Combination of water extraction with dilute-sulphuric acid pretreatment for enhancing the enzymatic hydrolysis of Jatropha curcas shells

• Acid pretreatment of Jatropha curcas shells is improved by a preliminary water extraction.
• Pretreatment conditions leading to maximal cellulose conversion were found.
• The improvement of the enzymatic conversion correlated well with the crystallinity.

Jatropha curcas shells were extracted with water in a pilot-scale reactor and then pretreated with dilute sulphuric acid. The pretreatment was initially investigated with a Box-Behnken experimental design in the range of 110–180 °C, 0.1–1.5% H2SO4 and 20–60 min, and then with complementary experiments at 190 °C. The glucan recovery was above 87% in all the experimental runs. Xylan solubilisation was 13–20% in the milder pretreatments and up to 45% in the most severe runs. Around 70% cellulose enzymatic conversion, evaluated with commercial cellulases during 72-h hydrolysis, was achieved for the pretreatments at 180 °C, and a region with maximal conversion was predicted for around 190 °C. For confirming that estimation, a 22-experiment augmented by one central point and parallel pretreatments of pre-extracted and non-extracted shells were performed. The highest cellulose conversion, reached at the central point, was 16.5% higher for the pre-extracted and pretreated material than for the directly pretreated one. The low cellulose crystallinity index (0.79) of the pre-extracted and pretreated shells correlated well with their better enzymatic convertibility.