-layer plywood. The moisture content of the veneers is 10-12%, and the length, width and thickness of the veneers are 145 mm, 110 mm and 1.5 mm respectively. The prepared adhesive is used to apply glue to the middle veneer. The glue application method is double-sided glue application, and the single-sided glue application amount is 300 g / m 2A sizing veneer is adhered with an unsized veneer on each of its upper and lower sides, such that the fiber directions of adjacent veneers are perpendicular to each other. The assembled three-layer plywood is placed on the heating plate of a hot press. The hot pressing temperature is 150 °C, the hot pressing pressure is 2 MPa, and the hot pressing time is 5 minutes. The bonding strength is tested according to Class II plywood of GB / T9846-2015 "General Plywood".

[0028] Example 1: A preparation process of a sulfonated lignin modified environmentally friendly adhesive based on straw biogas digested residue, comprising the following steps: Step 1: The straw biogas digested residue after biogas fermentation is stirred and washed with clear water three times. The mass ratio of the straw biogas digested residue to the clear water is 1:5 to remove sediment and soluble impurities, obtaining the washed digested residue; Step 2: The washed digested residue is dehydrated using a screw extrusion separator with a filter screen pore diameter of 0.2 mm and a pressure of 5.0 MPa, obtaining clean digested residue with a moisture content of 54.7% by mass; Step 3: The clean digested residue is mixed with a modification liquid. The modification liquid contains 5.0% by mass of sodium sulfite and 4.0% by mass of sodium hydroxide. The mass ratio of the clean digested residue to the modification liquid is 1:10. It is heated at 90 °C for 2 hours and centrifuged to obtain a crude sodium lignosulfonate liquid; Step 4: The crude sodium lignosulfonate liquid is concentrated through a vacuum spray concentrator tower with an atomization particle size of 50 μm and an inlet air temperature of 120 °C. The hot air inlet and the material flow direction are in reverse. After concentration, it is cooled to 50 °C for standby, with a solid content of 21.3%, obtaining a concentrated liquid; Step 5: An amino sulfonic acid composite catalyst is added to the concentrated liquid. The dosage of the amino sulfonic acid composite catalyst is 1.0% of the dry basis mass of the concentrated liquid. The amino sulfonic acid composite catalyst is prepared by compounding amino sulfonic acid and triethylamine at a mass ratio of 1:0.3. Then, epichlorohydrin is slowly added, with the amount of epichlorohydrin being 20% of the dry basis mass of the concentrated liquid. Under nitrogen protection, at pH = 9.0, it reacts at 70 °C for 3 hours to obtain an epoxy-sulfonated lignin copolymer; Step 6: Polystyrene sulfonic acid with a mass percentage of 2% of the solid content of the epoxy-sulfonated lignin copolymer is added, and the pH is adjusted to 8 to obtain an environmentally friendly adhesive.

[0029] In this example, the utilization rate of the straw biogas digested residue is 92.3%, the viscosity of the environmentally friendly adhesive is 15.2 mPa·s, the solid content is 21.3%, the storage stability at room temperature (25 °C) is 190 days, the bonding strength is 1.76 MPa, the residual free epichlorohydrin is 0.005%, and the free formaldehyde is 0.001%.

[0030] Among them, the utilization rate of the straw biogas digested residue = (total lignin content in the concentrated liquid - unreacted lignin content) / total lignin content in the concentrated liquid × 100%, the same hereinafter, and will not be elaborated further.

[0031] Example 2: The preparation process of the sulfonated lignin modified environmental protection adhesive based on straw biogas digested residue includes the following steps: Step 1: Stir and wash the straw biogas digested residue after biogas fermentation with clear water three times. The mass ratio of the straw biogas digested residue to the clear water is 1:4 to remove sediment and soluble impurities, and the washed digested residue is obtained. Step 2: Dehydrate the washed digested residue using a screw extrusion separator with a filter screen aperture of 0.3 mm and a pressure of 4.5 MPa to obtain clean digested residue with a moisture content of 60.6% by mass. Step 3: Mix the clean digested residue with a modification liquid. The modification liquid contains 4% by mass of sodium sulfite and 1% by mass of sodium hydroxide. The mass ratio of the clean digested residue to the modification liquid is 1:12. Heat at 95 °C for 1.5 hours and perform centrifugal separation to obtain a crude sodium lignosulfonate liquid. Step 4: Concentrate the crude sodium lignosulfonate liquid through a vacuum spray concentration tower with an atomization particle size of 50 μm and an inlet air temperature of 130 °C. The hot air inlet and the material flow are in the reverse direction. After concentration, cool down to 50 °C for standby with a solid content of 20.5% to obtain a concentrated liquid. Step 5: Add an amino sulfonic acid composite catalyst to the concentrated liquid. The dosage of the amino sulfonic acid composite catalyst is 0.5% of the dry basis mass of the concentrated liquid. The amino sulfonic acid composite catalyst is prepared by compounding amino sulfonic acid and triethylamine at a mass ratio of 1:0.2. Then slowly dropwise add epichlorohydrin, and the amount of epichlorohydrin is 10% of the dry basis mass of the concentrated liquid. Under nitrogen protection, at pH = 8.8, react at 50 °C for 3.5 hours to obtain an epoxy-sulfonated lignin copolymer. Step 6: Add polystyrene sulfonic acid with a mass percentage of 1% of the solid content of the epoxy-sulfonated lignin copolymer and adjust the pH to 7 to obtain an environmental protection adhesive.

