Catalytic Wet Air Oxidation Removal Of Phosphine Research

In this thesis, low concentrations of phosphine(PH3) were subject investigated and catalytic wet air oxidation was used to remove phosphine gas. The appropriate absorption solution and catalysts were screened, and the influence factors, such as reaction temperature, gas flow rate, O2 concentration and the pH of absorption solution, on the purification efficiency of PH3 were studied in detail. Kinetics of catalytic wet air oxidation of PH3 has been studied primarily, and the influences of pH and concentration of absorption solution, O2 concentration on the absorption rate were investigated. Finally, some techniques such as Fourier transform infrared spectrometry(FT-IR), X-ray photoelectron spectroscopy(XPS), X-ray powder Diffraction(XRD) and the atomic absorption spectrophotometry were adopted to analyse the solid products collected at different reaction time. The mechanism of catalytic wet air oxidation of phosphine was discussed. Main results obtained as follows:(1) Screening adsorption solution and catalystsBecause of the alkalescence and reducibility of PH3, acidity solution, oxidation solution and several salt solutions of active metals were chosen as adsorption solution. Results showed that Cu2+ was active, purification efficiency of PH3 removed by CuCl2,Cu(NO3)2,CuSO4 and Cu(CH3COO)2 were investigated, CuSO4 performed the most stability than others. Therefore, CUSO4 was chosen as the adsorption in this thesis.Purification efficiency of PH3 with a few catalysts supported metals and unsupported metals in CUSO4 solution were investigated. The unsupported catalysts were prepared with co-precipitation and the supported catalysts were prepared with impregnation. CuSO4-CuO performed best in all of catalysts for purification efficiency of PH3 under the same reaction conditions, which could keep 0 mg/m3 in the outlet for 600min.(2) The influence of reacting conditions on purification efficiency of PH3Catalytic wet air oxidation of PH3 with CuSO4-CuO was studied; the effects of reaction temperature, gas flow rate, O2 concentration and the pH of absorption solution on purification efficiency of PH3 were researched. Results showed that the purification efficiency of PH3 increased with the increasing of reaction temperature. Within the condition of high-temperature, the tendency of purification efficiency was slow. While the gas flow rate increased, the contact time of PH3 and absorption solution became short, the purification efficiency of PH3 decreased. The purification efficiency of PH3 was enhanced significantly by increasing the oxygen concentration. With the increasing of PH3 concentration, the PH3 handled in per unit time increased, which made the purification efficiency of PH3 decrease. The analysis indicated that the best purification efficiency of PH3 could be obtained at the pH of CuSO4 solution of 3-4. The purification efficiency of PH3 continuously increased with increasing the dosage of catalysts.(3) Kinetics and mechanism of catalytic wet air oxidation of phosphine with CuSO4-CuO was studiedKinetics of catalytic wet air oxidation of phosphine with CuSO4-CuO was studied. The process of this reaction was a gas-liquid-solid three-phase reaction and it was also revealed by double film theory. The results showed that this reaction of catalytic wet air oxidation of phosphine with CuSO4-CuO was an interface instantaneous reaction. It was found that there was a good linear correlation between the lognormal of phosphine concentration and the consumed time at various different temperatures. Therefore, this gas-liquid-solid three-phase reaction was first-order reaction at the range of the experimental temperature and the apparent activation energy was 36707.97 J/mol. When the Cu2+ concentration of absorption solution and the pH value ranged from 0.075 to 0.1mol/L and from 3 to 4, respectively, the absorption solution was beneficial to the absorption rate of PH3 with the oxygen concentration of 3%.Mechanism of catalytic wet air oxidation of phosphine with CuSO4-CuO was studied. Reaction products collected at different reaction time were analyzed by FT-IR, XPS, XRD and the atomic absorption spectrophotometry. The results showed that the P of PH3 was oxidized to+5, it existed with PO43-,HPO42-, H2PO4-. There were CuO, Cu2O, Cu in the solid reactant, CuO was decreased, and CU2O was added with reaction continuing. The Cu2+ concentration in absorption solution first increased and then decreased with reaction continuing. Results showed that CuO not only provided Cu2+ but also catalytic oxidation of low valent copper ion.