Description:FIELD OF THE INVENTION
The present disclosure broadly pertains to the field of carbon capture and storage (CCS). In particular, the present disclosure relates to a structure modified amine and a solvent system comprising the same. The present disclosure also pertains to the methods of obtaining the same and applications thereof.

BACKGROUND OF THE INVENTION
CO2 is one of the primary anthropogenic greenhouse gases (GHGs). Other anthropogenic GHGs are methane, nitrous oxide and chlorofluorocarbons and the concentration of these GHGs is increasing in recent years. Although the radiative effect of CO2 is much less than the other GHGs, CO2 is emitted in large quantities into the atmosphere and has a long atmospheric lifetime. The concentration of CO2 will increase to about 600 ppmv by 2050 if no emission and mitigation policies are enforced. Failing to control GHG emissions may consequently lead to dramatic changes in weather conditions, rise in sea levels, reduced availability of drinking water and migration of climate refugees. The emissions from coal-based power plants range between 0.825 -1.035 tons of CO2 per MWh, whereas emissions from natural gas-based power generation are in the range of 0.35–0.4 tons of CO2 per MWh. Also, in petroleum refinery, processing 1 ton of crude oil to finished products generates 0.2-0.25 tons of CO2. Development of decarbonising technologies for significant reduction of CO2 emissions is an essential requirement with the world’s growing energy demand and continued dependence on fossil fuels. Carbon capture and storage (CCS) is a technology where CO2 is separated from gaseous components and is transported through a pipeline to deep underground storage locations. CCS appears to be a promising system to combat global warming in the coming years.

Capturing CO2 from combustion flue gases /refinery off-gas streams is associated with high capital investment costs, highly variable operating costs and in most cases leads to a significant energy penalty. Various technologies based on physical/chemical absorption, adsorption, membrane and cryogenic separation are reported to remove or separate CO2 from industrial gases. Currently, chemical absorption is the most mature technology that comprises solvent mainly an aqueous solution of primary, secondary and tertiary amines and a combination of amines etc. These solvents have a CO2 absorption capacity of 1.5-2.5 moles/litre solution which leads to the requirement of the higher size of the columns and consequently higher capital costs. In the absorption process, CO2 present in the flue gas reacts with amine solvent (primary, secondary and tertiary) and forms carbamate and bicarbonate ions. To dissociate CO2 from bicarbonate and stable amine carbamates, high stripping temperature (120-150 ?) and pressure (>1 bar) are essential. Thus, the CO2 absorption process requires a high temperature for dissociation of CO2 from solvent in stripper, generally supplied by steam thus increasing electricity costs by >70%, and it is the costliest component of CO2 capture. Further, these solvents possess higher values of heat capacity which results in higher heating & cooling requirements and also large contact areas are required in the heat exchangers. As a result, both capital expenditure (CAPEX) and operating expenditure (OPEX) of CO2 capture systems will be increased. Thus, the regeneration energy requirement of such methods is high. Besides, high regeneration temperature promotes amine decomposition and equipment corrosion.
In the case of amines having both tertiary and primary nitrogen, polyamines and piperazine can absorb CO2 at faster rates and also at higher capacities. In the case of tertiary, alkali/alkali earth metal salts, carbamates and bicarbonates formed dissociates at low temperature. Therefore, the use of tertiary and alkali/alkali earth metal salts was encouraging. In alkaline salt-based processes, the most popular absorption solutions have been sodium and potassium carbonate-based solutions (US 4,112,051, US 4,397,660 and US 5,061,465).

In literature, polyamine derivatives developed from piperazine were effectively used in aqueous alkali solvents systems in patent US 8,388,855 (2013). The results clarified that the solvent with a minimum of 3.6% potassium salt and the same equivalent of piperazine derivative is required to achieve greater results compared to that of 5M-7M solution of MEA (monoethanolamine). The presence of higher amounts of potassium salts and piperazine derivatives leads to an increase in the possibility of precipitation, lower absorption rates, and the cost of the chemicals to increase in process cost.

Another prior art patent WO 2016/027164 Al (EP3183050B1, US201462040911) revealed the performance of a mixture of several polyamines and alkanol amines like 2-amino-2-methyl propanol, 2-piperazine-l-ethylamine, diethylenetriamine, 2-methylamino-2-methyl-l-propanol and used the potassium carbonate buffer aqueous solution. The patent evaluated the regeneration energies, chemical stability, vapour pressure, total heat consumption, net cyclic capacity, reaction kinetics etc during evaluation studies. However, a drawback of this prior art is the high cost of the chemical components used due to their tailor-made nature and the high cost of raw materials employed.

Thus, there is a need in the art for the development of highly efficient and cost-effective solvent combination system having superior mass transfer characteristics for CO2 capture from combustion flue gas mixture. The reaction parameters like kinetics, energy consumption, solvent capability, solvent recovery, low-cost chemicals and cyclic capacities play a critical role in the development of an efficient and potential solvent system for CO2 separation from flue gas streams.

SUMMARY OF THE INVENTION
The present invention provides a solvent composition for absorption of carbon dioxide from a gaseous mixture comprising:
- at least one alkyl polyamine, at least one tertiary alkanol amine, and at least one structure modified amine (SMA) having a structure represented by compound of formula I:

Formula I
wherein,
R is independently selected from H or CH3, and
n is independently selected from 1, 2, 3 or 4,
- an aqueous medium,
- optionally along with mineral carbonate.

