Take an organic or aqueous organic solvent such as formic acid, acetic acid, methanol, ethanol, acetone, ethylene glycol, oxalic acid, triethylene glycol or tetrahy — drofurfuryl alcohol and combine it with an inorganic acid catalyst such as hydrochloric acid or sulfuric acid and one can eliminate the internal lignin and hemicellu — lose bonds. This is known as an organosolv process (Pan et al., 2006; Sarkanen, 1980; Thring et al., 1990). Alterna­tively, an organic acid, such as oxalic acid, acetylsalicylic acid and salicylic acid may be substituted for the inor­ganic catalyst.

It has been observed that approximately 72% of xylose in untreated wood, in both its monomeric and oligomeric forms, could be recovered using an organo — solv pretreatment process (Pan et al., 2006). Pan et al. (2006) also investigated a bioconversion of hybrid pop­lar to ethanol at 180 °C, for 60 min, with 1.25% H2SO4, and 60% ethanol. They observed that nearly 74% of the lignin was removed as a precipitate in the ethanol extraction.

Raising the operational temperature above 185 °C eliminates the need for a catalyst, either for an inorganic acid or for an organic acid. At this condition, the amount of delignification is quite satisfactory. Adding acid yields a high quantity of xylose.

Since the organic solvents inhibit downstream biolog­ical processes, such as organism growth and enzymatic hydrolysis, it is necessary to remove these solvents from the system. This is quite difficult as some quantity of solvent is likely to reside in the system even after ef­forts to remove them. Organic solvents tend to evapo­rate into the atmosphere and are hazardous to the environment and one’s health. Containing the solvent is another challenge. Given these challenges, an organo — solv pretreatment is not necessarily ideal for large-scale or commercial operations.