Wood ash as a potential heterogeneous catalyst for biodiesel synthesis

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Wood ash as a potential heterogeneous catalyst for biodiesel synthesis Meeta Sharma a, Arif Ali Khan b,*, S.K. Puri a, D.K. Tuli a a b

Indian Oil Corporation Ltd., Research & Development Centre, Faridabad, India University School of Basic and Applied Sciences, Guru Govind Singh Indraprastha University, Kashmere Gate, Delhi 110403, India

article info

abstract

Article history:

Wood ash is a highly alkaline material comprises of inorganic constituents. A limited

Received 10 January 2011

information on use of wood ash as catalyst is available in literature. The present study was

Received in revised form

undertaken to investigate the catalytic activity of wood ash for transesterification of

17 January 2012

Jatropha oil. The thermal treatment (calcination) of wood ash was carried out at temper-

Accepted 17 February 2012

ature in the range of 500e1200
C to produce calcined wood ash catalysts (CWC). The wood

Available online 28 March 2012

ash was also chemically activated with K2CO3 and CaCO3 by double carbonate solid state reaction to yield activated wood ash catalysts (AWC). The prepared catalysts were char-

Keywords:

acterized by analytical techniques for surface morphology, crystalline phases, textural

Transesterification

characteristics and alkalinity. Methyl ester conversion of Jatropha oil was achieved in the

Biodiesel

range of 97e99% with CWC and AWC catalysts. The synthesized Jatropha methyl esters

Heterogeneous catalysis

using CWC and AWC catalysts have been found meeting the critical physico-chemical

Wood ash

properties of ASTM D-6751 standards of biodiesel. The present study revealed the possi-

Jatropha curcas (L)

bility of producing potential heterogeneous catalyst from wood ash for biodiesel synthesis, which can find a way to utilize abundant wood ash and reduce the overall cost of biodiesel production. ª 2012 Elsevier Ltd. All rights reserved.

1.

Introduction

In recent years, fatty acid methyl esters (FAME) derived from vegetable oils have gained importance as a promising alternate fuel known as biodiesel [1]. Unfortunately, in terms of commercial viability, the use of biodiesel is currently encountering extensive perplexities associated with food versus fuel dispute, solid residues generation and high price of biodiesel. Use of cheap non-edible oils and efficient catalysts have been considered to reduce the cost of biodiesel. Many attempts have been made to produce biodiesel from different feedstock [2], whereas search on catalyst is being perused for commercialization of biodiesel production.

Homogeneous catalysis (base and acid) is normally employed for biodiesel production, due to high yield and faster conversion of oils to methyl esters [3,4]. However, use of homogeneous catalysts lead to many problems such as equipment corrosion, emulsion formation during purification of biodiesel and some environmental problems, such as disposal of waste catalysts [5]. In order to circumvent these problems, several heterogeneous catalysts have been explored and widely accepted, because of generation of low waste effluent and consequent reduction in production cost. There are several comprehensive studies carried out on vegetable oil transesterification with heterogeneous catalysts, such as supported CaO [6e8], calcium ethoxide [9], NaX zeolite

* Corresponding author. Tel.: þ91 981974597; fax: þ91 23900305. E-mail address: [email protected] (A.A. Khan). 0961-9534/$ e see front matter ª 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.biombioe.2012.02.017

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loaded with KOH [10], MgO-functionalized mesoporous catalyst [11], MgO loaded with KOH and KF/CaeMgeAl Hydrotalcite [12] and as CaeZn mixed oxides [13]. Acid catalyst from fly ash has been reported for esterification of salicylic acid [14]. Similar study disclosed a value added utilization of oil palm ash in recycling of industrial waste [15]. A large number of developed heterogeneous catalysts have been reviewed for biodiesel production [16]. However, the higher cost of the developed catalysts were seen as major hindrance for their use on commercial scale. Wood fuel for generating heat and power is of great interest. However, wild fires burn thousands of hectares of forests all over the world, producing a large amount of wood ash as a waste. Beside this, the wood ash is a highly alkaline matter and its disposal is a growing problem, as environmental regulations have become more stringent [17]. Earlier studies [18,19] have shown that the dominant elements of wood ash are calcium, potassium, magnesium, silicon, manganese, aluminum, phosphorous, sulfur, iron, sodium and zinc. The wood ash has been considered for the agricultural application, as it is an excellent source of potash, lime and other plants nutrients [20]. Wood ash has also been used as binding agent, glazing agent in the ceramic industry, road base and alkaline material for the neutralization of waste [21]. The available chemical information on wood ash has revealed that the minerals present are the oxides of different elements. This information may be sufficient to identify the extent of alkalinity of wood ash, but gives little information about the thermal/chemical stability of actual compounds. According to report [22], the composition of forest wood ash depends on various factors, including type of forest species, part of plant (bark, stem, leaves) combusted, plant age, type of soil, climate, conditions of combustion etc. In the light of literature on definition of biomass samples, collected wood sample inorganic constituents composition depends upon the site differences factor, which is responsible for different thermo chemical conversion study of same wood sample for different site [23]. The aim of the present study is to obtain an active and cheap heterogeneous catalyst from waste wood ash for transesterification of non-edible oils, especially Jatropha oil. For this purpose, a series of catalysts were prepared from wood ash and characterized by analytical techniques. The present paper covers characterization and transesterification activity of wood ash products viz. pure wood ash, calcined wood ash and wood ash activated separately with K2CO3 and CaCO3. Chemical composition and mineralogy of the wood ash transformations into different selective compounds, after calcination and activation with metal carbonates have been studied. The produced biodiesel has been evaluated for critical properties as per ASTM D-6751 standard of biodiesel.

