Encyclopedia of Renewable Energy. James G. Speight

and un-reacted starting materials. The practical result of these sometimes conflicting demands are a wide range of conversion technologies and separation approaches, each more or less optimized for a specific end use application.

      Maximization of the conversion of feed to product can be accomplished by reducing the vapor pressure of the products in the reactor. A common practice is to add steam to the reactor. This not only reduces the partial pressure of the products driving the conversion higher; it is typically also utilized to import the needed heat of reaction into the reaction vessel. Steam is used because it can be easily separated from the reactor effluent through condensation. Another approach is to selectively remove one of the products of the reaction from the reactor, in this case the hydrogen.

      Hydrogen is removed by oxidation to produce water and also to supply some of the required heat of reaction. The direct addition of small amounts of oxygen into the reactor, typically in a specially designed reaction zone, usually with a catalyst present has been described. The risk with this solution is the indiscriminate reaction of the oxygen with either the reactants or the products.

      Another approach is to control the side reactions of products with oxygen is to use a membrane reactor to effectively segregate the reactant and product hydrocarbon molecules from the oxygen hydrogen scavenger. A third approach is to utilize redox agents along with the dehydrogenation catalysts that provide a supply of reactive but not free oxygen for reaction with the product hydrogen. One difficulty with this solution is that the redox agents are reduced and consumed in the process and must be regenerated in a separate processing step.