The yields and selectivities in both the catalyzed and non-catalyzed oxidative dehydrogenation of propane were found to increase with increasing pressure. The results showed that the maximum yields of valuable ODH products could be obtained by adjusting only reactants' partial pressure, while keeping their ratio constant

Kotanjac, Zeljko S.

Niederer, John P.M.

Versteeg, Geert F.

English

Kotanjac, Z. S.

Niederer, J. P. M.

Versteeg, G. F.

University of Groningen

   University of GroningenInfluence of the pressure on the product distribution in the oxidative dehydrogenation ofpropane over a Ga2O3/MoO3 catalystInfluence of the pressure on the product distribution inthe oxidative dehydrogenation of propane over a Ga2O3/MoO3 catalystKotanjac, Z. S.; Niederer, J. P. M.; Versteeg, G. F.Published in:International Journal of Chemical Reactor EngineeringIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:2007Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Kotanjac, Z. S., Niederer, J. P. M., & Versteeg, G. F. (2007). Influence of the pressure on the productdistribution in the oxidative dehydrogenation of propane over a Ga2O3/MoO3 catalystInfluence of thepressure on the product distribution in the oxidative dehydrogenation of propane over a Ga2O3/MoO3catalyst. International Journal of Chemical Reactor Engineering, 5(1).CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 12-11-2019INTERNATIONAL JOURNAL OF CHEMICALREACTOR ENGINEERINGVolume 5 2007 Note S6Influence of the Pressure on the ProductDistribution in the OxidativeDehydrogenation of Propane over aGa2O3/MoO3 CatalystZeljko S. Kotanjac∗ John P. M. Niederer†Geert F. Versteeg‡∗University of Twente, z.kotanjac@utwente.nl†University of Twente, john.niederer@frieslandfoods.com‡Clarkson University, geert.versteeg@procede.nlISSN 1542-6580Copyright c©2007 The Berkeley Electronic Press. All rights reserved.Influence of the Pressure on the Product Distributionin the Oxidative Dehydrogenation of Propane over aGa2O3/MoO3 Catalyst∗Zeljko S. Kotanjac, John P. M. Niederer, and Geert F. VersteegAbstractThe yields and selectivities in both the catalyzed and non-catalyzed oxida-tive dehydrogenation of propane were found to increase with increasing pressure.The results showed that the maximum yields of valuable ODH products could beobtained by adjusting only reactants’ partial pressure, while keeping their ratioconstant.KEYWORDS: oxidative dehydrogenation, heterogeneous catalysis, process de-velopment∗The authors gratefully acknowledge the financial support from the Netherlands Organisation forScientific Research (NWO).1. INTRODUCTIONThe oxidative dehydrogenation of propane as an alternative route for the production of propylene is drawing increasingattention due to the increasing demand for lower olefins. The present production capacity mainly consists of steamcrackers, which are usually operated to obtain maximum ethylene yields. (Dharia et al., 2004)The main alternatives are the dehydrogenation and oxidative dehydrogenation (ODH) of propane, with the firstone taking place at high temperatures of 800 – 900 K to obtain a favorable thermodynamic equilibrium. (Gussowet al., 1980) However, a high reaction temperature also leads to coke formation and cracking to ethylene, which bothcan be avoided with the ODH reaction. (Albonetti et al., 1996; Koc et al., 2005) In this process, which can forexample be catalyzed by Ga2O3/MoO3 mixtures, the main products are, besides propylene and ethylene, methane,carbon monoxide, carbon dioxide and water. Ga2O3/MoO3 catalyst was chosen because of its good performance(good alkane activation properties caused by Ga2O3 combined with a partial oxidation behavior of MoO3, as stated byDavies and Taylor (2004)) and ease of preparation, described in section 2.A problem in the further development of this system is the deep oxidation to COx. The actual mechanism ofthe overall process is still not known, while the fact that oxygen presence is the key for achieving the conversionsbeyond those expected based on the equilibrium of the simple dehydrogenation reaction is widely accepted. Althoughmany different and rather complex mechanisms for this reaction are investigated, as presented in Grabowski (2006),the reaction can be simplified to the network shown in Figure 1. (Leveles et al., 2003; Chen et al., 2001)C3H8C3H6COxk1k2k3Figure 1: Reaction network for the oxidative dehydrogenation of propaneAs already shown by Grabowski (2006), partial pressures of reactants determine the reaction kinetics, thereforealso the conversion and selectivities. Changing total pressure while keeping feed composition constant gives us apossibility to explore how conversion and selectivities change with partial pressure change, maintaining their ratioconstant.In attempts to find a catalyst which would both be active at low temperatures and avoid deep oxidation, variousmaterials such as supported molten salt catalysts (alkali chlorides), LiOH/LiI melts, metal sulphates and phosphates,as well as nickel molybdate, niobium pentoxide and TS-1 were investigated. (Fox and Lee, 1973; Dahl et al., 1991;Ushkov et al., 1988; Takita et al., 1989; Mazzocchia et al., 1991; Smits et al., 1991; Schuster et al., 2001) In this paperthe influence of pressure on the yields and selectivities in the ODH of propane over a Ga2O3/MoO3 catalyst will beinvestigated.2. EXPERIMENTALFor catalytic experiments, an equimolar mixture of Ga2O3 (Aldrich, 99.99 % ) and MoO3 (Aldrich, 99.99 %) wasground in a pestle and mortar, after which tablets were pressed, which were crushed and sieved to obtain a particlesize of 0.85 – 1.00 mm. Subsequently, the catalyst was calcined at 873 K for 3 hours in an oxidizing helium/oxygen(1:1 volume ratio) atmosphere.Experiments were performed in a stainless steel packed bed reactor of 70 cm length, equipped with a quartz linerof 10 mm in diameter to avoid possible side reactions with the steel reactor walls. The reactor was heated with twoseparate electrical ovens controlled by Eurotherm 91e controllers [K-type ChromelTM/AlumelTM thermocouples]. Acatalyst bed with a volume of 4 ml (1.1 g of catalyst) was used for all experiments. A gas mixture consisting of he-lium/propane/oxygen in a volume ratio of 8:2:1 was fed to the top of the reactor with a total flow rate of 110 ml/minusing Brooks R© 5850TR mass flow controllers. For non-catalytic experiments a similar volume of quartz beads was1Kotanjac et al.: Pressure Influence in the ODHPPublished by The Berkeley Electronic Press, 2007used to maintain the space velocity and contact time. Schematic overview of the experimental setup used for thisresearch is given in Figure 2.C1TT2MFC4MFC3AdditivePropane OxygenMFC2PCHeliumMFC1TT1PRC2GCR1R2Figure 2: Schematic overview of the experimental setup used in this research: R1–2 — Reactor sections, MFC1–4— Mass flow controllers, T1–2 — Temperature controllers/indicators, C1–2 — Condensers, PR — Pressure regulator,GC — Gas chromatographExperiments were carried out at 733 K and 773 K, varying the pressure from 1 to 6 bar in steps of 1 bar. Aftereach experiment of 5 hours the catalyst bed was regenerated for 2 hours at 873 K with a 1:1 helium/oxygen mixtureto remove any coke formed during the reaction. Reaction products were analyzed online on a Varian MicroGC 4900equipped with both a Molsieve 5 A˚ and a Al2O3/KCl column using thermal conductivity detectors. The carbon massbalance in all experiments was 100 ± 5 %.Propane conversion, Xp, has been calculated according to formulaXp =C0p−CpC0p(1)where C0p and Cp are the concentrations of propane at the inlet and outlet of the reactor, respectively.Selectivity to product i has been calculated according to formulaSi =ηi ·C f ormediCspentpropane(2)where ηi denotes a stoichiometric factor.3. RESULTSResults obtained from experiments performed at atmospheric pressure (see Table 1) were comparable to those of otherauthors: Grabowski and Słoczyn´ski (2005) obtained a selectivity to propylene of 76.5 % at a conversion of 1.2 %(733 K) and 72.8 % at a conversion of 1.5 % at 773 K, respectively, over VOx/SiO2 catalyst. Schuster et al. (2001)reported on a conversion of 19 % with a selectivity to propylene of over 70 % at 823 K, over the titanosilicalite TS-1catalyst, whereas the best result of Cadus and Ferretti (2002) was a selectivity of 31.8 % at 21.84 % of conversion at733 K, over Mo-MnO catalysts.Increasing the pressure from 1 to 4 bar (733 K) led to a significant increase in the conversion from ∼11 to∼40 mol%; a further increase from 4 to 6 bar led to a decrease of the conversion to ∼26 mol%, whereas at 773 K2 International Journal of Chemical Reactor Engineering Vol. 5 [2007], Note S6http://www.bepress.com/ijcre/vol5/S6an increase in the pressure of 1 to 3 bar led to an increase in the conversion from ∼15 to ∼45 mol% (see Table 1). Afurther increase from 3 to 6 bar led to a decrease to ∼34 mol%. Non-catalytic experiments at 773 K revealed a similartrend up to 3 bar, where the conversion was only 2.24 % at 1 bar and 41.61 % at 3 bar. Results at 733 K also