Hydrodesulfurization Research Articles

Low-valent germanium and tin hydrides as catalysts for hydroboration, hydrodeoxygenation (HDO), and hydrodesulfurization (HDS) of heterocumulenes

Low-valent Ge & Sn hydride catalysis: herein, we establish bis-guanidinato-supported Ge and Sn hydrides as selective catalysts for hydroboration of heteroallenes with HBpin. The catalytic cycle has been proposed based on stoichiometric experiments.

Fabrication of well-structured NiMo hydrodesulfurization catalysts using electropositive Mo-based nanoparticles

Using electropositive Mo-based nanoparticles (Mo-NPs) as precursor could realize the resulting catalyst with more uniform, shorter, higher layered, better Ni-promoted, and stable MoS2 slabs, thus holding excellent HDS performance.

Enhancing Mo leaching efficiency from spent catalyst via Fenton-like oxidation process: A comprehensive investigation of leaching effects, mechanism and environmental impacts

Spent hydrodesulfurization (HDS) catalyst contains considerable amounts of Mo, Ni and V, is an important secondary resource for these valuable metals. Direct acid solution leaching method exhibits poor separation effect from catalyst carrier for Mo due to greater stability of MoS2. This study explored Mo leaching efficiencies from spent HDS catalyst by Fenton-like oxidation systems (H2O2 and K2S2O8), which were frequently employed in the wastewater treatment. To further improve Mo leaching efficiency, nano zero-valent iron (nZVFe) was used to activate H2O2/K2S2O8 and produce more free radicals (·OH and ·SO4-). Approximate 96.0 % and 93.3 % of Mo were leached from spent HDS catalyst in nZVFe + H2O2 + H2SO4 and nZVFe + K2S2O8 + H2SO4 systems under optimal experimental conditions, increased by 16.2 % and 8.2 % than normal H2O2 (79.8 %) and K2S2O8 (85.1 %) system without nZVFe. The leaching process of Mo in both nZVFe + H2O2 + H2SO4 and nZVFe + K2S2O8 + H2SO4 systems conformed to the shrinkage core model. Kinetic analysis and molecular calculation demonstrated the leaching process of Mo in nZVFe + H2O2 + H2SO4 system was driven by chemical reaction and solid film diffusion, and the leaching and oxidation reactions of MoS2 occurred simultaneously. However, the leaching process of Mo in nZVFe + K2S2O8 + H2SO4 system was driven only by chemical reaction, solid MoS2 was firstly dissolved into Mo4+ by H+, and then oxidized into Mo6+ by ·SO4-. The economic and environmental impacts evaluation indicated that the separation of Mo from spent HDS catalysts by nZVFe + H2O2 + H2SO4 was assigned as a better choice than normal H2O2 and K2S2O8 system without nZVFe due to higher leaching efficiency and lower cost.

Monodisperse dendritic micro-mesoporous composite self-assembled with tiny TS-1 seeds as efficient catalysts for hydrodesulfurization of dibenzothiophenes

Novel TS-1/dendritic mesoporous silica nanoparticles (TS-1/DMSNs, TD) micro-mesoporous composites with different morphology were prepared for NiMo catalysts (NiMo/TD-TEA). Series catalysts were tested in dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) hydrodesulfurization (HDS) reactions in a fix-bed reactor. TS-1 were uniformly compounded with mesoporous materials in the form of Si-O-Ti bonds, which did not affect the typical dendritic morphology. The introduction of TEA could inhibit the growth of support particles, and modulate the acidity and the metal-support interaction (MSI) of catalysts. Optimized NiMo/TD-TEA catalyst showed the optimal DBT (98.0 %) and 4,6-DMDBT (92.3 %) desulfurization rate as well as the excellent hydrogenation (HYD) selectivity for DBT and 4,6-DMDBT HDS with the optimal reaction rate constant (12.2 mol·g−1·h−1, 6.7 mol·g−1·h−1) and turnover frequency (2.3 h−1, 1.4 h−1). By correlating to the catalyst acidity–activity and active phase–activity, the activity and selectivity were not only depended on the presence of Brønsted (B) acid and the total acid content but also associated with the dispersion and morphology of MoS2 slabs.

