C9 Aromatic Isomerization to Trimethylbenzenes

The patent changes the reaction parameter from carbon-removing reactions (dealkylation, hydrogenolysis) to carbon-preserving isomerization reactions. By using a bifunctional catalyst with specific properties (metal function for dehydrogenation, acid function for isomerization), the reaction pathway is changed to rearrange alkyl groups rather than remove them, thereby maximizing methyl group availability while avoiding carbon loss.

Instead of removing alkyl groups to produce methyl-substituted aromatics (conventional approach), the patent inverts the approach by isomerizing existing alkyl groups into methyl groups through rearrangement. This inversion of the reaction strategy transforms C9 aromatics with long alkyl chains into C9 aromatics with multiple methyl groups, achieving the desired product distribution without carbon loss.

The patent employs a bifunctional catalyst that combines two distinct functional components: a metal function (e.g., Pt, Pd, Ni) for dehydrogenation and an acid function (e.g., zeolite, alumina) for isomerization. This composite catalyst structure enables both reaction steps to occur in a single reactor, thereby increasing productivity and yield while the complexity is confined to the catalyst formulation rather than the overall process architecture.

The patent merges two separate reaction functions (dehydrogenation and isomerization) into a single catalytic system. By combining the metal catalyst for dehydrogenation with the acid catalyst for isomerization in one bifunctional catalyst, the process achieves higher productivity through integrated reaction pathways, while the operational complexity remains manageable as a single-reactor system.

The patent specifies precise parameter ranges for the bifunctional catalyst to achieve optimal performance: metal content at 0.01-5 wt% for sufficient dehydrogenation activity, acid site density controlled by Si/Al ratio (10-100) for appropriate isomerization activity, and particle size 0.1-5 mm for optimal mass transfer. These parameter specifications ensure high methyl group production while making the catalyst requirements quantifiable and controllable.

The patent applies local quality by creating distinct functional zones within the bifunctional catalyst: the metal sites provide localized dehydrogenation capability while the acid sites provide localized isomerization capability. This spatial differentiation of catalytic functions within the same catalyst particle allows simultaneous occurrence of both reactions, maximizing methyl group availability while managing catalyst complexity through functional specialization.