A MEMBRANE SYSTEM FOR NATURAL GAS DEHYDRATION

VIRTUALLY ALL NATURAL GAS MUST BE TREATED TO REMOVE WATER VAPOR BEFORE THE GAS ENTERS A PIPELINE. THE PRINCIPAL CURRENT TECHNOLOGY IS ABSORPTION WITH GLYCOL, BUT GLYCOL DEHYDRATORS COEXTRACT BENZENE, A KNOWN CARCINOGEN, WHICH IS THEN RELEASED TO THE ATMOSPHERE. NEW ENVIRONMENTAL REGULATIONS ARE LIKELY TO PROHIBIT THESE EMISSIONS WITHIN A FEW YEARS. THE NATURAL GAS INDUSTRY MUST, THEREFORE, EITHER CONTAIN THESE EMISSIONS OR REPLACE GLYCOL DEHYDRATORS. A MEMBRANE-BASED DEHYDRATOR WOULD BE AN EFFICIENT ALTERNATIVE, PRODUCING NO BENZENE EMISSIONS. THIS PROJECT AIMS TO PRODUCE SUCH A UNIT. DEHYDRATION OF BOTH SMALL AND LARGE NATURAL GAS STREAMS WOULD BE ECONOMICALLY FEASIBLE BECAUSE OF THE MODULAR NATURE OF MEMBRANE SYSTEMS. IN ADDITION, MEMBRANE SYSTEMS ARE MORE COMPACT THAN GLYCOL DEHYDRATORS AND DO NOT NEED THE GAS-FIRED BOILER USED TO REGENERATE THE GLYCOL, TWO IMPORTANT ADVANTAGES FOR OFFSHORE GAS PRODUCTION PLATFORMS. PREVIOUS RESEARCH HAS IDENTIFIED TWO HYDROPHILIC, RUBBERY POLYMERS WITH OUTSTANDING PROPERTIES AS MATERIALS FOR NATURAL GAS DEHYDRATION MEMBRANES. MEMBRANES PREPARED FROM THESE POLYMERS HAVE VERY HIGH SELECTIVITIES FOR WATER VAPOR OVER NATURAL GAS AND ARE COMPATIBLE WITH NATURAL GAS STREAMS AT PRESSURES OF AT LEAST 1,000 PSIG. ONE OF THE MEMBRANES ALSO HAS GOOD SELECTIVITY FOR CARBON DIOXIDE AND HYDROGEN SULFIDE, WHICH ALLOWS (PARTIAL) ACID GAS REMOVAL IN ADDITION TO DEHYDRATION. THE SELECTIVITIES FOR WATER VAPOR ARE SO HIGH THAT THE SEPARATION ACHIEVED IS LIMITED BY THE AVAILABLE PRESSURE RATIO ACROSS THE MEMBRANE AND THE OCCURRENCE OF BOUNDARY LAYERS ON THE FEED-SIDE MEMBRANE SURFACE. THIS MAKES THE PROPER DESIGN AND OPERATION OF THE MEMBRANE SYSTEM CRITICALLY IMPORTANT. THEREFORE, THE PHASE I EFFORT WILL (1) CONSTRUCT SMALL MEMBRANE MODULES THAT FULLY UTILIZE THE EXCELLENT SEPARATION PROPERTIES OF THE MEMBRANES ALREADY DEVELOPED AND (2) VERIFY THE PERFORMANCE OF THE MODULES IN A BENCH-SCALE TEST. IN PHASE II, THE PROCESS WOULD BE DEMONSTRATED IN A FIELD TEST. THE NATURAL GAS INDUSTRY HAS ALREADY INDICATED THAT HOST SITES WILL BE AVAILABLE FOR SUCH A DEMONSTRATION SYSTEM.