DESC:CONTINUITY
This application is a cognate application and claims priorities of Provisional Patent Application Nos. 202121048815 dated October 07, 2021 and 202221056264 dated September 30, 2022

FIELD OF THE INVENTION
The present invention relates to the production of alumina and, more particularly, to the production of dispersible alumina.

BACKGROUND OF THE INVENTION
The matrix of a refractory low cement castable contains fine and ultra-fine particles such as calcium aluminate cement, reactive aluminas and fumed silica. It is essential that all the matrix components are homogeneously distributed during mixing with water to take full advantage of the optimized particle size distribution and achieve the lowest water demand and desired rheological behavior. Dispersing agents are commonly used to de-agglomerate the fine particles of the matrix. Dispersing alumina is a highly- disperse reactive alumina containing organic components and used as deflocculating additives. Dispersing aluminas are complex organo mineral additives that controls the rheological properties of the low cement castable.

There has been much interest in the so-called dispersing aluminas, and a number of research are being carried out. The specific features and de-agglomerating efficiency of dispersing aluminas are advantageous over conventional dispersing additives. The traditional dispersing additives for low cement castable contained chemicals in small amounts such as phosphates, citric acid, sodium citrate, and organic additives. They were added, in amounts not exceeding 0.2%, which posed problems with their uniform distribution in dry concrete mixes.

Thus, the dispersing alumina plays the role of a carrier of organic de-agglomeration agents. Dispersing alumina also contains additives that serve to control the hardening rate (decelerating or accelerating). These types of dispersants are prepared by grinding dry mixtures of calcined alumina and additives (organic components, Na2O, CaO etc.).

Nonetheless, agglomeration still remains a major challenge for alumina ceramic. Due to this, particles are not fully dispersing in the matrix and makes the product inhomogeneous. The present invention overcomes the challenge by providing a process to develop dispersing alumina, for refractory castable application.

None of earlier reported work discusses about the process for producing surface treated alumina for improving the flowability in refractory castable application especially for micro-silica free castable.

OBJECTS OF THE INVENTION
It is an object of this invention to prepare a dispersing alumina which can readily be used in low cement castable.

It is an object of this invention to provide a facile and simple process to prepare dispersing alumina without employing complex process steps or reagents.

It is a further object of this invention to produce dispersing alumina which exhibits good flow behavior due to its dispersive nature.

These and further objects will become apparent as the description of the invention proceeds

SUMMARY OF THE INVENTION
The process for preparing dispersing alumina comprising:
i. milling calcined alumina in the presence of grinding agent and alumina grinding media,
ii. mixing the resultant alumina of step (i) with additives to obtain dispersing alumina
wherein the feed ratio of calcined alumina to the alumina grinding media is in a range from 1:40 to 1:50.

An aspect of the invention provides for a process for preparing dispersing alumina, comprising the steps of, drying of calcined alumina, milling of dried calcined alumina in the presence of grinding agent with 18 mm to 25 mm alumina grinding media for a duration of 4 hours at a predetermined rate of milling, followed by mixing with organometallic additives for 15 minutes to 20 minutes with 3 mm to 5 mm alumina ball.

BRIEF DESCRIPTION OF THE INVENTION
In describing and claiming the invention, the following terminology will be used in accordance with the definitions set forth below. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are described herein. As used herein, each of the following terms has the meaning associated with it in this section. Specific and preferred values listed below for individual process parameters, substituents, and ranges are for illustration only; they do not exclude other defined values or other values falling within the preferred defined ranges.

As used herein, the singular forms "a," "an," and "the" include plural reference unless the context clearly dictates otherwise.

The terms “preferred” and “preferably” refer to embodiments of the invention that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful and is not intended to exclude other embodiments from the scope of the invention.

As used herein, the terms “comprising” “including,” “having,” “containing,” “involving,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to.

The term “dispersing alumina” as used herein refers to efficient additives for optimizing rheological properties of castable.

The term “low cement castable” as used herein refers to classified as castable with less than 2.5% Lime (CaO) content in the formulation.

The term “organometallic compound/additive” as used herein refers to chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and sometimes broadened to include metalloids like boron, silicon, and selenium, as well.

The term “calcined alumina” as used herein refers to hard alumina and soft alumina.

The term “feed” as used herein refers to raw materials that are fed into the grinding media.

The term “micro silica” as used herein refers to fumed silica.

The present invention is directed towards making dispersible alumina by surface treating alumina that is obtained as a result of dry milling, with additives with the help of 3 mm to 5 mm alumina ball. Thus, the invention relates to the modification of surface of alumina by using polymeric additives such as poly carboxylate ether, organometallic compound, or mixture of both. The process which is economical and eco-friendly results in dispersing alumina having good flow behavior due to its surprising dispersive nature.