the northern part of Chhattisgarh state of India. Geographical coordinates are 23
37’250 ’ N and 81
34’400 ’ E, 244.62 km long east to west and total area of about 16,359 km2. The climate of the sample site is hot summer and well distributed rainfall during the monsoon season. The maximum temperature is 46
C in summer and 18
C in winter. After collection, dried fruits containing three seeds each were stored in perforated gunny bags (jute) below 7e8% moisture content to prevent the seeds from bacterial and fungal growth. Stored samples from the field immediately brought intact to the laboratory. b) Wood sample. The Acacia nilotica (babul) tree stem sample is used for wood ash preparation. The sample was collected from Matia village of Raipur district of India. Geographical coordinates are 21
19’55.170 ’ N and 81
450 25.240 ’ E, the height of the tree was approx. 16 m. The maximum temperature was 31.5
C and minimum temperature was 8.3
C (during sample collection period Dec. 2009), relative humidity 52e81% (at 8.30 h) and 43e60% (at 17.30 h) with annual rainfall of 1385 mm. The wood sample was dried prior to catalyst preparation. c) Methanol, n-hexane, potassium carbonate and calcium carbonate were of laboratory grade and procured from Merck Specialties Pvt. Ltd., and S.d. Fine Chemicals Ltd. All the chemicals and reagents were used as received.

2.

Experimental

2.3.

Characterization of catalyst

2.1.

Materials

2.3.1.

Soluble alkalinity measurements

a) Oil seed. The study was conducted on Jatropha curcas shrub bearing oilseeds. The yellow and brown stage of the fruit is considered as mature stage and collected in the 3rd year of plantation. Provenance of seed is Surguja district located in

2.2.

Catalyst preparation

2.2.1.

Calcined wood ash catalyst (CWC)

The wood sample was washed with deionized water and then dried at 60
C until the constant weight. The wood block was dry ashed separately and calcined at 500, 800, 1000 and 1200
C. The ash produced was observably coarse in nature. It was sieved and used as catalyst for transesterification of Jatropha oil. The prepared catalyst samples were denoted as W0, CWC500, CWC800, CWC1000 and CWC1200, where number 0 indicates W0 for wood ash as such (without calcination) and 500e1200 represents the temperature of calcination.

2.2.2.

Activated wood ash catalyst (AWC)

The activated wood ash catalysts were prepared by solid reaction method. Desired amount of finely ground K2CO3 or CaCO3 and wood ash were mixed together in a mortar and skived for half an hour. After drying in the oven at 80
C for 2 h, the solid was calcined at 800
C for 3 h. The prepared catalyst samples were denoted as AKWC0.25, AKWC0.5 and AKWC1, where number 0.25, 0.50 and 1.0 represents mass fraction percentage of K2CO3, in wood ash : K2CO3, mixture of activated wood ash catalysts. Catalysts, AKWC0.5 and AKWC1 were only taken for detailed analytical characterization. Similarly, only ACaWC0.5 was prepared by loading CaCO3 at optimum ratio of 0.5 mass fraction percentage in wood ash : CaCO3 mixture.

The wood ash sample (0.5 g) was mixed with 50 ml of distilled water and agitated for 48 h. The mixture was filtered through 0.2 mm membrane filter and titrated with 500 mol m3 HCl using 713 Metrohm pH Meter with Pt 1000/B/2/3 MKCl combined electrode. Based on titration, soluble alkalinity was

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determined by measuring the number of mmol of HCl required to neutralize 1 g of ash leachate to pH 7.

2.3.2.

Particle size analysis

A laser scattering particle distributor analyzer CILAS 1180 SL-5040 was employed for the determination of particle size of the prepared catalysts. For the determination, a dispersing liquid containing suspended particles circulates in a measuring cell intersected by a monochromatic laser beam collimated by a condenser on a window of analysis of a defined surface. The light of the laser is diffracted on the outside of the particles and the angles of diffraction are inversely proportional to the size of the particles.

2.3.3.

Surface area measurement

The surface area of prepared catalyst was measured by Micromeritics FLOW SORB-2301 instrument from adsorptiondesorption measurements. The sample was degassed under vacuum at 400
C for 2 h prior to adsorption measurements to evacuate the physisorbed moisture.

2.3.4.

Elemental analysis

Elemental analysis was carried out by Atomic Absorption Spectroscopy (AAS) with PerkineElmer (Optical Emission Spectrometer)eOPTIMA 5300V instrument. X-ray Fluorescence (XRF) technique was used for quantitative determination of elements, especially ‘P’ content by Petro axis, PANalytical 4 KW WDXRF.

2.3.5.

Surface morphology

Scanning Electron Microscopy (SEM) analysis was used to study the surface morphologies of catalysts. The topographical images of the catalyst sample were captured by HITACHIe3400 TypeeII, coupled with X-ray energy dispersive spectroscopy.

2.3.6.

Spectral analysis

The Infra Red (IR) spectroscopy of the wood ash catalyst samples were recorded on PerkineElmer 2000 FTIR instrument. About 2e3 mg of sample was mixed with 100 mg of KBr and grinded to uniform particle size and then pressed as KBr pellet using hydraulic press. The IR spectra were recorded in 4000e400 cm1 region at 4 cm1 resolution, 100 scans.

2.3.7.

Crystalline phases

X-Ray Diffraction (XRD) diffractogram of synthesized catalysts were recorded on 18 KW X-Ray Diffractometer (Rigaku, Japan). Various crystalline phases present in the samples were identified using search match software. The catalyst powder was grinded fine to ensure random orientation of the molecules so that there are sufficient amount of crystals to generate detectable signals of all angles respective of all the components present in the catalyst. The overall peak intensities are often used to estimate the amount of specific crystalline phase.

