Acid hydrolysis of the waste newspaper: Comparison of process variables for finding the best condition to produce quality fermentable sugars

Environmentally hazardous solid waste is renewed to the feedstock of bio-fuel through the recovery of good quality fermentable sugars by acid hydrolysis of the waste newspapers. Conflicting effects of the variables of acid hydrolysis on the yield of fermentable sugars; and that on the generation of undesired inhibitors to subsequent enzymatic hydrolysis for the production of bio-fuel are compared to select the best condition of hydrolysis. The roles of temperature, acid concentration, the ratio of inorganic to organic acids on the yield of desired total sugars (TS) and lignosulfonate (LS), and that on the reduction of inhibitors such as 5-hydroxymethyl furfural (HMF) and acetic acid with time are studied. The hydrolysis experiments are performed at two different temperatures (80 degrees C and 121 degrees C), in the acid concentration range of 0.25-1 % (w/v) and with different ratios of two types of acids. The maximum recovery of TS is obtained as 17 % (w/w) at an acid concentration of 1% (w/v), the temperature of 121 degrees C at a time of 60 min. Both of HMF and acetic acid are produced only at 121 degrees C. The best condition of acid hydrolysis is found as the temperature of 121 degrees C, a mixture of sulphuric acid to citric acid of the ratio 3:1 at a hydrolysis time of 60 min for higher values of desired TS and LS with a manageable production of inhibitors. The finer tuning of the hydrolysis variables to produce quality fermentable sugars is promising for the economical production of bio-fuel.