Preparation of a reusable and pore size controllable porous polymer monolith and its catalysis of biodiesel synthesis

Abstract

A sulfonated porous polymer monolith (PPM-SO₃H) has been prepared via the polymerisation of styrene (St) and divinyl benzene (DVB) with organic microspheres as pore-forming agents, followed by sulfonation with concentrated sulfuric acid. It was characterized by acid–base titration in order to determine its acid density, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, mercury intrusion porosimetry (MIP) and thermogravimetric analysis (TG). The PPM-SO₃H showed an acid density of 1.89 mmol g⁻¹ and pore cavities with an average diameter of 870 nm. The catalytic activity of PPM-SO₃H in practical biodiesel synthesis from waste fatty acids was investigated and the main reaction parameters were optimized through orthogonal experiment. The best reaction conditions obtained for the optimization of methanol to oil ratio, catalyst concentration, reaction temperature and reaction time were 1 : 1, 20%, 80 °C and 8 h, respectively. PPM-SO₃H showed excellent catalytic activity. In biodiesel synthesis, the esterification rate of PPM-SO₃H is 96.9%, which is much higher than that of commercial poly(sodium-p-styrenesulfonate) (esterification rate 29.0%). The PPM-SO₃H can be reused several times without significant loss of catalytic activity; the esterification rate was still 90.8% after 6 cycles. The pore size of this porous polymer monolith can be controlled. The dimension and shape of this porous polymer monolith were also adjustable by choosing a suitable polymerisation container.