Liquid-phase adsorption of nitrogen compounds from model diesel fuel on activated carbons

One of the great challenges in deep hydrodesulfurization (HDS) to produce ultra-low-sulfur diesel (ULSD) is the coexisting heterocyclic nitrogen-containing compounds in middle distillates, which significantly inhibit the HDS reactions. This study investigates various activated carbon (AC) samples for selectively removing nitrogen compounds from a model diesel fuel through adsorption. The physical and chemical properties of the AC samples were characterized using low-temperature N2 adsorption–desorption, SEM–EDS, and FT-IR to explore their impact on the adsorption performance. The results indicate that the adsorption performance is influenced not only by the surface area and by the number of oxygen-containing functional groups on the surface but also by the pore diameter distribution. Among all AC samples tested, AC-W exhibited the highest adsorption capacity, achieving a nitrogen removal rate of 97.8% with the addition of 10 wt.% of AC-W. The adsorption capacity was approximately 24.0 mg-N/g-A at a nitrogen equilibrium concentration of 200 ppmw. The adsorption isotherms for total nitrogen and individual nitrogen compounds in the fuel over AC can be described well by the Freundlich isotherm model. An approach for improving the ADN performance of AC is discussed based on the findings in this study.

In situ synthesis of mesoporous NiS2-MoS2 sphere-flower hybrid for hydrodesulfurization of thiophene and 4,6-dimethyl-dibenzothiophene

A series of new NiS2-MoS2-x (x = 0–0.5) sphere-flower hybrids with different Ni/Mo molar ratios, synthesized via a one-pot hydrothermal method, were used as catalysts for hydrodesulfurization (HDS) of thiophene (TP) and 4,6-dimethyl-dibenzothiophene (4,6-DMDBT). The characterizations show that the microstructure of MoS2, including the size of MoS2 nano-flowers, the length of MoS2 slabs, and the number of defects, was regulated by changing Ni/Mo ratios. Increasing the Ni/Mo ratio in the NiS2-MoS2-x catalysts significantly boosts their HDS activity, with the optimum ratio being 0.2. In addition, the NiS2-MoS2-0.2 catalyst exhibits the best direct desulfurization performance, which is associated with the minimum ratio of average slab length (Lav) to average stacking number (Nav) as well as the highest concentration of Ni-promoted Mo sites and sulfur vacancies. Moreover, Ni-containing NiS2-MoS2-x catalysts, characterized by a highly stable sphere-flower configuration, exhibit superior structural stability and catalytic durability than the Ni-free NiS2-MoS2-0 catalyst.

The organic–inorganic dual anchoring strategy based on organic chelators and lacunary polyoxometalates for the preparation of efficient CoWS hydrodesulfurization catalysts

Designing catalysts with bimetallic intimate synergistic effects to enhance catalytic activity has always been a focused problem for hydrodesulfurization (HDS) systems. Efficient HDS catalysts with abundant CoWS active phases were prepared through novel organic–inorganic ligand dual anchoring strategy based on the organic chelating agents and lacunary polyoxometalates (POMs). Citric acid (CA) chelating agent and Co2+ promoter are pre-coordinated in the impregnating solution, the trivacant Keggin [SiW9O34]10- (SiW9) POMs attract the promoter through the nucleophilic oxygen groups at the vacant sites to form the CA-Co@SiW9 “sandwich-like” structure, which allows the organic chelator-promoter-active center to be intimate interaction in a single molecule, thus achieving atomic-scale Co-W proximity on the precursor. In the subsequent sulfidation process, CA delayed the reduction temperature of cobalt species, enabling more Co promoter to be anchored at the edge sites of WS2 clusters to form abundant CoWS active phases, which fully exerted the bimetallic intimate synergism in the HDS reaction. Furthermore, the carbon deposits generated from CA carbonation acted as secondary support weakening the interaction of active metals with Al2O3 support and increasing the sulfidation degree as well as the dispersion of active metals. As a result, the S-Co(CA)W/Al2O3 catalyst achieves a remarkable turnover frequencies (TOF) value of 1.24 × 10-3 s−1 in HDS reaction of dibenzothiophene (DBT). This dual anchoring method based on POMs inorganic ligand and organic chelator ligand provides a new idea for designing novel HDS catalysts.