revealedan increasing conversion (0−29.1 %) with increasing pressure. At pressures higher than 3 bar (773 K) the situationwas the opposite: the conversion in non-catalytic experiments was 10.3 – 11.7 % higher than in catalytic experiments.Table 1: Conversion and selectivities for the catalyzed (top) and non-catalyzed (bottom) ODHP at 733 and 773 Kpressure, bar 1 2 3 4 5 6 1 2 3 4 5 6T = 733 K T = 773 K10.92 13.51 37.33 39.89 32.50 25.91 15.12 32.61 45.48 34.95 27.39 34.34X, mol% 0 1.31 15.08 28.01 29.49 29.10 2.24 12.16 41.61 38.55 30.29 40.3851.90 52.00 48.70 46.97 37.53 34.40 51.57 52.68 46.81 46.96 42.50 20.14C3H6 0 100 82.71 52.71 54.28 43.04 66.54 75.96 47.53 49.21 27.99 6.191.73 5.83 11.94 13.56 8.50 7.20 6.79 23.76 17.99 11.99 9.46 4.74C2H4 0 7.80 10.37 12.01 9.08 8.74 2.97 15.60 21.63 22.61 7.51 1.63S, mol% 0 3.03 6.19 6.22 7.00 11.19 2.08 7.70 7.76 7.72 8.14 10.20CH4 0 0 1.39 5.81 3.84 5.08 0 5.51 9.66 9.03 8.86 17.5155.74 45.55 21.85 20.34 27.18 37.71 42.77 19.96 14.56 14.75 15.36 20.74CO 0 0 10.80 26.55 23.11 29.48 5.46 6.79 15.92 12.39 35.44 27.93A similar change in the conversion was found at 733 K, where the drop in the conversion occurred at pressureshigher than 4 bar. The overall conversion in the catalyzed system was about 55 % higher than in the non-catalytic(26.68 % vs. 17.16 %) at 733 K, whereas the conversion under catalytic conditions was about 15 % higher at 773 Kthan in the non-catalytic (31.64 % vs. 27.53 %). This was probably due to Ga2O3, which is a well known promoter foralkane activation. (Iglesia and Baumgartner, 1993; Hargreaves et al., 2002)The selectivity to propylene based on propane at 773 K remained ∼42.5 – 52.5 % over the pressure range inves-tigated, although for non-catalytic experiments the scattering in the selectivity was large in the range ∼49 −76 %.At 733 K, the scattering was even larger, from 34.40 % to 52.00 % for catalytic and from 43.04 % to 100 % for non-catalytic experiments. The presence of MoO3 in the catalyst bed certainly had a large influence on the selectivity, asMoO3 is known to be a selective catalyst in the oxidative dehydrogenation of propane. (Meunier et al., 1997)At 773 K a significant drop in the selectivity to propylene was found at 6 bar for catalytic and 5 and 6 bar fornon-catalytic systems. At 733 K the drop in selectivity was not so drastic as for the catalytic system and decreasedfrom 46.97 % at 4 bar to 34.40 % at 6 bar, via 37.53 % at 5 bar. The non-catalytic system showed a constant decreasein selectivity from 100 % at 2 bar to 43.40 % at 6 bar.The selectivity to ethylene based on propane showed a comparable pattern at 773 K, reaching a maximum of23.76 mol% at 2 bar, whereas in non-catalytic experiments the maximum selectivity was 22.61 mol% at 4 bar. Bothcatalytic and non-catalytic systems showed a maximum ethylene selectivity at 4 bar of 13.56 % and 12.01 %, respec-tively.As can be seen from Figure 3, the maximum propylene yield was 18.74 % at 4 bar at 733 K and 21.29 mol% at3 bar at 773 K. In the non-catalytic system a maximum yield of 14.76 % at 4 bar and 733 K, and 19.78 % at 3 bar and773 K was found.The ethylene yield, which also is a valuable product, had a maximum of 8.18 % at 3 bar for the catalytic and8.99 % for the non-catalytic system at 773 K. At 733 K, the yield was found to be lower and reached 3.36 % in thecatalytic and 5.40 % in the non-catalytic system at 4 bar. Methane, and, more importantly, carbon monoxide yieldsonly showed a minor increase over the pressure range studied in these experiments. The maximum yields for methaneand carbon monoxide were 7.07 % and 12.06 % for the non-catalytic system at 773 K, respectively. At 733 K in boththe catalytic and non-catalytic system, as well as at 773 K in the catalytic system, methane and carbon monoxide yields3Kotanjac et al.: Pressure Influence in the ODHPPublished by The Berkeley Electronic Press, 2007     	     	 Figure 3: Product yields in the catalyzed ODH of propane at 773 K at different pressureswere significantly lower, with minimum of 1.63 % for methane in the non-catalytic and 2.90 % for CO in the catalyticsystem at 733 K.4. CONCLUSIONThe results clearly show that the high yields of valuable ODH products could be obtained by adjusting reactants’ partialpressure, while keeping their ratio constant. Maximum yields obtained in this system are comparable to maximumyields obtained from systems using a different catalyst (MgO, Li/MgO, xV/MgO, 18 % yield, Burch and Crabb (1993))and significantly higher than those obtained from systems with the same catalyst (a 5.7 % yield, Davies and Taylor(2004)).NOTATIONC concentration, mol/m3ODH oxidative dehydrogenationODHP oxidative dehydrogenation of propaneS selectivity, mol%X conversion, mol%Greek Lettersη stoichiometric factorSupercripts0 initial value of parameterSubscriptsp propanei species i4 International Journal of Chemical Reactor Engineering Vol. 5 [2007], Note S6http://www.bepress.com/ijcre/vol5/S6REFERENCESAlbonetti, S., Cavani, F., Trifiro`, F., Vedrine, J. C. “Key aspects of catalyst design for the selective oxidation ofparaffins”. Catalysis Reviews: Science and Engineering, Vol. 38, No. 4, 413 (1996).Burch, R., Crabb, E. M. “Homogeneous and heterogeneous contributions to the oxidative dehydrogenation of propaneon oxide catalysts”. Applied Catalysis A: General, Vol. 100, No. 1, 111–130 (1993).Cadus, L. E., Ferretti, O. “Characterization of Mo−MnO catalyst for propane oxidative dehydrogenation”. AppliedCatalysis A: General, Vol. 233, No. 1–2, 239–253 (2002).Chen, K., Xie, S., Bell, A. T., Iglesia, E. “Structure and properties of oxidative dehydrogenation catalysts based onMoO3/Al2O3”. Journal of Catalysis, Vol. 198, 232–242 (2001).Dahl, I. M., Grande, H., Jens, K. J., Rytter, E., Slagtern, A˚. “Oxidative dehydrogenation of propane in lithiumhydroxide/lithium iodide melts”. Applied Catalysis A: General, Vol. 77, 163–174 (1991).Davies, T., Taylor, S. H. “The oxidative dehydrogenation of propane using gallium-molybdenum oxide-based cata-lysts”. Journal of Molecular Catalysis A – Chemical, Vol. 220, No. 1, 77–84 (2004).Dharia, D., Letzsch, W., Kim, H., McCue, D., Chapin, L. “Increase light olefins production”. Hydrocarbon Processing,Vol. 83, No. 4, 61 (2004).Fox, D. B., Lee, E. H. “Supported molten salt catalysts for dehydrogenation”. Chemtech, Vol. 3, No. 3, 186–189(1973).Grabowski, R. “Kinetics of Oxidative Dehydrogenation of C2-C3 Alkanes on Oxide Catalysts”. Catalysis Reviews,Vol. 48, 199–268 (2006).Grabowski, R., Słoczyn´ski, J. “Kinetics of oxidative dehydrogenation of propane and ethane on VOx/SiO2 pure andwith potassium additive”. Chemical Engineering and Processing, Vol. 44, No. 10, 1082–1093 (2005).Gussow, S., Spence, D. C., White, E. A. “Dehydrogenation links LPG to more octanes”. Oil & Gas Journal, Vol. 78,No. 49, 96–101 (1980).Hargreaves, J. S. J., Hutchings, G. J., Joyner, R. W., Taylor, S. H. “A study of the methane-deuterium exchangereaction over a range of metal oxides”. Applied Catalysis A: General, Vol. 227, No. 1–2, 191–200 (2002).Iglesia, E., Baumgartner, J. E. “Hydrogen-transfer and activation of propane and methane on ZSM5-based catalysts”.Catalysis Letters, Vol. 21, No. 1–2, 55–70 (1993).Koc, S. N., Gurdag, G., Geissler, S., Guraya, M., Orbay, M., Muhler, M. “The oxidative dehydrogenation of pro-pane over potassium-promoted molybdenum oxide/sol-gel zirconia catalysts”. Journal of Molecular Catalysis A:Chemical, Vol. 225, 197–202 (2005).Leveles, L., Seshan, K., Lercher, J. A., Lefferts, L. “Oxidative conversion of propane over lithium promoted magnesiacatalyst: I. Kinetics and mechanism”. Journal of Catalysis, Vol. 218, 296–306 (2003).Mazzocchia, C., Aboumrad, C., Diagne, C., Tempesti, E., Herrmann, J., Thomas, G. “On the NiMoO4 oxidativedehydrogenation of propane to propene – some physical correlations with the catalytic activity”. Catalysis Letters,Vol. 10, No. 3–4, 181–191 (1991).Meunier, F. C., Yasmeen, A., Ross, J. R. H. “Oxidative dehydrogenation of propane over molybdenum-containingcatalysts”. Catalysis Today, Vol. 37, No. 1, 33–42 (1997).Schuster, W., Niederer, J. P. M., Hoelderich, W. F. “The gas phase oxidative dehydrogenation of propane over TS-1”.Applied Catalysis A: General, Vol. 209, No. 1–2, 131–143 (2001).Smits, R. H. H., Seshan, K., Ross, J. R. H. “The selective oxidative dehydrogenation of propane over niobiumpentoxide”. Journal of the Chemical Society — Chemical Communications, Vol. 20, No. 8, 558–559 (1991).5Kotanjac et al.: Pressure Influence in the ODHPPublished by The Berkeley Electronic Press, 2007Takita, Y., Yamashita, H., Moritaka, K. “Selective partial oxidation of propane over metal phosphate catalysts”.Chemistry Letters, Vol. 18, No. 10, 1733–1736 (1989).Ushkov, S. B., Osipova, Z. G., Sokolovskii, V. D., Ketchik, S. V. “Catalytic activity of some sulphates in the reactionof oxidative dehydrogenation of propane”. Kinetics and Catalysis, Vol. 29, No. 1, 195–198 (1988).6 International Journal of Chemical Reactor Engineering Vol. 5 [2007], Note S6http://www.bepress.com/ijcre/vol5/S6

