Title of Invention	"A PROCESS FOR OXIDATIVE DESULPHURIZATION OF LIQUID HYDROCARBON FUELS"
Abstract	The present invention provides a process for oxidative desulphurization of liquid hydrocarbon fuels, such as diesel fuel, gasoline, jet fuel, fuel oils, coal liquids and similar petroleum products to ultra low sulphur hydrocarbon fuels with sulphur content less than 10ppm. In this process, the sulfur compounds present in hydrocarbon fuel are first oxidised to more polar sulphones/sulphoxides and then removed by solvent extraction with NMP containing antisolvent followed by final polishing by passing through adsorption column.

Title of Invention

"A PROCESS FOR OXIDATIVE DESULPHURIZATION OF LIQUID HYDROCARBON FUELS"

Abstract

The present invention provides a process for oxidative desulphurization of liquid hydrocarbon fuels, such as diesel fuel, gasoline, jet fuel, fuel oils, coal liquids and similar petroleum products to ultra low sulphur hydrocarbon fuels with sulphur content less than 10ppm. In this process, the sulfur compounds present in hydrocarbon fuel are first oxidised to more polar sulphones/sulphoxides and then removed by solvent extraction with NMP containing antisolvent followed by final polishing by passing through adsorption column.

Full Text	FIELD OF THE INVENTION The present invention relates to a process for the desulphurization of liquid hydrocarbon fuels. Particularly the invention relates to a process for oxidative desulphurization of liquid hydrocarbon fuels such as diesel fuel, gasoline, jet fuel, fuel oils, coal liquids and similar petroleum products to ultra low sulphur hydrocarbon fuels with sulfur content less than 10 ppm. BACKGROUND OF THE INVENTION Because of their high energy densities and convenient physical form hydrocarbon fuel such as diesel fuel, gasoline, jet fuel, fuel oils and coal liquids are presently being consumed in vast quantities and their consumption continues to grow at alarming rates. Inevitably, this high consumption is having a major impact on the global environment. Most notably transport hydrocarbon fuels like diesel fuel, gasoline, jet fuels are receiving the highest scrutiny due to increased environmental concern. There is an increasing demand to reduce sulphur content in the hydrocarbon fuels to produce products, which have very low sulphur contents and are thereby marketable in the even more demanding market place. Conventionally hydrodesulphurization of hydrocarbon fuels which involves contacting of hydrogen with hydrocarbon streams in presence of catalysts at elevated temperature and pressure to convert sulphur compounds present therein to hydrogen sulfide is used to produce hydrocarbon fuels with lower sulphur content. Hydrodesulphurization can easily remove sulphur from several common classes of sulphur compounds such as sulphides, disulphides and thiols present in hydrocarbon fuels, because these are easily accessible to contact with hydrodesulphurization catalyst, however sulphur compounds like 4,6-dimethyldibenzothiophene (4,6-DMDBT) and others similar thiophene species are rigid to hydrodesulphurization and therefore are difficult to remove. Conventional hydrodesulphurization of diesel for example which operates at moderate temperatures (315-400 °C) and hydrogen pressure 3.0-9.0 MPa with Co/Mo/AI2O3 as catalyst can bring down their sulphur content 300-500ppm easily. However to bring down sulphur content further below 100ppm deep hydrodesulphurization of diesel requires very severe operating condition like the use of high temperature, high hydrogen pressure more active catalyst and long residence time. Deep hydrodesulphurization yield negative effects such as reduce catalyst life, high hydrogen consumption and high yield loss thereby resulting in higher operating cost. Apart from the cost involved the energy requirement for implementation of hydro processing technology also leads to increased level of CO2 emission from refinery itself. The US EPA has released new regulation that requires the sulphur content in the diesel fuel used in highway vehicle limited to 30ppm by 2005 and 15 ppm effective by 2006. Similarly in European country the sulphur content in the diesel fuel will be limited to 30-50 ppm by 2005. The necessity has therefore been felt for a process complementary to hydrodesulphurization to remove condensed thiophene, benzothiophene and dibenzothiophene type sulphur compounds present in hydrodesulphurized hydrocarbon fuel to yield ultra low hydrocarbon fuels. It is known that sulphur compound present in hydrocarbon fuels can be oxidized to sulphones, sulphoxides and subsequently removed by taking advantage of their different chemical and physical characteristics ( Tetsuo Aeda et. al., 20th American chemical society at San Diego California Mar 13-17 1994). US Pat No. 5958224 discloses a process for removal of refractory sulphur compounds from hydrotreater hydrocarbon stream by oxidizing them to sulphoxides and sulphones with peroxometal complexes like LMO(O2)2, where M is selected from the group consisting of Mo, W, Cr and L is alkyl phosphoric triamide like hexamethyl phosphoric triamide followed by adsorption on solid adsorbent like activated carbon, bauxite, clay, coke alumina or silica gel. The peroxometal complexes were prepared by reacting metal complexes with hydrogen peroxide. Collins et. al. (J.Mol. Catal A:Chem 117, (1977)397 ) reported their studies on oxidation of sulphur compounds present in gas oil with hydrogen peroxide using phosphotungstic acid as catalyst and subsequent removal of sulphones followed by solvent extraction using gamma- butyrolactone as solvent or by adsorption on silica gel to obtain ultra low sulphur gas oil. However large amounts of hydrogen peroxide were used for the oxidation of sulphur compounds present in gas oil. Mei et. al. ( Fuel 82(2003)405) reported their studies on ultrasound assisted oxidative desulphurization of diesel using hydrogen peroxide as oxidant, phosphotungstic acid as catalyst, methanol as solvent for extraction of sulphones and obtained 66.4% overall sulphur removal after 2.5 hr reaction. The sulphur removal efficiency could be improved to 91.8% by increasing the reaction time to 4 hours and using silica adsorption instead of solvent extraction to remove sulphones from diesel. U.S patent No: 6368495 discloses a process for oxidative desulfurization of petroleum fractions like gasoline, diesel fuel, kerosene which involves oxidation of thiophene and thiophene derivatives present in petroleum fraction to sulphones with alkyl hydroperoxide in presence of molybdenum on alumina as catalyst followed by decomposition of sulphones using catalyst like double layer hydroxides molecular sieves, inorganic metal oxides or a mixture thereof. Ishihara et al. (Applied Catalysis A: Gen 279(2005)279) reported oxidative desulfurization of desulfurized light gas oil with sulphur content 39 ppm involving oxidation of the sulphur compounds present therein with tert - butyl hydroperoxide in presence of 16 wt% MoO3/Al2O3 as catalyst followed by removal of the sulphones formed by adsorption over silica gel to obtain light gas oil with sulphur content less then 5 ppm. W O patent No: 2004029179 describes a process for oxidative desulfurization of hydrotreated hydrocarbon mixture boiling range 180 - 360°C containing less than 350 ppm thiophenic sulphur involving oxidation of sulfur compounds with organic peroxide in presence of a catalytic composition containing completely amorphous micro and /or mesoporous mixed oxide comprising a matrix selected from silica, alumina, ceria, magnesia and mixture thereof where in one or more metal oxides selected from transition metal oxides and group IV a metal oxides are uniformly dispersed followed by separation of the sulfur oxygenated products from the hydrocarbon mixture. Otsuki et al. (Energy & Fuels, 14 (2000) 1232) studied the oxidation of model sulfur compounds with a mixture of hydrogen peroxide and formic acid and found the reactivity of dibenzothiophene derivatives to increase with the increase of electron density. Thus the reactivity order for oxidation was found to be 4,6 -dimethyldibenzothiophene > 4 - methyl - dibenzothiophene > dibenzothiophene, whicsh is reverse to the order of reactivity for hydrodesulfurization. They further studied the oxidative desulfurization of light gas oil and vacuum gas oil using formic acid, hydrogen peroxide mixture as oxidant and N, N - dimethylformamide, acetonitrile, methanol, dimethylsulphoxide and sulpholane as solvents for extraction of sulphones. European patent No:0565324A1 describes a method for recovering organic sulfur compounds from liquid oil which involves oxidation of sulphur compounds present in liquid oil by mixture of a number of oxidants including formic acid and peroxide followed by removal of organic sulphones by adsorption on alumina or silica. W O patent No: 2005019386 discloses a process for desulphurization of hydrocarbonaceous oil which involves hydrodesulfurization to reduce sulphur level to a relatively low level then oxidation of sulphur compounds present in hydrodesulphurized hydrocarbonaceous oil to sulphones with an aqueous oxidizing solution like acetic acid, hydrogen peroxide mixture, decomposing residual oxidizing agent on supported transition metal and removal of sulphones by adsorption. U S patent No: 6402940 discloses a process for desulfurization of fuels such as diesel oil and similar products to reduce sulfur content to a range of from about 2 to 15ppm which involves oxidation of sulphur compounds present in fuels with a oxidizing/extracting solution of formic acid, a small amount of commercial hydrogen peroxide and preferably not more than 14wt% of water at slightly elevated temperature followed by separation of fuel from aqueous acid, flashed removal of residual acid water, neutralization of remaining acid with caustic solution or with anhydrous calcium oxide and removal of sulphones by adsorption on alumina. In our two pending patent applications we reported process for the oxidation of sulphur compounds present in liquid hydrocarbon fuels to sulphones with an oxidizing solution consisting of carboxylic acid such as formic acid, acetic acid, propionic acid, butyric acid containing 2 to 10 moles of urea hydrogen peroxide adduct or alkali metal peroxoborate like sodium, potassium, magnesium, calcium, barium or strontium peroxoborate per mole of sulphur. It is hitherto known that of carboxylic acid such as formic acid, acetic acid, propionic acid containing 2-10 moles of active oxygen containing species such as commercial 30/50% aqueous hydrogen peroxide, urea hydrogen peroxide adduct or alkali metal peroxoborate per mole of sulfur forms corresponding peracid which are powerful oxidants for oxidation of various types of sulphur compounds including 4,6- dimethyldibenzothiophene