(251a) Determination of the Effect of Water and Carbon Dioxide Addition into the Reactor Feed in Fischer-Tropsch Synthesis

Fischer Tropsch Synthesis (FTS) is an important chemical process whereby carbon monoxide and hydrogen are reacted over a supported metal catalyst to produce hydrocarbons and water. One of the side reactions in FTS is the water gas shift reaction (WGS) which is an equilibrium reaction in which water and carbon monoxide react to form carbon dioxide and hydrogen. It is thought that by expressing the mass balance corresponding to these reactions in terms of reaction extents a maximum possible reaction extent can be determined for the production of hydrocarbons. This is achieved by determining a region of possible reaction extents by plotting lines which correspond to the extents in which the number of moles of each species is zero and then setting the restriction that the number of moles must always be positive. It was found that one of the vertices of this region of possible extents represents the maximum production of hydrocarbons. The results show that the amounts of water and carbon dioxide in the feed had no effect on the maximum extent of hydrocarbon production. Therefore only the relative amounts of carbon monoxide and hydrogen have an effect on this maximum point. This is completely counter intuitive as it was has been thought that by adding H20 and/or CO2 to the reactor feed may decrease the amount of hydrocarbons produced. It was also found that equilibrium curves (at various temperatures) for the WGS reaction plotted in the extent region all passed through the maximum extent point.