Title of Invention

"A PROCESS FOR THE MANUFACTURE OF ZEOLITE-A USEFUL AS A DETERGENT BUILDER"

Abstract

The process of the present invention for the manufacture of Zeolite-A (detergent builder) involves utilization of sodium aluminate liquor (Bauxite leachate) obtained as stream of alumina refinery, reduction in reaction time, eliminating aging of gel as well as heat energy during gel preparation and crystallization of Zeolite-A powder from superalkaline crystallization bath consisting of aluminosilicate gel. This method avoids the use of closed hydrothermal system and homogenizer for dispersion of gel.

Full Text

This invention relates to a process for the manufacture of Zeolite-A useful as a detergent builder. This invention particularly relates to the field of chemical technology, wherein Zeolite-A powder, useful as detergent builder, is manufactured without amorphous or crystalline impurities, using soap grade sodium silicate, commercial grade sodium hydroxide or caustic lye, and sodium aluminate liquor (Bauxite leaohate)-an intermediate stream of alumina refinery. Synthesis of Zeol ites depend on the starting materials such as reactive a 1 urninosi1icate gels prepared by mixing sodium silicate & sodium aluminate solutions; or amorphous solids such as metakaolin, si 1 iceous earth, coal ash etc. , pH, alkal i concentration, hydrothermal conditions for crystallization with autogenous pressures and degree of super sa. tura t i on of the aluminosi 1 icate gel leading to the nucleation of zeolite crystals. Using Na2O-A12O3-SiO2-H2O system, formation of gel and subsequently zeolite can be represented as under : (Equation Removed) In the present context, the get is defined as hydrous alkali metal a1urninosi1icate prepared (a.) by reacting aqueous solutions of alkali metal silicates with alkali metal aluminates or using (b) reactive solids or (c) colloidal sols or (d) reactive aluminosi1icate such as derived from dehydroxy1 ation of kaolin. Hitherto known processes for the preparation of Zeolite-A (detergent builder) are described in brief as follows. German patent Ger, of fen 2,517,218 describes a process to prepare Zeo1ite-A suitable as phosphate substitute in detergent formulations, by treating NaOH solution simultaneously with waterglass solution and sodium aluminate solution, gelled during 0.5 h, added to sodium aluminate solution at 80*C, and then crystallized during 3.5 h at 93*C. The zeolite obtained was having 93 wt % particles In a French patent, French demande 2,384,716 aqueous sodium aluminate solution is cooled to below ambient temperature and aqueous sodium silicate is mixed therewith to keep the resultant solution below ambient temperature. Then the mass was heated to 60-100OC to form gel and maintained at this temperature for 12 min. to 3h. As claimed, the process allowed close control of particle size distribution of the product. ccording to a German Patent, Ger.Offen 2,951,192 Zeolite-A having average grain size 0.9 urn, calcium binding capacity 300 mg CaCO3/g and 134 mg MgCO3/g was prepared by holding a solution containing H2O 94.14, Na2O 3.77, SiO2 1.77, and Al2O3 0.52 mole at 60OC for 8h. As defined in a Japanese patent JP, 89,05,905, zeolite having fine grain size is prepared from a mixture containing sodium aluminal.c and si I ieale, by hyd ro I ..hernia 1 reaction a I. the following condi t i ons. 26-60 wt % zeolite concentration in reacting solution, 14-30 wt % alkal i (as Na20) concentration in mother liquor, 40*C at reactant solution mixing and 30-ll0OC for crystal 1 ization. Tn a Japanese patent JP 04,342,4 16 a method is described to manufacture Zeolite-A, avoiding formation of Hydroxysodalite. As per the patent, an aqueous solution containing 0.1-0.3 mole per litre aluminate ions and 0.05-3 mole/1 sodium ions is mixed with an aqueous solution containing 0.02-0.1 mole/1 silicate ions and 0.05-4 mole/1. Sodium ions at A-type zeolite useful as detergent builder is effectively manufactured, without generation of other types of zeolites (US), as described in Japanese patent JP 63,08,211. As per the patent, aqueous sodium silicate solution and aqueous sodium aluminate solution are mixed at 12 %, when the zeolite crystallization rate becomes > 60 % as determined by electron diffraction method (I) and Another .Japanese patent JP 63,26.5,808 describes a process for the manufacture of A-type zeolite as follows. The process comprises (a) adding an aqueous solution of alkaline Al(0H)3 [20-25 wt % Al(0H)3] at 70-90*C and an aqueous solution of alkali silicate (20-29 wt % SiO2) at Brit. UK Patent Appl. 2,005,653 describes a method to 2 + manufacture zeolite useful for Ca exchange without. amorphous or crystalline impurities by the hydrothermal crystallization of a completely dispersed a 1 urninosi1icate gel by combining solutions of silica, alumina and alkali. Following is one of the example given by the patentees. Sodium aluminate solution containing 59.3 % solids (Na20-Al203 molar ratio 1.2 : 1) prepared by dissolving AI2O3 hydrate in hot NaOH, and sodium-silicate solution containing 47 % solids (Si02:Na20: :2 . 