In Wisconsin, just off the main road, lies a lone silver structure surrounded by green pastures.
That structure houses Ethanol Ltd, a fictitious mid-sized ethanol manufacturing plant. It operates 24 hours a day, seven days a week, delivering over 50 million gallons of pure ethanol a year to its consumers.
An attractive candidate
As concern over climate change continues to grow, ethanol has received global attention as a suitable alternative to petroleum-based fuels.
One of the major contributors to earth’s increasing temperatures is transport pollution, which releases large amounts of carbon dioxide (CO2) into the atmosphere. CO2, a greenhouse gas (GHG), traps infrared radiation from the sun and emits it back onto the earth’s surface, warming it up.
Renewable energy sources are being explored as viable alternatives for reducing CO2 emissions. Biofuels, such as ethanol, can help to achieve this goal. Biofuels, such as ethanol, can help to achieve this goal. Ethanol is manufactured from living crops, usually by fermentation and distillation. The CO2 emitted during ethanol production and use is offset by the CO2 absorbed by the next generation of crops, neutralizing the carbon effect.
Within the United States, government efforts for reducing transport pollution have led to introduction of ethanol/gasoline blends into the vehicle market. The volume requirements for biofuels is regulated by the Environment Protection Agency (EPA) and have been increasing annually. The EPA has set a long-term target of producing 36 billion gallons of renewable fuels by 2022. Plants like Ethanol Ltd are partners in achieving this goal.
Beginning the manufacturing journey
Ethanol Ltd manufactures its ethanol from corn kernels using a dry milling production process, as described in this U.S. Department of Labor document. The process begins at the hammer mill, where the kernels are ground into a powder to increase the surface area. Next, hot water and enzymes are added to the dry powder in a propagation tank. Here, the water works to weaken the tough outer layer of the corn, and the enzymes break down the starch molecules into simple sugars. Another enzyme is added to break down the simple sugars to glucose. A mash is prepared, ready for the next stage.
When yeast and people work together
The mash is transferred to a fermentation tank, and dry yeast is added. The mixture is stirred to ensure that the yeast is fully hydrated, and conditions are adjusted to optimize yeast performance. This stage of production is crucial, because it is where ethanol is made.
For the production plant, two things are paramount – production speed, because this step can take up to 60 hours, and yield/purity of the ethanol generated by the yeast. To promote efficiency, plant employees like Melissa and Tony work together with various filtration tools. Their goal is to ensure that the fermentation stage moves along as quickly as possible to achieve high conversion of glucose to ethanol.
Melissa works as a lab technician in the in-house Quality Assurance team. Every 10 hours, one of her colleagues takes a sample from the fermentation tank and passes it through a Grade 4 qualitative cellulose filter paper. The high flow rate allows liquid components (the filtrate) to flow through the filter relatively quickly, leaving the solids behind.
Melissa examines the residue from the filter to check the breakdown progress of the mash. She cleans the filtrate further, passing it through a syringe filter to remove any trace solids that could still be present. This step prepares the liquid for a high-performance liquid chromatography (HPLC) test. It is important to filter the filtrate because any solids present will block the guard columns of the unit, slowing down the test. The clean filtrate is added to vials and injected into the HPLC system.
Within the system, the molecules in the filtrate are separated and identified through their ability to absorb ultraviolet light rays emitted from the unit’s ultraviolet lamp. The unabsorbed light is captured by the unit’s detector and translated into peaks on a chromatogram.
Melissa performs several of these HPLC tests for samples taken at different times, referring to each test’s chromatogram to understand the conditions within the fermentation tank at that time point. This understanding is key to determining how the yeast is performing.
Yeasts are living things that can generate ethanol from glucose under the right conditions for fermentation. A combination of stressors, such as high sugar concentrations, byproducts of bacterial contamination, and temperature changes can slow down the conversion process or kill it — halting ethanol production. Keeping optimal conditions for the yeast is key to maximizing the amount of glucose converted to ethanol. In the sample just removed from the fermentation tank, Melissa sees a peak in sugar concentration -this high sugar concentration could reduce the production efficacy of the yeast. She passes this information to Tony, the lead operation manager. Tony instructs his team to stop introducing new mash batches into the fermentation tank.
During fermentation, the CO2 produced in the glucose conversion reaction can be captured for use in beverage bottling or as dry ice.
After fermentation is complete, the fermented mash is pumped through a multi-column distillation system, where each column is heated to a specific temperature. Ethanol has a lower boiling point than water, so it vaporizes first. The dispelled vapor is condensed, collected and rectified, ready for the next stage.
The ethanol undergoes one final step to ensure its purity. It is put through a step that is based on size differences. It removes trace water molecules and associated impurities. Samples are then taken and placed into syringeless filters compatible with an autosampler. The autosampler injects the samples, drawing out enough liquid to perform an ion chromatography test. This test is vital, because the presence of water or other impurities can increase the electrical charge of the ethanol – causing problems later, when added to gasoline and ultimately within vehicle engines.
Before the ethanol is released to the market, a denaturant is added to make it undrinkable. But what happens to the leftover mash in the fermenter? This substance, now called stillage, is not wasted. Instead, it is put into centrifuges, then processed into products such as feed for farm animals.
Towards a cleaner environment
The production and use of this biofuel has been shown to benefit the environment. It yields minimal waste and has the potential to improve the efficiency of vehicle engines. According to the International Energy Agency, such use can potentially relieve the global environment of 2.1 billion metric tons of its C02 emissions by 2050. Ethanol is a major player in the fight against climate change, and the great news is that it is available now!