Experimental And Kinetic Modeling Study Of Furan And Its Derivatives Pyrolysis At Various Pressures

Pyrolysis of furan and its derivatives in flow reactor at various pressures were investigated. The pyrolysis intermediates, especially the free radicals and isomers were identified and quantified by using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) technique. Based on the previous and present theoretical studies, the detailed kinetic pyrolysis models were developed and validated against the present work and previous pyrolysis experimental data.In Chapter1, the purpose and significance of the research on the pyrolysis of furan and its derivatives at various pressures were presented. Large production and exploitation of biofuels were essential under the background of international energy and environmental crisis. Besides, as new kinds biofuels, the advantages and recent research progress of furan and its derivatives were summarized.In Chapter2, the experimental methods, theoretical calculations and kinetic model were introduced. A brief description of beamlines and pyrolysis appratus were also displayed in this chapter. And a brief discussion of the catalytic effects of α-alumina flow reactor was presented, and the experimental observation reveals the negligible surface catalytic effects of our α-alumina flow tube. Besides, the theoretical methods on quantum chemistry and calculating rate constants of key reactions in furan and its derivatives are briefly introduced, as well as the simulation methods using CHEMKIN-PRO software.In Chapter3, fuel decomposition and aromatic ring formation in furan pyrolysis at low pressure were discussed in detail. Specific products, which are directly related to the unimolecular decomposition reactions of furan, were observed, such as propyne+CO and acetylene+ketene. Using the calculated rate constants of unimolecular decomposition reactions of furan, a low pressure pyrolysis model, which consists of174species and950reactions was developed and validated against the mole fraction profiles of pyrolysis species measured in this work. The decomposition of furan is mainly controlled by the unimolecular decomposition reactions under the investigated conditions. Based on the experimental results and theoretical calculation, propargyl radical is suggested to be mainly formed from the unimolecular decomposition of propyne rather than furan. Furthermore, the temperature drop region close to the flow reactor outlet provides a sensitive circumstance at low to intermediate temperature region to validation high concentration radical combination reactions for aromatics formation, and the propargyl self-combination may be over-estimated at low to intermediate temperature regions according to the modeling analysis and experimental validation.In Chapter4, experimental and kinetic modeling study of2-methylfuran pyrolysis at various pressures were introduced in detail. The potienal energy surface of unimolecular decomposition of MF and2-furanylmethyl and reactions of H atom attack MF were calculated using CBS-QB3. The kinetic model were optimized according to the previous model and the validation against the present and previous pyrolysis data of MF. Based on the rate of production (ROP) and sensitivity analyses, main pathways in the decomposition of MF and the growth of aromatics were determined. The unimolecular decomposition to produce1-butyne+CO and acetyl+propargyl, H-atom abstraction to produce2-furanylmethyl radical, ipso-substitution by H to produce furan and H-atom attack to produce CH2CHCHCO+CH3and C4H7+CO were concluded to dominate the primary decomposition of MF. Further decomposition of2-furanylmethyl radical leads to great production of vinylacetylene. Many large aromatic hydrocarbons, including benzene, benzyl radical, toluene, phenylacetylene, styrene, indenyl radical, indene, and naphthalene, were also detected. Based on the ROP analysis, it is concluded that the higher concentrations of benzene, toluene and other aromatics in the MF pyrolysis result from the greater formation of propargyl radical and1,3-butadiene.In Chapter5, experimental and kinetic modeling study of2,5-dimethylfuran pyrolysis at various pressures were introduced in detail. Dozens of pyrolysis products, especially a series of radicals and aromatics, were identified from the measurement of photoionization efficiency spectra; and their mole fraction profiles were measured at790-1470K. Phenol,1,3-cyclopentadiene,2-methylfuran, vinylacetylene and1,3-butadiene were observed with high concentrations in the decomposition of DMF. The pressure-dependent rate constants of the major unimolecular decomposition reactions of DMF were theoretically calculated, and were adopted in the pyrolysis model of DMF with285species and1173reactions developed in the present work. The model was validated against the species profiles measured in both the present work and the previous pyrolysis studies of DMF. Based on the rate of production and sensitivity analyses, main pathways in the decomposition of DMF and the growth of aromatics were determined. The unimolecular decomposition to produce CH3CHCCH and acetyl radicals, H-atom abstraction to produce5-methyl-2-furanylmethyl radical, ipso substitution by H-atom to produce2-methylfuran and H-atom attack to produce1,3-butadiene and acetyl radical were concluded to dominate the primary decomposition of DMF. Further decomposition of5-methyl-2-furanylmethyl radical leads to great production of phenol and1,3-cyclopentadiene which can be readily converted to precursors of large aromatics such as cyclopentadienyl radical, phenyl radical and benzene. As a result, the formation of aromatics in the pyrolysis of DMF is promoted compared with the pyrolysis of cyclohexane and methylcyclohexane under very close conditions. Among furan and its derivatives, MF produces the highest concentration of aromatic species due to the large amounts formaiton of propargyl radical, benzene and toluene. Therefore, this observation emphasizes the necessity to investigate the sooting behavior and soot formation mechanism in MF and DMF combustion for the potential application as new biofuels. The experimental and modeling analyses on the formation of soot precursors in the pyrolysis of MF and DMF provide significant benefits to the design for the inhibition of their soot emissions. As a consequence, the investigations in the present work can help not only develop a detailed combustion model for furan and its derivatives, but also provide theoretical guidance for the reduction of the emissions in their practical applications.