Adsorption Technologies for Sustainable Reduction of CH4 and CO2 from Agricultural Livestock - Keynote lecture

INTRODUCTION Ruminants, mainly dairy cattle, are widely recognized as one of the main contributors to methane emissions in the environment, playing a significant role in the global warming phenomenon. Considering that a cow emits about 500 L/d of methane 1 and in view of the increasing population of cows due to the intensive farming activities, the daily methane emission is considerable. It is estimated that a cattle (600 kg of body weight) consumes 21 kg DMI /day and due to the enteric fermentation and respiration releases 23 g CH4 / kg DMI and 647 g CO2 / kg DMI 2. Extensive efforts have been made to reduce methane emissions from ruminants prior to their release into the environment; however, considering that the enteric fermentation process is unavoidable, it is crucial to establish methods for capturing the emitted methane. Given the common practice of implementing forced ventilation within barns for animal well-being, the discussed process aims to capture methane via adsorption on either synthetic or natural zeolites or different active carbons through the barn ventilation. The literature review has identified commercial zeolite 13X and Clinoptilolite as suitable materials. EXPERIMENTAL/THEORETICAL STUDY The adsorption isotherms of the gases on the selected adsorbent materials were first taken from the literature and then validated through experiments using a Hidden Catlab apparatus. Both saturation isotherms and dynamic breakthrough curves have been collected. Process design has been performed using Aspen Adsorption® V11 software after retrieving the relevant kinetic, transport and thermodynamic parameters. Different adsorbents have been exposed into a stable for 3-6-9 weeks in different locations and then characterized by thermogravimetry and by temperature programmed desorption couples with mass spectrometry. RESULTS AND DISCUSSION Carbon dioxide poses a significant challenge for methane capture on zeolite, because adsorption competition exists between CO2 and CH4. Therefore, it is suggested that the adsorption process is dominated by the carbon dioxide adsorption. This revealed the necessity of a two-stage adsorption system, with two beds in series. An initial “guard bed” filled with zeolite 13X was used to adsorb carbon dioxide and other gases from the barn, while efficiently adsorbing methane in the second bed of the same volume filled with Clinoptilolite, a cost-effective natural zeolite with excellent properties for methane adsorption. With the current design configuration, the first bed reaches saturation in 210 days whereas the second bed reaches saturation in 40 days; consequently, five replacements need to be executed while keeping the guard bed in operation. The designed plant allows to obtain an exiting flow consisting only of air, therefore mitigating the environmental impact of the agricultural sector. CONCLUSION Different adsorbents were tested in silico, then the selected ones in a controlled microreactor and in a real stable to design an adsorption-based process for the direct air capture of CO2 and CH4. A pilot scale (currently under realisation) and a full scale plant were designed from these data. ACKNOWLEDGMENTS This study was carried out within the Agritech National Research Center and received funding from the European Union Next-Generation EU (PIANO NAZIONALE DI RIPRESA E RESILIENZA (PNRR) – MISSIONE 4 COMPONENTE 2, INVESTIMENTO 1.4 – D.D. 1032 17/06/2022, CN00000022). G. Ramis and I. Rossetti gratefully acknowledge the Italian Ministry of Environment and Energy Sustainability (MASE) for funding the project “RSH2A_000018 - Hydrogen storage and distribution through power-to-gas strategy, with full carbon capture and utilization” in the frame the European Union Next-GenerationEU, Piano Nazionale di Ripresa e Resilienza (PNRR) – Missione 2 “Rivoluzione verde e transizione ecologica”, Componente 2 “Energia rinnovabile, idrogeno, rete e mobilità sostenibile”, Investimento 3.5 “Ricerca e sviluppo sull'idrogeno” (bando A)