Hemp MythBusters — Can hemp ethanol replace gasoline?
The Myth
Hemp ethanol can replace standard gasoline?
The Background
We have all probably heard of ethanol before. We drink it in our alcoholic beverages and we all consume it as a bio based additive in our gasoline. But diving in, what are the more specific characteristics of ethanol?
Ethanol is a two carbon molecule with an energy density of 76,330 BTU/gal in the E100 (100% ethanol) blend (Alternative Fuels Data Center, AFDC). For comparison, E10 (10% ethanol:90% gasoline) has an energy density of 112,114 to 116,090 BTU/gal (AFDC).
Most ethanol is made from glucose via fermentation. Fermentation is the process where yeast consume the sugars (glucose) and convert them into ethanol, carbon dioxide and heat. After fermentation the alcoholic solution contains up to 15% ethanol which is then purified via distillation and adsorption until a pure 100% ethanol product is achieved.
Ethanol is a domestically produced fuel and is produced from US agricultural crops, primarily corn. It features a higher octane rating, allowing for higher compression ratios and efficiency, helps oxygenate the fuel to reduce carbon monoxide emissions and emits less carbon dioxide than standard gasoline.
So, we are going to jump in, review the data, do a little math and see just how true this hemp myth really is.
The Data
For this myth, we will focus on a few primary data points including
- How much ethanol can be produced from hemp
- The opportunity cost for farmers to switch to hemp for ethanol production
- Production costs of cellulosic ethanol
- Technical challenges for ethanol use in vehicles
How much fuel?
To start off we need to look at the different ways that ethanol is produced and how the hemp plant can provide the required inputs for the process.
Ethanol is produced from the fermentation of glucose. Glucose can come from 2 primary sources:
- Starches — like corn kernels
- Cellulose — like plant stalks including corn, hemp, wheat, etc.
To produce ethanol from starch (a chain of glucose molecules bonded together), multiple enzymes are utilized to break the bonds to release the glucose molecules. These enzymes are low cost and require minimal energy to break the bond.
Cellulose is also a chain of glucose molecules bonded together. However, the bonds for cellulose are much stronger than those for starch. Because of this, a specific enzyme called cellulase is required to break the bonds.
It should be noted that, according to a Stanford paper, the energy required to produce cellulase (from bacteria) is higher than the energy generated from the hydrolyzed glucose.
Given the fact that the hemp plant really has no source of starch, the seeds are oil and protein, the flower is oil and plant matter and the stalks are lignin, hemicellulose and cellulose, the cellulosic pathway will have to be utilized.
We can calculate how much fuel can be produced from one acre of hemp and then figure out how many acres are needed to replace gasoline as this myth states.
According to the report “Cellulosic Ethanol: Status and Innovation”, cellulosic biomass can yield up to 82.5 gallons per metric tonne. If we model a production capacity of 8 tonnes per irrigated acre and consuming the entire plant stalk, up to 660 gallons of cellulosic ethanol fuel can be reduced per acre.
The Energy Information Administration (EIA) states that the United States consumed 142.86 billion gallons of gasoline in 2018. If we take that volume and divide by our gallon per acre value, we would need 216.45 million acres of land to grow enough hemp biomass to replace ethanol. As we know, the total available US farmland is 233.14 million acres (Farm Bureau Services, August 2019). Growing hemp for ethanol would consume 92.8% of all US farmland.
Now hemp can be grown on land not suitable for farming. However, the production yields would likely be lower and harvest costs would likely be higher.
So far we can see that hemp wouldn’t replace gasoline due to the amount of farmland needed but the potential yield per acre of irrigated land could be a good revenue generator for farmers, especially if they are already growing hemp for other uses. Let’s move on and see if those farmers would switch their crops to hemp with biomass offtake going to cellulosic ethanol production.
Will farmers switch crops?
