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In the present investigation, pyrolysis and gasification, two widely used thermochemical processes, are compared as potential chemical recycling methods for MWP and plastic rich MSW in terms of products of high value and their end uses. High temperature pyrolysis results in a wide spectrum of products which also contain monomers of C2-C4 range such as ethylene and 1,3-butadiene. Recovery of monomers from their isomers and other products is difficult and energy-intensive. Gasification breaks solid wastes into simple molecules (mainly CO & H2) which subsequently can be converted to value added liquid chemicals (namely alcohols) by a catalytic synthesis processes. Synthetic alcohol then can be converted to the desired petrochemical precursors. After reviewing different aspects of both pyrolysis and gasification, recycling through gasification is chosen as the preferred route for project SPORT as syngas product can be converted into several key petrochemical products in high yield.

This paper presents a thermodynamic model for the estimation of impurities in the raw synthesis gas and in the slag resulting from gasification of solid waste. Based on thermodynamic equilibrium calculations and mass balances, the model takes into account the possibility of each impurity becoming an oxide, a chloride, or remaining in its elemental form. The model includes a comprehensive set of thermodynamic data for a wide variety of chemical species used to estimate the equilibrium constants. By solving the equilibrium reaction equations, the model predicts which pollutants are formed and in what amounts as well as their distribution in the raw synthesis gas and in the slag. Predicting the distribution and fate of these pollutants is particularly important for the design of a gas cleaning system for the raw synthesis gas and for deciding on the disposal options of the slag. The model can be applied to different waste materials, including municipal solid waste, mixed plastics waste, auto-shredder residue (ASR) and biomass. A comparison between the model predictions and the operational data from a commercially-available gasification process (Thermoselect) shows a close agreement between the estimated and real data.

The pyrolysis behaviour of predried vegetable market waste has been investigated using TGA within the temperature range 523 to 923 K under inert atmosphere and a comparison has been made with other lignocellulosic materials in order to point out the difference between the pyrolysis of nearly homogeneous and perfectly mixed heterogeneous biomass. Kinetic parameters of the pyrolysis material have been evaluated from the simulation of the TG data. A reaction mechanism involving two parallel 1st order reactions evolving gaseous products lumped as volatiles and solid products lumped as char has been proposed for prediction of rate constants as a function of normalized fractional change. Four kinetic models incorporating the effect of deactivation have been used for this purpose. In another attempt, using concentration independent model of solid deactivation, simulation has been carried out to predict concentration time history of the system components as well as quantitative change of rate constants with the propagation of time.