Influence of the pressure on the product distribution in the oxidative dehydrogenation of propane over a Ga2O3/MoO3 catalystInfluence of the pressure on the product distribution in the oxidative dehydrogenation of propane over a Ga2O3/MoO3 catalyst

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   University of GroningenInfluence of the pressure on the product distribution in the oxidative dehydrogenation ofpropane over a Ga2O3/MoO3 catalystInfluence of the pressure on the product distribution inthe oxidative dehydrogenation of propane over a Ga2O3/MoO3 catalystKotanjac, Z. S.; Niederer, J. P. M.; Versteeg, G. F.Published in:International Journal of Chemical Reactor EngineeringIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:2007Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Kotanjac, Z. S., Niederer, J. P. M., & Versteeg, G. F. (2007). Influence of the pressure on the productdistribution in the oxidative dehydrogenation of propane over a Ga2O3/MoO3 catalystInfluence of thepressure on the product distribution in the oxidative dehydrogenation of propane over a Ga2O3/MoO3catalyst. International Journal of Chemical Reactor Engineering, 5(1).CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.INTERNATIONAL JOURNAL OF CHEMICALREACTOR ENGINEERINGVolume 5 2007 Note S6Influence of the Pressure on the ProductDistribution in the OxidativeDehydrogenation of Propane over aGa2O3/MoO3 CatalystZeljko S. Kotanjac∗ John P. M. Niederer†Geert F. Versteeg‡∗University of Twente, z.kotanjac@utwente.nl†University of Twente, john.niederer@frieslandfoods.com‡Clarkson University, geert.versteeg@procede.nlISSN 1542-6580Copyright c©2007 The Berkeley Electronic Press. All rights reserved.Influence of the Pressure on the Product Distributionin the Oxidative Dehydrogenation of Propane over aGa2O3/MoO3 Catalyst∗Zeljko S. Kotanjac, John P. M. Niederer, and Geert F. VersteegAbstractThe yields and selectivities in both the catalyzed and non-catalyzed oxida-tive dehydrogenation of propane were found to increase with increasing pressure.The results showed that the maximum yields of valuable ODH products could beobtained by adjusting only reactants’ partial pressure, while keeping their ratioconstant.KEYWORDS: oxidative dehydrogenation, heterogeneous catalysis, process de-velopment∗The authors gratefully acknowledge the financial support from the Netherlands Organisation forScientific Research (NWO).1. INTRODUCTIONThe oxidative dehydrogenation of propane as an alternative route for the production of propylene is drawing increasingattention due to the increasing demand for lower olefins. The present production capacity mainly consists of steamcrackers, which are usually operated to obtain maximum ethylene yields. (Dharia et al., 2004)The main alternatives are the dehydrogenation and oxidative dehydrogenation (ODH) of propane, with the firstone taking place at high temperatures of 800 – 900 K to obtain a favorable thermodynamic equilibrium. (Gussowet al., 1980) However, a high reaction temperature also leads to coke formation and cracking to ethylene, which bothcan be avoided with the ODH reaction. (Albonetti et al., 1996; Koc et al., 2005) In this process, which can forexample be catalyzed by Ga2O3/MoO3 mixtures, the main products are, besides propylene and ethylene, methane,carbon monoxide, carbon dioxide and water. Ga2O3/MoO3 catalyst was chosen because of its good performance(good alkane activation properties caused by Ga2O3 combined with a partial oxidation behavior of MoO3, as stated byDavies and Taylor (2004)) and ease of preparation, described in section 2.A problem in the further development of this system is the deep oxidation to COx. The actual mechanism ofthe overall process is still not known, while the fact that oxygen presence is the key for achieving the conversionsbeyond those expected based on the equilibrium of the simple dehydrogenation reaction is widely accepted. Althoughmany different and rather complex mechanisms for this reaction are investigated, as presented in Grabowski (2006),the reaction can be simplified to the network shown in Figure 1. (Leveles et al., 2003; Chen et al., 2001)C3H8C3H6COxk1k2k3Figure 1: Reaction network for the oxidative dehydrogenation of propaneAs already shown by Grabowski (2006), partial pressures of reactants determine the reaction kinetics, thereforealso the conversion and selectivities. Changing total pressure while keeping feed composition constant gives us apossibility to explore how conversion and selectivities change with partial pressure change, maintaining their ratioconstant.In attempts to find a catalyst which would both be active at low temperatures and avoid deep oxidation, variousmaterials such as supported molten salt catalysts (alkali chlorides), LiOH/LiI melts, metal sulphates and phosphates,as well as nickel molybdate, niobium pentoxide and TS-1 were investigated. (Fox and Lee, 1973; Dahl et al., 1991;Ushkov et al., 1988; Takita et al., 1989; Mazzocchia et al., 1991; Smits et al., 1991; Schuster et al., 2001) In this paperthe influence of pressure on the yields and selectivities in the ODH of propane over a Ga2O3/MoO3 catalyst will beinvestigated.2. EXPERIMENTALFor catalytic experiments, an equimolar mixture of Ga2O3 (Aldrich, 99.99 % ) and MoO3 (Aldrich, 99.99 %) wasground in a pestle and mortar, after which tablets were pressed, which were crushed and sieved to obtain a particlesize of 0.85 – 1.00 mm. Subsequently, the catalyst was calcined at 873 K for 3 hours in an oxidizing helium/oxygen(1:1 volume ratio) atmosphere.Experiments were performed in a stainless steel packed bed reactor of 70 cm length, equipped with a quartz linerof 10 mm in diameter to avoid possible side reactions with the steel reactor walls. The reactor was heated with twoseparate electrical ovens controlled by Eurotherm 91e controllers [K-type ChromelTM/AlumelTMthermocouples]. Acatalyst bed with a volume of 4 ml (1.1 g of catalyst) was used for all experiments. A gas mixture consisting of he-lium/propane/oxygen in a volume ratio of 8:2:1 was fed to the top of the reactor with a total flow rate of 110 ml/minusing Brooks R© 5850TR mass flow controllers. For non-catalytic experiments a similar volume of quartz beads was1Kotanjac et al.: Pressure Influence in the ODHPPublished by The Berkeley Electronic Press, 2007used to maintain the space velocity and contact time. Schematic overview of the experimental setup used for thisresearch is given in Figure 2.C1TT2MFC4MFC3AdditivePropane OxygenMFC2PCHeliumMFC1TT1PRC2GCR1R2Figure 2: Schematic overview of the experimental setup used in this research: R1–2 — Reactor sections, MFC1–4— Mass flow controllers, T1–2 — Temperature controllers/indicators, C1–2 — Condensers, PR — Pressure regulator,GC — Gas chromatographExperiments were carried out at 733 K and 773 K, varying the pressure from 1 to 6 bar in steps of 1 bar. Aftereach experiment of 5 hours the catalyst bed was regenerated for 2 hours at 873 K with a 1:1 helium/oxygen mixtureto remove any coke formed during the reaction. Reaction products were analyzed online on a Varian MicroGC 4900equipped with both a Molsieve 5 Å and a Al2O3/KCl column using thermal conductivity detectors. The carbon massbalance in all experiments was 100 ± 5 %.Propane conversion, Xp, has been calculated according to formulaXp =C0p −CpC0p(1)where C0p and Cp are the concentrations of propane at the inlet and outlet of the reactor, respectively.Selectivity to product i has been calculated according to formulaSi =ηi ·Cf ormediCspentpropane(2)where ηi denotes a stoichiometric factor.3. RESULTSResults obtained from experiments performed at atmospheric pressure (see Table 1) were comparable to those of otherauthors: Grabowski and Słoczyński (2005) obtained a selectivity to propylene of 76.5 % at a conversion of 1.2 %(733 K) and 72.8 % at a conversion of 1.5 % at 773 K, respectively, over VOx/SiO2 catalyst. Schuster et al. (2001)reported on a conversion of 19 % with a selectivity to propylene of over 70 % at 823 K, over the titanosilicalite TS-1catalyst, whereas the best result of Cadus and Ferretti (2002) was a selectivity of 31.8 % at 21.84 % of conversion at733 K, over Mo-MnO catalysts.Increasing the pressure from 1 to 4 bar (733 K) led to a significant increase in the conversion from ∼11 to∼40 mol%; a further increase from 4 to 6 bar led to a decrease of the conversion to ∼26 mol%, whereas at 773 K2 International Journal of Chemical Reactor Engineering Vol. 5 [2007], Note S6http://www.bepress.com/ijcre/vol5/S6an increase in the pressure of 1 to 3 bar led to an increase in the conversion from ∼15 to ∼45 mol% (see Table 1). Afurther increase from 3 to 6 bar led to a decrease to ∼34 mol%. Non-catalytic experiments at 773 K revealed a similartrend up to 3 bar, where the conversion was only 2.24 % at 1 bar and 41.61 % at 3 bar. Results at 733 K also revealedan increasing conversion (0−29.1 %) with increasing pressure. At pressures higher