Improving palm oil refining processes results in cleaner end products

By refining the crude palm oil, its odour and taste gets neutralized, while the colour becomes a more workable yellow to translucent white. Other benefits of the refining process are the improvement of the oil’s shelf life, thermal stability, and the removal of trace amounts of other unwanted compounds such as pesticides or biocides. On the other side, undesired, potential carcinogenic process contaminants can be formed during refining under certain conditions, such as high temperature and the presence of chlorine-containing molecules. In his thesis, Oey discusses the formation of three of these process contaminants (2-MCPD esters, 3-MCPD esters, and glycidyl esters) and suggests mitigation strategies aimed at elimination of these process contaminants in vegetable oil, but primarily palm oil.

Experimenting in a ‘mini factory’

During his research, Oey used a pilot plant, a mini factory, which simulates the oil refining process in small scale. This set-up can hold a maximum of 100 kg of crude oil. It allows them to manipulate the conditions of different refining stages and collect hot oil samples in a safe and controlled manner. The size of the experiments allows physical parameters and chemical reactions, such as the heating, cooling down, mixing, and filtration processes, to behave more closely to that of a full-scale refining set-up. Therefore, upscaling these pilot plant experiments should go much smoother and with less trial-and-error in comparison to an upscaling process starting from very small lab experiments.

Different refining methods

In this research, several refining methods have been adapted to to lower the levels of the three process contaminants. The methods are presented in two open-access, scientific publications. The first method was developed from the physical refining point-of-view and the second method was developed from the chemical refining point-of-view. The major difference between the two methods boils down to how the free fatty acids (FFA) are being removed from the oil. FFA have a negative impact on the shelf life and thermal stability of vegetable oils, for example during stir- or deep fry cooking processes.

With physical refining, the FFA are removed by means of steam distillation under vacuum and high temperatures. Chemical refining methods can include a pre-refining wash process where the crude oil are washed with deionized water to remove water soluble chlorine containing compounds and other potential precursors. The FFA are then removed by a saponification reaction with a lye, followed by removal of the formed soap stock. The advantage of chemical refining is that the required temperature for the entire process is much lower than what is needed during physical refining. By lowering the process temperature, the formation of the earlier mentioned process contaminants can also be kept to a minimum. However, chemical refining is prone to greater product losses due to the saponification reaction. The main key mitigation strategy for the physical refining methods can be found in the developed post-refining removal process of said contaminants. Finally, Oey performed a study to gain more in-depth insights in what kind of chlorine-containing molecules are present in the crude oil which may act as precursors in the formation of 2- and 3-MCPD esters.

The Key

In the discussion section of his thesis, Oey suggests that a combination of elements from both the physical and chemical refining process might be the key for a universal refining method. Such a universal refining method can be used to refine all sorts of vegetable oils with minimal fine-tuning efforts, while, most importantly, maintaining a low level of harmful process contaminants.