DESC:
RELATED PATENT APPLICATION
This application claims the priority to and benefit of Indian Provisional Patent Application No. 201941046191 filed on November 13, 2019; the disclosures of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to an improved process for the preparation of Sodium zirconium cyclosilicate. The improved process of the present invention includes the processes for the preparation of Sodium zirconium cyclosilicate from zirconium acetate with sodium silicate and colloidal silica solution respectively.

BACKGROUND OF THE INVENTION

Sodium zirconium cyclosilicate has the chemical formula Na~1.5H~0.5ZrSi3O9•2–3H2O. Sodium zirconium cyclosilicate exists in different forms. Among other forms, ZS-9 form of sodium zirconium cyclosilicate exhibits a high capacity to selectively entrap monovalent cations specifically excess potassium and ammonium ions in gastrointestinal tract. The high specificity of ZS-9 form is due to the chemical composition and diameter of the micro pores. ZS-9 form of sodium zirconium cyclosilicate microporous ion exchanger is approved for the treatment of hyperkalemia. Sodium zirconium cyclosilicate is non-absorbed, odorless and insoluble powder.

The Patent US 5338527 first disclose the product and a process for the preparation of product thereof. Different forms of sodium zirconium cyclosilicate are disclosed in the Patent US 5891417. Among the different forms, ZS-9 form is particularly used for absorption of potassium and ammonium ions from the gastrointestinal tract. During the preparation of ZS-9 form of Sodium zirconium cyclosilicate other undesired crystalline forms are also formed. The undesired forms have to be controlled during the manufacturing process itself since reprocessing the product is difficult.

The Patent US 9662352 discloses the preparation of Sodium zirconium cyclosilicate by hydrothermal crystallizing the reaction mixture prepared by combining zirconium acetate solution, source of silica, alkali metal hydroxide and water characterized by a specialized process and reactor configuration that more thoroughly suspends crystals throughout the reaction. This Patent also discloses the use and proper positioning of a baffle-like structure in relation to the agitator within the crystallization vessel produces the desired ZS-9 form.
Besides the availability of processes for the preparation of sodium zirconium cyclosilicate in state of the art, there is a need for an improved process for the preparation of predominantly ZS-9 of form of sodium zirconium cyclosilicate that is simple and economically significant.

OBJECTS OF THE INVENTION

The primary object of the invention is to provide an efficient and industry feasible process for the preparation of sodium zirconium cyclosilicate.

Another objective of the invention is to provide an improved process for the preparation of pure sodium zirconium cyclosilicate ZS-9 form.

Yet another object of the invention is to provide improved processes for the preparation of sodium zirconium cyclosilicate from zirconium acetate with sodium silicate and colloidal silica solution respectively.

SUMMARY OF THE INVENTION

One aspect of the present invention is to provide a process for the preparation of sodium zirconium cyclosilicate in a reactor comprising the steps of:
(i) providing a mixture of sodium silicate solution and sodium hydroxide solution in the reactor;
(ii) adding zirconium acetate solution to the mixture provided in step (i);
(iii) agitating the reaction mixture obtained in step (ii) with the agitator and baffle-like structure of the reactor at temperatures above 200°C; and
(iv) obtaining sodium zirconium cyclosilicate from the reactor,
wherein the reactor comprises
a reaction vessel having a volume of at least 2-L and an inside and outside wall;
an agitator within the reaction vessel;
a cooling jacket comprising serpentine-type coils proximate to the outside wall of the reaction vessel; or at least one baffle-like structure proximate the inside wall of the reaction vessel and placed in operative proximity to the agitator,
to provide uniform suspension of solids within the reaction vessel.

Another aspect of the present invention is to provide a process for the preparation of sodium zirconium cyclosilicate in a reactor comprising the steps of:
(i) providing a mixture of colloidal silica solution and sodium hydroxide solution in the reactor;
(ii) heating the reaction mixture obtained in step (i) in the reactor at temperatures above 200°C;
(iii) adding zirconium acetate solution to the mixture provided in step (ii) in the reactor by a specially designed high pressure addition funnel at temperatures above 200°C;
(iv) agitating the reaction mixture obtained in step (iii) with the agitator and baffle-like structure of the reactor at temperatures above 200°C; and
(v) obtaining sodium zirconium cyclosilicate from the reactor,
wherein the reactor comprises
a reaction vessel having a volume of 5-L and an inside and outside wall;
an agitator within the reaction vessel;
a cooling jacket comprising serpentine-type coils proximate to the outside wall of the reaction vessel; or at least one baffle-like structure proximate the inside wall of the reaction vessel and placed in operative proximity to the agitator,
to provide uniform suspension of solids within the reaction vessel.

