High Quality Biowaxes from Fatty Acids and Fatty Esters: Catalyst and Reaction Mechanism for Accompanying Reactions

Abstract

Biowaxes are interesting materials for pharmaceutical industry and consumer goods. Here the production of waxes from alternative renewable resources has been evaluated on the basis of the ketonic decarboxylation of fatty acids. The latter converts carboxylic acids (or their derivatives) into ketones with almost double chain length. Hence, sunflower oil was employed as starting material and passed over monoclinic zirconium. A wax fraction of 43% yield was obtained, though high content of molecules with more than 30 carbon atoms was not achieved due to prevalent carbon chain degradation. However, reaction of methyl stearate over zirconium oxide gave 60% wax fraction. Together with the waxes, an almost oxygen-free diesel fraction was obtained in more than 25% yield. Labeling experiments showed that the ketone intermediate is degraded by a radical chain mechanism. It is further concluded that methyl stearate radical formation is induced by carbon–carbon bond scission at high temperature whereas the glycerol part of the triglyceride may act as radical initiator. As a consequence, long linear alkane waxes should be produced in the absence of glycerol (moieties). The exploitation of the side-product as high quality diesel together with the waxes improves the economic feasibility of the process.

Catalytic advancements in carboxylic acid ketonization and its perspectives on biomass valorisation

“…FAME) on ketonization selectivity by carrying out isotopic labelling experiments. [163] Here, sunflower vegetable oil was used as triglyceride feedstock (93% C18 and 7% C16 fatty acids) for the ketonization on ZrO2 in a fixed bed reactor system at 400-550 °C under atmospheric H2 pressure. Under these conditions, full conversion resulted in a complex product mixture, which was divided into gasoline, diesel and wax fractions based on simulated distillation results.…”

Metal-Free Reduction Creates Highly Active TiO2 Surfaces for Fatty Acid Ketonization

“…However, their molecular composition is suitable for C−C coupling to renewable C 23 −C 35 "wax" ketones. 11 They can be used directly as end products 12 or may serve as intermediates to undergo hydrodeoxygenation and hydroisomerization reactions for the synthesis of bio-based paraffinic waxes and lubricants. 13−16 Ultimately, they can serve as platform molecules for a wide array of functionalized compounds such as amines, alcohols, sulfonates, olefins, etc.…”

“…This research topic has become increasingly trending in recent years. − On the contrary, the literature on the ketonization of long-chain C 12 –C 18 fatty acids is significantly less prevalent. However, their molecular composition is suitable for C–C coupling to renewable C 23 –C 35 “wax” ketones . They can be used directly as end products or may serve as intermediates to undergo hydrodeoxygenation and hydroisomerization reactions for the synthesis of bio-based paraffinic waxes and lubricants. − Ultimately, they can serve as platform molecules for a wide array of functionalized compounds such as amines, alcohols, sulfonates, olefins, etc. Since its discovery, metals, metal salts, zeolites, and metal oxides have been used as ketonization catalysts.…”

Preparation of Biowax Esters in Continuous Flow Conditions

“…In recent years, the focus has raised to the study of bio-based waxes obtained essentially from the structural modification of triglycerides of vegetable oils 5 carried out by partial or full hydrogenation of fatty acid chains or by interesterification to achieve the desired physical properties. 4,6 Several functional groups are commonly introduced on the acyl chains to improve cohesiveness and tune the wax physicochemical properties, such as hydroxyl or branched alkyl groups and short-chain fatty acids.…”

“…In recent years, the focus has raised to the study of bio-based waxes obtained essentially from the structural modification of triglycerides of vegetable oils carried out by partial or full hydrogenation of fatty acid chains or by interesterification to achieve the desired physical properties. , Several functional groups are commonly introduced on the acyl chains to improve cohesiveness and tune the wax physicochemical properties, such as hydroxyl or branched alkyl groups and short-chain fatty acids. , Another possible approach to prepare biowaxes is the direct esterification of long-chain acids with fatty alcohols to produce wax esters with chains longer than C30 that are normally harder, less greasy, and more brittle than those obtained by the abovementioned transesterification processes. , …”