The Thermal Stability And Hazard Of Ethyl Tert-butyl Ether And Methyl Tert-butyl Ether

Ethyl tert-butyl ether(ETBE)and methyl tert-butyl ether(MTBE)are oxygenated additives that have good miscibility with gasoline and are widely used in gasoline to improve the octane number of the fuel,anti-knocking ability and complete combustion of fuel to reduce the emission of carbon monoxide(CO),nitrogen oxides(NO,NO2)and particular matter(PM)and other harmful substances.Methyl tert-butyl ether is mainly used in China,and ethyl tert-butyl ether is mainly used in developed countries.The common feature of these two chemiclas is the alkyl ether compound with similar chemical structure.Lots of literatures on the combustion properties and chemical properties of ETBE and MTBE are available;however,the long-term storage stability,low temperature oxidation properties and the risk in air or oxygen are still insufficient and deserve systermitic study.In particular,the hazards of thermal oxidation of ETBE and MTBE have not paid full attention.Therefore,it is necessary to investigate the thermal oxidation characteristics and hazards of ETBE and MTBE for the safety of production,storage,transportation and applicationIn this thesis,thermal analysis methods:Differential Scanning Calorimetry(DSC)and Accelerating Rate Calorimeter(ARC)were used to detect the initial oxidation temperature,reaction heat,pressure and temperature behaviors of ETBE and MTBE thermal oxidation process,and a mini-closed-pressure-vessel-test(MCPVT)was designed to explore the pressure and temperature changes of the ETBE and MTBE oxidation reactions,moreover,the oxidation reaction products were analyed.The main research content and research results are as follows.(1)DSC characteristics of ETBE and MTBE thermal oxidation in air atmosphereDSC was applied to explore the thermal behavior of ETBE and MTBE in a closed standless still crucible,respectively.The experimental results showed that the initial exothermic temperature T0 of the ETBE oxidation reaction decreased with the increase of ETBE sample mass.When ETBE/O2=90(n/n),T0=122 ?.In the experimental range,the reaction heat QDSC increased with the increase of oxygen amount.When ETBE/O2=28,QDSC=130 J·g-1,the initial exothermic temperature T0 of MTBE had similar trend with ETBE.When ETBE/02=62(n/n),T0 and QDSC were 204 ? and 84 J·g-1,respectively.(2)Pressure and temperature behavior of ETBE and MTBE by a mini-closed-pressure-vessel-test(MCPVT)In order to investigate the hazards of ETBE and MTBE oxidation with large sample mass,a mini-closed-pressure-vessel-test instrument was designed.By the on-line detection of pressure and temperature changes of ETBE and MTBE in nitrogen atmosphere under dynamic temperature program and in oxygen atmosphere under isothermal mode,respectively,the oxidation characteristic can be clearly made.Experiment results indicated that,ETBE and MTBE are both stable in nitrogen atmosphere.In oxygen atmosphere,violent oxidation reaction in ETBE occurred at 110? and resulted a sharp temperature increasement of 28 ? and pressure increasement of 0.7 MPa.The maximum of pressure((dP/dt)Max)increasing rate was =1.2 MPa·h-1,and the rapid oxidation temperature was 94 ?.The oxidation of MTBE in oxygen atmosphere was mild and no marked temperature or pressure changed appeared.The oxidation temperature of MTBE was 140 ?.(3)The oxidation characteristic and kinetics of ETBE arid MTBE in adiabatic condition by ARC.To get the initial oxidation temperature and kinetics of ETBE and MTBE in adiabatic condition,ARC was applied to analyze the pressure and temperature behavior of ETBE and MTBE in nitrogen and oxygen atmosphere under adabtic condition.Experiment results indicated that no chemical reaction occurred in nitrogen atmosphere.In oxygen atmosphere,violent oxidation reaction in ETBE occurred and resulted in a sharp temperature increasement of 110 ? and pressure increasement of 1.3 MPa.The initial oxidation temperature of ETBE was 105.50?.The activation energy and pre-exponential factor of ETBE oxidation were 159.10 kJ mol-1 and 3.28×1021 s-1,respectively.The oxidation of MTBE was mild in oxygen atmosphere compared with ETBE,with temperature increasement of 52 ? and pressure increasement of 0.3 MPa.The initial oxidation temperature of MTBE was 149.21 ?.The activation energy and pre-exponential factor of MTBE oxidation were 236.75 kJ mol-1 and 6.02×1025 s-1,respectively.