Process for desulphurisation 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 10 ppm. 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.

1 . A process for oxidative desulphurization of liquid hydrocarbon fuel comprising the steps of: 
 (a) treating hydrocarbon fuel with an oxiding solution consisting of a mixture of oxygen containing species and an organosulphonic or carboxylic acid to oxidize sulphur compound(s) present therein to corresponding sulphones or sulphoxides, wherein the oxidizing agent is used in an amount in the range of 2-10 mole times of sulphur present in hydrocarbon fuel, and separating treated hydrocarbon fuel from the oxidizing solution;    (b) washing separated hydrocarbon fuel obtained in step (a) with water to remove sulphones or sulphoxides therefrom, and extracting the sulphones from hydrocarbon fuels to obtain desulphurised liquid hydrocarbon fuel.    
   
   
       2 . A process as claimed in  claim 1 , wherein step (a) is carried out at a temperature in the range 20-150° C., at a pressure in the range of atmospheric to 10 kg/cm 2 , and for a period of 2 to 60 min in a batch manner.  
   
   
       3 . A process as claimed in  claim 1 , wherein the sulphones/sulphoxides are removed from the hydrocarbon fuel in step (b) by solvent extraction.  
   
   
       4 . A process as claimed in  claim 1 , wherein in step (a) the carboxylic acid used is selected from the group consisting of formic acid, acetic acid, propionic acid and butyric acid, containing 2 to 10 moles of urea hydrogen peroxide adduct or alkali metal peroxoborate selected from the group consisting of sodium, potassium, magnesium, calcium, barium and strontium peroxoborate, per mole of sulphur to oxidize sulphur compounds to sulphones.  
   
   
       5 . A process as claimed in  claim 1 , wherein the sulphur compounds are oxidized to polar sulphones/sulphoxides in a continuous counter current oxidation reactor by passing the 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 of 20-150° C., at a pressure in the range of atmospheric to 10 kg/cm 2 , with residence time of 2 to 60 minutes, washing oxidised fuel with alkaline water followed by extracting resulting polar sulphones/sulphoxides with a mixture of N-methyl pyrrolidinone and 2-20% anti solvent in a continuous current column, at a temperature in the range of 20 to 80° C. to obtain an extract phase containing 4 to 5% hydrocarbons and a raffinate phase containing about 95% hydrocarbons, removing solvent from the extract phase and raffinate phase, followed by passing through a bed of alumina-silica or clay to obtain the desired sulphur free hydrocarbon fuel with 5-10 ppm sulfur.  
   
   
       6 . A process as claimed in  claim 1 , wherein the liquid hydrocarbon fuel is selected from the group consisting of diesel fuel, gasoline, jet fuel, fuel oil, coal liquids and similar petroleum products.  
   
   
       7 . A process as claimed in  claim 1 , wherein the liquid hydrocarbon fuel comprises untreated or hydrotreated liquid hydrocarbon fuel 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.  
   
   
       8 . A process as claimed in  claim 1 , wherein the carboxylic acid used is selected from formic acid, acetic acid, propionic acid and butyric acid.  
   
   
       9 . A process as claimed in  claim 1 , wherein the carboxylic acid used is 2 to 10 wt % of the hydrocarbon fuel.  
   
   
       10 . A process as claimed in  claim 1 , wherein the organosulphonic acid used is selected from the group consisting of p-toluenesulphonic acid, benzenesulphonic acid, methanesulphonic acid, trifluoromethane sulphonic acid and 3-nitrobenzene sulphonic acid.  
   
   
       11 . A process as claimed in  claim 1 , wherein the organosulphonic acid is used as organic solution in an organic solvent.  
   
   
       12 . A process as claimed in  claim 11 , wherein the organic solvent used is selected from acetonitrile and N-methylpyrrolidinone.  
   
   
       13 . A process as claimed in  claim 1 , wherein the oxidizing solution consists of organosulphonic or carboxylic acid and an oxygen containing species and is in the range of 3-5 mole times of sulphur present in hydrocarbon fuel.  
   
