Glycerol carbonate as a fuel additive for a sustainable future

Policy-makers and researchers have been considering a shift from conventional fossil fuels to renewable sources due to the growing concerns over global warming and diminishing oil reserves. Biodiesel, a renewable bio-driven fuel, can be derived from vegetable oils and animal fats, and is considered to be bio-degradable, non-toxic and environmentally friendly. The cetane number and calorific power of biodiesel are quite similar to those of conventional diesel. Crude glycerol of about 10-20% by volume appears as a byproduct in biodiesel production. The increasing demand for biodiesel has led to a substantial increase of glycerol supply in the global market and a dramatic fall in the price of glycerol which has warranted alternative uses of glycerol. One potential way to deal with the crude glycerol overflow is to convert it to glycerol carbonate (GC) and use GC as a fuel or fuel additive. Prior studies have indicated that carbonate esters can significantly reduce particulate emissions during engine combustion. In this work, we have explored possible reaction pathways in the initial stage of glycerol carbonate pyrolysis. Ab initio/RRKM-master equation methods are employed to differentiate various reaction pathways and to obtain the pressure- and temperature-dependence of the major channels. We have found that glycerol carbonate decomposes almost exclusively to produce CO2 and 3-hydroxypropanal over 800-2000 K and radical forming channels are unimportant. As 3-hydroxypropanal is one of the main products of GC decomposition, and aldehydes are known to have a very high impact on soot reduction, we conclude that GC has great potential for cleaner combustion as a fuel additive

On the high-temperature unimolecular decomposition of ethyl levulinate

Abstrac

An experimental and theoretical kinetic study of the reaction of OH radicals with tetrahydrofuran

Abstrac

A high temperature kinetic study for the thermal unimolecular decomposition of diethyl carbonate

Thermal unimolecular decomposition of diethyl carbonate (DEC) was investigated in a shock tube by measuring ethylene concentration with a CO2 gas laser over 900–1200K and 1.2–2.8bar. Rate coefficients were extracted using a simple kinetic scheme comprising of thermal decomposition of DEC as initial step followed by rapid thermal decomposition of the intermediate ethyl hydrogen carbonate. Our results were further analysed using ab initio and master equation calculations to obtain pressure- and temperature-dependence of rate coefficients. Similar to alkyl esters, unimolecular decomposition of DEC is found to undergo six-center retro-ene elimination of ethylene in a concerted manner

Insights into the Reactions of Hydroxyl Radical with Diolefins from Atmospheric to Combustion Environments

International audienc

A Combined High-Temperature Experimental and Theoretical Kinetic Study of Dimethyl Carbonate with OH Radicals

The reaction kinetics of dimethyl carbonate (DMC) and OH radicals was investigated behind reflected shock waves over the temperature range of 872-1295 K and pressures near 1.5 atm. The reaction progress was monitored by detecting OH radicals at 306.69 nm using a UV laser absorption technique. The rate coefficients for the reaction of DMC with OH radicals were extracted using a detailed kinetic model developed by Glaude et al. (Proc. Combust. Inst. 2005, 30 (1), 1111-1118). The experimental rate coefficients can be expressed in an Arrhenius form as: kexpt'l = 5.151013 exp(-2710.2/T) cm3 mol-1 s-1. To explore the detailed chemistry of DMC + OH reaction system, theoretical kinetic analyses were performed using high-level ab initio and master equation/Rice-Ramsperger-Kassel-Marcus (ME/RRKM) calculations. The geometry optimization and frequency calculations were carried out at the second-order Moller-Plesset (MP2) perturbation level of theory using the Dunning's augmented correlation consistent-polarized valence double-[small zeta] basis set (aug-cc-pVDZ). The energy was extrapolated to the complete basis set using the single point calculations performed at the CCSD(T)/cc-pVXZ (where X = D, T) level of theory. For comparison purposes, additional ab intio calculations were also carried out using the composite methods such as CBS-QB3, CBS-APNO, G3 and G4. Our calculations revealed that the H-abstraction reaction of DMC by OH radicals proceeds via an addition elimination mechanism in an overall exothermic process, eventually forming dimethyl carbonate radicals and H2O. The theoretical rate coefficiens were found to be in excellent agreement with those determined experimentally. The rate coefficients for DMC + OH reaction were combined with the literature rate coefficients of four straight chain methyl esters + OH reactions to extract the site-specific rates of H-abstraction from methyl esters by OH radicals

High-Temperature Experimental and Theoretical Study of the Unimolecular Dissociation of 1,3,5-Trioxane

Unimolecular dissociation of 1,3,5-trioxane was investigated experimentally and theoretically over a wide range of conditions. Experiments were performed behind reflected shock waves over the temperature range of 775–1082 K and pressures near 900 Torr using a high-repetition rate time of flight mass spectrometer (TOF-MS) coupled to a shock tube (ST). Reaction products were identified directly, and it was found that formaldehyde is the sole product of 1,3,5-trioxane dissociation. Reaction rate coefficients were extracted by the best fit to the experimentally measured concentration–time histories. Additionally, high-level quantum chemical and RRKM calculations were employed to study the falloff behavior of 1,3,5-trioxane dissociation. Molecular geometries and frequencies of all species were obtained at the B3LYP/cc-pVTZ, MP2/cc-pVTZ, and MP2/aug-cc-pVDZ levels of theory, whereas the single-point energies of the stationary points were calculated using coupled cluster with single and double excitations including the perturbative treatment of triple excitation (CCSD­(T)) level of theory. It was found that the dissociation occurs via a concerted mechanism requiring an energy barrier of 48.3 kcal/mol to be overcome. The new experimental data and theoretical calculations serve as a validation and extension of kinetic data published earlier by other groups. Calculated values for the pressure limiting rate coefficient can be expressed as log₁₀ <i>k</i>_∞ (s^–1) = [15.84 – (49.54 (kcal/mol)/2.3<i>RT</i>)] (500–1400 K)