RU2836916C1 - Method of producing fatty acids from vegetable oil soap stocks - Google Patents

Abstract

FIELD: oil and fat industry.

SUBSTANCE: method of producing fatty acids from vegetable oil soap stocks, characterized by that, first, alkaline saponification of hydrated vegetable oil is carried out with sodium hydroxide solution with concentration of 30-45% for 240 minutes at temperature of 90-95 °C to pH 10-11 while stirring with steam under pressure of up to 0.2 MPa to obtain a soap glue with excess alkali content of 0.2-0.3%, then the obtained mass is subjected to salting-out with sodium chloride with concentration of 16-20% for 75-80 minutes, after which the obtained mass is settled for 2 hours and divided into three layers – lower – soap alkali, middle – adhesive soap, upper – soap core; soap core is decomposed with sulphuric acid in two steps: at the first stage – sulphuric acid with concentration of 10-12% at hydrolysis temperature of 110-115 °C for 40 minutes and on the second – sulphuric acid with concentration of 80-92% at decomposition temperature of 90 °C for 85 minutes to pH 2.0-2.5, wherein sulphuric acid is fed in portions while stirring with live steam under pressure of 0.3 MPa until complete decomposition of soap. After separation of second sulphate water, obtained fatty acids are washed with water condensate until complete absence of sulphuric acid and sodium sulphate.

EFFECT: invention increases output of fatty acids, improves environmental situation by reducing waste water discharge, reduces energy consumption for obtaining fatty acids from vegetable oil soap stocks and reduces consumption of sodium hydroxide and sulphuric acid.

1 cl, 2 tbl

Description

The invention relates to the oil and fat industry, and specifically to methods for obtaining fatty acids from soapstocks formed during alkaline refining of vegetable oils.

A method for obtaining fatty acids from vegetable oil soap stocks is known (Patent of the Russian Federation No. 2048511. Method for obtaining fatty acids from vegetable oil soap stocks. Drozdov A.S., Didenko Z.V., Volkova L.D., Uvarova L.V., Kukhtitsky O.L., Aleinik V.M., Sorokin V.N., Gorbanev I.F., Kuznetsov V.A., Klochko N.D. IPC C11B 11/00. - No. 5064258/13. - Claimed 08.10.1992; Published 20.11.1995), according to which the soap stocks are preliminarily split by hydrolysis at 160-180°C and then the resulting emulsion is decomposed with sulfuric acid to a pH of 2-2.5 sulfate water at a temperature of 80-90°C. The decomposition product is settled and separated into two layers: fatty acids, which are sent for distillation, and sulfate water, which is sent to obtain sodium sulfate.

The disadvantages of the known method are the loss of fatty acids during numerous washings at the stages of decomposition and splitting and the formation of a large amount of wastewater.

The closest in technical essence to the invention is a method for processing soapstocks by decomposing them with sulfuric acid [Magazine "Fat and Oil Industry". - No. 8. - 1970. - Pp. 34-36], according to which the soapstock is diluted with water at a rate of 70-75% of its content in oil, the mass is heated to 80-85 ° C and, while mixing with air, is treated with sulfuric acid at a rate of 2-3% of its content in the aqueous layer at the end of the process. After adding the acid, the mass is mixed for 1-1.5 hours and left to settle at 88-94 ° C for 4-6 hours. The mass is separated into three layers: the aqueous phase is discharged into the sewer after neutralization, the intermediate phase (resinous substances) into the emulsion box, and the upper layer (soap stock fat) is washed with water and then split by contact or non-reactive methods into two phases. The splitting is carried out by adding condensate to the mass heated to 80-85°C and, while mixing with air, introducing the required amount of contact and sulfuric acid. After the first phase, the mass is settled, the aqueous phase is drained, and the remaining mass is subjected to the second phase of splitting. The depth of splitting after the second phase was 87.5-92.2%. After splitting, the crude fatty acids are washed with water until a neutral reaction and sent for distillation. The yield of acids was 80% of the mass of crude acids.

The disadvantages of this method are the loss of fatty acids during numerous washes at the stages of decomposition and splitting and the formation of a large amount of wastewater.

The aim of the invention is to reduce the loss of fatty acids and reduce the amount of wastewater.

The technical result of the invention consists in developing a method for obtaining fatty acids from vegetable oil soap stocks, which makes it possible to increase the yield of fatty acids, improve the environmental situation by reducing wastewater discharge, reduce energy costs for obtaining fatty acids from vegetable oil soap stocks and reduce the consumption of sodium hydroxide and sulfuric acid.

The distinctive features of the method are the sequence of technology stages and technological process modes.

