Click here for transcript of Lesson 9 Overview.
So in the good old days of Penn crude-- this is a simple now I'm holding in my hand of Pennsylvania crude. You can how fluid that is, or low viscosity. You can really see that it's almost drinkable. I'm tempted to actually take a sip from this now, but that's probably against regulations here in the museum.
Now for this you would not need any hydrotreatment because this has virtually no sulfur in it. But the current crude oil, which would be much more viscous than this, much more aromatic-- this essentially paraffinic crude-- then you would really need hydrotreatment 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 group that was drilled and produced in the United States. And Penn 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 Penn crude is pretty much extinct these days. This was so sweet that some entrepreneurs could actually sell this as a remedy.
There was one man who was Samuel Kier in Pittsburgh, I think he was in Canal Street. He put the Penn crude in pint bottles and sold them as remedies for different ailments, such as stomach aches, headaches, or growing mustaches on young boys who wanted to have a mustache 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 hydrotreatment to remove sulfur, unlike the sweet Penn crude grade 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 using 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 cetane number for diesel fuel. And also the 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 hydrotreatment and blending. We do categorized them into these two main categories. In hydrotreatment the point is to remove the heteroatom, 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 material. And, of course, hydrotreatment 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 hydrotreatment then we would need catalysts. These are typically supported catalysts. The support is alumina, silica, in some cases, mixed oxides. And the metals typically 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 heteroatom species. In hydrodesulfurization we remove sulfur as H 2 S, 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 heteroatom, and pull that out of the hydrocarbon structure as H 2 S, for sulfur, and ammonia from the nitrogen-containing species.
The metals typically of vanadium and nickel are separated as sulfides on catalyst surfaces-- a pretty interesting chemistry, as we will discuss this in lesson. So hydrotreatment would give us desirable heteroatom content, or regulated heteroatom 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 pour 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 pour 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 two, using essentially a linear mixing formula. So there are correlations that were developed to incorporate these non-linearities into calculating, determining, the final properties of the blends from multiple streams to make the final product from the refinery.