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       There are various methods for dewaxing vegetable oils, such as conventional method, volumetric method, and surfactant method.

　　1.conventional method

　　The conventional dewaxing method only relies on refrigerating the crystals, and then uses mechanical equipment to separate the oil and wax without all neutralizing agents and auxiliary dewaxing methods. When separating, use pressure-filled filtration, vacuum pump filtration and suction filtration separation machinery and equipment. The simplest method of this method is the primary crystal and filtration method. For example, the rice bran oil (temperature above 50°C) after film evaporation is moved into a storage tank with refrigeration equipment, mixed at a slow speed, and sufficiently cooled to 25°C under superheated steam. The total cooling and crystallization time is 48 hours, and then the oil and wax are separated by filtration. The pressure of the filtered gas is maintained at 0.3-0.35MPa, and the vegetable oils contained in the wax should be blown out with air compression immediately after filtering.

Because the dewaxing temperature is low, the viscosity is high, and the separation is difficult, for vegetable oils with high wax content such as rice bran oil, the secondary crystal filtration method is generally used. The cooling and crystallization time is 24 hours, and the first filtration is carried out with a vacuum oil filter to remove most of the fruit wax, and the gas pressure of the filter does not exceed 0.35MPa. The filtered oil enters the second refrigeration tank, and then enters the ultra-low temperature cold water again, so that the water temperature drops below 25°C. After 24 hours, the second filtration is carried out. The filtered oil is the dewaxed oil. After two filtrations, the wax content in the oil (indicated by toluene insoluble matter) is below 0.03%. Some companies use cloth bag filtration to obtain excellent dewaxing effects, but the speed of cloth bag filtration is slow and labor efficiency is also great.

　　 deacidified rice bran oil → cooling and crystallization → cloth bag filtration → dewaxing oil

　　                   ↓

　　            wax paste→melting→squeezing→crude wax

　　                   ↓

　　               soft fat

　　 Cooling and crystallization are carried out in the refrigeration room, the room temperature is 0-4 ℃, the oil is given at 70 ℃ and the heat insulation layer is applied in the refrigeration tank, the refrigeration time is 72 hours, and the final water temperature of the refrigeration tank is 6 -10 ℃. The temperature reduction rate is gradually within 24 hours, and the average value is 2°C/h; the following 24 hours r is 0.5°C/h, and the total temperature drop is about 1-2°C in the next 24 hours. Cloth bag filtration is carried out in the filtration room. The indoor temperature is maintained at 15-18℃, and the filtration time is 10-12hr. The cloth bag can be made of polyester card, vinyl cotton or pure cotton cloth, and the filtration rate is polyester card> vinyl cotton> pure Cotton cloth, the actual effect of dewaxing is very good. When the filtered oil is refrigerated at 0℃, it is completely transparent and clear for more than 1 hour, and the wax content in the dewaxed oil is below tens of mg/Kg. The compressive strength order of the filter material subjected to the cold storage experiment is: cotton cloth>vinyl cotton>polyester card.

The wax paste (accounting for 15%-17% of the total remaining oil) is poured into the melting pot, heated to 35-40°C, sealed and pressed. The press uses a 90-type hydraulic oil press, and the gas pressure of the press plate is 2.5- 5CPa, during actual operation, ensure squeezing, diligent pressure, and no wax paste. The squeezing time is 12 hr. The soft fat separated by squeezing accounts for about 61%, and the crude wax accounts for about 39%. The oil content in crude wax is 40%-45%.

       At this stage, most oil refineries in China use a plate filter press to separate the oil and wax paste after cooling and crystallization. Some small processing plants use cloth bags for filtration. Because of the standard restrictions, the cooling and crystallization temperature and time cannot be manipulated as specified above. Therefore, the actual effect of dewaxing is not ideal. Sunflower seed refined oil contains less wax than rice bran oil. , Can choose to open the glue, deacidified oil, refrigerate from above 50 ℃ to 10-15 ℃ in 2 days, and then use air compression to send the oil to the vacuum oil filter. The separated oil contains wax below tens of mg/Kg. Generally speaking, the conventional method of dewaxing equipment is simple, the project investment is low, and the actual operation is very easy, but the oil-wax separation is not complete, the dewaxing oil yield is low and the cloud point is high.