Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
,
CATALYTIC HYDROGEL
Field of the invention
The invention relates to materials used in the catalytic production of
hydrogen via hydrocarbon reforming. In particular, this invention relates to a
catalytic hydrogel, in which a hydrophilic polymer matrix supports an aqueous
hydrocarbon solution and a catalytically active ruthenium complex. The
invention
is best suited for low temperature, orientation independent reforming of
formic
acid.
Background of the invention
Hydrogen gas, H2, is a versatile energy carrier that can be used in energy
conversion devices such as fuel cells and combustion engines. The primary
challenges in the widespread adoption of H2 as an energy carrier lie in the
low
volumetric energy density of a gaseous fuel, especially in portable
applications
where high power density is required. The ideal solution is to utilize an
energy
dense liquid hydrocarbon fuel, and generate hydrogen on-demand in a fuel
processor via chemical reforming. Small chain alcohol and carboxylic acids
have
been widely exploited for this purpose, though formic acid in particular has
many
desirable properties, being liquid at nominal temperature and pressure, non-
toxic,
inflammable, and derivable in a carbon-neutral process. One major drawback
with traditional hydrocarbon reforming, however, is the high temperature (i.e.
>
200 C) environment required in attaining significant hydrogen production
rates,
which is problematic for safety and also inefficient, consuming a significant
portion of the energy produced. Catalysts for high temperature reforming are
conventionally supported or stored in a solid phase in solid support such as
Zeolite or Carbon, as the catalyst coating methods and processing (sintering)
typically require high temperatures unsuitable for polymers.
In addressing the limitations of high temperature reforming (>200 deg. C),
a number of recent publications have dealt with low temperature (i.e. < 150
C)
reforming of formic acid utilizing a class of ruthenium complexes in aqueous
1
CA 2733865 2018-06-08
ir
1,
,
,
solution. These homogeneous catalysts have several advantages for use in fuel
cell applications in particular, such as very high selectivity to H2, with ppm
levels
of carbon monoxide (CO); rapid start-up time due to low temperature operation;
and the ability to use a wide range of formic acid concentrations (15 ¨ 98%
w/w)
as feedstock.
For reformed H2 use in hydrogen fuel cells, it is important to have a
hydrogen gas production process producing high purity hydrogen on demand at
acceptable pressures, as carbon monoxide is poisonous to the catalyst in most
fuel cells. For the case of formic acid decomposition has two paths,
dehydrogenation producing H2 and CO2, or decarbonylation producing CO and
H20, as shown in the equations 1, 2 below.
HCOOH-4 H2 + CO2 Eq.1 Dehydrogenation
HCOOH4C0 + H20 Eq.2 Decarbonylation
Effective reforming of formic acid for fuel cells, then benefits from highly
selective dehydrogenation for increased H2 yield and low levels of CO
poisonous
to most proton exchange membrane (PEM) cells. This high selectivity has not
been shown using solid state catalyst with low temperature reforming of formic
acid.
New developments in liquid phase catalysis have demonstrated the
desired selective dehydrogenation. A novel process for high selectivity and
low
temperature formic acid decomposition has been recently published and patent
pending(US publication No: US2010/0068131] using a Ruthenium catalyst in
aqueous phase. This novel process achieves rapid low temperature
decomposition at rates up to 50X faster by the addition of sodium formate to >
95% conversion within 4 hours. Further recycling the catalyst led to 200X
faster
conversion within 1 hour.
2
CA 2733865 2018-06-08
ir
1,
This aqueous catalyst formulation ('8131 patent) has many advantages for
reforming formic acid through selective dehydrogenation efficiently to produce
high pressure hydrogen product for use in portable fuel cells with acceptable
trace amounts of CO poison, specifically active long life and producing a
positive
pressure of hydrogen and primarily all gas product, as reviewed in the
references.
In spite of this, liquid phase catalysts still suffer several drawbacks that
render them unsuitable for portable applications: the most serious of which
are
an inherent sensitivity to orientation, and difficulty maintaining an aqueous
reservoir near the normal boiling point of water. Hence, there is a need to
provide
a novel method of containing an aqueous catalyst that enables continuous
hydrogen production at a high rate, and in any orientation. The major
difficulty
with this class of aqueous catalyst arises from the fact that liquid water is
an
integral part of the reaction mechanism, and must be retained in the catalyst.
