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During mechanical defibration of wood, a minor fraction of the wood mass is dissolved in the process water. These dissolved substances represent an extra energy demand when they are treated in the mill's wastewater treatment plant. Galactoglucomannan, the main hemicellulose in spruce, can be recovered from thermomechanical pulp mill process water by a process based on microfiltration (MF) and ultrafiltration (UF). The purpose of this work was to study the scale-up of the process from laboratory scale to continuous industrial scale. MF was first studied in the laboratory, and then combined with UF in a continuous pilot process on-site at a pulp mill. The data obtained were used to estimate the cost of the membrane processes for galactoglucomannan recovery which was found to be about €1160 per ton hemicelluloses. [ABSTRACT FROM AUTHOR]

Hot-water extraction of hemicelluloses, especially galactoglucomannans, from fractions of ground spruce wood with different particle sizes was studied at 170°C with extraction times up to 60 min. Extraction of spruce sapwood, heartwood, and thermomechanical pulp (TMP) was also compared at 160 to 180°C. Static batch extractions were carried out in an accelerated solvent extractor (ASE). The extracted hemicelluloses were characterized by sugar unit analysis and determination of acetyl groups and molar masses. The particle size significantly affected the extraction of ground wood. The total extraction yield, as well as the yields of hemicelluloses and monosaccharides, was the highest from the finest ground wood fraction (< 0.1 mm). The release of acetic acid, average molar mass of extracted hemicelluloses, and end-pH of the extracts were also dependent of the particle size, although to a lower extent. Irrespectively of the ground wood particle size, the yield of hemicelluloses reached a plateau after 40 min extraction at 170°C. The results indicate that extraction of hemicelluloses is limited mainly by the diffusion in the fiber wall, and for coarse wood shives also by the mass transfer in the wood matrix. There were only small differences in the hot-water extraction yields of hemicelluloses from spruce sapwood, heartwood, and TMP, considering both poly- and monosaccharides.

Hemicelluloses dissolved in thermomechanical pulp (TMP) mill process streams can be used to manufacture high-value-added products. The molecular mass of the dissolved hemicelluloses is about 10 kDa. In some applications, it would be beneficial with larger molecules. It was therefore investigated whether it is possible to increase the size of hemicelluloses isolated by microfiltration and ultrafiltration from TMP process water using enzymatic treatment with laccase. No significant increase of the size of hemicelluloses was achieved, probably due to only a small percentage of lignin carbohydrate complexes in the process water. The molecular mass of lignin increased however markedly from a peak molecular mass of 1 kDa to about 60 kDa. Diafiltration was used to purify large molecules after the enzymatic treatment. Low-molecular-mass sugar and lignin molecules in the diafiltration permeate were concentrated by nanofiltration. The retention of sugars and lignin was about 98% during nanofiltration to a volume reduction of 80%. Average flux during nanofiltration was 49 l/m 2 h. [ABSTRACT FROM AUTHOR]

Galactoglucomannan is the major hemicellulose in process water from thermomechanical pulping of spruce. The recovery of hemicelluloses from this process water would both reduce the load on pulp mill water treatment plants and yield a biopolymer suitable as a raw material for renewable products. One method of recovering these hemicelluloses is two-stage filtration employing microfiltration to remove large contaminants, such as suspended matter and colloidal extractives, followed by ultrafiltration to concentrate and purify the hemicelluloses from low molecular mass contaminants. This investigation shows that a microfiltration membrane with a pore size of 0.1 μm removes colloidal extractives while still maintaining a high amount of high molecular mass hemicelluloses in the microfiltration permeate. The removal of extractives resulted in an increase in the initial flux during the subsequent ultrafiltration step from 90 L/m 2 h to over 200 L/m 2 h. [ABSTRACT FROM AUTHOR]

Abstract: Several valuable substances are released from wood during the production of thermomechanical pulp. These substances can be isolated and purified for use as value-added chemicals. The hemicellulose galactoglucomannan (GGM) has attracted a great deal of interest because of its possible applications as an oxygen barrier film in packaging materials, as a hydrogel in biomedical products and as an emulsion stabilizer in food and feed. In order to exploit GGM in pulp mill process water, it must be recovered at a high concentration and high purity. The first step in the purification process is the separation of GGM and dispersed substances. In this work, the influence of membrane pore size, cross-flow velocity and backpulsing on membrane performance during the microfiltration of thermomechanical pulp process water was investigated. The flux of 0.4 and 0.8μm membranes was lower than the flux of a 0.2μm membrane, and it was not possible to recover the pure water flux of the 0.4 and 0.8μm membranes. Increased cross-flow velocity and backpulsing had a positive effect on the flux, but only a minor influence on the retention. The mean molecular mass of GGM in the process water was 9kg/mol. The retention was therefore expected to be <10%. However, the retention of GGM was >50%, irrespective of the operating conditions. [Copyright &y& Elsevier]