The influence of storage time on relevant product properties of rubber seeds, rubber seed oil and rubber seed oil ethyl esters

Abstract

Background: 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. Results: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 nondried 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. Conclusions:Long-term seed storage led to an increase in the acid value of the oils present in the rubber seeds. Pretreatment (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.

Biofuel, Bioenergy and Feed Valorization of By-Products and Residues from Hevea brasiliensis Cultivation to Enhance Sustainability

“…Shell and kernel represent 47.5% w/w db and 52.3% w/w db of the whole seed, respectively, showing a low data variation among the tested varieties. The obtained results are in line with literature [2,13,31]. Table 3 reports characterization results for kernel, shell and capsule.…”

“…Different authors have found low ash and moisture contents for the shell fraction [10,26,31]. The results obtained from characterization analysis show negligible differences among varieties, suggesting a quite standardized feedstock.…”

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“…This may be due to the antioxidant in the formulation such as vitamin E and ascorbyl palmitate 21, which delayed the oxidation in the product. Also, the process of drying rubber seed before oil extraction helped the oil have good stability for long time storage 28 .…”

Techno-Economic Analysis for Small Scale Production of Rubber Seed Oil and Biodiesel in Palangkaraya, Indonesia

“…When assuming a 98 mol% biodiesel yield from RSO in combination with a molecular weight of 0.890 kg/mol and 0.298 kg/mol for RSO and RSO methyl esters [8], respectively, the estimated production scale of the biodiesel unit is approximately 15 kg/h, which is equivalent to 55 ton/y biodiesel (12 h operation per day for 306 days per year). An overview of the biodiesel process is presented in Fig.…”

“…By assuming the given composition and a rubber seed yield in the range of 100-1200 kg/(ha.y), the productivity of rubber seed oil (RSO) yield is estimated to be in the range 5-300 kg/(ha.y). The oil is a valuable source for the production of biodiesel (and by-product glycerol) and biopolymers [8], [9]. The protein rich press cake may find applications as a valuable source of protein [10], for instance to be used as cattle feed.…”