This is achieved by the fact that according to the method for obtaining fatty acids from vegetable oil soapstocks, characterized by the fact that first, alkaline saponification of hydrated vegetable oil is carried out with a sodium hydroxide solution of 30-45% concentration for 240 minutes at a temperature of 90-95 °C to a pH of 10-11 while stirring with steam under pressure up to 0.2 MPa until soap glue with an excess alkali content of 0.2-0.3% is obtained, then the resulting mass is salted out with sodium chloride of 16-20% concentration for 75-80 minutes, after which the resulting mass is settled for 2 hours and separated into three layers - the bottom - soap alkali, the middle - glue soap, the top - soap core; the soap core is decomposed with sulfuric acid in two stages: in the first - with sulfuric acid with a concentration of 10-12% at a hydrolysis temperature of 110-115°C for 40 minutes and in the second - with sulfuric acid with a concentration of 80-92% at a decomposition temperature of 90°C for 85 minutes to a pH of 2.0-2.5, with sulfuric acid being fed in portions while stirring the mass with live steam under a pressure of 0.3 MPa until the soap is completely decomposed, after separating the second sulfate water, the fatty acids obtained are washed with aqueous condensate until there is a complete absence of sulfuric acid and sodium sulfate.

The method is carried out as follows.

First, alkaline saponification of hydrated vegetable oil is carried out with a sodium hydroxide solution with a concentration of 30-45% for 240 minutes at a temperature of 90-95°C to a pH of 10-11 while stirring with steam under pressure of up to 0.2 MPa until soap glue with an excess alkali content of 0.2-0.3% is obtained.

The use of ranges of temperature, concentration, processing time, pH values is due to changes in the chemical composition of soapstocks obtained during the processing of various types of oils: sunflower, rapeseed, soybean, amaranth, linseed, hemp, etc. Each of the resulting soapstocks has variations in the quantitative content of certain fatty acids. Therefore, to give universality to the claimed method, ranges of temperature, concentration, processing time, pH values are specified, covering the entire range of processed soapstocks obtained from various oil crops.

The specified ranges of values of process parameters (temperature, concentration, processing time, pH) can also be used for processing a mixture of soapstocks of different oils in different proportions.

Alkaline refining (saponification) converts free fatty acids into insoluble soaps. Caustic soda (sodium hydroxide - NaOH) is used for alkaline saponification, since the highest degree of saponification of neutral fat is observed when using sodium hydroxide solutions.

As a result of neutralization of free fatty acids in oils with aqueous solutions of alkali, practically insoluble in oil or fatty acids (soaps) are formed, for example

RCOOH + NaOH ↔ RCOONa + H ₂ 0.

To accelerate the reaction and shift the equilibrium towards the formation of soaps, the amount of alkali is taken with some excess against the theoretically necessary for neutralizing free fatty acids. The theoretical consumption for neutralizing the amount of alkali (NaOH) is calculated using the formula

Щ _Т = Q⋅0.714 КЧ,

where Q is the amount of neutralized oil in kg, CN is the acid number.

The amount of excess alkali used varies depending on the nature and quality of the oil being refined, the initial acid number, the method of neutralization, and other neutralization conditions, such as temperature and concentration of the alkali solution.

The more thoroughly the initial oil is prepared, the less excess alkali is used. When using low-concentration alkali, the excess is less and for light oils it is from 5 to 50%, for difficult-to-refined oils (cotton) it reaches 200-300%. This is especially important to consider, since with a lack of alkali, soap hydrolysis increases and the probability of forming acidic soaps that are poorly soluble in water increases. Excess alkali is also necessary due to the fact that part of it is spent on interaction with other accompanying substances, for example, with acidic forms of phosphatides, etc. The consumption rate of caustic soda for additional saponification of soapstock is 108 kg per 1 ton of fatty acids.

Alkaline refining with caustic soda reduces the free fatty acid content to 0.01-0.03%. When using weaker alkali, it is difficult to obtain a free fatty acid content below 0.10%.

The concentration of the alkali solution is 30-45% depending on the type, quality of the oil and the neutralization method used.

The use of an alkali solution with a concentration below 30-45%, for example 25%, leads to incomplete alkali neutralization of the soapstock.

The use of an alkali solution with a concentration higher than 30-45%, for example 55%, leads to excessive consumption of alkali and an increase in the cost of the finished product, as well as the need to remove excess alkali from the wash water.

