Biomass-Derived Blue Pigment (Indigoidine) Could be Less Costly and Have Lower Carbon Footprint Than Synthetic Indigo

The current industrial production of indigo dye involves the use of toxic and hazardous compounds, resulting in the release of hazardous wastes and retention of toxic impurities in the indigo-dyed denim. To address these health and environmental concerns, and to meet the increasing demand for blue dye at a competitive price, we present a novel biologically-derived alternative to synthetic indigo dye called indigoidine. This alternative is produced using bioenergy sorghum feedstock and an ionic liquid-based one-pot high-gravity bioconversion process. We provide a comprehensive techno-economic analysis and lifecycle assessment of the biomass-derived indigoidine, which identifies areas for process improvement, cost reduction, and establishes performance targets for future research and development.

Currently, the yield of indigoidine in the one-pot batch process results in a high production cost and GHG emissions of $29.5/kg and 25.6 kgCO_2e/kg-indigoidine, respectively. We find that key cost and carbon footprint drivers for the biomass-derived indigoidine include the indigoidine yield from sugar and lignin monomers, the solid loading rate for bioconversion, the quality of biomass feedstocks, the retention time and aeration rate for the bioreactor, sugar yield, and ionic liquid recovery. By optimizing these parameters to near theoretical limits, we were able to achieve a significant reduction in both selling price and GHG emissions, resulting in a selling price and GHG emissions of $0.86/kg and 0.93 kgCO_2e/kg, respectively, representing a six- and five-fold reduction relative to synthetic indigo dye.

With further research and development efforts aimed at achieving the identified targets, we estimate a 95% likelihood of achieving a selling price and GHG emissions of indigoidine of less than $1.6/kg and 2.2 kgCO_2e/kg, respectively. These values are lower than the current market price and GHG emissions of synthetic indigo dye, which are $5.51/kg and 4.72 kgCO_2e/kg-indigoidine, respectively. Our findings suggest that the biomass-derived indigoidine could replace the fossil counterpart, saving several million dollars.