and other condensed thiophene derivatives which are most refractory in hydrodesulphurization, present in hydrocarbon fuels to their corresponding sulphones. It is also hitherto known that sulphones being more polar can be removed from liquid hydrocarbon fuels by solvent extraction using polar solvents like N, N -dimethylformamide, acetonitrile, methanol, dimethyl sulphoxide or sulpholane followed by final finishing by passing through alumina, silica, clay or by adsorption on alumina, silica to obtain ultra low sulphur (below 30 ppm) hydrocarbon fuels. In U S patent No: 6402940 oxidation of sulphur compounds present in hydrocarbon fuel is carried out with an oxidizing system consisting of a mixture of formic acid and aqueous hydrogen peroxide in a series of continuous stirred tank reactors (CSTR) followed by gravity separation of two phases in a settling tank. This type of system is not convenient for the handling of the bulk product like hydrocarbon fuel. Further this patent advocates the removal of oxidized sulphur compounds (sulphones, sulphoxides) from hydrocarbon fuel by adsorption on alumina in a packed bed column or circulating counter current fluidized alumina or mixer settler combination to obtain ultra low sulfur hydrocarbon fuel with sulphur content in the range 2-15 ppm. The removal of sulphones, sulphoxides from bulk oxidized hydrocarbon fuel by adsorption method will involve handling and regeneration of large amount of solid adsorbent and therefore is likely to be very inconvenient and practically difficult process. Further by using oxidative desulphurization process described in this U S patent No: 6402940, the cetane index of the hydrocarbon fuel which is a important characteristic of fuel like diesel can not be enhanced to an appreciable extent. N-Methylpyrrolidinone (NMP) a cyclic amine has excellent thermal stability is completely miscible with water in all proportions and can be handled in carbon, steel, nickel equipments. Although NMP has very high capacity but not high selectivity. However addition of antisolvent like water, ethylene glycol can increase the selectivity of NMP. In addition to selectivity the addition of water also decreases the boiling point of the solvent .NMP water mixture has been found to be the best solvent for dearomatization when raffinate is the product (E.Muller, Handbook of Solvent Extraction, Wiley Interscience 1983, p.523) and there are several commercial plants world over manufacturing Lube Oil Base Stocks (LOBS), Benzene, Toluene, Xylene (BTX); food grade hexane and special boiling point solvents by using NMP water mixture for solvent extraction of aromatics. However, incidentally, there are no literature report and use of NMP antisolvent like water mixture for solvent extraction/removal of sulphones/sulphoxides from oxidized hydrocarbon fuels. OBJECTS OF THE INVENTION The main object of the present invention is to provide a process for desulphurization of liquid hydrocarbon fuels which obviates the drawbacks as detailed above. Another object of the present invention is to provide a process for oxidative desulphurization of liquid hydrocarbon fuels such as diesel fuel, gasoline, jet fuel, fuel oil, coal liquid and similar petroleum products to ultra low sulphur hydrocarbon fuels with sulphur content less than 10 ppm. SUMMARY OF THE INVENTION Accordingly the present invention provides a process for the desulphurization of liquid hydrocarbon fuel which comprises oxidizing the sulphur compounds present in hydrocarbon fuel to polar sulphones/sulphoxides in a continuous counter current oxidation reactor by passing the said hydrocarbon fuel, as a continuous phase, and oxidizing solution containing carboxylic acid and active oxygen containing species, as a dispersed phase, at a temperature in the range 20-150 °C, at a pressure, atmospheric to 10 kg/cm2, with residence time of 2 to 60 minutes, washing of the oxidised diesel with alkaline water followed by extracting the above said resultant polar sulphones/sulphoxides with a mixture of N-methyl pyrrolidinone and about 2-20% anti solvent, in a continuous current column, at a temperature in the range of 20 to 80°C to obtain the extract phase containing 4 to 5 % hydrocarbons and a raffinate phase containing about 95% hydrocarbons, removing the solvent from the above said extract and raffinate phase by known method, followed by passing through a bed of alumina-silica or clay to obtain the desired sulphur free hydrocarbon fuel with 5-10 ppm sulfur. In an embodiment of the present invention the liquid hydrocarbon fuel includes diesel fuel, gasoline, jet fuel, fuel oil, coal liquids and similar petroleum products. In yet another embodiment the liquid hydrocarbon fuel used is untreated or hydrotreated containing thiophene, benzothiophene, dibenzothiophene type sulphur compounds which are refractory in nature in hydrodesulphurization (HDS), preferably hydrotreated liquid hydrocarbon fuels containing less than 500 ppm sulfur. In yet another embodiment the carboxylic acid used is selected from formic acid , acetic acid, propionic acid and butyric acid, preferably formic and acetic acid. In yet another embodiment the carboxylic acid used is 2 to 10 wt% of the hydrocarbon fuel. In yet another embodiment the active oxygen containing species used is selected from 30/50 wt% aqueous H2O2, alkali metal peroxoborate, urea hydrogen peroxide adduct, alkali and alkaline earth peroxide and alkali and alkaline earth hydroperoxide. In yet another embodiment the alkali metal peroxoborate used is selected from sodium, potassium, magnesium, calcium, barium, strontium peroxoborate. In yet another embodiment the alkali and alkaline earth peroxide used is selected from the group consisting of sodium, lithium, calcium, strontium, barium, magnesium and zinc peroxide. In yet another embodiment the alkali and alkaline earth hydroperoxide used is selected from potassium and sodium hydroperoxide. In yet another embodiment mole ratio of carboxylic acid to active oxygen containing species is in the range of 5:1 to 50:1, preferably 10:1 to 30:1. In yet another embodiment the use of continuous counter current oxidation reactor eliminate the need of settler as the settling zones are provided in the reactor itself. In yet another embodiment the active oxygen containing species used is preferably 2 to 5 mole times of the sulphur present in hydrocarbon fuel. A process as claimed in claim 1, wherein the oxidation of sulphur compounds present in hydrocarbon fuels is carried out preferably for 5 to 30 min residence time. In yet another embodiment the washing of the oxidized hydrocarbon fuel to remove residual carboxylic acid present is carried out water containing 0.1 to 10% alkali or alkaline earth metal oxides, hydroxide, carbonate or bicarbonate. In yet another embodiment the anti solvent used with NMP is selected from water, glycol and sulpholane, preferably water. In yet another embodiment the anti solvent used in a mixture with NMP is preferably in the range of 5 to 15 wt%. In yet another embodiment the recovery of NMP from NMP anti solvent mixture obtained as distillate is carried out by distillation of the solvent in drying column in the temperature range 80-250°C. In yet another embodiment the water is removed from carboxylic acid by distilling the overhead stream. In yet another embodiment the sulphones/sulphoxides adsorbed on alumina, silica, clay are removed by desorption and solubilization using polar solvent selected from the group consisting of methanol, acetone, acetonitrile preferably methanol. In still another embodiment the cetane index of the treated hydrocarbon fuel used is increased by 2-20 units. DETAILED DESCRIPTION OF THE INVENTION The present invention provides a process for oxidative desulphurization of liquid hydrocarbon fuels which comprises oxidation of sulphur compounds present in hydrocarbon fuels, to more polar sulphones/sulphoxides in a continuous counter current oxidation reactor in the temperature range 20-150°C with an oxidizing solution consisting of carboxylic acid containing 2 to 10 moles of active oxygen containing species, per mole of sulphur, washing of the oxidized diesel with alkaline water to remove carboxylic acid present followed by extraction of sulphones/sulphoxides in a counter current extractor with N-Methylpyrrolidinone antisolvent mixture, water washing to remove entrained NMP, drying through a salt filter and final finishing by passing through a bed of alumina/silica/clay. The liquid hydrocarbon fuels such as diesel fuel, gasoline, jet fuel, fuel oil, coal liquids and similar petroleum products may be both untreated or hydrotreated containing condensed thiophene, benzothiophene and dibenzothiophene type sulphur compounds which are refractory in nature in hydrodesulphurization (HDS) most preferably hydrodesulphurized diesel boiling range 167-376 °C containing 4,6-dimethyldibenzothiophene and other similar alkyldibenzothiophene sulphur compounds with total sulphur content less than 500 ppm. The use of continuous counter current oxidation reactor eliminates the need of settler as the settling zones are provided in the reactor itself and increases the efficiency of the oxidation process by providing highest concentration of the oxidant to the tail feed and optimum utilization of the oxidant. The present process is very common in the petroleum refining for various extraction processes like aromatic extraction for special boiling point solvent and production of benzene, toluene and xylenes. The active oxygen containing species used is selected from commercial aqueous hydrogen peroxide, alkali metal peroxoborate like sodium, potassium, magnesium, calcium, barium, strontium peroxoborate, urea hydrogen peroxide adduct, alkali and alkaline earth peroxide like sodium, lithium, calcium, strontium, barium, magnesium, zinc peroxide, alkali and alkaline earth hydrogen peroxide like potassium hydrogen peroxide preferably commercial aqueous hydrogen peroxide, sodium peroxoborate and urea hydrogen peroxide adduct. The final finishing of the diesel is carried out in adsorption column by passing diesel through a bed of adsorbent like alumina, silica, clay preferably nonactivated alumina.The sulphones/sulphoxides present in spent oxidized solution obtained from the continuous counter current oxidizer are separated from carboxylic acid and water by flashing. The present invention the invention as the consumption of active oxygen containing species is dependent upon the sulphur present in the hydrocarbon fuel and cost of this material can have a negative effect on the economics of the process. Therefore this process is most suitable for removal of small amounts of sulphur present in liquid hydrocarbon fuels preferably less than SOOppm sulphur. This process is capable of removing all types of sulphur such as thiols, disulphides, thiophenic from the liquid hydrocarbon fuel, the process is more suitable for liquid hydrocarbon fuel containing condensed thiophene, benzothiophene, dibenzothiophene and alkylated dibenzothiophene type sulphur which is refractory to hydrodesulphurization. MAIN ADVANTAGES OF THE PROCESS  The use of continuous counter current oxidation reactor eliminates the need of settler, as the settling zones are provided in the reactor itself and increases the efficiency of the oxidation process by providing highest concentration of the oxidant to the tail feed and optimum utilization of the oxidant.  