TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The first and second adsorption units are pressure swing adsorption units or vacuum swing adsorption units, where the adsorption unit comprises at least two adsorption beds and multi-layer adsorbent beds. The multilayer adsorbent beds contain an adsorbent material including silica gel, activated alumina, promoted activated alumina, carbon molecular sieves or molecular sieves including X and Y type zeolite materials. The adsorption beds include rotary beds or fixed beds. The power generation unit includes gas engine, microturbine or fuel cell.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: The natural gas stream is condensed twice and compressed to a pressure of 80-250 psig before entering the first adsorption unit. The purified natural gas from the first adsorption unit is fed to a guard bed, where the guard bed removes halogenated compounds, trace heavy metals, residual siloxanes and volatile organic compounds from the purified natural gas stream. The purified natural gas from the guard bed is fed to the second adsorption unit, where the second adsorption unit removes carbon dioxide and nitrogen from the purified natural gas. The purified natural gas is recovered from the second adsorption unit and was fed to the feed of natural gas to first adsorption unit. The waste gas stream from the second adsorption unit is fed to the first adsorption unit to regenerate adsorption beds. The depressurization gas from the first adsorption unit, the purified natural gas from the second adsorption unit and a tail gas from the first adsorption unit were fed to a power generation unit. The purified natural gas from the guard bed is fed to a membrane unit. The permeate stream from the membrane unit is: fed to second adsorption unit; fed to the first adsorption unit to regenerate adsorption beds, where the regeneration of adsorption beds is followed by regeneration of adsorption beds by tail gas from second adsorption unit; and combined with a tail gas stream from second adsorption unit and is fed to first adsorption unit to regenerate adsorption beds.    TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The membrane includes aromatic polyimide hollow fiber membrane, cellulose acetate, polyimides, polyamides, polysulfone, polycarbonates or polyetherimide. EXAMPLE - No suitable example given.