Process for producing ammonium thiosulfate

Abstract

A process for producing ammonium thiosulfate by reacting ammonia, sulfur dioxide and elemental sulfur in a reactor having a stirring device and a heating and cooling system, comprising: a) comminuting elemental sulfur to a particle size of less than 500 microns and feeding the comminuted sulfur into the reactor, b) feeding stoichiometric amounts of ammonia and sulfur dioxide into the reactor, and c) feeding ammonium thiosulfate into the reactor, the temperature of the reactor content is maintained not more than 70 DEG C, c) introducing an additional amount of ammonia while maintaining the temperature of the reactor content in the range of 90-120 DEG C, d) filtering the resulting ammonium thiosulfate solution wherein the elemental sulfur has a particle size of less than 100 microns. The process can improve the reaction rate of producing ammonium thiosulfate from ammonia, sulfur dioxide and elemental sulfur, shorten the total reaction time of producing ammonium thiosulfate, and improve the yield and purity of the obtained product.

Description

Technical Field

[0001] The present invention relates to a process for producing ammonium thiosulfate, and more particularly, to a process for producing ammonium thiosulfate from ammonia and sulfur dioxide by adding elemental sulfur. Background Art

[0002] US 3,473,891 discloses a two-step process for producing ammonium thiosulfate, wherein the first step comprises reacting an aqueous solution of ammonium bisulfite containing 32% sulfur dioxide with an equimolar amount of gaseous ammonia and sulfur in a reactor equipped with a stirrer at atmospheric pressure and a temperature of 20 - 50°C for 2 - 3 hours. The second step is to filter the resulting solution through a packed tubular reactor filled with sulfur to completely convert ammonium sulfite. The residence time in the filter is 0.5 hour. Then, final decolorization is carried out by adding ammonium bisulfite to a 60% ammonium thiosulfate solution in an amount of 1% by weight of the initial mixture. The pH value of the solution used in the first step is 8.8 - 9.2, and 0.1% by weight of hydrogen sulfide is used as a catalyst, and 0.05% by weight of polyethylene glycol ether is used as a sulfur wetting agent.

[0003] US 3,524,724 discloses a two-step process for producing ammonium thiosulfate, in which ammonia reacts with sulfur dioxide and ammonium bisulfite in a concentrated ammonia solution at a temperature of 60°C, a pressure of 30 bar, and a concentration of 80% or higher. Sulfur is dissolved in the ammonia solution, and the precipitated ammonium thiosulfate product is discharged in solid form. The ammonia solution of sulfur and water is transferred from the first reactor to the second reactor, saturated with sulfur dioxide at a pressure of 30 bar and a temperature of 20°C to form ammonium bisulfite, and then returned to the first reactor. The sulfur content in the solution is controlled, and the feed to the reactor is also regulated. Ammonium sulfate and ammonium sulfite are produced as impurities with a content of 3 - 10%, while the thiosulfate content is 85%. Sulfur dioxide is produced by burning sulfur in oxygen.

[0004] US 4,478,807 discloses a process for producing ammonium thiosulfate from sulfur dioxide, in which ammonium sulfite is formed by purifying the intermediate product formed by the reaction of purified ammonia and sulfur dioxide in the presence of water. Preferably, ammonia is added to sulfur dioxide at the bottom of the second washing reactor to keep sulfur dioxide and ammonia in a liquid phase state.

[0005] US2005002852 discloses a process for producing ammonium thiosulfate using a flue gas stream containing sulfur dioxide, comprising the following steps:

[0006] (a) contacting the flue gas stream with multiple streams of aqueous ammonia solution;

[0007] (b) generating a scrubber product stream containing ammonium bisulfite and ammonium sulfite;

[0008] (c) passing a scrubber product stream through a fluidized bed reactor containing solid sulfur; and

[0009] (d) contacting the reactor feed stream with ammonia; and

[0010] (e) reacting the scrubber feed stream, sulfur, and ammonia to produce a thiosulfate product stream.

