Optimization And Kinetics Of Catalytic Oxidation Ph₃ In Liquid Phase

Phosphorus tail gas and exhaust gases from confined calcium carbide furnace are precious resources which are rich in CO. They can become the raw material of Cl if they can be purified. The deep purification of phosphine is one of the main difficulties in the field of gas purification. The purification method of phosphine could be classified into dry method and wet method. Dry method mainly included physical adsorption, catalyzed oxidation with impregnated activated carbon and burning. Wet method mainly included chemical absorption method. It used the oxidative of the strong oxidant to react with PH3 to remove PH3, but the purification efficiency of which depended on the concentration of oxidant and the purification efficiency decreased rapidly. Thus there were several shortcomings in the method such as higher operating cost, uneven purification efficiency and poor operability for device. At present, using metal ions solution to purify phosphine has not been reported.The solution of metal ions was used as a self-screened catalyst of liquid phase catalytic oxidation to purify phosphine. Based on the purification efficiency of phosphine and stability, Pd(Ⅱ)-Mn(Ⅱ), Pd(Ⅱ)-Fe(Ⅲ) and Pd(Ⅱ)-Cu(Ⅱ) were screened as catalysts.The catalyst Pd(Ⅱ)-Cu(Ⅱ), which provided with high activity, good stability and easy regeneration, was the optimal selection by studying catalyst proportion, temperature, pH, oxygen content, inlet gas flow and PH3 concentration on the catalytic oxidation to phosphine. Mass transfer, reaction kinetics and the mechanism also have been further studied.(1) Screening of the catalysts and optimizing of the dynamics conditionsUsing metal ions solution purifying PH3 at low temperature, atmospheric pressure, a series of catalysts such as Pd(II)-Mn(II), Pd(II)-Fe(III) and Pd(II)-Cu(II) and so on were selected. The purification efficiency can reach percent.The purification efficiency of Pd(II)-Mn(II) and'Pd(II)-Fe(III) can reach 100%, but it declined rapidly in a short period of time and changing dynamics conditions seemed did no work to activity and stability. The ions changing from reduced state to oxidation was the control step. Pd(II)-Cu(II) has better activity and stability. The results showed that the optimal proportion of Pd(Ⅱ) and Cu(Ⅱ) was 1:10, the oxygen content 2% could meet the requirements and the optimal pH and temperature was 1.0 and 37℃respectively. When the concentration of Pd(Ⅱ) was 0.03mol/L, the purification efficiency of PH3 could reach 100% within 850min. Compared with N2, the purification efficiency and stability of CO was better as the carrier gas than that of N2, it was inferred that the CO could make oxygen activated.(2) Mass transfer and reaction kinetics of PH3 absorption with Pd(Ⅱ)-Cu(Ⅱ)The solution of Pd (Ⅱ)-Cu(II)was used as the catalyst of liquid-phase catalytic oxidation to purify phosphine, and the mass transfer and reaction kinetics of the catalytic oxidation of PH3 were studied in a double-stirred kettle. The experimental results indicated that the absorption reaction was instantaneous reaction at interphase of liquid and gases. The system was stable when the oxygen content was 20% and the proportion of Pd (Ⅱ) and Cu (Ⅱ) was 1:10. The Ha number was 552.56, the intrinsic reaction rate was very speedy and could make the transfer rate faster about 552.65 times; A comparison was made between the experimental enhancement factor and the computational enhancement factor from the models. The actual enhancement factor was 593.63; The disparity between actual enhancement factor and computational enhancement factor with double film model was 9.65%. But the deviation between actual and computational enhancement factor with surface renewal model or penetrating model. So the surface renewal model and penetrating model were more close to the real situation than double film model.(3) Mechanism of the catalytic oxidationIt was showed that phosphine could be smoothly oxidized into phosphates and the oxidation products were basically PO43- by Raman. And it was proved that selectivity ratio of the catalytic oxidation to PO43- reached 89%.These catalysts could purify phosphine in exhaust at low temperature and normal pressure. As a active, stable and miscellaneous catalyst, Pd(Ⅱ)-Cu(Ⅱ) worked in mild condition and the conditions was easy to manipulate.