Method for purifying vegetable oil

Abstract

The invention relates to the oil and fat industry. The technical result of the invention is an increase in the degree of purity of vegetable oil to a level that permits the use thereof for technical purposes. The claimed method includes the following operations: sedimentation / precipitation of heavy mechanical contaminants; filtration / purification to remove small suspended contaminants, food residues and resinous substances; refining with sulphuric acid to remove resinous substances and acid-containing and sulphur-containing compounds; alkali refining to remove free fatty acids, flavouring agents, aromatic substances, phospholipids and, to a small extent, waxes and carbohydrates; treatment with hydrogen peroxide; ultrasonic adsorption / retention of contaminants on the surface of an adsorber material for deep purification to remove colourants, metal ions, acidic compounds and esters; final filtration to provide for the fine purification of oils; and addition of a natural or synthetic antioxidant to prevent oxidation processes and prolong the storage life of the oil. The invention makes it possible to obtain purified vegetable oil that can be used for technical purposes.

Description

[0001] METHOD OF PURIFYING VEGETABLE OIL

[0002] The invention relates to the oil and fat industry.

[0003] Methods and compositions for purifying waste oil are known, wherein the reduction of the accumulation of contaminants, such as polar materials, free fatty acids, metals, colored bodies and soaps, is achieved by treating the oil with a composition containing effective amounts of silica, acidic aluminum oxide, clay and citric acid. Removal of contaminants from oil in accordance with the methods and compositions of the invention improves the quality of the oil and reduces costs, as well as various health and safety problems associated with the production of fried foods (Patent US 6638551. Methods and compositions for purifying edible oil. - 2003).

[0004] Rejuvenation of used cooking oil can be achieved on a small and large scale by using simple devices filled with a mixture of granular activated carbons of plant origin and antioxidants, and they can be immersed in a frying device such as a pot, vat, frying pan, fryers, etc. containing used oil (US 20080102181 Al. Rejuvenation of used cooking oil. Ramu M. Rao, Abdulrahman Foad Abdulfattah, Abdo A. Husseiny. - 2010).

[0005] A method for treating waste vegetable oil by filtration through a cellulose filter, drying with silica gel and esterification with methanol is known. In this process, the removal of solids was 78.63%. After filtration, the oil was adsorbed on silica gel. The experimental setup represented two adsorbent concentrations (0.025 g silica gel / mL oil and 0.11 g silica gel / mL oil) and two temperatures (15-60 °C). The best condition was a temperature of 15 °C and a ratio of 0.11 g silica gel / mL oil. The last step evaluated was esterification to convert free fatty acids to methyl esters. Two temperatures (40 °C and 60 °C), two sulfuric acid concentrations (1% w / w and 3% w / w) and two alcohol:oil molar ratios (4:1 and 6:1) were evaluated in this reaction.

[0006] According to the experimental results, the best conditions were 60 °C, 1% w / w sulfuric acid with an alcohol:oil molar ratio of 4:1 for 2 hours. The resulting oil had less than 1% moisture, 0.25% suspended solids, and 1.38 mg KOH / g oil with an acid value. These characteristics are in satisfactory agreement with ASTM and ISO standards, so it can be used as a feedstock for biodiesel production (Casallas ID et al. Pre-treatment of waste cooking oils for biodiesel production / / Chemical Engineering Transactions. - 2018. - V. 65. - P. 385-390).

[0007] The use of natural material zeolite B ayah for purification of waste vegetable oil is known. Zeolite is a natural rock or mineral that chemically has a large surface area for use in the adsorption process. Waste vegetable oil was purified in three stages: neutralization and bleaching in accordance with quality standards. The results of the research presented the optimal working conditions for the purification of waste oil: when adding NaOH with a concentration of 19% during the neutralization process and with a zeolite concentration of 90%, it is possible to reduce the acid number by 2.4 mg NaOH / g, the peroxide number by 7 meOg / kg, the color degradation of used vegetable oil was 51.83% (Rusdi R. et al. Purification of Used Cooking Oil by Alkali Neutralization and Bleaching of Bayah Natural Zeolite / / Jumal Bahan Alam Terbarukan. - 2021. - T. 10. - No. l. - P. 36-42).

