1. Prepared by: Ricki Chairil
Prepared for: Prof. Yong L. Joo
and Joseph Michael Carlin, Jr.
Cornell University
Electrospun Fiber-Integrated Catalyst
Membranes for H2S Removal in Gasification
Processes
CHEME 5650 Final Report
May 2015
Department of Chemical and Biomolecular Engineering

2. Abstract
The focus of this project was to optimize the morphology and surface adhesion of
electrospun polyacrylonitrile-polysilazane (PAN-OPSZ) nanofibers containing tungsten (VI)
oxide nanoparticles for use in membrane catalyst coatings for the removal of hydrogen sulfide in
industrial gas streams. All tested polymer solutions were electrospun at an infusion rate of 0.02
mL/min, target volume of 2 mL, voltage of 20 kV, and a distance 15 cm from the rectangular
collecting plate. We determined that a solution containing 7 wt% PAN in 4.5 g DMF, 0.68 g
tungsten oxide nanoparticles, and 0.339 g PMK OPSZ (i.e. 50:50 PAN:PMK ratio) produced
nanofibers with considerable scratch resistance and resists deforming by compressed air flows up
to 40 psi, applied 3 cm perpendicular to the surface of the fibers. These fibers contained about 50
mass% free WO3 nanoparticles. In general, solutions containing 6-7 wt% PAN in 4.5 g DMF
solvent, PMK masses of 0.31-0.47 g, and 3-20 mass% (without solvent) WO3 nanoparticles were
shown to produce scratch and compressed gas-resistant fibers that could potentially be used as
membrane catalysts. In order to be viable as catalysts, however, these solutions must be spun on
a cylindrical surface and then tested for H2S removal. Due to time constraint, these steps were
unable to be completed, but our findings here establish a foundation for the study of using
inexpensive polymer nanofibers in place of more costly transition metal catalysts currently used
in H2S removal.
Introduction
The removal of hydrogen sulfide (H2S), a toxic and environmentally harmful substance,
from process and waste gas streams is a vital concern in the energy industry. More stringent
environmental regulations passed worldwide have compelled numerous industries to integrate
H2S removal in their production processes, often via catalysis. During coal gasification or sour
gas processing, it is common for traditional metal and metal oxide catalysts to become poisoned
and deactivated by the entering H2S. In addition, typical solvent-based removal of H2S involves
the absorption of CO2 and H2S using liquid amines and the subsequent regeneration of these
amines for reuse, which occurs at elevated temperatures (115-125°C) and requires intensive
energy investment. As an alternative to high-temperature amine scrubbing or conventional
catalysis, this research project involves testing the efficacy of using membrane catalysts
consisting of tungsten (VI) oxide (WO3) nanoparticles (np) in conjunction with electrospun
polyacrylonitrile (PAN) nanofibers in H2S removal. Various types of organic polysilazane resins
(OPSZs), which are ceramic silicon-containing materials, will be added for adhesion and
structural support of the nanofibers. These novel catalysts will be heat-treated to increase the
number of active sites and are theoretically impervious to H2S poisoning.1,2
Successful
development of these catalysts could be applied to the petrochemical industry to remove sour
gases without the need for high-temperature regeneration.1

3. Because of time constraint and the unavailability of a working rotating cylindrical
collecting surface, hydrogen sulfide tests were unable to be conducted. This paper will thus focus
primarily on the optimization of the np-containing membrane catalyst itself, in terms of
adhesion, np concentration, and fiber morphology.
Theory
Solutions to be spun, which are typically organic polymers such as polyacrylonitrile,
polyethylene oxide, and polyvinyl alcohol, are collected in a plastic syringe and discharged via
mechanical syringe pump. A special 20 gauge needle is attached to the syringe to guide the
solution as it is spun, and to reduce the amount of surface tension the solution must overcome to
be spun correctly.3
Electrical clamps are then attached at the needle and the collector, which
consists either of a steel mesh or conductive surface covered in aluminum foil. A high voltage
(5,000 to 50,000 V typically) is applied to this system, which allows liquid droplets at the end of
the syringe to overcome its own surface tension. As the electrostatic repulsion energy of the
system counteracts the liquid surface tension, conical jets of solution nanometers in diameter,
called Taylor cones, begin to form.3
The liquid portion evaporates quickly and solid fiber
structures begin accumulate on the collector. These structures may be rather homogenous in fiber
diameter, which is ideal for our application due to the uniform distribution of fiber scaffold to
contain our catalyst nanoparticles,1,3
or they may have bead-like local accumulations of polymer
when examined under SEM. These beads are problematic because they indicate that the fiber
structure contains insufficient polymer distribution at certain locations, and tend to occur more
often when lower molecular weight polymers are spun.3,4
Materials and Methods
The main objective of this project is to test the H2S removal capability of electrospun
polyacrylonitrile (PAN) nanofibers, in conjunction with polysilazane resins (OPSZ), which are
silicon-containing organic ceramic precursors, and tungsten (VI) oxide nanoparticles (np). In
theory, these nanoparticles will react to remove H2S to form tungsten sulfides.4
These ceramic-
fiber hybrids will be incorporated into an existing tubular palladium catalyst bed. Figure 1 shows
a schematic of the test setup.

