Esterification of stearic acid using novel protonated and crosslinked amidoximated polyacrylonitrile ion exchange fibres

[Display omitted] •A protonated amidoximated polyacrylonitrile mesh was used as a heterogeneous acid catalyst for biodiesel production.•Esterification of long chain fatty acids were evaluated under a range of reaction conditions with catalyst reused for 13 cycles.•Conversion of stearic acid to methyl stearate was comparable to the 98% yield obtained with 1wt% H2SO4 homogenous catalyst•T•Catalyst is easy to re-use and replace with potential for application in continuous flow production of biodiesel•Waste Fats Oils and Grease (FOGs) have high Free Fatty Acid(FFA) content providing potential to esterify to produce biodiesel This study will demonstrate the conversion of stearic acid to methyl stearate (biodiesel) using for the first time crosslinked amidoximated polyacrylonitrile ion-exchanged mesh protonated by sulphuric acid. Quantitative analysis of conversion was by GC-FID, 1H NMR and ATR-FT-IR with GC-FID the most reliable. A molar ratio of methanol to stearic acid of 35.5: 1 gave 94 % conversion to the ester at 90 °C. At 65 °C and a greater ratio of 87.1:1 conversion was 94.1 % comparable to the 98 % yield obtained with 1wt% H2SO4. Re-use at 65 °C gently dropped to 57 % on the 13th cycle. Regeneration by washing with dichloromethane and re-acidification achieved 84 % conversion but quickly deactivated due to blocking of sites by methyl stearate as shown by ATR-FTIR. This protonated amidoxime PAN catalyst (distinct from sulfonated fibres) exhibited higher stability than other heterogeneous protonated catalysts (ion-exchange resins, zeolites, clays) used lower temperatures and shorter reaction times. Advantages of using a mesh in place of powders are its ease of removal/replacement for continuous flow reactors promoting quick changes in process parameters. This study is promising as providing a sustainable protonated catalyst for use in converting Fats, Oils and Greases (FOG’s) in waste oils and wastewater to biodiesel.