Description:FIELD OF THE INVENTION
The present invention pertains to the field of thermic fluids commonly referred to as heat transfer fluids (HTF). More specifically, the present invention relates adsorbent composition for reducing acidic species from heat transfer fluids (HTF) in batch and fixed bed mode and a process of preparing said composition. Further, the present invention pertains to a process for reducing the total acid number (TAN) from heat transfer fluid following either or both pre-treatment and post-treatment strategies.

BACKGROUND OF THE INVENTION
Heat transfer fluids are the fluids which acts as an intermediator for transferring heat from a heat source to other heat demands (or cold bodies). The transfer of heat is based on the ability of HTF to capture and transfer the heat from heat sources. During the circulation of fluids at high temperature, oxygenates are formed which results in the increase of acidic components in the system. These acidic components affect the properties of the fluid in the system as it can attack the material in contact with fluid and can lead to damage of pipe network due to corrosion effect. So, it is essential to monitor the acidic content of the fluid periodically and to remove the acidic components. This is done by measuring total acid number (TAN) value of the fluid. TAN value can be defined as parameter for measuring the acidic component in any fluid which is expressed in milligrams KOH/g which is required to completely neutralize the acidic components present in the fluid. TAN value of heat transfer fluid plays a vital role in the functioning of any equipment. Generally, a high TAN value (> 1.0 mg KOH/ g) can result in damaging of the material which is in contact with the fluid by corroding the material that can further lead to malfunctioning of the equipment of use. For finding out the reduction percentage of the TAN value, it is essential to measure TAN value before any process is used for reduction of TAN value. Then after employing the process, the TAN value of the fluid is measured again.

To enhance the lifespan of HTF, pre-treatment can be applied to remove acidic species formed during synthesis or due to moisture effects. Pre-treatment involves treating HTF with an adsorbent before utilizing it for any heat transfer application or placing it into any heat transfer loop. This treatment aims to reduce the TAN value of HTF close to 0, thereby increasing the number of cycles before the TAN value approaches 1.

Several processes, such as converting acids into esters, washing with a basic solution, and adsorption, can be employed to remove acidic components. Among these, the adsorption process stands out for its simplicity, cost-effectiveness, recyclability, reproducible results, unchanged fluid properties, and negligible material loss. Adsorption can be physical (physisorption) or chemical (chemisorption), influenced by factors like the number of vacant sites in the adsorbent, pore size, adsorption temperature, aging speed, aging time, and adsorbent-to-fluid ratio. The choice of an optimal adsorbent is crucial for enhancing the efficiency of the adsorption process.

WO2018211467A1 reveals an adsorbent composite for reducing TAN in heat transfer fluids, comprising layered double hydroxide, alumina, and activated bauxite. However, the preparation process for layered double hydroxide is lengthy and complex, and activated bauxite poses several health hazards.

Therefore, there is a need in the art to identify a suitable adsorbent which can adsorb the acidic components from the fluid and has a high surface area material as a support. There are various supports that are available such as silica, zeolites, alumina, activated carbon, metal organic framework, whose surface area can be varied from 100-900 m2/g depending upon the synthesis process, and reactants used. Apart from the surface area, the support should contain small size pores to provide space for the adsorbed species to fit in to it. Apart from the above mentioned characteristics, a suitable base is needed on the surface of a support material to attract acidic species through acidic base interactions phenomenon.

To achieve that, there is requirement of a suitable and optimized adsorbent composition by which maximum possible adsorption of acidic species can be done through pre-treatment and post-treatment of used heat transfer fluid.

SUMMARY OF THE INVENTION
This summary is provided to introduce a selection of concepts, in a simplified format, that are further described in the detailed description of the invention.

The present invention provides an adsorbent composition for reducing acidic species from heat transfer fluids (HTF), said adsorbent comprising:
i. an inorganic support; and
ii. an inorganic base,
wherein the base is in a range of about 1 weight % to about 30 weight % with respect to the inorganic support.

The present invention also provides a process for the preparation of an adsorbent composition, comprising:
i. adding an inorganic base to an inorganic support to form a mixture, wherein the inorganic base is added in a range of about 1 weight % to about 30 weight % with respect to the inorganic support;
ii. stirring the mixture;
iii. ageing the mixture;
iv. separating water from the mixture; and
v. drying the mixture to obtain the adsorbent composition.

