Purification Of Waste Lubricating Oil By Fulvic Acid And Its Composite Adsorbents

With the rapid growth of the global economy and people’s living standard, the generation of waste lubricating oil increases sharply. The characteristics of waste lubricating oil cause that recycling is one of the effective ways to solve the resources and environment problem. Adsorption is an important technology of regenerating for waste oil. As the core of that technology, adsorbents have been the hot spots in this field. With the seriousness of environmental pollution, the emergence of the defects of traditional adsorbents and the appearance of new adsorption materials, development and application of the alternative adsorbents have been the urgent problems in oil treatment field. Humic acid is a kind of natural polymer materials, which derives from a wealth of sources, has strong adsorption activity, is non-toxic to the environment and has environmental-friendly performance that other sorbents do not have. Fulvic acid is one of the key components of the humic acid. Having a variety of active functional groups and being easy to be extracted, fulvic acid has become a hotspot in research of humic acid. Therefore, three levels fulvic acid extracted from soil were used as new adsorbents and were characterized by FTIR. And then, composite adsorbents were prepared by loading the fulvic acid on the soil without humic acid, and were characterized by XRD respectively. Three levels of pure fulvic acid and composite adsorbents were used to regenerate waste lubricating oil. Using the decolorization rate as the main index, the effect of adsorbent dosage, mixing temperature, mixing time on the decolorization rate and the removal of asphaltene、Ca²⁺、Zn²⁺ were studied. Using batch equilibrium method, the kinetics and thermodynamics of asphaltene on fulvic acids were investigated. Combining with infrared spectrum of fulvic acid, its relationship with adsorption behavior of asphaltene was analyzed, which could help to explore the adsorption mechanism of asphaltene on fulvic acids and provide theoretical basis for the development and application of the new type of adsorbent in oil processing field and the oil pollution control.The infrared spectrum of fulvic acid showed that 3 levels fulvic acid had homogeneous functional groups, but the order of the number of oxygen-containing functional groups and the aromatic ring of the three levels fulvic acid was as follows: the first extractable fulvic acid > the third one> the second one. The result of the XRD indicated that the extracted fulvic acid had good crystallinity and high purity, and were load on the carrier soil steadily. But three levels fulvic acid differed in crystal structure and crystallinity.The single factor experiment of fulvic acid regenerating waste lubricating oil showed that fulvic acid extracted from the same source of soil had different treatment effect and processing parameters of waste lubricating oil. This may be associated with the structure of fulvic acid. The single factor experiment of composite adsorbents regenerating waste lubricating oil showed that the indexes of lubricating oil treated by the composite adsorbents were better than the oil treated by pure fulvic acid. And there were differences in processing condition and processing effect of waste lubricating oil. This may be related to the crystallinity and crystal structure of compound adsorbents, as well as the structure of fulvic acid.The kinetics experiments of asphaltene on fulvic acid showed that the order of adsorption capacity of asphaltene on three levels fulvic acid was as follows: the first level fulvic acid > the third one> the second one. The adsorption of asphaltene on first level fulvic acid was well described by first-order kinetic model, the adsorption kinetic of the second and third level fulvic acids were well described by second-order kinetic model. And the first level fulvic acid finished adsorption progress faster than the other one. The thermodynamics experiments of asphaltene on fulvic acid showed that high temperature favored the adsorption of asphaltene. Langmuir-Freundlich model provided the best fit for the equilibrium date.The relationships between infrared characteristics of fulvic acid and adsorption behavior of asphaltene were that the absorption of hydroxyl groups, aromatic groups and C-O groups were positively correlated with the sorption rate and binding force for asphaltene, and negatively correlated with the nonlinearity characteristics. Temperature rising could change adsorption characteristic parameters as adsorption of groups enhanced. Analysis suggests that molecular thermal motion enhancing and adsorption binding force changing caused by temperature rising could be the main reason of the phenomenon.