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Biodiesel production from waste frying oils and its quality control Article in Waste Management · May 2010 DOI: 10.1016/j.wasman.2010.01.007 · Source: PubMed

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Melahat Yildiz

Namık Kemal Üniversitesi

Utrecht University

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Waste Management 30 (2010) 799–803

Contents lists available at ScienceDirect

Waste Management journal homepage: www.elsevier.com/locate/wasman

Biodiesel production from waste frying oils and its quality control T. Sabudak a,*, M. Yildiz b a b

Department of Chemistry, Faculty of Science and Arts, Namik Kemal University, 59100 Tekirdag, Turkey Biodiesel Energy Ind. Trd. Inc., Velimese Industry Region, Corlu, Tekirdag, Turkey

a r t i c l e

i n f o

Article history: Accepted 7 January 2010 Available online 25 January 2010

a b s t r a c t The use of biodiesel as fuel from alternative sources has increased considerably over recent years, affording numerous environmental benefits. Biodiesel an alternative fuel for diesel engines is produced from renewable sources such as vegetable oils or animal fats. However, the high costs implicated in marketing biodiesel constitute a major obstacle. To this regard therefore, the use of waste frying oils (WFO) should produce a marked reduction in the cost of biodiesel due to the ready availability of WFO at a relatively low price. In the present study waste frying oils collected from several McDonald’s restaurants in Istanbul, were used to produce biodiesel. Biodiesel from WFO was prepared by means of three different transesterification processes: a one-step base-catalyzed, a two-step base-catalyzed and a two-step acid-catalyzed transesterification followed by base transesterification. No detailed previous studies providing information for a two-step acid-catalyzed transesterification followed by a base (CH3ONa) transesterification are present in literature. Each reaction was allowed to take place with and without tetrahydrofuran added as a co-solvent. Following production, three different procedures; washing with distilled water, dry wash with magnesol and using ion-exchange resin were applied to purify biodiesel and the best outcome determined. The biodiesel obtained to verify compliance with the European Standard 14214 (EN 14214), which also corresponds to Turkish Biodiesel Standards. Ó 2010 Elsevier Ltd. All rights reserved.

1. Introduction The increasing production of waste frying oils (WFO) from household and industrial sources is a growing problem worldwide. Oils are generally poured down the drain, resulting in problems for waste water treatment plants and energy loss, or integrated into the food chain through animal feeding, thus becoming a potential cause of human health problems (Costa Neto et al., 2000). Several end-uses for this type of waste have been identified, including soap manufacturing (Mittelbach and Tritthart, 1988) energy production by means of anaerobic digestion, thermal cracking (Zaher, 2003), and more recently the production of biodiesel, a fuel suited for use as a petroleum diesel substitute for engines. However, the majority of used oils are treated as waste materials frequently producing both ecological and economical problems. The catalytic conversion of waste frying oils by transesterification into biodiesel results in marked economic and environmental benefits. Biodiesel is biodegradable and nontoxic with low emission profiles thus being less, environmentally harmful than petroleum diesel. Biodiesel is capable of reducing the level of pollutants as well as of potential carcinogens (Zhang et al., 2003; Demibas, 2002). Particularly, waste oils represent an economical option for * Corresponding author. Tel.: +90 282 264 35 13; fax: +90 282 260 21 95. E-mail address: [email protected] (T. Sabudak). 0956-053X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.wasman.2010.01.007

use in biodiesel production, in view of their ready availability and low cost (Kulkarni and Dalai, 2006). Properties featured by used frying oils differ from those of refined and crude oils. The presence of heat and water accelerates the hydrolysis of tri-glycerides and increases the free fatty acid (FFA) content (Fennema, 1985). FFA and water content elicit significant effects on the transesterification of glycerides with alcohols. They also interfere with the separation of fatty acid esters and glycerol. Thus, tri-glycerides containing high amounts of water and FFA are not easily transesterified (Freedman et al., 1984). In literature, several published studies have investigated biodiesel produced from WFO by means of base or acid-catalyzed one-step transesterification reactions and base-catalyzed two-step transesterification reactions (Encinar et al., 2007; Caylı and Kusefoglu, 2008; Tomasevic and Siler-Marinkovic, 2003; Canakcı, 2007; Usta et al., 2005; Felizardo et al., 2006; Ozbay et al., 2008). No previous studies providing detailed information on two-step acid-catalyzed transesterification followed by base transesterification are available to date. The aim of this study was to establish the most appropriate method for use in the purification and characterization of biodiesel from WFO. Waste frying oils, collected from several McDonald’s restaurants by the Alternative Energy and Biodiesel Producers Association (ALBIYOBIR) in Istanbul, were used in the production of biodiesel using a one-step basic, two-step basic and two-step acid-basic transesterification. Each transesterification reaction

