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Thermal Decomposition of 2-Pentanol: A Shock Tube Study and RRKM Calculations Parandaman Arathala, and Balla Rajakumar J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.6b06386 • Publication Date (Web): 22 Sep 2016 Downloaded from http://pubs.acs.org on September 23, 2016

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The Journal of Physical Chemistry

Thermal Decomposition of 2-Pentanol: A Shock Tube Study and RRKM Calculations A. Parandaman and B. Rajakumar* Department of chemistry, Indian Institute of Technology Madras, Chennai-600036, India. *Address for correspondence: [email protected] Telephone number for the corresponding author(s) +91-44-2257-4231

Abstract Single pulse shock tube was used to study the thermal decomposition of 2-pentanol in the temperatures between 1110 and 1325 K. Three major decomposition products are methane, ethylene and propylene. The minor products detected in lower concentration are ethane, acetylene, acetaldehyde, 1-pentene and 2-pentene. The rate coefficient for the overall decomposition of 2-pentanol was found to be (1110-1325 K) = (4.01 ± 0.51) × 109 exp (-

(36.2 ± 4.7)/RT) s-1, where the activation energies are given in kcal mol-1. To simulate reactant and product distribution over the experimentally studied temperatures between 1110 and 1325 K, a reaction scheme was constructed with 34 species and 39 reactions. In addition to this, the temperature and pressure dependent rate coefficients were computed for various unimolecular dissociation pathways using RRKM theory. The high pressure limit rate coefficient for overall

decomposition of 2-pentanol was obtained to be (500-2500 K) = (9.67 ± 1.11) × 1014 exp (-(67.7 ± 2.9)/RT) s-1. The calculated high pressure rate coefficients and experimentally measured rate constants are in good agreement with each other. The reaction is majorly governed by the unimolecular elimination of water.

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1. Introduction The impact of fossil fuels on environment, increase in energy requirements and fuel cost have motivated serious search for alternative fuels in recent times. The suitable alternative fuels such as biofuels have been recommended in place of fossil fuels. Bioalcohol, biodiesel and biogas are known as biofuels, which are derived from biomass. It can be used in a pure form or in blend with fossil fuels.1-4 The interest in biofuels leads to consideration of alcohols as a fuel. The first generation biofuels, methanol and ethanol are extensively used in transportation sector all over the world. Approximately 90% of ethanol is used to produce biofuel all over the world,5,6 but ethanol have various drawbacks such as low energy density, high hygroscopicity and corrosiveness towards pipelines and engines.7,8 The next generation biofuels, butanol and pentanol were considered as potential biofuels,9-11 they exhibit better combustion properties including lower hygroscopicity and corrosivity, greater energy density and can be readily mixed with hydrocarbon fuels in fueling systems.12,13 The main disadvantage of biofuels is the formation of carbonyl compounds in the decomposition, which will further act as pollutants.6,14 Hence, the detailed mechanisms of the decomposition of these compounds are required in various conditions to get the best possible understanding of the combustion. The combustion of methanol and ethanol was studied by using various experimental techniques.15 The next generation alcohol is butanol, which is widely studied by combustion community over the last half a decade. Many experimental results on pyrolysis and oxidation of butanols were reported under various experimental conditions.9,16-18 Various computational methods were used to determine the rate coefficients and to understand various reaction 2 ACS Paragon Plus Environment

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pathways involved in combustion of butanol.19,20 As a consequence, several research groups have developed chemical kinetic models for combustion of butanol in different conditions.16,18,21 Studies on the combustion of pentanol are very limited. The oxidation mechanism of isopentanol was studied at lower temperatures between 550 and 750 K by Weltz et al.22 using time-resolved tunable synchrotron photo ionization mass spectrometry. Togbe et al.6 studied decomposition of n-pentanol and isopentanol using jet stirred reactor (JSR) and reported the complete kinetic models for n-pentanol and isopentanol. Zhao et al.23 studied thermal decomposition of 1-pentanol and its isomers using computational methods. There are no experimental and computational studies on thermal decomposition of 2pentanol are reported so far. Thermal decomposition of 2-pentanol, was carried out using shock tube for the first time in the temperatures between 1110 and 1325 K. In this study, the most suitable mechanism for the decomposition was proposed by following the complete degradation of reactant and formation of products. To understand the experimental results further, unimolecular decomposition reactions of 2-pentanol and their rate coefficients were explored with computational methods coupled with RRKM theory. The calculated and measured rate coefficients were compared with each other. The possible mechanism for overall decomposition was proposed and simulated. This present study reports complete decomposition mechanism of 2-pentanol in the studied temperature range.

2. Experimental Section Single Pulse Shock Tube (SPST) was used to carry out experiments in the present study. The detailed description of the SPST set-up used in this work were discussed elsewhere.24,25 The samples containing 6 Torr of 2-pentanol and 60 Torr of diluted (1.7% in argon) 1,1,1-



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trifluoroethane (CH3CF3) were added and diluted with argon up to the desired pressure (typically in the range of 200-600 Torr) depending on the required temperature in the test section. The temperatures behind the reflected shock waves were measured using chemical thermometric method.26,27 CH3CF3 was used as an internal standard to determine reaction temperature. It decomposes into CH2=CF2 + HF via a first order unimolecular reaction, whose rate constant of k = 8.14 × 1013exp (-71154/RT) s-1. Where the activation energy is given in cal mol-1 was reported earlier.28 The detailed description of measuring the reaction temperature using CH3CF3 as internal standard was given in our previous work.25 The experimental procedure was described in our recently reported articles24,25 and similar procedure was followed in the current experimentation. The post shock samples were withdrawn from the end of the driven section of the shock tube and were analyzed using gas chromatograph (Agilent Technologies 6890N) with a Flame Ionization Detector (FID). A 2 m long packed Hayesep-A column was used for the analysis and the oven temperature was programmed between 75 and 1500C. The method described in our previous work25 was followed here in measuring the concentrations of all the components of the post shocked mixture. The post shock mixture was also analyzed qualitatively using FTIR spectrometer (Bruker's VERTEX 70) as described earlier.24,25

3. Materials and chemicals The purities of the chemicals were as follows: Helium, HP certified to >99.995%, (Praxair); Argon (Ar), certified to >99.995%; 2-Pentanol, >99% (Sigma Aldrich); 1-pentene, >99.5% (Sigma Aldrich), 2-pentene, >99%, (Sigma Aldrich); acetaldehyde 99% (Sigma Aldrich), CH3CF3 (99%) and CH2CF2(99%) were purchased from SynQuest Laboratories are 4 ACS Paragon Plus Environment

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used in these experiments. Methane (99.5%), propylene (99.5%), ethane (99.5%) and ethylene (99.5%) are purchased from Praxair and were used without further purification in the present work.