than 3 bar (773 K) the situationwas the opposite: the conversion in non-catalytic experiments was 10.3 – 11.7 % higher than in catalytic experiments.Table 1: Conversion and selectivities for the catalyzed (top) and non-catalyzed (bottom) ODHP at 733 and 773 Kpressure, bar 1 2 3 4 5 6 1 2 3 4 5 6T = 733 K T = 773 K10.92 13.51 37.33 39.89 32.50 25.91 15.12 32.61 45.48 34.95 27.39 34.34X, mol%0 1.31 15.08 28.01 29.49 29.10 2.24 12.16 41.61 38.55 30.29 40.3851.90 52.00 48.70 46.97 37.53 34.40 51.57 52.68 46.81 46.96 42.50 20.14C3H6 0 100 82.71 52.71 54.28 43.04 66.54 75.96 47.53 49.21 27.99 6.191.73 5.83 11.94 13.56 8.50 7.20 6.79 23.76 17.99 11.99 9.46 4.74C2H4 0 7.80 10.37 12.01 9.08 8.74 2.97 15.60 21.63 22.61 7.51 1.63S, mol%0 3.03 6.19 6.22 7.00 11.19 2.08 7.70 7.76 7.72 8.14 10.20CH4 0 0 1.39 5.81 3.84 5.08 0 5.51 9.66 9.03 8.86 17.5155.74 45.55 21.85 20.34 27.18 37.71 42.77 19.96 14.56 14.75 15.36 20.74CO0 0 10.80 26.55 23.11 29.48 5.46 6.79 15.92 12.39 35.44 27.93A similar change in the conversion was found at 733 K, where the drop in the conversion occurred at pressureshigher than 4 bar. The overall conversion in the catalyzed system was about 55 % higher than in the non-catalytic(26.68 % vs. 17.16 %) at 733 K, whereas the conversion under catalytic conditions was about 15 % higher at 773 Kthan in the non-catalytic (31.64 % vs. 27.53 %). This was probably due to Ga2O3, which is a well known promoter foralkane activation. (Iglesia and Baumgartner, 1993; Hargreaves et al., 2002)The selectivity to propylene based on propane at 773 K remained ∼42.5 – 52.5 % over the pressure range inves-tigated, although for non-catalytic experiments the scattering in the selectivity was large in the range ∼49 −76 %.At 733 K, the scattering was even larger, from 34.40 % to 52.00 % for catalytic and from 43.04 % to 100 % for non-catalytic experiments. The presence of MoO3 in the catalyst bed certainly had a large influence on the selectivity, asMoO3 is known to be a selective catalyst in the oxidative dehydrogenation of propane. (Meunier et al., 1997)At 773 K a significant drop in the selectivity to propylene was found at 6 bar for catalytic and 5 and 6 bar fornon-catalytic systems. At 733 K the drop in selectivity was not so drastic as for the catalytic system and decreasedfrom 46.97 % at 4 bar to 34.40 % at 6 bar, via 37.53 % at 5 bar. The non-catalytic system showed a constant decreasein selectivity from 100 % at 2 bar to 43.40 % at 6 bar.The selectivity to ethylene based on propane showed a comparable pattern at 773 K, reaching a maximum of23.76 mol% at 2 bar, whereas in non-catalytic experiments the maximum selectivity was 22.61 mol% at 4 bar. Bothcatalytic and non-catalytic systems showed a maximum ethylene selectivity at 4 bar of 13.56 % and 12.01 %, respec-tively.As can be seen from Figure 3, the maximum propylene yield was 18.74 % at 4 bar at 733 K and 21.29 mol% at3 bar at 773 K. In the non-catalytic system a maximum yield of 14.76 % at 4 bar and 733 K, and 19.78 % at 3 bar and773 K was found.The ethylene yield, which also is a valuable product, had a maximum of 8.18 % at 3 bar for the catalytic and8.99 % for the non-catalytic system at 773 K. At 733 K, the yield was found to be lower and reached 3.36 % in thecatalytic and 5.40 % in the non-catalytic system at 4 bar. Methane, and, more importantly, carbon monoxide yieldsonly showed a minor increase over the pressure range studied in these experiments. The maximum yields for methaneand carbon monoxide were 7.07 % and 12.06 % for the non-catalytic system at 773 K, respectively. At 733 K in boththe catalytic and non-catalytic system, as well as at 773 K in the catalytic system, methane and carbon monoxide yields3Kotanjac et al.: Pressure Influence in the ODHPPublished by The Berkeley Electronic Press, 2007     	     	 Figure 3: Product yields in the catalyzed ODH of propane at 773 K at different pressureswere significantly lower, with minimum of 1.63 % for methane in the non-catalytic and 2.90 % for CO in the catalyticsystem at 733 K.4. CONCLUSIONThe results clearly show that the high yields of valuable ODH products could be obtained by adjusting reactants’ partialpressure, while keeping their ratio constant. Maximum yields obtained in this system are comparable to maximumyields obtained from systems using a different catalyst (MgO, Li/MgO, xV/MgO, 18 % yield, Burch and Crabb (1993))and significantly higher than those obtained from systems with the same catalyst (a 5.7 % yield, Davies and Taylor(2004)).NOTATIONC concentration, mol/m3ODH oxidative dehydrogenationODHP oxidative dehydrogenation of propaneS selectivity, mol%X conversion, mol%Greek Lettersη stoichiometric factorSupercripts0 initial value of parameterSubscriptsp propanei species i4 International Journal of Chemical Reactor Engineering Vol. 5 [2007], Note S6http://www.bepress.com/ijcre/vol5/S6REFERENCESAlbonetti, S., Cavani, F., Trifirò, F., Vedrine, J. C. “Key aspects of catalyst design for the selective oxidation ofparaffins”. Catalysis Reviews: Science and Engineering, Vol. 38, No. 4, 413 (1996).Burch, R., Crabb, E. M. “Homogeneous and heterogeneous contributions to the oxidative dehydrogenation of propaneon oxide catalysts”. Applied Catalysis A: General, Vol. 100, No. 1, 111–130 (1993).Cadus, L. E., Ferretti, O. “Characterization of Mo−MnO catalyst for propane oxidative dehydrogenation”. AppliedCatalysis A: General, Vol. 233, No. 1–2, 239–253 (2002).Chen, K., Xie, S., Bell, A. T., Iglesia, E. “Structure and properties of oxidative dehydrogenation catalysts based onMoO3/Al2O3”. Journal of Catalysis, Vol. 198, 232–242 (2001).Dahl, I. M., Grande, H., Jens, K. J., Rytter, E., Slagtern, Å. “Oxidative dehydrogenation of propane in lithiumhydroxide/lithium iodide melts”. Applied Catalysis A: General, Vol. 77, 163–174 (1991).Davies, T., Taylor, S. H. “The oxidative dehydrogenation of propane using gallium-molybdenum oxide-based cata-lysts”. Journal of Molecular Catalysis A – Chemical, Vol. 220, No. 1, 77–84 (2004).Dharia, D., Letzsch, W., Kim, H., McCue, D., Chapin, L. “Increase light olefins production”. Hydrocarbon Processing,Vol. 83, No. 4, 61 (2004).Fox, D. B., Lee, E. H. “Supported molten salt catalysts for dehydrogenation”. Chemtech, Vol. 3, No. 3, 186–189(1973).Grabowski, R. “Kinetics of Oxidative Dehydrogenation of C2-C3 Alkanes on Oxide Catalysts”. Catalysis Reviews,Vol. 48, 199–268 (2006).Grabowski, R., Słoczyński, J. “Kinetics of oxidative dehydrogenation of propane and ethane on VOx/SiO2 pure andwith potassium additive”. Chemical Engineering and Processing, Vol. 44, No. 10, 1082–1093 (2005).Gussow, S., Spence, D. C., White, E. A. “Dehydrogenation links LPG to more octanes”. Oil & Gas Journal, Vol. 78,No. 49, 96–101 (1980).Hargreaves, J. S. J., Hutchings, G. J., Joyner, R. W., Taylor, S. H. “A study of the methane-deuterium exchangereaction over a range of metal oxides”. Applied Catalysis A: General, Vol. 227, No. 1–2, 191–200 (2002).Iglesia, E., Baumgartner, J. E. “Hydrogen-transfer and activation of propane and methane on ZSM5-based catalysts”.Catalysis Letters, Vol. 21, No. 1–2, 55–70 (1993).Koc, S. N., Gurdag, G., Geissler, S., Guraya, M., Orbay, M., Muhler, M. “The oxidative dehydrogenation of pro-pane over potassium-promoted molybdenum oxide/sol-gel zirconia catalysts”. Journal of Molecular Catalysis A:Chemical, Vol. 225, 197–202 (2005).Leveles, L., Seshan, K., Lercher, J. A., Lefferts, L. “Oxidative conversion of propane over lithium promoted magnesiacatalyst: I. Kinetics and mechanism”. Journal of Catalysis, Vol. 218, 296–306 (2003).Mazzocchia, C., Aboumrad, C., Diagne, C., Tempesti, E., Herrmann, J., Thomas, G. “On the NiMoO4 oxidativedehydrogenation of propane to propene – some physical correlations with the catalytic activity”. Catalysis Letters,Vol. 10, No. 3–4, 181–191 (1991).Meunier, F. C., Yasmeen, A., Ross, J. R. H. “Oxidative dehydrogenation of propane over molybdenum-containingcatalysts”. Catalysis Today, Vol. 37, No. 1, 33–42 (1997).Schuster, W., Niederer, J. P. M., Hoelderich, W. F. “The gas phase oxidative dehydrogenation of propane over TS-1”.Applied Catalysis A: General, Vol. 209, No. 1–2, 131–143 (2001).Smits, R. H. H., Seshan, K., Ross, J. R. H. “The selective oxidative dehydrogenation of propane over niobiumpentoxide”. Journal of the Chemical Society — Chemical Communications, Vol. 20, No. 8, 558–559 (1991).5Kotanjac et al.: Pressure Influence in the ODHPPublished by The Berkeley Electronic Press, 2007Takita, Y., Yamashita, H., Moritaka, K. “Selective partial oxidation of propane over metal phosphate catalysts”.Chemistry Letters, Vol. 18, No. 10, 1733–1736 (1989).Ushkov, S. B., Osipova, Z. G., Sokolovskii, V. D., Ketchik, S. V. “Catalytic activity of some sulphates in the reactionof oxidative dehydrogenation of propane”. Kinetics and Catalysis, Vol. 29, No. 1, 195–198 (1988).6 International Journal of Chemical Reactor Engineering Vol. 5 [2007], Note S6http://www.bepress.com/ijcre/vol5/S6

