DE3822628A1 - Process for the treatment of lignin for obtaining aldehyde and/or phenolic acids - Google Patents

Abstract

The invention relates to a process for the treatment of lignin with ozone for the selective preparation of aldehydes and/or phenolic acid. This process consists in bringing the lignin into contact with ozone using a liquid solvent bath based on 1,1,2,-trichloro-1,2,2-trifluoroethane; the formation of aldehydes and/or phenolic acids is observed without noticeable decomposition into small molecules; these components are isolated from the solvent and the solid residual lignin mainly by filtration and distillation. The yield is improved by using a liquid solvent bath in which alcohol and 1,1,2-trichloro-1,2,2-trifluoroethane are mixed in a very small ratio. The process can be applied in particular to lignin which is derived from vegetable material containing fibre, such as, for example, wood, bagasses, straw; these plant fibres are exploited and give a high-grade product. <IMAGE>

Description

The invention relates to a treatment method for lignin Extraction of aldehydes and / or phenolic acids.

Lignin is known to be a by-product that occurs in large quantities the paper industry, which is mostly discarded or burned becomes.

Numerous studies have been conducted to try to utilize these very carbon-containing by-products. in the At the moment, the inventors are only aware of a few methods that are available and developed on an industrial level, the majority this by-product can only be used thermally will.

Some oxidation processes, mainly using copper oxide or nitrobenzene, are used by some companies anyway to make vanillin from guaiacol type lignin. But these procedures are essentially due to consumption and the price of the oxidants expensive, and theirs Profitability margin remains limited at best. You can e.g. B. on the following publications on these oxidation processes refer: K.V. Sarkanen; C. H. Ludwig, lignin: occurrence, Education, Structure and Responses, Wiley Interscience Edition, 1971.

Other publications also have the option demonstrated lignin ozonization in an aqueous environment perform; this leads to a breakdown of herbal substances in small molecules. Some of these publications suggest the kinetics of degradation to better understand the to investigate relevant phenomena (R.A.D. Mbachu, R.St. John Manley, Journal of Polymer Science 1981, 19, p. 2053-2089). Furthermore, the application of ozonization is proposed to To change or destroy lignin in its structure the attack on the plant substances in a biological way (J.J. Bono, G. Gas, A. Ouderni, R.S. Bes, J.C. Mora and A.M. Boudet, Syn. Ozone et Biologie, Revue Avril 1984 IOA Ed. "). The procedure exists in all these publications  in that lignin is in contact with ozone in an aqueous environment is brought, this leads to the formation of highly oxidized molecules with low molecular weight (oxalic acid, carbon dioxide...), that have no specific value. Such a procedure can thus for the utilization of lignin and for the extraction of commercializable products are not used. In addition, phenol aldehydes and phenolic acids are two products by the different sectors of the chemical industry, the pharmaceutical and agricultural food industries be heavily researched, especially as aroma or as a natural active ingredient base for medication. At the moment these essential compounds either by synthesis from basic chemicals produced (hydroxymethylation, chlorination...) or by splitting off mainly vanillin by lignin oxidation with oxidizing agents (copper oxide, nitrobenzene). The new invention is intended to provide a new method for the treatment of Supply lignin by ozonization, which is done in a selective manner leads to aldehyde and phenol formation.

An object of the invention is as a recovery process to deliver for lignin, which is very economical and which without strong degradation to the above compounds leads. The invented method can mainly be applied to lignin which are made from vegetable fibers such as wood, Bagasse, straw. . . was obtained to supply materials, namely Phenolaldehyde and / or phenolic acid or one of its own again a usable by-product like the residual lignin in so to speak activated form, which is due to its increased activity can use directly.

For this purpose, the method according to the invention is for lignin treatment by ozonization and for selective extraction characterized by phenol aldehydes and / or phenolic acids as follows:

• - Lignin is made in a solvent bath based on 1,1,2-trichloro-1,2,2-trifluoroethane in contact with ozone brought.
• - The resulting aldehydes and / or phenolic acids are then isolated from the solvent and from the solid residual lignin.

Unexpectedly, it is found that by exchanging the water by 1,1,2-trichloro-1,2,2-trifluoro-ethane the reaction of the ozone with lignin is completely changed and not too degraded higher molecular compounds leads to Phenolic aldehydes and / or phenolic acids. It also enables Procedure, a large part of starting lignin that is not yet reacting recover: this is much more reactive, like have shown various functionalization studies (so-called activated lignin).

