Adsorption Performance and Cold Plasma Activation of Biochar for On-Site CH₄ Storage and Energy Recovery in Oil Fields

Abstract

Routine flaring of associated petroleum gas (APG) remains a major source of greenhouse gas emissions in upstream oil production, particularly at remote or infrastructure-limited production sites where gas transportation and processing are uneconomic. Developing a field-deployable, integrated utilization pathway that captures methane (CH₄)-rich APG for on-site generation of electricity and heat at low cost could significantly reduce energy consumption and greenhouse gas (GHG) emissions across the oil industry. This thesis evaluates biochar as an adsorbent for capturing and storing CH₄ and cold plasma surface modification as a means of enhancing CH₄ adsorption, upgrading low-cost biomass-derived chars as effective adsorbents for such a system.

CH₄ adsorption performance was measured for four biochars and compared against that of three commercial activated carbons. While the pristine biochars exhibited adsorption capacities at least 50% lower than those of the tested activated carbons, they demonstrated more than twice the CH₄ storage capacity of compressed natural gas (CNG) at equivalent pressure and vessel volume (10-75 bar), demonstrating their potential to reduce compression requirements and avoid heavy high-pressure storage vessels in field applications. Adsorption thermodynamics and kinetics were analyzed to establish performance baselines and implications for adsorbed natural gas (ANG) storage.

To improve CH₄ storage performance of biochars, this work further investigated cold dielectric barrier discharge (DBD) plasma as a solvent-free, low-temperature surface modification technique. Three key findings emerged: the optimal plasma duration was 30 minutes; the initial volatile matter content of biochar directly governs plasma modification efficiency; and Ar plasma is the most effective source gas, increasing CH₄ adsorption capacity by up to 73%. It was also demonstrated that O₂ in plasma gas (i.e., air or O₂/He) led to a reduction in plasma effectiveness. Results indicate that the enhancement is associated with an increase in the specific surface area of biochars driven by the development of ultramicropores (<0.68 nm), which is in turn associated with the removal of organic impurities from biochar surfaces. Evidence indicates that the morphology, especially the width of pore entrances, may govern the adsorption effectiveness of biochars.

Finally, the research evaluated the end-of-life utilization of spent biochars. Multicycle adsorption tests showed that the adsorption performance of biochars degraded with repeated cycles. However, the degraded biochars can still store more methane volumetrically than compressed gas vessels at low to medium pressures relevant to oil and gas fields. Spent biochars retained residual CH₄, which increased calorific value (e.g. from 13.88 to 18.62 kJ/g) and reduced ignition temperatures (e.g. from 320 °C to 250 °C), supporting their reuse as an enhanced solid fuel.

This work demonstrates a laboratory-scale proof-of-concept that integrates emission abatement, energy recovery, and circular material use. If future work achieves techno-economic optimization, multicomponent gas validation, and successful scale-up of plasma treatment, this approach could potentially contribute to reducing the lifecycle GHG footprint of remote oil field operations. Significant engineering and economic development remains before field deployment feasibility can be assessed.