Process for preparing furfural from biomass

A method for producing furfural from biomass material containing pentosan:

• (a) providing a biomass containing pentosan;
• (b) contacting the biomass with a solution containing at least one α-hydroxysulfonic acid thereby hydrolyzing the biomass to produce a product stream containing at least one C5-carbohydrate compound in monomeric and/or oligomeric form, and α-hydroxysulfonic acid;
• (c) separating at least a portion of the α-hydroxysulfonic acid from the product stream containing at least one C5-carbohydrate compound to provide an acid-removed product stream containing the at least one C5-carbohydrate compound and recovering the a-hydroxysulfonic acid in its component form;
• (d) separating a liquid stream containing said at least one C5-carbohydrate compound and a wet solid stream containing remaining biomass from the acid-removed product;
• (e) dehydrating the C5-carbohydrate compound in at least a first portion of the liquid stream in the presence of a dehydration acid, in a biphasic reaction medium comprising an aqueous phase and a water-immiscible organic phase, at a temperature in the range of from about 100° C. to about 250° C.;
• (f) separating an organic phase stream containing furfural and an aqueous stream containing the acid from the dehydration product stream;
• (g) recycling at least a portion of the aqueous stream or a second portion of the liquid stream to step (b);
• (h) recovering furfural from the organic phase stream.