1. Field of the Invention
This invention relates to a process for the stream reforming of methanol, and particularly to a process for producing a reformed gas containing hydrogen gas and carbon dioxide gas in a good efficiency by vapor phase reaction of methanol and water in the presence of catalysts.
2. Description of the Prior Arts
Hydrogen gas is used in many industries. For instance, it is extensively used in ammonia synthesis, hydrogenation of various types of organic compounds, oil refining and desulfurization, etc. Also, it has a great demand for the metallurgical industry and the semiconductor industry.
Furthermore, hydrogen gas is expected to be a new energy source accompanying a recent advance in the fuel battery technologies. Thus, the demand for hydrogen gas has increasingly expanded.
Conventional methods for the production of hydrogen gas include steam reforming of hydrocarbons such as liquefied petroleum gas (LPG), liquefied natural gas (LNG) and naphtha. 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. The conventional methods have several drawbacks in that (1) the price of the raw material hydrocarbons continues to rise after the oil shock, and the supply of the raw material hydrocarbons is in unstable conditions, (2) desulfurization of the raw materials is required, (3) a high reaction temperature of 800.degree.-1,000.degree. C. is required for steam reforming, etc. Thus, 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 (1) the reaction temperature is relatively low, (2) separation of hydrogen gas from the reformed gas is easy, (3) no desulfurization is required because methanol is the raw material, etc. 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 (CH.sub.3 OH+H.sub.2 O.fwdarw.3H.sub.2 +CO.sub.2) itself has long been known, and some patents relating to the reaction are made open. In general, the reaction is carried out by adopting the molar ratio of water to methanol at 1.0 or more. The reaction yields a wet gas (hereinafter referred to as 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 as in FIG. 5, or the condensed liquid obtained by vapor-liquid separation treatment is recycled to the reaction system as in FIG. 6 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 amount 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.