BRIEF DESCRIPTION OF FIGURES

Figure-1: The PXRD pattern of sodium zirconium cyclosilicate resulted in Example-1
Figure 2: Reactor with a specifically designed high pressure addition funnel for performing the Example 2
Figure 3: Diagrammatic representation of the autoclave reactor of Figure 2.

DETAILED DESCRIPTION OF THE INVENTION

One embodiment of the present invention is to provide a process for the preparation of sodium zirconium cyclosilicate in a reactor comprising the steps of:
(i) providing a mixture of sodium silicate solution and sodium hydroxide solution in the reactor;
(ii) adding zirconium acetate solution to the mixture provided in step (i);
(iii) agitating the reaction mixture obtained in step (ii) with the agitator and baffle-like structure of the reactor at temperatures above 200°C; and
(iv) obtaining sodium zirconium cyclosilicate from the reactor,
wherein the reactor comprises
a reaction vessel having a volume of at least 2-L and an inside and outside wall;
an agitator within the reaction vessel;
a cooling jacket comprising serpentine-type coils proximate to the outside wall of the reaction vessel; or at least one baffle-like structure proximate the inside wall of the reaction vessel and placed in operative proximity to the agitator,
to provide uniform suspension of solids within the reaction vessel.

The step of providing a mixture of sodium silicate solution and sodium hydroxide solution in the reactor as in the step (i) of the present invention is preferably done by mixing sodium silicate solution with sodium hydroxide in the reactor is carried out in the range of 800 to 1000 RPM for at least 30 minutes.

The step of adding zirconium acetate solution to the mixture as in the step (ii) of the present invention may be done directly into the reactor or the addition through pressure funnel into the reactor.

Preferably more than 10 Kg nitrogen pressure was applied before step (iii) of the present invention.

The step of agitation of the reaction mixture as in step (iii) of the present invention is carried out at temperatures above 200°C, preferably in the range of 215°C to 225°C.

The agitation during the step (iii) of the present invention is carried out in the range of 800 to 1000 RPM.

The step (iii) of the present invention is carried out for about 48 hours.

Preferably the pH of the reaction mass is adjusted to 4.8 -5.3 before obtaining sodium zirconium cyclosilicate from the reactor as in step (iv) of the present invention. And optionally the obtained sodium zirconium cyclosilicate is washed with one or multiple washings with water.

The process for the preparation of sodium zirconium cyclosilicate from sodium silicate and zirconium acetate in a reactor of the present invention is capable of producing predominantly ZS-9 form of sodium zirconium cyclosilicate without using any seed crystals of ZS-9 form of sodium zirconium cyclosilicate.

Surprisingly the present inventors found that the process for achieving predominantly ZS-9 of sodium zirconium cyclosilicate from sodium silicate and zirconium acetate, could be performed in presence of either a cooling jacket comprising serpentine-type coils proximate to the outside wall of the reaction vessel; or at least one baffle-like structure proximate the inside wall of the reaction vessel and placed in operative proximity to the agitator, whereas the previous process as described in the Patent US 9457050 ensures the presence of both the cooling jacket comprising serpentine-type coils proximate to the outside wall of the reaction vessel; and at least one baffle-like structure proximate the inside wall of the reaction vessel and placed in operative proximity to the agitator for achieving predominantly ZS-9 of sodium zirconium cyclosilicate from sodium silicate and zirconium acetate.

Another embodiment of the present invention is to provide a process for the preparation of sodium zirconium cyclosilicate in a reactor comprising the steps of:
(i) providing a mixture of colloidal silica solution and sodium hydroxide solution in the reactor;
(ii) heating the reaction mixture obtained in step (i) in the reactor at temperatures above 200°C;
(iii) adding zirconium acetate solution to the mixture provided in step (ii) in the reactor by a specially designed high pressure addition funnel at temperatures above 200°C;
(iv) agitating the reaction mixture obtained in step (iii) with the agitator and baffle-like structure of the reactor at temperatures above 200°C; and
(v) obtaining sodium zirconium cyclosilicate from the reactor,
wherein the reactor comprises
a reaction vessel having a volume of 5-L and an inside and outside wall;
an agitator within the reaction vessel;
a cooling jacket comprising serpentine-type coils proximate to the outside wall of the reaction vessel; or at least one baffle-like structure proximate the inside wall of the reaction vessel and placed in operative proximity to the agitator,
to provide uniform suspension of solids within the reaction vessel.

The step of providing a mixture of colloidal silica solution and sodium hydroxide solution in the reactor as in the step (i) of the present invention is preferably done by mixing colloidal silica solution with sodium hydroxide in the reactor at the range of 800 to 1000 RPM for at least 30 minutes.

