Hydrogen separation approaches

FIGURE 6.36 Two hydrogen atoms approach one another. The protons are separated by the distance Rab-(a) At large values of Rab each electron interacts only with the proton to which it is bound, (b) As the atoms approach closer, both electrons interact with both protons. The distance of electron 1 from nuclei A and B is given by /"lA, /"ib the distance of electron 2 from nuclei A and B is given by r2B, the distance between the electrons is given by... 

The properties of the linear chain of atoms fall into three sets those for the intramolecular, the intermolecular and the closed-shell Ne-H interactions. The intramolecular bond lengths vary from Re = 1.39 au, the equilibrium value to 1.04 au obtained for the central molecule in the Ne H6 Ne vise at a pressure of 158 GPa. Only at the highest pressures do the intermolecular separations approach Re. Unlike the LDA calculations on solid hep hydrogen, no increase in separation over Re is found for high pressures. The Ne-H separations decrease at a slower rate. 

Atmospheric pressure CVD of NbCi-yN, using NbCl, NH3, and CH4 has been employed in three separate approaches toward the optimization of reaction characteristics [69]. These were (i) simultaneous deposition of niobium, carbon, and nitrogen by hydrogen reduction of NbCls with decomposition of methane and ammonia at a temperature of 900-1000°C (ii) deposition of a niobium amide complex derived from NbCl.s/NHi in nitrogen as a carrier gas at 250-350 °C, and subsequent conversion in ammonia/methane at 1 000-1 100 °C (iii) separate deposition of elemental niobium or NbCl.3 by hydrogen reduction at 500-1000°C and subsequent conversion to NbCi yNy in an ammonia/methane atmosphere at 1000-1 100°C. The results of these three approaches are given below. 

In this chapter, the most popular approaches for hydrogen production from H2S are reviewed before a novel open reactor architecture (OA) is presented, where the coupling of reaction and hydrogen separation is achieved in the series of consecutive conventional catalytic reactors (CR), each followed by a membrane separator (MS). Experimental study on the development of a suitable H2S decomposition catalyst is also presented, and the theoretical calculations for one... 

A same approach has been used by Karnik and co-workers who successfully produced Pd-based membrane via micro-fabrication and used it for hydrogen separation. The authors were able to design and fabricate a micro-reactor that was used for hydrogen separation however, the support (or a part of it) for the micro-membrane is made of copper, which is also active catalyst for WGS reaction. The reactor can be thus used for on-board hydrogen production for micro-fuel cell applications. 

Examples and Applications An example of the above approaches has been demonstrated for hydrogen separation. An SSF membrane (Sircar et al., 1999) was formed by coating a thin layer of polyvinylidene chloride-acrylate terpolymer latex containing 0.1 -0.14 mm polymer beads in an aqueous emulsion on the bore side of a macroporous alumina tube (0.56 cm internal diameter, 0.16 cm wall thickness). The latex was dried at 50°C under N2 and subsequently heated to 600°C followed by passivation by heating to 200-300°C in an oxidizing atmosphere. The resulting carbon membrane has a pore size of 5-7 A and a thickness of 2-3 p.m. 

The types of interactions that occur as two hydrogen atoms, infinitely separated, approach each other. The dashed lines represent the types of interactions (red for attractive interactions and blue and black for repulsive interactions). The solid black line represents the internuclear distance, r, between the two hydrogen atoms. 

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