Heating the soap stock with live steam to a temperature of 90-95°C reduces its viscosity and ensures efficient and uniform alkali refining (saponification). Heating the soap stock with live steam to a temperature below 90-95°C, for example 80°C, does not ensure a low enough viscosity for efficient alkali refining. Heating the soap stock with live steam to a temperature above 90-95°C, for example 100°C, is associated with significant excess steam consumption and significant energy costs; in addition, during steam condensation, an excessive amount of condensate is formed, reducing the concentration of alkali, which reduces the efficient flow of alkali refining.

Heating the soap stock with live steam for a period shorter than 240 min, for example 200 min, does not allow for complete alkaline refining to pH 10-11. Heating the soap stock with live steam for a period longer than 240 min, for example 260 min, will only increase the duration and, therefore, reduce the productivity without increasing the effect of alkaline refining to pH 10-11.

The use of live steam under pressure up to 0.2 MPa for mixing the reaction mass ensures the maintenance of the required temperature and the production of soap glue with an excess alkali content of 0.2-0.3%. The use of steam with less (for example, 0.15 MPa) or more (for example, 0.25 MPa) leads to high refining losses, high production costs, high energy consumption and significant volumes of greasy water.

Soapstock is a by-product of the neutralization stage of vegetable oils, which is a mixture of various valuable components. Of particular value are the fatty acids present in it, which are used in the production of soap, surfactants, biodiesel fuel, etc.

Soapstock, in terms of organoleptic and physicochemical indicators, must meet the requirements given in Table 1.

The resulting mass is then salted out with sodium chloride at a concentration of 16-20% for 75-80 minutes. The resulting viscous mass is thoroughly mixed, then water at a temperature of 60°C is added in an amount of 50% of the mass of the soap raw material. This is due to the fact that the salting out process maximizes the concentration of the soap component in the soap raw material obtained after preliminary saponification.

The use of sodium chloride with a concentration of 16-20% for salting out increases the yield and quantity of neutralized fatty acids, as well as the density of the solution. Reducing the concentration of sodium chloride to less than 16-20%, for example, 12%, reduces the concentration of the soap component in the soap raw material.

Increasing the concentration of sodium chloride above 16-20%, for example 24%, disrupts the homogeneity of the soap glue.

Carrying out salting for 75-80 minutes at a temperature of 60°C leads to the product of the concentrations of the stearate ion and the sodium ion being greater than the product of the solubility of sodium stearate. In this case, salting out occurs due to the influence of the common ion, the role of which is played by the sodium ion Na+. Electrolytes, in particular sodium chloride, when dissolved in water reduce the solubility of soap. The homogeneity of the soap glue is disrupted. The difference between the proportions of soap and sodium chloride solution leads to the fact that the soap, being lighter, separates and floats, forming a layer of concentrated, so-called basic soap.

Carrying out salting for 75-80 min and a sodium chloride concentration of 16-20% increases the yield and amount of neutralized acids due to the intensification of the salting out process and an increase in the density of the solution. With a process duration of 75-80 min and a sodium chloride concentration of 16-18%, the yield increases by 1.5 times. An increase in the sodium chloride concentration has a greater effect on the degree of neutralization, and an increase in the salting out duration - on the yield of fatty acids. The highest yield of acids is observed starting with a salting out duration of 75-80 min and a sodium chloride concentration of 16%.

The highest values and gradual decrease in the degree of neutralization are observed starting from the salting-out duration of 75-80 min. and the sodium chloride concentration of 16-20%. Under these conditions, the yield of fatty acids is 95.0%. Thus, preliminary saponification of soap raw materials allows for a more complete transformation of the fatty component into soap, salting-out allows for maximum concentration and isolation of the soap component, which is decomposed by sulfuric acid.

Failure to comply with the above rational salting-out modes (for 75-80 min and sodium chloride concentration of 16-20%) leads to additional loss of the fatty component of the soap raw material. In order to reduce and avoid losses, it is necessary to ensure the required duration of settling and the efficiency of phase separation after salting-out and washing of the final fatty acids from sulfuric acid residues.

After this, the resulting mass, as a result of settling for 2 hours, was divided into three layers: the bottom one was soapy alkali, the middle one was glue soap, and the top one was soap core.

Then the soap core is decomposed with sulfuric acid in two stages: in the first stage - with sulfuric acid with a concentration of 10-12% at a hydrolysis temperature of 110-115°C for 40 minutes and in the second stage - with sulfuric acid with a concentration of 80-92% at a decomposition temperature of 90°C for 85 minutes to a pH of 2.0-2.5.

