Lignin is the second most abundant biomass component on earth and is the major byproduct in the pulp and paper industry. Despite its interesting chemical structure, most lignin is today simply combusted for generation of process heat and power.
The structure of lignin is built by phenolic compounds, so it can be used as an alternative resource for the production of aromatic hydrocarbons. These might be used as feedstock for the production of plastics, synthetic rubbers and many more. Unfortunately, due to its complex structure, it is up to date infeasible to convert lignin by means of chemical and biochemical processes to valuable chemicals. But pyrolysis of lignin offers a chance for thermochemical conversion into valuable products. By heating the lignin to temperatures of 500-700°C – under the absence of oxygen – the molecules are being cracked to produce aromatics rich pyrolysis oil.
The aim of this research is to optimize the lignin pyrolysis. The energy for the reaction shall therefore be obtained by combustion of the by-products coke and permanent gases. The heat will be transported via the circulating bed material. Both reactions shall be integrated in one process to avoid heat loss. Furthermore, it is presumable that the yield of aromatic hydrocarbons will be increased by the reduction of the coke loading in the bed material.
To investigate the pyrolysis process a circulating fluidized bed riser 2 m in height and 80 mm in diameter is used. The lignin is fed pneumatically by nitrogen into the reactor, where it is pyrolyzed. The bed can be fluidized with nitrogen and/or steam. The solids are recirculated by a primary cyclone back into the riser. Char and ash are further separated by a secondary cyclone, before the hot vapors are quenched in a scrubber operated with a washing liquid like water, isoparaffin or sodium hydroxide. The gases leave the scrubber with temperatures below 90°C, before any residues are combusted.
The gas composition is continuously monitored behind the scrubber and side stream samples can be taken just before the scrubber to obtain information about the oil composition and with regard to the influence of operation time. The oil of both the side stream sampling as well as the scrubber sump are analyzed by gas chromatography (GC) and gel permeation chromatography (GPC) for oligomeric substances. Char samples are studied to investigate composition, particle size distribution, sorption properties and yield.
Additionally to the investigation of the experimental process, the pyrolysis process is modeled in the Aspen Custom Modeler®. A general model for scale up of the whole process is to be obtained. Through combination of the pyrolysis reactor model with other processes like a model for the combustion reactor used for regeneration of the bed material and the cyclone an overall process model is to be realized.
Franck M., Hartge E.-U., Heinrich S., Lorenz B., Werther J. (2011). Energetic Optimization of the Lignin Pyrolysis for the Production of Aromatic Hydrocarbons. Proc. of 10th Int. Conf. on Circ. Fluid. Beds&Fluidiz. Techn.
Franck M., Hartge E.-U., Heinrich S., Werther J., Eidam P., Fortmann I., Meier D. (2012). Gewinnung von Phenolen aus Lignin durch Flash-Pyrolyse in einer zirkulierenden Wirbelschicht (ZWS) - Prozessentwicklung und Produktanalytik. In Beiträge zur DGMK-Fachbereichstagung "Konversion von Biomassen“.
Franck M., Hartge E.-U., Heinrich S., Werther J., Meier D. (2014). Lignin Pyrolysis in a Circulating Fluidized Bed – Influence of Temperature and Char Formation on Bed Material. Proc. of 11th Int. Conf. on Fluidized Bed Techn.
• Thünen Institute of Wood Research
• Institute of Thermal Separation Processes, Hamburg University of Technology
• Institute of Environmental Technology and Energy Economics, Hamburg University of Technology
• tesa SE
• Sigmar Mothes Hochdrucktechnik GmbH