[0011] WO 03002455 discloses a process for producing ammonium thiosulfate by redox of sulfur compounds, which does not form elemental sulfur and does not convert more than 9% of the sulfur compounds into sulfate ions. The process includes oxidizing a thiosulfate solution with an oxidizing agent to produce a partially oxidized solution, adjusting the pH of the partially oxidized stream to 5 to 8, and reacting the partially oxidized solution with a stream containing a reduced sulfur compound to oxidize the reducing compound and reduce the partially oxidized stream.

[0012] RO 118279 discloses a process for producing ammonium thiosulfate by synthesis of ammonium hydroxide, sulfur dioxide, and elemental sulfur. The synthesis is carried out in one step by bubbling sulfur dioxide through a suspension containing an ammonium thiosulfate solution at a concentration of 50 - 60%, an ammonium hydroxide solution at a concentration of 25%, and elemental sulfur. The reaction mixture is heated to 75 - 85 °C. Sulfur dioxide and ammonium hydroxide are added until the sulfur is completely dissolved. The resulting ammonium thiosulfate solution is filtered and then crystallized.

[0013] Disadvantages of the known processes include: low process rate for producing ammonium thiosulfate; need to remove a large amount of heat generated when dissolving ammonia gas; complex design of the production line for ammonium thiosulfate due to the two-step process for producing ammonium thiosulfate.

[0014] The closest prior art to the present invention is GB 1175069, which discloses a continuous process for producing ammonium thiosulfate from ammonia, sulfur dioxide, water, and elemental sulfur in an aqueous reaction medium containing ammonium thiosulfate, including feeding ammonia and sulfur dioxide into the reaction medium in a first reactor to form ammonium sulfite, contacting the reaction medium containing ammonium sulfite with elemental sulfur in the first reactor, wherein the amount of elemental sulfur far exceeds the stoichiometric amount required to form ammonium thiosulfate, recycling most of the reaction medium in the first reactor, withdrawing a portion of the reaction medium from the first reactor, and feeding the withdrawn portion into a second reactor, where it is again contacted with excess sulfur to convert substantially all of the remaining ammonium sulfite into ammonium thiosulfate, and recovering ammonium thiosulfate from the second reactor.

[0015] Disadvantages of this known process include low process rate for producing ammonium thiosulfate, low yield of the target ammonium thiosulfate product, and complex design of the apparatus for producing ammonium thiosulfate due to the need for two reactors to produce ammonium thiosulfate in two steps. Summary of the Invention

[0016] The technical object of the present invention is to develop a process for the effective and rapid production of ammonium thiosulfate, with a high yield and high purity of the ammonium thiosulfate product.

[0017] The technical effects achieved by implementing the present invention include a higher reaction rate for the production of ammonium thiosulfate from ammonia, sulfur dioxide and elemental sulfur, a shorter reaction time for the production of ammonium thiosulfate, and a higher yield and purity of the resulting product.

[0018] To achieve the above technical effects, a process for the production of ammonium thiosulfate has been developed, which includes the interaction of ammonia and sulfur dioxide in a reactor equipped with a mixing device and a heating and cooling system. The process includes:

[0019] a) Crushing elemental sulfur and feeding the crushed elemental sulfur together with water into the reactor;

[0020] b) Feeding ammonia and sulfur dioxide into the reactor while maintaining the temperature of the reactor contents not exceeding 70 °C;

[0021] c) Introducing an additional amount of ammonia while maintaining the temperature of the reactor contents in the range of 90 - 120 °C;

[0022] d) Filtering the resulting ammonium thiosulfate solution, wherein the particle size of the elemental sulfur is less than 100 microns.

[0023] Elemental sulfur enters the reactor in the form of an aqueous suspension. In this case, the aqueous sulfur suspension contains at least 75% by weight of sulfur particles with a particle size less than 90 microns.

[0024] The molten sulfur sprayed into water through a pneumatic nozzle (5) is dispersed to prepare the aqueous sulfur suspension.

[0025] The dispersion is carried out as follows: Liquid hot sulfur is sprayed with a pneumatic nozzle. After the sulfur contacts the water, it further changes from the liquid phase to the solid phase. For this purpose, the initial massive sulfur is melted, mechanical impurities are filtered out, and then it is fed for spraying. When sprayed through the pneumatic nozzle (5), the liquid sulfur is dispersed into small droplets, and the small droplets contact the water and crystallize into a solid phase, with a main particle size less than 500 microns, preferably less than 100 microns, more specifically less than 90 microns. The minimum particle size is 2 microns.

[0026] The particle size of the elemental sulfur can be adjusted by changing the feeding rate of the molten sulfur and the air feeding rate of the pneumatic nozzle (5).

[0027] The particle size is further controlled by a hydrocyclone (3). The sulfur suspension is fed into the hydrocyclone (3) for classification. The fine fraction (less than 100 microns) from the upper outlet of the hydrocyclone is fed into the reactor (6) to synthesize ammonium thiosulfate, while the suspension of the coarse fraction (more than 100 microns) from the lower outlet of the hydrocyclone is fed into the ball mill (4) for wet grinding under the action of gravity.

[0028] The temperature in the reactor (6) is maintained by using water or steam through a heat exchanger or jacket (7).

[0029] The feeding rate of ammonia does not exceed 25 - 50 g / min, and the feeding rate of sulfur dioxide does not exceed 50 - 100 g / min.

[0030] The process is carried out continuously.

[0031] The conversion rate of sulfur dioxide to ammonium thiosulfate reaches 96 - 98%, the content of the main product ammonium thiosulfate in the solution is between 57 - 61% by weight, and the content of ammonium sulfite does not exceed 1% by weight. Therefore, the product meets the standard requirements for photography (DIN 19 080T82, ISO 3619), agrochemistry, and metallurgy.

[0032] Brief Description of the Drawings

[0033] Figure 1 shows a process flow diagram for the production of ammonium thiosulfate.

[0034] Figure 2 Shows the unit for producing the aqueous suspension of elemental sulfur.

[0035] Figure 3 Shows the particle size distribution curve of sulfur particles produced by dispersing sulfur.

[0036] Detailed Embodiments of the Invention

[0037] To produce ammonium thiosulfate, an aqueous suspension of elemental sulfur is produced in the unit for producing the suspension (Figure 1 and Figure 2 ).

[0038] To produce the aqueous suspension of elemental sulfur, the initial massive sulfur is melted, mechanical impurities are filtered out, and then it is fed into a pneumatic nozzle (5) for spraying. The filtered liquid sulfur enters the feed pipeline (8) of the contact crystallizer (1), and the above-mentioned liquid sulfur passes through the steam-heated nozzle (5) and is injected into the cold water stream that is also fed into the contact crystallizer (1) from the pipe network. When mixed with water, the liquid sulfur disperses and crystallizes into a solid phase, the main particle size of which is less than 100 microns. Preferably, the aqueous suspension of elemental sulfur contains at least 75% by weight of sulfur particles with a particle size less than 90 microns.

[0039] In addition, the crystalline sulfur water suspension from the crystallizer (1) is fed into the elemental sulfur suspension tank (2) equipped with a stirrer (9) and a submerged heat exchanger (10). By cooling the suspension with the submerged heat exchanger (10), the heat released after the liquid sulfur contacts water and crystallizes is absorbed by the elemental sulfur suspension tank (2).

[0040] The sulfur suspension is fed from the tank (2) to the hydrocyclone (3) by a pump (11) to classify the elemental sulfur particles by size. The fine sulfur fraction suspension (less than 100 microns) from the upper outlet of the hydrocyclone (3) is fed into the reactor (6) for synthesizing ammonium thiosulfate. Before entering the reactor (6), the elemental sulfur suspension enters the ammonia absorber (14). Since the elemental sulfur suspension contains water that can dissolve ammonia, in order to maintain the material balance of the ammonium thiosulfate process, the water suspension of elemental sulfur is used as a medium to absorb the excess ammonia circulating in the system. Using the ammonia absorber (14) can increase the production rate of ammonium thiosulfate and reduce the total reaction time for ammonium thiosulfate production.

[0041] The suspension of the coarse sulfur fraction (greater than 100 microns) from the lower outlet of the hydrocyclone (3) flows into the ball mill (4) by gravity for wet grinding, and the ground product is fed into the elemental sulfur suspension tank (2) by gravity.

[0042] The inner surface of the drum of the ball mill (4) is lined with Silex to avoid metal contamination of the crushed material. The grinding media are flint balls with a diameter of 30 - 90 mm, high alumina (amosite), and cylindrical zirconia bodies.

[0043] The resulting water suspension fed into the reactor (6) contains finely ground elemental sulfur with a particle size less than 100 microns, preferably less than 90 microns, and an excess ranging from 50 to 100 wt%.

[0044] The reaction is carried out by stirring the reaction mixture with a stirrer (12).

[0045] A stoichiometric amount of ammonia and sulfur dioxide are added to the reactor (6).

[0046] Ammonia and sulfur dioxide are fed into the reactor (6) simultaneously and continuously. Sulfur dioxide is fed in the form of wet gas, and ammonia is fed in the form of liquid ammonia.

[0047] Sulfur dioxide enters the reactor (6) through the compressor (16).

[0048] Since the reactants will be heated when feeding the reagents, to prevent the reaction materials from overheating, while feeding the initial reagents, the reactor contents are cooled with water to keep the reactor temperature not exceeding 70 °C. The cooling is provided by an immersion heat exchanger or a cooling jacket (7).

[0049] When the stoichiometric amounts of ammonia and sulfur dioxide are fed, an additional amount of ammonia is introduced from the absorber (14) to increase the system pressure to 2 - 3 atm. Meanwhile, due to the feed of excess ammonia, the reaction materials are heated to a temperature range of 90 to 120 °C. In this case, to maintain the temperature in the reactor (6) within the range of 90 - 120 °C, the feed of cooling water to the jacket (7) of the reactor (6) should be stopped, and steam (not shown in the figure) should be fed from the autonomous steam generator to the jacket (7) of the reactor (6).

[0050] Additional ammonia (excess dissolved ammonia) should be fed into the reactor to prevent the decomposition of the formed ammonium thiosulfate, because the uncontrolled decomposition of the formed ammonium thiosulfate can cause an explosion of the reaction mixture. In continuous production processes, it is preferably to use liquid ammonia because the heat of vaporization of liquid ammonia can be used to cool the reaction materials.

[0051] While sampling to monitor the completion of the ammonium thiosulfate synthesis reaction, the contents are mixed.

[0052] The evaporator (17) is used to separate excess ammonia from the finished product and then feed the finished product into the reactor to ensure the integrity of the reaction and prevent the decomposition of ammonium thiosulfate.

[0053] The settling centrifuge (15) is used to separate the excess unreacted sulfur from the finished product and send it back to the hydrocyclone (3) to ensure the continuity of the ammonium thiosulfate production process together with the fresh sulfur.

[0054] Using the evaporator (17) and the settling centrifuge (15) in the production of ammonium thiosulfate can increase the production rate of ammonium thiosulfate, reduce the total reaction time for producing ammonium thiosulfate, and improve the yield and purity of the obtained product.

[0055] The unreacted sulfur in the finished product solution is filtered and then recycled to step (a) of the ammonium thiosulfate production process.

[0056] Detailed description of the drawings

[0057] Figure 1 shows the process flow diagram for the production of ammonium thiosulfate solution, including

[0058] 1 - crystallizer

[0059] 2 - elemental sulfur suspension tank

[0060] 3 - hydrocyclone

[0061] 4 - ball mill

[0062] 5 - nozzle

[0063] 6 - reactor for synthesizing ammonium thiosulfate

[0064] 7 - Heat exchanger or jacket of the reactor (6)

[0065] 8 - Contact crystallizer feed pipeline

[0066] 9 - Agitator of the tank (2)

[0067] 10 - Submersible heat exchanger of the tank (2)

[0068] 11 - Pump of the tank (2)

[0069] 12 - Agitator of the reactor (6)

[0070] 13 - Container equipped with a finished product for sampling

[0071] 14 - Ammonia absorber

[0072] 15 - Settling centrifuge

[0073] 16 - Compressor

[0074] 17 - Evaporator

[0075] 18, 19, 20 - Pumps

[0076] Figure 2 A unit for producing an aqueous suspension of elemental sulfur is shown, including

[0077] 1 - Crystallizer

[0078] 2 - Elemental sulfur suspension tank

[0079] 3 - Hydrocyclone

[0080] 4 - Ball mill

[0081] 5 - Nozzle

[0082] Figure 3 A particle size distribution curve of sulfur particles produced by dispersing sulfur is shown, where

[0083] d is the effective particle size;

[0084] dQ (curve a) is a probability distribution that determines the probability of finding particles of a given particle size in a given set.

[0085] Q (curve b) is the proportion of particles with a particle size equal to or less than a given particle size at a given point.

[0086] Figure 3 A curve describing that the particle distribution approaches a normal distribution is shown.

[0087] Using finely dispersed elemental sulfur can enable the synthesis reaction of ammonium thiosulfate to be completed in one step without additional equipment and reagents, thereby shortening the reaction time and improving the process productivity.

[0088] The substantial content of the present invention will be described in detail in the embodiments.

[0089] Example 1

[0090] Water (500 ml) is charged into the reactor (6) for synthesizing ammonium thiosulfate through the hatch to provide a liquid medium in the reactor, and the stirrer is turned on.

[0091] In addition, an elemental sulfur aqueous suspension (pre-prepared in a unit for preparing an elemental sulfur aqueous suspension) is charged into the reactor (6) through the same hatch at a ratio of sulfur to water of 2:1 to 1:2.

[0092] For the experiment according to Example 1, a suspension of elemental sulfur with a particle size of 100 - 500 microns is used.

[0093] After all the elemental sulfur aqueous suspension is charged into the reactor (6), the remaining amount of water is added according to the experimental requirements.

[0094] After the charging of water and the elemental sulfur aqueous suspension into the reactor (6) is completed, cooling water is fed into the jacket (7) of the reactor, the reactor (6) is sealed and purged with nitrogen to remove the residual air entering the reactor from the open hatch, and the purge gas is discharged into a neutralization system (not shown in the figure).

[0095] When the temperature of the reaction medium in the reactor (6) reaches 12 - 18 °C, ammonia and sulfur dioxide are fed. The feeding rate of ammonia does not exceed 25 - 50 g / min. The feeding rate of sulfur dioxide does not exceed 50 - 100 g / min. During the feeding of the reagents, the changes in temperature and pressure in the reactor (6) are monitored. The maximum allowable temperature in the reactor (6) is 80 °C, and the maximum allowable pressure is 2.8 kgf / cm 2 .

[0096] When the amount of the reagents is fed into the reactor, the fed ammonia does not exceed 10% of the stoichiometric amount, the feeding of cooling water into the jacket (7) of the reactor (6) is stopped, and steam is started to be fed from an autonomous steam generator (not shown in the figure) into the jacket (7) of the reactor (6) to maintain the temperature in the reactor (6) within the range of 90 - 120 °C. The steam flow is set so that the temperature of the reaction material in the reactor (6) remains constant throughout the reaction time. Samples of the ammonium thiosulfate solution are taken regularly from the sampling container to analyze the contents of ammonium thiosulfate and ammonium sulfite in the mixture.

