Temperature and pretreatment effects on the drying of different collections of Jatropha curcas L. seeds

Abstract

Drying oilseeds to reduce their moisture content is crucial in order to preserve the seeds and their contents. However, due to the nature of conventional storage facilities, it is ideal to dry seeds just before using them for oil extraction and/ or in situ biodiesel production as the seeds dried in advance might recover the equilibrium moisture content due to the humidity from the air. Thus, drying the seeds immediately before oil extraction is vital to reduce the moisture content to its minimum. In the present study, the effects of five drying temperatures (313, 323, 333, 343 and 353 K) on the degree of moisture loss from Jatropha seeds at storage and the suitability of the drying processes to reduce the seed moisture to its minimum were investigated. The drying experiments of non-pretreated (whole seeds) and pretreated (crushed seeds) seeds were performed in a heating furnace. It was found that increasing in drying temperature promoted the rate of moisture loss, and the evaporation of moisture from the crushed seeds was faster than that of the whole seeds. However, the largest weight loss (6.47%) and the smallest seed residual moisture content (0.34%) were obtained when the whole seeds dried at 353 K. The findings of the present experiments suggested that drying the whole seeds of Jatropha at 353 K could provide dried seeds with suitable moisture content for oil extraction and/or in situ biodiesel production.

Effects of Different Extraction Solvents on Oil Extracted from Jatropha Seeds and the Potential of Seed Residues as a Heat Provider

“…Prior to oil extraction, the whole seeds (WS) at storage were dried in a heating furnace before crushing them. Accordingly, the WS with their seed coats were placed on Petri dishes and dried in the furnace at 80°C for 48 h to reduce their moisture content to the minimum following the previously published work [25]. According to Subroto [27], exposing the seed coat unprotected seed to temperatures higher than 60°C might cause jatropha oil peroxidation, and thus, in the current work, drying the WS with its seed coat and crushing it just before oil extraction was preferred.…”

“…After drying, the WS were crushed mechanically by hand using mortar and pestle. Then, the particle sizes of the crushed seeds (PSCS) were estimated using three different stainless steel sieves with openings of 500 μm, 1 mm, and 2 mm woven cloth (control group, 15-D2245/J, 15-D2215/J, and 15-D2185/J) following the studies published elsewhere [25]. Accordingly, the pulverized seeds used for this experiment was a mixture of four different particles sizes.…”

“…Then, the samples of all seed collection were treated with the selected solvent. Accordingly, all the thirteen seed collections were extracted with the selected solvent using cotton after drying the WS and crushing them [25].…”

“…Except a few researches on oil extraction using hexane and petroleum ether, no research has been reported on oil extraction from jatropha seeds from different parts of Ethiopia by drying the seeds at an appropriate temperature [25] and using different solvents. The objective of the present research was to determine the amount of oil that could be extracted from different jatropha seed collections from Ethiopia using different pre-treatments and solvents and measure the energy contents of the de-oiled seed residues.…”

“…The current paper presents some new issues that have not been reported in the other studies on oil extraction from jatropha seed collection from Ethiopia. Firstly, in the present study, the whole seeds (seeds with seed coat) were dried before oil extraction based on the results of our previously published work on jatropha seed drying [25]. In this seed drying study, drying the whole seeds at 80°C for 48 h was found to reduce the moisture contents of the seeds to below 1%, and this could eliminate heating of the oil at higher temperature after extraction to remove the residual moisture.…”