DESC:FIELD
The present disclosure relates to a process for the crystallization.
DEFINITION
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.
Raschig process: The term “Raschig process” refers to an industrial chemical method used for the production of hydroxylamine sulphate [(NH3OH)2 SO4] from Ammonia. It involves the oxidation of ammonia to prepare nitrous oxide followed by hydrogenation and subsequent reaction with sulphuric acid to prepare hydroxylamine sulphate solution.
Reichert MeF3: The term “Reichert MeF3” is used for a traditional inverted metallurgical microscope. The microscope offers multiple imaging modes, including bright field, dark field, polarized light, and differential interference contrast (DIC), providing versatility in material characterization.
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
Hydroxylamine sulphate is an odorless white crystalline solid. It is a stable form of hydroxylamine, a reactive compound that participates in many chemical reactions. Hydroxylamine sulphate is widely used in organic and inorganic synthesis. Hydroxylamine sulphate is also used for the manufacturing of hydroxylamine free base for radioactive industry, film photographic materials, photo reagents and as an oxidant in various formulations of liquid propellants.
In conventional crystallization methods, the resulting hydroxylamine sulphate (HAS) crystals are often small or have a wide size distribution, leading to suboptimal flowability. Poor flowability can cause operational issues such as blockages in handling equipment, inconsistent dosing, and difficulties in conveying materials. These problems are worsened when dealing with high-volume or automated processing environments, where precise control over material movement is essential.
The conventional methods for the preparation of hydroxylamine sulphate crystals using Swenson Walker crystallizer are known to produce more than 70% hydroxylamine sulphate crystals having a size of 150 µm or less. However, better control of flowability is observed when the size of hydroxylamine sulphate crystals is increased. Hence, it is required to enhance the crystal size and uniformity of the hydroxylamine sulphate crystals to increase its flowability.
Therefore, there is a need to provide a process for the crystallization of hydroxylamine sulphate that mitigates the drawbacks mentioned herein above or at least provides a 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 is to ameliorate one or more problems of the background or to at least provide a useful alternative.
Another object of the present disclosure is to provide a process for the crystallization of hydroxylamine sulphate.
Yet another object of the present disclosure is to provide a process for the crystallization of hydroxylamine sulphate that elevates the crystal size and reduces the excess consumption of the feed streams.
Still another object of the present disclosure is to provide a crystallization process that is simple and efficient.
Yet another object of the present disclosure is to provide a crystallization process that is commercially scalable.
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 crystallization of hydroxylamine sulphate, the process comprises the steps of:
a) obtaining a crude hydroxylamine sulphate solution;
b) evaporating the crude hydroxylamine sulphate solution at a first predetermined temperature to obtain a concentrated hydroxylamine sulphate solution having a predetermined density;
c) crystallizing the concentrated hydroxylamine sulphate solution under a predetermined agitation speed at a predetermined cooling condition to obtain a resultant mass;
d) centrifuging the resultant mass at a predetermined speed to obtain solids; and
e) drying the solids at a second predetermined temperature for a predetermined time period to obtain crystals of hydroxylamine sulphate having a predetermined particle size.
In an embodiment of the present disclosure, the crude hydroxylamine sulphate solution is a mixture of hydroxylamine sulphate, ammonium sulphate and sulphuric acid obtained by Raschig process.
In an embodiment of the present disclosure, the first predetermined temperature is in the range of 80 °C to 120 °C, preferably in the range of 100 °C to 110 °C.
In an embodiment of the present disclosure, the predetermined agitation speed is in the range of 3 rpm to 5 rpm.
In an embodiment of the present disclosure, the predetermined density is in the range of 1300 kg/m3 to 1450 kg/m3.
In an embodiment of the present disclosure, the predetermined density of the concentrated hydroxylamine sulphate solution is achieved through one or more evaporators.
In an embodiment of the present disclosure, the predetermined cooling condition comprises cooling with chilled water, cooling with ambient water and dual cooling.
In an embodiment of the present disclosure, the predetermined dual cooling condition comprises circulating ambient water in the cooling jacket for a time period in the range of 5 minutes to 150 minutes, followed by circulating chilled water for a time period in the range of 30 minutes to 120 minutes.