Currently, cellulosic ethanol is a product in production. Because of that, the feedstock used to make the product is openly purchased from farmers. According to farmprogress.com, corn stalks are being sold for $30-$50 per ton. If we are looking at hemp biomass replacing that, we can assume a similar cost structure. At the $30 rate, a hemp farmer selling biomass for ethanol can expect to receive $240 per acre to $400 per acre gross. The average value of corn per acre is $650. Within the scope of switching to hemp specifically for fuel, it is unlikely. However, there are other parts of the plant that a farmer could sell to achieve a higher overall value per acre allowing for the lower opportunity cost.
According to breakingenergy.com the total volume of cellulosic ethanol produced in 2017 was 10 million gallons which would have required 33,334 acres of hemp to be grown, given our 660 gallons per acre. This is important to note as it puts the market potential for farmers into perspective. Forbes estimates that the 2019 hemp harvest will be between 115,000–138,000 acres. This would yield about 4 times more hemp biomass than what the total cellulosic ethanol production demand is. Cellulosic ethanol production is increasing but it will take some time for that to consume the slack within the hemp market and reach an equilibrium point
We can see that in the context of an energy crop, hemp for cellulosic ethanol, really isn’t a larger revenue generator for farmers. However, if the value for the material were to increase, a revenue parity with other crops could be achieved or if the cellulosic material was a byproduct of another process. There is a limiting factor here, which is how much cellulosic biomass is required for production. This will be increasing over time but for now the supply of hemp will likely outpace the total demand for cellulosic fuel.
What is the cost of making cellulosic ethanol?
The production of cellulosic ethanol is identical as starch based ethanol except a pretreatment step is needed. The pretreatment step is what converts the cellulose into glucose.
The primary difference is the need to break the bonds on the cellulose molecules to produce glucose for the yeast. The primary method is a thermochemical process. The process starts with the application of acid and heat to ground cellulosic material. This is followed by hydrolysis where the cellulose bonds are broken by an enzyme called cellulase.
It is within these steps that cellulosic ethanol become less economical. The primary cost driver is the cost of the enzyme: cellulose. The white paper “Cellulosic Ethanol: Studies and Innovation” calculates the cost of cellulose at $1.82 per gallon. As of September 26, 2019, the spot price of ethanol is $1.435 per gallon. With those values, cellulase will consume 126% of the revenue generated from the sale of the final ethanol. This is just one of the production costs. The cost of feedstock, acid, heating, fermentation and distillation are not included.
The production costs of cellulosic ethanol, regardless of cellulose source, are above the current market price for ethanol. There are new technologies being developed and tested to reduce the cost of hydrolysis. Until those cost reductions are realized, cellulosic ethanol will likely struggle to achieve positive economics.
The technical issues
Regardless of feedstock source, cellulosic or starch/sugar, ethanol has a number of technical problems as it relates to performance and logistics as a gasoline replacement.
Ethanol is hygroscopic by nature, meaning it will absorb moisture from its surroundings. This leads to careful shipping and storage requirements to ensure that ethanol is not exposed to moisture. If it is, the ethanol will absorb the moisture and the purity will decrease. This characteristic can also lead to the absorption of water as the ethanol resides in a fuel tank and the absorption of moisture from rubber components such as seals and hoses.
Secondly, an EPA study indicated that E85 (85% ethanol: 15% gasoline) can produce up to 25.56% lower fuel economy compared to gasoline. The report also indicated that smaller ethanol levels such as E10 have minimal fuel economy effects.
Currently, most gasoline maintains 10% ethanol but that value is expected to increase over time due to the Renewable Fuel Standard.
We can see that even if hemp becomes the dominant cellulose source for cellulosic ethanol, there will still be various technical challenges inherent with ethanol.
The Myth — PARTIALLY BUSTED
Based on the information above, the myth that “Hemp ethanol can replace gasoline” is PARTIALLY BUSTED.
This myth is busted more so due to the specifics of cellulosic ethanol rather than the specifics of hemp. If technological advances can be made on the conversion of cellulose into glucose, then hemp could become a major feedstock source. The economics for hemp can become especially favorable if the cellulosic material is a waste product from oil, seed or cannabinoid production where most, if not all production costs can be applied to other products.
It does not appear that ethanol as a fuel additive will be phased out or replaced anytime soon, so anyone looking into the future of hemp ethanol could expect consistent demand for the feedstock for ethanol production.
