KR960010083B1 - Process for the preparation of ammonium thiosulfate - Google Patents

Abstract

The process includes the steps of; (a) oxidizing hydrogen sulfide and ammonia with air or oxygen in heterogeneous oxidation catalyst reactor(A); (b) condensing the product by condenser(B) and separating the condensed mixture solution into ammonium thiosulfate and sulfur by solid-liquid separator(c); (c) recovering the concentrated or crystallized ammonium thiosulfate by filtering and concentrating the separated ammonium thiosulfate; (d) recycling the ammonia, evaporated from the concentrator(E), and recycling the hydrogen sulfide made by hydrogenating the sulfur produced as a byproduct in hydrogenation catalyst reactor.

Description

Ammonium Thiosulfate ((NH4) 2S2O3)

1 is a schematic view of a process according to the manufacturing method of the present invention.

The present invention relates to a method of continuously producing ammonium thiosulfate (NH ₄ ) ₂ S ₂ O ₃ ) using hydrogen sulfide (H ₂ S) and ammonia (NH ₃ ) as raw materials. More specifically, the present invention relates to a method for producing ammonium thiosulfate from hydrogen sulfide and ammonia by gas phase oxidation using a heterogeneous catalyst.

Ammonium thiosulfate is white crystals, soluble in water and has a density of 1.679 g / cm 3. The ammonium thiosulfate solution is slowly decomposed at 50 ° C or lower, and decomposed into ammonium sulfite ((NH ₄ ) ₂ SO ₃ ) and elemental sulfur (S) at 100 ° C or higher. About 50% is a photographic developer and 50% is used for agriculture. Is being used. Originally, ammonium thiosulfate was prepared by the reaction of ammonium sulfite ((NH ₄ ) ₂ SO ₃ ) with sulfides or polysulfides, which is described in detail as follows.

(NH ₄ ) ₂ SO ₃ + (NH ₄ ) ₂ S ₈ → (NH ₄ ) ₂ S ₂ O ₃ + (NH ₄ ) ₂ S ₇ (1)

(NH ₄ ) ₂ SO ₃ + (NH ₄ ) ₂ S ₇ → (NH ₄ ) ₂ S ₂ O ₃ + (NH ₄ ) ₂ S ₆ (2)

The reactions of the above (1) and (2) types are continued until the final polysulfide (NH ₄ ) ₂ Sx becomes ammonium sulfide, and the final reaction is sulfurous acid (SO ₂ ) or Ammonium bisulffite is terminated as in Scheme (3).

3SO ₂ + (NH ₄ ) ₂ SO ₃ +2 (NH ₄ ) ₂ S → 3 (NH ₄ ) ₂ S ₂ O ₃ (3)

The solution thus made is cleared by activated carbon treatment and filtered to remove traces of sulfur. Ammonium thiosulfate in anhydrous crystalline form must be dried at low temperature in the presence of ammonia. Currently commercially prepared by using an excess of sulfur in a batch and a continuous reactor, reacted directly with ammonium sulfite as in Scheme (4) at 85 ~ 110 ℃ operating conditions (US Patent No. 3,473,891 (Oct. 21, 1969).

(NH ₄ ) ₂ SO ₃ + S → (NH ₄ ) ₂ S ₂ O ₃ (4)

The obtained ammonium thiosulfate is at a concentration of about 70% without concentration, unreacted excess sulfur is separated by filtration, and the color of the solution is cleared by treatment with activated carbon or sodium silicate.

The foregoing prior art uses ammonium sulfite and sulfides as reactants to produce ammonium thiosulfate. On the contrary, the present invention provides a method for continuously producing ammonium thiosulfate continuously by oxidizing with air or oxygen using hydrogen sulfide (H ₂ S) and ammonia (NH ₃ ) as raw materials. It is to provide. According to the present invention, a step of directly oxidizing hydrogen sulfide and ammonia to air or oxygen in a heterogeneous oxidation catalyst reactor (A); Condensing the reaction product through a cooler (B) and dissolving the condensed mixture of ammonium thiosulfate and elemental sulfur in water to separate the elemental sulfur and ammonium thiosulfate solution in the solid-liquid separator (C); Passing the separated ammonium thiosulfate solution through a filter (D) and then concentrating in a concentrator (E) to recover ammonium thiosulfate in a concentrated or crystalline state; And recycling the ammonia produced by evaporation in the concentrator and hydrogenating the elemental sulfur produced as a by-product on a hydrogenation catalytic reactor (F) to hydrogen sulfide. This is provided.

The present invention will now be described with reference to the accompanying drawings.

