AU2003282270A1 - An improved process for the preparation of bio-diesel - Google Patents

Description

WO 2005/052103 PCT/IB2003/005349 1 AN IMPROVED PROCESS FOR THE PREPARATION OF BIO-DIESEL Field of the invention: The present invention relates to an improved process for the preparation of bio-diesel. It has enormous potential application in automobile industry as a substitute fuel for diesel. 5 Background of the invention: Biodiesel has of late been recognized as an efficient fuel substitute. As reported by Anjana Srivastava and Ram Prasad (Renewable & Sustainable Energy Reviews - 4, 2000, p111 133,) renewable sources such as vegetable oils, animal fats and used cooking oils are normally used as the starting material for preparing this alternate source of fuel. There are 10 also reports that, the engine problems due to carbonization of combustion chamber and wax deposits & engine failure. As reported by Gerhard Vellguth (Society of Automobile Engines No. 831358 , 1983 ), the fuel injector modifications are needed in standard diesel engines while using vegetable oil as a fuel , otherwise fonns deposits on the injectors and in the cylinder head, leading to 15 poor performance, higher emissions and reduces engine life. This limitation has to some extent been resolved by way of transesterification. Reference may be made to Antolin et al., (Bioresource Technology 83, 2002, p 11 1-114), who transesterified sunflower oil with methanol at a temperature in the range of 40-70 'C under constant stirring for a period of 2-6 hrs. Similar efforts have been made by different 20 research groups to prepare biodiesel from multiple oil sources. As reported by Alcantara et al., (Biomass Bioenergy 18,p5l5-527,2000) several oils such as soybean, frying oil, tallow have been tried as substitutes for diesel. As reported by Widyan and Shyoukh (Bioresource Technology 85, p 2 5 3

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2 5 6 ,2 0 02), palm oil has also been tried as substitutes. Conventionally, biodiesel is prepared from oil by reacting with alcohol using a 25 acid/alkali/enzyme catalyst in the temperature range of 40-80 0 C under constant stirring for a period of 2-6 hrs. In order to achieve higher product conversion, 1-3 moles per moles of oil in excess to stoichemetric quantity of alcohol is normally used and the unreacted alcohol is removed in the subsequent process steps. The ester obtained is separated from glycerine by suitable separation process and the ester is washed with mild acid. The 30 product is purified further by evaporation to remove unreacted alcohol and traces of moisture. The final product is normally used in combination with regular petroleum fuels to overcome the viscosity and related problems., WO 2005/052103 PCT/IB2003/005349 2 The major limitation associated with all these processes is that the overall product conversion in most of the cases is limited to 60-85% only. Moreover, the temperature range limited up to 60'C results in prolonged time, which may be as high as 6 hrs and thereby enhancing the cost of the process significantly. 5 Another limitation associated with these processes is that the resulting product exhibits higher viscosity compared with conventional petroleum fuels, thereby necessitating it is blending with petroleum fuels for the use in diesel engines. Objects of the invention: The main object of the present invention is to provide an improved process for the 10 preparation of bio-diesel which obviates the limitations as stated above. Another object of the present invention is to provide a chemical process for biodiesel with renewable sources of energy. Still another object of the present invention is to provide a chemical process for biodiesel oil preparation from extracted from agricultural edible and non-edible products. 15 Yet another object of the present invention is to provide an environmentally friendly fuel. Still yet another object of the present invention is to provide an improved quality of biodiesel can be used with out any alteration in the diesel engine. Accordingly the present invention provides an improved process for the preparation of bio diesel, which comprises 20 i) heating oil, characterized by specific gravity in the range of 0.85 - 0.96 and iodine value not exceeding 208, to a temperature not exceeding 120'C for not less than 2hrs followed by transesterification with 8 to 42% w/w, of alcohol of general formula R-OH, where R represents (CH 2 n- ), n being any integer between 1 and 5, by known method in presence of not more than 0.55% w/w, 25 of a known catalyst, at a temperature higher than the boiling point of the alcohol but not exceeding 215'C for a period of not less than 30 minutes under continuous turbulent condition to get mixture of ester and glycerol, ii) subjecting the mixture, as formed in step(i) to separation of the esterified oil by known method for a period of not less than 4 hrs followed by conventional 30 purification for a period of not less than 8 hrs. and repeating the process of separation as well as purification in succession for not less than three times to get biodiesel.

