RU2525416C2 - Method of producing sorbent for extracting mercury compounds from aqueous solutions - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to production of sorbents for extracting mercury compounds from aqueous solutions Disclosed is a method of producing a sulphur-containing sorbent which includes polycondensation of sodium polysulphide with an organochlorine compound on the surface of petroleum coke particles. The organochlorine compound used is 1,4-dichlorobutyne-2.

EFFECT: method enables to obtain a sorbent with high mercury activity.

1 tbl, 11 ex

Description

The invention relates to the field of industrial ecology and specifically relates to a method for producing a sorbent for the extraction of mercury compounds from aqueous solutions, which can be used to purify mercury-containing waste and natural waters.

Despite its high toxicity, mercury and many of its compounds are widely used in various industries [1]. A steady decrease in the proportion of mercury used in the chlorine industry is observed against the background of an increase in the total amount of use of this element in connection with the expansion of the scope of its use in measuring instruments, electronic lamps, switches, relays and batteries [1, 2]. Due to the high microbiological activity, mercuric chloride and other inorganic mercury compounds have been used in medicine for many decades. The fungicidal properties of mercuric chloride contributed to its widespread use to protect plants from diseases [3].

The study of various organic compounds of mercury showed that by the strength of the bactericidal and fungicidal effects, they significantly exceed the inorganic compounds of this metal and chemical compounds of almost all other classes. Some organic derivatives of mercury have a favorable chemotherapeutic index, that is, the concentration of a substance that causes the death of pathogens is many times less than the concentration dangerous to plants, animals and humans [3]. Obtaining almost all mercury-containing pesticides is based on the use of various mercury salts (mercuric chloride, mercury sulfate, phosphate, acetate, etc.). However, the use of mercury compounds in agriculture contributes to the accumulation of this element in environmental objects, especially in water bodies [4]. The use of mercury compounds as catalysts also contributes to the formation of mercury-containing wastewater.

Mercury, like other heavy metals, belongs to thiol poisons, and in the tissues of organisms, mercury ions (into which metallic mercury are previously converted) combine with molecules containing SH groups, including protein macromolecules [5]. Various general approaches are used to remove mercury and its compounds from aqueous solutions: reagent treatment, flotation purification methods, the use of coagulants, ultrafiltration, biochemical methods, and membrane methods [6].

The most applicable and effective methods for the extraction of mercury compounds from aqueous solutions are sorption methods [7]. Commonly used carbon and ion-exchange sorbents have low efficiency with respect to mercury ions. Therefore, in this direction, studies are constantly being conducted to modify the known and the creation of new adsorbents.

A method is described for extracting mercury from solutions using silica gel as an adsorbent, treated with a mixture of petroleum organosulfur compounds with a molecular weight of 180-250, with a final sulfur content in the sorbent of 0.1-1.0% by weight. [8]. However, this sorbent has low chemical stability, especially in acidic environments. In addition, its composition is difficult to regulate.

To extract mercury, a method is described for producing an organo-mineral adsorbent obtained from spent oil refining zeolite by impregnating it with a solution of furfural with acid tar followed by carbonization with carbon dioxide (800 ± 10 ° С) and activation with water vapor (800 ± 10 ° С) [9] . The process of producing the sorbent is multi-stage, requires special equipment, the resulting sorbent has a not very high mercury activity (16.6 mg / g).

A known sorbent for the extraction of mercury (II) compounds obtained from silica gel by modifying it with an organosilicon monomer - bis-N, N '- (triotoxysilylpropyl) thiourea [10]. However, obtaining a sorbent requires the use of expensive reagents, and the resulting sorbent has low efficiency (36-40 mg / g).

The polycondensation products of functional organosilicon monomers, for example (3-thioacetamidopropyl) triethoxysilane, are used as the sorbent [11]. The statistical sorption capacity of the sorbent is 128-400 mg / g, however, an expensive and scarce monomer is required to obtain the sorbent.

Polyethylene monosulfide obtained by polycondensation of dichloroethane and sodium sulfide effectively absorbs mercury (up to 450 mg / g) [12]. This adsorbent is effective only for very acidic solutions (0.1 or 1 M HNO ₃ solution). However, on the surface of the sorbent there is a disproportionation of nitric acid nitrous mercury with the formation of metallic mercury. This is due to the low content of sulfur atoms in the monosulfide sorbent. An increase in sulfur content due to the lengthening of the sulfide chain leads to the formation of viscous polymers - thiocols, which cannot be used as sorbents.

Closest to the proposed technical solution is a method for producing sulfur-containing sorbents for wastewater treatment from heavy metals, which involves polycondensation of sodium polysulfide Na ₂ S _n obtained from elemental sulfur and sodium hydroxide in an aqueous solution in the presence of hydrazine hydrate, with waste from the production of epichlorohydrin, containing 1,2,3-trichloropropane, on the surface of fine particles of petroleum coke [13] (prototype). The sorbent is obtained in the form of granules, however, its activity with respect to mercury ions is not high enough and amounts to 152 mg per 1 g of sorbent.