The present invention also provides a structure modified amine (SMA) having a structure represented by compound of Formula I,

Formula I
wherein, R is independently selected from H or CH3, and n is independently selected from 1-4.

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 (A) NMR analysis of structure modified amines (SMA-1 & 2), and (B) IR spectrum of structure modified amines.
Figure 2 depicts experimental set-up for batch solvent screening system for continuous absorption-desorption screening evaluation of the solvent composition.
Figure 3 depicts experimental set-up for continuous solvent screening system.
Figure 4 depicts CO2 loading of different solvent composition under pressure conditions.
Figure 5 depicts CO2 absorption capacities of solvent composition.
Figure 6 depicts net cyclic loading of solvent composition in a continuous CO2 capture system.

DETAILED DESCRIPTION OF THE INVENTION
The present disclosure addresses the drawbacks of the art and provides for a novel activator and an improved solvent composition comprising the same which increases the absorption capacity of carbon dioxide and also reduces regeneration temperature. The present disclosure also provides for the method of synthesising the activator, method of obtaining the solvent composition, and applications thereof.

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, methods, 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.

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 “some” as used herein is defined as “none, or one, or more than one, or all”. Accordingly, the terms “none”, “one”, “more than one”, “more than one, but not all” or “all” would all fall under the definition of “some”. The term “some embodiments” may refer to no embodiments or to one embodiment or to several embodiments or to all embodiments. Accordingly, the term “some embodiments” is defined as meaning “no embodiment, or one embodiment, or more than one embodiment, or all embodiments”.

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.

More specifically, any terms used herein such as but not limited to “includes”, “comprises”, “has”, “consists” and grammatical variants thereof is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. The specification will be understood to also include embodiments which have the transitional phrase “consisting of” or “consisting essentially of” in place of the transitional phrase “comprising”. The transitional phrase “consisting of” excludes any element, step, or ingredient not specified in the claim, except for impurities associated therewith. The transitional phrase “consisting essentially of” limits the scope of a claim to the specified materials or steps “and those that do not materially affect the basic and novel characteristic(s)” of the claimed invention.

Whether or not a certain feature or element was limited to being used only once, either way it may still be referred to as “one or more features” or “one or more elements” or “at least one feature” or “at least one element”. Furthermore, the use of the terms “one or more” or “at least one” feature or element do NOT preclude there being none of that feature or element, unless otherwise specified by limiting language such as “there NEEDS to be one or more” or “one or more element is REQUIRED”.

Use of the phrases and/or terms such as but not limited to “a first embodiment”, “a further embodiment”, “an alternate embodiment”, “one embodiment”, “an embodiment”, “multiple embodiments”, “some embodiments”, “other embodiments”, “further embodiment”, “furthermore embodiment”, “additional embodiment” or variants thereof do NOT necessarily refer to the same embodiments. Unless otherwise specified, one or more particular features and/or elements described in connection with one or more embodiments may be found in one embodiment, or may be found in more than one embodiment, or may be found in all embodiments, or may be found in no embodiments. Although one or more features and/or elements may be described herein in the context of only a single embodiment, or alternatively in the context of more than one embodiment, or further alternatively in the context of all embodiments, the features and/or elements may instead be provided separately or in any appropriate combination or not at all. Conversely, any features and/or elements described in the context of separate embodiments may alternatively be realized as existing together in the context of a single embodiment.

As used herein, the term "about" is used to indicate a range or approximation that allows for slight variations or deviations from a specific value or parameter without departing from the scope of the present invention. When "about" is used in conjunction with numerical values, it signifies that the disclosed value or parameter may vary by ±10%, preferably ±5%, of the indicated values.

As used herein, the term “room temperature" is defined as the temperature range typically encountered in indoor environments where human activities take place. It refers to a temperature range between approximately 22°C and 27°C, which is considered comfortable for most individuals.

As used herein, the term "optionally" is used to indicate that a particular feature, component, step, or condition is not mandatory or required for the implementation or performance of the invention. It signifies that the presence or inclusion of the specified element is discretionary and dependent on the particular embodiment, preference, or desired outcome of the invention.

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 be used in the practice or testing of the disclosure, the preferred methods and materials are now described. All publications mentioned herein are incorporated herein by reference.

As used herein the terms “method” and “process” have been used interchangeably.

As used herein, the terms “solvent composition”, “solvent system”, “CO2-philic solvent” and “CO2-philic solvent system” are used interchangeably.

The major technical barriers affecting the performance of CO2 capture plant are high energy requirement for the stripper to desorb CO2 from the solvent, decrease in net power output from the power plant, the slow absorption rate of CO2 in solvents, solvent degradability etc. The primary characteristics of a solvent that make it a feasible candidate for post-combustion flue gas CO2 capture are fast reaction with CO2, large net-CO2 carrying capacity, low-enthalpy of reaction with CO2, low energy lost to heat and vaporize water. To overcome these challenges in capturing CO2 from flue gas/ hydrogen reformer flue gas, fluid catalytic regenerator flue gas streams etc., the present invention provides for solvent systems that are highly energy-efficient and/or cost-effective and have higher absorption capacities with better physico-chemical properties.

