Ultrasound-assisted oil removal of γ-Al2O3-based spent hydrodesulfurization catalyst and microwave roasting recovery of metal Mo

Mechanism of highly efficient oil removal from spent hydrodesulfurization catalysts by ultrasound-assisted surfactant cleaning methods

The removal of crude oil from spent hydrodesulfurization catalysts constitutes the preliminary stage in the recovery process of valuable metals. However, the traditional roasting method for the removal exhibits massive limitations. In view of this, the present study used an ultrasound-assisted surfactant cleaning method to remove crude oil from spent hydrodesulfurization catalysts, which demonstrated effectiveness. Furthermore, the study investigated the mechanism governing the process with calculation and experiments, so as to provide a comprehensive understanding of the cleaning method's efficacy. The surfactant selection was predicated on the performance in the IFT test, with SDBS and TX-100 finally being chosen. Subsequent calculations and analysis were then conducted to elucidate their frontier molecular orbitals, electrostatic potential, and polarity. It has been found that both SDBS and TX-100 possess the smallest LUMO-HOMO energy gap (ΔE), registering at 4.91 eV and 4.80 eV, respectively, and presenting the highest interfacial reactivity. The hydrophilic structure in the surfactant regulates the wettability of the oil-water interface, and the long-chain alkanes have excellent non-polar properties that promote the dissolution of crude oil. The ultrasonic-assisted process further improves the interface properties and enhances the oil removal effect. Surprisingly, the crude oil residue was reduced to 0.25% under optimal conditions. The final phase entailed the techno-economic evaluation of the entire process, revealing that, in comparison to the roasting method, this process saves $0.38 per kilogram of spent HDS catalyst, with the advantages of operational simplicity and emission-free. Generally, this study shed new light on the realization of efficient oil removal, with the salience of green, sustainable, and economical.

A facile method of treating spent catalysts via using solvent for recovering undamaged catalyst support

The process of washing and removing crude oil from spent catalysts is a serious issue in both catalyst regeneration and precious metals recovery. In this work, five different solvents with various polar and aromatic properties were chosen to evaluate their impact on the catalyst support structure and crude oil recovery from oil-contaminated spent catalysts. After the deoiling process, the spent catalyst was analyzed by scanning electron microscopy, X-ray diffraction (XRD), Fourier transform-infrared spectroscopy, elemental analyzer, contact angle measurement, gas chromatography-mass spectrometry, inductively coupled plasma-atomic emission spectroscopy, and Brunauer Emmet Teller (BET) method. Our findings demonstrate that p-xylene and kerosene are more effective in removing oil than other solvents. This is due to crude oil's similar polarity and molecular nature with kerosene and p-xylene. Considering the economical reason, kerosene is a better choice for deoiling spent catalyst compared to p-xylene as it is more affordable than p-xylene. XRD data show that the structure of the catalyst support was unaltered by the solvent treatment process, while BET data reveals that the surface area and pore volume are significantly enhanced after the deoiling process. These results imply that deoiling is a very crucial step for the recycling, regeneration, and reuse of spent catalysts. Our work is significant in developing sustainable approaches for managing spent catalysts, and minimizing waste and environmental pollution.

A comprehensive review on the ultrasound-enhanced leaching recovery of valuable metals: Applications, mechanisms and prospects

In recent two decades, ultrasound has been broadly applied to the hydrometallurgical leaching process to recover valuable metals within raw materials, aiming to solve the shortcomings of the conventional leaching process, including relatively low leaching recovery, long leaching duration, high reagent usage, high energy consumption and so on. The present work focuses on a comprehensive overview of the ultrasound-enhanced leaching of various metals, such as common nonferrous and ferrous metals, rare metals, rare earth elements, and precious metals, from raw metal ores and secondary resources. Moreover, the enhanced leaching mechanisms by ultrasound are discussed in detail and summarized based on the improvement of leaching kinetics, enhancement of the mass transfer and diffusion of lixiviants, and promotion of the oxidative conversion of metals from insoluble to soluble states. Lastly, the challenges and outlooks of future research on the leaching recovery for valuable metals with the assistance of ultrasound irradiation are proposed.

Self-circulation of oily spent hydrodesulphurization (HDS) catalyst by catalytic pyrolysis for high quality oil recovery

In this study, roasted spent HDS ash (sHDSc-A) was used for the first time to catalytically pyrolyze oily spent HDS catalysts (sHDSc) to improve the yield and quality of pyrolysis oil. The results showed that sHDSc-A promoted the decomposition of coke in oily sHDSc, resulting in the recovery of more oil and gas. Meanwhile, sHDSc-A significantly improved the quality of the pyrolysis oil. They inhibited the aromatization of alkanes to increase the saturation of the pyrolysis oil from 59.39% to 74.25% and the H/C radio from 1.62 to 1.72; promoted the decomposition of long-chain alkanes to increase the content of C11-C22 from 41.97% to 61.99%; enhanced the conversion of carboxylic acids to ketones led to the reduction of heteroatomic compounds such as N (56.10%-45.39%), S (66.95%-56.59%), and O (45.26%-26.70%) in the pyrolysis oil. The promotion of sHDSc-A in the pyrolysis process is attributed to the catalytic effect of the metal oxides in sHDSc-A. Among them, Al₂O₃ and Fe₂O₃ can promote decarboxylation of carboxylic acids and reduce O mobility, while MoO₃ and Fe₂O₃ play a significant role in reducing coke and increasing pyrolysis oil. NiO can also promote methane vapor reforming, and thus increase the production of H₂ in non-condensable gas. This study achieves self-circulation of oily sHDSc with a "waste-treatment-waste" strategy that presents the advantage of value-added energy recovery and waste reuse.

