Prof. Roger Ruan, University of Minnesota, USA
Title:Catalytic microwave assisted pyrolysis of solid waste for fuels, energy and chemicals production
Abstract: Our society currently faces the dual challenge of resource depletion and environmental pollution. Converting sustainable biomass and recycled plastic wastes into energy and fuel products provides an attractive solution to this challenge. Among the various conversion technologies, microwave assisted pyrolysis serves as a promising alternative to conventional pyrolysis technology due to several unique benefits inherent to its dielectric heating mechanism.
In order to improve feasibility and scalability of the microwave-assisted pyrolysis process, a novel system of continuous microwave-assisted pyrolysis (CMAP) featuring a mixing SiC ball bed was developed and first tested for fuel production from wood pellets. High quality syngas was produced from this process. Specifically, at temperature of 800oC, producer gas with a high energy content of 18.0 MJ/ Nm3 and a high syngas (H2+CO) content of 67 vol.% was obtained at a gas yield of 72.2 wt.% or 0.80 Nm3/kg d.a.f. wood pellets. Downstream condensation and physical adsorption lowered the tar concentration from 7.83 g/Nm3 at the exit of pyrolysis reactor to below the detection limit at the end of the process. Energy balance analysis showed that a cold gas efficiency of 73.3% was achieved at 800oC, which consumed 7.2 MJ electrical energy per kg of wood pellets. Further measures to improve the energy efficiency could potentially reduce the electricity consumption to 3.45 MJ/kg wood, enabling a net electricity production.
Then, pyrolysis of different plastic wastes for fuel production was conducted in the CMAP system. Overall, plastic wastes, especially polyolefin base plastics, produced much higher heating value byproducts, and relatively simpler compositions, compared to biomass, thus making plastic wastes a more desirable feedstock to produce high quality fuels, energy-efficiently. At 560oC, the highest liquid product yield, 47.4%, was obtained for thermal pyrolysis of HDPE, together with 24.5% wax product. The PP with fillers, (i.e. the mineral, talc) acted as a catalyst and showed noticeable cracking activity. The application of catalysts in the CMAP process has shown a significant impact on product yields and composition. Under a temperature of 620oC, incorporating ZSM-5 catalysts in a secondary catalyst bed, enabled the elimination of wax product and an increase of liquid yield to 48.9%, and the liquid products contained considerably higher contents of gasoline-range aromatics (45.0%) and isomerized aliphatic (24.6% ) contents. However, ZSM-5 catalysts also showed a tendency of rapid deactivation, and loss of activity at a feedstock/catalyst ratio of 5. Energy balance analysis of the process showed that 5 MJ of electrical energy were required to process 1kg of HDPE with the CMAP system, giving a total energy efficiency as high as 89.6%Furthermore, 6.1 MJ of electrical energy could potentially be generated from the gas products alone, making the process energy self-sufficient.
In order to address a series of issues facing the application of catalysts in scaled-up pyrolysis systems, a structured catalyst of SiC foam supporting ZSM-5, was developed and tested for ex-situ catalytic upgrading of biomass pyrolytic vapors. A hydrothermal synthesis method was used to synthesize the catalysts, which resulted in a thin layer of ZSM-5 crystals firmly attached to the structure of a microporous SiC foam material. Results suggest that the structured catalyst was more active and stable, compared to the randomly packed bed of catalysts, and also had the advantages of reduced pressure drop and enhanced heat and mass transfer. Therefore, this structured catalyst may serve as a promising candidate for future catalysts applied in large scale pyrolysis operations.
Lastly, a series of catalysts were tested to improve the yield and quality of the liquid hydrocarbon products from the plastic waste pyrolysis, with the aim of maximizing naphtha fractions for new plastic production. Notably, relay catalysis of Al2O3 followed by ZSM-5 achieved up to 100% conversion into monoaromatics and C5 -C12 alkanes/olefins at a catalyst to plastic ratio of 4:1. To further mitigate the aromatic formation, a novel approach of combining two catalytic reforming zones was developed and tested, where the first catalytic reforming zone was intended to improve the cracking of polyolefins into C5-C12 olefins, and the second, lower-temperature catalytic reforming zone was intended for the hydrogenation process to convert C5-C12 olefins to C5-C12 alkenes without high pressure or the use of external hydrogen. The tests were very successful and very promising results (60-75% C5-C12 alkanes, 3-5% C5-C12 olefins, 5-15% mono-aromatics) were obtained as hypothesized.
To conclude, our studies indicated that the catalytic microwave-assisted pyrolysis is a low-cost and highly efficient technology for solid wastes utilization.
Prof. Jun He, University of Nottingham Ningbo China, China
Title:Cost-effective Non-precious Metal Catalysts for Low-temperature Formaldehyde Oxidation
Abstract: Formaldehyde (HCHO) is one of the most common indoor air pollutants which causes adverse health effects, and a known carcinogen which has been proven to cause nasopharyngeal cancer and leukemia, over prolonged exposure. Catalytic oxidation, amongst the known techniques for HCHO removal, is the most promising, as it is capable of completely mineralizing HCHO into CO2 and H2O. Although noble metal based catalysts are very active for HCHO oxidation, their practical application is limited by cost and availability. Transition metal based catalyst offer a promising cost-effective alternative. However, improving their catalytic performance is critical to enhancing their competitiveness for practical and industrial application in indoor HCHO abatement. Birnessite-type manganese oxide (δ-MnO2) is a promising transition metal catalyst for HCHO removal from the indoor environment. Nonetheless, not much has been reported in the enhancement of its catalytic activity. This research focused on developing novel strategies to enhance the catalytic activity of δ-MnO2 through surface defect engineering using doping technique; the use of oxygen carrier; and fine-tuning the concentration of the cations present in its interlayer spaces. The developed catalysts were characterized and evaluated for HCHO oxidation. The surface reaction mechanism of HCHO oxidation was investigated via in situ Diffuse Reflectance Infrared Fourier Transform (DRIFTS).
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