Isolation of Lignocelluloses via Acidification of Hydrolysates Induced from Different Straws

Abstract

Hydrolysis has been commercially practiced for isolating hemicelluloses from wood chips. Acidification has also been reported as means to isolate lignocelluloses from hydrolysate. However, the performance of hydrolysis and subsequently acidification of induced hydrolysate on non-wood species is unclear. In this work, the hot water hydrolysis of wheat straw, rice straw and maize straw and the acidification of the generated hydrolysates were investigated. The hot water hydrolysis process of wheat, rice and maize straws were optimized. The effect of acidification on separating lignin from hydrolysates was also evaluated as a means to generate lignin. The properties of the collected lignocelluloses were determined to identify a potential application for them. The optimal conditions of the hydrolysis for straws were liquid/solid ratio of 12/1 (wt/wt), temperature of 170 °C and time of 60 min, which yielded rice straw hydrolysate containing more sugars than did the hydrolysates of wheat and maize straws. Acidification to pH 1.5 led to 27.49%, 29.17% and 23.38% lignin removals from the hydrolysates of wheat, rice and maize straws, respectively. Acidification decreased the furfural concentration of hydrolysates and increased the acetic acid concentration. The precipitates generated via acidification of hydrolysates had different heating values, thermal stability and ash content, and the precipitates of acidified rice straw hydrolysate had a higher heating value and thermal stability, but lower ash, than did those of acidified wheat and maize straws. The hot water hydrolysis of different straws could be conducted under the same conditions, but the acidification of hydrolysates would generate lignin with varied properties that may be suitable for altered applications. These results provide evidence for the impact of straw type on the thermal properties of extracted lignin of straw and thus its potential applications.