Fundamental kinetic modeling of the catalytic reforming process

In this work, a fundamental kinetic model for the catalytic reforming process has been developed. The complex network of elementary steps and molecular reactions occurring in catalytic reforming has been generated through a computer algorithm characterizing the various species by vectors and Boolean relation matrices. The algorithm is based on the fundamental chemistry occurring on both acid and metal sites of the catalyst. Rates are expressed for each of the elementary steps involved in the transformation of the intermediates. The Hougen-Watson approach is used to express the rates of the molecular reactions occurring on the metal sites of the catalyst. The single event approach is used to account for the effect of structure of reactant and activated complex on the rate coefficients of the elementary steps occurring on the acid sites. This approach recognizes that even if the number of elementary steps is very large they belong to a very limited number of types, and therefore it is possible to express the kinetics of elementary steps by a reduced number of parameters. In addition, the single event approach leads to rate coefficients that are independent of the feedstock, due to their fundamental chemical nature. The total number of parameters at isothermal conditions is 45. To estimate these parameters, an objective function based upon the sum of squares of the residuals was minimized through the Marquardt algorithm. Intraparticle mass transport limitations and deactivation of the catalyst by coke formation are considered in the model. Both the Wilke and the Stefan-Maxwell approaches were used to calculate the concentration gradients inside of the particle. The heterogeneous kinetic model was applied in the simulation of the process for typical industrial conditions for both axial and radial flow fixed bed reactors. The influence of the main process variables on the octane number and reformate volume was investigated and optimal conditions were obtained. Additional aspects studied with the kinetic model are the reduction of aromatics, mainly benzene. The results from the simulations agree with the typical performance found in the industrial process.