Patent ID: 6087545
Filing Date: 2000-07-11
Classification: B01J,Y02P

Abstract:
A process for the oxidative conversion of methane or natural gas to ethylene, ethane and higher hydrocarbons, operating in a most energy efficient and safe manner by allowing the endothermic hydrocarbon cracking reactions to occur simultaneously with the exothermic hydrocarbon oxidation reactions in a fixed diluted-catalyst bed reactor, using an improved supported catalyst, containing mixed strontium and other alkaline earth oxides deposited on a sintered low surface area porous inert support precoated with mixed lanthanum and other rare earth oxides, represented by the general formula:A.sub.a SrO.sub.b (x)/R.sub.c LaO.sub.d (y)/S,wherein, A is alkaline earth element selected from Be, Mg, Ca, Ba or a mixture thereof; Sr is strontium; O is oxygen; R is rare earth element selected from Ce, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu or a mixture thereof; La is lanthanum; S is catalyst support selected from sintered low surface area porous refractory inert solids comprising of alumina, silica, silica-alumina, silicon carbide, zirconia, hafnia or a mixture thereof; a is A/Sr mole ratio in the range of about 0.01 to about 10; b is number of oxygen atoms needed to fulfill the valence requirement of alkaline earth elements (A.sub.a Sr); c is R/La mole ratio in the range of about 0.01 to about 10; d is number of oxygen atoms needed to fulfill the valence requirement of rare earth elements, (R.sub.c La); y is weight percent loading of rare earth oxides (R.sub.c LaO.sub.d) precoated on the support in the range of about 0.5 wt % to about 50 wt % and x is wt % loading of alkaline earth oxides (A.sub.a SrO.sub.b) deposited on the precoated support in the range of about 0.4 wt % to about 40 wt % which is prepared by coating said support with the rare earth oxides (R.sub.c LaO.sub.d) and then depositing the alkaline earth oxides (A.sub.a SrO.sub.b) on the precoated support, the catalyst is diluted with an inert porous or non-porous refractory solid comprising of fused or highly sintered alumina, magnesia, silica, silica-alumina, silicon carbide, calcium oxide, zirconia, hafnia or a mixture thereof, in order to provide larger heat transfer area for the removal of heat of the exothermic hydrocarbon oxidation reactions and also larger contact time in the vicinity of the catalyst for the endothermic thermal hydrocarbon cracking reactions which utilize instantly the heat produced in the exothermic reactions, making the process most energy efficient and also making it lesser exothermic and hence more safer, in the presence of oxygen and steam in the feed the process comprises:(a) mixing oxygen with methane or natural gas at ambient temperature or below its ignition temperature,(b) preheating steam and the mixture of oxygen and methane or natural gas to a temperature between about 550.degree. C. and about 850.degree. C.,(c) admixing said preheated steam with said preheated mixture of oxygen and methane or natural gas,(d) passing continuously the resulting admixture feed over the said improved supported catalyst diluted with the said inert solid with the volume ratio of catalyst diluent to catalyst between about 0.5 and about 500 in a fixed reactor, maintaining the mole ratio of organic carbon to oxygen and steam in said admixture feed between about 3 and about 90 and between about 0.1 and about 100, respectively, a gas hourly space velocity of said admixture feed between about 5.times.10.sup.3 cm.sup.3 g.sup.-1 catalyst.g.sup.-1 and about 1.times.10.sup.6 cm.sup.3.g.sup.-1 catalyst.h.sup.1, a reaction temperature between about 700.degree. C. and about 1000.degree. C. and a pressure between about 1 atm and about 50 atm and separating the components of effluent produce gases by known methods and recycling the unconverted reactants.