Claims:We Claim
1. A compound of formula I

wherein
‘R’ is a carbon ranging from C5 to C10;
‘m’ is ethyl group ranging from 5 to 8 and
‘n’ is ranging from 3 to 5;
.
2. The compound of formula I as claimed in claim 1, wherein ‘R’ is a carbon ranging from C6 to C9; ‘m’ is ethyl group ranging from 6 to 7 and ‘n’ is ranging from 4 to 5.

3. The compound of formula I as claimed in claim 1, wherein the compound is compound A represented below

Compound A

4. A process for preparing compound of formula I as claimed in claim 1, wherein the process comprise steps of:
(i) reacting ethylene glycol derivative with sodium hydride in tetrahydrofuran;
(ii) adding propylene oxide at about 0? to about 5? in nitrogen environment to obtain a reaction mixture;
(iii) allowing the reaction mixture obtained in step (ii) to remain at room temperature for about 4h to about 8h;
(iv) monitoring the reaction followed by quenching the reaction with water and extracting with ethyl acetate; and
(v) evaporating the ethyl acetate layer to obtain compound of formula I;

5. The process as claimed in claim 4, wherein the solvent in step (i) is tetrahydrofuran.
6. The process as claimed in claim 4, wherein the addition of propylene oxide is at about 0? to about 2? in nitrogen environment.

7. The process as claimed in 4, wherein the compound of formula I has purity of about 90% to about 95%.

8. The process as claimed in 4, wherein the process provides about 75% to about 80% yield of the compound.

9. The process as claimed in claim 4, wherein the compound of formula I is compound of formula A.

10. The process as claimed in claim 9, wherein the process comprise steps of:
(i) reacting triethylene glycol with sodium hydride in tetrahydrofuran;
(ii) adding propylene oxide at about 0? in nitrogen environment to obtain a reaction mixture;
(iii) allowing the reaction mixture obtained in step (ii) to remain at room temperature for about 6h;
(iv) monitoring the reaction followed by quenching the reaction with water and extracting with ethyl acetate; and
(v) evaporating the ethyl acetate layer to obtain compound of formula A;

11. A process for flotation of coal, wherein the process comprises step of employing compound of formula I claimed in claim 1 as a frother.

12. The process as claimed in claim 11, wherein the coal is a low rank coal and the process yields lower ash clean coal.

13. The process as claimed in claim 11, wherein the compound of formula I is employed at a dosage of about 50ppm to about 200ppm.

, Description:TECHNICAL FIELD
The present disclosure relates generally to the field of coal flotation. More particularly, the present disclosure relates to a frother for flotation of lower rank coal to produce low ash containing product. The present disclosure also relates to process of preparation of said frother and to a process of flotation of coal using said frother.

BACKGROUND AND PRIOR ART
In the coal flotation process, the naturally hydrophobic coal particles are floated while the hydrophilic gangue particles are collected as tailings. For low ranked coal, single particle often contains both hydrophilic and hydrophobic sites which makes the flotation process difficult. Collector is added prior to flotation to enhance the surface hydrophobicity of the coal particles whereas frother is used for decreasing the surface tension of air bubbles, thereby assisting the formation of ultrafine bubbles. Diesel oil and pine oil are commonly used as collector and frother, respectively, in coal flotation processes adopted worldwide. At Tata Steel coal washeries treating captive coals, collector made by reputed suppliers is used in place of diesel as coal collectors. Commercially available frother is used for stabilizing air bubbles to enhance coal flotation process.

Generally, coal is formed mainly by the process of sedimentation and the organic composition of coal. The process differs based on the coalification i.e. metamorphic formation of coal. Organic matter of coal is formed from a variety of macerals with distinct physical and chemical properties. Subsequently, inorganic matter in coal mainly comprises of different mineral types. Approximately 70 different types of minerals are found in coal and some of the major minerals occur in the form of silicates, sulfides, carbonates and oxides.

Many researchers have showed that straight chain aliphatic oily collectors perform poorly for lower ranked coals and ionic collectors should be preferred in case of flotation of low ranked coals. A composite mixture of diesel no. 2 and diesel no. 6 in a ratio of 4:1 was found to be effective for floating low ranked coal (Wen & Sun, 1981). Oil droplets formed from this mixture are found to have a higher positive charge and this higher positive charge was attributed due to some polycyclic structures present in diesel no.6 containing amine, sulphur, salts of nickel and vanadium (Guthrie, 1960).

