Title of Invention

A PROCESS FOR THE PREPARATION OF SPECIAL GRADE LIGHT ALUMINIUM HYDROXIDE POWDER.

Abstract

The present invention relates to a process for the preparation of light hydrated alumina powder. More particularly the present invention relates to a process for the preparation of light hydrated alumina (light hydrate) powder, having a packed bulk density in the range 0.25 - 0.3g/ c.c. through gel precipitation. The process steps comprises characterized in that pouring an aqueous solution of aluminum sulfate into the reactor, agitating and stirring the said aqueous solution for a period ranging from 2 to 3 hrs, adding an aqueous solution of hydrazine in a mole ratio of hydrazine to aluminum sulfate ranging from 1:3-12 to 1:5-5 to the above said solution from a burette at a flow rate ranging from 1 - 2 ml/min, filtering and washing the precipitated slurry by standard method followed by drying in an air oven at a temperature ranging between 100 - 120°C for about 24h or till a constant weight of the aluminum hydroxide is obtained.

Full Text

The present invention relates to a process for the preparation of light hydrated alumina powder. More particularly the present invention relates to a process for the preparation of light hydrated alumina (light hydrate) powder, having a packed bulk density in the range 0.25 - 0.3 g/ c.c. through gel precipitation. Aluminium hydroxides and oxides in their normal and specialty forms have a wide variety of applications in many contemporary technological domains. The Bayer process produces aluminium trihydroxides as agglomerated particles having a packed bulk density of not less than 0.7g/cc. In recent years the market of normal hydroxides is quite competitive, there being a tremendous drop in the international price. However, special grade non-metallurgical hydroxides (light hydrated alumina), or its progenitor alumina, have a constant market, the demand being on an ever increasing trend year by year because of the advanced technological use of such materials in modern days. The major consumption of special grade light hydrate and derived materials are mostly in printing inks, boot polishes, wax polishes, paints, pigments, cosmetic products, extenders, filler in paper/pulp industries and in the preparation of high-tech ceramics/refractories/ composites, electroceramic and dielectric materials etc. Due to its non-toxic, high-temperature-resistant and easy-to-handle character, new areas of applications of such materials are also being explored regularly. The production of special grade aluminium hydroxide powder requires carefully controlled operations. Depending on its use in the production of the end material, aluminium hydroxide powder needfully requires high brightness, purity, fineness, and more particularly low bulk density. Though properties of such product can vary considerably, optimization of desired product is to be essentially achieved by suitable control of various precipitation parameters. In our country only about 1% of the total aluminium hydroxides/alumina is used for non-metallurgical purposes. Though India has a strong market base for special grade alumina hydrate powder, no easy and viable commercial production is available, and the requirements are met generally through imports. The earlier commercial/laboratory processes available so far for the production of hydroxide gels may be classified into two broad classes, (i) A sol-gel method in which an aluminium hydroxide precipitate is produced by aqueous hydrolysis of an Al- salt solution by sodium carbonate, (ii) Controlled reaction of aluminium sulfate with sodium aluminate liquor to produce hydroxides gels. The major disadvantages of the two above mentioned methods are : (a) Soda is present as a significant impurity impairing the quality of the product. (b) The hydrated alumina powder obtained in most of the commercially viable processes reported so far, are stubborn gels, hindering the successful use of such materials in later high-tech applications. (iii) No earlier worker has so far reported hydrated alumina powder having a loose and packed bulk density of 0.09 g/cc and 0.25 g/cc respectively. The present patent work utilizes hydrazine hydrate for precipitating light powder of aluminium hydroxide gel by reacting it with an aqueous solution of aluminium sulfate at room temperature under carefully controlled conditions. Control of various parameters such as concentrations of aluminium sulfate and hydrazine hydrate, the [N2H4]0 / [Al3+]0 ratio, final pH, and mode of addition of reactants, etc. determined the quality of the product powder. The major advantage of the present work is the production of a low bulk density material under ordinary laboratory conditions. The main object of the present invention is to provide a process for the preparation of special grade hydrated alumina powder Yet another object is to provide a process for the preparation of special grade hydrated alumina powder under ordinary laboratory conditions. Accordingly the present invention provides a process for the preparation of special grade light hydrated alumina powder which comprises characterized in that pouring an aqueous solution of aluminum sulfate into the reactor, agitating and stirring the said aqueous solution for a period ranging from 2 to 3 hrs, adding an aqueous solution of hydrazine in a mole ratio of hydrazine to aluminum sulfate ranging from 1:3-12 to 1:5-5 to the above said solution from a burette at a flow rate ranging from 1 - 2 ml/min, filtering and washing the precipitated slurry by standard method followed by drying in an air oven at a temperature ranging between 100 - 120°C for about 24h or till a constant weight of the desired aluminum hydroxide is obtained. In an embodiment of the present invention the density of the aluminium hydroxide obtained is in the range of 0.25 to 0.30 g/cm3. Analytical grade reagents and deionised water were used throughout the process. Hydrated aluminium sulfate [A12(SO4)3 .18 H2O, E.Merck, India Ltd.] and hydrazine hydrate[NH2.NH2.aq., Glaxo, India Ltd. ] were the main chemicals used for