Catalytic Phosphine Decomposition Catalyst For The Preparation Of High Purity Phosphorus

High purity Phosphor is the basic and precondition of fine chemical industry. In China, the high purity phosphorus especially semi-conductor level mainly depend on importation, so it is expensive. The technique of its preparation is significance to whole fine chemical industry of China. At present, there are two typical methods to prepare high purity Phosphorus: rectifying phosphor and decomposing PH₃ to attain high purity phosphor. The purity of phosphorus made by the former method is not high enough. The latter uses the by-production PH₃ purified and dried in producing hypophosphorous acid sodium as material. It is decomposed to high purity phosphor catalyzed by catalyst. The key of this technique is to prepare appropriate catalyst.In this dissertation, three series of Co-based amorphous alloy catalysts-- CoB, CoP, CoPB and ternary Fe-based alloy FeBP, FeCuP and FePdP particles were prepared by chemical-reduction method. ICP, BET, DSC, SEM and TEM technologies were used to characterize their compositions, surface areas, structures, thermal stabilities and morphologies. Decompositing PH₃ was selected as the probe reaction to investigate their catalytic performances. Effects of preparation methods and conditions on the structure,physical properties and catalytic activities of these amorphous alloys were studied. Main points of this paper are listed as follows:I. Research on the preparations, properties and applications of Co-P,Co-B,CoBP amorphous alloys and supported amorphous alloy CoP/TiO₂1. The preparation, properties and application in decomposing PH₃ of Co-Pâ‘ Co-P was prepared by chemical reduction deposition method. Reaction conditions have significant effects on the properties of alloy, e.g., the concentration and their molar ratio of reactants, the reaction temperature, the pH value of the reaction solution, the additive and inducement can all influence the reaction rate and composition of samples, especially the molar ratio of NaH₂PO₂·H₂O to the metal ions. â‘¡Supported alloy CoP/TiO₂ was prepared by inducement-sediment method. the mol ratios of Co to P in supported and unsupported Co-P amorphous catalysts are approximate due to the same prepared procedures and conditions, such as plating solution, temperature, PH value and stirring speed. The supported alloy Co-P/TiO₂ has smaller particle size, bigger surface area, higher thermal stability and catalytic activity than that of Co-P due to the introduction of TiO₂ .â‘¢All the series of Co-P by-prepared have catalytic activities on decomposition of PH₃. Their catalytic activities increased with the increase of P content in alloy. when P%≥7.7%, T<450℃. Given catalyst(Co_86.3 P_13.7), the decomposition rate first increased then decreased with the increase of temperature and decreased with the increase of total flow (Q_N2 +Q_PH3 ) and flow ratio(Q_N2 :Q_PH3). The decomposition rate of PH₃ is over 95% under proper conditions.The effect of conditions on catalytic activity of Co-P/TiO₂ is similar to Co-P. But the catalytic activity of Co-P/TiO₂ decreased slower than that of Co-P which was mainly attributed to the high dispersion of Co-P alloy particles on the support, the affinity of TiO₂ support for the Co-P alloy particles, and the heat sink of the support.2. Research on preparation and application of Co-B and Co-B-P amorphous alloysMetal Cobalt can form amorphous alloy with metalloid B, P and BP. Co-B and Co-B-P amorphous alloy were also prepared in this dissertation. There are some comparabilities and differences in their preparations, characters and applications in decomposing PH₃.â‘ the preparation of Co-B and Co-B-P amorphous alloy are much easier than that of Co-P amorphous alloy. The reaction of preparing Co-B and Co-B-P can take place at room temperature, even at zero, but heating the reaction solution to 80～90℃and adding inducement is necessary for preparation of Co-P.â‘¡CoB, CoBP and Co-P all present small spherical particles, but the sizes of them are different, so the surface areas are different too. The sizes of Co-B and Co-B-P are smaller than that of Co-P, about 10～20nm, while the particles of Co-P about 120nm.â‘¢the thermal stabilities of Co-B and Co-B-P are higher than that of Co-P. The catalytic activities of them are different due to the different characters. II. Research on the preparations, properties and applications of Ternary Fe-based alloy FeBP, FeCuP and FePdP particles1. The preparation of FeBP amorphous alloy and its application in decomposing PH₃The fresh FeBP amorphous alloy as-prepared is spherical in shape with an average size around 150nm. It has high thermal stability and high catalytic activity on decomposition of PH₃. Under proper conditions, the decomposition rate can approach 100%.2. The preparations and applications in decomposing PH₃ of FeCuP and FePdP catalystsâ‘ In the preparations of FeCuP and FePdP, reaction conditions such as the concentration and their molar ratio of reactants, the reaction temperature, the pH value of the reaction solution, the additive and inducement can all influence the reaction rates and compositions of samples, especially the molar ratio of NaH2 PO₂ ?H 2O to the metal ions.â‘¡Fresh Fe(Pd)P alloy particles present small spherical or flake with an average size around 20nm. After treated at 350℃⁵40℃, the particle size changed slightly, and the structure has no change, which shows that Fe(Pd)P alloy has high thermal stability; The fresh FeCuP alloy particles also present small spherical or flake with an average size around 20-50 nm. Treating at high temperature would result in big lumps in the SEM micrograph.â‘¢In the decomposition of PH₃ catalyzed by FeCuP and FePdP, reaction conditions have significant effects on the decomposition rate, e.g., decomposition temperature and P content, the total flow (Q_PH3 +Q_N2 ), the ratio of Q_N2 :Q_PH3. At a proper temperature range, the catalytic activity increased with the increasing of temperature; at the same temperature, the catalytic activity increased with the increasing of P content in samples.â‘£Relationship between catalytic activity and lifetime of alloy was investigated. Given temperature and rest conditions, the catalytic activity of 0.10g FeCuP catalyst begin to decrease after using 43h. III wiping off Arsenic and purity test of productWiping off Arsenic in PH₃ gas material through grade-heating was studied. Arsenic content in product and product purity were analyzed by Graphite furnace atomic absorption spectrometry (GF-AAS) and ICP. As a result, that both Zinc and alloy prepared can wipe off Arsenic in PH₃ gas, but the effect of Zinc is better than alloy.