A study on the production of biodiesel from used frying oil. (2024)

Introduction

Worldwide oil consumption was 3571.6 million tons, in 2000 but in2010, the consumption reached 4028.1 million tons, with average annualincrease of 3.1%. According to British Petroleum Statistical Review ofWorld Energy (2011), the world oil reserves were estimated 188.8 milliontons with a reserve to production ratio of 46.2 years at the end of 2010(Goldemberg, 2008). The first diesel engine that ran on vegetable oilwas built in 1893 by Rudolf Diesel and gave the idea of using vegetableoil as a transportation fuel. Current energy demand is hardly fulfilledby conventional energy resources such as petro-diesel, coal and naturalgas. The reserves of petroleum fuel will deplete in near future (Sheehanet al., 1998). Petroleum price has not only been increasing but alsocausing environmental pollution by producing hazardous gases due toincomplete combustion of these fuels (Marchetti et al., 2007). Balancebetween economic, agriculture and environmental development could bemade by using alternative fuel which should be economically competitive,technically feasible, readily available and environmentally acceptable.Biodiesel synthesized from renewable raw material has all theseproperties (Meher et al., 2006). In the recent years particular focushas been emphasized on biodiesel production from cheaper sources such asvegetable oil (Balat, 2008) because it is renewable, eco-friendly,biodegradable and non toxic in nature. Moreover, biodiesel is a cleanfuel having no sulphur emissions and lower heat of combustion thanpetro-diesel (Srivastava and Prasad 2000). Biodiesel produced fromanimal fat and used frying oil is eco-friendly and good alternative todiesel fuel (Demirbas, 2005). Recently scientists all over the world aretrying to produce more and more biodiesel because it can be used assubstitute for petro-diesel without the modification in diesel engines(Demirbas, 2002). Biomass, vegetable oil, animal fat and used frying oilcan be used to produce biodiesel by reacting with alcohol (methanol orethanol) and strong base catalyst such as potassium or sodium hydroxide(Kalam and Masjuki 2002).

Renewable raw material such as oil could be converted into itscorresponding fatty ester (biodiesel) by transesterification reactions.Transesterification process can proceed with or without alkali catalystby using primary or secondary monohydric aliphatic alcohols. However,for the production of biodiesel, various types of oils (as rawmaterial), hom*ogeneous catalysts (potassium hydroxide, sodium hydroxide,sulphuric acid and supercritical fluids), heterogeneous catalysts andenzyme (lipase) can be used (Marchetti et al., 2007).The blend ofbiodiesel with petro-diesel could also be used in transport sector. Theblend of biodiesel are denoted as Bxx, where xx shows the quantity ofbiodiesel blended with petro-diesel. For units, B100 is referred to 100%biodiesel and B80 is referred to 80% biodiesel and 20% petro-diesel andso on (Demirbas, 2007).

Used frying oil is the residue which can be collected fromrestaurants, kitchens and food processing factories for the productionof biodiesel. It is not recommended to be used again for cooking orfrying purpose. Normally it is disposed in water bodies, where it is notonly causing water pollution but also causing harm to aquatic organisms.Used frying oil can be a good option as raw material, because its priceis 2 to 3 times lower than fresh vegetable oils which in turn reduce theproduction cost of biodiesel (Hameed et al., 2009). Although thephysical and chemical characteristics of used frying oil are differentfrom fresh edible oil but both oils can be transformed into biodiesel byapplying same method i.e. transesterification reaction by alkalicatalyst, acid catalyst or using enzymes. The used frying oil can beeffectively converted into biodiesel by two-step transesterificationreaction. The two-step transesterification reaction consists of alkalicatalyzed reaction, and acid catalyzed reaction. The properties ofbiodiesel produced from used frying oil are certainly similar to thoseproduced from their respective fresh vegetable oil (Loh et al., 2006).

The present study was conducted to measure conversion efficiency ofused frying oil to biodiesel. Used frying oil was analyzed before itsconversion to biodiesel to measure its suitability for biodieselproduction. Biodiesel was analyzed after its production from used fryingoil and compared with ASTM standards (2002). Comparison of yield ofone-step and two-step transesterification reactions was another part ofthe study.