Firstly, this puts the practical operating temperature limit well below 100
C. at
atmospheric pressure, greatly restricting the potential hydrogen generation
rate.
Specifically, we have found in tests using 100% liquid catalyst that
pressurization
of 100PSI or more was required due to partial water vaporization from higher
temperatures required for adequate reaction rates, such pressure is unsuitable
for consumer or portable use. In addition to this, water balance
considerations
may limit the upper concentration of the fuel, thus reducing the effective
energy
density. Finally, a conventional liquid-filled vessel is inherently sensitive
to the
orientation in which it is placed; that is, a preferred orientation may meet a
specified design hydrogen output, while an off-axis orientation may produce
hydrogen sporadically or not at all. This is due to gravity separation in gas-
liquid
systems, whereby natural gravitational forces induce spatial non-uniformity in
gas-liquid systems. For example, the '8131 patent teaches a reactor vessel
impermeable to water and air and able to withstand acidic reaction conditions
and recommends glassware as discussed. In portable applications, where device
size, energy density, and orientation sensitivity are the key performance
metrics,
3
CA 2733865 2018-06-08
ir
1,
these challenges can be very difficult or impossible to overcome. In view of
this, a
passive method of liquid phase catalyst management is needed to increase
technical viability for portable applications. There is a need for designs and
materials to support and contain the catalyst adequately while maintaining
conditions for high reaction rates in any orientation.
There is a further need for a liquid catalyst support that enables the
generated hydrogen gas to easily permeate through the support when the
support is in any orientation. In addition to absorbing and retaining water
based
catalyst a material support is needed that can handle the chemical and
physical
requirements of reforming, including high absorption per unit weight of
material,
reliable under repeated cycles, substantially inert to the reaction process
and
formic acid, and meets standards for safe consumer use including recycling.
There are other low temperature formic acid processes in the early
stages of development. These additional liquid catalyst low temperature
formulations and methods are typically again demonstrated in a lab environment
with a beaker type reactor holding the liquid catalyst and fuel and with the
liquid
catalyst at the bottom due to gravity and the resulting hydrogen gas bubbling
up
and being trapped and processed, and have not met the needs described herein.
Some variations on solid state catalyst show conversion at low temperature
below 100 deg. C, however are estimated to have limited utility as they
require
extra salt/ionic liquids and resulting solid byproducts and lower reaction
rate per
unit volume and are orientation dependent
4
CA 2733865 2018-06-08
Existing solutions to contain aqueous catalyst include primarily
supported aqueous phase catalyst (SAPC). SAPC patents teach solid
support, which is inadequate to meet the needs as described earlier.
In reviewing use of highly absorbing materials with fuel cell
applications, use of hydrogels in fuel cells has been limited and for
unrelated
applications. Specifically for formic acid reforming in fuel cells, hydrogels
have
been limited in use as;
a) hydraulic barrier [US patent publication no. US 200810274393, US
patent publication no. US 200810248343, US patent publication no.
U520090035644]
b) as a temporary material phase in manufacturing membranes
potentially used in fuel cells [US patent no. 4664194]
c) forming solid catalyst as a hydrogel layer on nanomaterial
structure [US patent publication no. US 200110000889, US patent
no. 6531704],
d) holding a liquid electrolyte between anode and cathode in
microfluidic fuel cells [US patent publication no. US 201010196800].
As a class of hydrogels, the use of super absorbent polymers (SAP) more
generally within fuel cells and associated reforming shows unrelated uses.
US patent publication no. US 200810057381 references using a SAP to hold
electrolyte and formic acid fuel, however the catalyst is solid. US patent no.
6781249 references using SAP ancillary to a fuel cell system for water storage
and
disposal, but no mention of using liquid catalyst. US patent publication no.
US
2009/0071334 more generally references use of SAP in collection of water in
steam
reforming, however this is more general not related to liquid catalyst or
formic acid
fuel cells.
Date Recue/Date Received 2020-12-18
Summary of the Invention
A catalytic hydrogel is provided for the purpose of low temperature,
orientation independent hydrocarbon reforming. The catalytic hydrogel consists
of a network of hydrophilic polymer chains dispersed in an aqueous hydrocarbon
solution, preferably a formic acid solution; the catalytically active species
is
preferably a ruthenium complex.
