A NOVEL PROCESS FOR THE REMOVAL OF NITROGEN FROM NITROGEN-CONTAININGNATURAL GAS: DEVELOPMENT OF WATER-BASED ABSORBENTS

DOMESTIC NATURAL GAS PROVIDES AN INCREASINGLY IMPORTANT PORTION OF THE U.S. ENERGY SUPPLY. ESTIMATED U.S. GAS RESERVES ARE ABOUT 1000 TRILLON STANDARD CUBIN FEET (SCF)--OR ABOUT 1000 QUADS. FULLY 25% OF THE ESTIMATED U.S. NATURAL GAS RESERVES ARE CONTAMINATED WITH NITROGEN (N2) TO THE EXTENT THAT THE GAS CANNOT BE USED WITHOUT PROCESSING TO REDUCE THE N2 CONCENTRATION. NO TECHNOLOGY EXISTS TODAY FOR THE COST-EFFECTIVE REMOVAL OF N2 FROM NATURAL GAS AT THE WELLHEAD. IN PHASE I, THE N2 WILL BE SEPARATED FROM THE REST OF THE NATURAL GAS USING A REGENERABLE ABSORBENT. THE N2 ABSORBENTS ARE BASED ON SOLUTIONS OF TRANSITION-METAL COMPLEXES. THESE ABSORBENTS IDEALLY WILL HAVE THE FOLLOWING CHARACTERISTICS: (1) RAPID ABSORPTION OF NITROGEN AT THE PRESSURE AND TEMPERATURE OF THE NATURAL GAS FEED STREAM (HIGH PRESSURE AND AMBIENT TEMPERATURE), (2) RAPID DESORPTION OF NITROGEN UNDER MILD CONDITIONS (AMBIENT PRESSURE AND MODERATE TEMPERATURE), (3) EXTREMELY HIGH SELECTIVITY FOR NITROGEN OVER METHANE (AND THE OTHER NATURAL GAS COMPONENTS), AND (4) OTHER PROPERTIES THAT COMBINE TO YIELD AN ECONOMICAL PROCESS. THE UNDERSTANDING OF THE RELATIONSHIP BETWEEN THE MOLECULAR STRUCTURE OF N2-BINDING COMPOUNDS AND THEIR PROPERTIES WILL BE USED TO INCREASE THE SELECTIVITY OF THE N2ABSORBENT--THE KEY SHORTCOMING OF CURRENT ABSORBENTS. INCREASING SELECTIVITY WHILE RETAINING THE PROPERTIES OF LOW COST FOR REMOVAL OF N2 FROM NATURAL GAS OF LESS THAN $0.25/1000 SCF, THE COST TARGET FOR THIS PROCESS. HIGH SELECTIVITY WILL ALSO KEEP GAS LOSSES FOR TREATMENT BELOW A3% LIMIT IMPOSED BY ENVIRONMENTAL AND ECONOMIC CONSTRAINTS.