Materials and Methods

Collection of samples. Used frying oil was purchased from twodifferent chicken frying shops from different locations of ShahdaraTown, Lahore that was repeatedly used for frying from early morning tomid night and on closure of the restaurant it was put into a plastic canfor sale or thrown in sewage drain. The price of used frying oils was0.33 US$/L. The oil sample was collected in plastic bottles andtransferred to laboratory for further processing. The collected samplewas contaminated with suspended carbon particles and water content.Sieving and filtration were done to remove food contents and suspendedcarbon particles.

Analytical procedures. Before transesterification of the oil tomethyl esters all impurities were removed before its conversion tobiodiesel. For removing large solid particles a sieving plate with meshsize 170 mm was used and to remove all suspended particles Whattmanfilter paper was used. Used frying oil sample was heated at 60[degrees]Cfor 30 min to remove water content. Fatty acid profile was analyzed bygas chromatography mass spectrometry (GC-MS, Shimadzu GC-14-A).Properties of used frying oil sample such as, acid value free fatty acidvalue, iodine value and saponification value were analyzed by methods ofRaie (2008).

Experimental setup. Sodium methoxide was prepared by mixing NaOHand pure methanol. Sodium hydroxide was used 1% wt (dry weight basis) tooil and methanol was used 10% (dry weight basis) to used frying oil withmolar ratio 6:1 (Charoenchaitrakool and Thienmethangkoon, 2011). Themeasured amount of NaOH and pure methanol were mixed in beaker andstirred for 30 min.

Transesterification reaction was carried out by mixing oil withsodium methoxide to convert fatty acids (triglycerides) of used fryingoil to methyl esters (Biodiesel). Sodium methoxide was mixed in usedsample when its temperature reached to 60[degrees]C and stirredcontinuously for 30 min. The mixture was then allowed to stand inseparating funnel for at least 8 h. Two layers were produced, (a) withglycerol in the bottom and (b) methyl ester at the top. Upper layer wasmixed with hexane to dissolve methyl esters, and then hexane wasseparated by distillation afterwards to get pure biodiesel (Ahmad etal., 2009).

Two-step catalyzed process was used i.e. esterification andtransesterification. In the esterification process, free fatty acids(FFA) were reduced in the used frying oil using sulphuric acid as acatalyst. The optimum conditions were obtained using molar ratio ofmethanol to used frying oil 6:1 with 0.68% wt of sulphuric acid andreaction time 1 h at 51[degrees]C. In the transesterification reaction,methanol and alkali (NaOH) the catalyst was used to convert triglycerideportion of the used frying oil to methyl ester and glycerol. The optimumconditions were obtained using molar ratio of methanol to used sample9:1 with 1 %wt of base catalyst and reaction time 1 h at 55[degrees]C(Charoenchaitrakool and Thienmethangkoon, 2011; Lotero et al., 2005).

The final product of methyl ester was identified with the help ofthin layer chromatography (TLC) at Applied Chemistry Research Centre,Pakistan Council of Scientific and Industrial Research (ACRC-PCSIR)Laboratories, Lahore. Thin layer chromatogram was prepared withparticular length, width and thickness (20 cm x 20 cm x 0.25 mm) byutilizing water and silica gel. The plate was air dried and activated onheating at 105[degrees]C in the oven for 1 h. Biodiesel was dissolved inpure n-hexane as n-hexane, and diethyl ether (80:20) were used assolvent system. The 2, 7-dichlorofluorescein as non-destructive locatingagent was required to see colour bands (purple-yellow) under ultraviolet light of 366 nm wavelength.

Results and Discussion

Water content. Water content of oil sample was removed up to 0.43%by heating for 35 min (Table 1). The water content present in the usedoil sample decreased the efficiency of the transesterification process,because it decomposes the esters present in the oil and results in thesaponification of oil by base catalyst. Presence of high water contentin the oil can be tackled by acid catalyst, which increases theefficiency of transesterification process named as two content steptransesterification process. Water in pretreated used frying oil wasdetermined to be 0.1 % by weight (Charoenchaitrakool andThienmethangkoon, 2011). Minimum water content and free fatty acidcontent in oil were very important for getting optimal results in theprocess of transesterification. Basic catalyst can only be utilized intransesterification process, when there is low water and free fatty acidcontents. If the water content and fatty acid are high then two-steptransesterification process is suitable in which the first-step iscarried out with acid catalyst and the second-step with basic catalyst.Reaction rate can be increased by increasing reaction time (Ahmad etal., 2009). In this current study, both processes were used to measuretheir efficiency.

