WO2023084314A1

WO2023084314A1 - A process for the preparation of sulfamic acid

Info

Publication number: WO2023084314A1
Application number: PCT/IB2022/020068
Authority: WO
Inventors: Dhananjay Mahendra Lodha; Janardanan Kapyur NAMBOODIRI
Original assignee: Shree Sulphurics Pvt. Ltd.
Priority date: 2021-11-10
Filing date: 2022-11-10
Publication date: 2023-05-19

Abstract

The present disclosure relates to a process for the preparation of sulfamic acid. The process of the present disclosure has various advantages such as it avoids sudden pressurization of the reactor due to accumulation of reactants, prevents the uncontrolled temperature rise of reactants thus enhancing the efficiency of the reaction, hence controls exothermicity of the reaction. The process of the present disclosure substantially reduced the generation of the waste sulfuric acid during the process since liquid sulfur dioxide is recovered by distillation. Further, the excess sulfur trioxide is recovered and the wastage of sulfuric acid is reduced by reusing it, thereby making the process cost-efficient and environmental friendly.

Description

A PROCESS FOR THE PREPARATION OF SULFAMIC ACID

FIELD

The present disclosure relates to a process for the preparation of sulfamic acid.

DEFINITIONS

As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicates otherwise.

Exothermicity refers to the process wherein heat releases during the chemical reaction.

HP/M3 (Horse power per metre cube) refers to the agitator power per unit volume. It is a measure of the level of agitation.

BACKGROUND

The background information herein below relates to the present disclosure but is not necessarily prior art.

Sulfamic acid, also known as amidosulfonic acid, and amidosulfuric acid; is an important industrial chemical compound. It is used as such or as a component in cleaning agents, descaling agents and the like. Further, sulfamic acid is used as an intermediate in the manufacture of pharmaceutical products, sweeteners, dyes, pigments, and the like. Sulfamic acid has applications in the pulp and paper industry and resins. Sulfamic acid has desirable water-descaling properties, low volatility, and low toxicity.

The general method of manufacturing sulfamic acid is as represented below:

NH₂-CO-NH₂ + SO₃ + H2SO4 = 2 NH2.SO3H + CO₂

Typically, during the process for the preparation of sulfamic acid; urea and sulphur trioxide are mixed in a large excess of sulfuric acid and are heated to a temperature in the range of 70 °C to 120 °C wherein carbon dioxide is evolved and sulfamic acid is formed in the form of precipitated solids. The reaction is strongly exothermic and is accompanied by gas evolution. During the aforesaid process, the problems generally encountered are: (1) satisfactory cooling is required during the reaction to control the heat of the reaction to yield the desired product, (2) recovery of a pure product and (3) disposal of the acidic waste thus generated. In the conventional process, the so-obtained sulfamic acid is required to be purified by crystallization by using water. Further, the waste sulphuric acid generated during the preparation of sulfamic acid has a concentration of 70% which is typically more than 3 tons per ton of product and its disposal is a major challenge.

The literature is replete with processes for the preparation of sulfamic acid by various other routes/methods. However, these methods are associated with drawbacks such as low yield and/or low purity of the product. Further, these methods involve tedious purification stages, thereby resulting in an expensive process.

The conventional process for the preparation of sulfamic acid teaches either a fast addition of oleum or the addition of liquid sulphur trioxide and sulphuric acid at a lower temperature and later heating the mass. Although, both the aforesaid procedures are possible at the laboratory scale, they are dangerous to practice at an industrial scale where reactors of volume 5000 to 10000 liters are used and where the reactions are conducted at high pressures. The fast reaction of a large amount of unreacted urea may lead to accidents because of high pressures.

Moreover, the known processes with solvent for the preparation of sulfamic acid is carried out by using hazardous solvents like halofluorocarbons which may lead to difficulty in the removal of these solvents from the product and difficulty in recycling the solvents.

There is, therefore, felt a need to provide an alternative process for the preparation of sulfamic acid, which mitigates the drawbacks mentioned herein above or at least provide an useful alternative.

OBJECTS

Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:

It is an object of the present disclosure to ameliorate one or more problems of the background or to at least provide a useful alternative.

An object of the present disclosure is to provide a process for the preparation of sulfamic acid. Another object of the present disclosure is to provide a simple, economical, environmentfriendly process for the preparation of sulfamic acid.

Yet another object of the present disclosure is to provide a process for the preparation of sulfamic acid which ensures safety by controlling an exothermicity of the reaction and by controlling evolution of carbon dioxide.

