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ePaper created 2016-03-17, 15:06:18 | version 1.45.01
9 4 PROCESS UPSCALING FOR THE PRODUCTION OF BIOAROMATIC COMPOUNDS FROM LIGNIN Daniela Pufky-Heinrich, Björn Rößiger, Robert Röver, Gerd Unkelbach Lignin as a biobased raw material Current research is focusing on plant biomass that is not used as food, in food production or as animal feed and is available at competitive prices as a raw material for the production of platform chemicals. Herein, lignocellulosic biomass from wood is an important feedstock. In addition to cellulose, the other main constituent in wood is lignin. It is incorporated into plant cell walls and is responsible for the rigidity of wood. However, current processes for the production of chemical products from raw materials containing lignocellulose are generally designed to produce wood pulp and not to exploit all compo- nents in their entirety [1]. The wood pulp industry produces about 50 million metric tons of lignin as a by-product, mainly in the form of so-called kraft lignin. To date, the bulk of this lignin has mainly been used in energy production and burned directly in the pulping plants [2]. Small quantities of lignin in which the polymeric structure has been preserved are used in applications such as bonding agents, additives in cement or rubber. Moreover, due to its basic aromatic structure, it possesses enormous potential as a raw material for the production of aromatic building blocks for syntheses. Cleavage of lignin into aromatic structures Cleavage of the phenolic macromolecule lignin enables the production of mixtures of aromatic building blocks for synthesis. These can be used directly as raw material, e.g. for phenol formaldehyde resins, polyurethanes or in epoxides, or can be converted into the classic aromatic compounds, benzene, toluene, xylene or phenol, after further separation and defunctionalization. A variety of methods are suitable for this, such as hydrolysis, oxidative and reductive cleavage or enzymatic conversion. On an industrial scale, only the oxida- tive cleavage of lignosulfonates to vanillin has been realized. No other industrial processes have been described to date for other applications [3]. The process of base-catalyzed depolymerization (BCD) of lig- nin results in hydrolysis of the ether bonds in the lignin macro- molecule and thereby in the production of monomers, dimeric and oligomeric alkyl-functionalized aromatic compounds. The BCD process is carried out in aqueous or alcoholic solution at temperatures of up to 350°C and at 250 bar. Intensive research both on organosolv lignin and on technical lignin containing sulfur has been performed at the laboratory scale at Fraunhofer ICT and the process has been optimized. BCD of lignin is highly selective and results in high yields of aromatic cleavage products [4]. Piloting of the process at Fraunhofer CBP Scaling of this process at the pilot scale was carried out suc- cessfully at Fraunhofer CBP. We investigated and optimized the continuous process of chemical cleavage of lignin and the subse uent separation and purification of the aromatic fractions using a multi-stage process design. The alkaline solution was processed at a capacity of up to 20 kg/h. After depolymerization, the aromatic lignin fragments are processed by acidification of the reaction solution and separated into a liquid oil fraction (BCD oil) rich in monomers and a solid fraction rich in phenolic oligomers (BCD oligomers) during subse uent separation and purification using mechanical and thermal techni ues or this, a variety of filtration units and centrifuges are available at Fraunhofer CBP. BCD oil extraction 1 lignin BCD oil BCD BCD oligomers CHEMISTRY 94