Title of Invention

NOVEL CARBON SUPPORTED ACTIVATED ALUMINA ABSORBENT USEFUL FOR THE REMOVAL OF FLUORIDE IONS FROM WATER AND A PROCESS FOR THE PREPARATION THEREOF

Abstract

The present invention provides a novel adsorbent carbon supported activated alumina (CSAA) which posses both the advantageous characteristics of carbon and alumina viz., the high specific surface area associated with activated carbon and high sorption capacity of alumina towards F". Carbon supported activated alumina has an added advantage of its usage in the neutral pH unlike alumina and alumina impregnated carbon which are found to be efficient only in acidic pH. It is more efficient compared to carbon in terms of its sorption capacity towards F" and is therefore useful for the efficient removal of fluoride ions from water.

Full Text

The present invention relates to a carbon supported activated alumina adsorbent useful for the removal of fluoride ions from water. The present invention also relates to a process for the preparation of carbon supported activated alumina adsorbent useful for the removal of fluoride ions from water. Background of the invention Even though water is abundantly available on the earth in the form of oceans, lakes, rivers etc., only a little portion is fit for drinking purposes. Hence, most of the rural population depends on the ground water. The poor quality of ground water makes the people to suffer due to different diseases. The problem of excessive fluorides in drinking water is a matter of serious concern around the world. Fluoride as low as 1ppm (mg\L) causes breakdown of collagen, the most abundant of the body's protein at 30%. The concentration above 2ppm gives permanent teeth a chalky-white appearance or the mottled brown-satin coloration to children less than 10 years of age. Fluoride above 4ppm in drinking water can cause a condition of dense and brittle bones, known as osteoporosis, or marble bones called skeleton fluorosis. Fluoride replaces hydroxides in bones and thus is deposited in bones and causes chronic effect, known as skeleton fluorosis. The acceptable limits of fluoride ion in drinking water according to W. H. O. is 1.5 mg / litre of water. Hence it is utmost important to purify the water before its use. by Adsorption technology for removal of fluoride ion from water is one of the commercially viable technology. The present invention provides a process for the preparation of carbon supported activated alumina adsorbent useful for removal of fluoride ion from water. An invention relating to a process in removing fluoride ion from waste water from silicon processing, through neutralization was disclosed in a US patent No.US6436297 This invention highlights the method based on physicochemical processing for the removal of F'form water using milk of lime (Ca(OH)2 suspended in water) which is based on the spontaneous precipitation in the form of calcium fluoride (CaF2) of the fluoride ions in the presence of calcium ions following the equation: Reference may be made to another US patent 2059553 discloses the removal of fluoride by adsorption process on the activated alumina in presence of alkali metals. The pH of the water is maintained at 4-8. Reference may be made to yet another US patent 2043705 gave a comparative study of the adsorption properties of the hydroxides of aluminium, iron, zinc and manganese based on the precipitation method. Among all aluminium hydroxide is observed as the best. A publication by A.M.Raichur in separation and purification Technology (24 (2001) 121-127), explained about the removal of F" using rare earth oxides. Another publication by R. H. Me kee in Industrial Enganeering chemistry (26 (1934) 849) reveals the defluoridation by active carbon. Yet another reference may be made to a publication on defluoridation by R. Leyva Ramos , et al in Carbon (37 (1999) 609-619), which reports the use of Al impregnated on activated carbon using aluminum nitrate precursor. This catalyst adsorbs F" in acidic condition (i.e. pH- 3). The main limitations of the above mentioned patents and publications are: 1. Adsorption processes requires acidic conditions. 2. Addition of alkali metal ions for best adsorption. 