Removal of coke powders in coking diesel distillate using recyclable chitosan-grafted Fe3O4 magnetic nanoparticles

Abstract

Coking is an important process for heavy or residual oil treatment as coke powders carried by coking diesel distillate (CDD) could seriously affect the steady operation of downstream devices. In this work, chitosan (CS)-grafted Fe3O4 was used to prepare magnetic nanoparticles (MNPs), and characterization analyses, including X-ray diffractometry (XRD), Fourier-transform infrared spectrometry (FTIR), transmission electron microscopy (TEM), dynamic light scattering analysis (DLS), thermogravimetric analysis (TG), vibrating sample magnetometry (VSM), and water contact angle determination, were performed on the coking powders and MNPs. The mechanism of coke powder removal was determined through an experimental study on coke powder removal in CDD by using the MNPs. Grafting CS onto oleic acid (OA)-modified Fe3O4 yields Fe3O4@OA-CS nanoparticles with superparamagnetism, and the CS grafting quantity is an important factor influencing whether Fe3O4@OA-CS has high efficiency for coke powder removal. CS can enhance the hydrophilicity of Fe3O4@OA (water contact angle = 112°), and Fe3O4@OA-CS with some hydrophobicity (water contact angle = 105°) could satisfactorily remove coke powders (removal rate ≥96%) from the distillate. In addition, Fe3O4@OA-CS could be recycled and reused using light petroleum (LP). The new coke removal process involves the following principles: spatial distribution of CDD is taking coke powders as the core, coating with non-hydrocarbon compounds (polar layer), and dispersing into arenes and alkanes (non-polar layer). Fe3O4@OA-CS may show interfacial activity and could be directionally arranged on the interface between the polar and non-polar layers. Thus, non-hydrocarbon compounds may come into direct contact with the Fe3O4@OA-CS nanoparticles. When rinsed with LP, Fe3O4@OA-CS can enter the LP phase, together with these non-hydrocarbon compounds, and be effectively separated from the coke powders.