http://www.physorg.com/news/2010-12-formic-acid.html
http://www.physorg.com/print210417671.html
December 1st, 2010
Formic Acid in the Engine
Do ants hold the key to the fuel of the future? Formic acid provides
more efficient and safer storage of hydrogen. It is an ideal way to
store energy from renewable sources or to power 21st century cars.
Hydrogen is often referred to as the future replacement for fossil
fuels. Despite being environmentally-friendly and efficient, it
nevertheless has many drawbacks. Because it is extremely flammable,
it must be stored in bulky pressurized cylinders. Scientists from
the EPFL and their colleagues at the Leibniz-Institut für Katalyse
have found a way around these obstacles. Once converted to formic
acid, hydrogen can be stored easily and safely. This is an ideal
solution for storing energy from renewable sources like solar or
wind power, or to power the cars of tomorrow.
Hydrogen is easy to produce from electrical energy. With a catalyst
and the CO2 present in the atmosphere, scientists have been able to
convert it to formic acid. Rather than a heavy cast iron cylinder
filled with pressurized hydrogen, they obtain a non-flammable
substance that is liquid at room temperature.
In November 2010, EPFL laboratories produced the opposite reaction.
Through a catalytic process, the formic acid reverts to CO2 and
hydrogen, which can then be converted into electricity. A compact
working prototype producing 2 kilowatts of power has been developed,
and two companies have purchased a license to develop this
technology: Granit (Switzerland) and Tekion (Canada).
Storing Renewable Energy
“Imagine for example that you have solar panels on your roof,” says
Gabor Laurenczy, professor at the Laboratory of Organometallic and
Medicinal Chemistry and Head of the Group of Catalysis for Energy
and Environment.“In bad weather or at night, your formic acid
battery will release the excess energy stored while the sun was
shining.” In such a configuration, the method can restitute more
than 60% of the original electrical energy.
This solution is extremely safe. The formic acid continuously
releases very small amounts of hydrogen, “just what you need at the
time for your energy consumption,” says the researcher.
Another advantage over conventional storage is that the method can
store almost twice as much energy at equal volume. One liter of
formic acid contains more than 53 grams of hydrogen, compared to
just 28 grams for the same volume of pure hydrogen pressurized to
350 bars.
Finally, the researchers have developed a catalytic process using
iron, which is readily available and inexpensive compared to “noble”
metals such as platinum or ruthenium. As with all catalysts, no
material is degraded during the process.
Formic acid at the pump
It is probably in the automotive field that the invention has the
greatest potential. Currently, the prototypes produced by certain
carmakers store hydrogen in conventional form, which entails
problems such as risk of explosion, large volume pressurized tanks,
difficulties in filling the tank quickly, etc.
The vehicles of the 21st century may run on formic acid. This
solution allows for safer, more compact hydrogen storage as well as
easier filling at the pump – formic acid is liquid at room
temperature. “Technically, it is quite feasible. In fact, a number
of major automobile manufacturers contacted us in 2008, when oil
prices reached record highs,” says Gabor Laurenczy. “In my opinion,
the only obstacle is cost.” It will be several years before drivers
can pull up to any anthill and fill their tanks.
US Patent Application 2010068131
HYDROGEN PRODUCTION FROM FORMIC
ACID
Inventor: LAURENCZY GABOR [CH] ; FELLAY CELINE
EC: B01J31/02C; B01J31/24; (+2)
IPC: C01B3/02; C01B3/38; C01B3/00
Also published as: EP1918247
// KR20090073230 // JP2010506818 // WO2008047312
// EP2086873
Abstract -- The present
invention relates to a method of producing hydrogen gas and carbon
dioxide in a catalytic reaction from formic acid, said reaction
being conducted in an aqueous solution over a wide temperature range
and already at room temperature (25 DEG C.). The reaction is
advantageous because it can be tuned to take place at very high
rates, up to about 90 litre H2/minute/litre reactor volume. The gas
produced is free of carbon monoxide. The method of the present
invention is particularly suitable for providing hydrogen for a
motor, fuel cell or chemical synthesis.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method of producing
hydrogen gas and carbon dioxide from formic acid, and to a method of
producing energy.
PRIOR ART AND THE PROBLEM
UNDERLYING THE INVENTION
[0002] Hydrogen gas, H2, is a versatile source of energy and an
important starting material for many chemical reactions. Therefore,
hydrogen production is a large and growing industry, with globally
about 50 million tons being produced in 2004. As an energy source,
for example, it can be used in fuel cells, combustion motors and
chemical reactors for producing energy in the form of electric
energy, kinetic energy, and/or heat, just to mention a few. It is
for these many applications that hydrogen gas was recognised to be a
primary carrier that connects a host of energy sources to diverse
end uses (US Department of Energy 2003 report).
[0003] The high importance of hydrogen gas may be illustrated at the
example of the hydrogen fuel cell. Although water electrolysis gives
very pure H2, traditionally produced hydrogen gas often contains
carbon monoxide, which is deleterious to the catalyst in fuel cells.
This indicates how important it is to provide a process for
producing hydrogen gas at high purity locally, comprising no
contamination by CO.
[0004] Furthermore, hydrogen gas is extremely volatile. As a
consequence, hydrogen gas is stored at high pressure or low
temperature in gas containers made of steel, the weight of which is
exceeding by far the weight of the hydrogen gas stored in it.
[0005] Hydrogen gas reacts violently with oxygen in a wide
concentration range, making the storage of large quantities of
hydrogen dangerous.
[0006] Given the difficulty in storing the volatile hydrogen gas, it
is a particular objective to provide a process of preparing hydrogen
gas in situ, in other words, instantly upon demand of a selected,
hydrogen consuming device or process. For example, it would be
advantageous to provide a vehicle comprising a hydrogen fuel cell or
a hydrogen driven combustion motor, the vehicle being propelled by
energy generated in a reaction consuming hydrogen gas. Preferably,
such a vehicle does not require a heavy and dangerous container for
storage of hydrogen gas.
[0007] Generally, the present invention seeks to provide hydrogen
gas in an inexpensive, efficient manner, and, if necessary at high
pressure, in suitable reactors for direct use in a hydrogen
consuming process or device.
[0008] In JP 2005-289742 a method for producing hydrogen gas and
carbon dioxide from formic acid is disclosed. However, the reaction
is conducted at temperatures in the range of 250-600[deg.] C. and
is, therefore, not very practical.
[0009] U.S. Pat. No. 4,597,363 disclose a method of producing
hydrogen gas for a fuel cell by conversion of oxalic acid to formic
acid, followed by formation of hydrogen gas and carbon dioxide from
formic acid at elevated temperatures.
