Study On Hydrogen Production From Electro-oxidation Organic Wastewaters By A Packed-bed Electrode Reactor

Electrochemical oxidation as a debiodegradible organic wastewater treatment technology which has received much attention from researchers, especially the packed-bed electrode reactor(PBER) has been developing rapidly in recent years. However, the study on the mechanism of hydrogen production from PBER electro-oxidation organic is not yet in existence. In order to overcome this, ?-Al2O3 was used as substrate for fabricating of single component and composite type particulate electrodes with impregnation-calcination processes, that carried out phenol simulation wastewater, and analyzed energy consumption of PBER system. The phase composition, micro-morphology and electrocatalytic activity of the newly prepared particles were characterized by N2 adsorption stripping desorption, X-ray diffraction(XRD) and scanning electron microscopy(SEM) techniques as well as electrochemical test, and the best electrochemical performance of supported particulate electrodes was optimized to experimental operating conditions.Based on the above analysis, the mechanism of simultaneous hydrogen gas formation and phenol removal in packed bed electrode reactor was preliminarily investigated. The main conclusions of this paper are summarized as follows:(1) Bulk electrolysis experiments were conducted with simulated phenol wastewater using Mn/?-Al2O3,Cu/?-Al2O3,Sn/?-Al2O3,Ni/?-Al2O3 as fillings in packed bed electrochemical reactor. The results indicated that, the removal rate of phenol and COD showed negative growth due to the active components of Mn supported particulate electrode fall off seriously, and the degradation efficiency of Cu/ ?-Al2O3 was slightly better than that of activated alumina, Sn/?-Al2O3 and Ni/?-Al2O3 exhibited to highly electrocatalytic oxidation activity. At the same time, the UV spectrum suggested that the single component catalyst of Sn was less accumulated quinone intermediates compared with other particles.(2) The composite particle electrode with 0%, 6%, 12%, 20% molar quantity of Ni doped Sn and Sb metallic oxide was prepared, respectively(Ni relative Sn molar quantity, the molar ratio of Sn:Sb to 10:1). The water treatment experiment results determined that, the phenol removal efficiency of Ni content 6% particulate electrode showed the highest, it reached about 91.79%. At the time of COD was 79.64%, average current efficiency(ACE) and energy consumption(ESP) was 88.50%, 17.64 kWh/kgCOD, respectively. N2 adsorption desorption results described that supported ?-Al2O3 significantly reduced its specific surface area. XRD and SEM spectrum could be found that laboratory preparation of NiO/?-Al2O3, SnO2-Sb/?-Al2O3 particles surface did not appear obvious characteristics of metal oxide diffraction peaks, their SEM images also hadn’t significant morphology; it was the tin dioxide that had the strongest lattice diffraction peaks and the uniform distribution on the surface of SnO2/?-Al2O3. While, after doped with Ni, the crystallinity for SnO2-Sb/?-Al2O3 improved markedly, XRD diagram of SnO2 and Sb2O5 diffraction peaks increased with the increasing of Ni content, and a continuous immobilized membranes arose on composite particle electrode contained 6% content of Ni. The electrochemical test results revealed that, SnO2-Sb-Ni(6%)/?-Al2O3 possessed higher oxygen evolution potential(1.92V), the larger the voltammetric charge(3.670 C/cm2), the smallest charge transfer resistance(74.7 ?), and the maximum linear fitting curve slope(196.4) which iap(oxidation peak current) and v1/2(square root of the scan rate) of CV curve in potassium ferrocyanide/potassium ferricyanide system. All above illustrated that electrochemical activity of SnO2-Sb-Ni(6%)/?-Al2O3 particulate electrode was optimal.(3) The operating conditions optimization experiments of PBER system demonstrated that SnO2-Sb-Ni(6%) / ?-Al2O3 in the experimental range of the best current density was 5 mA/cm2, the optimal electrolyte content was 4%, the overall performance of the best influent flow rate was 1.2 L/h. Surveyed on degradation characteristics of phenol wastewater from current density, electrolyte content and flow rate can be found that these factors weren’t ignored, too low or too high was not conducive to the catalytic degradation of organic compounds.(4) The main reactions of degradation of organic compounds by the PBER when testing the CV curve of the particulate electrode system in different electrolyte, including the direct and indirect oxidation, and the modified ?-Al2O3 particles could significantly enhance its direct oxidation ability; SnO2-Sb-Ni(6%)/?-Al2O3 system had a maximum valid acidity accumulation concentration according to calculation of the specific capacitor value which the particulate electrodes. Simultaneously, the optimal state of hydrogen production coupled with organic matter electrochemical oxidation degradation by PBER system that the key was to particle electrode material with high specific capacitance and the pH value of the solution rose sharply corresponding concentration of COD critical point.