In an embodiment of the present disclosure, the predetermined cooling condition comprises a residence time of said concentrated hydroxylamine sulphate solution in the range of 30 minutes to 180 minutes.
In an embodiment of the present disclosure, the predetermined cooling condition comprises a cooling temperature of said concentrated hydroxylamine sulphate solution in the range of 8 °C to 30 °C.
In an embodiment of the present disclosure, the predetermined speed is in the range of 1000 rpm to 2500 rpm.
In an embodiment of the present disclosure, the second predetermined temperature is in the range of 90 °C to 110 °C.
In an embodiment of the present disclosure, the predetermined time period is in the range of 5 minutes to 25 minutes.
In an embodiment of the present disclosure, the hydroxylamine sulphate crystals are characterized by having:
• a predetermined particle size in the range of 300 µm to 1870 µm;
• free acid value of less than 0.4 mass%;
• ammonium sulphate content of less than 0.5 mass%; and
• a moisture content of less than 0.2%.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
The present disclosure will now be described with the help of the accompanying drawing, in which:
Figure 1A illustrates a Reichert MeF3 microscopic image of the hydroxylamine sulphate crystals prepared in accordance with the Example 1 (conventional process) of the present disclosure;
Figure 1B illustrates a Reichert MeF3 microscopic image of the hydroxylamine sulphate crystals prepared in accordance with Example 6 of the present disclosure;
Figure 2 illustrates the comparative graph between assay and crystallization temperature in accordance with Examples 7 to 13 of the present disclosure;
Figure 3A and Figure 3B illustrate the Reichert MeF3 microscopic images showing crystal size obtained by slightly decreasing the density to 1320 kg/m3 in accordance with the present disclosure;
Figure 4A illustrates a Reichert MeF3 microscopic image of a hydroxylamine sulphate crystal, wherein the crystal size is 399.39 µm in accordance with Example 16 of the present disclosure;
Figure 4B illustrates a Reichert MeF3 microscopic image of a hydroxylamine sulphate crystal, wherein the crystal size is 1131.55 µm in accordance with Example 16 of the present disclosure;
Figure 5 illustrates the comparative graph between assay values of the hydroxylamine sulphate solution at different densities in accordance with the present disclosure;
Figure 6 illustrates the graphical representation of the crystallization temperature Vs time in accordance with Example 17 of the present disclosure;
Figure 7 illustrates a particle size distribution graph of the obtained hydroxylamine sulphate crystals in continuously agitated crystallizer in accordance with Example 18 of the present disclosure;
Figure 8 illustrates a particle size distribution graph of the obtained hydroxylamine sulphate crystals in a crystallizer without agitation in accordance with the present disclosure;
Figure 9 illustrates a particle size distribution graph of the hydroxylamine sulphate crystals in two crystallizers in accordance with Example 19 of the present disclosure; and
Figure 10 illustrates the general process flow diagram for the production of hydroxylamine sulphate crystals, wherein (E) refers to an evaporator, (TK) refers to a holding tank, (C) refers to a crystallizer, (CF) refers to a centrifuge, and (D) refers to a dryer in accordance with the present disclosure.
DETAILED DESCRIPTION
The present disclosure relates to a process for the crystallization. Particularly, the present disclosure relates to a process for the crystallization of hydroxylamine sulphate.
Embodiments of the present disclosure will now be described with reference to the accompanying drawings.
Embodiments, of the present disclosure, will now be described herein. 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.
As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed elements.
The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third etc., when used herein do not imply a specific sequence or order unless clearly suggested by the present disclosure.
Conventional crystallization methods for producing hydroxylamine sulphate (HAS) crystals, particularly using a Swenson Walker crystallizer, tend to generate small crystals with a wide size distribution in which over 70% of the crystals being 150 µm or less. This results in poor flowability, leading to operational issues like blockages, inconsistent dosing, and handling difficulties, especially in high-volume or automated environments. To address these challenges, there is a need to enhance the size and uniformity of HAS crystals to improve their flowability and facilitate smoother processing.
