Perspectives on strategies for improving ultra-deep desulfurization of liquid fuels through hydrotreatment: Catalyst improvement and feedstock pre-treatment

Reliance on crude oil remains high while the transition to green and renewable sources of fuel is still slow. Developing and strengthening strategies for reducing sulfur emissions from crude oil is therefore imperative and makes it possible to sustainably meet stringent regulatory sulfur level legislations in end-user liquid fuels (mostly less than 10 ppm). The burden of achieving these ultra-low sulfur levels has been passed to fuel refiners who are battling to achieve ultra-deep desulfurization through conventional hydroprocessing technologies. Removal of refractory sulfur-containing compounds has been cited as the main challenge due to several limitations with the current hydroprocessing catalysts. The inhibitory effects of nitrogen-containing compounds (especially the basic ones) is one of the major concerns. Several advances have been made to develop better strategies for achieving ultra-deep desulfurization and these include: improving hydroprocessing infrastructure, improving hydroprocessing catalysts, having additional steps for removing refractory sulfur-containing compounds and improving the quality of feedstocks. Herein, we provide perspectives that emphasize the importance of further developing hydroprocessing catalysts and pre-treating feedstocks to remove nitrogen-containing compounds prior to hydroprocessing as promising strategies for sustainably achieving ultra-deep hydroprocessing

Oxovanadium (IV)-catalysed oxidation of dibenzothiophene and 4, 6-dimethyldibenzothiophene

The reaction between [VIVOSO4] and the tetradentate N2O2-donor Schiff base ligand, N,N-bis(o-hydroxybenzaldehyde)phenylenediamine (sal-HBPD), obtained by the condensation of salicylaldehyde and o-phenylenediamine in a molar ratio of 2 : 1 respectively, resulted in the formation of [VIVO(sal-HBPD)]. The molecular structure of [VIVO(sal-HBPD)] was determined by single crystal X-ray diffraction, and confirmed the distorted square pyramidal geometry of the complex with the N2O2 binding mode of the tetradentate ligand. The formation of the polymer-supported p[VIVO(sal-AHBPD)] proceeded via the nitrosation of sal-HBPD, followed by the reduction with hydrogen to form an amine group that was then linked to Merrifield beads followed by the reaction with [VIVOSO4]. XPS and EPR were used to confirm the presence of oxovanadium(IV) within the beads. The BET surface area and porosity of the heterogeneous catalyst p[VIVO(sal-AHBPD)] were found to be 6.9 m2 g−1 and 180.8 Å respectively. Microanalysis, TG, UV-Vis and FT-IR were used for further characterization of both [VIVO(sal-HBPD)] and p[VIVO(sal-AHBPD)]. Oxidation of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) was investigated using [VIVO(sal-HBPD)] and p[VIVO(sal-AHBPD)] as catalysts. Progress for oxidation of these model compounds was monitored with a gas chromatograph fitted with a flame ionization detector. The oxidation products were characterized using gas chromatography-mass spectrometry, microanalysis and NMR. Dibenzothiophene sulfone (DBTO2) and 4,6-dimethyldibenzothiophene sulfone (4,6-DMDBTO2) were found to be the main products of oxidation. Oxovanadium(IV) Schiff base microspherical beads, p[VIVO(sal-AHBPD)], were able to catalyse the oxidation of sulfur in dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) to a tune of 88.0% and 71.8% respectively after 3 h at 40 °C. These oxidation results show promise for potential application of this catalyst in the oxidative desulfurization of crude oils

Imidazole-functionalized polymer microspheres and fibers–useful materials for immobilization of oxovanadium (IV) catalysts