[0008] The closest technical solution, taken by us as a prototype, is a method for purifying waste vegetable oil, according to which waste oil is heated to 35-50 °C, neutralized with an alkali solution, kept under stirring for 10-30 minutes with a decrease in temperature to 20 °C, settled for 1.5-2.5 hours and decanted to separate liquid technical soap, heated again to a temperature of 80-90 °C, separated at this temperature with the supply of fresh water, normalized and cooled (RU Patent No. 2039796, IPC SPV 5 / 00, published on 20.07.1995).

[0009] The disadvantage of the prototype method is insufficient oil purification, i.e. the low efficiency of the method.

[0010] The objective of the invention is to achieve deeper purification of vegetable oils.

[0011] The technical result of the invention is to increase the degree of purification of vegetable oil to a level that allows it to be used for technical purposes.

[0012] The technical result is achieved in that in the method for purifying vegetable oil, including mechanical, physical and chemical processing methods, according to the invention, the following operations are performed: sedimentation - precipitation of heavy mechanical impurities; filtration - purification from small impurities in a suspended state, food residues, resinous substances; refining with sulfuric acid to remove resinous substances, acid- and sulfur-containing compounds; alkaline refining to purify from free fatty acids, flavoring and aromatic substances, phospholipids, to a small extent waxes, carbohydrates; treatment with hydrogen peroxide; ultrasonic adsorption - retention of impurities on the surface of the adsorber material for deep purification from pigments, metal ions, acidic compounds, esters; polishing filtration for fine purification of oils; addition of an antioxidant, natural or synthetic, to prevent oxidative processes and extend the shelf life of the oil.It is possible to replace refining with sulfuric acid with an alternative coagulation operation - the fusion of colloidal particles by mixing with an electrolyte liquid (trisodium phosphate, soda ash).

[0013] The method is carried out as follows.

[0014] Vegetable oil is subjected to sedimentation, that is, the precipitation of heavy mechanical impurities.

[0015] A filtration operation is carried out to clean the oil from small impurities in suspension, as well as food residues and resinous substances.

[0016] Refining is carried out with 15% sulfuric acid. This removes resinous substances, acid- and sulfur-containing compounds. As an alternative stage, coagulation is used - the fusion of colloidal particles by mixing with an electrolyte liquid (trisodium phosphate, soda ash). To do this, the oil is heated to 75-90 °C, and then mixed with a 10% coagulant solution for 20-30 minutes. Then it is settled for 1-2 days.

[0017] Next, alkali refining is carried out. This involves cleaning the oil from free fatty acids, flavoring and aromatic substances, phospholipids, and to a small extent waxes and carbohydrates. For refining, a solution of NaOH alkali with an excess of 15-30% is used. The oil is heated to a temperature of 65 °C with constant stirring. The rotation speed of the stirrer is 60 rpm. Then, the alkali solution is fed into the oil from the alkali measuring tank. Next, softened water is fed into the neutralizer with a continuously operating mixing device. Stirring is continued until well-settled soapstock flakes are formed. The required amount of alkali solution depends on the acid number of the original oil and the concentration of alkali. Theoretically, the required amount of alkaline agent for neutralizing oil is calculated using the formula:

[0018] NaOH = Q • 0.714 • CN where: Q is the amount of oil being neutralized; CN is the acid number of the oil being neutralized.

[0019] After the neutralization process is completed, an exposure is carried out - settling for 6 hours, as a result of which the soap stock settles to the bottom of the apparatus. As a result, all harmful substances that precipitate are removed along with the soap stock. To speed up settling, a solution of table salt (2-3% of the fat mass) with a strength of 8-10% is sprayed on the surface of the neutralized fat and to remove soap residues. The consumption of the salt solution is 15 liters per 1 ton of fat.

