Production of fatty acid methyl esters over a limestone-derived heterogeneous catalyst in a fixed-bed reactor

Journal of Industrial and Engineering Chemistry 20 (2014) 1665–1671

Contents lists available at ScienceDirect

Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec

Production of fatty acid methyl esters over a limestone-derived heterogeneous catalyst in a fixed-bed reactor Anawat Ketcong a, Warakorn Meechan a, Thikumporn Naree b, Issarapap Seneevong b, Anurak Winitsorn c, Suchada Butnark c, Chawalit Ngamcharussrivichai a,d,* a

Fuels Research Center, Department of Chemical Technology, Faculty of Science, Chulalongkorn University, Patumwan, Bangkok 10330, Thailand Program in Petrochemistry and Polymer Science, Faculty of Science, Chulalongkorn University, Patumwan, Bangkok 10330, Thailand PTT Research and Technology Institute, PTT Public Company Limited, Wangnoi, Ayutthaya 13170, Thailand d Center of Excellence on Petrochemical and Materials Technology, Chulalongkorn University, Patumwan, Bangkok 10330, Thailand b c

A R T I C L E I N F O

Article history: Received 3 April 2013 Accepted 6 August 2013 Available online 20 August 2013 Keywords: Biodiesel Transesterification Heterogeneous catalyst Limestone Fixed-bed reactor

A B S T R A C T

Production of fatty acid methyl esters (FAME) via the transesterification of different vegetable oils and methanol with a limestone-derived heterogeneous catalyst was investigated in a fixed-bed reactor at 65 8C and ambient pressure. This heterogeneous catalyst, as a 1 or 2 mm cross-sectional diameter extrudate, was prepared via a wet mixing of thermally treated limestone with Mg and Al compounds as binders and with or without hydroxyethyl cellulose (HEC) as a plasticizer, followed by calcination at 800 8C. The physicochemical properties of the prepared catalysts were characterized by various techniques. Palm kernel oil, palm oil, palm olein oil and waste cooking oil could be used as the feedstocks but the FFA and water content must be limited. The extrudate catalyst prepared with the HEC addition exhibited an enhanced formation of FAME due to an increased porosity and basicity of the catalyst. The FAME yield was increased with the methanol/oil molar ratio. The effect of addition of methyl esters as cosolvents on the FAME production was investigated. The structural and compositional change of the catalysts spent in different reaction conditions indicated that deactivation was mainly due to a deposition of glycerol and FFA (if present). The FAME yield of 94.1 wt.% was stably achieved over 1500 min by using the present fixed-bed system. ß 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

1. Introduction Transesterification of vegetable oils or animal fats with methanol in the presence of a homogenous base, such as NaOH or KOH, is the major route for the production of biodiesel as fatty acid methyl esters (FAME) due to the high conversion rate and the mild reaction conditions [1,2]. However, there are some serious drawbacks with homogeneously catalyzed reactions. The process requires neutralization, separation and purification steps that cause a significant increase in the production cycle time, capital investment and operation costs. Furthermore, a large amount of water is consumed and, from the required washing stages, produces environmentally unfriendly alkaline,

* Corresponding author at: Department of Chemical Technology, Faculty of Science, Chulalongkorn University, Patumwan, Bangkok 10330, Thailand. Tel.: +66 2 218 7528/2 218 7523x5; fax: +66 2 255 5831. E-mail address: [email protected] (C. Ngamcharussrivichai).

biodiesel-contaminated wastewater at significant levels (10% (v/ v) the amount of biodiesel produced) that requires detoxification treatment prior to discharge [3]. The use of soluble bases also affects the purity of the glycerol by-product, a versatile trihydric alcohol that is a starting substrate for the syntheses of valuable chemicals. Recently, Axens commercialized the first heterogeneously catalyzed biodiesel production process, invented by the French Institute of Petroleum (IFP), using a spinel mixed oxide of Zn and Al as a solid base catalyst [4]. The use of this catalyst simplifies the transesterification process by allowing the omission of the catalyst separation and product purification stages. The solid catalyst also reduces the loss of FAME yield from soap formation via the saponification reaction. As a result, a biodiesel with a FAME purity of 98% is produced concomitantly with 99% purity glycerol. Although the transesterification process is operated under high temperature and pressure conditions, resulting in a high operating cost, the plant gains benefit from selling the pharmaceutical grade glycerol.