The present invention thus provides a structure modified amine and a CO2-philic solvent system for the separation of CO2 from a gaseous mixture such as but not limiting to a flue gas mixture.

The present disclosure provides for an improved solvent composition using amines with different types of nitrogen atom containing polyamines, cyclic amines, alkanol amines along structure modified amine as a catalyst in high pH aqueous medium. The solvent system is highly effective for CO2 capture, low heat of absorption and desorption of CO2 and cost-effective chemicals. CO2 absorption with the solvent system of the present disclosure is cost-effective, highly efficient having CO2 recovery > 90%, higher net cyclic CO2 loading capacities with low solvent circulation rates, decrease in stripping temperatures etc compared to widely used solvent aqueous mono-ethanolamine (MEA).

The present invention provides a solvent composition for absorption of carbon dioxide from a gaseous mixture comprising:
- at least one alkyl polyamine, at least one tertiary alkanol amine, and at least one structure modified amine (SMA) having a structure represented by compound of formula I:

Formula I
wherein,
R is independently selected from H or CH3, and
n is independently selected from 1, 2, 3 or 4,
- an aqueous medium,
- optionally along with mineral carbonate.

In an embodiment of the present invention, the solvent composition comprises about 20-30 wt% of the at least one alkyl polyamine, about 10-15 wt% of the at least one tertiary alkanol amine, and about 1-5 wt% of the structure modified amine (SMA).

In another embodiment of the present invention, the at least one alkyl polyamine comprises an alkyl chain of C4-C8 carbon atoms and amine group, wherein the amine group is selected from primary, substituted or a combination thereof.

In yet another embodiment of the present invention, the at least one alkyl polyamine is selected from a group comprising 2,4 diethanol piperazine, diethylpropylamine, dimethyl propylamine, diethylenetriamine, triethylene tetramine, 3-Dimethylamino-1-propylamine (DMAPA, CO2PA-1), 3,3-diaminodipropylamine (CO2PA-2), Piperazine (PZ, CO2PA-3), Diisopropylamine (DIPA), Diethylenetriamine (DETA), and 1-(2-hydroxyethyl) piperidine (HEPD) or any combination thereof.

In still another embodiment of the present invention, the at least one tertiary alkanol amine is selected from a group comprising Methyl Diethanolamine (MDEA), 2-Methyl 2-Amino Propanol (AMP), Triethanolamine (TEA), 2-Dimethylaminoethanol (DMEA), 2-(Diethylamino) ethanol (DEEA), 2-(Dibutylamino) ethanol (DBAE) and 3-Dimethylamino-1-propanol (3DMAP) or any combination thereof.

In still another embodiment of the present invention, the mineral carbonate is selected from a group comprising potassium carbonate, calcium carbonate, calcium oxide and sodium carbonate or any combination thereof.

In still another embodiment of the present invention, the solvent composition comprises about 0-10% of the mineral carbonate.

In still another embodiment of the present invention, the aqueous medium is water, preferably demineralized water having mineral concentration less than about 1ppm.

In still another embodiment of the present invention, the solvent composition comprises about 50-70% of the aqueous medium.

The present invention also provides a structure modified amine (SMA) having a structure represented by compound of Formula I,

Formula I
wherein, R is independently selected from H or CH3, and n is independently selected from 1-4.

In some embodiments, the solvent system of the present disclosure comprises an aqueous mixture which includes at least one main agent of the (a) CO2-philic alkyl polyamine mixture (20-30% by wt) (CO2PA) (b) a tertiary amine/cyclic amine (10-15% by wt) and (c) structure modified amines (SMAs) as a chemical activator having a structure represented by the compound of Formula I (1-5% by wt). The CO2-philic alkyl polyamines (CO2PA) are mainly having amine groups of primary or substituted or both and having C4-C8 carbon atoms.

In a preferred embodiment, the structure modified amine (SMA) is present in a range of 3-5 % by weight of the solvent composition.

In another embodiment of the present invention, the structure modified amine (SMA) is added to the solvent composition as catalytic activator.

In some embodiments of the present invention, the gaseous mixture is a flue gas mixture, hydrogen reformer flue gas mixture, or fluid catalytic regenerator flue gas mixture.

In another embodiment of the present invention, a regeneration temperature of the CO2-philic solvent system for separating CO2 from the gaseous mixture is in a range of 100-110 ?.

In some embodiments, the solvent composition is in an aqueous medium having water up to 60-80% water, and the solvent composition is in clear and single phase at different temperatures ranging from about 20-100 ?.

In another embodiment of the present invention, the aqueous medium is demineralized (DM) water have mineral concentration less than 1ppm.

In another embodiment of the present invention, the total sum of the solvent composition is about 30-45 wt% of the total aqueous absorbent.

The present invention also provides a process for the synthesis of the solvent composition, comprising acts of:
- dissolving at least one alkyl polyamine, at least one tertiary alkanol amine, and at least one structure modified amine (SMA) in an aqueous medium;
- optionally, adding a mineral carbonate; and
- stirring to obtain a homogenous solvent composition.

