Solid effect in chemical cleaning treatment of oily sludge

Oil recovery from oily sludge generated from the petroleum industry was investigated using a chemical cleaning method. Four chemicals including three surfactants, cationic cetyltrimethylammonium bromide (CTAB), nonionic Tween 60, and anionic sodium dodecylbenzenesulfonate (SDBS), and an alkali, NaOH, were used for the deoiling of oily sludge. Special emphasis was placed on the effect of sludge (solid) concentration (Cs) on the deoiling efficiency (Ro) and oil distribution coefficient (KD). The results showed that the deoiling abilities of CTAB, Tween 60, NaOH, and SDBS reduced in turn. A “solid effect” (Cs-effect) was clearly observed in the deoiling equilibrium, i.e., the KD increased with increasing Cs. The SCA-KD function, derived from the surface component activity (SCA) model we developed recently, can describe the Cs-effect observed. The values of two model parameters, intrinsic distribution coefficient ( K D 0 ) and Cs-effect constant (γ), were obtained for the chemical-sludge systems at various temperatures (T). Interestingly, we found that the Cs-effect strength (or γ value) was independent of the chemicals used in our tests, while increased with increasing T. Furthermore, the KD of NaOH increased with increasing T, which was confirmed to arise from the Cs-effect. Possible reasons for these results were discussed. This work provides a better insight into the deoiling behavior from oily sludge and confirms that the SCA model is a mathematical tool for analyzing deoiling data with the Cs-effect.