خصوصیت و تبادل استری روغن بادام تلخ ایرانی برای تولید بیودیزل Characterization and transesterification of Iranian bitter almond oil for biodiesel production

Fossil fuels as energy resources are of vital importance to any country. There are limited resources of these fuels and therefore investigation of alternative renewable fuels is a necessary and increasing need. One of the renewable energy sources is biodiesel, which consists of mono alkyl esters of long chain fatty acids [1]. In addition of being renewable, biodiesel has other advantages such as having fuel properties close to petroleum diesel [2], reducing regulated air pollutants emissions [3,4], reducing greenhouse emissions [5], together with being non-toxic, environmentally safe and biodegradable [6]. There are several ways to produce biodiesel. Among them, transesterification is the most common one [7,8]. The transesterification is a reaction of oil with an alcohol in the presence of suitable catalysts such as acid or alkaline catalysts [9,10]. Methanol is the most common alcohol because of its properties and its low cost [11]. Alkaline catalysts, such as potassium hydroxide are more effective in the transesterification process [12]. The high cost of biodiesel is the major barrier for its commercialization [13,14]. Researchers have found out that the main part (85–۹۵%) of the total cost of biodiesel production is the cost of the raw material [15]. Therefore, production of biodiesel from low-cost feedstock, e.g., non-edible oils is necessary. Furthermore, most of the non-edible oil crops grow well on waste lands, can tolerate drought and dry conditions and do not need intensive care [16]. Many studies have been conducted on biodiesel production from non-edible oils, such as Jatropha curcas oil [17–۱۹], karanja seed oil [17,20], okra seed oil [21], rubber seed oil [22,23], castor oil [24], and mahua oil [25,26]. Generally, the effect of several operating variables on the transesterification reaction has been investigated and the fuel properties of produced biodiesels from non-edible oils have been determined, so that these oils were found to be appropriate viable sources for producing biodiesel. However, there are other non-edible oils that have not been investigated as a raw material for the production of biodiesel, so far. Bitter almond oil (BAO) is one of these oils. The almond tree (Prunus dulcis), which belongs to the family of Rosaceae, is a native to the Mediterranean climate region of the Middle East. But it was spread into other regions of the world by humans, so that it is cultivated in Europe, Asia and Northern Africa, and more recently also in California. Italy, Spain, Morocco, France, Greece, and Iran are the main countries that produce almond. The almond tree grows to a height between 3 and 8 m, with a trunk of up to 30 cm in diameter. Many varieties of almonds can be broadly divided into two types, namely sweet almond (with white flowers) and bitter almond (with pink flowers) [27]. The yield of the bitter almond oil, which is obtained from seeds of almond tree through a pressing process, is about 40–۴۵%. Bitter almond oil has a yellowish color and an acrid-burning taste. Bitter almond fruit contains amygdalin and an enzyme that decomposes it into glucose, benzaldehyde and hydrocyanic acid making the fruit non-edible [28]. In this work, the fatty acid composition and other physical and chemical properties of Iranian bitter almond oil were determined. The major purpose of the study was to investigate biodiesel production from the bitter almond oil by KOH-catalyzed transesterifi- cation. The effect of three important parameters including methanol to oil molar ratio, catalyst concentration and reaction temperature on the product yield, biodiesel purity and biodiesel yield were studied.