Environmental assessment of different integrated biorefinery scenarios using walnut shells as a source for lignin production

Conference Dates

June 5 – 10, 2022


Nowadays, the waste or loss of food produced along the supply chain is equivalent to approximately 33% of the total (FAO, 2013). However, the food sector can also contribute to solving the environmental problems it generates. The valorisation of food waste, with the aim of obtaining value-added compounds, represents a paradigm challenge within the framework of sustainable development. One of the products of high added value of greatest interest to the scientific community is lignin, due to its use as a source for obtaining chemical products. These lignin-based compounds must be competitive with petroleum derivatives from an economic and environmental aspect (Fernández-Rodríguez et al., 2021). In recent years, soda and organosolv processes have been placed at the centre of the biomass fractionation process spectrum. These processes make it possible to solubilise the lignin without altering its initial structure to any great extent (Fernández-Rodríguez et al., 2021). In the walnut processing industry, large quantities of shells are produced as by-products (approximately 400g per kilo of processed walnuts) which are either discarded or burned as fuel (Jahanban- Esfahlan et al., 2020). Nevertheless, under a circular economy approach, these wastes can be valorised to obtain lignin, due to their high lignin content by mass (approximately 40% of the total) (Jahanban-Esfahlan et al., 2020). Therefore, this study aims to environmentally analyse two different sequences of lignin extraction through the valorisation of walnut shells, considering the Life Cycle Assessment methodology. Lignin production involves the following steps: autohydrolysis, delignification, solid cleaning and precipitation. In the organosolv process, an ethanol/water mixture (70/30, v/v) is used at 200°C in a solid/liquid ratio of 1:6 while the soda process is carried out at 121°C using a 7.5% NaOH solution by weight as reagent in the same solid/liquid ratio as in the organosolv method (Fernández-Rodríguez et al., 2021). The valorisation system based was simulated with the use of Aspen Plus® software (Aspentech, 2020) and 100 kg of walnut shells were taken as the biomass input stream. The environmental study considered one kilogram of lignin as the target product, under a cradle-to-gate approach. The inventory is based on data taken from the simulation software. The environmental results suggest that the scenario based on the organosolv process presents the worst environmental profile for all impact categories mainly due to the total thermal energy required in the plant, requiring approximately five times more energy in this scenario than in the soda scenario. In addition, it is observed that the main equipment consuming the most thermal energy is the distillation column at the final stage of the valorisation process to recover the solvent for recirculation and the equipment for heating the large quantities of water needed in the autohydrolysis stage. As future work, it is proposed to reuse the internal streams of the valorisation plant to reduce the loads generated by the energy requirement as well as the use of renewable energy sources instead of using the national energy grid. -Aspentech, 2020. Aspen Plus. URL https://www.aspentech.com/products/engineering/aspen-plus/ (accessed 3.31.20). -FAO, 2013. Food wastage footprint: Impacts on natural resources - Summary report. -Fernández-Rodríguez, J., Erdocia, X., Alriols, M.G., Labidi, J., 2021. Techno-economic analysis of different integrated biorefinery scenarios using lignocellulosic waste streams as source for phenolic alcohols production. J. Clean. Prod. 285. https://doi.org/10.1016/j.jclepro.2020.124829 -Jahanban-Esfahlan, A., Jahanban-Esfahlan, R., Tabibiazar, M., Roufegarinejad, L., Amarowicz, R., 2020. Recent advances in the use of walnut (: Juglans regia L.) shell as a valuable plant-based bio-sorbent for the removal of hazardous materials. RSC Adv. 10, 7026–7047. https://doi.org/10.1039/c9ra10084a

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