FIELD OF THE INVENTION:
The present invention relates to a novel method of preparing flotation reagents for flotation of oxidized coal from the gangue materials.
It also describes the synthesis of polyethylene glycol derivative consisting of ester group and tetrahydrofurfuryl alcohol derivatives consisting of carbamate and ester groups. The disclosure also describes the applicability of these reagents as collectors for flotation of oxidized coal from gangue materials.
BACKGROUND OF THE INVENTION:
In the coal flotation process, the naturally hydrophobic coal particles are floated while the hydrophilic gangue particles are collected as tailings. 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. Standard No. 2 fuel oil and MIBC (methyl isobutyl carbinol) are commonly used as collector and frother, respectively, in coal flotation. Since flotation is based on particles’ surface properties, the petrographic study of coal is quite important.
Coal is formed mainly by the process of sedimentation and the organic composition of coal 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 60 different types of minerals are found in coal and some of the major minerals occur in form of silicates, sulfides, carbonates and oxides (Spackman, 1989).
Coal is considered as a complex cross-linked structure formed from aromatic structures connected through weak links as shown in Figure 1 (Davidson, 1980; Marzec, 1985). When such complex coal surface is exposed to atmosphere, it leads to oxidation of coal weathering, which can occur at the mine site or during storage and transportation. This oxidation results in formation of carboxylic or carbonyl groups (Figure 2) which further decreases

the hydrophobic character of coal particles. Therefore, in order to increase the floatability of oxidized coal particles, an extensive research has been conducted in past few decades to develop various chemical reagents. However, few of these chemicals have been used in the industry either due to economic feasibility or environmental regulations. Floating oxidized coal with acceptable combustible recovery and sufficient separation efficiency remains a difficult task confronting the coal preparation industry.
But none of the compounds provide substantial effective reagent for flotation of oxidized coal from the gangue materials.
The present invention meets the long-felt need.
SUMMARY OF THE INVENTION:
A novel compound to be used as flotation reagents for oxidized coal have two structure such as Formula I and Formula II, wherein Formula I is

wherein ‘Z’ can be an ester group having carbon atoms C19. Formula II is

wherein ‘Y’ can be a carbamate group or a ester group having carbon atoms ranging from C12 to C19.
OBJECTS OF THE INVENTION:
It is therefore, the primary object of the present invention to determine novel chemical reagents which can be used for floatation of oxidized hydrophilic coal particle effectively.

Another object of the present invention is to provide a method of producing the chemical reagents for flotation of oxidized coal from the gangue materials.
Yet another object of the present invention is to provide a method of producing chemical reagents with 90-95% purity and 75-80% yield, which is used for flotation of oxidized coal.
Another object of the present invention to provide a method of producing chemical reagent for flotation of oxidized coal, which is economic and environmentally friendly.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING:
It is to be noted, however, that the appended drawings illustrate only typical embodiments of the present subject matter and are therefore not to be considered for limiting of its scope, for the invention may admit to other equally effective embodiments. The detailed description is described with reference to the accompanying figures. Some embodiments of system or methods in accordance with embodiments of the present subject matter are now described, by way of example, and with reference to the accompanying figures, in which:
Fig. 1 illustrates typical structure of coal molecule.
Figure 2 illustrates the possible reactions during oxidation of coal when exposed to atmosphere.
Figure 3 illustrates the Fourier-transform infrared spectroscopy (FT-IR) of oxidised coal.
Figure 4 illustrates the yield vs ash content of the froth in coal flotation without addition of collector and MIBC.
Figure 5 illustrates the yield vs ash content of the froth in oxidised coal flotation with addition of synthesized collectors in absence of MIBC.
Figure 6 illustrates the yield vs ash content of the froth in oxidised coal flotation with addition of synthesized collectors in presence of MIBC.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:
The present invention relates to a novel method of preparing flotation reagents for flotation of oxidized coal from the gangue materials.
Three compounds are specifically designed for enhancing oxidized coal flotation, which contains hydrocarbon chain as well as oxygenated functional group. Those compounds are Tetrahydrofurfuryl (THF) oleate (compound- 1) Alkyl carbamate THF (compound-2) and polyethylene glycol mono oleate (compound-3).
In accordance to the embodiment of the present invention, there is provided a compound of formula I
The present disclosure describes a compound of formula-I

wherein ‘Z’ can be an ester group having carbon atoms C19. In an embodiment, the compound of Formula-I is


In an embodiment, the compound of Formula-I is
termed as poly (ethylene glycol) monooleate. The present disclosure describes a compound of formula-II

wherein ‘Y’ can be an ester group or a carbamate group having carbon atoms ranging from C12 to C19.

