Development of a novel chelation-based recycling strategy for the efficient decontamination of hazardous petroleum refinery spent catalysts.

The conventional hydrometallurgical methods for recycling refinery spent hydroprocessing catalysts are ineffective in simultaneously removing all metals (Ni, V, and Mo) in a single-stage operation. In this study, a novel octadentate chelating agent, diethylenetriaminepentaacetic acid (DTPA-C14H23N3O10), has been proposed for the first time to remove toxic metals (Ni, V, and Mo) in a single stage of operation from an industrial spent atmospheric residue desulfurization (ARDS) catalysts. It was discovered that the efficient formation of metal-DTPA complexes was attained under the optimum experimental conditions (60 °C, stirring - 150 rpm, S/L ration (w/v) of 2.5%, 7.5% DTPA, and medium pH-9) that resulted in the high removal of Mo (83.6%), V (81.3%) and Ni (64.1%) from the spent ARDS catalyst. Kinetic studies suggest that the leaching process followed a semi-empirical Avrami equation (R2 > 0.92), which predicted that the diffusion control reaction controlled the leaching. Species distribution and ecological risk analysis of the remaining metals in the insoluble residue (mostly Al2O3) indicated that the potential bioavailability of the remaining metals (except Ni) was significantly decreased, and residue poses a low ecological and contamination risk (individual contamination factor <1). Furthermore, the textural properties of the residue (BET surface area-103 m2/g and pore volume- 0.49 ml/g) were dramatically improved, suggesting that fresh hydroprocessing catalyst support can be synthesized using the leached residue. Compared to the conventional processes, the proposed chelating process is highly selective, closed-loop, and achieved high metal recovery in a single-stage operation while decreasing the environmental risks of the hazardous spent catalysts.

Synthesis of graphene derivatives from asphaltenes and effect of carbonization temperature on their structural parameters.

A method for synthesizing graphene derivatives from asphaltene is proposed in this work. The graphene derivatives are mainly composed of few-layer graphene-like nano-sheets of randomly distributed heteroatoms; mainly sulfur and nitrogen. The proposed method is based on a thermal treatment in which asphaltene is carbonized in a rotating quartz-tube furnace under an inert atmosphere at a temperature in the range of 400-950 °C. Asphaltenes from different origins were employed to verify the synthesis method. The results indicate that graphene derivatives obtained at high carbonization temperature have similar structural parameters, despite the evident differences in parent asphaltenes structures and compositions. The transformation of asphaltene to graphene derivatives mainly occurred due to three factors: the reduction in the average number of aromatic layers (n), the expansion in aromatic sheet diameter (L a), and the elimination of alkyl side chains. The reduction in the number of aromatic sheets per stack is primarily ascribed to thermal exfoliation, while the increase in the aromatic sheet diameter is attributed to secondary reactions in the aromatic core of asphaltene. The elimination of side chains, on the other hand, is mainly credited to thermal cracking. The quantification of defect density (L D) in the graphene derivatives suggests an association between defects and heteroatoms presence.