Thermochemical processes for the production of hydrogen by utilizing the catalytic steam-hydrocarbon process

Thermochemical processes present the most attractive means for the production of hydrogen. One such process utilizes the reforming reaction of a hydrocarbon fuel, for example, methane, with water to produce hydrogen. This process typically requires a significant amount of heat and must be carried out at elevated temperatures to attain the desired level of conversion. For example, the steam methane reforming reaction is strongly endothermic and the process is typically performed under high temperature conditions in order to increase the yield of the desired product. Unfortunately, these high temperatures and heat demands present a multitude of severe challenges for the design and operation of the system. Another such process utilizes the catalytic partial oxidation of a hydrocarbon fuel, for example, methane, with oxygen to produce hydrogen. However, the implementation of the process under high temperature conditions is also necessary to enable the catalytic reaction to proceed at short contact times in reduced scale reactors. Another such process, as described here, involves the reaction of an alcohol fuel, for example, methanol, with water to produce hydrogen under more moderate conditions. In comparison with methane, methanol permits operation of the system at much lower temperatures and with an insignificant amount of carbon monoxide. This feature offers certain advantages for reactor design and more compact usage, which is especially attractive for commercial applications. The most important industrial method for the production of hydrogen is the catalytic steam-hydrocarbon process, in which gaseous or vaporized hydrocarbons are treated with steam at high pressure over a catalyst to produce carbon oxides and hydrogen. The primary reaction products are processed further in various ways, depending on the desired application of the hydrogen. Another important process for hydrogen production is the noncatalytic partial oxidation of hydrocarbons under elevated pressures. This process requires a feed system for delivering precise rates of fuel and oxygen, burners of special design to give rapid mixing of the reactants, and a refractory-lined reactor. The latter process is exothermic, in contrast to the endothermic steam-hydrocarbon process. In a third process, called the pressure catalytic partial oxidation method, the two preceding processes are combined to maintain the required reaction temperature without external heating of the catalyst bed. Superheated steam and hydrocarbons are mixed, preheated, and blended with heated oxygen in a diffuser at the top of the catalytic reactor. The oxygen reacts with the hydrocarbons in a space above the catalyst. The reactants then pass through a bed of nickel catalyst in which the steam-hydrocarbon reactions proceed almost to equilibrium.