Eliminating gels in Film with ActivCat® Catalysts
W. R. Grace & Co. continues its legacy of supplying high-quality catalytic systems, while also offering customers access to its extensive technical support. This complementary combination has enhanced the production of polyethylene at Yangzi and Qilu, two subsidiaries of Sinopec, China’s largest manufacturer and distributor of petrochemicals.
Low Catalyst Activity Produces Low-Quality Polymers
In recent years, Yangzi and Qilu developed an interest in producing linear low-density polyethylene (LLDPE) for films and polyethylene of raised temperature (PERT) for pipes. Manufacture of these products relies on metallocene-based catalysts to initiate the polymerization process. Unfortunately, the catalyst acquired from the firms’ domestic supplier demonstrated poor activity and reoccurring gel defects.
These gels can impair a polymer. “Gels are, first of all, an appearance defect,” says J. Fernando Cevallos-Candau, a senior business development manager at Grace. “Even very low levels of gels are obvious in highly transparent films.” In addition, gels can form holes in films or create stress points that initiate cracks in a pipe.
Grace Technical Support Aids Efficient Implementation of ActivCat®
In 2019, Yangzi ran a small trial with ActivCat® Catalysts, a Grace technology that increases the activity of metallocene single-site catalysts. The technology is based on interactions with methylaluminoxane (MAO), a versatile activator of transition metal catalysts, including metallocene catalysts. ActivCat® catalysts allows MAO to activate more catalytic sites.
The trial solidified Yangzi’s interest in adopting ActivCat® catalysts. In turn, Grace lent on-site support to identify necessary updates and to optimize Yangzi’s system. In addition to evaluating Yangzi’s processing equipment, Grace provided detailed information about processing parameters for comonomer and hydrogen feeds, as well as information about feed-stream purification requirements. “Metallocene catalysts are much more sensitive to polar compounds in the feed stream, which results in electrostatic generation inside the reactor with very negative operability consequences,” Cevallos-Candau explains.
Grace also shared samples for common resin grades, provided feedback, and suggested improvements for their next commercial run.
ActivCat® Results in Superior Resins and Continued Collaboration
With assistance from Grace, Yangzi completed the upgrades less than a year after the first trial. As a result, gels were essentially eliminated, and the new resins have mechanical and optical properties comparable to the best in the market. Catalyst activity increased 30–40%. Throughput increased 3–5% at normal operating conditions because of improvements in bulk density.
“After Qilu saw their sister company having such a successful test, they moved [to incorporate ActivCat® catalyst] very quickly, maybe 6 months from decision to reactor start-up,” Cevallos-Candau says.
Collaboration with Grace has continued after these successes. “We have received product samples and shared evaluations,” Cevallos-Candau says. “We are looking into a potential modification of the catalyst that will be mutually beneficial.”
As a result, gels were essentially eliminated, and the new resins have mechanical and optical properties comparable to the best in the market.