Scholarly article on topic 'Kinetics of the Pre-Treatment of Used Cooking Oil Using Novozyme 435 for Biodiesel Production'

Kinetics of the Pre-Treatment of Used Cooking Oil Using Novozyme 435 for Biodiesel Production Academic research paper on "Chemical sciences"

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{Biodiesel / "liquid chromatography" / "Novozyme 435" / esterfication / transeterifcation}

Abstract of research paper on Chemical sciences, author of scientific article — K.F. Haigh, B. Saha, G.T. Vladisavljević, J.C. Reynolds

Abstract The pretreatment of used cooking oil (UCO) for the preparation of biodiesel has been investigated, using Novozyme 435, Candida antarctica Lipase B immobilized on acrylic resin, as the catalyst. The reactions in UCO were carried out using a jacketed batch reactor with a reflux condenser. The liquid chromatography mass spectrometry (LC-MS) method was developed to monitor the mono-, di and triglyceride concentrations for this work and it has been shown that it is possible to obtain linear calibration curves. This work showed that Novozyme 435 will catalyse the esterification of FFAs and the transesterification of mono- and diglycerides typically found in UCO when Novozyme 435 is used to catalyse the pretreatement of UCO for the formation of biodiesel.

Academic research paper on topic "Kinetics of the Pre-Treatment of Used Cooking Oil Using Novozyme 435 for Biodiesel Production"

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Engineering

Procedía

ELSEVIER

Procedía Engineering 42 (2012) 1211 - 1219

www.elsevier.com/locate/procedia

20th International Congress of Chemical and Process Engineering CHISA 2012 25 - 29 August 2012, Prague, Czech Republic

Kinetics of the pre-treatment of used cooking oil using Novozyme 435 for biodiesel production

K. F. Haigh33*, B. Sahab, G. T. Vladisavljevic3, J. C. Reynolds0

aDepartmentof ChemicalEngineering, Loughborough University, Loughborough, LE11 4LE, UnitedKingdom bDepartment ofApplied Sciences, Faculty ofEngineering, Science and the Built Environment, London South Bank University,

London, SE1 OAA, United Kingdom cDepartmentof Chemistry, Loughborough University, Loughborough, LE11 4LE, Unite dKingdom

The pretreatment of used cooking oil (UCO) for the preparation of biodiesel has been investigated, using Novozyme 435, Candida antarctica Lipase B immobilized on acrylic resin, as the catalyst. The reactions in UCO were carried out using ajacketed batch reactor with a reflux condenser. The liquid chromatography mass spectrometry (LC-MS) method was developed to monitor the mono-, di and triglyceride concentrations for this work and it has been shown that it is possible to obtain linear calibration curves. This work showed that Novozyme 435 will catalyse the esterification of FFAs and the transesterification of mono- and diglycerides typically found in UCO when Novozyme 435 is used to catalyse the pretreatement ofUCO for the formation of biodiesel.

©2012 Published by Elsevier Ltd. Selection under responsibility of the Congress Scientific Committee (Petr Kluson)

Keywords'. Biodiesel; liquid chromatography; Novozyme 435; esterfication; transeterifcation

a* Corresponding author. Tel.: +44-0-1509-222-528; E-mail address'. K.Haigh@lboro.ac.uk.

Abstract

1877-7058 © 2012 Published by Elsevier Ltd. doi:10.1016/j.proeng.2012.07.502

1. Introduction

Biodiesel is defined as mono-alkyl esters of long chain fatty acids derived from renewable sources, particularly vegetable oil and animal fats . The most common commercial process is to convert vegetable oil to biodiesel by means of a transesterification reaction, with methanol in the presence of a basic catalyst such as sodium hydroxide resulting in the formation of fatty acid methyl esters (FAME), as showninFig. 1.

> + s[ ] ™OH

Triglyceride R3

Glycerol

Fatty Acid Alkyl Esters (Biodiesel)

Fig. 1. Schematic representation of the transesterification reaction

Vegetable oil is an expensive raw material and there are ethical concerns with using a potential food source for fuel and alternative raw materials such as Jatropha Curacas , by-products from oil refining such as palm fatty acid distillate , animal fats, algal oil and used cooking oil (UCO) are currently being investigated to mitigate these issues. The advantage of UCO is that a waste material is diverted from landfill. The cooking process causes the vegetable oil, triglycerides, to breakdown to form, mono- and diglycerides, and free fatty acids (FFAs). The FFAs react with the basic catalysts used during transesterification in a saponification side reaction which can form an emulsion and reduce product yield. In addition most biodiesel specifications impose an upper limit on the FFAs content as FFAs can cause deposits and engine damage . Various methods have been investigated to remove FFAs from UCO including neutralization and water washing . However, these methods reduce the product yield and generate waste. Alternatively esterification can be used to convert the FFAs to biodiesel and a schematic of the esterification process is shown in Fig. 2. Currently the most common process is to use a homogenous acid catalyst such as sulfuric acid and methanol to produce FAME . Acid catalysts can also be used to catalyse the transesterification process, however, the reaction rate is much slower when compared to basic catalysts.

