WO2019082207A1

WO2019082207A1 - Energy efficient synthesis of sulphate of potash using ammonia as a catalyst

Info

Publication number: WO2019082207A1
Application number: PCT/IN2018/050689
Authority: WO
Inventors: Rahul Raju KANUMURU; Anil Kumar Kruthiventi; Prasad Babu MACIGI
Original assignee: Fertis India Pvt. Ltd.
Priority date: 2017-10-25
Filing date: 2018-10-25
Publication date: 2019-05-02

Abstract

The present invention describes an energy efficient method for the synthesis of Sulphate of Potash (K2SO4) from Muriate of Potash (KCl) using ammonia as a catalyst. This energy efficient process for production of potassium sulphate uses ammonia as a catalyst for reacting solution of potassium chloride with sulphuric acid. The advantage of the present invention is that the one of the main reactants i.e., potassium chloride can be use either in solid form or liquid form for the production of potassium sulphate. The reaction process can be conducted either in solid – liquid or liquid - liquid form for the production of potassium sulphate. Thus, the main advantage of using solid - liquid reaction results in minimizing the usage of water in the reactants and hence these kinds of reactions also eliminate the water evaporation step in the recovery process for recovering potassium sulphate.

Description

Energy Efficient Synthesis of Sulphate of Potash using Ammonia as a

Catalyst

Technical Filed:

The present invention relates to the manufacture of potassium sulphate and more particularly to a novel energy efficient method for the synthesis of Sulphate of Potash (K2SO4) from Muriate of Potash (KC1) using Ammonia as a catalyst.

Background and Prior Art:

Potassium Sulphate (K2SO4) also known as Sulphate of Potash (SOP) or Potash of Sulphur is a non-flammable white crystalline salt which is soluble in water. Potassium sulphate normally contains 48 to 54% potassium (as K2O) and supplies 17.5 - 18.2 % of sulphur. Potassium sulphate primarily used as fertilizer, is the second largest tonnage compound. Certain plants such as tobacco, fruits and vegetables that do not tolerate chloride ions are given the sulphate or other non- chloride forms of potassium. Potassium sulphate is a preferred fertilizer where, the intensive agriculture is required and the soil is deficient in both potash and sulphur. Where the soils are saline or acidic and where irrigation water may have higher chloride levels, SOP is the preferred form of potassium to use. When seeds or transplants are placed in direct contact with fertiliser, SOP is much less likely to cause root burn of plants. Potassium stimulates the growth of strong stems and gives the plant some disease resistance by promoting thickness of the outer cell walls. Adequate potassium can reduce moisture loss from growing plants, thereby giving some drought resistance. Potassium improves colour, flavour and storing quality of fruit and vegetables.

Approximately 6.0 million tons of potassium sulphate is used to be produced currently, typically by the reaction of potassium chloride with sulphuric acid, analogous to the Leblanc process. Potassium sulphate is also produced according to the following reaction, which is conducted in so-called Mannheim furnaces. Overall Reaction:

2 KC1 + H2SO4→ K2SO4 + 2 HC1

Potassium sulphate is manufactured traditionally either by the Mannheim process where potassium chloride reacts with sulphuric acid or manufactured from natural complex salts like kainite or langbeinite. Mannheim process is preferred over the recovery of potassium sulphate from natural complex salts, because, the mineral form of potassium sulphate is relatively rare in the natural complex salts.

The Mannheim process was originally developed for sodium sulphate production by reacting NaCl with sulphuric acid. Subsequently, the process has been used for the production of potassium sulphate by replacing NaCl with KC1. The Mannheim process is two stage processes, which are shown below in scheme 1.

Scheme 1

a) Exothermic reaction

b) Endothermic reaction

In the Mannheim process, potassium chloride reacts with sulphuric acid under slow mixing in the heated Mannheim furnace to produce gaseous HC1 and K2SO4. The Mannheim furnace is heated by natural gas or fuel oil. The product K2SO4 thus obtained is cooled in a cooling drum to obtain the product in the form of lumps. These lumps in the cooling drum are crushed and granulated. The byproduct HC1 gas is cooled and absorbed in water to obtain 30% hydrochloride acid.

