Extracção de óleo de grainha de uva com CO2 supercrítico

abstract

The main objective of this dissertation was the supercritical fluid extraction of grape seed oil using carbon dioxide, where the separation yield has been measured and the oil quality has been evaluated in terms of the composition and concentration of triacylglycerides. Furthermore, in order to increase the extraction yield, assays with pre-treated seed at high pressure have been carried out. With the purpose of accomplishing the cited objectives, the following working programme was established: (i) to obtain and prepare the seed (separation from musts, washing, drying, milling and classification); (ii) to carry out high pressure treatments (HPP) and measured the extraction yield via Soxhlet with n-hexane; (iii) to perform the supercritical fluid extraction (SFE) of the grape seed oil, using treated and untreated samples; (iv) to determine the triacylglycerides profile of the extracted oil by gas chromatography; (v) to model the experimental results. Firstly, the effect of the milled seed granulometry upon extraction yield has been studied, being confirmed that it is a fundamental process variable: h ( p d = 0.75 mm) =11.59% and h ( p d = 0.85 mm) =6.72%. From HPP experiments one concluded the final yield is not affected by treatments up to 3000 bar; at 5000 bar, final h was reduced by 6.7%. The supercritical fluid extractions carried out at 40 ºC and 180 bar with treated and untreated seed gave rise to yields equivalent to those obtained by Soxhlet using n-hexane, which proves the SFE is an efficient process. The cumulative extraction curves for both samples presented the two typical extraction periods: in the first one, approximately linear, it has been removed 90-92% of the available oil; the second, less important, reached a plateau rapidly. Comparing the first extraction periods of both SFEs performed, one concluded that the extraction rate for treated seed was 39.7% higher. Such fact allowed us to conclude that, although HPP does not influence final yield, the rate of the process is significantly improved, reducing the time needed to remove a fixed quantity of oil. With respect to the oil quality, the analysis showed it contains more than 92% of triacylglycerides and that it is particularly rich in unsaturated fatty acids (~80%), where oleic (C18:1) and linoleic (C18:2) acids are the most abundant (17-24% and 60-66%, respectively). Modelling has been performed on the basis of the works published by Perrut et al. (1997) and Sovová (2005). The model fitted data very well, giving rise to the following absolute average deviations: AAD(HPP) =2.36% e AAD(no HPP) =2.72%. With this model the concentration profiles in the bed and the breakthrough curves were determined, and the chief process parameters calculated. The mass transfer zone, defined using the limits of 5% and 95% of the maximum concentration, corresponds to 7.2% (no HPP) and ~4.9% (HPP) of the bed length. The velocities of the concentration waves through the bed were 96 and 35 times higher than the space time of CO2.

authors

Ana Luísa Carvalho Magalhães

supervisors

Carlos Manuel Santos Silva; Manuel António Coimbra Rodrigues da Silva

Groups