The primary method for separating oil from a mixture containing wax, particularly in petroleum processing, is solvent dewaxing.
Understanding Solvent Dewaxing
Solvent dewaxing is a widely used industrial process specifically designed to remove wax components from oil. This is crucial in various applications, such as producing lubricants, which require low wax content to maintain fluidity at cold temperatures.
The Process Explained
According to the provided reference, the commonly used method of separating wax from oil, particularly separating wax from petroleum fractions, is solvent dewaxing, in which the wax-containing oil is chilled in the presence of a selective solvent for the oil and filtered.
Here's a breakdown of the key steps involved:
- Mixing with a Solvent: A solvent is added to the oil-wax mixture. This solvent is carefully chosen because it selectively dissolves the oil but not the wax at low temperatures. Common solvents include mixtures of ketones (like methyl ethyl ketone) and aromatics (like toluene).
- Chilling: The mixture is then significantly cooled (chilled) to a very low temperature. As the temperature drops, the wax crystallizes or solidifies, while the oil remains dissolved in the solvent.
- Filtering: Once the wax has solidified, the mixture is passed through a filter. The solid wax crystals are captured by the filter, while the liquid mixture (oil dissolved in the solvent) passes through.
- Solvent Recovery: After filtration, the solvent is separated from the oil, usually through distillation, leaving behind the dewaxed oil. The recovered solvent is then typically recycled for use in the process.
Cost Considerations
The reference notes that the use and recovery of the solvent makes the process relatively expensive. This is because solvents themselves are a cost, and the energy required for distillation to recover the solvent adds to the operational expenses.
Why Separate Wax?
Wax is removed from oil primarily because it can solidify at lower temperatures, increasing the oil's viscosity and potentially causing it to gel or stop flowing. This is particularly problematic for oils used in engines or machinery operating in cold environments.
By employing methods like solvent dewaxing, manufacturers can produce oils with improved cold flow properties, ensuring they perform reliably even under frigid conditions.
