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• W2905629642 abstract "This thesis introduces the development of a novel and highly flexible process for the nonselective oligomerization of ethylene to linear alpha-olefins (LAO). The ability to separate chain growth from chain termination reactions in time and space enables the realization of enormous production flexibility. An easy and flexible product adjustment can be achieved through the selective influence on partial reaction rates.Herein, the (quasi) separation of the partial reactions by the combination of two catalysts, which are specialized in the respective reaction, is described. The chain growth from ethylene is mediated by coordinative chain transfer polymerization (CCTP) catalysts and the resulting alkyl chains are transferred on a chain transfer agent (CTA) based on Al or Zn. Another catalyst, based on nickel, catalyzes the chain termination step ( H elimination/transfer), that could be understood as a chain displacement reaction. The CTA bound alkyl chain gets displaced by ethylene and the corresponding alpha olefin is obtained. The chain transport between the two catalysts is mediated by the CTA (Scheme 1 a). The LAO can, thus, be produced from ethylene extremely flexible and highly efficient in a one-pot tandem reaction. The partial reactions were investigated in detail. The CCTP catalysts were examined in polymerization experiments without nickel, whereas the nickel-catalyzed chain termination reaction was described by 1H NMR experiments.Kinetic 1H NMR studies of the nickel(0)-catalyzed chain displacement reaction showed a first order reaction, depending on the Al or Ni concentration. A CCTP system based on yttrium(III)/triethylaluminum (TEA) showed a reversible chain transfer polymerization with very high transfer rates in the polymerization of ethylene without nickel. LAO could be obtained in the tandem reaction of CCTP and the nickel-catalyzed displacement reaction, which follow a Schulz-Flory distribution. The distribution of the resulting LAO can be regulated with outstanding flexibility by altering the process parameters (ethylene, Al, Y and Ni concentration). Thus, product distribution can be adjusted from 1-butene (90 mol-%) to LAO with an average molecular weight of 850 g mol 1. Furthermore, Al alkyls can be re used in a single batch experiment up to 78 times (TON), which increases the efficiency of the system significantly. Next, a titanium(IV)/TEA-based CCTP system was applied to produce Al capped alkyls chains from ethylene by irreversible chain transfer. The Ti catalyst shows low chain transfer rates and the products show a comparatively high molecular weight and polydispersities (Mw/Mn) of about 2. Relatively long-chain LAO were could thus be obtained in the tandem reaction with nickel. LAO with an average molecular weight from 260 g mol-1 to 7000 g mol 1 can be synthesized by altering the ethylene pressure and the aluminum concentration. This system, with a half-life of 126 min, has an outstanding long-term stability, and the Al alkyls applied can also be used substoichiometrically.As we…" @default.
• W2905629642 created "2019-01-01" @default.
• W2905629642 creator A5018742152 @default.
• W2905629642 date "2018-12-17" @default.
• W2905629642 modified "2023-09-23" @default.
• W2905629642 title "Highly Flexible Synthesis of Linear Alpha Olefins from Ethylene" @default.
• W2905629642 hasPublicationYear "2018" @default.
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