Abstract submitted to ICOSCAR3 with the topic: Modeling and scale-up of structured reactors and
microreactors
NUMERICAL SIMULATION OF CATALYTIC CRACKING OF N-HEPTANE
IN MONOLITH REACTOR
XU Min, LIU Hui*, JI Shengfu, and LI Chengyue
(State Key Laboratory of Chemical Resource Engineering，
Beijing University of Chemical Technology, Beijing 100029, China)
SHAO Qian, TIAN Huiping
(Research Institute of Petroleum Processing, SINOPEC, Beijing 100083, China)
Objective
Monolith catalyst (structured catalyst) and reactors have a lot of advantages over conventional
pellet catalyst in macro-kinetics of heterogeneous catalytic reactions and transport performances.
Many previous studies put emphasis on the investigation of mass transfer and reaction
characteristics of monolith catalyst for catalytic conversion of small organic molecules, however,
modeling and simulation of monolith reactors for chemical/petrochemical and petroleum refining
applications, have received little attention [1]. The major objective of the present work is to
numerically explore the applicability and potentials of monolith catalyst bed reactors to a complex
cracking reaction system.
Model and simulation method
A 1-D non-steady heterogeneous model for predicting the distribution of products of catalytic
cracking of n-heptane in monolith catalysts was developed, in which the cracking reactions within
the porous washcoat were described by a complex transient microkinetic model [2] that
incorporates the protolytic scission, β-scission, adsorption and desorption, chain-growth and
hydride-transfer events in the reaction scheme, and considers 55 reacting species (18 paraffins, 18
olefins and 19 carbenium ions). The set of model equations were solved by the method of lines.
Major results
Variation in reactive species concentration within the bulk gas phase with TOS
(time-on-stream) was computed, and the spatiotemporal concentration patterns of the species and
especially the carbenium intermediates adsorbed on the catalyst surface in the washcoat was
simulated. The effects of varying feed rates, washcoat thickness and material properties of
washcoat layer on reactor performance were investigated. Coupling of the internal mass transfer
resistance of the washcoat with the complicated chemical kinetics were analyzed. Coke formation
in the washcoat layer was also discussed. It is demonstrated that C3 and C4 olefin products are the
key products in catalytic cracking process of n-heptane. C3 and C4 products have a higher
selectivity than those heavier species, and C3 and C4 products increase with TOS. The feed rates
were found to be an important operation parameter influencing products distribution. Higher feed
rates or short contact times lead to higher selectivity to C3 and C4 olefins.
Reference
[1] J.W. Chen, H. Yang, N. Wanga, Z. Ring, T. Dabros, Mathematical modeling of monolith catalysts and reactors
for gas phase reactions. Applied Catalysis A: General 345 (2008) 1–11.
[2] H. Carabineiro, C.I.C. Pinheiro, F. Lemos, F. R. Ribeiro, Transient microkinetic modelling of n-heptane
catalytic cracking over H-USY zeolite. Chemical Engineering Science 59 (2004) 1221-1232.
*
Corresponding author: LIU Hui. E-mail: hliu@mail.buct.edu.cn (H. Liu)