Description:Field of the Invention
The present invention relates to a homogenous catalyst comprising esters of p-nitrobenzene carboxylic acid with pentaerythritol. The addition of the homogenous catalyst to Liquefied Petroleum Gas (LPG) fuel significantly improves the Laminar Flame Velocity (LFV) of LPG. The present invention also relates to a process for preparation of the homogenous catalyst and a process for preparation of a homogenous catalyst doped LPG fuel for use in spark ignition (SI) engine.

Background of the invention
In classical SI engines, a switch to Liquefied Petroleum Gas (LPG) offers several advantages over conventional fuels such as gasoline. Besides being economical it also offers operational and environmental benefits such as lower coking or deposit formations in engine; higher Brake Specific Energy Consumption (BSEC); about 40% less hydrocarbon emissions, 35% less NOx, 50% less CO emission compared to gasoline. Despite these significant benefits, use of LPG is severely limited in SI engines due to its low volumetric efficiencies that lead to issues such as poor thrust, low Brake Thermal Efficiency, low load bearing capacity etc.

These concerns can be addressed to a great extent by improving the flame velocity of LPG. Laminar Flame Velocity (LFV) is a fundamental property of a fuel which significantly impacts overall combustion performance. LFV dictates reactivity, exothermicity and diffusivity of the fuel–air mixture. Laminar Flame Velocity is inversely proportional to the total burn duration which in turn critically impacts the power output and engine efficiency.

WO2009105007A1 discloses a diesel fuel composition comprising at least one diesel fuel and at least one cetane number improving compound or at least one cetane number improving composition comprising at least one cetane number improving compound, said cetane number improving compound being at least one 2-alkylheptylnitrate, particularly 2-propylheptylnitrate. Disclosed are, furthermore, a cetane number improving additive comprising said 2-alkylheptylnitrate and the use thereof.

Sebbar et al. Energy & Fuels 2017 31 (3), 2260-2273 investigates the ignition/combustion of di-tertiary-butyl peroxide (DTBP) over a wide range of fuel/air ratios using numerical flame calculations to gain insight into species profiles and ignition/combustion characteristics of DTBP/air mixtures. The results are flame zone and reaction zone structures as well as the corresponding laminar flame speeds and propagation speeds of reaction zones. Several detailed reaction mechanisms are evaluated in the flame simulations, and sensitivity of the computed results to important reaction steps was evaluated.

WO2010134679A2 discloses a novel bicycloheptane-based compound. A cetane number improver containing the bicycloheptane-based compound and diesel fuel containing the cetane number improver are also provided. This cetane number improver has lower toxicity and superior stability, compared to a conventional cetane number improver, and can greatly improve the cetane number of fuel oil such as diesel, thus increasing combustion efficiency of fuel oil.

It has been well documented in literature that increased concentrations of oxo and peroxo radicals can improve flame velocities significantly. Organic nitrates and peroxides have often been popular choices to improve flame velocities and burn rates of diesel fuels. However, similar compounds which are essentially Cetane Improvers, have not found application in Spark Ignition engines due to obvious contradictory nature. Furthermore, such additives have not been reported for LPG, primarily attributed to the inadequate solubility of relatively polar compounds in LPG. Thus, there is a need to formulate additives that are sufficiently soluble in LPG and have the potential to enhance its flame velocity, consequently improving fuel efficiency.

Summary of the invention
The present invention provides hydrocarbon soluble, homogenous catalysts that increase the Flame Velocity of LPG, under different air to fuel ratios and engine relevant conditions. The increase in flame velocity is expected to improve burn rates, increase Mean Effective Pressure (MEP) and power output of a spark ignition engine.

In an aspect, the present invention provides a homogeneous catalyst for doping in LPG fuel of formula (1):
C(CH2OR1)2 (CH2OR2)2
(formula 1)
wherein:
R1 is selected from H, C6H4(NO2)CO-, or H3C-(CH2)5-CO-; and
R2 is C6H4(NO2)CO-.

