Susan M. Stagg-Williams

Pulsed electric field (PEF) as an intensification pretreatment for greener solvent lipid extraction from microalgae.

Microalgae, with their high lipid content, are a promising feedstock for renewable fuels. Traditionally, human and environmentally toxic solvents have been used to extract these lipids, diminishing the sustainability of this process. Herein, pulsed electric field technology was utilized as a process intensification strategy to enhance lipid extraction from Ankistrodesmus falcatus wet biomass using the green solvent, ethyl acetate. The extraction efficiency for ethyl acetate without PEF was lower (83–88%) than chloroform. In addition, the ethyl acetate exhibited a 2‐h induction period, while the chloroform showed no time dependence. Utilizing PEF technology resulted in 90% of the cells being lysed and a significant enhancement in the rate of lipid recovery using ethyl acetate. The increase in lipid recovery was due to the presence of the electric field and not due to temperature effects. The PEF technology uses less energy than other PEF systems reported in the literature. Biotechnol. Bioeng. 2013; 110: 1605–1615.

Catalytic Performance of Pt/ZrO2 and Pt/Ce-ZrO2 Catalysts on CO2 Reforming of CH4 Coupled with Steam Reforming or Under High Pressure

CO2 reforming of methane was performed on Pt/ZrO2 and Pt/Ce-ZrO2 catalysts at 1073 K under different reactions conditions: (i) atmospheric pressure and CH4:CO2 ratio of 1:1 and 2:1; (ii) in the presence of water and CH4:CO2 ratio of 2:1; (iii) under pressure (105 and 190 psig) and CH4:CO2 ratio of 2:1. The Pt supported on ceria-promoted ZrO2 catalyst was more stable than the Pt/ZrO2 catalyst under all reaction conditions. We ascribe this higher stability to the higher density of oxygen vacancies on the promoted support, which favors the cleaning mechanism of the metal particle. The increase of either the CH4:CO2 ratio or total pressure causes a decrease in activity for both catalysts, because under either case the rate of methane decomposition becomes higher than the rate of oxygen transfer. The Pt/Ce-ZrO2 catalyst was always more stable than the Pt/ZrO2 catalyst, demonstrating the important role of the support on this reaction.

Mixed-conducting oxygen permeable ceramic membranes for the carbon dioxide reforming of methane

Due to the high economic, environmental, and safety costs associated with pure oxygen, mixed-conducting oxygen-permeable ceramic membranes are being explored as an alternative oxygen source for hydrocarbon conversion reactors. This work reports a dramatic improvement in catalyst performance when an oxygen-permeable SrFeCo0.5Ox ceramic membrane is used in conjunction with a conventional powder Pt/ZrO2 catalyst for the CO2 reforming of CH4. Experiments comparing catalyst performance with up to 2% co-fed oxygen to catalyst performance with oxygen from the ceramic membrane demonstrated a conversion three times higher with the membrane than with any amount of co-fed oxygen. The results suggest that membrane oxygen is more beneficial for catalyst activity and stability than molecular gas-phase oxygen.

Metal-support interaction on Pt/ZrO2 catalysts for the CO2 reforming of CH4

Three forms of catalyst modification have been explored to elucidate the reaction mechanism and the role of the support in the CO2 reforming of CH4. The results of this study show that partial encapsulation of the metal does not significantly alter the catalytic performance and any differences in performance due to varying pretreatment conditions can be ascribed to variations in the particle size. In addition, promoters can be added to the support to increase the thermal stability, increase CO2 adsorption capacity, and decrease particle growth. Finally, a Pt/ZrO2-perovskite physical mixture has exhibited high stability for the reforming reaction in the presence of steam and under elevated pressures.

Waste Cooking Oil Biodiesel Use in Two Off-Road Diesel Engines

This study examines the composition and combustion performance of biodiesel produced from waste cooking oil. Six fuel batches produced from waste oil used in dining-hall fryers were examined to determine their physical and chemical properties, including their elemental and fatty acid methyl ester composition. Oleic and linoleic methyl esters accounted for more than 70% of the fuel composition, while the oxygen content averaged 10.2% by weight. Exhaust emissions were monitored for 5–100% biodiesel blends using two off-road engines: a 2007 Yanmar diesel generator and a 1993 John Deere front mower. Increasing biodiesel content resulted in reduced emissions of partial combustion products from the diesel generator but a rise in NOx, with the greatest changes occurring between 5 and 20% biodiesel content. For the riding mower, biodiesel content up to 50% had little effect on emissions, while NOx and total hydrocarbon emissions decreased with 100% biodiesel. The difference in NOx emissions is attributed to the two different fuel injection control designs used in the two engines. These results indicate that the effects of biodiesel use on nonroad engine exhaust emissions may be substantially lower in older engines optimized for performance over emissions control.

Promoting catalysis and high-value product streams by in situ hydroxyapatite crystallization during hydrothermal liquefaction of microalgae cultivated with reclaimed nutrients

Although algal biofuels hold great potential for renewable energy, production costs limit widespread technology adoption. Co-producing high-value products can ensure economic viability. We have discovered subcritical water will simultaneously convert algae, grown with reclaimed nutrients, into pure-phase substituted hydroxyapatite nanocrystals and a petroleum-like biocrude. The hydroxyapatite contains substitutions of carbonate, silicate, and magnesium, and can be easily modified to produce varying ratios of hydroxyapatite and tricalcium phosphate. The crystallization process is shown to undergo a nanoscale hierarchical order from long hexagonal crystals which aggregate to bundles, sheets, and flower-like microstructures. The hydroxyapatite promotes in situ catalytic upgrading of the biocrude product, particularly, the dehydration of fatty acid amides. Overall, in situ oil upgrading provides a superior quality biocrude by reducing the oxygen content to 96% of the oil boiling below 600 °C. Major compounds found within the biocrude include phenolics and unsaturated hydrocarbons. In addition to heterogeneous catalysis, the hydroxyapatite product has significant promise for biomedical engineering applications. Herein, we demonstrate live cell-adhesion of human Whartons jelly cells through extended filopodia on the hydroxyapatite product. This discovery establishes a new paradigm for water and nutrient reclamation systems and algae-based fuels and chemicals by producing a versatile high-value product, substituted hydroxyapatite, which can integrate into multiple markets and rapidly improve economic feasibility for algae biofuels.

Influence of Fuel Injection System and Engine-Timing Adjustments on Regulated Emissions from Four Biodiesel Fuels

The use of biofuels for transportation has grown substantially in the past decade in response to federal mandates and increased concern about the use of petroleum fuels. As biofuels become more common, it is imperative to assess their influence on mobile source emissions of regulated and hazardous pollutants. This assessment cannot be done without first obtaining a basic understanding of how biofuels affect the relationship between fuel properties, engine design, and combustion conditions. Combustion studies were conducted on biodiesel fuels from four feedstocks (palm oil, soybean oil, canola oil, and coconut oil) with two injection systems, mechanical and electronic. For the electronic system, fuel injection timing was adjusted to compensate for physical changes caused by different fuels. The emissions of nitrogen oxides (NOx) and partial combustion products were compared across both engine injection systems. The analysis showed differences in NOx emissions based on hydrocarbon chain length and degree of fuel unsaturation, with little to no NOx increase compared with ultra-low sulfur diesel fuel for most conditions. Adjusting the fuel injection timing provided some improvement in biodiesel emissions for NOx and particulate matter, particularly at lower engine loads. The results indicated that the introduction of biodiesel and biodiesel blends could have widely dissimilar effects in different types of vehicle fleets, depending on typical engine design, age, and the feedstock used for biofuel production.