2.4.

Extraction and characterization of jatropha oil

The morphological parameters of J. curcas seed was collected as length 17.75 mm 0.35 (SD); width 11.7 mm 0.28 (SD);

thickness 8.65 mm 0.21(SD) and kernel to seed shell ratio 1.43. For extraction of oil, mature fruits of J. curcas were dried in the sun and the kernels were isolated. Each fruit of J. curcas contains three set of Jatropha seeds. The oil was extracted from the J. curcas seed by soxhlet apparatus using n-hexane (bp. 68
C). After 16e18 h refluxing, the solvent was distilled off under vacuum and the oil content was calculated from the ratio of mass of oil to the mass of the crushed seed kernels used for extraction [24]. The oil content was found to be 40.1 mass fraction percentage of dry crushed seed kernels and 33 mass fraction percentage of dry crushed seed (kernel þ shell). The physico-chemical properties of the Jatropha oil were tested as per standard test methods and data are given in Table 1. Extracted Jatropha oil was used for transesterification reaction.

2.5.

Activity of catalyst

The activity of wood ash, CWC and AWC catalysts was evaluated by the transesterification of Jatropha oil with methanol. The reactions with pure K2CO3 and CaCO3 as catalyst were carried out to investigate the effect of loading ratio of metal carbonates with wood ash. Typical transesterification reaction was performed in a laboratory scale set-up, which consists of 250 ml glass flask equipped with magnetic stirrer and condenser, immersed in a constant temperature oil bath. The desired quantity of catalyst was first mixed with oilmethanol (1:12 M ratio) mixture to maintain catalytic activity at 40
C for 15 min. To the above stirred solution, desired quantity of vegetable oil was added and the reaction temperature was set at 65
C for the experiment. The progress of the reaction was monitored by Thin Layer Chromatography (TLC), using a composition of petroleum ether (85 ml): diethyl ether (13.5 ml): glacial acetic acid (1.5 ml) mixture as the mobile phase. After completion of the reaction, the material was transferred to separator and two phases were separated. Upper phase was biodiesel and lower was glycerin with

Table 1 e Physico-chemical properties of jatropha oil. Physical property

Test method

Fatty acid profile (%)

ASTM D-1983

Saturated fatty acids Palmitic acid C16: 0 Stearic acid C18: 0 Monounsaturated fatty acids Palmitoleic acid C16: 1 Oleic acid C18: 1 Polyunsaturated fatty acids Linoleic acid C18: 2 Linolenic acid C18: 3 Acid Value (KOH g kg1) Viscosity @ 40
C (mm2s1) Iodine value Density (kg m3) at 15
C Cloud point (
C) Pour point (
C) Oxidation stability (h) Water content (%)

Results

14.2 6.8 1.1 43.1

ASTM D-974 ASTM D-445 Cd 1c-85 ISO 3675 ASTM D-2500 ASTM D-97 EN14112 ASTM D-1123

34.3 0.5 3.80 37.0 99 910 8 3 2.56 0.17

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catalyst. Biodiesel layer was directly dried under reduced pressure to get rid of residual moisture.

2.6.

Methyl ester characterization and evaluation

The Jatropha oil methyl ester samples were characterized by IR and Proton Nuclear Magnetic Resonance (1H NMR) spectroscopy for functional groups. The purity and ester (product) conversion (%) was determined by Gel Permeation Chromatography (GPC) technique, which consists of the PL gel column (5 nm diameter of 600  7.5 mm dimensions) and refractive index detector operated with 1 cm3 min1 flow rate of THF as carrier solvent. GPC technique provides separation of components on the basis of molecular weight/size and helpful in monitoring of conversion of oil into biodiesel. Physicochemical properties of Jatropha methyl ester like TAN, viscosity etc. were analyzed as per standard ASTM test methods.

2.7.

Catalyst regeneration

After transesterification reaction, the spent catalyst from the reaction mixture was recovered by filtration and washed with methanol. The recovered catalyst was used for transesterification of Jatropha oil under similar reaction conditions to measure its activity in a number of cycles. The recovered catalyst was analyzed by XRD. Further the catalyst stability was also checked by leaching test and elemental analysis of the prepared biodiesel sample.

3.

Results and discussion

3.1. Characterization of calcined wood ash catalyst (CWC) and activated wood ash catalyst (AWC) 3.1.1.

Alkalinity

Data of the alkalinity of wood ash, CWC and AWC catalysts is given in Table 2. It is observed that ash calcination temperature affects alkalinity of the catalyst. The results showed that the soluble alkalinity of CWC catalysts increases from 1.6 to 2.6 mmol g1 ash with increase of calcination temperature from 500 to 800
C and decreases from 2.6 to 1.6 mmol g1 ash with increase of calcination temperature (1000e1200
C). The CWC800 has the highest value (2.6 mmol g1 ash) of soluble

Table 2 e Textural characteristics and alkalinity of wood ash, CWC and AWC catalysts. Catalyst

Surface area (m2g1)

Particle size, (mm)

Soluble alkalinity (mmol g1 ash)

