The Oxidation Characteristics And Safety Of Fuel Additive:Methylal And 2,5-Dimethylfuran

Methylal(DMM)and 2,5-dimethylfuran(DMF)have been widely proposed and tested as the promising fuel components in recent years.The oxidation stability and chemical safety of fuel are important research topics.It is necessary to carry out the oxidation characteristics and safety studies on the two kind of potential fuel candidates for the sake of their safety in production,storage,transportation and use,as well as the product quality control.(1)The oxidation characteristics of methylal at low temperature.It can track the changes of pressure and temperature in chemical reactions with the employment of the self-designed mini closed pressure test(MCPVT).The pressure and temperature behavior of DMM during the heating process under oxygen and nitrogen atmosphere were monitored by MCPVT for understanding the initial oxidation reaction and thermal decomposition reaction characteristics,and exploring the hazardous nature of oxidation reaction.Results show that DMM oxidation process can be divided into three stages:the initial auto-oxidation to form DMM peroxide,peroxide thermal decomposition and rapid deep oxidation.The generated peroxide has been successfully separated,and its structure is characterized as hydroperoxy(methoxymethoxy)methane.Its initial thermal decomposition temperature is 99.8 ?,and the decomposition heat is 2431.37 J·g-1.Above 100 ?,DMM oxidation undergoes the rapid thermal decomposition reaction,accompanying the rapid rise in temperature and pressure.Iodometry analysis for peroxide generated in DMM oxidation show that DMM can form high levels peroxides with the maximum peroxide value of 34,808 ppm.(2)The safety of DMM oxidation.The safety and stability of DMM oxidation was investigated by MCPVT using a step heating mode.There is no chemical reaction when DMM heated under a nitrogen atmosphere,but DMM is prone to oxidation under an oxygen atmosphere.Results show that the accumulation and rapid decomposition of DMM peroxides can lead to thermal runaway of DMM oxidation at temperature of 102 ?,accompanied by a sharp rise in temperature and pressure of the reaction system.The maximum temperature rise rate is 599.86 ?·min-1,the maximum pressure rise rate is 22.1 NMPa-min-1.(3)The oxidation products of DMM and its possible oxidation pathways.The low temperature oxidation mechanism of DMM was studied by comparing the products of initial oxidation and deep oxidation of GC-MS analysis.Results show that oxygen is consumed by 46.3%after deep oxidation,accompanied by significant increase in product composition of methane,formic acid,formaldehyde,methyl formate,dimethyl ether,methanol and acetaldehyde,and the decomposition of DMM peroxide.The initial oxidation is mainly caused by the dehydrogenation reaction of O-CH2-O group of DMM to form peroxides,such as hydroperoxy(methoxymethoxy)methane.Afterwards,DMM peroxide proceed rapid thermal decomposition,and lead to the deep oxidation of DMM It should be noted that the thermal decomposition in DMM oxidation can lead to thermal runaway,and probablely converting into an explosive reaction further,(4)The oxidation characteristics of DMF at low temperature.The temperature-time and pressure-time variation of DMF oxidation was monitored using MCPVT;the oxidation products were analyzed by GC-MS.The ring-opening reaction of DMF during oxidation was investigated by a situ 1H NMR.The results show that the DMF oxidation reaction is exothermic and oxygen-consuming process at under a high oxygen pressure;The initial exothermic temperature To is 81.9?,and the maximum exothermic rate is 23.4 ?·min-1.Under a low oxygen pressure,the oxidation of DMF at room temperature is a slow process,but the formation of peroxides and thermal decomposition at 52 ? will cause a rapid deep oxidation reaction of DMF at 60.4 ?.The main oxidation is product trans-3-hexene-2,5-dione;Its cis-trans isomerization under UV irradiation gives cis-3-hexene-2,5-dione,the ring opening process of DMF in oxidation is the opposite(5)The oxidation kinetics of DMF and its peroxides.The reaction kinetics of DMF with oxygen in the temperature range of 40-90 ? was investigated by an atmospheric pressure oxidation device.The peroxide concentration of DMF oxidation was determined by Iodometry,Results show that the reaction of DMF with oxygen at atmospheric pressure and low temperature exhibits an apparent first-order reaction.The apparent reaction activation energy is 29.08 kJ-mol-1.Iodometry analysis shows that DMF can be oxidized to forming a higher concentration of peroxide at 75 ? with a maximal peroxide value of 16348 ppm.Thin layer chromatography(TLC)analysis of DMF peroxides show that DMF produce a main primary peroxide in its auto-oxidation at below 60 ?As the temperature rises,the primary peroxide decomposes to produce a variety of peroxides;DMF peroxide decomposes rapidly at above 100 0C to form oxidation products(6)The risk of DMF oxidation and thermal decomposition.DMF oxidation will produce a variety of peroxides that contained in its solid product.The thermal decomposition characteristics and hazardous degree of DMF solid products were investigated by differential scanning calorimetry(DSC)and MCPVT.The DSC test shows that the initial decomposition temperature To of DMF peroxide is 58.8 ?,its decomposition heat is 1982.29 J·g-1.MCPVT test show that the thermal decomposition of DMF solid product is a violent exothermic,pressure rise process with high risk;the initial decomposition temperature is 90.2 ?,the maximum temperature rise rate is 9.9 ?·s-1,and the maximum pressure rise rate reaches 291 kPa-s-1.The thermal decomposition products are mainly carbon monoxide(16.8%),carbon dioxide(30.1%),formic acid(20.2%),acetic acid(12.6%)and methyl formate(8.9%).