Still another object of the present disclosure is to provide a process for the preparation of sulfamic acid that gives comparatively high purity and high yield.

Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.

SUMMARY

The present disclosure relates to a process for the preparation of sulfamic acid. The process for the preparation of sulfamic acid comprises adding predetermined amounts of liquid sulfur trioxide and a fluid medium in a reactor to obtain a solution. Separately, urea is reacted with sulfuric acid in a predetermined molar ratio at a first predetermined temperature to obtain a mixture of urea sulfate and unreacted sulfuric acid. The so obtained solution of liquid sulfur trioxide and fluid medium is heated at a second predetermined temperature and at a first predetermined pressure followed by the gradual addition of the mixture of urea sulfate and unreacted sulfuric acid over a first predetermined time period to obtain a reaction mass. The so-obtained reaction mass is maintained at a third predetermined temperature and at a second predetermined pressure for a second predetermined time period to obtain a product mixture. The product mixture is cooled to a temperature in the range of 20 °C to 50 °C followed by filtering to obtain a cake of sulfamic acid and a filtrate. The filtrate is distilled to recover the liquid sulfur trioxide and the fluid medium to obtain a residue followed by filtering to obtain a cake of sulfamic acid.

DETAILED DESCRIPTION

Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.

The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," “including,” and “having,” are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure is not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.

The literature is replete with the preparation of sulfamic acid by various other routes/methods. However, these methods are associated with drawbacks such as low yield and/ or low purity of the product. Further, these methods involve tedious purification stages, thereby resulting in an expensive process. Moreover, the conventional process for the preparation of sulfamic acid is carried out by using hazardous solvents like halofluorocarbons which may lead to difficulty in the removal of these solvents from the product and the difficulty in recycling the solvents. Further, these conventional processes are not feasible to carry out at a commercial scale.

The present disclosure provided a process for the preparation of sulfamic acid.

In an aspect, the process for the preparation of sulfamic acid comprises the following steps: a. adding predetermined amounts of liquid sulfur trioxide and a fluid medium in a reactor to obtain a solution; b. separately, reacting urea with sulfuric acid in a predetermined molar ratio at a first predetermined temperature to obtain a mixture of urea sulfate and unreacted sulfuric acid; c. heating said solution obtained in step a) at a second predetermined temperature and at a first predetermined pressure followed by gradual addition of the mixture of urea sulfate and unreacted sulfuric acid obtained in step b) over a first predetermined time period to obtain a reaction mass; d. maintaining the reaction mass at a third predetermined temperature and at a second predetermined pressure for a second predetermined time period to obtain a product mixture; e. cooling the product mixture to a temperature in the range of 20 to 50 °C followed by filtering to obtain a cake of sulfamic acid and a filtrate; and f. distilling the filtrate to recover said liquid sulfur trioxide and said fluid medium to obtain a residue followed by filtering to obtain the cake of sulfamic acid.

In accordance with the present disclosure, the process for preparing the sulfamic acid is described in detail.

In a first step, a predetermined amount of liquid sulfur trioxide and a predetermined amount of a fluid medium are added in a reactor to obtain a solution.

In accordance with the present disclosure, the fluid medium is liquid sulfur dioxide (SO2).

In accordance with the present disclosure, the predetermined amount of liquid sulfur trioxide is with respect to the predetermined amount of the urea.

In accordance with the present disclosure, the predetermined amount of the fluid medium is with respect to the predetermined amount of the urea.

In a second step, separately, urea is reacted with sulfuric acid in a predetermined molar ratio at a first predetermined temperature to obtain a mixture of urea sulfate and unreacted sulfuric acid.

In accordance with the present disclosure, the predetermined molar ratio of urea to sulfuric acid is in the range of 1:1 to 1:2. In an exemplary embodiment, the predetermined molar ratio of urea to sulfuric acid is 1:1.6. In accordance with the present disclosure, the first predetermined temperature is in the range of 40°C to 100°C. In an exemplary embodiment, the first predetermined temperature is 70°C. In another exemplary embodiment, the first predetermined temperature is 50°C.

In accordance with the present disclosure, a molar ratio of sulfur trioxide to urea can be in the range of 1:1 to 4:1. In an exemplary embodiment, the molar ratio of sulfur trioxide to urea is 2.96: 1. In another exemplary embodiment, the molar ratio of the sulfur trioxide to urea is 2.43:1. In yet another exemplary embodiment, the molar ratio of the sulfur trioxide to urea is 3.61:1. In still another exemplary embodiment, the molar ratio of the sulfur trioxide to urea is 2.74:1.

