Ethanol is a great compound. It keeps our hands clean during pandemics, it’s used as a feedstock for many industrial chemicals, it can power fuel cells, and it works well in combustion engines. And yes, it can also bring a special touch to celebrations. In addition, ethanol can be a front runner for developing carbon capture and storage (CCS) value chains. In this article from Endrava, we take a closer look at why this is so. Starting with production processes and the related greenhouse gas emissions, we then focus on production sites in the USA using CaptureMap, and share some thoughts about why CCS makes perfect sense in ethanol.
Ethanol has a wide range of uses
Ethanol, or C2H5OH, is an organic compound with many application areas. For medical use, it is frequently used as an antiseptic or as a medicinal solvent (think mouth wash). Its recreational use is well known. It has several use areas as an industrial ingredient to make other organic compounds. And last, but not least, it’s widely applied for engine fuel purposes, either nearly pure or in various blending proportions with regular gasoline.
Ethanol production volumes are impressive
In 2021 more than 100 billion liters of ethanol was produced globally, the vast majority of that coming from the USA and Brazil. Ethanol production takes different pathways depending on feedstocks. You can make it chemically, but we focus here on the biogenic production pathways.
Biogenic feedstocks include grain, beverage and food waste, and cellulosic biomass such as sugar cane. These are converted into ethanol in ethanol biorefineries. Most commonly, ethanol is made from corn through a dry mill production process in which the entire grain kernel is ground into a flour and then fermented.
What do you get out at the other end? Ethanol, sure. But that’s not all. In addition, you get distillers grain (think animal feed), distillers oil, and biogenic CO2. According to the Renewable Fuels Association, 25 kg of corn processed by in a dry mill ethanol refinery gives:
- 11 liters of ethanol
- 7 kg of distillers grain
- 0,4 kg of distillers oil
- 8 kg of biogenic CO2
In our line of work, it’s the CO2 that we’re interested in. So we made a handy conversion rule. The density of ethanol is 789 kg/m3. So 11 liters of ethanol, with a bit of kind rounding, is roughly 8 kg ethanol. That’s the same mass as the biogenic CO2 produced.
Production sites are located in the Midwest
We’re taking an American perspective in this article. That’s because many companies are now trying to align themselves with the announced 45Q tax credits for carbon capture and storage in the USA. And as we’ll get back to a bit later, ethanol sites are promising for CCS.
U.S. ethanol plants are typically located close to the raw material. This means the Midwest, because that’s where corn is produced. The map below shows U.S. ethanol production facilities from CaptureMap, counting 168 sites and 19,3 million tons of annual CO2 emissions. Production sites outside of the Midwest will either receive corn shipped by rail, or use other types of feedstocks.
While there are many sites, they are not that large in CO2 emissions. The illustration below shows the distribution of CO2 emissions across the different sites. The average CO2 emission size is 115 ktpa, while the median is just under 100 ktpa.
The details of fossil and biogenic CO2
In CaptureMap, we’re able to show both biogenic and fossil CO2. But, looking at these 168 sites, only six report biogenic emissions. From our understanding of the production processes, we would expect that all of them should show some level of biogenic CO2 emissions, but that’s not the case. What’s going on?
Ethanol production entails CO2 emissions from several different activities. Typically these sites have energy needs in the forms of heat and electricity. To get that energy, they use a combination of often fossil and sometimes biogenic sources. This could be natural gas, biogas or even waste wood chips. A good example is Poet‘s ethanol plant in Chancellor, South Dakota in which they get a substantial part of their energy needs from biogenic sources. Emissions from the sites energy needs (that are generated on-site) show up in CaptureMap. But where did the biogenic CO2 go from the fermentation process?
An interesting feature of the U.S. GHG Reporting program is that biogenic CO2 emissions from the fermentation process of ethanol production are not reported. It’s therefore not shown in the emission statistics. That means that biogenic CO2 is significantly underreported. How can we solve this conundrum?
First, we sourced production capacities for 154 ethanol plans in the U.S. from the Renewable Fuels Association. Then we matched these sites with the very same sites in CaptureMap, and sourced their annual CO2 emissions. By plotting the two against each other, we wanted to see if there’s a good correlation between production capacities and CO2 emissions. And the answer is yes!
As the illustration shows, each kg of ethanol produced gives about half of that (0,4394 to be precise) in mass of CO2. Now, production capacity is not the same as actual production, but for this analysis, it’s good enough. We can now make our second rule of thumb.
Why is this important to CCS?
Now, we’re getting to the core of the matter. The CO2 concentration from the fermentation in ethanol production is nearly 100%. It’s therefore a perfect starting point for CCS value chains, because the CO2 source is already high purity. This means you don’t need much additional and costly equipment on site to capture the CO2.
So, imagine having a high purity, biogenic CO2 stream ready for transport and storage? It’s the dream of any CCS business developer!
According to the Renewable Fuels Association, around 2,7 million tons of CO2 was captured from ethanol production in the U.S. in 2021. This was used for dry ice production, bottling, food processing and other uses (typically enhanced oil recovery). Using our rule of thumb, our overall analysis shows that the real biogenic volume of CO2 available from these sources is closer to 38 million tons per year (recall twice as much biogenic CO2 emissions from fermentation than from the rest of the site).
These volumes are not enormous in themselves, but it could be a strong starting point for establishing infrastructure for transport and storage. And that in turn could help other sites nearby with higher capture costs to join the same infrastructure for synergies of scale.
Cheers to that!
- Renewable Fuels Association, 2023: Biorefinery locations table
- Renewable Fuels Association, 2023: How is ethanol made
- State CO2-EOR Deployment Work Group, 2017: Capturing and Utilizing CO2 from Ethanol
- US DOE, Alternative Fuels Data Center, 2023: Global Ethanol Production by Country or Region
- US EPA, Greenhouse Gas Reporting Program
- Vital by Poet, 2014: Cleanest and Greenest of Them All
- Wikipedia, 2023: Ethanol