PhD Thesis Proposal: Low-Energy and Low-Cost Direct Air Capture

PhD Thesis Proposal: Low-Energy and Low-Cost Direct Air Capture (DAC) for Greenhouse Applications

Introduction

Greenhouse agriculture significantly benefits from CO2 fertilization, enabling off-season cultivation and increased yields for various crops. Optimal CO2 concentrations for most plants range from 600 to 1200 ppm [1]. Current CO2 enrichment technologies, such as compressed CO2 injection [2], biogas combustion [3], composting [4], and chemical enrichment processes [5], typically involve CO2 emissions to the atmosphere. However, the pressing challenge of global warming necessitates a paradigm shift in agricultural practices towards emission reduction. The next generation of enrichment technologies must transform greenhouses into local CO2 sinks. While agro-industrial symbiosis systems (AIS) can channel waste heat and CO2 to greenhouses via pipeline networks [6], their applicability is limited to specific sites. Direct Air Capture (DAC) technologies, on the other hand, have emerged as a promising Carbon Capture and Utilization (CCU) process suitable for any greenhouse location [7,8,9]. Despite their potential, the widespread adoption of DAC systems is hampered by high costs and significant energy consumption. This project proposes a cost-effective and energy-efficient carbon enrichment system for plant growth stimulation, leveraging low-temperature renewable energy sources for DAC to increase greenhouse CO2 concentrations to 2-3 times atmospheric levels. The core research hypothesis is that the relatively low CO2 enrichment levels required for greenhouse applications necessitate a low energy input and low operating temperatures. These requirements can be met by utilizing a blend of readily available, low-temperature renewable energy sources. Specifically, the energy for temperature swing absorption/adsorption and desorption will primarily be sourced from the temperature difference between the greenhouse interior and exterior during winter, a geothermal heat pump during intermediate climatic conditions, and a solar mat during summer.

Background and Problem Statement

For carbon capture applications, physical adsorbents or absorbents are generally preferred over chemical sorbents due to the high energy and temperature demands associated with chemical regeneration. A wide range of physical adsorbents exists, including carbonaceous materials, mesoporous silicas, zeolites, and Metal-Organic Frameworks (MOFs). However, careful selection is crucial as these materials can exhibit properties disadvantageous for greenhouse applications [10]. For example, activated carbon, while possessing high adsorption capacity and low humidity sensitivity, suffers from poor CO2/N2 selectivity. Zeolites offer higher selectivity but exhibit lower CO2 loading and significant efficiency reduction in the presence of water, also requiring energy-intensive regeneration. Some MOFs show promise for CO2 capture (DAC, flue gas) in terms of capacity and selectivity, are generally less water-sensitive, and easier to regenerate than zeolites, but are less mature and not yet widely available at low cost. Physical absorbents such as methanol, NMP (N-methyl-2-pyrrolidone), propylene carbonate, or DPEG (polyethylene glycol dimethylethers) offer the advantage of absorbing large quantities of CO2with less absorbent, thereby reducing solvent circulation rates. However, there is limited literature on their application in this context, with most applications focusing on H2S removal from syngas. Crucially, the performance of most sorbents in the literature has primarily been evaluated for industrial applications in high CO2 concentration, high-temperature environments (e.g., flue gas carbon capture) aimed at achieving high-purity separation for storage. Comprehensive studies on adsorption/desorption cycles under low-enrichment conditions, specifically to characterize sorbent behaviour for greenhouse applications, are largely lacking. A balance between cost, performance, and environmental impact of available sorbents also needs to be established through a techno-economic feasibility analysis coupled with a life cycle assessment. These investigations are critical for initiating the deployment of this new generation of enrichment technologies. The central challenge of this project is to validate the feasibility of a CO2 enrichment system for agricultural greenhouses that integrates a novel techno-environmental paradigm: very low carbon emissions, very low environmental impact, very low energy consumption, and economic viability.

Research Objectives

This project aims to promote the large-scale deployment of low-cost, low-tech CCU solutions operating with low-temperature energy sources. To achieve this, the following objectives will be pursued:

➢ Identify and select optimal physical sorbents (adsorbents or absorbents) suitable for low concentration CO2 capture in humid greenhouse environments, considering economic and environmental factors.

➢ Develop a robust experimental setup to accurately characterize the dynamic adsorption/desorption behaviour of selected sorbents under simulated greenhouse conditions.

➢ Design and dimension a low-energy, low-cost DAC system tailored for greenhouse CO2 enrichment, integrating various low-temperature renewable energy sources.

➢ Validate the proposed DAC system's ability to achieve target CO2 concentrations within a greenhouse using the available low-temperature renewable energy mix through comprehensive numerical simulations.

➢ Conduct a thorough techno-economic and life cycle assessment of the proposed DAC system to demonstrate its economic viability and environmental benefits.

Collaborative Framework

This project will be conducted in close partnership between the CEEP (Research Centre on Energy, Environment and Process) at Mines Paris - PSL and the Institute of Porous Material of Paris (IMAP), a joint research unit between ESPCI Paris - PSL and the Chemistry Department of ENS - PSL. IMAP will be involved in work packages requiring a microscopic understanding of adsorption/absorption phenomena, including molecular-scale sorbent characterization, and will have a strong involvement in the sorbent selection phase. IMAP may also functionalize a commercial zeolite and/or provide a batch of reference MOFs, formulated and industrially used for CO2 capture (e.g., CALF 20). CEEP will be involved in sorbent characterization, evaluating process performance at the laboratory scale, designing the virtual prototype at the system level and conducting the LCA and TEA. The thesis will be supervised by Dr. Maroun NEMER (CEEP) [13,14] with co-supervision by Pr. Christian SERRE (ESPCI/ENS) [11,12]. The starting of the PhD thesis is projected for February 2026.

Candidate Profile

The ideal candidate for this interdisciplinary PhD position will possess a strong academic background and a keen interest in sustainable technologies, particularly at the intersection of chemical engineering, materials science, process engineering and environmental sustainability. They should be highly motivated, intellectually curious, and capable of working effectively in a collaborative research environment.

The candidate is expected to be graduated with a Master's degree (or equivalent) in a relevant field such as: Chemical Engineering, Materials Science/Engineering, Process Engineering, Environmental Engineering, Chemistry (with a focus on materials or process chemistry), Energy Engineering

And have strong Foundational Knowledge in:

Thermodynamics and Heat Transfer: Essential for understanding energy flows, temperature swing processes, and designing efficient systems.

Mass Transfer and Separation Processes: Crucial for understanding adsorption/absorption, desorption, and overall capture efficiency.

Material Science (especially porous materials): Knowledge of various sorbent types (adsorbents like zeolites, MOFs, activated carbon; absorbents) and their properties is highly beneficial.

Reaction Engineering (basic understanding): For chemical processes, if any, and understanding sorbent regeneration.

Data Analysis and Scientific Computing: Proficiency in tools for data interpretation, modelling, and simulation.

Applications Procedure

Applications (CV and other relevant elements) are to be sent by mail to :

• Maroun NEMER:

• Ilango THIAGALINGAM:

• Christian SERRE:

Type d'emploi : CDD

Statut : Cadre

Durée du contrat : 36 mois

Rémunération : 1 800,00€ à 2 000,00€ par mois

Lieu du poste : Télétravail hybride Versailles)