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College of Engineering Unit(s): 
Chemical, Biological, and Environmental Engineering

Team: 
Wan Yi Ang, Rebekah Dumestre and Cathy Lim

Project Description: 

Our team was tasked by our sponsor, Vanguard Scientific, to design an expansion to a previous client’s ethanol extraction facility. We were asked to propose a use for the facility’s 10,000+ lb/day of spent hemp biomass, which is a byproduct of their process. Hemp is gaining popularity for its many eco-friendly and versatile applications. We are proposing a process to convert the biomass into activated carbon through a two-stage pyrolysis and activation setup. Activated carbon (also known as activated charcoal) consists of solid carbon which has very small holes, or pores, throughout its structure. These small pores can adsorb molecules such as heavy metals, which make activated carbon useful in water and air purification, pharmaceuticals, and other markets. 

The first stage of the process, pyrolysis, involves controlled burning of the biomass at 600℃ in the absence of air for two hours. These conditions encourage the formation of biochar, which is elemental carbon with a solid porous structure. The pores in the biochar, however, are too large for it to be used in water purification. This is where the activation stage comes into play. Exposing the biochar to steam at 850℃ for three hours instigates a gasification reaction where the steam reacts with some of the carbon in the biochar to form many more small pores in the structure. This structural change turns the biochar into activated carbon.

Throughout the design process, steps were taken to minimize environmental impact and production costs. As shown in our process flow diagram (see video linked below), we chose carbon dioxide as our carrier gas in the pyrolysis unit because we could recycle it from the emissions of the activation unit which cuts down raw material cost and byproduct outputs from the process. Additionally, steam was chosen as the activating agent due to its low environmental impact and its ability to be recycled because the unit produces more steam than it requires in the first place. The resulting design keeps utility and manufacturing costs low, and produces a high quality product that can be sold at a high market value.

Hemp Biomass to Activated Carbon - Engineering Expo Video

Industry Sponsor(s): 
Vanguard Scientific