Esterification of Glycerol with Acetic Acid Using Nitrogen-Based Brønsted-Acidic Ionic Liquids

Abstract

Glycerol esterification with acetic acid produces a mixture of mono, di, and triacetins, which are commercially important value-added products with a wide range of industrial uses including their application as fuel-additives, thus contributing to environmental sustainability and economic viability of the biorefinery concept. Glycerol esterification with acetic acid was studied using a range of nitrogen-based Brønsted-acidic ionic liquids. Cost-effective and easily synthesized Brønsted-acidic ionic liquids based on alkyl-pyrrolidone and alkyl-amine cations were synthesized and characterized using 1H NMR spectroscopy. The catalytic activity of the Brønsted-acidic ionic liquids produced were investigated for the production of di and triacetin from glycerol and acetic acid. Amongst all ionic liquids evaluated in this study, N-methyl-2-pyrrolidinium hydrogen sulfate [H-NMP]­[HSO4] was found to be the most active and cost-effective catalyst. The effect of significant reaction parameters on selectivity to the trisubstituted product, triacetin, was modeled using a design of experiment (DoE) approach with a response surface methodology involving a central composite design. The esterification process was optimized to maximize the production of triacetin. Optimizing the process this way naturally leads to lower levels of mono and diacetin. Amongst the reaction parameters evaluated, temperature had the greatest influence on product selectivity, followed by the glycerol to acetic acid molar ratio, and the model also showed dependence on the synergistic interaction between the temperature and mole ratio. It is worth noting that agitation speed had minimal influence on product selectivity. Under optimized reaction conditions, >99% glycerol conversion was achieved with 42.3% selectivity to triacetin, and a combined di and triacetin selectivity of >95% within 1 h.

Influence of Heterogeneous Catalysts and Reaction Parameters on the Acetylation of Glycerol to Acetin: A Review

“…The authors also reported that this transesterification method is cost-effective. The use of acid-functionalized ionic liquids as a catalyst in glycerol acetylation has been reported to be of high catalytic activity [136][137][138]. A >95% yield of triacetin was obtained in glycerol acetylation with acetic acid over 1-methyl-3-(3-sulfopropyl)-imidazolium hydrogen sulphate ([HSO 3 -pmim][HSO 4 ]) as the catalyst after 6 h of reaction time at 120 • C [136].…”

Glycerol Acetylation Mediated by Thermally Hydrolysed Biosolids-Based Material

“…Similar and even better results were achieved only using a high loading of thermally hydrolysed biosolids catalyst (from 8 wt% to 16 wt%). Other acid catalyst such as ionic liquids outperformed the biosolids-based catalyst, reaching conversions of up to 99% and selectivity for triacetin up to 47% [60]. Furthermore, nanostructured sulphated zirconia led to higher yields of triacetin (up to 40%) with low catalyst loading [61].…”

Optimization and Characterization of Mesoporous Sulfonated Carbon Catalyst and Its Application in Modeling and Optimization of Acetin Production

“…In recent times, efforts have been geared towards the use of low-priced feedstocks, namely inedible oils, waste cooking oils, and animal fats, to produce biodiesel [ 1 , 2 ]. Another alternative measure is to convert the byproduct, glycerol, to other more valuable products, thereby ameliorating the cost of biodiesel production and promoting a circular economy [ 3 ]. The worldwide production of glycerol is on the rise.…”

“…The trend of the above catalytic reactions is fast changing from the use of homogeneous catalysts due to environmental concerns, difficulty in its separation, corrosive effects, and nonrecyclability to more advantageous heterogeneous solid acids catalysts [ 3 , 6 , 8 ].…”

“…Similarly, the optimization of reaction parameters using a design of experiment (DOE) to improve triacetin selectivity has been scantly reported [ 3 , 11 , 28 ]. DOE has recently been employed in optimization studies, namely factorial design, Taguchi design, and response surface methodology (RSM), with each having advantages and otherwise.…”