Method of producing liquid hydrocarbons from natural gas, in the presence of a catalyst based on zeolite and gallium

#The invention concerns a method of producing liquid hydrocarbons from natural gas. More specifically, it concerns the conversion of natural gas, the main constituent of which is methane, to liquid products which can be transported more easily. The invention concerns a method characterised in that:

#(a) natural gas is separated into at least two fractions, a first fraction of gas enriched with methane and a second fraction enriched with C2+ alkanes (ethane, propane and higher alkanes);

#(b) at least part of the methane is oxidised selectively by molecular oxygen in the presence of a catalyst for oxidising linkage of methane

#FIGS. 1 and 2 are schematic embodiments of the invention, FIG. 1 relating to a vertical reactor and FIG. 2 relating to a horizontal reactor.

#A preferred embodiment of the invention comprises using a fluidized bed reactor for the selective oxidation and pyrolysis (oxypyrolysis) stages and a reactor of the moving bed type for aromatisation. In this embodiment the gas enriched with methane (3), emanating from separation of natural gas (1) in the separator (2), is mixed with molecular oxygen (5). In cases where it is advantageous to add water vapour to the charge, this is generally added either to the methane or to the oxygen, or to the methane and oxygen before the methane is mixed with the oxygen. It is very important to control the temperature of the gaseous mixture before it enters the reactor. For this purpose the gases containing methane (3) and the oxygen (5) may be heated independently or the gases (6) together. When the gases have been preheated to a temperature generally below 750.degree. C. and preferably below 600.degree. C. they are put into contact with the catalyst for oxidising coupling of methane in the lower part (7a) of the reactor (7) in FIG. 1 or in the upstream part (7a) of the reactor (7) in FIG. 2.

#The catalyst for this type of application must have good mechanical strength. The particles are generally from 20 microns to 4 mm in diameter. The size of the catalyst particles varies according to the operating conditions of the unit and the density of the catalyst. Although it is not possible to name all the catalysts for oxidising coupling of methane which are potentially of interest for an application in a boiling bed reactor, mention may be made of catalysts described in French patent 2 629 451, in Appl. Catal., vol. 76 (1990) 47, in Chem. Soc. Rev., vol. 18 (1989) 251 and, for example, catalysts such as: BaCO3/Al2O3 (generally though not necessarily in the presence of a few ppm of a chlorine source in the charge); Pb/Al2O3 (often in the Presence of an alkali metal and/or an anion containing sulphur or phosphorus); mixed oxides containing Na, B, Mg and Mn (such as NaB2Mg4Mn20x; La/MgO (often in the presence of one or more alkaline earth metal or alkali metal oxides and/or other lanthanide oxides and possibly boron); Na or K combinations, one or more alkaline earth metal oxides and possibly boron; MCeO3 perovskites (where M=Sr or Ba) and mixed oxides containing thorium or yttrium.

#After undergoing selective oxidation in the reactor (7) and at a location where at least 80% of the molecular oxygen introduced at stage (b) has been consumed, at least part of the gas fraction enriched with C2+ alkanes (4) is added in the reactor. This fraction may be added in the expanded bed of catalyst (FIG. 1) or at a level above the catalyst (such as the liberation zone).