Iodine value. Iodine value can be used to measure the unsaturationof oils. It is the percentage of iodine in centi-grams which 1 g ofsample absorbed. Iodine value of used frying oil sample was calculatedto be 52 mg/g (Table 1). Balat and Balat (2010) calculated iodine value35-61% for palm oil and 110-143 % for sunflower oil. According toOliveira et al. (2010) the oil showed iodine index 7.21g/100g. Low valueof iodine indicated lower unsaturated compounds of carbon and thebiodiesel produced from that oil was resistant to oxidation process.

Saponification value. The process of saponification of sodium soapobtained from vegetable oil can be described in the following chemicalequation:

vegetable oil + NaOH [right arrow] RCOONa + glycerin (Demirbas,2002).

The saponification value of used frying oil was measured to be 205mg/g (Table 1). Demirbas (2009b) calculated the sponification value188.2. High level of saponification required that sample must beesterified with sulphuric acid with methanol. If the free fatty acidlevel exceeds 0.5% by weight then the saponification reduces theformation and yield of methyl ester (biodiesel) and hindered settling ofproducts obtained (Canakci and Gerpen, 2001).

Acid and free fatty acid values. The free fatty acid (FFA) value isthe amount of milligram of KOH needed to neutralize fatty acids in 1g ofoil. The FFA value measured in used frying oil of current study was 8.7%(Table 1). Balat and Balat (2010) calculated FFA value 5.6 for fryingoil and >20 for waste palm oil while Berrios et al. (2010) measuredFFA value 2.14 for used frying oil. High free fatty acid content can beesterified using acid catalyst. Good quality methyle esters can beobtained by basic catalyst if free fatty acid content remained lowerthan 1.0 wt% (Meng et al., 2008).

The acid value is the amount in milligram (mg) of aqueous potassiumhydroxide (KOH) in 1 g of oil to neutralize the total free fatty acids.The acid value of sample studied was determined to be 0.8 mg KOH/g ofoil (Table 1). Berrios et al. (2010) measured acid value 0.14 mg forused frying oil. In the process of base catalyzed transesterificationthe acid value of the oil must be less than 1 mg (Demirbas, 2009c). Ifthe acid value exceeds 1 mg then additional alkali must be used toneutralize the free fatty acids (Canakci and Ozsezen, 2005).

Fatty acid composition and yield of reaction. Fatty acidcomposition of used frying oil was analyzed by gas chromatography. Itwas found that the used frying oil contained 0.1 wt% myristic acid, 7.88wt% palmitic acid, 0.35 wt% stearic acid, 54.54 wt% oleic acid, 28.96wt% linoleic acid, 7.546 wt% linolenic acid, 0.18 wt% arachidonic (Table2). Charoenchaitrakool and Thienmethangkoon (2011) reported thepercentage composition of fatty acids in waste frying oil as 1.1 wt%myristic acid, 25.8 wt% palmitic acid, 4.7 wt% stearic acid, 34.6 wt%oleic acid, 29.4 wt% linoleic acid, 2.5 wt% linolenic acid, and 0.2 wt%arachidonic acid. Demirbas (2009a) calculated fatty acid composition ofwaste cooking oil from sunflower seed oil as 6.8 wt% C16:0 (palmiticacid), 3.7 wt% C18:0 (stearic acid), 22.8 wt% C18:1 (oleic acid), 65.2wt% C18:2 (linoleic) and 0.1 wt% C18:3 (linolenic).

In one-step transesterification process, the yield of biodiesel wascalculated to be 88% with glycerine as a byproduct. In two-step process,the yield of biodiesel was higher (92%) than one step process (Table 3).Formation of soap during one-step reaction was the reason of its lowyield. However, in two-step reaction, sulphuric acid causedesterification of FFAs before biodiesel synthesis thus reducing thechances of soap formation. Zhang et al. (2003) described that high freefatty acid contents required to have pretreatment process in which theacid catalyst such as sulphuric acid was used to reduce the free fattyacid (FFA) contents.

Quality assessment of biodiesel. One step and two steptransesterification processes were used for the production of biodieselfrom used frying oil under reaction conditions shown in Table 4.