The superior HDS catalyst derived from a new Waugh Co-Mo polyoxometalate via cationic substitution

In this paper, the Waugh Co-Mo polyoxometalate (POM) (NH4)6[CoMo9O32] was prepared and cationic substituted to increase the Co/Mo ratio to 0.44 with Mo and Co atoms in a new Waugh Co-Mo POM molecule. The method was verified by X-ray diffraction, X-ray fluorescence, and infrared spectroscopy. Then, two series of Co-Mo hydrodesulfurization (HDS) catalysts were prepared using the Waugh Co-Mo POMs and traditional precursors, respectively. The HDS evaluation results showed the activities of catalysts prepared from the new Waugh Co-Mo POM is higher than the reference catalysts. For the catalyst prepared from the new Waugh Co-Mo POM, the cationic substitution provides a higher Co/Mo ratio and atomic-level proximity between Mo and Co atoms, leading to shorter and less stacked MoS2 nano-particles and more exposure of unsaturated edges and corner sites. In addition, a weak interaction between the new Waugh Co-Mo POM and Al2O3 leads to more CoMoS active phases. Catalysts prepared from the new Waugh Co-Mo POM showed excellent HDS performance, demonstrating the new Waugh Co-Mo POM is a superior precursor to construct the efficient HDS catalyst.

Modifying the active phase structure of Ni2P/Al2O3 by Ga introduction for improved hydrodesulfurization of diesel

Modifying the structure of active phase is an effective protocol to improve the catalytic activity of hydrodesulfurization (HDS) catalyst. Here, a variety of mesoporous GaAlOx supports with various Ga doping amount were synthesized by a facile hydrothermal strategy. The corresponding Ni2P supported catalysts were fabricated via a conventional impregnation and temperature-programmed reduction method, and their catalytic performances for 4,6-DMDBT HDS were examined. The experimental analyses show that the introduction of Ga substantially influences the geometric and electrical structure of Ni2P active phase on Ni2P/GaAlOx catalysts. The metal-support interaction is effectively abated with the elevation of Ga doping amount, thereby increasing the d-electron density of Ni species and boosting the pre-hydrogenation (HYD) route, thereupon enhancing the HDS performances of corresponding Ni2P/GaAlOx catalysts. Therein, Ni2P/GaAlOx-0.50 exhibits the highest activity with 70.1% 4,6-DMDBT conversion because of the optimal morphology and percentage of active phase, as well as distinguished redox and acid property. Further increasing the Ga loading, however, inhibits the HDS activity of Ni2P/GaAlOx-1.0 catalyst due to the decrease in the fraction and dispersion of active phases. Therefore, this work may shine light on the understanding of structure–activity of HDS catalyst and thereafter the preparation of HDS catalysts with high efficiency in future.

Machine learning-based optimization for catalytic sulfur removal: Computational modeling and analysis of fuel purification for reduction of environmental impacts

Hydrodesulfurization (HDS) process is an important process for separation of sulfur compounds from petroleum-based products due to operational and environmental problems that the sulfur compounds can cause. In this study, this process was evaluated to optimize its performance in removing sulfur compounds from petroleum to reduce its adverse effects. Multiple machine learning models were implemented for optimization of HDS process considering several inputs/outputs. Each data point has four input parameters: pressure, temperature, initial sulfur content of petroleum, and dosage of catalyst in the reactor. Sulfur concentration (ppm), SO2 emission percentage (%), and HDS cost ($) are also outputs to be optimized by the machine learning models. Multi-layered perceptron (MLP), Multi-task Lasso (MTL), and Gaussian process regression (GPR) are core models in this study developed for the first time for HDS process. These models were optimized utilizing Artificial Bee Colony (ABC) and applied on cleansed and normalized dataset. According to assessments done on final models, sulfur concentration, emission %, and HDS cost are predicted by R2-scores of 0.983, 0.999, and 0.990 respectively using models proposed in this study. Also, absence of overfitting can be guaranteed using these models according to analysis done in results section.