In an embodiment, the compound of Formula-II is

wherein ‘Y’ is and

In an embodiment, the compound of Formula-II is
, termed as
tetrahydrofurfuryl oleate.
In another embodiment, the compound of Formula-II is
termed as (tetrahydrofuran-2-yl)methyl decylcarbamate.
The compound of formula I is a flotation reagent for oxidized coal which possesses a perfect hydrophobic hydrophilic balance for effective flotation of oxidized coal.
The compound of formula II can also be successfully used as a flotation reagent for oxidized coal which possesses perfect hydrophobic hydrophilic balance for effective flotation of oxidized coal.
The process for preparing of compound of Formula I i.e., poly (ethylene glycol) mono-oleate (Compound 3) and compounds of formula II termed as tetrahydrofurfuryl oleate (Compound 1) and (tetrahydrofuran-2-yl) methyl decylcarbamate (Compound 2), comprises the steps of:

i) taking of carbonyl diimidazole(1.1eq) in a round bottom flask and adding tetrahydrofuran into it along with stirring for a suitable duration in a suitable atmosphere;
ii) cooling of the reaction mass at a suitable temperature alongwith dropwise addition of oleic acid (in case of Compound 1 and 3) or tetrahydrofurfuryl alcohol (in case of Compound 2) dissolved in 1 volume of tetrahydrofuran under a suitable atmosphere;
iii) allowing the reaction mass to warm upto room temperature with stirring for 2 hours in a suitable atmosphere and monitoring the reaction by using the TLC;
iv) adding tetrahydrofurfuryl alcohol (in case of Compound 1), dodecyl amine (in case of Compound 2) or polyethylene glycol (in case of Compound 3) dissolved in 1 volume of tetrahydrofuran and heating the mixture to a specific temperature such as 75°C along with stirring for 2 hour at 70°C;
v) cooling the reaction mass at a suitable temperature after completion of the reaction to remove the nitrogen and addition of ammonium chloride to it at a particular pH;
vi) evaporation of tetrahydrofuran and extraction of the compound.
As per the above-mentioned method, the tetrahydrofuran was mixed with carbonyl diimidazole alongwith stirring for 10 minutes at room temperature. The nitrogen atmosphere is used for all the reactions.
The reaction mass was cooled twice at temperature below 5°C. The used THF was evaporated with the help of vacuum rotavapor at temperature of 45°C.
The compound was extracted by adding dichloromethane (2 x 5 vol.). Extracted dichloromethane layer was evaporated under vacuum rotavapor at 45°C to obtain ~90 to 95% pure compound with 75 to 80% yield.
The reaction shows the preparation of tetrahydrofurfuryl alcohol derivative consisting of ester group termed as tetrahydrofurfuryl oleate


The reaction shows the preparation of tetrahydrofurfuryl alcohol derivative consisting of carbamate group termed as (tetrahydrofuran-2-yl)methyl decylcarbamate

The reaction shows the preparation of polyethylene glycol derivative consisting of ester group termed as poly (ethylene glycol) monooleate


In accordance with another embodiment of the present invention, the process is also provided for a flotation test, which clearly illustrates the collection of clean oxidized coal and also facilitates the removal of gangue, which comprises
i) mixing of oxidized coal with 2000ml of water in flotation cell with stirring for 5 minutes for proper wetting of coal in water;
ii) addition of 500ppm of collector and conditioning it for 2 minutes, followed by addition of 50ppm of methyl isobutyl carbinol (MIBC) with stirring for another 1 minute;
iii) opening of air valve of the floatation cell and supply of air at a fixed rate of 4 lpm;
iv) collection of froth for 4 minutes and separation of tailings; and
v) chemical analyses of the products after drying and weighing.
Results and discussions:
The flotation tests were performed on 200 g of oxidized coal sample (size: -200#, mesh). The feed sample had an ash content of 29.06 % and a contact angle of 57.02°.

FT-IR analysis of oxidized coal was done to analyse the oxygen functionalities present in the coal which can give an indication of the amount of oxygen present in the coal. As seen in the figure 3, the peaks at 3693 and 3650 cm-1 correspond to the vibrational stretching of alcoholic -OH group while that of 3619 cm-1 represents the vibrational stretching of phenolic -OH group. Presence of carboxylic group is confirmed by the stretching at 3044 cm-1. C=O aldehyde group was also present in the oxidized coal which was proved by the strong vibrational stretching at 1736 cm-1.
Fig 4 represents the yield and ash content of the froth after flotation of oxidized coal without addition of collector and frother. It was evident that the yield was quite low (~ 8 %) while the ash content was very high and was close to 25 %. This shows that the coal was not hydrophobic in nature and was not being able to attach to the bubbles and come to the froth.
Contact angle measurement of oxidized coal with addition of collectors
Change in contact angle of oxidized coal was analysed to determine the change in hydrophobicity of the oxidized coal. The oxidized coal had a contact angle of 57° and was much hydrophilic than good quality coal. The following table shows the change in contact angle (θ) of the coal after addition of the collectors. All the compounds showed high rise in contact angle among which proved that the coal became hydrophobic after addition of collectors. The rise in contact angle was least for compound 2 while it was highest for compound 1.
θ(Compound 3)> θ(Compound 1)> θ(Reagent 2)
Table 1: Change in contact angle of oxidized coal after addition of different collectors



