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Purification of Hydrogen Using Formulated Metal-Organic

Framework

Vicente I. Agueda 1, José A. Delgado 1, Aud I. Spjelkavik 2, Richard Blom 2 and Carlos
Grande 2*

1- Department of Chemical Engineering, Universidad Complutense de Madrid, 28040, Madrid, Spain

2- SINTEF Materials and Chemistry, Forskningsveien 1, 0373, Oslo, Norway

*Presenter: carlos.grande@sintef.no

Keywords: hydrogen production; carbon dioxide capture; metal organic framework;

UTSA-16; adsorption; diffusion; pressure swing adsorption
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1. Introduction

The recovery of hydrogen from steam methane reforming (SMR) off-gases is one of the largest points of industrial stationary emissions of carbon dioxide. If pre-combustion techniques for power production are adopted, the demand for hydrogen will considerably increase. For this reason, advances in H2 purification and CO2 capture from this application are important.
In the H2 purification from SMR off-gas, hydrogen is recovered from a mixture saturated with water vapour containing hydrogen and carbon monoxide, methane and carbon dioxide as impurities. Pressure Swing Adsorption (PSA) is mature technology for purification of hydrogen (Stöcker et al., 1998). The unit is composed by several columns, each of them comprising two or three layers of adsorbents to selectively remove impurities.
Recently, a novel microporous metal-organic framework, called UTSA-16, has been proposed for capturing carbon dioxide from gas mixtures by PSA in view of its high carbon dioxide adsorption capacity and selectivity at ambient conditions (Xiang et al. 2012). This material has small cages of about 0.45 nm in diameter, with pore openings of 0.33 x 5.4 nm2, and exhibits a carbon dioxide adsorption capacity which is one of the highest among MOF materials (Willis, 2010; Xiang et al 2012). The high capacity of this material with the zeolite-like density makes it a potential candidate for being used in purification of hydrogen from SMR off-gases.
The objectives of this work are the following:
(i) To develop a specific recipe to formulate UTSA-16 keeping high surface area, selective adsorption and fast diffusion.
(ii) To measure the adsorption Henry's law constants and reciprocal diffusion time constants of CO2, H2, CH4, CO and N2 on UTSA-16 extrudates.
(iii) To measure the high-pressure pure adsorption equilibrium isotherms of the cited gases in
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the prepared UTSA-16 extrudates at different temperatures (298, 313 and 338 K).
(iv) To evaluate the potential performance of the synthesized adsorbent on the recovery of hydrogen from SMR off-gases (composed of hydrogen, methane, carbon monoxide and carbon dioxide) by PSA using the measured adsorption properties.

2. Results and Discussion

2.1. Diffusion measurements

A chromatographic method has been used to measure the pure gas adsorption Henry's law constants and the reciprocal diffusion time constants of hydrogen, nitrogen, methane, carbon monoxide and carbon dioxide on UTSA-16 extrudates from pulse responses.
It was observed that diffusion within the UTSA-16 crystals is dominant within the studied conditions. For carbon dioxide, the time of the peak maximum is much higher than for the other gases because of the high value of K for this gas. It can be observed that the value of K correlates with the polarizability for H2, N2, CO and CH4, suggesting that dispersion forces determine the adsorption affinities of these gases in UTSA-16. Electrostatic interactions seem to be weak for these adsorbates. For carbon dioxide, although the polarizability is higher than for the rest of gases, the much higher value of K is due to the electrostatic interaction between its quadrupole moment and coordinated water molecules in UTSA-16 cavities (Xiang et al.
2012).

2.2. Adsorption equilibrium isotherms of hydrogen, nitrogen, methane, carbon monoxide and carbon dioxide in UTSA-16 extrudates

Adsorption of CO2, H2, CH4, CO and N2 were measured at three different temperatures and until high pressures. Figure 1 shows the adsorption isotherm of CO2 at 298 K in
UTSA-16 extrudates and zeolite and its comparison with zeolite 13X and activated carbon.
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The experimental adsorption isotherms were fitted adequately with the Dual Langmuir model in the studied pressure range.
The values of Henry constant determined from pulse and adsorption equilibrium experiments are quite similar, so the consistency of the results is verified.

