Abstract
Rubber seed oil (RSO) derived from rubber seeds is considered a promising plant oil. However, subsequent biodiesel synthesis from RSO was reported to be difficult due to the high acidity of the oil. Detailed studies on the effects of storage time of rubber seeds on relevant product properties such as acid value are not yet available. The authors here report a study on the influence of storage time on the moisture content of rubber seeds and the acid value of the oil within the seeds. In addition, the acidity of isolated rubber seed oil and the acidity of rubber seed oil ethyl esters versus time was determined. The moisture content as a function of the time for two different batches of rubber seeds, one with an initial water content of 3.1 wt% (obtained by drying the seeds at 60 °C for 3 days) and another with a moisture content 10.7 wt% (as received, non-dried) were determined at 27 °C and a relative humidity of 67 % for a period of 2 months. The moisture versus time curves were successfully modelled using an analytical solution of the instationary diffusion equation and allowed determination of the diffusion coefficient of water in the rubber seeds at 27 °C. The acid value of the isolated rubber seed oil increased considerably in time for both cases (from 0.84 to 4.19 mg KOH/g for the non-dried seeds and from 0.51 to 2.13 mg KOH/g for the dried seeds). Freshly isolated rubber seed oil and rubber seed ethyl esters derived thereof prepared using a transesterification reaction have a relatively low acid value of 0.52 and 0.32 mg KOH/g respectively. The acid value of rubber seed oil only slightly increased during storage (0.52–0.60 mg KOH/g), whereas the acid value of the rubber seed ethyl esters (0.32–0.33 mg KOH/g) does not change significantly. Long-term seed storage led to an increase in the acid value of the oils present in the rubber seeds. Pre-treatment (e.g. drying) of the rubber seeds showed a positive effect and the increase in acid value in time was lower than for the non-pretreated seeds. It is recommended to store the isolated rubber seed oil instead of the rubber seeds to minimize acid formation.
Highlights
Rubber seed oil (RSO) derived from rubber seeds is considered a promising plant oil
Rubber seed characteristics The experiments were carried out with fresh rubber seeds obtained from Bengkulu, Indonesia
The results indicate that the RSO ethyl esters (RSOEE) produced in this study has the potential be used for commercial applications
Summary
Rubber seed oil (RSO) derived from rubber seeds is considered a promising plant oil. subsequent biodiesel synthesis from RSO was reported to be difficult due to the high acidity of the oil. The authors here report a study on the influence of storage time on the moisture content of rubber seeds and the acid value of the oil within the seeds. Biodiesel is an important renewable transportation fuel produced from triglycerides like virgin plant oils and waste cooking oils [1,2,3] It is commercially available and widely used in many countries such as the US, Indonesia, Brazil, Germany and other European countries. Rubber seed oil (RSO), derived from rubber seeds, is considered a promising source because the seeds are reported to contain a high amount of oil (approximately 40–50 %) [10, 11] and are currently regarded as a waste. The valorization of rubber seeds by biodiesel production is highly relevant as it increases the economic attractiveness of the rubber plantations
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