Acid hydrolysis as a method to valorize cellulosic filter cake from industrial carrageenan processing

Abstract

Wastes generated from carrageenan processing industry include cellulosic filter cakes (CFC) which are mainly composed of structural sugar (0.25 w/w) and ash (0.75 w/w, primarily perlite). This study investigated the possible valorization of CFC by recovering the available sugars as glucose through direct acid hydrolysis. Five different sulfuric acid concentrations (5% v/v to 15% v/v) were used as catalyst for hydrolysis done at constant temperature and solvent-to-solid ratio of 95°C and 8 mL/g, respectively, over a reaction time of 5 to 300 minutes, to determine the effect of acid concentration on the hydrolysis yield. The maximum sugar yield achieved was only ~0.06 w/w, corresponding to a recovery of ~24%, for hydrolysis done with 10% v/v sulfuric acid for 120 minutes. Although the amount of sugar recovered was relatively low, hydrolysates obtained have a sugar concentration of ~7 g/L, a level considered adequate for substrates in some fermentation processes. In addition, none of the inhibitory compound, 5-hydroxymethylfurfural, was present in the hydrolysate. Drying of residual solids obtained after hydrolysis was found to result in the sulfonation of the remaining organic fraction, producing a sulfonated residue (with total acid density of 4 to 7 mmol H+/g) which may be used as solid acid catalyst.