In an embodiment, the invention provides for a process for preparing dispersing alumina. The process comprises of milling calcined alumina and grinding agent. Milling is carried out in presence of alumina grinding media. The resultant milled alumina is then mixed with at least one additive to obtain dispersing alumina.

The said calcined alumina, prior to milling, is subjected to drying, at a temperature in the range of 100oC to 150oC for duration of 2 hours.

Milling is carried out in jar mill or ball mill. The duration of milling is in the range of 3 hours to 5 hours. The grinding media is preferably alumina ball having ball size of 18 mm to 25 mm.

Resultant milled alumina and additives are mixed for 15 minutes to 20 minutes in the presence of 3 mm to 5 mm alumina ball for mixing.

Calcined alumina is a combination of hard calcined alumina and soft calcined alumina. The ratio of hard calcined alumina to the soft calcined alumina is in a range of 75:25 to 85:15; preferably, the feed ratio is 85:15. Using two types of alumina, that is, using a combination of hard and soft calcined alumina gives bimodal peak which helps in flowability of the alumina by making it easier, provides wide range of particle size distribution within the alumina and improves water absorption. The grinding agent is selected from propane diol, ethylene glycol, or triethanolamine. Preferably, the grinding agent is propane diol.

The additive is selected from polycarboxylate ether (PCE), an organometallic (OM) compound, or a combination thereof.

Polycarboxylate ether is preferably Castament FS 60/FS 40/FS 20/FS 10.

Castament is a polymerisation product based on polyethylene glycol.

The amount of poly carboxylate ether is in a range of 5.0 to 20.0 wt.% and, the amount of organometallic compound is in a range of 0.1 to 0.5 wt. % to the weight of mixture of calcined alumina (> 99 % Al2O3 content).

The organometallic additive is selected from calcium stearate or magnesium stearate.

The feed ratio of calcined alumina to the alumina grinding media is in a range from 1:40 to 1:50. The feed ratio plays an important role, as the alumina obtained is homogenous, and therefore the resultant alumina gives better packing in the castable matrix and is stronger than conventionally produced castable.

In a particular embodiment of the claimed process, the particle size of the resultant dispersed alumina is in a range from 1 µm to 3 µm (d50).

In yet another embodiment, the process for preparing dispersing alumina specifically comprises of drying hard and soft calcined alumina at a temperature in a range of 100°C to 150°C for a duration of 2 hours. Subjecting dried calcined alumina to milling in the presence of propanediol wherein milling is carried out in presence of alumina ball having size of 18 mm to 25 mm followed by mixing the resultant milled calcined alumina with polycarboxylate ether and calcium stearate for 15 minutes to 20 minutes in presence of 3mm to 5 mm alumina ball to obtain dispersing alumina.

It is known that micro silica (fumed silica) in refractory castable is a major impurity for liquid steel production. However, the dispersible alumina of the present invention is free from micro silica (fumed silica), used in high end refractory castable application to produce clean steel. Conventionally, inorganic additives such as sodium base, phosphate base, etc. were used which require more water for refractory castable application. However, in the present invention, as inorganic additives are not used, less water is required while using dispersing alumina of the present invention for refractory castable application. Requirement of more amount of water means that the mixture is porous and therefore, castable matrix is weak and does not have enough strength.

Further, no external dispersing agent is added in the present invention. The process makes the physical handling of the material easier. The grinding hours of the process is also decreased. Thus, a homogenous alumina, with good flowability and better water absorption is produced by using the present invention.

The rheological properties of the refractory castable are improved by using the dispersing alumina of the present invention. The dispersing alumina of the present invention provides better packing because of its homogenous distributive nature and therefore, demand for water is reduced and there is a reduction in water absorption time period. Improvement in the water absorption of the material is from a level of 15 % to 20 % to 6 % to 8 %.

The invention will now be described with reference to the following examples. It is to be understood that the examples are provided by way of illustration of the invention and that they are in no way limiting to the scope of the invention.

Examples

A. Samples of the present invention, DA-1 to DA-8 were prepared as follows:

125g of calcined alumina of both hard and soft alumina were dried at a temperature of 105°C for 2 hours. 125g of calcined alumina of both hard and soft alumina in a ratio of 85:15 (hard: soft) and 6 kg of alumina balls having size of 25 mm were milled for 4 hours wherein the calcined alumina (feed): grinding media ratio in the range of 1:48 which resulted in bimodal peak and good particle size distribution. Polycarboxylate ether (Castament FS 60/FS 40/FS 20/FS 10) and calcium stearate were added and mixed for 15 minutes in the presence of 3-5 mm alumina ball.