In some embodiments, the process for the synthesis of the solvent composition comprises:
- dissolving about 20-30 % of at least one alkyl polyamine, about 10-15 wt% of at least one tertiary alkanol amine, and about 1-5 wt% of a structure modified amine (SMA) in about 60-80% of an aqueous medium;
- optionally, adding a mineral carbonate; and
- stirring to obtain a homogenous solvent composition.

In an embodiment of the present invention, the synthesis of the solvent composition is performed at room temperature.

The present invention further provides for a structure modified amine (SMA) having a structure represented by the compound of Formula I:

Formula I
wherein, R is independently selected from H or CH3, and n is independently selected from 1, 2, 3 or 4.

In a preferred embodiment, the SMA has a structure represented by the compound of Formula I, wherein R is independently selected from H or CH3, and n is independently selected from 2, 3 or 4.

In some embodiments, the SMA has a structure represented by the compound of Formula I, wherein R is independently selected from H or CH3, and n is 2.

In some embodiments, the SMA has a structure represented by the compound of Formula I, wherein R is independently selected from H or CH3, and n is 3.

In some embodiments, the SMA has a structure represented by the compound of Formula I, wherein R is independently selected from H or CH3, and n is 4.

The SMA is employed as a catalytic activator and added as an enhancing agent for developing blended solvent composition of the present disclosure which further improves the absorption kinetics.

The present invention further provides a process for the synthesis of the aforesaid structure modified amine (SMA) represented by the compound of Formula I, wherein the process comprises:
- heating a primary alkyl amine in a closed system and adding a terminal alkylene oxirane to the same,
- stirring the mixture obtained for a period of about 10-15 h at a temperature ranging from about 50 ? to obtain the SMA; and
- optionally purifying the structure modified amine.

In some embodiments of the present invention, the primary alkyl amine has C4-C8 carbon atoms, and the terminal alkylene oxirane has C2-C4 carbon atoms.

In some embodiments of the present invention, the primary alkyl amine and the terminal alkylene oxirane are added in a ratio of 1:2.

In some embodiments, purification of the structure modified amine is carried out by employing a rotary evaporator.

In some embodiments, purification of the structure modified amine is carried out by techniques selected from a group comprising solvent evaporation.

Synthesis procedure for Structure Modified Amine (SMA):
In some embodiments, primary alkyl amine (C4-C8, about 0.5 to about 1.5 mole, preferably about 1.0 mole) is added to a clean, dry, three-neck round bottom flask and heated at a temperature ranging from about 22 ? to about 35 ?, preferably about 50 ? under closed system. A terminal oxirane compound (C2-C4, about 1.0 to about 3.5 mole, preferably about 2.0 moles) was slowly added to the primary alkylamine at a temperature ranging from about 35 ? to about 70 ? for about 20 minutes to about 45 minutes, preferably about 30 minutes. Stirring is continued at temperature ranging from about 35 ? to about 70 ?, preferably about 50 ? temperature for about 10 to 15 hours, preferably about 3 hours and then heating was removed and stirring continued for another 12 hours at room temperature. The reaction mixture is then subjected to rota vapour for removal of unreacted oxirane compound. A clean and colourless structure modified amine obtained in quantitative amount. The general scheme is presented in Scheme 1. The structure of the SMA compounds was analysed by Molecular spectroscopy techniques like Nuclear magnetic resonance (NMR) and Infrared (IR) spectra (Figure 1A & 1B).

Scheme1: Scheme for the synthesis of structure modified amine

Batch-scale Absorption Evaluation screening set-up:
In some embodiments, a batch experimental set-up consists of a cylindrical vessel of 200 mL capacity (MOC SS316) with a jacket system for the flow of coolant to maintain isothermal conditions for conducting the absorption studies as shown in Figure 2. The screening absorption system consists of provisions for gas inlets, liquid inlets, gas outlet, coolant outlet (107A, 109A), coolant inlet (107B, 109B), thermocouple (107) and pressure gauge (108) and pressure controller. The gas outlet is connected to a condenser tube (109) through which cooling fluid is circulated (109A, 109B). A chiller set-up is installed which can circulate coolant until about -10 ?. Two mass flow controllers for CO2 (103) and N2 (104) are connected to CO2 gas cylinder (101) and N2 gas cylinder (102) respectively, to measure the desired flow rates of both CO2 and N2 gases. A pressure control valve is used to maintain the desired pressure. The solvent of the measured quantity is charged in the vessel and purged with N2 gas. The mixture of CO2 and N2 gases are passed through the reactor at desired flow rates through the respective valves (105, 106) and bubbled through solvent homogeneously. The un-reacted gas passes through a pressure control valve (110) to wet gas flow meter (111) to measure the volume of the gas outlet.