4. Computational 4.1. Quantum chemical calculations Geometries of reactant (2-pentanol), transition states (TSs) and products of possible unimolecular dissociation channels of 2-pentanol were optimized at M06-2X level of theory with basis set29,30 6-31+G(d,p) which are internally available in Gaussian 09 program suite.31 The basis set 6-31+G(d,p) includes polarization functions on over all atoms and diffuse functions on non-hydrogen atoms. Various previous studies25,32,33 used 6-31+G(d,p) basis set for predicting reliable geometries and vibrational frequency calculations of the stationary points for the similar molecules. Therefore, 6-31+G(d,p) was used as a basis set in the present calculations. The optimized reactant and products were identified with zero imaginary frequency and transition states identified with one imaginary frequency. The Intrinsic Reaction Coordinate calculations34 was carried out to obtain the minimum energy path (MEP) at M06-2X functional with 631+G(d,p) basis set to confirm that the designated transition states connect the reactant and products. The normal modes of all the stationary points are viewed in Gauss View.35 The pressure and temperature dependentrate coefficients were calculated for unimolecular dissociation reactions of 2-pentanol with RRKM theory using KiSThelP program.36 Lennard-Jones (L-J) potential was used to model the interaction between reactant and bath gas Ar. The Lennard Jones parameters σ and ε/k for 2-pentanol and Ar were calculated using the following equations37



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σ = 2.44T ⁄P ⁄ = 0.77!" Where TC and PC are critical temperature and critical pressure respectively taken from NIST database.38 kB is the Boltzmann constant. The L-J parameters for 2-pentanol σ = 6.046 Å and ε/kb = 431.2 K were used in present study. The L-J parameters for Ar bath gas are σ = 3.47 Å and ε/kb = 113.5 K, which were taken from KiSThelP program.36

5. Results and discussion 5.1 Experimental Section In the present study, a total of 38 experiments were performed to determine the distribution of reaction products over the temperature range of 1110-1325 K. The normalized concentrations of reactant, all other products of each experiment and the experimental conditions are given in Table 1. The decomposition products of 2-pentanol and CH3CF3 were identified to be methane, ethane, ethylene, acetylene, 1,1-difluoroethylene, propylene, acetaldehyde, 1pentene and 2-pentene. 1,1-difluoroethylene (CH2CF2) is the decomposition product of CH3CF3, which was used as internal standard. Remaining products were formed solely from the decomposition of 2-pentanol. To confirm this, only 2-pentanol diluted with argon was decomposed using shock tube in the studied temperature range and all these products were identified. Typical chromatogram of the post shocked mixture obtained where the test mixture was heated to 1276 K is shown in Figure 1. The FTIR spectrum of the post shock mixture of 2-pentanol decomposed at 1276 K is shown in Figure 2. The IR spectrum analysis indicates the presence of 2-pentanol, methane, ethylene, acetylene and CO. The medium intense bands in the region 3100-3400 cm-1 and at 975 6 ACS Paragon Plus Environment

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cm-1 are assigned to the existence of 2-pentanol. The medium intensity bands in the region 20502220 cm-1 represents the presence of CO. The presence of acetylene was indicated by the bands at 3250-3300 cm-1 and high intense band at 750 cm-1. The distribution of the normalized concentrations of reactant and all other products in the studied temperature range are shown in Figure 3. Concentrations of products methane, ethylene, ethane, acetylene and acetaldehyde are found to be increasing with the increase in temperature. The concentrations of propylene was found to be increasing up to 1250 K and then started decreasing. The other products 1-pentene and 2-pentene are found to be increasing up to 1200 K and then decreasing. The first order rate coefficients for the total decomposition of 2-pentanol was determined by using the following equation, 1 (2 − )*'%+',&- = − &' % (2 − )*'%+',&-. Where [2-pentanol]t and [2-pentanol]0 are experimentally quantified concentrations of 2pentanol at the end of the reaction time ‘t’ and initial concentration respectively. The Arrhenius plot of the experimentally measured rate coefficients is shown in Figure 4. The rate coefficients data were fit by linear least square method. The obtained Arrhenius expression for the overall decomposition of 2-pentanol in the studied temperature range is (1110-1325 K) = (4.01 ±

0.51) × 109exp (-(36.2 ± 4.7)/RT) s-1. The rate coefficients obtained using RRKM theory, are also appended to Figure 4 for comparison. The experimentally measured and computed rate coefficients shows very good agreement with each other in the studied temperatures between 1110 and 1325 K, vide infra. The detailed error analysis was performed to quantify the total error in the experimentally measured rate coefficients in the studied temperature range. The procedure for the estimation of the errors was reported in our recent work.25 The total uncertainties from all sources in the 7 ACS Paragon Plus Environment


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experimental measurements were calculated using a root-sum-squared method. The estimated overall (2σ) uncertainty in the present experiments is ± 21%.

5.2 Computational 5.2.1 Electronic structures and energetics The geometries of all the stationary points optimized at M06-2X/6-31+G(d,p) level of theory are shown in Figure 5. The energy level diagram consists of reactant, transition states and products are labeled for the reactions R1-R7 is given in Figure S-I of the Supporting Information. The energy barriers for unimolecular decomposition of 2-pentanol estimated at same level of theory are given in Table 2. The structural parameters and vibrational frequencies of all the stationary points involved in the reactions R1-R7 obtained at the M06-2X/6-31+G(d,p) level of theory are given in the Supporting Information, SI (Tables S-I to S-II). Figure S-II in the Supporting Information reports R1-R7 reaction channels with corresponding structures identified for the unimolecular thermal decomposition of 2-pentanol. 2-pentanol undergoes seven unimolecular pathways which are labeled as R1-R7. These pathways yield stable reaction products through transition states. The molecular elimination channel R1 goes through four membered ring transition state (TS1) to form 1-pentene (P1) and H2O (P2) with barrier energy of 64.6 kcal mol-1. Similarly, reaction channel R2 goes through four membered ring transition state (TS2) to form 2-pentene (P3) and H2O (P4) but with the barrier of 66.9 kcal mol-1. Reaction channel R3 yields ethane (P5) and acetone (P6) by the transfer of –OH group hydrogen to methylene (-CH2-) group followed by C-C bond dissociation through transition state (TS3) with the energy barrier of 101 kcal mol-1. Reaction channel R4 forms ethylene (P7) and 2-hydroxy propane (P8) through transition state TS4 by intramolecular 8 ACS Paragon Plus Environment

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transfer of hydrogen atom from –CH3 group to –CH2 group followed by CH2-CH2 bond dissociation with a barrier of 113 kcal mol-1. Reaction R5 forms butyraldehyde (P9) and methane (P10) through transition state TS5 by migration of hydrogen atom from –OH group to –CH3 group followed by CH(OH)-CH3 bond dissociation with barrier of 84 kcal mol-1. The reaction R6 produces methane (P11), ethylene (P12) and acetaldehyde (P13) by transfer of H atom from –OH group to methyl group followed by CH3-CH2 bond dissociation with a barrier of 94 kcal mol-1. The reaction R7 produces propane (P14) and acetaldehyde (P15) via migration of hydrogen atom from –OH group to –CH2 group followed by CH2-CH(OH) bond dissociation with a barrier of 85 kcal mol-1. It is clear that the reaction pathways R3 and R4 are very high barrier reactions and are less possible in the current experimental conditions. However, they are included in our computations for the completeness. It is obvious from these seven channels that, the reaction channel R1 is energetically more favorable when compared with all the other possible reaction channels.

5.2.2. Kinetic analysis The pressure and temperature dependent rate coefficients for the seven unimolecular reaction channels (R1-R7) were calculated using RRKM theory in the temperatures between 500 and 2500 K with KiSThelP program. Among all the channels, formation of 1-pentene (R1) reaction pathway is the major one. The rate coefficients were calculated by varying the pressure from low to high pressures i.e. 0.01 atm, 0.1 atm, 1 atm, 10 atm and 100 atm for all the seven pathways. The computed high pressure limit rate coefficients for all the reaction channels R1-R7 are plotted over the temperature between 500 and 2500 K are shown in Figure 6. The pressure and temperature dependent Arrhenius plot over the temperatures between 1300 and 2500 K and



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pressure range of 0.01-100 atm for the major channel R1 is shown in Figure 7, as this channel is the major contributor. As seen from Figure 7, the rate coefficient is pressure independent at temperatures below 1400 K, but at temperatures above 1400 K the rate coefficient is found to be increasing with increase in pressure. The individual rate coefficients of the unimolecular reaction channels were added to obtain the overall rate coefficient for the title reaction. The comparison of reported rate coefficients with the current experimentally measured rate coefficients in the studied temperature range is shown in Figure 4. The linear least squares method was used to fit the computed rate coefficients between 500 and 2500 K. The obtained temperature dependent Arrhenius expression

is (500-2500 K) = (9.67 ± 1.11) × 1014exp [-(67.7 ± 2.9)/RT] s-1, where the activation energies are given in kcal mol-1. The rate coefficients calculated using RRKM theory and experimentally measured rate coefficients in the temperature between 1110 and 1325 K are in very good agreement with each other.