The step of adding zirconium acetate solution to the mixture in the reactor by a specially designed high pressure addition funnel at temperatures above 200°C as in step (iii) of the present invention is done by attaching the specially designed pressure addition funnel with reactor before the addition or the process. Preferably zirconium acetate solution is added to the reaction mass in the reactor by applying high pressure to the addition funnel without opening the reactor.

The step of agitation of the reaction mixture as in step (iv) of the present invention is carried out at temperatures above 200°C, preferably in the range of 215°C to 225°C.

Preferably more than 10 Kg nitrogen pressure was applied before step (iv) of the present invention.

The agitation during the step (iv) of the present invention is carried out in the range of 800 to 1000 RPM.

The step (iv) of the present invention is carried out for about 48 hours.

Preferably the pH of the reaction mass is adjusted to 4.8 -5.3 before obtaining sodium zirconium cyclosilicate from the reactor as in step (v) of the present invention. And optionally the obtained sodium zirconium cyclosilicate with one or multiple washings with water.

The process for the preparation of sodium zirconium cyclosilicate from colloidal silica solution and zirconium acetate in a reactor of the present invention is capable of producing predominantly ZS-9 form of sodium zirconium cyclosilicate without using any seed crystals of ZS-9 form of sodium zirconium cyclosilicate.

Surprisingly the present inventors found that the process for achieving predominantly ZS-9 of sodium zirconium cyclosilicate from colloidal silica and zirconium acetate could be performed by including the step of adding zirconium acetate solution to the mixture provided in step (ii) in the reactor by a specially designed high pressure addition funnel at temperatures above 200°C, whereas the previous process as described in the Patent US 9592253, the temperature was increased as quickly as possible after the addition of zirconium acetate solution to the mixture of colloidal silica and sodium hydroxide for achieving predominantly ZS-9 of sodium zirconium cyclosilicate.

The process provided in the invention could be achieved in smaller reaction vessels of volume such as 2L (2-Litre) and 5L (5-Litre) respectively.

The present invention is explained in detail with reference to the following examples described below, which are given for the purpose of illustration only and are not intended to limit the scope of the invention.

EXAMPLES

Example-1: Sodium zirconium cyclosilicate from Sodium silicate
Sodium silicate solution (206.2 gm) was mixed with sodium hydroxide solution (38.32 gm of sodium hydroxide in 150 ml of water) by stirring in 1000 to 1050 RPM for 30 minutes in the 2-Litre-autoclave reactor. Zirconium acetate solution (120 gm) was added to the reaction mass at 1000 to 1050 RPM, then the reaction mixture was heated to 220 ± 5°C under 10 Kg of nitrogen pressure. The reaction mixture was then stirred at 800 to 1000 RPM for 48 hours at 220 ± 5°C in 20-25 Kg pressure. After the completion of the reaction, the reaction mass was cooled to 40 ± 5°C and pH was adjusted to 4.8 to 5.3. The resultant solid was filtered, washed with water (3600 ml) and dried under vacuum to yield pure ZS-9 form of Sodium zirconium cyclosilicate (Fig-1). Yield: 65 gm

Example-2: Sodium zirconium cyclosilicate from colloidal silica
Colloidal silica solution (167.43 gm) was mixed with sodium hydroxide solution (167.43 gm of sodium hydroxide in 1250 ml of water) by stirring at 800 to 1000 RPM for 30 minutes in the 5-Litre-autoclave reactor and then heated to 200 ± 5°C. Zirconium acetate solution (125 gm) was added to the reaction mass through a pressure addition funnel without opening the reactor at 200 ± 5°C and then stirred at 800 to 1000 RPM for 48 hours at 220 ± 5°C in 20-25 Kg pressure. After the completion of the reaction, the reaction mass was cooled to 40 ± 5°C and pH was adjusted to 4.8 to 5.3. The resultant solid was filtered, washed with water (3750 ml) and dried under vacuum to yield predominantly ZS-9 form of Sodium zirconium cyclosilicate. Yield: 68 gm
,CLAIMS:

1. A process for the preparation of sodium zirconium cyclosilicate in a reactor, comprising the steps of:
(i) providing a mixture of sodium silicate solution and sodium hydroxide solution in the reactor;
(ii) adding zirconium acetate solution to the mixture provided in step (i);
(iii) agitating the reaction mixture obtained in step (ii) with the agitator and baffle-like structure of the reactor at temperatures above 200°C; and
(iv) obtaining sodium zirconium cyclosilicate from the reactor,
wherein the reactor comprises
a reaction vessel having a volume of at least 2-L and an inside and outside wall;
an agitator within the reaction vessel;
a cooling jacket comprising serpentine-type coils proximate to the outside wall of the reaction vessel; or at least one baffle-like structure proximate the inside wall of the reaction vessel and placed in operative proximity to the agitator,
to provide uniform suspension of solids within the reaction vessel.

