Article pubs.acs.org/EF
Biodiesel Production from Crude Jatropha Oil using a Highly Active Heterogeneous Nanocatalyst by Optimizing Transesterification Reaction Parameters Reddy ANR,*,† A. A. Saleh,† Md. Saiful Islam,‡ S. Hamdan,† and Md. Abdul Maleque§ †
Department of Mechanical Engineering, Faculty of Engineering, Universiti Malaysia Sarawak (UNIMAS), 94300 Kota Samarahan, Sarawak, Malaysia ‡ Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia § Department of Manufacturing & Materials Engineering, International Islamic University Malaysia 53100 Kuala Lumpur, Malaysia ABSTRACT: Various heterogeneous catalysts are often used to produce biodiesel from non-edible crude oils. In this study a highly active heterogeneous calcium oxide (CaO) nanocatalyst with a diameter and surface area of 66 ± 3 nm and 90.61 m2/g, respectively, was synthesized from Polymedosa erosa (P. erosa) seashells through a calcination−hydration−dehydration technique. The nano-CaO catalysis impact was investigated in a two-step transesterification of triglycerides from crude Jatropha oil as a biodiesel along with other reaction parameters such as catalyst ratio, reaction time, and methanol to oil ratio. Fourier transform infrared spectroscopy, transmission electron microscope, X-ray diffraction, and Brunauer−Emmett−Teller spectrographic techniques were utilized to evaluate the CaO nanocatalyst spectral and structural characteristics. The effect of the transesterification parameters on reaction kinetics and Jatropha biodiesel (JB) yield were analyzed by employing a three-factorfive-level response surface methodology model based on a full factorial, two-block, central composite design. The adequacy of the predicted model was verified, and a 98.54% JB yield was reported at optimal parametric conditions, i.e., 0.02:1 (w/w) catalyst ratio, 133.1 min reaction time, and 5.15:1 mol/mol of methanol to the pretreated oil. An average of 95.8% JB yield was obtained from the catalyst reusability up to the sixth cycle. Fuel property test results of JB were found to be highly commensurate with the biodiesel standard EN 14214. accelerate reaction rates13,14 due to an increased number of molecules that have the minimum required energy for the reaction to occur. Several researchers have explored calciumbased heterogeneous catalysts in pure 15−19 or mixed oxides15,16,20−22 for Jatropha biodiesel production and reported that heterogeneous CaO catalysts have advantages over homogeneous ones. Kawashima et al.17 investigated the trasesterification of rapseed oil using activated CaO with methanol and reported a 90% biodiesel yield. Islam et al.23 synthesized calcium carbonate nanoparticles with a 20 ± 5 nm diameter from cockle shells, while Margaretha et al.24 reported a surface area (SBET) of 17 m2/g and pore volume of 0.04 cm3/ (g of CaO) synthesized from Pomacea sp. shells that were utilized in biodiesel production from palm oil. Buasri et al.13 derived CaO from mussel shells (SBET = 89.91 m2/g), cockle shells (SBET = 59.87 m2/g), and scallop shells (SBET = 74.96 m2/ g) for biodiesel synthesis from palm oil. Tan et al.18 utilized CaO that was synthesized from waste chicken-eggshell with SBET = 54.6 m2/g and from calcinated ostrich-eggshell with SBET = 71.0 m2/g for the transesterification of waste cooking oil. Hwa et al.16 investigated the transesterification reaction catalyzed CaO (SBET = 9.2 ± 0.80 m2/g) that had a crystalline size of 66.3 ± 3.20 nm and obtained a 90% biodiesel yield from Jatropha oil. Taufiq-Yap et al.,15 with SBET = 9.5 m2/g, reported
1. INTRODUCTION The gradual depletion of the world’s petroleum reserves and impact of fuel combustion exhaust emissions on the environment and human health have therefore led to the search for substantial, environmentally friendly alternative energy sources such as biodiesel.1−4 Fatty acid methyl ester (FAME)known as biodieselcomprises monoalkyl esters of long chain fatty acids, produced by the transesterification of biologically produced feedstocks such as vegetable oils, animal fats, and microalgae oils.5 This has been introduced in the 1980s as a sustainable energy resource in reducing greenhouse emissions.6 Jatropha curcas (Linnaeus) is a fast growing plant in marginal and nonagriculture fields and is fully adaptable to tropical and subtropical climates,7 and, moreover, the oil content of the Jatropha seed is about 27−40% which has been reported as one of the best suited feedstocks for biodiesel production.7−9 Acid or base catalyzed transesterification has been reported extensively in literature,10 but many studies conclude an interaction of homogeneous acid catalysts11 and free fatty acids (FFAs) present in FAMEs during transesterification leads to reduced catalyst availability for the reaction and thus homogeneous catalysts are not recommended.9 The particle size of the catalyst is one of the most important factors for their catalytic activity.12 When the particle is small, the chemical reaction rate is increased since the diffusion forces would only be able to carry the product away from the surface of the catalyst particle. Many studies have confirmed that catalysts with a lower particle size and higher surface area © 2015 American Chemical Society
