Title of Invention

PROCESS FOR THE MANUFACTURE OF AN IMPROVED MOLECULAR SIEVE ADSORBENT TYPE X

Abstract

A process for the manufacture of an improved molecular sieve adsorbent type which comprises reacting a zeolite adsorbent in a pellet or powder form with an aqueous solution containing one or more sodium compound such as herein described, removing the excess solution, washing and drying the residue in any conventional manner and subjecting the dried residue to calcination in order to obtain said improved molecular sieve adsorbent type.

Full Text

FORM 2 THE PATENTS ACT, 1970 COMPLETE SPECIFICATION [See Section 10] "PROCESS FOR THE MANUFACTURE OF AN IMPROVED ADSORBENT TYPE X" INDIAN PETROCHEMICALS CORPORATION LIMITED, a Government Company, of P. O. Petrochemicals, District Vadodara - 391 346, Gujarat, INDIA, The following specification particularly describes the nature of the invention and the manner in which it is to be performed. A PROCESS FOR THE MANUFACTURE OF AN IMPROVED ADSORBENT TYPE X Field of the invention The present invention relates to a process for the manufacture of a molecular sieve adsorbent Type X with improved adsorption properties. The present invention particularly relates to a method for the preparation of an improved molecular sieve adsorbent Type X by treating zeolite X with an aqueous solution containing one or more sodium compounds to improve the adsorption and desorption properties thereof. Background of the invention Zeolite molecular sieve adsorbents are extensively used for drying and purification of gas streams such as air, light hydrocarbons and liquid streams. They find particular application in the separation of air by cryogenic distillation in order to obtain nitrogen and oxygen. In this process, the feed air is purified to remove moisture and carbon dioxide to a very low level generally below 1 part per million before subjecting it to cryogenic distillation. Zeolite molecular sieve type 13X, which is a sodium exchanged form of zeolite type X is widely used for this purpose due to its high adsorption capacity for water and carbon dioxide. In such an application, air purification is generally carried out using a two bed thermal swing adsorption (TSA) process. In a typical two bed TSA process, compressed air is passed through one of the beds at low temperature (5-20°C). At the same time the other bed undergoes regeneration at high temperature (70-250°C). The efficiency of the adsorbent in such applications depends on the capacity of the adsorbent for water and carbon dioxide at the adsorption temperature and the residual water adsorption capacity at the regeneration temperature, i.e., the difference in adsorption capacity of the adsorbent at the adsorption temperature and water retained at the regeneration temperature. Carbon dioxide due to its weak interaction with zeolite surface can be easily desorbed during regeneration even at low temperature. However, water can not be fully desorbed at low temperatures as it is strongly held on the zeolite surface. As a result, zeolite always possesses some residual water adsorption capacity even after regeneration at high temperature. Water retention capacity of the adsorbent depends on the regeneration temperature and on the nature of the adsorbent. The residual water adsorption capacity of the adsorbent decreases with the increase in the regeneration temperature. The higher the water adsorption capacity of the adsorbent at adsorption temperature and the lower the water retention capacity at the regeneration capacity at the regeneration temperature, the better are the adsorbent. Zeolite X is a crystalline aluminosilicate consisting of well-defined pore structure capable of adsorbing molecules with cross section diameters not greater than about 8 Angstroms. According to available art, zeolite X is prepared by the method disclosed in US Patent 2, 882, 244 and has the general formula: Na20:A1203:2.4Si02:w.H20 In commercial practice, the zeolite obtained by hydrothermal synthesis as a white powder is converted into pellets/granules/beads by mixing and pelletising with clay binders such as bentonite, attapulgite and kaolin. Such shaped bodies thus obtained are dried and then subjected to