Oxidation of hydrolysis lignin
Abstract Generated abstract
This study examines alkaline oxidation of hydrolysis lignin from cottonseed hulls, a lignin distinguished from wood lignins by its low methoxyl content, in the presence of vanadium pentoxide. Technical lignin and dimethyl sulfate methylated lignin were oxidized in sealed stainless steel ampoules under varied temperatures, alkali levels, and catalyst amounts, and the ether soluble products were separated into aldehyde, acidic, and phenolic fractions. The highest ether soluble yield from untreated lignin was 34.3% at 260°C for 4 hours with 33% sodium hydroxide and 5% vanadium pentoxide, while methylated lignin under comparable conditions gave about 50% ether soluble products. Chromatographic analysis detected vanillic and protocatechuic acids, pyrocatechol, and guaiacol among products from untreated lignin, and vanillic acid and guaiacol from methylated lignin.
Full Text
OXIDATION OF HYDROLYSIS LIGNIN
Communication IV. Oxidation of hydrolysis lignin from cottonseed hulls
L. A. PERSHINA, I. I. KLOCHAN, V. P. SHVACHEVA
(Presented by the scientific-methodological seminar of the Chemical-Engineering Faculty)
The lignin of cottonseed hulls differs sharply in its composition from wood lignins. It contains considerably fewer methoxyl groups; consequently, the content of aromatic elements usual for wood lignins is also lower. The lignin of cottonseed hulls includes elements containing aromatic nuclei of syringyl and guaiacyl structure, since vanillin and syringaldehyde were found in the products of oxidation with nitrobenzene [1].
Previously [3, 4] we carried out the oxidation of hydrolysis lignin of woody species in an alkaline medium in the presence of vanadium pentoxide.
The subject of the present work was the study of the oxidation of hydrolysis lignin from cottonseed hulls, and of the influence of the amount of vanadium pentoxide and the temperature of preliminary methylation of the lignin on the yield of ether-soluble substances.
Experimental part
Technical hydrolysis lignin from the Andizhan plant was extracted first with hot water for three hours, and then with an ether-benzene mixture for five hours.
Analysis data:
| No. | Component | Content |
|---|---|---|
| 1. | Moisture | 5.5% |
| 2. | Ash content | 2.4% |
| 3. | Lignin content | 84.5% |
| 4. | Carbon | 61.4% |
| 5. | Hydrogen | 4.9% |
| 6. | Methoxyl groups | 3.35% |
| 7. | Hydroxyl groups | 7.2% |
| 8. | Carboxyl groups | 3.1% |
Methylated lignin was obtained from hydrolysis lignin of cottonseed hulls. To 5 g of hydrolysis lignin, portions of 100 ml of 10% sodium hydroxide and 30 g of dimethyl sulfate were added. The reaction mixture was heated in a water bath (bath temperature 60°C) for 10 hours. The lignin was then filtered off, washed with a weak alkaline solution and several times with water.
Methylated hydrolysis lignin contains 5.7% hydroxyl groups and 14.9% methoxyl groups.
Vanadium pentoxide was obtained from reagent-grade (“ch.d.a.”) \(NH_4VO_3\) [2].
The oxidation was carried out in ampoules made of stainless steel \(1 \times 18N9T\), 20 mm in diameter and 160 mm high.
Weighed portions of lignin, alkali, vanadium pentoxide, and water were loaded into the ampoules, which were placed in a rotating autoclave.
The oxidation of cotton-husk hydrolysis lignin was carried out in the presence of various amounts of vanadium pentoxide and alkali, at different temperatures, for 4 hours. The hydromodule was \(1 : 10\). The oxidation of methylated cotton-husk hydrolysis lignin was carried out at \(260^\circ C\) for 4 hours in the presence of 33% caustic soda, calculated on the lignin charge, and various amounts of vanadium pentoxide.
The reaction mixture was treated by the method described by us in communications I and II [3, 4].
The quantities of the initial reagents, the conditions, and the yields of the reaction products are given in Tables 1 and 2.
