Furfural production from rice husks within a biorefinery framework

Furfural production at the industrial level began 100 years ago, but its reaction conditions continue to be studied. Data on furfural production from rice husks, a by-product of the rice-peeling process, are particularly limited. This raw material must be disposed of and is usually combusted for combined heat and power generation. However, in a biorefinery framework, this material can be used to generate value-added chemicals as well as power. This study evaluated furfural production from rice husks through acid hydrolysis the potential of the remaining solid to generate power and the formation of by-products. The variables were temperature (180–230 °C), sulphuric acid concentration (0.05–3% (w/w) sulphuric acid in the solution) and time (1–105 min). The results obtained for furfural yield, solid yield and particle size distribution indicated that the best conditions are 200 °C, 0.10% (w/w) acid and 40 min, which generated a furfural production amounting to 6.0% (w/w) of the oven-dried rice husk weight (55% of the theoretical yield) and a 60% solid yield. The gross heating value of the solid fraction remained considerably constant after the treatment, and the characteristics of the ash fraction were improved. This study gives furfural yields higher than those typically achieved at the industrial level (35–50% of the theoretical yield), with hydroxymethylfurfural and acetic, formic and levulinic acids as additional products, as well as the novelty of a remaining solid in good condition for power generation, making it a successful valorisation-prior-to-combustion approach.