I'm currently doing a research project on biodiesel. I'm wanting to find out if using different methods of production and different types of fats/oils can affect the effectiveness of the fuel however I'm not entirely sure which properties I should be looking for. I know that viscosity should be lower for the biodiesel to perform well however I was wondering what other properties I could investigate?
If anyone has any information they believe may help my understanding I would love to hear it.
Welcome to the forum.
Some other considerations are Cetane, Cloud point, completeness of conversion, energy content, Specific gravity...
An important factor in biodiesel use, in the real world is freezing point of components of the biodiesel. Biodiesel usually is not just one specific fatty acid ester, but it can be. For example anhydrous isopropyl alcohol will not transesterify with glyceryl fatty acid esters (vegetable oil) but via the Fischer esterification octadecanoic acid plus concentrated sulfuric acid plus anhydrous isopropyl alcohol yields isopropyl octadecanoate ( the isopropyl ester, a type of biodiesel ) plus water. A free fatty acid can be made into the ester with isopropanol to make a type of biodiesel, where isopropanol will not react to transesterify with fats/vegetable oils due to steric hinderance in the transesterification reaction. Why is that a big deal, you might ask? The normal methyl fatty acid ester, biodiesel molecule has a negative electron density volume at the carboxylic acid end (acid end) of the molecule attached to a methyl group by a single bond. The methyl group covers up the negative electron density some. Remember chloroform has carbon surrounded by chlorine. Chlorine had a high electronegativity, But 4 chlorine surrounding a carbon produces an even negative charge, not a polar a separated charge like sodium chrloride that has a high boiling point. Anyway , masking the carboxylic acid end of the fatty acid esters with bigger carbon functional groups changes the freezing points of the fatty acid esters present. I made methyl biodiesel (regular) , ethyl biodiesel , propyl biodiesel , and isopropyl biodiesel of vaying types. The flow properties (viscosity) of those different types of liquid fatty acid esters is different. Methyl Biodiesel made from beef grease and lard (swine grease) has a solid precipate at a room temperature of 76 degrees farenheit. The problem with using renderered animal fat to make biodiesel is that animal fat has up to a 22 carbon atom long chain of atoms in the fatty acids present. Even when made into a ester they have a low freezing point that will solidify at room temperature. Vegetable oils have a fatty acid with maximum length of 18 carbon atoms long. The higher the molecular weight in fatty acids the lower the melting point, except the number of double bonds in one molecule affects the melting point. I have bottles of methyl biodiesel made from beef grease and lard that have the lower melting components sitting in the bottom of the storage bottle as a precipitate. If water is present in the product methyl biodiesel, over time at room temperature, hydrolysis, a reverse reaction will occur that turms fatty acid esters and water into free fatty acids and methanol. If a biodiesel crude product is water washed in purifying it, if it is not used soon enough some of the fatty acid methyl esters plus water will decompose/hydrolyse into methanol and free fatty acids which will not vaporize in the engine's compustion chamber due to their high boiling and vaporization energy.
Looking at the oil being used to make biodiesel, there are several major properties that effect the finished product.
As you know, vegetable oil is made up of three fatty acid molecules attached to a glycerine molecule. The process of making biodiesel breaks that up so that individual fatty acid molecules are attached to methanol or rarely ethanol. It is the composition of those molecules that effect Cloud point and energy content.
The more carbons a fatty acid molecule has, the greater the energy content.
Fatty acids can be described as saturated, mono-unsaturated, and poly-unsaturated. How much of each of these types of fatty acids determine the cloud point, and how long the biodiesel can be stored before going rancid.
When the oil contains "stuff" besides oil and fatty acids, that stuff, may flow all the way through production and reduce the energy content, fuel filter life expectancy, and engine life expectancy.
In the real world, Used Vegetable Oil [UVO] is often used to cook animal parts. The fats from cooking poultry and pig are the primary source of precipitates that settle out of biodiesel in the vehicle tank when temperatures drop. These High Melting Point Esters [HMPE] will clog screens and filters and can disable the vehicle.
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