A Novel SiO₂‐Supported Fluorine Modified Chromium–Vanadium Bimetallic Catalyst for Ethylene Polymerization and Ethylene/1‐Hexene Copolymerization

Abstract

Phillips catalyst is one of the most significant industrial ethylene polymerization catalysts. Chemical modifications have been carried out to tune the Phillips catalyst performance and improve the polyethylene properties. After the modification of the catalyst by fluorine, the polyethylene product with higher molecular weight (MW) and narrower molecular weight distribution (MWD) is suitable for producing automobile fuel tanks. Vanadium containing Phillips catalyst enhances α‐olefin incorporation and MW regulation. In present work, fluorine modified and unmodified chromium–vanadium (Cr–V) bimetallic catalysts are prepared and explored. Compared with the fluorine‐free catalyst, the activities of F‐modified bimetallic catalysts slightly decrease with the increasing MW of the product and the hydrogen response increases slightly. Due to the synergistic effect of the chromium, vanadium and fluorine on the silica gel support, the short‐chain branch distribution (SCBD) of copolymers from F‐modified Cr–V bimetallic catalyst (Cr–V–F)600 is more beneficial than that of Cr–V bimetallic catalyst (Cr–V)600 and F‐modified Cr–V bimetallic catalyst (Cr–V–F)500. The fluorination of Cr–V bimetallic catalysts has not only preserved the high polyethylene activity of bimetallic active sites but also produced the advantage of the high MW ability from fluorine.

CrV Bimetallic Phillips Catalyst Prepared by Citric Acid‐Assisted Impregnation on Ethylene Polymerization

“…The fractionate of the ethylene/1‐hexene copolymers was carried on the temperature rising elution fractionation (TREF) system. [ 13 ] The system was mainly composed of an 850 mL column type fractionation bottle filled with quartz sand, a silicone oil bath with thermostat (Huber, POLYTSTAT CC2‐225B ± 0.02 °C), a pump (KNF Lab, STEPDOS 08 S), a rotary evaporator (EYELA), and a nitrogen gas container. About 1.5 g copolymer was added into a three‐necked flask and fully dissolved in 170 mL xylene with stirring for at least 4 h. Then it was quickly transferred into the preheated fractionation bottle, which was immersed in a silicone oil bath.…”

“…Combined the two strategies, we developed a fluorine‐modified CrV bimetallic catalyst. [ 13 ] The hydrogen response of the catalyst was more sensitive due to the synergistic effect of chromium, vanadium, and fluorine on the silica support. Unfortunately, the activity of the catalyst is reduced, mainly originated from the poor dispersion of the active centers on the limitation of the surface of the silica gel, as well as the agglomeration in the impregnation procedure during preparation.…”

Mechanistic Insights of Ethylene Polymerization on Phillips Chromium Catalysts

“…In the same year, Liu et al published the results of a study of fluorinated Cr/V catalysts [ 115 ]. Compared with a fluorine-free catalyst, the activities of fluorinated bimetallic catalysts slightly decreased with the increasing MW of the product, and the hydrogen response increased slightly.…”