So the invented process enables that from vegetable Lignin obtained from substances (especially in the paper industry) recycle because it provides high value compounds and also Residual materials that can in turn be used. Preferably the lignin as a powder in 1,1,2-trichloro-1,2,2-trifluoro-ethane suspended. The ozone is in suspension until saturated solved, especially by blowing, the blowing is during continued throughout the treatment. So you get a tight Contact between the heterogeneous components in the suspension. The optimal conditions could be determined by tests to get the best yield and reduce degradation:

• - Ozone consumption is between 10 and 30 milligrams of ozone per Minute and per liter of solvent,
• - Approximate starting amount of lignin is between 15 and 100 g per liter of solvent,
• - The duration of contact of lignin and ozone in the suspension is about 1 to 3 hours.

In general, it was found that with excess ozone in the Relationship to lignin the risk of lignin degradation in small molecules (oxalic acid ...) exist as well as the diminution the yield and pollution of the reaction environment; a deficit in ozone makes the reaction slower. It should be noted that the phenolic acids in a second stage the reaction by oxidation of aldehydes, which in a first stage of the reaction were formed: You can determine the relative ratio of the components by acting on one or more of the parameters already mentioned (Duration, ozone consumption, amount of lignin produced).

In addition, a preferential procedure leads to a remarkable one Increase in aldehyde and / or phenolic acid yield; there use a solvent bath made of alcohol, especially ethanol and methanol, and 1,1,2-trichloro-1,2,2-trifluoroethane. It is very advantageous to use a bath between the 10% and 25% alcohol to 1,1,2-trichloro-1,2,2-trifluoro-ethane is added.

The increase in the yield of desired compounds appears particularly explainable in that the connections according to their Education can be gradually dissolved in alcohol, and at the same time the reaction equilibrium shifts in a favorable direction. It also appears that the alcohol dissolves a small part of lignin is secured, which improves the Yield contributes.

Aldehydes and / or phenolic acids are from the solid residues (activated lignin) separated by filtration; the 1,1,2-trichloro 1,2,2-trifluoro-ethane can then be obtained simply by distillation the liquid phase as it is a very low Boiling point (47/48 ° C). Then you get an alcohol solution, from which the desired components are obtained in various ways especially by distillation after cleaning. This cleaning can be done in a conventional way, by percolation through a strongly basic resin to aldehydes and / or bind phenolic acid to said resin.  

The desorption then takes place by eluting the Resin with an acidified water / alcohol solution. (At the This solution of the extraction already mentioned emerges subjected to isolate aldehydes and / or phenolic acids).

The desorption solution is acidified so that the bound Components eluted and the resin is regenerated. In addition, the solid residual lignin that is filtered off was preferably washed with water for its recovery. The reactivity of this lignin enables it to be functionalized for use in various technical areas: Tanning agents, dispersions, carriers for natural active ingredients, Seed coating material, raw material for polymer production. . .

The treatment method of the invention is for the various existing lignin types can be used and enables selective Obtaining aldehydes and / or corresponding phenolic acids, especially

• - Parahydroxybenzaldehyde type lignin, which is mainly obtained from Annual plants come from (grass species...) And to parahydrobenzaldehyde and / or leads to parahydroxybenzic acid,
• - Guava cabbage-type lignin, which is mainly resin-rich Wood comes and to vanillin and / or vanillic acid leads,
• - Syringyl-type lignin, which is mainly hardwood is derived and leads to syringyl aldehyde and / or syringylic acid,
• - Mixture of these types of lignin, which correspond to corresponding Aldehydes and / or phenolic acids leads.

The invention is illustrated below by some application examples, which were carried out in a laboratory ozonization plant, as sketched in Figure 1 of the drawings; Figure 2 of these drawings shows a curve which was obtained according to Example 1 and which shows the development of the ozone concentration at the outlet of the ozonization reactor. The process is carried out in a closed reactor (1), which is equipped with an outlet for the gas enriched with ozone. This is released in the form of small bubbles through a diffuser ( 10 ). The outlet ( 3 ) is equipped with a separator and is intended for the residual gas.

In the examples, oxygen was used, which comes from a bottle ( 5 ) and flows through a conventional ozone generator ( 6 ) (cold plasma reactor).

The output ( 3 ) is connected to a conventional ozone analyzer (analyzer with an iodine-potassium solution) ( 7 ). A branch, which is provided with a valve ( 8 ), allows the gas to be passed to the analyzer ( 7 ) before the treatment in order to examine its composition.