3. In the precipitation method the separation of the pure water is a tedious process and there is no recovery of the catalyst. On the contrary, the present invention highlights the very simple way of making a highly efficient adsorbent for removal of fluoride ion without using alkali metal ions and easy way of operation i.e., in neutral pH-conditions. Objectives of the invention The main object of the present invention is to utilize the combined characteristics of alumina (aluminum hydroxide) and carbon prepared through deposition - precipitation route. Another object of the present invention is to prepare carbon supported activated alumina wherein the activated alumina precursor is selected from aluminum nitrate and the precipitating agent is selected from ammonia solution. Yet another object is to provide a process for the removal of high F" levels in the drinking water by using carbon supported activated alumina, as absorbent. Still another object is to provide a process wherein the defluoridation step can be performed at neutral PH. Summary of the invention Accordingly, the present invention provides a novel carbon supported activated alumina adsorbent comprising carbon content in the range of 1-80 wt%, having adsorbent capacity in the range of 91.4 to 98.7 % by wt. In an embodiment of the present invention the adsorbent has carbon content in the range of 5-50wt%. In yet another embodiment the adsorbent has carbon content preferably in the range of 5-25wt%. In yet another embodiment the adsorbent carbon supported activated alumina is useful for the removal of fluorides ions from water. The present process further provides a process for the preparation of carbon supported activated alumina adsorbent useful for the removal of fluoride ions from water, which comprises; adding activated carbon powder to an aqueous solution of 10-15 wt% of aluminum nitrate, followed by precipitation of the resultant solution mixture by adding drop wise 5% ammonia solution, under stirring, until pH of the solution mixture reaches to a value of 10, filtering the above said reaction mixture to obtain the aluminum hydroxide deposited activated carbon and washing it with water repeatedly till the filtrate reaches to a neutral pH value, and drying it at a temperature of 100-130°C, for a period of 24 hrs, followed by calcination at a temperature of 300-400°C, for a period of 2-5 hrs, under nitrogen atmosphere, activating the above said calcined aluminum hydroxide deposited activated carbon crystals with aluminum sulphate by soaking it in 3% aqueous solution of aluminum sulpahte, for a period of about 1 hr, followed by decantation and washing with water till the decant bring to neutral pH, drying the resultant product, at a temperature in the range of 100-130°C, for a period of about 4 hrs to obtain the desired product of carbon supported activated alumina. In yet another embodiment the temperature used for the calcination of aluminum hydroxide deposited activated carbon is irvthe range of 350-380°C. In yet another embodiment the temperature used for drying product is in the range of 120-130°C. In yet another embodiment the carbon supported activated alumina obtained has carbon content in the range of 5-50wt%, preferably in the range of 5-25Wt%. The present process further provides a process for the removal of fluoride ions from water using carbon supported activated alumina absorbent which comprises contacting fluoride ions containing water with a carbon supported activated alumina absorbent, at a neutral pH, at a temperature of 20-30°C, for a period of 1-24 hrs to obtain the fluoride ions depleted water. A In yet another embodiment the carbon supported activated alumina absorbent used is taken in a fixed bed reactor. In yet another embodiment the fluoride ions containing water used is continuously passed over the carbon supported activated alumina. In yet another embodiment the carbon supported activated alumina absorbent used has carbon content in the range of 5-50wt%, preferably 5-25Wt%. In yet another embodiment the carbon supported activated alumina having 25wt% carbon content used shows a maximum fluoride ions adsorption capacity of 98.7 wt% after contacting time period of 1 hr between the fluoride ions containing water and absorbent. In yet another embodiment the carbon supported activated alumina having 25wt% carbon content used shows a fluoride ions adsorption capacity of 98.3 wt% after contacting period of 5 hrs between the fluoride ions containing water and absorbent. In yet another embodiment the carbon supported activated alumina having 25wt% carbon content used shows a fluoride ions adsorption capacity of 92.4 wt% after a contacting period of 6 hrs between the fluoride ions containing water and absorbent. In still another embodiment the carbon supported activated alumina having 