Insight into the Synthesis Process of an Industrial Ziegler–Natta Catalyst

Abstract

In Ziegler–Natta catalysis, the catalyst particle size has a strong influence not only on catalyst performance but also on the morphology and particle size distribution of the final polymer particles. Fundamental insight into the catalyst particle formation process is therefore of industrial importance when addressing specific requirements in the final products. In the present work, we fully characterize a single-step catalyst preparation process, which comprises a reactive precipitation of a MgCl2-supported Ziegler–Natta catalyst, through decomposition of the hetero-bimetallic complex, Mg­(OR)2·Ti­(OR)4, by addition of ethyl aluminum dichloride (EADC). We track the evolution of both of the concentrations of the metals (Mg, Ti, Al) as well as Cl in the liquid phase and the size of the formed catalyst particles. It is observed that the liquid-phase composition is governed by the EADC feed rate under fully Cl-starved conditions. The process can be divided into two stages: The first stage is dominated by the precipitation of the Mg-based support, and the second stage involves complex adsorption–precipitation of the Ti species. The growth of the catalyst particle size occurs only in the first stage and is controlled by the aggregation and breakage events during the MgCl2 precipitation. It follows that the hydrodynamic stress in the reactor plays the essential role in controlling the catalyst size. In the second stage, no further particle growth occurs, not only because of the depletion of Mg in the liquid phase but also because the adsorbed Ti complex stabilizes the particles against aggregation. Finally, we have performed polymerization tests with the prepared catalysts and found that the size distribution of the polymer particles indeed closely replicates the one of the used catalyst particles.

Ultra-high molecular weight polyethylene: preparation and applications

“…Titanium is typically included as metal centers of the catalysts and magnesium chloride is widely used for supporting this type of catalysts (Fig. 2) [1,20,21]. Typically, other cocatalysts such as triethyl aluminium are required for activating ZN catalysts so that active sites are created for coordination between metal centers and double bonds of ethylene, after which additions of monomers are repeated for increasing molecular weights of products [22].…”

“…ZN catalysts feature a synthesis of linear UHMWPE due to the low tendency of bimolecular β-hydrogen transfer at low pressure of ethylene, which is one of the advantages over other types of catalysts [22]. While different kinds of ZN catalysts are prepared using distinct methods to optimize catalytic activities, the typical process of preparing this type of catalysts can be mainly generalized into two steps: preparations of supporting complexes and preparations of the catalysts based on the supporting complexes [21]. For example, Antoine et al reported that the addition of ethyl aluminum dichloride (DEAC) could increase particle sizes of catalysts and finally lead to a wider molecular weight distribution [21].…”

“…While different kinds of ZN catalysts are prepared using distinct methods to optimize catalytic activities, the typical process of preparing this type of catalysts can be mainly generalized into two steps: preparations of supporting complexes and preparations of the catalysts based on the supporting complexes [21]. For example, Antoine et al reported that the addition of ethyl aluminum dichloride (DEAC) could increase particle sizes of catalysts and finally lead to a wider molecular weight distribution [21]. During the synthesis of ZN catalysts, sizes of particles have great influences on both catalytic activities as well as polydispersity index of final products, which is mainly controlled during preparations of supporting materials [21].…”

“…For example, Antoine et al reported that the addition of ethyl aluminum dichloride (DEAC) could increase particle sizes of catalysts and finally lead to a wider molecular weight distribution [21]. During the synthesis of ZN catalysts, sizes of particles have great influences on both catalytic activities as well as polydispersity index of final products, which is mainly controlled during preparations of supporting materials [21]. Additionally, catalytic activities also increase dramatically with the existence of supporting materials since the supporting complexes contribute to slowing rates of decomposition of the active phase and increasing the stabilities of active centers [19].…”

Al(Salen) Metal Complexes in Stereoselective Catalysis

“…The heterogeneous conditions for the process use as principal catalytic system the MgCl 2 -supported Ziegler−Natta catalysts, composed of titanium complexes supported onto a MgCl 2 matrix. It is important to stress the use of aluminum alkyls AlR 3 (R = alkyl) as co-catalyst in the polymerization [18].…”