276792 The Pyrolysis of Lignin
Lignin is an organic polymer and it is the second most abundant renewable carbon source on Earth, after cellulose. Lignin is not one compound but many complex polymers; the commonality between all of them is their phenylpropane structure, that is, a benzene ring with a tail of three carbons. In their natural unprocessed form, their molecular weights may reach 15,000 or more.
In this work the kinetics of lignin pyrolysis is described by using a lumping model (G. Astarita, R.Ocone, “Lumping Nonlinear Kinetics”, AIChE Journal, 34, 129, 1988), where the lignin structure is simplified and assumed to be formed by repeating units (monomer) which can be identified with the basic benzene ring with the tail of three carbons. The bio-oil, produced by the pyrolysis of lignin, is then fractionated to obtain lighter components. Two different modelling approaches are attempted and comparisons are made; the bio-oil is considered as the feedstock for the fractionation and as one of the products from the primary thermal cracking. To model the products of the primary cracking we consider a discrete 3-lump approach and assume that the oil is one of the lumps (the other being the gas and the char). Successively, we model the fractionation in a continuum fashion by extending the approach of previous works on catalytic and thermal hydrocracking and we propose two different kinetic models. Prediction of the product distribution after pyrolysis is reported and the benefit of the lumping approach is assessed. Results are validated against experimental data taken at ICFAR, University of Western Ontario.