[0010] In both prior art documents, hydrogen gas is obtained at a
low conversion rate, relatively high temperatures and at a low gas
pressure. It is an objective of the present invention, to provide a
method for producing hydrogen gas at higher reaction rates,
temperatures in the range of 30-180[deg.] C. and at desired/very
high gas pressures.
[0011] Istvan Jószai and Ferenc Joó "Hydrogenation of aqueous
mixtures of calcium carbonate and carbon dioxide using a
water-soluble rhodium(I)-tertiary phosphine complex catalyst"
Journal of Molecular Catalysis A: Chemical 224 (2004) 87-91,
disclose a method in which calcium formate is obtained from calcium
carbonate under a gas phase containing both H2 and CO2. Also the
decomposition of Ca(HCOO)2 to H2 and CO2 by aid of the same catalyst
was reported. Again, only low conversion rates and low gas pressures
were obtained.
[0012] Jenner et al, Journal of Molecular Catalysis, 64 (1991)
337-347, disclose the decomposition of formic acid, more precisely
methyl formate in aqueous solution, to hydrogen, carbon dioxide and
carbon monoxide (1%). In this reaction, CO is produced in an
intermediate step, which accounts for its presence in the final
products. As catalysts, Ru3(CO)12 and tributylphosphine are
disclosed. Furthermore, no formate salt is added to the reaction
mixture. In view of this document, it is an objective of the present
invention to avoid CO impurities on the product side, use formic
acid as H2 and CO2 source, avoid the formation of methanol as
by-product and to be able to conduct the reaction at lower
temperatures with still high conversion efficiency and speed.
[0013] R. Laine et al., Journal of American Chemical Society, 99(1)
(1977) p. 252-253, disclose the use of a ruthenium carbonyl catalyst
in a water gas shift reaction conducted in very diluted
ethoxyethanol solvent. A relatively slow conversion of formic acid
or formate to hydrogen gas and CO2 in the same system is reported
(half life of formic acid is about 300 s). The very diluted
ethoxyethanol solution, with a molar ratio of KOH/HCOOH higher than
1.5 (mole/mole), renders this reaction unsuitable for practical
applications.
[0014] Khai et al., Journal of organometallic chemistry, 309 (1986)
p. C63-C66 disclose the reduction of nitro- and halo aromatic
compounds in presence of formic acid, the latter being decomposed in
the course of the reaction. The reaction takes place in organic
solvents (THF, benzene, DMF) and in presence of a water-insoluble
triphenyl ruthenium catalyst. The reduction of nitro- and halo
aromatic compounds is not the subject of the present invention.
[0015] King et al., Inorganica Chimica Acta, 237 (1-2) (1995), p.
65-69, report the decomposition of formic acid in a system
comprising a aqueous solution of rhodium(III) and NO<2->. In
this reaction, NO<2-> is used up and converted to N2O. The
catalyst is quickly deactivated during the reaction into insoluble
Rh metal. The present invention has the goal of converting formic
acid to hydrogen in a continuous way with catalyst recycling.
Furthermore, specific further products are not desired.
[0016] Gao et al., J. Chem. Soc., (2000), p. 3212-3217 and Chem.
Comm. (1998), 2365-2366, disclose the interconversion of formic acid
and H2/CO2 in acetone solution in presence of a binuclear ruthenium
catalyst comprising two bis-(diphenylphosphine)methane ligands. They
use air/oxygen sensitive system and catalyst, which releases CO
during the activation. Acetone is a volatile and flammable solvent.
[0017] FR 1228452 discloses the decomposition of formic acid in
mixtures comprising further aliphatic acids by the aid of a catalyst
comprising a metal such as platine bound on active carbon. The
reaction takes place slowly and conversion efficiencies are around
80-90%). The present invention has the objective of conducting the
conversion of formic acid in absence of other aliphatic acids and at
higher conversion efficiencies.
[0018] It is an objective of the present invention to provide a
method of producing hydrogen gas at a increased rate and at a high
conversion efficiency. It is a further objective to produce hydrogen
gas at higher pressures. Ideally, hydrogen gas is produced at
desired H2 partial pressures of up to 600 bar or more.
[0019] In particular, it is an objective to produce hydrogen in
situ, at a desired high rate for feeding a hydrogen consuming
device, for example a fuel cell or burning motor, or a hydrogen
consuming process directly, in an amount corresponding to the
hydrogen gas to be used.
SUMMARY OF INVENTION
[0020] The inventors of the present invention provided a method for
producing hydrogen gas from formic acid, which method meets the
objectives discussed above and which solves the problems of the
prior art.
[0021] In a first aspect, the present invention provides a method of
producing hydrogen gas and carbon dioxide in a chemical reaction
from formic acid, said reaction being conducted at a temperature in
the range of 20-200[deg.] C.
[0022] In a second aspect, the present invention provides a method
of producing hydrogen gas and carbon dioxide in a chemical reaction
from formic acid, said reaction being conducted in an aqueous
medium. Preferably, the reaction is conducted at a pH in the range
of 0-7, 1.5-5, more preferably 2.5-4.5.
[0023] In a third aspect, the present invention provides a method of
producing hydrogen gas and carbon dioxide in a chemical reaction
from formic acid, said reaction being conducted at a total gas
pressure in the range of 1-1200 bar, or higher.
[0024] In a fourth aspect, the present invention provides a method
of producing hydrogen gas and carbon dioxide in a chemical reaction
from formic acid, said reaction being conducted at a H2 partial
pressure in the range of 0.5-600 bar, or higher.
[0025] In a fifth aspect, the present invention provides a method of
producing hydrogen gas and carbon dioxide in a chemical reaction
from formic acid, said reaction being conducted in presence of a
formate salt.
[0026] In a sixth aspect, the present invention provides a method of
producing hydrogen gas and carbon dioxide in a chemical reaction
from formic acid, said reaction being conducted in presence of a
catalyst, said catalyst preferably being a complex of the general
formula (I):
[0000]
M(L)n (I)
[0000] in which,
M is a metal selected from Ru, Rh, Ir, Pt, Pd, and Os, preferably
Ru;
L is a ligand comprising at least one phosphorus atom or carbenes,
said phosphorus atom being bound by a complex bond to said metal, L
further comprising at least an aromatic group and a hydrophilic
group; and,
n is in the range of 1-4;
wherein the complex of formula (I) optionally comprises other
ligands and is provided in the form of a salt or is neutral.
[0030] In a seventh aspect, the present invention provides a method
for producing hydrogen gas at controlled quantity and/or gas
pressure comprising the reaction according to the present invention.
