Biodiesel
Senior User
Joined: Nov 2008
Posts: 460
Likes: 0
From: Gifford, IL
True biodiesel is WVO that goes through a chemical reaction called transesterfication to remove the glycerin from the WVO. The glycerin holds together triglycerides, but the glycerin is replace by methanol which holds the strands together. The glycerin falls to bottom, and after a lil TLC, you have pure biodiesel, which is alot thinner than WVO. It's alot better to run in your truck than WVO and doesnt require a two tank setup or fuel heater (unless its below 35* or so). It takes a little more work and costs about 1/4 whatever you can get methanol for ( usually 1$ to 1.25$ a gallon for each gallon of biodiesel made), but its alot easier on your injection system.
Mountain Pass
Joined: Dec 2008
Posts: 235
Likes: 1
From: Virginia
97biostroke, do you have any directions on making this biodiesel? That would be awesome. Bclay223@hotmail.com
Junior User
Joined: Dec 2005
Posts: 79
Likes: 1
From: Flint, MI
Biodiesel is not the product of mixing WVO and gas. It is not a mixture of Oil and a thinning agent.
The generally accepted definition of biodiesel is that it is a mono-alkyl ester of a fatty acid.
The fatty acid comes from the oil. The oil is either a vegetable oil or an animal fat. The reason is because these are what is typically called triglycerides, mean they are comprised of three fatty acids linked to a glycerine base. The oil molecule looks kind of like the letter E. Straight Vegetable Oil (SVO) and Waste Vegetable Oil (WVO) are most often used for this.
The mono-alkyl part comes from a short length alcohol; usually methanol but sometimes ethanol. Methanol is easiest to work with.
The 'ester' part refers to the way the alcohol molecule and the fatty acid molecule are linked. If I remember my chemistry correctly, an ester is essentially an oxygen atom with one thing linked to one of its two 'open spots' (in this case, an alcohol) and something else linked to its other 'open spot' (in this case, a fatty acid from the oil molecule).
So there is some chemical reaction which must take place to get this to work. In essence, you mix the oil with the methanol and also a 'catalyst'. The catalyst makes the reaction 'go' but is not used up in the process. For this reaction, the catalyst used is typically a strong base, either Sodium Hydroxide (NaOH) or Potassium Hydroxide (KOH).
So essentially you start with oil (3 fatty acid molecules and a glycerin molecule make up the oil molecule), methanol (a self-standing molecule for our purposes) and some catalyst. After the reaction you end up with biodiesel (three biodiesel molecules per oil molecule) glycerin (leftover from the oil molecule and not suitable as a diesel engine fuel), the catalyst, a little bit of methanol (you put extra in the force the chemical reaction along) and soap.
Where did the soap come from?
Soap is generally formed by the catalyst, a strong base, linking to fatty acid molecules which have already broken off the oil molecule. WVO will have more of these than SVO. Soap is generally considered to be a problem and the ASTM specification for soap in biodiesel is less than 200 ppm.
(side note: several homebrewers, including myself, run fuel with higher levels of soap than 200 ppm).
Generally after the reaction, everything will seperate into two layers. Top layer will have biodiesel, some of the leftover methanol and some of the soap. Bottom layer will have glycerin, most of the leftover methanol and the rest of the soap. The bottom layer is darker than the top layer.
Last thing to do is to get the methanol and soap out of the fuel. There are several methods to do this. One of the easiest is to run an air bubbler through the fuel. This will drive off the methanol over time. Methanol is a solvent which means it keeps the soap 'in solution' in the fuel. Getting it out means the soap will now be 'in suspension' in the fuel. From that point much (not all) of the soap can be filtered out. Often house-grade water filters are used for this purpose.
The finished fuel can be mixed in any ratio from 0 to 100% with petrodiesel.
This is a quick overview of the stuff and doesn't cover anomalies in the process or other ways to make biodiesel or the evils of contaminants in you oil (mostly water).
This did morph from a 'what it is and what it isn't' response into a 'what's the chemistry and how does it work' response - sorry for that.
Rory
The generally accepted definition of biodiesel is that it is a mono-alkyl ester of a fatty acid.
The fatty acid comes from the oil. The oil is either a vegetable oil or an animal fat. The reason is because these are what is typically called triglycerides, mean they are comprised of three fatty acids linked to a glycerine base. The oil molecule looks kind of like the letter E. Straight Vegetable Oil (SVO) and Waste Vegetable Oil (WVO) are most often used for this.
The mono-alkyl part comes from a short length alcohol; usually methanol but sometimes ethanol. Methanol is easiest to work with.
The 'ester' part refers to the way the alcohol molecule and the fatty acid molecule are linked. If I remember my chemistry correctly, an ester is essentially an oxygen atom with one thing linked to one of its two 'open spots' (in this case, an alcohol) and something else linked to its other 'open spot' (in this case, a fatty acid from the oil molecule).
So there is some chemical reaction which must take place to get this to work. In essence, you mix the oil with the methanol and also a 'catalyst'. The catalyst makes the reaction 'go' but is not used up in the process. For this reaction, the catalyst used is typically a strong base, either Sodium Hydroxide (NaOH) or Potassium Hydroxide (KOH).
So essentially you start with oil (3 fatty acid molecules and a glycerin molecule make up the oil molecule), methanol (a self-standing molecule for our purposes) and some catalyst. After the reaction you end up with biodiesel (three biodiesel molecules per oil molecule) glycerin (leftover from the oil molecule and not suitable as a diesel engine fuel), the catalyst, a little bit of methanol (you put extra in the force the chemical reaction along) and soap.
Where did the soap come from?
Soap is generally formed by the catalyst, a strong base, linking to fatty acid molecules which have already broken off the oil molecule. WVO will have more of these than SVO. Soap is generally considered to be a problem and the ASTM specification for soap in biodiesel is less than 200 ppm.
(side note: several homebrewers, including myself, run fuel with higher levels of soap than 200 ppm).
Generally after the reaction, everything will seperate into two layers. Top layer will have biodiesel, some of the leftover methanol and some of the soap. Bottom layer will have glycerin, most of the leftover methanol and the rest of the soap. The bottom layer is darker than the top layer.
Last thing to do is to get the methanol and soap out of the fuel. There are several methods to do this. One of the easiest is to run an air bubbler through the fuel. This will drive off the methanol over time. Methanol is a solvent which means it keeps the soap 'in solution' in the fuel. Getting it out means the soap will now be 'in suspension' in the fuel. From that point much (not all) of the soap can be filtered out. Often house-grade water filters are used for this purpose.
The finished fuel can be mixed in any ratio from 0 to 100% with petrodiesel.
This is a quick overview of the stuff and doesn't cover anomalies in the process or other ways to make biodiesel or the evils of contaminants in you oil (mostly water).
This did morph from a 'what it is and what it isn't' response into a 'what's the chemistry and how does it work' response - sorry for that.
Rory
Junior User
Joined: Dec 2005
Posts: 79
Likes: 1
From: Flint, MI
97biostroke, do you have any directions on making this biodiesel? That would be awesome. Bclay223@hotmail.com
Best (IMO) forum around on biodiesel. Cut your teeth on the Dr. Pepper method put forth by poster Tilly. Then work up.
Thread
Thread Starter
Forum
Replies
Last Post
Boss300
1999 - 2003 7.3L Power Stroke Diesel
11
Nov 18, 2004 08:18 AM