The present invention further provides a process for reducing total acidic number (TAN) of a heat transfer fluid by treating the heat transfer fluid with the adsorbent composition defined above, to obtain treated heat transfer fluid, and optionally regenerating the adsorbent composition.

OBJECTIVES OF THE PRESENT INVENTION:
The primary objective of the present invention is to provide a solid adsorbent composition which can reduce TAN value of various heat transfer liquids (HTF) arising from the oxygenates formed during oxidation of fluid occurring at high temperature or from any other known or unknown sources or processes; and provide a process for preparing the same.

Another objective of the present invention is to test the efficiency of the adsorbent composition in batch and fixed mode for its use as adsorbent in pre-treatment and post-treatment strategies of HTF.

Another objective of the present invention is to test the efficiency of the adsorbent in both acid spiked and industrially used HTF in heat transfer loop.

BRIEF DESCRIPTION OF THE DRAWINGS
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

Figure 1 depicts the agitation studies setup for reducing the total acid number in heat transfer fluid using agitation method in batch mode.
Figure 2 depicts the setup for reducing the total acid number in heat transfer fluid in fixed bed process.

DETAILED DESCRIPTION OF THE INVENTION
The present invention pertains to an adsorbent composition for reducing acidic species from heat transfer fluids (HTF). Adsorption phenomenon is utilized for adsorbing the acidic species from the heat transfer fluid. This is done either or both by decreasing the acidic content of the fresh heat transfer fluid or by decreasing the acidic content of the used heat transfer fluid. To adsorb acidic species from heat transfer fluid, a high surface area support is used to provide large number of vacant adsorption sites having mesopores for the adsorption process to occur. In addition to the support, some basic species is used to attract acidic species which results in acid base interactions.

For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiments in the specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated process, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skilled in the art to which this invention belongs. The composition, process, and examples provided herein are illustrative only and not intended to be limiting.

The articles “a”, “an” and “the” are used to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article.

The terms “comprise” and “comprising” are used in the inclusive, open sense, meaning that additional elements may be included. It is not intended to be construed as “consists of only”.

Throughout this specification, unless the context requires otherwise the word “comprise”, and variations such as “comprises” and “comprising”, will be understood to imply the inclusion of a stated element or step or group of element or steps but not the exclusion of any other element or step or group of element or steps.

The term “about” in the context of the present invention denotes an interval of accuracy that the person skilled in the art will understand to still ensure the technical effect of the feature in question. The term typically indicates deviation from the indicated numerical value of ±20%, preferably ±15%, more preferably ±10%, and even more preferably ±5%.

The term “optionally,” as used in the present invention, means that a feature or element described as ‘optional’ within the context of the invention is not required for the invention to function as claimed. It indicates that the presence or absence of the described feature or element does not alter the fundamental operation or scope of the invention, and its inclusion or exclusion may be determined based on the specific requirements or preferences of a practitioner skilled in the art or the application in question.

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 process and materials similar or equivalent to those described herein can be used in the practice or testing of the disclosure, the preferred process and materials are now described. All publications mentioned herein are incorporated herein by reference.

The terminology and structure employed herein is for describing, teaching, and illuminating some embodiments and their specific features and elements and does not limit, restrict, or reduce the spirit and scope of the invention.

The present invention provides an adsorbent composition for reducing acidic species from heat transfer fluids (HTF), said adsorbent comprising:
i. an inorganic support; and
ii. an inorganic base.
wherein the base is in a range of about 1-30 weight % with respect to the inorganic support.

In an embodiment of the present invention, the inorganic support is selected from a group comprising activated bare alumina, activated carbon and silica materials.

In an embodiment of the present invention, the inorganic support has a surface area greater than about 200 m2/g and a pore radius in a range of about 2 nm to about 10 nm.

In an embodiment of the present invention, the inorganic support consist of high surface area inorganic material as support and an inorganic base containing hydroxyl ions is impregnated on its surface.