Potassium sulphate is costlier than potassium chloride, due to removal chloride and addition of sulphate to potassium. Potassium sulphate thus obtained contains, over 50 % potassium (as K2O) and less than 1 % chlorine. A temperature of 550° to 600°C is required and has to be maintained within the furnace during the production of potassium sulphate.

Another method called Hargreaves process uses sulphur dioxide, oxygen and water and potassium chloride as the starting materials to produce potassium sulphate in a fixed bed reactor. For example, US2336180 discloses a process for the manufacture of alkali metal sulphate, which comprises dispersing crystalline particles of alkali metal chloride, maintained at a temperature substantially below reaction temperature immediately prior to dispersion, into a gaseous atmosphere of sulphur oxide, oxygen and water vapor at a reaction temperature of approximately 1450 °F to 2000 °F.

US3998935 discloses preparation of potassium sulphate (K2SO4) by contacting potassium chloride with an aqueous solution containing potassium bisulphate at a temperature of about 65 -110 °C, cooling the solution and permitting the potassium sulphate to crystallize from the solution. This process results in the production of 30 to 50% excess of potassium bisulphate.

US4588573 discloses yet another method, wherein, potassium chloride and sulphuric acid are reacted in a recycled aqueous solution in the stoichiometric ratio required for potassium sulphate production. Hydrogen chloride produced by the reaction of the potassium chloride and sulphuric acid is evaporated in admixture with water or in anhydrous form. The resulting solution is cooled to crystallize a potassium sulphate salt, preferably potassium bisulphate. The potassium sulphate salt is separated from the mother liquor and the mother liquor is recycled to the reaction step. The potassium sulphate salt is dissolved in an aqueous solution and sequentially decomposed to produce potassium sulphate and mother liquor rich in sulphuric acid. The mother liquor rich in sulphuric acid is concentrated and recycled to the reaction step. This process is an improvement over the process disclosed in US4045543. The process disclosed in this patent is cumbersome for industrial production, as the process demands the evaporation of about 3 tons of water per ton of potassium sulphate produced. Moreover, the steps involved in this process are required to be carried out at different temperatures and include recycling of at least three mother liquors. Moreover, the process calls for filtering potassium salt from a solution consisting of hydrochloric acid and hence, the product produced out of this process cannot be totally free from chloride content.

In the light of the above there remains a need in the art to provide an improved process for preparation of potassium sulphate salt that is free from chlorides and does not require high energy and easy to scale up for industrial production. The present invention aims to address these needs, for which protection is sought.

Objectives of the Invention:

The main object of the present invention is to eliminate the problems and inefficiencies of the prior art by providing a new and improved process for preparation of potassium sulphate free of chloride content and does not require higher energy.

A further object of this invention is to provide a simple, cost effective and highly energy efficient process for manufacture of high quality potassium sulphate fertilizer.

A further object of this invention is to provide suitable economical conditions whereby the new method may be effectively performed to produce the potassium sulphate. Summary of the Invention:

Accordingly, in line with the above objectives, the present invention provides an energy efficient process for preparation of potassium sulphate which comprises the reaction of potassium chloride with sulphuric acid in presence of ammonia as a catalyst at a temperature range 30°C to 100°C to obtain potassium sulphate. In the process of the present invention, the ammonium sulphate is generated in situ when the ammonia is reacted with sulphuric acid.

The process according to the invention comprises reaction of potassium chloride with sulphuric acid in the presence of ammonia as a catalyst to obtain a reaction mass consisting of potassium sulphate as a precipitate and ammonium chloride. The precipitated potassium sulphate is isolated and the reaction mass consisting of ammonium chloride is treated with calcium / sodium hydroxide solution to obtain ammonia gas, calcium / sodium chloride and water. The ammonia gas thus generated can be recycled for the subsequent batch reaction. The process can be conveniently conducted at a temperature range of 30 to 100 °C using suitable reactors on industrial scale.