[0020] The next step is to treat the vegetable oils with hydrogen peroxide to improve their color after cleaning the oils with a saline solution. This is achieved by the action of hydrogen peroxide on some pigments by releasing free oxygen. The oil is heated to 80 °C, a 10% hydrogen peroxide solution is added, mixed, and left to stand for 24 hours.

[0021] Next, adsorption is carried out using an ultrasonic device with a frequency of no more than 20 kHz, which allows impurities to be retained on the surface of the adsorber material for cleaning from acidic compounds, ethers and other products. Ultrasound and sonochemical equipment are used to create a cavitation effect in the liquid and ultrasonic processing of the material. Dispersion, homogenization and emulsification of adsorbent particles with oil are improved. Zeolite, silica gel or bentonite are used as an adsorbent.

[0022] The oil enters the adsorption tank. A vacuum of at least 0.08 MPa is created using a vacuum pump. The mixer is turned on, the oil is heated to 90 °C and dried for 50 minutes. Then the temperature is reduced to 70 °C and the device sucks in the adsorbent of the fraction 0.1-0.5 mm in the amount of 5% of the oil mass by vacuum. The entire adsorption process is carried out while maintaining a vacuum. The duration of mixing the oil with the adsorbent is 30 minutes. After that, the oil is cooled with cold water through a coil, and then filtered on a plate press to clean it from the adsorbent. The amount of the adsorbent introduced depends on the initial color of the oil, on the desired degree of clarification and on the activity of the adsorber.

[0023] The next stage is filtration on a polishing filter for fine cleaning of oils. An antioxidant is added to the finished oil to prevent oxidation processes and extend shelf life. The antioxidant used is Anthrancin 220 in an amount of 0.02 to 0.1%.

[0024] The purified vegetable oil is sent for sale.

[0025] The method is illustrated by the following examples.

[0026] Example 1.

[0027] Vegetable oil is subjected to sedimentation, that is, the precipitation of heavy mechanical impurities.

[0028] A filtration operation is carried out to clean the oil from small impurities in suspension, as well as food residues and resinous substances.

[0029] Refining is carried out with 15% sulfuric acid. This removes resinous substances, acid- and sulfur-containing compounds. As an alternative stage, coagulation is used - the fusion of colloidal particles by mixing with an electrolyte liquid (trisodium phosphate, soda ash). To do this, the oil is heated to 75-90 °C, and then mixed with a 10% coagulant solution for 20-30 minutes. Then it is settled for 1-2 days.

[0030] Next, alkali refining is carried out. This involves cleaning the oil from free fatty acids, flavoring and aromatic substances, phospholipids, and to a small extent waxes and carbohydrates. For refining, a solution of NaOH alkali with an excess of 15-30% is used. The oil is heated to a temperature of 65 °C with constant stirring. The rotation speed of the stirrer is 60 rpm. Then, the alkali solution is fed into the oil from the alkali measuring tank. Next, softened water is fed into the neutralizer with a continuously operating mixing device. Stirring is continued until well-settled soapstock flakes are formed. The required amount of alkali solution is calculated using the formula:

[0031] NaOH = Q • 0.714 • KN where: Q is the amount of oil to be neutralized;

[0032] CN – acid number of the neutralized oil.

[0033] After the neutralization process is completed, an exposure-settling is carried out for 6 hours, as a result of which the soap stock settles to the bottom of the apparatus. As a result, all harmful substances that precipitate are removed along with the soap stock. To speed up settling, a solution of table salt (2-3% of the fat mass) with a strength of 8-10% is sprayed on the surface of the neutralized fat and to remove soap residues. The consumption of the salt solution is 15 liters per 1 ton of fat.

