Template-derived mesoporous carbons with highly dispersed transition metals as media for the reactive adsorption of dibenzothiophene

Ultrasound-assisted adsorption approach for desulfurization of n-heptane using nitrogen-doped magnetic carbon dot nanocomposite

Desulfurization is an important process that not only affects the quality and performances of fuels but also is of great importance from environmental aspects. In this research, nitrogen-doped magnetic carbon dots nanocomposite was synthesized and characterized, and it's potential in adsorptive removal of thiophenes (i.e., thiophene, benzothiophene, and dibenzothiophene) from n-heptane (i.e., as model fuel) was investigated. After optimization of adsorption process, the removal efficiency was obtained above 95% for all of studied thiophenes. Besides that, it was concluded that using ultrasound during the adsorption process could enhance the maximum adsorption capacity. Langmuir model was able to appropriately describe the adsorption isotherm data, where the maximum equilibrium adsorption capacities for thiophene, benzothiophene and dibenzothiophene were obtained as 90.22, 96.51 and 100.38 mgg-1, respectively. The analysis of kinetic data also revealed that all thiophenes were being adsorbed following Pseudo-second-order model. To regenerate the adsorbent, the desorption process was also investigated using different solvents under different conditions, methanol was found as effective solvent for regeneration. The proposed adsorbent was used successfully for the removal of pollutants in a gasoline sample.

Preparation of Hollow Niobium Oxide Nanospheres with Enhanced Catalytic Activity for Oxidative Desulfurization

Hollow niobium oxide nanospheres were successfully synthesized by using prepared three-dimensional (3D) mesoporous carbon as the hard template. The 3D mesoporous carbon materials were prepared by using histidine as the carbon source and silica microspheres as the hard template. The samples were characterized by XRD, BET, SEM, TEM and other methods. The results show that the prepared niobium oxide nanospheres have a hollow spherical structure with an outer diameter of about 45 nm and possess a high specific surface area of 134.3 m2·g−1. Furthermore, the 3D mesoporous carbon materials have a typical porous structure with a high specific surface area of 893 m2·g−1. The hollow niobium oxide nanospheres exhibit high catalytic activity in oxidative desulfurization. Under optimal reaction conditions, the DBT conversion rate of the simulated oil is as high as 98.5%. Finally, a possible reaction mechanism is proposed.

Hydrogen-Assisted Thermocatalysis over Titanium Nanotube for Oxidative Desulfurization

Titanium nanotubes were hydrothermally synthesized via a two-step method for ODS (oxidative desulfurization). The catalysts’ structures were characterized by XRD (X-ray diffraction), FT-IR, UV-Vis (UV-Vis diffuse reflectance spectra), NH3-TPD, etc. The effects of O/S molar ratio and catalyst dosage, etc., were systematically investigated. The catalyst exhibited remarkable performance, so that the removal of DBT (dibenzothiophene) was nearly 100% under the optimal conditions in 10 min. Also, the catalysts could be easily reused for six consecutive cycles. The hydrogen-assisted thermocatalytic mechanism over titanium nanotubes for ODS was also studied and an effective reactant concentration (ERC) number of 70.8 was calculated.

Monitoring of Remaining Thiophenic Compounds in Liquid Fuel Desulphurization Studies Using a Fast HPLC-UV Method

Thiophenic compounds constitute a class of sulfur compounds derived by thiophene, containing at least one thiophenic ring. Their presence in fuels (crude oil, etc.) is important and can reach 3% m/m. The combustion of fuels leads to the formation of sulfur oxides a severe source of environmental pollution issues, such as acid rain with adverse effects both to humans and to the environment. To reduce such problems, the EU and other regulatory agencies worldwide set increasingly stringent regulations for sulfur content in fuels resulting in the necessity for intense desulphurization processes. However, most of these processes are inefficient in the total removal of sulfur compounds. Therefore, thiophenic compounds such as benzothiophenes and dibenzothiophenes are still present in heavier fractions of petroleum, therefore, their determination is of great importance. Until now, all HPLC methods applied in similar studies use gradient elution programs that may last more than 25 min with no validation results provided. To fill this gap, the aim of the present study was to develop and validate a simple and fast HPLC-UV method in order to be used as a useful monitoring tool in the evaluation studies of novel desulfurization technologies by means of simultaneous determination of dibenzothiophene (DBT) and 4,6-dimethyl-dibenzothiophene and dibenzothiophene sulfone in the desulfurization effluents.