In one of the aspects, the present invention provides a method of preparation of diester compound also referred as LPG C-1 and tetra-ester compound also referred as LPG C-2 comprising steps of:
dissolving a mixture of para nitro benzoic acid, dicyclohexylcarbodimide and 10 mol% 4-(Dimethylamino) pyridine in dichloromethane by constant stirring at room temperature under inert atmosphere;
adding pentaerythritol dissolved in dichloromethane to the mixture of step (a) followed by stirring to obtain final mixture; and
separating the diester product from final mixture of step (b) followed by its purification.
In another aspect, the present invention provides a method of preparation of mixed tetra-ester compound also referred as LPG C-3 comprising steps of:
dissolving a mixture of para nitro benzoic acid, dicyclohexylcarbodimide and 10 mol% 4-(Dimethylamino) pyridine in dichloromethane by constant stirring at room temperature under inert atmosphere;
adding pentaerythritol dissolved in dichloromethane to the mixture of step (a) followed by stirring to obtain final mixture;
separating the diester product from final mixture of step (b) followed by its purification;
dissolving a mixture of caprylic acid, dicyclohexylcarbodimide and 10 mol% 4-(Dimethylamino) pyridine in dichloromethane by constant stirring at room temperature under inert atmosphere;
adding pentaerythritol diester obtained in step (c) to the mixture of step (d) followed by stirring to obtain final mixture; and
separating the mixed tetraester product from final mixture of step (e) followed by its purification.
In another aspect, the present invention provides a process for the preparation of a homogenous catalyst doped LPG fuel, comprising steps of:
(a) mixing the homogeneous catalyst at room temperature in hexane to form a solution, wherein the homogeneous catalyst is selected from diester compound LPG C-1, tetra-ester compound (LPG C-2) or mixed tetra-ester compound LPG C-3; and
(b) adding the solution of step (a) to liquefied petroleum gas (LPG) in a compressed gas cylinder.

Detailed Description of the Invention
For the purpose of promoting an understanding of the principles of the disclosure, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the disclosure as illustrated therein being contemplated as would normally occur to one skilled in the art to which the disclosure 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 disclosure belongs. The system, methods, and examples provided herein are illustrative only and not intended to be limiting.

Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present disclosure, the preferred methods and materials are now described. All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited.

It must be noted that as used herein and in the appended claims, the singular forms "a", "and", and "the" include plural referents unless the context dictates otherwise. Thus, for example, reference to "a compound" includes a plurality of such compounds, and reference to "the step" includes reference to one or more steps and equivalents thereof known to those skilled in the art, and so forth.
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 claims or their equivalents.

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 disclosure.

The term "Liquefied Petroleum Gas (LPG)" refers to a combustible blend of hydrocarbon gases, typically consisting primarily of propane and butane in varying proportions, with common ratios ranging from approximately 50% to 70% propane and 30% to 50% butane. Additionally, LPG may contain trace amounts of impurities such as propylene and butylene. These impurities are present in concentrations generally below 5% and can vary depending on the source and processing methods used.

In an embodiment, the present invention provides a homogeneous catalyst for doping in LPG fuel of formula (1):
C(CH2OR1)2 (CH2OR2)2
(formula 1)
wherein:
R1 is selected from H, C6H4(NO2)CO-, or H3C-(CH2)5-CO-; and
R2 is C6H4(NO2)CO-.

In one of the embodiments of the present invention, the homogeneous catalyst for doping in LPG fuel of formula (1) the catalyst is a diester compound and it is also referred as LPG C-1 of the following chemical formula:

LPG C-1

In another embodiment of the present invention, the homogeneous catalyst for doping in LPG fuel of formula (1) the catalyst is a tetra-ester compound and it is also referred as LPG C-2 of the following chemical formula:

LPG C- 2

In another embodiment of the present invention, the homogeneous catalyst for doping in LPG fuel of formula (1) the catalyst is a mixed tetra-ester compound and it is also referred as LPG C-3 of the following chemical formula:

LPG C-3
In another embodiment, the present invention provides a method of preparation of diester compound also referred as LPG C-1 and tetra-ester compound also referred as LPG C-2 comprising steps of:
a. dissolving a mixture of para nitro benzoic acid, dicyclohexylcarbodimide and 10 mol% 4-(Dimethylamino) pyridine in dichloromethane by constant stirring at room temperature under inert atmosphere;
b. adding pentaerythritol dissolved in dichloromethane to the mixture of step (a) followed by stirring to obtain final mixture; and
c. separating the diester product from final mixture of step (b) followed by its purification.

