In a typical process for conversion of natural gas and associated light hydrocarbons into salable hydrocarbon products, methane, a gaseous oxidant, and C.sub.2 to C.sub.6 hydrocarbons from a gas well are fed to a reforming zone to produce a first product stream comprising carbon oxides (such as carbon monoxide and carbon dioxide), hydrogen, and some water. That first product stream is feed into a hydrocarbon synthesis zone with a hydrocarbon synthesis catalyst at elevated temperature and pressure to produce a second product stream having a wide range of products: from light hydrocarbons to heavy wax. The second product stream is separated in a distillation column into a light hydrocarbon fraction, at least one fraction of salable hydrocarbon products (such as a naphtha stream and a distillate fuels stream), and a waxy fraction. The waxy fraction is hydrotreated to remove heteroatoms and is hydrocracked, then the hydrotreated, hydrocracked waxy fraction is recycled to the distillation column. The light hydrocarbon fraction is recycled to the reforming zone.
A problem with such a process is that it requires that large volumes of light hydrocarbon fraction be fed to and recycled to the reforming zone, which means that both the reforming zone and the hydrocarbon synthesis zone have to be large to accommodate such large volumes of recycle gas. Therefore, it would be advantageous to develop processes that do not require such large volumes of recycle gas. In addition, processing C.sub.3+ hydrocarbons in the reforming zone can cause coking and metal dusting problems which make operation difficult.
Another problem with such a process is that a mixture of products is made which typically include LPG, naphtha, distillate fuel, and hydrocarbons in the lube base oil range. The hydrocarbons in the lube base oil range and distillate fuel are the most valuable products, but with the existing technology it is not practical to increase the yield of the most valuable products beyond a certain limit. In particular the export of the least valuable LPG product requires the use of pressurized containers for storage and shipment, which represent a significant expense, operational difficulties, and safety hazards. The naphtha from such a process typically has a very low octane value and makes a relatively poor feedstock to a reformer, and is only of moderate value when used as a feed to an ethylene naphtha cracker. While it is desirable to reduce or eliminate the production of LPG and naphtha, with the current process it is not possible to do so. Similarly, the diesel and hydrocarbons in the lube base oil range fractions are the most valuable, but with the current technology the yield of these most valuable fractions cannot be increased beyond a given value.
The disproportionation of saturated hydrocarbons has been described in the patent literature in U.S. Pat. Nos. 3,484,499; 3,668,268; 3,856,876; 3,864,417; and 3,953,537. In the general literature see Hughes, T. R., et. al., Proc. Int. Congr. Catal., 5th (Paper 87) 1972 and Burnett R. L., et. al., Jour. of Cat. 31, pp 55-64, 1973. In the petroleum industry, disproportionation has been proposed for the conversion of refinery gases (see, for example, U.S. Pat. No. 3,773,845) and for the reforming of distillate transportation fuels (see, for example, U.S. Pat. No. 4,676,885).
USPTO Backgrounds
USPTO Backgrounds