RU2671161C1 - Method of wood chemical processing - Google Patents

Abstract

FIELD: technological processes.SUBSTANCE: present invention relates to a process for the preparation of fine products – vanillin, syringaldehyde and cellulose. Method of chemical processing of wood includes acid prehydrolysis, followed by catalytic oxidation of the feedstock with oxygen in an alkaline medium at elevated temperature and pressure in vanillin, syringaldehyde and cellulose. In the catalytic oxidation step, oxygen is fed into the reactor in 2 to 5 separate portions of 8–22 % by weight, based on lignin, at regular intervals until the maximum concentration of aromatic aldehydes is reached.EFFECT: technical result of the invention consists in reducing the consumption of alkali and oxygen during the catalytic oxidation of lignocellulose to aromatic aldehydes and cellulose.1 cl, 1 tbl, 8 ex

Description

The invention relates to methods for producing products of fine organic synthesis of vanillin (B, 4-hydroxy-3-methoxybenzaldehyde), lilac aldehyde (CA, 4-hydroxy-3,5-dimethoxybenzaldehyde) and cellulose. Vanillin is widely used in the confectionery, pharmaceutical and perfumery and cosmetic industries. Lilac aldehyde can serve as a convenient starting compound for the synthesis of 3,4,5-trimethoxybenzaldehyde - raw materials for the production of various pharmaceutical preparations: trimethoprim, biseptol, bactrim.

A known method of producing vanillin and lilac aldehyde by oxidation of aspen wood with copper hydroxide or nitrobenzene [Pepper J.M. Casselman, B.W. Karapally J.C. Lignin oxidation. Preferential use of cupric oxide. Can. J. Chem., 1967, 45 (23), 3009-3012].

The main disadvantage of this method is the high cost of expensive oxidizing agents, as well as the difficulties in purifying B and SA from by-products of nitrobenzene reduction.

A known method of producing vanillin and lilac aldehyde by catalytic oxidation of wood of deciduous trees (oak, beech, hornbeam) with oxygen [Dardelet S., Froment P., Lacoste N., Robert A. Aldehyde syringique. Possibilites de production a partir de bois feuillus. Revue A.T.I.P., 1985, v. 39, No. 5, p. 267-274].

The main disadvantage of the method is the low yields of the target products due to the tendency of hardwood lignins to condensate.

A known method of chemical processing of coniferous wood by catalytic oxidation of raw materials in an alkaline environment at 170 ° C in vanillin and cellulose, followed by its acid hydrolysis [RU 2158192, publ. 10.27.2000].

The main disadvantage of this method is the high consumption of alkali (30 or more kg per kg of vanillin). This disadvantage is caused, in particular, by the oxidation of hemicelluloses, which requires an additional consumption of alkali and oxygen.

A known method of processing wood of small-leaved species into products of fine organic synthesis (vanillin, lilac aldehyde and levulinic acid) by catalytic oxidation by oxygen in an alkaline environment in the presence of copper hydroxide as a catalyst [RU 2119427, C1, 09/27/1998].

The main disadvantage of this method is the high consumption of alkali (12 kg per kg of aldehydes). This disadvantage is due to the fact that aspen and, moreover, birch contain a significant amount of hemicelluloses (up to 30 wt.%), And upon receipt of aromatic aldehydes they are oxidized, which requires an additional consumption of alkali and oxygen.

The closest in essence to the claimed method is a method of chemical processing of wood by acid prehydrolysis and subsequent catalytic oxidation of raw materials with oxygen in an alkaline environment at 170 ° C in vanillin, lilac aldehyde and cellulose [RU 2219048, publ. December 20, 2003]. Preliminary acid hydrolysis of wood reduces alkali consumption by removing hemicelluloses.

However, the main disadvantage of this method is the high consumption of alkali (11.5 kg per kg of aldehydes) and oxygen. The mentioned drawback is due to the fact that in the process of oxidation, oxygen is consumed not only for the formation of target aldehydes, but also for deep oxidation to carbon dioxide and carboxylic acids. These products bind alkali, which leads to a significant unproductive expenditure.

The objective of the invention is to reduce the consumption of alkali in the processing of wood into vanillin, lilac aldehyde and cellulose.

The technical result of the invention is to reduce the consumption of alkali and oxygen in the process of catalytic oxidation of lignocellulose to aromatic aldehydes and cellulose.

The technical result is achieved by the fact that in the method of chemical processing of wood by acid prehydrolysis and subsequent catalytic oxidation of lignocellulose with oxygen in an alkaline medium to vanillin, lilac aldehyde and cellulose, according to the claimed invention, oxygen is supplied to the reactor during the oxidation process in 2-5 separate portions of 8- 22 mass. % calculated on the lignin of the raw material at regular intervals until the maximum concentration of aromatic aldehydes is reached.