Continuous Absorption-Desorption Screening Evaluation for the solvent system:
In some embodiments, the experimental set-up for the continuous reactor system for evaluation of net cyclic capture capacity of CO2 and capture efficiency of different solvent systems from the gas mixture is depicted in Figure 3. The experimental set-up had mainly two columns absorber & stripper, feed section, rich and lean circulation pumps, condenser, and wet gas meters. The feed section includes CO2 and N2 streams. The CO2 line includes a heat traced line. All the gas feeds are fitted with pressure regulators, hand valves and mass flow controllers for ensuring the required feed ratio of CO2: N2 to the inlet of the absorber. All the gas streams to the absorber inlet are sufficiently pure (99.9 to 99.999%). The absorber/ desorber column consists of stainless steel packing material counter-current flow configuration. The flow rates of the individual gas streams are controlled by mass flow controllers. CO2 and N2 in the required composition are premixed in a gas mixer (201) before the absorber inlet and enter the CO2 absorber (202) at the bottom and move to the top of the column interacting counter-currently with lean amine solvent and came out from the top of the absorber outlet (203). The absorber outlet gas stream exits from the top of the absorber outlet (203) passes through a pressure control valve (210) and then passes to the wet gas meter (211) and finally gas is vented off. The liquid stream from the bottom of the absorber enters to rich amine through rich amine pump (204) and the rich amine is preheated then admitted to the CO2 stripper (205). The CO2 stripper is heated through an electrical line heater and the surface of the stripper is insulated to avoid heat loss. The lean amine stream from the stripper outlet passes to the condenser/heat exchanger (212) followed by the lean amine pump (213). The condenser has a cooling range of (0 to 20 ?) and cools the lean amine and then enters the absorber. The stripped off-gas from the stripper outlet (206) passes to condenser (207) and then admitted to pressure control valve (208) and passes to wet gas meter (209) for measuring stripped off the gas and finally vented off. The lean and rich amine streams were collected for analysis. Both gas streams from the absorber and stripper pass through wet gas flow meters for flow measurements and analyse individual gas compositions.

Typical Experimental conditions
Absorber Pressure - About 1.1- 1.3 bar.
Stripper Pressure- About 1.5-2 bar
Stripper Temperature - About 100-120 ?
Partial pressures of CO2 in Gas Mixture- About 12-17 Kpa

In some embodiments, advantages of the solvent system of the present disclosure include but are not limited to the following:
• The solvent composition has superior physico-chemical properties with respect to aqueous monoethanolamine (MEA) such as lower viscosity, density, higher acid dissociation constants (pKa), higher boiling point and lower melting point.
• The solvent composition is highly efficient having high absorption capacity and a superior rate of CO2 absorption for removal of CO2 from flue gas mixtures at various partial pressure levels of CO2.
• The developed CO2-philic solvent composition can separate CO2 in the flue gas at concentrations ranging from about 5-80 V% with a capture efficiency of >90%.
• The regeneration temperatures required for the developed solvent composition to strip CO2 ranges from 100-110 ?. It reduces regeneration temperature by about 10-15 ? to the conventional solvents. Therefore, heat stable salts will be minimized due to the thermal degradation of solvent. Also, reboiler duty and steam consumption will be decreased, and the operating cost of the process will be reduced.
• It has minimum solvent make-up requirement, low degradation & evaporation, low amine emissions to the atmosphere and corrosion of the equipment.
• The developed solvent composition has low solvent regeneration energy, higher net cyclic loading and lower solvent circulation rates compared to widely used solvent aqueous monoethanolamine. As the developed solvent system has higher absorption kinetics and lower circulation rates the height of the absorption column and area requirement for the heat exchanger can be reduced. Also, due to a decrease in column height, the pressure drop in the absorber reduces.
• The energy required for auxiliary equipment like rich/lean amine pumps, blowers etc. will be low as the solvent composition has low viscosity, density and low-pressure drop in a column.
• The developed CO2-philic solvent composition is cost-effective, energy-efficient and requires lower capital and operating costs and.

EXAMPLES:
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.

Synthesis procedure for Structure Modified Amine (SMA):
In a clean, dry, three-neck round bottom flask, primary alkyl amine (C4-C8, 1.0 mole) was added and heated at about 50 ? temperature under the closed system. Terminal oxirane compound (C2-C4, 2.0 moles) was slowly added to the primary alkylamine at 50 ? for 30 minutes. Stirring was continued at 50 ? temperature for 3 hours and then heating was removed and stirring was continued for another 12 hours at room temperature. Reaction mixture was then subjected to rota vapour for removal of unreacted oxirane compound. A clean and colourless structure modified amine was obtained in quantitative amount. The general scheme of the method for synthesis of the structure modified amine is presented in Scheme 1 below. The structure of the SMA compounds was analysed by Molecular spectroscopy techniques like NMR and Infrared IR spectra (Figures 1A & 1B).

Scheme1: Scheme for the synthesis of structure modified amine

From analysis of the NMR and IR spectra, the structure of reaction products i.e., structure modified amine was confirmed. In Figure 1A, the peak at d 3.90 indicates the opening of the epoxide group and the formation of the hydroxyl group by the C-C bond which confirmed the structure of the SMA-1 compound. In Figure 1B, the appearance of a peak at d 3.90 along with a peak at d 1.60 confirmed the structure of SMA-2 which has two CH2 groups more than that of SMA-1. In IR analysis, the peaks at 3353 and 3295 cm-1 indicate the presence of both amine and hydroxyl groups which support the formation of structure modified amines from oxirane and primary amines.

Screening of solvents for CO2 Absorption at different experimental conditions:
Solvent systems were prepared having varying concentrations using a combination of at least one tertiary alkanol, another alkyl polyamines by adding SMA’s as catalytic activators in an aqueous medium and the proportions of the components were fine tuned to improve CO2 capture capacity.

