Снижение энергопотребления и загрязнения: биоферменты ускоряют зелёную трансформацию бумажной промышленности

To achieve China's "dual carbon" goals, it is necessary to vigorously promote energy saving and emission reduction in key industries such as textiles, papermaking and pharmaceuticals, and the application of biotechnology will undoubtedly accelerate the pace of green transformation in these industries. To this end, this newspaper launches a series of reports titled "Green Biomanufacturing," focusing on how biotechnology helps traditional industries escape the trap of high energy consumption and high pollution.

If today's paper is compared with that of the past, it is not hard to find that over the years paper has become better and whiter.

However, behind the bright and glossy paper hides the "original sin" of high pollution and high energy consumption that the paper industry finds hard to shake off.

At the same time, China has many people and few trees, and wood-based pulp is extremely scarce; the paper industry has long relied on imported virgin pulp and waste paper for its raw materials. According to a joint announcement issued by the Ministry of Ecology and Environment and other ministries, China had basically achieved zero imports of solid waste by the end of 2020, so making paper by relying on imported waste paper is no longer feasible.

In recent years, under the dual pressure of environmental protection and cost, high-yield mechanical pulp made from non-wood raw materials such as straw with the aid of biological enzymes is quietly changing the raw material structure of the paper industry, bringing a transformation to this sector, especially the packaging paper industry.

The industry's pain behind paper

Papermaking is one of China's four great inventions, and China's paper industry has long ranked first in the world in both output and sales, accounting for about one quarter of the global total.

In recent years, with the development of internet technology, electronic reading has become widespread. But in the short term, paper is still irreplaceable in many fields, such as textbooks, advertising printing and household paper.

Whatever the type of paper, it all starts from a single wood fiber. "Papermaking raw materials mainly use the wood fibers found in plant materials," said Dai Hongqi, a professor at Nanjing Forestry University. To obtain wood fiber, plant raw materials must first be chipped or cut short; through high-temperature cooking in alkaline water or mechanical grinding, the fibers are separated to obtain pulp; the pulp is mechanically refined and, at a certain consistency, dewatered on a paper machine to form a wet web, which is further dewatered by pressing and dried into paper.

In order to obtain the wood fiber for making pulp, humans must input large amounts of water, electricity, alkali and other factors, while producing large quantities of black, foul and toxic wastewater, so that many paper companies repeatedly end up on environmental blacklists.

Although China is vast in territory and rich in resources, its forest resources are very scarce, with per-capita forest area only one seventh of the world average. In order to reduce domestic wood consumption and ease the environmental pressure caused by wastewater discharge, in recent years China has imported large quantities of foreign wood pulp and waste paper to meet the needs of national economic development.

"Imported wood pulp can be used directly for papermaking to produce white card, household paper, specialty paper and so on, while imported waste paper is mainly used to produce paperboard, packaging paper and newsprint, such as the boxes, corrugated board and kraft paper widely used in the e-commerce express delivery industry," Dai said.

At present, imported pulp accounts for as much as 40% of China's papermaking pulp. To ease the shortage of papermaking fiber raw materials and lower production costs, paper companies have begun to turn to rational use of cost-effective non-wood raw materials.

"Pulping raw materials fall into two categories, wood and non-wood; besides forest trees, straw, bamboo, reeds, reed canary grass and cotton stalks are all non-wood raw materials." Dai told the reporter of Science and Technology Daily that, limited by technology and processes in the past, the black liquor extraction rate and alkali recovery rate in chemical pulping from non-wood raw materials were low, and elemental chlorine bleaching was used for pulp, producing wastewater that was not only hard to treat but also extremely high in adsorbable organic halides (AOX), causing enormous damage to the ecological environment and posing a threat to human health.

With China's rapid economic development and strengthened ecological protection and pollution control, after 1990 almost all non-wood fiber pulping and papermaking enterprises were shut down. So far, only bamboo pulp papermaking enterprises in a few areas such as Sichuan are still operating.

Non-wood fiber pulping meets new opportunities

Although pulping production from non-wood raw materials has been completely banned, research into non-wood fiber utilization technology has not stopped. In recent years, biomass refining technology and high-yield chemi-mechanical pulping technology have become hot topics and gained attention in the industry, bringing non-wood pulp back onto the stage of the paper industry.