The oxidation step increases the polarity of the sulfur compounds present in the hydrocarbon fuel leading to their selective extraction by N-methyl pyrrolidinone antisolvent mixture  The process describes the first time use of industrially proven N-methyl pyrrolidinone antisolvent mixture as solvent for extraction of sulphones/sulphoxides from oxidised hydrocarbon fuels with minimum extraction of aromatics  Extraction of sulphones/ sulphoxides from oxidised hydrocarbon fuels reduces handling and regeneration of large amounts of adsorbent making the process convenient and more feasible Cetane index of the hydrocarbon fuels used is increased by 2-20 units due to partial removal of aromatics in extraction. BRIEF DESCRIPTION OF THE DRAWING Fig 1 shows a schematic flow sheet of the process and the invention wherein the sulphur removal is accomplished by oxidation, extraction followed by final finishing through adsorption. This discussion is for the points of example only and it should not be taken to be a dedication or waiver of any other modification or alternatives of the process which remain unsubstantially different from that as described here or claimed. The sulphur containing hydrocarbon fuel for example HDS diesel fuel containing less than 500 ppm sulphur is introduced to the continuous counter current oxidation reactor B through line 1. The feed entering through line 1, if required is passed through the heat exchanger to bring the feed to desired temperature. The continuous counter current oxidation reactor B is a packed reactor filled with proper size rasig rings and the desired temperature is maintained by circulating suitable fluid at temperature slightly above the desired reaction temperature. The continuous counter current oxidation reactor B has the provision for feeding sulphur containing liquid hydrocarbon fuel near the bottom and oxidant solution from near the top with suitable compartments for separation of oxidized hydrocarbon fuel and the spent oxidizing solution containing oxidized sulphur compounds extracted from hydrocarbon fuel during oxidation, organic acid, unused active oxygen containing species, and water formed during the reaction and added along with the oxidant. The active oxygen containing species (oxidant) enter the admixing tank A through line 2 and the organic acid through line 3 . In case of the recovered organic acid , it enters the admixing tank A through the line 4 and the balance of the organic acid if required is added through the line 3. The oxidant solution thus turned is fed to counter current oxidation reactor B near the top of the reactor. The carboxylic acid used for the preparation of oxidant solution is selected from formic, acetic, propionic and butyric acids preferably formic acid, acetic acid. The active oxygen containing species used for preparation of oxidant solution is selected from commercial aqueous hydrogen peroxide, alkali metal peroxoborate, urea hydrogen peroxide adduct, and alkali, alkaline earth peroxide preferably commercial aqueous hydrogen peroxide, urea hydrogen peroxide adduct and sodium peroxoborate. The active oxygen containing species used is 2 - 10 mole times preferably 2-5 mole times of the sulphur present in hydrocarbon fuel. The oxidant solution fed to the reactor B is 2 to 10 wt% of the hydrocarbon fuel. The oxidation in the reactor B is carried out at temperature 20-150°C preferably 30 -100°C at atmospheric pressure. The contact time between the hydrocarbon and oxidant solution is between 5 to 30 minutes. As determined by GC-SCD there was quantitative oxidation of sulphur compounds present in liquid hydrocarbon fuel to sulphones. The oxidized hydrocarbon fuel with sulphur content somewhat less than its original feed goes out of continuous counter current oxidizer B through line 5 and the spent oxidant solution coming out of the reactor B through line 6 is recirculated directly to admixing tank A till the water content of the spent oxidant solution exceeds a limit. This spent oxidant solution after adding makeup carboxylic acid through line 3 and active oxygen containing species through line 2 is again fed to the oxidizer B. When the water content of spent oxidant solution coming out through line 6 exceeds a limit it is fed to the flash distillation column C where sulphones fraction extracted by the oxidant solution in the oxidation reactor B is separated through line 7. The sulphones fraction thus obtained can find its way into coker, hot asphalt stream or any other suitable stream. The overhead stream from the flash distillation column C exiting through line 8 is fed to azeotropic distillation column D where water is removed through overhead line 9 and the recovered carboxylic acid after passing through cooler is fed to admixing tank A through line 4. The oxidized hydrocarbon fuel coming out of oxidizer B through line 5 is fed to acid neutralization column E where the acidic impurities present in oxidizing hydrocarbon fuel are neutralized and removed by washing with alkaline water stream 11. The washed oxidized diesel coming out of column E through line 10 is then taken to continuous counter current extraction column F where the sulphones present in oxidized liquid hydrocarbon fuel along with come of the polycyclic aromatic hydrocarbons are extracted by NMP containing 5-15 wt% antisolvent like water, which is fed through line 12 in the temperature range 20 - 80 °C. The raffinate phase, low sulphur hydrocarbon fuel leaves the extractor F through line 13 and the extract phase coming out through line 14 is fed to solvent recovery column G. In the solvent recovery column G the sulphones and polycyclic aromatic hydrocarbon extracted by NMP antisolvent mixture are recovered by distillation in the temperature range 90 - 360 °C. The sulphones fraction thus obtained through line 16 can be mixed with other sulphones fractions and can find its way into coker, hot asphalt stream or any other suitable stream. The overhead solvent fraction containing NMP and antisolvent coming out of column G through line 15 is taken to solvent dehydration column H, where antisolvent like water is removed from NMP by distillation in the range 80 - 250°C . The recovered NMP coming out from the bottom of solvent dehydration column H is recycled to the extraction column F after adding suitable amount of antisolvent like water. Low sulphur liquid hydrocarbon fuel coming out from the extractor column F through line 13 is taken to low sulphur hydrocarbon fuel wash column I, where it is washed with water to remove the entrained NMP. The water phase containing NMP coming out of column I through line 19 is fed to solvent dehydration column H to recover NMP. The washed low sulphur hydrocarbon fuel coming out of column I through line 18 is taken to salt filter column J where water present in the low sulphur hydrocarbon fuel is removed in presence of dehydrating agents like calcium chloride, calcium oxide etc.. The dry low sulfur hydrocarbon fuel coming out of the salt filter column J through line 20 is passed through adsorption column column K where the small amount of oxidized sulphur compounds contained in dry low sulphur hydrocarbon fuel are removed by adsorption on nonactivated alumina, silica or clay preferably nonactivated alumina and ultra low sulphur hydrocarbon fuel with sulphur content The following examples are given by way of illustration and therefore should not be construed to limit the scope of this investigation. Examples: Studies were carried out by using HDS diesel obtained from two Indian refineries as feedstocks and their characteristics are given in table 1 Table 1 Characteristics of feedstocks (Table Removed) ND = not determined Example 1 A series of experiments were carried out to optimize the sulphur to oxidant mole ratio, carboxylic acid to hydrocarbon ratio and reaction time. All these experiments were carried out in a jacketed mixer settler equipped with mechanical stirrer, thermowell , neck for addition of reactant and drain valve. The temperature of the reactants was maintained at desired level by circulating hot fluid in the jacket of the mixer settler. In the general experimental procedure, HDS diesel feedstock (l)(100 ml,83.34 g) was added to the mixer settler and stirrer, hot fluid were started to keep the temperature of the reactant at 50°C. Desired amount of formic Acid (99 - 100%) was then added to the diesel followed by addition of fixed amount of 30% aqueous Hydrogen peroxide. The mixture was then stirred vigorously at 50°C for a certain period and then taken out in the separating funnel through drain valves. The two layers namely hydrocarbon layer and formic acid layer were then separated. The diesel layer was then washed with water, aqueous sodium bicarbonate and water to remove entrained formic acid. The washed diesel layer was then dried on anhydrous sodium sulfate and analysed by G C SCO to determine the extent of oxidation of sulphur compounds present in it to sulphones. The results of these experiments are presented in Table 2. From these experiments it was established that for carrying out oxidation of HDS diesel at 50°C by using mixture of formic acid, 30% aqueous hydrogen peroxide as oxidant. Table 2 Oxidation of HDS diesel feedstock (I) bv using formic acid 30% aqueous hydrogen peroxide mixture as oxidant. (Table Removed) In a mixer settler, the minimum requirements for quantitative oxidation of sulphur compounds present to sulphones are: reaction time about 10 min, oxidant(H2O2) to sulphur mole ratio about 5 and formic acid about 6% of the HDS diesel. Example 2 After establishing the reaction parameters in mixer settler, experiments were carried out on oxidative desulphurization using HDS diesel feedstock (I) as feed as per the scheme shown in figure 1 in a blockout mode. The general discussion regarding fig 1 is given in Detailed description of the process. The oxidation of HDS diesel feedstock (I) was carried out in continuous counter current oxidation column B by using diesel as continuous phase at a flow rate 0.59 kg/hr and formic acid , 30%aqueous hydrogen peroxide mixture at a flow rate 0.29kg/hr as disperse phase. The temperature of the continuous counter current oxidation column