Fig. 7

General flow diagram of the supply chain of the chemical manufacturing of 2 main indigo products, a powdered dye, or a liquid pre-reduced solution. The light blue area marks the steps that would be different if a biological manufacturing platform would be employed, and these alternative operations may be found in the light green area. The final processing steps of the formulation are anticipated as similar to the chemical and biological platforms; therefore, they have not been included in the blue or green shading. ‘High T’ and a thermometer denote high temperature. The splitting arrows, numbered 2. (light blue) and 3., have been used to visualize the formulation of liquid indigo, which usually commences after the drying process has been performed to a certain extent. The numbered steps denote: 1.—the main chemical reaction chain toward the synthesis of synthetic indigo; nowadays in the majority of industrial factories, the core reaction relies on aniline or its precursors as the raw materials. 2.—the formulation toward powdered indigo; usually performed via drying. 3.—the formulation toward pre-reduced liquid indigo; usually performed via catalytic hydrogenation and the addition of strong reducing agents. 4.—the fermentation reaction that leads to the synthesis of biological indigo. The grey centrifuge represents the downstream processing sequence for product purification, for which the individual unit operations have been described in detail in “Downstream processing considerations” section. The dark blue writing represents the main substrates that are required to perform a certain manufacturing step, while the violet writing has been used to underline the potentially most expensive compounds. The figure has been created with the help of BioRender