Removal Of P-cresol From M-cresol By PJZ-299 Molecular Sieve

M-cresol is an important fine chemical,and m-cresol with high-purity can be used as a raw material for synthetic fragrances and cosmetics.Currently,domestic demands of high-purity m-cresol mainly depend on imports due to the limitation of technology.In this thesis,the molecular sieve PJZ-299 was used to adsorb p-cresol in mixed cresol（mixture of m-cresol and small amount of p-cresol）to prepare high-purity m-cresol,the results were shown as follows:（1）Analysis method of p-cresol concentration in mixed cresol.The concentration of p-cresol in mixed cresol was tested by high performance liquid chromatography（HPLC）.The conditions were shown as follows:Agilent HPLC ZORBAX SB-C18 column（4.6×150 mm,5μm）;UV detection wavelength:275 nm;injection volume:0.5μL;column temperature:30°C;mobile phase:ethanol+1.5×10^-2mol/Lβ-CD aqueous solution（volume ratio 2:8）;flow rate:1.0 m L/min.The standard curve with high correlation was drawn with a p-cresol concentration in the range of 8 to 60 mg/g,and the coefficient of correlation（R²）was 0.998.（2）The static adsorption process of p-cresol in mixed cresol solution by molecular sieve PJZ-299.The effects of time,temperature and initial concentration on the adsorption amount were investigated.The results show that:It needs 12 h to reach equilibrium at 25℃,and the amount of adsorption decreases with temperature increasing from 15 to 35℃;The equilibrium adsorption amounthas a linear correlation with the concentration of p-cresol in the solution.For mixed cresols with an initial p-cresol concentration of 25 mg/g（2.5%）,the equilibrium adsorption capacity is 5 mg/g.Thermodynamic and kinetic analysis shows that the enthalpy change（ΔH）of the adsorption process is less than 0,indicating that the adsorption is an exothermic process,which could be promoted by cooling;the chemical free energy changes（ΔG）is less than 0,which means the process is spontaneous;The adsorption process of p-cresol on PJZ-299 is controlled by internal diffusions.The apparent activation energy（E_a）is 34.72 k J/mol and the reaction order is 0.5212.（3）The regeneration processes of molecular sieve PJZ-299.The mixed cresol solution was recovered by vacuum distillation firstly,and then the molecular sieve was heated to be regenerated.The effects of distillation temperature and calcination temperature on the regeneration process were investigated.The results show that:In the vacuum distillation process,the residual amount on the molecular sieve gradually decreases and then increases slowly with the distillation temperature increasing.When the distillation temperature was 170℃,the residual quantity reached a minimum.Suitable conditions for the recovery of mixed cresol:the temperature is 170℃,the time is 6 h,and the residual quantity was 1.46%.Suitable conditions for thermal regeneration:calcination temperature is 600℃,calcination time is 3 to 4 h,and the regeneration efficiency is 97%.After five repetitions,the molecular sieve has a regeneration efficiency of 96%,indicating that the molecular sieve has good stability.Fluorescence microscopy shows that the surface morphology of the regenerated molecular sieve is not significantly different from that of fresh molecular sieves;Infrared spectroscopy showed that no new material formation after molecular sieve regeneration;The BET detection analysis showed that the regenerated molecular sieve did not change significantly compared to the fresh molecular sieve skeleton structure.（4）Based on the equilibrium level theory,the analytical formula of the breakthrough curve was obtained according to the linear relationship between the molecular sieve equilibrium adsorption amount（Q_e）and the concentration of p-cresol in the solution.The analytical formula is highly consistent with the measured breakthrough curve and can be used to predict the behavior of p-cresol in the adsorption of mixed cresol solution on molecular sieve PJZ-299.