4. Figure 1. Schematic of the hybrid nanofiber-ceramic modified catalyst bed. The H2S-rich process
stream will be introduced in cross-flow relative to the membrane.
Specifically, the solution to be electrospun contains varying amounts of PAN (MW =
150,000-200,000), dissolved in 4.5 g dimethylformamide (DMF). These solutions are stirred
between 2-8 hours to dissolve.
The breakdown of major project milestones is as follows:
(1) Electrospinning of PAN nanofibers onto a rectangular surface and testing of
relevant fiber specifications (fiber size, porosity, etc),
(2) The gradual addition of ceramic materials to these fibers, and the subsequent analysis
of the aforementioned properties, as well as narrowing the range of acceptable PAN and
OPSZ concentrations,
(3) Determination of tungsten nanoparticle concentration range that optimizes mechanical
fiber strength, surface adhesion, and H2S removal, as well as electrospin tests on a
cylindrical surface,
(4) Final performance evaluation of the ceramic and fiber-modified catalyst bed as
opposed to the control (unmodified with nanofibers).
Each phase is associated with an experiment series ID number and letter. As mentioned
previously, an appropriate cylindrical collector was unavailable, so phase (4) could not be
completed in time. However, in order to ultimately test the H2S removal capability of the
modified tubular catalyst bed, it has been proposed that a mixed-gas stream containing air,
hydrogen, and a controlled amount of H2S will be injected through the bed. The outlet hydrogen
sulfide concentration will be determined by stoichiometric analysis.

5. Phase 1 (Experiment series RC-1A). During this first stage of the project, a preliminary
PAN solution was spun and evaluated for fiber quality and to establish the standard conditions
for electrospinning. No OPSZ or tungsten np was added at this stage. This preliminary solution
was composed of 0.5 g 150,000 MW PAN (from Sigma-Aldrich) dissolved overnight at room
temperature in a 20 mL scintillation vial containing 4.5 g of DMF. Once the solution was
dissolved, about 3-4 mL of the solution was transferred to a 5 mL plastic Becton Dickinson (BD)
syringe. A 20 gauge spinneret needle was attached to the syringe. Next, the syringe was placed
inside a Harvard Apparatus PHD Infusion 2000 syringe pump, located inside a fume hood for
safety reasons. Meanwhile, a rectangular copper collecting slab was wrapped in heavy-duty
aluminum foil - this acted as the surface where the nanofibers accumulate. The collector was
placed 15 cm from the spinneret tip. Next, the tip of the spinneret and collector were clamped to
a high voltage source. While the voltage remained off, the pump was set to infuse 2 mL of the
solution at a rate of 0.02 mL/min. At this time, the pump was checked to ensure that a steady rate
of PAN solution flowed from the spinneret. Once no flow irregularities were detected, a
cardboard screen was first placed in front of the collector to capture unwanted solvent droplets
from collecting once the voltage was switched on. The high voltage was set to 20 kV, and the
stream of electrospun fibers was checked for flow irregularities. When the solvent was no longer
entrained by the propelled fibers and a steady stream of fiber was observed, the cardboard was
removed and the collection of the nanofibers began. The collector’s position was adjusted
accordingly based on where the bulk of the nanofibers were accumulating, but it always
remained 15 cm from the spinneret. Figure 1 shows a schematic of this setup.
Figure 1: Schematic of the basic electrospinning setup. The specified set of conditions was used
throughout the project.
Phase 2 (Experiment series RC-1B and RC-1C): Once the test fibers from Experiment
series RC-1A were confirmed to have acceptable morphology, we began adding OPSZ
(specifically, KiON HTA 1500 Rapid Cure) to the solutions. As mentioned, this stage of the
20 kV
Infusion conditions:
Flow rate = 0.02 mL/min
Target volume = 2 mL
Infusion time = 100 min
15 cm