The reactor ( 1 ) contains 1,1,2-trichloro-1,2,2-trifluoro-ethane, which in some examples is mixed with ethanol. This jar is shaken ( 9 ). The reactor is equipped with a sample outlet and an outlet.

example 1

In this example, the lignin used is resin-rich Wood (spruce wood) using that in the paper industry process known under the name "Organocell", which allows, without breaking down pulp, hemicelluloses and to extract lignin from the wood. The average Molar mass of this lignin is of the order of 990; it is essentially of the guaiacol type. His elementary analysis has delivered the following results (percentage by weight):

• - 61.7% carbon
• - 5.6% hydrogen
• - 30% oxygen

This lignin is in the form of a fine, brown powder. 30 g of lignin and 1 liter of 1,1,2-trichloro- 1,2,2-trifluoroethane solution.

The consumption of starting gas (oxygen) is set to 1 liter per minute. The input voltage of the ozone generator ( 5 ) is set so that a corresponding amount of ozone of 20 mg per liter of oxygen is developed, that is 20 milligrams of ozone per minute and liter of solvent. The gas concentration at the reactor outlet ( 1 ) is measured and plotted on the ordinate. The curve of Figure 1 is obtained. The saturation of the bath (indicated by C in the curve) is reached very quickly (approx. 5 minutes). An intermediate phase ( 2 ) or a section with a very slight gradient is then observed, during which the ozone consumption in the reactor can be regarded as very constant. A stable transformation reaction of lignin into vanillin and vanillic acid is achieved. It can be estimated that this reaction takes 1.2 hours in the example (up to point R) .

Then the curve becomes steeper, this shows a decrease in ozone consumption, that is, a decreasing reactivity (area B of the curve): The analyzes have shown that this area corresponds to an oxidation of the vanillin formed to vanillic acid. Depending on the desired products, the reaction is led past point R or stopped.

If 3 hours are exceeded, the analyzes show significantly increased breakdown of vanillin, vanillic acid and of residual lignin with the release of CO₂ in small oxidized molecules. The process is therefore ended before this dismantling begins. After this first series of experiments is carried out under the same conditions a renewed treatment with a contact duration of 2.5 Hours.

The ozonization reactor 1 is then emptied and the suspension is filtered through a frit. A solid residual material is obtained which is analyzed and a liquid phase.

The latter is subjected to distillation until the solvent completely evaporated. This is done with a cooling device recovered.

At the end of the distillation, the rest is made from a viscous There is liquid, dissolved in 0.1 liters of ethanol for cleaning. This cleaning is done with a strongly basic, anionic, "LEWATIT M 504" ion-exchange resin in the form of Chloride.  

Approximately 200 g of resin is used and percolation takes place within 2 hours with little loss. The components bound to the resin mentioned are then solved. by the enriched resin with a aqueous ethanol solution acidified with hydrochloric acid eluted. (Ethanol content: 90%; pH = 2)

The recovered solution is then replaced by high performance Liquid chromatography analyzed. It contains (in alcoholic Milieu solved):

• - 0.5% vanillin in relation to the weight of the used lignins,
• - 0.2% vanillic acid by weight of the used lignin.

The total weight of the recovered components is approximately 0.7% of the starting lignin.

In addition, the solid, recovered residues washed with water. They are examined with infrared spectroscopy and an elementary analysis is made. One poses found that these substances consist of hardly degraded lignin, which contain the following (weight-related portion):

• - 61.5% carbon
• - 5.8% hydrogen
• - 30.9% oxygen

About 70% of the starting material is recovered.
Functionalization studies (formylation, chlorination, alkylation reactions ...) show that the reactivity of this lignin is remarkably higher than that of the starting lignin which has not been subjected to treatment. A few weeks of storage and further examinations show that the activated lignin obtained retains its increased reactivity.

Example 2

The treatment is carried out in the same way as in the example 1 and under the following conditions:

• - starting lignin: identical,  
• - weight of treated lignin: identical,
• - consumption of ozone: identical,
• - Bath consists of a mixture of 1,1,2-trichloro- 1,2,2-trifluoroethane and ethanol, percentage by weight of ethanol: 10%
• - volume of the bath: identical,
• - Duration of treatment: 1.5 hours.

At the end of the treatment, an improved vanillin and Vanillic acid yield solid. You gain about 2.7% (weight percentage) of the original lignin. This improvement can be achieved by gradually dissolving the vanilla and the vanillic acid in ethanol explain the balance the reaction shifted in a favorable direction. It also seems much more of the original lignin in the bathroom to solve, and this has a favorable effect on the reaction. The solid residues are compared to (by weight) 60% of the original lignin recovered. The composition of the activated lignin is exactly identical to that of example 1.

Example 3

This example is carried out under the same conditions as example 2, only the amount of starting lignin in the reactor changed:

15 g, 30 g, 50 g and 100 g.

