Masters Degrees (Chemical Engineering)

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Browsing Masters Degrees (Chemical Engineering) by Subject "1-Octene"

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    Kinetic and Economic Potential Evaluation of Grubbs-type Precatalysts for 1-Octene Metathesis
    (Stellenbosch : Stellenbosch University, 2017-12) Visser, Chaney Gene; Van der Gryp, Percy; Goosen, N. J.; Vosloo, H. C. M.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering
    ENGLISH SUMMARY: The RSA olefins programme of the DST-NRF Centre of Excellence in Catalysis (c*change) aims to upgrade low-value linear 1-alkenes (also known as alpha-olefins) to high-value Guerbet-type surfactants via a proposed reaction sequence of which the initial step is the organometallic catalytic reaction of metathesis. Metathesis enables atom-efficient, green chemistry synthesis by reducing the number of synthesis steps required with current industry methods. Metathesis research has yielded a library of ruthenium carbene precatalysts, each with its own attributes and shortcomings. Previous work has designed and investigated the performance, kinetics, and industrial viability of precatalysts with the aim of improving thermal stability and efficiency for the metathesis of 1-octene, but has not compared precatalysts from an economic point of view. With the emergence of each new synthesised precatalyst, information such as the kinetic behaviour and performance is required before any economic evaluation can be made. In this study the combined catalytic, kinetic and economic performance of two chelating pyridinyl alcholato (O^N) ruthenium carbene precatalysts of the Grubbs 2nd generation type [RuCl (H2IMes) (O^N)(=CHPh) where O^N = 1-(2’-pyridinyl)-1-(cyclopentyl)-methanolato (GCYC) and O^N = 1-(2ʹ-pyridinyl)-1- (2ʹ-methyl-phenyl),1-phenyl-methanolato (GMPP) was evaluated for 1-octene metathesis. Metathesis reactions were conducted in a batch reactor with neat 1-octene (C8) while investigating the effects of temperature (40 - 100°C) and precatalyst load (C8/Ru: 5 000 - 14 000). Kinetic parameters were obtained by measuring concentration profiles for seven hours and fitting these profiles to fundamental kinetic models. The Douglas method was utilised for designing a conceptual process and estimating the economic potential of each precatalyst Peak performance was observed at 70°C for the GCYC precatalyst with turnover numbers (TONs) of 6631, 80% conversion of 1-octene (C8) and 42% selectivity towards primary metathesis products. In comparison, for the GMPP precatalyst TONs of 5888, 60% C8 conversion and 37% selectivity was obtained at peak temperatures between 70 and 90 °C. Latent thermo-switchable behaviour was observed where activation only occurred beyond the switching temperatures. Various reaction kinetic models were developed and could account for experimentally observed thermal precatalyst deactivation and competing isomerisation reactions with reasonable accuracy. Activation energies for 1-octene consumption were determined as 30.24 kcal.mol-1 and 13.10 kcal.mol-1 for the GCYC and GMPP precatalysts respectively. Similarly, the deactivation energies found for the precatalysts were 22.81 and 5.84 kcal.mol-1 respectively. The GMPP precatalyst was found to follow step-function behaviour and the Arrhenius relationship was followed where complete precatalyst deactivation did not occur. Economic evaluation over a Continuously Stirred Tank metathesis reactor – (CSTR -metathesis reactor) was found to be favourable for both precatalysts with an internal rate of return (IRR) of 73 and 53% respectively making them feasible choices for upgrading linear 1-alkenes to surfactants. The precatalyst with the best overall performance was found to be the GCYC precatalyst but the GMPP precatalyst still offers benefits of less stringent temperature control. Comparison studies with a commercial Hoveyda Grubbs 2nd generation catalyst HG2 proved the commercial catalyst to still be the best at low temperatures with an IRR of 91%. Future studies are recommended to conduct Density Functional Theory (DFT) investigations into the precatalysts, expand the scope of precatalysts for the economic potential evaluation and to consider development studies towards piloting the proposed process.