Following are the examples of the screening of solvents. Referral names of the code of the constituents employed are expanded below for reference:
- CO2PA-1 : 3-Dimethylamino-1-propylamine (DMAPA)
- CO2PA-2 : 3,3-diaminodipropylamine
- CO2PA-3 : Piperazine (PZ)
- MC-1 : Potassium carbonate
- SMA-1 : Structure modified amine represented by the compound of Formula I

Formula I
wherein R is independently selected from H or CH3, and n is 2.

Example-1: This solvent system was obtained by dissolving CO2-philic alkyl polyamine with carbon atoms C4-C8 (CO2PA-1) of 30% wt/wt and piperazine (PZ, CO2PA-3) of 10% wt/wt in demineralized water (DM) water (60% wt/wt) and stirring to obtain a homogenous solvent composition at room temperature.

Example-2: This solvent system contains Methyldiethanolamine of 20% wt/wt and CO2-philic alkyl polyamine with carbon atoms C4-C8 (CO2PA-1) of 10% wt/wt in DM water (70% wt/wt) and the mixture was stirred to obtain a homogenous solvent composition at room temperature.

Example-3: This solvent system contains Methyldiethanolamine of 15% wt/wt and CO2-philic alkyl polyamine with carbon atoms C4-C8 (CO2PA-2) of 30% wt/wt in DM water (55% wt/wt) and the mixture was stirred to obtain a homogenous solvent composition at room temperature.

Example-4: This solvent system was developed by dissolving Methyldiethanolamine of 30% wt/wt and CO2-philic alkyl polyamine with carbon atoms C4-C8 (CO2PA-3) of 10% wt/wt in DM water (60% wt/wt) and stirring to obtain a homogenous solvent composition at room temperature.

Example-5: The solvent system was developed by dissolving Methyldiethanolamine of 20% wt/wt and CO2-philic alkyl polyamine with carbon atoms C4-C8 (CO2PA-3) of 10% wt/wt in DM water (70% wt/wt) and stirring to obtain a homogenous solvent composition at room temperature.

Example-6: The solvent system was developed by dissolving CO2-philic alkyl polyamine with carbon atoms C4-C8 (CO2PA-2) of 15% wt/wt and Piperazine (PZ, CO2PA-3) of 15% wt/wt in DM water (70% wt/wt) and stirring to obtain a homogenous solvent composition at room temperature.

Example-7: The solvent system was obtained by dissolving CO2-philic alkyl polyamine with carbon atoms C4-C8 (CO2PA-2) of 30% wt/wt and potassium carbonate (MC-1) of 10% wt/wt in DM water (60% wt/wt) and stirring to obtain a homogenous solvent composition at room temperature.

Example-8: The solvent system was developed by dissolving CO2-philic alkyl polyamine with carbon atoms C4-C8 (CO2PA-2) of 15% wt/wt, Methyldiethanolamine of 10% wt/wt and potassium carbonate (MC-1) of 10% wt/wt in DM water (65% wt/wt) and stirring to obtain a homogenous solvent composition at room temperature.

Example-9: The solvent system was obtained by dissolving CO2-phillic alkyl polyamine with carbon atoms C4-C8 (CO2PA-2) of 20% wt/wt, 2-Methyl, 2-Amino Propanol (AMP) of 20% wt/wt and potassium carbonate (MC-1) of 10% wt/wt in DM water (60% wt/wt) and stirring to obtain a homogenous solvent composition at room temperature.

Example-10: The solvent system was obtained by dissolving CO2-philic alkyl polyamine with carbon atoms C4-C8 (CO2PA-2) of 10% wt/wt and Methyldiethanolamine of 30% wt/wt in DM water (60% wt/wt) and stirring to obtain a homogenous solvent composition at room temperature.

Example-11: The solvent system was prepared by dissolving CO2-philic alkyl polyamine with carbon atoms C4-C8 (CO2PA-2) of 20% wt/wt and methyldiethanolamine of 20% wt/wt in DM water (60% wt/wt) and stirring to obtain a homogenous solvent composition at room temperature.

Example-12: The solvent system was developed by dissolving Methyldiethanolamine of 15% wt/wt, CO2-philic alkyl polyamine with carbon atoms C4-C8 (CO2PA-2) of 30% wt/wt and catalyst amount of structure modified amine (SMA-1, 5% wt/wt) in DM water (50% wt/wt) and stirring to obtain a homogenous solvent composition at room temperature.

Example-13: The solvent system was developed by dissolving CO2-Philic alkyl polyamine with carbon atoms C4-C8 (CO2PA-1) of 30% wt/wt, piperazine (PZ, CO2PA-3) of 10% wt/wt and catalyst amount of structure modified amine (SMA-1, 5% wt/wt) in DM water (55% wt/wt) and stirring to obtain a homogenous solvent composition at room temperature.

Example-14: The solvent system was developed by dissolving CO2-Philic alkyl polyamine with carbon atoms C4-C8 (CO2PA-1) of 30% wt/wt and piperazine (PZ, CO2PA-3) of 10% wt/wt and catalyst amount of structure modified amine (SMA-2, 5% wt/wt) in DM water (55% wt/wt) and stirring to obtain a homogenous solvent composition at room temperature.