1226-086X/$ – see front matter ß 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jiec.2013.08.014

A. Ketcong et al. / Journal of Industrial and Engineering Chemistry 20 (2014) 1665–1671

1666

Transesterification can be actively performed under milder reaction conditions using an Al2O3-supported alkali metal oxide catalysts [5–9]. Unfortunately, the catalytically active centers are easily leached by methanol [10], limiting their economic application at a commercial scale. The use of CaO as an active solid basic catalyst has been widely investigated in alcoholysis [11–17]. In addition to its widespread availability and low cost, it possesses a high basic strength (H_ = 26.5) [18] and exhibits a low solubility in methanol [11]. The preparation of CaO can be done by a simple calcination of high-purity limestone at temperatures higher than 825 8C [19], as well as from other natural compounds, such as dolomite, cuttlebone, mollusk shells and eggshells [20,21]. However, CaO has been reported to form colloids of calcium glyceroxides (Ca(C3H7O3)2) during the transesterification of rapeseed oil with methanol in a batch reactor [11], and when the column reactor filled with only the calcined limestone was plugged after a long continuous run [22]. Dilution of the catalyst bed by adding active carbon extended the process lifetime. Recently, practical heterogeneous catalysts in an extrudate form were developed via a wet mixing of thermally treated limestone with Mg and Al compounds as binders, and then followed by calcination at high temperatures after extrudation [23]. No colloids were found in the transesterification reaction when performed under both batch and fixed-bed conditions. In the past decade, there have been a large number of works published on the development of heterogeneous base catalysts for the transesterification of triglycerides [24], of which a few studies have demonstrated the catalytic performance in continuous operation mode conditions [22,23,25]. Here, we reported the production of FAME from different oil feedstocks over a limestonederived heterogeneous base catalyst packed in a fixed-bed reactor at 65 8C and ambient pressure. Discussion on the system stability and the catalyst deactivation are also provided.

muffle furnace at 800 8C for 4 h. Hereafter, the typical catalyst formed from a distilled water paste is designated as CMA-I, whereas the catalysts prepared under the acidic condition without or with adding HEC are denoted as CMA-II and CMA-II-HEC. 2.2. Catalyst characterization The crystalline structures of the catalyst before and after being used in the transesterification were determined by means of powder X-ray diffraction (XRD) using a Bruker D8 ADVANCE X-ray diffractometer equipped with Cu Ka radiation using a 0.028 step size range at room temperature. The diffraction peaks were assigned after consulting the JCPDS powder diffraction files. Elemental analysis was performed by XRF on an Oxford ED2000 energy dispersive X-ray fluorescence spectrometer. The catalyst morphology was analyzed with a JEOL JSM-5800LV scanning electron microscope (SEM). A Perkin Elmer Pyris Diamond thermogravimetry (TG/DTA) was applied to investigate the catalyst deactivation using a temperature ramp rate of 8 8C min1 under a dry air flow at a rate of 20 mL min1. The textural properties of the catalysts were characterized by N2 adsorption-desorption measurement at 196 8C on a Micromeritics ASAP 2020 surface area and porosity analyzer. The catalyst was degassed at 200 8C for 2 h prior to the measurement. The total basicity of the catalyst was measured by a CO2-pulse chemisorption using a Micromeritics AutoChem II 2920 chemisorption analyzer. The solid sample (60 mg) was pretreated in situ at 400 8C for 1 h under an Ar flow (50 mL min1), after which CO2 (10 vol.% in Ar) was pulsed through the catalyst at 100 8C until reaching the saturation. Some physicochemical properties of the CMA-I, CMA-II and CMA-II-HEC catalysts are summarized in Table 1. 2.3. Transesterification reaction

