3.2. Supercritical fluid extraction
3.2.1. Effect of particle size on the extraction yield
Pre–treatments, e.g. grinding andclassificationaccording toparticle size, made before the extraction of RHSO from rosehip seeds which have a very hard outer shell by scCO2 extraction are of quite importance in terms of ensuring the mass transfer efficiency. By this way, the size of particles is reduced, and their surface area is increased, and the ligneous structure composed of lignin and cellulose surrounding the oil is damaged significantly. The effect of particle size (125 > Dp > 1000 m) on the extraction yield during the process of scCO2 extraction of RHSO in waste oilseeds of marmalade
production process was examined under the conditions of 30 MPa, 40 ◦C and 0.75 mL/min. The experimental findings are
shown in Fig. 2a. The extraction yield expressed in all graphics is defined as in Eq. (1).
Extraction yield = g extracted oil mass
100 g dry solid (1)
Considering the initial oil contents, it is seen that the extraction
yields achieved at 5 h in separation processes made with particles
with a size bigger than 500 m are about 1/2 fold less than
the yields achieved under other conditions. According to Reverchon
et al. [28], the reason of this at a microscopic level is that
the structures surrounding the oil with a diameter of 30 m and a
length of a few hundred microns cannot be damaged at a significant
level in bigger particle fractions and thus no significant increase
can be achieved in the extraction yield due to mass transfer limitations
inside the pores. del Valle and Uquiche [25] pointed that
each fraction classified according to particle size may have differ-ent oil content. They also reported that particularly the fractions
having a bigger particle size distribution consist of testae which
have low oil content. In this study, no significant mass transfer limitation
has been observed inside the pores in separation processes
made with particles with a size distribution of 125 < Dp < 355 m
and 355 < Dp < 500 m. Therefore, almost all of the initial oil content
of seeds can be extracted at the end of an extraction period of
about 2 h.