Example-15: The solvent system was developed by dissolving CO2-philic alkyl polyamine with carbon atoms C4-C8 (CO2PA-2) of 15% wt/wt, piperazine (PZ, CO2PA-3) of 15% wt/wt and catalyst amount of structure modified amine (SMA-1, 5% wt/wt) in DM water (65% wt/wt) and stirring to obtain a homogenous solvent composition at room temperature.

Example-16: The solvent system was developed by dissolving CO2-philic alkyl polyamine with carbon atoms C4-C8 (CO2PA-2) of 30% wt/wt, potassium carbonate (MC-1) of 10% wt/wt and catalyst amount of structure modified amine (SMA-1, 5% wt/wt) in DM water (55% wt/wt) and stirring to obtain a homogenous solvent composition at room temperature.

Example-17: The solvent system was developed by dissolving Methyldiethanolamine of 30% wt/wt, CO2-philic alkyl polyamine with carbon atoms C4-C8 (CO2PA-3) of 10% wt/wt and structure modified amine (SMA-1, 5% wt/wt) in DM water (55% wt/wt) and stirring to obtain a homogenous solvent composition at room temperature.

Example-18: The solvent system was developed by dissolving CO2-philic alkyl polyamine with carbon atoms C4-C8 (CO2PA-2) of 10% wt/wt, Methyldiethanolamine of 30% wt/wt and structure modified amine (SMA-1, 5% wt/wt) in DM water (55% wt/wt) and stirring to obtain a homogenous solvent composition at room temperature.

Example-19: The solvent system was prepared by dissolving CO2-philic alkyl polyamine with carbon atoms C4-C8 (CO2PA-2) of 20% wt/wt, methyl diethanolamine of 20% wt/wt and structure modified amine (SMA-1, 5% wt/wt) in DM water (60% wt/wt) and stirring to obtain a homogenous solvent composition at room temperature.

Screening results of CO2 absorbed solvent systems in the batch reactor:
Benchmark experiments were conducted in batch screening set-up as shown in Figure 2. Initially, baseline experiments were conducted with aqueous monoethanolamine which was used as a standard for CO2 separation applications. Further, screening of individual active components from alkanol amines, amines/polyamines, carbonates and a combination of CO2PAs were carried out at a temperature ranging from 30-40 ? and absorber pressure ranges from atmospheric to 130 kPa using 30%-50% wt/wt of various amine mixtures in an aqueous medium. The results of CO2 loading obtained for different solvent systems are shown in Figure 4.

The results displayed in Figure 4 shows the CO2 absorption capacities of different binary solvent recipes prepared by an amalgamation of different amines which includes alkanol/alkyl, alkyl polyamines and aqueous salts in different proportions. Amongst the solvent systems tested, Example 1, Example 3, Example 6 & Example 8 showed better CO2 absorption capacity which is in the range of 2.9 to 4.63 moles per litre solution and 1.1-1.21 moles per mole of amine as compared to that of a conventional aqueous solvent of monoethanolamine (MEA). The remaining binary solvents system of Examples 2, 4, 5, 7, 9, 10 & 11 showed a lower range of CO2 absorption capacities under similar experimental conditions in terms of both moles per mole and moles per litre solvent. The solvent system of Example 1 showcased a higher affinity towards CO2 due to a combination of primary and cyclic polyamines.

Other solvent systems like Example 3, Example 6 and Example 8, had lower CO2 absorption capacity in terms of moles per litre solvent as they have amines of tertiary alkanol amines which slows the rate kinetics of CO2 absorption in the solvent as compared to that of Example 1. Therefore, to improve the absorption kinetics of these solvent systems structure modified amines were synthesized and added as enhancing agents. These promoters improve the solubility and interaction of CO2 molecules with amine solvents. Also, tertiary amines have the advantage of low dissociation temperature for CO2.

Absorption evaluation studies were conducted by incorporating small amounts of structure modified amines (Examples 12 to 19) in a batch-scale absorption evaluation set-up.

Evaluation of structure modified amines (SMA) in amine solvents:
A catalytic amount of structure modified amines (SMA-1 & SMA-2) were added in solvent systems of Examples 1, 3, 4, 6, 8, 10 and 11 and evaluated for CO2 loading capacities. The results of the tests were summarized in Figure 6.

The test results given in Figure 5 reveal that the catalytic amount of structure modified amines (SMA 1 and SMA 2) improved the absorption of CO2 in solvent systems of Example 12 to Example 19 as compared to a solvent system without SMA blended. Whereas absorption capacities of solvent systems of Example 13 and 14 showed marginal improvement in CO2 absorption as compared to without SMA compound i.e., Example 1. Similarly, the solvent systems Example-15, 16, 17,18 & 19 achieved CO2 absorption capacities of 3.92, 3.70, 3.8, 4.21 and 3.23 moles per litre respectively as compared to the corresponding solvent systems (Example-5, 6, 8, 10 &11) without the addition of SMA compound.

The CO2 absorption capacities of solvent systems with 2.89 moles per litre (Example 3) was enhanced to 5.1 moles per litre by adding enhancing agents SMA-1. The improved absorption capacities in Example 12 are due to the synergistic effect of structure modified amines and combination of amines used which further improved the reaction kinetics and reached the maximum absorption capacities. Other physical-chemical parameters like viscosity, density and heat absorption are found within the required limit as compared to that of 30% of MEA solvent.

