(755e) Gas Storage in Superactivated Hydrochars Synthesized from Anaerobic Digested Food Waste

In the United States, 30-40% of food supplied is ultimately destined to be ‘food waste’ as estimated by U.S Department of Agriculture (USDA). This impacts the environment significantly by contributing to greenhouse gas (e.g., CO₂, CH₄, etc.) emissions during landfill disposal as well as resource depletion of water and energy. In addition, the greenhouse is coming from the burning of fossil fuel. As a result, the world is transitioning towards clean energy where, hydrogen (H₂) is a potential renewable and zero-emission energy carrier. Moreover, carbon dioxide (CO₂) capture, storage and utilization could reduce greenhouse gas emission from fossil fuel sectors. In order to adsorb either gases, a proper storage material is required. As a result, the gas storage materials are attracting great attention from researchers.

In the recent past, various efforts have been undertaken to store CO₂ and H₂ in metal-organic frameworks (MOFs), covalent organic frameworks (COFs) etc. due to their large specific surface area, small pore size, and large pore volume. However, it is not economically feasible to store bulk amounts of CO₂ and H₂ in MOFs or COFs, as they could be cost intensive. Hence, researchers have been focusing on producing storage material from waste material such as food waste, sewage sludge, etc. Anaerobically digested food waste could be a very low-cost feedstock to synthesize gas storage materials. The objective of this study was to produce superactivated hydrochars from food waste digestate for storing H₂ and CO₂. Hydrochar from food waste digestate was produced at 220 and 260 °C and activated using KOH in two methods. Produced hydrochars were chemically activated at 3 different temperatures (600, 700, 800 °C) and 4 different ratios (2:1, 3:1, 4:1, 5:1). BET analysis was conducted of the activated chars to determine the specific surface area, pore type, and corresponding pore volume. In addition, High-Pressure Volumetric Analyzer (HPVA) was used to measure the volumetric uptake of H₂ and CO₂. Analyses showed that activation ratio is the most important factor to control the material properties. Thus, an optimum ratio (4:1) was identified to work best for storing both H₂ and CO₂. Although the storage capacity in superactivated hydrochar is still lower than the MOFs and COFs, further investigation is required to improve the storage capacity on these waste-derived materials.