Research Group Caro

In catalytic membrane reactors, the expertise catalysis and membranes are combined synergistically. In such reactors, limitations by the equilibrium are circumvented for important reactions like dehydration, esterification etc., and conversion as well as yield can be improved.

RESEARCH EXPERTISE: CATALYSIS AND MEMBRANES

There is extensive experience with diverse catalytic reactions as steam reforming of methane, partial oxidation of methane to synthesis gas, aromatization and dimerization of methane, synthesis of dimethyl ether and dimethyl carbonate, oxidative and non-oxidative dehydration as well as Andrussow and Ostwald reactions.

Experience in the field of gas separation membranes is particularly with membranes based on zeolithes, metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs). Moreover, scale-up friendly mixed matrix membranes with MOF or COF nanoparticles as fillers in a pure polymer matrix are investigated as gas separation membranes.

Achievements are published in 360 scientific papers, 42 patents and have been recognized by national (Ostwal Medal) and international (Breck Award) awards. Research has been funded in collaborative projects by EU, BMBF, BMWi, DFG and directly by companies. Partly, investigations have been made at the European Nanoporous Materials Institute of Excellence (ENMIX).

SWITCHING GAS TRANSPORT IN A MEMBRANE BY EXTERNAL STIMULI

Two variants of switching the gas flux through a MOF membrane have been successfully realized:

An external electrical field acts on ions and dipols in the MOF structure, and it can be used to deform the crystal lattice and thus to control the gas flux through a MOF-based membrane.

Shining light of adjustable wavelength on the membrane surface, azo groups in the MOF membrane can be switched from trans to cis an vice versa. Thus, the pore size and so the gas flux can be varied.

  •  A. Knebel, B. Geppert, K. Volgmann, D.I. Kolokov, A.G. Stepanov, J. Twiefel, P. Heitjans, D. Volkmer, J. Caro, Defibrillation of soft porous metal-organic frameworks with electric fields, Science, 358 (2017) 347-351.
  • A. Knebel, C. Zhou, A. Huang, J. Zhang, L. Kustov, J. Caro, Smart metal-organic frameworks (MOFs): Switching gas permeation through MOF membranes by external stimuli, Chem. Eng. Technol. 41 (2018) 224-234.
  • A. Knebel, L. Sundermann, A. Mohmeyer, I. Strauß, S. Friebe, P. Behrens, J. Caro, Azobenzene guest molecules as light-switchable CO2 valves in an ultrathin UiO-67 membrane, Chemistry of Materials, 29 (2017) 3111-3117.
  • S. Zhou, Y. Wei, L. Li, Y. Duan, Q. Hou, L. Zhang, L.-X. Ding, J. Xue, H.H. Wang, J. Caro, Paralyzed membrane: Current-driven synthesis of a metal-organic framework with sharpened propene/propane separation,Science Adv. 4 (2018) eaau 1393.
  • Z. Wang, A. Knebel, S. Grosejan, D. Wagner, S. Bräse, C. Wöll, J. Caro, L. Heinke, Tunable molecular separation by nanoporous membranes, Nature Commun. 7:13872, 2016.
  • K. Müller, A. Knebel, F. Zhao, D. Bleger, J. Caro, L. Heinke, Switching thin films of azobenzene-containing metal-organic frameworks with visible light, Chem. Eur. J. 23 (2017) 5434-5438.

AROMATIZATION OF METHANE IN MEMBRANE REACTORS

Conversion of methane in liquid fuels and chemicals is technologically important. An established way is the aromatization of methane according to  6 CH4 ® C6H6 + 9 H2 at T>800°C. However, the so far obtained yield is far below 10 %. The problem can be solved by membrane reactors. Under equilibrium-controlled conditions membrane reactors can the act on the split-off hydrogen by

  • removing it from the reactor by a newly developed hydrogen-selective ceramic membrane, or by
  • burning it in-situ with a stoichiometric amount of oxygen, which is feed into the reactor by a newly developed oxygen-selective membrane from ambient air.

Lead by LUH, in national and international collaborative research groups, with contributions from universities, research institutes and industry, both variants have been practiced successfully.

  • Z. Cao, H. Jiang, H. Luo, S. Baumann, W.A. Meulenberg, J. Assmann, L. Mleczko, Y. Liu, J. Caro, Natural gas to fuels and chemicals: improved methane aromatization in the oxygen-permeable membrane reactor, Angew. Chem. Int. Ed. 52 (2013) 13794-13797.
  • J. Xue, Y. Chen, Y. Wei, A. Feldhoff, H.H. Wang, J. Caro, Gas to liquids: Natural gas conversion to aromatic fuels and chemicals in a hydrogen-permeable ceramic hollow fiber membrane reactor, ACS Catalysis, 6 (2016) 2448-2451.
  • S. Cheng, Y. Wang, L. Zhuang, J. Xue, Y. Wei, A. Feldhoff, J. Caro, H. Wang, A dual-phase ceramic membrane with extremely high H2 permeation flux prepared by autoseparation of a ceramic precursor, Angew. Chemie Int. Ed. 55 (2016) 10895-10898.

CONTACT

apl. Prof. Dr. rer. nat. habil. Armin Feldhoff
Group Leader
apl. Prof. Dr. rer. nat. habil. Armin Feldhoff
Group Leader