In an alternate process variant, the process for preparation of potassium sulphate comprises reaction of potassium chloride with ammonium sulphate at a temperature range 30°C to 100°C to obtain potassium sulphate as a precipitate and ammonium chloride. The precipitated potassium sulphate is isolated and the reaction mass consisting of ammonium chloride is treated with calcium / sodium hydroxide solution to obtain ammonia gas, calcium/sodium chloride and water. In this process variant, the recycling of the ammonia gas optionally comprising a step of hydrolysis in water followed by neutralization with sulphuric acid to yield ammonium sulphate that can be directly put to use for the next batch for the production of potassium sulphate. The process for manufacture of potassium sulphate as demonstrated in the present invention results in near 100% yields with highest purity, i.e., with the chloride content less than 2%.

The isolation of potassium sulphate according to the process of the present invention can be conducted at a temperature range of 30 to 50 °C.

The invention consists of certain novel features and a combination of parts hereinafter fully described and listed out in appended claims, it being understood that various changes in the details may be made without departing from the spirit, or sacrificing any of the advantages of the present invention.

Detailed Description of the Invention:

The invention will now be described in detail in connection with certain preferred and optional embodiments, so that various aspects thereof may be fully understood and appreciated.

Accordingly, in a preferred embodiment, the invention provides a process for preparation of potassium sulphate which comprises;

a) reacting potassium chloride in sulphuric acid in presence of ammonia as a catalyst to obtain a reaction mass consisting of potassium sulphate precipitate and ammonium chloride;

b) isolating the precipitated potassium sulphate;

c) treating the reaction mass consisting ammonium chloride with calcium/sodium hydroxide solution to generate ammonia gas, calcium / sodium chloride and water; and

d) recycling the ammonia gas thus generated for the subsequent batch reaction.

e) This reaction of the invention can be conducted at a temperature range of 30 to 100 °C.

The process of the present invention is shown in reaction scheme 2 as follows: Scheme 2

2 H4OH + H2SO4 ( H₄)₂S04 + 2 H2O

2 KC1 + ( H₄)₂S04 K2SO4 + 2 H4CI

2 H4CI + Ca(OH)₂ CaCl₂ + 2 H3 + 2 H₂0

The overall reaction is shown in scheme 3 below:

Scheme 3

2 KC1 + H₂S0₄ + Ca(OH)₂ K₂S0₄ + CaCl₂ + 2 H₂0

According to the process of the present invention, two moles of potassium chloride was reacted with one mole of sulphuric acid and two moles of ammonia at a temperature of 60 °C to obtain one mole of potassium sulphate and two moles of ammonium chloride. After isolating the precipitated potassium sulphate, the reaction mass comprising ammonium chloride was treated with two moles of calcium / sodium hydroxide to obtain 2 moles of ammonia gas, two moles of calcium / sodium chloride and two moles of water as by products. The ammonia gas thus generated is recycled to the next batch for the production of potassium sulphate. This method is demonstrated in examples 4 and 5.

In an alternate process variant, the process for preparation of potassium sulphate comprises reaction of potassium chloride with ammonium sulphate at a temperature range 30°C to 100°C to obtain potassium sulphate as a precipitate and ammonium chloride. The precipitated potassium sulphate is isolated and the reaction mass consisting of ammonium chloride is treated with calcium / sodium hydroxide solution to obtain ammonia, calcium/sodium chloride and water. In this process variant, the recycling of the ammonia gas optionally comprising a step of hydrolysis in water followed by neutralization with sulphuric acid to yield ammonium sulphate that can be directly put to use for the next batch for the production of potassium sulphate.

In performing this process variant, both the reactants, viz., potassium chloride and ammonium sulphate can be taken either in (liquid -liquid) solution form or potassium chloride can be taken as solid and ammonium sulphate can be taken as solution (solid-liquid) form or potassium chloride can be taken as liquid solution and ammonium sulphate can be taken as solid (liquid-solid) form.

