(657e) Novel Vacuum Pressure Swing Adsorption for Green Hydrogen Recovery from Natural Gas Grids Using Carbon Molecular Sieve | AIChE

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(657e) Novel Vacuum Pressure Swing Adsorption for Green Hydrogen Recovery from Natural Gas Grids Using Carbon Molecular Sieve

Authors 

Henrique, A. - Presenter, Faculty of Engineering University of Porto
Aly, E.
Zafanelli, L., Polytechnic Institute of Bragança
Rodrigues, A. E., LSRE - Laboratory of Separation and Reaction Engineering - Associate Laboratory LSRE/LCM
Silva, J. A. C., ESTiG-IPB
Mouchaham, G., Institut des Matériaux Poreux de Paris, Ecole Normale Supérieure de Paris, ESPCI Paris, CNRS, PSL University
Green hydrogen (GH), produced via water electrolysis, is widely recognized as a cost-effective fuel, and it plays a key role in the transition to a sustainable energy economy [1]. GH is a promising fuel for long-distance transportation, powering fuel cells in the mobility sector, and it helps to decarbonize heavy industries [2]. After GH production, it can be co-transported into the existing natural gas grids (NGG), thereby avoiding the need for extensive infrastructure investments [3]. However, upon blending GH into the NGG, it becomes important to recover and purify it to a high degree of purity to enable, for instance, fuel cell applications (H2 > 99,97%). One problem concerning the separation and purification of GH from NGG relates to the H2 feed concentration (< 20%), which differs greatly from conventional H2 purification processes (> 70%) [4]. Moreover, the high CH4 concentration and its relatively weak adsorption affinity on commonly used adsorbents further complicate achieving high-purity H2 and high recovery rates through conventional approaches.

In this work, we report a novel conceptual vacuum pressure swing adsorption (VPSA) process to separate H2 from CH4 by exploiting the kinetic selectivity of H2 over CH4 on CMS-3K-172, as shown in Figure 1A. To develop the conceptual VPSA cycle, a series of single and multicomponent breakthrough curves for H2 and CH4 were performed on CMS-3K-172 between 195 and 273 K, and pressures up to 18 bar. These experiments were performed in a cryogenic fixed-bed adsorption unit specially designed to work at lower temperatures (until 77 K) by using cryogenic baths [5]. The example shown in Figure 1B refers to single breakthrough curves of H2 and CH4 on CMS-3K-172 compared to a blank experiment (glass spheres inside the column) performed at 195 K and 12 bar, where a clear kinetic separation can be seen. CH4 has a limited diffusion, and it is blocked from entering the CMS-3K-172 for the short breakthrough time, which results in its early breakthrough compared to the blank experiment. On the other hand, the H2 breakthrough curve shows a delay compared to the blank experiment due to H2 being adsorbed on CMS-3K-172.

A fixed-bed adsorption mathematical model was validated through the fitting of binary experimental breakthrough curves (H2/CH4 - 20/80%), and, after that, it was used for the VPSA process simulations. The conceptual VPSA developed consists of 1 bed with 5 steps, namely (1) pressurization with feed, (2) feed, (3) H2 purge, (4) cocurrent depressurization (COD), and (5) countercurrent vacuum blowdown. The VPSA performance, i.e., H2 purity and recovery, was evaluated by changing the process variables such as step time, intermediate-to-high pressure ratio, purge-to-feed ratio, and VPSA type configuration. Figure 1C shows three VPSA types that were simulated: type I with the five steps mentioned above, type II without the COD step, and type III without the H2 purge step. The H2 purity-recover trade-off for the three VPSA types can be seen in Figure 1D. From a feed of 20% H2, the VPSA type II allows obtaining an H2 purity of up to 68% with a recovery of up to 92%, and the best trade-off between purity and recovery was 83% and 85%, respectively.

This work shows for the first time that an adsorbent that adsorbs preferentially H2 and blocks CH4 from entering its pores can be useful to enrich H2 from a low feed concentration. Moreover, this work provides insights for developing new materials with the same CMS characteristics but with higher H2 capacity, which could be beneficial to improve the VPSA process. In conclusion, the developed VPSA process is useful for increasing the H2 molar fraction from 20% to 60 - 70% with a high recovery. We are currently working on a second stage to be incorporated into the VPSA process to purify H2 for fuel cell applications (>99.97%).

Figure 1. A) VPSA based on the kinetic selectivity of H2 over CH4 on CMS-3K-172; B) Experimental single breakthrough curves of H2 and CH4on CMS-3K-172 compared to the blank experiment at 195 K and 12 bar; C) VPSA type configurations; and D) Trade-off between H2 purity and recovery for different VPSA types and sets of process variables. VPSA steps: (1) pressurization with feed, (2) feed, (3) H2 purge, (4) cocurrent depressurization (COD), and (5) countercurrent vacuum blowdown.

Acknowledgments

The authors are grateful to the Foundation for Science and Technology (FCT, Portugal) for financial support: (1) under project PTDC/EQU-EPQ/0467/2020 (DOI: 10.54499/PTDC/EQU-EPQ/0467/2020), (2) through the national funds FCT/MCTES (PIDDAC) to CIMO (UIDB/00690/2020 and UIDP/00690/2020), and SusTEC (LA/P/0007/2020), (3) by the national funds through FCT/MCTES (PIDDAC): LSRE-LCM, UIDB/50020/2020 (DOI: 10.54499/UIDB/50020/2020) and UIDP/50020/2020 (DOI: 10.54499/UIDP/50020/2020); and ALiCE, LA/P/0045/2020 (DOI: 10.54499/LA/P/0045/2020). Additionally, we thank national funding by FCT, Foundation for Science and Technology, through the individual research grant SFRH/BD/7925/2020 of Lucas F. A. S. Zafanelli. Moreover, the authors are grateful to Osaka Co. for kindly providing the CMS-3K-172 studied in this work.

References

[1] - IRENA. Decarbonising end-use sectors: Green hydrogen certification; International Renewable Energy Agency, 2022.

[2] - Atilhan, S.; Park, S.; El-Halwagi, M. M.; Atilhan, M.; Moore, M.; Nielsen, R. B. Green hydrogen as an alternative fuel for the shipping industry. Current Opinion in Chemical Engineering 2021, 31, 100668. DOI: https://doi.org/10.1016/j.coche.2020.100668.

[3] - Melaina, M. W.; Antonia, O.; Penev, M. Blending Hydrogen into Natural Gas Pipeline Networks: A Review of Key Issues; 2013. DOI: 10.2172/1068610.

[4] - Liemberger, W.; Gross, M.; Miltner, M.; Prazak-Reisinger, H.; Harasek, M. Extraction of Green Hydrogen at Fuel Cell Quality from Mixtures with Natural Gas. Chem Engineer Trans 2016, 52, 427-432. DOI: 10.3303/Cet1652072.

[5] - Zafanelli, L. F. A. S.; Aly, E.; Rodrigues, A. E.; Silva, J. A. C. A novel cryogenic fixed-bed adsorption apparatus for studying green hydrogen recovery from natural gas grids. Sep Purif Technol 2023, 307, 122824. DOI: 10.1016/j.seppur.2022.122824.

Topics 

Hydrogen Production & Storage
Adsorption
Materials

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