In the past ten years, edible oil refining develops rapidly and has become an important industry. Because of the low price of the crude oil and refined oil, the profit margin of the refinery is quite small. Production costs have increasingly determine the profitability of refineries. In addition, an increasing number of environmental protection policies are forcing manufacturers to reduce waste discharging as much as possible, especially solid waste like waste bleaching earth in decolorization.
The purpose and method of edible oil refining
In addition, higher quality requirements also strengthen the effects of cooking oil. Besides good sensory quality (no smell, taste, pale colour and excellent appearance) and high degree of stability (oxidation stability, freeze stability and shelf life), cooking oil also need to meet the requirements of various nutrition indicators: small amount of trans acid, rich natural vitamins and antioxidants, low polymer and foreign pollutants, such as heavy metals, pesticides, etc.
Compared with physical refining, chemical refining is still popular, especially for soft grease refining, such as soybean oil and vegetable oil. While stearin such as palm oil and cocoa butter are mostly processed by physical refining. Both physical refining and chemical refining can be used for sunflower oil and cottonseed oil. The choice of physical refining or chemical refining depends on the quality of crude oil. More and more refineries are close to the oil extraction factory, even combined with the crude oil factory that the overall quality of crude oil has been improved greatly. The modern new type soft grease refinery is often equipped with both physical refining and chemical refining process, and physical refining is the first choice.
Degumming is an important process of physical refining. In order to improve the effect of degumming (phosphorus content below 20pref.10ppm), special mixtures, reactants (acid, caustic soda), additives (such as EDTA) or enzymes are often added. The degumming process has been developed for many years, but all of them are based on the acid reaction classification degumming principle, that is to add acid to generate the hydratable phospholipids, then adjust PH value by adding quantitative caustic soda so as to improve the separation condition and reduce the oil loss. Typical examples include: Unilever’s super – joint degumming process, Vandemoortele’s TOP degumming process, Lurqi’s ENZYMAX process, DeSmet’s IMPAC degumming process and IPH’s ORP process.
Each kind of degumming process can ensure that the residual phosphorus residue is very small (even below 5%), which greatly improves the quality of crude oil and make it suitable for refining. For some poor or differentiated oils, chemical refining is still the best compromise for insurance purposes.
In order to overcome the disadvantages like dirty soap deposition and poor discharging in chemical refining, better refining process was developed. A typical example is the potassium hydroxide refining method from Agrotech company. In this process, free fatty acids turn into potassium soap, which can be used as the fertilizer. Another process is the sodium silicate refining process from Oxychem/Tamu company, in which the soap in the oil is separated by filtration rather than centrifugation.
The development of decoloring technology focuses on reducing the amount of bleaching clay, which is due to the fact that solid waste is becoming the biggest environmental pollution source in refining process. Several kinds of decoloring technology have been developed on the basis of the principle of multistage decoloring. In some decoloring process, decoloration can be achieved by two steps, or even three steps (such as Unilever and WEF); waste clay is reused for the pre-filter (DeSmet) in some process, while some even use complete reverse technology (Ohmi) for decoloring. The use of diatomaceous earth for predecolorization can also reduce the consumption of bleaching clay, because phospholipids, soaps and other impurities are absorbed and they will no longer interfere with decolorization during the operation. 30 to 50 percent saving of the consumption of bleaching earth has been reported and confirmed by industrial production.
The final process, also the most important working procedure in the refining process is deodorization. Most deodorization process is continuous, but the continuous process lacks flexibility under the condition of multi-item small sized production. Multstock process of DeSmet has solved the problem. There is almost no pollution in the replacement of refined oil products and the oil can be replaced up to 20 times a day.
In order to adapt to the change of the process, especially driven by reducing costs, new deodorization device has been put into market. The working efficiency of these new type of deodorizer is quite high. The efficient deodorizer with high efficiency heat recovery device has made the deodorization cost down to a fairly low level. A typical example is that the packing tower is introduced into the oil refining (Alfa Laval’s soft column), but some of the improvements have a negative effect on the quality of finished refined oil. Then, a new kind of deodorizer (Qualistock deodorizer from DeSmet) that cares not only the deodorization efficiency, but also the quality of refining was developed. It has unique design and easy to install (plug and play). All units that have deodorization function, including: the gas condensates, heat recovery, the final heating, deodorization, final cooling and steam blowing, are integrated in a specially designed container, which not only reduce the construction and installation costs, but also increase the efficiency of architectural space. In order to meet the various needs of different users, DeSmet has also developed a complete set of equipment to cooperate with this kind of equipment, such as the double temperature classification deodorization, double concentration and deep/shallow bed. Due to the modular design, the equipment can be combined when using. It can also be customized in the future.
In the process of oil modification, apart from hydrogenation and ester exchange, fractionation has already occupied a position. Many oil producers are increasingly pay attention to seek low or even zero transfer of fatty acids, including semisolid fat, such as margarine, candy butter, etc. The application of palm oil is getting wider especially through multi-stage fractionation. Extremely hard grease (melting point over 60°C) and soft oil (freezing point of less than 0°C) can be produced from a single species of oil by crystallization and filtration and the cost efficiency is higher.
These successful efforts have overcome the defect of the ester exchange partly, such as oil loss and consumption of crystallization. It has also opened up a new application of oil modification technology, which were forced to give up more than a decade ago when hydrogenation was quite popular.
There is no doubt that the new technology has a strong impact on oil refining, which will usher in a research and creative climax over the next decade or so. The development of oil processing technology would be thriving in the future. A typical example is the superfine microfiltration membrane technology. Once the industrialization of these technologies is successful, it will bring new opportunities for all kinds of oil physical refining.
Another challenge opportunity for the future oil refinery plants is the direction of development of non-edible oil. The high price of mineral oil and renewability of vegetable oils have attracted lots of attention, such as the chemical application of biofuels, fatty acid derivatives and other oils.
It can be assured that the oil processing technology would be further improved in different directions, but in a stable quality assurance, the benefit is the most important.