WO 2005/052103 PCT/IB2003/005349 3 In an embodiment of the present invention the oil used may be selected from ricebran oil, cottonseed oil , soybean oil, sunflower oil, castor oil, coconut oil. In another embodiment of the present invention the alcohol used may be selected from methanol, ethanol, n-propanol, n-butanol, n-pentanol 5 In yet another embodiment of the present invention the catalyst used may be selected from sodium hydroxide, potassium hydroxide. In still another embodiment of the present invention, the known method of separation used may be such as decanting, centrifuging, gravity separation, settling. In yet another embodiment of the present invention the conventional method of 10 purification used may be selected from bubble washing involving bubble size of 1-3mm, micro filtration with not less than 5micron filter, centrifuging, either alone or in any combination. In still another embodiment of the present invention, the Reynolds number (NRe) used for maintaining turbulence may be adjusted at not less than 4000 irrespective of the type of 15 reactor. The process of the present invention is described below in detail. Oil having specific gravity in the range of 0.85 - 0.96 and iodine value not exceeding 208 is heated to a temperature not exceeding 120*C for not less than 2hrs and is transesterified using 8 to 42% w/w, of alcohol of general formula R-OH, where R represents (CH 2 ,,+]), 20 n being any integer between 1 and 5, by known method in presence of not more than 0.5% w/w, of a known catalyst, at a temperature higher than the boiling point of the alcohol but not exceeding 215'C for not less than 30 minutes under continuous turbulent condition at. rpm in the range of 100-150 to get a mixture of ester and glycerol. The Reynolds number (NRe) is maintained at not less than 4000 irrespective of the type of the reactor. 25 The mixture of ester and glycerol is subjected to separation by known method for a period of not less than 4 hrs and the top layer ester is purified by conventional method for a period of not less than 8hrs. The process of separation as well as purification is repeated for not less than three times in succession to get biodiesel. The inventive step of the present invention lies not only in selecting the temperature of 30 transesterification at higher than the boiling point of the alcohol while not exceeding 215'C,but also in maintaining turbulence monitored by adjusting the Reynolds number (NRe) at not less than 4000 irrespective of the type of the reactor, to ensure about 97% WO 2005/052103 PCT/IB2003/005349 4 conversion of the oil into ester within a period of as low as 30 minutes, thereby enhancing the formation of fuel properties in the resulting product called biodiesel. The following examples are given by way of illustration only and therefore should not be construed to limit the scope of the present invention. 5 Example 1 100 ml of rice bran oil having a moisture content of 3% was heated at 1200 C for a period of 2 hrs. Later the moisture content of the oil was found to be 0.5%. This oil was taken in the specially modified batch Continuous Stirred Tank Reactor (CSTR) with provision for alcohol recycle/recovery system, condenser, thermometer and 10 feeding funnel. 20ml of methanol was taken in a beaker and 0.5gm sodium hydroxide was added to it under continuous stirring. The resulting solution was then added to the reactor rapidLy. The reactor system was maintained at turbulent condition by stirring at 100 rpm in order to maintaining the Reynolds number (NRe) at the minimum of 4000. The reaction was continued for 30 minutes. The excess methanol of 4 ml used for above reaction was later is 15 recovered. The resulting solution was taken in separating funnel, and two layers were found to form. The mixture was allowed to settle for 4 hrs and the top layer was taken for further processing. This was then subjected to bubble washing by aeration with 15ml of distilled water for a 20 period of 8 hrs and the resulting material was allowed to settle for 8hrs. It was taken for micro filtration to remove the micro particles present in the product. The bubble washing, settling and filtration operations were repeated for two more times to attain improved fuel properties. The resulting biodiesel was stored. 97% of rice bran oil was estimated to has been converted into biodiesel, which was found 25 to meet the specifications of conventional petroleum fuel. The biodiesel was used for running a test engines. The emission properties of this biodiesel were found to be better than of the conventional fuels. Example 2 100 ml of rice bran oil having a moisture content of 3% was heated at 1200 C for a period 30 of 2 hrs. Later the moisture content of the oil was found to be 0.5%. This oil was taken in the specially modified batch Continuous Stirred Tank Reactor (CSTR) with provision for alcohol recycle/recovery system, condenser, thermometer and feeding funnel. 