International Congress on Green Process Engineering (5º. 2016. Quebec, Canada)

Cellulose and hemicelluloses contained in woody biomass can be hydrolysed to monomeric sugars, which can be fermented to ethanol, or can be converted into higher value products [1].Hemicelluloses, when isolated from biomass, have unique properties.They can be used to produce films for packaging applications in substitution to synthetic plastics, as polysaccharides works as barriers against oxygen permeation; another important application is the production of aerogels to insulate products.Xylose from hemicellulose, for instance, can be converted to furfural, which is a precursor used in different fields, such as oil refining, plastics, pharmaceutical, and agrochemical industries.L-Xylose can be also hydrogenated or enzymatically transformed to xylitol, which is a sweetening agent and is also used for preventing tooth decay [2].The idea of transforming biomass to energy, materials, and chemicals, defines the concept of biorefinery, particularly interesting topic nowadays, considering the issues related to fossil combustibles and derivatives [3][4][5].A promising, clean and cheap way to depolymerize cellulose and hemicellulose into monosaccharides is the process called autohydrolysis, which simply consists on treating biomass with hot water/steam.During the reaction, most of the hemicellulose is extracted and hydrolysed to monomers, with a consequent release of acetic acid originated from the acetyl groups bonded to the oligosaccharides; a less amount of cellulose is released, due to the crystalline structure of the polymer, which make it more difficult to dissolve [6] .In our study, we investigate thoroughly the autohydrolysis of wood coming from different species of trees to produce expecially hemicelluloses.The experiments are carried out with different kinds of reactors:  a laboratory-scale semicontinuous tubular reactor , i.e. biomass wood chips in batch and fresh water pumped in continuous. a batch cascade reactor composed by 5 reactors connected in series, with water fully recirculated;  a continuous reactor with a homogeneous water-sawdust slurry, injected through a pipe together with a high temperature water stream, with low residence times;  a pilot-scale plant composed by 5 semi-continuous reactors working in series.Fractionation of biomass from Eucalyptus globulus, using subcritical water with a laboratory-scale semicontinuous tubular 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 southern Europe.Samples of 5g 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 2.5 and 20 mL/min and four temperatures between 135 and 285ºC 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 ºC and 5 mL/min, leading to a pentoses yield of 64.7%, with 0.7 of degradation products.Almost all the pulp is extracted at 285 ºC.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 30 % for sugar concentration.

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