Study On The Application Of Carbon-based Solid Acid With Large Surface Area In Catalytic Esterification Of Oleic Acid And Adsorption Of Pb(?)

In recent years,carbon-based solid acid?CSA?was widely used in the acid-catalyzed reactions.It is a kind of solid acid obtained by modifying acidic groups on its surface.Due to the high densities of SO₃H groups,simple separation process,low cost and environmentally friendly characteristics,CSA is a kind of novel strong acid catalyst which can replace the liquid acid of Br?nsted type.However,in most cases,the specific surface area of conventional CSA is less than 10 m²/g,and the number of acidic oxygen-containing functional groups on the surface is relatively small.So the molecules of reactants couldn't contact the acid sites of CSA efficiently,which shows negative effect on its catalytic activity.Therefore,it is of great significance to develop a carbon-based solid acid with large specific surface area and then to study its application.The carbon-based solid acid with large surface area?CSALA?was prepared by partially carbonization of H₃PO₄ pre-treated agricultural waste peanut shell and following sulfonation with concentrated H₂SO₄.The structure and acidity of CSALA was characterized by N₂isothermal adsorption-desorption,SEM,XRD,Raman,FT-IR,TG-DTA,XPS and acid-base titration.The specific surface area of CSALA was 329.3 m²/g,which was much higher than that of the traditional carbon-based solid acid?CSA,3.7 m²/g?.The density of acidic oxygen-containing functional groups?-SO₃H,-COOH,Ph-OH?on its surface was 0.52mmol/g,1.43 mmol/g and 0.33 mmol/g,respectively.The esterification of oleic acid with methanol was used as probe reaction to investigate the catalytic performance of CSALA.Under the conditions of 4 h,120?,n?methanol?/n?oleic acid?=10:1 and 3 wt%CSALA loading?percentage of the mass of oleic acid?,oleic acid conversion was up to 96.6%.The reusability of CSALA was poor.When it was for the fifth time,oleic acid conversion was only 27.8%.The density of-SO₃H group was seriously decreased,which was mainly due to the leaching of the-SO₃H group in the polar solvent methanol.The adsorption performance of CSALA on Pb???in water was investigated.Under the adsorption conditions of 120min,pH=5,0.5g/L and 100mg/L,the removal efficiency?R?of Pb???was up to 76%with 148.6 mg/g adsorption capacity?Q?to CSALA.It showed better adsorption performance than the activated carbon precursor?R and Q were 9.7%and 83.1mg/g,respectively?,which could be due to the high density of acidic oxygen-containing functional groups.In addition,the thermodynamics and kinetics of Pb???adsorption on CSALA were studied.The equilibrium adsorption capacity increased with increasing temperature,which indicates that the adsorption is an endothermic process.This is consistent with the thermodynamic analysis.The pseudo second-order kinetics model can well describe the adsorption characteristics of Pb???on CSALA,and the correlation coefficients R² were all more than 0.999.Moreover,the rate constant Kads and the equilibrium adsorption capacity qe increased with increasing temperature,which indicates that the high temperature is favorable for the adsorption of Pb???on the CSALA surface.