The present disclosure provides a process for the crystallization of hydroxyl amine sulphate.
The present disclosure relates to a process for the crystallization of hydroxylamine sulphate, the process comprising the steps of obtaining a crude hydroxylamine sulphate solution. The crude hydroxylamine sulphate solution is evaporated at a first predetermined temperature to obtain a concentrated hydroxylamine sulphate solution having a predetermined density. The concentrated hydroxylamine sulphate solution is crystallized under a predetermined agitation speed at a predetermined cooling condition to obtain a resultant mass. The resultant mass is centrifuged at a predetermined speed to obtain solids. The solids are dried at a second predetermined temperature for a predetermined time period to obtain crystals of hydroxylamine sulphate having predetermined particle size.
The process is described in detail below.
In a first step, a crude hydroxylamine sulphate solution is obtained.
In an embodiment of the present disclosure, the crude hydroxylamine sulphate solution is a mixture of hydroxylamine sulphate, ammonium sulphate and sulphuric acid obtained by Raschig process.
The crude hydroxylamine sulphate solution obtained by Raschig process is used as a raw material for the manufacturing of Caprolactam.
In a second step, the crude hydroxylamine sulphate solution is evaporated at a first predetermined temperature to obtain a concentrated hydroxylamine sulphate solution having a predetermined density.
In an embodiment of the present disclosure, the first predetermined temperature is in the range of 80 °C to 120 °C, preferably in the range of 100 °C to 110 °C. In an exemplary embodiment, the first predetermined temperature is 105°C.
In an embodiment of the present disclosure, the predetermined density is in the range of 1300 kg/m3 to 1450 kg/m3. In an exemplary embodiment, the predetermined density is 1400 kg/m3. In another exemplary embodiment, the predetermined density is 1380 kg/m3. In yet another exemplary embodiment, the predetermined density is 1320 kg/m3. In still another exemplary embodiment, the predetermined density is 1300 kg/m3. In yet another exemplary embodiment, the predetermined density is 1362 kg/m3. The density of the concentrated hydroxylamine solution before crystallization plays a critical role in determining both the yield and purity of the final product. If the solution's density falls below 1200 kg/m³, it leads to a reduction in production efficiency, resulting in lower yields of hydroxylamine sulphate crystals. Conversely, if the density exceeds 1450 kg/m³, it negatively impacts the chemical purity of the crystals, causing higher amounts of impurities such as ammonium sulphate and free sulfuric acid to remain. These impurities originate from the crude hydroxylamine sulphate solution produced by Raschig process, which includes not only hydroxylamine sulphate but also ammonium sulphate and sulfuric acid. Thus, maintaining an optimal density range between 1300 kg/m³ and 1450 kg/m³ is crucial for achieving high-quality hydroxylamine sulphate (HAS) crystals with minimal impurities.
In an embodiment of the present disclosure, the predetermined density of the concentrated hydroxylamine sulphate solution is achieved through one or more evaporators.
In a third step, the concentrated hydroxylamine sulphate solution is crystallized under a predetermined agitation speed at a predetermined cooling condition to obtain a resultant mass.
In an embodiment of the present disclosure, the predetermined agitation speed is in the range of 3 rpm to 5 rpm. In an exemplary embodiment, the predetermined speed is 4 rpm.
In an embodiment of the present disclosure, the predetermined cooling conditions comprises cooling with chilled water, cooling with ambient water, and dual cooling.
In an embodiment of the present disclosure, the predetermined dual cooling conditions comprise circulating ambient water in the cooling jacket for a time period in the range of 5 minutes to 150 minutes, followed by circulating chilled water for a time period in the range of 30 minutes to 120 minutes. In an exemplary embodiment, the ambient water is circulated in the cooling jacket for 120 minutes, followed by circulating chilled water for 60 minutes. In another exemplary embodiment, the ambient water is circulated in the cooling jacket for 45 minutes, followed by circulating chilled water for 60 minutes. In yet another exemplary embodiment, the ambient water is circulated in the cooling jacket for 45 minutes, followed by circulating chilled water for 45 minutes. In still another exemplary embodiment, the ambient water is circulated in the cooling jacket for 30 minutes, followed by circulating chilled water for 60 minutes. In yet another exemplary embodiment, the ambient water is circulated in the cooling jacket for 5 minutes, followed by circulating chilled water for 57 minutes. In still another exemplary embodiment, the ambient water is circulated in the cooling jacket for 14 minutes, followed by circulating chilled water for 95 minutes. In yet another exemplary embodiment, the ambient water is circulated in the cooling jacket for 14 minutes, followed by circulating chilled water for 115 minutes. In yet another exemplary embodiment, the ambient water is circulated in the cooling jacket for 45 minutes, followed by circulating chilled water for 60 minutes. In still another exemplary embodiment, the ambient water is circulated in the cooling jacket for 5 minutes, followed by circulating chilled water for 60 minutes.