The following table summarizes the results obtained (with repetition of the result from example 2):  

The delivers in the range of 15 g / 100 g of starting lignin per liter Treatment satisfactory results, the optimum is included 30 g / l.

Below 15 g per liter the dilution is too strong and has one Resulting reduction in yield. At over 100 g per liter the amount of lignin is too large to be even in the water distribute and cause satisfactory ozonization.

Example 4

This example is carried out under the same conditions as example 2, it will be the ethanol ratio in the solution between 10% and 25% changed. The following results were obtained:  

The optimum is at a value of 15%. That is below 10% Solution effect too low to considerably improve the yield; A decrease in the vanillin yield is observed above 25% due to increasing damage to this component or an oxidation of the vanillin and the vanillic acid.

Example 5

This example was carried out under the same conditions As in example 2, only the ozone flow in the bath per minute and changed per liter of bath. The following results were obtained:

Treatment times are very long under 10 milligrams to achieve acceptable yields. You put over 30 milligrams a remarkable percentage of mining compounds.

Example 6

The treatment is carried out in the same way as for the Example 1 under the following conditions:

• - starting lignin: identical,
• - Weight of treated lignin: 15 g
• - Ozone consumption: 22.5 mg / l
• - Bath consists of a mixture of 1,1,2- Trichloro-1,2,2-trifluoroethane and ethanol to 20%.

These conditions are very interesting because they yield vanillic acid of 1% and a vanillin yield of 4.3%, this means a total yield of more than 5% from the used lignin and a recovery of more as 60% reactivated lignin.

Claims (13)

1. A process for the recovery of aldehydes and / or phenolic acids by lignin and ozone, characterized in that

• that lignin is brought into contact with ozone in a solvent bath made from 1,1,2-trichloro-1,2,2-trifluoro-ethane,
• - That aldehydes and / or phenolic acids that have formed are then separated from the solvent and from the solid residual lignin.

2. The method according to claim 1, characterized in that the lignin in the form of powder in 1,1,2-trichloro-1,2,2-trifluoro Ethane bath occurs, with the ozone completely dissolved in the bath mentioned becomes. 3. The method according to claim 2, characterized in that a ozone-containing gas in lignin-containing 1,1,2-trichloro-1,2,2-trifluoro Ethane bath flows in until saturation and beyond. 4. The method according to claim 3, characterized in that the gas enriched with ozone diffuses into the solvent bath, that between 10 and 30 milligrams per minute and liter of solvent Ozone is released. 5. The method according to any one of claims 2, 3 and 4, characterized in that you have an amount of lignin in the range of 15 to 100 g per liter of solvent in the solvent bath. 6. The method according to claim 4 and 5, characterized in that the lignin with the ozone for a period of 1 to 3 hours remains in contact in the solvent bath. 7. The method according to any one of claims 1, 2, 3, 4, 5 and 6, characterized characterized in that a solvent bath made of 1,1,2-trichloro- 1,2,2-trifluoroethane used, which is mixed with alcohol, a solution of the resulting aldehydes and / or phenolic acids  secure; these components are isolated first by filtering the environment to obtain the solid residual lignins, then by distillation for recovery of 1,1,2-trichloro-1,2,2-trifluoroethane and finally through Purification of the alcohol solution and extraction of the aldehydes and / or Phenolic acids. 8. The method according to claim 7, characterized in that one uses a solvent bath that has a weight Contains 10% to 25% alcohol and with 1,1,2- Trichloro-1,2,2-trifluoro-ethane is mixed. 9. The method according to any one of claims 7 and 8, characterized in that the purification of the alcohol solution by percolation over a strongly basic resin to the aldehydes and / or bind the phenolic acids; to these components of to dissolve this resin, an acidified water / alcohol Percolated solution over said resin. 10. The method according to claim 9, characterized in that the Aldehydes and / or phenolic acids by distillation from the water / alcohol Solution can be obtained. 11. The method according to any one of the preceding claims, characterized characterized in that the solid residual lignin is separated off with water washed and recovered for recycling. 12. The method according to any one of claims 1 to 11, characterized in that it can be used for lignin which was obtained from plant material and contains fibers such as Wood, bagasse and straw. 13. The method according to any one of claims 1 to 12, characterized in that it is for parahydroxybenzaldehyde lignin and / or gujakol and / or syringyl can be used to corresponding phenol aldehydes (parahydroxybenzaldehyde, vanillin, Syringylaldehyde) and / or corresponding phenolic acids (parahydroxybenzic acid, Vanillic acid, syringylic acid).