Applied Catalysis A: General 223 (2002) 103–119 Synergy effects of ZSM-5 addition in fluid catalytic cracking of hydrotreated flashed distillate Marion A. den Hollander, Marieke Wissink, Michiel Makkee ∗ , Jacob A. Moulijn Department of Delft Chemical Process Technology, Section of Industrial Catalysis, Faculty of Applied Sciences, Delft University of Technology, Julianalaan 136, NL 2628 BL Delft, The Netherlands Received 20 April 2001; received in revised form 29 June 2001; accepted 3 July 2001 Abstract The effects of ZSM-5 addition in fluid catalytic cracking (FCC) are evaluated. Addition of ZSM-5 to the base catalyst in cracking of a hydrotreated flashed distillate at different residence times has as main result a higher production of LPG-range olefins. The results show that this is not solely caused by cracking of gasoline-range olefins by ZSM-5. ZSM-5 is able to produce LPG-range olefins (and gasoline) by cracking of feedstock-range hydrocarbons, probably after pre-cracking of a part of the paraffinic feedstock by the base catalyst or by thermal cracking. In the presence of the base catalyst, the activity of ZSM-5 for HCO cracking is comparable to the activity of the base catalyst and more than an order of magnitude larger than the activity of pure ZSM-5. Afterwards, when this pre-cracked feedstock has been consumed and significant amounts of gasoline-range olefins have become available, additional LPG-range olefins are produced by cracking of these gasoline-range olefins over the ZSM-5 additive. From a qualitative discussion of the results and a simple kinetic model it was concluded that the synergy is due to a combination of cracking of the feedstock molecules by the base catalyst and subsequently cracking of the olefins produced by the ZSM-5 catalyst. © 2002 Elsevier Science B.V. All rights reserved. Keywords: ZSM-5; Paraffinic feedstock; Gasoline; FCC-catalyst; Entrained flow reactor; Modelling 1. Introduction One of the incentives to use ZSM-5 additives in fluid catalytic cracking (FCC) operation is the in- creased yield of light, LPG-range, olefins that are important feedstocks for numerous petrochemical processes [1–6]. Typically, the addition of ZSM-5 results in a higher yield of light olefins, partly at Abbreviations: CCR, Conradson carbon residue; gln, gasoline; HCO, heavy cycle oil; HTFD, hydrotreated flashed distillate; LCO, light cycle oil; LPG, liquefied petroleum gas (C 3 and C 4 ); Ssres, sum of squared residuals ∗ Corresponding author. Tel.: +31-15-278-1391; fax: +31-15-278-5006. E-mail address: m.makkee@tnw.tudelft.nl (M. Makkee). the expense of gasoline yield, although the gasoline octane number increases [6–9]. ZSM-5 can be added as a separate additive, or it can be incorporated into the base FCC catalyst. The use of separate additives has the advantage of a higher flexi- bility; the ratio between the base catalyst and ZSM-5 can be relatively easy changed through a change in the addition rate of the ZSM-5 additive in comparison to the withdrawal of equilibrium catalyst from the indus- trial unit [6,9–11]. The ZSM-5 additives typically are a composite of ZSM-5 crystals in a non-active porous matrix of silica and/or alumina. The concentration of ZSM-5 crystals in such additives range from about 15 to 25 wt.%. The amount of ZSM-5 used in FCC units ranges from 0.2 to 3 wt.% of the total catalyst inven- tory [9,11,12]. 0926-860X/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S0926-860X(01)00746-3