Attempts have been made to improve overall process efficiency by combining the two individual pretreatments of rapid steam hydrolysis and organosolv. Rughani and McGinnis [53] have studied the effect of a combined RASH — organosolv process upon the rate of enzymatic hydrolysis and the yield of solubilized lignin and hemicellulose. A schematic diagram of the process is shown in Figure 4.10. For the organosolv pretreatment, the steam generator is disconnected and the condensate valve closed. The rest of the reactor setup is similar to the typical RASH procedure.

The organosolv processes at low temperature are generally ineffective in removing lignin, as explained earlier; however, combining the two processes leads to increased solubilization of lignin and hemicellulose. RASH temper­ature is the major factor in maximizing the percentage of cellulose in the

final product. The maximum yield of solubilized lignin was obtained at a temperature of 240°C for RASH and 160°C for the organosolv process.