If the reaction is conducted with solution of potassium chloride with solution of ammonium sulphate (liquid - liquid), then the isolation of the precipitated potassium sulphate can be recovered in two crops. The first crop can be recovered by cooling the reaction solution to crystallize potassium sulphate without vaporization of water and the second crop may be recovered from the solution with evaporation of water followed by crystallization. If both the reactants are taken in liquid form, then the process for preparation of potassium sulphate is conducted at a temperature range of 80 to 100 °C; however, the reaction can be accomplished within a shorter period of 30 to 60 minutes. This method is demonstrated in example 1 and example 4.

If the reaction is conducted with solid potassium chloride with solution of ammonium sulphate (solid-liquid), then the product, potassium sulphate can be isolated directly by cooling the reaction solution to crystallize potassium sulphate without vaporization of water. If the reactants are taken in solid-liquid form, then the process for preparation of potassium sulphate is conducted at a temperature range of 40 to 90 °C; however, the reaction will take a little longer time. In this method, the reaction can be accomplished within 150 to 180 minutes. This method is demonstrated in example 3 and 5. In yet another alternate embodiment, potassium chloride solution can be reacted with solid ammonium sulphate (liquid-solid) to obtain potassium sulphate. In this case, potassium sulphate can be isolated directly by crystallization without evaporation of water. This method is demonstrated in example 2.

The process for manufacture of potassium sulphate as demonstrated in the present invention results in near 100% yields with highest purity, i.e., with the chloride content less than 2%.

The process can be conveniently conducted at a temperature range of 30 to 100 °C using suitable reactors on industrial scale.

The process as described in the present invention is useful for the large scale industrial production of potassium sulphate fertilizer.

Unlike the Mannheim process where higher temperatures are used for the conversion of potassium chloride to potassium sulphate, the present invention has achieved the same using ambient pressures with much lower temperature when compared to Mannheim process. Further, use of ammonia as a recyclable raw material with a conversion range of 90 to 98% is the uniqueness of the process of the present invention. SOP as produced by the process of the present invention provides both potassium and sulphur in soluble forms and also devoid of chloride and hence has a much lower salt index than MOP.

Having described the basic concepts of the instant invention reference is made to the following examples which are provided to illustrate but not limit the preferred method of the invention and other similar methods of producing metal sulfates. Other features and embodiments of the invention will become apparent by the following examples which are given for illustration of the invention rather than limiting its intended scope. Various changes and modifications to the disclosed embodiments will be apparent to those skilled in the art.

Example

Example 1

2 KC1 (1) + ( H₄)₂S04 (1) K₂S0₄ (s) + 2 H₄C1 (1)

In the first example, which is liquid - liquid reaction where potassium chloride was reacted with ammonium sulphate to form the potassium sulphate and ammonium chloride. The reaction was conducted at 90 °C. Initially potassium chloride solution i.e., 856.3 grams of potassium chloride was dissolved in 1588.6 ml of water and ammonium sulphate solution i.e., 758.6 grams was dissolved in 770.1 ml of water. The two reactant mixtures were mixed slowly in batch reactor and allowed for reaction to take place to produce 1000 grams of potassium sulphate and 614.9 grams of ammonium chloride. After the reaction time say 30 minutes, the reaction mixture was cooled to 40 °C. In the first stage crystallization without any vaporization of water, 85% of total potassium sulphate i.e., 850 grams and 25.5 grams of ammonium chloride were recovered in dry solid product. In the second stage crystallization nearly 1016 ml of water evaporation and cooling to average temperature of 40 °C where it contains 150 grams of potassium sulphate and 5.0 grams of ammonium chloride in solid phase and the rest 584.4 grams of ammonium chloride was recovered from liquid phase. Nearly about 1016 grams of water was evaporated to recover the leftover 15% of potassium chloride. Chloride ion concentration was observed to be <2.0%.

