A single events microkinetic model for hydrocracking of vacuum gas oil

International audienceThe single events microkinetic modeling approach is extended to include saturated and unsaturated cyclic molecules, in addition to straight chained paraffins. The model is successfully applied to hydrocracking (HCK) of a hydrotreated Vacuum Gas Oil (VGO) residue in a pilot plant, under industrial operating conditions, on a commercial bi-functional catalyst. The molecular composition of the VGO feed is obtained by reconstruction based on a combination of analytical data (SIMDIS, GCxGC, mass spectroscopy). The necessary extensions to the single events methodology, which has previously only been applied to much simpler reacting systems (i.e. HCK of paraffins) are detailed in this work. Feeds typically used in the petrochemical industry typically contain a far more complex mixture of hydrocarbons, including cyclic species (i.e. naphtenes & aromatics). A more complex reaction network is therefore required in order to apply a single events model to such feeds. Hydrogenation, as well as endo-and exo-cyclic reactions have been added to the well-known acyclic β-scission and PCP-isomerization reactions. A model for aromatic ring hydrogenation was included in order to be able to simulate the reduction in aromatic rings, which is an important feature of HCK units. The model was then applied to 8 mass balances with a wide range of residue conversion (20 – 90%). The single events model is shown to be capable of correctly simulate the macroscopic effluent characteristics, such as residue conversion, yield structure, and weight distribution of paraffinic, naphthenic, and aromatic compounds in the standard cuts. This validates the overall model. The single events model provides far more detail about the fundamental chemistry of the system. This is shown in a detailed analysis of the reaction kinetics. The evolution of molecule size (i.e. carbon number), number of saturated/unsaturated rings, or the ratio of branched and un-branched species can be followed along the reactor. This demonstrates the explanatory power of this type of model. Calculations are performed on the IFPEN high performance computing cluster, with parallelization via MPI (message passing interface). This was very useful in order to reduce time consuming problems especially for the parameter fitting step.

Kinetic Modeling of Vacuum Gas Oil Hydrotreatment using a Molecular Reconstruction Approach

International audienceVacuum Gas Oils (VGO) are heavy petroleum cuts (boiling points ranging from 350 to 550 ˚C) that can be transformed into valuable fuels (gasolines, diesels) by fluid catalytic cracking or hydrocracking. Prior to these conversion processes, hydrotreating is required in order to eliminate the impurities in VGOs. The hydrotreatment process enables to meet the environmental specifications (total sulfur contents) and to prevent nitrogen poisoning of conversion catalysts. In order to develop a kinetic model based on an accurate VGOs molecular description, innovative analytical tools and molecular reconstruction techniques were used in this work. A lumped model using a Langmuir-Hinshelwood representation was developed for hydrodearomatization, hydrodesulfurization and hydrodenitrogenation of the VGO. This lumped model was successfully applied to the experimental feed pretreatment data and was able to predict evolution of concentration of the aromatics, nitrogen and sulfur species

New insight on competitive reactions during deep HDS of FCC gasoline

Dos Santos, N. Dulot, H. Marchal, N. Vrinat, M.In order to satisfy requests for high purity fuel, sulfur compounds have to be removed selectively from FCC gasoline with a minimum of olefins hydrogenation and recombination between olefins and H2S (product of hydrodesulfurization) to form thiols. Competition between hydrodesulfurization (HDS) and olefin hydrogenation (HYD) is truly a non-trivial subject. In this study, the impact of H2S on reactivity and selectivity has been studied for model compounds (3-methylthiophene and 1-hexene in heptame) under operating conditions allowing kinetic studies. Formation of C-6-thiols appears to be under thermodynamic control. Inhibition of H2S on both HDS and HYD reactions has been demonstrated. Moreover, inhibition of olefins on HDS and of 3MT on hydrogenation have been observed. This competition between HYD and HDS reactions is an argument in favor of an adsorption of both olefin and sulfur compounds on the same active sites. (C) 2008 Elsevier B.V. All rights reserved

Comparing hydrocracking models : continuous lumping vs. single events.

International audienceDevelopment of models for industrial hydrocrackers has received a great amount of attention by the scientific community over the past decades. Two fundamentally different modelling approaches are compared in this paper: a continuous lumping model with three families (paraffins, naphthenes, and aromatics) and a single events microkinetic model. The aim is to demonstrate the differences in the capabilities of the two modelling frameworks. Both models are capable of simulating experimental data from hydrocracking of a pre-treated Vacuum Gas Oil in a pilot plant at industrial conditions. The continuous lumping model provides better results of the macroscopic effluent characteristics, such as yield structure and PNA (Paraffin, Naphthene, Aromatic) distribution in the middle distillate cut. It requires only the feed SIMDIS (Simulated Distillation) and PNA composition to be known. The single events model, on the other hand, provides information which is not available in a simple continuous lumping model. An analysis of the reaction kinetics of paraffins and mono-naphthenes is performed to demonstrate this aspect. The single events model is far more complex and computationally expensive than the continuous lumping model. In conclusion, the two approaches should be considered complementary rather than competitive. In conjunction, they can be used to balance the drawbacks of each individual modelling approac