W0 CWC500 CWC800 CWC1000 CWC1200 AKWC1 AKWC0.5 ACaWC0.5

9.38 1.59 3.72 1.60 1.33 0.65 12.0 14.0

25 26 22 29 40 53 29 8

1.6 1.8 2.6 1.8 1.6 9.7 12.7 8.8

97

alkalinity. The possible reason for higher alkalinity may be the increase of thermal decomposition of CaCO3 to CaO with the increase of temperature, resulting in high CaO content [22]. The higher water solubility of CaO than CaCO3 resulted in an increase in soluble alkalinity value. Whereas the lowest value (1.6 mmol g1 ash) of soluble alkalinity observed with CWC1200 may be due to the formation of more stable silicate phases by the association of metal oxides (SiO2 and CaO) at higher temperature (1200
C). The lower water solubility of stable silicate phases causes decrease in soluble alkalinity [25]. The AWC catalysts (Table 2) AKWC1, AKWC0.5 and AcaWC0.5 posses 9.7, 12.7 and 8.8 mmol g1 ash soluble alkalinity respectively. Results showed that activated catalysts have higher values of soluble alkalinity than the calcined catalysts. High values of soluble alkalinity is due to the presence of metal carbonates K2CO3 and CaCO3 in excess. Among activated catalysts, AKWC0.5 has the highest value (12.7 mmol g1 ash) of soluble alkalinity. The reason for higher alkalinity is possibly because of the interaction of alkaline Kþ ions with wood ash during activation with K2CO3. Whilst in case of AKWC1, higher loading ratio of K2CO3 decreases the decomposition temperature of CaCO3 present in wood ash [26]. In case of AcaWC0.5 catalyst, only calcium carbonate is responsible for soluble alkalinity value of 8.8 mmol g1 ash.

3.1.2.

Textural characteristic

Textural characteristics of wood ash, CWC and AWC catalysts are given in Table 2. As seen from the Table, the surface area decreases markedly with calcination at higher temperature, as the values for W0, CWC500, CWC800, CWC1000 and CWC1200 are 9.38, 1.59, 3.72, 1.60 and 1.33 m2g1 respectively. The surface area value of 3.72 m2g1 for CWC800 is slightly higher than CWC500 and CWC1000. The possible reason may be the calcination temperature of 800
C, which is closer to CaCO3 decomposition temperature (825
C) and formation of CaO. The surface area value is matching with the reported value [27]. In case of CWC1200, the lower value of surface area (1.33 m2g1) may be due to reduction of CaO content, because of formation of silicate at higher temperature and so the surface area. The AWC catalysts, AKWC1, AKWC0.5 and ACaWC0.5 have surface area values of 0.65, 12.0 and 14.0 m2g1 respectively. The higher surface area value of AKWC0.5 is primarily may be due to the presence of K2CO3 as active component deposited inside the micro pores. To prove such conclusions the leaching test was carried out with the catalysts AKWC0.5 and AKWC1. These experiments revealed that active component (K2CO3) i.e. potassium was not leached with methanol from AKWC0.5 catalyst. However, the leaching in case of AKWC1 indicated that methanol contains some amount of Kþ ion deposited on the surface and start to decompose already at 700
C. The fact was also proved by FTIR spectra (Figs. 3 and 4) which shows the characteristic band of bulk K2CO3 at 1385 cm1. Above findings are in agreement with the earlier study [28]. While in case of AcaWC0.5, the presence of high CaO and Ca(OH)2 content form after CaCO3 decomposition may be responsible for high surface area. As shown in Table 2, the average particle size of W0, CWC500, CWC800, CWC1000, CWC1200 catalysts are 25, 26, 22, 29 and 40 mm respectively. The result revealed that with the increase of calcination temperature, the particle size

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Fig. 1 e SEM image calcined wood ash catalysts (CWC) at different temperatures.

increases. The possible reason may be the increase of sintering with the increase of temperature, leads to increase in particle size [26]. Sintering becomes apparent at 1000 and 1200
C temperature, the surface starts soften and contact, causes larger particle size [29]. The results are in agreement with the XRD analysis given in Figs. 5 and 6, which also supports the formation of Ca2SiO4.0.05Ca3(PO4)2 phase. In case of activated AKWC1, AKWC0.5 and ACaWC0.5 catalysts, the particle size are 53, 29 and 18 mm respectively. The largest particle size found for AKWC1 may be due to higher loaded amount of alkali compounds, as reported in earlier study [30]. The agglomeration of bulk carbonate on the surface due to hindrance of Kþ species may be responsible for formation of larger particle size on the surface [31]. The particle size of AKWC0.5 and ACaWC0.5 catalysts are similar to that of CWC catalysts calcined at 800 and 1000
C temperatures. SEM images of CWC and AWC catalysts are shown in Figs. 1 and 2, which illustrates the porous and spongy nature of ash particles [32]. As the calcination temperature increases, images show the presence of small mineral aggregates and agglomerated particles due to sintering of metal oxides. From the images, it is assumed to us that the spherical particles of different size accumulated on the ceramic surface [33].

3.1.3.

Elemental analysis

The mechanism by which the minerals are released as ash during combustion of wood is not clear, but is reasonable to assume that the conversion depends upon the combustion temperature and immediate environment. Table 3 gives elemental analysis of wood ash, CWC and AWC catalysts