the study. The precipitation apparatus consists of a 500 ml capacity glass vessel having a fitting lid. The lid had provision for accommodating a stirrer rod and an opening for reactant addition. A Remi make laboratory stirrer having a variable speed controller was used for agitating the solution . The stirrer speed was maintained between 275 + 25 rpm. A Julabo make thermostatic waterbath was used to maintain the temperature whenever required. Ice was used to maintain a temperature of around 6°C. In a typical experiment, an aqueous solution of aluminium sulfate of the desired concentration { e.g., 0.25 M, 0.5 M, and 0,75 M [Al3+ aq.]0} were poured into the reactor and agitated. A hydrazine hydrate solution of the required concentration {[N2H4.aq]0 = 0.78 to 3.51M} was added to it dropwise from a burette during the course of almost 2 hours at a hydrazine-hydrate-addition rate of about 1 ml/min. The product so obtained was washed thoroughly to free it off sulfate ion and other soluble impurities. Finally the product was washed with a little amount of acetone and dried in an air oven at about 110°C for overnight or until a constant weight was obtained . Table-1 shows a list of results obtained with varying experimental conditions at room temperature. It has been observed (Sl.No.8 entry) that a mole ratio {[N2H4.aq]0/[Al3+]0} of ~ 4:l,with[N2H4.aq]0 ~ 3.01 M and [Al3+.aq]0 ~ 0.75 M, resulted in the powder of the lowest measured packed bulk density ; the weight-loss on ignition at 1100°C(for lh) for the same product was found to be 49.5%. Furthermore, the same mole ratio (4:1) with different initial concentration of the reactants (Expt.Sl.No.5) produced a product of slightly higher packed bulk density, suggesting that the initial concentration(s) of reactant(s) and their mole ratio might be significant parameters for getting a product of low packed bulk density. Table-2 shows the effect of temperature on the loose and packed bulk density of the product. The concentration and mole ratio taken in these experiments are similar to those in SI. No.8 of Table-1. The temperature effect shows that up to about 50°C the packed bulk density remained almost the same, but it increased with increasing temperature, suggesting higher temperature may not be advantageous for getting the product of low bulk density. The novelty of the present invention lies in the preparation of light hydrated alumina powder of packed bulk density lying in the range of 0.25 - 0.3 g/cc starting from aqueous solutions of aluminium sulfate and hydrazine hydrate at normal pressure and temperature . The following examples are given by the way of illustration and should not be construed to limit % scope of the present invention. Example 1 Aluminium sulfate obtained from E.Merck, India Ltd., was dissolved in demineralised water to form a 0.75M Al aq. solution. Similarly, hydrazine hydrate (~ 3.0 M) was prepared. 125 ml of ~ 0.75M Al aqueous solution was poured into the reactor and agitated with a Remi make laboratory stirrer. Hydrazine hydrate solution (125ml) was taken in a burette and poured into the reactor dropwise at a rate of about 1ml/ min. The experiment was continued till the total hydrazine hydrate was added during the course of around 2hrs. The final pH was found to be around 7.35. After completion of the experiment the precipitated slurry was filtered in a Buchner funnel using Whatman filter paper no-1. The residue was repulped with 500 ml demineralized water and filtered again . This process was repeated several times to get the product free off sulfate ion and other soluble impurities. After this operation the product was washed with a few ml of acetone and was dried in an air-oven at 110°C for overnight or until a constant weight was obtained. The loose bulk density at room temperature was measured by introducing the product into a 25 ml-polycarbonate measuring cylinder without any tapping. Similarly, the packed bulk density was measured with sufficient tapping till no further reduction of volume was observed . Experiments on weight-loss on ignition were performed by taking each sample in a platinum crucible and introducing into a Muffle Furnace, (makdeal S.a.india amalgame Ltd.), maintained at the desired temperature/ duration (e.g., 1100°C,lh); the weights were measured by means of an electronic digital microbalance of Sartorius make with an accuracy limit within + 0.1 mg . TABLE - 1 Measured loose and packed bulk densities of products obtained under representative reaction conditions at room temperature(28 °C). (Table Removed) Weight loss on Ignition(LOI) at 1100°C for 1 hour = 55.0 % ( * ), 49.5% (#) TABLE - 2 Measured loose and packed bulk densities of products prepared at different temperatures {[N2H4.aq]0/[Al3+.aq]0 = 3.0/0.75 = 4:1} (Table Removed) We Claim: 1. A process for the preparation of special grade light hydrated alumina powder which comprises characterized in that pouring an aqueous solution of aluminum sulfate into the reactor, agitating and stirring the said aqueous solution for a period ranging from 2 to 3 hrs, adding an aqueous solution of hydrazine in a mole ratio of hydrazine to aluminum sulfate ranging from 1:3-12 to 1:5.5 to the above said solution from a burette at a flow rate ranging from 1 - 2 ml/min, filtering and washing the precipitated slurry by standard method followed by drying in an air oven at a temperature ranging between 100 - 120°C for about 24h or till a constant weight of the aluminum hydroxide is obtained. 2. A process as claimed in claim 1, wherein the density of the aluminum hydroxide obtained is in the range of 0.25 to 0.30 g/cm3. 3. A process for the preparation of a special grade light hydrated alumina powder substantially as herein described with reference to the examples.

Documents:

1000-del-2001-abstract.pdf

1000-del-2001-claims.pdf

1000-del-2001-complete specification (granted).pdf

1000-del-2001-correspondence-others.pdf

1000-del-2001-correspondence-po.pdf

1000-del-2001-description (complete).pdf

1000-del-2001-form-1.pdf

1000-del-2001-form-18.pdf

1000-del-2001-form-2.pdf

1000-del-2001-form-3.pdf