The present invention provides a method for producing a sorbent for the extraction of mercury compounds from aqueous solutions having a significantly higher adsorption activity. The proposed method consists in the polycondensation of sodium polysulfide on the surface of the particles of petroleum coke with 1,4-dichlorobutin-2, which can be represented by the following scheme:

1. Obtaining sodium polysulfide

2nS + 4 NaOH + N ₂ H ₄ · H ₂ O → 2Na ₂ S _n + N ₂ + 5H ₂ O, n = 2-3

на поверхности частиц нефтекокса2. Adsorption of anions $$S_n^{2-}$$

on the surface of petroleum coke particles

3. Polycondensation of polysulfide with 1,4-dichlorobutin-2

During polycondensation, the surface of Neftecox particles is coated with a layer of sulfur-containing polymer with polysulfide fragments -S _n - and triple bonds -C≡C-.

The sorbent is obtained in the form of particles of irregular shape of brown color with an average size of 1-1.5 mm.

An essential distinguishing feature of the proposed method is the use of organochlorine components for polycondensation - 1,4-dichlorobutin-2, which has not previously been used to obtain sulfur-containing sorbents of this type. In addition to the two chlorine atoms that provide polycondensation, dichlorobutin-2 contains a triple bond, the behavior of which under these reaction conditions is not predictable. However, the presence of triple bonds in the resulting sorbent creates additional conditions for the coordination of mercury ions and, possibly, this determines a significant increase in sorption activity in comparison with other sulfur-containing sorbents. 1,4-Dichlorobutin-2 is an available monomer derived from acetylene, formaldehyde and hydrogen chloride.

частично адсорбируются на поверхности нефтекокса. В поликонденсации участвуют адсорбированные ионы $$S_n^{2-}$$

, так и ионы, остающиеся в растворе. Коричневый цвет образующегося полимерного сорбента говорит о том, что макромолекулы полностью покрывают поверхность нефтекокса. Масса используемого нефтекокса определялась из соотношения нефтекокс: едкий натр (используемый для приготовления раствора Na₂Sn) и составляла 1:3-4. Величина n в полисульфидной цепочке Sn составляет от 2 до 3 и определяется соотношением NaOH: S. Увеличение длины полисульфидной цепочки n>3 не способствует повышению сорбционной активности (наблюдается даже ее уменьшение), а снижение n<2 также приводит к уменьшению сорбционной активности.Neftecox particles ≤0.15 mm in size were used as polycondensation centers. Neftecox is placed in a solution of sodium polysulfide, while the anions $$S_n^{2-}$$

partially adsorbed on the surface of petroleum coke. Adsorbed ions participate in polycondensation $$S_n^{2-}$$

, and ions remaining in solution. The brown color of the resulting polymer sorbent indicates that the macromolecules completely cover the surface of the petroleum coke. The mass of neftecox used was determined from the ratio of neftecox: sodium hydroxide (used to prepare the Na ₂ Sn solution) and was 1: 3-4. The n value in the polysulfide chain of Sn is from 2 to 3 and is determined by the ratio of NaOH: S. An increase in the length of the polysulfide chain n> 3 does not contribute to an increase in sorption activity (even a decrease is observed), and a decrease in n <2 also leads to a decrease in sorption activity.

The optimal molar ratio of 1,4-dichlorobutin-2 to the amount of sodium hydroxide used is 1.25-1: 2, that is, dichlorobutin is taken in a small excess. A decrease in the amount of dichlorobutin below 1: 2 leads to the formation of a polymer with SH or SNa groups at the ends, chemisorption of mercury ions on which leads to the formation of strong bonds and, possibly, to clogging of pores, which reduces the total sorption capacity. An increase in the amount of dichlorobutin relative to alkali more than 1.25: 2 requires an additional consumption of reagent and leads to the formation of a polymer sorbent with a high content of residual chlorine, which also causes a decrease in activity.

The sorption activity of the obtained sorbents was evaluated by the absorption of mercury compounds from model aqueous solutions of mercury (II) chloride or nitrate. For this, a weighed portion of the obtained sorbent (0.2 g) was shaken for 30 min with 25 ml of a mercury salt solution with an initial concentration of 4 g / l. Sorption capacity was calculated by changing the concentration of mercury ions in solution. The final concentration was determined photocolorimetrically [14].

The participation of the triple bond of the -C≡C-polymer fragment in coordination with mercury ions was confirmed by studies of sorbent samples before and after sorption by PC spectroscopy. It is known [15] that the non-terminal triple bond in organic molecules gives very weak absorption in the IR spectra. Therefore, a spectroscopic study was carried out using the method of impaired total internal reflection (ATR) [16] on a Varian 3100 (FTIR) instrument. For adsorbent samples, a weak band was detected before adsorption in the region of 2084–2087 cm ^–1 , which corresponds to stretching vibrations of С≡С and which completely disappears in samples of the sorbent saturated with mercury.

