JPS5851939B2 - Vanillin production method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Vanillin is currently produced primarily by alkaline oxidation of lignin obtained from the pulping of cellulose sulfite from soft water.

In a typical vanillin process, the oxidized pulping waste is extracted using, for example, a water-soluble alcohol (Sandborn, Finnish Patent No. 20078, 1944).

In this process vanillin as well as all other low molecular weight substances which form the sodium salt are dissolved in salt form in the alcohol phase.

This dissolution mainly occurs due to very high salt and alkali concentrations of the oxidized aqueous phase, which produce a so-called salting-out effect.

In another known method, the oxidized liquor is neutralized to liberate vanillin from its salts and extracted with an organic solvent at a pH below 7.

The organic solvent used may be benzene, xylene, or an aliphatic solvent.

This procedure is used, for example, in Finnish patent no. 17 of 1936.
It is described in the specification of No. 966.

In all known vanillin production methods, after dissolving vanillin together with its typical impurities, the next step is to separate vanillin from said impurities.

Most separation methods are of the type that convert vanillin as the main component to a purer form.

These separation steps primarily consist of physical separation and bisulfite complex formation that separates the aldehyde from other compounds.

Physical separation operations are often unsatisfactory for two reasons: they do not clearly separate vanillin and impurities.

These involve recycling large amounts of vanillin in their processes and therefore require more and more separation as impurities continue to accumulate.

On the other hand, if recycling of vanillin is to be avoided, large losses of vanillin will inevitably be encountered.

The manufacturing process for vanillin could be simplified if the amount of impurities could be reduced at the very beginning.

It is clear that if the starting material is one containing a higher than normal content of lignosulfonate, the oxidized liquor will also contain a higher than normal content of vanillin.

This oxidation method has been described in several patents and other publications and will not be discussed here.

Applicants have identified the impurities present in the highest amounts in vanillin,
It has now surprisingly been found that acetovanillin is primarily generated from low molecular weight lignin during oxidation.

By removing low molecular weight lignin from the liquid to be oxidized before oxidation, the amount of acetovanillin will be reduced by two-thirds compared to conventional methods.

This advantage leads to other improvements described below and simplifies the process for manufacturing vanillin.

In the vanillin production method, in which vanillin is extracted with alcohol, vanillin contains, in addition to the typical impurity acetovanillin, parahydroxybenzaldehyde, guaiacol, vanillic acid, O-vanillin, and large amounts of low molecular weight partially desulfonated lignin. .

Vanillin is naturally produced in several different ways.
It is removed from the alcohol, for example by evaporation or extraction in the form of the sodium salt, or as free vanillin.

If vanillin is extracted from alcohol as the sodium salt, it is convenient to process it manually to form the bisulfite complex of vanillin by using sulfur dioxide.

Non-aldehyde-non-complex impurities as well as partially desulfonated lignin (hereinafter referred to as "tar") can be readily extracted from this bisulfite complex.

The relatively pure bisulfite complex of vanillin thus obtained must be degraded.

This decomposition is most often carried out using sulfuric acid, liberating sulfur dioxide.

However, in such a decomposition, a significant portion of vanillin is destroyed, as it polymerizes partly with itself and partly with impurities.

It is also known to decompose the bisulfite complex of aldehydes by using alkali, whereby the bisulfite is converted to sulfite.

Furthermore, it is also known to extract aldehydes directly from such complex solutions with solvents at elevated temperatures.

Applicants have discovered that the best way to liberate vanillin is to combine the two methods described above, ie simultaneous decomposition with alkali and extraction with an organic solvent.

When sodium carbonate is used for the decomposition, the final pH value for the decomposition is 7.9, which has been proven in extensive experiments to be the best pH value also for the extraction.

Operating at said pH level, all tarry impurities will remain in the alkaline aqueous phase and only the aldehydes will migrate to the organic solvent.

The best organic solvents used here are aromatic solvents, especially toluene.

Aldehydes, in particular p-hydroxybenzaldehyde, which is more acidic than vanillin, are now very advantageously extracted from the vanillin/toluene solution obtained.

This is best done using slightly alkaline water.

Final purification is best accomplished by evaporating the toluene using a maximum temperature of 130'C and a pressure of 37.5 mm/Hg (approximately 5 kPa) for evaporation.

Such evaporation can be carried out in any apparatus, but is best accomplished in a thin film evaporator with several separate heating zones.

Evaporation is carried out at constant pressure with increasing temperature from about 60°C to 130°C towards the bottom of the apparatus.

Evaporation is then continued in a second similar device at almost the same temperature but now at an essentially lower pressure of 15 mm/Hg (0.2 kPa).

In this device, vanillin is vaporized from impurities of high molecular weight and from impurities with high boiling points, as described above.
Very pure crude vanillin is produced, with a purity of 99%.
．． It is 5% or more.

EXAMPLE 4525 kg of sodium oxybisulphite waste solution obtained from Finnish fir wood and containing 1.53% by weight of vanillin and having a density of 1,220 are first purified by ultrafiltration and then extracted successively with butanol.

The butanol extraction is carried out with water-saturated n-butanol having a density of 0.803 at a temperature of 53°C.

The raffinate obtained by extraction contains 0.002% vanillin.

The resulting extract contains 1.48% by weight of vanillin.

Furthermore, this extract contains 1.01% by weight of other dissolved organic substances, such as substances other than vanillin.