[0031] In an eight aspect, the present invention provides a method
for producing hydrogen for a hydrogen consuming process and/or
device, the method comprising the steps of:
producing hydrogen gas according to the method of the invention,
and,
directing the hydrogen gas to the hydrogen consuming process and/or
device.
[0034] In a ninth aspect, the present invention provides a method
producing energy, the method comprising the steps of:
producing hydrogen gas according to the invention;
optionally, separating the hydrogen gas from carbon dioxide;
directing the hydrogen gas to a process and/or device capable of
producing energy by using hydrogen gas; and,
producing energy by using the hydrogen gas.
[0039] In a further aspect, the present invention relates to a
method of producing a gas comprising hydrogen gas and being free of
carbon monoxide (CO), wherein the chemical reaction is conducted at
a temperature in the range of 15-220[deg.] C.
[0040] In another aspect, the present invention provides a method
for providing hydrogen gas as a reagent in a specific chemical
reaction, for example chemical synthesis, the method comprising the
step of producing hydrogen gas according to the present invention,
optionally, removing CO2 from the gas obtained, and directing the
hydrogen gas to provide it for the specific chemical reaction.
[0041] The reaction preferably takes place in an aqueous solution
and at relatively low temperatures. The chemical reaction of the
method of the present invention is believed to be highly
advantageous because, first, the reaction products, H2 and CO2, can
be easily separated from the reaction medium and from each other.
Actually, the gas just separates from the reaction medium when being
generated. Second, the catalyst is easily separated from the
reaction products, due to the high solubility of the catalyst in the
reaction medium and practically zero solubility in the reaction
products. The combination of these features render the method of the
present invention an extremely valuable tool for producing hydrogen
gas for any purpose one can envisage.
BRIEF DESCRIPTION OF THE DRAWINGS
[0042] In the drawings,
FIG. 1A schematically shows
a device in which the reaction of the present invention can be
conducted while simultaneously observing starting materials and
reaction products by NMR and by gas pressure measurements in the
same time.
FIG. 1B schematically shows
the reactor in which the reaction of the present invention can be
conducted.
FIG. 2 shows the influence
of temperature on the rate and conversion of the reaction of the
present invention over time. Different symbols stand for experiments
conducted at different temperatures: 100[deg.] C. (?); 90[deg.] C.
(-); 80[deg.] C. (-); and 70[deg.] C. (-).
FIG. 3 shows the influence
of HCOONa concentration on the rate and conversion of the reaction
of the present invention over time. Different symbols stand for
experiments conducted at different molar concentrations of HCOONa:
3.6 M (-); 1.2 M (?); 2.8 M (-); and 0.4 M (-).
FIG. 4 shows the conversion
of formic acid to hydrogen gas and carbon dioxide in a first
reaction cycle in dependence of different ruthenium phosphine
catalysts, co-catalyst systems: [Ru(H2O)6](tos)2+2 mTPPTS (-), 2
mTPPMS (?), 2 pTPPMS (-), RuCl3+2 mTPPTS (-), mTPPMS (-), pTPPMS
([Delta]).
FIG. 5 schematically shows a
device of the present invention: the formic acid tank, the reactor,
and the utilisation (fuel cell, motor a vehicle, heating, chemical
utilisation, etc).
DETAILED DESCRIPTION OF THE
PREFERRED EMBODIMENTS
[0049] The present invention provides a way to generate hydrogen gas
devoid of carbon monoxide not only at a unusually high rate, but
also at a rate that can be controlled easily by supply of formic
acid, and/or varying temperature in the reaction vessel, and/or by
varying other parameters of the reaction.
[0050] The reaction is robust, as the catalyst is completely
recycled and is effective for prolonged time without degradation.
The catalyst preferably used in the method of the present invention
is stable at the temperatures and in the acidic environment of the
reaction.
[0051] The reaction conditions are generally mild, as the reaction
was observed to take place at high conversion efficiency already at
temperatures of around 20[deg.] C., for example RT (25[deg.] C.) and
higher.
[0052] The reaction vessel in which the reaction takes place needs
to be substantially impermeably to water and air and preferably
withstand the acidic reaction conditions as defined further below.
Accordingly, glassware may constitute a material for a reaction
vessel in which the reaction of the method of the present invention
can be conducted.
[0053] If the reaction is conducted at high pressures, the reaction
vessel needs, of course, to be adapted to the pressures and further
conditions generated by the chemical reaction. Accordingly,
depending on the amount of pressure to be generated, vessels of
different materials and sizes may be constructed. At very high
pressures such as those described below, reactors made of hydrogen
resisting stainless steel may be used (Hastelloy, Inconel, etc).
[0054] Preferably, the reaction vessel comprises a formic acid inlet
and/or a gas outlet. The gas outlet may be provided as a valve, thus
allowing to control the pressure inside the reaction vessel may be
controlled by the valve properties. In case that the reaction is
conducted at above ambient pressures in the reaction vessel, the
formic acid inlet is preferably coupled to a pump so that formic
acid can be entered into the aqueous solution in the reaction vessel
albeit the high pressures inside it.
[0055] The reaction vessel preferably comprises means for measuring
the temperature and pressure inside the vessel, in particular a
thermometer and a pressure gage.
[0056] The chemical reaction of the present invention preferably
takes place in an aqueous solution, with water providing the
principle, preferably the only solvent (reaction medium). Preferably
the aqueous solution is a ionic aqueous solution. For the reaction
of the present invention to be carried out, only the starting
material, formic acid, and the catalyst are required. Preferably,
also a formate salt is present in the aqueous solution.
[0057] Accordingly, in the method of the present invention,
preferably a catalyst is used. In other words, the chemical reaction
of the method of the present invention is a catalytic reaction.
[0058] The catalyst to be used in the reaction of the present
invention is preferably soluble in water at least 50 g/L water at
25[deg.] C. More preferably it is soluble at least 100 g/L water,
even more preferably at 150 g L/water and most preferably at least
200 g L/water.
[0059] Of course, catalysts having lower solubilities could do as
well, for example with catalysts having higher efficiencies than
those reported herein.
[0060] Importantly, the catalyst is much more soluble in the
reaction medium, generally water, than in any of the products
produced, in particular in supercritical CO2, if the reaction is
conducted at a pressure sufficiently high for CO2 to be present in
the supercritical state. For example, above 31[deg.] C. and 73 bar
partial pressure, CO2 is present as a supercritical CO2. Since the
method of the present invention can be conveniently be conducted
under these conditions, the catalyst preferably is practically
insoluble in supercritical CO2, the latter serving as solvent in
many chemical reactions.