Example 1. In a reaction flask equipped with a stirrer, a thermometer, a reflux condenser and a device for introducing reagents, 8 g (0.2 mol) of NaOH were added, 20 ml of water, 2.5 ml of hydrazine hydrate were added. 6.4 g (0.2 mol) of finely dispersed sulfur (molar ratio of NaOH: S = 1: 1, which ensures the preferential production of sodium disulfide Na ₂ S ₂ ) was introduced into the resulting solution in portions. The reaction mixture was stirred for 1 h at a temperature of 80-85 ° C, cooled to 30 ° C, and 2.3 g of petroleum coke were poured (neftecox: NaOH mass ratio = 1: 1), with a particle size <0.15 mm. The resulting suspension was stirred for 30 min at a temperature of 25-30 ° C and 12.3 g (0.1 mol) of dichlorobutin (molar dichlorobutin: NaOH = 1: 2 ratio) was added with stirring. The precipitated brown precipitate of the sorbent is filtered off, washed with diluted (5%) hydrochloric acid, water, 10 ml of ethanol and dried, weight 13.8 g. Sulfur content 47%. The obtained sorbent under the above conditions showed sorption activity with respect to Hg ^{2+ ions} 412 mg / g.

Example 2. Under the conditions of example 1, but when using 2.7 g of petroleum coke, 14.2 g of sorbent containing 37% sulfur were obtained. Activity 364 mg / g.

Example 3. Under the conditions of example 1, but when using 2.7 g of petroleum coke, 14.2 g of sorbent containing 37% sulfur were obtained. Activity 386 mg / g.

Example 4. Under the conditions of example 1, but when using 3 g of neftekoks (NaOH: neftekoks ratio 2.7: 1, g / g), 15.6 g of sorbent containing 33.5% sulfur were obtained. Activity 301 mg / g.

Example 5. Under the conditions of example 1, but using 1.9 g of neftecox, 12.2 g of sorbent with a sulfur content of 50.4% was obtained. Activity 310 mg / g.

Example 6. Under the conditions of example 1, but using 9.6 g of sulfur (preferential production of Na ₂ S ₃ ), 16.8 g of a yellow sorbent with a sulfur content of 54% and an activity of 318 mg / g were obtained.

Example 7. Under the conditions of example 1, but using 8 g of sulfur (formation of a mixture of Na ₂ S ₂ and Na ₂ S ₃ ), 14.3 g of a sorbent with a sulfur content of 51% and sorption activity of 398 mg / g were obtained.

Example 8. Under the conditions of example 1, but when using 11.2 g of sulfur, 17.8 g of a sorbent with a sulfur content of 57% and an activity of 337 mg / g were obtained.

Example 9. Under the conditions of example 1, but when dropping 15.4 g of dichlorobutin, 16.4 g of a sorbent containing 43.2 percent sulfur were obtained. Activity 407 mg / g.

Example 10. Under the conditions of example 1, but when dropping 11.1 g of dichlorobutin, 12.2 g of sorbent containing 49% sulfur was obtained. Its activity is 316 mg / g.

Example 11. Under the conditions of example 1, but when dropping 17.2 g of dichlorobutin, 19.6 g of sorbent with a sulfur content of 31% was obtained. Activity 346 mg / g.

For a visual representation, the considered examples are summarized in a table.

Thus, using neftekoks, sulfur, alkali, hydrazine hydrate and 1,4-dichlorobutin, a method for producing a new sorbent for the absorption of mercury compounds from solutions has been developed. The sorbent has an activity of 2-2.5 times the activity of the sorbent obtained by the prototype method.

Table 1 Varying the conditions for obtaining the sorbent in accordance with the examples Example No. The ratio of NaOH: S (mol: mol) Neftecox: NaOH ratio (g / g) The ratio of dichlorobutin: NaOH (mol: mol) The activity of the obtained sorbent, mg / g one 1: 1 3.5: 1 1: 2 412 2 1: 1 4: 1 1: 2 364 3 1: 1 3: 1 1: 2 386 four 1: 1 2.7: 1 1: 2 301 5 1: 1 4.2: 1 1: 2 310 6 1: 1,5 3.5: 1 1: 2 318 7 1: 1.25 3.5: 1 1: 2 398 8 1: 1.75 3.5: 1 1: 2 337 9 1: 1 3.5: 1 1.25: 2 407 10 1: 1 3.5: 1 0.9: 2 316 eleven 1: 1 3.5: 1 1.4: 2 346

References

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Claims (1)

A method of producing a sorbent for the extraction of mercury compounds from aqueous solutions, including polycondensation of sodium polysulfide (Na ₂ S _n , where n = 2-3), obtained by the reaction of elemental sulfur and sodium hydroxide in an aqueous solution in the presence of hydrazine hydrate, with an organochlorine compound on the surface of petroleum coke particles characterized in that 1,4-dichlorobutin-2 is used as the organochlorine compound and the process is carried out with a petroleum coke: caustic soda mass ratio of 1: 3-4 and a 1,4-dichlorobutin-2: caustic soda molar ratio, equal to 1.25-1: 2.