As green fuel options continue to enter the heating and combustion industry, it's incredibly important for manufacturers, technicians, and consumers alike to to educate themselves about these cleaner and more sustainable fuel options and the opportunities they present. For anyone that's doing their research into green fuels, understanding the processes used to produce both biodiesel and renewable diesel are a huge piece of the puzzle. These processes actually impact the sustainability of the fuels they produce in several significant ways. In this post, we'll discuss the different green fuel production processes and how they affect the green potential of both biodiesel and renewable diesel as heating fuels.
Renewable Diesel and Biodiesel Production Processes
Renewable diesel can be refined from plant and animal oils and waste materials using three different processes. The most common process is called hydrotreating (or hydrogenation). Hydrotreating occurs when triglycerides (fats that are the building block for bio fuels) are hydrogenated in order to remove heavy metals that contain oxygen and nitrogen. Hydrogenated renewable diesel burns cleaner than renewable diesel produced using other processes. Hydrotreating is also a very similar process to the way petroleum diesel is produced, meaning that it can be used as a 1-1 substitute to petroleum diesel in existing systems.
Secondly, renewable diesel can be produced using another process called thermal conversion. During this process, also known as depolymerization, biomass and carbon-containing material is turned into a "bio-oil" that is refined into a type of green diesel fuel.
Finally, renewable diesel can be produced through a biomass-to-liquid process. This method involves converting the agricultural waste material through high-temperature gasification. The material becomes a synthetic gas mixture rich in hydrogen and carbon monoxide.
Biodiesel is produced using a chemical process called transesterification, where a glyceride will react with an alcohol in the presence of a catalyst. The process produces fatty acid esters with characteristics that are similar to petroleum/fossil diesel fuels. During transesterification, the plant- and animal-based oils and fat materials are purified into a viable fuel. However, transesterification does not remove oxygen from the fuel. Due to the potential complications caused by oxygen in the fuel, biodiesel is commonly blended with petroleum diesel in various percentages ranging from 5-20% (B5-B20).
While these blends cut back on the clean benefits of green fuel, it makes the oxygenated biodiesel manageable logistically. Transesterification is a production process that is unique to biodiesel in terms of fuel refining and cannot be used to create renewable diesel.
Different Processes, Different Green Fuels
While biodiesel and renewable diesel are made from the same types of agricultural waste products that serve as alternatives for fossil fuel, these differing production processes account for many of the differences between biodiesel and renewable diesel in application. One of the largest contrasts between the two fuels is the percentage of blends that manufacturers are able to produce due to the oxygen levels (or lack thereof) in the fuels. Because all oxygen can be removed from renewable diesel, this fuel can be refined in blends that are up to 100% renewable. There's no need to mix petroleum diesel with renewable.
However, because of the transesterification process, biodiesel cannot be rid of oxides, which can cause issues in transporting and storing the fuel, especially in extreme temperatures. Biodiesel does not have the same combustion characteristics of renewable diesel due to its oxygen content, so it tends to not burn as clean as renewable. However, both green fuels have the opportunity to become sustainable fuel options that cut back on emissions, recycle waste, and provide an alternative to fossil fuels that increase the heating industry's carbon footprint.