[0034] The next step is to treat the vegetable oils with hydrogen peroxide to improve their color after cleaning the oils with a saline solution. This is achieved by the action of hydrogen peroxide on some pigments by releasing free oxygen. The oil is heated to 80 °C, a 10% hydrogen peroxide solution is added, mixed, and left to stand for 24 hours.

[0035] Next, adsorption is carried out using an ultrasonic device with a frequency of no more than 20 kHz, which allows impurities to be retained on the surface of the adsorber material for cleaning from acidic compounds, ethers and other products. Ultrasound and sonochemical equipment are used to create a cavitation effect in the liquid and ultrasonic processing of the material. Dispersion, homogenization and emulsification of adsorbent particles with oil are improved. Zeolite is used as an adsorbent.

[0036] The oil enters the adsorption tank. A vacuum of at least 0.08 MPa is created using a vacuum pump. The mixer is turned on, the oil is heated to 90 °C and dried for 50 minutes. Then the temperature is reduced to 70 °C and the apparatus sucks in the 0.1-0.5 mm fraction zeolite adsorbent in the amount of 5% of the oil mass using vacuum. The entire adsorption process is carried out while maintaining a vacuum. The duration of mixing the oil with the adsorbent is 30 minutes. After that, the oil is cooled with cold water through a coil, and then filtered on a plate press to clean it from the adsorbent. The amount of adsorbent introduced depends on the initial color of the oil, the desired degree of clarification and the activity of the adsorber.

[0037] The next stage is filtration on a polishing filter for fine cleaning of oils. An antioxidant is added to the finished oil to prevent oxidation processes and extend shelf life. The antioxidant used is Anthrancin 220 in an amount of 0.02 to 0.1%.

[0038] The purified vegetable oil is sent for sale.

[0039] Example 2.

[0040] Example 2 is carried out in the same way as example 1, only silica gel is used as the adsorbent.

[0041] Example 3.

[0042] Example 3 is carried out in the same way as example 1, only bentonite is used as the adsorbent.

[0043] The cleaning results for three examples of using different adsorbents are shown in the table.

[0044] The use of the invention makes it possible to obtain purified vegetable oil for use in technical purposes.

[0045] In addition, vegetable oil as a renewable resource after purification can be converted into many derivatives such as alkyds, polyesteramides, polyesteramides, polyurethanes, epoxy resins and glycerin, which in a mixture with natural pigments can be used as biodegradable coatings and paints, polymers, composite materials. Table. Physicochemical properties of vegetable oils after purification using various adsorbents

[0046] Thus, our studies have shown that natural adsorbents from the series: zeolite, silica gel, bentonite, are distinguished by high sorption qualities, better selectivity in relation to accompanying substances of vegetable oils, availability, low cost and can be widely used in the purification of vegetable oils, which are a threat to both human health and the environment. Based on the above, it can be concluded that natural deposits with adsorbing properties can become a real alternative to synthetic zeolites not only in the purification of vegetable oils, but also have a wide range of applications.

Claims

CLAUSE OF INVENTION 1. A method for purifying vegetable oil that includes mechanical, physical and chemical processing methods, characterized in that the following are sequentially carried out: sedimentation - precipitation of heavy mechanical impurities, filtration - purification from small impurities in a suspended state and resinous substances, refining with 15% sulfuric acid to remove resinous substances, acid- and sulfur-containing compounds, alkaline refining to purify from free fatty acids, flavoring and aromatic substances, phospholipids, to a small extent waxes, carbohydrates, treatment with hydrogen peroxide, for which the oil is heated to 80 °C, a 10% hydrogen peroxide solution is added, mixed and settled for 24 hours, ultrasonic adsorption with a frequency of no more than 20 kHz - retention of impurities on the surface of the adsorber material for deep purification from acidic compounds, esters, polishing filtration for fine purification of the oil,adding a natural or synthetic antioxidant to prevent oxidation processes and extend the shelf life of the oil, 2. The method according to item 1, characterized in that natural adsorbents from the following series are used as the adsorbent: zeolite, silica gel, bentonite.

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