In an embodiment of the present disclosure, the predetermined cooling condition comprises a residence time of the concentrated hydroxylamine sulphate solution in the range of 30 minutes to 180 minutes. In an exemplary embodiment, the predetermined cooling condition comprises a residence time of 60 minutes.
In an embodiment of the present disclosure, the predetermined cooling conditions comprise a cooling temperature of the concentrated hydroxylamine sulphate solution in the range of 8 °C to 30 °C. In an exemplary embodiment, the predetermined cooling condition comprises a cooling temperature of 10 °C. In another exemplary embodiment, the predetermined cooling condition comprises a cooling temperature of 15 °C. In yet another exemplary embodiment, the predetermined cooling condition comprises a cooling temperature of 20 °C.
In a fourth step, the resultant mass is centrifuged at a predetermined speed to obtain solids.
In an embodiment of the present disclosure, the centrifugation speed is in the range of 1000 rpm to 2500 rpm. In an exemplary embodiment, the predetermined centrifugation speed is 1500 rpm.
In a fifth step, the solids are dried at a second predetermined temperature for a predetermined time period to obtain the hydroxylamine sulphate crystals having a predetermined particle size.
In an embodiment of the present disclosure, the predetermined particle size is in the range of 300 µm to 1870 µm.
In an embodiment of the present disclosure, the predetermined particle size is in the range of 300 µm to 800 µm.
In an exemplary embodiment, the predetermined particle size is 398.03 µm. In another exemplary embodiment, the predetermined particle size is 1866.74 µm. In yet another exemplary embodiment, the predetermined particle size is 399.39 µm. In still another exemplary embodiment, the predetermined particle size is 1143.60 µm.
In an embodiment of the present disclosure, the second predetermined temperature is in the range of 90 °C to 110 °C. In an exemplary embodiment, the second predetermined temperature is 105 °C.
In an embodiment of the present disclosure, the predetermined time period is in the range of 5 minutes to 25 minutes. In an exemplary embodiment, the second predetermined time period is 10 minutes.
In an embodiment of the present disclosure, the hydroxylamine sulphate crystals are characterized by having:
• a predetermined particle size in the range of 300 µm to 1870 µm;
• free acid value of less than 0.4 mass%;
• ammonium sulphate content of less than 0.5 mass%; and
• a moisture content of less than 0.2%.
In an exemplary embodiment, the hydroxylamine crystals are characterized by having a particle size of 1131.55 µm, free acid value of 0.08 mass%, ammonium sulphate content of 0.5 mass%, and moisture content of less than 0.19%.
The process of the present disclosure provides pure hydroxylamine sulphate crystals that exhibits enhanced flowability. The consistent particle size range (398 µm to 1866 µm) leads to uniform dosing and accurate measurement in automated processes. This consistency improves the reliability and precision of manufacturing operations, particularly in high-volume or automated environments. In addition to the enhanced flowability, the specified characteristics of the hydroxylamine sulphate (HAS) crystals provide several additional advantages such as improved chemical purity, greater stability, better handling and storage, and reduced environmental impact. With a free acid value of less than 0.4 mass% and ammonium sulphate content of less than 0.5 mass%, the HAS crystals are of higher chemical purity. This purity ensures better performance in downstream chemical reactions and reduces the need for additional purification steps, lowering production costs and improving efficiency.
