Jan Verstraete

Molecule-based kinetic modeling by Monte Carlo methods for heavy petroleum conversion

A methodology for kinetic modeling of conversion processes is presented. The proposed approach allows to overcome the lack of molecular detail of the petroleum fractions and to simulate the reactions of the process by means of a two-step procedure. In the first step, a synthetic mixture of molecules representing the feedstock is generated via a molecular reconstruction method, termed SR-REM molecular reconstruction. In the second step, a kinetic Monte Carlo method, termed stochastic simulation algorithm (SSA), is used to simulate the effect of the conversion reactions on the mixture of molecules. The resulting methodology is applied to the Athabasca vacuum residue hydrocracking. An adequate molecular representation of the vacuum residue is obtained using the SR-REM algorithm. The reaction simulations present a good agreement with the laboratory data for Athabasca vacuum residue conversion. In addition, the proposed methodology provides the molecular detail of the vacuum residue conversion throughout the reactions simulations.

Industrial Development and Operation of an Efficient Riser Separation System for FCC Units

With over 300 units in operation, Fluid Catalytic Cracking (FCC) is currently the dominant refinery conversion process. Over the last years, rapid separation of hydrocarbon vapors and catalyst at the riser outlet has been put forward to limit non-selective decomposition of reaction products, thus enhancing product selectivities.A new riser separator system, called RS², was developed to minimize post-riser cracking, while maintaining flexibility of operation. The development included cold flow testing, CFD and pilot plant testing, and aimed at minimizing both thermal degradation and catalytic overcracking. Cold flow testing was conducted at a representative scale (scale 1/10th) on a large cold flow mock-up. Testing various riser separator configurations provided a thorough understanding, both through visual observations, pressure drop measurements and tracer studies. Hot pilot plant testing was conducted to investigate the effect on yields of the riser separation system in the reactor-stripper under adiabatic operation as a function of operating conditions. The separator had a significant impact on the FCC heat balance and a large reduction of dry gas yield was observed.The resulting technology was successfully implemented on an industrial resid catalytic cracking unit. Operation of the separator was proven smooth and flexible with enhanced performance, while the industrial observations confirm the R&D conclusions. This paper therefore summarizes the R&D study and the industrial operation trends. In particular, the impact of stripper bed level on operation is discussed and explained based on the flow phenomena and design aspects.

Tortuosity and mass transfer limitations in industrial hydrotreating catalysts: effect of particle shape and size distribution

The tortuosity factor of γ-alumina supports and catalysts used in hydrotreating applications was evaluated in the liquid phase with three different techniques: pulse field gradient-NMR (PFG-NMR), inverse liquid chromatography (ILC) and catalytic experiments in a batch reactor. In order to satisfy the specific experimental constraints associated with each technique, tortuosity factors were evaluated in a wide range of operating conditions: temperature was varied from 295 K to 613 K, catalyst particles were used as-synthesized (trilobe extrudates) or crushed, and the liquid composition was either pure toluene, n-heptane/squalane mixtures, or squalane/2,5-bis-(octadecyl)thiophene mixtures. It is demonstrated that not taking into account both the shape factor and the size distribution of the particles can lead to significant errors in the tortuosity factor. For both parameters, the optimal mean spherical radius depends on the contribution of internal diffusion to the overall performance. When internal diffusion is the limiting step, a new expression for the mean radius of the distributed particle is proposed and validated by comparison between ILC and PFG-NMR results. This expression is transposable to any catalytic system, making it possible to measure the tortuosity factors using either microscopic or macroscopic methodologies. Moreover, the tortuosity factors obtained with ILC and NMR are in good agreement with the one estimated from the catalytic experiments, showing that mass transfer parameters can be extrapolated from non-reactive to reactive conditions.

Random porous network generation and 1D mass transfer simulation for gamma-alumina supports

A two or three-dimensional pore network is randomly generated by a Monte Carlo approach to represent γ-alumina supports. The network porous structure is obtained by the random interconnection of cylindrical pores. The proposed model allows to correctly represent the catalyst support pore size distribution, the porosity and internal surface area. Transient mass transfer is simulated in 1D within each pore of the network and tortuosity factors are estimated as a function of porosity. Confrontation of the predicted diffusion properties with both theoretical and experimental values from fixed-bed tracer experiments showed that the network structure agrees with theoretical tortuosity-porosity relations. However, real alumina supports exhibit higher tortuosities, which are probably due to the presence of two levels of porosities.