Purifying Yellow Phosphoric Tail Gas By Catalytic Oxidation And Investigation Of Its Theory

At present, producing yellow phosphorus by electric furnace is the main method at home and abroad. In recent years, the global yellow phosphorus production center has been transferred to China. The yearly production capability of yellow phosphorus in China has amounted to 1,750,000 tons. With the integration and technology advancement in yellow phosphorus enterprise, both single electric furnace's productivity and phosphorus enterprise's productivity have enlarged. Comprehensive utilization of yellow phosphoric tail gas, which is an important C₁ chemically raw material and environment protection have become an important task in the sustainable development of yellow phosphorus enterprises, providing the essential conditions for comprehensive and scaled utilization of yellow phosphoric tail gas.Yellow phosphoric tail gas contains high concentration carbon monoxide. For many years, the reason that yellow phosphoric tail gas has not well used is yellow phosphoric tail gas contained many impurities (such as sulfur, phosphorus, fluorine and so on). Because there wasn't mature depth purification technology, yellow phosphoric tail gas could not be used completely for a long time.In this article, catalytic purification of yellow phosphoric tail gas was studied and multivariate and highly active purification catalyst was developed. Emphasis is given to adsorption performance of PH₃, H₂S and reaction mechanism on transition metal oxide catalyst. Experiments were conducted to select catalyst carriers, to assess the efficiency of catalyst regeneration, and the influencing factors related to the purification of yellow phosphoric tail gas. Adsorption isotherm was used to calculate adsorption heat. Rate of adsorption curve was used to calculate activation energy. The thermodynamics and kinetics conditions and the trend of the interaction between metal oxides were found, and the main reaction constants were discovered. The adsorption samples of metal oxide catalyst were characterized by SEM, BET, XRD and XPS in order to find out catalyst's micro-mechanism and intermediate product generation disciplinarian. System of desulphorization and dephosphorization were established in this article. And the reaction mechanism and the chemically reaction equations were found. Firstly, Carbon was impregnated with different impregnants. It was 0.05mol/L Cu(AC)₂ for optimum impregnant, 80℃for optimum temperature, and 0.8% (vol%) for optimum oxygen content. The structure of materials after modification was determined using nitrogen adsorption. The modification resulted in a decrease in porosity, especially in micro-pore volume. Cu(AC)₂ significantly improves the performance of carbon as a PH3 and H₂S adsorbent when impregnation was applied whereas the effects of other materials used in this research were much less pronounced.The adsorption isotherm of PH₃ and H₂S showed the adsorption performance of metal oxide catalyst. The adsorption on metal oxide catalyst is mostly chemi-sorption of decalescence. Heat of adsorption and adsorption process all showed chemi-sorption degree. Combining characterization of catalyst and heat of adsorption, the catalytic purification mechanism of metal oxide catalyst was inferred. Analysis of XRD, XPS and pore size distribution indicates that CuO and Cu₂O present in the small pores act as a catalyst for oxygen activation causing PH₃ and H₂S oxidation. As a result of this process, P₂O₅, P₂O₃ and S are formed, which are strongly adsorbed and present in small pores from 0.3 nm to 2.0nm.Three-step regeneration (air oxidation, water vapor wash, air drying) method had optimum efficiency and secondary pollution was avoided.On-the-spot experiments were conducted to evaluate the catalyst. When catalyst was used to purify yellow phosphoric tail gas, total impurity content was lower than 1mg/m³ in 100h.This article examines a new yellow phosphoric tail gas purification process. The results indicated that catalytic oxidation technology might be more effective in purifying yellow phosphoric tail gas and exceed the purification limits of traditional processes. After purification, concentrations of PH₃, H₂S and HF in the tail gas were less than 1mg/m³ respectively, and meeting the need of returning raw material gas to C1 chemistry. Examination following an industrial application indicats that catalytic oxidation technology may have a service life longer than 500h with high stability and toxin immunity. Purification catalysts effective at relatively low temperatures were developed.The article get following innovative results. Firstly, yellow phosphoric tail gas purification catalyst is a new selective catalyst. Catalyst out of service can be regenerated easily. Secondly, phosphorus sulfur and other impurities can be purified at the same time. The difficulty of yellow phosphoric tail gas multivariate and highly active purification was overcomed. Thirdly, the purification was carried on in conditions with low-temperature range and low-oxygen content, and CO can not be oxidized. The achievements of this article successfully provide the sufficient condition for comprehensive utilization of yellow phosphoric tail gas, and also provided theoretical basis for phosphorus chemical industry tail gas for comprehensive utilization.