Simulation And Analysis Of Industrial Paraffins Separation Process On Molecular Sieve By Simulated Moving Bed Adsorption

The production of linear alkylbenzene was mainly established on UOP's patents, and the related process was composed of hydrofining, deparaffinating over molecular sieve, dehydrogenation and alkylation. Usually, n-paraffins are separated from i-paraffins and aromatic hydrocarbons by Molex process, which uses the simulated moving bed technology. In the present work, Simulation and analysis of industrial paraffins separation process on 5A molecular sieve had been carried out on the basis of true process conditions of Nanjing alkylbenzene factory. A model for the simulation of the cyclic steady-state performance of SMB was developed based on the analogy with the transients true moving bed (TMB) system. The model is composed of axial dispersion flow for bulk fluid phase, linear driving force (LDF) for mass transfer rate and competitive Langmuir adsorption equilibrium. The necessary parameters for simulation calculation were estimated and regressed on the basis of equilibrium data of monocomponent n-paraffins on 5A molecular sieve. Effects of operating variables, such as switch time of rotary valve, extract flow rate, feed flow rate and dsorbent flow rate on SMB performances were analyzed. The SMB performance is characterized by recovery and adsorbent productivity in the present study. The simulated results may provide reference for the optimization of technology design and for the reduction of energy consumption. Computation program of SMB for paraffins separation was compiled in Fortran language, wherein model equations were numerically solved by using the Pdecol package, which based on the method of finite-element collocation, and the complicated SMB process was approximated to TMB process. Simulation results showed that the calculated recovery and adsorbent productivity were in good agreement with those of the real system, which in turn verified the rationality of the adoptive models, computational methods and the corresponding parameters. Many major factors were taken into account in this model, which may be used in the dynamic simulation process for the paraffins separation on molecular sieve due to its higher computational efficiency. The established mathematical model could be applied to the process simulation with arbitrary steps, owing to its similarity with real system, simplicity and accuracy of computational method, and facility operation. Calculation results revealed the relationship between operation parameters and SMB performances, which were beneficial to the optimization and the modeling of the industrial process.