In this case, sulfuric acid is fed in portions while mixing the mass with live steam under a pressure of 0.3 MPa, avoiding violent foaming. After each portion of sulfuric acid is added, the mass is briefly mixed with low-pressure steam up to 0.3 MPa. Under the action of acid, the soap soap decomposes with the formation of fatty acids, while non-fatty impurities are destroyed and small flakes are formed at first, which, when mixed, become larger and are easily separated from the fatty acids during settling. The consumption rate of sulfuric acid is 186 kg per 1 ton of fatty acids. After the lumps disappear, sulfuric acid is added until the soap is completely decomposed, a sign of which is the formation of acidic water. The acidic water should be transparent, and after adding the methyl orange solution, it should be pink in color.

At pH below 2, the mass fraction of sulfuric acid increases, and pH above 2.5 leads to incomplete decomposition with the formation of an emulsion.

Decomposition at temperatures below 90°C requires long-term processing (more than 2 hours), and increasing the temperature above 90°C leads to an increase in heat costs and pressure.

After the required amount of sulfuric acid has been added, the contents are stirred with live steam so that the acid reacts most fully with the impurities. Acidic waters should contain no more than 1% free sulfuric acid. The mass is then allowed to settle for 1 hour, after which the mass is separated into fatty acids and sulfate water.

The fat content in drain water is no more than 100 mg/l.

Fatty acids are washed to remove traces of sodium sulfate and sulfuric acid and sent for distillation, while sulfate water is processed to produce commercial sodium sulfate.

Crude fatty acids obtained from soapstock must meet the organoleptic and physicochemical parameters specified in Table 2.

The method is illustrated by the following example.

Hydrated vegetable sunflower oil is subjected to alkaline saponification with a sodium hydroxide solution of 30-45% concentration to a pH of 10-11. The alkaline saponification process is carried out at a temperature of 90-95°C and is completed after 240 minutes. In this case, the mass is mixed with steam under pressure up to 0.2 MPa until soap glue with an excess alkali content of 0.2-0.3% is obtained.

Then the resulting mass is salted out with sodium chloride at a concentration of 16-20% for 75-80 minutes.

After standing for 2 hours, the resulting mass is divided into three layers: the bottom one is soap lye, the middle one is glue soap, and the top one is the soap core.

The upper soap core is decomposed with sulfuric acid in two stages: in the first stage - with sulfuric acid with a concentration of 10-12% at a hydrolysis temperature of 110-115°C for 40 minutes, and in the second stage - with sulfuric acid with a concentration of 80-92% at a decomposition temperature of 90°C for 85 minutes to a pH of 2.0-2.5.

Sulfuric acid is added in portions while stirring the mass with live steam under a pressure of 0.3 MPa until the soap is completely decomposed.

After separating the second sulfate water, the obtained fatty acids are washed with aqueous condensate until there is a complete absence of sulfuric acid and sodium sulfate.

The proposed method for obtaining fatty acids from vegetable oil soapstocks has the following advantages:

- increases the yield of fatty acids up to 95% by increasing the depth of acid cleavage by 7.1%;

- the use of the salting-out stage made it possible to improve the environmental situation by reducing the discharge of wastewater;

- reduces energy costs for obtaining fatty acids from vegetable oil soapstocks by intensifying the processes of alkaline saponification, salting out, hydrolysis and decomposition with sulfuric acid;

- reduces the consumption of sodium hydroxide and sulfuric acid;

- implementation of the soapstock hydrolysis process without the use of a catalyst at relatively low temperatures of 110-115°C and with complete utilization of wastewater.

Claims (1)

A method for obtaining fatty acids from vegetable oil soapstocks, characterized in that first, alkaline saponification of hydrated vegetable oil is carried out with a sodium hydroxide solution of 30-45% concentration for 240 min at a temperature of 90-95°C to a pH of 10-11 while stirring with steam under pressure of up to 0.2 MPa until soap glue with an excess alkali content of 0.2-0.3% is obtained, then the resulting mass is salted out with sodium chloride of 16-20% concentration for 75-80 min, after which the resulting mass is settled for 2 hours and separated into three layers - the bottom - soap alkali, the middle - glue soap, the top - soap core; the soap core is decomposed with sulfuric acid in two stages: in the first - with sulfuric acid with a concentration of 10-12% at a hydrolysis temperature of 110-115°C for 40 minutes and in the second - with sulfuric acid with a concentration of 80-92% at a decomposition temperature of 90°C for 85 minutes to a pH of 2.0-2.5, with sulfuric acid being fed in portions while stirring the mass with live steam under a pressure of 0.3 MPa until the soap is completely decomposed, after separating the second sulfate water, the fatty acids obtained are washed with aqueous condensate until there is a complete absence of sulfuric acid and sodium sulfate.