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The treatment of papermaking black liquor is a major issue in my country's environmental protection management. The current pulping and papermaking methods mainly include: Chemical methods, semi-chemical methods and chemical-mechanical methods, mechanical methods. Pulp raw materials are divided into: Wood pulp (softwood pulp and hardwood pulp), straw pulp (rice straw pulp, wheat straw pulp, reed pulp), etc. At present, there are many reports on the research and development of the use of lignin and lignin-based compounds, but there are not many studies on the utilization of mother liquor after lignin extraction. The combustion method is generally used for treatment. This method not only has high investment costs, but is also only suitable for large pulp and paper mills, and burns a large amount of organic raw materials. After several years of development and research on papermaking black liquor, this research group uses resource recovery methods to control the environmental pollution of black liquor, that is, comprehensive utilization of papermaking black liquor to completely eradicate the harm of black liquor to the environment. The process used in this article has product recovery in every step of the papermaking wastewater treatment process, that is, there is no emission, no combustion, and no secondary pollution. Therefore, whether it is from the perspective of protecting the environment or considering the use of waste resources, it has good social significance and economic value. Experimental research is now conducted using broadleaf semi-chemical pulp black liquor as raw material. 1 Experimental part 1.1 Experimental raw materials Raw materials: Broadleaf semi-chemical pulp black liquor is provided by Chaihe Paper Mill in Heilongjiang Province. The main components in black liquor are lignin, reducing sugars, organic acids, alkaloids and sodium salts. 1.2 The main equipment of the experiment is a self-made double-membrane three-chamber electrodialysis device (composed of anion and cation exchange membranes) 1.3 Experimental content 1.3.1 Separation and application of lignin in papermaking black liquor Papermaking black liquor contains a large amount of lignin. Lignin is a type of high molecular polymer with phenylpropane monomer as the skeleton and a network structure. Its main functional groups are methoxy groups, phenolic hydroxyl groups, alcoholic hydroxyl groups, carboxyl groups, etc. Therefore, lignin has properties similar to phenol, dissolving in alkaline solutions and precipitating in acidic solutions. Utilizing the characteristics of lignin, the papermaking black liquor is acidified to precipitate the lignin, and then filtered and washed to obtain a solid intrinsic product. This product is then used in rubber as a rubber coupling agent. 1.3.2 Recovery of acid, alkali and salt in the extraction solution. Send the filtrate after lignin extraction into the middle chamber of a double-membrane three-chamber electrolyzer composed of anion and cation exchange membranes. Water is placed in the cathode chamber and anode chamber respectively. Under the action of a DC electric field, the sodium in the liquid in the middle chamber Ions move to the cathode chamber through the cation exchange membrane and generate sodium hydroxide. Acid ions move to the anode chamber through the anion exchange membrane and generate acid. The electrolyte undergoes cyclic electrolysis. After the sodium hydroxide in the cathode chamber reaches a certain concentration, it returns to the pulping section. After the acid in the anode chamber reaches a certain concentration, it is returned to precipitate the lignin in the black liquor. A small amount of acid and alkali remain in the reducing sugar solution in the middle chamber. The salt precipitates out during the heating, evaporation and concentration process, and the salt in the sugar solution is recovered through filtration. 1.3.3 The caramel pigment is made from sugar liquid. The mother liquor after recovering the acid, alkali and salt by electrodialysis method has a sugar content of about 10%. Its main component is polyxylose. The polyxylose liquid is further concentrated and then spray-dried to obtain the caramel pigment. 1.3.4 Product performance evaluation (1) Lignin is used as a rubber coupling agent. Under different extraction conditions, different specifications of lignin solid particles were extracted from papermaking black liquor, and they were used as rubber coupling agents. Then various properties of the rubber were measured, and the properties of the vulcanized rubber were compared with the silane coupling agent KH-590. (2) Performance test of prepared caramel pigment. Performance testing of caramel pigments extracted from polysaccharide mother liquor using the People's Republic of China * * Standard - "Food Additive Caramel Color" GB8817-88 was tested. 2 Results and Discussion This process develops papermaking black liquor as a resource, treats the papermaking black liquor for the purpose of resource recovery, and recycles the acid and alkali obtained. ； The salt is recycled, while the lignin is used as a rubber coupling agent and the xylose polysaccharide is further used to produce caramel coloring. 