Energy Conversion and Management: X (Dec 2021)
Hydrocarbon yields and stability from Euphorbia tirucalli for quality energy use
Abstract
The present concerns on fossil fuels shortage, high price, and future exhaustion have necessitated the search for alternative energy sources using green plants. The study evaluated the yield and Oxidative Stability [OS] of liquid hydrocarbons from the E.tirucalli plant as a quality alternative energy source for future use. E.tirucalli stem bark samples were collected from 28 trees with similar stem Diameter at Breast Height (DBH) (60 cm) in the Bahi (semi-arid), Goba (coast), and Iyela (tropical) sites. Sample processing and analysis were done at the Department of Chemical and Mining Engineering (CME), University of Dar es Salaam. 20 g of the milled and dried stem bark sample has been used for extraction of liquid hydrocarbons using a Solid-liquid extraction technique with a Soxhlet extractor. The percentage yields (%) of the obtained liquid hydrocarbons were determined after rotary evaporation (60 °C) of the solvent. The hydrocarbon OS Indexes [OSI(s)] were determined by using a Metrohm 873 Biodiesel Rancimat, and the obtained OSI(s) were compared with 6 h EN 14214 standard Induction Time (IT). Differences in hydrocarbon yields (%) and, the OSI(s) among stem DBH in different study sites were determined by using One-way ANOVA (Minitab-v19: P ≤ 0.05). Results revealed higher hydrocarbon yields (5% – 17.5%) than 1% – 14% of the most laticiferous plants, 3% – 9% for most energy application substitutes, and 9% – 12% for long-term OSI quality products. Hydrocarbon OSI (s) was lower [3.50 h – 5.83 h (Bahi site] than recommended standards (6 hrs) in all study sites. Both hydrocarbon yields (%) and OSI (s) differed significantly, higher in the Bahi than Iyela and Goba sites. High hydrocarbon yields (%) and low OSI (s) indicate that E. tirucalli contained a high amount of low-quality high molecular weight unsaturated hydrocarbons susceptible to undergo auto-oxidation. They require pre-treatment to reduce their molecular weight to be suitable to replace fossil fuels, for energy use and conform to certified quality products of long-term oxidative stability.