3D Printing Technique Fortifies the Ultradeep Hydrodesulfurization Process of Diesel: A Journal of NiMo/Al2O3-MMT.

In this contribution, we rationally designed and controllably fabricated a NiMo/Al2O3-montmorillonite (3D-NiMo/Al2O3-MMT) monolithic catalyst via a 3D printing strategy with economical montmorillonite (MMT) as a binder. The catalytic performance of the resulting NiMo/Al2O3-MMT for 4,6-dimethyldibenzothiophene (4,6-DMDBT) hydrodesulfurization (HDS) was evaluated. The experimental results unveil that the 3D-NiMo/Al2O3-MMT monolithic catalyst exhibits robust stability and exceptional HDS activity with 99.2% 4,6-DMDBT conversion (residual 4 ppm of S), which is remarkably superior to that of conventional NiMo/Al2O3 (61.5%), NiMo/MMT (63.2%), and even NiMo/Al2O3-MMT (76.5%) prepared by the mechanical-mixing method. This should be ascribed to the synthetic effect between the MMT binder and the Al2O3 substrate, which effectively weakens the interaction between the Mo species and the Lewis acids on the original Al2O3 surface, thereby significantly increasing the content of reducible Mo species and considerably facilitating the formation of more highly active NiMoS phase (Type II) with optimal average stacking layers and thereafter remarkably enhancing the ultradeep HDS activity of the 3D-NiMo/Al2O3-MMT monolithic catalyst.

Effect of Zirconium modified Y zeolite via in situ synthesis and its regulation on the formation of excellent NiW catalyst for ultra-deep hydrodesulfurization of 4,6-DMDBT

Alternative support materials, such as Y zeolite, have been introduced to overcome the challenges associated with industrial alumina-supported hydrodesulfurization (HDS) catalysts. However, to improve catalytic activity while avoiding excessive hydrocarbon cracking, the properties of Y zeolite, including acidity, should be modulated. Herein, Zr-modified Y zeolite was prepared via in-situ synthesis, and the corresponding NiW catalyst was obtained by impregnating hybrid zeolite-alumina supports with metal precursors. The catalytic performance was tested using 4,6-dimethyldibenzothiophene (4,6-DMDBT) as an HDS probe. The position of the Zr species in the zeolites depended on the modification methods. The ZrHY zeolite prepared by impregnation mainly formed non-framework ZrO2 on the surface of zeolite, whereas the HZrY zeolite via in-situ synthesis exhibited Zr species dispersed in the zeolitic framework. Zr species in the zeolitic framework not only enhanced the acidities of the zeolite and hybrid-support (HZrY-Al2O3), but also regulated the interaction of active metals and hybrid support, which significantly enhancing the catalytic activity of the catalyst. Among the four investigated catalysts, the turnover frequency (TOF) and reaction rate constant (k) of 4,6-DMDBT HDS over NiW/HZrYA catalyst were higher efficient than those of other catalysts, and their isomerization selectivity was improved, reducing hydrogen consumption. This enhanced efficiency was attributed to the NiW/HZrYA catalyst having more suitable acid sites, a greater degree of active metals sulfidation, more NiWS phase, superior isomerization performance, and a higher matching degree between hydrogenation and hydrolysis activity. These findings are great meaning for design the ultra-deep low hydrogen consumption HDS catalysts.