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took place with and without THF as a co-solvent. However, three different purification procedures were applied in the production of biodiesel. Seven parameters were assessed in the biodiesel produced to test for compliance with European Standard 14214. 2. Materials and methods 2.1. Materials Waste frying oils were collected from several McDonald’s restaurants by ALBIYOBIR in Istanbul, Turkey. Two different waste frying oils with an FFA value 2% and 4.6%, respectively, were used in the study. Both waste oils were used in all three processes, onestep base, two-step base and two-step acid–base. Each process was performed twice, with and without co-solvent. Methanol, tetrahydrofuran (THF) and sulphuric acid, were supplied by Merck and magnesol (MgO:SiO2 (1:2.7)) from Dallas Group of America, whilst sodium methoxide was obtained from Biodiesel Energy Ind. Trd. Inc. Ion-exchange resins (PD-206) were purchased from Purolite Chemical Company and filter (XZF-103) from Zeren Textile Company. 2.2. Equipment Transesterification was carried out in a 50 L conical reactor, equipped with a 2500 watt resistance, a temperature controller, a mechanical stirrer with two 56 rpm propellers, a circulation pump (0.37 kw) for homogeneous mixing, a sampling valve and a methanol-acid mixture valve. In addition, density (EN ISO 3679), kinematic viscosity (EN ISO 3104), flash point (EN ISO 3679), water content (EN ISO 12937), acid value (EN 14104), iodine value (EN 14111) and methyl ester yield (EN 14103) tests were performed on biodiesel by using pycnometry (KEM-DA-130N), viscometry (USL-ASTM viscometer), flash point apparatus (Petrotest-Closed cup tester 30000-0), and Karl-Fischer moisture titrator (KEM, MKC-50) and GC (Perkin Elmer Clarus 500) with the conditions of inlet temperature: 240 °C, column flow: 2 mL/min, split flow: 50 mL/min, injection volume: 1 lL, oven program initial temperature: 195 °C, hold time (1): 0 min, hold time (2): 6 min, ramp (1): 5 °C/min, oven program final temperature: 240 °C, column: Carbowax 20 M, 30 m 320 lm 0.25 lm film, carrier gas: Helium, FID temperature: 240 °C, H2 flow: 45 mL/min, air flow: 450 mL/min. 2.3. Transesterification procedure The collected waste frying oil was first filtered to remove food residues and then heated at 105–110 °C to remove water. WFO contained 7% water and 1% solid particles. Water content was measured by Karl Fisher titration method and the percentage of solid particular residue was obtained subsequent to weighing after filtration percentage. Homogeneous WFO samples were used in the production of biodiesel in a one-step basic, two-step basic and two-step acid–base transesterification reaction. All transesterification reactions were carried out both using THF as a co-solvent and without THF. In the purification of biodiesel, three different methods, washing with distilled water, dry washing with magnesol and treating with ion-exchange resin were applied. Seven parameters were subsequently measured in biodiesel produced to test for compliance with the European Standards for biodiesel EN 14214. 2.3.1. Ones step base-catalyzed transesterification About 20 g (0.625 mol) of methanol and 1–1.5 g (0.0250– 0.0375 mol) of sodium hydroxide were used in the treatment of

