Location: Bioproducts Research
Project Number: 2030-41000-067-008-I
Project Type: Interagency Reimbursable Agreement
Start Date: Sep 1, 2020
End Date: Aug 31, 2024
Objective:
California produces 82% of the world’s almonds (estimated at 1.85 billion pounds of kernels for 2019), resulting in nearly 5 billion pounds of almond hulls and 1.4 billion pounds of shells with almost no market outlets for shells. The dairy cattle industry buys tree nut shells for animal bedding or feed extenders; however, that industry is shrinking or stable while tree nut production is expanding. There are very few large-scale viable markets for walnut, pistachio, almond and pecan shells. In fact, on occasion, processors have reported paying disposal fees of $10-$25/ton to dispose of excess shells – a direct hit to their profits. Research is needed to create alternate markets for these under-valued biomass feedstocks.
One new application for waste almond shells is the conversion to activated carbon. Through precise application of carbonization and activation processes, carbonaceous material can be converted to activated carbon with specific characteristics: high purity, high surface area material with application-specific pore structure. For example, silicon-based anode materials used in Li-ion batteries carbon with customized porosity to act as a scaffolding for further processes. Graphite, the incumbent anode carbon source, cannot meet next generation performance requirements of increased energy and power density. However, the battery industry is finding a promising next step by combining silicon with carbon to form a composite material. Currently, commercially available anodes are made from petroleum, coconut or synthetic precursors and are still very expensive (approx. $45-100/kg). The final yield of carbon precursors after activation is 12% to 20%. The low final yield and input price of precursors are the main reasons the current cost is so high.
Success of this program will result in new products from almond production agricultural residues. Transforming this “waste” stream into products with economic value ameliorates environmental and potential health risks of stockpiled waste, while improving economies of rural communities, and increasing revenues for almond growers. The proposed project will assess processing and manufacturing methods to convert waste almond biomass into carbon and activated carbon products for use in absorbed natural gas storage, Li-ion batteries, and ultracapacitors.
Approach:
1. Develop repeatable methods and processes to achieve microporous activated carbon structures from almond shells. Our hypothesis: Almonds possess a high cellulose content that will result in an activated carbon of high microporosity.
2. Develop product metrics for technology transfer to pilot scale . Our hypothesis: by working closely with our partners in the ultracapacitor, Li-ion battery and ANG storage sectors, we will be able to optimize activated carbons from almond shells to perform as well or better than current products.
3. Develop pilot-scale production process and manufacturing capability of multiple tons per month of activated carbon to start contributing to the targeted energy storage sectors at West Biofuels' facility (Woodland, CA). Our hypothesis: Carbonization and activation processes can be scaled but careful attention to operating conditions will be needed to ensure consistent product.
4. Perform techno-economic analysis of processing almond shells into advance carbon. Our hypothesis: Activated carbons for Li-ion batteries, ANG devices, and ultracapacitors can be manufactured using almond shells at prices significantly below those of current competitors.
