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Cracking of Vacuum Gas Oil onMicroporous and Mesoporous CatalystSystems*

By Heico Koch, Klaus Roos, Michael Stöcker, andWladimir Reschetilowski**

Dedicated to Professor Dr.-Ing. Gerhard Emig on theoccasion of his 60 th birthday

1 Introduction

The FCC process (Fluid Catalytic Cracking) has a keyfunction in the field of the more intense treatment of raw oilswith the catalyst being an important factor in the effective-ness of the process. The state-of-the-art catalysts containzeolite Y (gasoline production; 0.74 nm pore size) and ZSM-5 (olefin selective; 0.54 x 0.56 nm pore size) as activecompounds. They can not completely convert the bulkyhydrocarbons, since accessibility to the inner active sites isrestricted by geometrical hindrance. The extra large pore,zeotype materials of the MCM-41 type (2±10 nm pore size),which were developed at the beginning of the 1990s byMobil Oil Corp. [1,2], open up interesting perspectives forthe deeper cracking of heavy oil fractions [3].

In this work the catalytic behavior of microporous andmesoporous solid acids in industrially relevant compositesystems containing zeolite Y, MCM-41, and active SiO2/Al2O3 matrix on cracking hydrocarbons by MAT (Micro-activity Test), standardized by ASTM D-3907 [4a], has beeninvestigated. For the cracking investigations an industrialfeed stock, VGO (Vacuum Gas Oil), was used. Furthermorecomparisons to a state-of-the-art FCC catalyst with regard toselectivity, activity, stability, and the influence of the matrixwere performed. Special attention was paid to meet theprocess requirements of a FCC catalysts, e.g., thermalstability and hydrothermal stability up to 800 �C as well asa good regenerability.

2 Catalyst Systems and Methods

The commercial, stationary FCC catalyst (42.2 wt. %Al2O3; 56.2 wt. % SiO2), subsequently called standardcatalyst, was provided by Grace GmbH and the compositesystem (25 wt. % Al2O3; 75 wt. % SiO2) on the basis ofMCM-41 was provided by Sintef Applied Chemistry. For theformulation of the composite system, zeolite Y in the H formwith a Si/Al ratio of 2.6 and MCM-41 in the as synthesizedform with a Si/Al ratio of 17.3 were used.

The following temperature program was employed toremove the template: room temperature to 120 �C, 5 �Cmin±1, in N2, 10 l h±1; 120 �C for 3 h; 120±540 �C, 5 �C min±1;540 �C for 16 h, in air, 10 l h±1. A threefold ion exchange with0.1 N ammonium nitrate solution at 70 �C for 3 h stirredunder reflux was followed. Afterwards the solid was washedwith deionized water to constant conductivity of the washingsolution and then dried at 120 �C. Prior to catalytic andphysico-chemical measurements the prepared catalysts wereagain calcined as described above. In addition the MCM-41composite system (10 wt. % US-Y, 20 wt. % MCM-41, activematrix) was treated to obtain a second modification: steamtreatment with 100 % steam at 800 �C for 5 h in a movingbed reactor according to ASTM D-4463 [4b].

The thermal and hydrothermal stability of the investigatedcatalyst systems was checked by adsorption and desorptionmeasurements of N2 at ±196 �C after the various treatments.Regenerability was investigated by repeating catalytictesting in the MAT apparatus including a regeneration step.Table 1 summarizes detailed textural and structural data aswell as the nomenclature of the investigated catalystsamples. The stationary FCC catalyst exposes a high thermaland hydrothermal stability and shows no significant changeof textural properties. Results of the surface determinationof the MCM-41 composite systems (cf. Table 1) display highstability during calcination and catalytic testing. The steamtreated sample with 20 % MCM-41 content in the compositesystem shows a significant increase of specific surface, whichis lost after catalytic application. As all composite systemswere stable up to 1000 �C in air no further results will beshown here.

Chem. Eng. Technol. 21 (1998) 5 Ó WILEY-VCH Verlag GmbH, D-69469 Weinheim, 1998 0930-7516/98/0505-0401 $ 17.50+.50/0 401

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[*] Presented by H. Koch at ACHEMA '97, lecture group ReactionEngineering, 10 June 1997 in Frankfurt/Main, Germany.

