| http://www.w3.org/ns/prov#value | - C comprises cracked mainly unsaturated aliphatic hydrocarbons having 4 to 5 carbon atoms such as butene, butadiene, pentene, pentadiene, etc.The composition of the most preferred of such fractions is, for example, unsaturated C.sub.4 and C.sub.5 fraction having the following composition.______________________________________ C.sub.4 and C.sub.5 olefins 40 to 70 wt.% C.sub.4 and C.sub.5 diolefins 2
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