Example 2 2 KC1 (1) + ( H₄)₂S04 (s) K₂S0₄ (s) + 2 NH₄C1 (1)

In the second example, which is liquid - solid reaction where potassium chloride solution is reacted with solid ammonium sulphate to form the potassium sulphate and ammonium chloride. The reaction was conducted at 90 °C. Initially potassium chloride solution i.e., 856.3 grams of potassium chloride was dissolved in 1588.6 ml of water was prepared in batch reactor. Then slowly added the solid ammonium sulphate (758.6 grams) into the batch reactor and allowed for reaction to take place to produce 1000 grams of potassium sulphate and 614.9 grams of ammonium chloride. After the reaction time say 180 minutes, the reaction mixture was cooled to 25 °C. In the first stage crystallization without any vaporization of water, 100% of total potassium sulphate i.e. 1000 grams and 35 grams of ammonium chloride were recovered in dry solid product. The advantage of liquid - solid reaction is that there is no evaporation of water but the reaction time is longer because of slow multiphase reaction, which may follow shell progressive model. Chloride ion concentration was observed to be <1.5%.

Example 3

2 KC1 (s) + ( H₄)₂S0₄ (1) K₂S0₄ (s) + 2 H₄C1 (1)

In the third example, which is solid - liquid reaction where solid potassium chloride was reacted with ammonium sulphate solution to form the potassium sulphate and ammonium chloride. The reaction was conducted at 60 °C. Initially ammonium sulphate solution i.e., 758.6 grams of ammonium sulphate dissolved in 867.9 ml of water was prepared in batch reactor. Then slowly added the solid potassium chloride (856.3 grams) in the batch reactor and allowed for reaction to take place to produce 1000 grams of potassium sulphate and 614.9 grams of ammonium chloride. After the reaction time say 180 minutes, the reaction mixture was cooled to average temperature of 40 °C. In the first stage crystallization without any vaporization of water, 100% of total potassium sulphate i.e., 1000 grams and 35 grams of ammonium chloride were recovered in dry solid product. The advantage of solid - liquid reaction is that there is no evaporation of water but the reaction time is longer because of slow multiphase reaction, which may follow shell progressive model. Here, chloride ion concentration was observed to be <1.5%.

Example 4

2 KC1 (1) + ( H₄)₂S04 (1) K₂S0₄ (s) + 2 H₄C1 (1)

2 H₄C1 (1) + CaO (s) CaCl₂ (1) + 2 H₃ (g) + H₂0

2 H₃ (g) + H₂S0₄ (1) ( H₄)₂S0₄ (1)

In the fourth example, which is liquid - liquid reaction where potassium chloride solution was reacted with ammonium sulphate solution to form the potassium sulphate and ammonium chloride. The reaction was conducted at 90 °C. Initially potassium chloride solution i.e., 856.3 grams of potassium chloride was dissolved in 1588.6 ml of water and ammonium sulphate solution was prepared by reacting sulphuric acid with regenerated ammonia. During the reaction of ammonium chloride and slaked lime to produce 195.39 grams of ammonia which was dissolved in water to make 17.3 wt% ammonium hydroxide solution. 1129.4 grams of ammonium hydroxide solution was made to react with 563.2 grams of concentrated sulphuric acid to produce 758.6 grams of ammonium sulphate solution (934.2 ml of water). The two reactant mixtures were mixed slowly in batch reactor and allowed for reaction to take place to produce 1000 grams of potassium sulphate and 614.9 grams of ammonium chloride. After the reaction time say 30 minutes, the reaction mixture was cooled to average temperature of 40 °C. In the first stage crystallization without any vaporization of water, 82.5% of total potassium sulphate i.e. 825.3 grams and 25.5 grams of ammonium chloride were recovered in dry solid product. In the second stage crystallization nearly 1180 ml of water evaporation and cooling to average temperature of 40 °C where it contains 174.7 grams of potassium sulphate and 5.0 grams of ammonium chloride in solid phase and the rest 584.4 grams of ammonium chloride in liquid phase. Nearly about 1180 grams of water was evaporated to recover the leftover 17.5% of potassium sulphate.