6. Kinetic simulations The reaction scheme given in Table 3 was proposed for understanding the reaction mechanism and also to model the distribution of the concentrations of reactant and products. The proposed reaction scheme contains 34 species and 39 elementary reactions. The rate coefficients are expressed as k = A exp(-Ea/RT) or k = A Tnexp(-Ea/RT) and are given in Table 3. The experimentally determined temperatures and reaction times were used in kinetic simulations. The plot of the concentrations obtained in the simulation using proposed reaction mechanism and experimentally measured concentrations are shown in Figure 3a-i. The simulated concentrations


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of all the products and the reactants are in good agreement with experimentally measured concentrations. 2-pentanol decomposes via three possible channels, which are unimolecular. These reactions include water elimination, intramolecular hydrogen transfer and simple bond scission reactions (C-C, C-O, C-H and O-H). The rate coefficients for reactions R1-R7 were taken from the RRKM calculations and all other reactions rate coefficients were taken from past research works from various groups.39-52 The H2O elimination always has the lowest energy barrier than the other small molecular elimination reactions in thermal decomposition of 2-pentanol. The energy barrier for water elimination reactions is 10 kcal mol-1 lesser than the other molecular elimination reaction (methane, ethylene etc.). CH3-CH2-CH2-CH(OH)-CH3 → CH3-CH2-CH2-CH=CH2 + H2O k1 = 1.58 × 1014exp (-67.1/RT) s-1

(R1)

CH3-CH2-CH2-CH(OH)-CH3 → CH3-CH2-CH=CH-CH3 + H2O k2 = 3.01 × 1014exp (-69.5/RT) s-1

(R2)

In the decomposition of 2-pentanol, four homolytic C-C bond scissions and one C-O bond scission are quite possible, particularly in the studied temperature range. The C-C bond and C-O bond energies are much lower than those of C-H and O-H bonds.18,53,54 Therefore, the former type of bond scission processes would not compete with the latter ones and hence, they were not included in the proposed reaction scheme. CH3-CH2-CH2-CH(OH)-CH3 → CH3 + CH2-CH2-CH(OH)-CH3 k8 = 5.12 × 1026(T)-2.92exp (-90.5/RT) s-1 11 ACS Paragon Plus Environment

(R8)


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CH3-CH2-CH2-CH(OH)-CH3 → CH3-CH2 + CH2-CH(OH)-CH3 k9 = 8.54 × 1027 (T)-3.23exp (-91.7/RT) s-1

(R9)

CH3-CH2-CH2-CH(OH)-CH3 → CH3-CH2-CH2 + CH(OH)-CH3 k10 = 3.01 × 1025 (T)-2.57exp (-89.9/RT) s-1

(R10)

CH3-CH2-CH2-CH(OH)-CH3 → CH3-CH2-CH2-CH-CH3 + OH k11 = 2.82 × 1029 (T)-3.60exp (-101.9/RT) s-1

(R11)

CH3-CH2-CH2-CH(OH)-CH3 → CH3-CH2-CH2-CH(OH) + CH3 k12 = 5.13 × 1026 (T)-2.91exp (-90.5/RT) s-1

(R12)

6.1 Methane In the studied experimental temperature range, the maximum concentration of methane was found to beabout 24%. The methyl radicals formed in the decomposition of 2-pentanol play a major role in the formation of methane through reactions R8, R12 and R24. The formed CH3 radicals react with H atom (R16), abstract H atom from ethylene (R19) and water (R26) and form methane. CH3 + H → CH4

k16 = 6.93 × 1013(T)0.18cm3mol-1s-1

(R16)

C2H4 + CH3 → C2H3 + CH4

k19 = 4.16 × 1012exp (-11.1/RT) cm3mol-1s-1

(R19)

CH3 + H2O → CH4 + OH

k26 = 0.64 × 101(T)3.31exp (-12.6/RT) cm3mol-1s-1

(R26)

The reactions R5 and R6 are added to the reaction scheme for the direct formation of methane from 2-pentanol, whose rate coefficients were calculated using RRKM theory. In reaction R6, 12 ACS Paragon Plus Environment

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The transfer of H atom from –OH group to –CH3 group followed by CH3-CH2 bond dissociation by forming the products CH4 and CH3-CH(O)-CH2-CH2. The formed unstable biradical product CH3-CH(O)-CH2-CH2 will immediately undergo decomposition at CH(O)-CH bond by forming stable products acetaldehyde and ethylene. CH3-CH2-CH2-CH(OH)-CH3 → CH4 + CH3-CH2-CH2-CHO k5 = 1.92 × 1014exp (-86.2/RT) s-1

(R5)

CH3-CH2-CH2-CH(OH)-CH3 → CH4 + C2H4 + CH3-CHO k6 = 1.60 × 1014exp (-96.1/RT) s-1

(R6)

Methane is also formed from acetaldehyde via direct molecular elimination of CO (R17). The contribution of this reaction is very less, as maximum concentration of acetaldehyde formed in the reaction is 7%. In addition, the activation energy for this reaction is very high (85 kcal mol-1). CH3-C(O)-H → CH4 + CO

k17 = 1.00 × 1015exp (-85.0/RT) s-1

(R17)

On the other hand, the formed methane react with H atom (R37) and methyl radicals (R38) to regenerate methyl and ethyl radicals respectively. CH4 + H → H2 + CH3

k37 = 1.77 × 1014 exp (-13.8/RT) cm3mol-1s-1

(R37)

CH4 + CH3 → H2 + CH3-CH2

k38 = 1.00 × 1013exp (-23.1/RT) cm3mol-1s-1

(R38)

The rate coefficients of all the elementary reactions were varied by a factor of 10 in order to analyze the sensitivity towards the formation and decomposition of methane. The sensitivity of each reaction in terms of percentage change in the concentrations with respect to the reaction numbers are given in Table 4. The reactions R8 (C4-C5 bond scission in the reactant), R12 (C4C5 bond scission in the reactant) and R24 (C4-C5 bond scission in 1-pentene, which is formed 13 ACS Paragon Plus Environment


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via 1,2- unimolecular elimination of H2O from 2-pentanol through the reaction R1) are very sensitive to the formation of CH4. Therefore, methyl radicals plays major role for the formation of methane. Reactions R1 and R2 (2,3- unimolecular elimination of H2O from 2-pentanol) also shows major impact on the formation of methane.

6.2 Ethylene The decomposition of 2-pentanol leads to the formation of ethylene, which is one of the major product. Maximum concentrations of C2H4 were found to be 39% which is formed via reactions R4 and R6. The rate coefficients for these reactions were taken from the present RRKM calculations. R6 is a low barrier (96.1 kcal mol-1) reaction than that of R4 (115.9 kcal mol-1) and hence it contributes more to the formation of ethylene. CH3-CH2-CH2-CH(OH)-CH3 → C2H4 + CH3-CH(OH)-CH3 k4 = 6.01 × 1014exp (-115.9/RT) s-1

(R4)

CH3-CH2-CH2-CH(OH)-CH3 → CH4 + C2H4 + CH3-CHO k6 = 1.60 × 1014exp (-96.1/RT) s-1

(R6)

Initially, it was assumed that ethylene could be the product from reactions of methyl and other radicals formed in the decomposition of the reactant via following reactions CH3-CH2 → C2H4 + H

k14 = 3.06 × 1010(T)0.95exp (-36.9/RT) s-1

(R14)

2 CH3 → C2H4 + H2

k18 = 9.90 × 1015exp (-32.9/RT) cm3mol-1s-1

(R18)

C2H3 + H → C2H4

k20 = 3.88 × 1013(T)0.20cm3mol-1s-1

(R20)


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C2H2 + H2 → C2H4

k39 = 3.01 × 1011exp(-38.9/RT) cm3mol-1s-1

(R39)

All the above reactions involve CH3, C2H5, C2H3 radicals. Among all the above reactions involving CH3, C2H5, C2H3 radicals, reaction R14 and R18 are expected to contribute more as the concentrations of methyl and ethyl radicals are higher when compared to that of C2H3 radicals. The sensitivity analysis of the proposed reaction scheme is carried out for the formation of C2H4 and the results are given in Table 4. Reactions R1(1,2- unimolecular elimination of H2O from 2pentanol to form 1-pentene which further decompose via C-C bond scission to form C2H5 radicals in R25), R9 (C3-C4 bond scission in the reactant), R14 (decomposition of ethyl radical to form ethylene), R23 (ethane reacts with H atom to form C2H5 radicals) and R25 show significant sensitivity towards the formation of C2H4.