2.1 Lignin was used as a rubber coupling agent. Two specifications of lignin were selected.: 1# is a 10% solution prepared from large particle lignin ； 2# is an ultra-fine lignin product. These two lignins were used as coupling agents and added to different rubbers for mixing, and compared with the industrial KH-590 coupling agent. 2.1.1 Add nitrile rubber (1302#) mixed rubber. Add lignin 1#, 2# and KH-590 to the nitrile rubber (1302#) mixed rubber respectively for mixing, and measure the properties of the rubber. The results are shown in Table 1. Table 1 Performance comparison of lignin and KH-590 in nitrile rubber (1302#) mixed glue Formula characteristics Production formula Experimental formula Lignin 1# Lignin 2# KH-590 Additive dosage/portion 0 3.0 3.0 3.0 Tensile strength/MPa 13.0 14.6 14.0 13.0 Tensile elongation/% 280 270 270 260 Permanent deformation/% 13 13 13 17 Shore A hardness/degree 81 82 81 78 Note: The total amount of mixed glue is 200 g, each part is 2 g, the solid content of the lignin solution is 10%, the coupling agent is an additive for rubber, and KH-590 is one of the silane coupling agents. It can be seen from Table 1 that compared with the production formula, when the coupling agent is added in the same amount, both lignin 1# and 2# increase the tensile strength of rubber by 12.3% and 7.7% respectively. From the perspective of the tensile elongation, there is a decrease. ； The permanent deformation remains unchanged and the Shore A hardness does not change much. The addition of KH-590 has no obvious effect on the rubber. 2.1.2 Add 2# natural tobacco flake rubber. Add different parts of 1# lignin and KH-590 to 2# natural tobacco flake rubber to examine its performance. The results are shown in Table 2. Table 2 Comparison of properties of lignin powder and KH-590 in Ding 2# natural tobacco sheet gum basic formula project basic formula lignin 1# KH-590 0.5 1.0 1.5 0.5 1.0 1.5 Tensile strength/Mpa 17.5 19.5 21.7 18.37 16.85 18.84 21.0 Tensile elongation at break/% 179 178 179 177 134 125 140 300% elongation strength/MPa 5.68 6.21 6.70 6.47 11.2 13.3 12.7 Shore A hardness/degree 43.5 44.0 44 43.5 44 45 44 It can be clearly seen from Table 2 that the addition of lignin 1# significantly increases the tensile strength of butyl 2# natural smoke sheet rubber, and a peak appears with the increase in the amount added. That is, when 1.0 part is added, the tensile strength of the rubber reaches the maximum, which is 24% higher than the basic formula. ； It has little effect on the elongation at break of rubber, but also increases the 300% elongation strength to a certain extent. ； It has little effect on Shore A hardness. When using KH-590, adding 1.5 parts increases the tensile strength by only 20%. This shows that both KH-590 and lignin in natural rubber have a reinforcing effect on vulcanized rubber. Combining Table 1 and Table 2, it can be seen that lignin as a coupling agent not only has the function of KH-590, but also has good adaptability to various types of rubber. 2.2 Performance of the caramel pigment obtained. The polyxylose mother liquor is concentrated and dried to obtain the caramel pigment. After being diluted 100 times, this product becomes a reddish-brown transparent liquid without turbidity or sediment. ； Slightly sweet, tasteless or slightly sweet, no sour or astringent taste. The performance of the experimental products was measured and compared with * * Standard comparison, the results are shown in Table 3. It can be seen from Table 3 that all indicators of the homemade products are in line with the requirements of caramel pigments. * * standard. Therefore, it is feasible to use the mother liquor after lignin extraction to further obtain caramel pigment. Table 3 Comparative project indicators of self-made product performance and national standards (solid) Self-made products * * Standard color rate (EBC unit) ≥103160 ≥46000 Moisture/% ≤ 3.0 ≤ 3.0 Ammonia nitrogen (calculated as NH3)/% ≤0.02 ≤0.2 Sulfur dioxide (calculated as SO2) * /% None ≤0.1 Arsenic (calculated as As)/% ≤0.0001 ≤0.0003 Lead (calculated as Pb)/% ≤0.0001 ≤0.0005 Heavy metals/% ≤0.0004 ≤0.001 4-methylimidazole content/% None ≤0.02 2.3 Benefit estimation The use of this process can not only eliminate papermaking black liquor and solve environmental pollution problems, but also recover useful chemical products, so it has certain social and economic benefits. Using lignin as a coupling agent, the current price of silane coupling agent KH-590 is about 70,000 yuan/t, while the cost of producing 1 t of lignin products does not exceed 5,000 yuan. At the same time, the recovered acid and alkali as raw materials can be recycled, reducing production costs. 3 Conclusion (1) Using electrodialysis ion exchange membrane to treat delignification mother liquor, acids, alkali and salts can be recovered, and acids and alkali can be recycled. ； The final sugar solution can be concentrated and spray-dried to obtain caramel coloring. (2) The lignin compounds obtained by acid precipitation are used as rubber coupling agents and have better performance than the silane coupling agent KH-590. (3) Caramel pigment prepared from polyxylose liquid complies with * * standard. (4) This process has obvious social, environmental and economic benefits.