Design of active phase structure with high activity and stability in residue hydrotreating reactions

The catalyst with well-dispersed (Ni)MoS2 active phase characteristic of short slab length and low stacking numbers was designed by strengthening metal-support interaction (MSI) and metal dispersion, which displayed high activity and long-term stability in real-life residue hydrodesulfurization (HDS) reactions. Furthermore, the impacts of pseudo-boehmite and catalyst calcination temperature on surface properties were thoroughly investigated. Mo equilibrium adsorption method, Al27 NMR, XRD, Raman, UV–Vis DRS, and H2-TPR characterization showed that the hydroxyl groups concentration and tetrahedral cation vacancies increased upon reducing the pseudo-boehmite extrudates calcination temperature. Increasing calcination temperature of the catalysts further strengthened MSI, resulted in well-dispersed Mo species with enhanced MSI. Therefore, well-dispersed (Ni)MoS2 active phase was acquired on novel designed catalyst. XPS coupled with HRTEM indicated that the more potential active sites, less propensity for active phase evolution and gradual increase in sulfidation degree with processing time contributed to the high HDS performance of the designed active phase. This work can deepen our understanding toward evolution pattern of active phase during residue HDS catalysts, and give guidance for developing high performance catalyst by strengthening MSI and enhancing metal dispersion.

High-efficiency recycling of Mo and Ni from spent HDS catalysts: Enhanced oxidation with O2-rich roasting and selective separation with organic acid leaching- complexation extraction

Spent petroleum refining catalyst is regarded as the important secondary resource for valuable metals. However, common recycling strategies, including soda roasting, acid and alkaline solutions leaching and chemically precipitation, produced large quantities of high salinity wastewater. This study proposed an efficient method to recovery of Mo and Ni from the spent hydrodesulfurization (HDS) catalyst via O2-rich roasting and organic acid leaching with the advantage of less salinity wastewater production. The transformation of Mo(IV) into soluble Mo(VI) was enhanced by O2-rich atmosphere roasting, and 98.64% of Mo(IV) was oxidized at 650 ℃ for 2 h in atmosphere containing 30% of O2. The oxidation process of Mo(IV) was agreed with the shrinkage pore model, and regulated by surface reaction and internal diffusion. 97.97% of Mo(VI) was leached from roasted product by oxalic acid, separated with complexation extraction agent of Ala-TBP and recovered as (NH4)8Mo10O34 and (NH4)2Mo3O10 by evaporative crystallization. Ni was leached out from spent catalyst with 1 mol/L acetic acid, and precipitated as NiC2O4 with oxalic acid. 95.92% of Mo and 96.77% of Ni were recovered from spent HDS catalyst with this recycling route. This study provided a high-efficient and eco-friendly method to recovery of valuable metals from spent catalyst.

The Influence of Metal–Support Interactions on the Performance of Ni-MoS2/Al2O3 Catalysts for Dibenzothiophene Hydrodesulfurization

In this present work, a new kind of sulfurized hydrodesulfurization catalyst was synthesized via the hydrothermal treatment of MoS2, NiCO3·2Ni(OH)2·4H2O, and Al2O3 precursors, followed by annealing under a H2 atmosphere, which does not require a sulfurization process compared to traditional preparation methods. The influence of the annealing temperature and the type of Al2O3 precursor on the interactions between MoS2 and Al2O3 were studied using X-ray fluorescence spectroscopy, X-ray diffraction, N2 adsorption–desorption, Raman spectroscopy, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. The results indicated an increase in the number of stacked layers of the MoS2 catalyst, accompanied by a decrease in the degree of decoration of Ni atoms onto MoS2 nanoslabs, as a result of the strengthened MoS2–Al2O3 interaction. Subsequently, the efficiency of hydrodesulfurization (HDS) was evaluated using dibenzothiophene as a representative reactant, while establishing a correlation between the structure of the catalyst and its performance. The catalysts, using pseudo-boehmite as the precursor and calcined at 500 °C, synthesized by calcining pseudo-boehmite as the precursor for Al2O3 at a temperature of 500 °C and possessing suitable metal–support interactions, exhibited a reduced number of MoS2 stacking layers and lateral dimensions, along with an optimal decoration degree of Ni atoms, thereby resulting in the highest level of HDS activity.

