Upgrading bioethanol and, subsequently, butanol is a challenging science. Practitioners have to contend with numerous important considerations such as process safety, waste streams and chemical toxicity, recycling of solvents and catalysts, process economics, low oil prices, and a multitude of engineering and technology considerations. Nevertheless, despite the challenges, the ideal outcome of these efforts when accomplished is quite satisfying: a simple, efficient, green, robust and safe manufacturing process. Butanol, with a global market of about 350 million gallons per year, is an important industrial chemical. It is currently produced by the Oxo or Aldol processes. The Oxo process starts from propylene combined with hydrogen and carbon monoxide (usually in the form of synthesis gas) over an expensive rhodium catalyst.&nbsp; The Aldol process starts from acetaldehyde. These approaches using petroleum-derived components like propylene and synthesis gas are inherently &ldquo;not green.&rdquo; The Oxo process was developed and licensed to the industry beginning in 1971 in a collaboration among Johnson Matthey &amp; Co. Ltd., The Power-Gas Corporation Ltd. (formerly Davy Process Technology Ltd., now a subsidiary of Johnson Matthey PLC) and Union Carbide Corp. (now a subsidiary of The Dow Chemical Co.). A second, greener pathway is the ABE fermentation process (acetone, butanol, ethanol) that was pioneered by Chaim Weizmann during World War I. The petroleum-derived approach, however, proved to be economically advantageous and most of the facilities using fermentation processes closed, with a few exceptions, after World War II when the rapid development of the petrochemical industry took place. Today, as interest grows in transitioning from nonrenewable carbon to renewable resources, researchers and startups around the globe have made staggering progress toward the production of butanol from renewable resources. The ABE process is making a comeback to match mandates around the world. Since early 2000, the number of startups has been growing steadily and those pursuing various aspects of butanol production are flourishing more than ever&mdash;from capturing carbon dioxide or developing new microbial strains for efficient conversions to butanol, along with feedstock analysis and downstream processing.&nbsp; Butanol has successfully made the transition from a commodity chemical to a fuel additive, especially when compared to a more hygroscopic and less energy-dense ethanol. Butanol is versatile for many reasons. It can be used as a fuel additive or chemically transformed into to high-value, high-volume precursors such as butanal (global production around 6.6 million tons per year), glycol ethers, butyl acrylates or solvents.&nbsp; Butanol by itself can be used as a solvent or converted to the more widely used, workhorse plasticizer, 2-ethyl hexanol (global production around 2.5 million tons per year.)&nbsp; Jet Fuel Potential Another large-scale market attracts developers in alcohol-to-jet fuel blends. For example, a Boeing 747 consumes approximately 1 gallon of fuel per second. Over the course of a 10-hour flight, it burns about 36,000 gallons, or approximately 5 gallons per mile. Multitude volume of the fuel will be required to meet the blending requirements in the aviation department. Here we argue that: since the ethanol industry is relatively mature and represents a major chunk of biomass-derived biofuel, the annual volumes of ethanol production becomes the ideal proxy for potential volumes of alternative jet fuel. The consumption of Jet A-1 fuel used by commercial operators was 72.2 billion gallons in 2013, according to the Air Transport Action Group. The global production of ethanol in 2014 was 24.57 billion gallons. In considering the de novo design of systems that upgrade existing biofuels (such as ethanol to n-butanol or to Jet Fuel A-1), it is imperative to design working systems that are relatively inexpensive to keep investments, and final fuel cost, low. A simple back of the envelope calculation would suggest the following: With 100 percent conversion of ethanol to n-butanol the mass yield would be 80 percent. Similarly, for 100 percent conversion of ethanol to C16 hydrocarbon (carbon atoms per molecule; Jet Fuel A-1 contains C8 to C16) the mass yield would be 61 percent. If you started from butanol converted to Jet Fuel A-1, the mass yield would be 75 percent. Thus, theoretically, if all global ethanol produced in 2014 were converted, one would obtain 15 billion gallons of Jet Fuel A-1. That would amount to 21 percent of the 2013 Jet A-1 fuel consumption of 72.2 billion gallons. Fermentation Prospects Where does the ABE fermentation stand? The best results ever obtained for the ABE fermentation to date are in the vicinity of 20 grams per liter in butanol concentration from fermentation, 4.5 grams per liter per hour in butanol productivity and a butanol yield of less than 25 percent (w/w) from glucose, or about 1.29 gallons per bushel. Therefore, if the fermentation route were to be utilized, the limiting step would be a conversion of ethanol to butanol. Global ethanol production of 24.57 billion gallons would give only 4.6 billion gallons of Jet Fuel A-1, which amounts to 6.4 percent of the total requirement of the commercial operators. One critical policy hurdle for commercializing aviation biofuels is the difference in incentives for renewable fuels between on-road and aviation use. The on-road applications have been encouraged by measures such as tax breaks and mandates that do not differentiate between biofuel qualities. Under the EU&rsquo;s Renewable Energy Directive, it is left up to the market operators to use any biofuel as long as the sustainability criteria of the RED and the relevant technical specifications are met. Regarding aviation incentives, the Emission Trading Scheme qualifies aviation biofuel as noncarbon-dioxide emitting fuel, but the incentive is being undermined by the current difficulties with ETS application to the aviation sector. In the aviation sector, only high physical quality biofuels with low freezing points can be used to ensure the operability of the jet engines. The current political framework and international competition has led to a paradoxical situation, where high-quality biofuels are finding applications in road transport, although lesser-quality biofuels could also satisfy the road transport needs, while they can not be used in aviation due to the absence of incentives. A small- or medium-sized startup with a novel idea working on designing a proof-of-concept pilot has much to consider before venturing into a full-scale demo or commercial plant, or even just planning to expand its patent portfolio. Big conglomerates are also considering the technology, especially those planning to be brand ambassadors for developing sustainable solutions for tomorrow. All those considering an ethanol upgrading platform will want to consider a range of factors including market studies, value and volume chain analysis, process economics, industrial fermentation, separation technology, green chemistry, engineering technology, off-take agreements, and more. The growing number of developers is about to set up a chain of events that will be disruptive in how we look at energy and its utility. The list of factors to consider definitely presents a challenge, but it is a challenge that needs a global perspective and is most certainly not trivial. Author: Kapil S. Lokare, PhD Biomass Consultant, Emerging Technologies Division, Lee Enterprises Consulting Inc. Kapil.lokare@lee-enterprises.com 501-833-8511

Considering potential conversion volumes and the interest in renewable content in aviation fuels, there could be adequate volumes for blending.

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Developers make progress towards renewable aviation fuels. This contribution appears in the March issue of EPM. 

Promising jet fuel market looms for upgraded bioethanol, butanol

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