Preparation Of Encapsulated Heteropoly Acidic Ionic Liquid Composite Catalyst And Its Catalytic Performance In Ketalization

As a new perfume developed in recent years,ketals are widely used in food flavor,cosmetics,alcohol,ice cream,paint industry,pharmaceutical intermediates,special solvents and other fields by virtue of their soft and lasting aroma-like of mint.The traditional ketal reaction was catalyzed by common protonic acid（sulfuric acid,phosphate acid,etc.）,which always lead to side reactions,strong corrosion to equipment,and it is not easy to recover.At the moment,a large number of industrial waste water produced in the reaction process is more likely to lead to environmental pollution.Immobilized ionic liquids as green catalysts are widely used in the field of organic acid catalysis owning to excellent catalytic performance,strong stability of heat resistance and acid resistance,large specific surface area and relatively uniform pore size distribution.In recent years,a series of novel mesoporous molecular sieves have been synthesized.More highly efficient catalysts have been successfully prepared using ionic liquids with excellent catalytic performance as catalytic active components,and they have been applied to the organic acid catalysis.In this paper,SBA-16 mesoporous molecular sieves with uniform pore size distribution were synthesized by hydrothermal method,and a series of ionic liquids were synthesized and encapsulated into the ordered pores of mesoporous molecular sieves.Then,by further designing the carrier and catalytic active components（ionic liquid）,and strengthening the acidity of the catalysts,the catalytic performance of composite catalysts in the ketal reaction of cyclohexanone and glycol ethanol are more efficient.The main contents of the paper include:（1）A series of novel and efficient green catalysts consisting of different amounts of acidic ionic liquids and SBA-16 mesoporous molecular sieves with three dimensional structures（Im3m）have been successfully prepared by immersion method.Two kinds of Br?nsted ionic liquids are composed of sulfonic modified imidazole（organic cations）and sulfuric acid or tungstosilicic acid（anion）.The catalyst samples were characterized by FT-IR,SAXD,N₂ absorption-desorption isotherm,TEM and TG-DSC.The ketal reaction of cyclohexanone with ethylene glycol was carried out onto these catalysts.Particularly,the effects of loading,reaction temperature,reaction time,molar ratio of cyclohexanone（CYC）to ethylene glycol（EG）and catalyst dosage on the conversion of cyclohexanone and the yield of cyclohexanone ethylene glycol ketal（CGK）in reaction were investigated as well as the recycle of catalysts.The results show that when the reaction is in the optimum condition,the catalysts elicit best catalytic activity with conversion of cyclohexanone at 91.60%along with cyclohexanone ethylene glycol ketal yield of 82.73%.And after 5 times of reuse,the conversion of CYC still reached 85%and the yield of CGK is still above 65%.（2）A method for embedding boron atoms onto SBA-16 to increase acidic sites and enhance the acidity of the nano-cages was described.The tungstosilicic acid type ionic liquid（SWIL）was encaged into B-SBA-16 acidic nano-cages to obtain various composite catalysts.The acidic nano-cages and composite catalysts were characterized by FT-IR,TG-DSC,SAXD,BET,SEM,TEM,XPS and ¹H-NMR analyses.Research confirmed that boron was embedded onto the SBA-16 nano-cages in varying proportions and the obtained B-SBA-16 acidic nano-cages still maintained a high degree of pore ordering.The SWIL was successfully encapsulated into the acidic nano-cages via the immersion method.The cage-encapsulated tungstosilicic acid type ionic liquid catalysts SWIL/B（n）-SBA-16 were applied to catalyze the ketal reaction of CYC with ethylene glycol EG.The results showed that the conversion of CYC could reach 92.01%along with the yield of cyclohexanone ethylene glycol ketal（CGK）of 83.87%under ideal conditions.The CYC conversion was still nearly89.01%and the CGK yield was 72.81%even after 5 times of continuous reuse.（3）The dual-acid based phosphotungstic acid ionic liquids（M_nPWILs）modified by a variety of metal ions(Fe³⁺,Cu²⁺,Al³⁺)and sulfonic acid group（-SO₃）was explored and synthesized.Then,they were encapsulated into the B-SBA-16mesoporous nano-cages with acidic sites to obtain a plurality of encapsulating metal/sulfonic dual-acid based phosphotungstic acid ionic liquids（M_nPWIL/B-SBA-16s）composite catalysts.By means of FT-IR,BET,SAXD,TEM,SEM,TG-DSC,Py-IR and XPS,the structural properties,thermal stability and the encapsulation of M_n PWIL were investigated and confirmed.The composite catalysts were used to catalyze the ketal reaction of cyclohexanone（CYC）and ethylene glycol（EG）to investigate the catalytic performance and the optimum catalytic conditions with the aid of the orthogonal method.The experimental results showed that the conversion of CYC can reach about 94.05%,the yield of the product cyclohexanone ethylene glycol ketal（CGK）was up to 83.45%under the ideal catalytic reaction conditions catalyzed by Al_0.50PWIL/B-SBA-16 composite catalyst,and after 5 times of repeated operation,the catalyst still elicits prominent catalytic performance.