2. Experimental 2.1. Catalyst preparation The limestone used in the present study was donated by the Thai Dolomite Company Limited. Elemental analysis by X-ray fluorescence spectroscopy (XRF) indicated the presence of Ca and Mg as the major metals. The transesterification catalyst was prepared as described elsewhere [23] via a physical mixing of calcined limestone with precursors of Mg and Al in the presence of a solvent, followed by calcination. Typically, the limestone powder was calcined in a muffle furnace at 600–800 8C for 2 h, and the required amount of Mg(OH)2 and Al2O3 (AR grade, Ajax Finechem) was then mixed with the calcined rock and deionized water was slowly added under stirring until forming a paste. When hydroxyethyl cellulose (HEC, commercial grade) was used as a plasticizer, the catalyst preparation was carried out in a nitric acid solution. The paste was shaped into a continuous rod with a crosssectional diameter of 2 mm using a manual extruder and then dried in an oven at 100 8C overnight. Subsequently, the extruded catalyst was cut into 5-mm lengths, followed by calcination in a

Refined bleached deodorized palm oil (RPO) and palm kernel oil (RKO) were provided by the Chumporn Palm Oil Industry Public Co., Ltd. Food grade palm olein oil (POO) was donated by the Pathum Vegetable Oil Co., Ltd. Waste cooking oil (WCO), after being used for potato and chicken frying, was from Chester’s Grill. The fatty acid composition and some properties of the vegetable oils used in the present study are shown in Supplementary Information Tables S1 and S2, respectively, whilst the methanol and ethanol were commercial grade with >99% purity. The transesterification of various oils with methanol or ethanol under continuous conditions was performed in a glass column (20-mm inside diameter and 500-mm height) packed with 78 mL of the calcined catalyst extrudates, and with ca. 2 mm diameter glass beads as the bed support. In a typical reaction, oil and alcohol were separately fed upwards into the column by peristaltic pumps with a resident time of 60 min (Supplementary Information Fig. S1), maintaining a molar ratio of methanol/oil at 30. In some cases, tetrahydrofuran (THF) at 10% (v/v, based on the oil volume), was added into the oil reservoir to improve the cold flow properties of the feedstocks. The

Table 1 Physicochemical properties of the CMA-I, CMA-II and CMA-II-HEC extrudate catalysts after calcining at 800 8C for 2 h. Catalysta

CMA-I CMA-II CMA-II-HEC a b c

BET surface area

Average pore volume

Average pore diameter

Number of basic sites

(m2 g1)b

(cm3 g1)b

(nm)b

(mmol g1)c

34.5 30.3 24.1

0.148 0.155 0.239

21.5 20.4 39.8

45.9 29.2 35.0

The crystalline phases of all catalysts, as determined by XRD analysis, were CaO, Ca(OH)2, MgO, MgAl2O4, and Ca12Al14O33. Determined by N2 adsorption–desorption measurement. Determined by CO2-pulse chemisorption.

A. Ketcong et al. / Journal of Industrial and Engineering Chemistry 20 (2014) 1665–1671

column temperature was controlled at 65 8C using a heater jacket equipped with a thermocouple and connected to a temperature controller. The product mixture flowing from the top of the column passed into a water-cooled condenser, and was periodically collected in a 50-mL screw-cap glass bottle. The FAME phase was recovered without any washing after the excess alcohol was removed by rotary evaporator. The FAME composition was analyzed with a Shimadzu 14B gas chromatograph (GC) equipped with a flame ionization detector (FID) and a 30-m DB-Wax capillary column. The FAME yield (wt.%) was calculated according to the standard method (EN 14103) using methyl undecanoate (C12H24O2) as the reference standard in the analysis of the product transesterified from RKO, and methyl heptadecanoate (C18H36O2) for RPO, POO and WCO as the feedstocks. Quantitative analysis of the mono-, di-, and triglyceride remnants was performed on a Varian CP-3800 gas chromatograph equipped with a FID and a 15-m DB-1HT capillary column following the method described in EN 14105.

