Location: Bioproducts Research
Project Number: 2030-41000-067-006-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Oct 1, 2020
End Date: Jun 30, 2023
ARS and the cooperator will develop pyrolysis processes for making lab-scale activated carbon. We will produce samples of activated carbons that meet specifications for lithium ion, ultracapacitor and absorbed natural gas applications. We will manufacture and test product prototypes using the lab-scale activated carbon.
Conversion of almond shells into activated carbon products will be performed using a five-step process: 1) pyrolysis, 2) activation, 3) particle size optimization, 4) surface treatment, and 5) product testing. Several almond varieties will be selected for experimentation. 1) Pyrolysis will heat the almond shells in a low oxygen environment to remove volatiles and leave carbon and metal impurities. Nitrogen gas is used to replace oxygen in the pyrolysis process thereby eliminating combustion of the almond shell. Pyrolysis optimization will be performed by varying time and temperature to optimize pore development and produce biochar. 2) Activation uses carbon dioxide gas to etch the biochar surfaces by oxidation to increase micropore volume producing high surface area and resulting in a product with high-performance. Optimization of the activation process with include using a Design of Experiments program to measure effect of temperature, time and gas mixture on the pore development to maximize surface area and pore structure and create high value activated carbon. 3) Particle Size Optimization will be accomplished by using a precision-controlled pancake jet mill to obtain particle sizes of the activated carbon for specific applications. For example, lithium ion and ultracapacitor applications require a mean particle size of 8 µm with a narrow particle size distribution whereas, adsorbed natural gas applications require a mean particle size of 125 µm with bimodal particle size distribution. Milling process experiments will be performed to measure effect of input particle size, milling pressure, and gas temperature have on throughput, economic and energy costs, and final particle size distribution and produce ultracapacitor electrodes. 4) Surface treatment of ultracapacitor electrodes using thermal processing in nitrogen will decompose oxygen containing functional groups thereby reducing performance degradation and device failure. Functional groups on the surfaces will be quantified by x-ray photoelectron spectroscopy before and after treatment. Temperature, time, process gas will be evaluated in a full factorial experimental design to minimize surface functional groups including anhydride, ether, phenol, lactone, quinone, carboxylic and carbonyl groups. 5) Product Testing will include viability in commercial Li-ion batteries, adsorbed natural gas devices, or ultracapacitors. Samples for each application will be selected based on physical property characterization results compared to specifications for current market products. Materials meeting performance requirements will be used to develop market ready prototypes of almond derived energy storage products: Li-ion battery cells, adsorbed natural gas devices, and ultracapacitors. Simultaneous to the development of the steps 1-5, at the lab-scale, ongoing experimentation will be accomplished at the pilot scale.