[0061] Preferably, the molecular ratio of solubility of the catalyst
in water to the solubility of the catalyst in supercritical CO2 is
>99.5:0.5, more preferably >99.99:0.01, most preferably
>99.999:0.001.
[0062] Furthermore, the catalyst is stable at temperatures
>=60[deg.] C., preferably >=80[deg.] C., preferably
>=120[deg.] C., more preferably >=150[deg.] C. and most
preferably >=180[deg.] C. Stable, for the purpose of the present
invention, means that the catalyst catalyses at least 5, preferably
10 or more reaction cycles without measurable degradation or
measurable loss of activity.
[0063] Preferably, the catalyst is stable at the pH at which the
reaction is conducted, as defined further below.
[0064] Preferably, the catalyst is the catalyst of formula (I),
M(L)n as defined above. Preferably, M is Ru or Rh, more preferably
Ru (Ruthenium). Ru preferably is in the oxidation state Ru<II
>during the reaction, however, Ru<III>, which is more
easily available may also be used. It was observed that Ru<III
>is converted to Ru<II >during the reaction.
[0065] According to an embodiment of the method of the invention, if
n>1, each L may be different from another L.
[0066] L, in formula (I), is preferably selected from aryl
phosphines, more preferably phenyl phosphines, for example
triarylphosphines and/or triphenylphosphines. Preferably, the aryl
phosphine is substituted in order to increase its solubility in
water. Preferably, the aryl phosphine is substituted by a
hydrophilic group. The hydrophilic group is preferably selected from
sulphonate, carboxylate, and/or hydroxy, for example. Preferably it
is sulphonate.
[0067] Preferably, L in formula (I) above is a sulfonated triaryl
phosphine. It may be a mono-, di- or trisulphonated aryl phosphine.
Preferably, the triarylphosphine is trisulfonated.
[0068] Preferably, L is a sulfonated triphenylphosphine. It may be a
mono-, di- and/or trisulphonated triphenylphosphine. Preferably, the
triphenylphosphine is trisulfonated, as in this case solubility in
water is highest.
[0069] The sulfonyl group may be in the meta or para position of the
aryl/phenyl group bound to the phosphorus atom. Sulphonated
triphenylphosphines with the sulfonate group present at the meta
position are more easy to synthesise and are, therefore, preferably
used in the method of the present invention.
[0070] Preferably, L is TPPTS (tris(3-sulfophenyl)phosphine).
[0071] L can be also a carbene.
[0072] In formula (I) above, n is preferably 1, 2, 3 or 4, more
preferably it is 1, 2 or 3, most preferably it is 2. If n is 2, each
ligand L(1 to n) may be the same or different. An unlimited number
of combinations is technically possible in the context of the
present invention. Care has to be taken that, when selecting
ligands, the preferred water solubility of the ligand as defined
herein is obtained.
[0073] For illustrating the many possibilities of selecting ligands
for the catalyst of the present invention, one could imagine that n
is 2, with ligand L1 being a mono, bis, tris or non-sulfonated
triphenyl phosphine and ligand L2 being selected from a carbene, a
carbonated triphenyl phosphine or from a (mono, bis or tris)
sulphonated triphenyl phosphine, for example.
[0074] Preferably, if n=2, one ligand L1 is selected from a mono,
bis, or tris sulfonated triphenyl phosphine and ligand L2 is
selected from a carbene, a carbonated triphenyl phosphine or a
sulphonated triphenyl phosphine (in particular a mono, bis, or tris
sulfonated triphenyl phosphine).
[0075] Alternatively, if n=2, ligand L1 is selected from a mono,
bis, tris or non-sulfonated triphenyl phosphine and ligand L2 is
selected from a mono, bis, or tris sulfonated triphenyl phosphine).
[0076] For example, if n is 2, L1 may be TPPTS and L2 may be TPPMS
(mono sulfonated triphenyl phosphine). According to another example,
L1 may be TPPTS and L2 may be TTPDS (bis(3-sulfophenyl)phosphine).
According to a still other example, a non-sulfonated triphenyl
phosphine ligand may be combined with a trisulphonated triphenyl
phosphine ligand. Basically, all combinations of mono, bis, tris and
non-sulfonated triphenylphosphine ligands are possible.
[0077] If n>=2, there is preferably at least one sulfonated
triphenylphosphine ligand present. However, it is also possible to
use and combine triphenylphosphine ligands comprising carboxylate
groups.
[0078] It is worthwhile noting that, in general, catalysts with
twice the same ligand L, e.g. TPPTS, are much easier to prepare than
catalysts with different ligands L.
[0079] According to a preferred embodiment, the catalyst is
[Ru(TPPTS)2(H2O)4]XY, in which X is a non coordinating anion, for
example tosylate, triflate, and Y is 1 or 2, the overall charge of
XY being -2.
[0080] The catalyst may be conveniently synthesised by mixing
constituents (Ru<II >and/or Ru<III>, TPPTS, for example)
of the complex in water in the respective molecular quantity
followed by crystallisation. The individual constituents are
commercially available and are described in the literature.
Alternatively, the catalyst can be synthesised and partly generated
in situ, in the aqueous solution providing the reaction mixture by
adding said constituents first to an aqueous solution.
[0081] The reaction of the method of the present invention is
preferably conducted in presence of a formate salt. Surprisingly,
the presence of the formate salt can have a positive impact on the
rate of the reaction. On the other hand, with the ratio of formic
acid (HCOOH) to formate (HCOO<->) in the aqueous solution
decreasing, conversion efficiency decreases, in other words, the
percentage of formic acid that is converted becomes lower.
[0082] The formate salt may be any formic salt as long as the cation
does not substantially interfere with the chemical reaction.
Preferably, the cation is an inorganic cation, for example calcium
sodium preferably a metal ion. For example, the cation is sodium
and/or potassium, also possible are lithium, cesium, calcium and
ammonium. The use of different formate salts (with different
cations, for example) is not excluded.
[0083] Therefore, the molecular ratio of HCOOH:HCOO<- >can be
adjusted according to preferences on rate or conversion efficiency,
as is desired by the skilled person. The present inventors found an
optimum ratio in the range of 1:20 to 30:1, preferably 1:5 to 20:1,
more preferably 1:1 to 15:1, and even more preferably 5:1 to 14:1.
The most preferred ratio for having an optimal compromise between
reaction rate and conversion efficiency was found to be 9:1.
