Muskmelon (Cucumis melo) seed oil: A potential non-food oil source for biodiesel production
Highlights
► RSM (Response surface methodology) is used on muskmelon seed oil for biodiesel yield. ► Fuel properties of produced biodiesel satisfy the international specifications. ► The models developed using RSM will be highly useful for predicting the optimum biodiesel yield with good quality.
Introduction
World’s petroleum reserves are depleting due to rapidly growing demands by ever increasing population and industrialization coupled with environmental concerns. It has escalated the researcher’s efforts to explore alternative sources of fuels other than petroleum-based fuels [1], [2]. Currently, extensive work is being carried out toward the exploration of alternative renewable fuel sources. The researchers have found several types of biomass derived liquid fuels such as bio-ethanol, bio-methanol, methyl esters from vegetable oils and animal fats as an alternative to fossil fuel [3].
“Biodiesel” is defined as mono-alkyl esters of long-chain fatty acids derived from vegetable oils/animal fats. Biodiesel is prepared from various edible and non-edible oils apart from animal fat throughout the world. The use of biodiesel as a renewable, biodegradable, non-toxic, eco-friendly neat diesel fuel or in blends with petroleum-based fuels is intriguing [4], [5], [6]. The biodiesel is derived from the reaction between vegetable oil with methyl or ethyl alcohol in the presence of a catalyst. At present, most reliable process using transesterification reactions, employ an alkali-catalysis system. Transesterification process is the reaction of a triglyceride (vegetable oil/animal fat) with an alcohol to form esters and glycerin [7], [8]. It is a multiple reaction including three reversible steps in series as follows:where TG, DG, MG, RCO2R, ROH and GLY stands for triglycerides, diglycerides, monoglycerides, ester (biodiesel), alcohol and glycerin, respectively [9].
The climate and geography significantly determines the availability of raw materials for the production of biodiesel. The example of rapeseed and canola may be given in case of Europe, palm oil predominate the tropical countries (Malaysia), and fats from animal and soybean oil are more common in the United States [10], [11]. However, these existing raw material resources are insufficient which accommodates quite a small percentage of petro-diesel demand. Now resultantly for the past few years researchers are investing their efforts, on non-edible vegetable oils as sources for biodiesel synthesis. Moringa oleifera [12], Hevea brasiliensis [13], Pongamia pinnata [14], Jatropha curcas [15], [16], Hibiscus esculentus [17], Thlaspi arvense [11], Camelina sativa [18] and Coriandrum sativum [19] seed oils are few examples.
Muskmelon (Cucumis melo) belongs to the Cucurbitaceae family and is one of the popular fruits in the tropical countries. It is originated from Iran and Pakistan, mostly grown in the warmer regions of the world [20], [21]. In Pakistan, mainly in Sindh, farmers grow local varieties of muskmelon namely Golden and Dharidar [20]. In addition to a good source of protein, muskmelon seeds are a rich source of vegetable oil varying from 35 to 49% [21], [22] depending on varieties from different regions [22]. Despite being a rich source of oil and protein, its seeds are still being classified as waste product [22]. Several reports have been published on the composition of muskmelon seeds, as well as fatty acid profile [21], [22], [23] showing higher linoleic acid contents, which, though are variety dependent. Yanty et al. [23] reported that seed oil of Honeydew melon had a linoleic acid content of 69% as a principal fatty acid followed by oleic (16.8%), palmitic (8.4%) and stearic (4.6%) acids. Muskmelon seeds are also used in medicines for diabetes and chronic or acute eczema [23].
The muskmelon seeds are generally discarded as an agro-waste and can economically be utilized to extract muskmelon oil thus reducing the overall cost of muskmelon oil biodiesel production when compared with conventional vegetable oils. According to the agricultural statistics Government of Pakistan, total muskmelon production in (Sindh), Pakistan was 65,780 metric tons during the year 2008 with total area of 7653 ha [24]. Approximately 2–15% of muskmelon seeds are produced depending on seed weight and hybrid type [25]. Muskmelon contains 35–49% of oil, as per given estimation, approximately 1315.6–9867 metric tons of muskmelon seeds may be produced yielding an estimated minimum 460.5–3446.5 and maximum 644.5–4834.8 metric tons of muskmelon oil.
Deng et al. [16] used Jatropha oil as feedstock and hydrotalcite particles as catalyst for biodiesel production. Series of experiments under different reaction conditions, such as methanol/Jatropha-oil molar ratio, catalyst concentration, reaction temperature and ultrasonic power, were performed in order to optimize biodiesel yield without using RSM (response surface methodology). The purpose of the present study is to explore the muskmelon as a non-edible oil source for biodiesel production. The efforts have been made to explore the appropriateness of RSM to optimize methanolysis of muskmelon oil, aiming to develop a statistical model that could describe the effects and relationship of reaction parameters such as molar ratio of alcohol to oil, concentration of catalyst, reaction temperature and reaction time toward maximum biodiesel production yield. The main fuel properties of biodiesel from muskmelon oil have also been evaluated and compared with ASTM D 6751 and EU 14214 standards.
Section snippets
Materials
Muskmelon seeds were purchased from the local seed market of Faisalabad, Pakistan. Pure standards of FAMEs were obtained from Sigma Chemical Company (St. Louis, MO, USA). All other chemicals and reagents were analytical reagent grade and purchased from Merck Chemical Company (Darmstadt, Germany).
Extraction of muskmelon seeds
Muskmelon seeds (500 g) were crushed using a coffee grinder and then fed to a Soxhlet and extraction was carried out with 0.7 L n-hexane for 6 h. The solvent (n-hexane) was removed using lab scale rotary
Parent muskmelon oil characteristics
The AV of muskmelon crude oil was 0.29 mg KOH g−1 whereas muskmelon crude oil had 87.49 g I2/100 g of iodine value. The peroxide and saponification values of muskmelon oil were 3.45 m eq kg−1 and 216.59 mg KOH g−1, respectively.
Optimization of reaction conditions by RSM
In the current research work, RSM was used to appraise the effects between response (FAMEs yield) and four reaction variables (i.e. molar ratio of the methanol/oil, catalyst concentration, reaction temperature and time). The results at each point based on the experimental CCRD
Conclusions
The RSM based on CCRD was used for the optimization of alkali-catalyzed transesterification of muskmelon seed oil. The effect of methanol/oil molar ratio, catalyst concentration, reaction temperature and reaction time on biodiesel yields was appraised using RSM. Using the CCRD design, the maximum conversion for biodiesel produced from muskmelon oil was 89.5% under the optimum reaction variables: 5.8:1 methanol/oil molar ratio, 0.79% catalyst concentration, 55 °C reaction temperature and 72.50 min
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