- Open Access
Process optimization of Calophyllum inophyllum-waste cooking oil mixture for biodiesel production using Donax deltoides shells as heterogeneous catalyst
© The Author(s) 2019
- Received: 2 September 2018
- Accepted: 21 February 2019
- Published: 6 May 2019
In the present work, the waste material Donax deltoides shells (DDS) was utilized as a heterogeneous base catalyst for biodiesel production from Calophyllum inophyllum oil (CIO)-waste cooking oil (WCO) mixture. Non-edible CIO possessing 65 mg of KOH g− 1 of acid value was mixed with WCO of low acid value in different proportions. The acid value was reduced to 33.3 mg of KOH g− 1 of oil by using a volumetric ratio of 1:1 and it was further reduced to 5.6 mg of KOH g− 1 of oil by acid catalyzed esterification process and used for biodiesel production. DDS was converted into active CaO catalyst by calcination and the catalyst characterization was performed using different instrumental techniques. The impact of calcined DDS (catalyst) concentration, reaction time and methanol to esterified oil volumetric ratio on biodiesel conversion was investigated to optimize the transesterification reaction using response surface methodology based central composite design. The biodiesel conversion was determined by proton nuclear magnetic resonance spectroscopy and a maximum biodiesel conversion of 96.5% was achieved with catalyst concentration of 7.5 wt%, methanol to oil volumetric ratio of 63.8%, reaction time of 129.3 min, stirrer speed of 450 rpm and reaction temperature of 65 °C.
- Calophyllum inophyllum oil
- Waste cooking oil
- Donax deltoides shells
- Response surface methodology
World’s energy requirement is increasing as industrial, agricultural and transport sectors are dependent on conventional energy resources [1, 2]. This ever-increasing energy demand was met by utilizing conventional fossil fuel resources which are non-renewable in nature and are getting depleted day by day. In order to overcome the fossil fuel depletion and to meet the growing fuel demands, biofuels can be a better alternative. Biodiesel is one such fuel entails alkyl esters having long chain fatty acids obtained from lipids (oils) or animal fats . In addition, biodiesel is biodegradable, non-toxic, renewable, and sustainable to the environment [4, 5]. Biodiesel blended with conventional diesel fuel up to 30% can be directly used in diesel engines irrespective of any major engine alterations . Soybean oil, palm oil, and sunflower oil are few edible oils employed for biodiesel production and tested successfully in diesel engines [7, 8]. Exploiting such edible oils as feedstock leads to food versus fuel conflict and hence, non-edible feedstocks are turned out to be the pin interest for biodiesel production. Non-edible oils such as Moringa oleifera, Jatropha curcas, Croton megalocarpus, Ricinus communis, Pongamia pinnata, Azadirachta indica, Cerbera odllam, Sapium sebiferum, Calophyllum inophyllum were utilized as feedstock for biodiesel production [9, 10].
Among the different non-edible feedstocks, C. inophyllum oil (CIO) is the second most cultivated feedstock for biodiesel production . C. inophyllum belongs to the Clusiaceae family and its native range was distributed throughout India. It shows high tolerance to brackish water, salt spray, and winds . An adult plant can grow up to 20–30 m high. It bears fruits twice a year with the annual production of about 8000 fruits and its kernel contains 75% oil content [1, 7, 13, 14]. Hence, CIO can be exploited as a promising resource for the production of biodiesel [7, 15, 16]. Besides, 75–85% of production cost of biodiesel was attributed to the feedstock [17, 18] and hence, it is necessary to produce biodiesel economically. One such inexpensive feedstock is waste cooking oil (WCO) which is available in excess, dumped in landfills and rivers illegally . To manage the WCO disposal problem and to use WCO productively, it can be efficiently employed as biodiesel feedstock. Kulkarni and Dalai  reviewed methods of biodiesel production from WCO and discussed quality and performance of methyl esters derived from WCO. Few other researchers also investigated the utilization of WCO as biodiesel feedstocks [19, 21–24].