calcination at high temperatures in the range of 550 - 700°C. Calcination of the zeolite powder/formed bodies in the above temperature range may result in the damage to the adsorption properties such as adsorption capacity, rates of adsorption and desorption behaviour. We have now invented a process to restore adsorption and regeneration properties of both zeolite X powder and formed bodies that has lost part of its capacity during such manufacturing steps described above. Objects of the invention It is an object of the present invention to provide a process for the manufacture of a molecular sieve adsorbent Type X with improved adsorption properties It is a further object of the present invention of to provide a method of manufacture of a molecular sieve adsorbent Type X, particularly zeolite 13X having improved adsorption properties It is another object of the present invention to provide a method to improve the adsorption properties of zeolite 13X in powder or pellet form. It is yet another object of the invention to develop a method to improve the desorption or regeneration properties of the adsorbent zeolite 13X in powder or pellet form. It is a further object of the invention to develop a method to improve the adsorption and desorption /regeneration properties of molecular sieve adsorbent 13 X in powder or pellet form by chemical modification. It is a further object of the present invention to provide a method for restoring the adsorption and desorption properties of zeolite 13X in powder or pellet form which have lost oart such properties during manufacturing processes. Summary of the invention The above and the other objects of the present invention are achieved by the process of the present invention which involves chemical.modification of the Zeolite X powder and/or formed bodies manufactured by conventional processes involving calcination at high temperatures. The objects of the invention are particularly achieved by treating the zeolite X in a powder or pellet form and prepared by conventional process with an aqueous solution of a sodium compound. The present invention is based on the finding that treating Zeolite X in a powder or pellet form, which have lost part of their adsorption and / or desorption properties during their manufacturing process, with an aqueous solution of one or more sodium compound as described herein surprisingly restores such lost properties. Accordingly, the present invention provides a process for the manufacture of an improved molecular sieve adsorbent type 13X which comprises reacting a zeolite adsorbent in a pellet or powder form with an aqueous solution containing one or more sodium compound such as herein described, removing the excess solution, washing and drying the residue in any conventional manner and subjecting the dried residue to calcination in order to obtain said improved molecular sieve adsorbent type 13X. In a preferred embodiment, said aqueous solution of one or more sodium compound is selected from an aqueous solution of sodium hydroxide or a solution containing sodium hydroxide and sodium chloride. In one embodiment of the invention, the adsorbent is either NaX powder or formed bodies of NaX. In a further embodiment of the invention, the adsorbent is NaX bodies are selected from pellets, granules, extrudates or deactivated pellets. In a further embodiment of the invention, the size of the deactivated pellets is from 0.1 to 5.0 mm. In a further embodiment of the invention, the aqueous solution comprises of from 1 to 12 % w/w for sodium hydroxide and from 0 to 10 % w/w of sodium chloride. In a preferred embodiment of the invention, the reaction with said aqueous solution is carried out at a temperature in the range of from 10 to 100°C, more preferably in the range of 25 to l00°C. In another embodiment of the invention, the treatment time is in the range of 0.5 to 24 hours. In a further embodiment of the invention, the reaction/exposure is carried out with said solution with a solid/liquid ratio of 0.5 to 10. In yet another embodiment of the invention, the calcination step is carried out at a temperature ranging from 250 to 550°C. In yet another embodiment of the invention, the treatment/exposure is done by