An embodiment of an absorbent polymer for stably retaining liquid catalyst
in a hydrogel state for use in fuel reforming, is provided having, an
absorbent
polymer formable as a catalytic hydrogel, such that when contacted with a
liquid
phase catalyst, the polymer forms a hydrogel that absorbs liquid phase
catalyst in
a proportion greater than the polymer weight and retains the liquid catalyst
within
the hydrogel state independent of orientation. An additional detailed
embodiment
of a system is further provided, including the addition of a liquid phase
catalyst
absorbed and retained in the absorbent polymer forming a catalytic hydrogel.
A preferred embodiment involves the soluble ruthenium complex being
mixed with the aqueous formic acid solution, allowing free movement of the
complex throughout the catalytic hydrogel. Most significantly, catalyst
structures
as described above allow product gases and/or vapors to escape while retaining
liquid species within the polymer matrix. In other words, the catalytic
hydrogel is
not subject to, or dependent on, gravity separation of gas and liquid phases,
and
can easily be adapted for orientation independent operation in portable fuel
processors.
An additional benefit of using the catalytic hydrogel compared to an
aqueous solution can be ascribed to the ability of the hydrophilic polymer
chains
to retain water: it has been experimentally observed that a proper water
balance
can be maintained even at the normal boiling point of water. The relaxed
temperature restrictions allow higher operating temperatures than were
6
CA 2733865 2018-06-08
previously possible, resulting in higher catalyst output and a corresponding
decrease in both size and weight.
Further benefits of the catalytic hydrogel are absorbance of incoming fuel
to react homogenously with the catalyst and remaining stable during reforming
reaction and extended use and storage.
7
CA 2733865 2018-06-08
Brief Description of the Drawings
FIGURE 1 is a schematic illustration of a super absorbent polymer,
showing hydrophilic polymer backbone and light cross linking allowing swelling
when hydrated.
FIGURE 2 is an image of SAP crystalline dry pellets prior to interaction
with liquid catalyst solution.
FIGURE 3 is an image of SAP crystalline pellets following absorption of a
liquid catalyst solution to form a catalytic hydrogel.
FIGURE 4 is a perspective view of a layer formed of the catalytic hydrogel
illustrating use in a reformer reaction converting formic acid fuel to
hydrogen and
CO2 gases, while retaining excess water.
FIGURE 5 is a graph showing extended low temperature hydrogen
production from reforming formic acid using a catalytic hydrogel.
8
CA 2733865 2018-06-08
Detailed Description
A new class of aqueous catalysts has recently been described for low
temperature hydrogen production from hydrocarbon fuels, including formic acid.
These aqueous organo-metallic complexes display unusually high activity
towards formic acid decomposition. High purity hydrogen is produced via high
selectivity towards the dehydrogenation pathway ( 1 ), with little or no CO
production through dehydration ( 2 ).
liC0011 CO2.q- ( 1 )
FICOOff CO + 1120 ( 2 )
This quality makes the new catalyst formulations eminently suitable for
use in fuel cell applications, where CO content of the fuel gas can cause
rapid
deactivation. Specifically ruthenium formulations have achieved good yields of
H2 > 95% conversion from formic acid at fast rates suitable for use in real-
time
power applications. This catalyst composition results in the conversion of a
dehydrogenatable pre-cursor in an aqueous solution at high conversion rates of
near pure H2 for an extended period of time (and following very extended
storage
periods) , suitable for portable device use and commercial operations.
Use of the catalyst in liquid state in a vessel is orientation dependent so
doesn't meet the needs described. Attempts to use such a liquid catalyst with
a
solid state support (Zeolite) were found unsatisfactory, as the liquid
catalyst was
not properly contained (attracted and retained) such that when formic acid
fuel
was added, to approach adequate reaction rates and H2 production rates, the
reaction temperature had to be higher than the vaporization temperature of the
retained water, causing heated water vapor to expand and exhaust out of the
system at high pressure. The Zeolite or typical solid support then is found
unacceptable for use in compact portable reformers and fuel cell packs, as
safety
standards would not be met or cost feasibility and portability with this
constraint.
9
CA 2733865 2018-06-08
1,
Hence, to meet the needs described, a novel absorbing material is
provided that contains liquid catalyst and enables low temperature reforming
of
formic acid to be practically and commercially realized. Such absorbing
material
maintains reaction rates under various orientations, stable in use, maintains
water balance and finally has suitable material properties for reliable
repeated
use over long use cycles common in portable electronic power systems.
