Minimally-destructive evaluation of durian maturity based on electrical impedance measurement

Electrical impedance spectroscopy was investigated to model the dry matter content of durian using partial least squares regression. Measurements of the impedance were taken on the stem and the rind of durian samples at various stages of maturity based on the number of days after anthesis. Plots of the relationship between resistance and reactance, and the change in impedance and capacitance with respect to frequency in a range of 1–200 kHz were explored to determine the optimal frequencies associated with variation in the number of days after anthesis. The impedance parameters at frequencies of 1, 41 and 200 kHz were employed to model the dry matter content of the pulp. The reactance of the cross section of the stem and the capacitance of the rind were found to predominantly contribute to the prediction of the dry matter content. Selected impedance parameters using a stepwise regression could be used to classify durian samples into an immature class and mature class with less accuracy of 83.3%.     

Catalytic partial oxidation of CH4 over bimetallic Ni‐Re/Al2O3: Kinetic determination for application in microreactor

The activity of a novel Ni‐Re/Al₂O₃ catalyst toward partial oxidation of methane was investigated in comparison with that of a precious‐metal Rh/Al₂O₃ catalyst. Reactions involving CH₄/O₂/Ar, CH₄/H₂O/Ar, CH₄/CO₂/Ar, CO/O₂/Ar, and H₂/O₂/Ar were performed to determine the kinetic expressions based on indirect partial oxidation scheme. A mathematical model comprising of Ergun equation as well as mass and energy balances with lumped indirect partial oxidation network was applied to obtain the kinetic parameters and then used to predict the reactant and product concentrations as well as temperature profiles within a fixed‐bed microreactor. H₂ and CO production as well as H₂/CO₂ and CO/CO₂ ratios from the reaction over Ni‐Re/Al₂O₃ catalyst were higher than those over Rh/Al₂O₃ catalyst. Simulation revealed that much smoother temperature profiles along the microreactor length were obtained when using Ni‐Re/Al₂O₃ catalyst. Steep hot‐spot temperature gradients, particularly at the entrance of the reactor, were, conversely, noted when using Rh/Al₂O₃ catalyst. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1691–1701, 2018     

Comparative numerical evaluation of autothermal biogas reforming in conventional and split-and-recombine microreactors

A new microreactor design featuring embedded passive mixing elements was tested as a means to enhance autothermal reforming reaction of biogas over a novel ReNi/γ-Al₂O₃ catalyst. To determine an optimal condition that would result in completely converted biogas with H₂/CO product ratio of around one and minimal hot spot formation inside the reactor, use of various inlet O₂ and H₂O concentrations and inlet temperatures were numerically investigated. The influence of inlet reactant velocity on the reactor effectiveness was then studied at the optimal condition. Performance of a straight-channel microreactor was also studied and compared with that of the novel microreactor. The O₂:H₂O:CO₂:CH₄ ratio of 25:5:28:42% (v/v) and inlet temperature of 730 °C were noted as the optimal condition for the novel microreactor. Complete biogas conversion over a wider range of inlet Reynolds number, lower required catalyst loading to achieve the desired reactor performance, higher H₂ and CO selectivities and reduced hot spot formation were noted as the advantages of the novel microreactor.