Wide application of biotechnology in pulp and paper and future research directions

Progress in the application and research of biotechnology in pulp and paper

In recent years, emerging biotechnology has mainly included genetic engineering, bioengineering, fermentation engineering and enzyme engineering. Using biotechnology, new elite varieties and new species can be developed through the recombination of biological genetics; many useful new organic substances can be produced through metabolism; many existing production processes can be greatly improved by enzymatic reactions. Conditions and efficiency. Since the basic raw material of the paper industry is an organism (plant), the chemical pulping method is basically a chemical reaction process to the organism, and its environmental pollutants are mainly organic substances degraded from the organism, which can be fully utilized by the paper industry. An important basis for biotechnology.

The application of biotechnology in the pulp and paper process developed rapidly in the 1990s. The growing concern about environmental protection and reducing energy consumption has further promoted the application of biotechnology in the pulp and paper industry. The biotechnology currently used in the pulp and paper industry mainly includes genetic recombination to improve papermaking materials, biopulping, biobleaching, biological deinking of waste paper, biological treatment of waste liquids, enzymatic treatment, and biochemical control of pulp properties. Some studies The results have been used in industrial production.

1 Gene recombination technology to improve papermaking materials

Gene recombination technology is a technique for recombining genes and then transforming or transferring genes into cells for replication and expression. It is a powerful tool for improving biological traits. The purpose of genetically modified papermaking raw materials: to reduce the lignin content in papermaking raw materials, to increase the content of cellulose as much as possible, to improve the utilization rate of papermaking raw materials and shorten the age of trees. After 12 years of hard work, the Jiang Liquan Laboratory of the Michigan University of Technology finally found a way to reduce the lignin content of trees by genetic modification: using a group called Pt4CL1, which is called antisense technology to control lignin synthesis. , in a "suppressed state", the result obtained genetically modified trees. The eucalyptus content of the poplar tree was reduced by 45% compared with the control poplar, while the cellulose content was increased by 15%. The tree was found to grow fast and the tree height was 30% higher than that of the control tree. In addition, Zencea in the UK, Elserive Science in Belgium and the Biocell Research Center in France have successfully used GM engineering to develop papermaking materials that are more suitable for pulp and paper.

2 Biopulping

Pulp mills use chemical pulping to increase production scale and greatly improve the adaptability of raw materials. However, in recent years, the purification of pulp has exposed its shortcomings: large consumption of chemicals, high energy consumption, high equipment investment, especially the wastewater discharged from the pulping and bleaching process, with extremely high BOD, COD. The load, and it also contains highly toxic and carcinogenic substances, and the cost of the workers is registered to cause serious pollution to the environment. With the improvement of people's requirements for environmental protection, traditional chemical pulping is constantly improving, and bio-pulping technology will be rapidly developed.

Biological pulping is the use of microorganisms (mainly white rot fungi) or their products (enzymes) to pretreat plant fiber raw materials, replace biological routes or partial chemical routes with biological pathways, and then perform mechanical, chemical mechanical or chemical treatments. The vegetable fiber raw material is separated into pulp.

Biological pretreatment can significantly reduce the energy consumption of the refining and improve the performance of the slurry. Setliff used Ceriporiopsis subvemispora and P. chrysosporium to pretreat poplar, and the results showed that poplar could reduce energy consumption by 20% when the disc mill was ground to the same freeness compared to the fungal treatment. Norwegian spruce reduces energy consumption by 13%. Kashino used IZU-154 to study hardwood and softwood biomechanical pulp. It was found that the coarsely ground beech mechanical pulp can reduce the energy consumption of subsequent pulp by 1/3~1/2 after 7 days of fungal treatment. Improved; coarsely ground spruce mechanical pulp and red pine pulp are treated with fungi for 10 to 14 days, the energy consumption of refining is reduced by about 1/3, and the strength performance is also improved.

Biological methods for pretreatment of wood chips generally use white rot fungi, etc. These strains can produce lignin peroxidase, divalent peroxidase and laccase. The main influencing factors of pretreatment of wood chips are strain type, enzyme dosage and pH. Value, temperature and concentration, raw material species, etc.

3 Biobleaching

Bioenzymatic bleaching technology mainly uses hemicellulase to partially hydrolyze hemicellulose in fiber cells, making lignin easier to react with bleaching agent, thereby improving the whiteness of bleaching pulp and reducing the amount of bleaching agent. . Hemicellulase contributes to the bleaching of kraft pulp, enabling economical biotechnology to be applied to the bleaching of pulp. The basic principle is that hemicellulose (xylanase and mannosidase) can cause carbohydrates in pulp. The modification of the structure enhances the delignification effect. This enzyme depolymerizes some of the hemicellulose in the pulp and promotes bleaching chemicals to remove residual lignin from the pulp.