Kotanjac, Zeljko

Niederer, John

Versteeg, Geert

NARCIS 

Influence of the Pressure on the Product Distribution in the Oxidative Dehydrogenation of Propane over a Ga2O3/MoO3 Catalyst

The yields and selectivities in both the catalyzed and non-catalyzed oxidative dehydrogenation of propane were found to increase with increasing pressure. The results showed that the maximum yields of valuable ODH products could be obtained by adjusting only reactants' partial pressure, while keeping their ratio constant.

Versteeg, G. F.,

Niederer, J. P. M.,

Kotanjac, Z. S.,

University of Groningen Digital Archive

University of Twente Research Information

INTERNATIONAL JOURNAL OF CHEMICALREACTOR ENGINEERINGVolume 5 2007 Note S6Influence of the Pressure on the ProductDistribution in the OxidativeDehydrogenation of Propane over aGa2O3/MoO3 CatalystZeljko S. Kotanjac∗ John P. M. Niederer†Geert F. Versteeg‡∗University of Twente, z.kotanjac@utwente.nl†University of Twente, john.niederer@frieslandfoods.com‡Clarkson University, geert.versteeg@procede.nlISSN 1542-6580Copyright c©2007 The Berkeley Electronic Press. All rights reserved.Influence of the Pressure on the Product Distributionin the Oxidative Dehydrogenation of Propane over aGa2O3/MoO3 Catalyst∗Zeljko S. Kotanjac, John P. M. Niederer, and Geert F. VersteegAbstractThe yields and selectivities in both the catalyzed and non-catalyzed oxida-tive dehydrogenation of propane were found to increase with increasing pressure.The results showed that the maximum yields of valuable ODH products could beobtained by adjusting only reactants’ partial pressure, while keeping their ratioconstant.KEYWORDS: oxidative dehydrogenation, heterogeneous catalysis, process de-velopment∗The authors gratefully acknowledge the financial support from the Netherlands Organisation forScientific Research (NWO).1. INTRODUCTIONThe oxidative dehydrogenation of propane as an alternative route for the production of propylene is drawing increasingattention due to the increasing demand for lower olefins. The present production capacity mainly consists of steamcrackers, which are usually operated to obtain maximum ethylene yields. (Dharia et al., 2004)The main alternatives are the dehydrogenation and oxidative dehydrogenation (ODH) of propane, with the firstone taking place at high temperatures of 800 – 900 K to obtain a favorable thermodynamic equilibrium. (Gussowet al., 1980) However, a high reaction temperature also leads to coke formation and cracking to ethylene, which bothcan be avoided with the ODH reaction. (Albonetti et al., 1996; Koc et al., 2005) In this process, which can forexample be catalyzed by Ga2O3/MoO3 mixtures, the main products are, besides propylene and ethylene, methane,carbon monoxide, carbon dioxide and water. Ga2O3/MoO3 catalyst was chosen because of its good performance(good alkane activation properties caused by Ga2O3 combined with a partial oxidation behavior of MoO3, as stated byDavies and Taylor (2004)) and ease of preparation, described in section 2.A problem in the further development of this system is the deep oxidation to COx. The actual mechanism ofthe overall process is still not known, while the fact that oxygen presence is the key for achieving the conversionsbeyond those expected based on the equilibrium of the simple dehydrogenation reaction is widely accepted. Althoughmany different and rather complex mechanisms for this reaction are investigated, as presented in Grabowski (2006),the reaction can be simplified to the network shown in Figure 1. (Leveles et al., 2003; Chen et al., 2001)C3H8C3H6COxk1k2k3Figure 1: Reaction network for the oxidative dehydrogenation of propaneAs already shown by Grabowski (2006), partial pressures of reactants determine the reaction kinetics, thereforealso the conversion and selectivities. Changing total pressure while keeping feed composition constant gives us apossibility to explore how conversion and selectivities change with partial pressure change, maintaining their ratioconstant.In attempts to find a catalyst which would both be active at low temperatures and avoid deep oxidation, variousmaterials such as supported molten salt catalysts (alkali chlorides), LiOH/LiI melts, metal sulphates and phosphates,as well as nickel molybdate, niobium pentoxide and TS-1 were investigated. (Fox and Lee, 1973; Dahl et al., 1991;Ushkov et al., 1988; Takita et al., 1989; Mazzocchia et al., 1991; Smits et al., 1991; Schuster et al., 2001) In this paperthe influence of pressure on the yields and selectivities in the ODH of propane over a Ga2O3/MoO3 catalyst will beinvestigated.2. EXPERIMENTALFor catalytic experiments, an equimolar mixture of Ga2O3 (Aldrich, 99.99 % ) and MoO3 (Aldrich, 99.99 %) wasground in a pestle and mortar, after which tablets were pressed, which were crushed and sieved to obtain a particlesize of 0.85 – 1.00 mm. Subsequently, the catalyst was calcined at 873 K for 3 hours in an oxidizing helium/oxygen(1:1 volume ratio) atmosphere.Experiments were performed in a stainless steel packed bed reactor of 70 cm length, equipped with a quartz linerof 10 mm in diameter to avoid possible side reactions with the steel reactor walls. The reactor was heated with twoseparate electrical ovens controlled by Eurotherm 91e controllers [K-type ChromelTM/AlumelTMthermocouples]. Acatalyst bed with a volume of 4 ml (1.1 g of catalyst) was used for all experiments. A gas mixture consisting of he-lium/propane/oxygen in a volume ratio of 8:2:1 was fed to the top of the reactor with a total flow rate of 110 ml/minusing Brooks R© 5850TR mass flow controllers. For non-catalytic experiments a similar volume of quartz beads was1Kotanjac et al.: Pressure Influence in the ODHPPublished by The Berkeley Electronic Press, 2007used to maintain the space velocity and contact time. Schematic overview of the experimental setup used for thisresearch is given in Figure 2.C1TT2MFC4MFC3AdditivePropane OxygenMFC2PCHeliumMFC1TT1PRC2GCR1R2Figure 2: Schematic overview of the experimental setup used in this research: R1–2 — Reactor sections, MFC1–4— Mass flow controllers, T1–2 — Temperature controllers/indicators, C1–2 — Condensers, PR — Pressure regulator,GC — Gas chromatographExperiments were carried out at 733 K and 773 K, varying the pressure from 1 to 6 bar in steps of 1 bar. Aftereach experiment of 5 hours the catalyst bed was regenerated for 2 hours at 873 K with a 1:1 helium/oxygen mixtureto remove any coke formed during the reaction. Reaction products were analyzed online on a Varian MicroGC 4900equipped with both a Molsieve 5 Å and a Al2O3/KCl column using thermal conductivity detectors. The carbon massbalance in all experiments was 100 ± 5 %.Propane conversion, Xp, has been calculated according to formulaXp =C0p −CpC0p(1)where C0p and Cp are the concentrations of propane at the inlet and outlet of the reactor, respectively.Selectivity to product i has been calculated according to formulaSi =ηi ·Cf ormediCspentpropane(2)where ηi denotes a stoichiometric factor.3. RESULTSResults obtained from experiments performed at atmospheric pressure (see Table 1) were comparable to those of otherauthors: Grabowski and Słoczyński (2005) obtained a selectivity to propylene of 76.5 % at a conversion of 1.2 %(733 K) and 72.8 % at a conversion of 1.5 % at 773 K, respectively, over VOx/SiO2 catalyst. Schuster et al. (2001)reported on a conversion of 19 % with a selectivity to propylene of over 70 % at 823 K, over the titanosilicalite TS-1catalyst, whereas the best result of Cadus and Ferretti (2002) was a selectivity of 31.8 % at 21.84 % of conversion at733 K, over Mo-MnO catalysts.Increasing the pressure from 1 to 4 bar (733 K) led to a significant increase in the conversion from ∼11 to∼40 mol%; a further increase from 4 to 6 bar led to a decrease of the conversion to ∼26 mol%, whereas at 773 K2 International Journal of Chemical Reactor Engineering Vol. 5 [2007], Note S6http://www.bepress.com/ijcre/vol5/S6an increase in the pressure of 1 to 3 bar led to an increase in the conversion from ∼15 to ∼45 mol% (see Table 1). Afurther increase from 3 to 6 bar led to a decrease to ∼34 mol%. Non-catalytic experiments at 773 K revealed a similartrend up to 3 bar, where the conversion was only 2.24 % at 1 bar and 41.61 % at 3 bar. Results at 733 K also revealedan increasing conversion (0−29.1 %) with increasing pressure. At pressures higher than 3 bar (773 K) the situationwas the opposite: the conversion in non-catalytic experiments was 10.3 – 11.7 % higher than in catalytic experiments.Table 1: Conversion and selectivities for the catalyzed (top) and non-catalyzed (bottom) ODHP at 733 and 773 Kpressure, bar 1 2 3 4 5 6 1 2 3 