A process for producing an organic aliphatic product (such as butanol) from lignocellulosic biomass is provided, comprising: (a) fractionating lignocellulosic biomass in the presence of a solvent for lignin, a hydrolysis catalyst, and water, to produce a liquor containing hemicellulose, cellulose-rich solids, and lignin; (b) washing the cellulose-rich solids and separating the cellulose-rich solids from the liquor; (c) enzymatically hydrolyzing the cellulose-rich solids to generate a hydrolysate comprising glucose; (d) detoxifying the hydrolysate by neutralizing the hydrolysate, removing insoluble solids, and removing or oxidizing residual hydrolysis catalyst, thereby generating a purified hydrolysate; (e) fermenting the purified hydrolysate using a suitable microorganism to produce a dilute organic aliphatic product, wherein the microorganism is recycled with a membrane; (f) extracting the dilute organic aliphatic product into a water-immiscible extractant, to generate an intermediate material; and (g) disti