The prepared dispersing alumina was used in 95% alumina base low cement castable without any external dispersing agents (cement percent – 5%, lime – less than 2.5%).

Results of Samples DA-1 to DA-8 are given in terms of physical flow, water absorption, low cement castable (self-flow), specific surface area, particle size and loss on ignition as follows:

Measurement of physical flow
The sample was allowed to pass through the Ford flow cup by giving vibration using vibrating table. This method was specifically applicable for surface treated calcined alumina like SRM30F, NSR03F and SRM30FG. This was an arbitrary method.

A stand fitted with Ford flow cup (5 mm orifice) was placed on the vibrating table. The cup with fine calcined alumina was filled by closing the orifice by finger at bottom of Ford flow cup. The surface of alumina using flat end spatula was leveled and excess quantity of alumina was removed. An empty steel bowl under the Ford flow cup was kept to collect alumina during vibration. Vibrating table was switched on and the orifice was opened by removing the finger at a time. Fine alumina was allowed to fall into the steel bowl. The time taken for emptying out alumina from Ford flow cup was measured in seconds.

Determination of water absorption of calcined alumina and alumina tri-hydrate

10 g of sample (alumina) was weighed and transferred to 125 mL porcelain dish. 50 mL of water in a 100 mL beaker containing dropper was taken and weighed. Water with the help of dropper was added while stirring the material continuously with spatula. As the particles came in contact with water, they formed into small lumps and gradually coalesce. The rate of water addition was reduced, and the wetted lumps were squeezed into a single mass.

RESULTS

Calculate the oil/water absorption as follows :

W1 - W2
WA = ----------------------- x 100
g/100 g sample W

WA = water Absorption
W = Weight of the material
W1 = Initial weight of the beaker, water and dropper
W2 = Final weight of the beaker, water and dropper
W1 – W2 = Weight water consumed

For self-flow measurement of castable, the method was ASTM C230 and ASTM C1446-11.

Table 1:
Sample Name Additives composition Physical Flow (sec) Water Absorption (%) Low cement Castable Self-Flow (%) Specific surface area
SSA (m2/g) Particle size (d50) Loss on ignition
LOI (%)
DA-1 PCE (5%) 30 8.0 39 2.78 1.93 5.4
DA-2 PCE (10%) 38 7.2 45 2.53 1.89 9.3
DA-3 PCE (15%) 39 7.0 56 2.20 1.78 12.9
DA-4 PCE (20%) 47 7.8 61 2.12 1.72 16.5
DA-5 PCE (5%) + OM (0.1%) 39 7.2 32 2.91 1.95 5.4
DA-6 PCE (10%) +OM (0.1%) 30 7.0 64 2.56 1.86 9.5
DA-7 PCE (15%) +OM (0.1%) 35 6.8 78 2.34 1.78 13.2
DA-8 PCE (20%) +OM (0.1%) 45 8.0 51 2.18 1.69 16.2

Water absorption of conventionally used alumina’s for castable refractory are given below:

Table 2:
Alumina Name Water absorption (%)
HGRM 30 22
MRB37 17
NSR03 18
SRM30FG 20
MR10SG 21

From above Tables 1 and 2, it can be observed that conventionally used alumina namely HGRM 30, MRB37, NSR03, SRM30FG and MR10SG had higher water absorption in the range of 17% to 22%, whereas dispersing alumina (DA-1 to DA-8) of the present invention had reduced water absorption in the range of 6.8% to 8.0%.

From the above tables, it can be concluded that samples DA-1 to DA-8 provided similar results for flowability (physical flow), water absorption and self-flowability for low cement castable.

B. Samples DA-9 to DA-13 were prepared as follows:

Specific amounts of calcined alumina (both hard and soft alumina) were dried at a temperature of 105°C for 2 hours. The grinding media for all the samples DA-9 to DA-13 were alumina balls having size of 25mm.

In comparative sample DA-9, the feed: grinding media ratio was 1:30 and sample DA-9 was grinded for 6 hours.

In comparative sample DA-10, the feed: grinding media ratio was 1:35 and sample DA-10 was grinded for 5.5 hours.

In sample DA-11, the feed: grinding media ratio was 1:40 and sample DA-11 was grinded for 5 hours.

In sample DA-12, the feed: grinding media ratio was 1:45 and sample DA-12 was grinded for 4 hours.