6.3 Propylene It was observed that the propylene concentration was increasing up to 1250 K and further increase in the temperature leads to decrement in concentration of propylene. The main possible reaction for the formation of propylene is the decomposition of propyl radical through reaction R15. The other minor reaction channels for the formation of propylene are R30 and R33. CH3-CH2-CH2 → C3H6 + H

k15 = 4.14 × 1012(T)0.17exp(-35.6/RT) s-1

CH3-CH2-CH2-CH-CH3→ C3H6 + CH3-CH2 k30 = 1.22 × 1012(T)0.64exp(-29.4/RT) s-1 CH2-CH(OH)-CH3 → CH3-CH=CH2 + OH

k33 = 3.70 × 1012exp(-26.8/RT) s-1


(R15) (R30) (R33)


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The concentration of propylene decreases above 1250 K due to its own dissociation (R34) to form CH3 and C2H3 radicals and reaction with H atom to form n-C3H7 and iso-C3H7 radicals through reactions R35 and R36 respectively. C3H6 → CH3 + C2H3

k34 = 8.00 × 1014exp(-88.0/RT) s-1

(R34)

C3H6 + H → n-C3H7

k35 = 4.57 × 1012(T)0.51exp(-2.6/RT) cm3mol-1s-1

(R35)

C3H6 + H → iso-C3H7

k36 = 7.75 × 1012(T)0.51exp(-1.2/RT) cm3mol-1s-1

(R36)

The sensitivity analysis in Table 4 shows that reaction R10 (C2-C3 bond scission in the reactant to form C3H7 radicals) will have significant sensitivity towards the formation of propylene.

6.4 Minor products The detectedminor reaction products in the decomposition of 2-pentanol were ethane, acetylene, acetaldehyde, 1-pentene and 2-pentene. On comparing it with main reaction products, the concentrations of these individual minor products are found to be less than 10%. Another insignificant product that was identified was CO, which was qualitatively analyzed by FTIR spectroscopy. The concentrations of products ethane, acetylene and acetaldehyde were observed to be increasing in the studied temperature range. The concentrations of the other two products 1pentene and 2-pentene seem to be increasing up to 1200 K and beyond this the concentrations were found to be decreasing with the increase in temperature. The major channel for the production of C2H6 is the molecular elimination of ethane through reaction R3 and reaction between ethyl radical with H atom and water molecule through reactions R13 and R15 respectively. CH3-CH2-CH2-CH(OH)-CH3 → C2H6 + CH3-C(O)-CH3 16 ACS Paragon Plus Environment

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


k3 = 1.90 × 1014exp (-103.4/RT) s-1

(R3)

CH3-CH2 + H → C2H6

k13 = 5.44 × 1013(T)0.16cm3mol-1s-1

(R13)

C2H5 + H2O → C2H6 + OH

k52 = 3.39 × 106(T)1.44exp (-20.3/RT) cm3mol-1s-1

(R52)

The reaction channels through which acetylene can be formed using the present scheme are R22 and R31. The maximum concentration of acetylene in present experimental study was measured to be 6%. C2H3 + H → C2H2 + H2

k22 = 1.21 × 1013cm3mol-1s-1

(R22)

C3H5 → C2H2 + CH3

k31 = 1.26 × 1013exp (-33.7/RT) s-1

(R31)

Acetaldehyde concentration in the present experiments was measured to be around 7%. It was formed through reactions R7 and R21. CH3-CH2-CH2-CH(OH)-CH3 → C3H8 + CH3-CHO k7 = 9.44 × 1013exp (-86.4/RT) s-1 (R7) CH(OH)-CH3 → CH3-CHO + H

k21 = 5.00 × 1013exp (-21.9/RT) s-1

(R21)

1-pentene and 2-pentenewere formed through unimolecular elimination of water from 2pentanol through reactions R1 and R2. These two reaction products were observed to get decomposed beyond 1200 K and the reactions were added in the reaction scheme. The rate coefficients for C-C bond scission reactions of 1-pentene and 2-pentene are not available in the literature. Therefore, the rate coefficients for the C-C bond scissions were taken from the analogous systems such as 1-butene and 2-butene.47 CH3-CH2-CH2-CH=CH2 → CH3+ CH2-CH2-CH=CH2



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

k24 = 1.10 × 1016exp (-72.9/RT) s-1

Page 18 of 42

(R24)

CH3-CH2-CH2-CH=CH2 → CH3-CH2+ CH2-CH=CH2 k25 = 1.10 × 1016exp (-70.7/RT) s-1

(R25)

CH3-CH2-CH=CH-CH3 → CH3 + CH2-CH=CH-CH3 k28 = 3.16 × 1017exp (-99.4/RT) s-1

(R28)

CH3-CH2-CH=CH-CH3 → CH3 + CH3-CH2-CH=CH k27 = 3.16 × 1017exp (-99.4/RT) s-1

(R27)

CH3-CH2-CH=CH-CH3 → CH3-CH2 + CH3-CH=CH k29 = 1.00 × 1016exp (-75.7/RT) s-1

(R29)

Sensitivity analysis was carried out for the formation and decomposition of minor products and the results are given in Table 4. The reactions R1, R2, R9 and R32 shows more sensitivity towards the formation of ethane. Reaction R29 has shown more sensitivity towards the formation of C2H2. Reaction R10 is more sensitive for the formation of acetaldehyde. Reactions R1 and R2 have shown significant sensitivity towards the formation of 1-pentene and 2-pentene.

7. Conclusions Thermal decomposition of 2-pentanol was studied in the temperatures between 1110 and 1325 K. The main reaction products identified in the experiments were methane, ethylene and propylene; and the minor reaction products detected in lower concentrations were ethane, acetylene, acetaldehyde, 1-pentene and 2-pentene. The rate coefficient for the overall


Page 19 of 42

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decomposition of 2-pentanol was found to be (1110-1325 K) = (4.01 ± 0.51) × 109exp (-

(36.2 ± 4.7)/RT) s-1. The major unimolecular decomposition pathways of 2-pentanol were investigated using computational methods. The RRKM theory was used to calculate the rate coefficients for unimolecular decomposition reactions. Among the unimolecular decomposition pathways, elimination of H2O was found to be the major channel giving 1-pentene. The obtained

temperature dependent Arrhenius expression in studied temperature range is (500-2500 K) = (9.67 ± 1.11) × 1014exp (-(67.7 kcal mol-1 ± 2.9)/RT) s-1. A reaction scheme for the decomposition of 2-pentanol was constructed with 34 species and 39 reactions. The simulated concentrations of all the products and the reactants shows good agreement with experimentally measured concentrations using proposed reaction scheme and the results can be used for further improvement in the accuracy and completeness of the 2-pentanol kinetic mechanism. The formation of methane, ethane and other lower hydrocarbons could be explained only when C-C bond scission was taken into consideration in the kinetic mechanism. The decomposition of the test molecule by C-C bond scission at various positions was competing with H2O elimination. The formation of carbon monoxide in the decomposition of 2-pentanol should be taken into consideration, before its use as a biofuel additive.