3. Results and discussion 3.1. Influence of the reaction conditions As shown in Table 2, the transesterification of PKO and RPO in the fixed bed reactor gave a high FAME yield. The FAME yield decreased slightly when the total feed rate was increased, whilst a reaction temperature higher than the boiling point of methanol (64.7 8C) retarded the formation of FAME, presumably due to the reduction in the contact time between the reactants and between the reactants and the catalyst extrudates. Increasing the methanol/ oil molar ratio to 50 did not significantly alter the FAME yield, but allowed the reaction to be performed for a longer operating time of at least 1500 min without loss of the FAME production rate (see 3.2.4. Stability test). The addition of FFA, as 5 wt.% oleic acid, in the feedstock slightly hampered the transesterification, as reflected by the slight reduction in the FAME yield. The XRD pattern of the spent catalyst attained from the transesterification of RPO with the added oleic acid (Fig. 1(b)) is different to that of the catalyst used in the methanolysis of acid-free RPO (Fig. 1(a)), where the presence of Ca(OH)2 as the major Ca compound suggested that CaO was transformed via the formation of calcium methoxide (Ca(OCH3)2) [26] and subsequent hydrolysis, as shown in Eqs. (1) and (2). CaOðsÞ þ 2CH3 OHðlÞ $ CaðOCH3 Þ2ðsÞ þ H2 OðlÞ

(1)

1667

CaOðsÞ þ H2 OðlÞ $ CaðOHÞ2ðsÞ

(2)

However, there was no crystalline phase of Ca(OCH3)2 detected. Presumably, the Ca(OH)2 was derived from the CaO hydration by moisture in the ambient during the catalyst recovery and XRD analysis. The co-existence of oleic acid in the reaction generated calcium fatty acid salts (soap) on the catalyst surface, corresponding to the new XRD phase observed at 2u = 20.48, 21.78 and 26.58, that was concomitant with the decrease in CaO and Ca(OH)2 (Fig. 1(b)). This is consistent with catalyst deactivation via poisoning. The methanolysis of POO to FAME occurred at a lower extent compared to that of RPO, especially at the lower methanol/oil molar ratio of 30. This may be related to the presence of additive molecules in the food-grade oil. Although increasing the methanol/ oil ratio to 50 enhanced the FAME formation level at 120 min, a significant decrease in the FAME yield at longer reaction times was still observed. However, the transesterification reaction with POO could be carried out at 75 8C when ethanol was used as the alcohol to achieve a FAEE yield of 93% after 480 min reaction time. The relatively high reaction temperature and more hydrophobic character of ethanol may alter the solubility of the oil as well as the additive molecules. The present reactor system was able to synthesize FAME from WCO, but with relatively low FAME being obtained compared to those obtained with RPO and POO. Acid-base and Karl-Fischer titration based analysis indicated the existence of high FFA (4.1 wt.%) and water (1.8 wt.%) levels in in the WCO sample, both of which are harmful to the basic sites. The pre-esterification of WCO with methanol in the presence of H2SO4, according to the batch method reported by Patil et al. [27], reduced the amount of FFA and water to less than 1 wt.%, resulting in an improvement of the FAME yield to >90 wt.% in the subsequent transesterification under the fixed-bed conditions (data not shown). 3.2. Investigation of RPO methanolysis 3.2.1. Influence of the catalyst extrudate The sizes of the catalyst extrudates, i.e. nominal 1 and 2 mm cross sectional diameter by 5 mm long cylinders, were determined by the pore diameters of the die faced to the screw piston. To compare the effects of extrudate sizes, the weight of catalyst was kept constant. Glass beads, with an average diameter of 2 mm, were placed at the bottom of the reactor column to maintain a constant bed height between the different sized catalyst extru-

Table 2 Effect of varying the reaction conditions on the transesterificationa of vegetable oils with methanol or ethanol over CMA-I extrudates. Feedstock oilb

Alcohol

Alcohol/oil molar ratio

Total feed rate (mL min1)d

Reaction temperature (8C)

Run time (min)

PKO RPO RPO RPO RPO RPO + FFAc POO POO POO WCO

Methanol Methanol Methanol Methanol Methanol Methanol Methanol Methanol Ethanol Methanol

30 30 30 30 50 50 30 50 30 50

2.5 2.5 3.5 2.5 3.3 3.3 2.3 3.3 3.0 3.3

50 60 60 80 60 60 60 60 75 60

400 320 254 579 600 390 420 440 480 270

a b c d e

Reaction conditions: catalyst size, 2 mm cross-sectional diameter CMA-I catalyst. THF was added at 10% (v/v based on volume of oil) except for in the case of PKO and POO. Oleic acid, as a model free fatty acid (FFA), was added at 5 wt.% (based on weight of oil). Oil and alcohol were separately fed into the upward flow reactor at the combined total feed rate shown. Fatty acid methyl ester (FAME) or fatty acid ethyl ester (FAEE) yield, determined at 120 min and at the end of run time.