In sample DA-13, the feed: grinding media ratio was 1:50 and sample DA-13 was grinded for 3.5 hours.

Samples DA-11 to DA-13 resulted in bimodal peak and good particle size distribution.

Table 3: Results of samples DA-9 to DA-13
DA-9 DA-10 DA-11 DA-12 DA-13
Feed: grinding Media 1:30 1:35 1:40 1:45 1:50
Particle size (d50) (µm) 2.9 2.5 2.1 1.9 1.7
Bimodal Peak Absent Absent Present Present Present
Grinding hours (hours) 6 5.5 5 4 3.5

From the above table, it can be observed that when the feed: grinding media ratio was below 1:40 to 1:50, (sample DA-9 and DA-10) bimodal peak was absent, i.e., a homogenous mixture was not obtained. Further, from the above table, it can also be observed that even though the grinding hours are extended upto 6 hours, a bimodal peak was not obtained, and the mixture was a heterogenous in nature.

However, samples DA-11 to DA-13 showed a bimodal peak with reduced grinding hours when the feed: grinding media ratio was in the range of 1:40 to 1:50. In other words, a homogenous mixture was obtained with reduced grinding hours when the feed: grinding media ratio was in the range of 1:40 to 1:50.

From tables 1 to 3, it can therefore be concluded that grinding hours of the present invention process was decreased resulting into a homogenous alumina, with good flowability, better water absorption and easy handling of materials without adding any external dispersing agent.

The present invention, therefore, provides a clean and green process for preparing dispersing alumina and easily castable due to homogenous mixture, good flowability and better water absorption leading to reduction in water demand.

The castable material thus, prepared from the dispersing alumina of the present invention are not detrimental for steel production resulting in improved thermo-mechanical strength, abrasion resistance, etc.

The dispersing alumina of the present invention when used in 95% alumina base low cement castable without any external dispersing agents (cement percent – 5%, lime – less than 2.5%) provided improved and significant flowability (physical flow), reduced water demand, better self-flowability for low cement castable, reduced grinding hours.

The foregoing description of the invention has been set merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to a person skilled in the art, the invention should be construed to include everything within the scope of the disclosure.
,CLAIMS:
1. A process for preparing dispersing alumina comprising:
i. milling calcined alumina in the presence of grinding agent and alumina grinding media
ii. mixing the resultant alumina of step (i) with additives to obtain dispersing alumina
wherein the feed ratio of calcined alumina to the alumina grinding media is in a range from 1:40 to 1:50.

2. The process as claimed in claim 1, wherein the calcined alumina is milled for 3 to 5 hours.

3. The process as claimed in any one of the preceding claims, wherein the resultant alumina of step (i) and additives are mixed for 15 minutes to 20 minutes.

4. The process as claimed in any one of the preceding claims, wherein the calcined alumina is subjected to drying at a temperature in the range of 100°C to 150°C for a duration of 2 hours before milling.

5. The process as claimed in any one of the preceding claims, wherein the calcined alumina is a combination of hard calcined alumina and soft calcined alumina.

6. The process as claimed in claim 5, wherein the amount of hard calcined alumina to the soft calcined alumina is in a ratio of 75:25 to 85:15.

7. The process as claimed in claim 1, wherein the grinding agent is selected from propane diol, ethylene diol or triethanolamine.

8. The process as claimed in claim 1, wherein the alumina grinding media is alumina ball.
9. The process as claimed in claim 5, wherein the alumina ball size is of 18 mm to 25 mm for milling and 3mm to 5 mm for mixing.

10. The process as claimed in claim 1, wherein the additives are selected from polycarboxylate ether, organometallic compound or a combination thereof.

11. The process as claimed in claim 10, wherein the organometallic compound is selected from calcium stearate or magnesium stearate.

12. The process as claimed in 10, wherein the amount of polycarboxylate ether is in a range from 5 wt% to 20 wt%.

13. The process as claimed in claims 1 or 11, wherein the amount of organometallic compound is in a range from 0.1 wt% to 0.5 wt%.

14. The process as claimed in any one of the preceding claims, comprising the steps of:

i. drying hard and soft calcined alumina at a temperature in the range of 100°C to 150°C for a duration of 2 hours;
ii. milling hard and soft calcined alumina of step (i) with propanediol in an alumina ball for 3 hours to 5 hours;
iii. mixing the resultant alumina of step (ii) with polycarboxylate ether and calcium stearate for 15 minutes to 20 minutes to obtain dispersing alumina
wherein the feed ratio of calcined alumina to the alumina ball is in a range from 1:40 to 1:50.