The studies showed that the noted drawback of the known method, namely, high alkali consumption, can be eliminated by supplying oxygen to the reactor not in a continuous stream, maintaining its constant pressure, but in small portions (2-5 portions of 8-22% of the oxygen volume, absorbed in a known manner). As a result, the consumption of alkali per kilogram of aldehydes is reduced by 10-37% compared with the prototype.

Common features of the proposed method and prototype are:

- carrying out the process of acid prehydrolysis of wood;

- the process of oxidation in an alkaline environment with molecular oxygen in the presence of a catalyst under pressure at elevated temperature in aromatic aldehydes and cellulose.

A distinctive feature of the claimed invention lies in the fact that oxygen is supplied to the reactor during the process in 2-5 separate portions of 8-22 wt.% Per lignin at regular intervals until the maximum concentration of aromatic aldehydes is reached.

Due to the distinguishing feature in the claimed invention, the consumption of alkali (10-37%) and oxygen is significantly reduced compared with the known method for the catalytic oxidation of lignocellulose to aromatic aldehydes and cellulose.

The method is confirmed by specific examples.

Example 1. For the experiment used sawdust of birch wood, a fraction of 3-5 mm The wood contained lignin - 19.6 wt.%, Cellulose - 45 wt.%, Pentosans - 27 wt.%.

Prehydrolysis of 9 g of wood was carried out in a stainless steel reactor 12Kh18N10T with a capacity of 100 ml at 120 ° C for 30 min with 0.5% sulfuric acid, a water module of 1:10. The remaining wood was washed with water and dried, its yield was 71 wt.% Based on the used wood.

The oxidation of the wood residue after prehydrolysis (the content of lignin in it is 1.8 g) was carried out in a shake reactor made of stainless steel 12X18H10T with a capacity of 100 ml. The reactor is equipped with thermostatic control systems, controlled supply and registration of the absorbed oxygen volume and regulation of the working pressure in the autoclave.

6.0 g of prehydrolyzed wood (lignocellulose, 1.8 g of lignin) in 60 ml of a solution containing 100 g / l NaOH (the amount of alkali loaded is 6.0 g) with the addition of 4.0 g of copper pentahydrate as a catalyst, was charged argon was fed into the reactor to a pressure of 0.2 MPa and heated to 160 ° C.

At the time of heating up the reactor, 180 mg (10 wt% calculated on lignin) of oxygen from a calibrated tank was supplied to it. The next four 180 mg portions of oxygen were fed sequentially every 5 minutes after the previous portion. The reactor was held for 5 minutes after the fifth portion of oxygen and cooled.

The reaction mass was filtered, the filtrate was neutralized with 30% sulfuric acid to pH 3-4 and extracted twice with an equal volume of ethyl acetate. The combined extract was evaporated and analyzed by GLC. The result is: vanillin 0.18 g, lilac aldehyde 0.50 g. The total yield of vanillin and lilac aldehyde is 38 wt.% Calculated on the lignin of the source wood.

The solid residue (cellulosic residue) was washed with a small amount of 5% sulfuric acid, the filtrate copper sulfate solution was used as a catalyst in the following experiments.

The yield of acid washed cellulose residue was 3.78 g or 42 wt.% Based on the source wood.

As a result of the experiment, the following was calculated for wood lignin: vanillin - 0.18 g (10%); lilac aldehyde - 0.50 g (27.8%).

Alkali consumption in terms of kilogram of vanillin and lilac aldehyde was 8.82 kg (in the prototype - 11.5 kg), oxygen consumption - 1.32 kg / kg (see table).

Example 2. The experiment was carried out, as in example 1, but as a raw material used 8.9 g of aspen sawdust. 4.8 g of alkali were charged into the oxidation reactor, oxygen was fed into the reactor in two portions of 22 wt.% Per lignin (0.8 g in total) after 20 minutes.

The yield of acid washed cellulose residue was 3.40 g, or 38.2 wt.%, Based on the starting wood.

As a result of the experiment, the following was calculated for wood lignin: vanillin — 0.18 g (10 wt.% Based on wood lignin); lilac aldehyde - 0.40 g (22.2 wt.% calculated on wood lignin).

Alkali consumption in terms of kilogram of vanillin and lilac aldehyde was 8.28 kg, oxygen consumption was 1.38 kg / kg.

Example 3. The experiment was carried out, as in example 1, but 7.28 g of pine sawdust was used as raw material. 3.6 g of alkali was charged into the oxidation reactor, oxygen was fed into the reactor in three portions of 11 wt.% Per lignin (0.6 g in total) after 10 minutes.

