Dilute sulphuric acid pretreatment and enzymatic hydrolysis of Moringa oleifera empty pods

In this work, dilute sulphuric acid prehydrolysis of residual empty pods of Moringa oleifera fruits was investigated as pretreatment for enzymatic hydrolysis of cellulose. In experiments performed at 130–190 °C for 10–30 min, corresponding to a severity range between log Ro = 1.9 and log Ro = 4.2, the effect of pretreatment conditions on the recovery of polysaccharides and on the enzymatic convertibility of cellulose was evaluated. Overall cellulose recovery was above 95% in the pretreatments performed at 130 and 160 °C, and between 87 and 90% in the pretreatments at 190 °C, while xylan recovery in the most severe pretreatments was only 24.7–50.2%. The highest sugar concentration in the acid prehydrolysates (15.0 g/L) was obtained in the pretreatment performed at 160 °C and 20 min. The formation of degradation products was low at mild pretreatment conditions, but it increased with the severity. Furfural concentration reached 4.04 g/L at log Ro = 3.1 and decreased again with a further increase of the pretreatment severity. HMF, formic acid and levulinic acid were formed only in the most severe pretreatments. The pretreatment was effective for improving the enzymatic hydrolysis of cellulose, and the highest conversion (84.3%) was achieved in the material pretreated at mid severity (log Ro = 3.1).

► This is the first report on dilute-sulphuric acid pretreatment of Moringa oleifera empty pods.
► Pretreatment in the range between 130 and 190 °C was investigated.
► Pretreatments at mid severity led to high enzymatic convertibility of cellulose.
► Cellulose recovery was high for all pretreatment conditions.
► Pretreatments above 160 °C resulted in high losses of hemicelluloses.