The catalytic degradation of linear low-density (lldPE) polyethylene over HY-zeolite catalyst was studied in a semi-batch reactor. One of the important problems encountered during catalytic pyrolysis of macromolecules is the contact with the catalyst, which is known to affect the product distribution and the quality of the coke formed. A pre-degradation procedure was introduced to achieve efficient contact between the LLDPE macromolecules and the catalyst. The influence of the pre-degradation to the reaction conditions including holding time, temperature, polymer to catalyst ratio and flow rate of carrier gas was examined. Moreover, the pre-degradation results were compared with the results obtained using normal mixing procedure. The results obtained showed that, pre-degradation promotes the liquid fraction by a factor of more than one-fold increase at the expense of the gas fraction and the coke yield. The optimal liquid fraction with pre-degradation was obtained at low reaction temperature and catalyst amount respectively, i.e. high polymer to catalyst ratio, making it economically viable method for the degradation of lldPE.

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Biomass pyrolysis is a promising technology for fuel and chemical production from an abundant renewable source. It takes place usually in two stages; non-catalytic pyrolysis with further catalytic upgrading of the formed pyrolysis oil. The direct catalytic pyrolysis of biomass reduces the pyrolysis temperature, increase the yield to target products and improves their quality. However, in such one-stage process the contact between biomass and solid catalyst particles is poor leading to an excessively high degree of pure thermal pyrolysis reactions. The aim of this study was to enhance the catalyst-biomass contact via co-pressing of biomass and catalyst particles as a pre-treatment method. Catalytic pyrolysis of biomass components with HY and USY zeolites was studied using thermogravimetric analysis (TGA), as well as experiments in a pyrolysis reactor. The liquid and coke yields were characterized using gas chromatography, and TGA respectively. The TGA results showed that the degradation of the co-pressed cellulose occurred at lower temperatures compared to the pure thermal degradation, as well as catalytic degradation of non-pretreated cellulose. All biomass components produced better results using the co-pressing method, where the liquid yields increased while coke/char yields decreased. Bio-oil from catalytic pyrolysis of cellulose with HY catalyst mainly produced heavier fractions, while in the presence of USY catalyst medium fraction was mainly produced within the gasoline range. For hemicellulose catalytic pyrolysis, the catalysts had similar effects in enhancing the lighter fraction, but specifically, HY showed higher selectivity to middle fraction while USY has produced higher percentage of lighter fraction. Using with both catalysts, co-pressing had the best effect of eliminating the heavier fraction and improving the gasoline range fraction. Spent catalyst from co-pressed sample had lower concentrations of coke/char components due to the shorter residence times of volatiles, which suppresses the occurrence of secondary reactions leading to coke/char formations.

Catalytic and noncatalytic copyrolysis of plastic and heavy oil was studied using thermogravimetric analysis (TGA), pyrolysis reactor experiments, and GC analysis of the formed liquid. As revealed by the TGA experiments, predegradation as a pretreatment method had further lowered the decomposition temperature of polypropylene− (PP−) bitumen mixtures and reduced the severity of catalyst deactivation by coke. The presence of PP in the copyrolysis had increased the liquid yield and decreased the coke yield. The presence of PP in the copyrolysis had shifted the product distribution from heavier to lighter fractions while copyrolysis using predegradation displayed the highest percentage of C 5 −C 9 and C 9 −C 14 fractions. Based on the performance of the catalysts, C 5 − C 14 was produced in the following order, HY > 20% USY > APC > K30, while C 14 −C 20 was produced in the reverse order of K30 > 20% USY > APC > HY. Indepth analysis of the percentage product distribution confirmed the availability of synergies during the thermal copyrolysis of PP and Ex-Mwambe heavy oil. Predegradation as pretreatment method has intensified the contact between the two feed constituents, enabling synergistic effects to materialize. The excess percentage of C 5 −C 9 and the insignificant amount of C 20 + produced from the thermal copyrolysis affirmed the possibility that the presence of PP facilitates the conversion of waxy hydrocarbons into lighter products. the conversion of waxy hydrocarbons into lighter products. Coke components from predegradation method are more volatile while the coke formed during normal mixing pyrolysis contained a higher percentage of hard coke.

A mechanistic model on catalyst deactivation by coke formation in a continuous stirred tank reactor (CSTR) has been developed in the paper. Catalyst deactivation by coke formation was treated as a surface reaction. Four reaction mechanisms representing coke formation through different routes were proposed. The evolved system of ordinary differential equations (ODEs) was solved numerically using MATLAB. This approach was validated by applying it to the skeletal isomerization of 1-pentene over ferrierite. Simulation results were compared qualitatively to those obtained from the literature. Simulation results indicated that coke formation is an extremely rapid process with fast formation of coke components on the strongest acid sites leading to final coke. The coke deposition is slower at higher residence times resulting in more stable product formation and weaker deactivation. The results obtained from this work revealed that the developed model is indeed able to successfully demonstrate the most essential features of catalyst deactivation by coke formation and are in agreement with the findings in the literature. Future work is aimed to extend the study to different reactors such as a plug flow reactor, in addition to analysis of the reaction system’s sensitivity to variables such as temperature and pressure.