Oxidative desulfurization in diesel via a titanium dioxide triggered thermocatalytic mechanism

TiO₂ was prepared through a sol–gel method as the thermo-catalyst for oxidative desulfurization (ODS), and H₂O₂ was selected as the oxidant.

Zeolite-templated carbons - three-dimensional microporous graphene frameworks

Zeolite-templated carbons (ZTCs) are ordered microporous carbons synthesized by using zeolite as a sacrificial template. Unlike well-known ordered mesoporous carbons obtained by using mesoporous silica templates, ZTCs consist of curved and single-layer graphene frameworks, thereby affording uniform micropore size (ca. 1.2 nm), developed microporosity (∼1.7 cm3 g-1), very high surface area (∼4000 m2 g-1), good compatibility with chemical modification, and remarkable softness/elasticity. Thus, ZTCs have been used in many applications such as hydrogen storage, methane storage, CO2 capture, liquid-phase adsorption, catalysts, electrochemical capacitors, batteries, and fuel cells. Herein, the relevant research studies are summarized, and the properties as well as the performances of ZTCs are compared with those of other materials including metal-organic frameworks, to elucidate the intrinsic advantages of ZTCs and their future development.

Selective removal of dibenzothiophene from commercial diesel using manganese dioxide-modified activated carbon: a kinetic study

With a total concentration of 7055 mgS/kgfuel, the content of organosulphur compounds (OSCs) in local diesel is 20 times higher than the regulated value. Analysis revealed that 30% of OSC is originated from dibenzothiophene (DBT). It is known that DBT is a hardly removable compound and selective adsorbents are often needed for its removal with low affinity for other diesel components. In this work, a selective adsorbent based on surface modification of activated carbon (AC) by MnO2 is prepared for DBT removal from diesel. The porous nature of AC enabled carrying large amounts of MnO2 particles to end up with a selective adsorber for DBT. The best performance was observed at a surface loading of 26.8% of Mn and DBT is favourably removed over mono- and diaromatics hydrocarbons in diesel. Adsorption kinetics of DBT is studied under a high initial concentration of 835-11,890 mg/kg and at a ratio of 11 cm3/g (diesel:carbon). The results indicated a fast removal process after surface modification where 96% of the surface is occupied within 30 min of interaction. Kinetic data were best presented by reaction-based models with low prediction error sum of squares values 0.5-47.0, while, diffusion-based models showed limited application for modelling DBT adsorption. Accordingly, adsorption process is controlled by surface reactions and pore diffusion has a minor role in the overall process. The modified adsorbent is satisfactorily regenerated using n-hexane at 65°C.

Removal of organic sulfur compounds from diesel by adsorption on carbon materials

Removal of organic sulfur compounds from diesel by adsorption on different carbon materials, including activated carbons (ACs), carbon aerogels, carbon nanotubes, and AC cloths, was reviewed. The effect of the textural and surface chemistry property of carbon on desulfurization performance, carbon surface modification, adsorption mechanism, and adsorbent regeneration and the effect of other components, including aromatics, additives, nitrogen compounds, and moisture, on adsorptive desulfurization of diesel fuel were also discussed in detail. Carbon materials showed very high selectivity for removing the dibenzothiophenes, especially for 4,6-dimethyldibenzothiophene, which is very difficult with hydrodesulfurization and other adsorbents. Both the textural and chemical properties of AC have an important impact on the adsorption of DBTs. Adsorption selectivity and capacity can be enhanced further by carbon surface modification. Considering the effect of diffusion hindrance and regeneration, mesoporous carbon is more suitable than microporous carbon with pore size <2 nm. It is necessary to eliminate the inhibiting effect of fuel additive and nitrogen compounds on the DBTs before carbon materials are used for desulfurization of real diesel fuel. In the end, some useful suggestions are also made.