Flotation of oxidized coal with addition of collectors
Figure 5 represents the yield vs ash curve of froth after the oxidized coal was floated with different collectors in absence of MIBC. Addition of compound 1 gave a very high ash content in the froth (24 %), which was close to the ash content of feed sample and the yield reached a maximum of 27 %. On the other hand, using compound 2 as a collector decreased the ash content yield (20 %) but the yield also decreased slightly to 24 %. Compound 3 gave a relatively better performance in terms of ash content (19 %) and yield (32 %) amongst all the collectors.
Figure 6 represents the yield vs ash curve of froth after the oxidized coal was floated with different collectors in presence of MIBC. It was evident that after addition of MIBC, the ash content for compound 1 decreased from to 20 %, while the yield increased to 31 %. Although the ash content remained constant for compound 2 after addition of MIBC, but the yield decreased significantly to 14 % and therefore did not perform well due to interaction with the frother. Compound 3 gave best results with highest increase in yield to 51 % and decrease in ash content to 17 %.
From these test results, it has been found that, compound 3 (poly (ethylene glycol) mono-oleate) showed good selectivity for oxidized coal in comparison with compound 1 (tetrahydrofurfuryl oleate) and compound 2 (tetrahydrofurfuryl carbamate).

WE CLAIM:
1. A novel compound to be used as flotation reagents for oxidized coal have two
structure such as Formula I and Formula II, wherein Formula I is

wherein ‘Z’ can be an ester group having carbon atoms C19,

Formula II is

wherein ‘Y’ can be an ester group or a carbamate group having carbon atoms ranging from C12 to C19,

2. The compound as claimed in claim 1, wherein the compound of Formula I is poly (ethylene glycol) monooleate (compound 3) and compound of Formula II is tetrahydrofurfuryl oleate (compound 1) and tetrahydrofuran-2-yl)methyl decylcarbamate (compound 2).
3. A process for preparing compound of formula I and formula II comprises the steps of:
i) taking of carbonyl diimidazole(1.1eq) in a round bottom flask and adding tetrahydrofuran into it along with stirring for a suitable duration in a suitable atmosphere;

ii) cooling of the reaction mass at a suitable temperature alongwith dropwise addition of oleic acid (in case of Compound 1 and 3) or tetrahydrofurfuryl alcohol (in case of Compound 2) dissolved in 1 volume of tetrahydrofuran under a suitable atmosphere;
iii) allowing the reaction mass to warm upto room temperature with stirring for about 2 hours in a suitable atmosphere and monitoring the reaction by using the TLC;
iv) adding tetrahydrofurfuryl alcohol (in case of Compound 1), dodecyl amine (in case of Compound 2) or polyethylene glycol (in case of Compound 3) dissolved in 1 volume of tetrahydrofuran and heating the mixture to a specific temperature such as 75°C along with stirring for about 2 hour at approx. 70°C;
v) cooling the reaction mass at a suitable temperature after completion of the reaction to remove the nitrogen and addition of ammonium chloride to it at a particular pH;
vi) evaporation of tetrahydrofuran and extraction of the compound.
4. The method as claimed in claim 3, wherein tetrahydrofuran is mixed in
carbonyl diimidazole alongwith stirring for 10 minutes at room temperature.
5. The method as claimed in claim 3, wherein nitrogen atmosphere is used.
6. The method as claimed in claim 3, wherein the cooling temperature is maintained between 0°-5°C.
7. The method as claimed in claim 3, wherein the end compound is extracted with dichloromethane and the dichloromethane layer is being evaporated under vacuum rotavapor at 45°C.
8. The method as claimed in claim 1, wherein 90 to 95% pure compound is obtained with 75 to 80% yield.
9. A method of performing flotation test for facilitation of removal of gangue material comprises the steps of:

i) mixing of oxidized coal with 2000ml of water in flotation cell with stirring for 5 minutes for proper wetting of coal in water;
ii) addition of 500ppm of collector and conditioning it for 2 minutes, followed by addition of 50ppm of methyl isobutyl carbinol (MIBC) with stirring for another 1 minute;
iii) opening of air valve of the floatation cell and supply of air at a fixed rate of 4 lpm;
iv) collection of froth for 4 minutes and separation of tailings; and
v) chemical analyses of the products after drying and weighing.