The reduced free acid content contributes to the enhanced chemical stability of the crystals, minimizing the risk of unwanted reactions or degradation during storage or handling. A moisture content of less than 0.2% means the crystals are less prone to clumping, caking, or sticking together. This results in easier handling, more efficient storage, and lower chances of contamination or degradation from moisture, leading to extended shelf life. The high purity and controlled particle size can lead to improved reaction yields in organic and inorganic synthesis, as fewer impurities mean less interference in chemical processes. This is particularly advantageous in applications requiring precise control over reactants, such as in pharmaceuticals or the production of sensitive materials. Further, with fewer impurities, there is less generation of waste and by-products, contributing to a cleaner production process and reducing the environmental impact of downstream applications.
The foregoing description of the embodiments has been provided for purposes of illustration and 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 purpose only and not to be construed for limiting the scope of the disclosure. The following experiments are scalable to industrial/commercial process.
EXPERIMENTAL DETAILS
EXPERIMENT 1: A process for the crystallization of hydroxylamine sulphate (HAS) in accordance with the present disclosure
Examples 1- Crystallization with chilled water
Crude Hydroxylamine sulphate solution was obtained by Raschig process which was used for the production of Caprolactam. 75 Kg of the crude hydroxylamine sulphate solution was evaporated in an evaporator at 105 °C for 90 minutes to obtain a concentrated hydroxylamine sulphate solution having a density of 1350 kg/m3 (measured at 85 °C). The so-obtained concentrated hydroxylamine sulphate solution was transferred to a crystallizer and crystallized by continuously flowing chilled water as the cooling medium in the jacket of the crystallizer to obtain a resultant mass. The cooling temperature was maintained at 20°C. The resultant mass was centrifuged at 1500 rpm to obtain solids. The solids were dried at 105 °C for 10 minutes to obtain 32 kg of hydroxylamine sulphate crystals. The hydroxylamine sulphate crystals obtained in example 1 were analyzed for the following specification as summarized in Table 1:
Table 1: Quality Parameters for Hydroxylamine Sulphate Crystals obtained in Example 1
Components of the crystals Desired specifications (w/w) Actual results
Hydroxylamine sulphate Minimum 99.0% 99.59%
Free Sulphuric Acid Maximum 0.3% 0.05%
Ammonium Sulphate Maximum 0.5% 0.24%
Moisture Maximum 0.3% 0.15%
The obtained crystals have desired specifications.
Examples 2 to 4- Crystallization with chilled water with agitation at low speed
Example 2 was carried out in a similar manner to Example 1, except that chilled water was circulated for 30 minutes at 15 Hz and after 30 °C is obtained, one rotation per 10 minutes is given in the crystallizer. Example 3 was carried out in a similar manner as Example 2, except chilled water was supplied till 25 °C is obtained in the crystallizer. Example 4 was carried out in a similar manner to Example 2, except chilled water was supplied till 20 °C was obtained in the crystallizer.
The obtained crystals had the desired specification. A crystal size in the range of 300 µm to 800 µm was obtained from the hydroxylamine sulphate obtained in Examples 2 to 4.
EXPERIMENT 2: Optimization of the cooling condition
Example 5- Crystallization with ambient water
Example 5 was carried out in a similar manner to Example 1, except that the crystallization was carried out with ambient water in the jacket of the crystallizer while maintaining the cooling temperature at 47 °C.
The hydroxylamine sulphate crystals obtained in example 5 were analyzed for the following specification as summarized in Table 2:
Table 2: Quality Parameters for Hydroxylamine Sulphate Crystals obtained in Example 5
Components of the crystals Desired specifications (w/w) Actual results
Hydroxylamine sulphate Minimum 99.0% 98.0%
Free Sulphuric Acid Maximum 0.3% 0.93%
Ammonium Sulphate Maximum 0.5% 0.51%
Moisture Maximum 0.3% 0.53%
The specifications of the so-obtained hydroxylamine sulphate as illustrated in Figure 1A, did not meet with the desired specification.
Example 6- Crystallization with dual cooling conditions
Example 6 was carried out in a similar manner to Example 1, except that the initial crystallization was carried out with ambient and chilled water in the jacket of the crystallizer while maintaining the crystallization temperature at 10 °C.