Supporting Information Table S-I. Optimized geometries of the reactant, transition states and products at M06-2X level of theory with 6-31+G( d, p) basis set. Table S-II. Vibrational frequencies (cm-1) of the reactant, transition states and products at M062X level of theory with 6-31+G (d, p) basis set.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 42

Figure S-I. Potential energy surfaces of reaction pathways R1-R7 computed using the M062X/6-31+G(d,p) level of theory. The energies are given in the units of kcal mol-1. Figure S-II. The considered reaction pathways (R1-R7) for the unimolecular decomposition of 2-pentanol (The rate coefficients of these reactions were calculated using RRKM theory were used in the kinetic simulations).

Acknowledgment B.R. thanks Defence Research and Development Organization (DRDO), Government of India for funding. A.P. is very grateful to CSIR for providing a research fellowship. A.P. also thank Mr. G. Sudhakar and Mr. G. Srinivasulu for their help in doing the experiments.

References (1) Azad, A. K.; Rasul, M. G.; Khan, M. M. K.; Sharma, S. C.; Hazrat, M. A. Prospect of biofuels as an alternative transport fuel in Australia. Renew Sust Energy Rev 2015, 43, 331-351. (2) Varuvel, E. G.; Mrad, N.; Tazerout, M.; Aloui, F. Experimental analysis of biofuel as an alternative fuel for diesel engines. Appl Energy 2012, 94, 224-231. (3) Kohse-Hoinghaus, K.; Osswald, P.; Cool, T. A.; Kasper, T.; Hansen, N.; Qi, F.; Westbrook, C. K.; Westmoreland, P. R. Biofuel combustion chemistry: From ethanol to biodiesel. Angew. Chem.2010, 49, 3572-3597. (4) Christian, W.; Alexander, F.; Feline, B.; Dawid, B.; Heiko, D.; Thorsten, S.; Eckhard, B.; Trends and challenges in the microbial production of lingo cellulosic bioalcohol fuels. Appl. Microbiol. Biotechnol. 2010, 87, 1303-1315. (5) Tang, C.; Wei, L.; Man, X.; Zhang, J.; Huang, Z. High temperature ignition delay times of C5 primary alcohols. Combust. Flame 2012, 160, 520-529. (6) Togbe, C.; Halter, F.; Foucher, F.; Mounaim-Rousselle, C.; Dagaut, P. Experimental and detailed kinetic modeling study of 1-pentanol oxidation in a JSR and combustion in a bomb. Proc. Combust. Inst. 2011, 33, 367-374.


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(19) El-Nahas, A. M.; Mangood, A. H.; Takeuchi, H.; Taketsugu, T. Thermal decomposition of 2-butanol as a potential non fossil fuel: A computational study. J. Phys. Chem. A 2011, 115, 2837-2846. (20) Zhou, C. W.; Simmie, J. M.; Curran, H. J. Rate constants for hydrogen-abstraction by image from n-butanol. Combust. Flame 2011, 158, 726-731. (21) Black, G.; Curran, H. J.; Pichon, S.; Simmie, J. M.; Zhukov, V. Bio-butanol: combustion properties and detailed chemical kinetic model. Combust. Flame 2010, 157, 363-373. (22) Welz, O.; Zádor, J.; Savee, J. D.; Ng, M. Y.; Meloni, G.; Fernandes, R. X.; Sheps, L.; Simmons, B. A.; Lee, T. S.; Osborn, D. L.; Taatjes, C. A. Low-temperature combustion chemistry of biofuels: pathways in the initial low-temperature (550 K–750 K) oxidation chemistry of isopentanol. Phys. Chem. Chem. Phys. 2012, 14, 3112-3127. (23) Zhao, L.; Ye, L.; Zhang, F.; Zhang, L.Thermal decomposition of 1‑pentanol and Its isomers: A theoretical study. J. Phys. Chem. A 2012, 116, 9238-9244. (24) Sudhakar, G.; Rajakumar, B. Thermal decomposition of 1-chloropropane behind the reflected shock waves in the temperature range of 1015-1220 K: Single pulse shock tube and computational studies. J. Chem. Sci. 2014, 126, 897-909. (25) Parandaman, A.; Balaganesh, M.; Rajakumar, B. Experimental and theoretical study on thermal decomposition of methyl butanoate behind reflected shock waves. RSC Adv., 2015, 5, 86536–86550. (26) Lifshitz, A.; Tamburu, C.; Suslensky, A. Decomposition and isomerization of 1,2benzisoxazole: Single-pulse shock-tube experiments, quantum chemical and transition-state theory calculations. J. Phys. Chem. A 2006, 110, 11677-11683. (27) Manion, J. A.; Awan, I. A. Evaluated kinetics of terminal and non-terminal addition of hydrogen atoms to 1-alkene: a shock tube study of H + 1-butene. J. Phys. Chem. A, 2015, 119, 429-441. (28) Akira, M.; Kenji, Y.; Hiroumi, S. Thermal decomposition of 1,1,1-Trifluoroethane revisited. J. Phys. Chem. A 2014, 118, 11688-11695. (29) Zhao, Y.; Truhlar, D. G. Density functionals with broad applicability in chemistry. Acc. Chem. Res., 2008, 41, 157-161. (30) Zhao, Y.; Truhlar, D. G. The M06 suite of density functionals for main group thermochemistry, thermochemical kinetics, noncovalent interactions, excited states, and 22 ACS Paragon Plus Environment

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transition elements: two new functionals and systematic testing of four M06-class functionals and 12 other functional. Theor. Chem. Acc., 2008, 120, 215-241. (31) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A. Gaussian 09, Revision B.01, Gaussian, Inc., Wallingford, CT. 2010. (32) Li, Q. S.; Zhang,Y.; Zhang, S. Dual Level Direct ab Initio and Density-Functional Theory Dynamics Study on the Unimolecular Decomposition of CH3OCH2 Radical J. Phys. Chem. A 2004, 108, 2014-2019. (33) Mishra, B. K.; Chakrabartty, A. K.; Bhattacharjee, D.; Deka, R. C. Theoretical investigation on unimolecular decomposition of malonic acid: a potential sink for ketene. RSC Adv., 2014, 4, 38034–38039. (34) Gonzalez, C.; Schlegel, H. B. An improved algorithm for reaction path following. J. Chem. Phys. 1989, 90, 2154-2161. (35) Dennington, I. I. R.; Keith, T.; Millam, J.; Eppinnett, K.; Hovell, W. L.; Gilliland, R. Gauss View, Version 3.09; Semichem, Inc.: Shawnee Mission, KS.2003. (36) Canneaux, S.; Bohr, F.; Hénon, E. KiSThelP: a program to predict thermodynamic properties and rate constants from quantum chemistry results, J. Comp. Chem.2014, 35, 82-93. (37) Welty, J. R.; Wicks, C. E.; Wilson, R. E.; Rorrer, G. L. Fundamentals of Momentum, Heat and Mass Transfer, 4th ed.; JohnWiley and Sons Ltd.: New York, 2001. (38) Gude, M.; Teja, A. S. Vapor-liquid critical properties of elements and compounds. 4. aliphatic alkanols, J. Chem. Eng. Data,1995, 40, 1025-1036. (39) Harding, L. B.; Georgievskii, Y.; Klippenstein, S. J. Predictive theory for hydrogen atomHydrocarbon radical association kinetics. J. Phys. Chem. A 2005, 109, 4646-4656. (40) Curran, H. J. Rate constant estimation for C-1 to C-4 alkyl and alkoxyl radical decomposition. Int. J. Chem. Kinet. 2006, 38, 250-275. (41) Yasunaga, K.; Kubo, S.; Hoshikawa, H.; Kamesawa, T.; Hidaka, Y. Shock-tube and modeling study of acetaldehyde pyrolysis and oxidation. Int. J. Chem. Kinet. 2008, 40, 73-102. (42) Kern, R. D.; Singh, H. J.; Wu, C. H. Thermal decomposition of 1,2 butadiene. Int. J. Chem. Kinet.1988, 20, 731-747.