32ml of propanol was taken in a beaker and 0.5gm sodium hydroxide was WO 2005/052103 PCT/IB2003/005349 5 added to it under continuous stirring. The resulting solution was then added to the reactor rapidly. The reactor system maintained at turbulent condition by stirring at 100-rpm in order to maintaining the Reynolds number (Nae) at the minimum of 4000. The reaction was continued for 30 minutes. The excess methanol of 7 ml used for above reaction was later is 5 recovered by the special recovery system. The resulting solution was taken in separating funnel, and two layers were found to form. The mixture was allowed to settle for 4 hrs and the top layer was taken for further processing. This was then subjected to bubble washing by aeration with 25ml of distilled water for a 10 period of 8 hrs and the resulting material was allowed to settle for 8hrs. It was taken for micro filtration to remove the micro particles present in the product. The bubble washing, settling and filtration operations were repeated for two more times to attain improved fuel properties. The resulting biodiesel was stored. 95% of rice bran oil was estimated to has been converted into biodiesel, which was found 15 to meet the specifications of conventional petroleum fuel. The biodiesel was used for running a test engines. The emission properties of this biodiesel were found to be better than of the conventional fuels. Example 3 100 ml of sunflower oil having a moisture content of 1.5% was heated at 1200 C for a 20 period of 2 hrs. Later the moisture content of the oil was found to be 0.5%. This oil was taken in the specially modified batch Continuous Stirred Tank Reactor (CSTR) with provision for alcohol recycle/recovery system, condenser, thermometer and feeding funnel. 40 ml of butanol was taken in a beaker and 0.5gm sodium hydroxide was added to it under continuous stirring. The resulting solution was then added to the reactor 25 rapidly. The reactor system maintained at turbulent condition by stirring at 100-rpm in order to maintaining the Reynolds number (NRe) at the minimum of 4000. The reaction was continued for 30 minutes. The excess butanol of 8.3 ml used for above reaction was later is recovered by the special recovery system. The resulting solution was taken in separating funnel, and two layers were found to form. 30 The mixture was allowed to settle for 4 hrs and the top layer was taken for further processing. This was then subjected to bubble washing by aeration with 15ml of distilled water for a period of 8 hrs and the resulting material was allowed to settle for 8hrs. It was taken for WO 2005/052103 PCT/IB2003/005349 6 micro filtration to remove the micro particles present in the product The bubble washing, settling and filtration operations were repeated for two more times to attain improved fuel properties. The resulting biodiesel was stored. 98.0% of sunflower oil was estimated to have been converted into biodiesel, which was 5 found to meet the specifications of conventional petroleum fuel. The biodiesel was used for running a test engines. The emission properties of this biodiesel were found to be better than of the conventional fuels. Example 4 200 ml of coconut oil having a moisture content of 2% was heated at 1200 C for a period of 10 2 hrs. Later the moisture content of the oil was found to be 0.5%. This oil was taken in the specially modified batch Continuous Stirred Tank Reactor (CSTR) with provision for alcohol recycle/recovery system, condenser, thermometer and feeding funnel. 47 ml of methanol was taken in a beaker and 1gm sodium hydroxide was added to it under continuous stirring. The resulting solution was then added to the reactor 15 rapidly. The reactor system maintained at turbulent condition by stirring at 100-rpm in order to maintaining the Reynolds number (NRe) at the minimum of 4000. The reaction was continued for 60 minutes. The excess methanol of 10 ml used for above reaction was later is recovered by the special recovery system. The resulting solution was taken in separating funnel, and two layers were found to form. 20 The mixture was allowed to settle for 8 hrs and the top layer was taken for further processing. This was then subjected to bubble washing by aeration with 15ml of distilled water for a period of 8 hrs and the resulting material was allowed to settle for 8hrs. It was taken for micro filtration to remove the micro particles present in the product. The bubble washing, 25 settling and filtration operations were repeated for two more times to attain improved fuel properties. The resulting biodiesel was stored. 98.0% of coconut oil was estimated to have been converted into biodiesel, which was found to meet the specifications of conventional petroleum fuel. The biodiesel was used for running a test engines. The emission properties of this biodiesel were found to be better 30 than of the conventional fuels. Example 5 100 ml of coconut oil having a moisture content of 2% was heated at 1200 C for a period of 2 hrs. Later the moisture content of the oil was found to be 0.5%.