Fig. 2. Schematic representation of the esterification reaction

Novozyme 435, Candida antarctica Lipase B immobilized on acrylic resin, was investigated for the esterification pre-treatment of biodiesel from UCO . However it was found that at the higher reaction temperatures (50-60 C) the amount of FAME formed was greater than the amount of FFAs consumed based on the esterification reaction scheme shown in Fig. 2. Lipases including Novozyme 435 have also been investigated for transesterification, although it has been found that the reaction rate is slow. Kinetic modeling has been used to investigate the lipase catalysed transesterification reaction mechanism and it was found that there are parallel reaction pathways indicating that transesterification and esterification can occur simultaneously . This indicates that Novozyme 435 can simultaneously catalyse esterification and transesterification reaction in UCO.

In order to determine if Novozyme 435 can simultaneously catalyse esterification and transesterification reactions in UCO, it is necessary to monitor the mono-, di- and triglyceride concentrations in addition to the FAME and FFAs concentrations. Gas Chromatography (GC) and liquid chromatography (LC) are the most common methods for investigating the production of biodiesel . Substances with high molecular weights, high boiling points and low volatility are not easily vapourised and separated by GC, although this problem can be overcome by means of a silylation reaction and the use of internal standards . LC is a versatile analytical technique and most samples do not require derivitisation and as a result numerous methods have been investigated for the separation and quantification of biodiesel components . UV and Mass spectrometry (MS) detectors have been investigated for the detection of biodiesel components , however, UV detectors are not very versatile because the response is based on the concentration and number of double bonds. MS detectors are useful because they can also provide structural information.

This work has investigated the use of LC-MS to determine the concentration of mono-, di and trigclyerides in the reaction mixture during the esterification pretreatment of UCO for the production of biodiesel. This data has been used to improve the understanding of the reaction mechanism when Novozyme 435 is used as the esterification catalyst. In particular the aim is to determine which components and reactions are contributing to the additional FAME formation.

2. Experimental

2.1.Materials

Methyl ester, mono-, di and trigyceride standards were purchased from Sigma. Novozyme 435 was donated by Novozymes UK Ltd and used as supplied and stored in a refrigerator. The UCO was supplied by GreenFuel Oil Co Ltd., UK and has an average molecular weight of 278 g.mol"1 and an FFAs content of approximately 6.4 wt%. Analytical grade methanol, toluene and 2-propanol were purchased from Fisher Scientific UK Ltd. HPLC grade 2-propanol and acetonitrile were used for the HPLC work and purchased from Fisher Scientific UK Ltd. All solvents were used as supplied.

2.2. BatchExperimental Procedure

The esterification reactions were carried out using a jacketed batch reactor with a reflux condenser. The stirrer motor was a Eurostar Digital IKA-Werke. The temperature was monitored by means of a Digitron, 2751-K thermocouple and this information was used to set the temperature on the Techne, TE-10D Tempette water bath. The UCO and methanol were added to the reactor and heated to the required temperature, after sampling, the catalyst was added to initiate the esterification reaction. The sample tube was fitted with metal gauze to prevent withdrawal of catalyst when taking samples and the samples were withdrawn by means of a syringe. All samples were analyzed for FFAs, FAME, mono-, di and triglyceride concentrations.

2.3. FFA andFAME Analysis

The FAME concentration was determined using gas chromatography mass spectrometry (GC-MS) (Hewlett Packard HP-6890), equipped with a DB-WAX (J & W Scientific) capillary column, (30 m x 0.25 mm) packed with polyethylene glycol (0.25 ^m film thickness); Helium at a flow rate of 1.1 mL/min was used as the carrier gas. The amount of sample injected was 2 ^L. The temperature of the injector and detector was 250 °C. The initial oven temperature was 70 °C held for 2 min, then increased at 40 °C/min up to 210 °C, then increased at 7 °C/min up to 230 °C and the final temperature held for 11 minutes. Methyl heptadecanoate was used as the internal standard.

The %FFAs of all samples was determined by titration using the ASTM D974 method. 2gof sample was dissolved in 100 mL of a solution of toluene:2-propanol:water (volume ratio of 100:99:1) and titrated using p-naphtholbenzein indicator.

2.4. The LC-MS Procedure

The LC-MS was carried out using a Waters Acquity ultra performance liquid chromatography (UPLC) system interfaced to a Waters Synapt HDMS quadrupole time-of-flight (TOF) mass spectrometer, using positive ion. A Phenomenex Kinetix C18 UPLC column (150 mm x 2.1 mm x 2.1 ^m) was used for the separation. The chromatography used a binary method with acetonitrile as solvent A and 2-propanol as solvent B. The separation was carried out using a binary gradient with a flow rate of 0.15 ml/min starting with 90% acetonitrile and 10% 2-propanol changing to 30% acetonitrile in 20 min.

