SIMULATION OF FERMENTABLE SUGAR PRODUCTION FROM LIGNOCELLULOSICS TO FUEL ΒΙΟETHANOL Theocharis Tsoutsos, Dimitris Bethanis, Vasilis Gekas Environmental Engineering Dept, Technical University of Crete, University Campus GR 73100 Chania, Greece tel: (30 28210) 37825, fax: (30 28210) 37846, tsoutsos@mred.tuc.gr ABSTRACT: In this paper is studied the production of fermentable sugar solutions for bioethanol production. The process of acid hydrolysis was selected by using dilute H 2 SO 4 . Suitable lignocellulosics were investigated with high productivity in sugars, which are in abundance in the Mediterranean countries, so their exploitation could be economically feasible. The process was analyzed in two common reactor types (batch and continuous stirred tank). Also, a simulator was developed in Matlab environment for each material and each reactor. The simulation was applied in a wide range of temperatures (100 - 240 ºC) and acid concentrations (0.5 - 3.0% w/w), having as the fundamental objective to investigate the behaviour of pentosans and hexosans. It was confirmed that the production of rich-in-sugars solutions required the design of the process in two stages. In the first stage the degradation of sugars takes place, considering the fact that pentoses are formulated in softer conditions than hexoses; so the phenomenon can become very intense and the reaction time needs to be adjusted carefully. In the second stage of simulation, ranges of samples are tested with high concentration of sugar and products with low degradation; it is observed satisfactory sugar productivity. The xylose productivity is the range 85-95% in the most optimal conditions compared to the theoretical values, while large variations in glucose were frequent (10-55%) in comparison with the theoretical values, achieving best results for wheat straw hydrolysis in batch reactor. The simulation results agree with relevant experimental data from the international literature, verifying the reliability of the developed method, offering a functional tool for the study of process in the stage, before the practical implementation. Keywords: bio-ethanol, acid hydrolysis, straw, fermentation, reactor design 1. INTRODUCTION Biomass exploitation provides large challenges due to raw material abundance, particularly in the technological scheme to fuel bioethanol. Bioethanol is a fuel, friendly to the environment and immediately exploitable for substitution of petrochemicals, which today are used for the 97% of the transport needs [1]. The permanently worsened energy crisis has created favourable conditions for continuously bigger turn in such fuels. Besides the bioethanol production is greenhouse gas neutral, if will be used only renewable raw materials. The aim of the current study is the investigation of hydrolyzate production from lignocellulosics (LGC), as a microbial substrate to produce fuel bioethanol [2]. In the current study is simulated the dilute acid hydrolysis of various lignocellulosics (LGC) in order to identify the optimal conditions of the hydrolyzate production rich in fermentable sugars. The choice of LGC was made taking into consideration the design of a realistic process under Mediterranean conditions, so that is possible the composition of a realistic and sustainable technological scheme. The investigation realized by simulation of the hydrolysis reaction using computational Matlab environment. Various process conditions were assessed and were compared different types of raw materials and reactors. 2. LIGNOCELLULOSICS-TO-BIOETHANOL The production of LGC sugars is perhaps the most important stage in the process of ethanol production, because good quality solutions favour the efficient conversion to ethanol. However the process is not complete, because the lignin-semicellulose complex inhibits the penetration of the hydrolytic means, while the chemical breakdown of the cellulose is difficult due to its crystallinity. Consequently, for the improvement of the reaction activity, is essential the pretreatment of the raw material. Generally, after the pre-treatment process there are three hydrolysis alternatives: • Enzymatic hydrolysis • Concentrated acid hydrolysis • Dilute acid hydrolysis [3] Dilute acid hydrolysis is selected for the production of fermentable sugars via softer conditions than those in the case of concentrated acid. During this process is used dilute acid concentration (up to 3-4%) in temperatures 100 - 240 ο C. Several acids are able to be used, such as HCl, H 2 SO 4 , H 3 PO 4 and HNO 3 . In temperatures between 110-140 ο C semicellulose is hydrolyzed, while crystallic cellulose remains practically unchanging up to 170 o C and takes place up to 240 o C. The difference between these two parts dominates the design of a two-stage process. The hydrolysis, separately of the semicellulose and cellulose parts, has already been studied for wood biomass [4,5] and concerns initial semicellulose hydrolysis in low temperature (120-150 ο C) and then cellulose hydrolysis at higher temperature up to 240 ο C. During prehydrolysis the lignine-semicellulose complex is broken down, facilitating the semicellulose hydrolysis and the sugar production, mainly xylose, under relatively soft conditions. However at increased temperature xylose is broken down and are formulated undesirable byproducts. Also, for the same reason, is