James C. Ball

Biodiesel is a renewable fuel used in diesel engines that is typically blended with diesel fuel. However, biodiesel is susceptible to oxidation, which has the potential to produce higher molecular weight materials that may adversely impact vehicle fuel‐system performance. To investigate the chemical reactions potentially important in biodiesel oxidation, four different types of chemical reactions involving esters were studied: (1) ester formation (reactions of acids with alcohols), (2) alcoholysis (reactions of alcohols with esters), (3) acidolysis (reaction of acids with esters), and (4) ester exchange (reactions between two esters). Experiments with representative model compounds were used to evaluate these reactions at 90 °C with aeration; conditions previously used to simulate thermo‐oxidative degradation during biodiesel aging. Reactions were monitored using gas chromatography, fourier transform infrared (FTIR) spectroscopy, and total acid number (TAN). Evidence is presented suggesting that alcoholysis and ester formation (Reactions 1 and 2), catalyzed by carboxylic acids, are important reactions of esters that could lead to larger molecules. Acidolysis (Reaction 3) proceeded at a comparatively slow rate and ester exchange reaction products (Reaction 4) were not detected under these aging conditions.

An experimental study of the effects of partially-oxidized biodiesel fuel on the degradation of fresh fuel was performed. A blend of soybean oil fatty acid methyl esters (FAMEs) in petroleum diesel fuel (30% v:v biodiesel, B30) was aged under accelerated conditions (90°C with aeration). Aging conditions focused on three different degrees of initial oxidation: 1) reduced oxidation stability (Rancimat induction period, IP); 2) high peroxide values (PV); and 3) high total acid number (TAN). Aged B30 fuel was mixed with fresh B30 fuel at two concentrations (10% and 30% m:m) and degradation of the mixtures at the above aging conditions was monitored for IP, PV, TAN, and FAME composition. Greater content of aged fuel carryover (30% m:m) corresponded to stronger effects. Oxidation stability was most adversely affected by high peroxide concentration (Scenario 2), while peroxide content was most reduced for the high TAN scenario (Scenario 3). However, changes in TAN and FAME composition were modest with all four scenarios reaching a plateau in TAN formation at similar times and FAME concentrations showing similar declines. The results are discussed with respect to the chemistry of biodiesel fuel aging under high-temperature diesel fuel system conditions and considerations associated with the mixing of aged fuels with fresh fuels following vehicle refueling.

Effective bacterial control in cooling‐tower systems requires accurate and timely methods to count bacteria. Plate‐count methods are difficult to implement on‐site, because they are time‐ and labor‐intensive and require sterile techniques. Several field‐applicable methods (dipslides, Petrifilm, and adenosine triphosphate [ATP] bioluminescence) were compared with the plate count for two sample matrices—phosphate‐buffered saline solution containing a pure culture of Pseudomonas fluorescens and cooling‐tower water containing an undefined mixed bacterial culture. For the pure culture, (1) counts determined on nutrient agar and plate‐count agar (PCA) media and expressed as colony‐forming units (CFU) per milliliter were equivalent to those on R2A medium (p = 1.0 and p = 1.0, respectively); (2) Petrifilm counts were not significantly different from R2A plate counts (p = 0.99); (3) the dipslide counts were up to 2 log units higher than R2A plate counts, but this discrepancy was not statistically significant (p = 0.06); and (4) a discernable correlation (r ² = 0.67) existed between ATP readings and plate counts. For cooling‐tower water samples (n = 62), (1) bacterial counts using R2A medium were higher (but not significant; p = 0.63) than nutrient agar and significantly higher than tryptone‐glucose yeast extract (TGE; p = 0.03) and PCA (p < 0.001); (2) Petrifilm counts were significantly lower than nutrient agar or R2A (p = 0.02 and p < 0.001, respectively), but not statistically different from TGE, PCA, and dipslides (p = 0.55, p = 0.69, and p = 0.91, respectively); (3) the dipslide method yielded bacteria counts 1 to 3 log units lower than nutrient agar and R2A (p < 0.001), but was not significantly different from Petrifilm (p = 0.91), PCA (p = 1.00) or TGE (p = 0.07); (4) the differences between dipslides and the other methods became greater with a 6‐day incubation time; and (5) the correlation between ATP readings and plate counts varied from system to system, was poor (r ² values ranged from 4 CFU/mL.

