Almond and walnut shell activated carbon for methylene blue adsorption

Authors: McCaffrey, Zachariah; Torres, Lennard; Chiou, Bor Sen; Hart-Cooper, William; McMahan, Colleen; Orts, William

Submitted to: ACS Sustainable Resource Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/8/2024
Publication Date: 7/13/2024
Citation: McCaffrey, Z., Torres, L.F., Chiou, B., Hart-Cooper, W.M., McMahan, C.M., Orts, W.J. 2024. Almond and walnut shell activated carbon for methylene blue adsorption. ACS Sustainable Resource Management. 1(7):1421-1431. https://doi.org/10.1021/acssusresmgt.4c00080.
DOI: https://doi.org/10.1021/acssusresmgt.4c00080

Interpretive Summary: There are few markets for nutshells so research is needed to generate new uses for them to avoid landfilling. Activated carbon from almond shells is a potential option that would increase the value of raw almond shells while producing a product that can help solve wastewater problems such as methylene blue contaminated water. This research investigated manufacturing activated carbon from almond and walnut shells and compared their performance in adsorbing methylene blue from water with commercial activated carbons. The commercial carbons were made from coal and coconut shell. Conversion of nutshells to activated carbon used two processes: 1) pyrolysis - which converts raw biomass to a high carbon material, and 2) activation process that increases the materials surface area by etching pores in the carbon. Results showed the maximum surface area activated carbons from nutshells performed comparably with the commercial carbons.

Technical Abstract: Nut production in California is abundant and growing, with California having over 80% of the world's production of almonds and over 30% of the world's production of walnuts. Development of new products from agricultural residues would be beneficial to nut growers and processors, as well as eliminate an environmental problem due to the accumulation of billions of pounds of nutshells per year. Activated carbon (AC) from nutshells has the potential to be one of the more economically beneficial products, compared with electricity generation or as a filler in plastics, cement, and rubber. This study developed ACs from almond shells and walnut shells and compared their performance against two commercial ACs (Calgon Carbon Filtersorb 400 and Kuraray YP50) in adsorbing methylene blue (MB) at various concentrations. Activated carbons were generated from nutshell biochar using 2 levels of activation to investigate effect activation residence time has on material properties including pore development and MB adsorption. Raw nutshells, nutshell biochars, and nutshell ACs were characterized using CHNSO analysis, proximate analysis, thermogravimetric analysis, activation kinetics, FTIR, SEM, MB adsorption testing, BET surface area and pore size distribution, and linear regression analysis on incremental pore volume and methylene blue adsorption capacity. Results showed the maximum surface area ACs from nutshells performed comparably with the commercial carbons.