As one of the three major materials, plastics play an extremely important role in our daily life. However, the recycling rate of plastics after use is very low, and it is difficult to be degraded after being disposed of, which constitutes “white garbage†and has become a serious problem for major cities in the world. Polyethylene is the plastic product with the largest annual production (more than 100 million tons per year), and it is also one of the most inert and stable polymers. Compared with other types of polyolefins (such as polypropylene and polystyrene), it is even more difficult. degradation. At present, the vast majority of waste plastics are mainly disposed of by landfill and combustion methods: the former occupies land resources and is prone to cause groundwater pollution; the latter increases atmospheric carbon emissions and causes atmospheric pollution.
Recently, the Huang Zheng Group of the Shanghai Institute of Organic Chemistry of the Chinese Academy of Sciences and the Guan Zhibin Group of the University of California, Irvine Collaborated to achieve a breakthrough in the study of the degradation of polyethylene waste plastics. The relevant results were published online on June 18 in the "Scientific Progress "(Science Advances) magazine. The use of cross-alkane metathesis catalytic strategies, using inexpensive and large amounts of lower alkanes as reaction reagents and solvents (such low-carbon alkanes are produced in large amounts in petroleum refining, cannot be used as fuel or natural gas, have very limited use value), and polyethylene Recombination reactions occur, effectively reducing the molecular weight and length of the polyethylene. In the reaction system, low-carbon alkane is present in excess, so it can participate in the recombination reaction with polyethylene for many times until the molecular weight of tens of thousands or even millions of polyethylene is degraded into clean diesel.
This technology can degrade all types of polyethylene: including high density polyethylene (HDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), etc., and the catalyst can be compatible with various additives in commercial grade polyethylene. It has been proved that it can be applied to the degradation of various polyethylene waste plastics in real life, including waste plastic bottles, waste plastic films and waste plastic bags. Compared with the traditional pyrolysis method, the methods developed by Huang Zheng and Guan Zhibin have the advantages of mild reaction conditions and high product selectivity. High temperature pyrolysis methods often require reaction temperatures exceeding 400 degrees, producing very complex products including gases, oils, waxes, coke, etc. The molecular structure of the product includes straight chain alkanes, branched chain alkanes, olefins, aromatic hydrocarbons, etc., and the use value of products is low. The temperature of the degradation system developed by Huang Zheng and Guan Zhibin is relatively low (150-200 degrees). Regardless of the structure of the starting polyethylene waste plastics, straight chain alkanes are mainly produced and can be regulated by catalyst structure or reaction time. Controlling the selective production of C9-C22 alkanes that can be used as diesel fuels or polyethylene waxes with a narrow molecular weight distribution (these polyethylene waxes can be used as additives in polyolefin processing applications). The catalytic system provides a possible way to solve the "white waste" environmental pollution; on the other hand, "turn waste into treasure" to promote the recycling of carbon resources.
At present, the team is developing more efficient and lower-cost polyethylene degradation catalysts and is actively preparing for the polyolefin degradation test. The study was strongly supported by the State Fund Committee, the Ministry of Science, the Ministry of Science and Technology, and the State Key Laboratory of Organometallic Organic Chemistry of the Shanghai Institute of Organic Chemistry. In addition, Huang Zhenghe and Guan Zhibin are members of the Chinese Academy of Sciences innovation team "Alkenes and alkanes conversion and application" members were funded by the Chinese Academy of Sciences.
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