was maintained at70°C by passing hot water in the jacket of the column. The characteristics of the oxidized diesel obtained after acid neutralization column are given in table 3. As seen from the table 3 while there was no change in the cetane index of the HDS diesel after oxidation, the total sulphur present got reduced from 437 ppm to 365ppm due to the partial extraction of oxidized sulphur compounds from oxidized diesel into the spent oxidant solution. Also there was slight decrease in aromatic content from 24.5 to 23.2 wt% as determined by ASTM 2549 on oxidation of HDS diesel. Table 3 Characteristics of Oxidized Diesel feedstock (I) (Table Removed) The oxidized diesel thus obtained was extracted in the continuous counter current extraction column by using N - Methylpyrolidinone (NMP) containing 10% water as solvent at 50 °C at solvent to feed ratio ( S/F) = 1 and 2 and the data obtained are presented in table 4. Table 4 Continuous Counter Current Extraction Studies Feed: Oxidized Diesel Feedstock Solvent: NMP + 10% water Temperature: 50°C (Table Removed) The extract phases coming out of the extraction column F were found to contain 85.6 and 86.0 wt% solvent (NMP), 9.2 and 9.4 wt% water ,5.13 and 4.6 wt% hydrocarbons at S/F = 1 and S/F = 2 respectively. These extract phases were fed to solvent recovery and solvent drying columns to recover sulphone fractions and NMP as described in the "Detailed description of the process." The raffinate phases coming out of the extraction column F were found to contain 93.7 & 94.1 wt% of hydrocarbons, 6.3 & 5.9 wt% solvent NMP at S/F = 1 and S/F = 2 respectively. These phases were washed with water in the low sulphur diesel wash column I to remove entrained NMP and then subsequently dried by passing through salt filter column J containing anhydrous calcium chloride. The dried low sulphur diesel samples thus obtained were found to contain 42 & 24 ppm sulphur at S/F = 1 and S/F = 2 respectively and their cetane index were found to be 65.7 and 67.8 respectively. The dry low sulphur diesel samples thus obtained were polished by passing through adsorption column K filled with 6 to 20 mesh size silica gel. The ultra low sulphur diesel samples obtained from the adsorption column were found to contain 5 and 4 ppm total sulphur respectively, after the saturation of the adsorption column the diesel traped in the adsorbent was taken out by light naptha and the column was regenerated as described in " Detailed description of the process". Example 3 Oxidative desulfurization of HDS diesel from other refinery ( Feedstock ll)was carried out in the similar manner as described in the example 2 in a blockout mode. The oxidation of HDS diesel feedstock (II) was carried out in a continuous counter current oxidation column B by passing diesel as continuous phase at flow rate 0.59kg/hr. and formic acid , 30% aqueous hydrogen peroxide mixture at a flow rate 0.29kg/hr as discrete phase at 50 °C. The characteristics of the oxidised diesel obtained after and neutralization stepis given in Table-5 Table 5 Characteristics of Oxidized Diesel Feedstock(ll) (Table Removed) ND= not determined Again while there was no change in the cetane index of the HDS diesel after oxidation, the total sulphur got reduced from 541 ppm to 452 ppm due to partial extraction of the oxidized sulfur compounds from oxidized diesel into the spent oxidant solution. Also there was slight decrease in aromatic content from 27.4 to 26.2 an oxidation of HDS diesel. The oxidised diesel thus obtained was extracted in the continuous counter current extraction column by using NMP containing 10% water as solvent at 50°C at S/F 1&2 and the data obtained is presented in Table-6. The extract phases obtained from extraction column F were found to contain 85.71 & 86.33 wt% NMP, 9.25 and 9.26 wt% water, 5.02 and 4.41 wt % hydrocarbons at S/F 1 & 2 respectively. These extract phases were processed further to recover sulphone fraction and NMP as described in "Detailed description of the process". The raffinate phase obtained from the extraction column were found to contain 94.01 and 94.16 wt % hydrocarbons, 5.99 and 5.84 wt% NMP at S/F 1 & 2 respectively. These phases were washed with water in the low sulphur diesel wash column I to remove entrained NMP and then subsequently dried by passing through salt filter column J containing anhydrous calcium chloride. The dried low sulphur diesel samples thus obtained were found to contain 47 & 27 ppm total sulfur at S/F 1 & 2 respectively and their cetane index were found to be 63.2 and 64.8 respectively. Table 6 Continuous Counter Current Extraction Studies Feed: Oxidized Diesel Feedstock (II) Solvent: NMP + 10% water Temperature: 50°C (Table Removed) The dry low sulfur diesel samples thus obtained were polished by passing through adsorption column, filled with non-activated alumina. The ultra low sulphur diesel samples obtained from the adsorption column were found to contain 3 & 2 ppm sulfur respectively . After saturation of the adsorption column the diesel contained in it was recovered by displacement with light naphtha and the column was regenerated as described in "Detailed description of the process". commercial plants world over manufacturing Lube Oil Base Stocks (LOBS), Benzene, Toluene, Xylene (BTX); food grade hexane and special boiling point solvents by using NMP water mixture for solvent extraction of aromatics. However, incidentally, there are no literature report and use of NMP antisolvent like water mixture for solvent extraction/removal of sulphones/sulphoxides from oxidized hydrocarbon fuels. OBJECTS OF THE INVENTION The main object of the present invention is to provide a process for desulphurization of liquid hydrocarbon fuels which obviates the drawbacks as detailed above. Another object of the present invention is to provide a process for oxidative desulphurization of liquid hydrocarbon fuels such as diesel fuel, gasoline, jet fuel, fuel oil, coal liquid and similar petroleum products to ultra low sulphur hydrocarbon fuels with sulphur content less than 10 ppm. SUMMARY OF THE INVENTION Accordingly, the present invention provides We claim: 1. A process for the desulphurization of liquid hydrocarbon fuel which comprises; oxidizing the sulphur compounds present in hydrocarbon fuel to polar sulphones/sulphoxides in a continuous counter current oxidation reactor by passing the said hydrocarbon fuel, as a continuous phase, and oxidizing solution containing carboxylic acid and active oxygen containing species wherein mole ratio of carboxylic acid to active oxygen containing species is in the range of 5:1 to 50:1, as a dispersed phase, at a temperature in the range 20-150 °C, at a pressure atmospheric to 10 kg/cm2, with residence time 2 to 60 minutes, washing of the oxidised fuel with alkaline water followed by extracting the above said resultant polar sulphones/sulphoxides with a mixture of N-methyl pyrrolidone containing 2-20% anti solvent, in a continuous current column, at a temperature in the range of 20 to 80°C to obtain the extract phase containing 4 to 5 % hydrocarbons and a raffinate phase containing about 95% hydrocarbons, removing the solvent mixture from the above said extraction and raffinate phase by known method, followed by passing through a bed of alumina-silica or clay to obtain hydrocarbon fuel with 5-10 ppm sulfur. 2. A process as claimed in claim 1, wherein liquid hydrocarbon fuel includes diesel fuel, gasoline, jet fuel, fuel oil, coal liquids and similar petroleum products. 3. A process as claimed in claim 1, wherein liquid hydrocarbon fuel used is untreated or hydrotreated containing thiophene, benzothiophene, dibenzothiophene type sulphur compounds which are refractory in nature in hydrodesulphurization (HDS), preferably hydrotreated liquid hydrocarbon fuels containing less than 500 ppm sulfur. 4. A process as claimed in claim 1, wherein carboxylic acid used is selected from formic acid , acetic acid, propionic acid and butyric acid, preferably formic and acetic acid. 5. A process as claimed in claim 1, wherein carboxylic acid used is 2 to 10 wt% of the hydrocarbon fuel. 6. A process as claimed in claim 1, wherein the active oxygen containing species used is selected from 30/50 wt% aqueous H2O2, selected from alkali metal peroxoborate, alkali and alkaline earth peroxide, urea hydrogen peroxide adduct, and alkali and alkaline earth hydroperoxide. 7. A process as claimed in claim 6, wherein the alkali metal peroxoborate used is selected from sodium, potassium, magnesium, calcium, barium, strontium peroxoborate. 8. A process as claimed in claim 6, wherein the alkali and alkaline earth peroxide used is selected from the group consisting of sodium, lithium, calcium, strontium, barium, magnesium and zinc peroxide. 9. A process as claimed in claim 6, wherein the alkali and alkaline earth hydroperoxide used is selected from potassium and sodium hydroperoxide. 10. A process as claimed in claim 1, wherein mole ratio of carboxylic acid to active oxygen containing species is preferably in the range of 10:1 to 30:1. 11. A process as claimed in claim 1, wherein the use of continuous counter current oxidation reactor eliminate the need of settler as the settling zones are provided in the reactor itself. 12. A process as claimed in claim 1, wherein the active oxygen containing species used is preferably 2 to 5 mole times of the sulphur present in hydrocarbon fuel. 13. A process as claimed in claim 1, wherein the oxidation of sulphur compounds present in hydrocarbon fuels is carried out preferably for 5 to 30 min residence time. 14. A process as claimed in claim 1, wherein the washing of the oxidized hydrocarbon fuel to remove residual carboxylic acid present is carried out water containing 0.1 to 10% alkali or alkaline earth metal oxides, hydroxide, carbonate or bicarbonate. 15. A process as claimed in claim 1, wherein the anti solvent used with NMP is selected from water glycol and sulpholane, preferably water. 16. A process as claimed in claim 1, wherein the anti solvent used in a mixture with NMP is preferably in the range of 5 to 15 wt%. 17. A process as claimed in claim 1, wherein the recovery of NMP from NMP anti solvent mixture obtained as distillate is carried out by distillation of the solvent in drying column in the temperature range 80-250°C. 18. A process as claimed in claim 1, wherein water is removed from carboxylic acid by distilling the overhead stream. 19. A process as claimed in claim 1, wherein the sulphones/sulphoxides adsorbed on alumina, silica, clay are removed by desorption and solubilization using polar solvent selected from the group consisting of methanol, acetone, acetonitrile preferably methanol. 20. A process as claimed in claim 1, wherein the cetane index of the treated hydrocarbon fuel used is increased by 2-20 units.