In FIG. 1, the reaction in the oxidation catalyst reactor (A) in which ammonium thiosulfate is produced can be represented by the following reaction formula (5).

2H ₂ S + 2NH ₃ + 2O ₂ → (NH ₄ ) ₂ S ₂ O ₃ + H ₂ O (5)

Hydrogen sulfide and ammonia are passed together with oxygen through an oxidation catalyst reactor (A) to react at 180 to 550 ° C. Catalysts that can be used in the oxidation catalyst reactor (A) include those in which cobalt, molybdenum, vanadium, or mixtures thereof are supported on alumina or other acidic high surface minerals (eg, titania, silica-alumina, zeolite, etc.). In the oxidation catalyst reactor (A), in addition to ammonium thiosulfate, a small amount of elemental sulfur (S) and sulfur dioxide gas are generated as oxidation by-products. The product leaving the reactor is condensed into solid ammonium thiosulfate and elemental sulfur as it passes through a cooler (B) whose temperature is kept below 50 ° C. The condensed ammonium thiosulfate and elemental sulfur mixture is dissolved and washed with water and separated in a solid-liquid separator (C) into a solution of elemental sulfur and ammonium thiosulfate. The ammonium thiosulfate solution is then passed through an activated carbon fiber filter (D) to dry the color of the solution and remove some undissociated sulfur mist. As activated carbon fiber, it is preferable to activate pitch-based carbon fiber by the steam activation method, and the strength of about 100 to 250 MPa, the bulk density of about 0.01 to 0.1, and about 1000 to 2000 m 2 / g It is desirable to have a specific surface area. When passing ammonium thiosulfate solution containing about 100ppm total pollutant per unit of activated carbon fiber per unit time (approximately 10ml / g) within 600ml ~ 3000ml (LHSV = 60 ~ 300) within 3 ~ 15 hours The contaminants could be completely removed. The characteristic of such activated carbon fiber is that it is more than twice as effective in terms of liquid flow rate, bow mist removal efficiency and color improvement efficiency that can be treated under the same conditions as conventional activated carbon. In addition, activated carbon fibers that lost their ability to remove contaminants could be completely regenerated and reused after treatment at 400 ° C. for 6 hours under inert gas flow. The ammonium thiosulfate solution is slowly evaporated in the concentrator (E) at 100 ° C. or lower to obtain a concentrate or ammonium thiosulfate in crystalline form. At this time, the evaporated ammonia is recycled back to the source gas and used. Solid sulfur obtained as a by-product is evaporated and injected into a hydrogenation catalyst reactor (F). In the hydrogenation catalyst reactor (F) (Korean Patent Application No. 91-22218) having the property of converting all sulfur compounds to hydrogen sulfide, the introduced elemental sulfur is converted to hydrogen sulfide after reacting with hydrogen under a heterogeneous catalyst and recycled to the reactant. As a hydrogenation catalyst, elemental sulfur is converted into hydrogen sulfide through a hydrogenation reaction in a temperature range of 200 to 350 ° C. in a hydrogenation catalyst reactor using cobalt and molybdenum supported on alumina.

S + H ₂ → H ₂ S (6)

SO ₂ + 3H ₂ → H ₂ S + 2H ₂ O (7)

The amount of hydrogen is more than the amount that can be combined with the sulfur compound to be converted in an equivalent ratio.

According to the present invention, factors affecting the yield of ammonium thiosulfate are the amount of oxygen and the reaction temperature. As the amount of oxygen increases, the yield of ammonium thiosulfate increases, but the use of excess oxygen is undesirable because the by-product sulfur dioxide gas increases. This reduces the production of elemental sulfur. The amount of oxygen is suitably 0.2 to 5 times the amount of hydrogen sulfide, and the more preferable amount of oxygen to maximize the yield of ammonium thiosulfate is 0.3 to 3 times that of hydrogen sulfide. The reaction temperature is suitably between 160 ° C and 550 ° C. As the reaction temperature increases, the yield of ammonium thiosulfate increases. However, if the reaction temperature is higher than 500 ℃, sulfur dioxide, a by-product, increases, and the yield of ammonium thiosulfate decreases, and there is a risk of breakdown of the chip. It's faster and not desirable. Therefore, in the present invention, a more preferable reaction temperature for maximizing the yield of ammonium thiosulfate is 180 to 500 ° C.

The amount of ammonia required for the present invention is more than the equivalent ratio of the amount of hydrogen sulfide, but the equivalent ratio of ammonia may be used when the ammonia is present in the concentration of the produced ammonium thiosulfate to prevent the decomposition of ammonium thiosulfate so that the excess ammonia can be recycled (Figure 1). It is preferable to use about 2 to 5 times of ammonia. The presence of excess ammonia in an equivalent ratio did not significantly affect the deactivation of the catalyst or the yield of ammonium thiosulfate.

