27 de ago de 2015

Publicações: International Journal of Hydrogen Energy e Journal of Thermal Analysis and Calorimetry

This study aims at analyzing the potential application of the liquid effluent coming from acatalytic ethanol dehydrogenation reactor as a fuel blend or additive for internal combustion engines, and also of the hydrogen produced, as fuel for a polymer electrolyte fuel cell (PEMFC). The liquid effluent is obtained by the catalytic reaction of ethanol over Cu/ZrO2 at different contact times of the reactant with the catalyst bed. Subsequently, highperformanceliquid chromatography analysis and heat of combustion measurements are used to analyze the composition and the heat of combustion of the liquid effluent trapped by cold condensation at 271.65 K. In parallel, the effect of the presence of residual parts of the constituents of the liquid effluent in the H2 stream on the operational characteristics of a PEMFC having a Pt/C anode and cathode is investigated. Results show that the liquid fuel blend obtained from ethanol dehydrogenation has a heat of combustion higher than that of ethanol, and it is essentially formed by un-reacted ethanol, acetaldehyde and ethyl acetate. Thermodynamic calculations evidence a good agreement with the liquid effluent composition and its respective combustion enthalpy. Polarization curves of a PEMFC supplied with hydrogen containing 1000 ppm of acetaldehyde and ethyl acetate evidence performances comparable to that of the same system when fed with pure hydrogen, while with ethanol significant loss of activity is observed.

Isoconversional kinetic method (model- free kinetics) was used in this study to determine the activation energies (Ea) of the combustion process of five different biomass samples, namely pine sawdust, sugarcane bagasse, coffee husk, rice husk and tucuma˜ seeds, widely available in Brazil. Two different atmospheres with 20 % O2:N2/O2 (conventional combustion) and CO2/O2 (typical oxy-fuel combustion) were studied. Thermogravimetric (TG) and derivative thermogravimetric (DTG) curves were used to obtain experimental data on the thermal degradation behavior of the biomasses, and the activation energy values were obtained for hemicellulose, cellulose and residual lignin separately. The results show that the Ea obtained for N2/O2 ranged from 68 to 236 kJ mol-1 for hemicellulose, 119 to 209 kJ mol-1 for cellulose and 87 to 205 kJ mol-1 for residual lignin, depending on the type of biomass.  Under CO2/O2 atmosphere, Ea showed decreases, in average, 35 % for hemicellulose and 26 % for cellulose, in comparison with N2/O2 atmosphere. However, a 6 % increase was observed for the residual lignin. These changes can be understood by differences between CO2 and N2 gas properties. However, the results show that the variation in the Ea is more dependent on the type of biomass than on the atmosphere at which the combustion takes place.


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