4 5 6T = 733 K T = 773 K10.92 13.51 37.33 39.89 32.50 25.91 15.12 32.61 45.48 34.95 27.39 34.34X, mol%0 1.31 15.08 28.01 29.49 29.10 2.24 12.16 41.61 38.55 30.29 40.3851.90 52.00 48.70 46.97 37.53 34.40 51.57 52.68 46.81 46.96 42.50 20.14C3H6 0 100 82.71 52.71 54.28 43.04 66.54 75.96 47.53 49.21 27.99 6.191.73 5.83 11.94 13.56 8.50 7.20 6.79 23.76 17.99 11.99 9.46 4.74C2H4 0 7.80 10.37 12.01 9.08 8.74 2.97 15.60 21.63 22.61 7.51 1.63S, mol%0 3.03 6.19 6.22 7.00 11.19 2.08 7.70 7.76 7.72 8.14 10.20CH4 0 0 1.39 5.81 3.84 5.08 0 5.51 9.66 9.03 8.86 17.5155.74 45.55 21.85 20.34 27.18 37.71 42.77 19.96 14.56 14.75 15.36 20.74CO0 0 10.80 26.55 23.11 29.48 5.46 6.79 15.92 12.39 35.44 27.93A similar change in the conversion was found at 733 K, where the drop in the conversion occurred at pressureshigher than 4 bar. The overall conversion in the catalyzed system was about 55 % higher than in the non-catalytic(26.68 % vs. 17.16 %) at 733 K, whereas the conversion under catalytic conditions was about 15 % higher at 773 Kthan in the non-catalytic (31.64 % vs. 27.53 %). This was probably due to Ga2O3, which is a well known promoter foralkane activation. (Iglesia and Baumgartner, 1993; Hargreaves et al., 2002)The selectivity to propylene based on propane at 773 K remained ∼42.5 – 52.5 % over the pressure range inves-tigated, although for non-catalytic experiments the scattering in the selectivity was large in the range ∼49 −76 %.At 733 K, the scattering was even larger, from 34.40 % to 52.00 % for catalytic and from 43.04 % to 100 % for non-catalytic experiments. The presence of MoO3 in the catalyst bed certainly had a large influence on the selectivity, asMoO3 is known to be a selective catalyst in the oxidative dehydrogenation of propane. (Meunier et al., 1997)At 773 K a significant drop in the selectivity to propylene was found at 6 bar for catalytic and 5 and 6 bar fornon-catalytic systems. At 733 K the drop in selectivity was not so drastic as for the catalytic system and decreasedfrom 46.97 % at 4 bar to 34.40 % at 6 bar, via 37.53 % at 5 bar. The non-catalytic system showed a constant decreasein selectivity from 100 % at 2 bar to 43.40 % at 6 bar.The selectivity to ethylene based on propane showed a comparable pattern at 773 K, reaching a maximum of23.76 mol% at 2 bar, whereas in non-catalytic experiments the maximum selectivity was 22.61 mol% at 4 bar. Bothcatalytic and non-catalytic systems showed a maximum ethylene selectivity at 4 bar of 13.56 % and 12.01 %, respec-tively.As can be seen from Figure 3, the maximum propylene yield was 18.74 % at 4 bar at 733 K and 21.29 mol% at3 bar at 773 K. In the non-catalytic system a maximum yield of 14.76 % at 4 bar and 733 K, and 19.78 % at 3 bar and773 K was found.The ethylene yield, which also is a valuable product, had a maximum of 8.18 % at 3 bar for the catalytic and8.99 % for the non-catalytic system at 773 K. At 733 K, the yield was found to be lower and reached 3.36 % in thecatalytic and 5.40 % in the non-catalytic system at 4 bar. Methane, and, more importantly, carbon monoxide yieldsonly showed a minor increase over the pressure range studied in these experiments. The maximum yields for methaneand carbon monoxide were 7.07 % and 12.06 % for the non-catalytic system at 773 K, respectively. At 733 K in boththe catalytic and non-catalytic system, as well as at 773 K in the catalytic system, methane and carbon monoxide yields3Kotanjac et al.: Pressure Influence in the ODHPPublished by The Berkeley Electronic Press, 2007     	     	 Figure 3: Product yields in the catalyzed ODH of propane at 773 K at different pressureswere significantly lower, with minimum of 1.63 % for methane in the non-catalytic and 2.90 % for CO in the catalyticsystem at 733 K.4. CONCLUSIONThe results clearly show that the high yields of valuable ODH products could be obtained by adjusting reactants’ partialpressure, while keeping their ratio constant. Maximum yields obtained in this system are comparable to maximumyields obtained from systems using a different catalyst (MgO, Li/MgO, xV/MgO, 18 % yield, Burch and Crabb (1993))and significantly higher than those obtained from systems with the same catalyst (a 5.7 % yield, Davies and Taylor(2004)).NOTATIONC concentration, mol/m3ODH oxidative dehydrogenationODHP oxidative dehydrogenation of propaneS selectivity, mol%X conversion, mol%Greek Lettersη stoichiometric factorSupercripts0 initial value of parameterSubscriptsp propanei species i4 International Journal of Chemical Reactor Engineering Vol. 5 [2007], Note S6http://www.bepress.com/ijcre/vol5/S6REFERENCESAlbonetti, S., Cavani, F., Trifirò, F., Vedrine, J. C. “Key aspects of catalyst design for the selective oxidation ofparaffins”. Catalysis Reviews: Science and Engineering, Vol. 38, No. 4, 413 (1996).Burch, R., Crabb, E. M. “Homogeneous and heterogeneous contributions to the oxidative dehydrogenation of propaneon oxide catalysts”. Applied Catalysis A: General, Vol. 100, No. 1, 111–130 (1993).Cadus, L. E., Ferretti, O. “Characterization of Mo−MnO catalyst for propane oxidative dehydrogenation”. AppliedCatalysis A: General, Vol. 233, No. 1–2, 239–253 (2002).Chen, K., Xie, S., Bell, A. T., Iglesia, E. “Structure and properties of oxidative dehydrogenation catalysts based onMoO3/Al2O3”. Journal of Catalysis, Vol. 198, 232–242 (2001).Dahl, I. M., Grande, H., Jens, K. J., Rytter, E., Slagtern, Å. “Oxidative dehydrogenation of propane in lithiumhydroxide/lithium iodide melts”. Applied Catalysis A: General, Vol. 77, 163–174 (1991).Davies, T., Taylor, S. H. “The oxidative dehydrogenation of propane using gallium-molybdenum oxide-based cata-lysts”. Journal of Molecular Catalysis A – Chemical, Vol. 220, No. 1, 77–84 (2004).Dharia, D., Letzsch, W., Kim, H., McCue, D., Chapin, L. “Increase light olefins production”. Hydrocarbon Processing,Vol. 83, No. 4, 61 (2004).Fox, D. B., Lee, E. H. “Supported molten salt catalysts for dehydrogenation”. Chemtech, Vol. 3, No. 3, 186–189(1973).Grabowski, R. “Kinetics of Oxidative Dehydrogenation of C2-C3 Alkanes on Oxide Catalysts”. Catalysis Reviews,Vol. 48, 199–268 (2006).Grabowski, R., Słoczyński, J. “Kinetics of oxidative dehydrogenation of propane and ethane on VOx/SiO2 pure andwith potassium additive”. Chemical Engineering and Processing, Vol. 44, No. 10, 1082–1093 (2005).Gussow, S., Spence, D. C., White, E. A. “Dehydrogenation links LPG to more octanes”. Oil & Gas Journal, Vol. 78,No. 49, 96–101 (1980).Hargreaves, J. S. J., Hutchings, G. J., Joyner, R. W., Taylor, S. H. “A study of the methane-deuterium exchangereaction over a range of metal oxides”. Applied Catalysis A: General, Vol. 227, No. 1–2, 191–200 (2002).Iglesia, E., Baumgartner, J. E. “Hydrogen-transfer and activation of propane and methane on ZSM5-based catalysts”.Catalysis Letters, Vol. 21, No. 1–2, 55–70 (1993).Koc, S. N., Gurdag, G., Geissler, S., Guraya, M., Orbay, M., Muhler, M. “The oxidative dehydrogenation of pro-pane over potassium-promoted molybdenum oxide/sol-gel zirconia catalysts”. Journal of Molecular Catalysis A:Chemical, Vol. 225, 197–202 (2005).Leveles, L., Seshan, K., Lercher, J. A., Lefferts, L. “Oxidative conversion of propane over lithium promoted magnesiacatalyst: I. Kinetics and mechanism”. Journal of Catalysis, Vol. 218, 296–306 (2003).Mazzocchia, C., Aboumrad, C., Diagne, C., Tempesti, E., Herrmann, J., Thomas, G. “On the NiMoO4 oxidativedehydrogenation of propane to propene – some physical correlations with the catalytic activity”. Catalysis Letters,Vol. 10, No. 3–4, 181–191 (1991).Meunier, F. C., Yasmeen, A., Ross, J. R. H. “Oxidative dehydrogenation of propane over molybdenum-containingcatalysts”. Catalysis Today, Vol. 37, No. 1, 33–42 (1997).Schuster, W., Niederer, J. P. M., Hoelderich, W. F. “The gas phase oxidative dehydrogenation of propane over TS-1”.Applied Catalysis A: General, Vol. 209, No. 1–2, 131–143 (2001).Smits, R. H. H., Seshan, K., Ross, J. R. H. “The selective oxidative dehydrogenation of propane over niobiumpentoxide”. Journal of the Chemical Society — Chemical Communications, Vol. 20, No. 8, 558–559 (1991).5Kotanjac et al.: Pressure Influence in the ODHPPublished by The Berkeley Electronic Press, 2007Takita, Y., Yamashita, H., Moritaka, K. “Selective partial oxidation of propane over metal phosphate catalysts”.Chemistry Letters, Vol. 18, No. 10, 1733–1736 (1989).Ushkov, S. B., Osipova, Z. G., Sokolovskii, V. D., Ketchik, S. V. “Catalytic activity of some sulphates in the reactionof oxidative dehydrogenation of propane”. Kinetics and Catalysis, Vol. 29, No. 1, 195–198 (1988).6 International Journal of Chemical Reactor Engineering Vol. 5 [2007], Note S6http://www.bepress.com/ijcre/vol5/S6

