Reaction Intensification For Green Production Process Of Anhydrous Aluminum Fluoride

Known as the"gold industry",fluorine chemical industry is widely used in metallurgy,medicine,petroleum,chemical and other industries.As the largest inorganic fluoride product,aluminum fluoride plays an important role in electrolytic aluminum industry.Due to the limitation of fluorite resources and the sustainable development concept of energy conservation,emission reduction and clean production,improving the utilization rate of aluminum fluoride production raw materials and strengthening the reaction process have become the focus of research in recent years.In view of the above problems,the numerical simulation of anhydrous aluminum fluoride process was carried out in this paper.The thermodynamic values of the reactions involved were needed.Benson group contribution method was used to calculate the thermodynamic values of the reactions involved in anhydrous aluminum fluoride process within the temperature range of327～627℃.At the same time,the reaction rate and selectivity of Al（OH）₃ fluorination were discussed as a function of temperature,and the effects of temperature and feed ratio on the reaction rate and selectivity were studied.The results showed that the fluorination rate of Al（OH）₃ increased with the increase of the feed ratio at the same temperature,and the reaction rate increased with the increase of the reaction temperature at the same feed ratio.When the temperature reaches 477℃,the temperature change begins to cause the selectivity change,and the selectivity increases with the increase of temperature,indicating that Al（OH）₃ particles are more inclined to thermal decomposition reaction,so the reaction temperature of anhydrous aluminum fluoride should be set below 477℃.In this paper,Euler-Euler two-fluid model is used to simulate the cold state of two different gas-solid countercurrent fluidized beds.The gas velocity and the volume fraction of the solid phase in the straight fluidized bed and the variable fluidized bed are obtained and compared.It is found that the gas velocity in the straight fluidized bed is maintained at 0.1 m/s as a whole,and the flow velocity in the fine section of the variable fluidized bed is 0.04 m/s as the volume of the reactor increases compared with that in the straight fluidized bed.At the same time,the flow velocity in the variable fluidized bed is slower about 0.02 m/s due to the expansion of the cross-sectional area,and the gas has a longer residence time in the variable fluidized bed.For the solid phase volume fraction,the solid phase volume fraction in the straight fluidized bed is0.015～0.02,the fine section of the solid phase fraction in the variable diameter fluidized bed is0.03,and the variable diameter area is 0.04,which is one times higher than that in the straight fluidized bed.Therefore,under the same feeding conditions,the variable diameter fluidized bed has higher solid holdup,and the gas-solid contact efficiency is increased,so as to realize the process strengthening.Finally,the thermodynamic and kinetic equations were coupled with the cold model,and four kinds of variable diameter fluidized beds with different diameter ratioγwere established.The influence of diameter ratio on anhydrous aluminum fluoride process was analyzed and compared.The results show that under the same feeding conditions,Al（OH）₃ particles have better axial concentration distribution in the variable diameter fluidized bed,but with the increase of the diameter ratioγ,Al（OH）₃ particles cannot completely fill the whole variable diameter region,and can not strengthen the reaction process.For the reaction rate,straight in the fluidized bed Al（OH）₃ fluorination reaction rate is 1.96×10^-13mol/（m³·s）,γ=1.7,the reaction rate is 2.54×10^-13 mol/（m³·s）,γ=2.1,the reaction rate is 2.34×10^-13 mol/（m³·s）,γ=3.6,the reaction rate is 8.01×10^-14 mol/（m³·s）。It can be seen that the reaction rate can be improved by reducing the diameter of fluidized bed,but there is an optimal value of diameter ratioγbetween1 and 1.7,beyond which the strengthening effect of anhydrous aluminum fluoride process will be weakened or even negatively affected.