Mediterranean Biomass is an attractive lignocellulosic substrate for bioconversion to ethanol because it has high carbohydrate content and is present in large quantities in Andalucía (Spain). For efficient ethanol production from this kind of biomass it should be firstly pretreated to make the cellulose more accesible to enzymatic hydrolisis and to recover more effectively the hemicellulose. Although hydrotermal pretreatments have been studied only few papers can be found in the literature about the use of a high scale liquid hot water (LHW) treatment to fractionate this material. As main advantages, LHW improves the recovery of the pentosans and produces hydrolysate that results in little or no inhibition of solubilized sugar fermentation.

The objetive of this study is the optimization of the large-scale LHW pretreatment of Mediterranean biomass, in order to improve cellulose digestibility. LHW pretreatment was performed in a high scale reactor (designed and built by authors). The stainless-steel reactor has a total volume of 100 L, with an installation of thermal fluid to maintain the temperature constant inside the reactor. It is designed to reach to 240 ºC with an agitator composed of epicyclical motorized reduction gear with blades of 1.5 kW and 1500 rpm. A design of experiments will be projected with the purpose to evaluate the pretreatment process.

The amount of feedstock loaded will be varied. Solid/liquid ratio range between 1/10 (w/v) and 1/20 (w/v). The temperatures will range from 160 to 240 ºC; reaction times will vary between 10 and 45 min. The content of the reactor will cool down by unloading it into second reactor and it is estimated to 150 ºC in about 2 min. The reactor is kept sealed and the pretreated substrate is transferred to a second reactor where enzymatic hydrolysis is performed. In this second reactor a constant temperature (around 50 ºC) for enzymatic hydrolysis process is achieved by the same thermic fluid system as of the first reactor and an electric agitation system is available. After process pretreated and hydrolyzed slurry will be separated in a solid and liquid fraction both of which are analysed. 

LHW has been proved to be a suitable procedure to increase digestibility of a several biomass as is related in bibliography, although further improvements must be done to assess its viability at large scale production and to increase the hemicellulose sugars recovery.

The efectiveness of LHW pretreatment, as main purpose of this work, will be evaluated in terms of cellulose recovery in the solid fraction, hemicellulose derived sugar recovery in the liquid fraction and enzymatic hydrolysis yield of pretreated substrate using commercial cellulases. It is hoped that results show high values of enzymatic hydrolysis yields above 80 % (calculated as g glucose in EH assay/g potential glucose in pretreated material) for most pretreatment conditions tested. Nevertheless, high hemicellulose solubilizations values should be expected.