NOVELTY - The removal of sulfur compounds from hydrocarbon source involves passing the hydrocarbon source through low temperature sulfur trap containing an adsorbent which adsorbs sulfur compounds at low temperature and releases sulfur at elevated temperature.    USE - For removing sulfur compounds from hydrocarbon source, for producing hydrogen, and for generating electric power for fuel cells (all claimed), for producing ammonia, alcohols and ultra-clean hydrogen for electrical industry.    ADVANTAGE - The sulfur compounds are removed from the hydrocarbon source in a simple and easy manner, without risk of sulfur compounds reaching the catalytic reactors, and without need for separately heated nickel adsorbent in the start-up phase. Adsorption is carried out by an upstream adsorbent that operates at low temperature and is automatically regenerated once the operating temperature is reached. A very elegant and easy system is obtained, due to the automatic adsorption-desorption cycles. Replacement of adsorbent is not required. Sensitivity of adsorbent to sulfur poisoning decreases and upstream sulfur trap is unnecessary. Diffusion properties and speed of adsorption are increased by increasing the adsorbent surface area. Molten carbonate fuel cells are electrically efficient than phosphoric acid electrolyte fuel cells, and produce high quality steam as by-product due to significantly higher operating temperature.    DETAILED DESCRIPTION - The adsorbent in the low temperature sulfur trap is chosen from zeolites, carbon, clay materials, alumina and silica-alumina. The hydrocarbon source contains sulfur compounds, and is a liquid hydrocarbon or natural gas. The sulfur present in the sulfur compounds is not part of aromatic ring.    INDEPENDENT CLAIMS are included for:    (1) Production of hydrogen from hydrocarbon source containing sulfur compounds;    (2) Process for generating electricity from fuel cell;    (3) Use of adsorbent which adsorbs and releases sulfur compounds at low and high temperatures, respectively;    (4) Sulfur removal unit; and    (5) Fuel cell system.