The main composition of the edible oil is triglycerides. Pure triglyceride liquid is colorless and they become white when in solid form. But the common oil has different colors due to different amounts and varieties of pigments in oil, the pigments can be divided into three categories: Organic pigments such as chlorophyll, carotenoids, and gossypol; Organic degradants such as proteins, carbohydrates, and phospholipids; Some chromogens. Not all the pigments are bad, but the harmful pigments would damage oil quality and threaten human health, which should be removed.

why crude oil need bleaching process
Oil bleaching process can remove these harmful pigments from crude oil, as well as some trace metals, residual soap, odorous substances and residual pesticides. The purpose of oil bleaching is not to theoretically remove all pigments but to improve the color of oil and provide qualified materials for oil deodorization. What’s more, decolorization section can avoid oil color reversion and improve oil product’s shelf life.
Therefore, edible oil decolorization equipment is essential in oil refining plant for producing high-quality edible oils. After decolorizing, the bleached oil will look more transparent and brighter.

oil decolorizing equipment of refinery plant

Oil Bleaching Machine Features

  • Oil bleaching machine is made of 304L stainless steel material with mirror polishing treatment. Conform to the GMP standard.
  • The machine is equipped with stainless steel stirring blade, uniform stirring and convenient cleaning. Please note: the shape and size of the stirring blade can be customized according to customer needs.
  • Bleaching machine has electric control box which voltage is 220v/380v, button control and the temperature can be set.
  • Machine’s heating pipe is made of 304/316 stainless steel. Acid and alkali resistant, corrosion proof, high power and fast heating.detailes of oil bleaching machine
  • Wide application: oil decoloring machine is not only used in oil refining industry but also can apply to fine chemical industry, cosmetics market, the pharmaceutical industry, etc. With the advantages of reasonable design, great durability, high efficiency, stable operation, low noise and easy installation, our stainless steel decolorization tank has been widely used in medium and large material processing factory.

Common Methods of Oil Decolorization

In industrial cooking oil production plant, there are many methods for oil decolorization:  adsorption decolorization, heating decolorization, oxidation decolorization, chemical reagent decolorization and so on. Among them, adsorption decolorization is the mostly method in oil refining processes.

Adsorption Decolorization

oil decolorizing process
Oil adsorption decolorization is making use of some substances that have a strong adsorption effect on pigments(such as bleaching earth, activated clay and activated carbon) to adsorb pigments and other impurities in oil under certain conditions. Adsorption decolorization can not only achieve the purposes of improving oil color and removing gum but also effectively remove trace metal ions in oil and some substances that cause the poisoning of hydrogenated catalysts, so as to provide a good condition for further oil refining (hydrogenation, deodorization).

Comparison of different adsorption decolorization methods

Continuous type
Category of comparison Intermittent type Tube type Mechanical mixing Steam stirring
Clay consumption (%) 3-5 1-3 3-5 1-3
Decolorization temperature (℃) 90-110 100-110 90-110 105-120
Decolorization time (min) 30-50 20-30 30-40 20-30
Decolorizing vacuum degree (MPa) -0.095 -0.095 -0.095 -0.095
Bleaching oil color (Lovibond color) Y35R6 Y35R4 Y35R6 Y35R4
Equipment cost High Low High Low
Equipment maintenance cost High Low High Low
Steam consumption (%) 5 2-3 3 2-4
Power consumption High None High None

Other Decolorization Methods

Thermal decolorization is a decolorizing method that uses the thermal denaturation of certain heat-sensitive pigments to achieve decolorization by heating. However, high temperature inevitably leads to thermal oxidation of the oil. Therefore, this method is limited to the auxiliary decoloration of some low-value oil containing heat-sensitive dyes (palm oil, coconut oil), and is not used as a normal process for oil refining.

Air decolorization makes use of chromophores’ instability on oxygen to decolorize the oil by air-oxidizing pigments. For example, the carotenoid and chlorophyll in the oil are very unstable because of their structure, which is easy to be discolored under the action of oxygen. However, air decolorization leads to thermal oxidation of the oil, too. Thus, this method is generally limited to the auxiliary decolorization of high carotene oil (such as palm oil).

Reagent decolorization is a bleaching method which uses chemical reagents for oxidation and decolorization of the chromophores. The commonly used oxidants are sodium dichromate, hydrogen peroxide, and ozone. But reagent decolorization method exists a residual problem of chemical reagents, therefore, the bleaching process and washing separation conditions should be strictly controlled during operation, so that the residual amount of reagent can be controlled within the allowable range.

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