According to a preferred embodiment, the molecular ratio of
HCOOH:HCOO<- >is in the range of 1:9 to 15:1. The ratio of
HCOOH:HCOO<- >is a way of controlling the rate and conversion
efficiency of the present invention (see examples) and can be
adjusted according to the preferences of the skilled person.
[0084] For the purpose of the present specification, values
indicating the end-points of a range are considered to be included
in the range.
[0085] The presence of formic acid and the formate having, of
course, an influence on the pH, the reaction of the present
invention is preferably conducted at a pH in the range of 0-6, more
preferably 1-5, even more preferably 1.5-4.5 and most preferably 2-4
and 2-3.5. According to preferred embodiments, the pH is in the
range of 1-6, preferably 2.5-5.0.
[0086] The temperature of the reaction mixture (aqueous solution)
was found affect reaction rate. Accordingly, the chemical reaction
of the method of the present invention is preferably conducted at a
temperature in the range of 20[deg.] C.-200[deg.] C., preferably
60[deg.] C.-150[deg.] C., more preferably 70[deg.] C.-140[deg.] C.,
even more preferably 80[deg.] C.-130[deg.] C., most preferably
90[deg.] C.-125[deg.] C.
[0087] The temperature is preferably applied from outside the
reaction vessel by suitable heating/cooling equipment. For example,
heat exchangers, electric heating, an oil bath and or water bath may
be used to control the temperature in the interior of the reactor.
[0088] Other preferred ranges for the reaction of the method of the
invention are 25[deg.] C.-200[deg.] C., 80[deg.] C.-110[deg.] C.;
90[deg.] C.-120[deg.] C. and 80[deg.] C.-130[deg.] C.
[0089] It is clear that the reaction temperatures can be controlled
according to the preferences. If H2 production is to be very
cost-effective, it may be conducted at ambient temperatures for
prolonged time. This may be the case if cost is a more important
factor than time, for example when hydrogen is consumed in a low
rate. Under these conditions, temperature ranges of 20-90[deg.] C.,
25-70[deg.] C. may be selected, or even lower temperatures, for
producing hydrogen and CO2 gas at a relatively slow rate but still
pressures significantly above 1 bar.
[0090] In principle, the higher the temperature, the quicker the
reaction takes place. However, very high rates are obtained at
relatively low temperatures and therefore, temperatures around
100[deg.] C.+-20[deg.] C., preferably +-15[deg.] C. are preferred
for practical reasons.
[0091] A further way of controlling the reaction rate is, of course,
the supply of formic acid to the reaction vessel. The chemical
reaction of the method of the present invention can be conducted
batch-wise or continuously. In the batch-wise operation mode, the
amount of formic acid added per batch determines the amount of
hydrogen gas being produced. In the continuous mode, the rate of
adding formic acid into the reaction vessel can be used to determine
rate and/or amount of hydrogen being produced.
[0092] Temperature is thus one of the ways among others of
controlling the reaction of the method of the present invention. By
keeping the reaction vessel at a specific temperature, or by
modifying this temperature, the reaction rate can conveniently be
controlled.
[0093] Accordingly, in an embodiment, in the method of the present
invention, the hydrogen quantity and/or gas pressure is controlled,
optionally in the course of the reaction taking place, by varying
one, several, or all of factors selected from:
pH;
the molecular ratio of formic acid to formate in the reaction
medium;
the reaction temperature;
supply of formic acid;
these factors being varied, if applicable, according to the ranges
provided in the present description.
[0098] The hydrogen and carbon dioxide gas developed in the course
of the reaction can cause considerable pressure. Surprisingly, the
equilibrium of the reaction of the present invention lies so far at
the side of the products, that the increasing pressure does not stop
the reaction. So far, total gas pressures of up to 1200 bar have
been measured, which means that the method of the present invention
can be conducted under or at these pressures.
[0099] In terms of H2 partial pressure, the reaction was conducted
to produce H2 at partial pressures over to 600 bar. It is expected
that H2 higher partial pressure can be obtained, for example up to
1000 bar and more, in suitable reaction vessels. Accordingly, the
reaction of the present invention is preferably conducted at a H2
partial pressure in the range of 0.5-600 bar.
[0100] A pure H2 and CO2 mixture (50:50 vol. %) is produced.
[0101] The method of the present invention can be controlled to
produce from 0-90 litre H2/minute/litre reactor volume. For example,
the method produces from 10-60, 20-60, 30-55, or 40-55 litre
H2/minute/litre reactor volume, according to the preference of the
skilled person. In particular, the tuned reaction produces 80 litre
H2/minute/litre reactor volume. Any value in the ranges may be
obtained by adjusting parameters, for example the temperature,
catalyst concentration, formate concentration, the formic acid
supply rate, accordingly.
[0102] If required, CO2 can easily be separated from H2, by
exploiting physical properties such as melting temperature,
volatility and/or diffusion coefficient that differ with the two
gases.
[0103] The absence of any carbon monoxide in the produced gas, the
high rate and efficiency of conversion of formic acid to H2 under
the conditions described hereinabove, as well as the fact that the
reaction can be conveniently controlled provide important
advantages, for example if combined with the requirements of a fuel
cell. The fact that H2 at a high partial pressure is produced is
also an advantage, because it permits to control the amount of H2
conducted to a hydrogen gas consuming device, such as a fuel cell by
modifying the valve properties, with the reaction vessel functioning
as a reservoir for H2. The reaction vessel thus has two functions:
hydrogen gas is produced in it in accordance with requirements, and
hydrogen gas pressure is buffered in it under high pressure and thus
constitutes a buffer tank. Of course, if compared to a traditional
tank of hydrogen gas stored under pressure, a significantly smaller
and lighter vessel size can be used, with the actual tank of fuel
being constituted by a container of formic acid, which may be used
to produce hydrogen gas to meet short term requirements.
[0104] The present invention provides a method and/or device for
producing energy. The energy may be energy in any form, such as
kinetic energy, electric energy, heat, potential energy, or
combination of these at the same time.
[0105] For example, devices producing energy from hydrogen gas are
motors, such as a combustion motors and hydrogen fuel cells. Methods
for producing energy from hydrogen gas are the methods taking place
in the motor or the fuel cell. A fuel cell, for example, may produce
electric energy. A motor may produce kinetic energy and/or heat, for
example.
[0106] The present invention also provides a method for producing
hydrogen gas (H2) for chemical uses, that is, for using it in a
chemical reaction, in particular chemical synthesis. In this case,
the hydrogen gas may be produced according to the requirements in
the chemical reaction and be directly directed in the necessary
quantity to the place where the reaction/synthesis is supposed to
happen.