In another embodiment of the present invention, the stirring of the mixture of step (a) is carried out for 30 minutes; and stirring of the mixture of step (b) is carried out for 24 hours.
In another embodiment of the present invention, the 1:2 ratio of pentaerythritol: paranitrobenzoic acid is used for preparation of diester compound (I); and 1:4 ratio of pentaerythritol: paranitrobenzoic acid is used for preparation of tetra-ester compound also referred as LPG C-2.

In an embodiment, the present invention provides a method of preparation of mixed tetra-ester compound also referred as LPG C-3 comprising steps of:
a. dissolving a mixture of para nitro benzoic acid, dicyclohexylcarbodimide and 10 mol% 4-(Dimethylamino) pyridine in dichloromethane by constant stirring at room temperature under inert atmosphere;
b. adding pentaerythritol dissolved in dichloromethane to the mixture of step (a) followed by stirring to obtain final mixture; and
c. separating the diester product from final mixture of step (b) followed by its purification;
d. dissolving a mixture of caprylic acid, dicyclohexylcarbodimide and 10 mol% 4-(Dimethylamino) pyridine in dichloromethane by constant stirring at room temperature under inert atmosphere;
e. adding pentaerythritol diester obtained in step (c) to the mixture of step (d) followed by stirring to obtain final mixture; and
f. separating the mixed tetraester product from final mixture of step (e) followed by its purification.
In another embodiment of the present invention, the stirring of the mixture of step (a) is carried out for 30 minutes; stirring of the mixture of step (b) is carried out for 24 hours; stirring of the mixture of step (d) is carried out for 30 minutes; and stirring of the mixture of step (e) is carried out for 24 hours.
In an embodiment, the present invention provides a process for the preparation of a homogenous catalyst doped LPG fuel, comprising steps of:
(a) mixing the homogeneous catalyst at room temperature in hexane to form a solution, wherein the homogeneous catalyst is selected from diester compound also referred as LPG C-1, tetra-ester compound also referred as LPG C-2 or mixed tetra-ester compound also referred as LPG C-3; and
(b) adding the solution of step (a) to liquefied petroleum gas (LPG) in a compressed gas cylinder.
In another embodiment of the present invention, the tetra-ester compound also referred as LPG C-2 is present in a concentration in the range of 100 to 400 ppm and mixed tetra-ester compound also referred as LPG C-3 is present in a concentration in the range of 100 to 400 ppm.
In another embodiment of the present invention, the catalyst is used in improving the Laminar Flame Velocity of LPG by up to 24%.

Examples
The present disclosure is further illustrated by reference to the following examples which is for illustrative purpose only and does not limit the scope of the disclosure in any way. These examples are not intended to be inclusive of all aspects of the subject matter disclosed herein, but rather to illustrate representative features, methods, compositions, and results. These examples are not intended to exclude equivalents and variations of the present disclosure, which are apparent to one skilled in the art.

Example 1. Synthesis of diester compound LPG C-1 .

Scheme 1

The diester compound (I), derived from pentaerythritol (PE), was synthesized through the esterification of p-Nitrobenzoic acid (PNB) in dichloromethane (DCM). This reaction employed N,N'-Dicyclohexylcarbodiimide (DCC) and 4-(Dimethylamino)pyridine (DMAP) as catalysts at room temperature. PNB (25 g, 0.15 mol), DCC (31 g, 0.15 mol), and 10 mol% DMAP were dissolved in 40 ml of DCM in a 100 ml two-neck round-bottom flask equipped with a magnetic stirrer, maintaining an inert nitrogen atmosphere. The mixture was stirred at room temperature for 30 minutes. Subsequently, 10 g of PE (0.073 mol) in 20 ml of DCM was added, and the reaction continued for 24 hours, with DCC facilitating the activation of benzoic acid via O-acylisourea intermediate formation. DMAP was crucial to prevent unwanted acyl migration byproduct formation, which could compete with the nucleophilic attack of PE alcohol on the O-acylisourea intermediate.

