 Hello. In lesson four, we will start talking about separation processes. This is the first part of the separation processes. Remember, we have talked about having four different types of processes in the term you'll find. Separation is, of course, the first process. Now, the separation is very critical. The distillation process, which separates the crude oil with respect to the boiling point of the constituent compounds, is really the gateway to the refinery. There, we separate the crude oils into different fractions that are processed in downstream units until they end up as the desirable product that leave the refinery. Now, in laboratories, we could have different distillation methods to characterize crude oils so we can inform the industrial or commercial distillation process. There are three different distillation methods, and we will go through them in this lesson to see how different they are and what specific applications would each of these different distillation methods, the different laboratory methods, have in terms of applying to refinery processes. Now, in this lesson, we will also define distillation terms. What do we mean by cup points? What do we mean by yield and so forth so that we can have a more educated discussion on the distillation process. We will also introduce the vacuum distillation and talk about why one would need vacuum for distillation of the residue from the atmospheric crude tower. Distillation is perhaps the energy gosler of the refinery. It consumes the largest fraction of energy in a given refinery. That's why the efficiency of distillation is very important for the overall efficiency.