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(43) Baulch, D. L.; Cobos, C. J.; Cox, R. A.; Esser, C.; Frank, P.; Just, T.; Kerr, J. A.; Pilling, M. J.; Troe, J.; Walker, R. W et al. Evaluated kinetic data for combustion modelling. J. Phys. Chem. Ref. Data, 1992, 21, 411-429. (44) Natarajan, K.; Bhaskaran, K. A. Experimental and analytical investigation of high temperature ignition of ethanol. No. AD-P-000310/3. Indian Inst. of Tech., Madras. Dept. of Mechanical Engineering. 1981. (45) Cao, J. R.; Back, M. H. Kinetics of the reaction H + C2H6 → H2 + C2H5 in the temperature reaction of 1000 K. Can. J. Chem. 1984, 62, 86-91. (46) Ma, S.; Liu, R. Theoretical studies on the reaction path and dynamics of the reaction CH3+H2O → CH4 + OH. Sci. China Ser. B 1996, 39, 37-44. (47) Dean, A. M. Predictions of pressure and temperature effects upon radical addition and recombination reactions. J. Phys. Chem. 1985, 89, 4600-4608. (48) Tsang, W.; Hampson, R. F. Chemical kinetic data base for combustion chemistry. Part I. Methane and related compounds. J. Phys. Chem. Ref. Data, 1986, 15, 1087-1279. (49) Dunlop, J. R.; Tully, F. P. Catalytic dehydration of alcohols by OH. 2-propanol: an intermediate case. J. Phys. Chem. 1993, 97, 6457-6464. (50) Hidaka, Y.; Nakamura, T.; Tanaka, H.; Jinno, A.; Kawano, H. Shock tube and modeling study of propene pyrolysis. Int. J. Chem. Kinet. 1992, 24, 761-780. (51) Sutherland, J. W.; Su, M. C.; Michael, J. V. Rate constants for H + CH4, CH3 + H2, and CH4 dissociation at high temperature. Int J. Chem. Kinet. 2001, 33, 669-684. (52) Tabayashi, K.; Bauer, S. H. The early stages of pyrolysis and oxidation of methane. Combust. Flame 1979, 34, 63-83. (53) Park, J.; Zhu, R. S.; Lin, M. C. Thermal decomposition of ethanol. I. Ab Initio molecular orbital/Rice–Ramsperger–Kassel–Marcus prediction of rate constant and product branching ratios. J. Chem. Phys. 2002, 117, 3224-3230. (54) Bui, B. H.; Zhu, R. S.; Lin, M. C. Thermal decomposition of iso-propanol: First-principles prediction of total and product-branching rate constants. J. Chem. Phys. 2002, 117, 1118811195.


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F 1276 K

200

Current (pA)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


150 A

B G J

100

50

C

0

20

K

I

E D

H

40

60

80

100

120

Retention time (min) Figure 1. Gas chromatogram showing the products of the post shock mixture of the experiment carried out at 1276 K. The peaks labeled in the chromatogram are A: methane, B: ethane, C: ethylene, D: 1,1-difluoroethylene, E: acetylene, F: 1,1,1-trifluoroethane G: propylene, H: acetaldehyde, I: 1-pentene, J: 2-pentene and K: 2-pentanol. The peaks shown in black color corresponds to1,1-difluoroethylene and 1,1,1-trifluoroethane.



40

H 1276 K

-3

30 Absorbance×10

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 42

B 20

D E C A, D

10

C

A

F

G, B

G

0 500

1000

1500

2000

2500

3000

3500

4000

-1

wave number (cm )

Figure 2. FTIR spectrum showing the products of the post shock mixture of the experiment carried out at 1276 K. The peaks labeled in the spectrum are A: 2-pentanol, B: methane, C: ethane, D: ethylene, E: acetylene, F: acetaldehyde, G: CO and H: 1-pentene.


Page 27 of 42

0.25

1.0

(b)

(a) 0.20 [CH4]t/[C5H12O]0

[C5H12O]t/[C5H12O]0

0.8

0.6

0.4

0.15

0.10

0.2

0.05

0.0

0.00

1100

1150

1200 1250 1300 Temperature (K)

1350

1100

1150

1200 1250 Temperature (K)

1300

1350

0.4

(c)

(d)

-3

0.3

[C2H6]t/[C5H12O]0x10

[C2H4]t/[C5H12O]0

80

60

0.2

40

0.1

20

0.0

0

1100

1150


1100

1350


1300

1350

0.14

(e)

(f) 0.12

50 [C3H6]t/[C5H12O]0

-3

60

[C2H2]t/[C5H12O]0x10

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


40 30 20 10

0.10 0.08 0.06 0.04 0.02

0

0.00

1100

1150


1350

1100

1150



1300

1350


30

(h)

(g) [1-C5H10]t/[C5H12O]0x10

-3

-3

80 [C2H4O]t/[C5H12O]0x10

60

40

20

0

25 20 15 10 5 0

1100

1150


1350

1100

1150


1300

1350

0.12

(i) 0.10 [2-C5H10]t/[C5H12O]0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 42

0.08 0.06 0.04 0.02 0.00 1100

1150


1350

Figure 3. Comparison between the experimental and simulated concentrations of (a) 2-pentanol, (b) methane, (c) ethylene, (d) ethane, (e) acetylene, (f) propylene, (g) acetaldehyde, (h) 1-pentene and (i) 2-pentene. Filled circles are experimental concentrations and the unfilled circles are simulated concentrations.


Page 29 of 42

3000 2000 1500

1000

T (K) 800 700

600

500

40 20

This work (Experiment) This work (RRKM)

0

ln(k)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


-20 10 9

-40

8 7

-60

6 5

-80

4 0.75

0.80

0.85

0.90

-100 0.5

1.0

1.5 1000/T (K ) -1

2.0

Figure 4. Arrhenius plot for the overall decomposition of 2-pentanol in the temperature range of 1110-1325 K. The obtained temperature dependent rate coefficient is (1110-1325 K) =

(4.01 ± 0.51) × 109 exp (-(36.2 kcal mol-1 ± 4.7)/RT) s-1. The insert is the zoom of the data obtained in the present experiments.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Page 30 of 42

Page 31 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5. Geometries of the reactant, transition states, and products optimized at the M06-2X/631+G(d,p) level of theory. Blue color represents hydrogen, silver color represents carbon and red color represents oxygen in the structures. The bond lengths (Å) given on the structures are obtained at the M06-2X/6-31+G(d,p) level of theory.



T [K] 2500

1500

1000

800

700

40

600

500

R1 R2 R3 R4 R5 R6 R7

20 0 ln(k)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 42

-20 -40 -60 -80 -100 0.5

1.0

1.5

2.0

-1

1000/T [K ]

Figure 6. Calculated high pressure limit rate constants of reaction pathways R1-R7 over the temperature range of 500-2500 K.


Page 33 of 42

20

18

16

14 ln(k)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


12

TS1 0.01 atm 0.1 atm 1 atm 10 atm 100 atm

10

8

6 1400

1600

1800

2000 T [K]

2200

2400

2600

Figure 7. Arrhenius plot for the formation of 1-pentene via four membered ring transition state (TS1) through reaction channel R1 in the temperature range of 1300-2500 K and pressure range of 0.1-100 atm with Ar as diluent.



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Page 34 of 42

Table 1. Experimental conditions and distribution of normalized concentrations of reactant and reaction products in the decomposition of 2-pentanol.

