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Measurement and Testing


Introduction The 21st Century has been characterized by environmental consciousness and global eff orts towards biofuels. One promising alternative is bioethanol, which is already incorporated in gasoline blends worldwide. In the United States, up to 98% of gasoline contains 10% ethanol (E10). Most bioethanol production in the US is from corn grain starch at approximately 94% [1]. There are several diff erent methods for producing ethanol as well as various feedstocks, which diff er from country to country.


History E


thanol is in use because of its ability to increase the octane ratings in gasoline and has replaced several predecessors


due to their environmental and health detriments. In the 1900s, gasoline in the United States used lead as a primary additive but was phased out due to health risks until its full ban in 1990 by the Environmental Protection Agency (EPA). Following the ban, alternative additives became popular like methyl tertiary butyl ether (MTBE) and the hydrocarbon mixture BTEX (benzene, toluene, ethylbenzene, and xylene). Later research found associated health risks, leading to discontinuation of these additives. Currently, bioethanol is being used since it is considered cleaner [2]. The Renewable Fuel Standard (RFS1) was created by the EPA in 2005 which mandated at least 4 billion gallons of renewable fuel. RFS1 was implemented to reduce greenhouse gas emissions, as well as expand the alternative fuels sector to promote widespread environmental protections. RFS1 was amended in 2010, referred to as RFS2, which expanded the standard to 36 billion gallons of biofuel that would be in use by 2022. Within this amended standard, the EPA defi ned that no more than 15 billion gallons of biofuel was to be from corn grain ethanol and no less than 16 billion from cellulosic biofuel [3]. As of 2023, the EPA has defi ned a target production of 840 million barrels of cellulosic biofuel, and a total renewable biofuel output of 20.94 billion barrels [4]. While vastly undershooting total output, the RFS is implemented to promote alternative fuel industries, specifi cally biofuels, for better emissions output.


Ethanol in the US


In the US, about 90% of all ethanol production is done through dry milling, and 10% through wet milling [5]. The primary difference between these methods is how the corn grain is prepared. During dry milling, corn grain is fi rst ground up with no separation of its components. It is then mixed with water, where it is cooked with enzymes to induce its starch to undergo saccharifi cation into glucose. Yeast gets added to the mixture to ferment and forms the ethanol. Finally, separation is used to purify the ethanol mixture and remove unwanted products. In wet milling, corn grain is fi rst separated into its components: Starch, fi ber, germ, and gluten, through seeping corn grain in a water and sulfur dioxide mixture [6]. Figures 1 and 2 below show the wet and dry milling processes, respectively; both diagrams show their primary products, along with the unit operations required. Dry mills are often favored due to lower energy requirements. However, they primarily produce ethanol and animal feed, while wet mills also make food-grade ethanol. There is a much larger range of by-products that wet milling can produce. This is because wet milling is able to accomplish less amount of impurities in the ethanol due to properties in its separation[6].


RECENT ADVANCES AND IMPROVEMENT IN BIOETHANOL TECHNOLOGY


EFFECTS OF BIOETHANOL Air Quality


There has been much concern over whether or not ethanol is the safest choice as a potential gasoline alternative. Globally, countries have adopted different standards for ethanol-gasoline fuel percentages. An assessment was conducted in 2010 simulating certain emissions by 2022, using the RSF from the same year. The researchers assumed in this model that 15 billion gallons of corn grain ethanol and 16 billion gallons of cellulosic ethanol [3] would be used by this year, as mandated by the standard. Results indicated that particle matter (PM) and ground-level ozone were expected to increase over areas including the Midwest, but also expected to decrease in crowded cities. Corn fertilization and harvesting are responsible for this trend, while the tailpipe emissions from utilizing ethanol decrease the ambient PM and ozone in vehicle-dense cities. Sulfur dioxide levels were also found to increase due to the agricultural portion of ethanol production [8]. Figure 3 below visualizes the changes in ozone design values, modeled for 2022 in 2012 [8].Another simulation conducted in 2014 saw similar results despite utilizing a different methodology. In this simulation, the researchers used an estimation of the miles traveled by cars in 2020 all using E10 fuel, while the 2010 study used the RFS2 fuel predictions directly. Spikes in ambient PM2.5 in the “corn belt” areas of the Midwest are visible under corn grain ethanol predictions, affecting local air quality [9].


A more recent model from 2019 calculated emissions based on certain proposed ethanol standards in China, with predictions for 2030 [10]. Unlike previous studies, this simulation showed a decrease of PM2.5 emissions from 10% to 16% across certain Chinese regions, as well as the amount of aromatics and olefi ns present in the fuel modeled. However, researchers did not consider the upstream processes of ethanol production since the corn would be imported under Chinese standards. This accounts for the disagreement between studies since these


emissions primarily come from corn grain cultivation. As for carbon emissions, both black carbon [10] and carbon monoxide [8] were predicted to be reduced. Results from a second study regarding China’s fuel program saw a 7-38% decrease in black carbon emissions in ethanol fuel blends in comparison to traditional gasoline [11]. Emission levels for nitrogen oxides (NOx) and volatile organic compounds (VOCs) have been inconsistent across research most likely due to differences in engines and automotive technologies used for testing. These emissions depend on the vehicle’s technology [8].


Health Eff ects


One of the biggest concerns over ethanol usage in fuel is the increased risk of adverse health effects. Emissions of ethanol increase the formation of formaldehyde and acetaldehyde [8,12,10]. Formaldehyde is a known human carcinogen and acetaldehyde is a possible carcinogen [13]. In Brazil, until the early 2000s, there were many cars running on pure or high-percentage ethanol-gasoline blends [9]. As of 2023, the mandatory fuel blend percentage of ethanol in Brazil has decreased to be between 20% and 27% indicating that biofuel is still prevalent, albeit in decreased amounts [14]. Peak ethanol fuel program usage occurred during the 1980s and data has shown that ambient acetaldehyde and formaldehyde levels have decreased since then [12].


Improvements to Bioethanol


Most bioethanol produced worldwide is fi rst-generation at more than 99% of the total supply. First-generation bioethanol is produced from sugar and starches, typically from sugarcane, wheat, and corn [15]. As previously mentioned, the US predominantly produces ethanol from corn grain, classifying it as fi rst-generation [1]. The drawbacks of using fi rst-generation ethanol include high PM emissions and ground-level ozone spikes in areas where corn grain is cultivated [9]. In addition, food security concerns remain prevalent since many fi rst-generation ethanol plants double as food sources [16]. In the US, corn prices


Figure 1 (left): Depicts the wet milling process of corn [7]. PIN ANNUAL BUYERS’ GUIDE 2024


Figure 2 (right): Depicts the dry milling process of corn [7].


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