Microporous and Mesoporous Materials 25 (1998) 127–129

Is the catalytic activity of Al-MCM-41 sufficient for hydrocarboncracking?

Heico Koch a, Wladimir Reschetilowski b,*a Karl-Winnacker-Institut der DECHEMA e.V., Theodor-Heuss-Allee 25, D-60486 Frankfurt, Germany

b Institut fur Technische Chemie, Technische Universitat Dresden, D-01062 Dresden, Germany

Received 6 April 1998; accepted 30 April 1998

Abstract

This investigation shows a comparison of Al-MCM-41 with zeolite Y as FCC-catalyst compound. Comparablecracking activities for long-chain hydrocarbons and even increased cracking activities of MCM-41 for bulkyhydrocarbon molecules are observed. © 1998 Elsevier Science B.V. All rights reserved.

Keywords: FCC-catalyst; n-Hexadecane; 1,3,5-Triisopropylbenzene; MCM-41

1. Introduction investigated in a micro activity test (MAT ) accord-ing to ASTM D-3907 for their cracking activityon n-hexadecane and 1,3,5-triisopropylbenzene.The investigation of the mesoporous molecular

sieve, type MCM-41, has been the subject of manypublications in the past few years. A major reasonis their application, such as their catalytic behaviorin processing bulky molecules, e.g. catalytic crack- 2. Experimental and materials investigateding of hydrocarbons. Recently, discussions aboutthe sufficiency of cracking activity of hydrocarbons The materials used are MCM-41 with Si/Alon Al-MCM-41, e.g. the very interesting work of ratios of 3 and 17 compared with zeolite Y (Si/Al=Kim et al. [1], have arisen. Based on the work of 2.6) provided by Chemiewerke Bitterfeld. The syn-Roos et al. [2], cited in Ref. [1], the catalytic thesis, characterization and activation procedureactivity of n-hexadecane cracking has been consid- of the MCM-41 samples has been discussed in aered insufficient. In this study we made a closer previous work [3]. Table 1 shows the textural datainvestigation of the cracking activities of the pure of the MCM-41 in the activated H-form; zeoliteactive compound to show a distinction from the Y is also listed for comparison.optimized FCC catalyst used in Ref. [2] for com- Pretreatment of the catalysts consists of aparison. Therefore Al-MCM-41 and the active calcination step in a shallow bed reactor followedcompound in the FCC catalyst, zeolite Y, were by a temperature program starting at room tem-

perature: RT–120°C, 1°C min−1, in N2 (10 l h−1);* Corresponding author. 120°C for 3 h in N2 (10 l h−1); 120–540°C,

1387-1811/98/$ – see front matter © 1998 Elsevier Science B.V. All rights reserved.PII: S1387-1811 ( 98 ) 00184-X

128 H. Koch, W. Reschetilowski / Microporous and Mesoporous Materials 25 (1998) 127–129

Table 1Materials investigated

Catalyst sample BET surface (m2 g−1) Si/Al ratio Source

Before MAT After MAT

H-Y 985 854 2.6 BitterfeldMCM-41-3 822 607 3.2 IRMAMCM-41-17 849 818 17.3 SINTEF

1°C min−1 in synthetic air (10 l h−1) isothermal (according to ASTM D-3907) with a regenerationwithin the tests and n-hexadecane as model feed.for 12 h.

Catalytic testing was performed in an MAT With the investigated Al-MCM-41 materials it wasfound that the higher the aluminum content theapparatus according to ASTM D-3907 (fixed bed

reactor) and the following standard conditions: lower was the stable activity. However, a higheraluminum content also decreased the deactivationcatalyst mass, 4.0 g±0.05 g; feed, n-hexadecane or

1,3,5-triisopropylbenzene; feed rate, 1.33 g±0.03 g as well as the time to a constant conversion. Arapid partial deactivation of the catalyst samplesin 75 s; temperature, 482–582°C; catalyst-to-oil

ratio, 3; WHSV, 16 h−1; reactor N2 purge, MCM-41-3 and MCM-41-17 (Si/Al ratios 3 and17) to a stable activity was observed. A similar30 ml min−1 for 20 min. This standard was modi-

fied by varying the temperature and the catalyst- deactivation behavior in the first catalytic cycles isa common feature for all MCM-41 samples, whichto-oil ratio.