2.3. Simulation of the hydrogen purification from SMR-off gas by PSA with UTSA-16 as adsorbent

A four-column PSA cycle for hydrogen purification from SMR-off gas with UTSA-16 extrudates as adsorbent has been simulated. Connectivity between the steps and pressure levels of the different steps are presented in Figure 2. The studied cycle is similar to the one studied in a previous work using BPL activated carbon and 13X zeolite as adsorbents in a layered bed (Delgado et al. 2014). However, in this cycle a rinse step (a portion of tail gas rich in carbon dioxide is recycled as feed) has been introduced after the feed step. The rinse step is a heavy component recycle and thus it can be considered as a dual-reflux cycle (Yoshida et al., 2003; Reynolds et al., 2006). The rinse step has been included to take advantage of the higher carbon dioxide adsorption capacity of UTSA-16 with respect to BPL activated carbon, which could lead to a higher carbon dioxide concentration in the waste gas, resulting in a higher hydrogen recovery in the light product and a consequently higher purity of CO2 in the tail gas.
The design specification was either a hydrogen purity of 99.99+% or 99.999+%.
Simulation shows that the process can produce hydrogen with 99.999+% purity with high recovery (93%).
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3. Conclusions

The evaluation of a PSA process for H2 recovery and purification using metal-organic framework UTSA-16 was carried out. The evaluation was carried out by measuring fundamental adsorption equilibrium and kinetic data that was not available in literature.
Based on the obtained results, a four-bed PSA cycle for hydrogen purification from SMR-off gas has been simulated. Introducing a rinse step in the cycle, the process can yield hydrogen with 99.99-99.999% purity with 93-96% recovery and productivities between 2 and
2.8 mol kg-1 h-1.
An important feature of the positive initial evaluation of UTSA-16 for H2-PSA is its high volumetric density and that the species diffuse relatively easy through the pores of the extrudates. The results obtained from this work present a positive outcome of the utilization of metal-organic frameworks in H2-PSA utilization.
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References

Delgado, J. A., Agueda, V. I., Uguina, M. A., Sotelo, J. L., Brea, P. and C. A. Grande, 2014. Adsorption and Diffusion of H2, CO, CH4, and CO2 in BPL Activated Carbon and 13X Zeolite: Evaluation of Performance in Pressure Swing Adsorption Hydrogen Purification by Simulation. Ind. Eng. Chem. Res. 2014. DOI: 10.1021/ie403744u.
Reynolds, S. P., Ebner, A. D. and J. A. Ritter, 2006. Stripping PSA Cycles for CO2
Recovery from Flue Gas at High Temperature Using a Hydrotalcite-Like Adsorbent. Ind. Eng. Chem. Res., 45, 4278-4294
Stöcker, J., Whysall, M. and G. Q. Miller, 1998. 30 Years of PSA Technology for
Hydrogen Purification, UOP LLC, Des Plaines, Illinois.
Willis, R., 2010. Carbon Dioxide Removal from Flue Gases Using Microporous Metal-Organic Frameworks. Final Technical Report. Department of Energy, United States. Project contract: DE-FC26-07NT43092.
http://www.netl.doe.gov/technologies/coalpower/ewr/co2/pubs/43092F1.pdf.
Xiang, S., He, Y., Zhang, Z., Wu, H., Zhou, W., Krishna, R., Chen, B., 2012. Microporous Metal-Organic Framework with Potential for Carbon Dioxide Capture at Ambient Conditions. Nature Commun.3, 954.
Yoshida, M., Ritter, J. A., Kodama, A., Goto, M. and T. Hirose, 2003. Enriching Reflux and Parallel Equalization PSA Process for Concentrating Trace Components in Air. Ind. Eng.
Chem. Res., 42, 1795-1803
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Figures

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13X pellets

5 UTSA-16 pellets

4

BPL activated carbon

3 granules

2

1

0

0 1 2 3 4 5

p / bar

Figure 1. Comparison of carbon dioxide isotherms (in mol l-1) at 298 K in 13X zeolite

pellets, UTSA-16 extrudates and BPL activated carbon granules

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(a)

(b)

Duration, s	30	180	30	30	180	30	30	180	30	30	210
STEP	1	2	3	4	5	6	7	8	9	10
COLUMN 1	ADS	RIN	DEQ1	PP	DEQ2	BD	RP	PEQ2	PEQ1	BF
COLUMN 2	PEQ1	BF	ADS	RIN	DEQ1	PP	DEQ2	BD	RP	PEQ2
COLUMN 3	BD	RP	PEQ2	PEQ1	BF	ADS	RIN	DEQ1	PP	DEQ2
COLUMN 4	DEQ1	PP	DEQ2	BD	RP	PEQ2	PEQ1	BF	ADS	RIN

(c)

16

ADS

14

12

10

8

6

4

2

0

RIN DEQ1

PP DEQ2

BD RP

BF

PEQ1

PEQ2

0 120 240 360 480 600 720 840 960

t / s

Figure 2. (a) Connectivity between steps. F = feed gas, L = light product, T = tail gas. (b)

Cycle time schedule. (c) Pressure history for Simulation 4 in Table 6.

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