In the heart of Madrid, researchers at the Unit for Sustainable Thermochemical Valorization, part of the Energy Department at CIEMAT, are turning pistachio shells into a powerful tool for cleaning up industrial emissions. Led by Alejandro Márquez Negro, a team has developed a novel method to transform this agricultural waste into highly effective bioadsorbents for capturing carbon dioxide (CO2) and hydrogen sulfide (H2S), two of the most problematic gases in the energy sector.
The process begins with pyrolysis, a thermochemical treatment that heats the pistachio shells in the absence of oxygen, breaking them down into biochar, bio-oil, and gases. The biochar, a carbon-rich solid, is then activated using either chemical or physical methods to enhance its adsorption properties. “We found that chemical activation with potassium hydroxide (KOH) significantly boosted the biochar’s microporosity and surface area,” explains Márquez Negro. “This resulted in a remarkable adsorption capacity of 87 milligrams of CO2 per gram of adsorbent and 9.6 milligrams of H2S per gram of adsorbent.”
The implications for the energy sector are substantial. H2S is a common byproduct in processes like anaerobic digestion, where organic matter is broken down to produce biogas. Before this biogas can be used as a renewable energy source, it must be upgraded to remove contaminants like H2S. Similarly, capturing CO2 is crucial for reducing greenhouse gas emissions and mitigating climate change. The pistachio shell-based bioadsorbents offer a sustainable and cost-effective solution for both challenges.
The research, published in the journal ‘Molecules’ (translated to ‘Molecules’ in English), revealed that the chemical activation method not only enhanced the biochar’s adsorption capacity but also improved its performance in dynamic H2S capture tests. The presence of moisture in the adsorbent was found to favor H2S dissociation, further improving the capture process. “The hydrophilic properties of the chemically activated biochar play a significant role in its superior performance,” says Márquez Negro.
The study also highlighted the importance of using non-linear kinetic models to describe CO2 adsorption data, with the Avrami model providing the best fit. This finding could guide future research and development in the field of gas adsorption technologies.
As the demand for pistachios continues to grow, so does the abundance of pistachio shells. By converting this agricultural waste into valuable bioadsorbents, the research team is contributing to a circular economy, where waste from one process serves as a raw material for another. This approach not only reduces waste but also creates new opportunities for the energy sector.
The potential applications of this technology are vast. From biogas upgrading to carbon capture and storage, the pistachio shell-based bioadsorbents could revolutionize the way we manage industrial emissions. As the energy sector continues to evolve, innovative solutions like these will be crucial in achieving a more sustainable and efficient future.
The research team’s work is a testament to the power of interdisciplinary collaboration and the potential of waste valorization. By turning a seemingly insignificant agricultural byproduct into a powerful tool for environmental remediation, they are paving the way for a greener, more sustainable future. As the energy sector continues to grapple with the challenges of decarbonization and waste management, this research offers a glimmer of hope and a roadmap for future developments.