T5

P5

(K)

(atm)

1

1325

15.9

2

1272

3

Reaction

[CH4]t/

[C2H4]t/

[C2H6]t/

[C2H2]t/

[C3H6]t/

[C2H4O]t/

[1-C5H10]t/

[2-C5H10]t/

[2-C5H12O]t/

[C5H12O]0

[C5H12O]0

[C5H12O]0

[C5H12O]0

[C5H12O]0

[C5H12O]0

[C5H12O]0

[2-C5H12O]0

[2-C5H12O]0

620

0.2254

0.3517

0.0775

0.0529

0.0797

0.0658

0.0017

0.0170

0.1284

18.1

600

0.1849

0.3177

0.0794

0.0227

0.0977

0.0499

0.0103

0.0641

0.1734

1268

18.6

650

0.1983

0.3416

0.0702

0.0208

0.1089

0.0262

0.0112

0.0528

0.1700

4

1183

16.0

557

0.0624

0.1204

0.0204

0.0022

0.0631

0.0042

0.0157

0.1143

0.5973

5

1215

16.3

600

0.0991

0.1938

0.0366

0.0044

0.0896

0.0120

0.0140

0.0988

0.4518

6

1179

16.0

518

0.0476

0.0900

0.0169

0.0021

0.0503

0.0048

0.0156

0.0910

0.6815

7

1176

16.1

544

0.0609

0.1163

0.0196

0.0013

0.0617

0.0075

0.0184

0.0934

0.6209

8

1187

16.1

462

0.0709

0.1404

0.0235

0.0022

0.0689

0.0174

0.0128

0.0977

0.5661

9

1238

16.6

594

0.1280

0.2595

0.0526

0.0092

0.0997

0.0533

0.0105

0.0679

0.3194

10

1245

16.2

515

0.1248

0.2567

0.0501

0.0080

0.0988

0.0517

0.0079

0.0652

0.3369

11

1221

16.5

483

0.0867

0.1783

0.0372

0.0024

0.0792

0.0397

0.0178

0.0679

0.4907

12

1208

16.7

477

0.0797

0.1646

0.0269

0.0028

0.0763

0.0307

0.0189

0.0713

0.5289

13

1158

15.7

542

0.0305

0.0627

0.0067

0.0007

0.0359

0.0068

0.0126

0.0414

0.8026

14

1174

16.8

454

0.0486

0.0974

0.0131

0.0014

0.0498

0.0148

0.0311

0.0601

0.6837

15

1110

16.3

471

0.0191

0.0378

0.0045

0.0006

0.0214

0.0030

0.0086

0.0384

0.8667

16

1271

16.8

590

0.1638

0.3226

0.0647

0.0191

0.1012

0.0579

0.0109

0.0406

0.2193

S.No

time (µs)


Page 35 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48


17

1213

15.3

507

0.0801

0.1742

0.0275

0.0038

0.0809

0.0329

0.0160

0.0506

0.5340

18

1236

15.3

598

0.1198

0.2564

0.0487

0.0080

0.0991

0.0504

0.0183

0.0508

0.3486

19

1240

15.3

600

0.1138

0.2425

0.0455

0.0084

0.0944

0.0485

0.0151

0.0428

0.3889

20

1241

15.4

570

0.1326

0.2728

0.0496

0.0105

0.1027

0.0497

0.0120

0.0427

0.3273

21

1248

15.2

602

0.1264

0.2641

0.0470

0.0076

0.0999

0.0512

0.0149

0.0682

0.3208

22

1180

17.4

464

0.0480

0.1134

0.0119

0.0014

0.0583

0.0156

0.0124

0.0469

0.6922

23

1177

16.7

528

0.0512

0.1121

0.0162

0.0013

0.0572

0.0170

0.0212

0.0836

0.6402

24

1152

16.1

476

0.0303

0.0655

0.0070

0.0011

0.0376

0.0052

0.0098

0.0363

0.8072

25

1190

13.7

475

0.0602

0.1464

0.0227

0.0017

0.0747

0.0272

0.0180

0.0487

0.6005

26

1294

17.3

580

0.2008

0.3710

0.0725

0.0322

0.0968

0.0411

0.0045

0.0243

0.1567

27

1231

12.4

521

0.0933

0.1765

0.0337

0.0113

0.0535

0.0221

0.0058

0.0317

0.5720

28

1165

16.4

512

0.0301

0.0734

0.0088

0.0009

0.0422

0.0076

0.0130

0.0285

0.7954

29

1315

17.2

590

0.2016

0.3772

0.0751

0.0400

0.0860

0.0378

0.0046

0.0193

0.1586

30

1266

16.0

612

0.1461

0.3116

0.0577

0.0101

0.1015

0.0504

0.0164

0.0490

0.2573

31

1284

16.9

590

0.1731

0.3523

0.0745

0.0228

0.0950

0.0612

0.0076

0.0258

0.1877

32

1225

14.6

550

0.0998

0.2428

0.0373

0.0069

0.1006

0.0501

0.0171

0.0718

0.3736

33

1140

15.5

521

0.0145

0.0317

0.0042

0.0001

0.0236

0.0055

0.0116

0.1010

0.8077

34

1127

15.6

415

0.0198

0.0368

0.0035

0.0005

0.0226

0.0060

0.0105

0.0408

0.8595

35

1276

15.9

626

0.1781

0.3522

0.0667

0.0196

0.1036

0.0543

0.0088

0.0353

0.1813

36

1310

15.6

616

0.1926

0.3677

0.0768

0.0333

0.0929

0.0635

0.0077

0.0181

0.1473

37

1253

14.3

600

0.1475

0.3278

0.0629

0.0115

0.1124

0.0561

0.0141

0.0340

0.2337

38

1324

15.4

590

0.1963

0.3740

0.0791

0.0357

0.0894

0.0704

0.0076

0.0177

0.1299



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Table 2. Energy barriers (kcal mol-1) for thermal decomposition of 2-pentanol reaction via pathways R1-R7 calculated at M06-2X/6-31+G(d,p).

TSs

M06-2X/6-31+G(d,p)

TS1

64.6

TS2

66.9

TS3

101.1

TS4

112.8

TS5

84.1

TS6

93.6

TS7

84.7


Page 36 of 42

Page 37 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48


Table 3. Proposed reaction scheme for the decomposition of 2-pentanol with 39 reaction species and 37 elementary reactions.a

