Considerable research and development is underway to produce fuels from microalgae, one of several options being explored for increasing transportation fuel supplies and mitigating greenhouse gas emissions (GHG). This work models life-cycle GHG and on-site freshwater consumption for algal biofuels over a wide technology space, spanning both near- and long-term options. The environmental performance of algal biofuel production can vary considerably and is influenced by engineering, biological, siting, and land-use considerations. We have examined these considerations for open pond systems, to identify variables that have a strong influence on GHG and freshwater consumption. We conclude that algal biofuels can yield GHG reductions relative to fossil and other biobased fuels with the use of appropriate technology options. Further, freshwater consumption for algal biofuels produced using saline pond systems can be comparable to that of petroleum-derived fuels.
We have studied the reaction between CH and N2, (1) CH + N2 --> products, in shock tube experiments using CH and NCN laser absorption. CH was monitored by continuous-wave, narrow-line-width laser absorption at 431.1 nm. The overall rate coefficient of the CH + N2 reaction was measured between 1943 and 3543 K, in the 0.9-1.4 atm pressure range, using a CH perturbation approach. CH profiles recorded upon shock-heating dilute mixtures of ethane in argon and acetic anhydride in argon were perturbed by the addition of nitrogen. The perturbation in the CH concentration was principally due to the reaction between CH and N2. Rate coefficients for the overall reaction were inferred by kinetically modeling the perturbed CH profiles. A least-squares, two-parameter fit of the current overall rate coefficient measurements was k1 = 6.03 x 1012 exp(-11150/T [K]) (cm3 mol-1 s-1). The uncertainty in k1 was estimated to be approximately +/-25% and approximately +/-35% at approximately 3350 and approximately 2100 K, respectively. At high temperatures, there are two possible product channels for the reaction between CH and N2, (1a) CH + N2 --> HCN + N and (1b) CH + N2 --> H + NCN. The large difference in the rates of the reverse reactions enabled inference of the branching ratio of reaction 1, k1b/(k1b + k1a), in the 2228-2905 K temperature range by CH laser absorption in experiments in a nitrogen bath. The current CH measurements are consistent with a branching ratio of 1 and establish NCN and H as the primary products of the CH + N2 reaction. A detailed and systematic uncertainty analysis, taking into account experimental and mechanism-induced contributions, yields a conservative lower bound of 0.70 for the branching ratio. NCN was also detected by continuous-wave, narrow-line-width laser absorption at 329.13 nm. The measured NCN time histories were used to infer the rate coefficient of the reaction between H and NCN, H + NCN --> HCN + N, and to estimate an absorption coefficient for the NCN radical.
The reaction of hydroxyl [OH] radicals with formaldehyde [CH 2 O] was studied at temperatures ranging from 934 K to 1670 K behind reflected shock waves at an average total pressure of 1.6 atm. OH radicals were produced by shock-heating tert-butyl hydroperoxide [(CH 3 ) 3 CO OH], while 1,3,5-trioxane [(CH 2 O) 3 ] was used in the preshock mixtures to generate reproducible levels of CH 2 O. OH concentration time-histories were inferred from laser absorption using the well-characterized R 1 (5) line of the OH A-X (0, 0) band near 306.7 nm. Detailed error analyses, taking into account both experimental and mechanism-induced contributions, yielded uncertainty estimates of ±25% at 1595 K and ±15% at 1229 K for the rate of the reaction between CH 2 O and OH. These uncertainties are substantially lower than the factor of two uncertainty currently used for this reaction at high temperatures. The rate constants were fit with the recent low-temperature measurements of Sivakumaran et al. (Phys Chem Chem Phys 2003,5,4821-4827) to the three-parameter form shown below; this fit reconciles experimental data on the title reaction at low, intermediate, and high temperatures (200-1670 K).The reaction of OH with CH 2 O was also studied using quantum chemical methods at the CCSD(T) level of theory using the 6-311++G(d,p) basis set. The transition state for the H-atom metathesis reaction was located, and reaction rate coefficients were calculated. Reasonable agreement with the experimental measurements was obtained.
The reaction of hydroxyl [OH] radicals with toluene [C6H5CH3] was studied at temperatures between 911 and 1389 K behind reflected shock waves at pressures of approximately 2.25 atm. OH radicals were generated by rapid thermal decomposition of shock-heated tert-butyl hydroperoxide [(CH3)3-CO-OH], and monitored by narrow-line width ring dye laser absorption of the well-characterized R1(5) line of the OH A-X (0,0) band near 306.7 nm. OH time histories were modeled by using a comprehensive toluene oxidation mechanism. Rate constants for the reaction of C6H5CH3 with OH were extracted by matching modeled and measured OH concentration time histories in the reflected shock region. Detailed error analyses yielded an uncertainty estimate of +/-30% at 1115 K for the rate coefficient of this reaction. The current high-temperature data were fit with the lower temperature measurements of Tully et al. [J. Phys. Chem. 1981, 85, 2262-2269] to the following two-parameter form, applicable over 570-1389 K: k3 = (1.62 x 10(13)) exp(-1394/T [K]) [cm3 mol(-1) s(-1)]. The reaction between OH radicals and acetone [CH3COCH3] was one of the secondary reactions encountered in the toluene + OH experiments. Direct high-temperature measurements of this reaction were carried out at temperatures ranging from 982 to 1300 K in reflected shock wave experiments at an average total pressure of 1.65 atm. Uncertainty limits were estimated to be +/-25% at 1159 K. A two-parameter fit of the current data yields the following rate expression: k6 = (2.95 x 10(13)) exp(-2297/T [K]) [cm3 mol(-1) s(-1)].
Ignition delay times and OH radical concentration profiles were measured in toluene/O 2 /Ar mixtures behind reflected shock waves. Initial reflected shock conditions spanned 1400-2000 K and 1.5-5.0 atm, with equivalence ratios of 0.5-1.875 and toluene concentrations of 0.025-0.5%. OH time histories were monitored using narrow-linewidth ring dye laser absorption of the well-characterized R 1 (5) line of the OH A-X (0, 0) band at 306.7 nm. Ignition time data were extracted from the OH traces and were found to compare very well with measurements using sidewall pressure. These new data are in agreement with
The reaction between methyl and hydroxyl radicals has been studied in reflected shock wave experiments using narrow-linewidth OH laser absorption. OH radicals were generated by the rapid thermal decomposition of tert-butyl hydroperoxide. Two different species were used as CH 3 radical precursors, azomethane and methyl iodide. The overall rate coefficient of the CH 3 + OH reaction was determined in the temperature range 1081-1426 K under conditions of chemical isolation. The experimental data are in good agreement with a recent theoretical study of the reaction. The decomposition of methanol to methyl and OH radicals was also investigated behind reflected shock waves. The current measurements are in good agreement with a recent experimental study and a master equation simulation. C 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 488-495, 2008
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.