During the reaction, N,N'-dicyclohexylurea (DCU) was formed as a byproduct of the esterification process. To ensure full DCU precipitation, the reaction mixture was chilled in an ice bath. After separating the insoluble byproduct via suction filtration, the organic filtrate was treated with 2N HCl to eliminate DCC and DMAP. The organic layer was further washed with saturated NaHCO3 and brine solutions to neutralize excess acid. The product was then dried using anhydrous Na2SO4 and evaporated in a rotary evaporator.

The final product was purified through basic silica gel column chromatography using a hexane:ethyl acetate (3:1) eluent. After purification, the resulting eluent was evaporated using a rotary evaporator to obtain the final product. This synthesis method provides a comprehensive framework for the production of LPG C-1, with a focus on reaction conditions and purification steps.
Yield of the final product: 82%

Example 2. Synthesis of tetra ester compound LPG C-2 .

Scheme 2

Tetra-ester compound (LPG C-2) with PNB acid has been synthesized and purified based on the previous method (compound (I). In this reaction 4.7 eqv. PNB acid (78 g), 6 eqv. DCC (90 g) and 10 mol% DMAP (1 g) were mixed in 50 ml DCM. After 30 minutes 1 eqv. (13.6 g) PE was added and stirred the reaction for 24 hours at room temperature.
Work up are done as for example 1.
Yield of the final product: 76%

Example 3. Synthesis of mixed tetra ester compound LPG C-3 .

Scheme 3

Pentaerythritol diester, that is synthesized in scheme 1, was allowed to react with caprylic acid in 1:2 eqv ratio at room temperature to obtain the pentaerythritol mixed tetra-ester. In this reaction, 7.21 g caprylic acid (0.05 mol), 18.56 g DCC (0.09 mol) and 10 mol% DMAP were mixed in 40 ml DCM in a 100 ml two neck round-bottom flask equipped with a magnetic stirrer. The reaction mixture was stirred for 30 minutes at RT (room temperature) and N2 atmosphere inside the round bottom flask was maintained throughout the progress of reaction. After half an hour, required amount of pentaerythritol (PE) diester was added to the reaction mixture and was stirred for overnight at room temperature to get the final product, LPG C-3.
Work up & Purification: Same as for example 1.
Yield of the final product: 72 %

Example 4. Laminar Flame Velocity Measurement
Experimental Set Up:
In this experiment, the laminar flame velocity measurements of LPG (liquefied petroleum gas) and catalysts (LPG C-1, LPG C-2 and LPG C-3) are performed using an externally heated diverging channel (EHDC) method. The burning velocities are obtained at elevated temperatures (up to 600 K) at 1 atmospheric pressure for mixture equivalence ratios (?) of 0.8, 1 and 1.2. Diverging channel (of length 108 mm) is made of quartz and has inlet dimensions of 25 mm × 2 mm (aspect ratio of 12.5) with 10° divergence angle. This divergence decreases the mixture velocity along the flow direction and also facilitates in evading flame flashback. The high aspect ratio sustains the uniform flow field and planar flames, both being necessary criteria in defining the laminar flame velocity at different experimental conditions. The quartz material possesses desirable characteristics of high heat capacity, low thermal conductivity and wall transparency for the present experimental measurements.

An external infrared heater is placed 20 mm below the quartz channel to provide heat (to sustain adiabatic condition of the planar flame) and create a positive temperature gradient in the direction of fluid flow. An overlap distance of 30 mm is ensured between the heater and the channel. The horizontal alignment of the external heater is duly confirmed using a level indicator. The mass flow controllers (MFC) are operated at desired volumetric flow rate (in litres per minute) of fuel and air at a particular equivalence ratio. The gaseous fuels used are LPG, LPG C-1 and LPG C-2 with air being oxidizer. The MFC utilized for gaseous fuels (0-1 lpm) and air (0-5 lpm) was within an accuracy of ±1% of the full scale. The mass flow controller was controlled via computer using a command module system. K-type thermocouple was utilized to measure the temperature of channel’s inner wall with an accuracy of ±5 %. The final laminar flame velocity measurements include an uncertainty of ± 5%.

