A modular process for organosolv fractionation of lignocellulosic feedstocks into component parts and further processing of said component parts into one or more of a de-lignified cellulose stream, a sugar stream, small-chain alcohol streams and four structurally distinct classes of lignin derivatives. The modular process comprises a first processing module configured for digesting lignocellulosic feedstocks with an organic solvent thereby producing a cellulosic solids fraction and a liquid fraction, a second processing module configured for recovering small-chain alcohols and optionally a first class of lignin derivatives from the cellulosic solids fraction, a third processing module configured for recovering from the liquid fraction at least one of a second class and a third class of lignin derivatives or mixtures thereof, and waste stream comprising a fourth class of lignin derivatives. The fourth processing module may optionally recover the fourth class of lignin derivatives.