Described herein are compositions having an eight-membered monocyclic unsaturated hydrocarbon, methods and system to separate the eight-membered monocyclic unsaturated hydrocarbon at from a hydrocarbon mixture including additional nonlinear unsaturated C.sub.8H.sub.2m hydrocarbons with 4m8, by contacting the hydrocarbon mixture with a 10-ring pore molecular sieve having a sieving channel with a 10-ring sieving aperture with a minimum crystallographic free diameter greater than 3 and a ratio of the maximum crystallographic free diameter to the minimum crystallographic free diameter between 1 and 2, the molecular sieve having a T1/T2 ratio 20:1 wherein T1 is an element independently selected from Si and Ge, and T2 is an element independently selected from Al, B and Ga, the 10-ring pore molecular sieve further having a counterion selected from NH.sub.4.sup.+, Li.sup.+, Na.sup.+, K.sup.+ and Ca.sup.++.

A cyclic diene-containing composition having a content of a cyclic diene of 99.5 GC area % or less and a content of a cyclic monoene of 3.0 GC area % or less. A method for producing an aldehyde, the method including subjecting a cyclic diene in a cyclic diene-containing composition to a hydroformylation reaction to produce a corresponding aldehyde, wherein the method includes controlling a content of a cyclic monoene contained in the cyclic diene-containing composition to a predetermined threshold (1) or less. A method for producing a cyclic diene-containing composition, the method including performing distillation and purification of a hydrocarbon decomposition product obtained by thermal decomposition of a hydrocarbon-containing composition to produce a cyclic diene-containing composition containing a cyclic diene, wherein the method includes controlling a content of a cyclic monoene contained in the cyclic diene-containing composition to a predetermined threshold (1) or less.

A method for preparing paraxylene by biomass conversion includes the following steps: (1) contacting a biomass starting material with a hydrogenation catalyst for reaction in a multiphase system formed by an organic solvent, an inorganic salt and water, in the presence of hydrogen as a hydrogen source, and separating the resulting product to obtain an organic phase comprising 2,5-hexanedione; and (2) contacting the organic phase comprising 2,5-hexanedione obtained in the step (1) and ethylene with a molecular sieve catalyst for reaction to obtain paraxylene. The molecular sieve catalyst is at least one selected from the group consisting of aluminophosphate molecular sieves and SCM-14 molecular sieves.

A method for preparing paraxylene by biomass conversion includes the following steps: (1) contacting a biomass starting material with a hydrogenation catalyst for reaction in a multiphase system formed by an organic solvent, an inorganic salt and water, in the presence of hydrogen as a hydrogen source, and separating the resulting product to obtain an organic phase comprising 2,5-hexanedione; and (2) contacting the organic phase comprising 2,5-hexanedione obtained in the step (1) and ethylene with a molecular sieve catalyst for reaction to obtain paraxylene. The molecular sieve catalyst is at least one selected from the group consisting of aluminophosphate molecular sieves and SCM-14 molecular sieves.