双金属催化剂可催化乙烯聚合在单个反应器内制备双峰聚乙烯.考察了新型Cr-iV双金属催化剂及相应的单金属S-2和iV催化剂在不同实验条件下的乙烯均聚反应动力学.通过对Cr-iV催化剂聚合产物分子量分布曲线的解析发现铬钒活性中心之间存在相互作用,铬中心活性受到抑制,钒中心活性得到增强;聚合温度基本不改变铬钒活性中心生成的聚合物的质量分数.采用简化的单中心乙烯均聚动力学模型分别描述铬钒双活性中心的动力学行为,结合双金属催化剂的聚合实验结果确定了各个活性中心的动力学参数.相比单金属催化剂,Cr-iV 催化剂中铬活性中心链增长速率常数降低,说明其聚合活性降低;而钒活性中心链失活速率常数减小,稳定性增强,活性提高.%Bimetallic catalyst has been a hot research topic as it can realize one-pot synthesis of polyethylene with bimodal molecular weight distribution (MWD). The kinetics of ethylene homopolymerization with a novel Cr-iV bimetallic catalyst and corresponding monometallic S-2 and iV catalyst were studied at various experimental conditions. MWD deconvolution of polymers made by these catalysts showed interaction between Cr and V active centers in the Cr-iV bimetallic catalyst, reduced the activity of Cr centers, while activity of V centers was improved. Polymerization temperature almost did not change mass fractions of polymers produced by two active centers. The simplified single-center kinetic model for ethylene homopolymerization was employed to describe polymerization behaviors of Cr and V centers in Cr-iV bimetallic catalyst. Kinetic parameters of each active center were estimated by fitting experimental results of polymerization rates with model prediction. Compared to monometallic catalyst, Cr center in the Cr-iV catalyst had decreased chain propagation rate constant, which lead to reduction of polymerization activity, whereas V center in the Cr-iV catalyst had decreased chain deactivation rate constant, which signified more stable and active V center.
展开▼
