One, activated clay
Activated clay is bentonite as raw material processed into a highly active adsorbent, the most widely used in the decolorization of the oil industry. Activated clay has a strong adsorption capacity for pigments in oils and fats, especially chlorophyll and other colloidal impurities, and has stronger adsorption capacity for basic and polar atomic groups. After the grease is decolorized by the clay, there will be a little earthy odor that can be removed during the deodorization process.
Second, the composition
The active clay is mainly composed of silica (silica), alumina (alumina), and ferric oxide (iron oxide).
The main properties and uses of activated clay are:
1, has a wide range of decolorization, adsorption and purification, in the application of oil decolorization process has a good adsorption decolorization effect, a strong adsorption of pigments and impurities, the decolorization rate of various pigments in vegetable oil 85 ~ 95%.
2, with a specific adsorption, can remove all kinds of dark pigments and impurities such as oil, chlorophyll, lutein and carotene, decolorization and purification of the oil after the light color, clear, glossy, and good stability, low acid value.
3, Has the ability to adsorb and remove aflatoxins and benzopyrenes in oils and fats.
4, activated clay as a processing aid in the adsorption of the above-mentioned pigments, impurities and harmful substances, after strict filtration and oil completely separated, the filtering technology and control measures in the country as a mature technology.
5, activated clay has a certain shelf life, usually in December. The expired activated clay will not affect the quality of the oil, but it will absorb a certain amount of water in the air, which will reduce the decolorization power and increase the consumption of oil and grease, which will increase the cost of production and processing.
Fourth, production process
The bentonite-based active white clay processing production methods include the total wet method, the full dry method, and the semi-wet method.
The traditional all-wet method is to mix the bentonite, sulfuric acid, and water and heat it to 100° C. with stirring for a certain period of time to activate, dry, and crush the product. The biggest disadvantage of this method is that it consumes large amounts of acid, which results in large amounts of washing water, serious environmental pollution, and high costs.
The traditional dry-process production process involves mixing a small amount of sulfuric acid and water with bentonite, stirring it thoroughly, allowing it to stand for a period of time, and then drying it. Although this method reduces the amount of acid used, no waste water discharge and other environmental pollution, but its product quality is low, greatly limiting its use.
In the semi-wet process, a small amount of sulfuric acid and water are mixed with bentonite, stirred well, activated (placed) for a while at a certain temperature, and then acid and water are added for the second step of activation. The semi-wet production process solves the problems of the full wet process and the full dry process. The process is simple, the cost is low, and the product quality is high.
In general, the half-wet production process reduces the acid consumption by half to two thirds (1/2 to 2/3) compared to the traditional process, and the water consumption also decreases by 1/2 to 2/3. With a little treatment, there is no environmental pollution and the cost is low. Under the same circumstances, the product quality is 30% more than the conventional method.
Fifth, the application of oil refining decolorization
Activated clay has a strong selective adsorption effect on pigments, and absorbs pigments and other impurities in oils under certain conditions so as to achieve the purpose of decolorization. The adsorbent-treated oil not only achieves the purpose of improving oil color and removing colloids, but also effectively removes some trace metal ions in the oil and some substances that can cause poisoning by the hydrogenation catalyst. Further refinement of the oil provides good conditions.
Because of its large specific surface area, strong adsorption capacity, low activity, and no chemical interaction with oils and other chemical substances, activated clay has become the most widely used decoloring agent for edible oils. The amount of clay added during decolorization is based on the color of oils and fats. Determined by the requirements of refined oil products, the internal control standards for small packaged oils should be higher than the standard for the sale of bulk oils, and the use of white clay in the decolorization process should be slightly more. General decolorization usage is 2%-5% of oil weight. The amount of white clay added is more, and the better the decolorization effect is. However, excessive clay addition will also reduce the yield of refined oil. Because clay absorbs some pigments while also absorbing pigments, it increases the cost of refining and costs. Generally, the oil content of waste clay in the refinery is generally 20%-25%. . At present, a small number of companies use leaching to separate oil from activated waste white clay. However, due to the role of clay, the separated oil product is black and cannot be discolored to a good color. Therefore, the domestic oil refinery manufacturers regard the oil content of waste clay as an important indicator for the selection of active clay manufacturers.