prepared at different calcination temperature. The elements in wood ash are found to be Si, Ca, Mg, Na, K, Al and P. Among these elements, P, 1.1 mass fraction percentage; Mg, 2.9 mass fraction percentage and Na, 0.6 mass fraction percentage are present in relatively smaller amounts, while Ca, 14.7 mass fraction percentage; Si, 17.6 mass fraction percentage; K, 7.3 mass fraction percentage and Al, 9.0 mass fraction percentage are in higher amounts. In case of calcined wood ash catalysts, the variation in calcination temperature from 500 to 1200
C induces the modification in composition of prepared catalysts. As seen from the Table 3, after 500
C calcination, no major variation in composition of wood ash occurred. At 800
C calcination, the increase in Ca content was observed predominantly due to decomposition of CaCO3 (equation (1)) also confirmed by XRD pattern of CWC800 (Fig. 5). During the calcination temperature 1000e1200
C, maximum variation in the elemental composition was observed. At higher temperature, Na and Mg content decreases from 5.6 mass fraction percentage to nil and 4.5 mass fraction percentage to 0.5 mass fraction percentage respectively due to the decomposition of their carbonates to oxides and their subsequent volatilization [26]. The decrease in K content at 1000e1200
C is mainly due to vaporization of KCl (equation (2)). As seen from CWC catalysts data, the metal content of Ca are 14.7, 13.3, 17.8, 22.3 and 36.6 mass fraction percentage in W0, CWC500, CWC800, CWC1000 and CWC1200 respectively. The possible reason for increasing Ca concentration from 14.7 to 36.6 mass fraction percentage may be due to non-volatility of Ca element from the ash. Metal content of Si ranges from 17.6 to 20.1 mass fraction percentage remains almost constant and retained in

b i o m a s s a n d b i o e n e r g y 4 1 ( 2 0 1 2 ) 9 4 e1 0 6

99

Fig. 2 e SEM image of AKWC0.5 catalysts with different mass ratio to K2CO3 and ACaWC0.5.

the ash as silicates at higher temperature. Possibly, at higher temperature CaO and P2O5 might move to SiO2 to form CaeSiePeO phase as Ca2SiO40.05 Ca3(PO4)2 (equation (3)). CaCO3 /CaO þ CO2 ð500  800
CÞ

(1)

KClðlÞ/KClðgÞð1000  1200
CÞ

(2)

CaO þ P2 O5 þ SiO 2 /Ca2 SiO4 0:05Ca3 ðPO4 Þ2

(3)

The above results indicate that ashing temperature significantly affects catalysts chemical composition, as reported in earlier study [26]. As seen from Table 3, the elemental composition of AWC is similar, except the Ca and K content. The content of Ca is

Fig. 3 e FTIR spectra of calcined wood ash catalysts after calcination at 500e1200
C.

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Fig. 4 e FTIR spectra of activated wood ash catalysts after calcination at 800
C.

marginally higher (10.5 mass fraction percentage) in AKWC1 than in AKWC0.5 (8.5 mass fraction percentage). As the calcination was done only at 800
C temperature, so no major modification in composition of AWC catalysts was observed. The content of K in AWC is in line with the loaded ratios of K2CO3. In AcaWC0.5 catalyst, only Ca content is higher, 44.5 mass fraction percentage may be due to higher amount of CaCO3 added during activation.

3.1.4.

Spectral analysis

The FTIR spectra of calcined and activated wood ash catalysts are given in Figs. 3 and 4. The IR analysis of wood ash, W0 sample (Fig. 3) indicates the presence of carbonate, CO2 3 (broad peak at 1797, 1432, 874 and 712 cm1), PO3 4 and SiO2 components (broad peaks in the region of 1107,1037 cm1 along with 618 cm1), showing CaCO3, SiO2 and metal phosphate as main components. The IR spectrum of wood ash

Fig. 5 e XRD chromatogram of calcined wood ash catalysts (CWC) at different temperature.

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Fig. 6 e XRD chromatogram of activated wood ash catalysts (AWC) at different temperature.

calcined at 500
C (CWC500) shows similar spectral features. IR spectra of catalysts obtained after calcination at higher temperatures (CWC800 and CWC1000) show the characteristic bands at 1464, 1423, 997, 527 and 3643 cm1, indicating pres3 ence of CO2 3 , PO4 , SieOeSi and CaO functionalities [33]. All characteristic bands indicate the possible formation of metal silica phosphates as major component. The spectral feature of CWC1200 in 1100e800 cm1 region matches with CWC800 and CWC1000 catalysts, except presence of CaO. The spectral analysis of CWC revealed that various phases of silicon phosphates, metal carbonates and metal phosphates are formed with increase of calcination temperature. In AKWC1 and AKWC0.5 catalysts (Fig. 4), spectral features for presence of metal silica phosphate (1464, 1423, 620 cm1) and SieOeSi (1007 and 997 cm1) are prominent. The presence the characteristic bands at 3210, 864 and 707 cm1 supports

Table 3 e Elemental analysis of wood ash, CWC and AWC catalysts. Catalyst Calcin temp Elements, mass fraction percentage (
C) Si Ca Mg Na K Al P W0 CWC500 CWC800 CWC1000 CWC1200 AKWCI AKWC0.5 ACaWC0.5

e 500 800 1000 1200 800 800 800

17.6 15.7 21.5 22.9 20.1 31.9 31.9 30.5

14.7 13.3 17.8 22.3 36.6 10.5 8.5 44.5

2.9 2.7 4.5 3.1 0.5 3.0 2.6 2.7

0.6 0.6 5.7 5.6 e 8.5 8.3 1.0

7.3 9.0 6.7 8.3 5.7 1.2 7.0 1.3 2.5 0.2 36.8 1.1 10.8 1.3 3.0 1.5

1.15 0.80 0.50 0.50 0.50 0.55 0.47 0.40

the presence of K2CO3.1.5H2O. Additionally, the characteristic band at 1385 cm1 in AKWC1 catalyst confirms the presence of bulk K2CO3 [28]. In AcaWC0.5 catalyst, spectral feature for the presence of additional CaO (3644 cm1) and Ca(OH)2 (1759 and 1450 cm1) are observed. It can be seen that the band centered at 1400 cm1 could be assigned for the presence of B - type 2 carbonate substitution, (PO3 4 /CO3 ), which may be responsible for less reactivity of AcaWC0.5 catalyst.