In an embodiment of the present invention, the inorganic base is containing hydroxyl ions; the inorganic base is selected from a group comprising liquid ammonia in deionized water, potassium hydroxide (KOH) and sodium hydroxide (NaOH); preferably the inorganic base is liquid ammonia in deionized water.

The present invention also provides a process for the preparation of an adsorbent composition, comprising:
i. adding an inorganic base to an inorganic support to form a mixture, wherein the inorganic base is added in a range of about 1 weight % to about 30 weight % with respect to the inorganic support;
i. stirring the mixture;
ii. ageing the mixture;
iii. separating water from the mixture; and
iv. drying the mixture to obtain the adsorbent composition.

In an embodiment of the present invention, the inorganic base is prepared by adding liquid ammonia in deionized water.

In an embodiment of the present invention, the stirring is carried out for about 1to about 5 hours at a temperature not exceeding 50 °C.

In an embodiment of the present invention, the ageing is carried out at a temperature in a range of about 80 ? to about 120 °C.

In an embodiment of the present invention, the ageing is carried out for a period of about 12 to about 15 hours.

In an embodiment of the present invention, the mixture is dried at a temperature in a range of about 80 ? to about 120 °C.

The present invention also provides a process for reducing total acidic number (TAN) of a heat transfer fluid by treating the heat transfer fluid with the adsorbent composition defined above to obtain treated heat transfer fluid, and optionally regenerating the adsorbent composition.

In an embodiment of the present invention the process for reducing total acidic number (TAN) of a heat transfer fluid by treating the heat transfer fluid involves removing the acidic species from the heat transfer fluid by treating it with the adsorbent composition.

In an embodiment of the present invention, the process for reducing the acidic species and thereby reducing the total acid number (TAN) of the heat transfer fluid following either or both pre-treatment and post-treatment strategies.

In an embodiment of the present invention, the process for reducing total acidic number (TAN) of a heat transfer fluid by treating the heat transfer fluid with the adsorbent composition is carried out in batch mode and continuous fixed bed mode.

In an embodiment of the present invention, the process is an agitation process comprising:
i. adding the adsorbent composition to the heat transfer fluid to form a mixture;
ii. ageing the mixture;
iii. separating the treated heat transfer fluid from the mixture and optionally evaluating the total acidic number (TAN) in the fluid; and
iv. optionally regenerating the absorbent composition.

In an embodiment of the present invention, the adsorbent composition is added to the heat transfer fluid in a range of about 1-30 w/w%, preferably about 20 w/w%.

In an embodiment of the present invention, the ageing during the agitation process is carried out at an agitation speed in a range from about 100 to about 600 rpm at a temperature in a range from about 25 °C to about 80 °C.

In an embodiment of the present invention, the ageing during the agitation process is carried out at room temperature; wherein the room temperature is in a range of about 25 °C to about 30 °C.

In an embodiment of the present invention, the ageing during the agitation process is carried out for about 1 to about 6 hours.

In an embodiment of the present invention, the process is a fixed bed process comprising:
i. pre-heating the adsorbent composition in a quartz tube inside a furnace;
ii. passing the heat transfer fluid through one end of the quartz tube and contacting the heat transfer fluid with the adsorbent composition to obtain a treated heat transfer fluid;
iii. collecting the treated heat transfer fluid from another end of the quartz tube;
iv. optionally repeating the steps ii) and iii) with the treated heat transfer fluid;
v. separating the adsorbent composition from the treated heat transfer fluid; and
vi. optionally evaluating the total acidic number (TAN) of the treated heat transfer fluid.

In an embodiment of the present invention, the adsorbent composition in the fixed bed process is pre-heated at a temperature in a range of about 100 ? to about 200 ? under inert atmosphere.

In an embodiment of the present invention, the heat transfer fluid in the fixed bed process is passed through one end of the quartz tube with weight hour space velocities (WHSV) of about 2 h-1 to about 4 h-1; the furnace is maintained at a temperature between about 40 ? to about 200 ?.

In an embodiment of the present invention, the adsorbent composition is recyclable up to 5 times.

In an embodiment of the present invention, the adsorbent composition is regenerated by washing with a solvent followed by drying.

In an embodiment of the present invention, the solvent is selected from a group comprising hexane, n-heptane, n-octane, n-decane, n-dodecane or any combination thereof.

