Ethanol may be a simple molecule, but it has the potential to be a building block for a significant number of chemicals now made from petroleum.
About 40 billion gallons of ethanol would be needed to produce all of the organic chemicals currently made from petroleum, said Dennis Miller, department of chemical engineering, Michigan State University (MSU), East Lansing, Michigan, U.S. Miller spoke at the National Corn Grower Association’s Land Use and Carbon Impacts of Corn-based Ethanol Conference in August in St. Louis, Missouri, U.S.
Chemical production is a huge opportunity for the ethanol industry, assuming some challenges can be overcome.
"Biomass in many ways is the opposite of petroleum, which leads to a lot of challenges in the chemistry we have to do, the processes and breaking into the market for these materials," Miller said.
Petroleum is a robust, stable reactant with known physical properties and well-defined markets. In comparison, biomass is a reactive, thermally fragile reactant with unstudied physical properties and uncertain markets.
To be successful, efficient processes for converting ethanol into chemicals must be developed, Miller said, and ethanol facilities need the capital to add the equipment for these conversion processes. Finally, and most importantly, the markets have to be developed for these ethanol-based chemicals.
"A lot of these won’t be drop-in replacements," Miller said. "Those that are, maybe we can compete with."
When examining processes for producing various chemicals from ethanol, researchers at MSU analyze the raw material costs and whether a process would be economical.
For example, feedstock costs for producing butanol from ethanol (via acetaldehyde and Aldol condensation) would be about 31¢ per pound (assuming an ethanol price of $1.65 per gallon). This could be an attractive prospect since butanol is currently selling for 40¢ to 50¢ per pound. In comparison, feedstock costs for ethylene would be 41¢ per pound, but the finished chemical is currently selling at only 30¢ to 35¢ per pound.
In general, chemical production from ethanol becomes attractive when there is an abundant ethanol supply and petroleum prices are increasing, Miller said.
MSU has a reactive distillation facility that does both chemical reactions with catalysts and separations in a single piece of process equipment. The university’s two pilot-scale 5-meter columns are used to study possible processes for converting ethanol into chemicals.
One possible chemical is ethyl lactate, which has good solvent properties. It has low volatility, is stable to greater than 150 degrees C, has excellent solvent performance, is nontoxic, biodegradable and blendable, and generates minimal waste in production with only water as a byproduct.
Using reactive distillation, ethanol would be added to the bottom and lactic acid at the top of a column containing a catalyst in the middle. Because the ethanol is more volatile, it will move up the column and react with the lactic acid. The result is ethyl lactate and water, with excess ethanol recycled.
To date, MSU researchers have filed for a patent on the process and have evaluated the economics in collaboration with an industrial partner. The process could be added into an existing corn dry ethanol mill at a capital cost of between $8 million and $10 million and a three-to-five-year return on investment, Miller said.
If a 30-million-gallon-per-year ethanol facility diverted just 5% of its ethanol to ethyl lactate production, it could add $13 million to its bottom line per year (assuming production of 25 million pounds of ethyl lactate per year). A facility would either need to produce the lactic acid on site or purchase it remotely, Miller said.
The ethyl lactate selling price is heavily influenced by the lactic acid feed cost, he said. At the current lactic acid cost of 50¢ per pound, the ethyl lactate would have to sell for at least 70¢ per pound for the process to be economical.
Ethyl lactate is currently selling at $1.30 to $1.60 per pound. The catch is the current market for ethyl lactate is 10 to 20 million pounds per year as a specialty solvent in electronics manufacturing.
"The economics look good, and we’re comfortable with the process technology, but we have to develop the market," Miller said.
Another possibility for ethanol is in citric acid esterification, Miller said, which would produce citrate esters. These esters are non-toxic plasticizers that could replace phthalates. Citric acid itself is an inexpensive, bio-based organic acid made by fungal fermentation, he said.
This esterification process also could be integrated into existing dry mill ethanol plants. The required selling price for the esters would be about $1.15 per pound but would depend on ethanol and citric acid prices.
In addition to being a chemical feedstock, ethanol also could be used for creating advanced biofuels, Miller said. These advanced fuels have the potential to overcome some of the current concerns with biodiesel, in particular its tendency to gel at low temperatures.
One possible process is secondary transesterification of biodiesel via reactive distillation. Fatty acid methyl esters (FAME), otherwise known as biodiesel, would be added to ethanol to create fatty acid ethyl esters (FAEE) and methanol. The methanol could be recovered and used to make more biodiesel. Such a process could be added on to an existing biodiesel facility.
The benefit of the process is that there is no water in the system, and the resulting FAEE is an entirely renewable biofuel, Miller said. Additionally, the FAEE has a 5% higher energy content than methyl biodiesel.
A second approach is to convert ethanol to acetaldehyde and add it to glycerol (a byproduct of biodiesel production) to produce acetal compounds. Adding the acetaldehyde to the glycerol eliminates the concern of what to do with this byproduct, as it can be added back into the fuel.
Producing biodiesel with methanol results in production of 1.05 gallons of biodiesel per gallon of oil, while using ethanol results in 1.1 gallons of biodiesel per gallon of oil. Adding in the acetals increases production to 1.24 gallons of biodiesel per gallon of oil.
A full B20 buildout in the U.S. would require 1.5 billion gallons of ethanol per year, or 2.4 billion gallons per year with acetals, Miller said.
"There is a substantial opportunity to look at ethanol as a feedstock for biodiesel," he said.
Co-products of the ethanol process also have potential as feedstocks, Miller said. Using a thermal conversion process, the distiller’s grains could be converted into an additional 1.05 gallons of hydrocarbon fuel per bushel. The process is thermal neutral because the energy comes from the chemical reactions, and it increases the fuel energy yield of the ethanol conversion process by 50%.
The challenges to overcome include removing the nitrogen and sulfur from the distiller’s grains and the economics of processing the grains versus drying and selling them as a feed.
Carbon dioxide, another ethanol byproduct, also has some possibilities. It is a pure, distributed feedstock that can be used to accelerate plant growth in a greenhouse; as a dry cleaning solvent; for beverage carbonation; or dry ice.
Beyond those physical uses, carbon dioxide also has chemical applications. A lot of energy has to be added to make it useful, Miller said, but there may be opportunities for value addition that overcome that requirement.
For example, carbon dioxide could possibly be used as a replacement for phosgene, a highly toxic agent, in the synthesis of isocyanate. Isocyanate is used to create polymers such as polyurethane, which has a market of nearly 25 billion pounds per year worldwide.
Carbon dioxide also could be used to create propylene carbonate, which is the preferred electrolyte in lithium batteries. It has excellent solvent properties and is an ingredient in elastomers and adhesives.