In accordance with the present disclosure, a molar ratio of the fluid medium to urea can be in the range of 10:1 to 30:1. In an exemplary embodiment, the molar ratio of the fluid medium to urea is 17.2:1. In another exemplary embodiment, the molar ratio of the fluid medium to urea is 17.32:1. In yet another exemplary embodiment, the molar ratio of the fluid medium to urea is 17.74:1. In still another exemplary embodiment, the molar ratio of the fluid medium to urea is 24.88:1.

In a third step, the solution of liquid sulfur trioxide and the fluid medium is heated to a second predetermined temperature and at a first predetermined pressure followed by the gradual addition of the mixture of urea sulfate and unreacted sulfuric acid over a first predetermined time period to obtain a reaction mass.

In accordance with the present disclosure, carbon dioxide is evolved in the third step.

In accordance with the present disclosure, the second predetermined temperature is in the range of 60°C to 120°C. In an exemplary embodiment, the second predetermined temperature is 80°C.

In accordance with the present disclosure, the first predetermined pressure is in the range of 10 to 45 Kg/cm g. In an exemplary embodiment, the first predetermined pressure is 20 Kg/cm g.

In accordance with the present disclosure, the first predetermined time period is in the range of 2 hours to 8 hours. In an exemplary embodiment, the first predetermined time period is 3 hours. In another exemplary embodiment, the first predetermined time period is 2.5 hours. In yet another exemplary embodiment, the first predetermined time period is 2 hours. In a fourth step, the reaction mass is maintained at a third predetermined temperature and at a second predetermined pressure for a second predetermined time period to obtain a product mixture.

In accordance with the present disclosure, the third predetermined temperature is in the range of 60°C to 120°C. In an exemplary embodiment, the third predetermined temperature is 80°C.

In accordance with the present disclosure, the second predetermined pressure is in the range of 10 to 45 Kg/cm g. In an exemplary embodiment, the second predetermined pressure is 20 Kg/cm g.

In accordance with the present disclosure, the second predetermined time period is in the range of 30 minutes to 180 minutes. In an exemplary embodiment, the second predetermined time period is 60 minutes.

In a fifth step, the product mixture is cooled to a temperature in the range of 20 to 50 °C followed by filtering to obtain a cake of sulfamic acid.

In an exemplary embodiment, the product mixture is cooled to 35 °C. In another exemplary embodiment, the product mixture is cooled to 32°C. In yet another exemplary embodiment, the product mixture is cooled to 30°C.

In accordance with the present disclosure, the cake of sulfamic acid is dried to obtain sulfamic acid having a yield in the range of 81 to 87% and purity in the range of 80 to 90%.

In an exemplary embodiment, the yield of sulfamic acid is 84.4 %. In another exemplary embodiment, the yield of sulfamic acid is 81.53%. In yet another exemplary embodiment, the yield of sulfamic acid is 81.07%. In still another exemplary embodiment, the yield of sulfamic acid is 86.7%.

In an exemplary embodiment, the purity of sulfamic acid is 85 %. In another exemplary embodiment, the purity of sulfamic acid is 84%. In yet another exemplary embodiment, the purity of sulfamic acid is 86.5%. In still another exemplary embodiment, the purity of sulfamic acid is 89.4%.

Finally, the filtrate of sulfamic acid is distilled to recover the liquid sulphur dioxide (SO2) and the excess liquid sulphur trioxide (SO3) which is reused in the next batch. The residue left after the removal of SO2 and SO3 is filtered to get 2 to 5% yield of sulfamic acid. The recovery and reuse of the liquid sulphur dioxide (SO2) and the excess liquid sulphur trioxide (SO3) makes the process environment friendly.

The residue, after distillation of sulfur dioxide contains sulfuric acid, sulfur trioxide, sulfamic acid and impurities. Sulfur trioxide is recovered and sulfuric acid is reused for several cycles. Hence, the sulfuric acid in the form of waste is achieved in a very less amount i.e., less than 0.7 Kg/Kg product. The yield and the purity of the sulfamic acid are improved by varying the process conditions such as by increasing the agitation, by increasing the addition time per mol and by increasing the sulfur dioxide to urea ratio which results in the formation of slurry in lesser amount.