Desulfurization of 2-phenylcyclohexanethiol over Pd and Pt catalysts on γ-Al2O3

The desulfurization of 2-phenylcyclohexanethiol (2-PCHT) was studied over Pd and Pt catalysts supported on γ-Al2O3 under 5.0 MPa H2 or Ar at 240 °C. The infrared spectra of the two catalysts during the reactions of 2-PCHT (PCHT-IR) were measured between 180 and 300 °C at 0.2 MPa H2 and Ar. The hydrodesulfurization (HDS) of 2-PCHT over Pd/Al2O3 and Pt/Al2O3 followed pseudo-first-order kinetics, and occurred mainly through β-elimination. Pd/Al2O3 was more active than Pt/Al2O3, mainly due to its higher β-elimination activity. Piperidine showed different inhibiting effects on their HDS performances. The species adsorbed on Pd/Al2O3 and Pt/Al2O3 were different under H2. Strong adsorption of 1-phenyl-1-cyclohexene on both catalysts was observed under Ar, which could be responsible for Langmuir-Hinshelwood kinetics and low activities. Pd/Al2O3 and Pt/Al2O3 were less active than transition-metal phosphides in the HDS of 2-PCHT, but were more active than the Mo-based sulfides.

Targeted fabrication of 1T-MoS2 enriched nanosheets vertically oriented on spiny-shaped nanospheres with sufficient sulfur vacancies and “rim” sites for co-enhancing the hydrodesulfurization activity and hydrogenation selectivity

The 1T-enriched spiny-shaped nanospheres with vertically oriented MoS2 nanosheets over the surface was successfully prepared with the novel solvent induced micelle-limited Mo-CTA+ composites self-assembly (SIMMS) strategy under the dual effects of mixed sulfur sources (thiourea and thioacetamide) and cetyltrimethylammonium bromide (CTAB). In the proposed strategy, the molybdenum source and CTAB are firstly assembled to Mo-CTA+ by strong electrostatic attraction to avoid the molybdenum source from polymerization and forming large polymolybdate anions. Meanwhile, the CTAB moleculars self-assemble to spherical micelles, which can adsorb Mo-CTA+ through van der Waals force and obtain spherical precursors with a controllable number of nucleation sites. Under the sulfurization from mixed sulfur source, appropriate reducibility can control the formation of crystal seeds and crystal growth during the crystallization process of MoS2, whereas CTAB can regulate and control the growth behavior and micro-morphology of MoS2, which is ultimately also retained between the MoS2 nanolayersto expand their interlayer spacing and stabilize the 1T phase. Therefore, the 1T-enriched spiny-shaped nanospheres with vertically oriented MoS2 nanosheets can be controllably prepared. In the hydrodesulfurization (HDS) reaction of dibenzothiophene (DBT) over these catalysts, the MoS2-75%/0.25 catalyst with the highest concentration of sulfur vacancies as well as “rim” and “rim-like” sites can reach the highest HDS activity (99.1%) and HYD/DDS ratio (4.76), which are much higher than those of the MoS2-H catalyst prepared by conventional hydrothermal method (HDSDBT%=46.0%, HYD/DDS ratio=0.90).

Molecular modeling of 1-butyl-3-methylimidazolium based ionic liquids for potential applications in the desulfurization of diesel fuel