In the ammonia regeneration reactor, initially 321.8 grams of slake lime and makeup 30.5 grams of ammonium chloride is taken. Then added the generated ammonium chloride solution and allow the reaction to take place for generating ammonia gas. The generated ammonia gas was passed into another cooled reactor to make 17.3 concentration of ammonium hydroxide. After completion of reaction the generated ammonium hydroxide was neutralized with concentrated sulphuric acid to make ammonium sulphate. The produced ammonium sulphate solution was used for the initial reaction to take place to produce potassium sulphate and ammonium chloride. Here, the chloride ion concentration was observed to be <2.0%.

Example 5

2 KC1 (s) + (NH₄)₂S04 (1) K₂S0₄ (s) + 2 NH₄C1 (1)

2NH₄C1 (1) + CaO (s) CaCl₂ (1) + 2NH₃ (g) + H₂0

2NH₃ (g) + H₂S0₄ (1) (NH )₂S0₄ (1)

In the fifth example, which is solid - liquid reaction where solid potassium chloride was reacted with ammonium sulphate solution to form the potassium sulphate and ammonium chloride. The reaction was conducted at 90 °C. Initially ammonium sulphate solution was prepared by reacting sulphuric acid with regenerated ammonia. During the reaction of ammonium chloride and slaked lime to produce 195.39 grams of ammonia which was dissolved in water to make 12.7 wt% ammonium hydroxide solution. 1537.9 grams of ammonium hydroxide solution was made to react with 563.2 grams of concentrated sulphuric acid to produce 758.6 grams of ammonium sulphate solution (1342.5 ml of water). The two reactant solid potassium chloride and ammonium sulphate solution mixtures were mixed slowly in batch reactor and allowed for reaction to take place to produce 1000 grams of potassium sulphate and 614.9 grams of ammonium chloride. After the reaction time say 180 minutes, the reaction mixture was cooled to average temperature of 40 °C. In the first stage crystallization without any vaporization of water, 100% of total potassium sulphate i.e. 1000 grams and 32.5 grams of ammonium chloride were recovered in dry solid product and the rest 582.4 grams of ammonium chloride in liquid phase.

In the ammonia regeneration reactor, initially 321.8 grams of slake lime and makeup 32.5 grams of ammonium chloride were taken. Then added the generated ammonium chloride solution and allowed the reaction to take place for generating ammonia gas. The generated ammonia gas was passed in another cooled reactor to make 12.7 concentration of ammonium hydroxide. After completion of reaction the generated ammonium hydroxide was neutralized with concentrated sulphuric acid to make ammonium sulphate. The produced ammonium sulphate solution was used for the initial reaction to take place to produce potassium sulphate and ammonium chloride. Here, the chloride ion concentration was observed to be <2.0%.

A by product of 637.59 grams of calcium chloride with a purity of approximately 95% was formed. Therefore, by this process though theoretically we have recovered the whole of ammonia consumed in step one, practically we were achieving around 90% efficiency, alongside producing 0.63 ton of calcium chloride per ton of the main product potassium sulphate.

The advantage of the present invention is that one of the main reactants i.e., potassium chloride or ammonium sulphate can be used either in solid form or liquid form for the production of potassium sulphate. The reaction process can be conducted either in solid - liquid or liquid - liquid form for the production of potassium sulphate. Thus, the main advantage of using solid - liquid reaction is that it results in minimizing the usage of water in the reaction and hence these kind of reactions also eliminates the water evaporation step in the recovery process for recovering 100% potassium sulphate.

While there has been disclosed what is considered to be the preferred embodiment of the present invention, it is understood that various changes in the details may be made without departing from the spirit, or sacrificing any of the advantages of the present invention.