virgin oil or waste frying oil featuring a free fatty acid content of less than 1% per 100 g (0.12 mol) (Gerpen, 2005). Free fatty acid content of the waste frying oil used in this study was 4.6%. During the production process, 32 kg (37.6 mol) of waste oils were mixed with 6.4 kg (200 mol) of methanol and 640 g (11.85 mol) of sodium methoxide solution in methanol at a 30% concentration. Waste frying oils were mixed with methanol and sodium methoxide for 2 h at a temperature of 58 °C to allow the transesterification reaction to take place (Acaroglu, 2003). However, at the end of the reaction time, neither biodiesel nor glycerine was produced, due to the high free fatty acid content. The same experiment was repeated using different waste frying oil samples featuring, a 2% FFA content. Following completion of the reaction the mixture was left to settle for approximately 10 h. Following this period, the glycerine phase was drained out from the bottom of the reactor. The biodiesel phase, separated from glycerine, was heated to 110 °C and left for 30 min to permit evaporation of excess methanol. Magnesol was added to methanol-free biodiesel and the mixture reactor stirred for 1 h in the reactor. The biodiesel and magnesol mixture was then filtered. 2.3.2. Two-step base-catalyzed transesterification In this method, the transesterification reaction took place in two-steps. 75% of the methanol and methoxide was used at the first step and the rest was used in the second step. Between the first and the second steps, the mixture was left to settle for 2 h and the glycerine phase subsequently separated out. In this study, 32 kg (37.6 mol) of WFO was used. For the reaction, 4.8 kg (150 mol) of methanol and 480 g (8.88 mol) of sodium methoxide were used at the first step and 1.6 kg (50 mol) of methanol and 160 g (2.96 mol) of sodium methoxide at the second step. Temperatures of both reaction media were adjusted to 58 °C, with each reaction time lasting 1 h. No biodiesel production was obtained from the experiment performed using waste frying oil having an FFA value of 4.6%. Subsequently, the same procedure was applied using frying oil having an FFA value of 2%. At the end of the reaction, the glycerine phase was separated from biodiesel, and excess methanol was evaporated. Methanol and glycerine free biodiesel was then mixed with magnesol for 1 h and the mixture obtained subsequently filtered. 2.3.3. Two-step acid–base catalyzed transesterification In this study, a two-step process was selected for biodiesel production. The process was started with an acid-catalyzed esterification procedure followed by base-catalyzed transesterification process. Acid esterification, mainly used as a pretreatment process, was performed as a first step remove FFA from waste frying oil. During the esterification reaction, 32 kg (37.6 mol) of WFO, FFA value 4.6%, 3.3 kg (103.1 mol) methanol and 73 g (0.74 mol) of sulphuric acid (98%) were stirred for 1 h at a temperature of 58 °C. During stirring, a 100 ml sample was taken every 15 min and checked for FFA value. FFA values obtained for samples 3 and 4 were remarkably similar indicating that over a 1 h stirring period the reactions reached an equilibrium. After 1 h, stirring was stopped and the reaction mixture allowed to settle for 1 h. After 1 h settling, methanol, acid and water mixture phase was separated from oil phase. The oil phase was analysed and new FFA value obtained as 2.2%. The same procedure was performed repeatedly until an FFA value lower than 1% was achieved. For the second reaction, 1.6 kg (50 mol) of methanol and 35 g (0.35 mol) of sulphuric acid were used. Following this reaction FFA value decreased to 0.7% and alcohol, water and acid mixture phase was separated from the oil. Subsequent to phase separation, 6.4 kg (200 mol) of methanol and 640 g (11.85 mol) of 30% sodium methoxide were added to oil and mixture was stirred for 1 h at 58 °C. On completion of the reaction, the mixture was left to settle