Reactivity of Alkyldibenzothiophenes Using Theoretical Descriptors

Theoretical calculations of the reactivity of dibenzothiophene and its methyl, dimethyl, and trimethyl derivatives show that local reactivity descriptors reproduce their experimental desulfurization reactivity trend if the first desulfurization step involves directly the sulfur atom, which only occurs if the sulfur atom is blocked at most by one methyl group. In the series of molecules{4,7-dimethyldibenzothiophene,x,4,7-trimethyldibenzothiophene (x=1,2,3)}, the most reactive molecule is 2,4,7-trimethyldibenzothiophene, and local descriptors show that the reactivity is linked to the activity of the sulfur atom, which is higher in 2,4,7-trimethyldibenzothiophene due to the position of the third methyl substitute, located in theparaposition with respect to the carbon bonded to the sulfur atom. The electrostatic potential of 2,4,7-trimethyldibenzothiophene shows one effective adsorption site, while 1,4,7-trimethyldibenzothiophene and 3,4,7-trimethyldibenzothiophene have more sites, contributing to the higher reactivity of 2,4,7-trimethyldibenzothiophene. The index of reactivity of other descriptors was evaluated and the effect of the position of the methyl substituents on adsorption parameters, as the dipole moment and the atomic charges were also studied.

Cr(VI) removal from aqueous solution with bamboo charcoal chemically modified by iron and cobalt with the assistance of microwave

Bamboo charcoal (BC) was used as starting material to prepare Co-Fe binary oxideloaded adsorbent (Co-Fe-MBC) through its impregnation in Co(NO3)2, FeCl3 and HNO3 solutions simultaneously, followed by microwave heating. The low-cost composite was characterized and used as an adsorbent for Cr(VI) removal from water. The results showed that a cobalt and iron binary oxide (CoFe2O4) was uniformly formed on the BC through redox reactions. The composite exhibited higher surface area (331 m2/g) than that of BC or BC loaded with Fe alone (Fe-MBC). The adsorption of Cr(VI) strongly depended on solution pH, temperature and ionic strength. The adsorption isotherms followed the Langmuir isotherm model well, and the maximum adsorption capacities for Cr(VI) at 288 K and pH 5.0 were 35.7 and 51.7 mg/g for Fe-MBC and Co-Fe-MBC, respectively. The adsorption processes were well fitted by the pseudo second-order kinetic model. Thermodynamic parameters showed that the adsorption of Cr(VI) onto both adsorbents was feasible, spontaneous, and exothermic under the studied conditions. The spent Co-Fe-MBC could be readily regenerated for reuse.

Effect of the incorporation of nitrogen to a carbon matrix on the selectivity and capacity for adsorption of dibenzothiophenes from model diesel fuel

Two synthetic, polymer-derived carbons were modified with urea to incorporate nitrogen surface functional groups. Then they were investigated as adsorbents of dibenzothiophene (DBT) and 4, 6-dimethyldibenzothiophene (DMDBT) from simulated diesel fuel under dynamic conditions with the total concentration of sulfur being 20 ppmw. The materials before and after adsorption were characterized using elemental analysis, XPS, adsorption of nitrogen, potentiometric titration, and thermal analysis. The incorporation of nitrogen species caused a visible increase in the adsorption capacity. However, selectivity evaluated on the basis of the adsorption of naphthalene decreased. Whereas at low surface coverage the volume of pores smaller than 10 A is important, with the progress of adsorption the surface chemistry gradually starts to play a more important role via either polar or acid/base interactions. The latter are important for the selectivity of adsorption when the aromatic hydrocarbons are present. Although polar interactions are weaker than the acid-base ones, the centers that they represent seem to be more favorable to attract DBT and DMDBT than arenes. There is an indication that nitrogen-containing groups contribute to chemical transformations of DBT and DMDBT/oxidation and promote the involvement of oxygen from the surface groups in the reactive adsorption.

Interactions of 4,6-dimethyldibenzothiophene with the surface of activated carbons

Two carbon samples, commercial wood-based carbons and laboratory-derived polymer-based carbon, were oxidized to two different levels of surface acidity. The resulting adsorbents were characterized using adsorption of nitrogen, potentiometric titration, FTIR, SEM/EDAX, and elemental analysis. On the carbons obtained, the adsorption of 4,6-dimethyldibenzothiophene (4,6-DMDBT) from hexadecane was carried out in the range of the initial concentrations between 10 and 150 ppmw sulfur. The results indicate that pores with diameters less than 10 A are important for adsorption of 4,6-DMDBT. Chemical transformations, likely oxidation, occur in larger pores, and the extent of this process is governed by the availability of oxidants. Those oxidants might be either chemisorbed oxygen and/or iron oxides present in an inorganic matter. Surface acidic groups, when located in larger pores, attract 4,6-DMDBT via specific interactions, and this can increase the amount adsorbed. When the density of these groups is high, they create obstacles for the effective packing of the adsorbate in the pore space and, thus, the amount adsorbed decreases.