4 : 1 ) were heated to 72*C, diluted and mixed for 7 minutes in a homogenizer to produce a. dispersed gel with no visible particles and viscosity 110 ops at 60°C. Zeolite-A seed material was added and the gel was heated 80 minutes at 100*C. The crystalline Zeolite-A was separated, washed, dried for 5h at 105*C to give an uncontaminated material with Ca-exchange capacity 289 mg CaCO3/g. Tn our earlier patents no. 576/DEL/92 and 577/DEL/92, an improved process for the preparation of a1urninosi1icate gel and detergent grade zeolite from this gel has been described, wherein commercial sodium aluminate powder is used to prepare sodium aluminate solution having pre-optimised concentration of Na2O and Al2O3- This sodium aluminate solution having ambient temperature is reacted with sodium silicate solution at ambient: temperature to form aluminosilicate gel useful for the manufacturer of detergent grade zeolite having calcium binding capacity within the range of 150 to 160 mg CaO/gm. The drawbacks associated with the above mentioned known processes are : i) Complex unit operations such as simultaneous addition of reacting solutions, maintaining the temperature of reactants and/or reaction mixture above or below ambient temperature, are involved in the preparation method. ii) Gel formation at 60-110OC or below ambient temperature makes the preparation method energy consuming which adds to the production cost. iii) Aging of gel, dispersing gel using homogenizer, prolonged crystallization time, hydrothermal conditions for crystallization etc. also contribute to make the process uneconom i ca1 . iv) Precise pH control is required to obtain zeolite of uniform and small grain size. v) Dilute solutions are used which is not favourable for large scale production of Zeolite-A. vi) Lowering the alkali concentration during the process and monitoring by sophisticated instruments (e.g. electron diffraction & XRD) is a tideous job. Even it requires much more time to obtain the product. vii) Preparation of sodium-alurninate solution by dissolving Al2O3 hydrate in hot NaOH solution add to the production cost. viii)High energy inputs are involved for the preparation a alumino silicate gel, since the raw material sodium aluminate powder has util ized more energy as compared to sodium aluminate liquor from which it was prepared. The gel of ambient temperature also requires more energy to achieve the crystallization temperature of more than 90*C. The main object of the present invention is to provide of process for the manufacture of Zeolite-A useful as a detergent builder. Another object of the present invention is to provide an eeo-friend 1y, competitive process for the manufacture of Zeolite-A (detergent builder), using sodium aluminate liquor (Bauxite leachate) which is an intermediate stream of alumina refinery and also eliminate the drawbacks of the known processes. Tn the present invention, sodium aluminate liquor (Bauxite leachate) is used as received from the Bauxite leaching plant, to react with sodium silicate solution to form a 1 urninosi1 ieate gel which is subjected to crystallization to obtain Zeolite-A (detergent builder) powder with the composition t.O +. 0.2 Na20 : Al2O3 : 1.8 + 0.2 Si02 : Y H2O (Y = up to 5) with 100 wt % particles below 20 urn, 90 wt % particles in the range 1-5 urn. Average particle s i 7,e ^50 (sedigraph) maximum 4 urn and calcium binding capacity of minimum 160 mg CaO/g absolute dry zeolite. Specifications of Sodium Aluminate liquor (Bauxite leachate) - an intermediate stream of alumina refinery used in the present invention is given in Table? 1 below : Tab1e 1 (Table Removed) The process of the present invention for the manufacture of Zeolite-A (detergent builder) involves utilization of sodium aluminate liquor (Bauxite leachate) obtained as stream of alumina refinery, reduction in reaction time, eliminating aging of gel as well as heat energy during gel preparation and crystallization of Zeolite-A powder from superalkaline crystallization bath consisting of aluminosilicate gel. This method avoids the use of closed hydrothermal system and homogenizer for dispersion of gel. The mother liquor/filtrate of the product contains mainly alkali, which can be recycled for Bauxite leaching or for the preparation in reactant solutions. Thus, the present invention provides economical, eco-friendly, simple, less time and energy consuming, competitive process for manufacturing Zeolite-A (detergent builder). Accordingly, the present invention provides a process for the manufacture