[0107] The present invention also provides a process and/or
apparatus consuming energy, whereby the energy is produced by the
method and/or device of the present invention. Apparatuses consuming
energy are, for example, vehicles, such as cars, trains, aircrafts
or boats. Of course, any energy consuming apparatus is referred to,
not only transport vessels. Accordingly, the energy consuming
apparatus is understood to also refer to plants, households, and so
forth.
[0108] Preferably, with respect to the method and/or device
producing energy from hydrogen gas, said hydrogen gas is preferably
produced in, or in close vicinity to said device for the purpose of
producing energy. "Vicinity", in the context of the present
invention, refers to the fact that the hydrogen gas may be directly
guided to the method and/or device without need to be stored in a
storage container, such as a gas bottle, which has to be brought to
the device and which needs to be exchanged as soon as it is empty.
In other words, "vicinity" refers to a system in which hydrogen gas
is produced from a formic acid storage, in a way that hydrogen gas
can be produced continuously or batch-wise as long as formic acid is
present for providing hydrogen gas to the energy producing method
and/or device.
[0109] FIG. 5 schematically illustrates a device and/or method
producing energy. In this figure, 11 illustrates a HCOOH reservoir,
which is connected to a pump 12, which pumps formic acid into
reactor 10, from which hydrogen gas is directed to the desired
application 20, which may be a motor, a fuel cell, a reactor for a
further chemical reaction, for example. An optional CO2-separator 5
is indicated with doted lines, and may be used whenever pure
hydrogen gas or hydrogen gas free of CO2 is required for application
20.
[0110] For example, the energy may be electric energy produced by a
fuel cell, the method comprising the steps of:
producing hydrogen gas according to the method of the present
invention;
optionally, separating the hydrogen gas from the carbon dioxide;
directing the hydrogen gas to a fuel cell; and,
oxidizing the hydrogen gas with oxygen gas in said fuel cell and
thus creating electric energy.
[0115] In general, the process and/or apparatus consuming energy is
preferably situated in vicinity to the method and/or device
producing energy, for example on the vehicle, if the energy
consuming apparatus is a vehicle. The energy may, of course, be
stored in a suitable form, if desired, before being consumed by the
method and/or apparatus consuming energy. Preferably, however, the
energy is produced, by the method of the present invention,
according to the energy requirements of the process and/or
apparatus, and hydrogen gas is produced and guided to the energy
producing method and/or device for producing energy as a function of
said energy requirement.
[0116] The present invention is described more concretely with
reference to the following examples, which, however, are not
intended to restrict the scope of the invention.
EXAMPLES
Example 1
Preparation of Catalyst
[Ru(TPPTS)2(H2O)4](tos)2]
[0117] The catalyst precursor [Ru(TPPTS)2(H2O)4](tos)2], was
prepared by dissolving [Ru(H2O)6](tos)2, in which tos=tosylate
(4-methylbenzenesulfonate ion) and TPPTS, where TPPTS is
tris(3-sulfophenyl)phosphine tri sodium salt, in a molar ratio of
1:2 in water, slightly acidified with tosylic acid.
[0118] [Ru(H2O)6](tos)2] is synthesised according to the method of
Bernhardt (Bernhardt, P.; Biner, M.; Ludi, A. Polyhedron 1990, 9,
1095-1097). TPPTS is commercially obtained from Aldrich (N<o
>444979) CAS 63995-70-0.
[0119] 2.1 g (0.0038 mol) [Ru(H2O)6](tos)2 was mixed with 4.3 g
(0.0076 mol) TPPTS in 20 mL water (containing 0.2 g tosylic acid) at
55[deg.] C. until the complex formation was complete (NMR check, J.
Kovács, F. Joó, A. C. Bényei, G. Laurenczy, Dalton Transac., 2004,
2336), after the water was evaporated in vacuum.
Example 2
Experimental Setting for the
Preparation of Hydrogen from Formic Acid
[0120] The reaction was carried out in two different reactors:
[0000] A) In high pressure sapphire NMR tubes (A. Cusanelli, U.
Frey, D. T. Richens, A. E. Merbach, J. Am. Chem. Soc., 1996, 118,
5265) equipped with a manometer, in batch mode. The reaction was
followed simultaneously by multinuclear NMR (<1>H,
<13>C, <31>P) and in the same time by the pressure
evolution of the H2 and CO2. This setting 1 is schematically
illustrated in FIG. 1A, in which the NMR tube 3, serving as a
reaction vessel, comprising the reactants is placed in the NMR
spectrometer 2 and wherein a pressure measurement device 4 placed on
top of the tube, can be monitored from outside.
B) In a high pressure autoclave of the type Parr 47, equipped with
manometer, thermometer, modified for inlet/outlet, connected to a
HPLC pump for supplying formic acid with the required pressure. It
was used both in batch mode and in continuous mode. The reactor was
prepared according to the schematic illustration shown in FIG. 1B,
in which 10 stands for the reaction vessel/reactor. A formic acid
reservoir 11 is connected to a pump 12, which pumps the formic acid
through an inlet 13 directly into a glass container placed in the
autoclave 14. The autoclave is equipped with a manometer 15 and a
thermometer 16 that permit monitoring of the conditions inside the
reactor while the reaction takes place. A gas outlet 17 comprises a
valve 19 in order to control the gas outflow. A heater 18 is
provided for controlling the temperature in the reactor, where the
reaction takes place.
[0121] In a standard experimental setting, in high pressure sapphire
NMR tube reactors, 2.5 mL of an aqueous solution of 4 M
HCOOH/HCOONa, with a initial molar formic acid to formate ratio of
9:1 (that is 3.6 M HCOOH and 0.4 M HCOONa) is prepared at RT
(=25[deg.] C.) in a 10 mm sapphire NMR tube. The pH of the solution
was about 2.8.
[0122] The catalyst is formed in situ by adding [Ru(H2O)6](tos)2 (30
mg, 0.054 mmol) and TPPTS at (61 mg, 0.108 mmol) to the aqueous
solution (catalyst concentration: 0.022 mM).
[0123] Oxygen is removed previously from all solutions by bubbling
N2 into the solution, since both, [Ru(H2O)6](tos)2 and the
phosphines can be oxidized.
[0124] The sapphire tube is put into the NMR spectrometer, connected
to a manometer and the reaction is started by heating to a
temperature of 90[deg.] C.
[0125] Reactions are followed by analysing the species in solution
by multinuclear (<1>H, <13>C, <31>P) NMR
spectroscopy. In general, the pressure in the sapphire NMR tube and
the species in solution in each of the experiments were measured
simultaneously as a function of time. There is no other product
detected during the reaction beside H2 and CO2. As expected, it was
found that pressure correlates directly with conversion.
