Desulfurization efficiency of polydimethylsiloxane/silica nanoparticle nanocomposite membranes: MD simulations

Abstract

The effect of SiO2 nanoparticles on the efficiency of polydimethylsiloxane membranes to separate n-octane from benzothiophene was investigated using molecular dynamics simulations. The non-bond energies were more negative (by∼4000kcal/mol) compared with their corresponding potential energies. Further, adding 2–10vol% silica particles to the membrane led to increase in the potential and non-bond energies so that the 10vol% SiO2 membrane had the greatest negative potential as well as non-bond energies of nearly −35,000 and −39,000kcal/mol, respectively. It was found that the free volume was increased from 82764.23Å3 in the pure polydimethylsiloxane membrane to 99362.47–208186.38Å3 in 2–10vol% SiO2 nanocomposite membranes. The X-ray diffraction patterns of all membranes exhibited one peak at about 23° proving the presence of amorphous silica structures. Increasing the silica content into the polymeric matrix caused enhancement in the surface area so that it was changed within the range of 37421.00–43812.95Å2 which may be related to the presence of greater accessible surfaces on the total molecules by increasing amount of the SiO2 particles. The radial distribution function analysis revealed the interactions of benzothiophene molecules with SiO2, n-octane and polydimethylsiloxane were strong, moderate and weak, respectively suggesting the benzothiophene molecules would diffuse and transfer more easily within the polydimethylsiloxane membrane in the presence of SiO2 nanoparticles. The lowest n-octane diffusion coefficient (0.0037×10−4 cm2/s) was measured for the 6vol% SiO2 membrane while the largest BT diffusion coefficient was obtained for the 6vol% SiO2 membrane (0.0071×10−4 cm2/s) confirming this membrane was the most appropriate nanocomposite to separate benzothiophene from n-octane (desulfurization process).