 Hello, welcome to lesson 8. We will talk about more catalytic conversion processes. We'll talk about in this class about alkylation, about polymerization, catalytic reforming, and isomerization. All of these processes are catalytic processes to produce high octane number gasoline. Remember for high performance, high power, we need it to produce high octane number gasoline. FCC obviously is the principal process in a refinery to produce high octane gasoline. Catalytic reforming developed also during the Second World War was really a popular, very popular process. Now the feedstock for catalytic cracking comes from the light ends unit. You will remember the NAFTA fractionator in the light ends unit. The heaviest product from the light ends unit is the heavy NAFTA. The reason it's heavy, it has a lot of NAF teams or cycloalkanes in its composition. So what happens in catalytic reforming is essentially converting these NAFTAs or cycloalkanes into aromatics. Aromatics have very large octane numbers. Benzene for example has an octane number of 100. So that is highly, highly desirable high octane number component in the refinery blending scheme if you will. So dehydrogenation of NAF teams using a precious metal catalyst like platen is pretty straightforward. If you do have a clean NAFTA heavy NAFTA, if you have sulfur associated with clean or with NAFTA feed, you need to hydratrate it to remove because platen is very susceptible to poisoning by sulfur. So you need pre-hydrotreatment before catalytic reforming. Now up until the 1990s, cat reforming was one of the most popular processes in the refinery as far as producing high octane number gasoline. But with the introduction of 1990 Clean Air Act amendments, the amount of gasoline or benzene and aromatics in gasoline were limited because of environmental issues or reasons of toxicity. So all of a sudden now catalytic reforming produces high aromatic content wasn't so desirable, but the refiners could not give up catalytic reforming. Why? Because there is a byproduct from cat reforming that is very, very valuable for the refinery. It has become of course increasingly valuable in the recent times and that is hydrogen. If you do dehydrogenate NAFTAs, the byproduct is hydrogen in addition to making aromatics. And hydrogen is needed in hydratreating processes and finishing processes that we will be talking about in the next lesson. So that is the cheapest source of hydrogen. Obviously you can make hydrogen from natural gas by reforming natural gas and that is done in refineries as well to produce additional hydrogen. But the cheapest source of hydrogen in a refinery comes from catalytic reforming. So it's still used in US refineries to make gasoline. That is a reformate and of course the byproduct hydrogen. The second process we will talk about is alkylation. Alkylation is in a sense the opposite of cracking where you have a larger molecule, you crack it into smaller molecules. In alkylation we do the opposite. We take the smaller molecules and combine them into larger molecules that would fall in the boiling range for gasoline. So the feedstocks for alkylation are 3 to 4 carbon atoms, alkanes, isoalkanes, isobutane is the principle feedstock that comes from FCC and also olefins, 3 to 4 carbon atom olefins that is propene and butane. So combining isobutane with propene or propene or butane will put you in the gasoline boiling range with 7, 8 carbon atoms and the resulting product will be an isoalkane with a high octane number. That would be essentially making up the alkylate. So alkylation is an alternative to catalytic reforming to make high octane gasoline without the aromatic. So that looks like really a nice alternative but there is one problem and the problem is for alkylation you would need as catalyst highly concentrated acids like highly concentrated sulfuric acid or highly concentrated hydrofluoric acid. These are of course not easy to work with or to transport or to have around because of the risks involved with using this highly acidic materials. Another process that generates larger hydrocarbons from smaller fragments are called polymerization. The difference between alkylation and polymerization is that we use just olefins in polymerization. No isobutane here so we use 3 to 4 carbon atom olefins typically again come from FCC process combine them using a milder acid as a catalyst this time so phosphoric acid. So the problems with handling phosphoric acids are not as severe as those with highly concentrated sulfuric or hydrogen fluoride used in alkylation. So polymerization produces branched olefins which also have respectable octane numbers. The last process we will talk about is isomerization. That's actually adding branching to straight run paraffins. This is essentially the light NAFTA that comes from the light ends unit as opposed to heavy NAFTA that is NAFTANIC like NAFTA is paraffinic but it has only straight chain paraffins with low octane numbers. So isomerization add branching to these straight chains to increase the octane number. So all these processes just make high octane gasoline which is of course the most important fuel in US refineries.