Full Text

FIELD OF THE INVENTION
The present invention relates to a process for the desulphurization of liquid hydrocarbon fuels. Particularly the invention relates to a process for oxidative desulphurization of liquid hydrocarbon fuels such as diesel fuel, gasoline, jet fuel, fuel oils, coal liquids and similar petroleum products to ultra low sulphur hydrocarbon fuels with sulfur content less than 10 ppm.
BACKGROUND OF THE INVENTION
Because of their high energy densities and convenient physical form hydrocarbon fuel such as diesel fuel, gasoline, jet fuel, fuel oils and coal liquids are presently being consumed in vast quantities and their consumption continues to grow at alarming rates. Inevitably, this high consumption is having a major impact on the global environment. Most notably transport hydrocarbon fuels like diesel fuel, gasoline, jet fuels are receiving the highest scrutiny due to increased environmental concern. There is an increasing demand to reduce sulphur content in the hydrocarbon fuels to produce products, which have very low sulphur contents and are thereby marketable in the even more demanding market place.
Conventionally hydrodesulphurization of hydrocarbon fuels which involves contacting of hydrogen with hydrocarbon streams in presence of catalysts at elevated temperature and pressure to convert sulphur compounds present therein to hydrogen sulfide is used to produce hydrocarbon fuels with lower sulphur content. Hydrodesulphurization can easily remove sulphur from several common classes of sulphur compounds such as sulphides, disulphides and thiols present in hydrocarbon fuels, because these are easily accessible to contact with hydrodesulphurization catalyst, however sulphur compounds like 4,6-dimethyldibenzothiophene (4,6-DMDBT) and others similar thiophene species are rigid to hydrodesulphurization and therefore are difficult to remove. Conventional hydrodesulphurization of diesel for example which operates at moderate temperatures (315-400 °C) and hydrogen pressure 3.0-9.0 MPa with Co/Mo/AI2O3 as catalyst can bring down their sulphur content 300-500ppm easily. However to bring down sulphur content further below 100ppm deep hydrodesulphurization of diesel requires very severe operating condition like the use of high temperature, high hydrogen pressure more active catalyst and long residence time. Deep
hydrodesulphurization yield negative effects such as reduce catalyst life, high hydrogen consumption and high yield loss thereby resulting in higher operating cost. Apart from the cost involved the energy requirement for implementation of hydro processing technology also leads to increased level of CO2 emission from refinery itself. The US EPA has released new regulation that requires the sulphur content in the diesel fuel used in highway vehicle limited to 30ppm by 2005 and 15 ppm effective by 2006. Similarly in European country the sulphur content in the diesel fuel will be limited to 30-50 ppm by 2005. The necessity has therefore been felt for a process complementary to hydrodesulphurization to remove condensed thiophene, benzothiophene and dibenzothiophene type sulphur compounds present in hydrodesulphurized hydrocarbon fuel to yield ultra low hydrocarbon fuels.
It is known that sulphur compound present in hydrocarbon fuels can be oxidized to sulphones, sulphoxides and subsequently removed by taking advantage of their different chemical and physical characteristics ( Tetsuo Aeda et. al., 20th American chemical society at San Diego California Mar 13-17 1994). US Pat No. 5958224 discloses a process for removal of refractory sulphur compounds from hydrotreater hydrocarbon stream by oxidizing them to sulphoxides and sulphones with peroxometal complexes like LMO(O2)2, where M is selected from the group consisting of Mo, W, Cr and L is alkyl phosphoric triamide like hexamethyl phosphoric triamide followed by adsorption on solid adsorbent like activated carbon, bauxite, clay, coke alumina or silica gel. The peroxometal complexes were prepared by reacting metal complexes with hydrogen peroxide. Collins et. al. (J.Mol. Catal A:Chem 117, (1977)397 ) reported their studies on oxidation of sulphur compounds present in gas oil with hydrogen peroxide using phosphotungstic acid as catalyst and subsequent removal of sulphones followed by solvent extraction using gamma- butyrolactone as solvent or by adsorption on silica gel to obtain ultra low sulphur gas oil. However large amounts of hydrogen peroxide were used for the oxidation of sulphur compounds present in gas oil.
Mei et. al. ( Fuel 82(2003)405) reported their studies on ultrasound assisted oxidative desulphurization of diesel using hydrogen peroxide as oxidant, phosphotungstic acid as catalyst, methanol as solvent for extraction of sulphones and obtained 66.4% overall sulphur removal after 2.5 hr reaction. The sulphur
removal efficiency could be improved to 91.8% by increasing the reaction time to 4 hours and using silica adsorption instead of solvent extraction to remove sulphones from diesel.
U.S patent No: 6368495 discloses a process for oxidative desulfurization of petroleum fractions like gasoline, diesel fuel, kerosene which involves oxidation of thiophene and thiophene derivatives present in petroleum fraction to sulphones with alkyl hydroperoxide in presence of molybdenum on alumina as catalyst followed by decomposition of sulphones using catalyst like double layer hydroxides molecular sieves, inorganic metal oxides or a mixture thereof. Ishihara et al. (Applied Catalysis A: Gen 279(2005)279) reported oxidative desulfurization of desulfurized light gas oil with sulphur content 39 ppm involving oxidation of the sulphur compounds present therein with tert - butyl hydroperoxide in presence of 16 wt% MoO3/Al2O3 as catalyst followed by removal of the sulphones formed by adsorption over silica gel to obtain light gas oil with sulphur content less then 5 ppm.
W O patent No: 2004029179 describes a process for oxidative desulfurization of hydrotreated hydrocarbon mixture boiling range 180 - 360°C containing less than 350 ppm thiophenic sulphur involving oxidation of sulfur compounds with organic peroxide in presence of a catalytic composition containing completely amorphous micro and /or mesoporous mixed oxide comprising a matrix selected from silica, alumina, ceria, magnesia and mixture thereof where in one or more metal oxides selected from transition metal oxides and group IV a metal oxides are uniformly dispersed followed by separation of the sulfur oxygenated products from the hydrocarbon mixture.
Otsuki et al. (Energy & Fuels, 14 (2000) 1232) studied the oxidation of model sulfur compounds with a mixture of hydrogen peroxide and formic acid and found the reactivity of dibenzothiophene derivatives to increase with the increase of electron density. Thus the reactivity order for oxidation was found to be 4,6 -dimethyldibenzothiophene > 4 - methyl - dibenzothiophene > dibenzothiophene, whicsh is reverse to the order of reactivity for hydrodesulfurization. They further studied the oxidative desulfurization of light gas oil and vacuum gas oil using formic acid, hydrogen peroxide mixture as oxidant and N, N - dimethylformamide,
acetonitrile, methanol, dimethylsulphoxide and sulpholane as solvents for extraction of sulphones.
European patent No:0565324A1 describes a method for recovering organic sulfur compounds from liquid oil which involves oxidation of sulphur compounds present in liquid oil by mixture of a number of oxidants including formic acid and peroxide followed by removal of organic sulphones by adsorption on alumina or silica.
W O patent No: 2005019386 discloses a process for desulphurization of hydrocarbonaceous oil which involves hydrodesulfurization to reduce sulphur level to a relatively low level then oxidation of sulphur compounds present in hydrodesulphurized hydrocarbonaceous oil to sulphones with an aqueous oxidizing solution like acetic acid, hydrogen peroxide mixture, decomposing residual oxidizing agent on supported transition metal and removal of sulphones by adsorption.
U S patent No: 6402940 discloses a process for desulfurization of fuels such as diesel oil and similar products to reduce sulfur content to a range of from about 2 to 15ppm which involves oxidation of sulphur compounds present in fuels with a oxidizing/extracting solution of formic acid, a small amount of commercial hydrogen peroxide and preferably not more than 14wt% of water at slightly elevated temperature followed by separation of fuel from aqueous acid, flashed removal of residual acid water, neutralization of remaining acid with caustic solution or with anhydrous calcium oxide and removal of sulphones by adsorption on alumina. In our two pending patent applications we reported process for the oxidation of sulphur compounds present in liquid hydrocarbon fuels to sulphones with an oxidizing solution consisting of carboxylic acid such as formic acid, acetic acid, propionic acid, butyric acid containing 2 to 10 moles of urea hydrogen peroxide adduct or alkali metal peroxoborate like sodium, potassium, magnesium, calcium, barium or strontium peroxoborate per mole of sulphur.
It is hitherto known that of carboxylic acid such as formic acid, acetic acid, propionic acid containing 2-10 moles of active oxygen containing species such as commercial 30/50% aqueous hydrogen peroxide, urea hydrogen peroxide adduct or alkali metal peroxoborate per mole of sulfur forms corresponding peracid which are powerful oxidants for oxidation of various types of sulphur compounds including
4,6- dimethyldibenzothiophene and other condensed thiophene derivatives which are most refractory in hydrodesulphurization, present in hydrocarbon fuels to their corresponding sulphones.
It is also hitherto known that sulphones being more polar can be removed from liquid hydrocarbon fuels by solvent extraction using polar solvents like N, N -dimethylformamide, acetonitrile, methanol, dimethyl sulphoxide or sulpholane followed by final finishing by passing through alumina, silica, clay or by adsorption on alumina, silica to obtain ultra low sulphur (below 30 ppm) hydrocarbon fuels.
In U S patent No: 6402940 oxidation of sulphur compounds present in hydrocarbon fuel is carried out with an oxidizing system consisting of a mixture of formic acid and aqueous hydrogen peroxide in a series of continuous stirred tank reactors (CSTR) followed by gravity separation of two phases in a settling tank. This type of system is not convenient for the handling of the bulk product like hydrocarbon fuel. Further this patent advocates the removal of oxidized sulphur compounds (sulphones, sulphoxides) from hydrocarbon fuel by adsorption on alumina in a packed bed column or circulating counter current fluidized alumina or mixer settler combination to obtain ultra low sulfur hydrocarbon fuel with sulphur content in the range 2-15 ppm. The removal of sulphones, sulphoxides from bulk oxidized hydrocarbon fuel by adsorption method will involve handling and regeneration of large amount of solid adsorbent and therefore is likely to be very inconvenient and practically difficult process.
Further by using oxidative desulphurization process described in this U S patent No: 6402940, the cetane index of the hydrocarbon fuel which is a important characteristic of fuel like diesel can not be enhanced to an appreciable extent.
N-Methylpyrrolidinone (NMP) a cyclic amine has excellent thermal stability is completely miscible with water in all proportions and can be handled in carbon, steel, nickel equipments. Although NMP has very high capacity but not high selectivity. However addition of antisolvent like water, ethylene glycol can increase the selectivity of NMP. In addition to selectivity the addition of water also decreases the boiling point of the solvent .NMP water mixture has been found to be the best solvent for dearomatization when raffinate is the product (E.Muller, Handbook of Solvent Extraction, Wiley Interscience 1983, p.523) and there are several

