 We have talked about in many occasions the evolution of refinery, based on of course the demands for the products, all the way from a one-pot distillation refinery, or we can call it a separation refinery, just to make kerosene for the lamps, for lighting. Now it's widely considered and in claim that that very process saved the whales from extinction, because instead of now using whale oil in lamps one could use kerosene without much smoke, and the light or the light to actually let people extend the daylight in essence. Of course with the electric light, now kerosene was not demanded, but as you know, as we've talked about before, the demand for another fuel or gasoline was increasing. So from separation or distillation refinery we went to the thermal refinery to make more gasoline for the increasing number of automobiles, and of course the lubricating oil that is needed in these engines. So the thermal refinery performed quite well up until the Second World War to use just heat to make the chemical changes that are needed to change the composition of the crude oil to fit with the product demand in essence. With the Second World War raging with the demand for high performance fuels, the catalytic processes were introduced. So we are in the catalytic refinery taking over from the thermal refinery, and the catalytic refinery continued of course after the Second World War. An interesting historical note, the companies, oil companies that were competing before the Second World War in the United States and in Western Europe got together to develop these catalytic, many of these catalytic processes that are still used today in an effort obviously to develop more powerful fuels for the war effort. So that is a very interesting era in the history of petroleum refining where competition turns into collaboration to make of course more powerful fuels for the more powerful war machine. Until the end of the century, obviously this trend continued, and the next stage is referred in some text as the end of the century refinery where the focus now is really on the very heavy end because as we are using crude oil in the marketplace the crude oil available for refining becomes heavier. So when you do the distillation there is a huge amount of vac of distillation that is separated. So the end of the century refinery focuses on treating these heavy ends, essentially hydro processing using different reactor configurations, using essentially the chemistry chemical modeling to determine the reaction chemistry kinetics for more optimum conversion of these very heavy ends. The most challenging parts of the crude oil to be converted into the light distillates. So on one hand we have an increasing demand for lighter fuels like gasoline diesel jet fuel and on the other hand we do have a crude oil base that is getting increasingly heavier and dirtier. So the end of the century refinery focused on treating and hydro treating these heavy ends to make the lighter and cleaner products. As we have mentioned at the beginning of this course there is a new trend, that is the hydrofracking to make essentially to produce shale gas. But there is a liquid byproduct and it won't be too long before hydrofracking is used to produce oil also. So in the 21st century we may see yet another significant change in the refinery scheme to incorporate shale oil that is produced by hydrofracking into the refinery to be refined into the mix of the fuels and materials that are needed in the marketplace.