Figure 6. Steam mole fraction contour maps in the integrated combustion-reforming reactor in which combustion chambers are in direct thermal contact to reaction chambers for an endothermic steam-methanol reforming reaction.
The effect of catalyst layer thickness on the methanol conversion is illustrated in Figure 7 in which combustion chambers are in direct thermal contact to reaction chambers for an endothermic steam reforming reaction. Within the reformer, the methanol and steam react endothermically at high temperature to produce a gaseous product consisting primarily of steam, hydrogen, and carbon dioxide. Methanol is passed with steam over a catalyst at pressure typically ranging from 14.7 to 150 psia and temperatures in the range of about 373 K to about 548 K. Typical steam to methanol mole ratio are in the range of about 2.5:1 to about 4:1. The conversion of methanol may be affected in one pass over the catalyst bed contained in the reformer. Conventional methods for the production of hydrogen gas include steam reforming of hydrocarbons [45, 46]. According to the usual method, carbon monoxide and carbon dioxide are removed from a reformed gas containing hydrogen gas, carbon monoxide and carbon dioxide obtained by the above methods so as to produce hydrogen gas [47, 48]. The conventional methods have several drawbacks in that the price of the raw material hydrocarbons continues to rise, and the supply of the raw material hydrocarbons is in unstable conditions, desulfurization of the raw materials is required, and a high reaction temperature of 1100-1300 K is required for the steam reforming process. Consequently, the conventional methods are suitable for large scale hydrogen gas production, but they are not adequate for middle to small scale hydrogen gas production. In contrast, hydrogen gas production by the steam reforming of methanol has various advantages in that the reaction temperature is relatively low, separation of hydrogen gas from the reformed gas is easy, and no desulfurization is required because methanol is the raw material. Also, the method can easily cope with large to small scale plants, since it uses inexpensive and easily transportable methanol as the raw material. The steam reforming reaction of methanol yields a wet gas containing condensable components such as methanol and water, and a reformed gas. After the reaction, the reformed gas containing hydrogen and carbon dioxide is taken out by cooling of the wet gas. Here, an industrial problem is the treatment of the condensed liquid. Conventionally, the condensed liquid is disposed without treatment or the condensed liquid obtained by vapor-liquid separation treatment is recycled to the reaction system so as to make reuse of the condensed liquid together with the raw material methanol and water. However, the former has a big problem from the view-point of pollution since the condensed liquid contains a considerable number of organic components such as unreacted methanol and high boiling point components. In the latter, a trace amount of ethanol contained in the raw material methanol accumulates because it is hardly converted by the usual reaction method. If the treated condensed liquid is reused in the reforming reaction system, it is necessary to adjust the amount of water so as to make the methanol-water ratio at a predetermined value. Therefore, if steam reforming of methanol is continuously carried out, a portion or the whole of a predetermined amount of raw material water may be allotted for water to be added to the condensed liquid. The steam reforming reaction of methanol which discharges the condensed liquid or makes reuse of the treated condensed liquid should not particularly be limited, but the reaction is usually carried out as follows. Known catalysts are used for the steam reforming reaction of methanol. For example, they include copper catalysts such as those containing copper oxides, chromium oxides and manganese oxides. The conditions of steam reforming reaction of methanol vary with the catalysts used, and cannot absolutely be specified. The reformed gas mainly contains hydrogen gas and carbon dioxide gas. When carbon dioxide gas is removed from the reformed gas by a conventional method such as absorptive removal with an aqueous sodium carbonate solution, an aqueous potassium carbonate solution or an aqueous monoethanolamide solution, a high purity of hydrogen gas is obtained. Also, when the condensed liquid is reused after treatment for the steam reforming reaction of methanol, it has no bad effect due to ethanol and high boiling point components on the reaction. The conversion of methanol is usually maintained high. The durability of catalysts is increased, and the process causes no pollution.