6. project involves determination of an optimal range of PAN and RC OPSZ concentrations for our
membrane catalyst. For series RC-1B, six solutions, each with varying RC OPSZ concentrations,
were created. The solution preparation and electrospinning procedures were identical to the
methods outlined in phase 1, except that RC OPSZ was slowly added to the solution after PAN
was dissolved. The mixture of PAN and RC OPSZ was stirred for 15 minutes to dissolve. After
SEM analysis of the RC-1B solutions, which contained 150,000 MW PAN, it was determined
that a majority of the solutions had very poor fiber morphology due to the formation of localized
polymer beads. As such, four of these six solutions were remade with 200,000 MW PAN (from
Polysciences, Inc.) instead. This series of solutions (RC-1C) otherwise contained the same
masses of PAN, RC OPSZ, and DMF as their RC-1B counterparts. Only solutions with relatively
higher concentrations of OPSZ were considered for the RC-1C series, since it has been shown
that silicon-containing materials in nanofibers improves thermal and mechanical stability.6
Table
1 summarizes the compositions of the RC-1B and RC-1C series solutions.
Table 1. Compositions of RC-1B and RC-1C series solutions. RC-1B solutions contained
150,000 MW PAN, while RC-1C solutions contained 200,000 MW PAN.
Solution
number
mPAN/mOPSZ
PAN
concentration
in DMF
(wt%)
mDMF (g) mPAN (g) mOPSZ (g)
RC-1B-1 80:20 8 4.5 0.39 0.098
RC-1B-2 70:30 8 4.5 0.39 0.17
RC-1B-3
RC-1C-1
60:40 8 4.5 0.39 0.26
RC-1B-4
RC-1C-3
40:60 6.5 4.5 0.31 0.46
RC-1B-5
RC-1C-4
30:70 5 4.5 0.24 0.56
RC-1B-6
RC-1C-2
50:50 8 4.5 0.39 0.39
Phase 3 (Experiment series RC-4A, RC-4B, and RC-4C): Because of the acceptable
fiber morphology of the RC-1C solutions, it was determined that only the 70:30, 60:40, 50:50,
and 40:60 PAN:OPSZ solutions could be viable as the final membrane catalyst. These solutions
were be loaded with tungsten oxide nanoparticles and tested for their adhesion to the collecting
surface, which is a key desirable quality in our final catalysts. For these trials, the solution
preparation method was modified to accommodate for the addition of nanoparticles. First, the
appropriate amount of nanoparticles was added to 4.5 g of DMF. Next, the solution was ultra-
sonicated using a Q-Sonica Q-500 Probe Sonicator at 50% amplitude for 30 minutes per solution
- this prevents the nanoparticles from aggregating. After ultra-sonication, 200,000 MW PAN was
added to the solutions and dissolved overnight. When the solutions were ready to spin, they were

7. Parafilmed shut, placed inside a 30ºC water bath sonicator, and sonicated for 60 minutes to
ensure uniform mixing of PAN and np.
Because of previous observations that OPSZ RC produced fibers of poor adhesion to the
collecting surface, we opted at this phase to use PMK, a solid variant of OPSZ, instead of liquid
OPSZ RC. The PMK was added and dissolved into the solutions after they were sonicated in the
water bath, after which the solutions were electrospun per the conditions described in Phase 1.
After spinning, the fiber mats were subjected to two adhesion tests - for RC-4A and RC-4B
solutions, the fibers were scratched with increasing pressure both by finger and by a pencil tip.
For RC-4C solutions, the fibers were also subjected to crossflow by compressed air. The fibers
were graded on a scale of 1-5 based on their performance in the adhesion scratch tests, with 5
being the best adhesion.
Qualitative descriptions for the scores are as follows:
1: Very little adhesion. Fibers can be removed by lightly dragging a fingertip over the
surface.
2: Minimal adhesion. Can be removed by light pencil scratching. Resists light fingertip
drags but peels off with higher finger pressure.
3: Moderate adhesion. Resists finger pressure. Requires moderate effort to scratch off
with pencil tip. May peel a little when light pencil scratches applied.
4: Good adhesion. Generally resists most writing-pressure pencil drags.
5: Excellent adhesion. Requires great effort to scratch off with pencil tip.
To conduct the compressed air test, the air pressure was set at 10 psi intervals and air was blown
both parallel and perpendicular to the fiber (which was left attached on the aluminum foil
collector). Specifically, during the crossflow tests, the air outlet was initially placed at 10 cm
from the fiber surface, then moved gradually closer. If the fiber did not deform or peel from the
foil when the air outlet was 3 cm from the surface, it was considered resistant to that particular
air pressure, and the pressure was increased for additional trials until all fibers began showing
signs of structural weakness.
Results
Because optimization of the fibers as applied to membrane catalysis of H2S was the main
focus of this project, we will only report in-depth results most relevant to this final optimization.
Specifically, the fiber characteristics and adhesion qualities of nanoparticle-loaded, PMK-
containing nanofibers - the very same fibers that would likely be employed in our final