[**] Dipl.-Ing. H. Koch, Karl-Winnacker-Institut der DECHEMA e.V.,Theodor-Heuss-Allee 25, D-60486 Frankfurt am Main, Germany; Dr.-Ing. K. Roos, Rotan GmbH, Riedstraûe 3, D-67125 Dannstadt,Germany; Dr. rer. nat. M. Stöcker, SINTEF Applied Chemistry, P.O.Box 124 Blindern, N-0314 Oslo, Norway; Prof. Dr. rer. nat. habil. W.Reschetilowski, Technische Universität Dresden, Institut für TechnischeChemie, D-01062 Dresden, Germany.

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Table 1. Investigated catalyst samples.

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Catalytic investigations were performed in a microactivitytest apparatus using VGO as the feed, according to ASTMD-3907, at 482 �C with 1.33 g VGO for 75 s and with 4 g ofcatalyst in a fixed bed (Fig. 1). After completing the feedinjection the reactor is stripped with flowing nitrogen (30 mlmin±1 for 20 min). Analysis of the gaseous fraction wasperformed on a GC-FID (VEGA 6300-01, Carlo Erba) withhydrogen as the carrier on a PLOT-Megabore column (GS-Al 50 m x 0.53 id). For the analysis of the liquid fraction aD2887-Megabore column (10 m x 0.53 id) was selected andthe procedure of the gas chromatographic simulateddistillation according to ASTM D-2887 [4c] used. The testsunder standard conditions were repeated before and aftervariation of the catalyst/oil ratio and temperature to confirmreproducibility and constant activity. Therefore, the catalystswere regenerated after every catalytic cycle with syntheticair (150 ml min±1 for 12 h) and tested again.

3 Results and Discussion

The catalytic behavior of the steam treated compositesystem in cracking of an industrially relevant feed stock,vacuum gas oil, was compared to a calcined only compositesystem and the stationary FCC catalyst.

Fig. 2 shows the conversion rates of the investigatedcatalyst samples vs. the catalyst/oil ratio. The catalyticactivity of the steam treated MCM-41 composite system athigher catalyst/oil ratios is comparable to the standardcatalyst or even higher at a catalyst/oil ratio of 3. Furtherinvestigations also proved a deeper cracking of the feedstock. The catalytic activity of the calcined MCM-41composite system is significantly lower at low catalyst/oilratios. Deactivation by catalytic application can not beobserved for any of the tested materials.

Fig. 3 displays product yields of the investigated catalystsamples at a comparable conversion rate of ca. 45-47 wt. %.It is evident that the MCM-41 composite system produceshigher gas yields and a significantly lower liquid fractioncompared to the other catalyst samples. The standardcatalyst and the steam treated MCM-41 composite systemshow no difference in terms of gas and liquid fraction incracking of VGO. The composite system shows a productshift within the liquid fraction to lighter products, LCO andgasoline, whereas the HCO fraction is found mainly in theproducts of the standard catalyst.

Figure 3. Comparison of the product composition of cracked vacuum gas oilon investigated catalysts at comparable conversion rates.

The calcined MCM-41 composite system yields moresaturated (Fig. 4) and branched (Fig. 5) hydrocarbons incatalytic cracking of VGO compared to the standardcatalyst. Such a significant production of branched andsaturated products is neither known from ultrastable zeoliteY nor from pure MCM-41 in the H form [5] and can beexplained by special catalytic effects of the matrix. Due tosteam treating the MCM-41 composite system lowers theratios of iso-C4/total-C4 and (C3+C4) paraffin/olefin in thecrack product compared to the results of the calcined only

Figure 1. Schematic arrangement of the microactivity test apparatus accordingto ASTM D-3907 with additional regeneration for cyclic testing of catalystsamples.

Figure 2. Catalytic activity in cracking vacuum gas oil (VGO) on MCM-41composite systems in comparison to the standard catalyst.

