Process for the two-stage decomposition of hemi-celluloses to xylose

DETAILED DESCRIPTION What is claimed is: 1.
In a process for the two-stage decomposition of a hemi-cellulose of a xylan-containing natural product for the purpose of obtaining xylose wherein the hemi-cellulose of xylan is treated in a first stage with a basic medium and the obtained solid residue is thereafter subjected in a subsequent stage to an acid treatment, the improvement wherein the treatment with said basic medium and said acid are carried out in a single reaction vessel and: a.
in the first stage the hemi-cellulose of xylan-containing material is treated at an atmospheric or elevated pressure and at an elevated temperature with an alkali hydroxide solution, the alkali content of which is sufficient to split off and neutralize acetic acid bound in the hemi-cellulose of the xylan-containing material, and the resultant alkaline solution is filtered off from the reaction vessel to leave behind the solid residue; b.
following the alkali treatment, the solid residue is extracted within the reaction vessel with at least one liquid surge at a temperature of about 20 to 120.
degree.
C; c.
in the subsequent stage the so-extracted solid residue is subjected at an elevated pressure and at an elevated temperature to an acid treatment, the acid treatment being effected employing an acid solution, said acid solution being filtered off following contact with said solid extraction residue from the reaction vessel; d.
the resultant acid treated residue is extracted afresh within the reaction vessel with at least one liquid surge at a temperature of about 20.
degree.
to 120.
degree.
C; e.
the extract obtained from said extraction and the solution obtained from the acid treatment are processed for the recovery of xylose or xylitol.
2.
A process according to claim 1 wherein said subsequent stage is a second stage following extraction of the solid residue obtained from said first stage.
3.
A process according to claim 1 wherein the alkaline solution filtered off from the reaction vessel is processed for the recovery of organic acids and lignin