The process of the present disclosure involves the gradual addition of a preformed mixture of urea sulphate and unreacted sulfuric acid to the solution of sulphur trioxide dissolved in the fluid medium (sulfur dioxide medium) under pressure over 2 to 8 hours at a temperature in the range of 40°C to 100°C where the reaction proceeds at a substantial rate, to form sulfamic acid with the continuous evolution of carbon dioxide. This results in good control of the reaction rate since the reaction starts as soon as urea sulphate enters the reactor. Therefore, there is no accumulation of urea in the reactor, which ensures there is no sudden reaction resulting in the sudden generation of carbon dioxide. Further, the process of the present disclosure results in a comparatively very less amount of waste sulfuric acid. Thus, the process of the present disclosure is environment friendly.

The process of the present disclosure is simple and employs inexpensive, easily available reagents. Thus, the process of the present disclosure is economical.

The process of the present disclosure has the following advantages:

• the gradual addition of the mixture of urea sulfate and unreacted sulfuric acid to the solution of sulfur trioxide and sulfur dioxide medium avoids conditions for sudden pressurization of the reactor due to accumulation of reactants and later increase in the reaction rate, which is important when operating at large reactors under high pressure in a commercial plant; simplifies the heating and cooling arrangements and reduces the area of the condenser required to remove the heat, since, the heat of the reaction is about 45 Kcal/gmol urea, it is estimated that the mass gets heated to 170°C and the pressure rise to more than 79 Kg/cm²g in case of an instantaneous addition and reaction. Hence, to operate under pressure it is essential to control the reaction;

• the gradual addition of urea sulfate to a mixture of sulfur trioxide and sulfur dioxide medium also prevents the uncontrolled temperature rise of reactants (exothermicity of the reaction is in control);

• generation of the waste sulfuric acid during the process is substantially reduced since liquid sulfur dioxide is used as the medium of reaction and liquid sulfur dioxide is recovered by distillation, whereas sulfuric acid used in the conventional process is not recovered easily; and

• recovery of excess sulfur trioxide and reuse of sulfuric acid bring down the wastage of sulfuric acid and the cost of the process.

The foregoing description of the embodiments has been provided for purposes of illustration and is not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.

The present disclosure is further described in light of the following experiments which are set forth for illustration purposes only and not to be construed for limiting the scope of the disclosure. The following experiments can be scaled up to an industrial/commercial scale and the results obtained can be extrapolated to industrial scale.

EXPERIMENTAL DETAILS

Experiment 1: Preparation of sulfamic acid in accordance with the process of the present disclosure.

Example 1:

685 g of liquid sulfur trioxide and 3185 g of liquid sulfur dioxide were added to an autoclave (5 lit capacity) to obtain a solution. Separately, 600 g of urea was added gradually to 1568 g of 100% sulfuric acid at 70°C to obtain a mixture of urea sulfate and excess sulfuric acid. The solution of sulfur trioxide and sulfur dioxide was heated to 80°C and stirred at a pressure of 20 Kg/cm²g followed by the gradual addition of 628 g of the mixture of urea sulfate and sulfuric acid (corresponding to 2.9 moles urea) over 3 hours to obtain a reaction mass with the evolution of carbon dioxide which is vented off via a condenser. The reaction mass was maintained at 80°C and at a pressure of 20 Kg/cm g for an additional 1 hour to obtain a product mixture. The product mixture was cooled to 35 °C followed by filtering to obtain a cake of sulfamic acid and a filtrate. The cake of sulfamic acid was dried to obtain 547 g of sulfamic acid (yield = 82.2 %).

The filtrate was distilled to recover liquid SO2 and excess liquid SO3 which is reused in the next batch. The residue left after the removal of SO2 and SO3 was filtered to obtain 13 g of sulfamic acid (yield = 2.2 %).

Thus, the total yield of sulfamic acid was 84.4 %.

The purity of sulfamic acid was 85%.

Examples 2 to 4: Same procedure was followed as in Example 1 except for a change in the molar ratios and the reaction conditions as given in Table 1.

Table 1:

Inference:

It is evident from table 1 that the amount of the fluid medium, time of addition and agitation level are factors which influence yield. The present disclosure uses less amount of urea and higher amount of the fluid medium which is recovered easily by the distillation and reused, hence the process of the present disclosure is cost-effective, simple and environment-friendly.

TECHNICAL ADVANCEMENTS

The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a process for the preparation of sulfamic acid, which:

- is less hazardous and hence safe;

- controls the exothermicity, removes chances of pressurization, and ensures control of the reaction on the industrial scale without dangers of runaway of reaction due to the gradual addition of urea sulfate since the process uses sulfur dioxide under pressure as a medium of reaction;

- is simple and environment-friendly;

- recovers the fluid medium used by distillation and reused;

- produces the product in good yield and purity; and

- involves simple workup methodology giving high productivity.

