Bioresource Technology 100 (2009) 2883–2885

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Bioresource Technology

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Application of waste eggshell as low-cost solid catalyst for biodiesel production

Ziku Wei a,b, Chunli Xu a,b,*, Baoxin Li c

a Key Laboratory of Applied Surface and Colloid Chemistry (Shaanxi Normal University), Ministry of Education, Xi’an 710062, PR Chinab School of Chemistry and Materials Science, Shaanxi Normal University, Chang’an South Road 199, Xi’an 710062, PR Chinac Key Laboratory of Analytical Chemistry for Life Science of Shaanxi Province, School of Chemistry and Materials Science, Shaanxi Normal University, Xi’an, 710062, PR China

a r t i c l e i n f o a b s t r a c t

Article history:Received 11 September 2008Received in revised form 18 December 2008Accepted 18 December 2008Available online 7 February 2009

Keywords:Eggshell wasteBiodieselCatalysisHeterogeneous catalysisTransesterification

0960-8524/$ - see front matter � 2008 Elsevier Ltd. Adoi:10.1016/j.biortech.2008.12.039

* Corresponding author. Address: School of ChemShaanxi Normal University, Chang’an South Road 199+86 29 85300970; fax: +86 29 85307774.

E-mail address: xuchunli@snnu.edu.cn (C. Xu).

Waste eggshell was investigated in triglyceride transesterification with a view to determine its viabilityas a solid catalyst for use in biodiesel synthesis. Effect of calcination temperature on structure and activityof eggshell catalysts was investigated. Reusability of eggshell catalysts was also examined. It was foundthat high active, reusable solid catalyst was obtained by just calcining eggshell. Utilization of eggshell as acatalyst for biodiesel production not only provides a cost-effective and environmental friendly way ofrecycling this solid eggshell waste, significantly reducing its environmental effects, but also reducesthe price of biodiesel to make biodiesel competitive with petroleum diesel.

� 2008 Elsevier Ltd. All rights reserved.

1. Introduction

Eggshell weighs approximately 10% of the total mass (ca. 60 g)of hen egg, and eggshell is the significant solid waste producedfrom food processing and manufacturing plants (Stadelman,2000). In China, for example, it is estimated that annually about4,000,000 tones is generated and will continue to grow in future(MOA, 2006). Most of the eggshell waste is commonly disposedin landfills without any pretreatment because it was traditionallyuseless (Tsai et al., 2008a). However, the waste management isnot a desirable practice in view of the environmental odor frombiodegradation (Tsai et al., 2008b). In recent years, a great deal ofeffort has been conducted for the application of eggshell as va-lue-added products. These major applications included a possiblebone substitute (Dupoirieux et al., 1995), the starting material forpreparing calcium phosphate bioceramics (e.g., hydroxyapatite)(Balazsi et al., 2007), and a low-cost adsorbent for removal of ionicpollutant from the aqueous solution (Tsai et al., 2008a). Eggshellhas a little developed porosity and pure CaCO3 as an importantconstituent. The chemical composition (by weight) of eggshellhas been reported as follows: calcium carbonate (94%), magnesiumcarbonate (1%), calcium phosphate (1%) and organic matter (4%)(Stadelman, 2000). Due to its intrinsic pore structure in the calci-fied eggshell, high content of CaCO3 and the amount in abundance,

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istry and Materials Science,, Xi’an 710062, PR China. Tel.:

it is possible to prepare active heterogeneous catalyst from egg-shell. However, to our best knowledge, there is no report about cat-alyst prepared from eggshell in the open literature.

The price of petroleum diesel has soared in recent years and theavailable reserves of this important fuel will eventually be ex-hausted if large-scale use continues, and greenhouse gas emissionby the usage of fossil fuels is also becoming a greater concern. So,research is now being directed towards the use of alternativerenewable and environmentally friendly fuels that are capable offulfilling an increasing energy demand (Ma and Hanna, 1999). Bio-diesel is a renewable alternative to petroleum diesel that is com-posed of monoalkyl esters of fatty acids, and it has similarphysical properties to petroleum diesel but unique advantagesincluding being renewable, biodegradable, non-toxic and lowemissions. Biodiesel is generally produced by transesterificationof vegetable oils or animal fats with short-chain alcohols (generallymethanol) in the presence of catalysts (Ma and Hanna, 1999; DiSerio et al., 2008; Huber et al., 2006). The conventional catalystsfor this transesterification reaction are homogeneous strong bases(such as alkali metal hydroxides and alkoxides) and homogeneousacids (such as H2SO4). However, alkaline catalysts are generallycorrosive to equipment and also react with free fatty acid to formunwanted soap by-products that require expensive separation;homogeneous acid catalysts are difficult to recycle and operate athigh temperatures, and also give rise to serious environmentaland corrosion problems. Therefore, the development of solid cata-lysts has recently gained much attention in view of their ease ofseparation and lack of corrosion or toxicity problems (Lópezet al., 2007; DaSilveira Neto et al., 2007). Unfortunately, the

2884 Z. Wei et al. / Bioresource Technology 100 (2009) 2883–2885

preparation of the highly effective solid catalysts is complex,costly, and requires experienced people to operate it (Zong et al.,2007). The cost of fabricating a catalyst can be a critical factor inits industrial applications. The production of biodiesel calls for anefficient and cheap catalyst to make the process economic and fullyecologically friendly, accordingly reducing its price and making itcompetitive with petroleum diesel (Di Serio et al., 2008; Kawashi-ma et al., 2008; Zong et al., 2007; Toda et al., 2005).

