Organic-inorganic hybrid porous sulfonated zinc phosphonate material: efficient catalyst for biodiesel synthesis at room temperature

A new porous zinc phosphonate material (HZnP-1) has been synthesized via the reaction between p-xylenediphosphonic acid and anhydrous ZnCl2 under hydrothermal and mildly acidic conditions (pH similar to 5) in the absence of any structure directing agent. The phenyl group of this material has been sulfonated with concentrated sulfuric acid to obtain sulfonic acid functionalized material HZnPS-1. Powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE SEM), N-2 sorption, solid state C-13 CP MAS and P-31 MAS NMR, and FT IR spectroscopic tools are employed to characterize these materials. The crystal structures of both the materials are indexed corresponding to the new orthorhombic phases with unit cell parameters a = 11.00, b = 8.74, c = 14.62 angstrom, alpha = beta = gamma = 90 degrees for HZnP-1, and a = 10.65, b = 13.52, c = 15.30 angstrom and alpha = beta = gamma = 90 degrees for HZnPS-1. HZnPS-1 showed outstanding catalytic activity and high recycling efficiency for the synthesis of different biodiesel compounds via esterification of long chain fatty acids by using methanol as both reactant and solvent at room temperature. The green and eco-friendly catalytic system described herein can overcome the problem faced by the existing catalytic systems known in biodiesel synthesis, such as drastic conditions (high reaction temperature) and requirement of hazardous organic solvents.