The present invention makes use of super absorbent polymers (SAPs),
that, when mixed with aqueous catalyst solutions and/or an active ruthenium
complex, form a stable hydrogel state. Specifically, we have discovered an
effective liquid catalyst support material that holds aqueous Ru catalyst in a
hydrogel state and is super absorbing, has temperature stability, holds the
liquid
at standard pressure during reaction, and enables high rates of hydrogen
production when reforming formic acid. The catalyst support enables
orientation
independence of reforming reactions for generating hydrogen for PEM fuel cell
systems.
The present invention is described using terms of definitions below:
"Catalysis," as the term used herein, is the acceleration of any physical or
chemical or biological reaction by a small quantity of a substance-herein
referred
to as "catalyst"-the amount and nature of which remain essentially unchanged
during the reaction. For teachings contained herein, a raw material is
considered
catalyzed by a substance into a product if the substance is a catalyst for one
or
more intermediate steps of associated physical or chemical or biological
reaction.
"Chemical transformation," as the term used herein, is the rearrangement,
change, addition, or removal of chemical bonds in any substance or substances
such as but not limiting to compounds, chemicals, materials, fuels,
pollutants,
biomaterials, biochemicals, and biologically active species. The terms also
includes bonds that some in the art prefer to not call as chemical bonds such
as
but not limiting to Van der Weals bonds and hydrogen bonds.
CA 2733865 2018-06-08
ir
"Activity" of a catalyst, as the term used herein, is a measure of the rate of
conversion of the starting material by the catalyst.
"Selectivity" of a catalyst, as the term used herein, is a measure of the
relative
rate of formation of each product from two or more competing reactions. Often,
selectivity of a specific product is of interest, though multiple products may
interest some applications.
"Stability" of a catalyst, as the term used herein, is a measure of the
catalyst's
ability to retain useful life, activity and selectivity above predetermined
levels in
presence of factors that can cause chemical, thermal, or mechanical
degradation
or decomposition. Illustrative, but not limiting, factors include coking,
poisoning,
oxidation, reduction, thermal run away, expansion-contraction, flow, handling,
and charging of catalyst.
"Porous" as used herein means a structure with sufficient interstitial space
to
allow transport of reactant and product materials within the structure to
expose
the reactant materials to the constituent compositions contained within the
porous structure.
"Hydrogel" as used herein means a colloid gel in which water is the continuous
phase. The gel remains swelled without leaking solvent/solution, unlike fiber
based absorbers. Equivalent terms to hydrogel include sponge, fibrous
filaments,
soft polymer or co-polymer or gel.
For H2 use in hydrogen fuel cells, it is important to have a hydrogen gas
production process producing high purity hydrogen on demand at acceptable
pressures, as carbon monoxide is poisonous to the catalyst in most fuel cells.
Formic acid decomposition has two paths, dehydrogenation producing H2 and
002, or decarbonylation producing CO and H20, as shown in the equations 1, 2
previously. Effective reforming of formic acid for fuel cells, then benefits
from
highly selective dehydrogenation for increased H2 yield and low levels of CO
poisonous to most PEM cells.
11
CA 2733865 2018-06-08
ir
A novel process for high selectivity and low temperature formic acid
decomposition has been recently published and patent pending (US
publication No: US201010068131) using a Ruthenium catalyst in aqueous
phase. This reaction achieves fast selective formic acid decomposition by
homogenous catalysis, with very low levels of carbon monoxide poison.
This method of producing hydrogen gas and carbon dioxide in a
chemical reaction from formic acid uses a catalyst in aqueous solution in
the presence of added formate salt where the catalyst has the form;
M(L) n (I) Eq. 3
in which, M is a metal selected from Ru, Rh, Ir, Pt, Pd, and Os, preferably
Ru;
n is in the range of 1-4; L is a carbine, or a ligand comprising at least one
phosphorus atom, said phosphorus atom being bound by a complex bond to
said metal, the phosphorus ligand further comprising at least an aromatic
group and a hydrophilic group, wherein, if n> 1, each L may be different from
another L; and wherein the complex of formula (I) optionally comprises other
ligands and is provided in the form of a salt or is neutral.
A brief description of the reaction of the preferred formulations of the
'8131 patent are included as useful for illustrating how the novel catalytic
hydrogel meets the required needs, by rapid production of hydrogen gas (up
to 90 liter H2/minute) with high purity and little to no carbon monoxide. The
amount of hydrogen gas produced can be controlled and varied by fuel
quality, temperature and pH, and also produced continuously with the
addition of fuel to replace the consumed HCOOH. The preferred catalyst
metal is Ruthenium [Ru].
