Valorization of black liquor lignin into renewable absorber coatings for thermal performance enhancement of solar dryers

Solar drying is a low energy‐consuming technology in agricultural processing; however, its application has been limited by the low absorption capacity and thermal destruction of traditional petroleum‐based absorbent coatings. This research discusses the heroization of kraft black liquor lignin as a renewable photothermal absorber coating of mixed‐mode solar dryers. Lignin was extract of acid precipitation, then formulated into absorber coats, and fully characterized by physicochemical and optical means of FTIR, XRD, SEM, TGA, and UV–VIS–NIR. Lignin‐based formulations were found to have much higher hemispherical absorptance, up to 0.94, and a higher photothermal conversion efficiency η ₚₜ ≈0.46 when compared to a commercial black coating. The evaluation of the solar dryer through an experiment showed improvement in total thermal efficiency as the value changed to about 54–56% of the lignin optimization formulations with reference being about 36%. Response Surface Methodology was used to model and optimize the coating formulation parameters, and the obtained model had R 2 = 0.962 and a statistically insignificant lack‐of‐fit term. These results support the hypothesis of the conversion of black liquor lignin into high‐performance absorber coating successfully to increase solar dryer performance and at the same time increase sustainable biorefinery waste valorization.