The butanol extract is re-extracted with water containing 0.2% by weight NaOH.

The purpose of this is to prevent the formation of harmful emulsion systems during the extraction.

The resulting aqueous raffinate now contains 2.88% by weight of vanillin and the butanol extract contains 0.03% vanillin.

The same butanol is used six times to extract vanillin from the oxidized raw material.

No difference was observed in butanol after the first and sixth extraction.

The aqueous phase containing vanillin sodium salt, amounting to a total of 2370 kg, obtained in this way is evaporated in a vacuum evaporator at a temperature of 35° C. to 453 kg.

The evaporated product contained approximately 15 O117 kg of vanillin, while the total dry matter content was greater than 300 f/kg.

A sodium bisulfite complex of vanillin is prepared in a known manner by treating a concentrated aqueous solution of sodium vanillin with sulfur dioxide gas in a mixer-equipped reaction volume.

Sulfur dioxide gas is fed to the reactor until the pH drops to 4.5.

The aqueous solution of the bisulfite complex becomes pale in color and a tar-like substance begins to separate from the aqueous solution.

The solution is passed into an extraction column where it is treated countercurrently with n-butanol at a temperature of 25°C.

Non-aldehyde impurities as well as tarry substances are extracted from the aqueous solution with butanol.

The bisulfite complex purified in this way is clean and light in color.

The n-butanol used for extraction is, for example, 30? /l guaiacol, 35? /l of acetovanillin, and 5 f/l of vanillin, and about 140 t/l of other mainly tarry desulfonated lignin.

Purified bisulfite complex of vanillin at pH 7.9
Decompose by adding NaOH until .

The aqueous solution thus obtained is heated to a temperature of 65° C. and extracted continuously with toluene to obtain a clear toluene extract.

Is the extract liquid 81? /l of vanillin, while the bottom biomass contains 24 F? /l: Contains vanillin.

The resulting toluene extract is washed twice with a small amount of pure water to remove the residues of the sodium salts and the heavy phase that may have migrated during the extraction.

The purity of vanillin in the toluene solution thus obtained is greater than 98%.

During the evaporation of the toluene solution, a small amount of guaiacol also evaporates together with the toluene.

Solid brown-yellow crude vanillin having a melting point of 79.5°C is vacuum distilled at a temperature of 140°C and a pressure of 1 to 2 mmHg.

In this distillation all distillate is recovered, while the amount of bottom product remaining is about 5% of the feed.

The bottom product can be rubbed into an alkaline solution and recycled to the process.

The distillate is pale yellow in color and has a melting point of 80°C.

The distillate obtained is dissolved in water to give a 5% solution, the yellow color disappears upon filtration through activated carbon, and it is crystallized from water in the usual manner by cooling to 5°C.

The crystals are separated from P and dried at a temperature of 60° C. and a pressure of 4 to 5 mmHg for 4 hours.

The melting point of the crystals obtained is 81.4 to 82.2°C.

Gas chromatography analysis shows that there are no impurities in the crystals.
．． 0.05% acetovanillin and 0.05% orthovanillin.

No traces of other impurities were found.

[Brief explanation of the drawing]

The drawing is a process flow diagram of the method of the present invention.

Claims (1)

[Claims] 1 Lignosulfonate is air oxidized in the presence of sodium hydroxide and isolated by alcohol extraction, the resulting sodium vanillin is converted to a bisulfite complex using SO2, and sodium carbonate is added. This complex is decomposed and extracted as free vanillin with an organic solvent in conjunction with or immediately after the decomposition, the free vanillin in the organic solvent is washed with slightly alkaline water, and the organic solvent is extracted from the solution thus treated. A method for producing vanillin, which comprises evaporating it in a low vacuum to remove not only the organic solvent but also guaiacol from vanillin. 2. The method according to item 1, characterized in that the lignosulfonate raw material is produced by ultrafiltration at a pH of 7.0. 3. Evaporate the aqueous solution of vanillin, which has been removed as the sodium salt from the alcohol product, to a concentration of 5 to 15 times, preferably 10 times, compared to the original concentration, and at this concentration use 802 to 2. Process according to claim 1, characterized in that the conversion into a sulfite complex is carried out. 4 A concentrated aqueous solution of vanillin bisulfite complex,
Non-aldehyde impurities were removed from the aqueous solution by extraction with the same alcohol used to separate vanillin from the reaction mixture, and the extract thus obtained was fed alcohol-free to the feed of the oxidation reactor. or the first, characterized in that it is recycled together with alcohol;
The method according to any one of paragraphs 3 to 3. 5. The first method, characterized in that the purified bisulfite complex is decomposed in alkaline conditions using sodium carbonate for decomposition, and the decomposition is carried out at the boiling point of the mixture to distill off the dissolved alcohol.
4. The method according to any one of paragraphs 4 to 4. 6. Bring vanillin from the decomposed reaction mixture to the decomposition temperature.
- The method according to any one of items 1 to 5, characterized in that the organic solvent is extracted with an organic solvent, and the organic solvent consists of toluene. I From a mixture of vanillin and an organic solvent, preferably toluene, complete evaporation of the solvent is carried out using temperatures up to 130°C and at the same time a pressure of up to 37.5 mm/Hg (5 KPa) during the evaporation. The method according to any one of paragraphs 1 to 6, characterized in that: