JPS58156505A - Process for separating and recovering hydrogen chloride and ammonia from ammonium chloride - Google Patents

Abstract

PURPOSE:To separate and to recover HCl and NH3 on an industrial scale in high yield, by bringing an NH4Cl gas into contact with NH4HSO4 so that HCl is recorvered, decomposing thermally formed (NH4)2SO4. CONSTITUTION:In a process wherein HCl and NH3 are separated and recovered from NH4Cl using NH4HSO4, a molten salt consisting essentially of NH4HSO4 is brought into contact with an NH4Cl gas, NH3 is absorbed in the molten salt, HCl is separated and recovered. While, a formed molten salt of (NH4)2 SO4 is thermally decomposed, to separate and to recover NH3. A molten salt consisting essentially of NH4HSO4 obtained from the NH3 recovery process is circulated through the HCl recovery process and used. Sublimation of NH4Cl can be suppressed, a specific device for elimination, etc. is not required, and stable operation can be carried out for a long time. This process causes no loss of HCl, NH3 and energy, is economically improved, and suitable for production of industrial scale.

Description

Detailed Description of the Invention The present invention relates to a method for separating and recovering ammonium chloride into hydrogen chloride and ammonia using ammonium hydrogen sulfate. Specifically, the present invention relates to a method for separating and recovering ammonium chloride into hydrogen chloride and ammonia using ammonium hydrogen sulfate. The present invention relates to a method that can sufficiently separate and recover hydrogen chloride and ammonia from ammonium chloride in high yields on an industrial scale, by thermally decomposing the ammonium 9-sulfate produced after the 9-year-old process and recovering ammonia.

Currently, ammonium chloride is produced using the ammonium chloride/some production method.
It is produced on a large scale as a byproduct of soda ash production, but much of it is used only as a cheap fertilizer. Previous attempts have been proposed to recover ammonium chloride by decomposing ammonium chloride to produce high value-added products such as chlorine or hydrogen chloride, but each method has serious drawbacks and has not yet been put to practical use. do not have.

For example, a method that utilizes the reaction of metal oxides such as iron, manganese, and magnesium with ammonium chloride requires 50%
KFi is a technology that is far from being put to practical use because it requires a high temperature of 0° C. or higher, and the reactants are mainly solids.

In addition, nine methods have been proposed that utilize the reaction between acidic sulfates such as ammonium and sodium and ammonium chloride.

According to JP-A-55-162405, when ammonium sulfate is used as the acidic sulfate, the reaction proceeds according to the following formulas.

am, as o, + MTIaOL→(NH4)t 8
04+ HOt↑ (1)()iH4), 80(+1
%H804+ NTi Hatake ↑ (2) The reaction of equation (1) is carried out at 200 to 260°C, and the reaction of equation -) is carried out at 320 to 380°C, respectively, above the SOO°C required for the method using metal oxides. Hydrogen chloride and ammonia can be efficiently recovered at lower temperatures than at higher temperatures. Furthermore, since most of the reaction is carried out in the state of a molten salt, it is very advantageous in terms of operation compared to a solid state.

The present inventors conducted a detailed study on the technology utilizing this reaction with ammonium hydrogen sulfate. As a result, K, who put this technology into practical use, found that it is essential to improve the recovery rate of hydrogen chloride and ammonia recovered from ammonium chloride to substantially stoichiometric amounts.

According to the publication, the amount of hydrogen chloride and ammonia recovered is the maximum compared to the ammonium chloride used! The present inventors have found that this decrease in recovery rate is due to the sublimation of ammonium chloride that occurs when hydrogen chloride is generated and the undecomposed ammonium chloride remaining in the molten salt. This undecomposed ammonium chloride has a molten salt of 320~
During heating to 3110°C, sublimation occurs during the ammonia recovery process.

It is natural that the sublimation of ammonium chloride causes economic disadvantages such as a decrease in the amount of hydrogen chloride and ammonia to be recovered and an increase in the required energy, but moreover, the sublimation of ammonium chloride hinders the continuation of stable operation. This is a more serious problem in practical terms. Circular ammonium sublimes during the process and precipitates on the walls of the reactor and hydrogen chloride or ammonia recovery pipe, clogging the pipe and interfering with normal operation.

To avoid such problems, heat or keep warm the areas in the reactor and tubes where ammonium chloride is precipitated.
The precipitated ammonium chloride can be re-sublimated, but this requires a device for temperature maintenance, a device for removing ammonium chloride from circular cyclized hydrogen or ammonia, and a sample material. many.

The present inventors discovered a new problem to be solved in a method using the reaction of acidic sulfate and ammonium chloride,
As a result of extensive research, we found that when molten ammonium hydrogen sulfate and gaseous ammonium chloride are brought into contact, ammonia is absorbed into the molten ammonium hydrogen sulfate extremely efficiently;
The present invention was completed based on the discovery that hydrogen chloride, which does not contain any ammonium chloride, can be efficiently recovered because hydrogen chloride Fi is not absorbed at all.

That is, the method of the present invention includes a hydrogen chloride recovery step in which a molten salt mainly consisting of ammonium hydrogen sulfate is brought into contact with ammonium chloride gas, and ammonia is absorbed into the molten salt to recover hydrogen chloride; An ammonia recovery step in which ammonia is separated and recovered from the molten salt by heating the salt, and a molten salt mainly consisting of ammonium hydrogen sulfate obtained from the ammonia recovery step is recycled to a hydrogen chloride recovery facility. be.

Since the method of the present invention can substantially suppress the sublimation of ammonium chloride in the process, it does not require special equipment for rounding such as removing sublimated ammonium chloride, and stable operation can be achieved over a long period of time. This technology is extremely suitable for industrial-scale production, as it is highly economical and has no loss of hydrogen chloride, ammonia, or energy.

The present invention will be explained in more detail below.

The most important feature of the process of the invention is the use of gaseous heptammonium chloride. That is, the ammonium nonachloride gas obtained by sublimating solid ammonium chloride at a temperature of 200° C. or higher, preferably 290-350° C., is brought into contact with a molten salt mainly consisting of ammonium hydrogen sulfate after being circulated from the ammonia recovery step. The objective is to recover hydrogen chloride.

As mentioned above, when ammonium chloride is supplied in solid form, at least 45% of ammonium chloride sublimes during the process and becomes contained in hydrogen chloride or ammonia. On the other hand, when gaseous ammonium chloride rum is supplied, hydrogen chloride and ammonia containing no ammonium chloride can be obtained, and problems due to sublimation and precipitation of ammonium chloride do not occur. Depending on the sublimation temperature of ammonium chloride and the carrier gas flow rate, the hydrogen chloride recovery rate is improved by 10 to 100 times compared to the case where solid ammonium chloride is supplied. The amount of salt is ',/! O = '7'! -You can save up to twice as much.

It is surprising that the problems of the conventional method could be solved by simply changing the supplied ammonium chloride from solid to gas, improving reaction efficiency and making it possible to significantly downsize the device. . Although the reason for this is not clear, it is inferred as follows.

The reaction when supplying solid ammonium chloride is as described in JP-A-55-162405, MH41180, +4kOL → ('Ha%804+M
This is a reaction in which ammonium chloride, represented by ol↑, is decomposed with ammonium hydrogen sulfate. On the other hand, the reaction when gaseous ammonium chloride is supplied is expressed by the following reaction formula.

)iH4H804+ IH, → (aH4)*soa It is thought that the reaction mechanism is completely different. That is, ammonium chloride gas is a mixed gas that exists in a substantially dissociated state into #i hydrogen chloride and ammonia, and when this mixed gas is brought into contact with a molten salt of ammonium hydrogen sulfate, ammonia is absorbed by the above neutralization reaction. It is thought that only hydrogen chloride can be recovered. This difference in reaction mechanism results in a large difference in the amount of sublimation of ammonium chloride, the rate of recovery of hydrogen chloride, and the amount of circulating molten salt, as described above.

Ammonium chloride gas is solid ammonium chloride
It is obtained by heating and sublimating at 0°C or higher, preferably Fi 290 to 550°C, but usually a carrier gas such as nitrogen or air is passed into the sublimation process or mixed to contain 10 to 50 vol- of ammonium chloride. A mixed gas is used. This is very effective in suppressing the precipitation of sublimed ammonium chloride in the piping and at the feed inlet to the molten salt.

Since ammonium hydrogen sulfate molten salt absorbs ammonia from ammonium chloride gas very efficiently, no special measures are required, but the amount of molten salt used can be reduced, and the hydrogen chloride recovery rate can be improved, increasing the equipment volume. A method in which ammonium chloride gas and molten salt are brought into countercurrent contact is preferred because it can reduce the amount of gas.

The contact temperature may range from 200 to 290°C, but in consideration of the concentration of ammonium chloride gas to be supplied, prevention of scale generation at the supply inlet, and the amount of energy required, it is preferably as high as possible, that is, about 250 to 290°C. .

Temperatures above 290°C should be avoided as ammonium sulfate begins to decompose.

There is no 4IK limit for the ammonium sulfate content in the molten salt, as long as ammonium hydrogen sulfate absorbs ammonia very efficiently. However, although there are some differences depending on the temperature, if the ammonium sulfate content exceeds 70 mall, ammonium sulfate will precipitate in the molten salt as a solid, and the viscosity of the molten salt will rapidly increase, making handling difficult. Undesirable. Usually, the fused salt obtained from one hydrogen chloride recovery product contains 50 to 40 mobs of ammonium sulfate.

The molten salt obtained from the hydrogen chloride recovery rate does not contain ammonium chloride, but contains 50 to 40 mol of ammonium sulfate, so there will be no problems if it is heated to 300°C or higher, which is higher than the decomposition temperature of ammonium sulfate. Ammonia can be recovered.

Since there is an equilibrium between ammonium sulfate and ammonium hydrogen sulfate, high temperature sintering is preferred to increase ammonia recovery. However, high temperatures above 380"C, where ammonium hydrogen sulfate begins to decompose, should be avoided, preferably in the range of 350 to 370°C. The molten salt obtained from an ammonia recovery plant is usually 85mol19G of ammonium hydrogensulfate, It has a composition of 15 molq II of ammonium sulfate, and can be recycled to the hydrogen chloride recovery plant without requiring any treatment other than cooling to the temperature that corresponds to the hydrogen chloride recovery rate.In addition, 1 air is required to efficiently recover ammonia.

A method of supplying a carrier gas, such as nitrogen, into the molten salt is commonly used.

The method of the present invention not only solves the problem of sublimation of ammonium chloride during the process, which is a major obstacle to practical application, but also achieves a huge improvement over the method using solid ammonium chloride. That is, in the method of the present invention, which is not a reaction in which ammonium chloride is decomposed with ammonium hydrogen sulfate, the hydrogen chloride recovery rate is 10 to 100 times faster than that of a method that supplies solid ammonium chloride.
If the seismic intensity is 50 times higher than normal, the reactor required for unit hydrogen chloride recovery will be 115 degrees. 9, if solid ammonium chloride is supplied, 1 completely decomposes the ammonium chloride in the hydrogen chloride recovery process and obtains a molten salt that does not contain ammonium chloride. Rounding K is ammonium sulfate content, the amount is 4
The amount of ammonia recovered per unit molten salt is less than the amount compared to the method of the present invention.

As is clear from the above explanation, in the method of the present invention,
By using solid ammonium chloride, the required amount of molten salt is reduced to less than 90% compared with the conventional method, and the problem caused by ammonium chloride sublimation during the process is solved, resulting in stoichiometric hydrogen chloride. Separation and recovery of ammonia and ammonia were achieved. As a result, the reactor volume for the hydrogen chloride recovery rate is 1 Ao, and the amount of energy required for the sensible portion of the molten salt at the ammonia recovery plant is less than η. In other words, the method of the present invention is extremely suitable for use on an industrial scale, and makes it possible to effectively utilize chloride atomium, whose use was limited to fertilizers.

Hereinafter, the present invention will be specifically explained based on Examples. .

Example 1 2.0 mol of ammonium hydrogen sulfate was packed into a reactor with a gas inlet at the bottom, 5 mol of ammonium monochloride was packed into each sublimator, and nitrogen gas was introduced into the sublimator at a flow rate of 400 in. Introduced into the shoes of absorption tubes. The reactor is heated to melt ammonium sulfur/hydrogen at 280°C.
℃, and then heated the sublimator to a predetermined temperature to sublimate ammonium chloride and blow into the molten salt together with nitrogen gas. The circular cyclized hydrogen separated from ammonia is introduced into a gas absorption tube filled with pure water9. Round cyclized ammonium sublimated in 1 hour in experiment A1 with cL41 mol, A
The hydrogen chloride recovery rate was 7.41s in experiment A1 and 1001.A3ftt1 in experiment A2.

Next, in experiments A2 and A3, after cooling the sublimator to room temperature and completing hydrogen chloride recovery, only nitrogen gas was introduced into the reactor to raise the temperature of the reactor to s6o''C and keep it constant. The generated ammonia was captured in a gas absorption tube filled with dilute sulfuric acid.As a result, in A2, the amount of ammonia recovered in 2 hours after raising the temperature to !40''CK was 1139 mol, and the ammonium sulfate content in the molten salt was The amount is 140mo
It was 1gII. Similarly, in A5, the amount of ammonia recovered was (L64 mol), and the ammonium sulfate content in the molten salt was 2 t 5 mol. White scale was deposited inside the recovery tube during hydrogen chloride recovery and hyammonia recovery. There was nothing to do.

Comparative Example "Reactor 1 similar to Example 1 (filled with 2.0 mol of ammonium hydrogen sulfate, heated and melted at 250°C and 280°C, and mixed with 7 mol of ammonium chloride LO. Nitrogen gas flow rate was 4001 As blood, the generated hydrogen chloride can be introduced into a gas absorption tube filled with pure water.

At both molten salt temperatures* of 250°C and 280°C, white scale increased over time in the upper part of the reactor and in the recovery tube, and the increase in scale was particularly significant at 280°C. Recovery rate in 5 hours was 89.7% at 250℃
, at 280°C Table 2 Sat- and 9. Ammonium chloride remaining in the molten salt after hydrogen chloride recovery was 101 mol and 28
It was not detected at 0°C.

Example 2 Continuous operation for 10 hours was carried out using the reaction apparatus schematically shown in FIG. The OO sublimator was filled with solid ammonium chloride, and molten ammonium hydrogen sulfate containing 15 mal11 of ammonium sulfate was circulated to reactor M, preheater 9, reactor B, and cooling tank 011. Reactor size is 280
The temperature of the 9°C reactors was set at 560°C, and the temperature of the molten salt was lowered to s00°C in the cooling tank. The residence time of the molten salt was set to 20 minutes in reactor chamber B and 3 hours in chamber B. The capacity of reactor B was rhsl, and the capacity of reactor B was tOt.

Keep the temperature of the ammonium chloride sublimator at 550℃,
A mixed gas of 4/nin of nitrogen gas and ammonium chloride was introduced into the reactor, and the recovered gas was filled with an aqueous solution of caustic soda through a recovery tube and captured in a gas absorption tube. i
9. Blow nitrogen gas into the reactor BK41AS,
Introduce the recovered gas into a gas absorption tube filled with an aqueous sulfuric acid solution. As a result of 10 hours of continuous operation, the amount of sublimated ammonium chloride was 11! What is the recovery rate for hydrogen chloride recovered in s moles per 1 ton and 1 mole? The amount of ammonia recovered was 111 moles, and the recovery rate was ttS-. After 10 hours of continuous operation, no white scale was found to be deposited in the upper part of the 4 reactors, B, or the collection tube.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the nine reactor used in Example 2. The solid line shows the flow of molten salt, and the broken line shows the flow of gas. M: hydrogen chloride recovery reactor, B = ammonia recovery reactor,
C: ammonium chloride sublimator, 'D = preheater. 1: Cooling tank, 't: Hydrogen chloride gas absorption pipe, G: Ammonia gas absorption pipe, P: Pump patent applicant Toyo Ichida Kogyo Co., Ltd.

Claims (1)

[Claims] 0) A method for separating and recovering hydrogen chloride and ammonia from ammonium chloride using ammonium hydrogen sulfate, in which a molten salt mainly consisting of ammonium hydrogen sulfate is brought into contact with ammonium chloride gas, and ammonia is added to the molten salt. The hydrogen chloride recovery process consists of a hydrogen chloride recovery process in which hydrogen chloride is separated and recovered by absorption, and an ammonia recovery process in which ammonia is absorbed and the molten salt is heated to separate and recover ammonia from the molten salt. Hydrogen chloride recovery process 11 for molten salt consisting of ammonium hydrogen
A method for separating and recovering hydrogen chloride and ammonia from ammonium chloride using Kli rings as a q# track. (2) The method according to claim 1, characterized in that a molten salt mainly consisting of ammonium hydrogen sulfate and ammonium chloride gas are brought into countercurrent contact. (2) As ammonium chloride gas, use a carrier gas such as nitrogen or air for 50~! 3. The method according to claim 1 or 2, characterized in that a mixed gas containing O□VOW- is used. 44) Any one of claims 1 to 3, characterized in that hydrogen chloride is recovered at a temperature of 200°C to 290°C, and ammonia is recovered at a temperature of 11 degrees, from 300°C to 580°C. The method described in.