Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Engineering Science

Program

Chemical and Biochemical Engineering

Supervisor

Charpentier, Paul

Abstract

The production of green diesel through waste fats and oils is a promising route to producing renewable transportation fuels that are energy dense, have low oxygen content, low nitrogen content, and possess excellent cold flow properties. However, producing green diesel can be expensive, as most methods use expensive noble metals catalysts such as platinum or palladium, use expensive hydrogen gas, and/or use pyrolysis and thermal cracking to reduce hydrocarbon chain length and lose energetic carbon-hydrogen bonds. This thesis studies the continuous thermo-catalytic decarboxylation of fatty acids and their derivatives to create liquid transportation fuels using an inexpensive MoOx/Al2O3 catalyst with no addition of hydrogen gas to produce hydrocarbons with minimal cracking. MoOx/Al2O3 catalyst was found to decarboxylate oleic acid up to 99% at 375 ºC and decarboxylate stearic acid up to 99% at 390 ºC. A feedstock of 50:50 oleic:stearic acid processed at 375ºC and 3.5 h residence time had a minimum decarboxylation of 90 %, heptadecane selectivity of 55 %, and a liquid yield of 86 %. The addition of glycerol and ethanol to the reaction, which is thought to undergo reforming, lowered the necessary reaction temperature for stearic acid from 375 ºC to 390 ºC. Changing the reaction solvent from steam to toluene, without added glycerol/ethanol, lowered the necessary reaction temperature for stearic acid from 390 ºC to 375 ºC. A third-party fuel analysis confirmed that product from the process was suitable as a commercial diesel fuel, which makes this a possible route for green diesel production.

Summary for Lay Audience

The use of fossil fuels is associated with the emission of greenhouse gases and therefore, global warming. A greenhouse gas increases the amount of heat our atmosphere is able to retain and effectively increases average global temperatures, helping to cause global warming. When fossil fuels are burned for energy, they produce carbon dioxide (CO2), a gas known to be a potent greenhouse gas. An increase in global average temperatures is correlated to an increase in droughts, larger category storms, and other adverse environmental events. Decreasing the use of fossil fuels for energy is essential for reducing the impact of global warming.

Biofuels are renewable and CO2 neutral alternatives to fossil fuels. Biofuels are carbon neutral because the CO2 that is absorbed by the biomass is equal to the CO2 that is released when the fuel is burned. When fossil fuels are burned, the CO2 is sourced from underground reserves that result in a net positive amount of CO2 in the atmosphere.

There are several challenges associated with producing a biofuel that has properties that are ideal for our current engines, climates, and infrastructure. Promising biomass sources for biofuels are waste fats and oils such as corn distiller’s oil, yellow grease, and brown grease. These sources are composed of molecules that have long hydrocarbon chains with oxygen atoms at the head of the chain. The removal of these oxygen atoms from fats and oils improves fuel properties and makes these biofuels look and behave more akin to diesel, jet fuel, and gasoline. Decarboxylation, which uses a catalyst for the removal of the oxygen atoms in the form of CO2, is a promising method for production of liquid transportation fuels.

This thesis explored the potential of MoOx/Al2O3 catalysts for the continuous production of green diesel from corn distiller’s oil, oleic acid, and stearic acid. By modifying reaction conditions such as temperature, pressure, residence time, and additives, fuel was produced that was deemed suitable as diesel.

Biofuels are renewable and CO2 neutral alternatives to fossil fuels. Biofuels are sourced from plants and other biomasses that absorb atmospheric CO2. When biofuels are burned for energy, the released CO2 from these fuels are absorbed by the biomass sources, creating a cycle of CO2 release and sequestration. When fossil fuels are burned, the CO2 is sourced from underground reserves that do not undergo the cycle of “en-masse” re-sequestration, resulting in a net positive amount of CO2 in the atmosphere.

There are several challenges associated with producing a biofuel that has properties that are ideal for our current engines, climates, and infrastructure. Promising biomass sources for biofuels are waste fats and oils such as corn distiller’s oil, yellow grease, and brown grease. These sources are composed of molecules that have long hydrocarbon chains with oxygen atoms at the head of the chain. The removal of these oxygen atoms from fats and oils improves fuel properties and makes these biofuels look more akin to fuels like diesel, jet fuel, and gasoline. Decarboxylation, which is the removal of the oxygen atoms in the form of CO2, is a promising method for production of liquid transportation.

This thesis explored the potential of MoOx/Al2O3 catalysts for the continuous production of liquid hydrocarbons from corn distiller’s oil, oleic acid, and stearic acid. The addition of glycerol and ethanol to the process was explored and was found the reduce the temperature requirement for the decarboxylation of stearic acid. We were able to produce a fuel that is a suitable as a diesel.

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