Molecular sieves hydrogen purification with

The separation factors are relatively low and consequently the MR is not able to approach full conversion. With a molecular sieve silica (MSS) or a supported palladium film membrane, an (almost) absolute separation can be obtained (Table 10.1). The MSS membranes however, suffer from a flux/selectivity trade-off meaning that a high separation factor is combined with a relative low flux. Pd membranes do not suffer from this trade-off and can combine an absolute separation factor with very high fluxes. A favorable aspect for zeoHte membranes is their thermal and chemical stability. Pd membranes can become unstable due to impurities like CO, H2S, and carbonaceous deposits, and for the MSS membrane, hydrothermal stability is a major concern [62]. But the performance of the currently used zeolite membranes is insufficient to compete with other inorganic membranes, as was also concluded by Caro et al. [63] for the use of zeolite membranes for hydrogen purification. 

Purification. The commercial solvent, made by addition of SOj to butadiene and hydrogenation, contains various contaminants. One method of purification is by passage through a column of Linde molecular sieves and fractionation. Another is by repeated vacuum distillation from sodium hydroxide pellets until a mixture of 1 ml. with 1 ml. of 100% sulfuric acid developes no color in 5 min. the solvent is then distilled again from calcium hydride. Another involves treatment with permanganate and sulfuric acid to remove oxidizable impurities, addition of enough sodium pyrosulfite to give a clear solution, extraction with methylene chloride, treatment with P Os, decantation, and distillation. 

Commercially available chlorosilanes can be used normally without further purification. Chlorosilanes stored in a laboratory for a long time may contain siloxanes by hydrolysis. They are purified by distillation before use. Hydrogen chloride contained in chlorosilanes sometimes prohibits reactions. In this case, chlorosilanes are treated with molecular sieves and potassium carbonate. 

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