efficiency was compared to that of static extraction using solvents mixture, namely methanol-chloroform (1:1). Sample of different sizes were tested. It is important to note that the in the static mode, the extraction was assisted by ultra-sonication, which was not the case in Soxhlet tests. Table 1 shows the percentage of extracted oils from the different particle sizes. The performances of
Figure 1. TGA and DTG curves of date pits.
both methods were comparable, with Soxhlet extraction showing better performance for smaller sizes samples. When large particles were used, Soxhlet extraction was less effective than the static method. This was expected as ultrasonic- cation enhanced the extraction efficiency by a caustic-induced cavitation that can disrupt the sample and facilitate solvent penetration, and therefore enhanced the contact between the solvent and the solute. The comparison revealed that dynamic extraction was 18% and 31% higher than the static mode when medium and small particle size samples were used, respectively. By decreasing samples particle sizes, the extraction yield increased dramatically for more than 3 folds, reaching 11.67% when n-hexane was used with small size particles, compared to the large particles. The effect was less when the static mode was tested, where only 8.9% yield of oil was obtained with small size samples (equivalent to 75% of total extractable oils using n-hexane). Generally, by reducing particle size, the increased specific surface area enhances oils exposure to the solvent, therefore dissolving and extracting more oils. The results found in this work are in agreement with previously reported oil contents in date pits     .
The composition of extracted oils was determined, and the results are shown in Table 2. As shown, extracted oils contained mainly of trans-9-elaidic and linoleic acids. These together accounts for more than 45% of the total fatty acids present in the oil. Palmitic acid is the second highest acid in accounting for around 20% followed by myristic and stearic acids. The results found in this work were in agreement with previous results on date pits   and other potentials biodiesel feed stocks, such as microalgae lipids  .
Table 1. Effect of samples particle size on extracted oil yield.
Table 2. Date-pits oil composition.
3.3. Biodiesel Production
The production of biodiesel from extracted date pits oils was tested using different catalysts; namely NaOH, Eversa®Transform and Novozym®435. Reactions were carried out with methanol to oil molar ratio of 5:1 for six hours. Produced FAMEs were dissolved in 10 ml n-hexane before being analyzed. Comparable yields were obtained when the reaction was carried using Novozym®435 and NaOH. As shown in Figure 2, the highest yield, reaching 30%, was achieved in the presence of Novozym®435. A slightly lower yield of 27% was obtained in NaOH. By using Eversa®Transform a yield of only 11% was achieved.
Despite the comparable yields obtained using Novozym®435 and NaOH, the profiles of the produced esters were different, as shown in Figure 2. It was found that the selectivity of NaOH was high toward transesterifyingtrans-9-elaidic acids compared to other acids. Whereas Novozym®435 equally transestrified most acids present in the oil sample. Similar observation was also found using the liquid Eversa®Transform lipase. It is important to mention that this is the first work to test the use of this lipase in biodiesel production
The potential of using waste date-pits as a new source for oil to be used in biodiesel production was examined. From grinded date pits, in size ranging of 0.5 - 0.35 mm, maximum extraction yields of 11% and 7.9% were achieved using Soxhlet and methanol-chloroform solvent mixture extraction methods, respectively. The effectiveness of using lipase from different sources in producing the biodiesel was investigated, and compared to that of conventional alkaline catalyst. The highest biodiesel yield of 30% was obtained at 40˚C, 5:1 methanol to molar ratio after 6 hrs using Novozym®435. The possibility of using liquid
Figure 2. Biodiesel production yield after six hours from oils extracted from date pits using different enzymes.
Eversa®Transform lipase was also examined; however, a lower yield was obtained.
Cite this paper
Al-Zuhair, S., Taher, H., Al Dhaheri, S., Wajeeh, S., Nour, M. and El-Najjar, E. (2017) Biodiesel Production from Oils Extracted from Date Pits. Green and Sustainable Chemistry, 7, 48-56. https://doi.org/10.4236/gsc.2017.71004