WO 2005/052103 PCT/IB2003/005349 7 This oil was taken in the specially modified batch Continuous Stirred Tank Reactor (CSTR) with provision for alcohol recycle/recovery system, condenser, thermometer and feeding funnel. 35 ml of ethanol was taken in a beaker and 0.5gm sodium hydroxide was added to it under continuous stirring. The resulting solution was then added to the reactor 5 rapidly. The reactor system maintained at turbulent condition by stirring at 100-rpm in order to maintaining the Reynolds number (NRe) at the minimum of 4000. The reaction was continued for 45 minutes. The excess ethanol of 8 ml used for above reaction was later is recovered by the special recovery system. The resulting solution was taken in separating funnel, and two layers were found to form. 10 The mixture was allowed to settle for 8 hrs and the top layer was taken for further processing. This was then subjected to bubble washing by aeration with 15ml of distilled water for a period of 8 hrs and the resulting material was allowed to settle for 8hrs. It was taken for micro filtration to remove the micro particles present in the product. The bubble washing, 15 settling and filtration operations were repeated for two more times to attain improved fuel properties. The resulting biodiesel was stored. 97.0% of coconut oil was estimated to have been converted into biodiesel, which was found to meet the specifications of conventional petroleum fuel. The biodiesel was used for running a test engines. The emission properties of this biodiesel were found to be better 20 than of the conventional fuels. Example 6 100 ml of sunflower oil having a moisture content of 1.5% was heated at 1200 C for a period of 2 hrs. Later the moisture content of the oil was found to be 0.5%. This oil was taken in the specially modified batch Continuous Stirred Tank Reactor 25 (CSTR) with provision for alcohol recycle/recovery system, condenser, thermometer and feeding funnel. 20 ml of methanol was taken in a beaker and 0.5gm sodium hydroxide was added to it under continuous stirring. The resulting solution was then added to the reactor rapidly. The reactor system maintained at turbulent condition by stirring at 100-rpm in order to maintaining the Reynolds number (NRe) at the minimum of 4000. The reaction was 30 continued for 30 minutes. The excess methanol of 4 ml used for above reaction was later is recovered by the special recovery system. The resulting solution was taken in separating funnel, and two layers were found to fonn. The mixture was allowed to settle for 4 hrs and the top layer was taken for further nrocessin2.

