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Biofuels and Environmental Catalysis

Research

Biofuels and Environmental Catalysis Research

Research in the Biofuels and Environmental Catalysis group is focused on two principal objectives: to reduce the environmental impacts of fuel use and to develop renewable fuel sources. Central to these goals is the application of catalysis. In addition to the synthesis of novel catalysts, studies are conducted to probe catalyst structure, mode of action and deactivation mechanisms. The optimization of reaction conditions and the application of novel reactor technologies are also important activities.

Research is conducted in collaboration with a number of other university departments and external institutions, and is performed by both CAER staff and students. Collaboration between CAER and the various science and engineering departments at UK allows students to receive traditional graduate and undergraduate education, while being exposed to the unique multidisciplinary environment at CAER. The following provides an overview of the main topics currently being researched.

Microalgae for CO2 Capture and Utilization

Algae Tubes

Beginning in 2008, CAER and the UK Department of Biosystems and Agricultural Engineering, with the support of the Kentucky Department of Energy Development and Independence, have been studying the use of microalgae for the capture and utilization of carbon dioxide. During the early stages of this project, it was quickly determined that while open pond technologies were relatively well understood, the regional constraints (climate, geography, land availability, etc.) associated with most Kentucky-located power plants would provide significant barriers to large-scale algae cultivation. Consequently, initial work in this project has focused on the design of a low cost, closed-loop photobioreactor.

This work will culminate in a pilot-plant demonstration at a coal-fired power plant in Kentucky (Duke Energy's East Bend Power Plant), slated for start-up in summer 2012. While the mitigation of CO2 emissions forms the main focus of this project, in order to determine the overall process economics, the production of biofuels and other bioproducts from algae is also being examined at CAER. Conversion technologies under study include lipid extraction and processing to liquid hydrocarbons, as well as fast pyrolysis. The resulting process data will be incorporated in a techno-economic model which will enable the costs associated with CO2 capture and utilization to be calculated at different operating scales.

Biomass/Bio-oil Upgrading

Currently the production of ethanol by fermentation of corn-derived carbohydrates is the main technology used for the production of liquid fuels from biomass resources. Alternatively, biomass can be converted into fuels and chemicals indirectly (by gasification to syngas followed by catalytic conversion to liquid fuels) or directly to a liquid product by thermochemical means. Direct thermochemical conversion processes include pyrolysis, liquefaction, and solvolysis. Given that biomass is expensive to transport, being able to pre-process and densify the biomass before transport to a centralized bio-refinery will save significant costs and potentially increase rural income. However, the crude bio-oils afforded by thermochemical conversion processes such as pyrolysis are chemically complex and are typified by a high oxygen content.

Biomass Examples

The oxygenated compounds present in raw bio-oils impart a number of unwanted characteristics such as thermal instability (reflected in increasing viscosity upon storage), corrosivity and low heating value. This instability is associated with the presence of reactive chemical species, notably alkenes, aldehydes, ketones, carboxylic acids and guaiacol-type molecules. Upon prolonged storage, condensation reactions involving these functional groups result in the formation of heavier compounds. The quality of bio-oils can be improved by the partial or total elimination of the oxygenated functionalities present. In this context, we are studying new approaches for catalyst-assisted stabilization of crude biomass-derived pyrolysis oils, for the ultimate production of fuels and high value chemicals.

Lignin Deconstruction for the Production of Fuels and Chemicals

Given the promise of biofuels derived from plant material, it is important to find creative and efficient ways of utilizing all of the potential energy sources contained within this form of biomass. Lignin, one of the three primary constituents of most plant material, is still relatively poorly understood and is highly resistant to deconstruction by chemical means. As the biofuels industry continues to grow, huge quantities of waste lignin will begin to be produced unless effective methods of using this material are found. Despite its recalcitrance, lignin contains component monomers that could potentially function as platform molecules for the synthesis of high-value chemicals, in addition to liquid fuels.

The overarching goal of this project is to develop improved processes for the direct conversion of lignin to fuels and chemicals. In collaboration with Drs. Seth Debolt (Horticulture) and Mark Meier (Chemistry), and with guidance from molecular studies of lignin deconstruction, combined with directed molecular engineering of critical crop properties, researchers in this project aim to overcome lignin's resistance to chemical and biological manipulation. At CAER, research is focused two main pathways for lignin deconstruction: controlled thermolysis in appropriate solvents (e.g., ionic liquids) and (catalytic) oxidative cleavage.

Decarboxylation of Fats and Oils for the Production of Hydrocarbon Fuels

Trucks

Currently, hydrocarbon-based biofuels are mainly produced by deoxygenating renewable feedstocks through hydrotreating. However, this approach has two important drawbacks: 1) it requires high pressures of hydrogen which are only available at centralized facilities to which biomass would have to be transported; and 2) it employs catalysts consisting of metal sulfides that usually need careful handling and risk contaminating the products with sulfur. Deoxygenation via decarbonylation and/or decarboxylation (deCOx) is a promising alternative to deoxygenation through hydrotreating. Indeed, this approach has the significant advantages of requiring considerably lower hydrogen pressures and hydrogen consumption, and of employing simple supported metal catalysts. Initial reports have focused on supported Pd and Pt, the cost of which is prohibitive. However, work at CAER has shown that inexpensive Ni catalysts can display comparable performance to precious metals in the deoxygenation of vegetable oils and animal fats to drop-in hydrocarbon fuels via deCOx. Current work in the BEC group aims at further developing these findings.

Automotive Catalysis

Fuel Converter

On-going work at CAER is focused on reducing emissions of nitrogen oxides (NOx) present in lean exhaust gases (i.e., gases in which excess oxygen is present) such as those emitted by diesel and lean-burn gasoline engines. Lean-burn engines provide more efficient fuel combustion and lower CO2 emissions compared with traditional stoichiometric engines. However, the effective removal of NOx from lean exhaust represents a challenge to the automotive industry. Recent years have witnessed concerted efforts to reduce NOx emissions from mobile sources of lean exhaust gas using lean NOx trap (LNT) or selective catalytic reduction (SCR) catalysts. Although both technologies have many positive features, each approach has drawbacks which have slowed their deployment. For LNT catalysts, one of the main disadvantages is the cost associated with the use of platinum group metals, while for SCR, the cost of the injection system and refilling of the NH3 source adds to the consumer's costs.

However, recent studies have shown that by combining LNT and SCR catalysts in series, these drawbacks can be lessened. In this configuration the SCR catalyst functions in a passive or in situ mode, i.e., with the storage and utilization of NH3 generated by the LNT during rich purge events. Given that the presence of the SCR catalyst relaxes the NOx conversion requirements of the LNT catalyst, the volume of the LNT in the LNT-SCR system can, in principle, be lower than for an LNT-only system, thereby reducing the precious metal costs. Furthermore, the need for a urea injection system is eliminated.

Car Exhaust

Neither the optimal engine control strategy nor the optimal catalyst formulations for generating and reacting NH3 in an LNT + in situ SCR application are obvious, however. Consequently, work at CAER is focused on ascertaining the optimal catalyst architecture and operating strategy of LNT-SCR catalyst systems, with the goal of maximizing NOx conversion levels with minimum fuel penalty. This involves both fundamental and applied studies, utilizing analytical techniques such as spatially resolved capillary inlet mass spectrometry (spaciMS) and diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS).

Contact: Mark Crocker