In general, biodiesel synthesized via transesterification reaction necessitates a catalyst to uphold the reaction . Homogeneous catalysts (NaOH and KOH) are generally exercised owing to its higher yield under mild reaction conditions and minimum reaction time [25, 26]. Conversely, exploiting such catalysts has numerous problems such as excess wastewater generated during water wash in order to remove the alkaline catalyst from biodiesel . Also, it is difficult to recover the homogeneous catalyst and may corrode the pipelines and reactors. Alternatively, heterogeneous basic catalysts have shown several merits such as non-toxic, low-cost, and eco-friendly nature [24, 28]. Furthermore, it can be reused, recycled and the product (biodiesel) needs less or no water wash and also produces by-product (glycerol) with high purity [5, 19]. Hence, heterogeneous catalysts are preferred over homogeneous catalysts. Alkaline earth metal oxides can serve as solid catalyst because of its high basicity and minimal solubility in oil . Calcium oxide (CaO) is one such catalyst which is non-toxic, available naturally, environmental friendly and low solubility in methanol. Utilization of seashells as a heterogeneous catalyst is an economical means of biodiesel production and also serves as an effective waste disposal strategy [5, 30, 31].
Among the various sources, sea shell derived catalyst has an excellent reusability . Recently, CaO derived from Gallus domesticus shells , ostrich egg shell and chicken egg shell , waste scallop shell , white bivalve clam shell , Tellina tenuis , river snail shell , mussel shell , and crab shell  has been exploited as heterogeneous catalysts in transesterification process. Donax deltoides shells (DDS) is one such sea shell of bivalve type which is distributed throughout Indo-West Pacific from Andaman and Nicobar Islands to Indonesia and throughout Australia .
Process optimization is an important step in the production process to obtain the maximum biodiesel yield and conversion but it is time-devouring and laborious. Response surface methodology (RSM) is a statistical approach to optimize the complex processes which helps to understand the interaction between the process parameters and also minimizes the number of experimental runs essential to obtain maximum conversion and also to acquire adequate data to prove that the result is statistically significant [36–39]. Several authors optimized biodiesel production using RSM techniques [24, 40–43].
The present study aimed to explore the possibility of utilizing DDS as a suitable heterogeneous alkali catalyst for methyl ester (biodiesel) production from CIO-WCO mixture. DDS was converted into the active form of CaO catalyst via calcination process. The calcined DDS was studied using Fourier Transform Infrared (FTIR) spectroscopy, X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive Atomic X-ray (EDAX) spectrometry. Optimization of biodiesel process parameters using central composite design (CCD) based RSM was employed to understand the effect of reaction time, calcined DDS concentration and methanol to esterified CIO-WCO oil volumetric ratio on biodiesel conversion. The synthesized biodiesel was analyzed by proton nuclear magnetic resonance spectroscopy (1H-NMR) for determining biodiesel conversion.
DDS was collected from the sea shore of Mahabalipuram, Chennai. CIO was purchased from Tamil traders, Coimbatore, while WCO was obtained from the canteen, PSG College of Technology, Coimbatore, Tamil Nadu, India. Sulfuric acid (≥ 97%), petroleum ether (40–60 °C), and potassium hydroxide (≥ 85%) used in the present study were purchased from HiMedia Laboratories Pvt., Mumbai, India, while methanol, ethanol (99.9%), and phenolphthalein pH indicator solution were purchased from S.D. Fine Chemicals, Mumbai, India. Acid value of the various oil samples was determined using a standard titration method by titrating 0.1 N 95% ethanolic KOH (Burette) solution against the mixture containing 2 g of oil sample, 30 mL (equal amounts) of ethanol and petroleum ether mixture, and few drops of phenolphthalein indicator.
SEM analysis on a Carl Zeiss (Model: Sigma V) was performed in order to analyze the surface morphology of the uncalcined and calcined DDS. EDAX was done to reveal the elemental composition of the catalyst. Formation of calcium oxide in calcined DDS was confirmed using XRD (Rigaku; Model, DMAX 2200/Ultima C) furnished with Cu Kα radiation (Kα = 1.54 Å). XPERT-3 diffractometer system was employed in order to acquire diffraction patterns with the scan range from 2θ = 10 to 90°, step size of 0.0130, step time of 48.19 s and at the rate of 30 mA and 45 kV. FTIR spectroscopy on ATR-FTIR (Model: BRUKER, Germany) in scan range of 600–4000 cm− 1 was accomplished to compare the functional groups present in uncalcined and calcined DDS.
A two-step esterification-transesterification reaction was employed since the acid value of CIO-WCO mixture was determined as 33.4 mg of KOH g− 1 of oil. Acid value reduction was performed by using 250 mL three-necked round bottom flask placed in a water bath maintained at 60 °C. After esterification reaction, the acid value of CIO-WCO mixture was decreased to 5.6 mg of KOH g− 1 of oil using the optimum esterification conditions of 1:3 methanol to CIO-WCO volumetric ratio, 1% (v/v) of sulphuric acid, 90 min of reaction time and stirrer speed of 450 rpm. The excess methanol present in the esterified mixture was eliminated by heating and the resulting mixture was allowed to settle for phase separation. The bottom layer containing impurities (water and excess catalyst) was disposed and the top layer was subjected to transesterification reaction.
