The importance of filtration in ethanol production quality assurance and its impact on fighting climate change

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. First generation bioethanol is manufactured from living crops, usually by fermentation and distillation while second generation is produced from non-edible agricultural residues, lignocellulosic biomass, and municipal solid waste. Third-generation bioethanol is still in the early stages of development and uses algae as feedstock, and the latest generation involves the use of genetically modified microorganisms and feedstocks. 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 to reduce transport pollution have led to the introduction of ethanol/gasoline blends in the vehicle market. The volume requirements for biofuels are regulated by the Environment Protection Agency (EPA) and have been increasing annually. The EPA proposed and finalized rules that establish required Renewable Volume Obligation targets and percentages standards: 22.33 billion gallons by 2025, up by 1.7 billion gallons, or 8% from 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 described in this U.S. Department of Labor document. The process begins at the hammer mill, where kernels are ground into a powder to increase surface area. Next, hot water and enzymes are added to the dry powder in a propagation tank. Here, water works to weaken the tough outer layer of the corn, and 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. This mixture is stirred to ensure that the yeast is fully hydrated, and conditions are adjusted to optimize yeast performance. This stage is crucial because it’s where ethanol production occurs.

There are two fundamentals for the ethanol production plant — production speed, and yield/purity. This step can take up to 60 hours, so high yield and purity of ethanol generated by the yeast is important to capitalize on this time investment. 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 and achieves a high conversion level 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 (MashPrep™ or Puradisc™ syringe filter or Whatman GD/X™ filter) to remove any trace solids that are present. This step prepares the liquid for a high-performance liquid chromatography (HPLC) test. It is important to filter the ethanol filtrate as any solids present will block guard columns of the unit, slowing down testing. The clean filtrate is added to vials and injected into the HPLC system. Good laboratory practice includes filtering buffers, called mobile phase, which are used in this analytical technique. Filtering both sample and mobile phase are simple, economical practices that extend the life of consumable HPLC parts and preserve 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 is key for determining how the yeast is performing.

Yeasts are living organisms that generate ethanol from glucose under fermentation conditions. A combination of stressors, such as high sugar concentrations, byproducts of bacterial contamination, and temperature changes can slow down the conversion process or halt ethanol production. Maintaining optimal conditions for the yeast is key to maximize the amount of glucose converted to ethanol. In the sample just removed from the fermentation tank, Melissa sees a peak in sugar concentration — this 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.

Using a PolyVENT™ or HEPA-Cap™ vent filter to vent a bioethanol fermentation tank can protect the product from airborne contamination. This ensures product quality and safety and protects the environment from aerosols produced in the tank.

Minimizing waste

During fermentation, 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 and vaporizes first. The dispelled vapor is condensed, collected and rectified, ready for the next stage.

The ethanol then undergoes a final step called separation, based on molecule size. It removes trace water molecules and associated impurities. Samples are then filtered by dedicated ion chromatography syringe filters (Acrodisc™ IC PES syringe filter) and injected to perform an ion chromatography test. This test is vital, because the presence of water or other impurities can increase the electrical charge of ethanol which causes problems later when added to gasoline and burned within vehicle engines. Before ethanol is released to the market, a denaturant is added to make it undrinkable. What happens to the leftover mash from the fermenter? This substance, called stillage is put into centrifuges and processed into products such as feed for farm animals.

For advice on filter material properties and compatibility, contact Cytiva support.

Alternatively, request a sample by completing the form using the following link.

Additional resources

Renewable Fuels Association website: http://www.ethanolrfa.org/
Ethanol Producer website (Reboot global debate on biofuels): https://ethanolproducer.com/articles/reboot-global-debate-on-biofuels-12864