In this work, we explored the possibility of application of egg-shell as a catalyst in catalytic process of biodiesel production. Re-use of eggshell as low-cost catalyst for biodiesel production wasinvestigated in the viewpoint of the recycle of eggshell waste, min-imization of contaminants, reducing the production costs of bio-diesel and making the process to produce biodiesel fullyecologically friendly.

1000 oC

900 oC

Inte

nsity

(a.

u.)

800 oC

CaO

CaCO3

700 oC

600 oC

500 oC

300 oCInte

nsity

(a.

u.)

2. Methods

2.1. Materials

Eggshell was collected from the local bakeries. To remove impu-rity and interference material, the eggshell was rinsed severaltimes with deionized water. Then, the eggshell was dried at100 �C for 24 h in the dry oven. Calcination was performed in themuffle furnace at different temperatures (200 �C–1000 �C) for 2 hunder static air after crushing the dried eggshell.

2.2. Characterizations

TGA experiments were carried out using Q600 SDT thermalanalysis machine (TA Instruments, USA) under a flow of nitrogen.The sample weight used was about 20 mg, and the temperatureranged from 38 �C to 1000 �C with a ramping rate of 20 �C min�1.X-ray diffraction patterns were recorded on a D/Max-3C X-raypowder diffractometer (Rigalcu Co., Japan), using a Cu-K a sourcefitted with an Inel CPS 120 hemispherical detector. SEM micro-graphs were performed using a Quanta 200 scanning electronmicroscope equipped with an energy dispersive spectrometer (Phi-lips-FEI Co., the Netherlands).

2.3. Reaction procedure

The reactions were carried out in a batch reactor at 65 �C or150 �C under vigorous stirring. Typical reactions were performedwith 25 ml of vegetable oil (100% soybean oil; Xi’an Jiali GreaseIndustrial Co., Ltd., Xi’an, China) and 9 ml of methanol (methanol/vegetable oil molar ratio 9:1; molecular weight of soybean oil‘‘871 g/mol” was used) using 3 wt% (catalyst/oil weight ratio) ofeggshell derived catalyst at 65 �C for the specified time. The reac-tion products were analysed using the following procedure. Thesamples were separated from catalyst and glycerol by centrifuge.The glycerol could be separated because it was insoluble in the es-ters and had a much higher density. Then methanol was removedusing a vacuum pump and the obtained product was added todeuterated chloroform for 1H NMR to determine the yield to methylester.

20 30 40 50 60 70 80

natural

200 oC

2θ (°)

Fig. 1. XRD patterns of natural eggshell and the materials obtained by calciningnatural eggshell in the range of 200 �C–1000 �C.

3. Results and discussion

3.1. Characterization of eggshell waste-derived catalysts

The heterogeneous catalyst was prepared by calcining eggshellwaste at high temperature. The textural structure of eggshell cal-cined at different temperatures can be observed from the scanningelectron micrograph (SEM) images. Natural eggshell had macrop-

ores and a generally irregular crystal structure. The SEM imagesindicated that the structure of eggshell changed with calcinationtemperature. Below 700 �C, the size and shape of particles wassimilar to that of natural eggshell. Above 800 �C, the size of parti-cles decreased and the particle shape became more regular. Thechange of structure of eggshell may be resulted from the changeof composition.

In order to explain the effect of calcination temperature, weinvestigated the calcination process of eggshell with thermal grav-ity analysis (TGA) technology. TGA result showed the tempera-tures, at which the eggshell precursors decomposed when heatedin a controlled environment. Water and organics was removedfrom the precursors below 600 �C, whereas carbon dioxide was lostbetween 700–800 �C.

The thermal pre-treatment resulted in a change in the X-ray dif-fraction (XRD) pattern, caused by the removal of CO2 from thestarting material (Fig. 1). The diffraction patterns of the samplesheated at temperatures <700 �C were characteristic of CaCO3, whilesamples activated at temperatures >700 �C displayed diffractionreflections characteristic of CaO. Samples calcined at 700 �C for2 h contain CaCO3 as the major phase and CaO as a minor phase.

3.2. Transesterification over eggshell waste-derived catalysts

3.2.1. Effect of calcination temperatureTo determine the influence of the calcination temperature on

the activity of the eggshell-derived catalyst, eggshell was calcinedat different temperatures between 200 �C and 1000 �C and then

Z. Wei et al. / Bioresource Technology 100 (2009) 2883–2885 2885

tested for the transesterification of soybean oil to produce biodie-sel. These results showed that eggshell sample calcined above800 �C was the most active catalyst. A yield of 97–99% was ob-tained in the presence of eggshell sample calcined above 800 �C.When the calcination temperature was 700 �C, a yield of 90% wasachieved, whereas, a low level of activity was observed when thecalcination temperature was <600 �C. A yield of <30% was gainedin the presence of eggshell sample calcined <600 �C.

