RU2494085C1 - Method of purifying vanillin obtained from lignin oxidation products - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a method of purifying vanillin obtained from lignin oxidation products, by reacting vinillin-containing extracts with aqueous solutions sodium bisulphite, followed by decomposition of the vanillin-bisulphite derivative. The method is characterised by that the vanillin-bisulphite derivative is heated in an autoclave to 120-170°C, the vapour-gas phase is released and vanillin is extracted from the obtained mixture or solution, followed by recycling the obtained aqueous solution of sulphurous anhydride and sodium sulphate into a solution of sodium bisulphite.

EFFECT: method enables to avoid the use of sulphuric acid and alkali when purifying vanillin, widely used in food, perfume, cosmetic and pharmaceutical industry.

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Description

The invention relates to methods for the isolation of vanillin from lignin-containing raw materials and for the purification of vanillin extracts obtained by extraction of oxidized alkaline solutions of lignins, followed by isolation of the target product.

Vanillin (B, 4-hydroxy-3-methoxybenzaldehyde) is widely used in the food, perfumery, cosmetic and pharmaceutical industries.

A known method of purification of vanillin extracts by recrystallization from water-methanol solutions [US 3049566, 1962]. The disadvantage of this method is the low degree of purification of raw vanillin, which requires multiple recrystallization to achieve satisfactory purification. The mentioned drawback is due to the low separation coefficients of the vanillin – impurity system during their crystallization from aqueous methanol solutions.

A known method of separating vanillin and lilac aldehyde from a solution obtained by oxidation of lignin-containing raw materials, extraction with high-boiling alcohols or esters with a boiling point of more than 130 ° C with further re-extraction with an aqueous alkaline solution (alkali or soda) at pH 10-14 and the isolation of vanillin and lilac aldehyde acidification with sulfuric acid to pH 5 (RU 2177935, publ. 10.01.2002).

The disadvantage of this method is the high resin content in the resulting concentrate - 33-44 wt.% And the need for further purification.

A known method of purification of raw vanillin by extraction with hydrocarbon solvents followed by crystallization of the target product by cooling the solution [US 3686322, 1972].

The disadvantage of this method is the low solubility of vanillin in non-polar hydrocarbons and the need to use the latter in large volumes.

The closest to the claimed method is the method of separation of vanillin from one stripped off benzene extract by its interaction with an aqueous solution of sodium hydrosulfite NaHSО ₃ , used on a semi-industrial scale at Syassky PPM [Kamaldina OD, Massov Y.A. Obtaining vanillin from lignosulfonates. - M.: CBTI ZINIS, 1959, 38 pp.]. In accordance with the known method, vanillin from one stripped off extract is re-extracted with an aqueous solution of NaHSO _{3 at a} concentration of 29 wt.%. Sodium hydrosulfite chemically interacts with the carbonyl group of vanillin with the formation of a fairly strong vanillin-sulfite derivative:

$$Ar-CH{O}_{org}+NaHS{O}_{3aq}\leftrightarrow Ar-CH\left(OH\right)S{O}_{3}N{a}_{aq},(\mathrm{one})$$

where Ar-CHO is vanillin.

This method has two main advantages: the ability to concentrate vanillin at the stages of extraction-stripping and its purification in the process of formation of a vanillin-hydrosulfite derivative. The latter is due to the fact that the reaction proceeds along the carbonyl group of vanillin, while carbonyl groups are practically absent in the accompanying impurities. As a result, the majority of the resins after bisulfitation remain in the organic phase, and vanillin passes into the aqueous phase. Vanillin from an aqueous solution of a hydrosulfite derivative is isolated by acidification with sulfuric acid. In this case, purified vanillin precipitates, sulfur dioxide is released into the gas phase and is then absorbed by an alkali solution to regenerate the sodium hydrosulfite solution:

$$2Ar-CH\left(OH\right)S{O}_{3}Na+H_{2}S{O}_{\mathrm{four}}\leftrightarrow 2Ar-CHO+N{a}_{2}S{O}_{\mathrm{four}}+2S{O}_2+2H_{2}O(2)$$

$$NaOH+S{O}_2\leftrightarrow NaHS{O}_3(3)$$

The main disadvantage of this method is the high consumption of sulfuric acid for the isolation of vanillin from the obtained hydrosulfite derivative and alkali for the regeneration of a solution of sodium bisulfite.

