Fluid Catalytic Cracking V

M.L. Occelli, P. O'Connor

• Editore: Elsevier Science
• Anno: 2001
• ISBN:
  9780080531717
• Argomento: Technology & Engineering
• Categoria: Chemical & Biochemical Engineering

Catalyst production for the transformation of crudes into gasoline and other fuel products is a billion dollar/year business and fluid cracking catalysts (FCCs) represent almost half of the refinery catalyst market. During the cracking reactions, the FCC surface is contaminated by metals (Ni, V, Fe, Cu, Na) and by coke deposition. As a result, the catalyst activity and product selectivity is reduced to unacceptable levels thus forcing refiners to replace part of the recirculating equilibrium FCC inventory with fresh FCC to compensate for losses in catalyst performance. About 1, 100 tons/day of FCC are used worldwide in over 200 fluid cracking catalyst units (FCCUs). It is for these reasons that refiners' interest in FCC research has remained high through the years almost independantly, of crude oil prices. However, recent oil company mergers and the dissolution of research laboratories, have drastically decreased the number of researchers involved in petroleum refining research projects; as a result the emphasis of research has shifted from new materials to process improvements and this trend is clearly reflected in the type of papers contained in this volume. Modern spectroscopic techniques continue to be essential in the understanding of catalyst performance and several chapters in the book describe the use of 27 Al, 29 Si and 13 C NMR to study variation in FCC acidity during aging and coke deposition. In addition several chapters have been dedicated to the modeling of FCC deactivation, and to the understanding of contact times on FCC performance. Refiners efforts to conform with environmental regulations are reflected in chapters dealing with sulfur removal, metals contaminants and olefin generation.

Development of a Kinetic Model for FCC valid from Ultra-Short Residence Times

M.A. den Hollander^{† †} Current address: Shell Global Solutions International, P.O. Box 38000, 1030 BN, Amsterdam, The Netherlands

M. Makkee*; J.A. Moulijn Industrial Catalysis, Department of Chemical Technology, Faculty of Applied Sciences, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands
^* Corresponding author email address: [email protected]

Abstract

Experimental data from Hydrowax cracking using the microriser equipment have been used to develop a kinetic model that adequately describes the experimental data from 0.05 to 5 s residence time. To account for different time scales of the reactions, different activity functions were used for coke formation and for conversion to the other products. The activity for coke formation was described by an exponentially decreasing function of the residence time with a very short characteristic time of 0.02 s. The activity for formation of the other products was also described by an exponentially decreasing function, in this case of the coke content of the catalyst.

The model was used to predict the residual activity of the catalyst in a second experiment with flesh Hydrowax feedstock. Using the assumption that in the second run no further deactivation of the catalyst took place, the model predictions agreed well with the experimental data.

The applicability of the model to data from other feedstocks, a hydrotreated flashed distillate and a vacuum gas oil, was successfully demonstrated.

Keywords

riser reactor

modeling

deactivation

coke

residual activity

1 INTRODUCTION

An industrial FCC unit is operated in a heat-balanced mode; in the regenerator coke is burnt from the catalyst thereby providing the heat that is needed for the evaporation and cracking of the feed in the reactor. Therefore, an important operating parameter is the amount of coke deposited on the catalyst in the reactor. Generally, coke formation in FCC can take place in two different time scales: firstly, deposition of coke upon the first contact of the catalyst with a feedstock that contains coke precursors (thermal coke, soaking coke from liquid droplets, extremely reactive hydrocarbons, etc.), and secondly, the catalytic formation of coke as a side-product of cracking due to hydrogen transfer, condensation, and dehydrogenation reactions [1,2]. To be able to discriminate between these two coking regimes, the experimental set-up should have the ability to discriminate between reactions on a millisecond time scale (deposition of coke) and reactions on a longer time scale (cracking reactions with coke as a side product).

The microriser is a laboratory-scal...