The preferred complexes of the liquid catalysts are water soluble
phosphine TPPTS [meta-trisulfonated triphenyl-phosphine], and include
active species;
12
Date Recue/Date Received 2021-10-07
[Ru(H20)6]2+ , [Ru(H20)6]3+ and RuC13.xH20.
Specifically a Ruthenium complex selected from the group of
RuCI3xH20/TPPTS, [Ru(H20)6][tosy112/TPPTS and [Ru(H20)6][tosylpiTPPTS is
preferred. These catalyst complexes are stable at the pH the reaction is
conducted at, and at the reaction temperatures, and have been shown to have no
loss in activity over 12 cycles, 1 year storage. Exposure to air did not
deactivate
the catalyst. These results are ideal for portable commercial use.
The reaction rate and conversion efficiency are influenced by pH level of
the incoming formic acid fuel ¨ this is controlled by adding a formate to the
catalyst complex. The preferred formulation has optimum ratio of
HCOOH:HCOONa in terms of reaction rate and conversion efficiency is identified
to be around 9:1, providing pH in the range of 2.6-3.1.
The reaction rate also directly correlates with temperature, over a wide
range. Conversion higher than 90% is achieved at 70deg C and higher, i.e.
considered in a low temperature range for Hydrocarbon reforming. The reaction
is endothermic enabling novel low temperature reforming. Ru complex
formulations are preferred for adequate reaction rates at low temperature
range,
to retain the water in liquid phase, to meet safety standards and to reduce
design
complexity and cost required to filter the water vapor out of the product gas.
The
preferred operating range of the novel catalytic hydrogel is then 70-100 deg.
C. In
some embodiments it may be acceptable to use reaction temperatures lower or
higher than this preferred range.
Realizing benefits of such aqueous catalyst for low temperature
hydrocarbon reforming has to overcome challenges of containing liquid phase
catalyst. As outlined earlier these challenges include, reaction rate
sensitive to
orientation, maintaining an optimum homogenous phase for extended production,
selectively permeable to product H2 gas, inert under operating temperature
range and acidity.
13
CA 2733865 2018-06-08
A hydrogel material is discovered that provides an unusual and
unexpected solution to the needs of the fuel reforming process and chemistry,
in
particular for suitably containing both the liquid catalyst and formic acid
fuel, both
passively in storage and actively in use. Hydrogels absorb many times their
body
weight in water. A class of hydrogels is "superabsorbent polymers [SAP's]. A
super absorbent polymer as defined herein is a lightly cross-linked, partially
neutralized, hydrophilic three dimensional polymer network which can increase
in
weight up to several hundred times on absorption of aqueous solutions. Various
combinations of grafting different co-monomers such as acrylic acid,
acrylamide,
and PVA, have been used. SAPs may also be formed of sodium polyacrylate,
polyacrylamide copolymer, ethylene maleic anhydride copolymer, cross-linked
carboxymethylcellulose, polyvinyl alcohol copolymers, cross-linked
polyethylene
oxide, or starch grafted copolymer of polyacrylonitrile. For consumer
products,
the most suitable choice is found to be poly(acrylic acids), providing the
best
performance to cost.
Illustrated in FIG. 1 is a super absorbent polymer formed of poly (acrylic
acids), showing a hydrophilic polymer backbone and light cross linking
allowing
swelling when hydrated. The poly (acrylic acids) structure contains ionizable
carboxylic acid groups, -COOH, on each repeating unit, making the polymer
backbone hydrophilic. The structure of the polyacrylate is [-CH2-CH(000X)An,
where X is one or more Alkali metals such as Na. The alkali terminated polymer
is soluble. The backbone is cross-linked with hydrophilic crossliners to
enable
expansion without dissolution. When water is absorbed, hydration and formation
of hydrogen bonds creates solvent-polymer interactions.
