Preparation of Cation Exchangers Based on Hydrolysis Lignin
Abstract Generated abstract
This study examines the use of hydrolysis lignin, a large-scale waste product of the alcohol-hydrolysis industry, as a raw material for preparing cation-exchange materials. Air-dry lignin was sulfonated with concentrated sulfuric acid under varied temperatures and heating times, and the resulting sulfolignins were evaluated for static exchange capacity toward sodium ions, sulfur content, swelling, and mechanical strength. The experiments indicate that elevated sulfonation temperatures, especially 130 to 220 °C, produce materials that are sparingly soluble or insoluble in dilute alkali and acid solutions and have exchange capacities of about 3.7 to 4.0 mg-eq/g with adequate mechanical strength. The work suggests a possible chemical route for converting inexpensive hydrolysis lignin into useful ion-exchange sorbents.
Full Text
ON THE PREPARATION OF CATION EXCHANGERS BASED ON HYDROLYSIS LIGNIN
F. Z. Gorfinkel, O. N. Kuzmina
(Submitted by the organic section of the scientific seminar of the CTF)
Lignin is a significant waste product of the alcohol-hydrolysis industry.
Wood contains 25–31% lignin. Unlike cellulose, lignin still has no practical application; only an insignificant portion of it is burned together with coal, while the remaining mass goes to waste dumps. At the hydrolysis plants of the Soviet Union, 400,000 tons of lignin accumulate annually (calculated as absolutely dry material). By 1965 this quantity will reach 1,300,000 tons.
The economics of production in the alcohol-hydrolysis industry now requires the search for ways of utilizing hydrolysis lignin based on its chemical processing. The aim of the present work is to study the possibility of synthesizing ion-exchange resins (cation exchangers) from hydrolysis lignin. Cation exchangers—solid natural or artificial materials, practically insoluble in water and organic solvents, capable of exchanging the cations or anions contained in them for other ions present in solution—are now finding broad and varied application (for desalination of water, recovery of valuable metals from various wastes, in the sugar industry, as catalysts in the synthesis of organic compounds, etc. [1]).
The first part of our investigation consisted in enhancing the adsorption properties of hydrolysis lignin by sulfonating it with concentrated sulfuric acid under various conditions. In its structure, lignin is a high-molecular compound of aromatic character containing phenolic hydroxyls.
In the opinion of many investigators, the principal structural unit of lignin is coniferyl alcohol, which, according to our assumption, should readily undergo sulfonation, thereby contributing to an increase in the adsorption properties of hydrolysis lignin. We carried out sulfonation of hydrolysis lignin by the action of concentrated sulfuric acid of specific gravity 1.84 on air-dry lignin at various temperatures (20°, 40, 65, 95, 130, 165, 175, and 220°) and heating times (30′, 80′, 2, 3, 5 hours).
Experimental Part
In a 100 ml round-bottom flask equipped with a reflux air condenser, 10 g of air-dry hydrolysis lignin and 40–50 g of concentrated sulfuric acid of specific gravity 1.84 were placed.
The mixture was thoroughly stirred and heated in a glycerin bath at temperatures of 20°, 40°, 65°, 95°, 130°, 165°, 175°, and 220°.
The resulting sulfolignins were washed with distilled water until the wash waters gave a negative reaction for the ion \(\mathrm{SO_4^{II}}\), and were dried at a temperature of 16–18°. In the samples obtained, the static exchange capacity, in mg-eq/g, for the sodium ion was determined; in some tests the swelling and mechanical strength were determined, and the sulfur content was determined by the microchemical method according to Korshun and Gelman.
The static exchange capacity was determined in the following manner.