of Zeolite-A useful as a detergent builder which comprises i) diluting sodium aluminate liquor with water or alkali hydroxide such as herein described so as to get molar ratio of Na20 : Al203 at a range 1.95 to 2.05. ii) mixing sodium silicate with alkali and water to obtain a mixture wherein molar ratios of Na20 - Si02 is in the range of 0.6 - 0.8 and H20 - N20 is in the range of 35 - 45, iii) adding hot ( 50°C - 60°C) sodium aluminate solution of step (i) to the sodium silicate solution of step (ii) at ambient temperature molar ratios of Si02 - AI2O3 is in the range of 1.6 - 2.0, Na20 - Si02 is in the range of 1.6 - 2.0, and H20 - Na20 is in the range of 3 - 4, iv) heating the crystallization bath and the gel obtained at step (iii) from ambient temperature to 95°C for a period in the range of 45 to 75 minutes under continuous stirring to get crystals, v) recovering Zeolite-A from the crystal mass of step (iv) by filtration and washing till the pH of filtrate is basic, followed by drying and pulverizing, such as herein described. The sodium aluminate liquor used may be an intermediate stream from, Bauxite leaching plant of alumina refinery. The sodium aluminate liquor may be diluted to adjust the Na2O - Al2O3 molar ratio to 2.0 + 0.05 by adding water and alkali hydroxide such as caustic soda, caustic lye. The sodium silicate solution may be prepared by mixing water, alkali such as caustic soda, caustic or lye and sodium silicate. In an embodiment of the present invention, the sodium silicate used is selected from soap grade sodium silicate (Mole Si02/Na20 = 2.4 - 2.5) and Neutral sodium silicate (Mole SiO2/Na2O = 3.2 - 3.3). The sodium silicat used may be selected from commercially available sodium ailicales such as soap grade (mole SiO2/Na2O =2.4 2.5) and Neutral (Mole SiO2/Na2O = 3.2-3.3). The dosing time may be in the range of eo to 120 minutes. The Zeolite-A (detergent builder) may be crystallized by maintaining the temperature or crystallization bath from above 90OC to about 95OC. The washing may be carried out till the pH of the filtrate i s around 11. The drying may be carried out at least for 6 h at 110'C in air dryer. The, process of the present invention is illustrated by the following examples which should not be construed to limit the scope of the present invention. a) 300.7 L of sodium aluminate liquor (Na2O =168.18 gpl, Al2O3 = 169.6 gpl),14.74 Kgs of NaOH flakes and 199.3 I of water are mixed in a stirred tank equlped with steam jacket/heat mixed m a stirred tank equiped with steam jacket/heating coil. solution so prepared is heated to 50-60*C to simulate the conditions oT temperature of sodium aluminate solnl. ion prepared using sodium aluminate liquor (Bauxite leaohate) available in alumina refinery. b) 155.25 Kgs sodium silicate (34.79 % SiC>2, 14.24 % Na20, Si02/Na20 mole ratio 2.4), 19.48 Kgs of NaOH flakes and 355 L water are mixed in a tank equipped with stirrer and stirred for 15 minutes. c) Solul ion prepared in (a.-) is added to so 1 u I ion (b) within 1.5 h at ambient temperature with constant stirring to form aluminosilicate gel having molar ratios Si02-Al203 1-8 ± 0.2, Na20-Si02 1.6-2.0, H20-Na20 30-40. d) The alurainosi1icate gel thus prepared is heated from ambient temperature to 93 + 2OC in the same vessel as in (c) and the same temperature is maintained for 1 h under continuous stirring. e) The Zeolite-A powder produced in (d) is filtered using plate and frame type filter press. f) 560 L filtrate obtained in (e) contains 82.42 gpl Na20 and less than 2 gpl Si02 & A1203. This filtrate can be recycled in alumina refinery for Bauxite leaching process or can be partially used in preparation of reactant solutions. g) The cake is washed w i I. h water till the pH of the wash water i s around 1 1 . 1)) The product is dried in a cabinet type tray dryer at 110OC for about 6 h. The dried powder is pulverised and passed through 300 mesh BSS . The product Zeolite-A (detergent builder) powder obtained was grit free having following specifications. (Equation Removed) Example 2 a) 5.8 T. of sodium aluminate liquor (Na2O = 182.0 gp], A12O3 = l76 gpl). 