Vegetable oil (sunflower, rapeseed, flax, etc.) is the main raw material for production of biodiesel. The type of oil used gives some particular properties to the final product. For example, rapeseed oil-based biodiesel has a relatively low calorific value and high pour point and filterability.
Generally speaking, the process of biodiesel production is aimed at the reduction of vegetable oil viscosity. This effect can be achieved using various methods.
The composition of vegetable oil includes triglycerides (esters, connected to a glycerol molecule) and trihydric alcohol. Glycerol is mainly responsible for viscosity and density. Making biodiesel involves removing of this component by displacing it with alcohol. This process is called transesterification.
A positive feature of biodiesel is the possibility to use waste vegetable oil for production. The primary product must be pre-filtered to remove impurities and water. In the case when water is not completely removed, there is a risk that transesterification reaction will be replaced with hydrolysis of triglycerides. This is very undesirable since at the output we’ll get not biodiesel, but fatty acid salts.
The general scheme of biodiesel production looks as follows. Vegetable oil is heated to a certain temperature, after which it is mixed with alcohol and catalyst. In some cases, acid is used to accelerate the reactions. The resulting mixture should be stirred and settled. Then the mixture should break down into layers: the upper layer is biodiesel, the middle layer is soap, and the lower layer is glycerol.
The other layers are separated from biodiesel and then it should be washed to remove soap residues, catalysts and other undesirable impurities. This is followed by drying with magnesium sulfate. The drying agent is removed by conventional filtration.
Mathematics of biodiesel production is simple enough: if you have one ton of vegetable oil, 111 kg of alcohol and 12 kg of catalyst agent, the output can amount to 970 kg of biodiesel and 153 kg of glycerin.
The color of good biodiesel should resemble the color of honey, while glycerin is darker. If waste vegetable oil was used as feedstock, the resulting glycerin is usually brown and may solidify at the temperature of 38°C. If using fresh vegetable oil, glycerin remains liquid even at lower temperatures.
Visual inspection and control of pH is used to evaluate the quality of the resulting biodiesel. Externally, quality biodiesel should be similar to pure sunflower oil, should not contain any impurities, suspended solids and contaminants, as well as turbidity. If turbidity is present, this means that the product contains water, and it must be removed by heating.
GlobeCore offers UBT-type plants, designed to produce biodiesel. This equipment works based on hydrodynamic ultrasonic high frequency controlled cavitation principle. This makes it possible to achieve significant advantages:
- Minimum feedstock requirements.
- Instantaneous transesterification reaction.
- No need for washing and drying of biodiesel.
- Minimal power consumption.
- Compact dimensions and flexibility in plant design.