An SAP particle 2 is shown in FIG.1, with a hydrophilic backbone 8 and
light cross linking between the chains as represented by crosslink region 6
and
others (not numbered). In a dry state, Positive counter ions are balanced with
the
negative carboxylic groups. Hydrated counter ions move more freely within the
particle 2 as part of bigger network (not shown), which increases the osmotic
14
CA 2733865 2018-06-08
pressure within the polymer, however they are still weakly bound along the
polymer backbone and do not exit the polymer to surrounding solution (not
shown). This resultant difference in osmotic pressure pulls more water
molecules
inside the polymer and enables relatively uniform diffusion. The charged
groups
repel as shown in repulsion region 4 which expands the polymer and adds to
swelling capacity. The absorbing capacity of the SAP is greatest with water
and
decreases with ionic solutions, such as electrolytes. For example, when
absorbing an aqueous catalyst solution based on Ruthenium, absorption may
drop on the order of 5 times dry weight. Various polymerization techniques
have
been used for synthesizing SAP's such as inverse suspension polymerization,
solution polymerization, suspension polymerization, bulk polymerization,
foamed
polymerization and graft polymerization.
It is desired to achieve a continuous absorption of aqueous catalyst and
fuel within the hydrogel and various modifications can be made to tailor a
specific
SAP material. For example, techniques to introduce structural porosity by use
of
foaming agents, surfactants or grafting comb like chains with improved
molecular
mobility. Reducing the smallest dimension of the SAP particles within the
hydrogel can achieve rapid kinetics, for example by suspended polymerization
techniques.
FIG.2 shows an image of a hydrogel 10 using a SAP formed of sodium
polacrylate crystals in a dry state before addition of liquid catalyst.
Individual
polycrystalline pellets 12 are shown for illustration, however the hydrogel 10
can
be formed by known techniques to a wide range of forms including as a thin
sheet, powder, segments of thin sheets, weave, mesh, laminate, pellets, sponge
or non-uniform layers. For applications in reformers for fuel cells, a
laminate or
thin sheet is preferred, as shown in FIG. 4.
FIG. 3 shows a catalytic hydrogel 14, following contact and absorption of
an aqueous ruthenium-based catalyst (not numbered), formed as individual
pellets 12. The SAP has expanded approximately 10 times by weight compared
CA 2733865 2018-06-08
ir
1,
to the dry volume weight, and shows the dark color of the Ruthenium based
solution. The degree of absorption varies with solution concentration and
typically
for the preferred ruthenium based solution is greater than 5 times dry weight.
We
further observed that the aqueous solution is retained independent of
orientation
of the SAP material as is shown by various pellet surfaces at different
orientations and the lack of observed excess solution underlying the catalytic
hydrogel 14, i.e. the solution is fully absorbed by each pellet and not
flowing out
with gravity.
This orientation independence is further confirmed during reforming
operation where the rate of hydrogen production is shown to be independent of
orientation of the material. The catalytic hydrogel 14 holds the catalyst for
long
periods in any orientation and allow repeated uses, with minimal reduction in
reactivity. Therefore the catalytic hydrogel 14 is suitable to safely and
efficiently
store reformer catalyst which can be used in any orientation, enabling use
with
formic acid fuel to power consumer mobile products.
The catalytic hydrogel further contains the aqueous catalyst in a "gel-like"
state ("hydrogel state") between solid and liquid, which is advantageous to
allowing extended high reaction rates. There are several novel benefits of the
catalytic hydrogel. Firstly, this catalytic hydrogel retains aqueous solution
regardless of orientation. Secondly, it is stable under high temperatures and
does
not suffer hot spots or breakdown under reforming reaction. Thirdly, in
comparison to rigid solid supports, the catalytic hydrogel is flexible and
absorbs
a high capacity of fuel relative to its weight, for rapid ongoing production
of.
hydrogen. Fourthly, the material is commercially produced in high volumes with
reliable consistency.
The use of the catalytic hydrogel in reforming formic acid fuel is shown in
FIG. 4. Catalytic hydrogel layer 26 is placed for receiving an incoming formic
acid
fuel formulation which reacts with the catalyst as per Eq. 2 in a
dehydrogenation
process, producing a positive pressure of H2 and CO2 gases which exit the
16
CA 2733865 2018-06-08
1,
catalytic hydrogel layer 26. The hydrophilicity and osmotic properties of the
resulting catalytic hydrogel 26 allow the hydrogel to retain both water
solutions
and fuel.