commercial plants world over manufacturing Lube Oil Base Stocks (LOBS), Benzene, Toluene, Xylene (BTX); food grade hexane and special boiling point solvents by using NMP water mixture for solvent extraction of aromatics. However, incidentally, there are no literature report and use of NMP antisolvent like water mixture for solvent extraction/removal of sulphones/sulphoxides from oxidized hydrocarbon fuels.
OBJECTS OF THE INVENTION
The main object of the present invention is to provide a process for desulphurization of liquid hydrocarbon fuels which obviates the drawbacks as detailed above.
Another object of the present invention is to provide a process for oxidative desulphurization of liquid hydrocarbon fuels such as diesel fuel, gasoline, jet fuel, fuel oil, coal liquid and similar petroleum products to ultra low sulphur hydrocarbon fuels with sulphur content less than 10 ppm.
SUMMARY OF THE INVENTION
Accordingly the present invention provides a process for the desulphurization of liquid hydrocarbon fuel which comprises oxidizing the sulphur compounds present in hydrocarbon fuel to polar sulphones/sulphoxides in a continuous counter current oxidation reactor by passing the said hydrocarbon fuel, as a continuous phase, and oxidizing solution containing carboxylic acid and active oxygen containing species, as a dispersed phase, at a temperature in the range 20-150 °C, at a pressure, atmospheric to 10 kg/cm2, with residence time of 2 to 60 minutes, washing of the oxidised diesel with alkaline water followed by extracting the above said resultant polar sulphones/sulphoxides with a mixture of N-methyl pyrrolidinone and about 2-20% anti solvent, in a continuous current column, at a temperature in the range of 20 to 80°C to obtain the extract phase containing 4 to 5 % hydrocarbons and a raffinate phase containing about 95% hydrocarbons, removing the solvent from the above said extract and raffinate phase by known method, followed by passing through a bed of alumina-silica or clay to obtain the desired sulphur free hydrocarbon fuel with 5-10 ppm sulfur.
In an embodiment of the present invention the liquid hydrocarbon fuel includes diesel fuel, gasoline, jet fuel, fuel oil, coal liquids and similar petroleum products.
In yet another embodiment the liquid hydrocarbon fuel used is untreated or hydrotreated containing thiophene, benzothiophene, dibenzothiophene type sulphur compounds which are refractory in nature in hydrodesulphurization (HDS), preferably hydrotreated liquid hydrocarbon fuels containing less than 500 ppm sulfur.
In yet another embodiment the carboxylic acid used is selected from formic acid , acetic acid, propionic acid and butyric acid, preferably formic and acetic acid.
In yet another embodiment the carboxylic acid used is 2 to 10 wt% of the hydrocarbon fuel.
In yet another embodiment the active oxygen containing species used is selected from 30/50 wt% aqueous H2O2, alkali metal peroxoborate, urea hydrogen peroxide adduct, alkali and alkaline earth peroxide and alkali and alkaline earth hydroperoxide.
In yet another embodiment the alkali metal peroxoborate used is selected from sodium, potassium, magnesium, calcium, barium, strontium peroxoborate.
In yet another embodiment the alkali and alkaline earth peroxide used is selected from the group consisting of sodium, lithium, calcium, strontium, barium, magnesium and zinc peroxide.
In yet another embodiment the alkali and alkaline earth hydroperoxide used is selected from potassium and sodium hydroperoxide.
In yet another embodiment mole ratio of carboxylic acid to active oxygen containing species is in the range of 5:1 to 50:1, preferably 10:1 to 30:1.
In yet another embodiment the use of continuous counter current oxidation reactor eliminate the need of settler as the settling zones are provided in the reactor itself.
In yet another embodiment the active oxygen containing species used is preferably 2 to 5 mole times of the sulphur present in hydrocarbon fuel. A process as claimed in claim 1, wherein the oxidation of sulphur compounds present in hydrocarbon fuels is carried out preferably for 5 to 30 min residence time.