WO 2005/052103 PCT/IB2003/005349 8 This was then subjected to bubble washing by aeration with 15ml of distilled water for a period of 8 hrs and the resulting material was allowed to settle for 8hrs. It was taken for micro filtration to remove the micro particles present in the product. The bubble washing, settling and filtration operations were repeated for two more times to attain improved fuel 5 properties. The resulting biodiesel was stored. 98.0% of sunflower oil was estimated to have been converted into biodiesel, which was found to meet the specifications of conventional petroleum fuel. The biodiesel was used for running a test engines.The emission properties of this biodiesel were found to be better than of the conventional fuels. 10 Example 7 100 ml of sunflower oil having a moisture content of 1.5% was heated at 120' C for a period of 2 hrs. Later the moisture content of the oil was found to be 0.5%. This oil was taken in the specially modified batch Continuous Stirred Tank Reactor (CSTR) with provision for alcohol recycle/recovery system, condenser, thermometer and 15 feeding funnel. 25 ml of ethanol was taken in a beaker and 0.5gm sodium hydroxide was added to it under continuous stirring. The resulting solution was then added to the reactor rapidly. The reactor system maintained at turbulent condition by stirring at 100-rpm in order to maintaining the Reynolds number (NRe) at the minimum of 4000. The reaction was continued for 30 minutes. The excess ethanol of 8ml used for above reaction was later is 20 recovered by the special recovery system. The resulting solution was taken in separating funnel, and two layers were found to form. The mixture was allowed to settle for 4 hrs and the top layer was taken for further processing. This was then subjected to bubble washing by aeration with 15ml of distilled water for a 25 period of 8 hrs and the resulting material was allowed to settle for 8hrs. It was taken for micro filtration to remove the micro particles present in the product. The bubble washing, settling and filtration operations were repeated for two more times to attain improved fuel properties. The resulting biodiesel was stored. 98.0% of sunflower oil was estimated to have been converted into biodiesel, which was 30 found to meet the specifications of conventional petroleum fuel. The biodiesel was used for running a test engines.The emission properties of this biodiesel were found to be better than of the conventional fuels.

