A continuous flow method for generation of hydrogen from formic acid

1. A continuous flow method for generation of hydrogen from formic acid Artur Majewski [a], David J. Morris [b], Kevin Kendall [a], and Martin Wills [b] [a]Department of Chemical Engineering, The University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK. fax: (+44) 121 414 2739, e-mail: K.kendall@bham.ac.uk [b] Department of Chemistry, The University of Warwick, Coventry, CV4 7AL, UK. fax: (+44) 24 7652 4112, e-mail: M. wills@warwick.ac.uk HDelivery Introduction A method is described for the continuous-flow generation of hydrogen from the ruthenium-catalysed decomposition of formic acid (FA) in the presence of an amine base. The rate of addition of formic acid may be mediated by either a temperature feedback mechanism or through the use of impedence measurements. Procedure Results on the use of ruthenium complexes for hydrogen generation from FA/amine systems at around 120oC are disclosed. In order to establish which amines were worthy of further examination as a base in hydrogen production, a series (1-6) were screened for compatibility with formic acid. The best result, was achieved using N,N-dimethyloctylamine 3, which gave a smooth increase and then decrease of gas generation over time. For larger scale continuous flow reactions a test rig was constructed containing a 2L reaction flask mounted on a stirrer/hotplate. The reaction vessel was fitted with an inlet tube into which formic acid could be replenished using a peristaltic pump. The reaction temperature (or resistance) was monitored using the LabVIEW programme. The reactor was charged with ca. 100 mL of a 5:2 (molar) mixture of FA and the amine, together with a ruthenium(II) complex. Results and Discussion A continuous flow addition reaction was carried out each day for between 1 and 6 days and measurements of the gas flow rate were taken using the flow meter. Selected results are illustrated in Figure below. Since the control of the reaction using a temperature feedback mechanism had proved to be difficult due to a delay in the response time, the use of impedence as a feedback response mechanism was investigated. Because the formate salt is a strong electrolyte and amines are dielectric, we tested impedence measurement to control the reaction. Replenishment was programmed for when the impedence rose above 80Ω. Using RuCl2(DMSO)4 the reaction was very effective on the first day, with an average gas production of over 1.5L/min. This rate reduced each day, in line with the temperature-controlled reaction. Flow meter Condensers Peristaltic pump Computer - pump controlling and data recording Refrigerator circulator Reactor Impedance meter Fuel cell Conclusions and Acknowledgements We have demonstrated that efficient continuous generation of hydrogen and CO2 can be achieved from a formic acid/tertiary amine base mixture using either a temperature or impedence-based feedback system. We thank the EPSRC for funding through a feasibility grant and via the SUPERGEN 14 H-Delivery grant. • References • Artur Majewski, David J. Morris, Kevin Kendall, and Martin Wills, ChemSusChem 2010, 3, 431-434. • a) T. C. Johnson, D. J. Morris, M. Wills, Chem. Soc. Rev. 2010, 39, 81-88; b) F. Joó, ChemSusChem 2008, 1, 805-808; c) S. Enthaler, ChemSusChem 2008, 1, 801-804. • D. J. Morris, G. J. Clarkson, M. Wills, Organometallics 2009, 28, 4133-4140.