The hydroxylamine sulphate crystals obtained in example 6 were analyzed for the following specification as summarized in Table 3:
Table 3: Quality Parameters for Hydroxylamine Sulphate Crystals obtained in Example 6
Components of the crystals Desired specifications (w/w) Actual results
Hydroxylamine sulphate Minimum 99.0% 99.31%
Free Sulphuric Acid Maximum 0.3% 0.10%
Ammonium Sulphate Maximum 0.5% 0.37%
Moisture Maximum 0.3% 0.18%
The specifications of the so-obtained hydroxylamine sulphate met with the desired specification with particle size of the hydroxylamine sulphate crystals ranging from 550 µm to 1200 µm as illustrated in Figure 1B.
Optimization of dual cooling conditions
Examples 7 to 13
Examples 7 to 13 were carried out in a similar manner to Example 6, except that 100 kg of hydroxylamine sulphate solution was used, the density of the concentrated hydroxylamine sulphate solution was kept at 1380 kg/m3, and the cooling conditions were maintained in accordance with Table 4.
Table 4: Optimization of dual cooling conditions
Example Dual Cooling Conditions Cooling temperature (°C)
Circulation of Ambient water Circulation of Chilled water
7 120 minutes 60 minutes 15
8 45 minutes 60 minutes 10
9 45 minutes 45 minutes 10
10 30 minutes 60 minutes 10
11 5 minutes till 60 °C is obtained 57 minutes 20
12 Till 50 °C is obtained 60 minutes 15
13 14 minutes till 60 °C is obtained 115 minutes 15
The observed crystal size was in the range of 300 µm to 1200 µm. Figure 2 illustrates the comparative graph between assay and crystallization temperature. The observed yield in Examples 7 to 13 were in the range of 9.5% to 11%.
Optimization of dual cooling condition with slight variation of density
Example 14
Example 14 was carried out in a similar manner to Example 9, except that the density was slightly reduced to 1320 kg/m3. The observed particle size was in the range of 398.03 µm to 1866.74 µm with 10.5% yield as illustrated in Figure 3A and Figure 3B.
Example 15
Example 15 was carried out in a similar manner to Example 8, except that the density was slightly lowered to 1320 kg/m3. The observed particle size was in the desired range. However, the free sulphuric acid was up to 0.3 mass%.
To decrease the amount of sulphuric acid, controlled heat transfer is required, which aids the sufficient heat transfer between the two mediums and ultimately helps to lower the percentage of free sulphuric acid and increase the crystal growth.
Example 16
Example 16 was carried out in a similar manner to Example 11, except that the density was slightly lowered to 1300 kg/m3. The observed parameters are summarized in Table 5.
Table 5: Quality Parameters for Hydroxylamine Sulphate Crystals obtained in Example 16
Components of the crystals Desired specifications (w/w) Actual results
Hydroxylamine sulphate Minimum 99.0% 99.37%
Free Sulphuric Acid Maximum 0.3% 0.08%
Ammonium Sulphate Maximum 0.5% 0.30%
Moisture Maximum 0.3% 0.19%
All the specifications were in range and the observed crystal size was in the range of 399.39 µm to 1131.55 µm as illustrated in Figure 4A and Figure 4B respectively.
Figure 5 illustrates the comparative graph between assay values of the hydroxylamine sulphate solution.
The dual cooling condition initially used in the crystallization process presented significant challenges during scale-up to the pilot plant. Key issues included non-replicability, prolonged operation time, the need for additional crystallizers, low production yield, and increased operational costs. These drawbacks stemmed from the complexity of managing two distinct cooling mechanisms simultaneously, which introduced variability and inefficiency in the process.
To address these challenges, the process was adapted to use only chilled water cooling to simplify the operation, to ensure consistency, and to improve scalability.
Optimization of cooling condition with chilled water circulation in crystallizer
Example 17- Crystallization with residence time
Example 17 was carried out in a similar manner to Example 1, except that the density of the concentrated hydroxylamine sulphate solution was maintained between 1350 kg/m3 to 1360 kg/m3 and a residence time of 1 hour was provided in the crystallizer to facilitate crystal growth. The crystallization was carried out till 20°C temperature was obtained. Figure 6 illustrates a graph of average crystallization temperature Vs time.
