Preparation,Characterization Of Soild Acid Catalysts And Its Application For Alkylation

Aromatics are important raw materials for chemical fiber industry,and the production of aromatics is considered as benchmark of chemical industry for a country.However,due to the refining and thermal cracking process,the aromatic streams contain some olefins which lead broming index of aromatics over required value.These olefins components must be removed,as they will cause negative effects on following operations.Currently,the primary method to reduce olefins is clay treatment,however,frequent replacement of clay caused by rapid deactivation results in high labor and monetary costs,more importantly,it results serious environmental problems.In China,large numbers of aromatics units are being build,the growing awareness of environmental protection in chemical industry requests us developing environment friendly and cost-effective catalysts to substitute clay to remove olefins in aromatics.Our works focused on the following aspects:Using different Lewis acid agents to modify clay,and finally choose ZnBr2 as the best candidate.ZnBr2 modified Inner Mongolia clay shows the highest activity in the reaction for reducing bromine index of aromatics.Based on different characterization methods such as XRD,TEM,SEM and FTIR,a hypothesis about mechanism for the preparation of ZnBr2 modified clay is put forward.Both thermal analysis and furnace test indicated that the reasonable dry temperature for ZnBr2-Clay is 150?,and the calcination temperature is 350?.Pyridine adsorbed FTIR spectra demonstrated the amount of surface Lewis acid on ZnBr2-Clay was improved significantly,the amount of weak Lewis acid sites were increased 654%?the amount of total Lewis acid sites were increased 380%.The reaction used to reducing bromine index in aromatics was confirmed belongs to alkylation,reaction mechanisms on different acid sites were also proposed.As the activity of ZnBr2-Clay was so outstanding,we conducted industrial test with it.The industrial test showed that the ability of ZnBr2-Clay in reducing bromine index is 17.7 times higher than unmodified clay,and it has no big effect on the component of aromatics.The second solid acid catalyst is methanesulfonic acid functionalised silica material.This kind of catalyst was synthesised by method of sol-gel.The most important feature for this catalyst is anhydrous formic acid is used to hydrolysis tetraethylorthosilicate(TEOS),no water is added in the whole preparation,so the active component can be anchored in silica matrix more effectively instead of dissolving in water,more than 98%methanesulfonic acid can be anchored on the silica matrix.Furthermore,no surfactant species or precursors were involved in the whole process,the synthesis process is environment friendly.This new organic/inorganic hybrid catalyst was characterized by XRD,EDS,BET,TGA/DSC and Pyridine-FTIR.The catalytic activity was also tested by alkylation of olefins and aromatics which is same reaction as we used for ZnBr2-Clay.The activity test showed that the lifetime for methanesulfonic acid functionalised silica material is double then ZnBr2-Clay,so methanesulfonic acid functionalised silica material also has a bright industrial application prospect.Combined thermal stability analysis and surface acid sites analysis,the mechanism for the preparation of methanesulfonic acid functionalised silica material is put forward.When the calcination temperature lower than 300 ?,there are two kinds of interaction between methanesulfonic acid and silica,one is the source for Lewis acid sites and another is for Bronsted acid sites.When the calcination temperature is higher than 500?,methanesulfonic acid decomposed and released SO3,which can react with silica again and form new active site.High content of both Lewis and Bronsted acid sites,abundant pores and large surface area made the activity of methanesulfonic acid functionalised silica higher than MCM-22,ZSM-5 and industrial acidity clay.Pyridine-FTIR indicated that this catalyst has abundant Lewis acid sites,especially weak acid sites.29Si and 27A1 MAS NMR confirmed that aluminium methanesulphonate was anchored on the surface of the silica matrix by the covalent bond of Si-O-Al Al serves as a bridge connected methanesulfonate and silica matrix.A series of sulfated zirconia(SZ)catalysts was synthesized by immersion of amorphous zirconium hydroxide in sulfuric acid of various concentrations(1 to 5 N).These samples were fully characterized by XRD,thermogravimetric analysis and mass spectrometry,and aqueous sulfuric acid immersion and high temperature oxide melt solution calorimetry.The catalytic activity was also tested by alkylation of olefins and aromatics.We investigated the enthalpies of the complex interactions between sulfur species and the zirconia surface(?Hsz)for the sulfated zirconia precursor(SZP),ranging from-109.46 ± 7.33(1 N)to-42.50 ± 0.89(4 N)kJ/mol S.Mass spectrometry showed that there are two kinds of interactions between sulfur species and zirconia.?Hsz appears to be a roughly exponential function of sulfuric concentration.The enthalpy of SZ formation(?Hf),becomes more exothermic linearly as sulfur surface coverage increases,from-147.90 ± 4.16(2.29 nm-2)to-317.03 ± 4.20(2.14 nm-2)kJ/mol S.Moreover,water adsorption behavior was also studied and the water adsorption enthalpy on sulfated zirconia under different water coverage was calculated.