In sample 1 (two-step process) the used frying oil was almostcompletely converted to biodiesel (methyl ester) and was according toASTM standard (2002) of biodiesel because there were no fatty acids andglycerides found in final product (biodiesel). Biodiesel produced byone-step transesterification process (sample 2) contained fatty acidsand glycerides along with methyl ester. Therefore, the biodieselproduced from used frying oil was of good quality by two-steptransesterification process using acid and base catalyst than by usingone-step transesterification process using base catalyst as the finalproduct contained some amount of fatty acids and glycerides (Fig. 1).

Kinematic viscosity. Kinematic viscosity is the quotient of thedynamic viscosity divided by density (Va/d) at same temperature. Theviscosity of biodiesel produced from used samples determined by ASTMD445 method was 4.86 at 40[degrees]C (Table 5). Charoenchaitrakool andThienmethangkoon (2011) reported the viscosity of biodiesel 4.61. Balat(2008) reported that the biodiesel has viscosity close to diesel fuel.Viscosity effects the injection equipment at the time of operation offuel and at low temperature the increase in the viscosity effectsfluidity of fuel. By increasing the temperature of reaction, viscositydecreased and miscibility of methanol and oil increased that ultimatelyincreased the free fatty acid conversions (Park et al., 2010).

Flash point. Flash point is the temperature recorded on thermometerat the time of application that causes a distinct flash in the interiorof cup. The flash point of biodiesel produced in this study wasdetermined by ASTM D93 testing method and the value obtained was185[degrees]C (Table 5). Charoenchaitrakool and Thienmethangkoon (2011)reported the flash point of biodiesel was 160. The ASTM D6751-02standard for flash point of biodiesel is more than 130[degrees]C.Demirbas (2009c) reported the flash point for biodiesel prepared fromwaste cooking oil was 469 K (196[degrees]C).

Specific gravity. Specific gravity is the ratio of weight of givenvolume of material to weight of an equal volume of water. In this methodboth weights recorded in vacuum condition and the standard referencetemperature for both, material and water was 60 F. The specific gravityof biodiesel measured by ASTM D1298 testing method was 0.884 g/mL (Table5). The minimum values of specific gravity indicate the removal of heavyglycerine and thus completion of reaction (Sharma et al., 2008). Balatand Balat (2010) calculated the specific gravity of biodiesel 0.88 g/mL.Berrios et al., (2010) measured the specific gravity of biodieselobtained from used frying oil in pressure system was 0.875 g/cm.Demirbas (2009c) measured density of biodiesel from waste cooking oil as0.897 kg/L at 288K0.

Conclusion

Energy crises and environmental impacts of fossil fuel are forcingworld to search its alternatives such as biofuels. Therefore, biodieselproduction from cheaper raw material can be a fruitful technology. Usedfrying oil could be the suitable raw material otherwise it is disposedoff in water bodies or soil causing environmental and health problems.Synthesis of biodiesel from this waste oil could be the best use of it.In the present study, biodiesel was produced from used frying oil by twomethods and it was found that the biodiesel produced from two-steptransesterification method gives good quality in comparison to one-steptransesterification process as soap formation took place in one-stepprocess. Properties of biodiesel such as kinematic viscosity, flashpoint and specific gravity were analyzed and found within ASTM (2002)standards limits for biodiesel.

Recommendations

* Repeated use of frying oil should be banned to avoid health riskand its market value could be created by using it for biodieselproduction.

* Following results of current study for biodiesel production fromused frying oil should be launched at commercial scale as it is anefficient, cheaper and feasible raw material.

* Further research is needed on conversion of used frying oil tobiodiesel by using various catalysts to enhance its yield.

Acknowledgement

The authors acknowledge Sustainable Development Study Centre atGovernment College University Lahore for providing funding for thiscurrent study and Dr. Muhammad Zeeshan at Applied Chemistry ResearchCentre (ACRC), PCSIR Laboratories Lahore for guiding and providingtesting facilities of oil and biodiesel. Authors are also thankful toTahir Sattar and Ikram Hussain Arain, Chief Chemist at Southern ElectricPower Company Limited, Lahore for their cooperation in biodieseltesting.