Sixth, the acceptance criteria for refined vegetable oil bleaching clay
Color: white or gray, light pink
Appearance: Powdered solid
Decolorization rate: ≥90%
Particle size (over 200 mesh screen, %): ≥ 90%
Free acid (calculated as H2SO4, %): ≤ 0.3
The national standard GB25571-2011 stipulates the physical and chemical indicators of activated clay as follows:
Seven other decolorizers for decoloration of vegetable oils
China is rich in bentonite resources and is the world's largest producer of bentonite. The annual consumption of bentonite in China is about 5 million tons, of which 40% is used in the iron ore pellet market, 30% is used in the foundry market, and activated clay accounts for about 10%. It is mainly used for the refining of edible oils and fats and for the petroleum industry for petroleum. , Oil, paraffin, wax, kerosene and other minerals, refining the decolorization and purification, food, pharmaceutical industry also have applications.
The demand for active white clay for oil refining is about 200,000 tons per year. In 2016, China’s consumption of edible oils and oils has reached a record 30 million tons. The demand for decolorizing agents has increased year by year, but there are many active clay producers, and the quality is uneven. In addition, due to the fact that the price of activated clay is higher than that of attapulgite, the current application of activated clay in the oil refining industry is not only fiercely competitive within the industry, but it is also always faced with the challenge of other decolorizing materials such as attapulgite clay.
1) Activated carbon
Activated carbon is mainly composed of sawdust, bagasse, husks, hard husks, etc., and then subjected to chemical or physical activation. Its carbon content is as high as 90 to 98%, its density is 1.9 to 2.1 ton/m3, and its bulk density. 0.08 ~ 0.45 ton / M3, with loose pores, large specific surface area, high decolorization coefficient, and hydrophobicity, capable of adsorbing macromolecules, especially effective for removal of blue and green pigments, also capable of removing trace minerals The oil gives flashes of grease. In addition, there is also a strong adsorption capacity for gases, PAHs and pesticide residues. Because of its high price and high oil absorption rate, it is often used with bleaching or activated clay in decolorization operations of oils. Mixing ratios of 1:10 to 20 can significantly improve the decolorization ability and remove the smell of bleaching soil.
The attapulgite clay is a magnesium-rich fibrous mineral whose main component is silicon dioxide. This soil is delicate and the appearance is grayish gray or grayish white. The farmers in the producing area did not find any animal disease as a feed additive. The decolorization effect of attapulgite clay is good. Compared with activated clay, the amount of decolorization is small, the oil loss is small, and the price is low. The problem is that filtration is more difficult and the fineness of the soil should be appropriately thickened.
3) Natural bleaching
Natural drifting earth, learning name bentonite. Its main component is (Al4Si8O20 (OH) 4 • NH2O), and it also contains a small amount of calcium, magnesium, iron, sodium and potassium. The pH value of the suspension is 5-6 and it is acidic, so it is also called acidic clay. The natural bleaching soil is graded from mining to final grinding and is only processed by physical methods. Its structure is microporous crystalline or amorphous, specific surface area is much larger than other clays, has a certain activity, but its decolorization coefficient is low (refer to before and after decolorization of the same batch of oil, while observing the ratio of the oil column when reaching the same color) The oil absorption rate is also high, so it gradually replaced by activated clay.
The zeolite is an acidic volcanic lava and intercalation layer of intertidal multi-cycle, multi-ore lake basin sedimentation, melting or hydrolyzation of multi-series volcanic glass from the clinoptilolite deposit, after mining, screening, grinding, screening Zeolite adsorbent. Its chemical composition is mainly silica, followed by alumina. Zeolite has a good decolorization effect, decolorization can also reduce the acid value and moisture of the oil, the price is cheaper than activated clay, is a new material for oil decolorization.
5) Diatomaceous earth
Diatomaceous earth is evolved from the single-cell type potassium silicate shell remains under natural forces. Diatomaceous earth with good purity is white, usually light gray or reddish-brown. The main chemical composition is silica. It has a certain adsorption capacity for pigments, but it has a low decolorization coefficient and a high oil absorption rate. Used as a filter aid.
6) Other decolorants
The adsorbents used for the decolorization of oils are activated alumina and alumina treated with sulfurous acid.