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Influence of the pressure on the product distribution in the oxidative dehydrogenation of
propane over a Ga2O3/MoO3 catalystInfluence of the pressure on the product distribution in
the oxidative dehydrogenation of propane over a Ga2O3/MoO3 catalyst
Kotanjac, Z. S.; Niederer, J. P. M.; Versteeg, Geert
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International Journal of Chemical Reactor Engineering
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Kotanjac, Z. S., Niederer, J. P. M., & Versteeg, G. F. (2007). Influence of the pressure on the product
distribution in the oxidative dehydrogenation of propane over a Ga2O3/MoO3 catalystInfluence of the
pressure on the product distribution in the oxidative dehydrogenation of propane over a Ga2O3/MoO3
catalyst. International Journal of Chemical Reactor Engineering, 5(1).
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INTERNATIONAL JOURNAL OF CHEMICAL
REACTOR ENGINEERING
Volume 5 2007 Note S6
Influence of the Pressure on the Product
Distribution in the Oxidative
Dehydrogenation of Propane over a
Ga2O3/MoO3 Catalyst
Zeljko S. Kotanjac∗ John P. M. Niederer†
Geert F. Versteeg‡
∗University of Twente, z.kotanjac@utwente.nl
†University of Twente, john.niederer@frieslandfoods.com
‡Clarkson University, geert.versteeg@procede.nl
ISSN 1542-6580
Copyright c©2007 The Berkeley Electronic Press. All rights reserved.
Influence of the Pressure on the Product Distribution
in the Oxidative Dehydrogenation of Propane over a
Ga2O3/MoO3 Catalyst∗
Zeljko S. Kotanjac, John P. M. Niederer, and Geert F. Versteeg
Abstract
The yields and selectivities in both the catalyzed and non-catalyzed oxida-
tive dehydrogenation of propane were found to increase with increasing pressure.
The results showed that the maximum yields of valuable ODH products could be
obtained by adjusting only reactants’ partial pressure, while keeping their ratio
constant.
KEYWORDS: oxidative dehydrogenation, heterogeneous catalysis, process de-
velopment
∗The authors gratefully acknowledge the financial support from the Netherlands Organisation for
Scientific Research (NWO).
1. INTRODUCTION
The oxidative dehydrogenation of propane as an alternative route for the production of propylene is drawing increasing
attention due to the increasing demand for lower olefins. The present production capacity mainly consists of steam
crackers, which are usually operated to obtain maximum ethylene yields. (Dharia et al., 2004)
The main alternatives are the dehydrogenation and oxidative dehydrogenation (ODH) of propane, with the first
one taking place at high temperatures of 800 – 900 K to obtain a favorable thermodynamic equilibrium. (Gussow
et al., 1980) However, a high reaction temperature also leads to coke formation and cracking to ethylene, which both
can be avoided with the ODH reaction. (Albonetti et al., 1996; Koc et al., 2005) In this process, which can for
example be catalyzed by Ga2O3/MoO3 mixtures, the main products are, besides propylene and ethylene, methane,
carbon monoxide, carbon dioxide and water. Ga2O3/MoO3 catalyst was chosen because of its good performance
(good alkane activation properties caused by Ga2O3 combined with a partial oxidation behavior of MoO3, as stated by
Davies and Taylor (2004)) and ease of preparation, described in section 2.
A problem in the further development of this system is the deep oxidation to COx. The actual mechanism of
the overall process is still not known, while the fact that oxygen presence is the key for achieving the conversions
beyond those expected based on the equilibrium of the simple dehydrogenation reaction is widely accepted. Although
many different and rather complex mechanisms for this reaction are investigated, as presented in Grabowski (2006),
the reaction can be simplified to the network shown in Figure 1. (Leveles et al., 2003; Chen et al., 2001)
C3H8
C3H6
COx
k1
k2
k3
Figure 1: Reaction network for the oxidative dehydrogenation of propane
As already shown by Grabowski (2006), partial pressures of reactants determine the reaction kinetics, therefore
also the conversion and selectivities. Changing total pressure while keeping feed composition constant gives us a
possibility to explore how conversion and selectivities change with partial pressure change, maintaining their ratio
constant.
In attempts to find a catalyst which would both be active at low temperatures and avoid deep oxidation, various
materials such as supported molten salt catalysts (alkali chlorides), LiOH/LiI melts, metal sulphates and phosphates,
as well as nickel molybdate, niobium pentoxide and TS-1 were investigated. (Fox and Lee, 1973; Dahl et al., 1991;
Ushkov et al., 1988; Takita et al., 1989; Mazzocchia et al., 1991; Smits et al., 1991; Schuster et al., 2001) In this paper
the influence of pressure on the yields and selectivities in the ODH of propane over a Ga2O3/MoO3 catalyst will be
investigated.
2. EXPERIMENTAL
For catalytic experiments, an equimolar mixture of Ga2O3 (Aldrich, 99.99 % ) and MoO3 (Aldrich, 99.99 %) was
ground in a pestle and mortar, after which tablets were pressed, which were crushed and sieved to obtain a particle
size of 0.85 – 1.00 mm. Subsequently, the catalyst was calcined at 873 K for 3 hours in an oxidizing helium/oxygen
(1:1 volume ratio) atmosphere.
Experiments were performed in a stainless steel packed bed reactor of 70 cm length, equipped with a quartz liner
of 10 mm in diameter to avoid possible side reactions with the steel reactor walls. The reactor was heated with two
separate electrical ovens controlled by Eurotherm 91e controllers [K-type ChromelTM/AlumelTM thermocouples]. A
catalyst bed with a volume of 4 ml (1.1 g of catalyst) was used for all experiments. A gas mixture consisting of he-
lium/propane/oxygen in a volume ratio of 8:2:1 was fed to the top of the reactor with a total flow rate of 110 ml/min
using Brooks R© 5850TR mass flow controllers. For non-catalytic experiments a similar volume of quartz beads was
1Kotanjac et al.: Pressure Influence in the ODHP
Published by The Berkeley Electronic Press, 2007
used to maintain the space velocity and contact time. Schematic overview of the experimental setup used for this
research is given in Figure 2.
C1
T
T2
MFC4MFC3
AdditivePropane Oxygen
MFC2
PC
Helium
MFC1
T
T1
PRC2
GC
R1
R2
Figure 2: Schematic overview of the experimental setup used in this research: R1–2 — Reactor sections, MFC1–4
— Mass flow controllers, T1–2 — Temperature controllers/indicators, C1–2 — Condensers, PR — Pressure regulator,
GC — Gas chromatograph
Experiments were carried out at 733 K and 773 K, varying the pressure from 1 to 6 bar in steps of 1 bar. After
each experiment of 5 hours the catalyst bed was regenerated for 2 hours at 873 K with a 1:1 helium/oxygen mixture
to remove any coke formed during the reaction. Reaction products were analyzed online on a Varian MicroGC 4900
equipped with both a Molsieve 5 A˚ and a Al2O3/KCl column using thermal conductivity detectors. The carbon mass
