(737c) Tandem Catalysis: A Prospective Method for Producing Ethylene-α-Olefin Copolymers from Ethylene Stock

Polyolefins take up the biggest share in global plastic market. Ethylene-based copolymers, e.g. linear low density polyethylene (LLDPE) and polyolefin elastomer (POE), are both very important branches of polyolefin family. Tandem catalytic method for preparing ethylene-based copolymer is of great interest to chemists and chemical engineers. The real value of tandem catalyst system lies in that comonomer could be generated in situ and that give a saving of cost in comonomer production, purification, transport and storage. In the past decade, the development of catalysts for ethylene trimerization and tetramerization has achieved a tremendous progress,¹ attracting a number of researchers to exploit new tandem catalyst systems for preparing ethylene-α-olefin copolymers. However, less effort was focused on the production process which was quite concerned by industry. The production process was commonly dependent on the feature of the product. Soft product such as POE prefers using solution phase process under high temperature and hard product such as LLDPE prefers using gas phase or slurry phase process under comparatively lower temperature. With the great success in the utilization of metallocene catalyst, the feature of the oligomerization catalyst decides whether or not the tandem catalyst system is practical. We are making efforts in seeking tandem catalyst systems with good potential for application.

  In our research, a high temperature tandem catalyst system was developed using SNS-Cr and CGC-Ti in a solution reactor. Ethylene trimerization catalyst SNS-Cr could show high 1-hexene selectivity (>98%) and high activity under 110 ^oC and high pressure. The polyethylene as byproduct having melting point about 125 ^oC was less than 0.5 wt% in the oligomerization. The resulting copolymer exhibited comparable mechanical properties in comparison to commercial 1-octene based POE.

  The combination of SNS-Cr and supported Ziegler-Natta catalyst in a slurry reactor under 75 ^oC also showed good potential in preparing 1-hexene based LLDPE. A mixing of triethyl aluminum (TEA) and methylaluminoxane (MAO) was used as cocatalyst in order to reduce the cost in MAO. SNS-Cr still exhibited high activity in preparing 1-hexene. The melting point of the product located in the range of LLDPE. The SEM photos showed that the morphology of the product was well kept.

[1] D. S. McGuinness. Chem. Rev. 2011, 111, 2321–2341.

Acknowledgment This work was supported by the National Natural Science Foundation of China (No. 20936006 and No.20976152), and the National Basic Research Program of China (2011CB606001).