Reduce energy consumption for refining, reduce environmental pollution
biological enzymes or scrub the "original sin" of the paper industry
Green Biological Manufacturing①
Editor's comment To achieve China's "dual carbon" goal, it is necessary to vigorously promote energy conservation and emission reduction in key industries such as textiles, papermaking, and pharmaceuticals. The application of biotechnology will undoubtedly accelerate the pace of green transformation in these industries.
To this end, this newspaper launched a series of reports on "Green Biological Manufacturing", focusing on how biotechnology can help traditional industries get out of the difficulties of high energy consumption and high pollution.
If you compare the current paper with the past, it is not difficult to find that the paper quality has become better and whiter over the years.
However, behind the glamorous paper, there is the “original sin” of high pollution and high energy consumption that the paper industry cannot get rid of.
At the same time, China has a large population and few trees, and an extreme shortage of wood raw material pulp. Paper raw materials have long relied on imported virgin pulp and waste paper.
According to the requirements of the announcement jointly issued by the Ministry of Ecology and Environment and other ministries and commissions, China has basically achieved zero import of solid waste by the end of 2020, and it is no longer feasible to rely on imported waste paper to make paper.
In recent years, under the dual pressures of environmental protection and cost, non-wood materials such as straw, and high-yield mechanical pulp assisted by biological enzymes are making subtle changes in the raw material structure of the paper industry, which has brought the industry, especially the packaging paper industry, to subtle changes. Come a revolution.
The pain of the industry behind paper
Papermaking is one of China's four major inventions. The annual production and sales volume of China's papermaking industry ranks first in the world, accounting for about a quarter of the global total.
In recent years, with the development of Internet technology, electronic reading has become popular.
However, in a short period of time, paper is still irreplaceable in many fields, such as teaching materials, advertising printing, and household paper.
No matter what type of paper, you must start with a piece of wood fiber.
"Paper-making raw materials are mainly wood fibers in plant materials." said Dai Hongqi, a professor at Nanjing Forestry University. In order to obtain wood fibers, the plant materials need to be chipped or cut into short lengths; they are separated by high-temperature cooking in alkaline water or mechanical grinding. The fiber is used to obtain pulp; the pulp is mechanically refined and dewatered on a paper machine at a certain concentration to form a wet paper sheet, which is further dewatered by pressing and dried into paper.
In order to obtain the wood fiber for making paper pulp, humans must invest a lot of water, electricity, alkali and other elements. At the same time, a large amount of black, smelly, and toxic waste water will be produced, so that many paper companies have repeatedly boarded the environmental black list.
Although China has a vast land and abundant resources, forest resources are very scarce. The per capita forest area is only 1/7 of the world average. In order to reduce domestic wood resource consumption and reduce the environmental pressure caused by waste water discharge, China has imported a large number of foreign wood pulp and waste paper in recent years. To meet the needs of China's national economic development.
"Imported wood pulp can be directly used for paper making, white cardboard, household paper, specialty paper, etc.; while imported waste paper is mainly used for the production of cardboard, packaging paper, newsprint, etc., such as packaging boxes, Corrugated paper, kraft paper, etc." said Dai Hongqi.
At present, the proportion of China's paper pulp imports is as high as 40%.
In order to alleviate the shortage of paper-making fiber raw materials and reduce production costs, paper-making companies have begun to use non-wood raw materials that are cost-effective and reasonable.
"Pulping raw materials are divided into two categories: wood and non-wood. In addition to forest trees, straw, bamboo, reed, awn stalk, and cotton stalk are all non-wood raw materials." Dai Hongqi told a reporter from Science and Technology Daily that it was limited by technology and technology in the past. , The extraction rate of black liquor and alkali recovery rate for the production of chemical pulp from non-wood raw materials is low. The pulp is bleached with elemental chlorine. The waste water produced is not only difficult to treat, but also has a high content of adsorbable organic halide (AOX), which causes great damage to the ecological environment. There are also threats to human health.
With the rapid development of China's economy and the strengthening of ecological environment protection and pollution control, after 1990, almost all non-wood fiber pulping and papermaking enterprises have been shut down.
So far, only a small number of bamboo pulp and paper enterprises in Sichuan and other regions are still operating.
Non-wood fiber pulping usher in new opportunities
Although the pulping production of non-wood raw materials has been completely banned, the research on non-wood fiber utilization technology has not stopped because of this.
In recent years, biomass refining technology and high-yield chemical mechanical pulp technology have become hotspots and have received the attention of the industry, allowing non-wood pulp to return to the stage of the paper industry.
