Abstract
This work aims to shed light on the use of two biochars, obtained from the pyrolysis at 550 °C of heavy-metal-contaminated Jatropha curcas L. roots, as heterogeneous catalysts for glycerol esterification using residual glycerine. To do this, glycerine from biodiesel production was purified. In a first step, H3PO4 or H2SO4 was used to remove non-glycerol organic matter. The glycerol-rich phase was then extracted with ethanol or propanol, which increased the glycerol content from 43.2% to up to 100%. Subsequently, the esterification of both purified glycerine and commercial USP glycerine was assayed with acetic acid (AA) or with acetic anhydride (AH) at 9:1 molar ratio to glycerol using Amberlyst-15 as catalyst. Different reaction times (from 1.5 to 3 h) and temperatures (100–115 °C when using AA and 80–135 °C when using AH) were assessed. Results revealed that the most suitable conditions were 80 °C and 1.5 h reaction time using AH, achieving 100% yield and selectivity towards triacetylglycerol (TAG) almost with both glycerines. Finally, the performance and reuse of the two heterogeneous biocatalysts was assessed. Under these conditions, one of the biocatalysts also achieved 100% TAG yield.
Highlights
The increasing production of biodiesel has resulted in an oversupply of its by-product, glycerine [1]
When glycerine was acidified with H3 PO4, three phases were found after decantation: an upper layer containing MONG, and intermediate glycerol-rich phase, and an inorganic salts phase on the bottom
Only 2 phases were found when working with H2 SO4 because the inorganic salts layer was not observed, which agrees with the results of Manosak et al [3] but contradictory with those reported by Kongjao et al [2]
Summary
The increasing production of biodiesel has resulted in an oversupply of its by-product, glycerine [1]. 1 kg glycerine (crude glycerol) is produced from every 10 kg biodiesel produced by transesterification [2]. As 42 billion liters biodiesel will be produced in 2020, according to projections, it is estimated that 4.2 billion liters glycerine will be available that year [1]. Glycerine or crude glycerol obtained from biodiesel production is composed of glycerol (40–70% wt.) and methanol, water, salts, and soap as well as other triglycerides that have not entirely reacted (di- and mono-glycerides). The most commonly used methods for glycerine purification are based on simple distillation. The main hindrances of these purification methods are the high energy required for glycerol vaporization and the low process yield [3,4]
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