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sample. The steam treated composite system now shows aselectivity behavior typical for pure, not steamed MCM-41materials [5]. Therefore, a reduction of the number of strongacid sites by steaming (deactivating) preferentially in theactive matrix of the MCM-41 composite system (comparedto the standard catalyst) can be assumed.

Comparison of the C3/C4 product ratio in Fig. 6 showscatalytic behavior (for the steam treated MCM-41 compositesystem), which points out a superimposition of the catalyticproperties of MCM-41 and zeolite Y. The catalytic behavior atconversion rates up to ca. 47 wt. % is comparable to thestandard catalyst which is the behavior of zeolite Y. Higherconversion rates increase the C3/C4 product ratio of thesteamed MCM-41 composite system. It approaches the MCM-41 typical level, which implies the partial retention of theMCM-41 structure in the composite system after steaming.

4 Conclusions

The intense characteristics of the calcined MCM-41composite system in cracking vacuum gas oil to produce

branched and saturated hydrocarbons shows a clear influ-ence of the active matrix. This tendency of the compositesystem is lost by steam treating the material. It can beassumed that the strong acid sites of the matrix aredeactivated. The selectivity behavior of the MCM-41composite system after steaming is analogous to pure, notsteamed MCM-41 materials. Therefore, it can be figured thatthe MCM-41 structure in the composite system under theconditions of the steam treatment in contrast to pure MCM-41 materials is not completly and irreversibly damaged andremains able to develop its typical catalytic behavior.

The obtained results show the application of mesoporousmaterials of type MCM-41 as active compounds in FCCcatalysts with good perspectives to achieve a deeper crackingof heavy oil fractions.

Acknowledgment

The authors thank the Commission of the EuropeanUnion for financial support in the frame of the Joule IIprogram and Grace GmbH for helpful cooperation.

Received: November 27, 1997 [K 2340]

References

[1] Beck, J. S.; Vartuli, J. C.; Roth, W. J.; Leonowicz, M. E.; Kresge, C. T.;Schmitt, K. D.; Chu, C. T.-W.; Olson, D. H.; Sheppard, E. W.; McCullen,S. B.; Higgins, J.B.; Schlenker, J. L.; J. Am. Chem. Soc. 114 (1992)pp. 10834±10843 .

[2] Kresge, C. T.; Leonowicz, M.E.; Roth, W. J.; Vartuli, J. C; Beck, J. S.;Nature 359 (1992) pp. 710±712.

[3] Roos, K.; Liepold, A.; Koch, H.; Reschetilowski, W.; Chem. Eng.Technol. 20 (1997) pp. 326±332.

[4] (a) ASTM D-3907: Standard Method for Testing Fluid CrackingCatalysts by Microactivity Test; (b) ASTM D-4463: Standard Guide forSteam Deactivation of Fresh Fluid Cracking Catalysts; (c) ASTM D-2887: Test Method for Boiling Range Distribution of Petroleum Fractionsby Gas Chromatography.

[5] Roos, K.; Liepold, A.; Reschetilowski, W.; Schmidt, R.; Karlsson, A.;Stöcker, M.; Stud. Surf. Sci. Catal. 94 (1995) pp. 389±396.

This paper will also be published in German in Chem. Ing Tech. 70 (1998) No. 6.

Chem. Eng. Technol. 21 (1998) 5 Ó WILEY-VCH Verlag GmbH, D-69469 Weinheim, 1998 0930-7516/98/0505-0403 $ 17.50+.50/0 403

Figure 4. (C3+C4) paraffin/olefin ratio as function of the conversion rate(varied by temperature adjustment) in cracking of vacuum gas oil on MCM-41composite systems compared to the standard catalyst.

Figure 5. Iso-C4/total-C4 ratio as function of the conversion rate (varied bytemperature adjustment) in cracking of vacuum gas oil on MCM-41 compositesystems compared to the standard catalyst.

Figure 6. C3/C4 product ratio as function of the conversion rate (varied bytemperature adjustment) in cracking of vacuum gas oil on MCM-41 compositesystems compared to the standard catalyst.

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