Received: August 20, 2015 Revised: December 11, 2015 Published: December 14, 2015 334
DOI: 10.1021/acs.energyfuels.5b01899 Energy Fuels 2016, 30, 334−343
Article
Energy & Fuels
dehydration of the P. erosa shells to obtain a fine powder following a technique reported previously by Niju et al.38,39 Briefly, approximately 500 g of P. erosa seashells was cleaned to remove the edible portion and any other impurities, rinsed thoroughly with distilled water, and then dried in a hot air oven at 105 °C for 24 h.40 The P. erosa shells were finely ground using a blender (Khind blender BL 1512, Shah Alam, Malaysia) and then passed through an 80 μm sieve mesh. The micrometer-sized powdered P. erosa shells were then calcinated in a chamber furnace (CWF23/13 23 Lt−1300 °C, Carbolite Ltd., Hope, U.K.) at 900 °C for 2.5 h. At 850 °C, the calcium carbonate of the P. erosa shell powder decomposed to calcium oxide and carbon dioxide as presented in the following reaction.
an 85% biodiesel production from Jatropha oil, while Choudhury et al.19 reported a 89.36% biodiesel yield with a CaO catalyst of SBET = 7.114 m2/g using an ultrasound effect with crude Jatropha oil. These studies show that CaO can be a promising catalyst for biodiesel production since catalysts with lower particle sizes and a higher surface area contribute to enhancing the transesterification reaction rate. Very scant work, however, has been devoted to the synthesis of CaO as a nanocatalyst that focuses on reducing the particle size and increasing the surface area for biodiesel production25−31 especially from the largely available sustainable waste resources such as seashells. Polymesoda erosa (P. erosa) has been widely reported throughout the Indo-Pacific geographic region as a prominent fishery source in many tropical and subtropical islands and is locally known as “Lokan”.32 From the works of Hossen et al.33 and Rahim et al.,34 it was obvious that P. erosa shells are abundantly available in the coastal regions of east and west Malaysia. However, to the best of our knowledge no research has reported on synthesis of CaO nanocatalyst from P. erosa seashells. Many state-of-the-art works have been performed on optimizing the primary transesterification process parameters such as manipulating the catalyst ratio, methanol ratio, and reaction time, etc., and their potential interactions to achieve optimal biodiesel yield using response surface methodology (RSM) as a statistical and optimization tool.19,25−31,35 Kumar Tiwari et al.25 have reported the use of RSM−CCRD to curtail FFA percent from Jatropha using H2SO4 and KOH as catalysts. Meanwhile, CCD-based RSM was utilized for optimizing biodiesel yields from Jatropha oil using catalysts such as sulfated zirconia−alumina,26 H2SO4, and NaOH.27 In addition a RSM Box−Behnken design was utilized for studying the effect of ultrasound in biodiesel synthesis from Jatropha19,35,36 and soybean37 oils. In the present study CaO was synthesized with a low particle size and high surface area in order to obtain a highly active heterogeneous CaO nanocatalyst. In addition optimization of the two-step transesterification reaction parameters such as catalyst ratio, reaction time, and methanol ratio were explored for maximum biodiesel yield from crude Jatropha oil (CJO). Highly active heterogeneous CaO nanocatalyst that was synthesized from a new seashell species P. erosa through calcination−hydration−dehydration technique was characterized by evaluating their catalyst morphological features. The nano-CaO catalytic activity and transesterification reaction kinetics were analyzed by employing a three-factor-five-level CCD-based full factorial, two-block RSM model. Calcium oxide leaching, catalyst reusability, and stability were also studied. The resulting fuel properties of JB were then investigated to compare with EN 14214 biodiesel standards.
