| This paper resumed the characteristics and treatment status of MDEA wastewater that generated in the process of natural gas purification. Aiming at the characteristics of oxidation resistance and biological toxicity of MDEA, three dimensional electrode technology was proposed to efficiently treat this kind wastewater. In this paper, using DC and pulse square wave as power supply modes, MDEA wastewater was treated by the self-made three-dimensional electrode device.The wave characteristics of DC and pulse square wave in water were comparative studied. The results indicated that the waveforms of the two power supply modes would not be distorted in the three-dimensional electrode reactor. For pulse power supply, the input voltage, frequency and duty cycle were independent and without interference each other. But changing any one parameter would lead to the variation of output energy, which would result in different electrochemical treatment effect. In addition, there was an obvious oscillation and attenuation of the peak of pulse discharge between the filled particles, which indicated the existence of pulse capacitor in the system. And the capacitance value increased with the increase of filled particles. The increased capacitance with stronger charge storage capability would generate greater output voltage and current.The OH, H2O2 and O3 created in three-dimensional electrode reaction system were detected through clear water experiments, which concluded that the generation of active substances were higher under pulse power supply. This moment, the OH production was about 2 times of DC power supply, the yield of H2O2 was 0.322 mmol/L and 0.224 mmol/L, and the output of O3 was 0.19 μmol/L and 0.05 μmol/L, respectively. By SEM analysis of electrodes treated, the titanium anode coated ruthenium and iridium appeared many surface cracks, the surfaces of graphite cathode and particle electrode were attached with more massive and spherical particles, and the pore structure was blocked, which indicated that under the DC power supply the electrode system developed more serious passivation and corrosion. By cyclic voltammetry and polarization curves analysis, the peak currents were 0.071 A and 0.092 A and the corrosion currents were 0.0196 mA and 0.0108 mA, respectively, for the processed electrodes in three electrode system. So, the titanium anode with pulse power supply had better catalytic activity. Moreover, with the increase of cell voltage, the particle current amplitudes were 5.16～9.22 mA and 5.88～11.75 mA, respectively. Therefore, particle current was greater when using pulse power supply.The degradation effect of MDEA wastewater was different using three-dimensional electrode of different power supply mode. Compared with the DC power supply, under pulse power supply the COD removal efficiency was increased by 12% and the degradation rate increased by 46.6%. Under the optimal condition of pulse electrolysis with current density of 80 A/m3, frequency of 3 kHz, duty ratio of 50%, the maximum removal rate of wastewater COD obtained was 57.8%, the minimum energy consumption per unit volume reached was 21.1 kw/m3, the highest energy use efficiency achieved was 23.9 g/kwh. Based on the analysis of IR and GC-MS, it was concluded that the degradation pathway of MDEA under DC power supply was like ①.①:The bond of MDEA breaking only occurred in the C-N of -CH2- to generate MMEA first, and formed ethanol amine and ethylene glycol. The degradation pathway of MDEA under pulse power supply was also included ②.②:There was bond breaking between C and N of-CH3, and MDEA degraded into diethanolamine first, and be further oxidation degradation relied on OH, H2O2, O3, etc. Through establishment of dynamic model and test of equation, the degradation of MDEA were according with the first order kinetic equation by three dimensional electrode methods of DC and pulse power supply. |
PDF Full Text Request