|ARNOLD D R1 , BUZZARD JL1,2 |
1School of Chemical Engineering, University of Natal, 2International Furan Technology (Pty) Ltd.
Correspondence to: D R Arnold, School of Chemical Engineering, University of Natal, Durban, 4041 Tel: (031) 260 1228, Fax: (031) 260 1118
Furfural has been made from agricultural waste products since the 1920's and is one of the few bio-based chemicals that compete with crude oil. Until 2001, it was used as a precursor for Spandex (Lycra®), foundry resins, lubricating oils and as a process chemical. Furfural has recently been registered in South Africa and Spain as a nematicide, with a potential to replace methyl bromide, carbamates and phosphide-based chemicals. Furfural is produced by the acid hydrolysis of the pentosan in woody vegetable waste products such as bagasse, corncobs, wood chips and oilseed husks and stalks. Presently the only available furfural production technology is the Chinese batch process, which is inefficient and achieves yields around 30-40% of theoretical with a digester residence time of 4½-5½ hours. The reaction sequence taking place is a simple hydrolysis of the pentosan polymers (e.g.xylan) to the pentoses (e.g. xylose) followed by catalytic dehydration to form furfural. Yield-loss reactions occur while the furfural is in the liquid phase, by polymerisation and by reaction with the precursor pentose, accounting for the low yield figure. All furfural production processes world-wide strip the furfural from the biomass substrate using live steam. This is inefficient because the diffusion of furfural though the liquid surrounding the solid substrate into the stripping steam is slow. This high furfural residence time allows the yield-loss reactions to occur. In addition, by-products such as acetic acid, 5-methyl furfural and methyl furyl ketone that form due to side-reactions are stripped out of the substrate and contaminate the final product. The newly patented SupraYield® process that has been developed overcomes all of these problems, producing furfural devoid of these by-products. Instead of steam stripping, adiabatic flash distillation releases furfural into the vapour phase as soon as it is produced. Yield-loss reactions are avoided, and by-products remain in the liquid phase. The development of the process is described, together with the theoretical considerations that led to its perfection.
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