"Biorefining can turn the various components of non-wood fiber raw materials into resources separately, especially the high-value utilization of hemicellulose and lignin," Dai told the reporter.

Lignin accounts for roughly 20%-40% of the composition of non-wood fiber raw materials; conventional pulping removes lignin to obtain the pulp fiber used as a papermaking raw material. Lignin is a high-molecular polymer in which phenylpropane units are linked through ether bonds and carbon-carbon bonds into a three-dimensional network structure; depending on the type of plant fiber raw material, the aromatic monomers that basically make up lignin can gain and lose electrons, can absorb ultraviolet light, and are also energy storage materials with application potential.

In the past, the value of lignin was never well developed and utilized; the traditional practice of pulp mills was to burn it to recover heat energy. Dai explained that in recent years, based on the special functions of lignin's phenolic hydroxyl aromatic monomers, researchers have used lignin to replace phenol as a green adhesive, energy-storage electrolyte/electrode material, UV-resistant film material and so on.

Another technology direction that is currently favored is high-yield chemi-mechanical pulping. This technology can not only ease the bottleneck of China's shortage of papermaking fiber raw materials, but also has the advantages of lower difficulty and lower cost in wastewater treatment.

"This technology abandons the old approach of extracting cellulose and leaving behind hemicellulose and lignin, and instead uses all the wood fiber components together as pulp for papermaking," Dai explained. High-yield chemi-mechanical pulping relies mainly on mechanical methods, supplemented by a small amount of biological enzymes and chemical additives; this greatly simplifies the pulping wastewater treatment process and lowers costs, and can not only replace large quantities of imported commercial wood pulp and waste paper raw materials, but also eliminate the huge air pollution caused by burning crop straw.

Dai revealed that the paper industry has already carried out many research projects and conducted pilot trials at individual companies, using wheat-straw biological pulping to make household paper, packaging paper and so on.

Biological enzymes may promote the green transformation of the paper industry

In fact, under the dual pressure of cost and environment, the paper industry also yearns to transform from a major polluter into a model of energy saving and emission reduction.

In turning the high-pollution, high-energy-consumption paper industry "back onto the right path," biological enzyme preparations are playing an increasingly large role.

Dai said that biological enzymes have the characteristics of specificity and high efficiency. At present, technical research on the application of biological enzymes in the paper industry focuses mainly on 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, making the fibers swell and soften faster, promoting the effect of refining, reducing refining energy consumption and improving paper strength. Research shows that biological enzymes can reduce the energy consumption per tonne of refined pulp by 41.4%.

In addition, when the paper industry recycles large quantities of waste paper, deinking treatment is required.

The traditional deinking method uses chemicals to separate ink particles from the fibers under appropriate temperature and mechanical action, and then removes the detached ink particles from the pulp by flotation, washing or a combination of the two. Enzymatic deinking, by contrast, uses enzymes to treat waste paper, aided by flotation or washing or a combination of both processes, thereby removing the ink.

Bleaching is also an important step in the papermaking process. Using enzyme preparations can produce a "biological bleaching aid" effect, reducing the use of chlorine-containing bleaching chemicals, thereby reducing the discharge of adsorbable organic halides in bleaching wastewater and lowering environmental pollution.

However, the application of biological enzymes in the paper industry has not been all smooth sailing.

Dai said that R&D on biological enzyme technology has achieved some results, but application still faces bottlenecks. So far, there is no truly biological pulping mill anywhere in the world. The reason is that applying biological enzymes to complex, large-scale pulping production still involves a series of technical difficulties.

"In addition, the pretreatment of raw materials with biological enzymes takes a long time, while manufacturers need efficiency to ensure continuous production, so they tend to prefer more efficient physical or chemical pretreatment methods," Dai said, noting that some enzyme preparations themselves also have problems such as high cost, limited variety, great sensitivity to temperature and pH environment, and inconspicuous effects. Therefore, at the present stage the application of biological enzyme technology is still auxiliary and cannot play a leading role.

At the same time, he is optimistic about the application prospects of biological enzymes in the paper industry: "Overall, biological enzymes are highly specific and efficient; especially for the high-pollution, high-energy-consumption paper industry, their environmental benefits are obvious, and they have unique advantages over chemicals. With technological progress, they will certainly occupy a leading position in the paper industry in the future."

——This article is reprinted from China Packaging Network (pack.cn). Original link: http://news.pack.cn/show-378529.html