Ni/γ-Al_2O_3催化剂上丙烯齐聚反应研究——Ⅰ.性能研究和机理初探

Propene Oligomerization on Ni/γ-Al2O3 I. Reaction Behavior and Preliminary Study of Catalytic Mechanism

丙烯齐聚产物,特别是三、四聚产物是合成洗涤剂、增塑剂、表面活性剂、润滑油添加剂等精细化工产品的重要原料。目前,工业上该反应主要采用美国UOP公司开发的固体磷酸催化剂。该催化剂的主要缺点是易泥化结块,堵塞管道。故开发新型丙烯齐聚催化剂并进行相应的理论研究具有重要意义。1984年,美国专利报导了用镍盐负载在γ-Al_2O_3上的催化剂,用于烯烃二聚具有较高的催化活性,但将其用于低碳烯烃三、四聚反应的研究尚未见到。本文考察了Ni/γ-Al_2O_3催化剂用于丙烯三、四聚反应的催化性能,并初步探讨了其催化反应机理。

The propene oligomerization over Ni/ γ- Al2O3 catalyst is studied by using fixed bed reaction apparatus, and ESR is employed to investigate the valence and coordination state of nickel ions in the course of catalytic reaction. The effect of reaction temperature and pressure, LHSV on catalytic activity and selectivity of trimer and tetramer have been studied. It is found that the optimum reaction conditions are T=373 K, P=2. 5 MPa, LHSV=1. 5 h-1. Under optimum reaction conditions, liquid yield is 83% and selectivity of trimer and tetramer are 54% and 25%, respectively. We also investigate the behavior of nickel ions with ESR, the result shows that the bi-valent nickel ions are reduced to uni-valent nickel ions by propene during the propene oligomerization, and that the uni-valent nickel ions form unsaturated complexes with propene. The apprearance of reaction induction period is not only due to the coordination of Ni+ ions with propene to form active complexes, but also due to the reduction of Ni2+ ions into Ni+ ions. At the initial stage of oligomerization, a new species of ESR signal is observed, g1 = 2. 014, g2=2. 040, g3=2. 061. We assume that this signal is due to the species [=Ni(CsH6)2]+. But the new signal disappeared after outgassing at 723 K. It is suggested that the catalytic active centers for the oligomerizati6n of propene over Ni/γ-Al2O3 catalyst are the unsaturated complex with propene of the uni-valent nickel ions. The activation mechanism for the catalyst is proposed to be: / reduction s coordination /