The world cottonseed yield ranks only second to soybean in all oil plants. However, cotton seed oil ranks 5th in all edible oils, since about 16% of the cotton seed is used as feed. The whole cottonseed contains 15% ~25% of oil, while its kernel contains 32% ~ 46% oil and 30%protein, so it is an important resource of edible oil and vegetable protein. Cotton seed oil contains 60% ~ 90% of unsaturated fatty acids (linoleic acid and oleic acid), which has the functions lowering cholesterol, preventing atherosclerosis, etc. Cottonseed oil is an also important kind of edible vegetable oil.
Cottonseed oil production process
Cotton seed oil production process
There three methods,we can get cottonseed oil: mechanical screw oil pressing, pre-pressing & solvent extraction, and direct solvent extraction.
Cotton seed oil pressing mainly rose in 1960s when cottonseed oil was pressed by small batch type cold oil press machine and sold in the form of crude oil. This kind of crude oil does not go through heat treatment, so it contains large quantity of free gossypol, which would cause male infertility if directly consumed. Therefore, it was banned to directly consume crude cottonseed oil.
Pre-pressing & solvent extraction method is a common oil making method in our country at present, and this method is also applied to other high oil content materials. The latest progress of cottonseed oil processing technology is the use of the extruder. The extruded material then goes through solvent extraction, which simplifies processing technology, and reduces the loss of solvent, reduces residual oil in meal, and improves the feeding property of cottonseed meal. The extracted oil meal contains 0.10% to 0.20% free gossypol, which is only half of the pre-pressed cottonseed material.
The crude cottonseed oil contains about 2% or more gossypol, phospholipids, fatty acids and other non glyceride composition that affect the flavor and sensory index; therefore, it must go through degumming, deacidification, bleaching and deodorization process to achieve food standards. Commonly used refining methods are: traditional chemical alkali refining process and the mixed oil refining process. Refining is a very important step in cottonseed oil production, which directly affects the quality, yield and consumption of oil. Different oil refining technologies have different results.
The traditional alkali refining process is based on the cotton seed oil as raw material, and through twice neutralization and alkali refining to get light color neutralized oil; but this process needs high consumption and the oil color cannot reach standards. Mixed oil refining use the extracted mixed cotton seed oil for evaporation and alkali refining, which can increase oil yield, improve oil color and leave out conventional alkali refining washing steps. Since 1960s, mixed oil refining technology has become the most commonly used method of cottonseed oil refining in the United States and other western countries, since it eliminates the deacidification of crude cottonseed oil. Its color is lighter than conventional neutralized cottonseed oil, which is conducive to subsequent processing.
Cotton seed mixed oil refining technology
Cottonseed mixed oil refining is to degum and deacidify the mixed oil (the mixture of solvent and oil) gained from the first vaporization system in cotton seed extraction technology before it is not totally evaporated and desolventized, and before its viscosity and density are lower than crude oil. As there is no high-temperature exsolution, the gossypol or other pigments contained in mixed oil are not yet fully fixed and easy for removal. The specific gravities of mixed oil and soap stock have great difference, which can reduce the neutral oil in soap stock, and at the same time easy to separate from soap, so that the handling capacity is increased.
As this cotton seed oil refining technology is to deacidify the mixture of oils and solvents, therefore all devices must be sealed and explosion-proof, and must be constructed inside the solvent extraction plant. In order to prevent the solvent gas leakage from bringing safety hazard, usually the centrifugal machine adopts nitrogen seal design, so that its internal is filled with nitrogen and isolate from oxygen to improve safety.
The key point of mixed cottonseed oil refining is to control the concentration of cottonseed oil mixture. The best concentration is 65% ~ 70%: the acid-base concentration and the added quantity can be determined by raw material phospholipid content and free fatty acid content. the alkali solution concentration used in mixed oil alkali refining is lower than that used in conventional alkali refining, generally 11% ~ 14%; the reaction temperature cannot exceed the boiling point of the solvent, control at 55~ 60℃; acid reaction time is generally 15~ 20 min, alkali reaction time is relatively longer, general control at 1~ 2h. All the parameters can be adjusted according to the actual color of the oil.
Mixed cottonseed oil refining technology advantages
Compared with the traditional chemical method of alkali oil refining, the main advantages of mixed oil refining are:
The cotton seed oil color produced by this refined technology is better than the conventional alkali refined cottonseed oil.
Mixed oil refining does not need to be washed, which does not need centrifuge and auxiliary facilities.
As the mixed oil is not easy to emulsify in alkali refining, so soap is not easy to take away the oil, in consequence the oil yield is high.
The mixed oil refining removes colloid, pigments and other impurities, reduces the loss in evaporation process.
The same as conventional refining, soap stock is added to the oil meal in evapo-separated machine, which can recycle the solvent in soapstock, while at the same time increase the use value of meal.
The cotton seed oil from mixed oil refining reaches the Nation 3rd Grade standard (China), which can be directly put into the market; the refined oil after decolorization and deodorization can reach National 1st Grade Standard (China).
Conclusion
The combination use of the cottonseed extrusion, oil extraction and the mixed oil refining process can make the production of our cottonseed oil plant reach 350 t/d. The extrusion & extraction technology can improve the oil yield and reduce the solvent loss. Firstly, the mixed oil refining technology eliminates the conventional washing process in alkali refining, which not only saves water, but also reduces the wastewater discharge capacity of 40 m3/d. Secondly, this technology dephenolizes from raw oil extraction, and the decolorization and deodorization can enhance dephenolization effect. Thirdly, this technology moves deacidification to solvent extraction process, which can greatly simplifies cottonseed oil making technology, decreases construction area and production cost. This oil making technology can also be applied to rapeseed oil and rice bran oil.