3.1.5.

XRD analysis

The crystalline compounds in wood ash, CWC and AWC were identified by XRD diffraction, as shown in the Figs. 5 and 6 respectively. The results of XRD analysis were reviewed with elemental analysis to observe the modification in the composition of the prepared catalysts with the variation in calcination temperature. In case of CWC catalysts, as seen from the Fig. 5, the XRD pattern of W0 indicates the presence of CaCO3, SiO2 and KCl compounds. On calcination of W0 at 500
C (CWC500), the pattern of crystalline compounds remains same, which indicates that low temperature ash shows strong peaks corresponding to calcium carbonate. On calcination at 800
C (CWC800), the corresponding XRD pattern shows the presence of KCl, CaO and Ca2SiO4.0.05Ca3(PO4)2 phases. The increase in Ca content also supported by elemental analysis. After calcination at higher temperature (1000 and 1200
C), XRD pattern shows that intensity of peaks corresponding to Ca2SiO4.0.05Ca3(PO4)2 phase increases and found prominent, which is in good agreement with search match analysis of calcium phosphate silicate, Ca2SiO4.0.05Ca3(PO4)2 phase. As per XRD pattern, search match analysis indicates the presence of several compounds with peaks at the same angle. The presence of Ca2SiO4.0.05Ca3(PO4)2 phase is further confirmed by

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XRF analysis of above samples. XRF analysis shows the presence of ‘P’ in all the samples in low concentration (approx. 0.5 mass fraction percentage), which matches with calculated ‘P’ content. The possible reason may be that during the calcination at higher temperature, low volatile compounds are removed as discussed in elemental analysis Section 3.1.3. and proportion of probable peaks matching with Ca2SiO4.0.05Ca3(PO4)2 increases. Secondly, above 800
C temperature, the ash composition can also be modified by the presence of Si as SiO2, which in association with metal oxide as CaO give ceramic like silicate compound as Ca2SiO4.0.05Ca3(PO4)2 and showed signs of sintering. The extent of sintering increases with the increase in temperature and confirms the presence of only Ca2SiO4.0.05Ca3(PO4)2 in CWC1200 catalyst. In case of activated wood ash catalysts, AKWC1, XRD pattern (Fig. 6) also shows the presence of Ca2SiO4.0.05Ca3(PO4)2 phase along with KCl and K2CO3.1.5H2O, while in AKWC0.5 the KCl is absent. In case of ACaWC0.5, XRD pattern indicates presence of peaks corresponding to CaO, Ca (OH)2, Ca2SiO4.0.05Ca3(PO4)2 and KCl phases.

3.2.

Activity of catalyst in transesterification

The activity of W0, CWC and AWC catalysts was evaluated in terms of ester conversion during transesterification of Jatropha oil. In order to compare the activity of the prepared catalysts, the reactions were carried out at catalyst concentration of 5 mass fraction percentage and oil to methanol molar ratio of 1:12 and reaction time of 180 min. The effective catalysts, CWC800 and AKWC0.5 were also studied at lower concentration of 1 and 3 mass fraction percentage. Table 4 shows the catalytic activity of wood ash (W0), calcined wood ash (CWC) and activated wood ash (AWC) for transesterification of Jatropha oil with methanol. Data for pure K2CO3 and CaCO3 is also included for comparision.

3.2.1.

Activity of calcined wood ash catalysts (CWC)

Basically the wood ash is an alkaline matter, partly soluble in water and insoluble in methanol. The partly water solubility

characteristic of prepared catalysts was considered a critical factor and was used to determine a possible correlation with catalytic activity of wood ash catalyst. Therefore, in the present study, soluble alkalinity method was used to determine the basic nature of the catalyst. The data given in Table 2, revealed the extractive soluble alkalinity of the catalysts due to metal ion. It may be seen from the Tables 2and 4 that ash temperature affects catalysts alkalinity and hence the catalytic activity of the prepared catalysts. It has been observed that wood ash as such (W0) and calcined at 500
C (CWC500) exhibit poor activity of ester conversion of 38.7 and 40.2% respectively. Catalysts obtained by calcination at 800 and 1000
C (CWC800 and CWC1000) show increased activity, giving 98.7% and 98.2% ester conversion respectively at 5 mass fraction percentage catalyst dosage. The possible reason may be the higher dispersion of active basic sites on the catalyst, results in maximum catalytic activity. However, calcination at 1200
C (CWC1200), results in reduced alkalinity and thus the lower activity of catalyst, giving ester conversion of 60.5%. This observation is also in line with the reported literature, which indicates that calcination at higher temperature deactivates catalyst activity [31]. The degree of heterogeneity is very important for the economical application of heterogeneous wood ash catalyst for biodiesel synthesis. It is desirable that active species are not leached from the catalyst. In order to confirm heterogeneity, the alkalinity test was performed in methanol medium and soluble alkalinity of the filtrate was determined as less than 0.1 mmol g1. Since, the transesterification was carried out in methanol medium instead of water, the alkalinity of the catalyst was nonextractable. Additionally, the loss of recovered catalyst was found negligible. The observations were further confirmed by transesterification reaction with methanol extracted catalyst after alkalinity test. The catalyst showed similar activity as fresh catalyst and revealed the heterogeneous and basic nature of the catalyst. Further, the XRD pattern of recovered catalyst after alkalinity test in methanol confirms the presence of stable CaO and Ca2SiO4.0.05Ca3(PO4)2 basic active phase.

