In recent years, the use of mechanistic modeling to identify the underlying kinetics of complex systems has increased greatly. One of the challenges to kinetic modeling is the construction of a model which can capture the essential chemistry of a system while a manageable size is retained. The rate-based generation of mechanistic models is an attractive approach because kinetically significant species can be determined and selectively included in the final mechanism. An algorithm for the rate-based generation of reaction mechanisms developed previously 1 was improved and used to construct a compact mechanistic model for low-pressure tetradecane pyrolysis. Though thousands of species and reactions were generated, only a small portion of these (2% of species and 20% of reactions) was deemed necessary and incorporated into the final model. Experimental data were used to determine frequency factors for a subset of the reaction families, while all other kinetic parameters were set on the basis of literature values. With no adjustment to the optimized frequency factors, the mechanistic model was able to accurately predict reactant conversions and product yields for varying reaction conditions and initial reactant loadings. It was also observed that increasing the quantity of species initially seeded resulted in a smaller mechanism that had comparable fitting and predicting abilities as those of the models seeding only the reactant. Subsequent regeneration of the reaction mechanisms using the optimized values for the frequency factors resulted in smaller models with comparable capabilities.

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Environmental and economical concerns over diminishing landfill space and the growing abundance of mixed plastic waste mandate development of viable strategies for recovering highvalued resources from waste polymers. Co-processing of waste polymer mixtures with coal allows for the simultaneous conversion of coal and plastics into high-valued fuels. However, there is limited information about the underlying reaction pathways, kinetics, and mechanisms controlling coal liquefaction in the presence of polymeric materials.A series of model compound experiments has been conducted, providing a starting point for unraveling the complex, underlying chemistry. Neat pyrolysis studies of model compounds of polyethylene and coal were conducted in batch reactors. Tetradecane (C 14 H 30 ) was used as a polyethylene mimic, and 4-(naphthylmethyl)bibenzyl (NBBM) was used as a coal model compound. Reaction temperatures were 420 and 500˚C, and batch reaction times ranged from 5-150 minutes. Detailed product analysis using gas chromatography and mass spectrometry enabled the reactant conversion and product selectivities to be determined. Reaction of single components and binary mixtures allowed the kinetic coupling between feedstocks to be examined.2

Low-and high-pressure "pyrolysis experiments employing tetradecane .aqd 4-(1naphthylmethyl)-bibenzyl (NBBM) as "model compounds-for polyethylene and coal, respectively; were conducted at 420"C at different reaetmit loadings both neat and in binary mixtures. These reaetion" sets demonstrated that when reacted in binary m!xtures, the conversion of.tetradecane increased while the selectivities to primary products of NBBM were enhanced in the gas phase. Variation of the relative concentrations of the components revealed that the effat was'indeed a chemical one and not simply a result of dilution. As the polymer mimic to coal model compound ratio increased, there was a decrease in selfinteraetions of NBBM with minimal changes in the degradation products of tetradecane. Increasing the overall reaetion pressure in the system through addition of an inert gas from atmospheric pressure to 2360 psig resulted in small decreases in reactant conversions and altered product distributions only. slightIy. Overall, the experiments canied out demonstrated that favorable hiteraetions exist in the gas phz+e during coprocessing, and thẽ primary reaction 'pathways. ,apd mechanism governing~the interactions be@veen the feedstocks were elucidated.~L 'Because of me~o-phase nature of I$13BMand .~BM/tetradecane reactions, new capabilities had to be developed for model solution. 'A parsing algorithm was developed that automatically, 'duplicates all reactions in the mechanism, writing one instarice of the reaction for the gas phase"and one for the liquid phase. The parser~SO adh WUMPOrt reactions, allowing for communication between the gas phase and the liquid phase. Equilibrium between the phiises for each species was enforced by determining the value of the distribution' coefficient.~HYSIS was used to develop correlations for K* values of different compound classes is a @nction of molecular weight. Fu@errnore, values for the mass transfer coei%cients from the vapor to th~liquid phase were identified that ensured that equilibrium would be maintained. ". . .'.

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