[0032] In this example, the utilization rate of the straw biogas digested residue is 94.1%, the viscosity of the environmental protection adhesive is 16.8 mPa·s, the solid content is 22.9%, the storage stability at room temperature (25 °C) is 187 days, the bonding strength is 1.85 MPa, the residual free epichlorohydrin is 0.007%, and the free formaldehyde is 0.003%.

[0033] Example 3: The preparation process of the sulfonated lignin modified environmental protection adhesive based on straw biogas digested residue includes the following steps: Step 1: Stir and wash the straw biogas digested residue after biogas fermentation with clear water three times. The mass ratio of the straw biogas digested residue to the clear water is 1:6 to remove sediment and soluble impurities, and the washed digested residue is obtained. Step 2: Dehydrate the washed digested residue using a screw extrusion separator with a filter screen aperture of 0.1 mm and a pressure of 5.5 MPa to obtain clean digested residue with a moisture content of 50.3% by mass. Step 3: Mix the clean biogas residue with the modification liquid. The modification liquid contains 10% sodium sulfite and 10% sodium hydroxide by mass percentage. The mass ratio of the clean biogas residue to the modification liquid is 1:8. Heat at 85°C for 2.5 hours, then perform centrifugal separation to obtain the crude sodium lignosulfonate solution; Step 4: Concentrate the crude sodium lignosulfonate solution through a vacuum spray concentration tower. The atomization particle size is 50 μm, the inlet air temperature is 100°C, and the hot air inlet is in the reverse direction of the material flow. After concentration, cool down to 50°C for standby. The solid content is 21.6% to obtain the concentrated solution; Step 5: Add an amino sulfonic acid composite catalyst to the concentrated solution. The dosage of the amino sulfonic acid composite catalyst is 1.5% of the dry basis mass of the concentrated solution. The amino sulfonic acid composite catalyst is prepared by compounding amino sulfonic acid and triethylamine in a mass ratio of 1:0.5. Then slowly dropwise add epichlorohydrin, and the amount of epichlorohydrin is 30% of the dry basis mass of the concentrated solution. Under nitrogen protection, at pH = 9.2, react at 90°C for 2.5 hours to obtain the epoxy-sulfonated lignin copolymer; Step 6: Add polystyrene sulfonic acid with a mass percentage of 3% of the solid content of the epoxy-sulfonated lignin copolymer, and adjust the pH to 9 to obtain the environmental protection adhesive.

[0034] In this example, the utilization rate of the straw biogas residue is 90.1%. The viscosity of the environmental protection adhesive is 13.5 mPa·s, the solid content is 20.4%, the storage stability at room temperature (25°C) is 185 days, the bonding strength is 1.58 MPa, the residual free epichlorohydrin is 0.008%, and the free formaldehyde is 0.001%.

[0035] Example 4: The preparation process of the sulfonated lignin modified environmental protection adhesive based on straw biogas residue is only different from Example 1 in that in Step 1, the straw biogas residue after biogas fermentation is stirred and washed with water 4 times. The mass ratio of the straw biogas residue to water is 1:6 to remove sediment and soluble impurities to obtain the washed biogas residue.

[0036] In this example, the utilization rate of the straw biogas residue is 89.4%. The viscosity of the environmental protection adhesive is 12.3 mPa·s, the solid content is 21.1%, the storage stability is 183 days, the bonding strength is 1.63 MPa, the residual free epichlorohydrin is 0.006%, and the free formaldehyde is 0.002%.

