How to produce biodiesel easily using a green biocatalytic approach in sponge-like ionic liquids

Abstract

Hydrophobic ionic liquids (ILs) based on cations with long alkyl side-chains (e.g. N-octadecyl-N 0 ,N 00 ,N 000trimethylammonium bis(trifluoromethylsulfonyl)imide ([C 18 tma][NTf 2 ])) are switchable ionic liquid/solid phases with temperature that behave as sponges. As liquid phases, they are excellent monophasic reaction media for lipase-catalyzed methanolysis of triolein, resulting in fast and efficient biodiesel synthesis, e.g. up to 100% yield in 8 h at 60 C, with exceptional enzyme stability (up to 1370 days halflife time at 60 C). As solid phases, the reaction mixture can easily be fractionated by iterative centrifugations at controlled temperature into three phases, i.e. solid IL, glycerol and pure biodiesel. A straightforward and sustainable approach for producing biodiesel has been developed, allowing full recovery and reuse of the biocatalyst-IL system for successive cycles and suitable for scaling-up. Broader contextA clean biocatalytic approach for producing biodiesel using temperature switchable ionic liquid/solid phases as reaction/separation media has been developed. This paper demonstrates a novel property of ionic liquids (ILs) based on cations with long alkyl side-chains (e.g. N-octadecyl-N 0 ,N 00 ,N 000 -trimethylammonium bis(triuoromethylsulfonyl)imide ([C 18 tma][NTf 2 ])) that behave as sponge-like systems for soaking and releasing (wringing) hydrophobic compounds (triolein and methyl oleate). As liquid phases, these ILs are excellent monophasic reaction media for the lipase-catalyzed methanolysis of triolein, resulting in fast and efficient biodiesel synthesis: up to 100% yield in 8 h at 60 C, accompanied by exceptional enzyme stability (up to 1370 days half-life time at 60 C). As solid phases, the reaction mixture can easily be fractionated by iterative centrifugations at controlled temperature into three phases: solid IL, glycerol and pure biodiesel. This represents a straightforward and sustainable approach for producing biodiesel, allowing full recovery and reuse of the biocatalyst-IL system for successive cycles and suitable for scaling-up. The unique properties of hydrophobic ILs, based on cations with long alkyl side chains (e.g. [C 18 tma][NTf 2 ]), allow the combined biotransformation and straightforward separation of the product opening up new opportunities to develop new reaction platforms for green industrial processes.

Sponge-like ionic liquids: a new platform for green biocatalytic chemical processes

“…37b Other authors reported how 1alkyl-3-methylimidazolium ILs (e.g. 30 The IL net could be considered as a nano-sponge with holes of variable volume, which are suitable for housing or releasing hydrophobic molecules as a function of their liquid or solid phase, respectively. 37c Ohno and co-workers reported several interesting poly(IL)s showing temperature-dependent phase behaviour after mixing with pure water, and also with aqueous salts solutions.…”

A Raman spectroscopic approach to investigate the production of biodiesel from soybean oil using 1-alkyl-3-methylimidazolium ionic liquids with intermediate chain length

“…Reaction yield estimated by Raman spectroscopy for the transesterification of soybean oil by methanol using 10 wt.% of the enzyme pseudomonas cepacia at 40°C using C 8 C 1 ImTFSI (#) or C 10 C 1 ImTFSI (Ã). For comparison, reaction rates observed by other authors are also shown, while using: C 12 C 1 ImTFSI and 10 wt.% of the enzyme candida antarctica at 60°C (blue, reproduced from reference [25]); C 16 C 1 ImTFSI and 10 wt.% of the enzyme candida antarctica at 60°C (red, reproduced from reference [26]); C 4 tmaTFSI and 18 wt.% of the enzyme candida antarctica at 60°C (green, reproduced from reference [27]); C 8 C 1 Im:TFSI and 2 wt.% of the enzyme candida antarctica at 50°C (yellow, reproduced from reference [21]); C 4 C 1 ImTFSI and 20 wt.% of the enzyme pseudomonas cepacia at room temperature (violet, reproduced from reference [5]), and a Brønsted acidic ionic liquid for increasing temperatures between 80 and 160°C (gray, reproduced with permission from reference [19]). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)…”

“…SI-3. The benefits of long alkyl chains have recently been observed by Lozano et al [27] when substituting the butyl (n = 4) chain with a dodecyl (n = 12) in ammonium based ionic liquids. The same authors have also reported that when varying the chain length from decyl (n = 10) to octodecyl (n = 18) in imidazolium based ionic liquids the reaction yield varied only slightly [26].…”

“…More precisely, we focus on imidazolium cations with alkyl chains varied from ethyl (n = 2) to decyl (n = 10), this n-range representing ionic liquids with both a relatively low viscosity and a good affinity to the oil/biodiesel. Moreover, as opposed to the majority of previous studies that have focused on temperatures well above 60°C [25][26][27]16,17,19], we deliberately limit our study to a process temperature of 40°C. In fact, the current challenge is to identify ionic liquids suitable for mild reaction conditions, such that fossil-free fuel alternatives (i.e.…”

“…The use of ionic liquids in green industrial processes is very appealing, since they can be designed to fully take into account versatility, easy separation of the products, and recyclability of the reaction medium [11]. More specifically, the use of pyridinium, pyrrolidinium, and imidazolium based ionic liquids as catalysts [14][15][16][17][18][19] or catalyst-supports [5,13,[20][21][22][23][24][25][26][27] in the transesterification of vegetable oils can result in higher reaction yields, higher catalytic effect, and feasibility of milder process conditions than for conventional organic solvents. It has also been shown that the choice of the anion has an impact on the reaction yield, which for instance can increase from 55% to 83% by substituting PF À 6 with InCl À 4 while keeping the 1-butyl-3-methylimidazolium (C 4 C 1 Im) cation [28,22].…”