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for 10 h. Glycerine phase was drained out from the bottom of the reactor. The rest of the mixture, containing biodiesel and methanol, was heated to evaporate excess methanol. After the evaporation, magnesol was added to the methanol-free biodiesel and was mixed for 1 h, subsequent to which the mixture was filtered to separate biodiesel and magnesol. 2.3.4. Transesterification reactions with co-solvent (THF) In the present study, tetrahydrofuran (THF) was used as a cosolvent in each transesterification reaction. The amount of THF used in each reaction was equal to the quantity of oil employed a ratio of 1 kg THF to 1 kg waste frying oil (Boocock et al., 1998). The results of the reactions are provided in Table 1. 2.3.5. Purification by washing with water Washing was carried out using soft hot water at a temperature of 50–60 °C. The amount of water used in the washing process was equal to the quantity of biodiesel. Subsequent to washing biodiesel was left to settle for 10 h and the water was then separated from biodiesel. The washed biodiesel was dried by means of agitation at 110 °C for 20 min. 2.3.6. Purification by magnesol Magnesol corresponding to 1% the total amount of biodiesel was added following separation from glycerine and methanol. The resulting magnesol and biodiesel mixture was stirred for 1 h at 70–80 °C. Magnesol was subsequently separated from biodiesel by filtering. 2.3.7. Purification by ion-exchange resin The flow velocity of biodiesel passing through the resin colon was dependent on the amount of resin. In this process no temperature limitations were applied when using biodiesel. The temperature of biodiesel passing through the ion-exchange resins should however not exceed 150 °C. The present study was performed at room temperature and biodiesel corresponding to one and half times the amount of resin was passed through the ion-exchange resins (Purolite-PD 206) at 1 h. 2.3.8. Characterization of the produced biodiesel A series of tests were performed to characterize the properties of the produced biodiesel according to EN 14214. These properties include density (EN ISO 36799, viscosity (EN ISO 3104), flash point (EN ISO 3679), water content (EN ISO 12937), acid number (EN 14104), iodine value (EN 14111) and methyl ester content (EN 14103).

According to the results shown in Table 1, the use of a co-solvent does not produce a significant increase in reaction yield. The highest yield increase obtained was 0.8%. From an economical point of view, the use of THF in this study is not feasible as THF is applied mainly to increase the solubility of methanol in oil. However, the mixing ability of the reactor is sufficient to achieve homogenization of the methanol oil mixture.

3.2. Effect of purification methods on reaction yield The biodiesel produced following transesterification reaction may contain impurities such as soap, mono- di- tri-glycerides, glycerine, methanol and salts. Washing with water, use of an absorbent such as magnesol (this purification method is known as dry wash) or ion-exchange resin can then be performed to achieve separation impurities from biodiesel. The effect of purification methods on transesterification reaction yield is shown in Table 2. The lowest yield is obtained by water wash and the highest yield by ion-exchange resin. The present study revealed how use of ion-exchange resin proved to be the best method in purification of biodiesel produced from waste frying oil.

3.3. Characterization of the produced biodiesel In order to increase the commercial value of biodiesel, standards for fuel quality and control have been established by the ASTM and European (EN) standards, among the most prominent (Mahajan et al., 2007). The biodiesel market is regulated by the Energy Market Regulatory Authority (EMRA) in Turkey. Marketed biodiesel must comply with EN 14214 standards. Although 25 parameters are taken into account by the Standard EN 14214, EMRA requires all biodiesel producers to analyse a minimum of seven parameters; accordingly, density, viscosity, flash point, water content, acid value, iodine value and methyl ester content were analysed in this study. The results of the analysis are illustrated in Tables 3–5. Limits reported in these tables represent limit values of experimental methods establish by EN 14214.

Table 1 The effect of reaction types without and with co-solvent on reaction yield. Types of transesterification reactions

FFA values (%)

Yield (%) Without cosolvent

With cosolvent

3. Results and discussion

One-step base

2 4.6

76.8 0

77.3 0

3.1. Effect of reaction types with and without co-solvent on reaction yield

Two-step base

2 4.6

85 0

85.8 0

Two-step acid–base

4.6

90.3

90.4

Vegetable oil does not dissolve in methanol; it is therefore necessary to stir methanol and oil mixture well to obtain a homogeneous mixture. If the mixing process is not sufficient to homogenize the mixture, the reaction yield reaction decreases. To solve mixing problems, a co-solvent such as n-hexane or tetrahydrofuran (THF) may be used (Boocock et al., 1998). The results obtained from transesterification reactions carried out with and without co-solvent, one-step basic, two-step basic and two-step acid–base transesterification, are shown in Table 1. No biodiesel is produced by means of one-step and two-step base transesterifation processes, from oil with FFA value 4.6%. Biodiesel production yield, by two-step acid–base reaction process, is obtained as 90.4%.