"Bio-refining can separately resource utilization of various components of non-wood fiber raw materials, especially the high-value utilization of hemicellulose and lignin." Dai Hongqi told reporters.
Lignin accounts for about 20%-40% of the composition of non-wood fiber raw materials. Traditional pulping is to remove lignin to obtain pulp fibers that are used as raw materials for papermaking.
Lignin is a high-molecular polymer with a three-dimensional network structure connected by phenylpropane units through ether bonds and carbon-carbon bonds. Depending on the type of plant fiber raw materials, the aromatic monomers basically composed of lignin have the function of gaining and losing electrons, and can absorb ultraviolet rays. , Is also an energy storage material with application potential.
In the past, the value of lignin has not been well developed and utilized. The traditional practice of pulp mills is to use it to recover heat energy through combustion.
Dai Hongqi said that in recent years, based on the special functions of ligninphenol hydroxy aromatic monomers, researchers have replaced phenol with lignin as a green adhesive, energy storage electrolyte/electrode material, and anti-ultraviolet membrane material.
Another technical direction that is currently promising is the high-yield chemical mechanical pulp technology.
This technology can not only alleviate the bottleneck of the shortage of paper fiber raw materials in China, but also has the advantages of low difficulty and low cost in wastewater treatment.
"This technology discards the idea of extracting cellulose and leaving hemicellulose and lignin in the past. Instead, it uses all lignocellulosic components and uses them as pulp for papermaking." Dai Hongqi said, high-yield chemical mechanical pulp Mainly by mechanical methods, supplemented by a small amount of biological enzymes and chemical additives, this greatly simplifies the process of pulping wastewater treatment and reduces costs. It can not only replace imported wood pulp and waste paper materials in large quantities, but also eliminate crop stalks. The huge air pollution problem caused by incineration.
Dai Hongqi revealed that the paper industry has implemented many scientific research projects and conducted pilot projects in individual companies to use wheat straw bio-pulping for household paper and packaging paper.
Biological enzymes may promote the green transformation of the paper industry
In fact, under the dual pressure of cost and environment, the paper industry is also eager to transform from a major polluter to a model of energy conservation and emission reduction.
Bio-enzyme preparations are playing an increasingly important role in "recovering evil and returning to the right" in the highly polluting and energy-consuming paper industry.
Dai Hongqi said that biological enzymes have the characteristics of specificity and high efficiency.
At present, the technical research on the application of biological enzymes in the papermaking industry mainly focuses on the aspects of refining, deinking, bleaching, and removing stickies in the papermaking process.
For example, biological enzymes can be used to modify the cell walls of pulp fibers to accelerate the swelling and softness of the fibers, promote the effect of refining, reduce the energy consumption of refining, and increase the strength of paper.
Studies have shown that biological enzymes can reduce the energy consumption per ton of pulp milled by 41.4%.
In addition, when the paper industry recycles a large amount of waste paper, it needs to be deinked.
The traditional deinking method is to use chemicals to separate the ink particles from the fibers under appropriate temperature and mechanical action, and then use flotation, washing or a combination of the two methods to remove the peeled ink particles from the pulp Remove.
Biological enzymatic deinking is the use of enzymes to treat waste paper, assisted by flotation or washing, and a combination of the two processes to remove ink.
Bleaching is also an important step in the papermaking process.
The use of enzyme preparations can achieve the effect of "biological bleaching assistance" and reduce the amount of chlorine-containing bleaching chemicals, thereby reducing the discharge of adsorbable organic halides in bleaching wastewater and reducing environmental pollution.
However, the application of biological enzymes in the paper industry has not been smooth sailing.
Dai Hongqi said that some results have been achieved in the research and development of biological enzyme technology, but there are still bottlenecks in the application.
So far, there is no real biological pulp mill in the world.
The reason is that there are still a series of technical problems in the application of biological enzymes to complex and large-scale pulping production.
"In addition, biological enzymes take a long time to pretreat raw materials, and manufacturers need efficiency to ensure continuous production, so they are more inclined to adopt more efficient physical or chemical pretreatment methods." Dai Hongqi said, some enzyme preparations It also has problems such as high cost, limited variety, greater influence by temperature and acid-base environment, and insignificant effect.
Therefore, the application of biological enzyme technology at this stage is still supplementary and does not play a leading role.
At the same time, he expressed optimism about the application prospects of biological enzymes in the paper industry: “In general, biological enzymes are highly specific and efficient. Especially for the paper industry with high pollution and high energy consumption, the environmental protection effect is obvious, and Compared with chemicals, it has unique advantages. With technological advancement, it will surely occupy a leading position in the paper industry in the future."