Evaluation of the fractionation processes .1 Crystal growth rate

Figure 4.28: Crystal growth rate of coconut stearins as a function of (A) cold finger temperature and (B) melting points.

The overall growth rates of coconut stearin crystals calculated based on Equation 3.14 from emulsion fractionation are compared to that of the dry fractionation process (Figure 4.28A). From all fractionation processes, it can be seen that the operation of the fractionation must be done at slow crystal growth rates in the range of 10^-8 to 10^-7 m/s in order to achieve the fractionation of the high melting coconut stearins. The crystal growth rate of the coconut stearins decreased with increasing the cold finger temperature. The addition of the emulsifier (L-195) in the coconut oil fractionations either with or without water results in the retardation of the crystal growth rate in comparison to the process without L-195 at all cold finger temperatures. This can be explained by a kinetic study of L-195 on the crystallization of coconut oil. L-195 inhibited the crystallization kinetics of coconut oil (see Chapter 4.1.2). And the crystal growth rates of the emulsion fractionation process regardless water concentration are relatively in the same range as the dry fractionation of coconut oil containing L-195.

This gives a hint that an increase in the supercooling value might not be significantly needed for the crystallization of the water-in-oil emulsion drops since the continuous phase is the oil phase, unlike oil-in-water emulsion systems [Huc09].

Faster growth rates in the range of 10^-7 m/s leads to the low melting point of the coconut stearin indicating low separation efficiency (Figure 4.28B). The results at the slow growth rate range of 10^-8 m/s reveal that the coconut stearins obtained from emulsion fractionation process have significantly higher melting points than that of the dry fractionation process. This implies that in order to produce coconut stearin via a dry fractionation with the same purity as that of the emulsion fractionation, extremely slow growth rate probably in the magnitude of 10^-10 m/s, which is time and energy consuming, is needed. The reduction of the viscosity effects via the emulsion production and the modification of coconut oil crystal habit via L-195 addition enhance the solid-liquid separation by lowering the content of low melting liquid inclusions.

A B

4.4.2.2 Yield

Yields of the coconut stearin obtained from the emulsion fractionation processes in comparison to that of the dry fractionation processes are plot against the cold finger temperatures as shown in Figure 4.29.

Figure 4.29: Yield of the coconut stearins obtained from different fractionation processes.

In consequence to the crystal growth rate, the coconut stearins of the fractionation process involving with L-195 addition are lower than those from the fractionation of the pure RBD coconut oil. However, the stearin yields of the emulsion fractionations increase with the increasing water concentration. This is due to the fact that the stearin yield based on the relation of the solid fraction to the initial oil amount (Equation 3.15).

Increasing water concentration in the emulsion refers to the reduction of the oil phase.

Consequently, the stearin yield from the emulsion fractionations increased with the increasing water concentration. Especially, the stearin yield of the fractionation of coconut emulsion containing 35 wt-% water can be produced at the similar ranges of the yield obtained from the dry fractionation of the pure RBD coconut oil.

4.4.2.3 Effective distribution coefficient

The effective distribution coefficient (Keff) is introduced as a measure to evaluate the separation efficiency of the fractionation process in terms of the purities of the fractionated products. In this case, the coconut stearin fraction is the main product.

As defined in the previous chapter, the low melting fatty acid group of medium chain fatty acids and unsaturated fatty acids is considered to be the impurities which lower the SFC and the melting point of the coconut stearins. To obtain high melting coconut stearins, the low melting fatty acid group must be retained in the coconut stearin composition as low as possible, indicating a good separation of the process. The effective distribution coefficient is calculated based on the ratio of the impurities of the coconut stearin to the impurities of the initial feed oil. Therefore, Keff is a

dimensionless parameter where the lower Keff is, the higher is the purities as well as the separation efficiency of the fractionation process. In this case, Keff of both emulsion fractionation and dry fractionation processes were examined and used to evaluate the separation efficiency.

Figure 4.30: Effective distribution coefficient of the emulsion fractionation process with 3 water concentrations and the dry fractionation of RBD coconut oil and in the presence of L-195 as a function of the melting point of coconut stearins.

The effective distribution coefficients of the fractionation process of coconut oil emulsion with 3 water concentrations and the dry fractionation of coconut oil melt as a function of the melting point of coconut stearins are shown in Figure 4.30. The diagram clearly indicates that the Keff of the fractionation process decreases as the melting point of the coconut stearin increases. Furthermore, Keff of the emulsion fractionation is lower than that of the dry fractionation process with the higher melting point of the coconut stearins. As a consequence, the emulsion fractionation has a better separation efficiency than the dry fractionation process in terms of product quality.

Considering only the emulsion fractionation systems, Keff of the process decreases as a water concentration increases. However, increasing of the water concentration above 20 wt-% has no further effect on the Keff since the Keff of the emulsion fractionation of both 20 wt-% and 35 wt-% water concentration are in the same ranges.

4.4.2.4 Mass-related distribution coefficient

From an economical point of view, not only the product quality, but also the product quantity must be taken into account. In order to define if the emulsion fractionation process is more cost effective than the conventional dry fractionation, the concept of the mass-related distribution coefficient (Km-eff) is further extended from Keff. This dimensionless Km-eff parameter is therefore calculated by relating coconut stearin yields of these fractionation processes to the product purity according to Equation 3.17.

Figure 4.31 is the diagram showing the Km-eff of the emulsion fractionation process comparing to that of the dry fractionation process as a function of melting point of the coconut stearins.

Figure 4.31: Mass related distribution coefficient of the emulsion fractionation in comparison to the dry fractionation as a function of the melting point of coconut stearins.

The evaluation of this diagram can be made by comparing the Km-eff of emulsion fractionation and the dry fractionation process. Km-eff of the emulsion fractionation is lower than that of dry fractionation process indicating a higher efficiency. It is clear that the emulsion fractionation meets the requirement as the better cost effective process.

To point out, at the same purity of the coconut stearin, higher amount of yield can be obtained from the emulsion fractionation process. The melting point of the coconut stearins from the emulsion fractionation is approached 30 °C, at the same time; the amount of the stearin yield is acceptable. For the emulsion fractionation, the increasing of water content of an emulsion mixture resulted in a slight reduction of the Km-eff. This is because higher amounts of the coconut stearin were obtained as explained in chapter 4.4.2.2. For this reason, it can be concluded that an emulsion fraction process is the more cost effective process compared to a dry fractionation process from the economical point of view by taking the purity as well as yield of the product into account.