Oxidation of hydrolysis lignin
Abstract Generated abstract
This study examines how the amount of vanadium pentoxide affects the alkaline oxidation of sulfuric-acid hydrolysis lignin and the formation of low-molecular-weight ether-soluble products. Lignin was oxidized with 1 to 180% vanadium pentoxide relative to lignin under fixed alkaline conditions, and the products were separated into alkali-soluble, ether-soluble, and water-soluble fractions, with the ether-soluble material further divided into aldehyde, acid, and phenolic fractions. The results indicate that increasing vanadium pentoxide decreases the yield of alkali-soluble lignin acids, while the maximum yield of ether-soluble products is obtained at about 5% vanadium pentoxide relative to lignin.
Full Text
OXIDATION OF HYDROLYSIS LIGNIN
Report II
OXIDATION WITH VANADIUM PENTOXIDE
L. A. PERSHINA, V. N. KUKSINA, V. P. VASIL’EVA
(Submitted by the Department of Organic Chemistry)
In the oxidation of sulfuric-acid hydrolysis lignin in the presence of oxides and hydrated oxides of metals of variable valence (report 1), we came to the conclusion that vanadium pentoxide significantly (by a factor of more than 2) increases the yield of low-molecular-weight substances soluble in ether.
The aim of the present work is to determine the effect of the amount of vanadium pentoxide on the yield of ether-soluble substances.
There are indications in the literature that, in the oxidation of hydrolysis and other lignins, the highest yields of ether-soluble products are obtained when considerable quantities of oxidizing agent are used [1, 2, 3]. It was natural to assume that, with an increase in the amount of \(V_2O_5\), the yield of ether-soluble products would increase.
A series of experiments was carried out with different amounts of vanadium pentoxide, from 1 to 180% relative to lignin, with 30% caustic alkali, at a hydromodule of 1/10, \(T = 180^\circ\), and a time of 4 hours.
The reaction products were separated into substances soluble in alkali, ether, and water.
The ether-soluble substances are low-molecular-weight compounds, which we separated into aldehydes, acids, and phenols. For this purpose the ether solution was extracted with 10% sodium bisulfite 2–4 times. The bisulfite extract was acidified with \(H_2SO_4\) (1:1), and \(SO_2\) was removed by a stream of carbon dioxide while heating on a water bath for 3 hours. The solution was saturated with sodium chloride and extracted with ether 8 times. The ether extracts were dried over sodium sulfate, the ether was distilled off, and the residue was weighed. To isolate the acid fraction, the ether solution remaining after treatment with sodium bisulfite was extracted four times with an 8% solution of \(NaHCO_3\); the solution was acidified with sulfuric acid and extracted with ether. The same ether solution was treated with 5% caustic sodium, and the phenols were isolated analogously.
The amounts of the initial substances, the yields of substances soluble in alkali and ether, and also the results of their analysis are given in Table 1.
Conclusions
- With an increase in the amount of vanadium pentoxide, the yield of lignin acids soluble in alkali decreases.
Table 1
| No. | Amount of \(V_2O_5\), % relative to lignin | Soluble in alkali, % relative to lignin | Soluble in acetone, % C | Soluble in acetone, % H | Reaction products soluble in ether: from filtrate, % relative to lignin | Reaction products soluble in ether: from precipitate I, % relative to lignin | Reaction products soluble in ether: from precipitate II, % relative to lignin | Reaction products soluble in ether: total | Bisulfite fraction, % | Bicarbonate fraction, % | Alkaline fraction, % |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 180.0 | 0 | — | — | 3.5 | 6.2 | 0 | 9.7 | 13.2 | — | — |
| 2 | 90.0 | 2.0 | — | — | 3.3 | 1.0 | 0 | 4.3 | 10.0 | 5.0 | 10.0 |
| 3 | 50.0 | 3.3 | 61.5 | 4.97 | 6.0 | 1.0 | 0 | 7.0 | 17.0 | 13.5 | 7.0 |
| 4 | 25.0 | 10.0 | — | — | 9.0 | 4.5 | 5.3 | 18.8 | 8.8 | 8.8 | 12.3 |
| 5 | 18.0 | 15.0 | 67.7 | 5.97 | 5.0 | 0.53 | 10.5 | 16.03 | 30.0 | 16.7 | 3.3 |
| 6 | 10.0 | 20.0 | 58.6 | 4.62 | 3.3 | 4.5 | 10.6 | 18.4 | — | — | — |
| 7 | 7.5 | 14.7 | — | — | 4.3 | — | — | — | — | — | — |
| 8 | 5.0 | 21.3 | 66.7 | 5.6 | 16.0 | 3.0 | 18.3 | 37.3 | 3.0 | 3.5 | 8.4 |
| 9 | 4.0 | 30.0 | — | — | 4.0 | 2.0 | 6.7 | 12.7 | — | — | — |
| 10 | 2.5 | 36.0 | 68.5 | 6.3 | 7.0 | 2.0 | 6.0 | 15.0 | 4.6 | 33.0 | 28.0 |
| 11 | 1.0 | 76.0 | 64.6 | 5.5 | 10.0 | 0 | 4.3 | 14.3 | — | — | — |
| 12 | without catalyst | 87.7 | — | — | 3.3 | 0 | 5.0 | 8.3 | 8.0 | 12.0 | 32.0 |
- The greatest yield of ether-soluble products is obtained with an amount of vanadium pentoxide equal to 5% of the weight of the lignin.
References
- J. A. Pearl, Studies of lignin, J. Am. Chem. Soc. 71, 2196, 1949.
- A. D. Grigor'ev. Comparative study of methods for obtaining vanillin from hydrolysis lignin and coniferous-wood sawdust, Proceedings of the Ural Polytechnic Institute, collection 96, 4–7, 1960.
- A. D. Grigor'ev, Z. V. Pushkareva. Preparation of vanillin from coniferous-wood sawdust and hydrolysis lignin using copper oxide, Proceedings of the Ural Polytechnic Institute, collection 96, 8–18, 1960.