   
       14 . A process as claimed in  claim 1 , wherein the temperature in oxidation of sulphur compound present in hydrocarbon fuel is in the range of 30-100° C.  
   
   
       15 . A process as claimed in  claim 4 , wherein the water content of the oxidizing solution containing carboxylic acid and alkali metal peroxoborate is in the range 0-14%.  
   
   
       16 . A process as claimed in  claim 4 , wherein the mole ratio of carboxylic acid or organosulphonic acid to alkali metal peroxoborate used in the oxidizing solution is in the range of 5:1 to 50:1.  
   
   
       17 . A process as claimed in  claim 4 , wherein the mole ratio of carboxylic acid or organosulphonic acid to alkali metal peroxoborate used in the oxidizing solution is in the range of 10:1 to 30:1.  
   
   
       18 . A process as claimed in  claim 1 , wherein the reaction time for oxidation of sulphur compounds present in hydrocarbon fuel is in the range of 7 to 20 minutes.  
   
   
       19 . A process as claimed in  claim 1 , wherein the solvent used for extraction of sulphones/sulphoxides from oxidized hydrocarbon fuel is selected from the group consisting of N,N-dimethylformamide, acetonitrile, methanol, dimethylsulfoxide, sulpholane, and N-methylpyrolidinone containing 2-20% water as antisolvent.  
   
   
       20 . A process as claimed in  claim 1 , wherein the oxygen containing species is selected from 30/50 wt % aqueous H 2 O 2 , alkali metal peroxoborate, urea hydrogen peroxide adduct, alkali metal peroxoborate, alkali and alkaline earth peroxide and alkali and alkaline earth hydroperoxide.  
   
   
       21 . A process as claimed in  claim 20 , wherein the alkali metal peroxoborate used is selected from sodium, potassium, magnesium, calcium, barium and strontium peroxoborate.  
   
   
       22 . A process as claimed in  claim 20 , wherein the alkali and alkaline earth peroxide is selected from the group consisting of sodium, lithium, calcium, strontium, barium, magnesium and zinc peroxide.  
   
   
       23 . A process as claimed in  claim 20 , wherein the alkali and alkaline earth hydroperoxide is selected from potassium and sodium hydroperoxide.  
   
   
       24 . A process as claimed in  claim 1 , wherein the mole ratio of carboxylic acid or organosulphonic acid to active oxygen containing species is in the range of 5:1 to 50:1, preferably 10:1 to 30:1.  
   
   
       25 . A process as claimed in  claim 5 , wherein continuous counter current oxidation reactor is used to provide settling zones in the reactor in order to eliminate a settler.  
   
   
       26 . A process as claimed in  claim 1 , wherein the active oxygen containing species is in the range of 2 to 5 mole times of the sulphur present in hydrocarbon fuel.  
   
   
       27 . A process as claimed in  claim 1 , wherein the oxidation of sulphur compounds present in hydrocarbon fuels is carried out for 5 to 30 min residence time.  
   
   
       28 . A process as claimed in  claim 1 , wherein the washing of the oxidized hydrocarbon fuel to remove residual carboxylic acid present is carried out with water containing 0.1 to 10% alkali or alkaline earth metal oxides, hydroxide, carbonate or bicarbonate.  
   
   
       29 . A process as claimed in  claim 5 , wherein the antisolvent used with NMP is selected from water, glycol and sulpholane, preferably water.  
   
   
       30 . A process as claimed in  claim 29 , wherein the anti solvent used in a mixture with NMP is in the range of 5 to 15 wt %.  
   
   
       31 . A process as claimed in  claim 5 , 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.  
   
   
       32 . A process as claimed in  claim 5 , wherein the water is removed from carboxylic acid by distilling the overhead stream.  
   
   
       33 . A process as claimed in  claim 5 , 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 and acetonitrile, preferably methanol.  
   
   
       34 . A process as claimed in  claim 1 , wherein the cetane index of the treated hydrocarbon fuel used is increased by 2-20 units.