4.1. Experimental procedure
Before conducting the experiments, a settling time of 20 min is assigned to ensure uniform heating of the diverging channel. Once all the preliminary arrangements are put forth, ignition for fuel-air mixture is provided close to the channel outlet using an electric spark positioned above the channel. The other electrode (also earthed for safety) is positioned exactly below the electrode of the ignition transformer with a gap of 3-4 mm. Once the ignition is provided at the exit of the channel, a flame is established. The flame then propagates inside the channel, and it continues to propagate until a location is reached where incoming mixture velocity equals the mixture burning velocity, thus leading to the formation of a stabilized planar flame at this location. The position of a stabilized flame depends on incoming reactants velocity and external heat input which govern the temperature distribution in the channel. The stabilized flame image is captured using a DSLR camera and processed to measure the location. The capture area of the camera (and hence resolution) was calibrated with the physical dimensions on a measuring scale. Any uncertainty in this process stems from the uncertainty in the measurement of the measuring scale and has been accounted for in the mass balance based uncertainty calculations. For a fixed equivalence ratio, the external heat input and flow rate are varied to establish a planar flame inside the channel. The process is repeated similarly for other equivalence ratios. An unvarying velocity profile in the transverse direction subjected from a high aspect ratio of the channel and the channel divergence angle help to establish planar flames. The data retrieved from the stabilized planar flame location are then employed to determine the laminar flame velocity of the given fuel-air mixture. In this study, particularly planar flames are examined to evaluate the laminar burning velocities.
The laminar flame velocity (Su) is determined using the following modified mass conservation equation:

S_u=U_in×(A_in/A_f )(T_f/T_in ) (1)

where Ain and Uin represents the channel area and mixture velocity at inlet respectively, Tf and Af represents the unburnt mixture temperature and channel area at the flame position respectively, and Tin represents the inlet mixture temperature of the channel.

Result and discussion:
In order to improve flame velocity, all esters derivatives (di, tetra and mixed) of nitrobenzene were tested. In order to benchmark the results, p-nitrobenzoic acid was used as a control. The dosage rates of the catalysts were maintained at 300 ppm in LPG (W/V).

The laminar flame velocity measurements are reported using equation 1 for all fuel compositions. The measurements at Uin = 1 m/s are detailed in table 1. Af was calculated using the following equation:
Af=[2 X {x (Flame front distance from inlet).tan10°}mm +25 mm] X 2 mm
Table 1: Measurement of laminar flame velocity
Fuel Additive (in 300 ppm W/V in LPG) Distance from inlet, x (mm) Inlet
temperature, Tin (K) Mixture temperature, Tf (K) Channel Area, Af @Flame front (mm2) Laminar Flame Velocity, Su (m/s)
LPG Blank LPG 84 312 485 109.2368 0.71
2-Ethylhexyl-nitrate 84 312 488 109.2368 0.72
LPG C-1 88 312 545 112.0576 0.78
LPG C-2 82 288 509 107.8264 0.82
LPG C-3 85 288 541 109.942 0.85
*2-Ethylhexyl-nitrate is a cetane booster

It can be seen from the results, while p-nitro benzoic acid failed to produce any appreciable improvement in the LFV of LPG, the corresponding pentaerythritol esters have shown significant improvements. It was also demonstrated that tetra-ester compound LPG C-2 was significantly more efficient in increasing LFV compared to the mono-ester. However, LPG C-3, with fewer nitrobenzene units have shown best LFV improvement overall. This can presumably be attributed to the higher solubility of LPG C-3 in nonpolar propane/butane.

Furthermore, variation of LFV with varying concentration of additive was measured and shown in Table 2.