Analytical characterization of the gaseous pro- implies they have the same types of catalytic activesites. The catalytic activity of MCM-41 materialsduct was carried out using GC-FID. Liquid pro-

ducts were analyzed by detailed hydrocarbon in n-hexadecane cracking at the steady state islower than or at the same level as the acidic zeoliteanalysis (DHA), which means a gas chromato-

graphic system specially optimized for Y, showing that the catalytic activity for theAl-MCM-41 used is not clearly insufficient.hydrocarbons.Detailed characterization data of the samples canbe found in the literature [3], as well as detaileddiscussions of selectivity investigations [4].3. Results and discussion

The large mesopores have not been taken advan-tage of by using n-hexadecane as the model feed,Fig. 1 displays the catalytic activity of cyclic

tested Al-MCM-41 materials and zeolite Y

Fig. 2. Cracking activity of MCM-41 in comparison with thoseFig. 1. Deactivation behavior of different materials in n-hexade- of zeolite Y and of an FCC catalyst under ASTM D-3907 condi-

tions with a bulky feed molecule (1,3,5-triisopropylbenzene).cane cracking under ASTM D-3907 conditions.

129H. Koch, W. Reschetilowski / Microporous and Mesoporous Materials 25 (1998) 127–129

since there is no geometrical hindrance to the inner 4. Conclusionsactive sites of zeolite Y. Conclusively, using

The Al-MCM-41 materials possess a catalytic1,3,5-triisopropylbenzene as the model feed, withcracking activity for long-chain hydrocarbonsa kinetic diameter of 0.94 nm and therefore geo-which is comparable with that of zeolite Y, and ametrical restrictions to the inner centers of zeolitesignificantly increased activity in cracking theY, a complete shift of the cracking activities wasbulky 1,3,5-triisopropylbenze.observed. Fig. 2 shows a comparison of zeolite Y

Therefore we conclude that there is a highand Al-MCM-41 with a similar Si/Al ratio in theirpotential of mesoporous MCM-41 in hydrocarboncracking activity of 1,3,5-triisopropylbenzenecracking activity. Optimization of structural and

under ASTM D-3907 conditions. In addition, the chemical properties might even increase the appli-cracking activity of the stationary FCC catalyst, cation potential.also used by Roos et al. [2], is shown for compari-son. Al-MCM-41 clearly shows a higher crackingactivity at 95 wt.% conversion rate. The conversion Acknowledgementis increased by 27 wt.% in comparison with thatfor zeolite Y. From a comparison of the FCC The authors thank the Commission of the EUcatalyst with Al-MCM-41 the advantage of the for their financial support in the frame of theMCM-41 mesopores is obvious since Al-MCM-41 JOULE II programme as well as SINTEF Appliedalso shows a higher cracking activity of about Chemistry and GRACE GmbH for their helpful

cooperation.15 wt.%.Considering the investigations with the two

different model feeds, it can be deduced that aReferencesgeneral cracking activity of MCM-41 up to the

level of zeolite Y is achievable while the level of[1] J.-H. Kim, M. Tanabe, M. Niwa, Microporous Mater. 10an FCC catalyst with an active matrix for pre-

(1997) 85.cracking cannot be reached (shown by n-hexade- [2] K. Roos, A. Liepold, W. Reschetilowski, R. Schmidt, A.cane cracking). Taking advantage of the meso- Karlsson, M. Stocker, Stud. Surf. Sci. Catal. 94 (1995) 389.

[3] H. Koch, U. Bohmer, A. Klemt, W. Reschetilowski, M.pores, the best cracking rates are obtained usingStocker, J. Chem. Soc., Faraday Trans. 94 (1998) 817.Al-MCM-41, with even better rates than zeolite Y

[4] H. Koch, A. Klemt, A. Taouli, W. Reschetilowski,or an optimized FCC catalyst (shown by Proceedings DGMK Conference C4 Chemistry —

Manufacture and Use of C4 Hydrocarbons, 1997, p. 197.1,3,5-triisopropylbenzene cracking).