Objective Optimize the process flow of an industrialized isobutylene selective dimerization unit.

Methods (1) Add water washing tower to remove metal cations and alkali nitrogen compounds from C₄ raw materials. (2) Remove the related pipelines and equipment used to directly inject TBA into the catalytic distillation tower. (3) Use a three-tower pressure-swing distillation process including "catalytic distillation tower + high pressure tower + low pressure tower" to separate TBA-diisobutylene azeotropes. (4) Remove the external circulating loops used to control the temperature rise of the reactors.

Results (1) Reduced the mass fraction of metal ions and basic nitrides in C₄ to less than 1 mg/kg, which could ensure the long-term operation of the catalyst. (2) The dissolved water and free water from the water washing tower, which were azeotropic with C₄ components, were used as inhibitors for the dimerization reactions of catalytic distillation tower, which reduced the TBA consumption and equipment cost and simplified the process. (3) Dimers with TBA mass fraction equal or lesser than 100 mg/kg and TBA with purity greater than 99.99% could be obtained from high-pressure tower and low-pressure tower respectively. (4) Under the same conditions, the amount of side reaction products caused by the backmixing of reaction products was reduced, the selectivity of diisobutylene was increased by 3%-7%, and the amount of catalyst used in the reactors was reduced by 20%-40%.

Conclusion After optimizations, the unit could produce high purity diisobutylene product and reduce energy consumption.