Victor Diakov

Methanol oxidative dehydrogenation in a catalytic packed-bed membrane reactor: experiments and model

Abstract Methanol oxidative dehydrogenation to formaldehyde over a Fe–Mo oxide catalyst was studied experimentally in three reactor configurations: the conventional fixed-bed reactor (FBR) and the packed-bed membrane reactor (PBMR), with either methanol (PBMR-M) or oxygen (PBMR-O) as the permeating component. The kinetics of methanol and formaldehyde partial oxidation reactions were determined independently from FBR experiments. A steady state plug-flow PBMR model, utilizing these kinetics and no adjustable parameters, fit the experiments accurately. It is shown experimentally and in accordance with the model that for given overall feed conditions, the reactor performance for methanol conversion and formaldehyde yield is in the order PBMR-M

Methanol oxidative dehydrogenation in a catalytic packed-bed membrane reactor

Abstract Methanol oxidative dehydrogenation to formaldehyde over a Fe-Mo oxide catalyst was studied experimentally in a packed-bed membrane reactor (PBMR) as well as in a conventional fixed-bed reactor (FBR) under identical overall reaction conditions. Two configurations for PBMR were investigated, using either oxygen (PBMR-O) or methanol (PBMR-M) as permeate, and the other reactant flowing over the catalyst bed. The influence of temperature, reactant residence time, feed concentration and nitrogen diluent split were studied. In the FBR experiments, selectivity to formaldehyde increased for increasing feed concentration of methanol and decreased when oxygen concentration was increased. This behavior indicated that the relative reactor performance should be in the order PBMR-O>FBR>PBMR-M, and this was confirmed experimentally.

Reactant distribution by inert membrane enhances packed-bed reactor stability

Abstract Operational stability of the packed-bed membrane reactor (PBMR) in methanol partial oxidation reaction over industrially used Fe–Mo oxide catalyst was studied at temperatures 200–250°C and excess oxygen feed conditions. The reaction network is as follows: CH 3 OH → (1) +1/2 O 2 HCHO + H 2 O → (2) +1/2 O 2 CO + H 2 O . Oscillations in carbon monoxide production were observed and their amplitude was taken as a measure of reactor operational instability. Three reactor configurations were investigated. The conventional fixed-bed reactor (FBR), with both reactants fed directly to the catalyst bed, exhibited the largest oscillation amplitude. The PBMR with oxygen permeating through the membrane (PBMR-O) and methanol sent directly to the catalyst bed, exhibited decreased oscillation amplitudes, while the PBMR with methanol permeating the membrane (PBMR-M) and oxygen fed directly, was found to be stable in most cases. It is hypothesized that the instability in reactor operation is generated by the spatial non-uniformity in reaction conditions along the catalyst bed coupled with strong methanol adsorption. The consumption of methanol along the reactor alters the propagation rate of deviations in methanol concentration from its steady-state value. As shown by model considerations, this may result in packed-bed operational instability. Stability enhancement, obtained when using an inert membrane for distributed addition of methanol in the PBMR-M, is due to a more uniform methanol concentration profile along the catalyst bed. It is shown that distributed addition of a reactant to catalyst bed is an effective remedy from spatial nonuniformity induced instabilities.

Methanol oxidative dehydrogenation in a packed-bed membrane reactor: yield optimization experiments and model

For the reaction involving methanol oxidative dehydrogenation to formaldehyde: CH 3 OH+1/2O2→CH 2 O+H 2 O+1/2O2→CO+2H 2 O, the performance of the packed-bed membrane reactor (PBMR) is compared with that of the conventional fixed-bed reactor (FBR) over a wide range of operating conditions. An experimentally validated reactor model is used for this purpose. It is found, both by simulations and experimental observations, that relative reactor performance depends strongly on the operating conditions. Using formaldehyde yield as the basis for optimization, optimal reactor performances for a fixed catalyst mass are determined and compared. The results predict higher optimal formaldehyde yield for the PBMR with oxygen fed via the membrane. The optimal reactor performance in this configuration is also less sensitive to variations in operating conditions and exhibits essentially 100% formaldehyde yield over a wide temperature range.

Novel Chemical Mixtures for Hydrogen Generation by Combustion

*† ‡ Fuel cells are attractive power sources for various terrestrial and aerospace applications, since they provide much higher specific energy than batteries. Their deployment, however, is hindered by the lack of efficient methods for hydrogen storage. Metal borohydrides, such as sodium borohydride, are efficient hydrogen-storing compounds but their use requires either expensive catalysts or mixing with solid oxidizer salts, which can produce harmful byproducts. To solve this problem, we propose sodium borohydride/aluminum/water mixtures for combustion-based generation of hydrogen. In the proposed mixtures, the highly exothermic reaction of aluminum with water assists hydrolysis of sodium borohydride, eliminating the need of catalyst. Upon ignition, such mixtures exhibit selfsustained propagation of combustion wave with simultaneous release of hydrogen stored in sodium borohydride and water. We report mixture ingredients and sodium borohydride/metal mass ratios required for stable generation of hydrogen, with ~7 wt% yield and environmentally benign solid byproducts.