0.240 Kg NaOH flakes and 4.1 I, water are mixed in a vessel to obtain 10 T. of sodium aluminate solution having Na2O-Al2O3 molar ratio 2.0. Heated to ROT before adding to sodium silicate so 1 u I. i on . b) 3.07 5 Kgs sodium silicate (Si02 35.12 %, Na20 = 14.69 %, & H20 = 50.19 %), 0.367 Kgs NaOII Makes, and 7.1. L water are mixed i n a vosse 1 for I 5 in i nu tes . c) Sodium aluminate solution as prepared in (a) is added to sodium silicate solution prepared as in (b) within 1.5 h at ambient temperature with constant stirring to form alurninosi1icate gel having molar ratios Si02-Al203 1.8 + 0.2, Na20-Si02 1.6-2.0, H20-Na20 30-40. d) The gel thus formed was heated upto 93 + 2*C in the same vessel as prepared in (c) arid the temperature maintained for lh under continuous stirring. e) The Zeolite-A powder produced in (d) is . obtained as described in example 1. (page no 15 Removed) & 102 gpl Al2O3. The solution is heated to 60OC prior to mixing with sodium silicate solution. b) 66.5 Kgs sod i urn s i 1 i ca t e (34.53 % S i 02, 14.85 % Na20 and 50.62 % H20), 7.664 Kgs NaOH flakes and 150.2 1. water are mixed to obtain sodium silicate solution. c) Solution prepared in (a) is added to solution prepared in (b) within 90 minutes at ambient temperature so as to obtain a gel suitable to manufacture Zeolite-A (detergent builder). d) The gel is heated to 93 + 2*C and maintained at this temperature for 1 h under continuous stirring. e) The procedures followed thereafter are similar to those described in earlier examples. Zeolite-A powder obtained according to this example was having following properties. (Equation Removed) Specifications of Zeolite-A (detergent builder) produced by the process of the present invention are given at Table 2 below : Table 2 (Table Removed) Zeolite-A powder* produced by the present invention is free of grit particles (i.e. particles > 45 um) having narrow particle size distribution (90 % particles between 1-5 um), average particle size (d50 , sedigraph) for the potential application as detergent builder to replace phosphates in detergent formulations. The present invention has the following advantages. 1 ) An intermediate stream of alumina refinery as received from Bauxite leaching plant containing many impurities (see Table 2) has been used as source of alumina and alkali. This makes the final product cheaper as no extra processing is required for the preparation of sodium aluminatc solution. 2) The unit operations involved in the process are so simple that it reduces the plant machinery cost and smooth production is possible. 3) The byproduct obtained in this process, i.e. filtrate, contains mainly alkali, which can be reutilised in Bauxite leaching or in the preparation of reactant sojution. Thus making the process eco-friend 1y. 4) Fven wash water which is slightly alkaline can be reused for the preparation of rea.ctanl solutions. 5) The process does not require any precise pH control or monitoring the crystallization by using sophisticated instruments. The only precise control required is that f temperature during crys ta11ization. We Claim: 1. A process for the manufacture of Zeolite-A useful as a detergent builder which comprises i) diluting sodium aluminate liquor with water or alkali hydroxide such as herein described so as to get molar ratio of Na20 : Al203 at a range 1.95 to 2.05. ii) mixing sodium silicate with alkali and water to obtain a mixture wherein molar ratios of Na2O- SiO is in the range of 0.6 - 0.8 and H2O- N2O is in the range of 35 - 45, iii) adding hot ( 50°C - 60OC) sodium aluminate solution of step (i) to the sodium silicate solution of step (ii) at ambient temperature with continuous stirring, using crystallization bath to obtain a gel wherein molar ratios of Si02 - Al2O3 is in the range of 1.6 - 2.0, Na2O - SiO2 is in the range of 1.6 - 2.0, and H2O - Na2O is in the range of 3 - 4, iv) heating the crystallization bath and the gel obtained at step (iii) from ambient temperature to 95°C for a period in the range of 45 to 75 minutes under continuous stirring to get crystals, v) recovering Zeolite-A from the crystal mass of step (iv) by filtration and washing till the pH of filtrate is basic, followed by drying and pulverizing, such as herein described. 2. A process as claimed in claim 1 wherein the sodium aluminate liquor is diluted by adding water and alkali hydroxide selected from sodium hydroxide or potassium hydroxide. 3. A process as claimed in claims 1 and 2 wherein the sodium silicate used is selected from soap grade sodium silicate (Mole SiO2/Na2O = 2.4 - 2.5) and Neutral sodium silicate (Mole SiO2/Na2O = 3.2 - 3.3). 4. A process as claimed in claims 1 to 3 wherein the crystallization at step (iv) is effected by maintaining the temperature of crystallization bath from 90°C to 95°C. 5. A process as claimed in claims 1 to 4 wherein the washing carried out till the pH of the f filtrate is around 11. 6. A process as claimed in claims 1 to 5 wherein the drying carried out at least for 6 h at 110°C in air dryer. 7. A process for the manufacture of Zeolite - A used as a detergent builder substantially as herein described with reference to the examples.

Documents:

1865-del-1997-abstract.pdf

1865-del-1997-assignment.pdf

1865-del-1997-claims.pdf

1865-del-1997-correspondence-others.pdf

1865-del-1997-correspondence-po.pdf

1865-del-1997-description (complete).pdf

1865-del-1997-form-1.pdf

1865-del-1997-form-19.pdf

1865-del-1997-form-2.pdf

1865-del-1997-form-3.pdf

1865-del-1997-form-6.pdf