We Claim:
1. A process for isolating fermentable sugars from the hydrolyzate obtained from the acid hydrolysis of a material containing cellulose, hemicellulose and lignin; wherein the process comprises:
(a) neutralizing the hydrolyzate with an alkali and filtering the resultant mixture to recover lignin as a solid;
(b) drying the filtrate of step (a) to obtain a residue comprising fermentable sugars and salts;
(c) extracting fermentable sugars from the residue with C1-C6 alcohol or their mixtures; and
(d) evaporating the alcohol to yield fermentable sugars.
2. The process as claimed in claim 1, wherein the alkali is selected from a group comprising alkaline hydroxides, alkaline salts, amines and combinations thereof.
3. The process as claimed in claim 1, wherein the alkali is alkaline hydroxide, preferably ammonium hydroxide.
4. The process as claimed in claim 1, wherein the alcohol is ethanol.
5. The process as claimed in claim 1, wherein the alcohol concentration is more than 70% v/v in water.
6. The process as claimed in claim 1, wherein the neutralization is carried out at ambient temperature or below.
7. The process as claimed in claim 1, wherein the neutralization is carried out at a temperature of about 0 ºC to 10 ºC.
8. The process as claimed in claim 1, wherein the sugar is selected from a group comprising glucose, xylose and arabinose.