Optimal conditions for hemicelluloses extraction from Eucalyptus globulus wood: hydrothermal treatment in a semi-continuous reactor

Optimal conditions for hemicellulose extraction from wooden biomass in a semi-continuous system have been assessed in this work. This study would constitute the first stage for a profitable and green industrial process. Eucalyptus globulus was selected as raw material due to its low water consumption, high growth and its efficiency in lignocellulose production. Moreover its cultivation is very popular in southern Europe. Samples of 5.0 g of wood were fractioned using a pressurized hot water semi-continuous system, to produce sugars (pentoses and hexoses) and a solid residue enriched in lignin.

Five flow rates between 2.50 and 20.00 mL/min and four temperatures between 135.0 and 285.0 °C were tested in order to maximize the production of sugars, avoiding the formation of degradation products.

Optimum conditions for the extraction of hemicellulose were identified at 185.0 °C and 5.00 mL/min, leading to a pentoses yield of 67.409 wt%, with 0.702 wt% of degradation products. Almost all the pulp is extracted at 285.0 °C.

SEM images show very well the changes in the wood structure at different temperatures.

A kinetic model was developed, describing the extraction and hydrolysis of hemicellulose and cellulose with absolute average deviations around 10% for sugar extracted mass.