8. membrane catalysts - will be presented here, and detailed analysis of preliminary and test fibers
that lacked nanoparticles (i.e. RC-1 series solutions) will not be considered.
Tables 2 and 3 present the compositions of the final solutions to be considered as
candidates for the final H2S membrane catalysts, as well as their performance on adhesion tests.
Table 2. Compositions and adhesion scores for RC-4B solutions.
Solution number mDMF (g) mPAN (g) mPMK (g) mnp (g) Adhesion score
RC-4B-1 4.50 0.313 0.313 0.0313 3
RC-4B-2 4.50 0.339 0.339 0.0339 4
RC-4B-3 4.50 0.290 0.435 0.029 4
RC-4B-4 4.50 0.313 0.470 0.0313 5
RC-4B-5 4.50 0.313 0.313 0.0626 4
RC-4B-6 4.50 0.339 0.339 0.0678 5
RC-4B-13 4.50 0.339 0.339 0.271 4
RC-4B-14 4.50 0.339 0.339 0.339 3.5
Solution number PAN:PMK mass ratio PAN wt% in DMF mnp/ mPAN Xnp = mnp/ mF
RC-4B-1 50:50 6.5 10% 4.8%
RC-4B-2 50:50 7 10% 4.8%
RC-4B-3 40:60 6 10% 3.8%
RC-4B-4 40:60 6.5 10% 3.8%
RC-4B-5 50:50 6.5 20% 10%
RC-4B-6 50:50 7 20% 10%
RC-4B-13 50:50 7 80% 29%
RC-4B-14 50:50 7 100% 33%
Table 3. Compositions and adhesion scores for RC-4C solutions.
Solution number mPAN (g) mPMK (g) mnp (g) Adhesion
score
Compressed air
resistance
RC-4C-1 0.339 0.339 0.68 3.5 up to 40 psig
RC-4C-2 0.339 0.339 1.02 3 up to 20 psig
RC-4C-3 0.339 0.339 1.58 2 < 10 psig
Solution number PAN:PMK mass ratio PAN wt% in DMF mnp/ mPAN Xnp = mnp/ mF
RC-4C-1 50:50 7 200% 50%
RC-4C-2 50:50 7 300% 60%
RC-4C-3 50:50 7 466% 70%
Figures 2-3 give a visual representation of these scores, using RC-4A solutions as examples. The
RC-4A series of experiments was used to establish the ideal amounts of PAN, PMK, and
tungsten oxide nanoparticles for trials RC-4B and RC-4C.

