Study On The Synthesis Of Polyoxymethylene Dimethyl Ethers From Methanol

With more attention has been paid to the air quality and humanhealth, there are more and more strict emission standards for diesel fuelhave implemented, and it is necessary to develop a new type ofeconomic and environmental clean diesel. Polyoxymethylene dimethylethers(DMM3～8) as a new exploration of oxygenated diesel blendcomponent, which create a new route to synthetise the clean fuel insteadof diesel oil. Using methanol which is serious surplus productioncapacity in the domestic market as the main raw material in the processengineering, which prolongs methanol industry chain and improves theadded value of methanol. Polyoxymethylene dimethyl ethers are a verypromising oxygenated diesel complement component, which improvethe diesel combustion performance and make up for the deficiency oftraditional diesel fuel additive.Polyoxymethylene dimethyl ethers are regarded as a attractivetailoring diesel fuels, which have high oxygen content(47.0%～50.3%)and average cetane number of above76. DMM3～8has goodcompatibility with petroleum diesel and biodiesel.When10%-30%DMM3～8was added in the diesel oil, their stability physical propertiesallows the use in modern diesel engines without significant change ofthe engines infrastructure. It can greatly reduce the amounts of carbonmonoxide and nitrogen oxides released upon combustion and reduce theexhaust pollution more than50%, which can meet the very strictnational IV standard on diesel emission requirements and close to thenational V standard. This paper developed a new process for polyoxymethylenedimethyl ethers. The acidic function ionic liquid which is studied moreand more in recent years is used as catalyst. The ionic liquid overcomesthe shortcomings of traditional inorganic acid and super acid, such aswaste water pollution, the corrosion of the equipment and it is not easyto separate from the product, which is an environmentally friendly,non-toxic, high selective, recycled green catalyst. polyoxymethylenedimethyl ethers were synthetised by one pot reaction at the constanttemperature and pressure conditions in a high-pressure reactionkettle.DMM3～8are degrees of polymerization of3to8inpolyoxymethylene dimethyl ethers, which was obtained by phaseseparation, extraction, distillation and so on. Different degree ofpolymerization of polyoxymethylene dimethyl ethers fractions werequalitative and quantitative analyzed by the effective carbon numbersand internal standard.The experiment of synthesis of polyoxymethylene dimethyl ethersfrom methanol and trioxane. The selection of catalyst, catalyst amount,raw material ratio, reaction time, reaction temperature, reaction pressureand other factors were studied in the experiment. Thus the appropriateoperating conditions were obtained. At temperature110℃,trioxane/methanol mass ratio1.5:1, pressure2.0MPa in1500ml stainless steelreaction kettle, and when catalyst is the hydrogen sulfate imidazoleionic liquid, the dosage of which is5%,which is the optimum reactionconditions. The yield of DMMnand the selectivity of DMM3～8were68.92%and32.18%, respectively. When the other conditions remainunchanged and polyoxymethylene dimethyl ethers were synthetisedfrom methylal and trioxane, the optimum proportionthe of methylal andtrioxane is1.6.The yield of DMM2-8and the selectivity of DMM3～8were51.37%and60.67%.When20%DMM3～8was added in the0#diesel oil, which was completely miscibility with diesel oil without adding any auxiliarysolvent, and the mixed density was in the range of0#diesel standardrange. DMM3～8was added to diesel fuels which improved the flashpoint of0#diesel oil and cetane number and reduced the sulfur contentin diesel engine, which can improve the combustion properties of dieselfuel and environmental benefits.