In 1989, Finland took the lead in industrial trials using xylanase pretreatment of kraft pulp. Currently, many pulp and paper mills in Northern Europe and North America apply this biotechnology to the industrial production of bleached kraft pulp. The Chilean pulp mill uses commercial xylanase to pretreat unbleached eucalyptus kraft pulp during the bleaching process of blue eucalyptus and bright blue eucalyptus kraft pulp, and combines the elemental chlorine bleaching sequence DEopD results to save chlorine dioxide. 12% to 40%, but has no effect on the strength of the bleached pulp, and the whiteness reaches 90% ISO.

4 Waste paper bio-deinking

Due to the shortage of wood fiber raw materials, the demand for using waste paper resources as raw materials for papermaking is increasing. The key to the recycling of waste paper is deinking. The traditional deinking process is divided into two major categories: washing method and flotation method. The washing method is simple in equipment and small in investment, but the water consumption is large and the environmental pollution load is large, which is mostly seen in small and medium-sized enterprises. Modern large-scale deinking production lines usually use a flotation method or a flotation method as a supplement to the main washing method. Both of these deinking processes are used for chemical deinking, while chemical deinking chemicals are expensive, causing serious environmental pollution, and pulp is prone to "alkaline blackening". With the development of biotechnology, the research of enzymes used in waste paper deinking technology came into being.

First acts on the interface between the fibers. Construction News loosens the connection between the ink and the fiber, and detaches the ink from the fiber surface under moderate mechanical action. The biological enzyme deinking agent is a high-efficiency compound enzyme preparation. The biological enzyme deinking has the following advantages: (1) It can adapt to any ink, the ink and the fiber are completely separated, the deinking pulp has high whiteness and less dust; (2) the fiber has High rate; (3) can reduce the amount of chemicals such as sodium hydroxide, sodium silicate, hydrogen peroxide, etc.; (4) The deinking wastewater load is much lower than chemical deinking, which is conducive to environmental protection.

Putz et al. compared the enzymatic deinking and chemical deinking of offset printing paper, and found that enzymatic deinking can save a lot of chemicals and reduce the COD content of wastewater. Domestic research on deinking of waste newsprint also shows that enzymatic deinked pulp has higher whiteness and similar physical properties.

5 Biological treatment of pulping industry wastewater

The application of biotechnology in the treatment of pulping industry wastewater can be the decolorization, deodorization, detoxification and removal of organic matter BOD from wastewater, and the effect is obvious. The biological treatment pulping industry wastewater has aerobic treatment (such as aeration method, activated sludge method, biological turntable method, etc.) and anaerobic treatment. Anaerobic treatment of pulping wastewater produces methane and recovers energy.

At present, the main research is to use enzymes to destroy the chlorinated organic matter in the chlorine bleaching wastewater, to reduce the content of organic chloride as much as possible, and to have a higher chroma removal rate. Messner et al. immobilized white rot fungus P. chrysosporium BKM/F-1767 on the porous foam carrier of the drip filter (MYCOPOR process) with a residence time of 6-12 h, and the AOX removal rate, COD removal rate and decolorization rate reached 80% respectively. 40% and 87%. The Swedish monosulfate pulping plant combined with ultrafiltration uses an anaerobic-aerobic biological process to treat pulp bleaching wastewater, which reduces BOD by 95%, AOX by 80%, and a decolorization rate of 50%. In addition, the United States, Canada and Japan used white rot fungi to decolorize the kraft pulp bleaching wastewater, and achieved remarkable results.

6 Enzyme treatment improves slurry performance

In recent years, researchers have devoted themselves to the use of enzymes to improve fiber properties, improve the water filtration performance of pulp and the strength of pulp. The traditional method is to modify the fibers using cellulase and hemicellulase. However, the water filtration performance of the modified pulp has decreased. Recently, the use of laccase in lignin-degrading enzymes to modify fibers to increase pulp strength has been widely recognized.

According to foreign reports, the laccase mediator system was used to improve the performance of the unbleached kraft pulp, and it was found that the wet strength of the pulp was significantly improved. Tang Zhenjiang [8] and other laccase treatment of grinding stone wood pulp, found that paper strength and dry strength effect. GatenhplmP [9] found that the grafting of laccase with the acid groups on the surface of the fiber can improve pulp strength and swelling properties.

7 Resin biological control

Resin barriers have always been a major problem plaguing newsprint production. The resin component in the vegetable fiber raw material is some hydrophobic substance dissolved in a neutral organic solvent, and these hydrophobic substances will be in the process of papermaking.