(37a) Assessing Alternatives for Biorefineries

Human activity has been increasingly releasing more carbon dioxide emissions into our atmosphere. These carbon dioxide emissions trap heat, steadily drive up the planet’s temperature, and create significant and harmful impacts on our health, environment, and climate. If left unchecked, these emissions are expected to cause irreversible damage to communities throughout the United States and the world. This damage includes increased urban air pollution, flooding due to rising sea-levels, erosion in coastal communities, extreme weather including more intense droughts and hurricanes, reduced productivity of some agricultural regions, and loss of treasured landscapes such as coral reefs.

The United States alone contributes to nearly 25% of world’s annual global CO₂ emissions, with electricity and transportation each accounting for roughly one third of these emissions. The majority of the electricity is generated by coal-fired power plants, which produce roughly 25% of the total U.S. CO₂ emissions, while the majority of transportation emissions come from the combustion of petroleum-based products such as gasoline. Transportation CO₂ emissions also account for roughly 25% of the U.S. total U.S.. In contrast, most renewable energy sources do not emit carbon that originate in the ground (fossil carbon). These renewable energy sources include wind, solar, geothermal, hydroelectric, and biomass. Reduction in the use of fossil-fuel energy sources and increased use of renewable energy sources will help to reduce overall fossil-derived CO₂emissions.

Recent years have seen an increased quantity of U.S. CO₂emissions from transportation. This is due to the increased demand for travel, and the limited gains in fuel efficiency across the U.S. vehicle fleet. As the demand for travel increases, so does the demand for renewable transportation fuels to try to help solve the carbon dioxide emission crisis. First generation biofuels were the first response to this increased demand, but they are physically and chemically different than their petroleum counterparts. These major differences have motivated the development of processes that are capable of producing drop-in compatible renewable fuels. These drop-in fuels are engine ready, and have essentially the same properties as their petroleum counterparts, but significantly reduce the overall carbon dioxide emission footprint.

One of the new technologies for producing drop-in compatible renewable fuels and associated chemicals is based on the non-catalytic cracking of fatty acid based oils, such as animal fats and waste cooking oils, as well as triglyceride based (TAG) oils such as crop oils, bacteriological oils, and algae lipids.

 Over the past ten years, research has been conducted on the each of the various unit operations needed to design a comprehensive facility capable of producing drop-in compatible renewable fuels and various by-product chemical products in a variety of configurations using this technology. This research included determination of the optimized yields of organic liquid products (OLP) produced from the conversion of the inlet oil.  This OLP can then be further processed and separated into transportation fuels such as jet fuel and diesel fuel as well as fuel intermediates like naphtha and butane plus other by-products.  A model that accurately represents the reactions completed by the noncatalytic cracking of the TAG oils was developed through substantial testing in continuous, scalable reactors. 

In the present study, all of the previous work conducted by previous researchers was reexamined from a process design perspective in order to develop technically viable, commercially relevant process pathways that can be evaluated for economic feasibility under a number of scenarios.

The noncatalytic cracking process consists of four core subsystems used to convert triglyceride oils into petroleum equivalent renewable fuels:  non-catalytic cracking, purification, decarboxylation, and trim purification. The non-catalytic cracking system is where the TAG and/or fatty acid oils are cleaved into smaller molecules, with the majority of the molecules in the C5-C16 range. The molecules are then sent to purification. The light non-condensable (against room temperature water) gases and heavy ends are separated from the middle distillate in the purification section. The light gases and heavy ends are then sent to further processing and purification to produce usable and saleable byproducts while the middle distillates are routed through decarboxylation reactors. Decarboxylation removes the carboxylic acid group that remain on some of the fatty acid fragments after cracking. Following decarboxylation, the fuel intermediates are sent to trim purification where the transportation fuel products are purified. 

Among the by-products generated are syngas, propane, butane, pentane, and high purity carbon either in the form of anode grade coke or a mesophase pitch suitable for the production of continuous carbon fibers.  Other process options can generate high purity short chain fatty acid by-products, such as acetic and propionic acid, and high concentrations of alkylated aromatics.

The research presented here takes all the information gathered from the various research over the past ten years, and consolidates this information in the form of preliminary designs of various process pathways. These preliminary designs can then be used assess the practicality of implementing a world scale plant capable of producing renewable fuels through the noncatalytic cracking of TAG and/or fatty acid oils. Previously developed in-house fundamental data and literature available on this topic were used to develop ChemCAD simulations for this process. These simulations were then used to develop the preliminary design of the process.

Implementation of world scale biorefineries capable of producing quantities of gasoline, kerosene, and diesel using this technology would help lower the world’s dependence upon petroleum-based transportation fuels.  This in turn can assist in the global efforts to mitigate climate change.