Effects of redox additives on the fuel properties of oil refined from oily sludge via non-thermal plasma treatment

Abstract

Oily sludge, composed of complex substances including various amounts of water, hydrocarbons, metallic debris, solid residue, and inorganic compounds, is a by-product of petroleum refining, waste lubricating oil from vehicles, and mechanical lubricants from various-sized vessels. Due to its heavy content, oily sludge causes high viscosity and results in a sluggish liquid state. In the recycling industry, oily sludge is considered industrial waste. Although its content is complex and difficult to separate, its heating value could reach 33.5 MJ/kg, about 70% of that of diesel fuel, and thus has a high recycling value. Solvent extraction was used in a pretreatment process to extract the oily content of the sludge. The dielectric barrier discharge (DBD) type of non-thermal plasma reactor was thereafter applied to pyrolyze and excite the oily sludge to produce liquid products. The fuel oils produced from the action of non-thermal plasma on the treated oily sludge, with the addition of a reductant or oxidant agent, were analyzed for their fuel compositions and properties, such as elemental contents and chemical compounds, and heating value. The experimental results showed that the pretreatment procedures effectively improved the recovery yield of the discarded oily sludge; for example, its heating value reached 44.37 MJ/kg after the pretreatment process. Finally, after comparing the fuel properties of the oily sludge with the addition of an oxidizing or reducing agent at various weight ratios of the dielectric to the oily sludge, it was found that the oily sludge with 50 wt% sodium hypophosphite improved the fuel properties more than that with ferric nitrate hydroxide. The carbon residue and moisture content of the treated oily sludge were reduced by 1.1 wt% and 0.12 wt%, respectively. Moreover, a higher yield of 84.05% fuel product from the oily sludge was achieved. The non-thermal plasma reaction effectively converted discarded oily sludge into beneficial fuel oil for industrial combustors.