Cryogenic hydrogen

Pressurized hydrogen vessels made of steel is too weighty to carry with cars, and liquefied hydrogen cryogenic method has no infrastructures yet. Metalhydrides is meritorious for Vd, but not for Wd-... 

Ahuja V, Green R. Application of matrix heat exchangers to thermomechanical energy recovery from liquid hydrogen. Cryogenics 1998 38(9) 857-867. 

Ohira, K. (2004) Development of density and mass flow rate measurement technologies for slush hydrogen. Cryogenics, 44, 59-68. 

Williams, Laurence O., "Hydrogen Fueled Automobiles Must Use Liquid Hydrogen", Cryogenics, Vol. 13, No. 12, Efecember 1973, Page 693... 

Liquid hydrogen is important in cryogenics and in the study of superconductivity, as its melting point is only 20 degrees above absolute zero. 

The cmde product from the gasifier contains CO2 and H2S, which must be removed before the gas can be used to produce chemicals. The Rectisol process is used to remove these contaminants from the gas. This is accompHshed by scmbbing the product with cold methanol which dissolves the CO2 and H2S and lets the H2 and CO pass through the scmbber. The H2S is sent to a Claus sulfur plant where over 99.7% of the sulfur in the coal feed is recovered in the form of elemental sulfur. A portion of the clean H2 and CO are separated in a cryogenic distillation process. The main product from the cryogenic distillation is a purified CO stream for use in the acetic anhydride process. The remaining CO and hydrogen are used in the methanol plant. 

A wide range and a number of purification steps are required to make available hydrogen/synthesis gas having the desired purity that depends on use. Technology is available in many forms and combinations for specific hydrogen purification requirements. Methods include physical and chemical treatments (solvent scmbbing) low temperature (cryogenic) systems adsorption on soHds, such as active carbon, metal oxides, and molecular sieves, and various membrane systems. Composition of the raw gas and the amount of impurities that can be tolerated in the product determine the selection of the most suitable process. 

Polyurethane, PVC, and extruded polystyrene provide the bulk of the cellular plastics used for low and cryogenic temperature appHcations. In some cases, eg, the insulation of Hquid hydrogen tanks on space systems, foams have been reinforced with continuous glass fibers throughout the matrix. This improves strength without affecting thermal performance significantly. 

NASA is also considering a more advanced aircraft such as Mach 5 to cut Pacific travel time to about three hours, but in this case kerosene fuel is no longer acceptable, and Hquefted natural gas or Hquefted hydrogen would be needed to provide the necessary cooling and stabiUty. However, a completely new fueling system would be required at every international airport to handle these cryogenic fluids. 

As in the case of the salt complexation processes, the cryogenic systems require prepuriftcation of the feed gas. Bulk water, hydrogen sulfide, and carbon dioxide are removed by standard techniques. Final removal of these materials is accompHshed by adsorption. After prepuriftcation, the gases are ready for cryogenic processing. 

Most refinery/petrochemical processes produce ethylene that contains trace amounts of acetylene, which is difficult to remove even with cryogenic distillation. Frequently it is necessary to lower the acetylene concentration from several hundreds ppm to < 10 ppm in order to avoid poisoning catalysts used in subsequent ethylene consuming processes, such as polymeri2ation to polyethylene. This can be accompHshed with catalytic hydrogenation according to the equation. 

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