Polyethyleneimine-modified alkali lignin semi-interpenetrating polymer network for oil/water separation

Abstract

Oily wastewater is produced throughout the petroleum extraction process, from drilling and oil production to collection and transportation. Such effluent comprises not only large amounts of free and emulsified oil, but also a variety of poisonous and hazardous compounds. When these compounds are released without appropriate treatment, contaminating drinking water sources via groundwater penetration, and causing irreparable damage to ecosystems and human health it is difficult to be reversed. With global petroleum demand rising and environmental standards tightening, the scientific and efficient treatment of such oily wastewater to achieve the dual objectives of ‘compliant discharge’ and ‘resource recovery’ has emerged as an urgent global challenge for both the petroleum industry and the environmental sectors worldwide. Separation of components in oily wastewater presents a pressing challenge, extending beyond mere oil-water separation to encompass the isolation of other harmful constituents. Developing an economical, environmentally sound, and highly efficient membrane remains a significant technical hurdle. This study presents a semi-interpenetrating polymer network (semi-IPN) hydrogel with oil-water separation functionality, fabricated from the renewable green resource alkanolamine (AL). Lignin was first modified using polyethyleneimine (PEI), followed by incorporation of semi-IPN polyvinyl alcohol (PVA) linear molecules, after adding SiO₂ nanoparticles, the resulting semi-IPN hydrogel exhibited remarkable superhydrophilicity (OCA = 156°) and strong chemical stability. This superhydrophilic behaviour was attributed to low surface energy and the roughness imparted by the SiO₂ nanoparticles. With a stable average efficiency of 99%, it overcomes the difficulty of attaining stable separation across various oil phases while retaining continuously high separation efficiency.

Graphical abstract