WO 2005/052103 PCT/IB2003/005349 9 Emission Analysis of Diesel, Biodiesel and Various Blends Load Sample Time for CO CO 2 HC 02 NOx Noise Texii KW lOcc(sec) (%vol) (%vol) (ppm) (%VOL) (ppm) (db) ( 0 c) Diesel 65 0.08 2.1 28 17.53 180 145 140 Biodiesel 65 0.04 2.55 10 17.10 111 116 182 BS1 66 0.02 2.31 0 17.30 154 145 153 0 BS2 71 '0.02 2.14 0 17.50 96 112 154 BS3 69 0.03 2.13 0 17.36 125 113 145 BS4 69 0.03 2.42 5 17.28 113 120 170 BSS 78 0.04 2.09 0 17.47 84 115 169 Diesel 49 0.12 3.5 43 15.62 397 145 210 Biodiesel 45 0.04 3.95 20 15.27 118 119 202 BS1 51 0.03 3.61 0 15.70 369 120 190 4 BS2 49 0.03 3.49 27.5 15.57 277 112 196 BS3 48 0.03 3.84 20 14.94 300 115 180 BS4 49 0.04 3.90 17.5 16.39 283 129 245 BS5 48 0.045 4.02 2.5 14.99 300 116 242 Diesel 42 0.13 4.3 63 14.68 582 146 243 Biodiesel 36 0.03 5.06 10 13.53 525 121 277 BS1 46 0.04 4.11 35 14.73 473 117 210 7 BS2 39 0.04 4.87 12.5 13.56 502 114 225 BS3 38 0.05 5.44 10 12.67 479 116 243 BS4 38 0.05 5.20 10 13.18 496 126 285 BS5 38 0.06 5.46 32.5 12.85 451 119 315 Diesel 32 0.2 6.3 85 11.2, 689 159 287 Biodiesel 30 0.05 6.74 20 10.99 727 123 329 BS1 32 0.06 6.79 37.5 10.53 800 119 250 11 BS2 29 0.06 6.91 15 10.43 728 118 240 BS3 30 0.10 7.05 15 10.15 608 119 285 BS4 30 0.10 7.35 45 9.83 605 126 296 BS5 30 0.11 7.01 30 10.36 616 121 362 Diesel 27 0.34 7.7 89 9.12 942 169 294 Biodiesel 25 0.09 8.30 35 8.74 904 124 411 BSI 27 0.07 7.58 35 9.24 977 120 266 14 BS2 26 0.18 8.04 47.5 8.54 858 119 363 BS3 23 , 0.27 9.03 52.5 6.86 782 122 342 BS4 27 0.14 8.10 45 8.60 782 127 395 BS5 24 0.24 8.30 45 8.22 660 123 380 Note: BS- Blended with Diesel BS1- B20, BS2- B80, BS3-B50, BS4-B40, BS5- B60 5 OIL SPECIFICATION Specific gravity : 0.916 - 0.912 Refractive .Index :1.470 - 1.473 Iodine value : 99 - 108 WO 2005/052103 PCT/IB2003/005349 10 Saponification value :181 - 189 Acid value : 4 - 120 Titer : 24 - 28'c Unsaponifiable matter : 3.5 % 5 Tocopherols average : 400 mg/kg of oil Fuel properties Property DIESEL Biodiesel (RBOE) Density (gm/cc) 0.82 0.865 Viscosity (Cst) 2.4 3.46 Heat Of Combustion 42.57 45.09 (MJ/Kg) Flash Point ('C) 74 182 Fire Point ('C) 87 194 Copper strip Corrosion No.3 < No.1 @ 100 (*C) Engine Efficiency Load Specific Fuel Break Thermal Mechanical Indicative (kW) Consumption Efficiency (%) Efficiency (%) Thermal (kWh) Efficiency (%) _ Diesel Biodiesel Diesel Biodiesel Diesel Biodiesel Diesel Biodiesel 0 oo oo 0 0 0 0 20.65 30.22 4 0.556 0.611 15.07 14.01 47.41 37.54 31.77 37.33 7 0.378 0.419 22.17 20.08 62.22 51.27 36.22 40.46 11 0.314 0.333 26.67 25.69 71.26 62.31 37.42 41.23 14 0.292 0.328 28.65 26.07 75.94 67.78 37.73 38.45 A comparative study of the Complete specification relating to P03ceO4 ( an improved 10 process for the preparation of bio-diesel) and the US patent No. 6,015,440 apparently reveals the following differences. SI.No US patent No. 6,015,440 Bio-diesel Process - Ref No. P03ceO4/CLRI I Temperature range of the More than the boiling point of the alcohol but reaction 70-80' C less than 2150 C 2 Pressure at 20 psig Atmospheric pressure 3. Separation alkali using ion Separation of alkali using water exchange column, 4 Top layer approximately 80% More than 80% WO 2005/052103 PCT/IB2003/005349 11 5 Un-reacted methanol removal Un-reacted methanol has separated immediately by an addition process step of after the reaction by a specially modified flash recovery system (in a provision built within on within the reactor separate reactor) 6 Fixed bed/Plug flow reactor Batch reactor 7 Multiple reactor Single reactor consists of special provision for excess alcohol recovery 8 Continuous process Batch process 9 Increased final product The final product contains only higher fatty acid volume due to blending of esters. higher fatty acid ester with glyceryl ether. 10 Reaction with isobutylene No such reaction 11. Oxidative process Base catalysed transesterification 12 Product is Mixture of Bio- The final product contains higher fatty acid diesel and Ester glycerol esters. 13. Transesterifying at least a Almost all portion. portion only 14. This end product of this The end product is bio-diesel, no mixing with process is a mixture of ester glycerol. In fact glycerol is obtained as by and the etherified glycerol, product which is converted into bio diesel by blending. 15. Only by mixing the etherified This is a bio-diesel process, without mixing the glycerol to the esterified oil glycerol, with all required bio-diesel properties may gives the viscosity and emission norms similar to the nonnal diesel reduction. fuel. 16 Strong acid catalyst process Alkali/ base catalyst process 17. Approximately 80% of the More than 95% in pure form bio-diesel is in pure form 1& Effect of mixing of etherified No engine difficulties. No need of any change in crude glycerol's effect in the the engine needed, no engine block etc. engine is not defined, shown only the viscosity reduction 19. Low waste process, not More than 95% conversion. Glycerol formed as separating the 20% crude a by-product can be used in other industries. glycerol formed. 2a Formation of 20% glycerol, Glycerol formed as a by-product can be used in for economical purpose, after other industries. reacting with isobutylene mixing with the bio-diesel 21. After mixing the crude The final product after the reaction is similar to glycerol only, the product diesel fuel gives properties closely resembling to have of diesel fuel In our opinion, the inventive step of the present invention vis-i-vis the aforesaid US Patent document, however, essentially lies in conducting the reaction at a temperature WO 2005/052103 PCT/IB2003/005349 12 higher than the boiling point of the alcohol used, besides maintaining the turbulence (NRe = 4000 or more), that is applicable irrespective of the type of the reactor used, to enhance the fuel properties of the resulting product. This step ensures that no blending, as described in 5 the US Patent document. Following are some of the advantages of the present invention: 1. The high temperature with turbulent condition (Reynolds number more than 4000), reduces the reaction time significantly. 2. The special provision in the reactor enables the effective recovery of excess alcohol 10 added for the reaction. 3. Bubble washing and microfiltration achieved the high quality of the biodiesel. 4. The product is based on renewable source. 5. The product can be used as substitute fuel for diesel engines without any major modification of engines. 15 6. The final product is a substitute fuel for diesel without blending with other conventional petroleum fuels. 7. The products fuel properties and the engine efficiency are comparable with nonnal diesel engine fuels. 8. The emission characteristics are like those of normal fuels.

