Abstract

The Dung Quat refinery is exploring solutions to increase the yields of light olefins, especially propylene, to meet the rising demand for petrochemical industry materials, specifically for the Polypropylene plant. This study also investigates the yields of other products, such as gasoline and LCO. Although various methods can be used to address this issue, such as changing operating parameters or using catalysts with high Si/Al ratios, adjusting the ZSM-5 additive ratio has been found to be the most effective and flexible approach. Because an experimental study of this kind would require a Residue Fluid Catalytic Cracking (RFCC) pilot plant and would be both time-consuming and expensive, a steady-state model of the R2R (Reactor - two Regenerators) configuration of the RFCC unit at Dung Quat refinery was developed in Aspen Hysys, using the built-in FCC module together with the Peng-Robinson fluid package. The model was set up for the atmospheric residue of Bach Ho crude oil and was calibrated against plant operating data: the deviations in the flow rates of light ends, naphtha, LCO and bottoms, as well as in the riser outlet temperature, all remained below 5.5%, which confirms that the model is reliable for parametric investigation. The ZSM-5 content in the catalyst inventory was then varied from 0 to 20 wt% and the resulting product yield structure was analysed. The simulation results from the Hysys program indicate that adding less than 2.5% ZSM-5 additive can make the mass flow of LPG in the outlet gas stream increase by nearly 7% higher than initial capacity without changing the configuration of the related unit in the refinery. By adding 20% ZSM-5 additive leads to nearly triple the propylene yields and increase the yield of LPG to 31.15 wt%. However, gasoline yields decreased by 15 wt%. The gasoline composition was also analyzed, revealing that the amount of paraffins and olefins decreased while cyclic components, such as naphthene and aromatics, increased. Furthermore, the addition of ZSM-5 additive increased olefin branching, improving gasoline quality with a higher octane number. Quantitatively, the propylene yield rises from 3.80 wt% to 10.74 wt% and the octane number of the cracked gasoline increases from 89.82 to 98.64 when the ZSM-5 content is raised from 0 to 20 wt%. These results provide a quantitative basis for selecting a suitable ZSM-5 dosing strategy at Dung Quat refinery, balancing the propylene demand of the downstream Polypropylene plant against the loss of gasoline yield and the capacity limit of the Propylene Recovery Unit.