FAME/FAEE yield (wt.%)e 120 min

End of run

86.5 93.2 92.5 88.8 94.7 93.7 80.0 92.3 91.6 86.5

85.7 93.0 91.4 90.4 93.3 90.0 69.1 80.4 93.1 85.7

A. Ketcong et al. / Journal of Industrial and Engineering Chemistry 20 (2014) 1665–1671

Intensity/ a.u.

1668

(c)

(b)

(a) 10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

2 /º Fig. 1. XRD patterns of the spent CMA-I catalysts: (a) typical reaction, (b) reaction in the presence of oleic acid, and (c) reaction with adding MEA-75. (Symbols: * = CaO, ~ = Ca(OH)2, = Ca12Al14O33, ^ = MgO and * = Ca soap species).

dates. A higher FAME yield was achieved with the 1-mm catalyst extrudates (Fig. 2). The enhanced level of FAME formation could be attributed to the higher surface area-to-volume ratio found inside the reactor bed with the smaller catalyst extrudates due to their smaller void fraction that improves the contact between the reactants and the catalyst surface. Note that the cross-sectional cut-down extrudates after being used for up to 10 h of time on stream possessed a pale yellow external surface radiance, similar to the color of RPO, but remained white at the center. Possibly, the bulky triglyceride molecules rarely diffused inside the extrudates and so only the active sites located near the external surface were accessible for the catalytic transesterification. The addition of HEC as a plasticizer in the catalyst formulation enhanced the level of FAME production by the 2-mm cross-

100

FAME yield/ wt.%

95 90 85 80 75 70 100

200

300 400 500 Time on stream/ min

600

Fig. 2. The FAME yield attained from the transesterification of RPO with methanol over different sized CMA-I, CMA-II and CMA-II-HEC catalysts. Reaction conditions: methanol/oil molar ratio, 30; temperature, 65 8C. (Symbols: ~ = 1-mm CMA-I, ^ = 2-mm CMA-I, & = 2-mm CMA-II and * = 2-mm CMA-II-HEC).

sectional diameter catalyst extrudates (Fig. 2). The inclusion of HEC decreased the BET surface area but increased the average pore size, average pore volume and basicity (Table 1). In support of this is that, from the BJH plots in Fig. 3, the catalyst prepared with HEC addition exhibited a shift in the pore size distribution to higher diameters including the generation of new larger pores (diameters >100 A˚). Moreover, SEM analysis revealed the larger secondary pores, with an average diameter of 1.7 mm, in the catalyst prepared in the presence of HEC (Fig. 4). Therefore, the removal (burning off) of the HEC from the shaped catalyst upon its calcination in air provided the extrudates with a higher number of larger secondary pores that essentially promoted the diffusion of triglycerides and methanol into the interior active sites of the catalyst extrudates. However, the loss of mechanical strength of the catalyst particles from their increased porosity would explain why the catalyst extrudates were damaged after the long reaction run. 3.2.2. Influence of the methanol/oil molar ratio Generally, a large molar excess of methanol to oil is required to drive the equilibrium of the transesterification of triglycerides to a high FAME conversion [1]. Most of the reported batch studies over heterogeneous base catalysts have revealed that the FAME formation is increased with increasing methanol/oil molar ratios up to 15 and then remained constant at higher ratios [5–8], although a suitable ratio as high as 30 was reported in some studies [20,28]. Indeed, the EsterFip-H commercial FAME production plant is operated at a similar high methanol/oil molar ratio [4]. Despite being unfavorable from the economic point of view, such a high methanol/oil ratio seems to have no detrimental effect on the surface reaction. However, the potential role of such a high molar excess of methanol remains unclear. Instead of performing the reaction in a large amount of methanol, it was reported that using THF as a co-solvent relieved the mass transfer limitation and promoted the conversion of triglycerides [11]. However, in contrast, in this study, under batch conditions using the CMA-I catalyst and a methanol/oil molar ratio of 30, the addition of THF at 10% (v/v based on the oil volume) only increased the FAME yield 5%, whereas increasing the methanol/oil molar ratio to 50 cause a 12% increase in the obtained FAME yield. As shown in Fig. 5, the FAME production was slightly and significantly enhanced when the methanol/oil molar ratio was

