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In this paper we report the kinetics and chemistry of cellulose pyrolysis using both a Pyroprobe reactor and a thermogravimetric analyzer mass spectrometer (TGA-MS). We have identified more than 90% of the products from cellulose pyrolysis in a Pyroprobe reactor with a liquid nitrogen trap. The first step in the cellulose pyrolysis is the depolymerization of solid cellulose to form levoglucosan (LGA; 6,8-dioxabicyclo[3.2.1]octane-2,3,4-triol).LGA can undergo dehydration and isomerization reactions to form other anhydrosugars including levoglucosenone (LGO; 6,8-dioxabicyclo[3.2.1]oct-2-en-4-one), 1,4:3,6-dianhydro--D-glucopyranose (DGP) and 1,6-anhydro--D-glucofuranose (AGF; 2,8-dioxabicyclo[3.2.1]octane-4,6,7-triol). The anhydrosugars can react further to form furans, such as furfural (furan-2-carbaldehyde) and hydroxymethylfurfural (HMF; 5-(hydroxymethyl)furan-2-carbaldehyde) by dehydration reactions or hydroxyacetone (1-hydroxypropan-2-one), glycolaldehyde (2-hydroxyacetaldehyde), and glyceraldehyde (2,3-dihydroxypropanal) by fragmentation and retroaldol condensation reactions. Carbon monoxide and carbon dioxide are formed from decarbonylation and decarboxylation reactions. Char is formed from polymerization of the pyrolysis products. The pyrolytic conversion of cellulose was fitted to two different reaction models. The first model (Model I) combined the first-order kinetic model with a thermal-lag model that assumed the temperature difference between the thermocouple and specimen in TGA to be directly proportional to the heating rate. The second model (Model II) combined the first-order kinetic model with an energy balance that took into account the heat transfer at the sample boundary including the heat flow by endothermic pyrolysis reaction. Both models were able to adequately fit the empirical data. The kinetic parameters obtained from both models were similar. Cellulose pyrolysis had an activation energy of 198 kJ mol . Model I is computationally easier, however Model II is physically more realistic. Importantly, our results indicate that the intrinsic kinetics for cellulose pyrolysis are not a function of heating rate. During the pyrolysis of cellulose a thermal temperature gradient between the cellulose and heater can occur due to the endothermic pyrolysis reaction. A faster heating rate can magnify the thermal-lag, which leads kinetic derivations to artificial outcomes.

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The conversion of biomass compounds to aromatics by thermal decomposition in the presence of catalysts was investigated using a pyroprobe analytical pyrolyzer. The first step in this process is the thermal decomposition of the biomass to smaller oxygenates that then enter the catalysts pores where they are converted to CO, CO 2 , water, coke and volatile aromatics. The desired reaction is the conversion of biomass into aromatics, CO 2 and water with the undesired products being coke and water. Both the reaction conditions and catalyst properties are critical in maximizing the desired product selectivity. High heating rates and high catalyst to feed ratio favor aromatic production over coke formation. Aromatics with carbon yields in excess of 30 molar carbon% were obtained from glucose, xylitol, cellobiose, and cellulose with ZSM-5 (Si/Al = 60) at the optimal reactor conditions. The aromatic yield for all the products was similar suggesting that all of these biomass-derived oxygenates go through a common intermediate. At lower catalyst to feed ratios volatile oxygenates are formed including furan type compounds, acetic acid and hydroxyacetaldehyde. The product selectivity is dependent on both the size of the catalyst pores and the nature of the active sites. Five catalysts were tested including ZSM-5, silicalite, beta, Y-zeolite and silica-alumina. ZSM-5 had the highest aromatic yields (30% carbon yield) and the least amount of coke.

Studies in the last decade suggest that microwave energy may have a unique ability to influence chemical processes. These include chemical and materials syntheses as well as separations. Specifically, recent studies have documented a significantly reduced time for fabricating zeolites, mixed oxide and mesoporous molecular sieves by employing microwave energy. In many cases, microwave syntheses have proven to synthesize new nanoporous structures. By reducing the times by over an order of magnitude, continuous production would be possible to replace batch synthesis. This lowering of the cost would make more nanoporous materials readily available for many chemical, environmental, and biological applications. Further, microwave syntheses have often proven to create more uniform (defect-free) products than from conventional hydrothermal synthesis. However, the mechanism and engineering for the enhanced rates of syntheses are unknown. We review the many studies that have demonstrated the enhanced syntheses of nanoporous oxides and analyze the proposals to explain differences in microwave reactions. Finally, the microwave reactor engineering is discussed, as it explains the discrepancies between many microwave studies.