(232d) Evaluation of Alternative Processes for Grapeseed Oil Production from a Techno-Economic and Environmental Perspective

Circular economy principles serve as the vehicle to establishing sustainable consumption and production patterns within the manufacturing sector. A more efficient use of the existing resources, including the revalorization of residues, facilitates the reduction of the environmental impact while fostering innovation and resilience in the process industry. As part of the food manufacturing sector, wine production is one of the largest contributors to solid waste generation, producing 0.2 kg solid residue per bottle of wine dispatched. This residue, comprising skins, seed, grape stalks, and wine lees, holds high intrinsic value and can be transformed into a wide range of high added value products.¹ The production of grapeseed oil for culinary and medicinal purposes using this residue has been investigated as a supplementary process for small and large wineries. Conventional oil extraction methods employing organic solvents like n-hexane offer simple recovery, low vaporization heat and high selectivity², but also involve negative human-health, safety, and environmental impacts.³ To mitigate these issues, supercritical fluids, particularly CO₂, were suggested as safer and greener alternatives due to their recyclability, non-toxicity, and non-flammability features. Supercritical (SC) CO₂ extraction proved to prevent product degradation and yields highly pure oil with minimal solvent residue.⁴ Furthermore, incorporation an organic co-solvent can improve the solubility and extraction efficiency of the targeted compounds. Ethanol, a green and safe compound widely used in food and drugs processing, has been proposed as a safe co-solvent to improve the yield of the SC-CO₂ extraction technology.⁵

This work systematically evaluated the performance of SC-CO₂ extraction, and combined SC-CO₂ and ethanol co-solvent extraction, which were compared with the conventional process using hexane for grapeseed oil recovery. Each solvent-oil system necessitated an appropriate prediction method to accurately replicate the thermodynamic equilibrium occurring during the extraction process, and thus estimate yield and optimal operating conditions. The assessment included conceptualization of the extraction process, process modeling and simulation, techno-economic analysis (TEA), and cradle-to-gate life cycle assessment (LCA). Aspen Plus modeled system performance and estimated costs, while SimaPro conducted LCA. These methods formed the basis for techno-economic and environmental assessment.

The three extraction systems were designed to process 15% of the seed residue generated in California, i.e. a production capacity of 900 kg/h. Results showed that hexane extraction technology can achieve the highest yield, recovering 130.6 g grapeseed oil per kg of grape seed entering the process. Using solely SC-CO₂ as extracting agent reduced by 12% the efficiency of the extraction (114.6 g_oil kg_seed ^-1), while incorporating ethanol as co-solvent system in a 10% mass ratio could achieve a comparable yield to hexane extraction, reporting 129.8 g_oil kg_seed ^-1. The advantage of the latter with respect to the conventional extraction is the absence of traces of toxic solvent. Oil produced via hexane extraction reported a residual hexane content of 500ppm, while CO₂ (45 ppm) and ethanol (0.3%) residual content is harmless to human health. The TEA performed to the hexane process estimated a total capital cost of $4.95 MM and a production cost of 6.31 USD per kg of extracted grape oil. The SC-CO₂+ethanol extraction system almost doubled capital cost ($9.72 MM) while the production cost was 36% superior (8.61 USD kg_oil^-1). However, the level of purity achieved with the SC-CO₂+ethanol system increases the selling price of the grapeseed oil,⁶ so the profit of the former resulted approximately 3 to 4 times higher than the oil recovered using hexane. Finally, a cradle-to-gate LCA was performed to track both biogenic and fossil carbon dynamics. Different operating conditions of each extraction method identified resulted in a dissimilar environmental impact. Hexane extraction operated at atmospheric pressure and mild temperature conditions, thus reporting relatively low heat and power demands. Assuming biogenic carbon as climate neutral, hexane extraction generated 2.78 fossil kgCO₂-eq per kg oil produced. The use of supercritical CO₂ requires operating pressures above 150 bar, and elevated solvent to seed ratios. The greater solvent to grape seed mass ratio involved, together with the pressurisation and heating/refrigeration requirements caused the superior carbon emission score for the alternative processes. SC-CO₂ oil-extraction agent generated 7.35 kg CO₂-eq kg_oil^-1, while the CO₂-ethanol system reported the highest score estimated in 8.48 kg CO2-eq kg_oil^-1. However, when the electrification of utilities and renewable energy supply were assumed, the CO₂-ethanol scenario incurred the lowest GWP (i.e. 1.44 kg CO₂-eq kg_oil^-1) reducing by 25% the environmental impact of the conventional technology.

References

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