Table 4 e Comparative catalytic activity of wood ash, CWC and AWC catalysts in transesterification of jatropha oil. Catalyst

Catalytic activity ester conversion, %

Observation (during work-up of reaction)

W0

40.2

CWC500 CWC800 CWC1000

42.2 98.7 98.2

CWC1200 K2CO3

60.5 98.5

AKWC1 AKWC0.5 AKWC0.25 CaCO3 ACaWC0.5

99.0 99.0 97.5 2.9 91.7

Slow reaction, require more settling time for catalyst and glycerine -doFast reaction, required no refining after catalyst and glycerin separation Slow reaction, more reaction time, required no refining after catalyst and glycerin separation Slow reaction, required no refining Very fast reaction, catalyst leached, act as homogeneous catalyst, product change to viscous material after glycerin separation Fast reaction, fast glycerin and catalyst separation, no refining Fast reaction, fast glycerin and catalyst separation, no refining Slow reaction, fast glycerin and catalyst separation, no refining Slow reaction, emulsion formation, Vegetable oil remains unreacted Slow reaction, emulsion formation, methyl ester refined by washing with brine

Reaction conditions: Oil to methanol ratio, 1:12; Catalyst dosage, 5 mass fraction percentage; Reaction time, 3 h under reflux conditions.

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Amongst the calcined wood ash catalysts, CWC800 was selected for optimization study, considering its marginal superior performance.

3.2.2. Activity of activated wood ash catalysts (AWC) 3.2.2.1. Effect of loading content and type of metal carbonates. Comparative transesterification performance of activated wood ash catalysts, K2CO3 and CaCO3 is given in Table 4. The results show that K2CO3 salt alone is found extremely active catalyst, giving 98% ester conversion within 1 h reaction time. It is known that K2CO3 catalyst acts as a homogeneous catalyst in the reaction medium and remains about 55% soluble in methanol at the end of the reaction [34]. However, in the present study, the biodiesel produced with K2CO3 catalyst changed into viscous material, which restricts the use of K2CO3. Activation of wood ash with K2CO3 in different concentration of 0.25, 0.5 and 1 mass fraction percentage resulted in products free from the above drawback. As can be seen from the Table that activated wood ash catalysts (AKWC), provides more than 97% ester conversion. The ester conversion achieved with activated catalysts, AKWC0.25, AKWC0.5 and AKWC1 are 97.5%, 99.0% and 99.0% respectively at 5 mass fraction percentage catalyst dosage. The catalyst with 0.5 mass fraction percentage loading content of K2CO3 on wood ash (AKWC0.5) gives optimum ester conversion of 99.0% and therefore, 0.5 mass fraction percentage optimum loading ratio was chosen for the preparation of CaCO3 loaded wood ash catalyst (ACaWC0.5). In case of AWC catalysts, as seen from the Table 4, the soluble alkalinity of the catalysts affected by the amount of loading of K2CO3 or CaCO3. In case of AKWC1, even the catalysts has reasonable alkalinity, higher loading amount of K2CO3 cover the surface and thus could cause decreased catalytic activity. When the active sites are inaccessible to reactants, it is expected to decrease the conversion. While in case of AcaWC0.5 catalyst, lower activity (91.7% ester conversion) was found in comparison to AKWC0.5 (99%) catalysts in spite of having higher surface area. The higher soluble alkalinity (12.7 mmol g1) of AKWC0.5 catalyst than ACaWC0.5

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catalyst (8.8 mmol g1) may be the possible reason for difference in performance of two catalysts. In addition to above, generating strong basic sites and their high dispersion during activation with K2CO3 is also responsible for better performance. The catalyst AKWC0.5 was selected for optimization study, as it showed good activity at lower K2CO3 loading ratio of 0.5 mass fraction percentage in the mixture.

3.2.3.

Optimization of CWC800 and AKWC0.5 catalysts

In view of the good catalytic activity of CWC800 and AKWC0.5, a detailed study on optimization with these catalysts was carried out for transesterification of Jatropha oil. In this study, influence of reaction time (30e210 min) and catalyst concentration (1e3 mass fraction percentage) were studied to optimize the ester conversion. However, the temperature in all experiments was kept constant i.e. 65
C. The effect of reaction time on ester conversion was studied by drawing samples at the interval of 30 min, 60 min, 120 min, 180 min and 210 min and their ester conversion was determined by GPC and data is summarized in Fig. 7. As can be noticed from the data that in general, the progress of reaction increases with the increase in reaction time up to 180 min, beyond that a marginal increase of ester conversion is noticed. In the case of CWC800 catalyst, maximum level of 97.7% ester conversion is achieved at 3 mass fraction percentage of catalyst dosage after 180 min. While in case of AKWC0.5 catalyst, 98.5% ester conversion is obtained after 210 min. Ester conversion data for two catalysts at 1 and 3 mass fraction percentage concentration revealed that as expected the ester conversion increases with increase in catalyst dosage. In case of CWC800 catalyst, maximum level of 93% and 97.7% ester conversion is achieved at 1 and 3 mass fraction percentage catalyst dosage respectively, whereas 97.6% and 98.5% ester conversion is obtained with AKWC0.5 at its corresponding concentration. The catalyst characterization and ester conversion data of different wood ash catalysts given in Tables 2and 4 were reviewed to find a possible correlation between the two. It is

Fig. 7 e Effect of reaction time and catalyst concentration of CWC800 and AKWC0.5 catalysts on jatropha oil transesterification.