[0126] There are no traces of CO is found in the reaction product
gas as it is tested by <13>C NMR and FT-IR spectroscopy.
[0127] In the batch-wise mode, for recycling, as one reaction cycle
is completed (checked by NMR and no further increase in pressure-or
release of gas through the outlet valve), the sapphire tube is moved
out from the NMR spectrometer, opened and formic acid is added to
restore the initial concentration of HCOOH.
[0128] In the continuous mode, the autoclave containing of an
initial concentration of 4 M HCOOH/HCOONa (9:1), and 0.022 M
[Ru(TPPTS)2(H2O)6](tos)2 in 12 mL water, is put in an oil bath and
the reaction is started by heating the oil bath and therewith the
temperature in the autoclave to a temperature of 100[deg.] C.
[0129] In the continuous mode, when the initial amount of formic
acid is fully converted (no more increase in pressure), formic acid
is added continuously at a constant rate of 0.1 mL/min. Non-degassed
HCOOH is added without protection against oxygen. No effect on the
activity is observed, indicating that the catalytically active
species are not sensitive to oxygen. The H2 (+CO2) gas is released
at 130 bar at a rate of about 150 mL/min in order to maintain the
pressure constant. When addition is stopped and the gas out valve
closed, no pressure increase is observed, which means that all
formic acid has been converted. The continuous process was run for
several weeks without any loss of activity, even if the process is
interrupted and restarted.
[0130] In the following examples, batch-wise or continuous mode was
selected for studying the effects of varying different reaction
parameters provided in Example 2.
Example 3
Effect of Temperature on Hydrogen
Production from Formic Acid
[0131] The experimental setting of Example 2 is modified to evaluate
the effect of temperature on the pressure in the sapphire tube
reactor.
[0132] Accordingly, 1.25 mL H2O and 1.25 mL D2O were supplied with 2
mM of the catalyst concentration obtained in Example 1. Formic acid
and formate were initially added at a molar ratio of 9:1 and at a
total concentration of 4 M. The pH of the solution was about 2.8.
[0133] The reaction was operated batch-wise, by closing the
gas-outlet. Cycles 3-6 were conducted at different temperatures and
the conversion over time was monitored. Accordingly, the 3<rd
>cycle was conducted at 90[deg.] C., the 4thcycle was conducted
at 100[deg.] C., the 5thcycle was conducted at 80[deg.] C. and the
6thcycle at 70[deg.] C.
[0134] Each cycle was considered terminated when conversion was more
than 90% and no further increase in pressure was observed and no
more change in the HCOOH/HCOONa concentration was detected by NMR.
Then, for the next cycle, the pressure was released, new formic acid
was added to restore the initial concentration of 4 M HCOOH/HCOONa
and the reaction started by setting temperature.
[0135] At all temperatures, total pressure (and accordingly,
conversion) increased with time, the HCOOH concentration decreased,
with the reaction performed at 100[deg.] C. being completed fastest,
after 30-40 minutes, when a pressure of about 120 bars was observed.
[0136] The results of this example are shown in FIG. 2, which shows
the influence of temperature during different cycles on reaction
rate. It can be seen that the reaction is completed most rapidly at
100[deg.] C. (?), whereby at 70[deg.] C. (-), the reaction is
slowest, but still above 90% conversion is obtained. The reaction
rate thus directly correlates with temperature.
Example 4
Effect of pH on Hydrogen Production
from Formic Acid
Example 4.1
Ratio of HCOOH:HCOONa
[0137] Influence of pH to the reaction rate and conversion
efficiency is measured with the experimental setting of Example 2,
which is operated batch-wise and in which the initial ratio of HCOOH
to HCOONa is varied, while keeping the overall concentration of
substrate at 4 M, thus varying pH. Accordingly, HCOOH:HCOONa
mixtures of 100:0 mol %, 90:10 mol %, 70:30 mol %, 40:60 mol %,
10:90 mol % and 0:100 mol % were prepared and added to the aqueous
solution at 4 M.
[0138] After each completed reaction cycle, HCOOH was added to
obtain a total concentration of 4 M, thus restoring HCOOH that was
used up.
[0139] It was found that when only HCOOH or only HCOONa was used
(100:0; 0:100), reactions were very slow.
[0140] It was found that the presence of HCOONa positively affects
the reaction rate in a wide concentration range, with the conversion
efficiency becoming lower at lower concentrations of HCOOH.
[0141] The optimum ratio of HCOOH:HCOONa in terms of reaction rate
and conversion efficiency was identified to be around 9:1.
[0142] At this ratio, the pH was in the range of 2.6-3.1
Example 4.2
Effect of HCOONa Concentration on
Conversion Efficiency and Reaction Rate
[0143] Example 4.1 is conducted batch-wise with a concentration of
22 mM [Ru(H2O6](tos)2, 44 mM TPPTS (catalyst formed in situ), 4 M
HCOOH (10 mmol) with variable initial contents of HCOONa.
[0144] The experiment was repeated with 0.4, 1.2, 1.6, 3.6 M HCOONa
and conversion was monitored over time.
[0145] After each reaction cycle, initial HCOOH concentration was
restored to 4 M HCOOH.
[0146] The result is shown in FIG. 3, were it can be seen that with
lowest initial HCOONa concentration (0.4 M, -), the reaction
advances slowest, but conversion of HCOOH to H2 and CO2 gets close
to 100%. The reaction rate is higher at HCOONa concentrations of 1.6
(?), 2.8 (-) and 3.6 M (O), but overall conversion decreases. In
summary, HCOONa concentration is inversely proportional with
conversion. It increases the reaction rate, but only up to 2.8 M
concentration. An optimum concentration of formate salt can be
selected according to preferences of the skilled person.
Example 5
Effect of Catalyst on the Reaction
Example 5.1
Effect of Catalyst Concentration on
Conversion Efficiency and Reaction Rate
[0147] The experiment of Example 2, is modified by adding different
initial concentrations (2.3 mM, 22 mM, 45 nM, 67 nM, 90 mM, 112 mM
and 123 mM) of [Ru(H2O)6](tos)2 and 2 equivalents of TPPTS.
[0148] It was observed that increase in catalyst concentration
accelerates the rate of the HCOOH decomposition reactions until a
catalyst concentration of is about 90 mM reached.
