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.