It was later found that low grade coal surface layer can be dissolved using caustic soda solution. In alkaline medium, hydration of low ranked coal surface could be reduced, which can increase the hydrophobicity of low rank coal particles. A cationic organic compound such as benzidine in benzoyl alcohol was used at 850 °C for reduction of oxidized groups and coal electro-kinetic behaviour was found to be restored (Wen & Sun, 1977). Cyclic hydrocarbons (Xuebao etal., 2012) such as cyclodecane (C10H18) was found to have a slightly better performance as compared to dodecane.

It was later found that introduction of benzene ring in collector can increase the collector performance as it tends to form strong p bonding with coal aromatic structure. Also, presence of hydrophilic groups such as ethoxy and phenol groups on collector can further enhance the collector capability to interact with hydrophilic groups on coal surface through hydrogen bonding.

Coal collector molecule having benzene ring

Ethoxylated nonyl phenol was found to be better collector than dodecane for Illinois No. 6 coal (Harris, Diao, & Fuerstenau, 1995) as it was found to be adsorbed both on hydrophobic and hydrophilic surfaces (Aston, Lane, & Healy, 1989). Therefore, a combination of hydrophobic aliphatic hydrocarbon chain along with aromatic compounds and hydrophilic groups could be effective as collector for low grade coals. However, the number of hydrophilic groups in the collector should be kept limited as an increased number of hydrophilic groups surrounding coal could negatively impact the coal flotation.

US4582596 discloses a process for recovering coal or mineral values from raw coal or mineral ore which comprises subjecting the raw coal or mineral ore in the form of an aqueous pulp, to a floatation process in the presence of a flotation collector, and a floatation frother which comprises the reaction product of an aliphatic C6 alcohol and between about 1 and 5 moles of propylene oxide, butylene oxide or mixtures thereof, under conditions such that the coal or mineral values are recovered.

US4272364 discloses use of 4,4-dimethyl-1-pentanol as a froth flotation agent for coal recovery processes.

US4761223 discloses a process for recovering coal from raw coal which comprises subjecting the raw coal in the form of an aqueous pulp, to a flotation process in the presence of a flotation collector, and a floating amount of a flotation frother which comprises the reaction product of a polyhydroxy C1-20 alkane or polyhydroxy C3-20 cycloalkane and propylene oxide, or a mixture of propylene oxide and ethylene oxide, with the proviso that at least 50 mole percent of the mixture is propylene oxide, and the reaction product has a molecular weight of between about 150 and 1400, under conditions such that the coal is recovered.

US4915825 discloses an improved froth flotation process wherein solid coal particles are selectively separated under coal froth flotation conditions as a froth phase from remaining solid feed particles as an aqueous phase in the presence of a frother, the improvement comprising a frother of at least 4-methyl cyclohexane methanol.

Coal is considered as a complex carbon structure having both aromatic and aliphatic structures connected through weak links. Lower rank coal contains impurities which are difficult to float as well as produce low ash concentrate in the flotation process. Therefore, in order to increase the floatability of lower rank coal particles, extensive research has been conducted in past few decades to develop various chemical reagents as discussed above. However, few of these chemicals have been used in the industry either due to economic feasibility or environmental regulations. Floating coal with acceptable combustible recovery and sufficient separation efficiency remains a difficult task confronting the coal preparation industry. The present disclosure overcomes the limitation associated with the prior art by providing a frother and methods thereof.

SUMMARY OF THE DISCLOSURE
Accordingly, the present disclosure provides a compound of formula I to be used as frother for flotation of coal, wherein the compound has the structure

wherein
‘R’ is ranging from C5 to C10;
‘m’ is ethyl group ranging from 5 to 8;
and n is ranging from 3 to 5.

In another aspect, is the present disclosure provides a process for preparing compound of formula I.

In yet another aspect, the present disclosure provides a process for flotation of coal wherein said process comprises step of employing the compound of formula I.

In yet another aspect, the present disclosure provides a process for flotation of lower rank coal to obtain lower ash clean coal by applying compound of formula I as frother.

In yet another aspect, the present disclosure provides a process for flotation of lower rank coal which is economic and environmentally friendly.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
Figure 1: illustrates 1H-NMR of 1-(2-(2-(2-hydroxyethoxy)ethoxy)ethoxy)propan-2-ol.
Figure 2: illustrates FT-IR of coal used in the present disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE
It is to be understood that the present disclosure is not limited in its application to the details of compound and process set forth in the following description. The present disclosure is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

The use of “including”, “comprising” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.

Before disclosure is described in greater detail, it is to be understood that the present disclosure is not limited to particular embodiments described, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting disclosure.

Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range, is encompassed within the disclosure. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges and are also encompassed within the disclosure, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the disclosure.