In an embodiment of the present invention, drying during regeneration of the adsorbent composition is carried out at a temperature in a range of about 80 to about 120 ?.

In an embodiment of the present invention, the adsorbent composition is regenerated by washing with hexane and drying it in oven.

In an embodiment of the present invention, the heat transfer fluid comprises synthetic aromatics phenyls blended with esters and olefins or a mixture of acids in major proportions.

In an embodiment of the present invention, the heat transfer fluid comprises biphenyl, cyclohexyl benzene, diphenyl ether, ethylene, and propylene.

In an embodiment of the present invention, heat transfer fluid is a mixture of acids selected from a group comprising a monocarboxylic acid, a dicarboxylic aliphatic acid, an aromatic acid or any combination thereof.

In an embodiment of the present invention, the mono carboxylic acids is selected from a group comprising 2-ethyl hexanoic acid, hexanoic acid, heptanoic acid, octanoic acid, neodecanoic acid, decanoic acid, nonanoic acid, isoheptanoic acid, dodecanoic acid or any combination thereof.

In an embodiment of the present invention, the dicarboxylic aliphatic acid is selected from a group comprising sebacic acid, adipic acid, pimelic acid, suberic acid, azelaic acid, dodecanedioic acid or any combination thereof.

In an embodiment of the present invention, the aromatic acid is phthalic acid.

In an embodiment of the present invention, the adsorbent composition reduces the TAN values of phenyl and terphenyls mixture based thermic fluids using agitation up to about 95%. However, the adsorbent composition reduces the total TAN values up to only about 74.51 % when the inorganic support was used without modification or without impregnation in inorganic base.

In an embodiment, the present invention provide the process of agitation study such as optimizing temperature, adsorbent dosage, time duration of experiments, concentration of the base on support, and agitation speed to attain TAN reduction as high as about 95%.

In some embodiment, the present invention provide the adsorbent composition comprising of inorganic support having surface area less than about 200 m2/g and pore radius less than about 2 nm to about 10 nm under similar conditions provides 5-10 % less TAN reduction as compared to 95 % TAN reduction.

In an embodiment of the present invention, the adsorbent composition reduces the TAN values of a heat transfer fluid by at least 50%, more preferably at least 60%, at least 65% at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, at least 98% or at least 99%.

In an embodiment of the present invention, the adsorbent composition reduces the TAN values up to about 95% in the sample fluid spiked using naphthenic acid using the agitation process.

In an embodiment of the present invention, the adsorbent composition reduces the TAN values up to about 80 % in pre-treated HTF using the agitation process.

In an embodiment of the present invention, the adsorbent composition reduces the TAN values up to about 60 % in industrially used HTF (Sigma THERM G) containing Terphenyls group using the agitation process.

In an embodiment of the present invention, TAN can be reduced up to 88 % using the fixed bed process.

In an embodiment of the present invention, the adsorbent recycles up to 5 times and attain TAN reduction close to about 80 %.

The present disclosure with reference to the accompanying examples describes the present invention. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention. It is understood that the examples are provided for the purpose of illustrating the invention only and are not intended to limit the scope of the invention in any way.

EXAMPLES:

EXAMPLE 1: ADSORBENT SYNTHESIS
Inorganic base which contain 2 g liquid ammonia (30% purity) in 50 ml water was added to 10 g of grounded alumina in a beaker and stirred on hot plate containing magnetic stirrer for 2 hours at a temperature which should not be more than 50 °C. After the required time for heating and stirring, mixture was aged at a suitable temperature of 80 to 120 ? overnight to remove the water content from the mixture and dried at 90 ?. The adsorbent synthesized contains hydroxyl ions on the surface and it is observed that the surface area decreases compared to unmodified support.

EFFECT OF AGITATION ON THE TOTAL ACID NUMBER
A fresh, contaminants free 250 ml vessel purged with nitrogen was used for the adsorption. In the vessel, 20-50 gm of heat transfer fluid with pre-determined TAN was taken and kept for heating on magnetic hot plate as shown in Figure 1. The finely grounded adsorbent composition was added to the pre-heated heat transfer fluid the in W/W % (adsorbent/heat transfer fluid) of 1 to 20 wt.%. The ageing speed and temperature was varied between 100-600 rpm, and 25-80 °C, respectively. The adsorption experiment efficiency varied when it is performed between 1-6 hours. After the experiment, adsorbed fluid was centrifuged, and supernatant liquid was evaluated for TAN using ASTM D664 titration process.