Hereinafter, the present invention will be described in detail through examples.

Example 1

2 g of a catalyst having 5 wt% cobalt and 5 wt% molybdenum supported on alumina was added to a U-tube reactor made of quartz, and the reaction temperature was raised to 350 ° C., followed by hydrogen sulfide 6 ml / min, ammonia 12 ml / min and oxygen 3 ml / min was injected into the reactor. The product was condensed in a cooler maintained below 50 ° C. at the back of the reactor. The non-condensed gas was heated to 160 ° C. and unreacted hydrogen sulfide, ammonia gas, and generated sulfur dioxide gas were analyzed every 30 minutes. At this time, the gas analysis result always showed a constant composition regardless of time. After the reaction for 24 hours, the condensed product was dissolved in water, filtered, and solid sulfur and ammonium thiosulfate were separated and weighed. When calculated based on sulfur, the conversion rate (X) of hydrogen sulfide in the mixed gas is 99%, the selectivity for ammonium thiosulfate (S ₁ ) is 70%, and the selectivity for elemental sulfur (S ₂ ) is 29%. , Selectivity to sulfur dioxide (S ₃ ) was 1%.

EXAMPLES 2-4

Except for changing the flow rate of oxygen was carried out in the same manner as in Example 1, hydrogen sulfide conversion (X), selectivity for ammonium thiosulfate (S ₁ ), selectivity for sulfur, calculated on the basis of sulfur (S ₂ ), selectivity (S ₃ ) for sulfur dioxide is shown in Table 1.

TABLE 1

[Examples 6-15]

The conversion and selectivity according to the reaction temperature in the same reaction conditions as in Example 1 are shown in Table 2.

As shown in Table 2, the yield of ammonium thiosulfate increased as the reaction temperature increased.

TABLE 2

Example 16

In Example 1, the product passing through the reactor was passed through a cooler maintained at 50 ° C. or lower to precipitate a solid, washed with water to dissolve it, and sulfur was separated. The filtrate was slowly dried at 60 ° C. with a vacuum dryer to give a white powder crystal. As a result of elemental analysis, the molar ratio of N: H: S: O was 1: 4: 1: 1.5, which corresponded to ammonium thiosulfate accurately, and X-ray diffraction analysis showed no other impurities except ammonium thiosulfate crystals. . The residual concentrations of hydrogen sulfide and sulfur dioxide in the mixed gas separated from the concentrator were 250ppm and 720ppm, respectively, and the total SOx concentration in the exhaust gas after incineration was kept below 100ppm at 12%.

Example 17

In Example 1, the amount of water was added up to 20 ml / min (about 50 vol%) and the amount of ammonia was increased up to 60 ml / min, but there was no significant change in the activity of the catalyst and the yield for ammonium thiosulfate. .

As shown in the above examples, the advantages of the present manufacturing process are that the manufacturing process is simpler than the conventional process, and the ammonia and sulfur compounds which evaporate when the ammonium thiosulfate solution is concentrated are recycled back to the reactor and reused so as not to cause pollution by waste water. to be. In addition, it is a feature of the present invention that high conversion and little SO ₂ generation during the reaction.

Claims (3)

Directly oxidizing hydrogen sulfide and ammonia to air or oxygen in a heterogeneous oxidation catalyst reactor (A); Condensing the reaction product through a cooler (B) and dissolving the condensed mixture of ammonium thiosulfate and elemental sulfur in water to separate the elemental sulfur and ammonium thiosulfate solution in the solid-liquid separator (C); Passing the separated ammonium thiosulfate solution through a filter (D) and then concentrating in a concentrator (E) to recover ammonium thiosulfate in a concentrated or crystalline state; And recycling the ammonia produced by evaporation in the concentrator and hydrogenating elemental sulfur produced as a by-product on a hydrogenation catalyst reactor (F) to recycle hydrogen sulfide to produce ammonium thiosulfate from hydrogen sulfide and ammonia. Way. The method according to claim 1, wherein the amount of oxygen used is 0.5-5 times the amount of hydrogen sulfide and the catalytic reaction temperature is 180-500 ° C. The catalyst used in the oxidation catalyst reactor according to claim 1 or 2, wherein the catalyst used in the oxidation catalyst reactor is an acidic high surface area inorganic material selected from the group consisting of alumina, titania, silica-alumina and zeolite or cobalt molybdenum, vanadium or Characterized in that the mixtures are supported.