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 disclosure belongs. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present disclosure, representative illustrative process and materials are now described.

All publications and patents cited in this specification are herein incorporated by reference as if each individual publication or patent were specifically and individually indicated to be incorporated by reference and are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited. The citation of any publication is for its disclosure prior to the filing date and should not be construed as an admission that the present disclosure is not entitled to antedate such publication by virtue of prior disclosure. Further, the dates of publication provided may be different from the actual publication dates which may need to be independently confirmed.

It is noted that, as used herein and in the appended claims, the singular forms "a", "an", and "the" include plural referents unless the context clearly dictates otherwise. It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as "solely," "only" and the like in connection with the recitation of claim elements or use of a "negative" limitation.

As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present disclosure.

For convenience, certain terms used in the specification, examples, and appended claims are collected in this section.

As used herein, the term 'compound(s)' comprises the compounds disclosed in the present disclosure.

The present disclosure relates to a compound of formula I

wherein
‘R’ is a carbon ranging from C5 to C10;
‘m’ is ethyl group ranging from 5 to 8 and
‘n’ is ranging from 3 to 5;

In an embodiment of the present disclosure, the compound of formula I acts as a frother for flotation of lower rank coal to produce low ash containing product.

In an embodiment of the present disclosure, ‘R’ is a carbon ranging from C6 to C9; ‘m’ is ethyl group ranging from 6 to 7 and ‘n’ is ranging from 4 to 5.

In an embodiment of the present disclosure, the compound is compound A represented below

Compound A

The present disclosure relates to a process for preparing compound of formula I , wherein the process comprise steps of:
(i) reacting ethylene glycol derivative with sodium hydride in a solvent;
(ii) adding propylene oxide at about 0? to about 5? in nitrogen environment to obtain a reaction mixture;
(iii) allowing the reaction mixture obtained in step (ii) to remain at room temperature for about 4h to about 8h;
(iv) monitoring the reaction followed by quenching the reaction with water and extracting with ethyl acetate; and
(v) evaporating the ethyl acetate layer to obtain compound of formula I;

In an embodiment of the present disclosure, wherein ethylene glycol derivative is but not limiting to triethylene glycol.

In an embodiment of the present disclosure, the solvent in step (i) is but not limiting to tetrahydrofuran.

In an embodiment of the present disclosure, the addition of propylene oxide is at about 0?, at about 0.5?, at about 1?, at about 1.5?, at about 2?, at about 2.5?, at about 3?, at about 3.5?, at about 4?, at about 4.5? or at about 5? in nitrogen environment.

In an embodiment of the present disclosure, the addition of propylene oxide is at about 0? to about 2? in nitrogen environment.

In an embodiment of the present disclosure, the nitrogen environment maintains inert atmosphere.

In an embodiment of the present disclosure, the compound of formula I has purity of about 90% to about 95%.

In an embodiment of the present disclosure, the compound of formula I has purity of about 90%, about 91%, about 92%, about 93%, about 94% or about 95%.

In an embodiment of the present disclosure, the process provides about 75% to about 80% yield of the compound.

In an embodiment of the present disclosure, the process provides about 75%, about 76%, about 77%, about 78%, about 79% or about 80% yield of the compound.

In an embodiment of the present disclosure, the process comprise steps of:
(i) reacting triethylene glycol with sodium hydride in tetrahydrofuran;
(ii) adding propylene oxide at about 0? in nitrogen environment to obtain a reaction mixture;
(iii) allowing the reaction mixture obtained in step (ii) to remain at room temperature for about 6h;
(iv) monitoring the reaction followed by quenching the reaction with water and extracting with ethyl acetate;
(v) evaporating the ethyl acetate layer to obtain compound of formula A;

The present disclosure also relates to a process for flotation of coal, wherein the process comprises step of employing compound of formula I as a frother.

In an embodiment of the present disclosure, the coal is a low rank coal and the process yields lower ash clean coal.

In an embodiment of the present disclosure, the compound of formula I is employed at a dosage of about 50ppm to about 200ppm.

In an embodiment of the present disclosure, the process is economic and environmentally friendly.

The present disclosure also relates to use of the compound of formula I as a frother for floatation of coal.

The present disclosure also relates to a composition comprising compound of formula I.

In an embodiment of the present disclosure, the composition comprises compound of formula I and collectors for flotation of coal.

In another embodiment, the composition comprises compound of formula I optionally along with additional frothers for flotation of coal.

