Experimental Study On Separation Of C₃H₆/C₃H₈ Mixtures Using Slurry

Propylene is an important chemical raw material with high economic,which can be used to produce polypropylene and acrylonitrile,etc.However,the production of propylene in industry is often accompanied by the appearance of propane.Because the properties of propylene and propane are similar,the separation process has the disadvantage of high energy consumption.The existing separation methods all have some shortcomings,so,it is necessary to develop a separation method with simple operation and low energy consumption.In this work,the kinetic separation of C₃H₆/C₃H₈ gas mixture was carried out using ZIF-8/M-water slurry.The differences of solubility and sorption rate of C₃H₆ and C₃H₈ in ZIF-8 slurry were investigated.In addition,the optimal ratio of ZIF-8 slurry was studied,and the separation effect of ZIF-8 slurry on C₃H₆/C₃H₈ gas mixture was investigated under different conditions.The reusability of ZIF-8 slurry was measured,and the recovered materials were characterized.Furthermore,a continuous breakthrough experiment on the C₃H₆/C₃H₈ gas mixture was carried out using a bubble column to further explore the separation performance of slurry.The main research contents of this work are as follows:（1）The solubility and sorption rates of C₃H₆ and C₃H₈ in ZIF-8/M-water slurry were measured at 293.15 K.It was found that the solubility difference between the two in ZIF-8 slurry is very small.The desorption heat values of C₃H₆ and C₃H₈ are maintained at about-30 k J/mol and-25 k J/mol,respectively,but the sorption rate of C₃H₆ is significantly higher than that of C₃H₈.Therefore,the C₃H₆/C₃H₈ gas mixture can be separated by using their difference in sorption rate in ZIF-8 slurry.（2）The kinetic separation of C₃H₆/C₃H₈ gas mixture was carried out using ZIF-8/M-water slurry.The effects of ZIF-8 solid content in ZIF-8 slurry and M content in liquid phase on the separation performance were investigated systematically.The results show that with the increase of the solid content of ZIF-8,the separation effect gradually increases,but the high solid content will make the slurry viscosity increase and seriously affect the gas-liquid mass transfer,so the solid content of the slurry was set at 30 wt%.The increase of M content in the liquid phase is not conducive to the separation of C₃H₆/C₃H₈ gas mixture,but the addition of M can effectively suppress the foaming phenomenon in the desorption process of ZIF-8 slurry,which is conducive to the experimental operation.Considering the separation effect and the foaming problem of the slurry,the M content in the liquid phase was set at 20 wt%.In addition,the effects of temperature,sorption time,and initial gas-liquid ratio on the separation effect were investigated.The results show that with the decrease of temperature,the separation effect increases gradually.With the increase of sorption time,the separation effect first increases and then decreases.With the increase of initial gas-liquid ratio,the separation effect of slurry on gas mixture gradually decreases,but when the gas-liquid ratio is small,the slurry has little effect on the separation effect of the gas mixture.In addition,the reusability of ZIF-8 slurry was investigated,and the recovered materials were characterized by XRD.The results show that the ZIF-8 slurry can still maintain a high separation effect on the gas mixture after repeated use,and the structure of ZIF-8 remains intact.（3）A breakthrough separation of C₃H₆/C₃H₈ gas mixture was carried out using a bubble column.The results show that when the content of M is 50 wt%in the liquid phase,the relative sorption rate difference between C₃H₆ and C₃H₈ can be maintained at a high level for a long time.Considering the foaming problem of slurry,ZIF-8 slurry with 50 wt%M content in the liquid phase was selected for continuous breakthrough experiments.The effects of inlet flow rate,temperature,pressure and gas composition on breakthrough results were investigated systematically.The results show that with the increase of the inlet flow rate,the breakthrough time becomes shorter,and the separation effect firstly increases and then decreases.Temperature has little effect on the breakthrough time,and the separation effect is the best at 293.15 K.With the increase of pressure,the breakthrough time became longer,and the separation effect firstly increase and then decreases.Under the conditions of the inlet flow rate of 44.9m L/min,temperature of 293.15 K,and the gauge pressure of 200 k Pa,the breakthrough experiment was carried out.The results show that the selected gas composition can maintain more than 95%of the C₃H₈ outlet content for a period of time after breakthrough separation.After desorption of ZIF-8 slurry for 11 h,propylene content can be reduced to 0.1%and propane content can be reduced to 0.8%.The reusability of ZIF-8 slurry was investigated and the results show that after three repeated experiments,ZIF-8 slurry can still maintain good separation ablity.