Both polymer microspheres and microfibers containing the imidazole functionality have been prepared and used to immobilize oxovanadium(IV). The average diameters and BET surface areas of the microspheres were 322 μm and 155 m2 g−1 while the fibers were 1.85 μm and 52 m2 g−1, respectively. XPS and microanalysis confirmed the incorporation of imidazole and vanadium in the polymeric materials. The catalytic activity of both materials was evaluated using the hydrogen peroxide facilitated oxidation of thioanisole. The microspheres were applied in a typical laboratory batch reactor set-up and quantitative conversions (>99%) were obtained in under 240 min with turn-over frequencies ranging from 21.89 to 265.53 h−1, depending on the quantity of catalyst and temperature. The microspherical catalysts also proved to be recyclable with no drop in activity being observed after three successive reactions. The vanadium functionalized fibers were applied in a pseudo continuous flow set-up. Factors influencing the overall conversion and product selectivity, including flow rate and catalyst quantity, were investigated. At flow rates of 1–4 mL h−1 near quantitative conversion was maintained over an extended period. Keeping the mass of catalyst constant (0.025 g) and varying the flow rate from 1–6 mL h−1 resulted in a shift in the formation of the oxidation product methyl phenyl sulfone from 60.1 to 18.6%

Adsorption and separation of platinum and palladium by polyamine functionalized polystyrene-based beads and nanofibers

Adsorption and separation of platinum and palladium chlorido species (PtCl62- and PdCl42-) on polystyrene beads as well as nanofibers functionalized with ammonium centres based on ethylenediamine (EDA), diethylenetriamine (DETA), triethylenetetramine (TETA) and tris-(2-aminoethyl)amine (TAEA) are described. The functionalized sorbent materials were characterized by microanalysis, SEM, XPS, BET and FTIR. The surface area of the functionalized fibers was in the range 69–241 m2/g while it was 73–107 m2/g for the beads. The adsorption and loading capacities of the sorption materials were investigated using both the batch and column studies at 1 M HCl concentration. The adsorption studies for both PtCl62- and PdCl42- on the different sorbent materials fit the Langmuir isotherm with R2 values >0.99. The highest loading capacity of Pt and Pd were 7.4 mg/g and 4.3 mg/g respectively for the nanofiber sorbent material based on ethylenediamine (EDA) while the beads with ethylenediamine (EDA) gave 1.0 mg/g and 0.2 mg/g for Pt and Pd respectively. Metals loaded on the sorbent materials were recovered by using 3% m/v thiourea solution as the eluting agent with quantitative desorption efficiency under the selected experimental conditions. Separation of platinum from palladium was partially achieved by selective stripping of PtCl62- with 0.5 M of NaClO4 in 1.0 M HCl while PdCl42- was eluted with 0.5 M thiourea in 1.0 M HCl. Separation of platinum from iridium and rhodium under 1 M HCl concentration was successful on triethylenetriamine (TETA)-functionalized Merrifield beads. This material (M-TETA) showed selectivity for platinum albeit the low loading capacity

Synthesis and crystal structures of zinc(II) coordination polymers of trimethylenedipyridine (tmdp), 4-nitrobenzoic (Hnba) and 4-biphenylcarboxylic acid (Hbiphen) for adsorptive removal of methyl orange from aqueous solution

Two novel Zn(II) coordination polymers (CPs), [Zn(nba)2(tmdp)]n (1) and [Zn(biphen)2(tmdp)]n (2), were synthesised by reacting Zn(NO3)2·6H2O and 4,4′-trimethylenedipyridine (tmdp) with corresponding carboxylates: 4-nitrobenzoic (Hnba) and 4-biphenylcarboxylic acid (Hbiphen). Their structures were characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD) and single-crystal X-ray diffraction. Compounds 1 and 2 are one-dimensional CPs with the zinc(II) carboxylate units bridged through the N-donor spacer ligand. The zinc (II) atom adopts a tetrahedral arrangement in 1 and 2 coordinated by two nitrogen atoms from two tmdp ligand molecules and two deprotonated oxygen atoms from two carboxylate ligand molecules. The adsorption capacities of MO in this study was found to be 546.31 mg/g and 22.67 mg/g for 1 and 2, respectively. DFT studies confirmed that adsorption is primarily due to π-π stacking and electrostatic interactions between MO and 1. It is noteworthy that binding energy (BE) values for 1 (-74.14 KJ/mol) and 2 (-61.11 KJ/mol) correlate reasonably well with the observed adsorption capacities of MO. The study demonstrated that 1 has higher adsorption efficiency in comparison to 2 and could be an effective and easily reusable adsorbent for the removal of MO from wastewater