[0037] Example 5: The preparation process of the sulfonated lignin modified environmental protection adhesive based on straw biogas residue is only different from Example 1 in that in Step 2, the washed biogas residue is dehydrated using a screw extrusion separator with a filter screen aperture of 0.1 mm and a pressure of 5.2 MPa to obtain clean biogas residue with a moisture content of 58.1% by mass percentage.

[0038] In this example, the utilization rate of straw biogas marsh slag is 91.4%, the viscosity of the environmental protection adhesive is 14.2 mPa·s, the solid content is 20.8%, the storage stability at room temperature (25°C) is 189 days, the bonding strength is 1.70 MPa, the residual free epichlorohydrin is 0.008%, and the free formaldehyde is 0.001%.

[0039] Example 6: The preparation process of the sulfonated lignin modified environmental protection adhesive based on straw biogas marsh slag is only different from Example 1 in that: in step 3, the clean marsh slag is mixed with the modification liquid. The modification liquid contains 8% by mass of sodium sulfite and 5% by mass of sodium hydroxide. The mass ratio of the clean marsh slag to the modification liquid is 1:9. Heat at 87°C for 2 hours, and then perform centrifugal separation to obtain the crude sodium lignosulfonate solution.

[0040] In this example, the utilization rate of straw biogas marsh slag is 90.5%, the viscosity of the environmental protection adhesive is 14.3 mPa·s, the solid content is 21.3%, the storage stability at room temperature (25°C) is 191 days, the bonding strength is 1.65 MPa, the residual free epichlorohydrin is 0.006%, and the free formaldehyde is 0.002%.

[0041] Example 7: The preparation process of the sulfonated lignin modified environmental protection adhesive based on straw biogas marsh slag is only different from Example 1 in that: in step 4, the crude sodium lignosulfonate solution is concentrated through a vacuum spray concentrator tower. The atomization particle size is 50 μm, the inlet air temperature is 110°C, and the flow direction of the hot air inlet is opposite to that of the material. After concentration, cool down to 45°C for standby, with a solid content of 20.7% to obtain the concentrated solution.

[0042] In this example, the utilization rate of straw biogas marsh slag is 89.7%, the viscosity of the environmental protection adhesive is 14.7 mPa·s, the solid content is 20.6%, the storage stability at room temperature (25°C) is 186 days, the bonding strength is 1.62 MPa, the residual free epichlorohydrin is 0.007%, and the free formaldehyde is 0.001%.

[0043] Example 8: The preparation process of the sulfonated lignin modified environmental protection adhesive based on straw biogas marsh slag is only different from Example 1 in that: in step 5, an amino sulfonic acid composite catalyst is added to the concentrated solution. The dosage of the amino sulfonic acid composite catalyst is 0.8% of the dry basis mass of the concentrated solution. The amino sulfonic acid composite catalyst is prepared by compounding amino sulfonic acid and triethylamine according to a mass ratio of 1:0.4. Then, epichlorohydrin is slowly added dropwise. The amount of epichlorohydrin is 15% of the dry basis mass of the concentrated solution. Under nitrogen protection, at pH = 9.0, react at 60°C for 3.5 hours to obtain the epoxy-sulfonated lignin copolymer.

[0044] In this embodiment, the utilization rate of straw biogas digested residues is 91.3%, the viscosity of the environmental protection adhesive is 15.0 mPa·s, the solid content is 21.7%, the storage stability at room temperature (25°C) is 183 days, the bonding strength is 1.67 MPa, the residual free epichlorohydrin is 0.005%, and the free formaldehyde is 0.002%.

[0045] Example 9: The preparation process of the sulfonated lignin modified environmental protection adhesive based on straw biogas digested residues is different from that of Example 1 only in that: in Step 5, an amino sulfonic acid composite catalyst is added to the concentrated solution, and the dosage of the amino sulfonic acid composite catalyst is 1.2% of the dry basis mass of the concentrated solution. The amino sulfonic acid composite catalyst is prepared by compounding amino sulfonic acid and triethylamine according to a mass ratio of 1:0.3. Then, epichlorohydrin is slowly added dropwise, and the amount of epichlorohydrin is 25% of the dry basis mass of the concentrated solution. Under nitrogen protection, at pH = 9.1 and 80°C, the reaction is carried out for 3 hours to obtain an epoxy-sulfonated lignin copolymer.

[0046] In this embodiment, the utilization rate of straw biogas digested residues is 89.5%, the viscosity of the environmental protection adhesive is 15.4 mPa·s, the solid content is 20.9%, the storage stability at room temperature (25°C) is 190 days, the bonding strength is 1.70 MPa, the residual free epichlorohydrin is 0.007%, and the free formaldehyde is 0.002%.

