| Biofuels play an important role in offering renewable energy worldwide, which poses the cardinal environmentally friendly energy solution in many fields. Hydrogenation is an essential process for aqueous bio-oil to be transformed into biofuel. Electrochemical hydrogen pump (EHP) reactor, with the same configuration as a polymer electrolyte membrane fuel cell, has provided an alternative to heterogeneous catalytic hydrogenation, due to its ability to produce dissociated hydrogen in situ on a catalyst surface with high efficiency. However, there are few concerns about the source of hydrogen for the anode of EHP hydrogenation reactors. In most cases, pure hydrogen is used as an anode feedstock to provide protons to the cathode hydrogenation reaction, which is mainly derived from non-renewable coal and natural gas.In this paper, it is proposed for the first time that EHP is used as a reactor to complete organic dehydrogenation and biomass derivative hydrogenation simultaneously. Owing to the unique membrane barrier effect of EHP reactors, dehydrogenation and hydrogenation reactions could run simultaneously at the anode and cathode compartments without interference. Incorporation of two reactions into one EHP reactor greatly simplifies the reactor equipment. Organic dehydrogenation reactants usually have lower electrochemical energy barriers than water, which contributes to the reduction of the electrolysis potential and energy consumptionBased on the proposal of bilateral EHP reactor,2-propanol EHP reactor and phenol EHP reactor catalyzed by Pt were investigated separately, then Pt-Nafion-Pt bilateral EHP reactor was run to couple two reactions. At anode, the effects of reaction temperature, current density, concentrations and reaction time on 2-propanol dehydrogenation catalyzed by Pt were investigated. Meanwhile, at cathode, the phenol hydrogenation process catalyzed by Pt in EHP reactor is studied, which has high catalytic selectivity to cyclohexanol (95.4%) and reaction rate (17.0 nmol cm-2 s-1). It is concluded that lower temperature and higher current density could promote selectivity to cyclohexanol.Due to high applied potential of 2-propanol dehydrogantion catalyzed by Pt, PtRu was chosen to obtain lower applied potential. Two methods are proposed in this work to get low and stable potential:one is to increase PtRu loadings to supply more activity sites, the other is pulse current operation to relief the potential jump and help to keep stable of the applied potential. As the result, the applied potential for 2-propanol dehydrogenation in EHP reactor can be controlled below 0.2 V, which is only 10% of the thermodynamic dissociation potential of water. At the cathode, Pt was replaced by Pd to increase cyclohexanone rate. After optimization of operation conditions and diffusion layers, it exhibits cyclohexanone as 11.0 nmol cm-2 s-1 at 80℃ under 18.9 mA cm’2, which is much higher than that reported in conventional three-phase reactor as well as the elevated hydrogenation rate by aqueous phase catalyzed by PVP-Pd. Then PtRu-Nafion-Pt/Pd bilateral EHP reactor were coupled successfully to gain comparable hydrogenation rate as phenol EHP reactor.Furthermore, bilateral EHP reactor coupled ethylene glycor and levulinic acid was investgaed. Compared with 2-propanol, ethylene glycol could provide higher available current density, reaching 130 mA cm-2 at 80℃. In the study of levulinic acid, it is founded that PtRu shows more excellent performance in hydrogenation process. Moreover, PtRu-Nafion-PtRu/Pt bilateral EHP reactor coupled those two reactions exhibits higher hydrogenation rate, due to avoiding the hydrogen permeation in hydrogenation EHP reactor. |
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