How to Make Biodiesel Fuel - An Overview
Posed By Future Fuels
From the What is Biodiesel section we know that the process of making biodiesel is known as transesterification and is achieved by adding methanol to vegetable oil. The process requires a catalyst to increase the rate of the chemical reaction between the methanol and vegetable oil. The catalyst used in the creation of biodiesel is an alkaline one, either Sodium Hydroxide or Potassium Hydroxide.
When the process is complete the catalyst can be recovered unaffected by the chemical reaction that it accelerated, along with the glycerol separated from the vegetable oil.
If waste vegetable oil is used then we have another situation to deal with. Waste vegetable oil will have been been reheated several times during the course of its usage. The reheating will cause some of the fatty acids bonded to the glycerol to break away and float freely in the vegetable oil - hence the name Free Fatty Acid (FFA). There are two ways of dealing with free fatty acids:
- Esterify the FFAs creating methyl esters then proceeding with the transesterification.
- Increase the amount of catalyst in the single transesterifaction process so that the additional catalyst neutralises the FFAs creating soap as an additional by-product.
Option 1 is used in the commercial production of biodiesel, but for smaller scale production option 2 is favoured as it reduces the complexity of the process. Following option 2, we would have to perform a titration on a sample of the waste vegetable oil in order to calculate the amount of additional catalyst required to neutralise the FFAs.
The additional catalyst would then react with the FFAs creating soap in the process.
Transesterification is a reversible reaction. This means that the process is working both ways simultaneously until a balance between the vegetable oil and biodiesel is reached. Consequently we need to ensure that the process continues the creation of biodiesel rather than stall once it reaches this point of equilibrium.
In commercial production we would tap off the output as it is created thus ensuring that there is a greater quantity of input vegetable oil to keep the reaction producing the biodiesel. For smaller scale production, however, it is more practical to use an increased volume of methanol to ensure that the reaction continues in the direction of producing biodiesel.
Like the catalyst, this excess methanol will be left over after completion of the reaction.
Step by Step from the Top
The commencement of the production process depends upon the type of oil employed, and whether it is fresh oil or used oils from the catering industry. In the case of the latter, a titration process takes place, the result of which determines the proportions of methanol to sodium hydroxide used in the preparation of the reaction catalyst. (Inadequate or omitted titration on used vegetable oil is the single biggest cause of fatty deposits in fuel filters).
There are then the following steps in the process of producing the biodiesel:
- Filtration of inbound waste oil
- Drying the fuel (i.e. removing water content, especially in the case of used oils)
- Transesterification (specifically, the separation of the methyl esters from the glycerol)
- Settling period
- Separation of the biodiesel fuel from the glycerine layer [containing glycerol, catalyst, soap and methanol]
- Washing the biodiesel fuel
- Filtration to 5 microns
- Drying the fuel again
- Final products of biodiesel fuel and the by-products
If you want to learn how to make biodiesel we can help guide you in the right direction and avoid the costly mistakes! For a pictorial overview of the process of making biodiesel, this is definitely worth looking at...
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Print | posted on Thursday, October 11, 2007 3:17 PM