Patent GB-1431540-A (GB)
Title: Production of methane
IPC: C07C9/04
Filed: 1974-04-16
Abstract: 1431540 High methane content gas TEXACO DEVELOPMENT CORP 16 April 1974 [25 June 1973] 16634/74 Heading C5E A gas stream comprising at least 90 mole per cent methane is produced by (1) producing a raw process gas stream principally comprising CO, H 2 , CO 2  H 2 O with minor amounts of CH 4 , A, H 2 S, and particulate carbon and containing 30 to 60 mole per cent of N 2  (dry basis) by the partial oxidation in a free flow non-catalytic gas generator of a hydrocarbonaceous feedstock with air or oxygen-enriched air comprising 21 to 50 mole per cent O 2  and 50 to 79 mole per cent N 2 ; (2) cooling, cleaning and purifying the gas stream from (1) to produce a feed gas for catalytic methanation comprising CO and H 2  and containing 32 to 62 mole per cent nitrogen; (3) reacting the gas stream from (2) in a first catalytic methanation zone at 400‹ to 1500‹ F. and a pressure of 1 to 350 atm. abs. until substantially all of the H 2  is reacted with a portion of the CO to produce CH 4  and H 2 O; (4) introducing the gas stream from (3) and supplemental H 2 O into a water-gas shift conversion zone, and reacting H 2 O with a portion of the CO to produce a process gas stream comprising H 2 , CO, CO 2 , CH 4  and N 2 , and removing any excess water therefrom; (5) adjusting the temperature of the gas stream from (4) to 400‹ to 1000‹ F. and reacting the H 2  and CO in a second catalytic methanation zone to produce a gas stream principally comprising CH 4 , and containing CO 2 , H 2 O, N 2  and optionally minor amounts of H 2 , CO and A as impurities; and (6) cooling the gas stream from (5) and separating said impurities therefrom by conventional processes to produce the product gas stream. The raw process gas stream of step (1) is produced at an autogenous temperature of 1500‹ to 3500‹ F. and a pressure of 1 to 350 atm. abs. and the pressure in steps (2) to (6) is substantially that of step (1) less ordinary line drop. The hydrocarbonaceous fuel may be a liquid hydrocarbon selected from liquefied petroleum gas, petroleum distillates and residues, gasoline, naphtha, kerosine, crude petroleum, asphalt, gas oil, residual oil, tar-sand oil, shale oil, coal oil; aromatic hydrocarbons such as benzene, toluene, xylene fractions, coal tar, cycle gas oil from fluid-catalyticcracking operation; furfural extract of coker gas oil; and mixtures thereof; a gaseous hydrocarbon selected from ethane, propane, butane, pentane, water gas, coke-oven gas, refinery gas, acetylene tail gas, ethylene off-gas and mixtures thereof; an oxygenated hydrocarbonaceous organic material selected from carbohydrates, cellulosic materials, aldehydes, organic acids, alcohols, ketones, oxygenated fuel oil, waste liquids and by-products from chemical processes containing oxygenated hydrocarbonaceous organic materials and mixtures thereof; or a pumpable slurry, in a vaporizable carrier, e.g. water, liquid hydrocarbon fuel or a mixture thereof, of coal, particulate carbon, petroleum coke, and/or concentrated sewer sludge. The hydrocarbonaceous fuel is preheated to a temperature up to 1200‹ F. but below its cracking temperature, before it is introduced into a gas generator in step (1). Step (1) may be conducted in the presence of a temperature moderator, e.g. H 2 O, CO 2 , a portion of cooled clean process gas, recycled from a later step of the process by-product nitrogen from an air separation unit or from a cryogenic gas purification zone, or a mixture thereof. The mole ratio H 2 O/CO of the reacting stream in step (4) is 2 to 4:1. Step (4) may be conducted in a catalytic water-gas shift conversion zone using a fixed or fluidized bed or catalytic tubes at 600 to 1000‹F. or in a non-catalytic thermal direct water-gas shift conversion zone at 1500‹ to 2800‹ F. The raw process gas stream is cooled in step (2) by indirect heat exchange with water in a waste heat boiler thereby producing steam, and at least a portion of the steam is introduced into the water-gas shift conversion zone in step (4) as the supplemental H 2 O. The methanation catalyst in steps (3) and (5) may be sulphur-sensitive or -resistant and may be a Group VIII transition element, mainly iron, nickel and cobalt, nickel oxide-aluminium oxide, or nickel oxide-magnesium oxide precipitated on kaolin and reduced with hydrogen, nickel-thorium oxide-magnesium oxide and kieselguhr reduced with hydrogen, and the space velocity in each methanation zone is 100 to 10,000 standard volumes of gas per volume of catalyst per hour.