50wt% carbon content shows a fluoride ions adsorption capacity of 91.4 wt% after a contacting period of 6 hrs between the fluoride ions containing water and absorbent. Detail description of the invention Activated alumina can be applied as a successful defluoridation medium. Out of the several advantages associated with the usage of alumina, its specificity for F" and a relatively high exchange capacity of this ion are the major ones for it to acts as an efficient defluoridation material. The mechanism behind its action is chemisorption where activated alumina acts as an anianite, charged with S042" ions. During the processes of activation of alumina with aluminum sulphate, the formation of a complex-ligand takes place in the initial stage which then acts as an anion exchanger in the next stage for the removal of F" by the exchange of SO42" with F". Further, the sorption capacity of the material may be restored by using a regeneration solution like NaOH. The common adsorbents viz., carbon and alumina have certain advantages and drawbacks in terms of their performance towards the removal of fluoride. The present report discloses the use of a novel adsorbent carbon supported activated alumina (CSAA) which posses both the advantageous characteristics of carbon and alumina viz., the high specific surface area associated with activated carbon and high sorption capacity of alumina towards F'. Carbon supported activated alumina has an added advantage of its usage in the neutral pH unlike alumina and alumina impregnated carbon which are found to be efficient only in acidic pH. It is more efficient compared to carbon in terms of its sorption capacity towards F". However the working principle of CSAA is similar to that of alumina but more efficient and works even in the neutral pH. The advantage of carbon supported activated alumina is the formation smaller activated alumina crystallites on the carbon. Activated alumina is better dispersed on activated carbon because activated carbon is a high surface area material. The following examples are given by the way of illustration and therefore should not be construed to limit the scope of the invention Example-1 A series of carbon supported activated alumina with varying carbon loading 5 to 50 wt. %, are prepared by deposition precipitation method. Finely powdered activated carbon is added to the aqueous solution containing requisite amount of 10% aluminum nitrate by weight. It is precipitated with 5% ammonia solution by adding drop-wise slowly under vigorous stirring conditions until the pH reaches to a value of 10. The precipitated aluminum hydroxide deposited on activated carbon is filtered with thorough washings until the pH of the filtrate reaches to neutral. These precipitates are kept for drying at 120 °c for over night in the oven. The dried catalysts are calcined at 350°C for 3h under nitrogen atmosphere. These calcined catalysts are activated with aluminum sulphate. 10 gm catalyst is soaked in a 100 ml of 3 % aluminum sulphate solution for 1h followed by decantation and washings thoroughly with deionised water to bring the neutral pH. The catalysts are dried for 4h in oven at 120°C. The catalysts thus prepared are ready for the reaction. The catalyst with carbon contents of 5%, 15%, 25% and 50% by weight are designated as CSAA 5, CSAA 15, CSAA 25 and CSAA 50 respectively. Example-2 The defluoridation ability of the three catalysts, two are commercially available alumina (obtained from M/S Sude Chemie, India) and activated carbon (Source : Norrit obtained from M/S. Fluka, Netherlands) and the other is CSAA 25 as prepared in Example-l are shown in Table - 1. The fluoridated water with F" concentration of 20ppm is prepared by dissolving requisite amount of NaF in deionized water. The 20ppm F" containing water is passed continuously over the catalyst of 1 gram, taken in a fixed bed glass reactor (10 mm diameter and 200 mm long). The concentration of the fluoride ion present in the out let water after 5h is analyzed using a Advanced lon-Chromatograph (M/S. Metrohm Switzerland) with conductivity detector and with anion column Sup - 5 and mixture of aqueous solution containing sodium carbonate and bicarbonate. It is clearly observed that the catalyst prepared in the Example-l is the best adsorbent among the three adsorbents. The fluoride adsorption capacity of CSAA 25 as prepared in the Example-l is twice than that of the y-AfeOa and is approximately 25 times more active than activated carbon which is given in the