The sulfur compounds in diesel fuel produce harmful environmental pollutants during combustion. Hydrodesulfurization (HDS) is the most common technique to reduce the sulfur content of diesel fuel but cannot effectively remove aromatic sulfur compounds to produce ultra-low-sulfur diesel. Ionic liquids (ILs) show potential as alternative solvents for extractive desulfurization to be implemented after a conventional HDS process, but the mechanism is not well understood. This work focuses on using a combination of molecular simulation free energy calculations and detailed structural analysis to better understand the molecular-level interactions between dibenzothiophene and seven common imidazolium-based ILs. The free energy calculations suggest that the ILs interact differently with thiophene and dibenzothiophene. No specific interactions were observed between the anion and dibenzothiophene; varying the anion showed no remarkable differences in the observed interactions. It was determined that interactions between dibenzothiophene and the cation were more significant; π-π stacking between the imidazole ring and thiophene ring plus favorable electrostatic interactions between the alkyl chain and benzene rings were observed. The primary goal of this work is to use molecular simulations to complement current experimental research to identify suitable ILs for potential extractive desulfurization applications.

A novel method to leach vanadium, molybdenum and nickel from spent hydrodesulfurization catalysts using hydroxyl radicals (HO•) in Fe2O3-assisted oxygen microbubble process

As one of hazardous wastes, the ever-increasing number of spent hydrodesulfurization (HDS) catalysts which consists of a considerable amount of heavy metals, such as vanadium (V), molybdenum (Mo) along with nickel (Ni) and other organic contaminant has presented a serious waste-management challenge. In this study, we propose the Fe2O3-assisted oxygen microbubble Fenton-like process for spent HDS catalysts recovery. The leaching efficiencies of vanadium, molybdenum, and nickel are close to 89%, 90%, and 97%, respectively, under the optimum operating conditions (Fe2O3/raw materials mass ratio 4%, pH 3.2, temperature 80 °C, liquid to solid mass ratio 15/1 and leaching time of 90 min). The advantages of this strategy are two fold: (i) using commercial oxygen and Fe2O3 as oxidants, avoid high costs and consumption of oxidants, (ii) oxygen microbubbles are introduced into the system and the free radicals (HO•) generated by microbubbles collapsing during aeration enhance the mass transfer and oxidizing rates. However, the presence of strong reductive free radicals (H•) makes microbubbles incompatible for use. Moreover, Fe2O3 is proven to promote the generation of HO• from collapsing oxygen microbubbles under acidic conditions. These findings significantly increase the potential use of microbubble technique in resource recovery and provide fundamental information for peer researches to facilitate their future research on the development of more efficient and cleaner technologies.

Kinetics of biodesulfurization of South African diesel using Pseudomonas aeruginosa

As a result of several environmental and health challenges associated with the emission of SOx during the direct combustion of diesel, stringent regulations have been issued by the Environmental Protection Agency (EPA) and the South African government to all refineries in South Africa. Therefore, the development of an effective, affordable, and less energy-intensive technique is therefore urgently required. In this recent study, real South African diesel (obtained after HDS, 120 ppm) was degraded by resting cells of Pseudomonas aeruginosa in a batch experiment. About 5 mL of diesel was measured into a 250 mL Erlenmeyer flask with 5 mL of resting cell in glycerol/NaCl (1:1) and 20 mL of Basal Salt Media (BSM). The mixture was incubated for 8 h, at 37 °C, and agitated at 130 rpm, with an initial hydrodesulfurized diesel concentration of 120 mg/L and cell mass of 1.2 gDCW/L. High-Liquid Chromatography and Gas/Mass (GC/MS) chromatography were used to determine the initial and final concentrations of the synthetic and real diesel samples. Findings showed about 70.54 % removal of DBT in 120 ppm desulfurized diesel. Meanwhile, Pseudomonas aeruginosa selectively converted sulfur atoms in DBT compound to 2-HBP. Michaelis-Menten for modeling the growth of the bacteria fitted well into the experimental data. Similarly, First-order kinetic fitted and described well the behavior of the bacteria for degradation of DBT in synthetic and real diesel samples. The findings of this investigation indicated that biodesulfurization would be a more effective method to complement the hydrodesulfurization (HDS) technique as opposed to the primary methods for desulfurizing organo-sulfur compounds in diesel oil. This will assist the refineries to meet up with the stringent regulation to minimize the emission of sulfur compounds, which cause environmental pollution and health problems in South Africa and all over the world.