The yield of acid washed cellulose residue was 3.12 g, or 42.8 wt.%, Calculated on the source wood.

As a result of the experiment, obtained based on wood lignin: vanillin - 0.36 g (20 wt.% Based on wood lignin).

Alkali consumption in terms of kilogram of vanillin was 10.0 kg, oxygen consumption was 1.67 kg / kg.

Example 4. The experiment was carried out, as in example 1, but 6.0 g of fir sawdust was used as raw material. 3.6 g of alkali was charged into the oxidation reactor, oxygen was fed into the reactor in four portions of 8 wt.% Per lignin (0.6 g in total) after 7 minutes.

The yield of acid washed cellulosic residue was 2.30 g or 38.3 wt.% Based on the source wood.

As a result of the experiment, obtained per wood lignin: vanillin - 0.38 g (21.1 wt.% Per wood lignin).

Alkali consumption in terms of kilogram of vanillin was 9.47 kg, oxygen consumption was 1.53 kg / kg.

Example 5. The experiment was carried out, as in example 1, but 6.5 g of spruce sawdust was used as raw material. 3.6 g of alkali was charged into the oxidation reactor, oxygen was fed into the reactor in three portions of 11 wt.% Per lignin (0.6 g in total) after 10 minutes.

The yield of acid washed cellulose residue was 2.93 g, or 45.1 wt.%, Based on the starting wood.

As a result of the experiment, obtained per wood lignin: vanillin - 0.35 g (19.4 wt.% Per wood lignin).

Alkali consumption in terms of kilogram of vanillin was 10.3 kg, oxygen consumption was 1.71 kg / kg.

Example 6. The experiment was carried out, as in example 1, but 6.6 g of larch sawdust was used as raw material. 3.6 g of alkali were charged into the oxidation reactor, oxygen was fed into the reactor in three portions of 10 wt.% Per lignin (0.54 g in total) after 10 minutes.

The yield of acid washed cellulosic residue was 2.09 g or 31.7 wt.% Based on the starting wood.

As a result of the experiment, obtained per wood lignin: vanillin - 0.40 g (22.2 wt.% Per wood lignin).

Alkali consumption in terms of kilogram of vanillin was 9.0 kg, oxygen consumption was 1.35 kg / kg.

Example 7. The experiment was carried out, as in example 1, but 9.0 g of birch sawdust was used as raw material. 5.0 g of alkali was charged into the oxidation reactor, oxygen was fed into the reactor in three portions of 15 wt.% Per lignin (0.81 g in total) after 10 minutes.

The yield of acid washed cellulose residue was 3.68 g, or 40.9 wt.%, Based on the starting wood.

As a result of the experiment, the following was calculated for wood lignin: vanillin — 0.14 g (7.8 wt.% Based on wood lignin); lilac aldehyde - 0.44 g (24.4 wt.% calculated on wood lignin).

Alkali consumption in terms of kilogram of vanillin and lilac aldehyde was 8.6 kg, oxygen consumption was 1.40 kg / kg.

Example 8. The experiment was carried out, as in example 1, but 9.0 g of birch sawdust was used as raw material. 5.0 g of alkali were charged into the oxidation reactor, oxygen was fed into the reactor in four portions of 8 wt.% Per lignin (0.58 g in total) after 7 minutes.

The yield of acid washed cellulosic residue was 3.75 g or 41.7 wt.% Based on the starting wood.

As a result of the experiment, the following was calculated for wood lignin: vanillin - 0.20 g (11.1 wt.% Based on wood lignin); lilac aldehyde - 0.49 g (27.2 wt.% calculated on wood lignin).

Alkali consumption in terms of kilogram of vanillin and lilac aldehyde was 7.5 kg, oxygen consumption was 0.84 kg / kg.

Thus, in the claimed invention, the consumption of alkali is reduced in comparison with the prototype by 10-37% (see table).

The consumption of alkali and oxygen during the catalytic oxidation of prehydrolyzed wood of various species with oxygen to vanillin, lilac aldehyde and cellulose

Notes: * the mass of lignin loaded into the reactor in all experiments was 1.8 g. ** the number of portions of oxygen supplied to the reactor and its amount, in mass. % calculated on lignin, *** alkali consumption, in kg per kg of aldehydes.

Claims (1)

A method of chemical processing of wood, including acid prehydrolysis followed by catalytic oxidation of the feed with oxygen in an alkaline environment at elevated temperature and pressure in vanillin, lilac aldehyde and cellulose, characterized in that at the stage of catalytic oxidation, oxygen is fed into the reactor in 2-5 separate portions of 8- 22 wt.% Calculated on lignin at regular intervals until the maximum concentration of aromatic aldehydes is reached.