S.No Reaction

A

n

Ea

Reference

R1

CH3-CH2-CH2-CH(OH)-CH3 → CH3-CH2-CH2-CH=CH2 + H2O

1.58 × 1014

0.00

67.1

This work

R2

CH3-CH2-CH2-CH(OH)-CH3 → CH3-CH2-CH=CH-CH3 + H2O

3.01 × 1014

0.00

69.5

This work

R3

CH3-CH2-CH2-CH(OH)-CH3 → C2H6 + CH3-C(O)-CH3

1.90 × 1014

0.00

103.4

This work

14

R4

CH3-CH2-CH2-CH(OH)-CH3 → C2H4 + CH3-CH(OH)-CH3

6.01 × 10

0.00

115.9

This work

R5

CH3-CH2-CH2-CH(OH)-CH3 → CH4 + CH3-CH2-CH2-CHO

1.92 × 1014

0.00

86.2

This work

R6

CH3-CH2-CH2-CH(OH)-CH3 → CH4 + C2H4 + CH3-CHO

1.60 × 1014

0.00

96.1

This work

R7

CH3-CH2-CH2-CH(OH)-CH3 → C3H8 + CH3-CHO

9.44 × 1013

0.00

86.4

This work

R8

CH3-CH2-CH2-CH(OH)-CH3 → CH3 + CH2-CH2-CH(OH)-CH3

5.12 × 1026

-2.92

90.5

23

R9

CH3-CH2-CH2-CH(OH)-CH3 → CH3-CH2 + CH2-CH(OH)-CH3

8.54 × 1027

-3.23

91.7

23

R10

CH3-CH2-CH2-CH(OH)-CH3 → CH3-CH2-CH2 + CH(OH)-CH3

3.01 × 1025

-2.57

89.9

23

R11

CH3-CH2-CH2-CH(OH)-CH3 → CH3-CH2-CH2-CH-CH3 + OH

2.82 × 1029

-3.60

101.9

23

R12

CH3-CH2-CH2-CH(OH)-CH3 → CH3-CH2-CH2-CH(OH) + CH3

5.13 × 1026

-2.91

90.5

23

R13

CH3-CH2 + H → C2H6

5.44 × 1013

0.16

0.0

39

R14

CH3-CH2 → C2H4 + H

10

3.06 × 10

0.95

36.9

40

R15

CH3-CH2-CH2 → C3H6 + H

4.14 × 1012

0.17

35.6

40

R16

CH3 + H → CH4

6.93 × 1013

0.18

0.0

39



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Page 38 of 42

R17

CH3-C(O)-H → CH4 + CO

1.00 × 1015

0.00

85.0

41

R18

2 CH3 → C2H4 + H2

9.90 × 1015

0.00

32.9

42

R19

C2H4 + CH3 → C2H3 + CH4

4.16 × 1012

0.00

11.1

43

R20

C2H3 + H → C2H4

3.88 × 1013

0.20

0.00

39

R21

CH(OH)-CH3 → CH3-C(O)-H + H

5.00 × 1013

0.00

21.9

44

R22

C2H3 + H → C2H2 + H2

1.21 × 1013

0.00

0.00

43

R23

C2H6 + H → C2H5 + H2

5.95 × 1014

0.00

12.9

45

R24

CH3-CH2-CH2-CH=CH2 → CH3+ CH2-CH2-CH=CH2

1.00 × 1016

0.00

72.9

47

R25

CH3-CH2-CH2-CH=CH2 → CH3-CH2 + CH2-CH=CH2

1.00 × 1016

0.00

70.7

47

R26


0.64 × 101

3.31

12.6

46

17

R27

CH3-CH2-CH=CH-CH3 → CH3 + CH3-CH2-CH=CH

3.16 × 10

0.00

99.4

47

R28

CH3-CH2-CH=CH-CH3 → CH3 + CH2-CH=CH-CH3

3.16 × 1017

0.00

99.4

47

R29

CH3-CH2-CH=CH-CH3 → CH3-CH2 + CH=CH-CH3

1.00 × 1016

0.00

75.7

47

R30

CH3-CH2-CH2-CH-CH3→ C3H6 + CH3-CH2

1.22 × 1012

0.64

29.4

40

R31

C3H5 → C2H2 + CH3

1.26 × 1013

0.00

33.7

47

R32

C2H5 + H2O → C2H6 + OH

3.39 × 106

1.44

20.3

48

R33

CH2-CH(OH)-CH3 → CH3-CH=CH2 + OH

3.70 × 1012

0.00

26.8

49

R34

C3H6 → CH3 + C2H3

8.00 × 1014

0.00

88.0

50

R35

C3H6 + H → n-C3H7

4.57 × 1012

0.51

2.6

40

R36

C3H6 + H → iso-C3H7

7.75 × 1012

0.51

1.2

40


Page 39 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48


a

R37

CH4 + H → H2 + CH3

1.77 × 1014

0.00

13.8

51

R38

CH4 + CH3 → H2 + CH3-CH2

1.00 × 1013

0.00

23.1

52

R39

C2H2 + H2 → C2H4

3.01 × 1011

0.00

38.9

48

Rate expressions are given in the form of k = A exp(-Ea/RT) and k = ATnexp(-Ea/RT). The units of the rate coefficients are s-1 and

cm3mol-1s-1 for first and second order reactions respectively. The units for the activation barrier are kcal mol-1.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Page 40 of 42

Table 4. The percentage changes in the concentrations of individual species, when the rate coefficients of the reactions in the proposed reaction scheme were varied by a factor of 10 in order to analyze the sensitivity towards the formation of all the products at 1268 K. No

Reaction

CH4

C2H4

C3H6

1-C5H10

CH3CHO

C2H6

C2H2

2-C5H10

R1

CH3-CH2-CH2-CH(OH)-CH3 → CH3-CH2-CH2-CH=CH2 + H2O

101

149

-58

15

-29

202

-19

-66

R2

CH3-CH2-CH2-CH(OH)-CH3 → CH3-CH2-CH=CH-CH3 + H2O

114

-89

-51

-14

-26

138

181

377

R5

CH3-CH2-CH2-CH(OH)-CH3 → CH4 + CH3-CH2-CH2-CHO

0

0

0

2

-1

-1

0

0

R6

CH3-CH2-CH2-CH(OH)-CH3 → CH4 + C2H4 + CH3-CHO

0

0

0

3

-1

-1

0

0

R8

CH3-CH2-CH2-CH(OH)-CH3 → CH3 + CH2-CH2-CH(OH)-CH3

178

-130

-22

-6

-15

10

-5

-31

R9

CH3-CH2-CH2-CH(OH)-CH3 → CH3-CH2 + CH2-CH(OH)-CH3

-30

306

354

-8

-12

35

-20

-31

R10

CH3-CH2-CH2-CH(OH)-CH3 → CH3-CH2-CH2 + CH(OH)-CH3

-49

19

306

-8

317

-41

-23

-25

R11

CH3-CH2-CH2-CH(OH)-CH3 → CH3-CH2-CH2-CH-CH3 + OH

-4

-10

-22

0

0

0

0

0

R12

CH3-CH2-CH2-CH(OH)-CH3 → CH3-CH2-CH2-CH(OH) + CH3

180

-130

-28

-6

-13

9

-6

-27

R14

CH3-CH2 → C2H4 + H

6

48

4

0

-4

-41

0

0

R15

CH3-CH2-CH2 → C3H6 + H

0

0

0

4

-1

-3

0

0

R19

C2H4 + CH3 → C2H3 + CH4

8

-18

1

0

0

0

5

1

R21

CH(OH)-CH3 → CH3-C(O)-H + H

0

0

0

3

0

-1

0

0

R22

C2H3 + H → C2H2 + H2

1

-23

-2

5

-2

4

19

0

R23

C2H6 + H → C2H5 + H2

3

38

-1

3

1

-35

-6

-1

R24

CH3-CH2-CH2-CH=CH2 → CH3+ CH2-CH2-CH=CH2

72

-133

3

-15

-2

-5

10

-1

R25

CH3-CH2-CH2-CH=CH2 → CH3-CH2 + CH2-CH=CH2

-34

78

0

-17

-2

-6

-9

0


Page 41 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48


R26


6

16

-6

2

-4

-9

-4

5

R27

CH3-CH2-CH=CH-CH3 → CH3 + CH3-CH2-CH=CH

0

0

0

0

0

0

-3

2

R28

CH3-CH2-CH=CH-CH3 → CH3 + CH2-CH=CH-CH3

0

0

0

0

0

0

-3

2

R29

CH3-CH2-CH=CH-CH3 → CH3-CH2 + CH=CH-CH3

87

48

6

5

-5

37

69

-85

R31

C3H5 → C2H2 + CH3

0

0

0

0

0

0

-1

0

R32

C2H5 + H2O → C2H6 + OH

-11

-147

-2

5

-2

111

6

3

R34

C3H6 → CH3 + C2H3

0

0

0

0

0

0

0

0

R37

CH4 + H → H2 + CH3

-8

-38

2

1

0

18

0

0

R38

CH4 + CH3 → H2 + CH3-CH2

-43

31

-3

0

0

0

0

0

R39

C2H2 + H2 → C2H4

3

13

-4

0

0

0

-21

-1



Table of content (TOC)

3000 2000 1500

1000

T (K) 800 700

600

500

40 20

This work (Experiment) This work (RRKM)

0

ln(k)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 42 of 42

-20 10 9

-40

8 7

-60

6 5

-80

4 0.75

0.80

0.85

0.90

-100 0.5

1.0

1.5 1000/T (K ) -1


2.0

Thermal Decomposition of 2-Pentanol: A Shock ... - ACS Publications

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