Construction Of Nanoreactor And Its Application In Catalytic Synthesis Of Polyoxymethylene Dimethyl Ethers

Polyoxymethylene dimethyl ethers(PODE_n)are environmentally friendly diesel additives with high cetane number and oxygen content,which can greatly improve the combustion performance of diesel engines and reduce the emissions of nitrogen oxides and solid particles produced by diesel combustion,have broad prospects.The synthesis of PODE_n is a typical acid catalyzed reaction.As the green catalyst,ionic liquids have great catalytic performance and high selectivity,but ionic liquids are expensive and difficult to recover,which restrict the wide application.In the paper,the nanoreactor was synthesized by encapsulation of ionic liquids with the nanocage of KIT-5.PODE_n were synthesized by the nanoreactor in different raw material systems.In order to study the influence of acidity for the synthesis of PODE_n,bis-sulfonic ionic liquids were prepared.This effectively solved the problem that the difficult recovery of ionic liquids,and cost savings.(1)The nanoreactor was prepared by encapsulation,with KIT-5 as a carrier,N-sulfonate imidazole ionic liquids as active components.The catalytic performances of nanoreactors in different reaction systems were synthesized.The optimal conditions for the synthesis of PODE_n with methanol and trioxane as raw materials:reaction time 2 h,reaction temperature 110?,the molar ratio of methanol and trioxane 2,catalyst dosage 4 wt%.Under the conditions,the conversion of trioxane and the selectivity to the PODE_3-5 were as high as 89.94%and 45.04%.The catalyst can be reused four times.The optimal reaction conditions for the synthesis of PODE_n with dimethoxymethane and trioxane as raw materials:reaction time 2 h,reaction temperature 100?,molar ratio of dimethoxymethane and trioxane 1.5,catalyst dosage 3 wt%.the conversion of trioxane and the selectivity to the PODE_3-5 were as high as 84.52%and 51.14%.The catalyst can be reused six times without any significant effect.In an anhydrous system,the selectivity of the target product was better,the recycling performance of the catalyst was higher.Under the optimal conditions,the catalytic activity of ionic liquid and nanoreactor were compared.It was found that the catalytic activity of the nanoreactor prepared by encapsulating the ionic liquid was as good as the ionic liquid,and can be recycled to reduce costs.By studying the relationship between reaction time and product distribution,the synthesis of PODE_n was discussed.PODE_n is formed one by one as the increase of degree of aggregation(n).(2)The nanoreactor was prepared by encapsulating three kinds of phosphonium ionic liquids with different anions,and the catalytic activity of three kinds of nanoreactor was compared.It was showed that the nanoreactor prepared with triphenyl sulfonic acid butyl phosphonium trifluoromethanesulfonate ionic liquid as the active component has the best catalytic activity.the conversion of trioxane and the selectivity to the PODE_3-5 were as high as 98.89%and 44.57%.The catalyst can be reused four times without any significant effect.(3)Four kinds of bis-sulfonic imidazole ionic liquids were synthesized.The structure of four ionic liquids was characterized by the NMR spectrometer,and the acidity of these ionic liquids was determined by UV-vis spectra.The acidity of the bis-sulfonic imidazole ionic liquids is stronger than that of the mono-sulfonic acid ionic liquids.A series of single factor experiments were designed,the optimal conditions for synthesis of PODE_n were as follows:reaction time 2 h,reaction temperature 110?,the molar ratio of methanol and trioxane 2,catalyst dosage 2 wt%.Under the conditions,the conversion of trioxane and the selectivity to the PODE_3-5 were as high as 98.39%and 56.67%.Under the optimal conditions,the catalytic activity of ionic liquids in the synthesis of PODE_n with methanol and trioxane was compared.The catalytic activity of the bis-sulfonic acid ionic liquid was stronger than that of the mono-sulfonic acid ionic liquid.