The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

The foregoing description of the specific embodiments so fully reveals the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.

Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.

The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.

While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.

Claims

CLAIMS:

1. A process for the preparation of sulfamic acid, said process comprising the steps of: a. adding predetermined amounts of liquid sulfur trioxide and a fluid medium in a reactor to obtain a solution; b. separately, reacting urea with sulfuric acid in a predetermined molar ratio at a first predetermined temperature to obtain a mixture of urea sulfate and unreacted sulfuric acid; c. heating said solution obtained in step a) at a second predetermined temperature and at a first predetermined pressure followed by gradual addition of said mixture of urea sulfate and unreacted sulfuric acid obtained in step b) over a first predetermined time period to obtain a reaction mass; d. maintaining said reaction mass at a third predetermined temperature and at a second predetermined pressure for a second predetermined time period to obtain a product mixture; e. cooling said product mixture to a temperature in the range of 20 to 50 °C followed by filtering to obtain a cake of sulfamic acid and a filtrate; and f. distilling said filtrate to recover said liquid sulfur trioxide and said fluid medium to obtain a residue followed by filtering to obtain a cake of sulfamic acid.

2. The process as claimed in claim 1, wherein said predetermined amount of liquid sulfur trioxide is with respect to the predetermined amount of urea.

3. The process as claimed in claim 1, wherein said predetermined amount of fluid medium is with respect to the predetermined amount of urea.

4. The process as claimed in claim 1, wherein a molar ratio of sulfur trioxide to urea is in the range of 1:1 to 4:1.

5. The process as claimed in claim 1, wherein a molar ratio of sulfur trioxide to urea is 2.96: 1.

6. The process as claimed in claim 1, wherein a molar ratio of sulfur trioxide to urea is 2.43: 1.

7. The process as claimed in claim 1, wherein a molar ratio of sulfur trioxide to urea is 3.61: 1.

8. The process as claimed in claim 1, wherein a molar ratio of sulfur trioxide to urea is 2.74: 1.

9. The process as claimed in claim 1, wherein a molar ratio of said fluid medium to urea is in the range of 10:1 to 30:1.

10. The process as claimed in claim 1, wherein a molar ratio of said fluid medium to urea is 17.2:1.

11. The process as claimed in claim 1, wherein a molar ratio of said fluid medium to urea is 17.32:1.

12. The process as claimed in claim 1, wherein a molar ratio of said fluid medium to urea is 17.74:1.

13. The process as claimed in claim 1, wherein a molar ratio of said fluid medium to urea is 24.88:1.

14. The process as claimed in claim 1, wherein said predetermined molar ratio of urea to sulfuric acid is in the range of 1 : 1 to 1 : 2.

15. The process as claimed in claim 1, wherein said predetermined molar ratio of urea to sulfuric acid is 1:1.6.

16. The process as claimed in claim 1, wherein said first predetermined temperature is in the range of 40°C to 100°C.

17. The process as claimed in claim 1, wherein the first predetermined temperature is 70°C.

18. The process as claimed in claim 1, wherein said second predetermined temperature and said third predetermined temperature are independently selected in the range of 60°C to 120°C.

19. The process as claimed in claim 1, wherein said second predetermined temperature and said third predetermined temperature is 80°C.

20. The process as claimed in claim 1 , wherein said first predetermined pressure and said second predetermined pressure are independently selected in the range of 10 to 45 Kg/cm g.

21. The process as claimed in claim 1, wherein said first predetermined pressure and said second predetermined pressure is 20 Kg/cm g.

22. The process as claimed in claim 1, wherein said first predetermined time period is in the range of 2 hours to 8 hours.

23. The process as claimed in claim 1, wherein said first predetermined time period is in the range of 2 hours to 3 hours.

24. The process as claimed in claim 1 , wherein said second predetermined time period is in the range of 30 minutes to 180 minutes.

25. The process as claimed in claim 1, wherein said second predetermined time period is 60 minutes.

26. The process as claimed in claim 1 , wherein said sulfamic acid has a yield in the range of 81 to 87% and a purity in the range of 80 to 90%.

27. A sulfamic acid produced by the process as claimed in any one of claims 1 to 26.

28. The sulfamic acid as claimed in claim 27 has purity in the range of 80 to 90%.

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