A. Ketcong et al. / Journal of Industrial and Engineering Chemistry 20 (2014) 1665–1671

5

5

(A)

(B)

4

4

3

3

dVp/dDp

dVp/dDp

1669

2

1

2

1

0

0

1

10

100

1000

Dp/nm

1

10

100

1000

Dp/nm

Fig. 3. BJH pore size distribution attained from the 2-mm cross-sectional diameter (A) CMA-II and (B) CMA-II-HEC extrudate catalysts.

increased from 30 to 50 or to 60, respectively, with a >95% FAME yield achieved at the methanol/oil ratio of 60. A high methanol/oil ratio is required for the efficient transesterification in a fixed bed reactor operating at a low reactants flow rate where the laminar flow of oil and methanol greatly limits the molecular transfer between the two liquid phases and between the liquid reactants and the solid catalyst. Polar products, such as the diglycerides, monoglycerides and glycerol, can accumulate on the hydrophilic surface of the catalyst. A long contact time of glycerol with the CaO phase may seriously deactivate the active sites by forming calcium glyceroxides [22]. A large molar excess of methanol increases the polarity and can leach and dissolve the glycerol and the glyceride derivatives away from the active sites on the catalyst surface. 3.2.3. Influence of methyl ester addition The addition of methyl esters as co-solvents to enhance the miscibility of the reactants in the ethanolysis of soybean oil over

CaCO3 packed in a fixed-bed reactor was reported to improve the level of obtained FAME conversion [25]. In addition, an increase in the transesterification rate by directly mixing a small amount of biodiesel (B100) with activated CaO powder was observed under batch conditions [29], whilst the residual mono- and di-glycerides in the incompletely transesterified oil possess emulsifying properties that are expected to modify the solubility of the feedstock oil and methanol. The effect of adding a methyl ester mixture, evaluated as two different glyceride compositions (Supplementary Information Table S3), on the transesterification of POO with methanol was investigated (Fig. 6). Each selected methyl ester mixture (15 wt.%) was co-fed with the oil into the reactor. The FAME yield was slightly improved in the presence of MEA-96, as was the initial FAME yield (up to 200 min reaction time) obtained with the addition of MEA-75, but in both cases the increased amount of FAME corresponded to the amount of FAME that would be

Fig. 4. SEM micrographs of the 2-mm cross-sectional diameter (A) & (B) CMA-II and (C) & (D) CMA-II-HEC extrudate catalysts (5000 and 15,000 magnifications).

A. Ketcong et al. / Journal of Industrial and Engineering Chemistry 20 (2014) 1665–1671

1670

950

100

10

95

0

DTG/ g min

-1

750

90 85

-10

650 550

-20

450 -30

350 250

80

Weight loss/ wt.%

FAME yield/ wt.% ww

850

-40

150 -50

50

75

-50

-60 0

70 100

200

300 400 500 Time on stream/ min

600

100

200

300 400 500 Temperature/ °C

600

700

800

Fig. 7. Weight loss and DTG curves of CMA-I catalysts spent in the transesterification of POO with methanol in the absence (thick line) or the presence of MEA-75 (thin line) as a co-solvent.

Fig. 5. Effect of varying the methanol/oil molar ratio on the FAME yield attained from the transesterification of RPO with methanol over CMA-I extrudates. Reaction conditions: catalyst size, 2-mm cross-sectional diameter; temperature, 65 8C. (Symbols: ^ = 30, 4 = 50 and * = 60).

expected to be produced from the transesterification of the residual mono- and di-glycerides in the added methyl ester mixture (Supplementary Information Table S3). That is, no beneficial effect was seen, in contrast to that previously reported [25]. This discrepancy may, however, be due to the higher methanol/oil molar ratio used in the present study. Moreover, when MEA-75 was added, a severe drop in the FAME yield at later time points was observed, the potential cause of which is addressed next. The weight loss and DTG curves of the spent CMA-I catalysts, used in the transesterification of POO with methanol, with and

