Process for purifying a contaminated hydrochloric acid composition

A process for the hydrolysis of a lignocellulosic material comprising:

• contacting a particulate lignocellulosic material with hydrochloric acid to yield a hydrolysate comprising saccharides, hydrochloric acid, water and contaminants,
• separating the saccharides from the hydrolysate to leave a contaminated hydrochloric acid composition having a first hydrochloric acid concentration, optionally, the first hydrochloric acid concentration is obtained after a hydrochloric acid concentration in the contaminated hydrochloric acid composition,
• feeding a part of the stream of the contaminated hydrochloric acid composition into the first distillation column to yield a first bottom product comprising water and hydrochloric acid with the hydrochloric acid concentration below the first hydrochloric acid concentration and a first top product comprising hydrochloric acid in a concentration based on weight above the azeotropic hydrochloric acid composition at the first pressure;
• wherein the first distillation column is operated at a first pressure so that the first hydrochloric acid concentration of the contaminated hydrochloric acid composition is above an azeotropic composition of hydrochloric acid and water at the first pressure;
• feeding at least a portion of the first bottom product and another part of the stream of the contaminated hydrochloric acid composition to the second distillation column to yield a second top product comprising contaminants and water, and a second bottom product comprising water and hydrochloric acid;
• wherein the second distillation column is operated at a second pressure that is lower than the first pressure and the hydrochloric acid concentration of the combined stream comprising the first bottom product and the contaminated hydrochloric acid composition in the second distillation is less than the azeotropic composition of hydrochloric acid and water at the second pressure;
• recycling at least a part of the second bottom product into the first distillation column, wherein a concentration of the combination of the part of the stream of the contaminated hydrochloric acid composition fed into the first distillation and the part of the second bottom product recycled into the first distillation column is above the azeotropic composition of hydrochloric acid and water at the first pressure;
• and
• recycling at least part of the first top product to the contacting step.

A purified hydrochloric acid composition comprising:

• from 85 to 95% wt of hydrochloric acid;
• from 5 to 15% wt of water;
• from 0.001 to 0.1% wt of methanol;
• and
• from 0.25 to 4% wt of acetic acid,
• the percentages being based on the amounts of methanol, acetic acid, water and hydrochloric acid.