Extraction Process Design by Single Factor Experiments
E ffect of Water Added on Oil Recovery
The effect of water added on OR is shown in Fig. 2. The OR was only 37%
without the addition of water. It gradually increased as the quantity of
added water was augmented from 0.00 to 1.40 mL, but failed to increase
further when water was increased to 1.60 ml.. Among all of the water
dosages investigated, 1.40 mL per 10.00 g slurry resulted in the highest
OR.
Technically, the water added is necessary for extracting pecan oil and
its amount of addition was found to be a critical factor of obtaining a
reasonably high OR. The separation of oils by the addition of water may
be involved with the mechanism that the cohesion work of oils and solid
particles overcomes the adhesion work of oils to the solid particle
surface. When the pecan kernels were converted to a slurry by grinding,
the formation of a continuous oily phase occured because of release of
free oils. Such compounds as proteins, phospholipids, and free fatty
acids compose many small solid particles dispersed which have
hydrophobic surfaces covered by oils. At this state, the work of
adhering to the solid particle surface by oils is larger than that of
cohesion of oils plus that of centrifugation force (1435 g). When water
is added, it binds to the hydrophilic groups the surface of the small
solid particles facilitated by mechanical agitation and therefore
hydrogen bonds are formed. A rigid, sticky and particle is formed
because of the aggregation of all the hydrophilic groups and water
driven by hydrogen bond. At this state, inter surface tension is
increased. The work of adhering to the solid particle surface by oils is
less than that of cohesion of oils so that free oils are released.