Juana M. Bernal

Immobilised Lipase on Structured Supports Containing Covalently Attached Ionic Liquids for the Continuous Synthesis of Biodiesel in scCO2

Different nanostructured supports, based on 1-decyl-2-methyimidazolium cations covalently attached to a polystyrene divinylbenzene porous matrix, were used as carriers to immobilise Candida antarctica lipase B. The suitability of these immobilised lipase derivatives for the synthesis of biodiesel (methyl oleate) by the methanolysis of triolein has been tested in both tert-butanol and supercritical (sc)CO(2) (18 MPa, 45 °C) as reaction media. The use of modified supports with low ionic-liquid loading covalently attached to the main polymeric backbone chains provide structured materials that led to the best biodiesel yields (up to 95 %) and operational stability (85 % biodiesel yield after 45 cycles of 8-4 h) in scCO(2) (45 °C, 18 MPa). The presence of tert-butanol as an inert cosolvent in the scCO(2) phase at the same concentration as triolein was key to avoid poisoning the biocatalyst through the blockage of its active sites by the polar byproduct (glycerol) produced in the biodiesel synthesis.

Stabilizing immobilized cellulase by ionic liquids for saccharification of cellulose solutions in 1-butyl-3-methylimidazolium chloride

A new approach to improve the cellulase stability against 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]), based on coating of immobilized enzyme particles with hydrophobic ILs, is proposed. The stability of commercial cellulase (Celluclast®), immobilized onto a polymeric support (Amberlite XAD4), was first studied in ten different ionic liquids (ILs) at 50 and 80 °C. Hydrophobic ILs clearly enhanced the enzyme thermal stability. Butyltrimethyl-ammonium bis(trifluoromethylsulfonyl)imide ([N1114][NTf2]) enhances half-life time of the immobilized enzyme at 50 °C up to 4 times, while [Bmim][Cl] behaved as a powerful enzyme deactivating agent. Thus, the stability of cellulase in hydrophobic IL/[Bmim][Cl] mixtures was greatly improved with respect to [Bmim][Cl] alone. A stabilized cellulase derivative obtained by coating immobilized enzyme particles with [N1114][NTf2], has been then successfully used for the saccharification of dissolved cellulose in [Bmim][Cl] (i.e. up to 50% hydrolysis in 24 h) at 50 °C and 1.5 w/v water content.

A clean enzymatic process for producing flavour esters by direct esterification in switchable ionic liquid/solid phases

A clean biocatalytic approach for producing flavour esters using switchable ionic liquid/solid phases as reaction/separation media has been developed. The phase behaviour of different IL/flavour acetyl ester (geranyl acetate, citronellyl acetate, neryl acetate and isoamyl acetate) mixtures was studied at several concentrations, resulting for all cases in fully homogeneous liquid media at 50 °C, and solid systems at room temperature. By using an iterative centrifugation protocol on the solid IL/flavour ester mixtures at controlled temperatures, the solid IL phase and the liquid flavour ester phase can be easily separated. The excellent suitability of an immobilized Candida antarctica lipase B (Novozym 435) catalyst in the esterification reaction between an aliphatic carboxylic acid (acetic, propionic, butyric or valeric) and a flavour alcohol (isoamyl alcohol, nerol, citronellol or geraniol) in N,N′,N′′,N′′′-hexadecyltrimethyl-ammonium bis(trifluoromethylsulfonyl)imide ([C16tma][NTf2])IL has been demonstrated, the product yield being improved up to 100% under appropriate reaction conditions (enzyme amount, dehydrating molecular sieves, etc.) at 50 °C. The enzymatic synthesis of sixteen different flavour esters was carried out in [C16tma][NTf2] by means of this approach, providing products of up to 0.757 g mL−1 concentration after IL separation. The residual activity of the enzyme/IL system during seven consecutive operation cycles was shown to be practically unchanged after reuse.

Supercritical synthesis of biodiesel.

The synthesis of biodiesel fuel from lipids (vegetable oils and animal fats) has gained in importance as a possible source of renewable non-fossil energy in an attempt to reduce our dependence on petroleum-based fuels. The catalytic processes commonly used for the production of biodiesel fuel present a series of limitations and drawbacks, among them the high energy consumption required for complex purification operations and undesirable side reactions. Supercritical fluid (SCF) technologies offer an interesting alternative to conventional processes for preparing biodiesel. This review highlights the advances, advantages, drawbacks and new tendencies involved in the use of supercritical fluids (SCFs) for biodiesel synthesis.

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

To build a green chemical industry it is necessary to develop integrated processes of selective transformation and separation capable of directly providing pure products, including the reuse of all the elements of the reaction system, e.g. catalysts, solvents, etc. In recent years, the unsurpassed selectivity of enzymes for chemical reactions, combined with the excellent solvent properties of ionic liquids (ILs), has provided an excellent setting for carrying out sustainable chemical transformations. However, implementation of this to industrial chemical processes needs the development of straightforward, cheap and/or sustainable approaches for pure product extraction, including the reuse of ILs. Hydrophobic ILs based on cations with long alkyl side-chains, e.g. octadecyldecyltrimethylammonium bis(trifluoromethylsulfonyl)imide, ([C18tma][NTf2]), are temperature switchable ionic liquid/solid phases that behave as sponge-like systems (Sponge-Like Ionic Liquids, SLILs). Based on this newly found property, SLILs have been used to develop straightforward and clean approaches for producing nearly pure synthetic liquid compounds of high added value (e.g. flavour esters, biodiesel, etc.) in two steps: a biocatalytic step that occurs as monophasic liquid systems, followed by a product separation step carried out by cooling/centrifugation/filtration of the solid reaction system. SLILs therefore might be considered a new green platform for easy preparation of pure products.

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

Hydrophobic ionic liquids (ILs) based on cations with long alkyl side-chains (e.g. N-octadecyl-N′,N′′,N′′′-trimethylammonium bis(trifluoromethylsulfonyl)imide ([C18tma][NTf2])) 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 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, 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.

An efficient microwave-assisted enzymatic resolution of alcohols using a lipase immobilised on supported ionic liquid-like phases (SILLPs)

The combined action of microwave irradiation and CALB immobilised onto polymeric SILLPs leads to an excellent activity improvement (28 fold) and operational stability towards reuse (12 operation cycles). This procedure also allows the microwave-assisted one-pot DKR by the combination with a solid acid catalyst.