circulating said solution through a column containing the said zeolite. Detailed Description In a typical process, the adsorbent is in the form of powder or formed bodies and is subjected to chemical reaction and/or exchange with an aqueous solution containing 1 to 12 % w/w of sodium hydroxide and 0 to 10 % w/w of sodium chloride for 1 to 24 hours at 25 to 100°C. the resulting adsorbent is washed with water and dried at 80 to 120°C and then calcined at 250 to 450°C for 2 to 15 hours. The crystallinity of the adsorbent is measured by comparing the X-ray diffraction data with literature X-ray diffraction data. The X-ray diffractions at the 'd' values 14.465, 8.845, 7.538, 5.731, 4.811, 4.419, 3.946, 3.808, 3.765, 3.338, 3.051, 2.944, 2.885, 2.794 and 2.743 A0 were used for comparison. Water adsorption capacity of the resultant adsorbent is measured by gravimetric method using a McBain-Bakr quartz spring balance. Adsorption capacity for carbon dioxide is also measured in McBain-Bakr balance by noting the weight increase of a known weight of the adsorbent when the latter is exposed to 760 torr of carbon dioxide gas pressure for a period of one hour. Water or carbon dioxide retention values of the adsorbent are measured by subjecting the samples to evacuation at required temperature. The present invention is useful for improving the adsorbing/regeneration properties of the adsorbent. The present invention can also be used for increasing the adsorption capacity of the adsorbent 13X which has lost part of its water adsorption capacity due to high temperature calcination. The invention will now be illustrated with reference to the following Examples. It must, however, be understood that the following Examples do not constitute a limitation on the scope of the invention and are merely illustrative. It is possible to work the invention" outside the parameters specified in the following Examples. EXAMPLE 1 200 g commercial adsorbent 13X obtained supplied by CAT AD Division IPCL, Thane in 1.5 mm cylindrical pellet form was treated with 1000 ml of 2 wt % sodium hydroxide solution at 90°C for 6 hours followed by thorough washing with distilled water. The resulting solid was then dried at 110°C and calcined at 350°C. The adsorption properties measured on the resultant adsorbent bodies are given below: Property Starting 13X 13X obtained from Example 1 Water adsorption capacity at 30°C and 75 % relative humidity, g/100g 26.0 30.1 Water retained at 120°C and 0.5 mm Hg g/lOOg 6.4 3.7 Carbon dioxide capacity at 30°C and 1 atm 18.8 21.0 Improvement in the adsorption/regeneration (retention properties) is apparent from the above adsorption data. EXAMPLE 2 100 g commercial adsorbent 13X in 1.5 mm cylindrical pellet form was treated with 500 ml of aqueous solution containing 1 wt % sodium hydroxide and 4 wt% of sodium chloride at 90°C for 4 hours. The adsorbent pellets were then washed and dried at 110°C followed by activation at 400°C for 5 hours. The adsorption and regeneration properties measured on the resultant adsorbent bodies are given below: Property Starting 13X 13X obtained from Example 2 Water adsorption capacity at 30°C and 75 % relative humidity, g/lOOg 26.0 30.5 Water retained at 120°C and 0.5 mm Hg g/100g 6.4 2.6 Carbon dioxide capacity at 30°C and 1 atm 18.8 21.2 The above results show excellent improvement in adsorption and regeneration properties of the adsorbent on treatment according to the present invention. EXAMPLE 3 100 g commercial adsorbent 13X (Is/Al ratio = 2.4) was treated with 1000 ml of 2 wt % sodium hydroxide solution at 80°C for 4 hours followed by thorough washing with distilled water. The resultant adsorbent powder was then dried at 110°C and calcined at 350°C. The adsorption properties measured of the powder are given below: Property Starting 13X 13X obtained from Example 3 Water adsorption capacity at 30°C and 75 % relative humidity, g/100g 32.3 35.0 Water retained at 120°C and 0.5 mm Hg g/lOOg 7.0 5.5 Carbon dioxide capacity at 30°C and 1 atm 21.3 24.6 EXAMPLE 4 200 g commercial adsorbent 13X same as that used in Example 1 was calcined for 4 hours in a muffle furnace. Water adsorption capacity measured on this adsorbent showed loss in capacity. The adsorbent resulting from the above calcination was treated with 1000 ml of 2 wt % sodium hydroxide solution at 90°C for 6 hours followed by thorough washing with distilled water. The adsorbent thus obtained was then dried at 110°C and calcined at 350°C. The adsorption properties measured on the resultant adsorbent bodies are given below: Property Starting 13X 13X calcined at 650°C for 4 hours 13X obtained from Example 4 Water adsorption capacity at 30°C and 75 % relative humidity, g/lOOg 26.0 22.2 30.5 Water retained at 120°C and 0.5 mmHgg/lOOg 6.4 5.3 3.5 Carbon dioxide capacity at 30°C and 1 atm 18.8 . 