Various processes based on phase change, absorption, adsorption, permeation through
membranes, and chemical reactions are available for separation, recovery and
purification of hydrogen. Some of these processes are employed in practical operations
according to operating conditions, specifications, and end uses for removed and
recovered components. The prime technology is the pressure swing adsorption
processes, which have several advantages over the other methods. Technical progress
for improvement of hydrogen recovery and energy consumption can be made mainly byresearch and development of separation media such as absorbents, adsorbents, polymer
membranes and hydrogen storage alloys to achieve superior performances in selectivity,
rate-capability, capacity, and durability.Addition of hydrogen to natural gas is a possible way to enlarge the use of hydrogen
into energy fields. For this purpose, a beneficial effect in terms of improving
combustion properties and reducing polluting emissions can be obtained for burner
combustion of town gas and lean-burn operation of internal combustion engines.
Safe handling of hydrogen and its mixtures, and the hazards and damage resulting from
its physical and chemical properties and combustion characteristics are outlined with
respect to its three forms of gas, liquid, and metal hydride. As hydrogen is colorless and
odorless, burns with a nearly invisible flame, and can embrittle some metals, detectors
of gaseous hydrogen and its flame and materials suitable for equipment are also
described. Hydrogen can be handled as safely as other fuels. However, gaseous
hydrogen is a highly flammable and explosive gas with wide flammability limits, a low
minimum ignition energy, and a fast burning velocity. Liquid hydrogen is an extremely
low-temperature liquid with a normal boiling point of 20 K. Adequate handling and
safety measures of hydrogen are obviously important for both current and emerging
uses of hydrogen as a feedstock and a fuel.