Experiments conducted for finding out the composition of suitable adsorbent for reducing TAN value of HTF is being performed using HP Therm a, HP Therm ?, HP Therm ß, and commercial Terphenyls mixture fluid. The adsorbent that used was activated alumina. The specific examples are listed below:

EXAMPLE 2:
To 50 g of H P Therm ? fluid, 50 mg of naphthenic acid (0.1 wt. % of the heat transfer fluid) was added to spike the acid number. Then after using certain amount for recording initial TAN value, to the remaining fluid, 1.3 g of base impregnated adsorbent composition was added. Then it was kept for agitation at 100 RPM and 80 °C for 1 hour.
Total acid number of thermic fluid feed before adsorption: 0.445-0.510 mg KOH/g
Total acid number of thermic fluid after adsorption: 0.111-0.212 mg KOH/g
Total acid number reduction (%): 69.12-75.50 %

EXAMPLE 3:
The procedure was essentially same as given in Example 2, except the adsorption temperature was carried out at 60 °C instead of 80 °C.
Total acid number of thermic fluid feed before adsorption: 0.445-0.510 mg KOH/g
Total acid number of thermic fluid after adsorption: 0.04-0.09 mg KOH/g
Effective total acid number reduction (%): 85.01-92.90 %

EXAMPLE 4:
The procedure was essentially same as given in Example 2, except the adsorption temperature was maintained at room temperature instead of 80 °C.
Total acid number of thermic fluid feed before adsorption: 0.445-0.510 mg KOH/g
Total acid number of thermic fluid after the adsorption: 0.180-0.230 mg KOH/g
Total Acid number reduction (%): 62.00-67.00 %

EXAMPLE 5:
The procedure was essentially same as given in Example 3, and agitation speed was maintained in the range of 200 rpm.
Total acid number of thermic fluid feed before adsorption: 0.445-0.510 mg KOH/g
Total acid number of thermic fluid after the adsorption: 0.032-0.070 mg KOH/g
Total acid number reduction (%): 85.00-95.00 %

EXAMPLE 6:
The procedure was essentially same as given in Example 5, and adsorbent composition used was impregnated with 5 % concentration of inorganic base to activate the high surface area support.
Total acid number of thermic fluid feed before adsorption: 0.445-0.510 mg KOH/g
Total acid number of thermic fluid after adsorption: 0.050-0.100 mg KOH/g
Total acid number reduction (%): 75.50-80.00 %

EXAMPLE 7:
The procedure was essentially same as given in Example 5, and duration of experiment was 6 h.
Total acid number of thermic fluid feed before adsorption: 0.445-0.510 mg KOH/g
Total acid number of thermic fluid after adsorption: 0.111-0.142 mg KOH/g
Total Acid number reduction (%): 70.00-75.01 %

EXAMPLE 8: The procedure was essentially same as given in Example 5, and 0.25g adsorbent was used.
Total acid number of thermic fluid feed before adsorption: 0.445-0.510 mg KOH/g
Total acid number of thermic fluid after adsorption: 0.250-0.300 mg KOH/g
Total acid number reduction (%): 45.00-50.01 %

EXAMPLE 9:
The procedure was essentially same as given in Example 5, and instead of HP Therm ?, HP Therm a fluid was used.
Total acid number of thermic fluid feed before adsorption: 0.345-0.370 mg KOH/g
Total acid number of thermic fluid after the adsorption: 0.041-0.078 mg KOH/g
Total Acid number reduction (%): 85.10-88.90 %.

