Kinetic and Economic Potential Evaluation of Grubbs-type Precatalysts for 1-Octene Metathesis

[摘要] ENGLISH SUMMARY: The RSA olefins programme of the DST-NRF Centre of Excellence in Catalysis (c*change) aimsto upgrade low-value linear 1-alkenes (also known as alpha-olefins) to high-value Guerbet-typesurfactants via a proposed reaction sequence of which the initial step is the organometalliccatalytic reaction of metathesis. Metathesis enables atom-efficient, green chemistry synthesis byreducing the number of synthesis steps required with current industry methods. Metathesisresearch has yielded a library of ruthenium carbene precatalysts, each with its own attributes andshortcomings. Previous work has designed and investigated the performance, kinetics, andindustrial viability of precatalysts with the aim of improving thermal stability and efficiency for themetathesis of 1-octene, but has not compared precatalysts from an economic point of view. Withthe emergence of each new synthesised precatalyst, information such as the kinetic behaviourand performance is required before any economic evaluation can be made. In this study thecombined 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 investigatingthe effects of temperature (40 - 100°C) and precatalyst load (C8/Ru: 5 000 - 14 000). Kineticparameters were obtained by measuring concentration profiles for seven hours and fitting theseprofiles to fundamental kinetic models. The Douglas method was utilised for designing aconceptual process and estimating the economic potential of each precatalystPeak 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 metathesisproducts. 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-switchablebehaviour was observed where activation only occurred beyond the switching temperatures.Various reaction kinetic models were developed and could account for experimentally observedthermal precatalyst deactivation and competing isomerisation reactions with reasonableaccuracy. Activation energies for 1-octene consumption were determined as 30.24 kcal.mol-1 and13.10 kcal.mol-1 for the GCYC and GMPP precatalysts respectively. Similarly, the deactivationenergies 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 wasfollowed where complete precatalyst deactivation did not occur.Economic evaluation over a Continuously Stirred Tank metathesis reactor – (CSTR -metathesisreactor) was found to be favourable for both precatalysts with an internal rate of return (IRR) of73 and 53% respectively making them feasible choices for upgrading linear 1-alkenes tosurfactants. The precatalyst with the best overall performance was found to be the GCYCprecatalyst but the GMPP precatalyst still offers benefits of less stringent temperature control.Comparison studies with a commercial Hoveyda Grubbs 2nd generation catalyst HG2 proved thecommercial catalyst to still be the best at low temperatures with an IRR of 91%. Future studiesare recommended to conduct Density Functional Theory (DFT) investigations into theprecatalysts, expand the scope of precatalysts for the economic potential evaluation and toconsider development studies towards piloting the proposed process.

[发布机构] Stellenbosch University