The changes observed in the XRD patterns (Fig. 1) coincidedwith a change in the catalytic activity of eggshell calcined at differ-ent temperatures. Calcinations below 600 �C did not lead to theformation of CaO, and, consequently, the catalytic activity was verylow. The best catalytic performance was obtained for calcinationtemperatures above 800 �C, when the XRD patterns showed a crys-talline CaO. Samples calcined at 700 �C for 2 h contain CaCO3 as themajor phase and CaO as a minor phase, hence middle yield wereobtained. Therefore, CaO were the active phase of the eggshell de-rived catalysts.

3.2.2. Effect of reaction variablesThe yield of biodiesel was affected by reaction variables, such as

methanol/oil ratio, catalyst amount or reaction time. The reactionvariables were associated with the type of catalysts used (Maand Hanna, 1999). Therefore, the effect of reaction variables wasstudied in the presence of eggshell-derived catalyst. For the follow-ing reactions, all the catalyst was prepared by calcinning eggshellat 1000 �C for 2 h.

The experimental results showed that the yield increased withincreasing the methanol/oil molar ratio, and reached a maximumwhen the ratio was above 9. When a small amount of catalyst(<1 wt%) was used, the maximum product yield could not bereached. However, increasing the amount of catalyst to more than10 wt% lead to the slurry (mixture of catalyst and reactants)becoming too viscous, giving rise to a problem of mixing and a de-mand of higher power consumption for adequate stirring. To avoidthis kind of problem, an optimum amount of catalyst loading wasdetermined. The results showed that the yield increased withincreasing the catalyst loading weight up to 3 wt%. However, theyield did not increase when the catalyst loading weight was above3 wt%. Getting the reactants to and from the catalyst became therate determining step (mass transport limitation) which was whyadding more catalyst didn’t have an effect. Therefore, the optimumcatalyst loadings was found to be 3 wt% in this system. The effect ofreaction time was tested. The results showed that the yield in-creased with time, reaching maximum value (yield >95%) after 3 h.

The experimental results showed that a 9:1 molar ratio ofmethanol to oil, addition of 3 wt% eggshell-derived catalysts (cal-cined at 1000 �C, CaO), 65 �C reaction temperatures gave the bestresults, and the biodiesel yield exceeded 95% at 3 h. Both the reac-tion condition and yield of biodiesel were almost similar to that ofhomogeneous catalytic system (Ma and Hanna, 1999). Hence, egg-shell-derived heterogeneous catalyst showed high activity.

3.2.3. Reusability of eggshell waste-derived catalystsWe also investigated the reusability of the catalyst. The results

indicated that the eggshell-derived catalyst can be repeated use for13 times with no apparent loss of activity. After being used formore than 13 times, eggshell-derived catalyst lost activity gradu-ally. The eggshell-derived catalyst was completely deactivatedafter being used more than 17 times. The deactivation of egg-shell-derived catalyst may be ascribed to its structure change.The XRD patterns of the eggshell-derived catalyst used more than17 times were characteristic of Ca(OH)2, while fresh eggshell-de-rived catalyst displayed diffraction reflections characteristic ofCaO. This showed that the major phase of catalyst has changedfrom CaO (fresh catalyst, Fig. 1) to Ca(OH)2 (catalyst used more

than 17 times). The structure change of catalyst could result fromthe reaction between H2O and CaO, because the reactants (soybeanoil and methanol) contain a little amount of water. However, thecatalyst can be regenerated just by simple calcination. Therefore,eggshell-derived catalyst can be reused and regenerated.

4. Conclusions

High active, reusable solid catalyst was obtained by just calcin-ing eggshell. Calcined eggshell exhibited high activity towards thetransesterification of vegetable oil with methanol to produce bio-diesel. The method of reusing eggshell waste to prepare catalystcould recycle the waste, minimizing contaminants, reducing thecost of catalyst, and making the catalyst environmentally friendly.This high efficient and low-cost eggshell catalyst could make theprocess of biodiesel production economic and fully ecologicallyfriendly. The ecologically friendly and economic process couldeffectively reduce the processing cost of biodiesel, making it com-petitive with petroleum diesel. We anticipate that the low-costcatalyst could be used in a large-scale industrial process of biodie-sel, making the process cheap and ecologically benign. In additionto biodiesel production, such environmentally benign eggshell-de-rived catalysts should find application in a wide range of otherbase-catalysed important organic reactions.

Acknowledgements

This work was supported by the Scientific Research Foundationfor the Returned Overseas Chinese Scholars, State EducationMinistry.

Appendix A. Supplementary material

Supplementary data associated with this article can be found, inthe online version, at doi:10.1016/j.biortech.2008.12.039.

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