C. ECHIM, R. VERHP and C. STEVENS, Ghent University, Belgium and W. DE GREYT, Desmet Ballestra Group, Belgium

Abstract: The valorization of by-products helps to reduce waste, to minimize the footprint of the technology and to add value through the production of biodiesel as an energy carrier. Alternative resources such as deodorizer distillates can partially replace the traditional feedstocks for the production of biodiesel, but require application of new technologies and/or additional purification steps. This chapter proposes to offer an overview of different methodologies used to convert deodorized distillates to biodiesel/biofuels and to recover the valuable minor components such as sterols, squalene and tocopherols.

Key words: biodiesel production from deodorizer distillates, conversion routes for high-acidity feedstocks, recovery of the minor components.

22.1 Composition of deodorizer distillate

Crude vegetable oils contain triacylglycerols (TAG) as major component and various minor components such as diacylglycerols (DAG), monoacylglycerols (MAG), free fatty acids (FFA), phospholipids, tocopherols, sterols, squalene, color pigments, waxes, aldehydes, ketones, triterpene alcohols and metals which may affect the quality of the final product. These minor components are removed partially or entirely by either physical (RBD) or chemical (NBD) refining.

Deodorizer distillate (DD) is one of the side streams obtained in the final step of refining of vegetable oils used to remove odoriferous components and to reduce the free acidity in order to make the vegetable oils suitable for human consumption.

It was observed that the composition of DD is dependent on the oil source, the refining routes (physical or chemical) and the deodorizer operating conditions (De Greyt and Kellens, 2000; Kellens and De Greyt, 2000). Determination of the DD composition or stability was studied by different authors (Haas and Scott, 1996; Verleyen et al, 2001; Dumont and Narine, 2007; Dumont and Narine, 2008). DD obtained from physical (RBD) and chemical (NBD) refining of different feedstocks contains typically 30-90% FFA, an important unsaponifiable matter such as tocopherols, sterols and squalene (5-33%), but also acylglycerols (<1-14%) (Table 22.1).

Physical (RBD) and chemical (NBD) refining differ both in the composition of the deodorized oil and of the distillate.

It was observed that physically refined oils have a higher retention of unsaponifiables in the oil compared with the chemically refined oils. A sterol retention varying

between 68% and 90% in the physical and 79% and 87% in chemical refining is observed while tocopherol retention between 23% and 92% in the physical and 21% and 73% in chemical refining was found. The higher retention of unsaponifiables in the physically refined oil is attributed to the lower vapor pressure of these components due to the advance of FFA during deodorization (Verleyen et al., 2002).

DDs obtained from the chemical refining are rich in tocopherols and sterols and contain little FFA. On the contrary, distillates derived from physical refining contain mainly FFA and consequently little tocopherols and sterols representing little economic value.

Deodorization has an important effect on the overall refined oil quality and distillate composition. The last decade’s increased attention has therefore been paid to the optimization of the deodorizing process conditions and the development of improved deodorizing technology (Verleyen et al., 2002).

The development of a new type of scrubber operating at two different tempera­tures (dual condensation concept) allows the production of DDs with a unique com­position (high in tocopherols and sterols) and higher value (Kellens et al., 2005).

A modification to the condenser unit was made for the collection of the distillate in two separate fractions. The first fraction contains mainly FFA (80%) where the second fraction contains concentrated sterols and tocopherols (17% and 15%, respectively) and residual FFA (43%) with a similar composition as DD from chemical refining (Verleyen et al., 2002).