[0097] After the specified reaction time ends, stop the steam feed and start feeding cold water into the jacket (7) of the reactor (6). After cooling the reaction material in the reactor to a temperature not exceeding 40 °C, stop the water flow to the jacket (7) of the reactor (6) and stop the mixer (12), discharge the liquid reaction product into the sampling container (13), filter the finished product solution to separate ammonium thiosulfate and unreacted sulfur, and analyze the finished product filtrate and precipitate. Use nitrogen from the inert gas purge system to purge the gaseous product from the reactor into the neutralization system.

[0098] Table 1 shows the amounts of the components and the reaction time for producing ammonium thiosulfate according to Example 1.

[0099] Table 1

[0100] Ammonia, g Sulfur dioxide, g Sulfur, g Water, ml Reaction time, min 700 1300 1000 2000 30

[0101] As a result of the reaction, an ammonium thiosulfate solution was produced, in which the content of ammonium thiosulfate was 57 wt% and the content of ammonium sulfite was 0.98 wt%. In this case, the conversion rate of sulfur dioxide to ammonium thiosulfate was 96%.

[0102] Example 2

[0103] The production process of ammonium thiosulfate is similar to the process in Example 1.

[0104] In addition, in Example 2, to obtain ammonium thiosulfate, a sulfur suspension was used in which the particle size of the sulfur particles did not exceed 90 microns.

[0105] Table 2 shows the amounts of the components and the reaction time for producing ammonium thiosulfate according to Example 2.

[0106] Table 2

[0107] Ammonia, g Sulfur dioxide, g Sulfur, g Water, ml Reaction time, min 700 1300 1000 2000 15

[0108] As a result of the reaction, an ammonium thiosulfate solution was produced, in which the content of ammonium thiosulfate was 61 wt% and the content of ammonium sulfite was 0.95 wt%. In this case, the conversion rate of sulfur dioxide to ammonium thiosulfate was 98%.

[0109] From the obtained results, it can be seen that in the process of producing ammonium thiosulfate, using a sulfur water suspension with a particle size less than 100 microns (preferably less than 90 microns) can shorten the total reaction time for producing ammonium thiosulfate and improve the yield and purity of the obtained product.

Claims

1. A process for producing ammonium thiosulfate by reacting ammonia, sulfur dioxide and elemental sulfur in a reactor equipped with a mixing device and a heating and cooling system, comprising: a) pulverizing elemental sulfur and feeding the pulverized elemental sulfur together with water into the reactor; b) feeding stoichiometric amounts of ammonia and sulfur dioxide into the reactor while maintaining the temperature of the reactor contents at no more than 70 °C; c) introducing an additional amount of ammonia while maintaining the temperature of the reactor contents in the range of 90 - 120 °C; d) filtering the resulting ammonium thiosulfate solution; characterized in that the particle size of the elemental sulfur is less than 100 microns, wherein the minimum particle size of the elemental sulfur is 2 microns.

2. The process according to claim 1, characterized in that the elemental sulfur is fed into the reactor in the form of an aqueous suspension.

3. The process according to claim 2, characterized in that the aqueous suspension of sulfur contains at least 75% by weight of sulfur particles with a particle size less than 90 microns.

4. The process according to claim 2, characterized in that the aqueous suspension of sulfur is produced by dispersing molten sulfur by spraying the molten sulfur through a pneumatic nozzle into water.

5. The process according to claim 4, characterized in that the size of the sulfur particles is adjusted by the rate of feeding the molten sulfur to the nozzle and the rate of feeding air, and is controlled by using a hydrocyclone.

6. The process according to claim 1, characterized in that the ammonia fed in step (c) does not exceed 10% of the stoichiometric amount.

7. The process according to claim 1, characterized in that the temperature in the reactor is maintained by water or steam using a heat exchanger or a jacket.

8. The process according to claim 1, characterized in that the feeding rate of the ammonia does not exceed 25 - 50 g / min, and the feeding rate of the sulfur dioxide does not exceed 50 - 100 g / min.

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