(4)Separation and structural characterization of ETBE and MTBE peroxides and analysis of oxidation productsThe peroxides formed in ETBE and MTBE oxidation were isolated by column chromatography.The separation conditions were as follows:the eluent was a mixture of cyclohexane and ethyl acetate(V/V,10:1),and the column packing was:silicon.The primary peroxides of ETBE and MTBE were characterized by HPLC-MS,1H and 13C nuclear magnetic resonance(NMR)and Fourier transform infrared spectrometer(FTIR).The HPLC-MS analysis of ETBE peroxide showed that the(M+1)peak was 135 and the molecular weight M was 134;the NMR spectrum analysis showed that the 1H NMR chemical shifts were:8.03,5.25,1.38 and 1.28 ppm,respectively.The 13C NMR chemical shifts were:98.44,74.79,28.68 and 19.99 ppm,respectively;the FTIR characteristic absorption peaks were:3375,1260 and 842 cm-1,respectively.The chemical structure of ETBE peroxide was identified as 1-tert-butoxy-ethyl,hydroperoxide(TBEHP).The HPLC-MS analysis of MTBE peroxide showed that its(M+1)peak was 121 and the molecular weight was 120;the 1H NMR chemical shifts were:8.87,5.18,and 1.22 ppm,respectively,and the 13C NMR chemical shifts were:94.2,75.3,and 29.6 ppm,respectively;The FTIR characteristic absorption peaks were:3350,1137 and 848 cm-1,respectively.The chemical structure of MTBE peroxide was characterized as 1-tert-butoxy-methyl,hydroperoxide(TBMHP).Both those peroxides were new compounds.The ETBE and MTBE oxidation products were analyzed qualitatively and quantitatively by gas chromatography-mass spectrometry(GC-MS).At 110 ?,the main oxidation products of ETBE were:Methanol(24.63%),tert-butyl formate(18.33%),acetone(22.05%),isopropanol(3.75%),and water(2.68%),respectively;the main oxidation products of MTBE at 150? were:Tert-butyl alcohol(27.56%),tert-butyl acetate(19.44%),acetic acid(9.61%),methyl formate(8.97%),formic acid(8.76%),acetone(5.37%),and water(3.26%),respectively.(5)Thermal decomposition characteristics and decomposition kinetics of ETBE peroxide(TBEHP)and MTBE peroxide(TBMHP)DSC was used to investigate the thermal decomposition characteristics of TBEHP and TBMHP.The experimental results showed that the initial decomposition temperature T0,self-decomposition temperature Tonset and decomposition heat QDSC of TBEHP were 60.12 ?,99.12 ? and 1523.99 J g-1,respectively.The initial decomposition temperature To,self-decomposition temperature Tonset and decomposition heat QDSC of TBMHP were 52.63 ?,74.01 ? and 1529.36 J·g-1,respectively.The thermal decomposition kinetics of TBEHP and TBMHP were calculated using Kissinger,Friedman and O-F-W three kinetic models,respectively with DSC experimental results.The thermal decomposition activation energy Ea and pre-exponential factor of TBEHP calculated by Kissinger was 76.01 kJ·mol-1 and 3.14×1012 s-1,respectively.The thermal decomposition activation energy Ea and pre-exponential factor of TBMHP calculated by Kissinger were 47.23 kJ·mol-1 and 2.85×1012 s-1,respectively.(6)Experimental evaluation of oxidative explosion risk of ETBE and MTBEThe explosive risk of 5.00 g sample of ETBE and MTBE were assessed by a 500-mL autoclave in 1.00 MPa oxygen atmospheres.Experimental results showed that explosive occurred when temperature increased to 140 ? with feature of explosive sound in autoclave and the glass sample container was crushed.However,no explosion was detected even temperature increased to 200 ? in MTBE.MTBE is more stable and safer than ETBE.