In an embodiment, the processes of the present disclosure involves characterizing frother molecules into two phase (air-water interphase) flotation parameters and selectively recovering concentrate and tailings during flotation experiments. The selectivity and kinetics aspect of frother is demonstrated by the results obtained through the flotation experiments conducted in the lab. The flotation process and the collection methodology is given below:
After conditioning the coal slurry with collector and frother, the air is bubbled through the compressed air line connected to the rotor of the mechanical flotation cell. The cell is filled with water up to the marked height; air inlet valve is opened and kept at 2 lpm. The froth samples (concentrate) are collected after 30 (F1), 60 (F2), 120 (F3), and 240 (F4) seconds of flotation. After the final froth sample is collected, the machine is stopped. The froth products and the tailings (the part that remaining inside the flotation cell) is dried, weighed and analyzed for their ash content. Based on the quantity (% of concentrate/feed) for the flotation duration along with concentrate assay, efficiency of the frother is determined. Lower the ash in the concentrate, the reagent is more selective while amount of froth recovered in the concentrate after 30 sec showed the kinetics part of the reagent. The frothers are characterized through FTIR to ascertain the functional groups present in the reagent followed by NMR to know the exact position of the functional groups for confirming the structure of the reagent.
The present disclosure is further exemplified by following examples. However, these examples should not be construed as limiting the scope of the embodiments herein.
Each embodiment is provided by way of explanation of the disclosure and not by way of limitation of the disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made to the compounds, compositions and methods described herein without departing from the scope or spirit of the disclosure. For instance, features illustrated or described as part of one embodiment can be applied to another embodiment to yield a still further embodiment. Thus, it is intended that the present disclosure includes such modifications and variations and their equivalents. Other objects, features, and aspects of the present disclosure are disclosed in or are obvious from, the following detailed description. It is to be understood by one of ordinary skill in the art that the present disclosure is a description of exemplary embodiments only and is not to be construed as limiting the broader aspects of the present disclosure.

EXAMPLES
EXAMPLE 1: SYNTHETIC SCHEME OF COMPOUNDS

Compound A [1-(2-(2-(2-hydroxyethoxy)ethoxy)ethoxy)propan-2-ol]

Experimental procedure for preparation of the above compound (Compound A):
1.2 equivalent of Triethylene glycol is reacted with 1.2 equivalent of sodium hydride in tetrahydrofuran to generate sodium alkoxide. 1.2 equivalent of propylene oxide at 0? is added in nitrogen environment. The reaction mixture is kept at room temperature for 6 h. Reaction with TLC is monitored and after completion, the reaction is quenched with water and extracted with ethyl acetate twice. The ethyl acetate layer is evaporated using vacuum rotary vapour to obtained pale yellow with 60% yield. The compound is then submitted for 1H-NMR analysis [Figure 1]. In this process, changing of parameters (reaction temperature and time of reaction) resulted in synthesis of other compounds namely, compound B and C. The flotation tests are also performed with these compounds as done with compound A (frother as claimed in this disclosure) with lower rank coal and commercial collector in the laboratory.

The structure of compound B and compound C are given below:

compound B

compound C

Solubility of the compounds:
The compound extracted by the process described above is sparingly soluble in water.

Contact angle:
As the compound is intended to use as surface acting agents with frothing capabilities to support coal flotation application, it was subjected to contact angle measurements. The contact angle is found to be 930.

EXAMPLE 2: CHARACTERIZATION OF COAL
Raw coal is collected from the feed material of Tata Steel washery present in West Bokaro,Ramgarh, Jharkhand. The raw coal is then taken to R&D laboratory of Tata Steel for further study. Raw coal is screened at 0.5mm to collect the undersize of the screen which is feed to flotation cell. The feed to flotation is then subjected to FT-IR analysis [Figure 2] as well as proximate analysis to understand the mineral oxides present in the coal [Table 2].

Table 1: Ash content and contact angle of coal:
Ash content 29.06%
Contact angle 57.02 o

Table 2: Mineral oxides present in the coal
Mineral oxides present in ash produced from coal Element Quant (%) Element Quant (%)
Fe (T) 2.25 P 0.12
Al2O3 6.95 TiO2 0.67
SiO2 17.16 MnO 0.43
CaO 0.51 Ce2O3 0.0070
MgO 0.22 C & O Rest
EXAMPLE 3: FLOTATION EXPERIMENTS

Materials for the flotation test:
A f1otatIon cell Denver D-12, 2.5-lit capacity is used for flotation test. This unit has a baffle arrangement at bottom to avoid swirling of the slurry within the cell and an impeller is provided for proper mixing of the slurry, the speed of which can be controlled by a speed regulator.