Example 18- Crystallization with agitation
Example 18 was carried out in a similar manner to Example 1, except that the crystallizer was continuously agitated at 4 rpm till the temperature of the crystallizer reached 20 °C. The agitation speed is important and needs to be controlled as high speed of the agitator leads to the breakage of the crystals.
The specifications of the crystals were within the desired range with 80% of the crystals having the particle size more than 500 µm. Figure 7 illustrates the particle size distribution of the obtained hydroxylamine sulphate crystals.
Figure 8 illustrates a particle size distribution graph of the obtained hydroxylamine sulphate crystals in a crystallizer without agitation.
Example 19- Crystallization in two large scale crystallizers
Example 19 was carried out in a in a similar manner to Example 1, except that the crystallization was carried out in two large scale crystallizers, and the density of the concentrated hydroxylamine sulphate solution was maintained at 1350 kg/m3 at 85 °C. After the desired density was achieved, the hydroxylamine sulphate solution was pumped from a holding tank (TK) to the crystallizers (C1) and (C2). Here, the crystallization of the solution was carried out in both the crystallizers. The temperature of the crystallizers were maintained at 25 °C by circulating the chilled water in jacket of crystallizers. After that, a residence time of 60 minutes was provided to decrease the temperature from 25 °C to 20 °C to obtain a resultant mass. The resultant mass was further, centrifuged to obtain solids and the wet solids were dried to obtain hydroxylamine sulphate crystals.
Figure 9 illustrates the particle size distribution of the hydroxylamine sulphate crystals in two crystallizers.
Example 20- Scale up process for the crystallization of hydroxylamine sulphate (HAS) in accordance with the present disclosure
The scale up trials at hydroxylamine sulphate crystal plant was performed. A schematic depiction of the process is illustrated in Figure 10. The hydroxylamine sulphate solution was evaporated in an evaporator (E), till the obtained density at 85 °C was 1350 kg/m3. The hydroxylamine sulphate solution was pumped from the holding tank (TK) to a crystallizer (C) via heat exchanger to carry out the crystallization. The temperature of the crystallizer was frequently monitored and agitation at 4 rpm was executed till the temperature of the hydroxylamine sulphate solution was 25 °C. After reaching the desired temperature, the shaft of the crystallizer was stopped and the residence time of 1 hour was provided to decrease the temperature till 20 °C to obtain a resultant mass. The resultant mass was centrifuged in a centrifuge (CF) to obtain solids. The solids were dried in a steam jacketed drier (D).
The analysis of the single crystallizer trial batch is summarized in Table 6.
Table 6: Quality Parameters for Hydroxylamine Sulphate Crystals obtained in Example 20
Components of the crystals Desired specifications (w/w) Actual results
Hydroxylamine sulphate Minimum 99.0% 99.38%
Free Sulphuric Acid Maximum 0.3% 0.08%
Ammonium Sulphate Maximum 0.5% 0.27%
Moisture Maximum 0.3% 0.19%
This confirms that the optimized conditions and techniques used in the process of the present disclosure are effective and reliable. As a result, the process can be successfully scaled up from a laboratory or pilot scale to an industrial level for the efficient production of high-purity hydroxylamine sulphate crystals. These crystals are derived by the crystallization of crude hydroxylamine sulphate solution obtained by Raschig process, which is typically employed for the synthesis of caprolactam. The scalability of this process ensures consistent quality and performance, making it suitable for large-scale applications in pharmaceutical and other chemical processes requiring high-purity hydroxylamine sulphate. The particle size of the hydroxylamine sulphate crystals were obtained in the range of 350 µm to 550 µm.
