Synergistic co-processing of Red Mud waste from the Bayer process and a crude untreated waste stream from bio-diesel production

Abstract

The production of the aluminum metal from bauxite ore and bio-diesel from triglyceride oils both generate large waste streams, and their management and valuation is therefore of great interest in Brazil and any other country with established or developing bio-fuel and aluminum industries. The integration of these two waste streams into the development of alternative technologies that utilize wastes as low-cost materials could potentially contribute to economic development as well as chemical sustainability and minimize the environmental and ecological impact of these industries. In this study, a crude untreated bio-diesel plant waste stream consisting of glycerol, methanol, free fatty acid salts and water was co-processed with Red Mud, the highly alkaline by-product of bauxite refining through the Bayer Process, at elevated temperature and pressure (350 to 400 °C; 0–500 psi hydrogen gas) in an attempt to synergistically produce value-added products from these two waste streams. Comparative analysis between untreated and upgraded materials was performed by CHN EA, TGA, TPR, SEM, MS, FT-IR, Karl-Fischer-Titration, and ¹H/¹³C NMR. The products obtained showed an increase in carbon and hydrogen content in both the organic product phase and the Red Mud catalyst recovered. Also observed in the organic phases was an increase in the paraffin content relative to starting material as determined by NMR with a concomitant reduction of the alcohol content confirming glycerol and methanol conversion. The Red Mud recovered after every upgrading reaction showed a change of color to dark gray to black, magnetic and amphiphilic properties, as well as a substantial decrease in its alkalinity and an increase in its carbon content. Catalyst recycling reactions were performed highlighting the possibility that the Red Mud could be reused as a catalyst promoting an increase in the observed crude glycerol conversion to paraffins potentially usable as a low-grade heavy fuel oil.