High Productive Ethylene Trimerization Catalyst Based on CrCl 3 /SNS Ligands
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High Productive Ethylene Trimerization Catalyst Based on CrCl3/SNS Ligands Ebrahim Ahmadi • Zahra Mohamadnia Mehdi Nekoomanesh Haghighi
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Received: 27 December 2010 / Accepted: 27 March 2011 / Published online: 3 May 2011 Ó Springer Science+Business Media, LLC 2011
Abstract Methylaluminoxane (MAO)-activated chromium (III) complexes of tridentate SNS ligands of the form (RSCH2–CH2)2NH (R = alkyl, aryl) have been prepared and tested for the trimerization of ethylene to 1-hexene. The effect of ethylene pressure, Al/Cr ratio and S donor substitution on 1-C6 selectivity and productivity has been examined. It is shown that when the substitution on S is pentyl group it will lead to the highest productivity, 174200 g 1-C6/g Cr h, due to the synergistic effect of this group. Keywords Ethylene Trimerization 1-Hexene SNS ligands
1 Introduction Linear a-olefins, such as 1-hexene and 1-octene, are used, among other applications, as co-monomers in the production of linear low density polyethylene (LLDPE). The
E. Ahmadi (&) Polymer Synthesis Laboratory, Chemistry Department, Zanjan University, PO Box 45195-313, Zanjan, Iran e-mail: [email protected] Z. Mohamadnia M. N. Haghighi Department of Polymerization Engineering, Iran Polymer and Petrochemical Institute (IPPI), PO Box 14965-115, Tehran, Iran e-mail: [email protected] Z. Mohamadnia Department of Chemical Engineering, Zanjan University, PO Box 45195-313, Zanjan, Iran
conventional method of producing 1-hexene and 1-octene is by oligomerization of ethylene, which yields a wide spectrum of linear a-olefins (LAOs) [1]. A more selective route to 1-hexene is via trimerization of ethylene. In this regard, a number of trimerization catalyst systems have been developed [2], most of them based on chromium catalysts, including the Phillips pyrrolide system [3], the Sasol mixed heteroatomic systems [4, 5], and the BP diphosphine system [6, 7], although other metals such as Ti [8] and Ta [9] have also been employed. The Sasol trimerization catalyst [CrCl3(SNS)][SNS = RSCH2CH2N(H) CH2CH2SR, R = Me, Et, n-Bu, or n-Dec] has been shown to be not only active but also 98% selective for 1-hexene [5, 10, 11]. McGuinness and coworkers [2, 12] reported the mixed-donor tridentate (PNP, SNS) complexes of CrIII, which act as highly selective and efficient precatalysts for ethylene trimerization when activated with MAO. Both the PNP and SNS systems were capable of total 1-hexene selectivities of over 97%, making them among the most selective systems available. Most importantly, the dramatically lower costs of these ligands compared to PNP ligands make their superior in terms of potential technical application. In fact, there are only three features in these complexes that may be responsible for the exceptional selectivity: the metal oxidation state of the catalytically active species, the N–H function, and the particular nature of the sulfur donor atoms. Substitutions at the S donors have an influential effect on catalyst productivity and selectivity. Alkyl groups with low steric dema
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