Constructing Nanoreactor By Ship In A Bottle Methed And Synthesis Of Polyoxymethylene Dimethyl Ethers

Polyoxymethylene dimethyl ethers?PODEn?as the world's most promising environment-friendly diesel additives,can significantly improve the diesel combustion performance and the effect of thermal efficiency,reduce the pollutant emissions.In addition,the raw materials for synthesis of polyoxymethylene dimethyl ethers are methanol and its derivatives,so the development of this technology is also conducive to extend the methanol industry chain and alleviate the problem of methanol overcapacity in China,has remarkable economic benefits and environmental benefits.The synthesis of polyoxymethylene dimethyl ethers is an acid catalytic reaction,combined with the catalysts reported in the literature,the acidity of ionic liquids is adjustable,the activity and selectivity of ionic liquids in synthesis of polyoxymethylene dimethyl ethers are relatively high.However,due to the inherent shortcomings of ionic liquids such as high price and difficult recovery,they are unable to large-scale application in the industry.In this paper,MIL-100?Fe?,a synthetic material with low price and environmental protection,was selected as the carrier material,and the catalytic active component ionic liquids were encapsulated in the nanocage of the carrier by the method of"ship in a bottle"to prepared a nanoreactor.The synthesis of polyoxymethylene dimethyl ethers by the nanoreactor was studied in different raw material system,and more,bisulfonic acid ionic liquids were prepared to study the effect of acidity on the synthesis of polyoxymethylene dimethyl ethers.This effectively solved the problem that ionic liquids are expensive and can not be recycled.At the same time,the pore size of MIL-100?Fe?is relatively matched with the size of target product,so the prepared nanoreactor has a shape-selective catalytic effect,which can effectively restrict the generation of products with high degree of polymerization and improve the selectivity of the target product.The main contents of this paper are as follows:?1?The nanoreactor was prepared with four kinds of N-sulfonic acid butylimidazole ionic liquids with different anions as active component,MIL-100?Fe?as the carrier by"ship in a bottle"method.A series of single factor experiments were designed to obtain the optimum conditions for catalytic synthesis of polyoxymethylene dimethyl ethers in aqueous system,the optimal conditions as follows:reaction temperature of 110°C,reaction time 2 h,methanol and trioxane mole ratio 2:1,the dosage of catalyst 4 wt%.Under the conditions,the conversion of trioxane was 93.07%,the selectivity of PODE355 was 44.2%.The catalytic activities of nanoreactor with four kinds of N-sulfonic acid butylimidazole ionic liquids as active components were compared and studied,the recycling ability of the catalyst and the reasons for the decrease of the catalytic activity were preliminarily analyzed.It was found that the catalyst still maintained high catalytic activity after recycling six times,had a good ability of reuse.?2?Two kinds of ionic liquids with different carbon chain lengths were used as active components and MIL-100?Fe?as carrier to prepare nanoreactor by"ship in a bottle"method.A series of single factor experiments were designed in anhydrous system,the optimum conditions for synthesis of polyoxymethylene dimethyl ethers by dimethoxymethane and trioxane were as follows:reaction temperature 100°C,reaction time 1 h,dimethoxymethane to trioxane molar ratio 1.5:1,catalyst dosage 3 wt%.Under these conditions,the conversion of trioxane was 91.26%,and the selectivity of PODE355 was48.86%,and the catalytic activity of the nanoreactor constructed by ionic liquids with short carbon chain lengths as active components was obviously poor.Using nanoreactor MIL-100?Fe?@[BSO3HIm][HSO4]as catalyst,the effect of catalytic synthesis of polyoxymethylene dimethyl ethers in aqueous system and anhydrous system was studied comparatively.It was found that anhydrous system was superior to aqueous system in terms of reaction conditions and selectivity of target products.The chain growth mechanism of the synthesis of polyoxymethylene dimethyl ethers was discussed.It was found that the products of polyoxymethylene dimethyl ether satisfied the Schulz-Flory distribution rule.It showed that in the process of synthesis of polyoxymethylene dimethyl ether,trioxane was first decomposed into a single formaldehyde unit,and then inserted into PODEn chain one by one.?3?In order to further explore the effect of acidity on the synthesis of polyoxymethylene dimethyl ethers,four kinds of bisulfonate imidazole ionic liquids were synthesized.The acidity of the investigated ionic liquids was evaluated from the determination of the Hammett acidity functions using UV-visible spectroscopy.In aqueous system,polyoxymethylene dimethyl ethers were synthesized by the ionic liquids with different acidity,and the effect of acidity on catalytic activity was analyzed,it was found that the acidity of the catalyst should be controlled within a suitable range.