Example 5.2
Different Sulfonated Phosphine
Ligands Tested
[0149] TPPTS (tris(3-sulfophenyl)phosphine trisodium salt) has been
chosen as ligand because of its very high water solubility and
stability. The catalysis was further tested with less soluble
mono-sulfonated triphenyl phosphines, with the sulfonyl group in
para and meta position (pTPPMS and mTPPMS), as a ligand for the
[Ru(H2O)6](tos)2 complex. Two equivalents mTPPMS and pTPPMS,
respectively were added to each Ru- equivalent.
[0150] The experiments were conducted in the batch-wise mode in the
sapphire NMR-tube as indicated in Example 2.
[0151] The results are shown in FIG. 4. As can be seen, the reaction
works with all catalysts. The rate is slightly faster with
monosulfonated triphenylphosphines (?, -) than with the
trisulfonated one (-), but since the former are only partially
soluble in water, handling is less convenient. When ruthenium is
added as RuCl3, the reactions are slower and the catalyst less
stable over repeated cycles, specially with the monosulfonated
triphenylphosphines (-, [Delta]).
Example 5.3
Ru<III >and Ru<II >
[0152] [Ru<III>(H2O)6](tos)3 is tested with two equivalents of
TPPTS according to the batch-wise operation mode set out in Example
2. In presence of two equivalents of TPPTS, the reaction is as fast
as [Ru<II>(H2O)6](tos)2 with two TPPTS.
[0153] In the cycles following the first reaction cycle, no
difference in reaction rate or conversion was found between
[Ru<II>(H2O)6](tos)2 and [Ru<III>(H2O)6](tos)3. The
species observed during the reaction with Ru<III >are similar
to what is observed with Ru<II>, indicating that the Ru<III
>is reduced during the process.
Example 5.4
Further Ru Catalysts with or
without TPPTS Ligands
[0154] Example 2 was conducted for one reaction cycle in the
NMR-sapphire tube, whereby [Ru(TPPTS)2(H2O)4](tos)2 as prepared in
Example 1 was used (5.4 a)) or replaced by another catalyst as
listed below:
Experiment 5.4 a): Ru(TPPTS)2
Experiment 5.4 b): Ru(TPPTS)
Experiment 5.4 c): Ru(TPPTS)2+10 TPPTS
Experiment 5.4 d): Ru(H2O)6
[0155] Experiment 5.4 e): Ru(H2O)6+2 equivalents TPPTS
[0156] All catalysts showed certain activity, but catalysts 5.4 a)
and e) showed the fastest rate, already in the first reaction cycle.
Example 5.5
Further Catalysts
[0157] Example 2 was repeated in the batch-wise mode whereby the
catalyst was replaced, at the same concentrations, by one of the
catalysts listed below.
Experiment 5.5 a)
[0158] Catalyst [Ru<II>(H2O)6](tos)2 in presence of one
equivalent of the diphosphine
1,2-bis(di-4-sulfonatophenylphosphino)benzene tetrasodium salt,
Strem Chemicals, 15-0155
Experiment 5.5 b):
[0159] Catalyst [Ru<II>(H2O)6](tos)2 in presence of one
equivalent of 2,2'-bipyridine (Merck).
Experiment 5.5 c):
[0160] Catalyst of an arene derivative
[Cl2Ru(PPh3)(1-(2-benzylethyl)-3-methylimidazolium]Cl (ref: T.
Geldbach, G. Laurenczy, R. Scopelliti, P. J. Dyson; Organomet.,
2006, 25, 733.).
Experiment 5.5 d):
[0161] Catalyst [RuCl2(PTA)(9S3)], where
9S3=1,4,7-trithiacyclononane and
PTA=1,3,5-triaza-7-phosphaadamantane (ref.: B. Serli, E. Zangrando,
T. Gianferrara, C. Scolaro, P. J. Dyson, A. Bergamo, E. Alessio;
Eur. J. Inorg. Chem., 2005, 3423.).
Results:
[0162] In general, all catalysts 5.5 a)-d) were much slower than
Ru(H2O)6 with two TPPTS.
[0163] With the bipyridine ligand (5.5 b)), there is decomposition
of the catalyst, observable by the change of the red solution to
black and also by the loss of activity during recycling.
[0164] The arene compound (5.5 c)), initially soluble in the
reaction mixtures, precipitates out during the reaction.
Example 6
Susceptibility of Catalyst to
Poisoning
6.1 Poisoning by Mercury
[0165] Example 2 was run in the batch-wise mode with 22 mM
[Ru(TPPTS)2(H2O)4](tos)2.
[0166] After the 3<rd >recycling of [Ru(TPPTS)2(H2O)4](tos)2,
mercury is added to the solution. The following recycling cycles are
not affected by the presence of Hg, giving a strong evidence that
the catalytic reaction is homogeneous.
6.2 Carbon Monoxide (CO)
[0167] Example 2 was run in the batch-wise mode with 22 mM
[Ru(TPPTS)2(H2O)4](tos)2.
[0168] After the 16threcycling of the [Ru(H2O)6](tos)2+2 TPPTS
solution (without loss of activity), the reactor is pressurised with
50 bar of CO and mixed for 15 minutes. The gas is then released and
the reaction restarted. The first two recyclings (the 17thand 18th)
are significantly slowed down but the catalyst is not completely
poisoned. During further recycling cycles, the CO is being slowly
eliminated and the original activity of the catalyst is almost fully
recovered.
6.3 Oxygen
[0169] As mentioned in Example 2 above, oxygen is removed from all
the solutions by bubbling N2 into the solution before the filling of
the reactor. These precautions are taken since both [Ru(H2O)6](tos)2
and the phosphines can be oxidized. However, during the recycling
cycles, non-degassed HCOOH is added without protection against
oxygen. In case of Ru(TPPTS)2 it is not necessary to degas.
6.4 Chloride
[0170] Example 2 was run in the batch-wise mode. Further to the two
equivalents of TPPTS, two equivalents of NaCl were added. No effect
on the rate of reaction were observed during recycling in presence
of NaCl.
Example 7
Pressure in Reaction Vessel
[0171] In order to verify that the reaction can still be done at a
higher pressures, a high pressure autoclave was prepared in similar
conditions.
[0172] At optimum temperature, pH and with the catalyst of Example
2, in batch mode the total gas pressures of over 750 bar were
registered, with hydrogen gas partial pressures up to 370 bar.
CONCLUSIONS
[0173] From the series of experiments conducted described herein
above it can be concluded that the method of the invention permits
the quick production of hydrogen gas very pure from carbon monoxide.
The amount of hydrogen gas to be produced can be determined and
varied at very short terms by substrate quantity, temperature and
pH. The hydrogen generation is easily controllable and the catalyst
is robust. The reaction can conveniently be conducted at batch-wise
or continuous mode without catalyst loss.
