Preparation of normally liquid hydrocarbons and a synthesis gas to make the same, from a normally gaseous hydrocarbon feed

A process of preparing from a normally gaseous hydrocarbon feed a synthesis gas comprising hydrogen and carbon oxides and suitable for the synthesis of normally liquid hydrocarbons therefrom, the process comprising the steps of:

• (a) preheating an inlet stream comprising a normally gaseous hydrocarbon feed, by-product hydrocarbons obtained from a hydrocarbon synthesis operation, H.sub.2 O, oxygen and recycled carbon dioxide obtained as defined below, to a preheat temperature of about 800.degree. F. to 1400.degree. F. (427.degree. C. to 760.degree. C.) and introducing the preheated inlet stream at a pressure of from about 100 to 1,000 psig into a first catalyst zone comprising a monolithic body having a plurality of gas flow passages extending therethrough and having a catalytically effective amount of palladium and platinum catalytic components dispersed therein, the amount of feed, H.sub.2 O and oxygen introduced into said first catalyst zone being controlled to maintain in said inlet stream an H.sub.2 O to C ratio of from about 0.5 to 5, and an O.sub.2 to C ratio of from about 0.4 to 0.65;
• (b) contacting the preheated inlet stream within said first catalyst zone with said platinum group metal catalyst at a volumetric hourly rate of at least about 100,000 volumes of throughput per volume of catalyst per hour to initiate and sustain therein catalytic oxidation of said feed to produce hydrogen and carbon oxides therefrom, and oxidizing in said first catalyst zone a quantity, less than all, of said feed, which quantity is sufficient to heat such first zone effluent to an elevated temperature of from about 1750.degree. F. to 2400.degree. F. (954.degree. C. to 1316.degree. C.);
• (c) passing the first zone effluent, while still at said elevated temperature, from said first catalyst zone to the second catalyst zone containing a platinum group metal steam reforming catalyst therein and contacting the first zone effluent in said second catalyst zone with said steam reforming catalyst at an hourly volumetric rate of from about 2,000 to 20,000 volumes of throughput per volume of catalyst, to react hydrocarbons therein with H.sub.2 O to produce hydrogen and carbon oxides therefrom and thereby provide a gas mixture including hydrogen, carbon monoxide and carbon dioxide;
• (d) passing the effluent of said second catalyst zone to a carbon dioxide removal zone and separating carbon dioxide from the second zone effluent;
• (e) recycling the carbon dioxide separated in step (d) to said inlet stream in an amount sufficient so that said inlet stream comprises from about 5 to 20 mole percent carbon dioxide., and
• (f) withdrawing the carbon dioxide-depleted second zone effluent obtained in step (d) as said synthesis gas and passing said synthesis gas to a hydrocarbon synthesis operation from which said by-product hydrocarbons are obtained.