Advance of Polyolefin Technology in China   

By Zhong Weike, China Rubber & Plastic Research Institute, CNCIC

In 2010, China's output of polyolefin resins reached more than 19 million tons, up 20.8% year on year. Meanwhile, its import volume of polyolefin resins in 2010 also reached 11.69 million tons, slightly smaller than 2009. During 2005 - 2010, the average annual growth rate of the country's apparent consumption of polyolefin was 9.81%, while it reached 15% during 2000 - 2005. Such a slowdown may have caused by the global financial crisis and other factors. But it also shows that China's polyolefin market is maturing.
    In a maturing market, the demand growth for general polyolefin resins will be gradually slowing down. Instead, it will need more specialized and customized resins. Designing and tailor-made products according to the end users' requirements will be a development direction of China's polyolefin industry. In this regard, developed countries which have entered the mature stage of polyolefin consumption have provided a lot of successful experiences. As Dr. CP Chen from Germany-based Sud-Chemie AG pointed out, the current development route of a polymer is: first determine the structure of the polymer according to the end user's requirements, then find out the catalyst and polymerization conditions for the polymer, and then make product design, and finally return to the end user for verification.
    Although catalysts account for a small proportion in the cost of polyolefin production, they have a significant impact on the market value of the polymers. It can be said that the improvement of the catalysts has contributed greatly to the progress of polyolefin technologies, especially of special resin technologies. Catalysts have huge impacts on both micro-and macro-structures of polymers and directly determine the nature (such as relative molecular weight and its distribution, product form, random polymer content) and uses of products. Of course, for the grade of the target polyolefin resin, the process conditions also have a great impact on the selection of the catalysts.
    Currently, there are mainly three series of polyolefin catalysts that have large industrial applications: chromium-based catalysts, Ziegler-Natta (ZN) catalysts, and metallocene and non-metallocene single-active-center catalysts.
   Chromium-based catalysts are mainly used in the Phillips loop process and The Dow Chemical's Unipol process. The Phillips loop process, which now accounts for more than 1/2 of the global HDPE output, uses the chromium-based catalysts.
    The Ziegler-Natta catalyst that was invented 60 years ago still plays an important role in the production of polyolefin resins. Now, many polyethylene (PE) producers in the world are still constantly improving their Ziegler-Natta catalysts. For example, the activity of the industrial catalyst UCAT-J recently developed by Univation Corp reaches 650 000 g (PE) / g (catalyst). In August 2009, the company started to build a plant in Zhangjiagang, Jiangsu Province to produce the catalyst. The plant will be put into production in 2011. This catalyst can be used for the production of linear low density polyethylene (LLDPE) and high density polyethylene (HDPE). About half of PE technologies and catalysts that Univation has sold in recent years were bought by Chinese companies. Ziegler-Natta polypropylene (PP) catalysts are the mainstream catalysts for the production of PP. Their overall performance is improving. Some new-type special Ziegler-Natta catalysts are being constantly applied in industrial production. Various major companies at home and abroad mainly use different electron donors to constantly improve the activity of the Ziegler-Natta catalysts. Sinopec has made significant progress in this regard. Sinopec Beijing Research Institute of Chemical Industry has done a large amount of research in Ziegler - Natta PP catalysts. The catalysts developed by this institute, such as NA catalyst used for the production of anti-impact copolymers and NA-II catalyst used for the production of BOPP film and propylene copolymers, have been tested and used in many domestic PP plants.
    Metallocene catalysts are the most important type of single-active-center catalysts. They are used to produce polymers with a narrow molecular weight distribution. The research area of metallocene catalysts has expanded to non- metallocene catalysts which also feature the single active center. In the past 20 years, the single-active-center catalysts have played the largest role in the production of PP, especially of the high-pressure polyethylene (HPPE). But they do not have very satisfactory applications results in other areas, such as in the production of PP. Since 1993, China has started the research and development of metallocene catalysts but still lags much behind developed countries in this aspect.
   In terms of production capacity and output of polyolefin resins, Sinopec and CNPC have ranked among the forefronts in the world. The two giants still have a lot of polyolefin projects under construction. Sinopec has made rapid progress in the polyolefin technology. In recent years, Sinopec has developed many new grades of polyolefin resins and also made remarkable achievements in the development of olefin polymerization processes, the improvement of catalysts and the application of high-efficiency nucleating agents. Sinopec has developed HA-series PP catalysts with an activity of more than 200 000 g (PP) / g (catalyst). The ND PP catalyst and high-activity BCE catalyst developed by Sinopec have passed industrial tests and verification. In the aspect of polyolefin polymerization processes, Sinopec has invented the asymmetric electron donor-adding technology and the third-generation PP loop technology. Its large-scale gas-phase-process-based PE technology packet has got successful industrial applications. Based on resin structure characterization and molecular structure design, Sinopec has successfully developed special PE resins for fuel gas pipes and automobile bumpers.
    CNPC has also made considerable progress in the development of polyolefin catalysts. The group's first proprietary PSP-01 spherical PP catalyst had successful industrial tests at CNPC Fushun Petrochemical Company's 100 000 t/a PP unit in 2010. Two grades of special resins have successfully been developed with the catalyst. This means that CNPC will be able to substantially reduce its procurement of PP catalysts and enhance its development capability of new PP products. This will lay a firm foundation for its important R & D project - "Vehicle-purposed polyolefin material unification technology".
    Although China has made a lot of achievements in the R & D and production of polyolefin catalysts and the localization rate of Ziegler-Natta catalysts in China has reached about 90%, Chinese enterprises do not have very strong capability in the development of high-performance polyolefin resins and urgently need to make great efforts in the research and development of proprietary polyolefin processes and technologies. Relevant domestic experts point out that in the aspect of PE, China's polyolefin industry should increase the production of special resins for pressure-proof pipes, cables and large-scale hollow products, and in the aspect of PP, it need focus on the development of transparent food packaging, flexible cast and low-heat-seal & high-tear functional resins. In the aspect of new polyolefin catalysts, China needs to focus on the research and development of metallocene catalysts and non-metallocene single-active-center catalysts and catalysts for functional polyolefin resins.
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