900 ° C
CaCO3(s) ⎯⎯⎯⎯⎯⎯→ CaO(s) + CO2 (g) The CaO derived from the P. erosa shells was refluxed in water at 60 °C for 6 h, and the solid particles were filtered and dried in a hot air oven at 120 °C overnight.40 The solid powder was further ground in a Planetary ball mill (Ritesh) at 200 rpm for 3 h and dehydrated by performing calcination at 600 °C for 3 h to change the hydroxide form to the oxide form. Thus, a highly active CaO nanocatalyst was synthesized from P. erosa shells subjected to the calcination− hydration−dehydration treatment. 2.3. Characterization of CaO Nanocatalyst. In order to investigate the chemical structure of the newly synthesized CaO nanocatalyst, powder samples of CaO were tested using a Fourier transform infrared (FT-IR) spectrophotometer (Model 100 series, PerkinElmer) over a 4000 to 280 cm−1 region. The sizes and shapes of the CaO nanocatalyst were obtained by using a transmission electron microscope (TEM; Hitachi H-7100, Tokyo, Japan). The surface area of nano-CaO, uncalcined P. erosa shell, and reference-CaO catalyst were studied using the Brunauer−Emmett−Teller (BET) and Barrett−Joyner−Halenda (BJH) methods which were applied to obtain the pore volume and diameter (Quantachrome instruments: autosorb iQ-AG-C). Nanocatalyst crystalline properties were investigated using the X-ray diffraction (XRD) test from a Shimadzu 6000 X-ray machine with nickel filtered Cu Kα (λ = 1.542 Å) radiation. The average crystallite size of the CaO nanoparticles was calculated from line broadening using Scherrer’s equation: D=
0.9λ β cos θ
where D = crystalline size (nm), λ = wavelength of X-ray (λ = 1.542 Å), β = full width at half-maximum (fwhm; rad) intensity, and θ = Bragg diffraction angle (deg). XRD analysis was carried out over 20− 80 °C at a rate of 2 °C min−1 and a scanning angle of 2θ. 2.4. Biodiesel Production. Biodiesel production from CJO was carried out using the newly synthesized CaO nanocatalyst by following standard laboratory procedures. The important tranesterification reaction paramenters were ascertained and analyzed in contrast with previous studies reported in literature.41−43 The major steps involved in biodiesel production included FFA estimation, acid pretreatment, and transesterification using CaO as the nanocatalyst, and are comprehensively discussed in the following sections. 2.4.1. Acid Pretreatment. CJO acid pretreatment was carried out by designing an experimental protocol as reported by Deng et al.42 and Yee.43 The FFA content was estimated in terms of KOH in milligrams in order to neutralize 1 g of fatty acid methyl ester; i.e., 0.1 M of KOH was diluted with ethanol, as reported in literature.44,45 Next, 2 ± 0.5 g of CJO together with 50 mL of solvent consisting of 95% ethanol and diethyl ether in a 1:1 molar ratio were thoroughly mixed in a conical flask using a magnetic stirrer. Titration was carried out by adding a few drops of phenolphthalein to the mixture with the KOH solution when continuously stirred until the color of the solution turned pink and lasted for 10 s. This was repeated three times for accuracy, and the FFA content was measured at 29.466%. In order to improve the conversion rate for maximum biodiesel yield, the FFA content in CJO was minimized or removed by following a two-step transesterification.46 For the first step, acid esterification known as acid pretreatment was performed with H2SO4. Filtered 25 mL of CJO was heated over
2. EXPERIMENTAL SECTION 2.1. Materials. Raw Jatropha seeds were purchased from a local Jatropha agriculture farm situated in Asajaya, Sarawak, Malaysia. Crude Jatropha oil (CJO) was extracted from their seeds using a hand operated nut and seed oil expeller at a mechanical engineering workshop, University Malaysia Sarawak (UNIMAS). Laboratory grade chemicals that included methanol (MeOH; >99% pure), H2SO4 (95− 97%), KOH, double distilled deionized water, and calcium oxide (UNI-CHEM chemical reagents; CAS No. 1305-78-8; MW = 56.08) were used as a reference catalyst. 2.2. Preparation of CaO Nanocatalyst. P. erosa seashells were collected from a local village Muara Tebas, Sawarak, Malaysia. The CaO nanocatalyst was prepared using calcination−hydration− 335