Table 2 The effect of purification methods on reaction yield. Types of transesterification reactions

Yield before purification (%)

Yield after purification (%) Washing with water

Dry washing by magnesol

Ionexchange resin

One-step base Two-step base Two-step acid– base

76.8 85 90.3

80.8 91.0 95.6

84.9 92.3 96.9

85.8 93.4 98.4

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Table 3 The analysis results of produced biodiesel from a one-step base-catalyzed transesterification with co-solvent of WFO (FFA value: 2%). Parameter

Unit

Limits

Analysis results

Experimental method

Minimum

Maximum

washing with water


Ion-exchange resin

Density, 15 °C Viscosity, 40 °C Flash point Water content Fatty acid number Iodine value Methyl ester

kg/m3 mm2/s °C mg/kg mg KOH/g g iodine/100 g % (m/m)

860 3.5 120 – – – 96.5

900 5 – 500 0.5 120 –

884 5.82 155 422 0.41 106 80.8

882 5.32 151 637 0.29 106 84.9

886 5.46 159 381 0.33 106 84.1

EN EN EN EN EN EN EN

ISO 3679 ISO 3104 ISO 3679 ISO 12937 14104 14111 ISO 14103

Table 4 The analysis results of produced biodiesel from two-step base-catalyzed transesterification without co-solvent of WFO (FFA value: 2%). Parameter


Unit

kg/m3 mm2/s °C mg/kg mg KOH/g g iodine / 100 g % (m/m)

Limits

Analysis Results

Experimental method

Minimum

Maximum

Washing with water


Ion-exchange resin

860 3.5 120 – – – 96.5

900 5 – 500 0.5 120 –

883 5.31 159 398 0.39 106 91.0

880 5.14 163 526 0.26 106 92.3

884 5.22 161 317 0.30 106 91.7



Table 5 The analysis results of produced biodiesel from two-step acid–base catalyzed transesterification without co-solvent of WFO (FFA value: 4.6%). Parameter


Unit

kg/m3 mm2/s °C mg/kg mg KOH/g g iodine/100 g % (m/m)

Limits

Analysis results

Experimental method

Minimum

Maximum

Washing with water


Ion-exchange resin

860 3.5 120 – – – 96.5

900 5 – 500 0.5 120 –

885 4.92 148 422 0.38 106 95.6

882 4.74 146 487 0.26 106 96.9

882 4.63 151 372 0.23 106 97.2

4. Conclusions Waste frying oil used in this study was obtained from several McDonalds branches in Istanbul. Biodiesel was produced by three different methods, one-step basic, two-step basic and two-step acid-basic transesterification, each method being performed twice, both with and without co-solvent (THF). The effect of THF on reaction yield was found to be very low due to the use of a reactor equipped with a mechanical agitator and circulation pump for mixing, capable of homogenizing the mixture sufficiently even without co-solvent. As an alternative to use of co-solvent, which reduces reactor capacity and requires additional energy for distillation of co-solvent, it is more economical to improve the mixing ability of the reactor. Three different purification methods, washing with water, addition of magnesol and ion-exchange resin were applied to biodiesel. The most effective purification method was determined to be ionexchange resin. Although purification ability of magnesol was comparable to that of ion-exchange resin, the clay used to filter magnesol subsequently represents a toxic waste the disposal of which is particularly costly. Furthermore, purified biodiesel was analysed to check for compliance with the standard EN 14214. The outcome of experiments performed underlined the impossibility of producing, biodiesel from waste frying oils with an FFA value higher than 2%, without acid esterification. In the present study, biodiesel produced from



waste frying oil with an FFA value of 4.6% by means of two-step acid base reactions and purification by ion-exchange resin met requirements established by EN 14214. Consequently, the findings obtained in the present study endorse the feasibility of producing biodiesel by means of a two-step acid base process from WFO with FFA value higher than 2% and ion-exchange resin for purification.

Acknowledgement The authors would like to thank Biodiesel Energy Ind. Trd. Inc. for the kind assistance provided during in this study.

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