Abstract
Oxygenated organic compounds derived from biomass (biofuel) are a promising alternative renewable energy resource. Alcohols are widely used as biofuels, but studies on bifunctional alcohols are still limited. This work investigates the unimolecular thermal degradation of 2-methoxyethanol (2ME) using DFT/BMK and ab initio (CBS-QB3 and G3) methods. Enthalpies of the formation of 2ME and its decomposition species have been calculated. Conventional transition state theory has been used to estimate the rate constant of the pyrolysis of 2ME over a temperature range of 298–2000 K. Production of methoxyethene via 1,3-H atom transfer represents the most kinetically favored path in the course of 2ME pyrolysis at room temperature and requires less energy than the weakest Cα − Cβ simple bond fission. Thermodynamically, the most preferred channel is methane and glycoladhyde formation. A ninefold frequency factor gives a superiority of the Cα − Cβ bond breaking over the Cγ − Oβ bond fission despite comparable activation energies of these two processes.
Highlights
Among biofuels, the most popular bioethanol suffers from some drawbacks such as low internal energy, water absorption, very high ignition temperature, lower combustion efficiency, and high vapor pressure causing massive emissions to the atmosphere[8,9,10] giving rise to adverse effects on the human health[11]
Geometry optimization for 2ME, its decomposition products, and transition states have been performed using density functional theory (DFT) employing the Bose-Martin functional developed for kinetics (BMK)[30] (42% electron correlation) in conjunction with the 6–31+G(d,p) basis set
Kinetic parameters for different channels of 2ME pyrolysis have been estimated over a wide range of temperatures using the Kisthelp package program[42], where the classical transition state theory (TST)[43] is coupled with Eckart tunneling correction[44] to compute rate constants (k) for H-atom transfer reactions of 2ME pyrolysis over the applied range of temperatures (298–2000 K)
Summary
Ethylene glycol had recently become available from different biomass categories using various procedures with high yield[13,14,15,16,17,18,19] as a biofuel, but there still some concerns related to its low carbon content, low melting point (−13 °C), high viscosity, high toxicity, and high hydrophilic nature[20] Those issues can be avoided by using alone in the current engine infrastructure. Kinetic parameters for different channels of 2ME pyrolysis have been estimated over a wide range of temperatures using the Kisthelp package program[42], where the classical transition state theory (TST)[43] is coupled with Eckart tunneling correction[44] to compute rate constants (k) for H-atom transfer reactions of 2ME pyrolysis over the applied range of temperatures (298–2000 K).
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