References

Ahmad, M., Zafar, M., Khan, M.A., Sultana, S. 2009. Biodiesel fromPongamia pinnata L. oil: A promising alternative bioenergy source, PartA: Energy Sources, 31: 1436-1442.

ASTM D6751 2002. Standard Specification for Biodiesel Fuel (B100)Blend Stock for Distillate Fuels. www.astm.org/DATABASE.CART/HISTORICALD6751-02.htm. DOI: 10.1520/D6751-02.

Balat, M., Balat, H. 2010. Progress in biodiesel processing.Applied Energy, 87: 1815-1835.

Balat, M. 2008. Modeling vegetable oil viscosity. Energy Source,Part A: Recovery, Utilization and Environment Effects, 30: 1856-1869.

Berrios, M., Martin, M.A., Chica, A.F., Martin A. 2010. Study ofesterification and transesterification in biodiesel production from usedfrying oils in a closed system. Chemical Engineering Journal, 160:473-479.

Canakci M., Ozsezen A. N. 2005. Evaluating waste cooking oils asalternative diesel fuel. Gazi University Journal of Science, 18: 81-91.

Canakci, M., Van Gerpen, J. 2001. Biodiesel production from oilsand fats with high free fatty acids, Transactions of the AmericanSociety of Agricultural Engineerings, 44: 1429-1436.

Charoenchaitrakool, M., Thienmethangkoon, J. 2011. Statisticaloptimization for biodiesel production from waste frying oil throughtwo-step catalyzed process. Fuel Processing Technology, 92: 112-118.

Demirbas., A. 2009a. Production of biodiesel fuels from linseed oilusing methanol and ethanol in non-catalytic SCF conditions. BiomassBioenergy, 33: 113-118.

Demirbas., A. 2009b. Progress and recent trends in biodiesel fuels.Energy Conversion and Management, 50: 14-34.

Demirbas., A. 2009c. Biodiesel from waste cooking oil viabase-catalytic and supercritical methanol transesterification. EnergyConversion and Management, 50: 923-927.

Demirbas., A. 2007. Importance of biodiesel as transportation fuel.Energy Policy, 35: 4661-4670.

Demirbas., A. 2005. Biodiesel production from vegetable oils viacatalytic and noncatalytic supercritical methanol transesterificationmethods. Progress in Energy Combustion Science, 31: 466-487.

Demirbas A. 2002. Diesel fuel from vegetable oil viatransesterification and soap pyrolysis. Energy Source, 24: 835-841.

Goldemberg., J. 2008. Environmental and ecological dimensions ofbiofuels. In: Conference on the Ecological Dimensions of Biofuels,Washington, D.C., USA.

Hameed, B. H., Goh C. S., Chin, L.H. 2009. Process optimization formethyl ester production from waste cooking oil using activated carbonsupported potassium fluoride. Fuel Processing Technology, 90: 1532-1537.

Kalam M.A., Masjuki, H.H. 2002. Biodiesel from palm oil an analysisof its properties and potential. Biomass Bioenergy, 23: 471-479.

Loh, S.K., Choo, Y. M., Cheng, S.F., Ma, A. N. 2006. Recovery andconversion of palm olein derived used frying oil to methyl esters forBiodiesel. Journal Oil Palm Research, 18: 247-252.

Lotero, E., Liu, Y., Lopez, D.E., Suwannakarn, K., Bruce, D.A.,Goodwin, J.G. 2005. Synthesis of Biodiesel via Acid Catalysis.Industrial & Engineering Chemistry Research, 44: 5353-5363.

Marchetti, J.M., Miguel, V.U., Errazu, A.F. 2007. Possible methodsfor biodiesel production. Renewable and Sustainable Energy Reviews, 11:1300-1311.

Meher, L.C., Sagar, V.D., Naik, S.N. 2006. Technical aspects ofbiodiesel production by transesterification; A review. Renewable andSustainable Energy Review, 10: 248-268.

Menga, X., Chen, G., Wang, Y. 2008. Biodiesel production from wastecooking oil via alkali catalyst and its engine test. Fuel ProcessingTechnology, 89: 851-857.

Oliveira, J.F.G., Lucena, I.L., Saboya, R.M.A., Rodrigues, M.L.,Torres, A.E.B., Fernandes, F.A.N., Cavalcante Jr, C.L., ParenteJr,E.J.S. 2010. Biodiesel production from waste coconut oil byesterification with ethanol: The effect of water removal by adsorption.Renewable Energy, 35: 2581-2584.

