 So, in the good old days of Pen Crude, this is a sample now I'm holding in my hand of Pennsylvania Crude, you can see how fluid that is, or law of viscosity. You can really see that it's almost drinkable. I'm tempted actually to take a sip from this now, but that's probably against regulations here in the museum. Now for this you would not need any hydro treatment because this is virtually no sulfur in it, but the current crude oils, which would be much more viscous than this, much more aromatic, this is essentially paraffinic crude, then you would really need hydro treatment to remove sulfur, nitrogen, or metals associated with this. This is an extinct crude oil. This is the early Pennsylvania crude. Here we see some samples of Pennsylvania crude oil, the first crude that was drilled and produced in the United States. And Pen Crude, or Pennsylvania crude, is a very special crude oil. It is the sweetest. The sweet means in this case, not really, with a lot of sugar, but very low sulfur. So you can see the light color of the crude oil. This is actually, as it came from underground without any refining. This is very rare now, and Pen Crude is pretty much extinct these days. This was so sweet that some entrepreneurs could actually sell this as a remedy. One man was Samuel Kears in Pittsburgh. I think he was in Canal Street. He put the Pen Crude in pint bottles and sold them as remedies for different ailments, such as stomach aches, headaches, or growing moustache on young boys who wanted to have moustache to show off. So sour crude oils obviously are what we have today. That means high sulfur crude oil, which would require quite a bit of hydro treatment to remove sulfur, unlike the sweet Pen Crude great oil. Having talked about the separation processes and the conversion units, we are now ready to talk about the finishing processes. That's the third kind of processes used in petroleum refining. Now finishing is done essentially to make sure that the product that is leaving the refinery is compliant with the required performance specifications, such as octane number for gasoline or c-tane number for diesel fuel, and also with environmental regulations like sulfur, nitrogen, or metal contents of these fuels that are leaving the refinery to be sold in the marketplace. So the finishing processes are hydro treatment and blending. We do categorize them into these two main categories. In hydro treatment, the point is to remove the hydro atom, whatever that is, sulfur, nitrogen, or metal, with the help of a catalyst and hydrogen. So the objective is to use the minimum amount of hydrogen and make the minimum amount of change in the hydrocarbon structure of your feed materials to remove the sulfur, nitrogen, or metal out. Minimizing hydrogen is important because hydrogen is a very expensive chemical or material. And of course, hydro treatment or finishing is not a place to make the chemical changes desired in the hydrocarbon skeleton or hydrocarbon structure. Conversion processes do that. So in hydro treatment then, we would need catalysts. These are typically supportive catalysts. The support is alumina, silica, in some cases mixed oxides. And the metals, typically a molybdenum cobalt or nickel that are put on these supports. We need these metals to dissociate molecular hydrogen so that it can actually react with these hydro atom species. In hydro disulfurization, we remove sulfur as H2S, which is an acidic gas. Nitrogen as ammonia, which is a base. So the purpose of hydrogen is to really seek out and find that hydro atom and pull that out of the hydrocarbon structure as H2S or sulfur and ammonia from the nitrogen containing species. The metals, typically vanadium and nickel, are separated as sulfides on catalyst surfaces. A pretty interesting chemistry as we will discuss in this lesson. So hydro treatment would give us the desirable hydro atom content or regulated hydro atom content in the products. With blending, we need to look into all the specifications that are needed for a given product. For example, for diesel fuel, the viscosity or pore point could be important. And typically in a refinery to make a product like gasoline or diesel you will be blending a large number of streams. Remember, there are quite a few different streams coming from different conversion processes or separation processes to be blended to make these final products. For gasoline, it's the octane number. So we will go through some of the procedures we can use to calculate the physical properties like pore point or viscosity of these blends to make sure that they actually follow the specifications needed for these products. You would see that many of these calculations are nonlinear. If you take, say, sample A and sample B, blend them. Together the viscosity of that blend would not be the average of the two using essentially a linear mixing formula. So there are correlations that were developed to incorporate these nonlinearities into calculating, determining the final properties of the blends from multiple streams to make the final products from the refinery.