Techno-economic and life cycle assessment of tannin production from spruce bark for leather industry applications

Abstract

Bark, which is currently far from being utilised to the maximum, has the potential to be a sustainable source of chemicals in the future. For instance, bark contains a significant amount of tannin which has a wide range of applications in various industries. Tannins extracted from spruce bark have been proposed for use in the leather industry to achieve more sustainable and environmentally friendly tanning processes. In this work, a novel industrial-scale extraction process for tannins from spruce bark is described and its feasibility and environmental impacts evaluated. The process concept includes hot water extraction of tannins from spruce bark and after-treatment sections, with the final product a powder with a high concentration of polyphenolic compounds. The process and its equipment were dimensioned based on the estimated available bark volume of a pulp mill located in the Nordic countries. The study included a techno-economic analysis and sensitivity study, and the plant project to be implemented using this tannin extraction process was assessed to be feasible in terms of dimensions, raw material and consumption of utilities. Based on the techno-economic analysis, tannins extracted from Norway spruce for leather industry applications show promising economic potential. The minimum selling price for the tannin product was 2.1 €/kg, and the most prominent economic risks within said plant project stemmed from achieving a high enough overall process yield. The global warming potential of the extracted spruce bark tannin was 4.6 kg CO2-eq per kg of tannin product. The most significant contributor to the potential was process steam, meaning that optimising the energy consumption of the process would be important for increased environmental benefits. If the extraction of tannin from spruce bark can be successfully scaled up to industrial level, there is significant potential for the future, improving the value of underutilised biomass fractions and thus providing an alternative to the most commonly used, environmentally harmful tanning agents.