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observed, the activity of the catalysts has been found reasonable correlation with the alkalinity of the respective catalyst. The data of surface area and particle size were not found correlating with the activity of the catalysts. Most probably, the basic sites available on the catalyst surface cause high alkalinity of catalyst in the reaction medium leading to increased catalytic activity. It is observed that the catalyst with lower surface area, increased particle size and higher alkalinity, exhibit good catalytic activity and supports the earlier findings [30]. Thus, it is reasonable to conclude from the present study that the active component and its location in the catalysts is the main reason for catalysts activity.

rates of 10
C min1, up to 800
C. The results given in Fig. 8 show that in AKWC0.5, there is a weight loss at 190
C corresponding to the removal of loosely absorbed water on the surface and found stable up to 800
C temperature. While in case of ACaWC0.5 catalyst, the decomposition takes place in two steps. In the first step, moisture is removed at 190
C associated with 3.14% weight loss. In the second step, decomposition of calcium carbonate occurres at 450
C and 661
C producing calcium oxide associated with 7.91% weight loss. Further, the stability of AKWC0.5 catalyst is confirmed by the metal analysis of biodiesel sample prepared and found all the metals were <1 mg kg1.

3.2.4.

4. Characterization and properties of synthesized biodiesel

Catalyst stability

The reusability of the CWC800 catalyst was checked by using leaching test. The activated catalyst was placed in contact with methanol, for 2 h at 65
C. The methanol was filtered to remove solids and then Jatropha oil was placed in contact with the clear methanol solution at 65
C for 2 h. The methanol extract of catalyst did not show any reactivity, confirming non-leaching behavior of the catalyst. Above findings are in line with earlier study [28]. The stability of active basic sites present on the catalyst was supported by methanol filtrate negligible soluble alkalinity and leached catalyst residue activity that confirmed the heterogeneous nature of the catalyst. Additionally, the biodiesel produced from CWC800 catalyst was analyzed for metal analysis and found to contain negligible content (<1 mg kg1) of metals like, P, K, Ca, and Mg. The results indicate that the CWC acts as a stable heterogeneous catalyst for methanolysis of Jatropha oil. The stability of AKWC0.5 and ACaWC0.5 was measured by TG analysis and data are shown in Fig. 8. These studies were done on TG model 2950 Hi Resolution modulated TGA, with heating

The synthesized jatropha methyl ester was characterized by IR and 1H NMR spectroscopy. The IR of the transesterified jatropha oil shows characteristic bands of fatty acid methyl ester at 1742, 1462, 1436, 1361 and 1170 cm1. Typical 1H NMR spectra after transesterification showed the shift of glycerol eCH2OH signal from d 4.2 ppm in jatropha oil to a sharp eOCH3 signal at d 3.65 ppm of jatropha methyl ester. The Jatropha methyl esters synthesized separately with CWC800 and AKWC0.5 catalysts were also evaluated for critical parameters against the ASTM D-6751 standard specification of biodiesel and the data are given in Table 5. It is clear from the Table that values of all the parameters are within the range of specified limits of standard. The most critical parameter, oxidation stability found for two samples are 3.31 and 3.11 h respectively against the specified limit of 3 h. However, the stability can be further improved by blending with an antioxidant [35].

Fig. 8 e TGA curves of thermal decomposition of AKWC0.5 and ACaWC0.5 catalysts.

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Table 5 e Key physico-chemical properties of synthesized jatropha methyl ester as per ASTM D-6751 standard. Property (units)




Flash Point ( C) Viscosity at 40
C (mm2s1) Neutralization value (KOH g kg1) Sulfated ash (% mass) CCR (% mass) Free glycerin (% mass) Total glycerin (% mass) Methanol content (% mass) Ester content (% mass) Oxidation stability (h) Sulfur (mg kg1) Copper corrosion (No.) Cetane no Calcium & magnesium (mg kg1) Sodium & potassium (mg kg1)

Test methods

ASTM D-93 ASTMD-445 ASTM D-664 ASTMD-874 ASTMD-4530 ASTMD-6584 ASTMD-6584 EN 14110 EN 14103 EN 14112 ASTMD-5453 ASTM D-130 ASTM D-613 EN 14538 EN 14538

Test limit

Min 130 1.9e6.0 Max 0.50 Max 0.02 Max 0.05 Max 0.02 Max 0.24 Max 0.20 Min 96.5 Min 3 Max 50 Max 3 Min 47 Max 5 Max 5

Jatropha methyl ester using catalyst CWC800

AkWC0.5

164 4.21 0.05 0.009 0.037 0.0025 0.017 0.023 98.5 3.21 20 1 57.1 <1 <1

162 4.66 0.03 0.019 0.036 0.0042 0.017 0.052 98.6 3.11 12 1 49.0 <1 <1

CWC800 (calcined wood ash catalyst at 800
C). AKWC0.5 (activated wood ash catalyst with 1:0.5 mass fraction percentage ratio of K2CO3).

5.

Conclusions

The present study covers the synthesis of new heterogeneous catalysts from calcined wood ash which mainly composed of calcium phosphate silicate Ca2SiO4.0.05Ca3(PO4)2. The thermally and chemically synthesized wood ash catalysts exhibited good catalytic activity in transesterification of Jatropha oil with methanol for preparation of biodiesel. Ester conversion in the range of 97e99% could be achieved with wood ash catalysts. The synthesized Jatropha methyl ester met the ASTM D-6751 standards of biodiesel. The study revealed the possibility of producing potential cheaper heterogeneous catalyst from wood ash for biodiesel synthesis, which can find a way to utilize abundant wood ash.

Acknowledgments The authors wish to thank Dr. J. Christopher, Dr. M. I. S. Shastri of Analytical Division and Dr. A. C. Pulikottil of Catalyst Division for providing analytical support and the management of Indian Oil Corporation, R&D Centre for allowing me to publish this work.

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