2. The process for the preparation of sodium zirconium cyclosilicate as claimed in claim 1, wherein in step (i) the mixing of sodium silicate solution with sodium hydroxide solution in the reactor is carried out in the range of 800 to 1000 RPM for at least 30 minutes.

3. The process for the preparation of sodium zirconium cyclosilicate as claimed in claim 1, wherein the step of adding zirconium acetate solution to the mixture as in the step (ii) is preferably done directly into the reactor.

4. The process for the preparation of sodium zirconium cyclosilicate as claimed in claim 1, wherein the step of agitating the reaction mixture with the agitator and baffle-like structure of the reactor at temperatures above 200°C as in step (iii) is preferably done after applying more than 10 Kg nitrogen pressure.

5. The process for the preparation of sodium zirconium cyclosilicate as claimed in claim 1, wherein the step (iii) is preferably carried out at temperatures in the range of 215°C to 225°C.

6. The process for the preparation of sodium zirconium cyclosilicate as claimed in claim 1, wherein the agitation of the reaction mixture as in step (iii) is carried out in the range of 800 to 1000 RPM.

7. The process for the preparation of sodium zirconium cyclosilicate as claimed in claim 1, wherein the step (iii) is carried out for about 48 hours.

8. The process for the preparation of sodium zirconium cyclosilicate as claimed in claim 1, wherein the sodium zirconium cyclosilicate is obtained as in step (iv) after adjusting the pH of the reaction mass to 4.8 -5.3.

9. The process for the preparation of sodium zirconium cyclosilicate as claimed in claim 1, wherein the process is capable of producing predominantly ZS-9 form of sodium zirconium cyclosilicate without using any seed crystals of ZS-9 form of sodium zirconium cyclosilicate.

10. A process for the preparation of sodium zirconium cyclosilicate in a reactor, comprising the steps of:

(i) providing a mixture of colloidal silica solution and sodium hydroxide solution in the reactor;
(ii) heating the reaction mixture obtained in step (i) in the reactor at temperatures above 200°C;
(iii) adding zirconium acetate solution to the mixture provided in step (ii) in the reactor by a specially designed high pressure addition funnel at temperatures above 200°C;
(iv) agitating the reaction mixture obtained in step (iii) with the agitator and baffle-like structure of the reactor at temperatures above 200°C; and
(v) obtaining sodium zirconium cyclosilicate from the reactor,
wherein the reactor comprises
a reaction vessel having a volume of 5-L and an inside and outside wall;
an agitator within the reaction vessel;

a cooling jacket comprising serpentine-type coils proximate to the outside wall of the reaction vessel; or at least one baffle-like structure proximate the inside wall of the reaction vessel and placed in operative proximity to the agitator,
to provide uniform suspension of solids within the reaction vessel.

11. The process for the preparation of sodium zirconium cyclosilicate as claimed in claim 10, wherein the reactor comprises a specifically designed high pressure addition funnel.

12. The process for the preparation of sodium zirconium cyclosilicate as claimed in claim 10, wherein the step of adding zirconium acetate solution to the mixture in the reactor by a specially designed high pressure addition funnel at temperatures above 200°C as in step (iii) is done by attaching the specially designed pressure addition funnel with reactor before the addition or the process.

13. The process for the preparation of sodium zirconium cyclosilicate as claimed in claim 10, wherein the step (iii) is preferably done by applying high pressure to the addition funnel without opening the reactor.

14. The process for the preparation of sodium zirconium cyclosilicate as claimed in claim 10, wherein the step of agitating the reaction mixture with the agitator and baffle-like structure of the reactor as in step (iv) is preferably carried out at temperatures in the range of 215°C to 225°C.

15. The process for the preparation of sodium zirconium cyclosilicate as claimed in claim 10, wherein the step (iv) is preferably carried out after applying more than 10 Kg nitrogen pressure.

16. The process for the preparation of sodium zirconium cyclosilicate as claimed in claim 10, wherein the agitation of the reaction mixture as in step (iv) is carried out in the range of 800 to 1000 RPM.

17. The process for the preparation of sodium zirconium cyclosilicate as claimed in claim 10, wherein the step (iv) is carried out for about 48 hours.

18. The process for the preparation of sodium zirconium cyclosilicate as claimed in claim 10, wherein the sodium zirconium cyclosilicate is obtained as in step (v) after adjusting the pH of the reaction mass to 4.8 -5.3.

19. The process for the preparation of sodium zirconium cyclosilicate as claimed in the claim 10, wherein the process is capable of producing predominantly ZS-9 form of sodium zirconium cyclosilicate without using any seed crystals of ZS-9 form of sodium zirconium cyclosilicate.