9. Figures 2-3. Adhesion/scratch test on Solutions RC-4A-3 (left, rated 2.5/5) and RC-4A-9 (right,
rated 5/5). The semicircular marks are finger drags, while the straight-line marks are from
pencil tips. Note that RC-4A-3 and 9 both generally resist finger drags but only RC-4A-3 begins
to peel under light pencil pressure. There is an increase in scratch pressure from top to bottom.
In Tables 2 and 3, we report the total loading mass ratio Xnp. This is the ratio of
nanoparticle mass to the total mass of the fiber (mF = mPAN + mPMK + mnp) not including the mass
of the DMF solvent, which evaporates during electrospinning. This total loading mass ratio will
likely determine the extent of conversion of H2S in our final catalyst membranes. As a reference,
prior research on transition metal phosphide catalysts report that at total mass loading of 14-20%,
H2S removal was improved by 10-20% on average compared to commercially available
catalyst.5
However, to maximize H2S removal, we wanted to determine if Xnp levels greater than
50% were viable as membrane catalysts, since theoretically, higher loading yields more active
sites and higher rates of conversion. Additionally, because the final membrane catalyst would
need to endure large gas flow rates perpendicular to the surface, we attempted to simulate these
high flow rates using compressed air for these highly loaded fibers.
Initially, because nanoparticle loading increases solution viscosity, which can make
electrospinning more difficult, very low nanoparticle loadings were used. However, once it was
discovered that nanoparticle loading generally does not adversely affect electrospinning or
adhesion below a mnp to mPAN mass ratio of 80%, nanoparticle loading was eventually greatly
increased. This was the main rationale behind the RC-4C trials, and explains the large difference
in nanoparticle loading between trials RC-4B and RC-4C. Finally, in the interests of time, only
solutions containing a 50:50 PAN:PMK ratio at 7% PAN in DMF were considered at higher np
loading, since these solutions produced the best adhesion in RC-4B trials.

10. Discussion
We note from Tables 2 and 3 that a solution containing 7% PAN in 4.5 g DMF, in a
50:50 PAN:PMK mass ratio (i.e. 4.5 g DMF, 0.339 g 200,000 MW PAN, and 0.339 g PMK)
produced the best base solution for nanoparticle loading in terms of adhesion and gas flow
resistance. In general, we noticed that the higher the PMK mass added, the better the adhesion
(up to a certain point), but the more papery the fiber mats. Furthermore, contrary to what was
hypothesized, nanoparticle loading had little bearing on fiber quality or adhesion unless very
high loadings (Xnp > 50%) were used. This adhesion was retained despite higher solution
viscosity, as mentioned previously. Figure 4 gives a visual representation of how adhesion and
total nanoparticle loading were related.
Figure 4. Plot of average adhesion score as function of nanoparticle concentration for 7 mass%
PAN in DMF and 1:1 (50:50) PAN:PMK solutions.
Table 2 also reveals that PAN concentrations of 6-7 wt% in 4.5 g DMF and PMK masses
of 0.31-0.47 g produced fibers that scored 4 or higher on the scratch adhesion tests. Depending
on the physical stress that the membrane catalysts endure during handling and normal operation,
it is likely that the fiber composition can deviate slightly from the optimal makeup described
above.
In Table 3, we see that our optimized fibers (7% PAN in 4.5 g DMF, 50:50 PAN:PMK
mass ratio) can be loaded with up to 50 mass% nanoparticles and still resist compressed air
crossflow of 40 psi. Assuming this pressure resistance is not lost when electrospinning is
ultimately conducted on a cylindrical surface, it is adequate for H2S removal in industrial flue
gases, which have pressures slightly above atmospheric (15-20 psia).7
For more pressurized H2S-
rich gas streams, it may be necessary to add polyethylene oxide to the solution, then immerse the
spin fibers in water, to enhance adhesion.
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
0 20 40 60 80
AverageAdhesionScore
Xnp (mass% of nanoparticles in fiber)

11. Conclusion and Recommendations
In closing, we have successfully synthesized tungsten oxide nanoparticle-loaded PAN-
OPSZ nanofibers which have been shown to possess considerable scratch resistance and
resistance to gas flows up to 40 psig. However, these fibers have yet to be spun on a cylindrical
surface and tested for sulfide conversion. Additionally, there are a few shortcomings to the
methodology presented here that must be addressed. Firstly, the scratch adhesion tests were
mostly qualitative by nature, and the scores assigned to each fiber were assigned based only on
qualitative properties. For future studies, it is recommended that these scratch tests be conducted
using known scratch pressures and hardness. Furthermore, it is also necessary to determine the
typical stresses these final catalyst membranes must endure, not only during normal operation
but also during handling. While these fibers were shown to be mostly resistant to scratching and
tearing, they may be peeled from the surface when being installed or maintained. In these cases it
is necessary to add additional adhesion enhancers (such as PEO). Finally, the issue of scale-up is
also a factor to consider. While these solutions produced excellent fibers on aluminum foil-
covered copper plate in lab-scale, their properties may change when spun on a different substrate
or over a larger surface area.
Acknowledgements
I would like to thank Prof. Yong Lak Joo and Joseph M. Carlin, Jr. of the Cornell
University Department of Chemical Engineering for their excellent instruction and guidance over
the course of this project.

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