The objective of the invention is to reduce the cost of sulfuric acid and alkali in the processes of separation of vanillin from a vanillin-bisulfite derivative and the regeneration of a solution of sodium hydrosulfite.

The objective of the invention is achieved by the fact that in the method of purification of vanillin obtained from the oxidation products of lignins, the interaction of vanillin-containing extracts with aqueous solutions of sodium hydrosulfite, followed by decomposition of the vanillin-hydrosulfite derivative, according to the invention, the vanillin-hydrosulfite derivative is heated in an autoclave to 120-170 ° C , the vapor-gas phase is discarded and vanillin is extracted from the resulting mixture or solution, followed by recycling of the resulting aqueous solution of sulfur dioxide and sul phi sodium in sodium hydrogensulfite solution.

Common features of the claimed invention and prototype are the purification of vanillin obtained from the oxidation products of lignins by the interaction of vanillin-containing extracts with aqueous solutions of sodium hydrosulfite NaHSO ₃ followed by decomposition of the vanillin-hydrosulfite derivative.

Distinctive features of the claimed invention are that the vanillin-hydrosulfite derivative is heated in an autoclave to 120-170 ° C, the vapor-gas phase is discarded and the vanillin is extracted from the resulting mixture or solution, followed by recycling of the resulting aqueous solution of sulfur dioxide and sodium sulfite to sodium hydrosulfite solution.

The technical result of the claimed invention is to fundamentally reduce the cost of sulfuric acid and alkali in the process of separation of vanillin from its sodium bisulfite derivative. So, in accordance with the known method, the consumption of sodium hydrosulfite is 3.2 kg per kilogram of vanillin, which corresponds to a 4.6-fold excess from stoichiometry. To acidify it, 3 kg of concentrated sulfuric acid are needed, and 1.2 kg of sodium alkali to absorb the released sulfur dioxide. According to the claimed method, the costs of these reagents are reduced to zero, more precisely, to the level of technological losses, i.e. about a hundred times.

These distinguishing features determine the achievement of the technical results of the claimed invention, since it is precisely due to the heating of the sodium hydrosulfite solution and the vanillin-hydrosulfite derivative to high temperatures, 120-170 ° C, that the hydrosulfite ion is hydrolyzed with water to remove sulfur dioxide in the vapor phase along with excess water :

$$2NaHS{O}_3\leftrightarrow N{a}_{2}S{O}_3+S{O}_2+H_{2}O.(\mathrm{four})$$

As a result of a decrease in the concentration of the hydrosulfite ion in the solution, the vanillin-hydrosulfite derivative decomposes to vanillin and sodium sulfite:

$$2Ar-CH\left(OH\right)S{O}_{3}N{a}_{aq}\leftrightarrow 2Ar-CH{O}_{aq}+N{a}_{2}S{O}_3+S{O}_3+H_{2}O.(5)$$

After vanillin extraction, the residue of sodium sulfite (reaction (4)) is sufficient to mix with condensate, a solution of sulfur dioxide obtained in reactions (4) and (5), and a regenerated solution of sodium hydrosulfite is obtained to clean new portions of vanillin:

$$N{a}_{2}S{O}_3+S{O}_2+H_{2}O\leftrightarrow 2NaHS{O}_3.(6)$$

Reactions (4) - (5) proceed to a sufficient depth only at elevated temperatures, where the acidity of water increases so much that water, like sulfuric acid at low temperatures, protonates the bisulfite ion into sulfuric acid, which decomposes into sulfur dioxide and water. Therefore, the technical results and distinguishing features of the proposed method are in a causal relationship with each other.

The method is confirmed by specific examples:

Example 1. In the examples listed, the reaction mixture obtained by the oxidation of Syassky PPM lignosulfonates in an alkali solution with atmospheric oxygen at 160 ° C with a vanillin concentration of 7.2 g / L was used. 1 l of the reaction mixture was acidified to pH 4 and extracted three times with 100 ml of octanol. The combined extract contained 6.9 g of vanillin.

The combined extract was re-extracted three times with 20 ml of sodium hydrosulfite solution at a concentration of 250 g / l. The residual vanillin content in the octanol solution was 0.21 g, and 6.69 g of vanillin passed into the hydrosulfite solution.

The resulting solution of the vanillin-hydrosulfite derivative was loaded into an autoclave with a capacity of 0.5 L and heated to 140 ° C, after which the vapor-gas phase was released through the valve into the refrigerator-condenser. The autoclave was cooled, the solid residue was extracted with ethanol, and vanillin from this extract was obtained by distillation of the solvent. Received 6.35 g of vanillin (95% of the hydrosulfite contained in the solution). The solid sodium sulfite residue was analyzed for residual vanillin. Found in the solid residue 0.31 g of vanillin (4.6% of the hydrosulfite contained in the solution).