Evaluation of structure modified amines (SMA) in continuous absorber/desorber CO2 capture plant:
Further, the evaluation studies were extended with the solvent combination of the present invention in continuous absorber/desorber CO2 capture plant as mentioned in the experimental set-up in Figure 3 and as described above.

The CO2 absorption/desorption experiments were conducted in a continuous absorber-stripper system using shortlisted amine solvent systems described above. The typical operating conditions for conducting experiments as per stabilized conditions are as follows:
Absorber Pressure - About 1.1- 1.3 bar.
Stripper Pressure- About 1.5-2 bar
Stripper Temperature - About 100-120 ?
Partial pressures of CO2 in Gas Mixture- About 12-17 Kpa

Base data was generated for net cyclic loading for 90% CO2 recovery by varying the solvent circulation rates with an aqueous mono-ethanol amine at temperature of 120 ?. Further data for net cyclic CO2 loading was generated with solvent systems of Example 3 (without the addition of SMA activator) and corresponding Example 12 (with the addition of SMA activator) at stripping temperatures of 105 to 110? and compared to standard aqueous MEA solvent system, as shown in Figure 6.

Solvent circulation rates with solvent system of Example 3 and Example 12 were low w.r.t aqueous MEA and net cyclic loading for proposed solvent system of Example 12 was almost 50% greater than an aqueous MEA. As the regeneration temperatures for the proposed solvent system of Example 12 was reduced by 10-15 ? w.r.t aqueous MEA, the re-boiler duty and steam required will be lower for the proposed solvents to strip the CO2. As the stripper temperature was low, the thermal degradation of the solvent will be less and also amines emitting to the atmosphere will be low.

Referral Numerals:
Component Reference Numeral
CO2 gas supply cylinder 101
N2 gas supply cylinder 102
Mass flow controller (MFC-1) 103
Mass flow controller (MFC-1) 104
Valve 1 105
Valve 2 106
Thermocouple 107
Coolant out 107A
Coolant in 107B
Pressure gauge 108
Condenser tube 109
Coolant out 109A
Coolant in 109B
Pressure control valve 110
Wet gas meter 111
Gas mixer 201
CO2 Absorber 202
Absorber outlet 203
Rich amine pump 204
CO2 stripper 205
Stripper outlet 206
Heat exchanger 207
BPR 208
Wet gas meter 209
BPR 210
Wet gas meter 211
Heat exchanger 212
Lean amine pump 213
, Claims:1. A solvent composition for absorption of carbon dioxide from a gaseous mixture comprising:
- at least one alkyl polyamine, at least one tertiary alkanol amine, and at least one structure modified amine (SMA) having a structure represented by compound of formula I:

Formula I
wherein,
R is independently selected from H or CH3, and
n is independently selected from 1, 2, 3 or 4,
- an aqueous medium,
- optionally along with mineral carbonate.

2. The solvent composition as claimed in claim 1, wherein the solvent composition comprises about 20-30 wt% of the at least one alkyl polyamine, about 10-15 wt% of the at least one tertiary alkanol amine, and about 1-5 wt% of the structure modified amine (SMA).

3. The solvent composition as claimed in claim 1 or 2, wherein the at least one alkyl polyamine comprises an alkyl chain of C4-C8 carbon atoms and amine group, wherein the amine group is selected from primary, substituted or a combination thereof.

4. The solvent composition as claimed in any of claims 1-3, wherein the at least one alkyl polyamine is selected from a group comprising 2,4 diethanol piperazine, diethylpropylamine, dimethyl propylamine, diethylenetriamine, triethylene tetramine, 3-Dimethylamino-1-propylamine (DMAPA, CO2PA-1), 3,3-diaminodipropylamine (CO2PA-2), Piperazine (PZ, CO2PA-3), Diisopropylamine (DIPA), Diethylenetriamine (DETA), and 1-(2-hydroxyethyl) piperidine (HEPD) or any combination thereof.

5. The solvent composition as claimed in any of claims 1-4, wherein the at least one tertiary alkanol amine is selected from a group comprising Methyl Diethanolamine (MDEA), 2-Methyl 2-Amino Propanol (AMP), Triethanolamine (TEA), 2-Dimethylaminoethanol (DMEA), 2-(Diethylamino) ethanol (DEEA), 2-(Dibutylamino) ethanol (DBAE) and 3-Dimethylamino-1-propanol (3DMAP) or any combination thereof.

6. The solvent composition as claimed in claim 1, wherein the mineral carbonate is selected from a group comprising potassium carbonate, calcium carbonate, calcium oxide and sodium carbonate or any combination thereof.

7. The solvent composition as claimed in claim 1, wherein the solvent composition comprises about 0-10% of the mineral carbonate.

8. The solvent composition as claimed in claim 1, wherein the aqueous medium is water, preferably demineralized water having mineral concentration less than about 1ppm.

9. The solvent composition as claimed in claim 1, wherein the solvent composition comprises about 50-70% of the aqueous medium.

10. A structure modified amine (SMA) having a structure represented by compound of Formula I,

Formula I
wherein, R is independently selected from H or CH3, and n is independently selected from 1-4.