TECHNICAL ADVANCEMENTS
The present disclosure described hereinabove has several technical advantages including, but not limited to, the realization of:
- A process for the crystallization of hydroxylamine sulphate, that:
• is simple and economical;
• produces hydroxylamine sulphate crystals having particle size in the range of 300 µm to 1870 µm, free acid value of less than 0.4 mass%, ammonium sulphate content of less than 0.5 mass%, and moisture content of less than 0.2%;
• utilize crude hydroxylamine sulphate solution obtained as a by-product in the process for the preparation of Caprolactam; and
• exhibits enhanced flowability and reduces the specific consumption of feed.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising, will be understood to imply the inclusion of a stated element, integer or step,” or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
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 invention to achieve one or more of the desired objects or results. While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Variations or modifications to the formulation of this invention, within the scope of the invention, may occur to those skilled in the art upon reviewing the disclosure herein. Such variations or modifications are well within the spirit of this invention.
The numerical values given for various physical parameters, dimensions and quantities are only approximate values and it is envisaged that the values higher than the numerical value assigned to the physical parameters, dimensions and quantities fall within the scope of the invention unless there is a statement in the specification to the contrary.
While considerable emphasis has been placed herein on the specific features of the preferred embodiment, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiment without departing from the principles of the disclosure. These and other changes in the preferred embodiment 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:WE CLAIM:
1. A process for the crystallization of hydroxylamine sulphate, the process comprising the following steps:
a) obtaining a crude hydroxylamine sulphate solution;
b) evaporating said crude hydroxylamine sulphate solution at a first predetermined temperature to obtain a concentrated hydroxylamine sulphate solution having a predetermined density;
c) crystallizing said concentrated hydroxylamine sulphate solution under a predetermined agitation speed at a predetermined cooling condition to obtain a resultant mass;
d) centrifuging said resultant mass at a predetermined speed to obtain solids; and
e) drying said solids at a second predetermined temperature for a predetermined time period to obtain hydroxylamine sulphate crystals having a predetermined particle size.
2. The process as claimed in claim 1, wherein said crude hydroxylamine sulphate solution is a mixture of hydroxylamine sulphate, ammonium sulphate and sulphuric acid obtained by Raschig process.
3. The process as claimed in claim 1, wherein said first predetermined temperature is in the range of 80 °C to 120 °C.
4. The process as claimed in claim 1, wherein said predetermined agitation speed is in the range of 3 rpm to 5 rpm.
5. The process as claimed in claim 1, wherein said predetermined density is in the range of 1300 kg/m3 to 1450 kg/m3.
6. The process as claimed in claim 1, wherein said predetermined density of the concentrated hydroxylamine sulphate solution is achieved through one or more evaporators.
7. The process as claimed in claim 1, wherein said predetermined cooling conditions comprises cooling with chilled water, cooling with ambient water, and dual cooling.
8. The process as claimed in claim 7, wherein said predetermined dual cooling condition comprises circulating ambient water in the cooling jacket for a time period in the range of 5 minutes to 150 minutes, followed by circulating chilled water for a time period in the range of 30 minutes to 120 minutes.
9. The process as claimed in claim 1, wherein said predetermined cooling condition comprises a residence time of said concentrated hydroxylamine sulphate solution in the range of 30 minutes to 180 minutes.
10. The process as claimed in claim 1, wherein said predetermined cooling condition comprises a cooling temperature of said concentrated hydroxylamine sulphate solution in the range of 8 °C to 30 °C.
11. The process as claimed in claim 1, wherein said predetermined speed is in the range of 1000 rpm to 2500 rpm.
12. The process as claimed in claim 1, wherein said second predetermined temperature is in the range of 90 °C to 110 °C.
13. The process as claimed in claim 1, wherein said predetermined time period is in the range of 5 minutes to 25 minutes.
14. The process as claimed in claim 1, wherein said hydroxylamine sulphate crystals are characterized by having:
• a predetermined particle size in the range of 300 µm to 1870 µm;
• free acid value of less than 0.4 mass%;
• ammonium sulphate content of less than 0.5 mass%; and
• a moisture content of less than 0.2%.

Dated this 04th Day of March 2025

_______________________________
MOHAN RAJKUMAR DEWAN, IN/PA – 25
OF R. K. DEWAN & CO.
AUTHORIZED AGENT OF APPLICANT

TO,
THE CONTROLLER OF PATENTS
THE PATENT OFFICE, AT MUMBAI