Feasibility and concurrent remediation of red mud as an in situ pyrolysis catalyst

Authors: LEPORE, ANDREW - Oak Ridge National Laboratory; Ashworth, Amanda; PYOUNGCHUNG, KIM - University Of Tennessee; LABBE, NICOLE - University Of Tennessee; CONNATSER, RAYNELLA - National Transportation Research Center; ALLEN, FRED - University Of Tennessee

Submitted to: BioResources
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/22/2019
Publication Date: 4/24/2019
Citation: Lepore, A., Ashworth, A.J., Pyoungchung, K., Labbe, N., Connatser, R.M., Allen, F.L. 2019. Feasibility and concurrent remediation of red mud as an in situ pyrolysis catalyst. BioResources. 14(2):4696-4707.

Interpretive Summary: Red mud, or bauxite residue, is a well-known industrial waste product generated by the Bayer process during the production of aluminum. This waste stream is generated at a massive scale annually and may serve as a sustainable catalyst for bioenergy production. This technology has the potential to generate revenue from unwanted materials, both crop and bauxite residues. However, red mud’s toxicity must be neutralized during pyrolysis in order to be used downstream as a soil amendment. To test this, researchers evaluated various ratios of red mud and plant residue during bioenergy conversion. The findings suggest that red mud is able to produce a better liquid fuel than plant residues alone, however, the loadings must be considered carefully. The use of the byproduct in this process resulted in a high-quality soil amendment. Therefore, this technology has the potential to create multiple revenue streams from a longstanding waste material, however, future investigation of red mud’s catalytic ability and its ability to improve plant yield need further investigation.

Technical Abstract: Catalytic pyrolysis may be an alternative production strategy to petroleum-derived fuels and chemicals. Furthermore, red mud, a toxic industrial bauxite byproduct, may serve as a sustainable catalyst, thereby overcoming the need for more robust catalysts. To test this, in situ catalytic pyrolysis was run on a semi-pilot scale with various ratios of red mud and switchgrass (Panicum virgatum) feedstock. Authors hypothesized that the coking process would render red mud environmentally benign and could, like biochar, improve soil quality and health for bioenergy crop production. Therefore this work investigated i) red mud’s capability to enhance bio-oil quality, and ii) how the modified biochar produced from in situ pyrolysis affected switchgrass establishment, seedling vigor, and root and shoot mass. Results indicate that red mud is effective at increasing soil pH and reducing the total acid number in bio-oil. While high loading of reacted red mud had a negative impact on plant yield, adding uncatalyzed biochar to pure red mud significantly improved seedling yield on marginal soils. These results suggest that this technology has potential for valorizing a waste stream and creating a soil amendment from red mud; thereby closing nutrient and bioenergy production cycles.