Table 2. Measurement of variation of LFV with varying concentration of catalyst.

Concentration of additive LPG C-2 (in ppm) Distance from inlet, x (mm) Inlet temperature, Tin (K) Mixture temperature, Tf (K) Channel Area, Af @Flame front (mm2) Laminar Flame Velocity, Su (m/s)

0 84 312 485 109.24 0.71
100 79 304 493 105.71 0.77
200 81 304 511 107.12 0.78
300 84 304 544 109.24 0.82
400 86 304 571 110.65 0.85
Concentration of additive LPG C-3(in ppm) Distance from inlet, x (mm) Inlet temperature, Tin (K) Mixture temperature, Tf (K) Channel Area, Af @Flame front (mm2) Laminar Flame Velocity, Su (m/s)

0 84 312 485 109.24 0.71
100 79 296 482 105.71 0.77
200 80 296 512 106.42 0.81
300 83 296 548 108.53 0.85
400 85 296 572 109.94 0.88

Since, LPG has lower volumetric efficiency compared to conventional gasoline, Combustion chambers typically have lower than stoichiometric (?=1) air to fuel ratio during combustion cycle. In order to simulate the real-life engine conditions and evaluate effect of temperature on the LFVs, the additized LPG (300 ppm) were also tested under different air-to fuel ratio and under different temperatures to examine the efficacy of the catalysts. The results are given in Table 3.

Table 3. Evaluation of catalysts under different ? and temperature
LPG with LPG C-2 (300 ppm)
Laminar Velocity (m/s) @different temperatures


Temperature Exponent, a
? (Air to Fuel Equivalence ratio) 300K (Su,0) 400 K 500 K 600 K
0.80 0.33 0.50 0.70 0.93 1.51
1.00 0.34 0.53 0.75 0.99 1.54
1.20 0.33 0.52 0.73 0.96 1.54
LPG with LPG C-3 (300 ppm)
Laminar Velocity (m/s) @different temperatures


? (Air to Fuel Equivalence ratio) 300K (Su,0) 400 K 500 K 600 K Temperature Exponent, a
0.80 0.33 0.51 0.72 0.94 1.52
1.00 0.35 0.54 0.77 1.02 1.55
1.20 0.34 0.53 0.75 0.99 1.54

Temperature exponents (a) were calculated from the fitting the data in the power-law, Su= {S u,0.( Tu/Tu,0 )}a . Higher temperature exponents indicate a greater increase in LFV with increase in temperature at a constant ?.

It was imperative to evaluate the performance of the additized LPG under actual field conditions. For this purpose, Dibenzoyl peroxide dosed LPG was tested in an extensive sea trial in two-stroke, two-cylinder Suzuki engine powered boats. The details are listed below in Table 4.

As can be seen from the data, additized LPG provided much better power output and much improved fuel efficiency compared to blank LPG. The performance is almost on par with gasoline. However, owing to the significantly higher H-C ratio of LPG (considering 1:1 C3/C4 ratio) compared to gasoline, considerable CO2 reduction (25.5%) can be achieved through replacing gasoline.
Table 4. Engine Tests
Engine details
Engine Specification: TWO STROKE 9.9 HP
Make YAMAHA / SUZUKI
Model 9.9 HP / DT9.9AK/DT15AK
Cylinder volume: 280 to 300 CC
No of Cylinders: 2
No of Strokes: 2
Engine Load 4000 RPM
Test Duration 100 hrs

Results
Parameter Blank LPG LPG C-3 dosed LPG (300 ppm) Gasoline (RON91)
Average Maximum Power Output 6.9 KW (9.9 PS) 7.1KW (9.9 PS) 7.2 KW (9.9 PS)
Average Fuel consumption/hr 7.9 7.6 7.3
Average CO2 emission/Litre of Fuel (Kg) 1.65 1.65 2.3
Average CO2 emission (Kg/hr) 13 12.5 16.8

