Study of biopolymers and silica recovery from pre-hydrolyzed rice husks.

The production of rice husks, abundant agro-waste rich in biopolymers and minerals, already at a rate of 120 million tons/year, is expected to further increase to meet the demand of a growing world population. It is the most common use as fuel pollutes air, water, and soil. However, there is still a significant lack of methods for fractionation of all of its compounds. We are presenting here a biorefinery process based on successive extraction of extractives (xylose, lignin, cellulose, and silica) from rice husk through pre-extraction, hydrolysis, organosolv pulping, and demineralization while assessing the effect of these processes on the extracted biopolymers. The optimized conditions for pulping of hydrolyzed rice husks are 3% of FeCl₃·6H₂O as catalyst, a biomass/solvent ratio of 1:10 (m/v), and a 50% ethanol:water as cooking liquor treated in a reactor at 200 °C for 60 min. The conditions for demineralization of the pulp resulting from organosolv pulping are 10% of Na₂CO₃ as base, a biomass/solvent ratio of 1:15 (m/v), and treated in a reactor at 115 °C for 30 min. The properties of the lignin and cellulose recovered from hydrolyzed rice husk were almost identical to those of untreated rice husk. We successfully obtained lignin with a recovery of 47% and a purity of 94%, cellulose recovered after silica removal with only 1% ash and a purity of 82%, while also recovering silica. The recovery of lignin and cellulose, along with silica, offers an opportunity for further valorization while also proposing an alternative solution to rice husk disposal and implicated pollution. [ABSTRACT FROM AUTHOR]