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US 7,022,302 B2Granted
Process for preparing hydrotalcite and brucite type posite charged layers
AssigneeCouncil of Scientific and Industrial Research
InventorsPravinchandra M. Oza, Satishbhai H. Mehta, Murnalben V. Sheth, Pushpito K. Ghosh, Mahesh R. Gandhi, Jatin R. Chunawala
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Abstract
An improved process is described for the preparation of surface modified hydrotalcite. The process comprises reacting a precursor of magnesium and aluminium in the presence of suitable alkali carbonate at high temperature. The product has a BET surface area of ≦20 m2/gm and average particle size of ≦0.5 μm and is useful as halogen scavenger and fire retardant.
Claims25
A process for the preparation of hydrotalcite which comprises,
- (i) diluting bittern with water to obtain a solution with about 2% (w/v) magnesium ion concentration and clarifying the diluted bittern by treating with equivalent amounts of alum solution and caustic soda solution to precipitate aluminium and magnesium hydroxide in the range of 75–100 ppm and 200–300 ppm respectively;
- (ii) separating the sedimented hydroxides and obtaining a clear solution of bittern with a magnesium ion concentration in the range of 0.53–0.90 molar;
- (iii) reacting clear bittern obtained in step (ii) above with alkali carbonate while keeping mole ratio of carbonate ions to magnesium ions in the range of 1.1–1.4 to obtain an aqueous slurry of a magnesium precursor;
- (iv) reacting a solution of alum or soluble aluminium salts having not more than 100 ppm of iron with alkali carbonate under continuous stirring while keeping mole ratio of carbonate ions to aluminium ions in the range of 1.70–1.95 to obtain an aqueous slurry of aluminium precursor;
- (v) separating the precursors obtained in steps (iii) and (iv) above in form of cakes, and washing the cakes till washed liquor of magnesium precursor and aluminium precursor show less than 0.1% (w/v) of chloride and sulphate respectively;
- (vi) heating well dispersed aqueous slurry of magnesium precursor and adding caustic soda equivalent to 0.90–0.95 of magnesium ion present under continuous stirring;
- (vii) maintaining the temperature of slurry obtained in step (vi) and then allowing it to cool;
- (viii) re-dispersing aluminium precursor in 0.05 molar sodium carbonate solution to obtain an aqueous aluminium slurry;
- (ix) adding aqueous aluminium slurry obtained in step (viii) to a magnesium slurry obtained in step (vii) keeping ratio of mole of aluminium ions to total moles of aluminium and magnesium ions in the range of 0.28–0.33 under continuing agitation to obtain an amorphous magnesium-aluminium complex;
- (x) crystallizing mixed slurry of 3–5% (w/v on product basis) under agitation and cooling;
- (xi) adding stearic acid of 3–6% (w/v on product basis) to a slurry obtained in step (x) with continuous stirring;
- (xii) agitating the slurry obtained in step (xi) while allowing to cool, filtering the slurry and washing the cake till filtrate indicated pH of 8.5 to 10.5;
- (xiii) drying the said wet cake and pulverizing to obtain hydrophobic hydrotalcite in powder form.
10 more elements
A process for the preparation of hydrotalcite which comprises, (i) diluting sea bittern with water to obtain a solution with nearly 2% (w/v) magnesium ion concentration and clarifying the bittern by treating with equivalent amount of alum solution and caustic soda solution to precipitate aluminium and magnesium hydroxide in the range of 75–1000 ppm and 200–300 ppm respectively;
- (ii) separating the sedimented hydroxides and obtaining a clear solution of bittern having magnesium ions concentration in the range of 0.53–0.90 molar;
- (iii) preparing an aqueous slurry of magnesium precursor by reacting clear bittern obtained in (ii) with alkali carbonate while keeping mole ratio of carbonate ions to magnesium ions in the range of 1.1–1.4 at ambient temperature in stipulated time range of 30–60 minutes;
- (iv) preparing an aqueous slurry of aluminium precursor by reacting a solution of alum or soluble aluminium salts having not more than 100 ppm of iron with alkali carbonate in 30 minutes under continuous stirring while keeping mole ratio of carbonate ions to aluminium ions in the range of 1.70–1.95;
- (v) separating two precursors obtained in (iii) and (iv) by filtration, and washing the cakes till washed liquor of magnesium precursor and aluminium precursor showed less than 0.1% (w/v) of chloride and sulphate, respectively;
- (vi) heating well dispersed aqueous slurry of magnesium precursor to 60–70° C. and adding caustic soda equivalent to 0.90–0.95 of magnesium ion present, in 15 minutes time under continuous stirring;
- (vii) maintaining the temperature of slurry obtained in (vi) to 60–70° C. for 15 minutes and allowing to cool to nearly 40° C.;
- (viii) re-dispersing aluminium precursor in 0.05 molar sodium carbonate solution;
- (ix) adding aqueous aluminium slurry obtained in (viii) to a magnesium slurry obtained in (vii) in 30 minutes keeping ratio of mole of aluminium ions to total moles of aluminium and magnesium ions in the range of 0.28–0.33 and continuing agitation for 30 minutes;
- (x) crystallizing mixed slurry of 3–5% (w/v on product basis) in the temperature range of 140–150° C. for 4–5 hrs under agitation and cooling to 80° C.;
- (xi) adding stearic acid of 3–6% (w/w on product basis) to a slurry obtained in (x) with continuous stirring;
- (xii) agitating the slurry obtained in (xi) while allowing to cool to nearly 55° C., filtering the slurry at nearly 40° C. and washing the cake till filtrate indicated pH of 10;
- (xiii) drying the said wet cake at 110° C. and pulverizing to obtain hydrophobic hydrotalcite in powder form.
9 more elements
Dependencies are inferred from the claim text.