Claims

We claim,

1. An energy efficient process for preparation of potassium sulphate comprising reacting potassium chloride with sulphuric acid in presence of ammonia as a catalyst at a temperature ranging from 30°C to 100°C.

2. The energy efficient process for preparation of potassium sulphate as claimed in claim 1, wherein, ammonium sulphate is generated in situ by reacting ammonia with sulphuric acid.

3. The energy efficient process for preparation of potassium sulphate as claimed in claim 1 or claim 2, wherein, the process comprises a reaction of potassium chloride with ammonium sulphate.

4. The energy efficient process for preparation of potassium sulphate as claimed in claim 1 or claim 2, wherein the said process comprises ;

a) reacting potassium chloride with sulphuric acid in presence of ammonia as a catalyst to obtain a reaction mass consisting of potassium sulphate precipitate and ammonium chloride;

b) isolating the precipitated potassium sulphate;

c) treating the reaction mass consisting ammonium chloride with calcium / sodium hydroxide solution to generate ammonia, calcium / sodium chloride and water; and

d) recycling the ammonia thus generated for the step a) in subsequent batch reaction for ammonium sulphate production.

5. The energy efficient process for preparation of potassium sulphate as claimed in claim 3, wherein the said process comprises;

a) reacting potassium chloride with ammonium sulphate to obtain a reaction mass consisting of potassium sulphate precipitate and ammonium chloride; b) isolating the precipitated potassium sulphate;

c) treating the reaction mass consisting ammonium chloride with calcium / sodium hydroxide solution to generate ammonia, calcium / sodium chloride and water; and d) recycling the ammonia thus generated for the step a) in subsequent batch reaction for ammonium sulphate production.

6. The energy efficient process for preparation of potassium sulphate as claimed in claim 4 or claim 5, wherein, the recycling of the ammonia gas optionally comprising a step of hydrolysis in water followed by neutralization with sulphuric acid to yield ammonium sulphate.

7. The energy efficient process for preparation of potassium sulphate as claimed in claim5, wherein, the potassium chloride and ammonium sulphate are reacted both in solution form (liquid - liquid).

8. The energy efficient process for preparation of potassium sulphate as claimed in claim 7, wherein, the isolation of the precipitated potassium sulphate of step b) as first crop is carried out by cooling the reaction solution to crystallize potassium sulphate without vaporization of water.

9. The energy efficient process for preparation of potassium sulphate as claimed in claim 7, wherein, the isolation of the potassium sulphate of step b) as a second crop from the solution with partial evaporation of water followed by crystallization.

10. The energy efficient process for preparation of potassium sulphate as claimed in claim 7, wherein the reaction of potassium chloride solution with ammonium sulphate solution (liquid - liquid) is conducted at a temperature range of 80 to 100 °C.

11. The energy efficient process for preparation of potassium sulphate as claimed in claim 7, wherein the reaction of potassium chloride solution and ammonium sulphate solution (liquid - liquid) is conducted for a time period between 30 to 60 minutes.

12. The energy efficient process for preparation of potassium sulphate as claimed in claim 5, wherein, the potassium chloride and ammonium sulphate are reacted in solid-liquid form.

13. The energy efficient process for preparation of potassium sulphate as claimed in claim 12, wherein the isolation of the precipitated potassium sulphate of step b) is carried out by cooling the reaction solution to crystallize potassium sulphate without vaporization of water.

14. The energy efficient process for preparation of potassium sulphate as claimed in claim 12 and claim 13, wherein the reaction of solid potassium chloride with ammonium sulphate solution (solid - liquid) is conducted at a temperature range 40 to 90 °C.

15. The energy efficient process for preparation of potassium sulphate as claimed in claim 12 and claim 13, wherein the reaction of solid potassium chloride and ammonium sulphate solution is conducted for a time period between 150 to 180 minutes.

16. The energy efficient process for preparation of potassium sulphate as claimed in any one of the preceding claims 1 to 15, wherein isolation of potassium sulphate can be conducted at a temperature range of 30 to 50 °C.