DOI: 10.1021/acs.energyfuels.5b01899 Energy Fuels 2016, 30, 334−343
Article
Energy & Fuels 100 °C to remove the water content. A mixture of H2SO4 and MeOH was prepared by adding the catalyst/alcohol at a proportional ratio with CJO, by volume, in a three-neck flask fitted with a water cooled condenser setup and heated to 50 °C. The CJO sample was added to the mixture, for which heating was continued at 50 °C and a magnetic stirrer at 200 rpm was used. The contents were allowed to settle for 1 h after the reaction. The oil was washed three times with distilled water, and then the oil was separated and heated to remove the water content. Within the CJO, the FFA value was reduced to a minimum value, i.e., 1%, which is suitable for base catalyzed transesterification.45 2.4.2. Transesterification Using CaO Nanocatalyst. The pretreated oil, as obtained in acid pretreatment, which had a minimum FFA value was used together with a highly active CaO nanocatalyst for catalyzed transesterification. A mixture of the CaO nanocatalyst (0.01−0.03 (w/w)) in powder form and methanol (4−6 mol/mol) by ratio were prepared and added to the pretreated CJO. The reactants were allowed to react at a stirring speed of 500 rpm and at 60 °C for a period of 60−180 min. The mixture was shaken at 250 rpm for 2 h using an orbital shaker at room temperature and then allowed to settle for 24 h. Biodiesel was separated from glycerol, while the methanol− water layer was washed using distilled water. The filtered biodiesel was heated to 100 °C while being continuously stirred using a magnetic stirrer in order to get pure biodiesel. 2.5. Design of Experiments for Maximum JB Yield. An experimental model designed to analyze the transesterification reaction kinetics along with the effects of different reaction parameters, including catalyst ratio, reaction time, and methanol ratios, were used to optimize the JB yield. A typical RSM three-factor-five-level CCD full factorial two-block model was utilized for the experimental design. Using the designed model objective function, JB yield was fitted as a quadratic surface to further optimize dependent factors within a specific sphere for an optimum number of experimental iterations and to analyze linear, quadratic, and factorial interactions among different factors.25 The model was built to maximize the dependent factor, and JB yield was the response during transesterification. The catalyst-topretreated oil ratio (C), reaction time (T), and methanol-to-pretreated oil ratio (M) were input as the independent parameters (factors) of the transesterification process to explore their effects on the response. In Table 1, the actual levels of the three independent factors together
factorial and axial levels. Random run order was used for all experimental iterations to minimize redundancy. For CCD, the distance between the central and axial points is denoted with an “α”, which acts as a key element in the metamorphosis of the factor levels.25 The present model default α was 1.633. Metamorphosis of the factors into coded (X) levels to the uncoded levels were obtained from the equations C = 0.02 + 0.006X, T = 120 + 36.7X, and M = 5 + 0.61X. 2.6. Model Fitting and Statistical Analysis. The experimental data obtained were analyzed by response surface regression procedure using second-order polynomial as stated in 3
Y = β0 +
i=1
level factor
C T, min M
−1.633
−1
0
1
1.633
0.01 60 4
0.014 83.3 4.39
0.02 120 5
0.026 156.7 5.61
0.03 180 6
3
i=1
i101
