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ePaper created 2014-05-07, 13:23:14 | version 1.30.01
98 Sustainable use of renewable resources Rising prices for raw materials and the increasing scarcity of mineral oil resources are boosting the interest in renewable resources and in strategies for the sustainable production of special materials, fine chemicals or platform chemicals. Emulating the concept from the petrochemical industry these biobased materials will in future be made available by bio- refineries. Native hardwoods offer themselves as a chemical feedstock that is available sustainably and without competing with foodstuff production. For the conversion of wood or lig- nocellulose into platform chemicals for the chemical industry of the future, the wood first of all has to be broken down and separated into its basic chemical components. Organosolv lignin for a wide range of applications In the second phase of the collaborative project “Lignocel- lulose Biorefinery” the concept of a wood-based biorefin- ery was successfully implemented on the pilot scale at the Fraunhofer CBP in Leuna. The necessary preliminary work for this was carried out together with the Fraunhofer Institutes IGB and ICT as well as twelve other industrial and research project partners. The “organosolv process” developed in the first phase of the project uses mixtures of alcohol and water to fractionate wood under pressure and at high temperature into its basic components cellulose, hemicelluloses and lignin. Cellulose and hemicelluloses can then be converted to sugars with the help of enzymes. Unlike with other fractionation processes, the resulting lignin is very pure and neither con- taminated with sulfur nor with inorganic salts. This permits applications for a wide range of materials. Scaling of the fractionation process to the pilot plant The work at the Fraunhofer CBP focused on the scaling of the fractionation process to the pilot scale. The basic questions concerning the process specifications were worked on in joint preliminary work with the project partners. The plant was de- signed and planned in detail on the basis of these results. The pilot plant comprises a large number of individual process steps for the production of concentrated sugar solutions and lignin powder obtained from wood chips. Up to 70 kg of wood (oven dry weight) can be processed in one batch. The plant was designed in such a way that the material and energy cycles are closed. The simplified diagram of the plant in Fig. 2 shows that the wood is first of all digested in a 400-liter reac- tor at up to 200°C; here lignin and hemicelluloses are solubi- lized in an ethanol-water mixture. The additional tanks and heat exchangers of the “tank farm” permit a fractional wash- ing of the material under reaction conditions and the recovery of energy during the pulping process. From the pulping liquor enriched with lignin and hemicelluloses lignin is precipitated by adding water or distilling the ethanol; it is then filtered off and, after washing, dried. The ethanol used is entirely recovered by distillation from the filtrate and the hemicellu- lose sugars remain as an aqueous solution. The solid fibrous residue of the pulping process is disintegrated and washed, dewatered, enzymes are added and then, in stirred reactors specially designed at the Fraunhofer IGB, it is saccharified with a high concentration of the pulp. After a filtration step a glu- cose solution is obtained which is concentrated into a sirup to stabilize it. CHEMISTRY LIGNOCELLULOSE BIOREFINERY – SUCCESS- FUL IMPLEMENTATION ON THE PILOT SCALE Dr. rer. nat. Moritz Leschinsky, Dipl.-Chem. (FH) Gerd Unkelbach 1 2 pulping lignin precipation/ solvent recovery lignin washing digester 400 L 200°C tank farm fiber washing enzymatic hydrolysis concentration lignin drying dewatering dewatering ethanol / water ethanol / water mother liquor wood chips fiber fraction xylose fraction conc. glucose solution hydrolysis lignin organosolv ligninlignin hydrolysis residue glucose solution