IMPROVED COATED-METAL HYDROGEN EXTRACTION MEMBRANES

COATED REFRACTORY-METAL MEMBRANES ARE SUGGESTED FOR HYDROGEN EXTRACTION FROM GAS MIXTURES FOR HYDROGEN PURIFICATION, FOR PRODUCING REFORMULATED GASOLINE AND FOR MEMBRANE-REACTOR USE. PALLADIUM-BASED MEMBRANES HAVE BEEN USED FOR DECADES FOR HYDROGEN PURIFICATION AND MEMBRANE REACTORS BECAUSE PALLADIUM COMBINES HIGH PERMEABILITY, 100% SSELECTIVITY, AND GOOD SURFACE PROPERTIES. SEVERAL REFRACTORY METALS ARE HIGHER IN PERMEABILITY, AND ARE STRONGER AND CHEAPER THAN PALLADIUM; THEY ARE NOT ORDINARILY USED FOR THESE APPLICATIONS BECAUSE POOR SURFACE PROPERTIES REDUCE HYDROGEN TRANSPORT. WHEN THESE REFRACTORY METALS ARE COATED WITH PALLADIUM, HOWEVER, THE SURFACE BARRIERS ARE REDUCED. MEMBRANES THAT RESULT SHOW HYDROGEN FLUXES AS HIGH AS 0.095 MOL/M(2)S FOR A DRIVING PRESSURE OF 0.78 ATM AND A THICKNESS OF 0.25 MM, MORE THAN TEN TIMES GREATER THAN THOSE AVAILABLE WITH PALLADIUM AT 420 DEGREES CENTIGRADE, AT LOWER COST AND WITH THE SAME 100% SELECTIVITY. SUCH MEMBRANES CAN BE MADE THINNER THAN 0.1 MM BECAUSE OF THE STRENGTH OF THE REFRACTORY METALS. THINNER MEMBRANES SHOULD SHOW STILL HIGHER HYDROGEN FLUXES BECAUSE FLUX INCREASES AS MEMBRANE THICKNESS DECREASES. MEMBRANE COSTS ARE ESTIMATED AS $2500/M(2) IF THE MEMBRANES ARE MASS-PRODUCED. CURRENT MEMBRANES ARE STILL LABORATORY PROTOTYPES, TOO THICK AND TOO SMALL FOR MOST APPLICATIONS. IN PHASE I THINNER-WALLED, LARGER-SURFACE MEMBRANES WILL BE MADE, AND THEIR HYDROGEN TRANSPORT AND DURABILITY MEASURED. THIS WILL PROVIDE PRACTICAL MEMBRANES FOR USE IN BENCH-SCALE INDUSTRIAL TESTS AND WILL PROVIDE BENCHMARK TRANSPORT AND COST DATA.