100 90

FAME yield/ wt.%

80 70 60 50 40 30 20 10 0 100

200 300 400 Time on stream/ min

500

Fig. 6. Effect of the addition of two different methyl ester mixtures (15 wt.%) on the FAME yield attained from the transesterification of POO with methanol over CMA-I extrudates. Reaction conditions: catalyst size, 2-mm cross-sectional diameter; methanol/oil molar ratio, 30; temperature, 65 8C. (Symbols: ^ = none, ~ = MEA-75 and * = MEA-96).

without the addition of MEA-75 (Fig. 7) indicated that the used catalyst in the presence of the MEA-75 exhibited a much higher amount of organic species, especially as glycerol (15.1 wt.%), corresponding to the weight loss found at 205 8C, while the amount of glyceride derivatives, evidenced by the decomposition temperature of 312 8C, were comparable between both used catalysts (ca. 7 wt.%). Accordingly, the XRD analysis of the spent catalyst formed with MEA-75 indicated a decreased crystallinity of the metal phases (Fig. 1), and so suggests that the glycerol and glyceride derivatives contained in the MEA can deactivate the catalyst. 3.2.4. Stability test As a stability test, the transesterification of RPO with methanol using the CMA-I catalyst developed in this study was carried out in a modified fixed-bed system for 1500 min. The effluent product from the top of the reactor column was directly fed into an evaporator, made of a glass column packed with 2-mm diameter glass beads and covered by a heater jacket, to continuously remove the excess methanol. The separate FAME and glycerol phases were discharged from the bottom of the evaporator, and then collected and subjected to GC analysis without prior washing. FAMEs were stably produced throughout the 1500 min reaction period with an average purity of 94.1% (Supplementary Information Fig. S2). According to the standard method EN14105, the amount of diglycerides and triglycerides remaining in the biodiesel product was quantified to be 0.12 and 0.03 wt.%, respectively, both of which passed the standard specification issued by the Department of Energy Business, the Ministry of Energy, Thailand. However, the monoglycerides content was 0.53 wt.% higher than the maximum level allowed by the current biodiesel specifications. The amount of alkali earth metal ions, as Ca2+ and Mg2+, was less than 300 ppm, as evidenced by the XRF analysis. These results suggested that a reasonably good quality of biodiesel can be obtained, at this laboratory scale, using this heterogeneous catalysis system. To enhance the purity of the obtained FAME and to reduce the monoglycerides content, the FAME produced should be fed again into the reaction column after which the FAME yield can be increased to >98 wt.%. Moreover, a column packed with a cation-exchange resin can be used to adsorb the soluble metal ions from the final ester product [30].

A. Ketcong et al. / Journal of Industrial and Engineering Chemistry 20 (2014) 1665–1671

1671

4. Conclusions

References

The production of FAME via the transesterification of different vegetable oils with methanol over a heterogeneous base catalyst derived from limestone was successfully performed in a fixed-bed reactor using a separate feeding configuration into the reaction column with an upward one-pass flow of the reaction mixture at 65 8C and ambient pressure. The presence of FFA and water in the starting oil hampered the transesterification via the formation of calcium fatty acid salts (soap). Despite the loss of mechanical properties, the addition of HEC as a plasticizer in the catalyst formulation improved the porosity and the basicity of the catalyst extrudates, resulting in an enhanced FAME yield. With RPO as the feedstock, increasing the methanol/oil molar ratio above 30 increased the level of FAME formation, but no beneficial effect of the co-addition of methyl esters as a co-solvent was observed under the studied conditions. Catalyst deactivation was principally related to the deposition of glycerol and glyceride derivatives on the active surface. By using the present fixed-bed system, the FAME yield of 94.1 wt.% was stably achieved over 1500 min.

