Isobutene dimerisation in a miniplant-scale reactor

A miniplant-scale tubular reactor with an inside diameter of 0.016 m and length of 1.3 m was used to produce 2,4,4-trimethylpentene (isooctene) by dimerizing 2-methylpropene (isobutene). The reaction took place in liquid phase in presence of a solid macroporous ion exchange resin catalyst. The reactor system included an external heating coil with temperature-controlled heat transfer fluid and an axial internal thermowell for temperature probes.The reaction was studied with two reactors in series, varying the feed compositions and temperature set points of the reactors. In addition to the feed and product compositions, the temperature profiles of the reactor were measured.A two-dimensional pseudohomogeneous model for the catalyst bed and separate models for the reaction kinetics and liquid phase activity coefficients were combined with a hardware-specific model, which took both the heating coil and the thermowell into account. Kinetic models for the reactions involved were liquid-phase activity-based, Langmuir–Hinselwood-type models.The simulation model predicted well the measured axial temperature and concentration gradients in the reactor. Calculations revealed significant radial temperature variations inside the catalyst bed, necessitating the use of a two-dimensional model in reactor simulations.Conversions and selectivities of diisobutene given by the model matched well with those obtained from the experiments. Once-through yields up to 65% were measured for diisobutene.