(698f) Multicomponent Breakthrough Curve Dynamics of Novel Carbon Xerogel Materials for Blue Hydrogen Production

Today, fossil fuels are responsible for over 90% of global hydrogen (H₂) production with the largest contributor being steam methane reforming (SMR), however, SMR is associated with large carbon dioxide (CO₂) emissions, emitting 11 kg of CO₂ for every kg of H₂ produced [1]. In order to achieve climate change targets, current production facilities must be retrofitted with carbon capture technologies. MEA absorption, an established carbon capture (CC) technology, uses a toxic material and occupies large volumes of space [2]. Therefore, new innovative CC technologies must be developed.

Pressure swing technologies, have been proposed as an alternative to the commercialised technologies due to their rapid cycle times and low operating costs. To improve the performance of pressure swing technologies, active carbon xerogels (ACXs) as an adsorbent material, have shown their versatility in the ability to tune their surface area, adsorption sites, and pore structures to optimise adsorption capacity and selectivity [3]. Furthermore, multi-component adsorption systems experience unique adsorption breakthrough curve (BTC) dynamics resulting in the displacement of lighter components which, with the influence of non-isothermal conditions, can result in various BTC characteristics, including plateaus and adsorption hysteresis at normalised adsorbate outlet concentrations over inlet concentrations (C/C₀) other than 1 (i.e. at non equilibrium conditions) [4][5].

This work presents a series of ACXs which were activated at temperatures ranging from 600°C to 800°C that showed CO₂ adsorption capacities between 2.41 mmol g^-1 and 3.03 mmol g^-1, with selectivity of CO₂ greater than 77%, from BTC experiments using a typical SMR hydrogen PSA tail gas (i.e. 50% CO_­2; 15% CH₄; 10% CO balanced in N₂) at STP conditions. The material activated at the highest temperature (i.e. 800°C) exhibited the highest specific surface area at 882 m² g^-1 and subsequently the highest adsorption capacity of CO₂ during dry BTC experiments at 3.03 mmol g^-1.

The distinctive characteristics of the non-isothermal multicomponent adsorption BTC for a typical tail gas displayed various dynamic properties of ACXs. The affinity of the adsorbates followed a trend of CO₂>CH₄>CO. Further, it was observed that prior to CO₂ breakthrough, both CH₄ and CO experienced displacement where – due to the non-isothermal conditions of the breakthrough curve – plateaus were observed at C/C₀ other than 1. The specific properties of this system can be leveraged in the design and optimisation of a pressure swing adsorption cycle to enhance the selectivity of CO₂ capture for small-scale blue hydrogen production.

[1] T. K. Blank, P. Molly, Hydrogen’s Decarbonization Impact for Industry, Rocky Mountain Institute (2020).

[2] IEA, Global Hydrogen Review (2023). Available at https://www.iea.org/reports/global-hydrogen-review-2023.

[3] C. Larkin, J. Morrison, et al., Hollow Fibre Adsorption Unit for On-Board Carbon Capture: The Key to Reducing Transport Emissions, Carbon Capture Science & Technology 2 (2022), 100034.

[4] M. Jurkiewicz, M. Musik, R. Pelech, Adsorption of a Four-Component Mixture of Volatile Organic Compound Vapors on Modified Activated Carbons, Ind. Eng. Chem. Res. 62 (2023), 3716-3723.

[5] I. Pentchev, K. Paev, I. Seikova, Dynamics of non-isothermal adsorption in packed bed of biporous zeolites, Chemical Engineering Journal 85 (2002), 245-257.