A homogeneous catalyst based on esters of nitroaromatic additive was evaluated for LPG to improve its performance in outboard SI engines of fishing boats. The catalyst improves the Laminar Flame Velocities of LPG by almost 24%. This in turn improves the mean effective pressure in the cylinder during compression cycle translating in superior performance. During extensive sea trials the catalyst was shown to effectively bridge the performance gap between gasoline and LPG, both in terms of power output and fuel consumption that otherwise arises out of poor volumetric efficiencies. Most importantly, replacement of gasoline with LPG results in significant reduction of carbon footprint and a prominent step towards sustainability.
, Claims:1. A homogeneous catalyst for doping in LPG fuel of formula (1):
C(CH2OR1)2 (CH2OR2)2
(formula 1)
wherein:
R1 is selected from H, C6H4(NO2)CO-, or H3C-(CH2)5-CO-; and
R2 is C6H4(NO2)CO-.

2. The catalyst as claimed in claim 1, wherein the catalyst is a diester compound LPG C-1:

LPG C-1

3. The catalyst as claimed in claim 1, wherein the catalyst is a tetra-ester compound LPG C-2:

LPG C-2

4. The catalyst as claimed in claim 1, wherein the catalyst is a mixed tetra-ester compound LPG C-3:

LPG C-3

5. A method of preparation of compounds as defined in claims 2 and 3, comprising steps of:
a. dissolving a mixture of para nitro benzoic acid, dicyclohexylcarbodimide and 10 mol% 4-(Dimethylamino) pyridine in dichloromethane by constant stirring at room temperature under inert atmosphere;
b. adding pentaerythritol dissolved in dichloromethane to the mixture of step (a) followed by stirring to obtain final mixture; and
c. separating the diester product from final mixture of step (b) followed by its purification.

6. The method as claimed in claim 5, wherein 1:2 ratio of pentaerythritol: paranitrobenzoic acid is used for preparation of diester compound (I); and 1:4 ratio of pentaerythritol: paranitrobenzoic acid is used for preparation of tetra-ester compound LPG C-2.

7. The method as claimed in claim 5, wherein stirring of the mixture of step (a) is carried out for 30 minutes; and stirring of the mixture of step (b) is carried out for 24 hours.

8. A method of preparation of compound as defined in claim 4, comprising steps of:
a. dissolving a mixture of para nitro benzoic acid, dicyclohexylcarbodimide and 10 mol% 4-(Dimethylamino) pyridine in dichloromethane by constant stirring at room temperature under inert atmosphere;
b. adding pentaerythritol dissolved in dichloromethane to the mixture of step (a) followed by stirring to obtain final mixture; and
c. separating the diester product from final mixture of step (b) followed by its purification;
d. dissolving a mixture of caprylic acid, dicyclohexylcarbodimide and 10 mol% 4-(Dimethylamino) pyridine in dichloromethane by constant stirring at room temperature under inert atmosphere;
e. adding pentaerythritol diester obtained in step (c) to the mixture of step (d) followed by stirring to obtain final mixture; and
f. separating the mixed tetraester product from final mixture of step (e) followed by its purification.

9. The method as claimed in claim 8, wherein stirring of the mixture of step (a) is carried out for 30 minutes; stirring of the mixture of step (b) is carried out for 24 hours; stirring of the mixture of step (d) is carried out for 30 minutes; and stirring of the mixture of step (e) is carried out for 24 hours.

10. A process for the preparation of a homogenous catalyst doped LPG fuel, comprising steps of:
(a) mixing the homogeneous catalyst in hexane at room temperature to form a solution, wherein the homogeneous catalyst is selected from diester compound LPG C-1, tetra-ester compound LPG C-2 or mixed tetra-ester compound LPG C-3; and
(b) adding the solution of step (a) to liquefied petroleum gas (LPG) in a compressed gas cylinder.
11. The process as claimed in claim 10, wherein tetra-ester compound LPG C-2 is present in a concentration in the range of 100 to 400 ppm and mixed tetra-ester compound LPG C-3 is present in a concentration in the range of 100 to 400 ppm.

12. The catalyst as claimed in claim 1, for use in improving the Laminar Flame Velocity of LPG by up to 24%.