William C. McCaffrey

The dynamics of heterotrophic algal cultures.

In this work, the time varying characteristics of microalgal cultures are investigated. Microalgae are a promising source of biofuels and other valuable chemicals; a better understanding of their dynamic behavior is, however, required to facilitate process scale-up, optimization and control. Growth and oil production rates are evaluated as a function of carbon and nitrogen sources concentration. It is found that nitrogen has a major role in controlling the productivity of microalgae. Moreover, it is shown that there exists a nitrogen source concentration at which biomass and oil production can be maximized. A mathematical model that describes the effect of nitrogen and carbon source on growth and oil production is proposed. The model considers the uncoupling between nutrient uptake and growth, a characteristic of algal cells. Validity of the proposed model is tested on fed-batch cultures.

Optimization of microalgal productivity using an adaptive, non-linear model based strategy

The optimization of biomass and oil productivities in heterotrophic cultures of Auxenochlorella protothecoides was achieved using a non-linear model-based approach. A 10-fold increase in the average biomass productivity, and a 16-fold increase in the maximum productivity, was observed with respect to batch cultures as a result of the proposed optimization strategy. Final cell density in the optimized culture was 144 g/L (dry weight), with 49.4%w/w oil content. Maximum lipid productivity was 20.16 g/L d, achieved during the exponential growth phase at an average cell density of 86 g/L. Lipid productivity in the optimized microalgal culture was higher than previously reported values for other oleaginous microorganisms. Oil composition analysis showed that the oil has a high quality as biodiesel precursor. The higher productivity and excellent lipid profile of the optimized microalgal culture make A. protothecoides an exceptional source for biodiesel production and a potential source of single cell oil for other applications.

Kinetics of hydrocracking and hydrotreating of coker and oilsands gas oils

Abstract Two-stage hydrocracking of gas oils involves a complex set of hydrogenation, heteroatom removal, and cracking reactions. Feeds from coking processes and oilsands bitumen are richer in aromatics and heteroatoms, which increases the importance of the reactions of these components. The hydrocracking and hydrotreating kinetics of a series of conventional, coker and oilsands gas oils were measured using a laboratory microreactor. The kinetics were then correlated with the composition of the feed oils. The conversion of gas oil to middle distillate during hydrotreating was correlated with sulfur content and polyaromatic hydrocarbon content. Hydrocracking of the gas oil in the second stage of reaction followed a Langmuir-Hinshelwood rate expression based on the inlet concentration of total nitrogen. The resulting composite rate expression gave good prediction of gas oil conversion kinetics for the full range of gas oils. The inhibition of hydrocracking by nitrogen was more important for cracking than the differences in the homologous series in the gas oils of different origins.

Chabazite-Clay Composite for Bitumen Upgrading

Abstract The Alberta oilsands resource is increasingly recognized as a strategic source for North American energy supply. We synthesized a novel chabazite-clay composite for improved oilsand bitumen upgrading by growing chabazite on kaolin under alkaline conditions. XRD, SEM, TEM, N 2 physical adsorption, and XPS surface elemental analysis confirmed that the chabazite-clay composite has a unique exterior surface, accessible to large hydrocarbon molecules, that could moderate bitumen upgrading reaction with high performance contaminant (sulfur, nitrogen, nickel, and vanadium) removal.

A simple and rapid protocol for measuring neutral lipids in algal cells using fluorescence.

Algae are considered excellent candidates for renewable fuel sources due to their natural lipid storage capabilities. Robust monitoring of algal fermentation processes and screening for new oil-rich strains requires a fast and reliable protocol for determination of intracellular lipid content. Current practices rely largely on gravimetric methods to determine oil content, techniques developed decades ago that are time consuming and require large sample volumes. In this paper, Nile Red, a fluorescent dye that has been used to identify the presence of lipid bodies in numerous types of organisms, is incorporated into a simple, fast, and reliable protocol for measuring the neutral lipid content of Auxenochlorella protothecoides, a green alga. The method uses ethanol, a relatively mild solvent, to permeabilize the cell membrane before staining and a 96 well micro-plate to increase sample capacity during fluorescence intensity measurements. It has been designed with the specific application of monitoring bioprocess performance. Previously dried samples or live samples from a growing culture can be used in the assay.