20.2 Improvement in the adsorption/regeneration (retention properties) is apparent from the above adsorption data. EXAMPLE 5 100 g commercial adsorbent 13X (UOP's) which was in use in an air drier of N2/02 plant which has lost part of its adsorption capacity was treated with 500 ml of 2 wt % sodium hydroxide solution at 95°C for 6 hours followed by thorough washing with distilled water. The resulting solid is then dried at 110°C and calcined at 350°C. The adsorption properties measured on the resultant adsorbent bodies are given below: Property Starting 13X 13X obtained from Example 5 Water adsorption capacity at 30°C and 75 % relative humidity, g/lOOg 24.0 31.2 Water retained at 120°C and 0.5 mm Hg g/100g 4.9 3.1 Carbon dioxide capacity at 30°C and 1 atm 16.7 20.4 Improvement in the adsorption/regeneration (retention properties) is apparent from the above adsorption data. We Claim: 1. A process for the manufacture of an improved molecular sieve adsorbent type which comprises reacting a zeolite adsorbent in a pellet or powder form with an aqueous solution containing one or more sodium compound such as herein described, removing the excess solution, washing and drying the residue in any conventional manner and subjecting the dried residue to calcination in order to obtain said improved molecular sieve adsorbent type. 2. A process as claimed in claim 1 wherein said aqueous solution of one or more sodium compound is selected from an aqueous solution of sodium hydroxide and a solution containing sodium hydroxide and sodium chloride. 3. A process as claimed in claim 2 wherein aqueous solution comprises of from 1 to 12 % w/w for sodium hydroxide and from 0 to 10 % w/w of sodium chloride. 4. A process as claimed in any preceding claim wherein said zeolite adsorbent is either NaX powder or formed bodies of NaX. 5. A process as claimed in claim 4 wherein said NaX bodies are selected from pellets, granules, extrudates or deactivated pellets. 6. A process as claimed in claim 5 wherein said deactivated pellets have a particle size in the range of from 0.1 to 5.0 mm. 7. A process as claimed in any preceding claim wherein the reaction of said zeolite adsorbent with said aqueous solution of one or more sodium compound is carried out at a temperature in the range of from 10 to 100°C. 8. A process as claimed in claim 7 wherein said reaction temperature is in the range of 25 to l00°C. 9. A process as claimed in claim 7 or 8 wherein the reaction is carried out for from 0.5 to 24 hours. A process as claimed in any preceding claim wherein the solid/liquid ratio in the reaction mixture is in the range of 0.5 to 10. A process as claimed in any preceding claim wherein said calcination step is carried out at a temperature ranging from 250 to 550°C. A process for the manufacture of an improved molecular sieve adsorbent type 13X substantially as herein described with reference to and as illustrated in the foregoing examples. Dated this the 7th day of December, 1999 H SUBRAMANIAM, Of SUBRAMANIAM, NATATARAJ & ASSOCIATES ATTORNEYS FOR THE APPLICANTS

Documents:

947-bom-1999-claim(granted)-(23-12-1999).doc

947-bom-1999-claim(granted)-(23-12-1999).pdf

947-bom-1999-correspondence(27-05-2004).pdf

947-bom-1999-correspondence(ipo)-(24-06-2004).pdf

947-bom-1999-form 1(23-12-1999).pdf

947-bom-1999-form 2(granted)-(23-12-1999).doc

947-bom-1999-form 2(granted)-(23-12-1999).pdf

947-bom-1999-form 3(23-12-1999).pdf

947-bom-1999-form 4(27-05-2004).pdf

947-bom-1999-petition under rule 138(15-03-2004).pdf

947-bom-1999-petition under rule 138(20-01-2004).pdf

947-bom-1999-power of authority(20-04-2000).pdf