The obtained solid sodium sulfite residue with vanillin residues was mixed with condensate, an aqueous solution of sulfur dioxide obtained after condensation of the steam-gas mixture from the autoclave, water was added to a volume of 60 ml and the sodium hydrosulfite solution used in Example 2 was obtained.

Example 2. The experiment was carried out, as in example 1, including the stage of vanillin reextraction, but for this, the sodium hydrosulfite solution obtained in example 1 was used. 6.95 g of vanillin was found in the hydrosulfite solution after reextraction.

The resulting solution of the vanillin-hydrosulfite derivative was loaded into an autoclave with a capacity of 0.5 L and heated to 170 ° C, after which the vapor-gas phase was released through the valve into the refrigerator-condenser.

Received 6.67 g of vanillin (96% of the hydrosulfite contained in the solution). The solid sodium sulfite residue was analyzed for residual vanillin. Found in the solid residue 0.24 g of vanillin (3.4% of the hydrosulfite contained in the solution).

Example 3. The experiment was carried out as in example 1, but the solution of the vanillin-hydrosulfite derivative in the autoclave was heated to 120 ° C, and the vapor-gas phase was released through the valve into the refrigerator-condenser so that approximately half of the water remained in the autoclave. The resulting suspension of vanillin in a solution of sulfite, hydrosulfite and a vanillin-hydrosulfite derivative was extracted with ethyl acetate.

Obtained 5.28 g of vanillin (79% of the hydrosulfite contained in the solution). The solid sodium sulfite residue was analyzed for residual vanillin. Found in the solid residue 1.31 g of vanillin (19.6% of the hydrosulfite contained in the solution).

Example 4. The experiment was carried out, as in example 1, but the solution of the vanillin-hydrosulfite derivative was boiled at atmospheric pressure and 102-105 ° C until the water was completely evaporated, and the vapor-gas phase was condensed into a refrigerator-condenser. The resulting precipitate was extracted with methanol, and the extract was evaporated.

Received 2.13 g of vanillin (31.8% of the hydrosulfite contained in the solution). The solid sodium sulfite residue was analyzed for residual vanillin (in the form of an undecomposed vanillin-hydrosulfite derivative). Found in the solid residue 4.42 g of vanillin (66% of the hydrosulfite contained in the solution).

Example 5. The experiment was carried out as in example 1, but the solution of the vanillin-hydrosulfite derivative in the autoclave was heated to 180 ° C, and the vapor-gas phase was released through the valve into the refrigerator-condenser so that approximately half of the water remained in the autoclave. The resulting suspension of vanillin in a solution of sulfite, hydrosulfite and a vanillin-hydrosulfite derivative was extracted with ethyl acetate.

Received 5.64 g of vanillin (84% of the hydrosulfite contained in the solution). The resulting vanillin was dark in color and required additional purification. The solid sodium sulfite residue was analyzed for residual vanillin. Found in the solid residue 0.27 g of vanillin (4% of the hydrosulfite contained in the solution). Loss of vanillin due to its milling at high process temperatures was 12%.

Thus, the presented examples show that in the proposed method for the isolation of vanillin from lignin oxidation products, in comparison with the prototype, the consumption of sulfuric acid and sodium alkali in the process of vanillin purification by bisulfitation is practically eliminated and sodium hydrosulfite is returned to the production cycle without reagents. The key stage of the process, hydrolysis of the vanillin-hydrosulfite derivative, proceeds efficiently in an autoclave at 120-170 ° C. At lower temperatures, the degree of hydrolysis is small, and most of the vanillin cannot be isolated by simple extraction, and at temperatures above 170 ° C, the vanillin is partially resinized.

Claims (1)

The method of purification of vanillin obtained from the products of lignin oxidation by the interaction of vanillin-containing extracts with aqueous solutions of sodium hydrosulfite followed by decomposition of the vanillin-hydrosulfite derivative, characterized in that the vanillin-hydrosulfite derivative is heated in an autoclave to 120-170 ° C, the vapor-gas phase is removed and the extragene phase from the resulting mixture or solution, followed by recycling of the resulting aqueous solution of sulfur dioxide and sodium sulfite in a solution of sodium hydrosulfite.