EXAMPLE 10:
The procedure was essentially same as given in Example 5, and instead of HP Therm ?, industrially used HP Therm ß fluid was used.
Total acid number of thermic fluid feed before adsorption: 0.589-0.626 mg KOH/g
Total acid number of thermic fluid after adsorption: 0.200-0.234 mg KOH/g
Total acid number reduction (%): 60.00-69.00 %

EXAMPLE 11:
The procedure essentially was same as given in Example 5, and thermic fluid used was from modified terphenyls with thermal stress in custom built solar line concentrators in steam generation plant. 20 % concentration of inorganic base was used for the impregnation of inorganic support.
Total acid number of thermic fluid feed before adsorption: 0.250-0.300 mg KOH/g
Total acid number of thermic fluid after adsorption: 0.090-0.120 mg KOH/g
Total acid number reduction (%): 60.00-65.00 %

EXAMPLE 12:
The procedure was essentially same as given in Example 5 and is repeated with regenerated catalyst.
Total acid number of thermic fluid feed before adsorption: 0.485-0.550 mg KOH/g
Total acid number of thermic Fluid after the adsorption: 0.048-0.089 mg KOH/g
Total acid number reduction (%): 78.2-90.10 %

EXAMPLE 13:
The procedure was essentially same as given in Example 5, except the adsorbent alumina is not activated using the inorganic base.
Total acid number of thermic fluid feed before adsorption: 0.485-0.550 mg KOH/g
Total acid number of thermic fluid after the adsorption: 0.110-0.144 mg KOH/g
Total acid number reduction (%): 72.14-77.10 %

EXAMPLE 14:
Fixed bed studies were performed in a quartz reactor equipped with a furnace, quartz tube, condenser, flow meter, and gas passing facility. The setup for reducing the total acid number in heat transfer fluid in fixed bed process is shown in Figure 2. HTF was passed and contacted with an adsorbent composition described above. Before passing, the adsorbent was preheated in the temperature range of 100-200 ? under inert atmosphere to remove moisture or any volatile species present on the surface of adsorbent. The temperature of the furnace was maintained between 40-200 ?. Then, HTF was allowed to flow through the adsorbent with a pre-determined WHSV of 2-4 h-1. The adsorbed fluid was collected and again passed through the same adsorbent till saturation level is reached in adsorbing acid contaminants. After the experiment, adsorbed fluid is centrifuged, and supernatant liquid was evaluated for TAN using ASTM D664 titration process.

The HTF was passed (WHSV = 2.0152 h-1) through a fixed bed maintained at temperature of 100 ? containing the adsorbent which was preheated at 200 ? under nitrogen atmosphere. After passing through bed, TAN of HTF was recorded.
Total acid number of thermic fluid feed before the adsorption: 0.445-0.555 mg KOH/g
Total acid number of thermic fluid after the adsorption: 0.03-0.075 mg KOH/g
Total Acid number reduction (%): 83-90 %

Example 15:
The procedure was essentially same as Example 17, WHSV was maintained at 2.2296 h-1 and temperature was increased to 150 ?.
Total acid number of thermic fluid feed before adsorption: 0.445-0.510 mg KOH/g
Total acid number of thermic fluid after adsorption: 0.080-0.109 mg KOH/g
Total acid number reduction (%): 78-83 % , Claims:1. An adsorbent composition for reducing acidic species from heat transfer fluids (HTF), said adsorbent comprising:
i. an inorganic support; and
ii. an inorganic base,
wherein the base is in a range of about 1 weight % to about 30 weight % with respect to the inorganic support.

2. The adsorbent composition as claimed in claim 1, wherein the inorganic support is selected from a group comprising activated alumina, activated carbon and silica materials; the inorganic support has a surface area greater than about 200 m2/g and a pore radius in a range of about 2 nm to about 10 nm.

3. The adsorbent composition as claimed in claim 1, wherein the inorganic base is containing hydroxyl ions; the inorganic base is selected from a group comprising liquid ammonia in deionized water, potassium hydroxide (KOH) and sodium hydroxide (NaOH); preferably the inorganic base is liquid ammonia in deionized water.

4. A process for the preparation of an adsorbent composition, comprising:
i. adding an inorganic base to an inorganic support to form a mixture, wherein the inorganic base is added in a range of about 1 weight % to about 30 weight % with respect to the inorganic support;
ii. stirring the mixture;
iii. ageing the mixture;
iv. separating water from the mixture; and
v. drying the mixture to obtain the adsorbent composition.