Optimization of the transesterification process
Design of experiments
Range and levels of independent variables
Methanol to oil ratio
SEM and EDAX analysis
Physicochemical properties of CIO and WCO
Physicochemical properties and fatty acid composition of CIO and WCO
Waste cooking oil
Calophyllum inophyllum oil
Mixture of WCO and CIO (50–50%)
Acid value = (mg of KOH g− 1 of oil)
Density at 27 °C (kg m− 3)
Kinematic viscosity at 40 °C (mm2 s−1)
Saponification value (mg of KOH g−1)
Palmitic acid (%)
Oleic acid (%)
Linoleic acid (%)
Stearic acid (%)
Different blends of CIO and WCO and its corresponding acid values
Calophyllum inophyllum oil (%)
Waste cooking oil (%)
Acid value (mg of KOH g−1 of oil)
Optimization of biodiesel production
Central composite design based RSM
CCD matrix for the biodiesel production from CIO-WCO mixture
A: Catalyst concentration
B: Methanol to oil ratio
C: Reaction time
Experimental biodiesel conversion
Predicted biodiesel conversion
ANOVA table for transesterification process
Sum of Squares
B-Methanol to oil ratio
Lack of Fit
Impact of calcined DDS concentration and methanol to esterified CIO-WCO ratio on methyl ester conversion
Impact of calcined DDS concentration and reaction time on methyl ester conversion
Figure 6b illustrates the impact of catalyst concentration and reaction time on the conversion of CIO-WCO to methyl esters. At 6 wt% calcined DDS and 120 min reaction time, methyl ester conversion was found to be 70%. Conversely, a minor decline in conversion (57%) was seen when the time was increased to 180 min. Besides, increasing catalyst concentration beyond 8 wt% and holding the time at 150 min, the methyl ester conversion was around 76%. However, increasing the time resulted in decreased methyl ester conversion (70%). At 10 wt% calcined DDS loading and 120 min transesterification time, 60% conversion was achieved. Furthermore, increasing the transesterification time from 120 to 180 min exhibited decreased conversion (54%). From the Fig. 6b, it was observed that between 7 and 8 wt% of catalyst concentration and transesterification time of 120 min, maximum methyl ester conversion (81%) was achieved. This clearly indicated that excess reaction time resulted in decreased biodiesel conversion . From ANOVA table, it was observed that the interactive effect between calcined DDS concentration (A) and reaction time (C) on methyl ester conversion is insignificant since the p-value (0.0734) was found to be slightly greater than 0.05.
Impact of methanol to esterified CIO-WCO oil ratio and reaction time on methyl ester conversion
1H-NMR spectrum of CIO-WCO derived methyl esters
In the present study, DDS derived CaO was employed as a cost effective heterogeneous catalyst for methyl esters production from CIO-WCO via transesterification process. Utilizing low-cost WCO as feedstock makes biodiesel production more economical and also prevents illegal landfilling thereby creating a safe environment. Also, the mixing of WCO with non-edible oil like CIO will act as a potential feedstock owing to the limited prevalence of CIO throughout the year. Blending of CIO with WCO at different proportions was evaluated to lower the acid value and the opted CIO-WCO (1:1 volumetric) mixture showed a moderate acid value of 33.4 mg of KOH g− 1 oil. Further, to diminish the acid value of CIO-WCO mixture, the esterification reaction was executed using sulphuric acid as homogeneous catalyst and the acid value was further decreased to 5.6 mg of KOH g− 1 of oil. In transesterification process, the effect of transesterification time, volumetric ratio of methanol to esterified CIO-WCO and calcined DDS concentration on biodiesel conversion was investigated using CCD of RSM. The ANOVA analysis indicated that the volumetric ratio of methanol to esterified CIO-WCO had a greater impact on methyl esters conversion. 1H-NMR results revealed the maximum experimental methyl esters conversion of 96.5% at a catalyst concentration of 7.5 wt%, methanol to esterified (CIO-WCO) oil volumetric ratio of 63.8%, reaction time of 129.3 min, stirrer speed of 450 rpm and transesterification temperature of 65 °C. The observed experimental methyl esters (biodiesel) conversion results were in agreement with the predicted biodiesel conversion of 97.5%.
SN is grateful to Science and Engineering Research Board (SERB), New Delhi, India for Early Career Research Award (ECR) and MB is thankful to SERB for the award of Junior Research Fellowship (JRF).
All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
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