At long last we dive into the details of how biodiesel is made. The raw material, referred to as feedstock, used in biodiesel production can be obtained from used cooking oils, from fresh or new vegetable oils, and from animal fats/oils. We will examine the issues & processes involved with new vegetable oil feedstocks at a later time. Today we will focus on biodiesel production based upon used vegetable cooking oils. In addition, the video at the end of the post also contains a segment on the process for obtaining animal fats. On a mass production scale, biodiesel production breaks down into the following steps: Feedstock Collection, Feedstock Filtration/Purification, Transesterification (Biodiesel Production), and Biodiesel Distribution & Sales. The processes for homebrewing and/or co-op biodiesel processes are similar to those used in biodiesel industrial processes. We will discuss smaller scale biodiesel production in a later post.
The collection of used vegetable cooking oils is typically handled by companies which solely collect used oils from restaurants. Most restaurants dump their used cooking oil into collection drums (some restaurants use 55 gallon drums) or large covered bins located outside of the restaurant. The biggest source of restaurant oil is the waste oil from deep fryers. Any restaurant, bakery, social club (VFW, American Legion, Knights of Columbus, etc.) that deep fries food is a potential source of used cooking oil. Waste oil collection is accomplished via specialty tanker trucks. A tanker truck pumps or sucks the used oil from the waste drum into the tanker. Once a collection run is completed the tanker truck will deliver the used oil to a filtration plant.
Regarding how biodiesel is made, the next step in the biodiesel production process involves the filtration and purification of the collected used cooking oil. Why must you filter & purify the oil? The number of fry cycles and overall fryer times that a batch of deep fryer oil is exposed to varies from restaurant to restaurant. For example, many American Legion Posts and VFW Posts will use a fryer vat of oil for only one event, such as a one night Steak Fry. Said oil has much less contamination that the oil used at a commercial restaurant. Some restaurants will use a single vat of oil up to 5-7 days (although by the then the oil conveys a bad flavor to the cooked food). Cooking oil undergoes several transitions over the times a single vat is used to deep fry food. First, cooking oil becomes contaminated or collects water during each fry cycle. The greater the number of fry cycles for a given batch of oil, the greater the amount of trace water that contaminates the oil. This water comes from the vegetable, poultry, fish, & meats that are fried in the oil. In addition, waste particles from the cooked food collect in the oil over time: i.e. waste breading, broken pieces of meat/fish/chicken, small pieces of vegetables, etc. In addition, the PH of the oil changes as the fry cycles continue or increase. The oil molecules “crack” with the prolonged exposure to heat. In short, used oil becomes more acidic over time. But this change in PH only comes into play during the actual biodiesel production process.
The equipment & processes used to purify the used oil will vary from plant to plant. This multi-stage process involves the use of filters to remove contaminant particles and the use of heat to remove unwanted water. The video at the end of this post provides some excellent footage of an actual filtration plant. Once the used oil is purified it is then delivered to the biodiesel plant. Please not that some facilities actually perform both used oil purification processes and biodiesel production within the same plant.
Transesterification (Biodiesel Production)
The technical term for biodiesel production is called transesterification. Don’t let this long scary term fool you. The process is actually quite simple. Cooking oil is just composed of triglyceride molecules. I know what you are thinking. You are thinking “Kill Me Know, he is talking Klingon techno-speak!” Just bear with me it is not that bad. A triglyceride molecule is composed of 1 glycerol molecule connected to 3 fatty acid chains. To convert the fats into fuel, one chemically reacts an alcohol, either methanol or ethanol, with the cooking oil. The chemical reaction requires catalyst, heat, and physical mixing. For example, when the methanol-based process requires use of sodium hydroxide (lye) as a catalyst. Back to our triglyceride molecule. The catalyst causes the alcohol to react with the triglyceride molecule producing 1 glycerol molecule and 3 long chain ester molecules. the ester molecules are the actual biodiesel molecules. When using methanol, one obtains methyl ester, a common form of biodiesel. The cool thing about biodiesel production is that the process involves essentially zero waste. The glycerol by product can & is used in the production of soaps & cosmetics. Watch this brief video segment for a visual illustration of this chemical reaction.
Biodiesel Distribution & Sales
The final stage in how biodiesel is made is the distribution stage. In biodiesel mass production, an actual distribution infrastructure exists which is invisible to the consumer. Depending upon the supply chain, this step can actually consist of brokers/brokerages, storage facilities, biodiesel delivery, & consumer sales. For example, a brokerage may handle the supply chain transactions between multiple independent biodiesel refineries and fuel distributors. The distributor will provide bulk biodiesel fuel management & delivery services. The goal is to economically deliver biodiesel to a fueling station in order to supply the end user. Our next post will provide an inside look into the process underway in New York City.
How Biodiesel is Made: The Video
Let’s watch a great video showing how biodiesel is made on a mass production scale. This video is provided free by the Discovery Channel’s How It’s Made YouTube Channel.