Cycling with impure hydrogen

May use impure gases (rather than UHP hydrogen) and cycle with fresh charges or use the same impure gas. 

It is important to remove all oxygen, dienes and acetylenes from the feed to the metathesis reactor. Furthermore, the C4 stream needs to contain the minimum practical level of butene-1 and isobutene to minimize the metathesis reaction of the C4 hydrocarbons, which results in the formation of C5 and Ce olefins. The higher olefins lead to polymer formation and catalyst deactivation. An excess of ethylene normally suppresses the C4 reactions. A typical steam cracker C4 stream, which has been subjected to selective hydrogenation to remove impurities and fractionation to provide a suitable butene-2 rich raffinate-2, or the butene-2 rich efflnent from an MTBE unit, can provide a suitable feed for the metathesis reactor. The catalyst operating cycle with a rhenium catalyst is usually fairly long. Regular catalyst regeneration may be necessary and the catalyst can last for several years. 

Active Carbon. The process of adsorbiag impurities from carbon dioxide on active carbon or charcoal has been described ia connection with the Backus process of purifyiag carbon dioxide from fermentation processes. Space velocity and reactivation cycle vary with each appHcation. The use of active carbon need not be limited to the fermentation iadustries but, where hydrogen sulfide is the only impurity to be removed, the latter two processes are usually employed (see Carbon, activated carbon). 

The lead precursor in PbSe film deposition was lead acetate complexed with triethanolamine. The growth rate for PbSe was 0.18-0.16nm/cycle. The films were polycrystalline (i.e., cubic) without preferred orientation. The stoichiometry of SILAR-grown PbSe was found to be 1 1 within the limits of the RBS technique. Impurities detected were 5 at.% of oxygen and 8 at.% of hydrogen.103... 

Ilmenite ore is treated with sulfuric acid the sediment of iron sulfate is filtered off. The solution is cooled to 0 °C, saturated with hydrogen chloride and mixed with solid potassium chloride. This forms a deposit of potassium chlorotitanate K2TiCU., which is not soluble in water. The salt is separated (in the filter) and sent into a rotating furnace to be heated to 300-500 °C and disintegrated. The disintegration releases vapours of titanium tetrachloride, which are sent to condense the sediment of potassium chloride is returned into the cycle. The titanium tetrachloride produced by this technique is veiy pure, since most impurities remain in the mother waters. 

Hydrogen, which is highly volatile and non-polar or polarizable, is, when mixed with various impurities, practically unadsorbable, and is hence easy to purify by this method. The regeneration of adsorbent beds which have fi.xed the other components is usually carried out by raising the temperature obtained by a stream of hot gas which also acts as the desorbent the restoration of adsorption conditions then requires the beds to be cooled. These heat transfers are slow, making the process inapplicable to rapid cycles, and restricts it to the separation of small amounts of impurities. 

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