Table-1. Example-3 The F" adsorption capacities of different samples of activated alumina with varying compositions of carbon are listed in Table-2. A flow of 20ppm F" water is passed continuously over the catalysts CSAA 5, CSAA 15, CSAA 25 and CSAA 50 separately and the concentration of F" at the out let after 6h, is analyzed by advanced ion-Chromatograph with conductivity detector and with anion column Sup - 5 and mixture of aqueous solution containing sodium carbonate and bicarbonate . The increase in carbon content up to 50 wt% by weight enhanced the adsorption capacity. Example-4 The defluoridation capability of CSAA 25 at regular internals is listed in the Table-3. The 20ppm F" containing water is passed continuously over the catalyst of 1 gram, taken in a fixed bed glass reactor (10 mm diameter and 200 mm long). The concentration of the fluoride ion present in the out let water at regular intervals is analyzed using an Advanced lon-Chromatograph with conductivity detector and with anion column Sup - 5 and mixture of aqueous solution containing sodium carbonate and bicarbonate. The data explains the excellent defluoridation capability of CSAA We claim: 1. An activated carbon supported activated alumina adsorbent comprising: an activated carbon support onto which alumina is adsorbed; wherein the activated carbon supported activated alumina adsorbent has an activated carbon content in the range of 25-50 wt %; wherein the alumina adsorbed onto the carbon support is not activated prior to adsorption but is activated after adsorption onto said support and prior to use of said adsorbent and wherein the fluoride ion adsorption capacity of said activated carbon supported activated alumina adsorbent is in a range of 91.4 wt % to 92.4 wt% after contacting period of 6 hours between the fluoride ions containing water and adsorbent. 2. An adsorbent as claimed in claim 1, wherein the carbon content is 25 wt%. 3. An adsorbent as claimed in claim 1, wherein the adsorbent is brought in contact with water containing fluoride ions to remove said ions from water. 4. A process for the preparation of activated carbon supported activated alumina adsorbent as claimed in claim 1 which comprises; adding activated carbon powder to an aqueous solution of 10-15 wt% of aluminum nitrate, followed by precipitation of the resultant solution mixture by adding drop wise 5% ammonia solution, under stirring, until pH of the solution mixture reaches to a value of 10, filtering the above said reaction mixture to obtain the aluminum hydroxide deposited activated carbon and washing it with water repeatedly till the filtrate reaches to a neutral pH value, and drying it at a temperature of 100-130°C, for a period of 24 hrs, followed by calcination at a temperature of 300-400°C, for a period of 2-5 hrs, under nitrogen atmosphere, activating the above said calcined aluminum hydroxide deposited activated carbon crystals with aluminum sulphate by soaking it in 3% aqueous solution of aluminum sulpahte, for a period of 1 hr, followed by decantation and washing with water till the decant bring to neutral pH, drying the resultant product, at a temperature in the range of 100-130°C, for a period of 4 hrs to obtain the desired product of activated carbon supported activated alumina. 5. A process as claimed in claim 4, wherein the temperature used for the calcination of aluminum hydroxide deposited activated carbon is in the range of 350-380°C. 6. A process as claimed in claim 4, wherein the temperature used for drying product is in the range of 120-130°C. 7. A process as claimed in claim 4, wherein the carbon supported activated alumina obtained has carbon content in the range of 5-50wt%, preferably in the range of 5-25Wt%.

Documents:

657-DEL-2006-Abstract-(25-07-2012).pdf

657-del-2006-abstract.pdf

657-del-2006-Claims-(10-10-2012).pdf

657-DEL-2006-Claims-(25-07-2012).pdf

657-del-2006-claims.pdf

657-del-2006-Correspondence Others-(07-08-2012).pdf

657-DEL-2006-Correspondence Others-(25-07-2012).pdf

657-del-2006-correspondence-others 1.pdf

657-del-2006-Correspondence-Others-(10-10-2012).pdf

657-del-2006-correspondence-others.pdf

657-DEL-2006-Description (Complete)-(25-07-2012).pdf

657-del-2006-description (complete).pdf

657-del-2006-form-1.pdf

657-del-2006-form-18.pdf

657-DEL-2006-Form-2-(25-07-2012).pdf

657-del-2006-form-2.pdf

657-del-2006-Form-3-(10-10-2012).pdf

657-DEL-2006-Form-3-(25-07-2012).pdf

657-del-2006-form-3.pdf

657-del-2006-form-5.pdf

657-del-2006-Petition-137-(07-08-2012).pdf