Browsing by Author "Peddie, Waylin Lee"

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    Separation of homogeneous hydroformylation catalysts using organic solvent nanofiltration
    (Stellenbosch : Stellenbosch University, 2016-03) Peddie, Waylin Lee; Van der Gryp, Percy; Vosloo, H. C. M.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: The upgrade of inter alia syngas and short chain olefins to high value commodities in the surfactant and detergent range, finds relevance worldwide due to the abundance of feedstock. These commodities are manufactured systematically through an innovative network of homogeneously-catalysed reactions, i.e. metathesis, hydroformylation and hydrogenation, and forms part of the overarching theme of the RSA Olefins programme of the South African Department of Science and Technology (DST) and National Research Foundation (NRF) Centre of Excellence in Catalysis (c*change). Homogeneous catalysts are generally preferred over its heterogeneous counterpart due to inter alia superior catalytic performance, higher product selectivity and negligible diffusional problems. However, the prevalence of homogeneous catalysts is hampered by the expensive, waste generating and destructive thermal separation methods required for the recovery of these catalysts. The main aim of this study is therefore to demonstrate the non-destructive recovery of homogeneous catalysts, in a state allowing for their recycle and reuse, from hydroformylation post-reaction mixtures as well as the potential for further solvent purification using organic solvent nanofiltration (OSN). Furthermore, confirmation is afforded to the cost- and energy-efficiency of OSN for homogeneous catalyst recovery commonly alluded to in literature by performing an economic and energy evaluation between OSN and classical downstream recovery units, i.e. distillation. Focus was placed on the recovery of two well-known and commercially available hydroformylation catalysts, HRh(CO)(PPh3)3 and Co(C5H7O2)3, and the solvents considered include those representative of the hydroformylation and hydrogenation reactions (1-octene, 1-decene, 1-nonanal, 1-undecanal, 1-nonanol, 1-undecanol), using the Duramem 150 (DM-150), Duramem 200 (DM-200) and STARMEM 240 (ST-240) membranes. Parameters such as applied pressure, feed concentration, solvent type and catalyst load were varied and its effects on the ST-240 membrane’s performance investigated. The main contributions and conclusions from this study were threefold regarding, 1) the capability of OSN to recover and reuse homogeneous catalysts, 2), the characterisation of OSN performance in terms of permeance and separation, and 3) the modelling of OSN performance. 1) OSN catalyst recovery: It was found that the presence of the rhodium-based catalyst, HRh(CO)(PPh3)3, resulted in the hydroformylation reaction having a high regioselectivity toward the linear aldehyde product and produced mainly 1-nonanal with a yield of approximately 66 mol% in the case of 1-octene as substrate. Additionally, linear to branched (n/iso) product molar ratios of greater than 2 were observed. It was also found that cost and energy savings of greater than 90% can be attained upon using OSN systems for homogeneous catalyst recovery as compared to conventional distillation systems. 2) OSN permeation and separation: It was found that the ST-240 membrane was able to successfully separate homogeneous catalysts from different reaction systems with catalyst recoveries up to 99%. Moreover, the recovered catalyst was found to be in a condition suitable for reuse for at least three consecutive hydroformylation reaction cycles, thereby improving upon its overall catalytic performance in excess of 30%. Flux of pure reaction species (1-octene, 1-decene, 1-nonanal, 1-undecanal, 1-nonanol and 1-undecanol) were shown to range between 1.83 L.m-2.h-1 to 135 L.m-2.h-1. Flux was also found to be highly dependent on applied pressure, solvent viscosity and interaction parameters indicative of the solvent-membrane and solute-solvent interactions. Minimal separation was attainable between binary mixtures consisting of 1-octene/1-nonanal, 1-decene/1-undecanal and 1-nonanal/1-nonanol. 3) OSN modelling: The OSN separation process for the different solvents were described using literature-based transport models based on the pore-flow and solution-diffusion models with the latter performing relatively better than the former in terms of predictive capacity. Moreover, a newly postulated model which incorporated an additional solubility parameter term was found to improve predictive capacity of the solution-diffusion model by approximately 3%. KEYWORDS: Organic Solvent Nanofiltration, Hydroformylation, Homogeneous catalyst, Catalyst separation