What is biofuel? Derived from residual plant and animal matter, biofuels are simply organic fuels that act in the same manner as fossil fuels like oil, natural gas, or coal. Also known as biomass, this organic matter is processed directly into liquid fuels that can provide energy for transportation, power plants, or other applications that utilize carbon-based energy sources. As a renewable resource produced primarily from plant matter, biofuels offer a means to make liquid fuel that is carbon neutral and thus reduce carbon emissions responsible for climate change.
What is Biofuel Made From?
Instead of undergoing a geological process, biofuels are extracted much quicker from biomass made from plants that include corn, soy, sunflowers, sorghum, or wheat, along with animal waste from domesticated herbivores like cattle. Biofuels can also be made from just about any organic waste, including wood.
The most common ethanol production method involves fermentation in biorefineries, made in much the same way as drinkable alcohol. Usually blended into gasoline to increase octane levels, ethanol is clear and colorless alcohol, also known as ethyl or grain alcohol. The most common gasoline blend uses 10 percent ethanol and 90 percent gasoline, while specially designed vehicles can run on a blend called E85 that contains 51% to 83% ethanol. According to the US Department of Energy (DOE), over 98 percent of gasoline in the country contains ethanol.
Regardless of the plant matter from which it is made, all ethanol has the same chemical formula. The United States primarily uses ethanol made from corn grain, while Brazil mainly uses sugar cane. Still, ethanol can also be made from dedicated crops of switchgrass or miscanthus, which use less water and fertilizer. It can even be produced from wood chips, crop residue, or other plant-based waste. Though generally made from sugars and starches found in edible parts of plants, increasingly, researchers seek to use non-edible fibrous material found in many plants for ethanol production to reduce the use of plant matter from edible crops.
As a replacement fuel in compression-ignition (diesel) engines, the fact that biodiesel burns more cleanly makes it a very desirable replacement for petroleum-based diesel fuel. Non-toxic and biodegradable, it blends with petroleum diesel at any ratio, most commonly at 20 percent biodiesel and 80 percent petroleum diesel. However, diesel engines are fully capable of running on pure biodiesel with no alterations.
Biodiesel can be used wherever regular diesel is used, including in:
- Boats and ships of all sizes
- Construction equipment
- Fire engines, ambulances, and other emergency vehicles
- Freight (and other) diesel-powered locomotives
- Passenger vehicles
- Tanks, armored trucks, and other military vehicles
Made from mixing various vegetable and plant oils, animal fat, and even recycled cooking oil with methanol or other alcohol, it offers a way to reduce carbon emissions throughout the shipping industry.
A gaseous type of biofuel, biogas burns just like natural gas. Because of this, it can replace natural gas for heating water and in buildings. Mainly composed of methane, it is produced by a natural microbiological process using bacteria that converts it into a usable gas in stages through decomposition in an oxygen-absent environment. Agricultural companies currently package and sell biogas for household use in gas cylinders like those used for gas grills. It is made using a mixture of animal and plant waste, with carbon and hydrogen found in plants combined with nitrogen from animal waste.
Like ethanol, methanol is also a type of alcohol that can be used as a clean fuel. It can be combined with gasoline to produce higher octane blends, better fuel efficiency, and lower emissions. Used widely in China, methanol has a similar chemical composition to methane, though it is liquid rather than a gas. Through the use of a catalyst, it converts biomass through gasification at very high temperatures.
Methanol is used as a fuel for:
- Industrial boilers
- Marine gasoline engines
- Motor vehicles
- Racing cars
Methanol is also a key ingredient in biodiesel production.
Also produced through fermentation, butanol is alcohol that offers greater energy output than ethanol or methanol. Similar in chemical structure to gasoline, it can be used in gasoline engines without modification, though butanol is much more challenging to produce. Butanol is made from wheat, sorghum, and other high-energy grains.
How are Biofuels Made?
Biomass must undergo a multi-step process to make it usable as fuel.
The tough outer walls of plant cells include cellulose, hemicellulose, and lignin, which are bound together tightly and must be broken down to produce biofuel. To break down these tough cell walls, they must undergo a process called deconstruction, either at high or low temperatures.
Using extreme heat and pressure, high-temperature deconstruction breaks down solid biomass into either liquid or gaseous form. This is accomplished through:
- Pyrolysis involves the chemical decomposition of organic matter, using high temperatures to produce a liquid oil, which can be processed further into a standalone hydrocarbon fuel or used as feedstock to mix with crude oil at a standard refinery. In an oxygen-free environment, biomass is heated to between 932-1292°F (500-700°C), vaporizing its useful elements. Impurities are then separated from the vapor before being cooled and condensed into liquid biocrude oil.
- Gasification involves converting biomass by heating the feedstock to temperatures greater than 932°F (700°C), then converting it via a chemical reaction into syngas, consisting primarily of carbon monoxide and hydrogen. Unlike pyrolysis, this does not involve an oxygen-free environment.
- Hydrothermal liquefaction uses high pressure and temperatures between 392-662°F (200-350°C) to start the chemical decomposition of biomass or wet waste to produce biocrude oil that can then be upgraded into hydrocarbon fuel. This method works well for wet feedstocks such as algae.
This method typically utilizes chemicals or enzymes to break feedstocks down by stages. Biomass first goes through a pretreatment step to open the physical structure of the plant’s cell walls. This makes cellulose and hemicellulose more accessible, allowing it to break the polymers into simple sugars using a process called hydrolysis.
After deconstruction, the intermediary fuel stock must be upgraded further, which involves different biological or chemical processes. This can involve a biological process that uses bacteria, yeast, or other microorganisms to ferment the sugar or gaseous intermediaries into useable fuels. These intermediaries can alternatively be processed chemically to remove contaminants, making them easier to store and handle. This process results in either biofuel ready for commercial sale or intermediary fuel stock suitable for finishing as per standard petroleum refinement.
How are Biofuels Made with Hammermills
Milling is used as a pre-treatment for producing biofuels that undergo combustion, gasification, and densification processes. Hammermills play a crucial role in converting biomass into useable form through this initial pulverizing of the biomass into specific particle size ranges. Particle size plays a vital role in the end product, which is also affected by the machine’s parameters.
The angular hammer speed affects both irregularity and distribution of particle sizes. At higher angular speeds, dispersion in particle size is lower, while the opposite is true for lower speeds. Consistency in the shapes and sizes of particles is important in producing any biofuel, with finer particles tending to create more valuable biofuels. Hammermills offer a particularly effective means to control particle reduction, particularly for biomass with high water content.