Ahmed H. Mangood

Thermal Decomposition of 2-Butanol as a Potential Nonfossil Fuel: A Computational Study

The thermochemistry and kinetics of the pyrolysis of 2-butanol have been conducted using ab initio methods (CBS-QB3 and CCSD(T)) and density functional theory (DFT). The enthalpies of formation and bond dissociation energies of some alcohols including 2-butanol and its derived radicals have been calculated. A variety of simple and complex dissociations have been examined. The results indicated that dehydration to 1- and 2-butene through four-center transition states is the most dominant channel at low to moderate temperatures (T ≤ 700 K), where formation of butenes is kinetically and thermodynamically more favorable than other complex and simple bond scission reactions. Although the C-C bond fission channels require more energy than needed for some complex decomposition reactions, the former pathways predominate at higher temperatures (T ≥ 800 K) due to the higher values of the pre-exponential factors. The progress of the complex decomposition reactions has been followed through intrinsic reaction coordinate (IRC) calculations to understand the mechanism of transformation of 2-butanol to different products.

Effect of some amino acids on the rate of dissolution of calcite crystals in aqueous systems

Abstract The dissolution of calcite seed crystals has been investigated in the presence of some amino acids by constant composition method in which the undersaturation and ionic strength were maintained constant. The crystal dissolution rates are markedly inhibited by the addition of amino acids. The order of the degree of inhibition is L-arginine > glycine > phenyl alanine > alanine. Application to a kinetic Langmuir-type model suggests that adsorption of the amino acids at the active dissolution sites is the cause of the reduction in the dissolution rates.

Structures and energetics of unimolecular thermal degradation of isopropyl butanoate as a model biofuel: density functional theory and ab initio studies.

Density functional theory (DFT)/BMK and CBS-QB3 ab initio calculations have been carried out to study the structures and energetics of unimolecular decomposition reactions of isopropyl butanoate (IPB, C(3)H(7)C(O)OCH(CH(3))(2)) as a model biofuel. The results show a good performance of the BMK method. Among seven different dissociation channels of IPB, formation of butanoic acid and propene via a six-membered ring transition state is the most favorable reaction. On the other hand, formation of lower esters is hindered by high-energy barriers and unlikely occurs except at elevated temperatures. Simple bond scission costs less energy than lower ester formation. A comparison with methyl and ethyl esters indicates faster decomposition of IPB. The changes in bond lengths along minimum energy paths are discussed.

Assessment of hybrid, meta-hybrid-GGA, and long-range corrected density functionals for the estimation of enthalpies of formation, barrier heights, and ionisation potentials of selected C1–C5 oxygenates

The enthalpies of formation for some selected oxygenates have been calculated by the atomisation energy approach using B3LYP, BHandHLYP, MPW3LYP, MPW1K, MPWB1K, BB1K, MPW1B95, BMK, and long-range corrected (LC-ωPBE, LC-BOP, LCgau-BOP, LC-BOP12, LCgau-B97) density functionals, as well as the composite CBS-QB3 method. Compared with experiment, BMK, LC-ωPBE, LCgau-BOP, LC-BOP12, LCgau-B97, MPW195, MPW3LYP functionals and CBS-QB3 give root mean square errors (RMSE) in enthalpies of formation no greater than 4 kcal/mol, whilst MPW1K and BHandHLYP show much worse performance (RMSE of 20–40 kcal/mol). The B3LYP, MPWB1K, and BB1K results fall between the two extremes. Energy barriers for the dominant paths in the unimolecular decomposition of simple esters (HCO2CH3, C2H5CO2C2H5), C1–C3 acids, and 1-butanol are reproduced well by CBS-QB3, BMK, BB1K, LCgau-B97, and PW1B95 (RMSE = 1–2 kcal/mol), while other LC methods (LC-ωPBE, LC-BOP, LCgau-BOP, and LC-BOP12) show a deviation of up to 4 kcal/mol. For the ionisation potentials, calculated from Koopmans theorem, all of the investigated LC-methods give good results compared with other density functional theory functionals with a maximum deviation of 0.4 eV, except for LCgau-B97, which has an RMSE of 0.7 eV.