[0047] Example 10: The preparation process of the sulfonated lignin modified environmental protection adhesive based on straw biogas digested residues is different from that of Example 1 only in that: in Step 6, polystyrene sulfonic acid with a mass percentage of 1.8% of the solid content of the epoxy-sulfonated lignin copolymer is added, and the pH is adjusted to 8.5 to obtain the environmental protection adhesive.

[0048] In this embodiment, the utilization rate of straw biogas digested residues is 89.5%, the viscosity of the environmental protection adhesive is 14.8 mPa·s, the solid content is 21.5%, the storage stability at room temperature (25°C) is 182 days, the bonding strength is 1.68 MPa, the residual free epichlorohydrin is 0.006%, and the free formaldehyde is 0.001%.

[0049] Comparative Example 1: The preparation process of the sulfonated lignin modified adhesive based on straw biogas digested residues is different from that of Example 1 only in that: in Step 1, the straw biogas digested residues after biogas fermentation are stirred and washed once with clear water.

[0050] In this comparative example, the utilization rate of straw biogas digested residues is 72.4%, the viscosity of the environmental protection adhesive is 15.2 mPa·s, the solid content is 20.7%, the storage stability at room temperature (25°C) is 90 days, the bonding strength is 0.95 MPa, the residual free epichlorohydrin is 0.034%, and the free formaldehyde is 0.003%.

[0051] Comparative Example 2: The preparation process of the sulfonated lignin modified adhesive based on the biogas residue of straw biogas is only different from that of Example 1 in that: in step 2, the dehydration pressure is 3.0 MPa, and clean biogas residue with a moisture content of 73.1% by mass is obtained.

[0052] The utilization rate of the straw biogas residue in this comparative example is 68.5%, the viscosity of the environmental protection adhesive is 13.5 mPa·s, the solid content is 21.3%, the storage stability at room temperature (25 °C) is 102 days, the bonding strength is 0.88 MPa, the residual free epichlorohydrin is 0.041%, and the free formaldehyde is 0.002%.

[0053] Comparative Example 3: The preparation process of the sulfonated lignin modified adhesive based on the biogas residue of straw biogas is only different from that of Example 1 in that: in step 3, the addition of sodium sulfite is omitted.

[0054] The utilization rate of the straw biogas residue in this comparative example is 53.2%, the viscosity of the environmental protection adhesive is 12.7 mPa·s, the solid content is 20.5%, the storage stability at room temperature (25 °C) is 40 days, the bonding strength is 0.62 MPa, the residual free epichlorohydrin is 0.058%, and the free formaldehyde is 0.003%.

[0055] Comparative Example 4: The preparation process of the sulfonated lignin modified adhesive based on the biogas residue of straw biogas is only different from that of Example 1 in that: in step 5, the dosage of the amino sulfonic acid composite catalyst is 3.0% of the dry basis mass of the concentrated liquid.

[0056] The utilization rate of the straw biogas residue in this comparative example is 87.6%, the viscosity of the environmental protection adhesive is 15.1 mPa·s, the solid content is 21.3%, the storage stability at room temperature (25 °C) is 120 days, the bonding strength is 1.32 MPa, the residual free epichlorohydrin is 0.015%, and the free formaldehyde is 0.005%.

[0057] Comparative Example 5: The preparation process of the sulfonated lignin modified adhesive based on the biogas residue of straw biogas is only different from that of Example 1 in that: in step 5, pH = 8.0.

[0058] The utilization rate of the straw biogas residue in this comparative example is 81.4%, the viscosity of the environmental protection adhesive is 14.3 mPa·s, the solid content is 21.5%, the storage stability at room temperature (25 °C) is 117 days, the bonding strength is 1.12 MPa, the residual free epichlorohydrin is 0.028%, and the free formaldehyde is 0.004%.

[0059] Comparative Example 6: The preparation process of the sulfonated lignin modified adhesive based on the biogas residue of straw biogas is only different from that of Example 1 in that: in step 3, the clean biogas residue is directly mixed with equal amounts of sodium sulfite and equal amounts of sodium hydroxide, then equal amounts of water are added and mixed, and heated at 90 °C for 2 hours, followed by centrifugal separation to obtain the crude sodium lignin sulfonate solution.

[0060] The utilization rate of the straw biogas residue in this comparative example is 62.6%, the viscosity of the environmental protection adhesive is 11.5 mPa·s, the solid content is 20.1%, the storage stability at room temperature (25°C) is 105 days, the bonding strength is 0.35 MPa, the residual free epichlorohydrin is 0.009%, and the free formaldehyde is 0.005%.