The catalytic hydrogel is found to hold the Ru based solution in a suitable
partial "liquid-solid" state. The Ru based catalyst solution and fuel are
retained
independent of gravitational direction, suitable for mobile use, while not
substantially restricting the further absorbance of new incoming fuel
throughout
the catalytic hydrogel. The catalytic hydrogel is an unusual and fortunate
discovery due to common support materials being limited by not retaining
aqueous solution and being orientation dependent. Hence, the catalytic
hydrogel
represents an ideal novel catalytic material suitable for mobile reforming,
orientation independence, and multiple cycles.
Measurement data of a low temperature formic acid reforming process
using catalytic hydrogel is shown in FIG.5, with hydrogen production as a
function of time over 500 hours of operation. Assuming typical mobile power
use
of 3 hours of H2 generation a day, this test range is equivalent to 160 days
of
mobile device power requirements. Reaction temperature is shown (lower line)
and is maintained between approximately 90-100 deg. C,. This test is done
using
the catalytic hydrogel described and shown in FIG. 3, specifically aqueous
Ruthenium based solution absorbed in polyacrylate SAP hydrogel. The catalytic
hydrogel is formed using discrete pellets of polyacrylate stored in a glass
bottle
container in which formic acid fuel is introduced (-15% aqueous). The glass
bottle container (not shown) is heated using a conventional electrical heater
(not
shown), and production of hydrogen gas is shown in mVmin. The catalytic
hydrogel test demonstrates conversion of > 95%, as measured by remaining
unused formic acid fuel found to be less than 5% by weight indirectly, and the
hydrogel remains substantially unchanged over this period. A suitable ongoing
water balance is shown to be maintained even around the normal boiling point
of
water. This relaxed temperature restriction allows higher operating
temperatures
17
CA 2733865 2018-06-08
than were previously possible, resulting in higher catalyst output and a
corresponding decrease in both size and weight. .As the catalytic hydrogel in
this
test is not a continuous single-part, but discrete pellets in liquid fuel, and
heating
is not fully distributed, the resulting experimental variance is larger than
can be
achieved. Consistent uniform gas production in this prototype test is
improvable
with better heating integration, process optimization, and using continuous
hydrogel material with uniform fuel distribution, however this test is
suitable to
demonstrate operation.
Another benefit and novelty of using the catalytic hydrogel in formic acid
reforming is there are only trace elements of CO produced. Further benefits of
the catalytic hydrogel are absorbance of incoming fuel to react homogenously
with the catalyst and remaining stable during reforming reaction and extended
use and storage.
Alternate formulations for aqueous catalysts are known that can produce
hydrogen from formic acid at low temperature and are included herein as
operable to form a catalytic hydrogel. Such liquid phase catalysts have
similar
requirements for a supporting material, and can be substituted equivalently.
One
of these is a soluble Ruthenium phosphine complex, RuCl2
(triphenylphosphane)2. This formulation has performance 93% conversion at
ambient pressure and 25-40 deg., C. Another formulation results in 100%
conversion at ambient pressure and temperature with a soluble Rhodium
complex; Rh" (Cpl(bP0(H20)SO4CP*=Pentamethyl-cycloPentadienyl. This
formulation similarly uses pH control to optimize the reaction rate by
diluting the
reactant formic acid with HCOONa. Either of these alternate formulations
above,
and any other aqueous catalyst formulations for homogenous liquid phase
reactions can be substituted equivalently for the formulation described in
detail.
18
CA 2733865 2018-06-08
While the embodiments are described for use with the aqueous
Ruthenium based catalytic hydrogel with formic acid fuel, they may be also be
used in a wider range of liquid catalysts for reforming hydrocarbons in
general.
The embodiments described herein have solved these various unmet needs in an
efficient, effective and integrated manner
Alternatives to using polyacrylate SAP in the catalytic hydrogel, may
include combinations of other polymers or co-polymers for tuning material
properties. Additionally hybrid blends of other materials with a super
absorbent
polymer may be used. The catalytic hydrogel can be used with liquid catalysts
for
other hydrocarbon fuels, such as catalysts to reform methanol and the like.
The advantage of using the catalytic hydrogel described in the
embodiments is that a liquid catalyst is held in an ideal contained state for
high
efficiency fuel conversion, with extended stable use to produce high rates of
hydrogen gas. While particular elements, embodiments and applications for the
present invention have been shown and described, it will be understood, of
course, that the invention is not limited thereto since modifications may be
made
by those skilled in the art without departing from the scope of the present
disclosure, particularly in light of the foregoing teachings.
19
CA 2733865 2018-06-08