3. Results of the LC-MS Analysis

A typical chromatogram generated by LC-MS for UCO is shown in Fig. 3. UCO is known to consist of a mixture of various mono-, di and triglycerides and as a result the chromatogram for UCO has a large number of peaks. This analysis was carried out using a mass spectrometer and therefore an extracted ion chromatogram for each species can be generated based on their mass-to-charge ratio. The extracted ion chromatogram for glycerol dioleate linoleate is shown as an inset in Fig. 3. This chromatogram has two significant peaks that correspond to two isomers of glycerol dioleate linoleate separated by the UPLC column.

g 00 (2011) 000-000

^^Diglycerides ^^

Triglycerides

UCO has many components and in order to simplify the method it has been assumed that each component of a given species gives a similar mass spectrometric response. Two calibration standards were used for each of the mono-, di and triglyceride species. It can be seen from the inset in Fig. 3. that many of the components form multiple peaks due to isomerization and as a result the total area under all peaks for the relevant component was used as the peak area. A typical calibration curve is shown in Fig. 4(a). A linear trend has been fitted to this data and the equation and R2 value are shown on Fig. 4(a). From this data it can be seen that the calibration curve is linear. In theory calibration curves should pass through the origin. A non-zero intercept at the Y-axis indicates that there is an interaction with the solvent.

Fig. 3. A typical UPLC chromatogram of used cooking oil (UCO) using the base peak ion (BPI) setting. The inset shows the extracted ion chromatogram for glycerol dioleate linoleate which gives a protonated molecular ion [M+H]+at m/z 905.8

It has been found that most of the diglycerides separate into two peaks and during the reaction these peaks disappear at different rates. An example is shown in Fig. 4(b). for glycerol palmitate linoleate (PL). An enzyme catalyst, Novozyme 435, is being used to catalyse this reaction and this data shows that this catalyst has some stereoselectivity. Enzymes have been investigated for the manufacture of biodiesel but this data indicates that information on the fatty acid composition of a particular oil may not be sufficient to determine how well the enzyme will catalyse a particular reaction. A different mix of isomers could affect how well the reaction proceeds.

Fig. 4. (a) a typical calibration curve for diolein; (b) a comparison of the rate of disappearance ofdiglyceride peaks (glycerol palmitate linoleate (PL))

4. Results of the Batch Experiments

A comparison of the FAME formation compared to FFAs consumption at 60 C using Novozyme 435 as the esterification catalyst is shown in Fig. 5. A schematic of the esterification of FFAs to FAME for the pretreatment of UCO is shown in Fig. 2. From this data it can be seen that the FAME formation exceeds the FFAs consumptionby a factor of3.

It has been proposed that transesterification also taking place and a reaction schematic involving triglycerides is shown in Fig. 1. A similar transesterification reaction is possible involving the mono- and diglcyeride species. The change in concentration of the mono-, di- and trigclyerides, FAME and FFAs is shown in Fig. 6. From this data it can be seen that the monoglyceride concentration increases slightly and then decreases, which is typical of a reaction intermediate. The diglyceride concentration decreases steadily during the course of the reaction. This means that at the end of the 6 h reaction time most of the mono- and diglycerides have been consumed and this would account for the additional formation of FAME. In contrast the change in triglyceride concentration is very small and there is some variation in the experimental data although it appears that overall there is a slight decrease. Thus while triglycerides will react in the transesterification reaction the rate is much slower when compared to the transesterification of mono- and diglycerides. This is consistent with previous experiments where it was found that when Novozyme 435 was used as a transesterification catalyst, the transesterification of triglycerides was the rate limiting step with no accumulation of mono- or diglycerides during the reaction . This data shows that simultaneous esterification and transesterification reactions are occurring during the pretreatement of UCO for the preparation of biodiesel when Novozyme 435 is used as the catalyst.

Fig. 5. Comparison of the FFAs consumption and FAME formation using Novozyme 435 as the esterification catalyst at 60 C

Fig. 6. Change in the concentration of the triglycerides (TG), diglycerides (DG), monoglycerides (MG), fatty acid methyl esters (FAME I biodiesel) and fatty acids (FFAs) during the pretreatment of UCO for biodiesel. This experiment was carried out using Novozyme 435 as the catalyst at 60 C

5. Conclusions

The pretreatment of UCO, using Novozyme 435 as the catalyst, for the preparation of biodiesel has been investigated using LC-MS to monitor the mono-, di and triglyceride concentrations. It was found that it is possible to get linear calibration curves and that LC-MS can be used to monitor the mono-, di and triglyceride concentrations. In addition it has been shown that the LC-MS method has sufficient sensitivity to monitor the progress of specific isomers which may be relevant when working with enzyme catalysts.

This work was carried out because earlier experiments focused on the esterification pretreatment of UCO to form biodiesel showed that there was an excessive formation of FAME at high temperatures due to side reactions. The mono-, di and triglyceride results have shown that the mono-, and diglycerides are consumed during the reaction while the triglyceride concentration decreases slightly. These results show that during the pretreatment of UCO for the preparation of biodiesel with Novozyme 435 as the catalyst esterification and transesterification take place simultaneously.

Acknowledgements

We would like to thank EPSRC for the PhD scholarship to KH. We would also like to thank GreenFuel Oil Co Ltd., UK for supplying the UCO and Novozymes UK. Ltd. (Dr. David Cowan) for supplying the enzyme catalyst and his help and advice with using Novozyme 435 for this project.

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