In yet another embodiment the washing of the oxidized hydrocarbon fuel to remove residual carboxylic acid present is carried out water containing 0.1 to 10% alkali or alkaline earth metal oxides, hydroxide, carbonate or bicarbonate.
In yet another embodiment the anti solvent used with NMP is selected from water, glycol and sulpholane, preferably water.
In yet another embodiment the anti solvent used in a mixture with NMP is preferably in the range of 5 to 15 wt%.
In yet another embodiment the recovery of NMP from NMP anti solvent mixture obtained as distillate is carried out by distillation of the solvent in drying column in the temperature range 80-250°C.
In yet another embodiment the water is removed from carboxylic acid by distilling the overhead stream.
In yet another embodiment the sulphones/sulphoxides adsorbed on alumina, silica, clay are removed by desorption and solubilization using polar solvent selected from the group consisting of methanol, acetone, acetonitrile preferably methanol.
In still another embodiment the cetane index of the treated hydrocarbon fuel used is increased by 2-20 units.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a process for oxidative desulphurization of liquid hydrocarbon fuels which comprises oxidation of sulphur compounds present in hydrocarbon fuels, to more polar sulphones/sulphoxides in a continuous counter current oxidation reactor in the temperature range 20-150°C with an oxidizing solution consisting of carboxylic acid containing 2 to 10 moles of active oxygen containing species, per mole of sulphur, washing of the oxidized diesel with alkaline water to remove carboxylic acid present followed by extraction of sulphones/sulphoxides in a counter current extractor with N-Methylpyrrolidinone antisolvent mixture, water washing to remove entrained NMP, drying through a salt filter and final finishing by passing through a bed of alumina/silica/clay. The liquid hydrocarbon fuels such as diesel fuel, gasoline, jet fuel, fuel oil, coal liquids and similar petroleum products may be both untreated or hydrotreated containing condensed thiophene, benzothiophene and dibenzothiophene type sulphur
compounds which are refractory in nature in hydrodesulphurization (HDS) most preferably hydrodesulphurized diesel boiling range 167-376 °C containing 4,6-dimethyldibenzothiophene and other similar alkyldibenzothiophene sulphur compounds with total sulphur content less than 500 ppm. The use of continuous counter current oxidation reactor eliminates the need of settler as the settling zones are provided in the reactor itself and increases the efficiency of the oxidation process by providing highest concentration of the oxidant to the tail feed and optimum utilization of the oxidant. The present process is very common in the petroleum refining for various extraction processes like aromatic extraction for special boiling point solvent and production of benzene, toluene and xylenes. The active oxygen containing species used is selected from commercial aqueous hydrogen peroxide, alkali metal peroxoborate like sodium, potassium, magnesium, calcium, barium, strontium peroxoborate, urea hydrogen peroxide adduct, alkali and alkaline earth peroxide like sodium, lithium, calcium, strontium, barium, magnesium, zinc peroxide, alkali and alkaline earth hydrogen peroxide like potassium hydrogen peroxide preferably commercial aqueous hydrogen peroxide, sodium peroxoborate and urea hydrogen peroxide adduct.
The final finishing of the diesel is carried out in adsorption column by passing diesel through a bed of adsorbent like alumina, silica, clay preferably nonactivated alumina.The sulphones/sulphoxides present in spent oxidized solution obtained from the continuous counter current oxidizer are separated from carboxylic acid and water by flashing. The present invention the invention as the consumption of active oxygen containing species is dependent upon the sulphur present in the hydrocarbon fuel and cost of this material can have a negative effect on the economics of the process. Therefore this process is most suitable for removal of small amounts of sulphur present in liquid hydrocarbon fuels preferably less than SOOppm sulphur. This process is capable of removing all types of sulphur such as thiols, disulphides, thiophenic from the liquid hydrocarbon fuel, the process is more suitable for liquid hydrocarbon fuel containing condensed thiophene, benzothiophene, dibenzothiophene and alkylated dibenzothiophene type sulphur which is refractory to hydrodesulphurization.
MAIN ADVANTAGES OF THE PROCESS
 The use of continuous counter current oxidation reactor eliminates the need
of settler, as the settling zones are provided in the reactor itself and
increases the efficiency of the oxidation process by providing highest
concentration of the oxidant to the tail feed and optimum utilization of the
oxidant.
 The oxidation step increases the polarity of the sulfur compounds present in
the hydrocarbon fuel leading to their selective extraction by N-methyl
pyrrolidinone antisolvent mixture
 The process describes the first time use of industrially proven N-methyl pyrrolidinone antisolvent mixture as solvent for extraction of sulphones/sulphoxides from oxidised hydrocarbon fuels with minimum extraction of aromatics
 Extraction of sulphones/ sulphoxides from oxidised hydrocarbon fuels reduces handling and regeneration of large amounts of adsorbent making the process convenient and more feasible
Cetane index of the hydrocarbon fuels used is increased by 2-20 units due to partial removal of aromatics in extraction.
BRIEF DESCRIPTION OF THE DRAWING
Fig 1 shows a schematic flow sheet of the process and the invention wherein the sulphur removal is accomplished by oxidation, extraction followed by final finishing through adsorption.
This discussion is for the points of example only and it should not be taken to be a dedication or waiver of any other modification or alternatives of the process which remain unsubstantially different from that as described here or claimed. The sulphur containing hydrocarbon fuel for example HDS diesel fuel containing less than 500 ppm sulphur is introduced to the continuous counter current oxidation reactor B through line 1. The feed entering through line 1, if required is passed through the heat exchanger to bring the feed to desired temperature. The continuous counter current oxidation reactor B is a packed reactor filled with proper size rasig rings and the desired temperature is maintained by circulating suitable
fluid at temperature slightly above the desired reaction temperature. The continuous counter current oxidation reactor B has the provision for feeding sulphur containing liquid hydrocarbon fuel near the bottom and oxidant solution from near the top with suitable compartments for separation of oxidized hydrocarbon fuel and the spent oxidizing solution containing oxidized sulphur compounds extracted from hydrocarbon fuel during oxidation, organic acid, unused active oxygen containing species, and water formed during the reaction and added along with the oxidant. The active oxygen containing species (oxidant) enter the admixing tank A through line 2 and the organic acid through line 3 . In case of the recovered organic acid , it enters the admixing tank A through the line 4 and the balance of the organic acid if required is added through the line 3. The oxidant solution thus turned is fed to counter current oxidation reactor B near the top of the reactor.
The carboxylic acid used for the preparation of oxidant solution is selected from formic, acetic, propionic and butyric acids preferably formic acid, acetic acid. The active oxygen containing species used for preparation of oxidant solution is selected from commercial aqueous hydrogen peroxide, alkali metal peroxoborate, urea hydrogen peroxide adduct, and alkali, alkaline earth peroxide preferably commercial aqueous hydrogen peroxide, urea hydrogen peroxide adduct and sodium peroxoborate. The active oxygen containing species used is 2 - 10 mole times preferably 2-5 mole times of the sulphur present in hydrocarbon fuel. The oxidant solution fed to the reactor B is 2 to 10 wt% of the hydrocarbon fuel. The oxidation in the reactor B is carried out at temperature 20-150°C preferably 30 -100°C at atmospheric pressure. The contact time between the hydrocarbon and oxidant solution is between 5 to 30 minutes. As determined by GC-SCD there was quantitative oxidation of sulphur compounds present in liquid hydrocarbon fuel to sulphones.
The oxidized hydrocarbon fuel with sulphur content somewhat less than its original feed goes out of continuous counter current oxidizer B through line 5 and the spent oxidant solution coming out of the reactor B through line 6 is recirculated directly to admixing tank A till the water content of the spent oxidant solution exceeds a limit. This spent oxidant solution after adding makeup carboxylic acid through line 3 and active oxygen containing species through line 2 is again fed to the oxidizer B. When the water content of spent oxidant solution coming out
through line 6 exceeds a limit it is fed to the flash distillation column C where sulphones fraction extracted by the oxidant solution in the oxidation reactor B is separated through line 7. The sulphones fraction thus obtained can find its way into coker, hot asphalt stream or any other suitable stream. The overhead stream from the flash distillation column C exiting through line 8 is fed to azeotropic distillation column D where water is removed through overhead line 9 and the recovered carboxylic acid after passing through cooler is fed to admixing tank A through line 4.
The oxidized hydrocarbon fuel coming out of oxidizer B through line 5 is fed to acid neutralization column E where the acidic impurities present in oxidizing hydrocarbon fuel are neutralized and removed by washing with alkaline water stream 11. The washed oxidized diesel coming out of column E through line 10 is then taken to continuous counter current extraction column F where the sulphones present in oxidized liquid hydrocarbon fuel along with come of the polycyclic aromatic hydrocarbons are extracted by NMP containing 5-15 wt% antisolvent like water, which is fed through line 12 in the temperature range 20 - 80 °C. The raffinate phase, low sulphur hydrocarbon fuel leaves the extractor F through line 13 and the extract phase coming out through line 14 is fed to solvent recovery column G. In the solvent recovery column G the sulphones and polycyclic aromatic hydrocarbon extracted by NMP antisolvent mixture are recovered by distillation in the temperature range 90 - 360 °C. The sulphones fraction thus obtained through line 16 can be mixed with other sulphones fractions and can find its way into coker, hot asphalt stream or any other suitable stream. The overhead solvent fraction containing NMP and antisolvent coming out of column G through line 15 is taken to solvent dehydration column H, where antisolvent like water is removed from NMP by distillation in the range 80 - 250°C . The recovered NMP coming out from the bottom of solvent dehydration column H is recycled to the extraction column F after adding suitable amount of antisolvent like water.
Low sulphur liquid hydrocarbon fuel coming out from the extractor column F through line 13 is taken to low sulphur hydrocarbon fuel wash column I, where it is washed with water to remove the entrained NMP. The water phase containing NMP coming out of column I through line 19 is fed to solvent dehydration column H to recover NMP. The washed low sulphur hydrocarbon fuel coming out of column I through line 18 is taken to salt filter column J where water
present in the low sulphur hydrocarbon fuel is removed in presence of dehydrating agents like calcium chloride, calcium oxide etc..
The dry low sulfur hydrocarbon fuel coming out of the salt filter column J through line 20 is passed through adsorption column column K where the small amount of oxidized sulphur compounds contained in dry low sulphur hydrocarbon fuel are removed by adsorption on nonactivated alumina, silica or clay preferably nonactivated alumina and ultra low sulphur hydrocarbon fuel with sulphur content The following examples are given by way of illustration and therefore should not be construed to limit the scope of this investigation.
Examples:
Studies were carried out by using HDS diesel obtained from two Indian refineries as feedstocks and their characteristics are given in table 1
Table 1
Characteristics of feedstocks
(Table Removed)
ND = not determined
Example 1
A series of experiments were carried out to optimize the sulphur to oxidant mole ratio, carboxylic acid to hydrocarbon ratio and reaction time. All these experiments were carried out in a jacketed mixer settler equipped with mechanical stirrer, thermowell , neck for addition of reactant and drain valve. The temperature of the reactants was maintained at desired level by circulating hot fluid in the jacket of the mixer settler. In the general experimental procedure, HDS diesel feedstock (l)(100 ml,83.34 g) was added to the mixer settler and stirrer, hot fluid were started to keep the temperature of the reactant at 50°C. Desired amount of formic Acid (99 - 100%) was then added to the diesel followed by addition of fixed amount of 30% aqueous Hydrogen peroxide. The mixture was then stirred vigorously at 50°C for a certain period and then taken out in the separating funnel through drain valves. The two layers namely hydrocarbon layer and formic acid layer were then separated. The diesel layer was then washed with water, aqueous sodium bicarbonate and water to remove entrained formic acid. The washed diesel layer was then dried on anhydrous sodium sulfate and analysed by G C SCO to determine the extent of oxidation of sulphur compounds present in it to sulphones. The results of these experiments are presented in Table 2. From these experiments it was established that for carrying out oxidation of HDS diesel at 50°C by using mixture of formic acid, 30% aqueous hydrogen peroxide as oxidant.
Table 2
Oxidation of HDS diesel feedstock (I) bv using formic acid 30% aqueous
hydrogen peroxide mixture as oxidant.
(Table Removed)
In a mixer settler, the minimum requirements for quantitative oxidation of sulphur compounds present to sulphones are: reaction time about 10 min, oxidant(H2O2) to sulphur mole ratio about 5 and formic acid about 6% of the HDS diesel.
Example 2
After establishing the reaction parameters in mixer settler, experiments were carried out on oxidative desulphurization using HDS diesel feedstock (I) as feed as per the scheme shown in figure 1 in a blockout mode. The general discussion regarding fig 1 is given in Detailed description of the process. The oxidation of HDS
diesel feedstock (I) was carried out in continuous counter current oxidation column B by using diesel as continuous phase at a flow rate 0.59 kg/hr and formic acid , 30%aqueous hydrogen peroxide mixture at a flow rate 0.29kg/hr as disperse phase. The temperature of the continuous counter current oxidation column was maintained at70°C by passing hot water in the jacket of the column. The characteristics of the oxidized diesel obtained after acid neutralization column are given in table 3. As seen from the table 3 while there was no change in the cetane index of the HDS diesel after oxidation, the total sulphur present got reduced from 437 ppm to 365ppm due to the partial extraction of oxidized sulphur compounds from oxidized diesel into the spent oxidant solution. Also there was slight decrease in aromatic content from 24.5 to 23.2 wt% as determined by ASTM 2549 on oxidation of HDS diesel. Table 3
Characteristics of Oxidized Diesel feedstock (I)
(Table Removed)
The oxidized diesel thus obtained was extracted in the continuous counter current extraction column by using N - Methylpyrolidinone (NMP) containing 10% water as solvent at 50 °C at solvent to feed ratio ( S/F) = 1 and 2 and the data obtained are presented in table 4.
Table 4
Continuous Counter Current Extraction Studies
Feed: Oxidized Diesel Feedstock
Solvent: NMP + 10% water Temperature: 50°C
(Table Removed) The extract phases coming out of the extraction column F were found to contain 85.6 and 86.0 wt% solvent (NMP), 9.2 and 9.4 wt% water ,5.13 and 4.6 wt% hydrocarbons at S/F = 1 and S/F = 2 respectively. These extract phases were fed to solvent recovery and solvent drying columns to recover sulphone fractions and NMP as described in the "Detailed description of the process."
The raffinate phases coming out of the extraction column F were found to contain 93.7 & 94.1 wt% of hydrocarbons, 6.3 & 5.9 wt% solvent NMP at S/F = 1 and S/F = 2 respectively. These phases were washed with water in the low sulphur diesel wash column I to remove entrained NMP and then subsequently dried by
passing through salt filter column J containing anhydrous calcium chloride. The dried low sulphur diesel samples thus obtained were found to contain 42 & 24 ppm sulphur at S/F = 1 and S/F = 2 respectively and their cetane index were found to be 65.7 and 67.8 respectively.
The dry low sulphur diesel samples thus obtained were polished by passing through adsorption column K filled with 6 to 20 mesh size silica gel. The ultra low sulphur diesel samples obtained from the adsorption column were found to contain 5 and 4 ppm total sulphur respectively, after the saturation of the adsorption column the diesel traped in the adsorbent was taken out by light naptha and the column was regenerated as described in " Detailed description of the process". Example 3
Oxidative desulfurization of HDS diesel from other refinery ( Feedstock ll)was carried out in the similar manner as described in the example 2 in a blockout mode. The oxidation of HDS diesel feedstock (II) was carried out in a continuous counter current oxidation column B by passing diesel as continuous phase at flow rate 0.59kg/hr. and formic acid , 30% aqueous hydrogen peroxide mixture at a flow rate 0.29kg/hr as discrete phase at 50 °C. The characteristics of the oxidised diesel obtained after and neutralization stepis given in Table-5
Table 5
Characteristics of Oxidized Diesel Feedstock(ll)
(Table Removed)
ND= not determined
Again while there was no change in the cetane index of the HDS diesel after oxidation, the total sulphur got reduced from 541 ppm to 452 ppm due to partial extraction of the oxidized sulfur compounds from oxidized diesel into the spent oxidant solution. Also there was slight decrease in aromatic content from 27.4 to 26.2 an oxidation of HDS diesel.
The oxidised diesel thus obtained was extracted in the continuous counter current extraction column by using NMP containing 10% water as solvent at 50°C at S/F 1&2 and the data obtained is presented in Table-6.
The extract phases obtained from extraction column F were found to contain 85.71 & 86.33 wt% NMP, 9.25 and 9.26 wt% water, 5.02 and 4.41 wt % hydrocarbons at S/F 1 & 2 respectively. These extract phases were processed further to recover sulphone fraction and NMP as described in "Detailed description of the process".
The raffinate phase obtained from the extraction column were found to contain 94.01 and 94.16 wt % hydrocarbons, 5.99 and 5.84 wt% NMP at S/F 1 & 2 respectively. These phases were washed with water in the low sulphur diesel wash
column I to remove entrained NMP and then subsequently dried by passing through salt filter column J containing anhydrous calcium chloride. The dried low sulphur diesel samples thus obtained were found to contain 47 & 27 ppm total sulfur at S/F 1 & 2 respectively and their cetane index were found to be 63.2 and 64.8 respectively.
Table 6
Continuous Counter Current Extraction Studies
Feed: Oxidized Diesel Feedstock (II)
Solvent: NMP + 10% water
Temperature: 50°C
(Table Removed)
The dry low sulfur diesel samples thus obtained were polished by passing through adsorption column, filled with non-activated alumina. The ultra low sulphur diesel samples obtained from the adsorption column were found to contain 3 & 2 ppm sulfur respectively . After saturation of the adsorption column the diesel contained in it was recovered by displacement with light naphtha and the column was regenerated as described in "Detailed description of the process".
commercial plants world over manufacturing Lube Oil Base Stocks (LOBS), Benzene, Toluene, Xylene (BTX); food grade hexane and special boiling point solvents by using NMP water mixture for solvent extraction of aromatics. However, incidentally, there are no literature report and use of NMP antisolvent like water mixture for solvent extraction/removal of sulphones/sulphoxides from oxidized hydrocarbon fuels. OBJECTS OF THE INVENTION
The main object of the present invention is to provide a process for desulphurization of liquid hydrocarbon fuels which obviates the drawbacks as detailed above.
Another object of the present invention is to provide a process for oxidative desulphurization of liquid hydrocarbon fuels such as diesel fuel, gasoline, jet fuel, fuel oil, coal liquid and similar petroleum products to ultra low sulphur hydrocarbon fuels with sulphur content less than 10 ppm.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides

We claim:
1. A process for the desulphurization of liquid hydrocarbon fuel which comprises; oxidizing the sulphur compounds present in hydrocarbon fuel to polar sulphones/sulphoxides in a continuous counter current oxidation reactor by passing the said hydrocarbon fuel, as a continuous phase, and oxidizing solution containing carboxylic acid and active oxygen containing species wherein mole ratio of carboxylic acid to active oxygen containing species is in the range of 5:1 to 50:1, as a dispersed phase, at a temperature in the range 20-150 °C, at a pressure atmospheric to 10 kg/cm2, with residence time 2 to 60 minutes, washing of the oxidised fuel with alkaline water followed by extracting the above said resultant polar sulphones/sulphoxides with a mixture of N-methyl pyrrolidone containing 2-20% anti solvent, in a continuous current column, at a temperature in the range of 20 to 80°C to obtain the extract phase containing 4 to 5 % hydrocarbons and a raffinate phase containing about 95% hydrocarbons, removing the solvent mixture from the above said extraction and raffinate phase by known method, followed by passing through a bed of alumina-silica or clay to obtain hydrocarbon fuel with 5-10 ppm sulfur.
2. A process as claimed in claim 1, wherein liquid hydrocarbon fuel includes diesel fuel, gasoline, jet fuel, fuel oil, coal liquids and similar petroleum products.
3. A process as claimed in claim 1, wherein liquid hydrocarbon fuel used is untreated or hydrotreated containing thiophene, benzothiophene, dibenzothiophene type sulphur compounds which are refractory in nature in hydrodesulphurization (HDS), preferably hydrotreated liquid hydrocarbon fuels containing less than 500 ppm sulfur.
4. A process as claimed in claim 1, wherein carboxylic acid used is selected from formic acid , acetic acid, propionic acid and butyric acid, preferably formic and acetic acid.
5. A process as claimed in claim 1, wherein carboxylic acid used is 2 to 10 wt% of the hydrocarbon fuel.
6. A process as claimed in claim 1, wherein the active oxygen containing species used is selected from 30/50 wt% aqueous H2O2, selected from alkali metal peroxoborate, alkali and alkaline earth peroxide, urea hydrogen peroxide adduct, and alkali and alkaline earth hydroperoxide.
7. A process as claimed in claim 6, wherein the alkali metal peroxoborate used is selected from sodium, potassium, magnesium, calcium, barium, strontium peroxoborate.
8. A process as claimed in claim 6, wherein the alkali and alkaline earth peroxide used is selected from the group consisting of sodium, lithium, calcium, strontium, barium, magnesium and zinc peroxide.
9. A process as claimed in claim 6, wherein the alkali and alkaline earth hydroperoxide used is selected from potassium and sodium hydroperoxide.
10. A process as claimed in claim 1, wherein mole ratio of carboxylic acid to active oxygen containing species is preferably in the range of 10:1 to 30:1.
11. A process as claimed in claim 1, wherein the use of continuous counter current oxidation reactor eliminate the need of settler as the settling zones are provided in the reactor itself.
12. A process as claimed in claim 1, wherein the active oxygen containing species used is preferably 2 to 5 mole times of the sulphur present in hydrocarbon fuel.
13. A process as claimed in claim 1, wherein the oxidation of sulphur compounds present in hydrocarbon fuels is carried out preferably for 5 to 30 min residence time.
14. A process as claimed in claim 1, wherein the washing of the oxidized hydrocarbon fuel to remove residual carboxylic acid present is carried out water containing 0.1 to 10% alkali or alkaline earth metal oxides, hydroxide, carbonate or bicarbonate.
15. A process as claimed in claim 1, wherein the anti solvent used with NMP is selected from water glycol and sulpholane, preferably water.
16. A process as claimed in claim 1, wherein the anti solvent used in a mixture with NMP is preferably in the range of 5 to 15 wt%.
17. A process as claimed in claim 1, wherein the recovery of NMP from NMP anti solvent mixture obtained as distillate is carried out by distillation of the solvent in drying column in the temperature range 80-250°C.
18. A process as claimed in claim 1, wherein water is removed from carboxylic acid by distilling the overhead stream.
19. A process as claimed in claim 1, wherein the sulphones/sulphoxides adsorbed on alumina, silica, clay are removed by desorption and solubilization using polar solvent selected from the group consisting of methanol, acetone, acetonitrile preferably methanol.
20. A process as claimed in claim 1, wherein the cetane index of the treated hydrocarbon fuel used is increased by 2-20 units.

Documents:

1891-del-2005-abstract.pdf

1891-DEL-2005-Claims-(10-01-2012).pdf

1891-del-2005-claims.pdf

1891-DEL-2005-Correspondence Others-(10-01-2012).pdf

1891-DEL-2005-Correspondence Others-(19-01-2012).pdf

1891-del-2005-correspondence-others.pdf

1891-DEL-2005-Description (Complete)-(10-01-2012).pdf

1891-DEL-2005-Description (Complete).pdf

1891-del-2005-description (provisional).pdf

1891-del-2005-drawigns.pdf

1891-del-2005-form-1.pdf

1891-del-2005-form-18.pdf

1891-del-2005-form-2.pdf

1891-DEL-2005-Form-3-(10-01-2012).pdf

1891-del-2005-form-3.pdf

1891-del-2005-form-5.pdf

1891-DEL-2005-Petition-137-(19-01-2012).pdf

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Patent Number

251607

Indian Patent Application Number

1891/DEL/2005

PG Journal Number

13/2012

Publication Date

30-Mar-2012

Grant Date

26-Mar-2012

Date of Filing

20-Jul-2005

Name of Patentee

COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH

Applicant Address

ANUSANDHAN BHAWAN, RAFI MARG, NEW DELHI - 110001, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	GARG MADHUKAR ONKARNATH	INDIAN INSTITUTE OF PETROLEUM, MOHKAMPUT, DEHRADUM 248005, UTTRANCHAL, INDIA
2	BIR SAIN	INDIAN INSTITUTE OF PETROLEUM, MOHKAMPUT, DEHRADUM 248005, UTTRANCHAL, INDIA
3	KHANNA MOHAN KRISHAN	INDIAN INSTITUTE OF PETROLEUM, MOHKAMPUT, DEHRADUM 248005, UTTRANCHAL, INDIA
4	NAUTIYAL BHAGAT RAM	INDIAN INSTITUTE OF PETROLEUM, MOHKAMPUT, DEHRADUM 248005, UTTRANCHAL, INDIA
5	NANOTI SHRIKANT MADHUSUDAN	INDIAN INSTITUTE OF PETROLEUM, MOHKAMPUT, DEHRADUM 248005, UTTRANCHAL, INDIA
6	TUMULA VENKATESHWAR RAO	INDIAN INSTITUTE OF PETROLEUM, MOHKAMPUT, DEHRADUM 248005, UTTRANCHAL, INDIA
7	DHARAM PAUL	INDIAN INSTITUTE OF PETROLEUM, MOHKAMPUT, DEHRADUM 248005, UTTRANCHAL, INDIA
8	SHARMA YOGENDRA KUMAR	INDIAN INSTITUTE OF PETROLEUM, MOHKAMPUT, DEHRADUM 248005, UTTRANCHAL, INDIA
9	DAS GAUTAM	INDIAN INSTITUTE OF PETROLEUM, MOHKAMPUT, DEHRADUM 248005, UTTRANCHAL, INDIA
10	SINGH JASVINDER	INDIAN INSTITUTE OF PETROLEUM, MOHKAMPUT, DEHRADUM 248005, UTTRANCHAL, INDIA
11	SHARMA CHANDRA DUTT	INDIAN INSTITUTE OF PETROLEUM, MOHKAMPUT, DEHRADUM 248005, UTTRANCHAL, INDIA
12	BASANT KUMAR	INDIAN INSTITUTE OF PETROLEUM, MOHKAMPUT, DEHRADUM 248005, UTTRANCHAL, INDIA
13	GUPTA ASHOK KUMAR	INDIAN INSTITUTE OF PETROLEUM, MOHKAMPUT, DEHRADUM 248005, UTTRANCHAL, INDIA

PCT International Classification Number

C10G

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA