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Poster

Catalytic Study of Template-Ion Exchanged Ni/MCM-41 as Used for the Direct Transformation of Ethene Into Propene

MPG-Autoren
http://pubman.mpdl.mpg.de/cone/persons/resource/persons86519

Wolff,  T.
Physical and Chemical Foundations of Process Engineering, Max Planck Institute for Dynamics of Complex Technical Systems, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons86315

Hamel,  C.
Physical and Chemical Foundations of Process Engineering, Max Planck Institute for Dynamics of Complex Technical Systems, Max Planck Society;
Otto-von-Guericke-Universität Magdeburg, External Organizations;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons86525

Zahn,  V. M.
Physical and Chemical Foundations of Process Engineering, Max Planck Institute for Dynamics of Complex Technical Systems, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons86477

Seidel-Morgenstern,  A.
Physical and Chemical Foundations of Process Engineering, Max Planck Institute for Dynamics of Complex Technical Systems, Max Planck Society;
Otto-von-Guericke-Universität Magdeburg, External Organizations;

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Zitation

Lehmann, T., Wolff, T., Hamel, C., Zahn, V. M., & Seidel-Morgenstern, A. (2010). Catalytic Study of Template-Ion Exchanged Ni/MCM-41 as Used for the Direct Transformation of Ethene Into Propene. Poster presented at 2010 AIChE Annual Meeting, Salt Lake City, USA.


Zitierlink: http://hdl.handle.net/11858/00-001M-0000-0013-8E93-B
Zusammenfassung
Propene is, in contrast to ethene, a side product in huge industrial processes like steam cracking or catalytic cracking. The availability of propene is therefore to a large extent directly coupled to the production of ethene. However, the demand for propene has been constantly growing in past years since propene is used for the production of a number of large volume chemicals (e. g. polypropylene). This growth – even exceeding a similar development for ethene – led to a considerable gap between propene supply and demand [1]. The situation can be expected to aggravate further as soon as the global economy regains impetus. In this context intensive research for new synthetic approaches regarding propene generation is currently underway. One of the potential alternatives is to alter the overall product spectrum of cracking processes via the direct conversion of the cracker main product ethene to propene (ETP). Very recently a number of promising catalysts, zeolites [2,3] as well as supported metal catalysts [4,5], have been employed for this ETP reaction. Moreover, some of these catalysts may provide a route to propene based on renewable feed stocks, i. e., dehydration of bio-ethanol to ethene and subsequent transformation of ethene into propene [6,7]. The focus of the study at hand is on supported bifunctional nickel catalysts. As-synthesized mesoporous MCM-41 has been used as support material which was then doped with nickel via a template-ion exchange method developed by Iwamoto and co-workers (see [4] and references therein). The resulting catalyst Ni/MCM-41 simultaneously contains metal (nickel) and acid functions. It is reported in the literature that the ETP reaction may proceed via three consecutive reaction steps [4,5]. First of all, ethene dimerizes to 1-butene (metal function) followed by a double bond shift to 2-butenes (acid function). Subsequent metathesis between ethene and 2-butenes (metal function) generates propene. A possible mechanistic pathway for Ni/MCM-41 is proposed in Fig. 1. This contribution presents the results of a comprehensive experimental study dealing with the preparation and the characterization of template-ion exchanged Ni/MCM-41 as a possible catalytic system for the ETP reaction. The goal was to gather further knowledge about this system in addition to what has already been published in the literature [4]. In the field of catalyst preparation, the influence of different silica sources for the synthesis of the support material, different nickel precursors and metal content was investigated. In particular, the kind of silica source had a surprisingly strong influence on the catalyst performance. Catalysts prepared with colloidal silica of small particle diameter gave the best results. Furthermore, the catalyst system was thoroughly characterized by using chemical analysis, XRD, TEM, EDX, BET measurements, TPD and TPR. One of the important findings here is that the active nickel phase does not seem to be nickel oxide but rather some cationic form of nickel on the support surface. Apart from catalyst characterization, reaction studies have been carried out. Fig. 2 depicts ethene conversion and propene selectivity in a temperature range between 50 and 450 °C. Significant ethene conversion can already be observed at temperatures as low as 75 °C. At this temperature, ethene consumption corresponds mainly to the formation of 1-butene via dimerization. Double-bond isomerization of butenes also occurs at low temperatures. The metathesis of 2-butene with additional ethene sets in between 250 and 300 °C. Remarkable ethene conversion of 75 % and a propene selectivity of 50 % could be obtained at approximately 400 °C (see Fig. 2). Another point of investigation was the influence of water vapor in the feed gas. It has been reported that water is a necessary prerequisite for catalytic activity of Ni/MCM-41 [4]. This would be somewhat detrimental since the hydrothermal stability of MCM-41 is questionable over longer operating periods (especially important for potential industrial application). However, no positive influence of water vapor was found for our catalysts. In fact, the prepared catalysts exhibited highest activity in a water-free environment (see Fig. 2). Long-time activity measurements revealed moderate deactivation. Ethene conversion dropped roughly from 80 to 60 % over 50 hours of continuous operation at 340 °C, while propene selectivity decreased in the same time interval from 26 to 21 % (typical curves are shown in the insets of Fig. 2). Moreover, catalytic tests were performed to investigate the influence of residence time and initial ethene concentration which gave some preliminary support for the suspected reaction mechanism (Fig. 1). In addition, we studied the coupled reaction equilibria of the system of ETP reactions to gain an objective standard for catalyst evaluation. Based on the experimental results, the direct conversion of ethene to propene using supported bifunctional nickel catalysts shows promising potential to contribute to an improved propene supply. Compared to other catalysts described in the literature, Ni/MCM-41 seems to be one of the most stable systems for the conversion of ethene to propene. This justifies more detailed kinetic investigations on a quantitative basis which are planned for the future. References: [1] H. A. Wittcoff, B. G. Reuben, J. S. Plotkin, Industrial Organic Chemicals, 2nd ed., Wiley (2004). [2] H. Oikawa, Y. Shibata, K. Inazu, Y. Iwase, K. Murai, S. Hyodo, G. Kobayashi, T. Baba, Appl. Catal. A, 312, 181-185 (2006). [3] B. Lin, Q. Zhang, Y. Wang, Ind. Eng. Chem. Res., 48, 10788-10795 (2009). [4] M. Iwamoto, Catal. Surv. Asia, 12, 28-37 (2008). [5] M. Taoufik, E. Le Roux, J. Thivolle-Cazat, J.-M. Basset, Angew. Chemie Int. Ed., 46, 7202-7205 (2007). [6] K. Inoue, M. Inaba, I. Takahara, K. Murata, Catal. Lett., 136, 14-19 (2010). [7] S. Sugiyama, Y. Kato, T. Wada, S. Ogawa, K. Nakagawa, K.-I. Sotowa, Top. Catal., article in press (2010).