Combined membrane filtration and enzymatic treatment for recovery of high molecular mass hemicelluloses from chemithermomechanical pulp process water

• Hemicelluloses were recovered from chemithermomechanical pulp process water.
• Membrane filtration and enzymatic treatment were used in an innovative process.
• Membrane filtration provided a hemicellulose fraction suitable for enzymatic treatment.
• Enzymatic laccase treatment increased the molecular mass of hemicelluloses markedly.
• Large hemicelluloses were separated from small hemicelluloses by ultrafiltration.

Hemicelluloses with high molecular mass are needed for the manufacture of value added products such as food packaging barrier films. In this work such molecules were recovered from chemithermomechanical pulp (CTMP) process water using an innovative three-stage process comprising membrane separation and enzymatic treatment with laccase. Microfiltration followed by ultrafiltration was found to be a suitable combination in the first stage, providing a concentrated and purified hemicellulose fraction suitable for enzymatic treatment. In both membrane processes a high average flux (260 and 115 l/m2 h) and a low fouling tendency were observed. A marked increase in the average molecular mass of hemicelluloses with bound lignin moieties was achieved by laccase treatment in the second stage. The enzymatically crosslinked hemicelluloses were finally recovered in the third stage using ultrafiltration. In the final high molecular mass solution the hemicellulose concentration was 54 g/l, the contribution of hemicelluloses to the total solids content 43%, and the viscosity of the solution 27 mPa s. The results demonstrate that a hemicellulose fraction of high quality can be produced from CTMP process water, and that this could constitute a suitable feedstock for the production of, for example, barrier films for renewable packaging.