[1] K.H. Chung, J. Ind. Eng. Chem. 16 (2010) 506. [2] I.M. Atadashi, M.K. Aroua, A.R. Abdul Aziz, N.M.N. Sulaiman, J. Ind. Eng. Chem. 19 (2013) 14. [3] F. Ma, M.A. Hanna, Bioresour. Technol. 70 (1999) 1. [4] L. Bournay, D. Casanave, B. Delfort, G. Hillion, J.A. Chodorge, Catal. Today 106 (2005) 190. [5] H.J. Kim, B.S. Kang, M.J. Kim, Y.M. Park, D.K. Kim, J.S. Lee, K.Y. Lee, Catal. Today 93– 95 (2004) 315. [6] T. Ebiura, T. Echizen, A. Ishikawa, K. Murai, T. Baba, Appl. Catal. A 283 (2005) 111. [7] X. Xie, H. Peng, L. Chen, Appl. Catal. A 300 (2006) 67. [8] X. Xie, H. Li, J. Mol. Catal. A 255 (2006) 1. [9] S. Benjapornkulaphong, C. Ngamcharussrivichai, K. Bunyakiat, Chem. Eng. J. 145 (2009) 468. [10] D. Martı´n Alonso, R. Mariscal, R. Moreno-Tost, M.D. Zafra Poves, M. Lo´pez Granados, Catal. Commun. 8 (2007) 2074. [11] S. Gryglewicz, Bioresour. Technol. 70 (1999) 249. [12] G.R. Peterson, W.P. Scarrach, J. Am. Oil Chem. Soc. 61 (1984) 1593. [13] S. Gryglewicz, Appl. Catal. A 192 (1999) 23. [14] C. Reddy, V. Reddy, R. Oshel, J.G. Verkade, Energy Fuel 20 (2006) 1310. [15] A. Demirbas, Energy Convers. Manage. 48 (2007) 937. [16] M. Lo´pez Granados, M.D. Zafra Poves, D. Martı´n Aloson, R. Mariscal, F. Cabello Galisteo, R. Moreno-Tost, J. Santamarı´a, J.L.G. Fierro, Appl. Catal. B 73 (2007) 317. [17] X. Liu, H. He, Y. Wang, S. Zhu, X. Piao, Fuel 87 (2008) 216. [18] H. Hattori, Chem. Rev. 95 (1995) 537. [19] R.S. Boynton, Chemistry and Technology of Lime and Limestone, John Wiley & Sons, Inc., New York, 1980. [20] C. Ngamcharussrivichai, W. Wiwatnimit, S. Wangnoi, J. Mol. Catal. A 276 (2007) 24. [21] N. Viriya-empikul, P. Krasae, B. Puttasawat, B. Yoosuk, N. Chollacoop, K. Faungnawakij, Bioresour. Technol. 101 (2010) 3765. [22] M. Kouzu, J. Hidaka, Y. Komichi, H. Nakano, M. Yamamoto, Fuel 88 (2009) 1983. [23] C. Ngamcharussrivichai, W. Meechan, A. Ketcong, K. Kangwansaichon, S. Butnark, J. Ind. Eng. Chem. 17 (2011) 587. [24] Y.C. Sharma, B. Singh, J. Korstad, Fuel 90 (2011) 1309. [25] G.J. Suppes, K. Bockwinkel, S. Lucas, J.B. Mason, J.A. Heppert, J. Am. Oil Chem. Soc. 78 (2011) 139. [26] M. Kouzu, T. Kasuno, M. Tajika, S. Yamanaka, J. Hidaka, Appl. Catal. A 334 (2008) 357. [27] P.D. Patil, V.G. Gude, S. Deng, Ind. Eng. Chem. Res. 48 (2009) 10850. [28] C. Ngamcharussrivichai, P. Totarat, K. Bunyakiat, Appl. Catal. A 341 (2008) 77. [29] M. Lo´pez Granados, D. Martı´n Alonso, A.C. Alba-Rubio, R. Mariscal, M. Ojeda, P. Brettes, Energy Fuel 23 (2009) 2259. [30] M. Kouzu, S. Yamanaka, J. Hidaka, M. Tsunomori, Appl. Catal. A 355 (2009) 94.

Acknowledgements The authors are grateful to the PTT Public Co., Ltd., the Center of Excellence on Petrochemical and Materials Technology (PETROMAT), Chulalongkorn University, and the Thai Government Stimulus Package 2 (TKK 2555) under the Project for Establishment of Comprehensive Center for Innovative Food, Health Products and Agriculture (PERFECTA) for financial and technical support. The authors also thank the Chumporn Palm Oil Industry Public Co., Ltd. and the Pratum Vegetable Oils Co., Ltd. for providing the vegetable oils, and the Thai Dolomite Co., Ltd. for donating the natural limestone. The authors wish to express their thanks to Dr. Robert Douglas John Butcher for English language editing. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.jiec.2013.08.014.