Table
| No. | Lignin | \(\mathrm{H_2SO_4}\) | Reaction temperature, °C | S.E.C. | Heating duration, minutes | Heating duration, hours | Color of solution | Swelling | Mechanical strength, % | Sulfur content, % |
|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 10 | — | 16—18° | 2,2 | — | — | brown | 0,4 | ||
| 2 | 10 | 50 | 20° | 2,95 | — | 2 | ” | 5,26 | ||
| 3 | 10 | 50 | 20 | 3,17 | — | 5 | ” | 5,76 | ||
| 4 | 10 | 40 | 40 | 3,12 | — | 2 | ” | |||
| 5 | 10 | 50 | 40 | 3,17 | — | 2 | ” | |||
| 6 | 10 | 50 | 40 | 3,00 | — | 5 | ” | |||
| 7 | 10 | 40 | 65 | 3,00 | 30 | — | ” | |||
| 8 | 10 | 40 | 65 | 3,82 | — | 3 | yellow | |||
| 9 | 10 | 40 | 65 | 3,75 | — | 5 | ” | 3,46 | ||
| 10 | 10 | 40 | 95 | 3,47 | 30 | — | ” | |||
| 11 | 10 | 40 | 95 | 3,43 | 80 | — | ” | |||
| 12 | 10 | 40 | 95 | 3,50 | — | 2 | ” | 87,2 | ||
| 13 | 10 | 40 | 95 | 3,52 | — | 3 | ” | |||
| 14 | 10 | 40 | 95 | 3,77 | — | 5 | ” | |||
| 15 | 10 | 50 | 95 | 3,45 | 30 | — | ” | |||
| 16 | 10 | 50 | 95 | 3,81 | — | 5 | ” | |||
| 17 | 10 | 50 | 130 | 3,72 | — | 3 | almost colorless | 1,2 | 88,5 | |
| 18 | 10 | 50 | 130 | 3,85 | — | 5 | ” | |||
| 19 | 10 | 50 | 165 | 3,65 | — | 3 | colorless | 1,4 | ||
| 20 | 10 | 50 | 165 | 3,69 | — | 5 | ” | |||
| 21 | 10 | 50 | 175 | 3,75 | — | 3 | ” | |||
| 22 | 10 | 50 | 175 | 3,75 | — | 5 | ” | 86,7 | 3,24 | |
| 23 | 10 | 50 | 220 | 4,00 | — | 3 | ” | |||
| 24 | 10 | 50 | 220 | 4,00 | — | 5 | ” |
A weighed portion of dried sulfonated lignin, passed through sieves with openings of 0.5 and 0.25 mm, was placed in a flat-bottomed flask, 50 ml of 0.1 N alkali solution (NaOH) was added, the flask was stoppered, and it was left for 24 hours with periodic shaking. At the end of the experiment the cation exchanger was separated from the solution by filtration, and part of the solution was titrated with 0.1 N sulfuric acid solution in the presence of phenolphthalein indicator. The static exchange capacity was determined from the difference between the amount of acid consumed in titrating the solution from the control experiment and that from the sample, and was expressed in mg-eq of sorbed ion per 1 g of sulfonated lignin. Mechanical strength was determined by the method for testing the granulometric stability of swollen sorbent grains [2]. Swelling was determined by the method recommended by Trostyanskaya.
The data obtained are presented in the table (see p. 42).
Conclusions
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The possibility has been demonstrated of sulfonating sulfuric-acid hydrolysis lignin with concentrated $H_2SO_4$ of specific gravity 1.84 at temperatures of $(20^\circ, 40^\circ, 65^\circ, 95^\circ, 130^\circ, 165^\circ, 175^\circ, 220^\circ)$; however, only at elevated temperature $(130–220^\circ)$ are sulfolignins obtained that are very sparingly or completely insoluble in dilute alkali and acid solutions.
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From the inexpensive raw material sulfuric-acid hydrolysis lignin, by sulfonating it with concentrated sulfuric acid, cation exchangers can be obtained with sufficient exchange capacity (3.7–4.0) and mechanical strength.
LITERATURE
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K. M. Saladze, A. B. Pankov, V. S. Titov. Ion-exchange high-molecular compounds. State Scientific-Technical Publishing House of Chemical Literature, 1960.
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N. B. Trostyanskaya. Ion-exchange resins. Ion Exchange. Collection of articles, Publishing House of the Academy of Sciences of the USSR, 29, 1959.