Park, Y.M., Lee, J.Y., Chung, S.H., Park, I.S., Lee, S.Y., Kim,D.K., Lee, J.S., Lee, K.Y. 2010. Esterification of used vegetable oilsusing the heterogeneous W[O.sub.3]/Zr[O.sub.2] catalyst for productionof biodiesel. Bioresource Technology, 101: 59-61.

Raie, M.Y. 2008. Oil, Fats and Waxes, 1st edition, National BookFoundation, Islamabad, Pakistan.

Sharma, Y.C., Singh, B., Upadhyay, S.N. 2008. Advancements indevelopment and characterization of biodiesel: A review. Fuel, 87:2355-2373.

Sheehan, J., Cambreco, V., Duffield, J., Garboski, M., Shapouri, H.1998. An overview of biodiesel and petroleum diesel life cycles. AReport by US Department of Agriculture and Energy, pp. 1-35, Washington,D.C., USA.

Srivastava, A., Prasad, R. 2000. Triglycerides-based diesel fuels.Renewable and Sustainable Energy Reviews, 4: 111-133.

Thai standard EN 14214. 2004. Biofuels Standard & Regulationsin Thailand. Thailand Institute of Scientific and Technological Research(TISTR). http://www.tistr.or.th.

Zhang, Y., Dube, M.A., McLean, D.D., Kates, M. 2003. Biodieselproduction from waste cooking oil: Process design and technologicalassessment. Bioresource Technology, 89: 1-16.

Mehmood Abbas (a), Farooq Ahmad (a) *, Adnan Skhawat Ali (a),Maqsood Ahmed (a), Muhammad Farhan (a), Syed Ahtisham Shabbir (b), AqsaIftikhar (a) and Nazish Mohy-u-Din (a)

(a) Sustainable Development Study Centre, GC University, Lahore,Pakistan

(b) Directorate General of Health, Lahore, Government of Punjab,Pakistan

(received February 28, 2012; revised December 29, 2012; acceptedJanuary 4, 2013)

* Author for correspondence; E-mail: [emailprotected]

Table 1: Analysis of pretreated frying oil sampleParameters tested ResultsWater content (%) 0.43Nature of food (fried) Chicken meatIodine value (mg/g) 52Saponification value (mg/g) 205Free fatty acid (%) 8.7Acid value (mg KOH/g) 0.8Table 2. Percentage composition of fatty acids in usedfrying oilFatty acid profile Result (%)C14:0 Tetradecanoic (myristic) Traces (0.1)C16:0 Hexadecanoic (palmitic) 7.88C18:0 Octadecanoic (stearic) 0.35C18:1 Octadecenoic (oleic) 54.54C18:2 Octadecadienoic (linoleic) 28.96C18:3 Octadecatrienoic (linolenic) 7.546C20:0 Eicosanoic (arachidonic) 0.18Total saturated fatty acids 8.51Total unsaturated fatty acids 91.046Others 0.444Table 3. Measurement of amount and yield of productsfrom 200 mL of used frying oilProducts of the processes One-step Two-step process processBiodiesel produced (mL) 176 184Glycerin and other 24 16 byproduct (mL)Yield of biodiesel (%) 88 92Table 4. Optimization of reaction conditions fortransesterification of used frying oilReaction One-step Two-step processconditions process trans esterification Esterification Trans esterificationCatalyst NaOH [H.sub.2] NaOH S[O.sub.4]Methanol to 3:1 6:1 9:1 oil ratioTemperature 60 51 55 ([degrees]C)Reaction 30 60 60 time (min)increased that ultimately increased the free fatty acidconversions (Park et al., 2010).Table 5. Analysis of biodiesel produced from used frying oil andits comparison with international standardsProperties of Testing Biodiesel ASTM Thaibiodiesel methods of this D6751 Standard EN study 14214 (2004)Kinematic viscosity (2002) at 40 [degrees]C ASTM ([mm.sup.2]/s) D445 4.86 1.9-6.0 3.5-5.0Flash point ASTM ([degrees]C) D93 185 >130 >101Specific gravity ASTM (g/mL) D1298 0.884 -- 0.860-0.900created by using it for biodiesel production.