A compressor is provided to supply air to the cell in the range of 0-20 litres/min (lpm) in an interval of 1 lpm. The cell has an automatic pulp level controller through make up water tank and froth removal system. For each batch flotation, 250-300 gm fine coal sample of size <0.5mm is allowed to wet for 1 hour in known volume of water. It is transferred into the 2.5-lit capacity Denver cell. Additional water is added to maintain required pulp density i.e. 10-12% solid content. Slurry is allowed to wet for 3 minutes at the impeller speed of 850 rpm. Commercial collector is added and conditioned for 3 minutes. After conditioning, requisite amount of frother (Commercial as well as compound A of the present disclosure) is added. It is again conditioned for another 3 minutes. The cell is filled with water up to the marked height; air inlet valve is opened and kept at 2 lpm. The froth samples are collected after 30 (F1), 60 (F2), 120 (F3), and 240 (F4) seconds of flotation. After the final froth sample is collected [F1+F2+F3+F4], the machine is stopped. The froth products and the tailings (the part that remaining inside the flotation cell) are dried, weighed and analyzed for their ash content.

Table 3: Parameters of laboratory flotation tests
Parameters
Weight of coal 250 -300 gm
Pulp density 10 -12 %
Collector dosage (synthetic collector of Commercial Chemicals) 400-600 ppm
Frother dosage (Commercial chemicals and compound A) 50-200ppm
Agitator speed 800 -1200 rpm
Air supply rate 3-6 lpm

Laboratory flotation tests are done with commercial collector and compound A as frother at dosages of 50 - 200ppm. The results obtained for Compond A as a frother are compared with that of commercial collector and commercial frother at the same dosages as mentioned above. The results are given in Tables 4-9 below:

Table 4: Commercial collector: 500ppm and Commercial frother: 50ppm

Cum. yield. % Cum. ash%
Final Froth Sample 62.07 13.76
Tailings 100.00 24.90

Table 5: Commercial collector: 500ppm and compound A as frother: 50ppm

Cum. yield. % Cum. ash%
Final Froth Sample 55.76 12.24
Tailings 100.00 24.90

Table 6: Commercial collector: 500ppm and Commercial frother: 100ppm

Cum. yield. % Cum. ash%
Final Froth Sample 64.98 14.76
Tailings 100.00 24.90

Table 7: Commercial collector: 500ppm and compound A as frother: 100ppm

Cum. yield. % Cum. ash%
Final Froth Sample 56.94 12.57
Tailings 100.00 24.90

Table 8: Commercial collector: 500ppm and Commercial frother: 200ppm

Cum. yield. % Cum. ash%
Final Froth Sample 63.45 15.39
Tailings 100.00 24.90

Table 9: Commercial collector: 500ppm and compound A as frother: 200ppm

Cum. yield. % Cum. ash%
Final Froth Sample 64.86 14.57
Tailings 100.00 24.07

At low frother dosage of 50 ppm, it is observed that ash content of concentrate for the application of compound A as frother is lower by around 1.5 units from commercial frother based on the ash content of the cumulative froth product (concentrate fractions F1 to F4). At median dosage of 100 ppm (used in coal washeries of Tata Steel), clean coal ash content obtained for commercial frother is 14.76% at yield of 64.98% whereas clean coal ash content for compound A as frother reduced by 2.19 units [12.57%]. The corresponding yield drop is around 8 units. If normalisation of ash content of clean coal is done at 14.76%, predicted yield for compound A as frother through linear regression would be 68.2% which is 3.2 units higher than that obtained for commercial frother. At higher frother dose of 200ppm, yield obtained for compound A as frother is observed to be higher by1.41 units at lower clean coal ash level of 14.57% compared to 15.39% ash content measured with application of commercial frother. From the experimental result, it is evident that the compound A is capable of lowering concentrate ash content of froth product compared to the commercial frother.

The laboratory flotation tests are also conducted with compounds B and C at commercial collector dose of 500ppm and frother dosage of 100 ppm. The results with these compounds are given below:

Table 10: Commercial collector: 500ppm and compound B as frother:
100ppm

Cum. yield. % Cum. ash%
Final Froth Sample 69.08 17.57
Tailings 100.00 24.9
Table 11: Commercial collector: 500ppm and compound C as frother:
100ppm
Cum. yield. % Cum. ash%
Final Froth Sample 74.31 19.34
Tailings 100.00 24.9

It is observed from the laboratory flotation tests conducted with the same coal at identical conditions for frothers (compound B and compound C) along with commercial collector, these compounds could not perform like compound A.