Novel photocatalyst system to deep desulfurization of petroleum model and gas condensate by Box–Behnken design

In this research, cobalt (Co)/molybdenum (Mo) and nickel (Ni) doped with titanium dioxide (TiO2) were loaded onto multi-walled carbon nanotubes (MWCNTs). Then, the magnetization catalyst, iron oxide (Fe3O4), was loaded on them, which was used for the deep desulfurization of dibenzothiophene (DBT). These catalysts were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, differential reflectance spectroscopy, and Brunauer–Emmett–Teller, Barrett–Joyner–Halenda, and vibrating sample magnetometer techniques. The photocatalytic activity of these catalysts was experienced under visible light using DBT. The response surface methodology based on the Box–Behnken design was used to evaluate parameters, including catalyst dosage (g), time (min), and concentration of DBT (mg L−1). The highest degradation efficiency under optimal conditions for CoMoNi/TiO2/MWCNTs/Fe3O4 catalysts with a catalyst dosage of 0.3 g, a time of 180 min, and a concentration of 50 mg L−1 was 99.99%. Optimum conditions were studied for desulfurization of the gas condensate. The highest desulfurization efficiency (90.33%) was obtained by the CoMoNi/TiO2/MWCNTs/Fe3O4 catalyst.

Ultrasound and microwave-assisted recycling of spent mercuric chloride catalyst

It is urgent to develop a high-efficient process for recycling the spent mercuric chlorides catalyst (SMC) from vinyl chloride monomer (VCM) production with the implementation of the 'Minamata Convention on mercury'. A ultrasound and microwave-assisted technology were developed to treat SMC in this study. Firstly, organic carbon deposition was separated from SMC by pretreatment (ultrasonic-assisted ethanol extraction). The optimized extraction conditions were: ultrasonic time 2 h, ultrasonic power 700 W, extraction temperature 65°C, and liquid-solid ratio 7:1. Under these conditions, 90% of hazardous Cl-containing organics were separated from SMC. Then the pretreated SMC was treated by microwave heating for mercury removal. Residual mercury concentration of SMC decreased from original 1.33% to only 11.92 mg/kg at the preferred conditions of 500°C for 60 min and the treated SMC passed the Toxicity Characteristics Leaching Procedure (TCLP) test. Simultaneously, catalyst support activated carbon (AC) was regenerated with specific surface area increasing from original 263.85 to 627.5 m²/g. The organics from macropores and surface of AC was removed by pretreatment, intensifying the subsequent Hg removal and regeneration of AC as revealed by the comparative studies. Finally, SMC was subjected to water leaching for recovering metal values. 88.7% of Ba and 95.3% of Ce were leached with ultrasonic power 500 W and ultrasonic time 120 min. SMC was detoxified and valuable components Hg, AC, Ba, Ce were recovered by this new process, which may provide a new idea for industrial treatment of SMC.

Wax Separated Effectively from Fischer-Tropsch Wax Residue by Solvent Desorption: Thermodynamic and Kinetic Analysis

The separation and recycling of effective resources in Fischer-Tropsch wax residue (FTWR) are urgent because of the environmental hazards and energy waste they bring. In this study, organic solvents are used to separate recyclable resources from FTWR efficiently, achieving the goals of “Energy Recycle” and “Fisher-Tropsch Wax Residue Treatment”. The response surface methodology (RSM) response surface analysis model accurately evaluates the relationship among temperature, residence time, liquid–solid ratio, and desorption rate and obtains the best process parameters. The results show that the product yield can reach 82.28% under the conditions of 80 °C, 4 h, and the liquid–solid ratio of 24.4 mL/g. Through the kinetic analysis of the desorption process of FTWR, the results show that the desorption process conforms to the pseudo second-order kinetic model and the internal diffusion model. The thermodynamic function results showed that there were not only van der Waals forces in the desorption process, but other strong interaction forces such as hydrogen bonds. In addition, Langmuir, Freundlich, and BET equations are used to describe the desorption equilibrium. Scanning electron microscopy (SEM) were used to analyze the pore structure of FTWR during desorption. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and Gas chromatography-mass spectrometer (GC-MS) analysis confirmed that the desorption product’s main component was hydrocarbons (50.38 wt%). Furthermore, naphthenic (22.95 wt%), primary alcohol (11.62 wt%), esters (8.7 wt%), and aromatic hydrocarbons (6.35 wt%) compounds were found and can be further purified and applied to other industrial fields. This study shows that using petroleum ether to separate and recover clean resources from Fischer-Tropsch wax residue is feasible and efficient and has potential industrial application prospects.

Microwave field: High temperature dielectric properties and heating characteristics of waste hydrodesulfurization catalysts

The exploration of the dielectric properties of waste hydrodesulfurization catalysts has important guiding significance for the development of microwave heat treatment of waste hydrodesulfurization catalysts for the recovery of valuable metals. The resonant cavity perturbation technique was used to measure the dielectric properties of waste catalyst and the mixture of waste catalyst and Na₂CO₃ during roasting from room temperature to 700 °C at 2450 MHz. The heating properties of the waste catalyst and mixture of waste catalyst and Na₂CO₃ were determined in the microwave field. The results show that the waste catalyst and the mixture of waste catalyst and Na₂CO₃ exhibit strong microwave response capability, and the dielectric constant, dielectric loss factor, and dielectric loss tangent increase with increasing temperature; from 20 to 300 °C, the waste catalyst and the mixture of waste catalyst and Na₂CO₃ heated at a slower rate, while the material heated rapidly from 300 to 700 °C. In addition, the mechanism of microwave action has been proposed based on the study of dielectric properties and heating properties in the microwave field.