Investigation On Pyrolysis Kinetics Of Iso-pentanol And Fuel Isomeric Effects Of Pentanol

Nowadays bio-alcohols are the most important renewable biofuels which are important for mitigating the energy crisis caused by the drastic consumption of fossil fuels.Compared with ethanol,the most commonly used bio-alcohol,pentanol isomers represented by iso-pentanol,2-methyl-1-butanol and n-pentanol have higher energy density,higher boiling point,better mixing with fossil fuels,lower water solubility,and stronger applicability to conventional engines.Bio-pentanol can be extracted by distilling off the by-products of fusel oil produced from the fermentation of rice,wheat and other crops.Due to the above advantages,pentanol has become a promising second-generation biofuel.However,experimental and kinetic modeling studies on pentanol isomers are still not comprehensive enough,especially iso-pentanol that is the most abundant in fusel oil except ethanol.Therefore,iso-pentanol,one of the representative pentanol isomers,was selected as the target fuel in this work.The pyrolysis kinetics of iso-pentanol was studied thoroughly with both experimental and kinetic modeling methods.Besides,the isomeric effect was also revealed based on the comparision studies among iso-pentanol,2-methyl-1-butanol and n-pentanol.In terms of the experiment,pyrolysis of three pentanol isomers including iso-pentanol,2-methyl-1-butanol and n-pentanol was conducted in a flow reactor at 30 and 760 Torr.Synchrotron vacuum ultraviolet photo ionization mass spectrometry(SVUV-PIMS)method combined with ultrasonic molecular beam sampling was used to identify and quantify the pyrolysis products.Photoionization efficiency(PIE)spectra of pyrolysis products were obtained by scanning photon energy at fixed temperature,and more than 20 species were detected in the pyrolysis of three pentanol isomers,including linear and cyclic olefins,alkanes,enols,aldehydes,and aromatic hydrocarbons,etc.Particularly,the reactive species like propargyl and allyl radicals were also measured,and several isomers such as propadiene and propyne,acetaldehyde and vinyl alcohol were separated.In the pyrolysis experiments of 2-methyl-1-butanol and n-pentanol,benzene,fulvene,and C5 diolefin were also observed.By scanning the temperature at fixed photon energy,the mole fraction profiles of the fuel and pyrolysis products as a function of temperature were obtained.In terms of the kinetic modeling,a kinetic modeling for iso-pentanol pyrolysis was constructed,containing 178 species and 1344 elementary reactions based on our newly developed modeling for butane isomers.The experimental results obtained in this work were used to test the performance of the present model,as well as previous models(i.e.Sarathy model and Dayma model).It is found that the Sarathy model overpredicts the formation of isobutene and vinyl alcohol while underpredicts that of isopentene,1,3-butadiene,etc.In contrast,based on Dayma model,the formation of 1,3-butadiene and vinyl alcohol was significantly overpredicted,while the prediction of isobutylene and formaldehyde was underestimated.Compared with previous models,the present model has a much better performance against present pyrolysis data.Based on the rate of production(ROP)analysis and sensitivity analysis,the main reaction pathways in the pyrolysis of iso-pentanol were revealed.It shows that the contribution of unimolecular dissociation reactions to the consumption of fuel is far less than H abstraction reactions in the pyrolysis of iso-pentanol,which is similar to 2-methyl-1-butanol and iso-butanol,while different from n-pentanol and n-butanol.This result indicates that both carbon chain length and carbon chain structure have an important influence on the pyrolysis kinetics of alcohol fuels.Isomeric effect of three pentanol fuels was systematically studied based on the pyrolysis experiments of three pentanol isomers in this work,present model for iso-pentanol and our previous models for 2-methyl-1-butanol and n-pentanol.The experimental results show that the temperature window of two branched amyl alcohols is about 20 K earlier than that of linear amyl alcohol.This is mainly because the contributions of hydrogen abstraction reactions and unimolecular dissociation reactions to the consumption of fuel are different among different alcohols.In the pyrolysis of two branched amyl alcohols,the contribution of hydrogen abstraction reactions is much higher than that of unimolecular dissociation reactions to the consumption of fuel under 30 and 760 Torr.While the contribution of hydrogen abstraction reactions to the consumption of fuel in the pyrolysis of n-pentanol is lower than that in the pyrolysis of two branched amyl alcohols.Because of the isomeric effect,the dehydration products of three pentanol isomers are significantly different in their molecular structure and concentration.According to modeling analysis,it shows that in the pyrolysis of two branched amyl alcohols,the H abstraction reaction at C? site and subsequent ?-scission reaction contributes a lot to the consumption of fuel,and C5 olefins are mainly produced in this way.In the pyrolysis of n-pentanol,the dehydration reaction has a greater contribution to the formation of n-pentene.The contribution of H abstraction and subsequent ?-scission reaction of fuel radical is 2/3 lower than that in the pyrolysis of two branched amyl alcohols.Therefore,the highest mole fractions of 3-methyl-1-butene and 2-methyl-1-butene are both 2-3 times higher than that of n-pentene.The C4 olefins produced in pyrolysis of the three fuels are also significantly different.The ROP analysis shows that formation of C4 olefins are mainly dependent on the ?-C-C and ?-C-0 bond fission reactions of the fuel radicals.The pyrolysis of iso-pentanol,2-methyl-1-butanol,and n-pentanol mainly produce 3-methyl-1-butene,1-butene and 2-butene,and 1-butene,respectively.In terms of C1-C3 products,the most abundant hydrocarbon product is propene in the pyrolysis of iso-pentanol,while ethylene is the major product in the pyrolysis of 2-methyl-1-butanol and n-pentanol.In terms of oxygenated products,1-propenol and 2-propenol were detected in the pyrolysis 2-methyl-1-butanol and only 2-propenol was measured in n-pentanol.No C3 enol was detected in the pyrolysis of iso-pentanol due to the presence of methyl branch at the C? site.Finally,the production of benzene and fulvene in the pyrolysis of two branched amyl alcohols is significantly higher than that in the pyrolysis of linear alcohol,which is due to the higher production of propadiene and propyne in the pyrolysis of two branched amyl alcohols.In terms of C5 diolefins,2-methyl-1,3-butadiene can be generated only in the pyrolysis of two branched amyl alcohols,and the production of 1,3-cyclopentadiene is almost the same in the pyrolysis of three pentanol fuels.