(415g) Experimental Evaluation of Catalytic Transients Involved in Reservoir Natural Gas Reforming

Hydrogen is considered a flexible energy carrier and a clean reagent/reactant for many sectors (transport, heating, chemicals production) seeking to move towards net zero emission.¹ Hydrogen already plays a key role in the refinery and chemicals industries but its potential application in other sectors has significantly increased demand. As a result, there is worldwide interests in developing technologies to produce clean and cost-effective hydrogen. The current commercial practice for hydrogen production is mostly through steam methane reforming (SMR) resulting in annual greenhouse gas (GHG) emissions of 830 Mt.^1–3

Subsurface hydrogen generation in a natural gas reservoir involving steam reforming and retaining the GHGs associated with the commercial (above ground) process in the reservoir is an alternative pathway to produce clean hydrogen. The concept here is to inject a catalyst precursor into the gas reservoir, heat the reservoir to reach reaction temperature using thermal enhanced oil recovery technologies and finally initiate the steam methane reforming to produce hydrogen.⁴

In this study we investigate the feasibility of clean hydrogen production using the catalytic SMR reaction at subsurface conditions through transient behavior studies (temperature programmed techniques). To this effect, Ni and Fe based catalyst precursors are immobilised on reservoir materials using incipient wetness impregnation methods. The concentrations are commensurate with expected field implementation. Catalyst calcination, reduction/activation, SMR reaction and deactivation occur almost simultaneously as oxidants are used to initiate either a thermal front that moves through the reservoir or in a huff-and-puff operation that oscillates between oxidation and SMR reaction. In order to simulate these conditions, the dried catalysts in this study were subjected to using temperature programmed (TP) experiments followed by steady-state experiments at the final temperature for a specific period of time.

Reference experiments (see Figure 1) were devoted to the individual catalyst calcination step, catalyst reduction step, and SMR reaction step to characterize the catalyst and determine the best performance envelope. Catalyst testing was continued with combining these three experimental steps in one-step experiment and thus mimicking the subsurface transient conditions. The effect of active metals (Ni, Fe or Ni-Fe), CH₄/H₂O ratio, space time and temperature ramp rates using one-step experiments were investigated. The TP reaction data were used to estimate the apparent activation energy for each catalyst. The catalyst characterization before and after one-step experiments were carried out to determine possible catalyst deactivation mechanisms. The results have provided insights into optimized operating conditions for subsurface hydrogen generation that can be used for pilot field studies.

Figure 1. (a) TP calcination of 1 wt% Ni/sand in Ar at 10°C/min and (b) Energy-dispersive X-ray spectroscopy (EDS) mapping of a calcined 1 wt% Ni/sand.

References

1 International Energy Agency, The future of hydrogen, https://iea.blob.core.windows.net/assets/9e3a3493-b9a6-4b7d-b499-7ca48e3..., (accessed 11 April 2022).

2 M. H. Ali Khan, R. Daiyan, P. Neal, N. Haque, I. MacGill and R. Amal, Int. J. Hydrogen Energy, 2021, 46, 22685–22706.

3 Z. Ou, Z. Zhang, C. Qin, H. Xia, T. Deng, J. Niu, J. Ran and C. Wu, Sustain. Energy Fuels, 2021, 5, 1845–1856.

4 L. Surguchev, R. Berenblym, A. Dmitrievsky, US8763697B2, 2010.