5. The process as claimed in claim 4, wherein the inorganic support is selected from a group comprising activated alumina, activated carbon and silica materials; the inorganic base is an inorganic base containing hydroxyl ions, the inorganic base is selected from a group comprising liquid ammonia in deionized water, potassium hydroxide (KOH) and sodium hydroxide (NaOH), preferably the inorganic base is prepared by adding liquid ammonia in deionized water; the inorganic support has a surface area greater than about 200 m2/g and a pore radius in a range of about 2 nm to about 10 nm.

6. The process as claimed in claim 4, wherein the stirring is carried out for about 1 to about 5 hours at a temperature not exceeding 50 °C; the ageing is carried out at a temperature in a range of about 80 °C to about 120 °C for a period of about 12 to about 15 hours; the mixture is dried at a temperature in a range of about 80 °C to about 120 °C.

7. A process for reducing total acidic number (TAN) of a heat transfer fluid by treating the heat transfer fluid with the adsorbent composition defined in any of claims 1-3, to obtain treated heat transfer fluid, and optionally regenerating the adsorbent composition.

8. The process as claimed in claim 7, wherein the process is an agitation process comprising:
i. adding the adsorbent composition to the heat transfer fluid to form a mixture;
ii. ageing the mixture;
iii. separating the treated heat transfer fluid from the mixture and optionally evaluating the total acidic number (TAN) in the fluid; and
iv. optionally regenerating the absorbent composition.

9. The process as claimed in claim 7 or 8, wherein the adsorbent composition is added to the heat transfer fluid in a range of about 1-30 w/w%, preferably about 20 w/w%; the ageing is carried out at an agitation speed in a range from about 100 to about 600 rpm at a temperature in a range from about 25 ? to about 80 °C for about 1 to about 6 hours; wherein the process is carried out in batch mode.

10. The process as claimed in claim 7, wherein the process is a fixed bed process comprising:
i. pre-heating the adsorbent composition in a quartz tube inside a furnace;
ii. passing the heat transfer fluid through one end of the quartz tube and contacting the heat transfer fluid with the adsorbent composition to obtain a treated heat transfer fluid;
iii. collecting the treated heat transfer fluid from another end of the quartz tube;
iv. optionally repeating the steps ii) and iii) with the treated heat transfer fluid;
v. separating the adsorbent composition from the treated heat transfer fluid; and
vi. optionally evaluating the total acidic number (TAN) of the treated heat transfer fluid.

11. The process as claimed in claim 7 or 10, wherein the adsorbent composition in the fixed bed process is pre-heated at a temperature in a range from about 100 ? to about 200 ? under inert atmosphere; wherein the heat transfer fluid in the fixed bed process is passed through one end of the quartz tube with weight hour space velocities (WHSV) of about 2 h-1 to about 4 h-1; the furnace is maintained at a temperature between about 40 ? to about 200 ?; wherein the process is carried out in continuous fixed bed mode.

12. The process as claimed in any of claims 7-9, wherein the adsorbent composition is regenerated by washing with a solvent followed by drying; the solvent is selected from a group comprising hexane, n-heptane, n-octane, n-decane, n-dodecane or any combination thereof; wherein drying during regeneration of the adsorbent composition is carried out at a temperature in a range of about 80 ? to about 120 ?.

13. The process as claimed in claim 7, wherein the heat transfer fluid comprises phenyls blended with esters and olefins, or a mixture of acids selected from a group comprising a monocarboxylic acid, a dicarboxylic aliphatic acid, an aromatic acid or any combination thereof.

14. The process as claimed in claim 13, wherein the aromatic phenyl is selected from a group comprising biphenyl, cyclohexyl benzene, diphenyl ether, olefin is selected from a group comprising ethylene and propylene; the mono carboxylic acid is selected from a group comprising 2-ethyl hexanoic acid, hexanoic acid, heptanoic acid, octanoic acid, neodecanoic acid, decanoic acid, nonanoic acid, isoheptanoic acid, dodecanoic acid or any combination thereof; the dicarboxylic aliphatic acid is selected from a group comprising sebacic acid, adipic acid, pimelic acid, suberic acid, azelaic acid, dodecanedioic acid or any combination thereof; the aromatic acid is phthalic acid.