balance in all experiments was 100 ± 5 %.
Propane conversion, Xp, has been calculated according to formula
Xp =
C0p−Cp
C0p
(1)
where C0p and Cp are the concentrations of propane at the inlet and outlet of the reactor, respectively.
Selectivity to product i has been calculated according to formula
Si =
ηi ·C f ormedi
Cspentpropane
(2)
where ηi denotes a stoichiometric factor.
3. RESULTS
Results obtained from experiments performed at atmospheric pressure (see Table 1) were comparable to those of other
authors: Grabowski and Słoczyn´ski (2005) obtained a selectivity to propylene of 76.5 % at a conversion of 1.2 %
(733 K) and 72.8 % at a conversion of 1.5 % at 773 K, respectively, over VOx/SiO2 catalyst. Schuster et al. (2001)
reported on a conversion of 19 % with a selectivity to propylene of over 70 % at 823 K, over the titanosilicalite TS-1
catalyst, whereas the best result of Cadus and Ferretti (2002) was a selectivity of 31.8 % at 21.84 % of conversion at
733 K, over Mo-MnO catalysts.
Increasing the pressure from 1 to 4 bar (733 K) led to a significant increase in the conversion from ∼11 to
∼40 mol%; a further increase from 4 to 6 bar led to a decrease of the conversion to ∼26 mol%, whereas at 773 K
2 International Journal of Chemical Reactor Engineering Vol. 5 [2007], Note S6
http://www.bepress.com/ijcre/vol5/S6
an increase in the pressure of 1 to 3 bar led to an increase in the conversion from ∼15 to ∼45 mol% (see Table 1). A
further increase from 3 to 6 bar led to a decrease to ∼34 mol%. Non-catalytic experiments at 773 K revealed a similar
trend up to 3 bar, where the conversion was only 2.24 % at 1 bar and 41.61 % at 3 bar. Results at 733 K also revealed
an increasing conversion (0−29.1 %) with increasing pressure. At pressures higher than 3 bar (773 K) the situation
was the opposite: the conversion in non-catalytic experiments was 10.3 – 11.7 % higher than in catalytic experiments.
Table 1: Conversion and selectivities for the catalyzed (top) and non-catalyzed (bottom) ODHP at 733 and 773 K
pressure, bar 1 2 3 4 5 6 1 2 3 4 5 6
T = 733 K T = 773 K
10.92 13.51 37.33 39.89 32.50 25.91 15.12 32.61 45.48 34.95 27.39 34.34
X, mol% 0 1.31 15.08 28.01 29.49 29.10 2.24 12.16 41.61 38.55 30.29 40.38
51.90 52.00 48.70 46.97 37.53 34.40 51.57 52.68 46.81 46.96 42.50 20.14
C3H6 0 100 82.71 52.71 54.28 43.04 66.54 75.96 47.53 49.21 27.99 6.19
1.73 5.83 11.94 13.56 8.50 7.20 6.79 23.76 17.99 11.99 9.46 4.74
C2H4 0 7.80 10.37 12.01 9.08 8.74 2.97 15.60 21.63 22.61 7.51 1.63
S, mol% 0 3.03 6.19 6.22 7.00 11.19 2.08 7.70 7.76 7.72 8.14 10.20
CH4 0 0 1.39 5.81 3.84 5.08 0 5.51 9.66 9.03 8.86 17.51
55.74 45.55 21.85 20.34 27.18 37.71 42.77 19.96 14.56 14.75 15.36 20.74
CO 0 0 10.80 26.55 23.11 29.48 5.46 6.79 15.92 12.39 35.44 27.93
A similar change in the conversion was found at 733 K, where the drop in the conversion occurred at pressures
higher than 4 bar. The overall conversion in the catalyzed system was about 55 % higher than in the non-catalytic
(26.68 % vs. 17.16 %) at 733 K, whereas the conversion under catalytic conditions was about 15 % higher at 773 K
than in the non-catalytic (31.64 % vs. 27.53 %). This was probably due to Ga2O3, which is a well known promoter for
alkane activation. (Iglesia and Baumgartner, 1993; Hargreaves et al., 2002)
The selectivity to propylene based on propane at 773 K remained ∼42.5 – 52.5 % over the pressure range inves-
tigated, although for non-catalytic experiments the scattering in the selectivity was large in the range ∼49 −76 %.
At 733 K, the scattering was even larger, from 34.40 % to 52.00 % for catalytic and from 43.04 % to 100 % for non-
catalytic experiments. The presence of MoO3 in the catalyst bed certainly had a large influence on the selectivity, as
MoO3 is known to be a selective catalyst in the oxidative dehydrogenation of propane. (Meunier et al., 1997)
At 773 K a significant drop in the selectivity to propylene was found at 6 bar for catalytic and 5 and 6 bar for
non-catalytic systems. At 733 K the drop in selectivity was not so drastic as for the catalytic system and decreased
from 46.97 % at 4 bar to 34.40 % at 6 bar, via 37.53 % at 5 bar. The non-catalytic system showed a constant decrease
in selectivity from 100 % at 2 bar to 43.40 % at 6 bar.
The selectivity to ethylene based on propane showed a comparable pattern at 773 K, reaching a maximum of
23.76 mol% at 2 bar, whereas in non-catalytic experiments the maximum selectivity was 22.61 mol% at 4 bar. Both
catalytic and non-catalytic systems showed a maximum ethylene selectivity at 4 bar of 13.56 % and 12.01 %, respec-
tively.
As can be seen from Figure 3, the maximum propylene yield was 18.74 % at 4 bar at 733 K and 21.29 mol% at
3 bar at 773 K. In the non-catalytic system a maximum yield of 14.76 % at 4 bar and 733 K, and 19.78 % at 3 bar and
773 K was found.
The ethylene yield, which also is a valuable product, had a maximum of 8.18 % at 3 bar for the catalytic and
8.99 % for the non-catalytic system at 773 K. At 733 K, the yield was found to be lower and reached 3.36 % in the
catalytic and 5.40 % in the non-catalytic system at 4 bar. Methane, and, more importantly, carbon monoxide yields
only showed a minor increase over the pressure range studied in these experiments. The maximum yields for methane
and carbon monoxide were 7.07 % and 12.06 % for the non-catalytic system at 773 K, respectively. At 733 K in both
the catalytic and non-catalytic system, as well as at 773 K in the catalytic system, methane and carbon monoxide yields
3Kotanjac et al.: Pressure Influence in the ODHP
Published by The Berkeley Electronic Press, 2007
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 
 
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Figure 3: Product yields in the catalyzed ODH of propane at 773 K at different pressures
were significantly lower, with minimum of 1.63 % for methane in the non-catalytic and 2.90 % for CO in the catalytic
system at 733 K.
4. CONCLUSION
The results clearly show that the high yields of valuable ODH products could be obtained by adjusting reactants’ partial
pressure, while keeping their ratio constant. Maximum yields obtained in this system are comparable to maximum
yields obtained from systems using a different catalyst (MgO, Li/MgO, xV/MgO, 18 % yield, Burch and Crabb (1993))
and significantly higher than those obtained from systems with the same catalyst (a 5.7 % yield, Davies and Taylor
(2004)).
NOTATION
C concentration, mol/m3
ODH oxidative dehydrogenation
ODHP oxidative dehydrogenation of propane
S selectivity, mol%
X conversion, mol%
Greek Letters
η stoichiometric factor
Supercripts
0 initial value of parameter
Subscripts
p propane
i species i
4 International Journal of Chemical Reactor Engineering Vol. 5 [2007], Note S6
http://www.bepress.com/ijcre/vol5/S6
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Influence of the Pressure on the Product Distribution in the Oxidative Dehydrogenation of Propane over a Ga2O3/MoO3 Catalyst

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