Table 1
Oxidation of hydrolysis lignin
| No. | Lignin, g | NaOH, g | \(V_2O_5\), g | Temperature, °C | Alkali-soluble products: yield, % of lignin | Ether-soluble products: from precipitate I, % of lignin | Ether-soluble products: from precipitate II, % of lignin | Ether-soluble products: from filtrate, % of lignin | Total |
|---|---|---|---|---|---|---|---|---|---|
| 1 | 2.0 | 0.66 | 0.1 | 150 | 1.03 | 0 | 0 | 1.6 | 1.6 |
| 2 | 2.0 | 0.66 | 0.1 | 180 | 58.1 | 0 | 1.3 | 3.44 | 4.74 |
| 3 | 2.0 | 0.66 | 0.1 | 220 | 53.6 | 0 | 4.3 | 4.96 | 9.26 |
| 4 | 2.0 | 0.66 | 0.1 | 260 | 23.3 | 0 | 10.0 | 24.3 | 34.3 |
| 5 | 2.0 | 0.66 | 1.0 | 260 | 21.5 | 0 | 8.5 | 18.5 | 27.0 |
| 6 | 2.0 | 0.66 | 1.0 | 260 | 2.0 | 0 | 4.0 | 29.0 | 33.0 |
| 7 | 2.0 | 1.04 | 0.1 | 260 | 2.0 | 5.0 | 13.5 | 15.0 | 33.5 |
| 8 | 2.0 | 1.4 | 1.0 | 260 | 1.0 | 10.0 | 5.0 | 16.0 | 31.0 |
Table 2
Oxidation of methylated hydrolysis lignin
| No. | Amount of \(V_2O_5\), % of lignin | Alkali-soluble products: yield, % of lignin | Ether-soluble products: from precipitate I, % of lignin | Ether-soluble products: from precipitate II, % of lignin | Ether-soluble products: from filtrate, % of lignin | Total |
|---|---|---|---|---|---|---|
| 1 | 0 | 19.2 | 2.7 | 10.33 | 11.0 | 24.03 |
| 2 | 5.0 | 8.03 | 6.0 | 23.2 | 21.0 | 50.2 |
| 3 | 6.25 | 8.05 | 0.0 | 19.79 | 30.6 | 50.15 |
The greatest yield of ether-soluble substances (34.3%) was obtained in the oxidation of cotton-husk hydrolysis lignin under the following conditions: temperature 260°C, time 4 hours, 33% caustic soda based on the lignin charge, 5% vanadium pentoxide, hydromodule 1:10. Under these conditions, hydrolysis lignin methylated with dimethyl sulfate is oxidized with the formation of 50.2% ether-soluble substances.
The substances soluble in ether were separated into aldehyde, acidic, and phenolic fractions, the yields of which are given in Table 3.
Table 3
| No. | Lignin | Aldehyde fraction, % of lignin | Acidic fraction, % of lignin | Phenolic fraction, % of lignin |
|---|---|---|---|---|
| 1 | Hydrolysis lignin of cotton husks | 2.37 | 14.3 | 9.5 |
| 2 | Methylated hydrolysis lignin of cotton husks | 1.02 | 7.17 | 24.8 |
By the methods of paper and thin-layer chromatography, vanillic and protocatechuic acids were detected in the acidic fraction obtained upon oxidation of hydrolysis lignin; upon oxidation of the methylated lignin—vanillic acid. In the phenolic fraction, in the first case pyrocatechol and guaiacol were detected; in the second—guaiacol.
REFERENCES
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A. F. Semechkina, N. N. Shorygina. Study of the lignin of cotton-seed hulls, ZhOKh, issue 1, 1958.
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Yu. V. Karyakin, I. I. Anilov. Pure Chemical Reagents, Goskhimizdat, 1953.
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L. A. Pershina, V. P. Vasil’eva. Oxidation of hydrolysis lignin. I communication, Izv. TPI, vol. 136, 1965.
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L. A. Pershina, V. N. Kuksina, V. P. Vasil’eva. Oxidation of hydrolysis lignin. II. Communication, Izv. TPI, vol. 136, 1965.