Claims (7)

1. An improved process for the preparation of bio-diesel, which comprises i) heating oil having by specific gravity in the range of 0.85 - 0.96 and iodine value not exceeding 208, to a temperature not exceeding 120C for not less 5 than 2hrs followed by transesterification with 8 to 42% w/w, of alcohol of general formula R-OH, where R represents (C,,H2n 1 ), n being any integer between 1 and 5, in presence of not more than 0.55% w/w, of a catalyst, at a temperature higher than the boiling point of the alcohol but not exceeding 215C for a period of not less than 30 minutes under continuous turbulent 10 conditions to obtain a mixture of ester and glycerol, ii) Subjecting the mixture, as formed in step (i) to separation of the esterified oil for a period of not less than 4 hrs followed by purification for a period of not less than 8 hrs. and repeating the process of separation as well as purification in succession for not less than three times to obtain biodiesel. 15

2. A process, as claimed in claim 1 wherein the oil is selected from ricebran oil, cottonseed oil , soybean oil, sunflower oil, castor oil, coconut oil.

3. A process, as claimed in claim 1, wherein the alcohol is selected from methanol, ethanol, n-propanol, n-butanol, and n-pentanol

4. A process, as claimed in claim 1 wherein the catalyst is selected from sodium 20 hydroxide, potassium hydroxide.

5. A process, as claimed in claim 1 wherein the esterified oil is separated by decanting, centrifuging, gravity separation, settling, either alone or in any combination.

6. A process, as claimed in claim 1 wherein the purification of the mixture is by 25 bubble washing involving bubble size of 1-3mm, micro filtration with not less than micron filter, centrifuging, either alone or in any combination.

7. A process, as claimed in claim 1 wherein the Reynolds number (NRe) for maintaining turbulence is adjusted at not less than 4000 irrespective of the type of reactor.