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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.