Smog chamber/FTIR techniques were used to study the atmospheric chemistry of the Z and E isomers of CF₃CFCHF, which we refer to as CF₃CFCHF(Z) and CF₃CFCHF(E). The rate constants k(Cl + CF₃CFCHF(Z)) = (4.36 ± 0.48) × 10^-11, k(OH + CF₃CFCHF(Z)) = (1.22 ± 0.14) × 10^-12, and k(O₃ + CF₃CFCHF(Z)) = (1.45 ± 0.15) × 10^-21 cm³ molecule^-1 s^-1 were determined for the Z isomer of CF₃CFCHF in 700 Torr air diluent at 296 ± 2 K. The rate constants k(Cl + CF₃CFCHF(E)) = (5.00 ± 0.56) × 10^-11, k(OH + CF₃CFCHF(E)) = (2.15 ± 0.23) × 10^-12, and k(O₃ + CF₃CFCHF(E)) = (1.98 ± 0.15) × 10^-20 cm³ molecule^-1 s^-1 were determined for the E isomer of CF₃CFCHF in 700 Torr air diluent at 296 ± 2 K. Both the Cl-atom and OH-radical-initiated atmospheric oxidation of CF₃CFCHF give CF₃C(O)F and HC(O)F in molar yields indistinguishable from 100% for both the Z and E isomer. CF₃CFCHF(Z) has an atmospheric lifetime of approximately 18 days and a global warming potential (100 year time horizon) of approximately 6. CF₃CFCHF(E) has an atmospheric lifetime of approximately 10 days and a global warming potential (100 year time horizon) of approximately 3. CF₃CFCHF has a negligible global warming potential and will not make any significant contribution to radiative forcing of climate change.

Relative rate techniques were used to study the kinetics of the reactions of Cl atoms and OH radicals with ethylene glycol diacetate, CH3C(O)O(CH2)2OC(O)CH3, in 700 Torr of N2/O2 diluent at 296 K. The rate constants measured were k(Cl + CH3C(O)O(CH2)2OC(O)CH3) = (5.7 +/- 1.1) x 10(-12) and k(OH + CH3C(O)O(CH2)2OC(O)CH3) = (2.36 +/- 0.34) x 10(-12) cm3 molecule-1 s-1. Product studies of the Cl atom initiated oxidation of ethylene glycol diacetate in the absence of NO in 700 Torr of O2/N2 diluent at 296 K show the primary products to be CH3C(O)OC(O)CH2OC(O)CH3, CH3C(O)OC(O)H, and CH3C(O)OH. Product studies of the Cl atom initiated oxidation of ethylene glycol diacetate in the presence of NO in 700 Torr of O2/N2 diluent at 296 K show the primary products to be CH3C(O)OC(O)H and CH3C(O)OH. The CH3C(O)OCH2O* radical is formed during the Cl atom initiated oxidation of ethylene glycol diacetate, and two loss mechanisms were identified: reaction with O2 to give CH3C(O)OC(O)H and alpha-ester rearrangement to give CH3C(O)OH and HC(O) radicals. The reaction of CH3C(O)OCH2O2* with NO gives chemically activated CH3C(O)OCH2O* radicals which are more likely to undergo decomposition via the alpha-ester rearrangement than CH3C(O)OCH2O* radicals produced in the peroxy radical self-reaction.

Smog chamber/FTIR techniques were used to study the atmospheric fate of n-C_xF_2x+1C(O) (x = 1, 2, 3, 4) radicals in 700 Torr O₂/N₂ diluent at 298 ± 3 K. A competition is observed between reaction with O₂ to form n-C_xF_2x+1C(O)O₂ radicals and decomposition to form n-C_xF_2x+1 radicals and CO. In 700 Torr O₂/N₂ diluent at 298 ± 3 K, the rate constant ratio, k(n-C_xF_2x+1C(O) + O₂ → n-C_xF_2x+1C(O)O₂)/k(n-C_xF_2x+1C(O) → n-C_xF_2x+1 + CO) = (1.30 ± 0.05) × 10^-17, (1.90 ± 0.17) × 10^-19, (5.04 ± 0.40) × 10^-20, and (2.67 ± 0.42) × 10^-20 cm³ molecule^-1 for x = 1, 2, 3, 4, respectively. In one atmosphere of air at 298 K, reaction with O₂ accounts for 99%, 50%, 21%, and 12% of the loss of n-C_xF_2x+1C(O) radicals for x = 1, 2, 3, 4, respectively. Results are discussed with respect to the atmospheric chemistry of n-C_xF_2x+1C(O) radicals and their possible role in contributing to the formation of perfluorocarboxylic acids in the environment.