Spent coffee grounds oil extraction using short-chain alcohols: kinetics extraction, equilibrium data, and process intensification

Author(s)

Tatiane Akemi Toda

• Document type: Doctoral Thesis
• Press: Pirassununga.
• Institution: Universidade de São Paulo (USP). Faculdade de Zootecnica e Engenharia de Alimentos (FZE/BT)
• Defense date: 2022-01-18

Examining board members

Christianne Elisabete da Costa Rodrigues; Pedro Esteves Duarte Augusto; Rodrigo Corrêa Basso; Rosemary Aparecida de Carvalho; Elias de Souza Monteiro Filho; Fernanda Maria Vanin

• Advisor: Christianne Elisabete da Costa Rodrigues

Abstract

The main aim of this Ph.D. thesis was the valorization of the spent coffee grounds (SCG), a material result of the beverage preparation and by-product of the soluble coffee processing industry. The valuation strategy proposed was through the extraction of the spent coffee grounds oil (SCGO) using ethanol (absolute ET0 and hydrated ET6) and isopropanol (absolute IPA0 and hydrated IPA12) as solvents. A study of the kinetics of SCGO extraction was carried out under atmospheric pressure and with pressurized ethanol (PLE). In addition, it was performed the experimental determination of the SCGO partition coefficients between the extract and raffinate phases. The mathematical modeling of these data using the Langmuir type and linear equations, together with the mass balances, allowed calculating of the minimum solvent flow and the ideal number of stages of continuous extractor configured in countercurrent. This study was performed with the four types of proposed solvents. The evaluation of process intensification strategies using pressurized liquid extraction (PLE) or ultrasound-assisted extraction (UAE) was also carried out. Increasing temperature favored SCGO extraction, while solvent hydration resulted in a negative impact on lipid extraction. The mass transfer coefficients for the washing step were higher than the coefficients for the diffusion step. The pressurization of the system accelerated the extraction of the compounds, with a shorter time to reach the steady-state and higher diffusion and mass transfer coefficients of the SCGO. PLE at high temperature (150 °C) enabled SCGO extraction with lower levels of free fatty acids (FFA), which demonstrates that under these operating conditions, the physicochemical characteristics of ET6 were modified. The use of ET0 and ET6 made it possible to obtain comparable yields under these conditions, revealing that the solvent with the lowest price, ET6, can be used for extraction processes. The study of SCGO partition in systems containing SCG and short-chain alcohols allowed us to verify that for ethanol, especially ET6, there is a limit of solubilization of SCGO in the extract phase, indicating liquid saturation. The minimum flow and number of ideal stages of countercurrent extractors were higher for ET6 and lower for IPA0. Depending on the conditions, the use of ET0 can make it possible to obtain more concentrated final extracts, with similar or even better results than with IPA0. The evaluation of the UAE and PLE, at 50 °C was performed through the morphology and physical characteristics of the solid phases and the dimensioning of cross-current configured extractors. The results indicated that the intensification of the process with the sonication or pressurization did not allow for significant gains in terms of SCGO extraction yield when compared to conventional extraction. (AU)

• FAPESP's process: 17/10034-0 - Spent coffee grounds oil extraction using ethanol: Kinetics extraction, equilibrium data and process intensification
• Grantee: Tatiane Akemi Toda
• Support Opportunities: Scholarships in Brazil - Doctorate