[0061] It can be seen that through precise parameter control and process optimization, the utilization rate of straw biogas residue in the technical solution of the present invention is increased from <50% in the traditional method to >90%; at the same time, the adhesive has low viscosity, high bonding strength, good storage stability, and basically does not contain free epichlorohydrin and free formaldehyde, with excellent environmental protection and safety; the performance of the plywood made with the adhesive of the present invention meets the requirements of Class II plywood in the industrial standard (GB / T 9846-2015).

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Any other modifications or equivalent replacements made by those of ordinary skill in the art to the technical solutions of the present invention shall be covered within the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solutions of the present invention.

Claims

1. The preparation process of sulfonated lignin modified environmentally friendly adhesive based on straw biogas residue is characterized by: The following steps are involved: Step 1: Stir and wash the straw residue after biogas fermentation with clean water for multiple times to remove sediment and soluble impurities to obtain washed residue; Step 2: dehydrating the washed biogas residue to obtain clean biogas residue with a moisture content of ≤70% by mass; Step 3: mixing the clean biogas residue with the modified liquid, heating at 85-95° C. for 1.5-2.5 hours, and centrifuging to obtain a crude sodium lignin sulfonate liquid; Step 4: Concentrating the crude sodium lignin sulfonate solution to make the solid content ≥ 20% to obtain a concentrated solution; Step 5: Add aminosulfonic acid composite catalyst to the concentrated solution, then slowly drop epichlorohydrin, under nitrogen protection, pH = 8.8-9.2, 50° C.-90° C. for reaction for 2.5-3.5 hours to obtain epoxy-sulfonated lignin copolymer; Step 6: Add surfactant and adjust pH to obtain environmentally friendly adhesive.

2. The preparation process of the sulfonated lignin modified environmentally friendly adhesive based on straw biogas and biogas residue as claimed in claim 1, characterized in that: The stirring and washing is performed for more than 3 times, and the mass ratio of the straw biogas residue to the clean water is 1:(4-6).

3. The preparation process of the sulfonated lignin modified environmentally friendly adhesive based on straw biogas and biogas residue according to claim 1, characterized in that: The dehydration adopts a spiral extrusion separator with a filter mesh aperture of 0.1-0.3 mm and a pressure of 4.5-5.5 MPa.

4. The preparation process of the sulfonated lignin modified environmentally friendly adhesive based on straw biogas and biogas residue according to claim 1, characterized in that: The modified liquid contains 4-10% by mass of sodium sulfite and 1-10% by mass of sodium hydroxide, and the mass ratio of the clean biogas residue to the modified liquid is 1:(8-12).

5. The preparation process of the sulfonated lignin modified environmentally friendly adhesive based on straw biogas and biogas residue according to claim 1, characterized in that: The concentration treatment is to concentrate the crude sodium lignin sulfonate liquid through a reduced pressure spray concentration tower, and the process parameters include: atomization particle size ≤ 50 μm, air inlet temperature 100-130° C., hot air inlet and material flow are in the opposite direction, and after the concentration is completed, the temperature is cooled to below 50° C. for standby use.

6. The preparation process of the sulfonated lignin modified environmentally friendly adhesive based on straw biogas and biogas residue according to claim 1, characterized in that: The dosage of the aminosulfonic acid composite catalyst is 0.5%-1.5% of the dry basis mass of the concentrated solution.

7. The preparation process of the sulfonated lignin modified environmentally friendly adhesive based on straw biogas and biogas residue as claimed in claim 1, characterized in that: The epichlorohydrin accounts for 10-30% of the dry mass of the concentrate.

8. The preparation process of the sulfonated lignin modified environmentally friendly adhesive based on straw biogas and biogas residue as claimed in claim 1, characterized in that: The surfactant is polystyrene sulfonic acid, and the added mass of the surfactant is 1%-3% of the solid content of the epoxy-sulfonated lignin copolymer.

9. The process for preparing the sulfonated lignin modified environmentally friendly adhesive based on straw biogas and biogas residue according to any one of claims 1 to 8, characterized in that: The environmentally friendly adhesive has a viscosity of ≥10 mPa·s, a pH of 7-9, a solid content of ≥20%, a storage stability of ≥180 days, a bonding strength of ≥1.5 MPa, a free epichlorohydrin residue of ≤0.01%, and a free formaldehyde content of ≤0.01%.

10. The environmentally friendly adhesive obtained by the preparation process of the sulfonated lignin modified environmentally friendly adhesive based on straw biogas and biogas residue according to claim 9.