Chu et al. (2004) separated tocopherols from PFAD using silica in a stirred batch adsorption reactor. The equilibrium of the adsorption process as a function of the reaction temperature, the agitation rate and the silica mass on tocopherols adsorption onto silica was investigated over a concentration range of tocopherols. A lower reaction temperature led to a higher tocopherols uptake at equilibrium, indicating that the adsorption process in this study was exothermic. The adsorption capacity increased with the rise in agitation rate. However, in this study the maximum adsorption capacity remained unchanged when the silica mass was increased. The thermodynamic parameters of the adsorption process helped in predicting how the retention of vitamin E might vary with a temperature change. However, information on the separation performance, such as tocopherols recoveries, is not available.

Fabian et al. (2009) described a new approach for the separation of a NPLF from SODD using a stirred batch-wise hexane desorption to achieve the same degree of separation as that obtained by a modified Soxhlet extraction that was reported in a previous study by Gunawan et al. (2008). The effects of the operation parameters, such as the silica gel to SODD mass ratio, the solvent volume to SODD mass ratio and the adsorption-desorption temperature on separation, were systematically investigated. Starting with SODD that contains 4% FASEs, 2% squalene, 13% tocopherols and 9% free phytosterols, it was possible to obtain an NPLF enriched with FASEs (19%, recovery 97%) and squalene (9%, recovery 100%). The contents of FFAs, TAGs, tocopherols and free phytosterols remained in the NPLF were 12%, 1%, 5% and 1%, respectively. In addition, the NPLF contained squalene and FAS Es that could be processed further to obtain pure squalene and FASEs as described in the previous work (Gunawan et al., 2008). The batch extraction employed in this study yielded about the same degree of separation as compared to that of modified Soxhlet extraction. However, the advantage of the method of this study is that it can be scaled-up easily.

22.5 Future trends

Economic consideration is a key driving force behind the development of the technologies to process inexpensive biodiesel feedstocks and to recover the minor components.

The purification of minor components from DDs is a complex process that implies multiple steps and techniques. When a desired material is produced industrially, the way of processing affects the cost of production. Therefore, in order to make a process industrially viable, the number of steps has to be reduced. However, their valorization should be considered when the DD from chemical refining is used for the production of biodiesel.

There are different routes (direct conversion or acylglycerol route) to convert the DDs to biodiesel/biofuel, some of which have found industrial application. A pretreatment of the feedstock or post-treatment of the final biodiesel are necessary in order to meet the quality specifications.

A combination of technologies opens broad opportunities to convert low-price lipid resources into biodiesel/biofuel that complies with the EU and ASTM specifications and to valorize minor components for different applications.