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 and Discussion
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.
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.
n
N
N
N
N
7
2.0
80
1.5
60
40
20
50
8
100
150
0
200
Flow
meter
0
Condensers
Peristaltic
pump
0.5
0
time [min]
The
best
result,
was
achieved
using
N,Ndimethyloctylamine 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.
1.0
gas volume (388L)
temperature
gases flow
50
20
0
6
100
40
0
4 (n=1), 5 (n=5)
150
100
100
200
time [min]
gas flow [L/min]
60
2.5
0.0
400
300
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.
1800
1st day
FA:DMOA 5:2
140
average performances from 5
hours work at resistance ~80
FA:DMOA 5:2 100ml reactor
0.1g RuCl2DMSO4
1600
5000
140
1400
120
130
4000
100
3000
80
60
2000
40
0
0
50
100
150
1000
120
800
600
1000
temperature
resistance
gas flow
20
1200
110
400
200
time [min]
250
0
300
reaction temperature [oC]
N
3
temperature
gas volume (5.9 L)
gas flow
80
120
gas flow [ml/min]
2
100
temperature [oC] or resistance []
1
200
gas flow [mL/min]
N
N
temperature [oC]
N
3.0
gas flow [ml/min]
120
140
250
temperature [oC]
FA:Dimethyloctylamine 5:2
140
3rd day
FA:DMOA 5:2
temp
gas flow
200
0
100
1
2
3
4
5
day
Computer
- pump
controlling
and data
recording
Refrigerator
circulator
Fuel cell
Impedance
meter
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.
Reactor
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.
1.
2.
3.
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.