Desulfurization Cycles Research Articles

Catalytic fixation of hydrogen sulfide over CuO-CaCO3 co-impregnated tea stalk-derived biochar

Catalytic fixation of hydrogen sulfide over CuO-CaCO3 co-impregnated tea stalk-derived biochar

High-Degree Oxidative Desulfurization of a Commercial Marine Fuel Using Deep Eutectic Solvents and Their Recycling Process

Escalating environmental concerns have dictated the need to develop innovative methods for efficiently desulfurizing marine fuels (heavy fuel oils). In this work, the oxidative desulfurization method using deep eutectic solvents (DESs) was applied to reduce the sulfur content in a commercially available heavy fuel oil (HFO) below 0.5 wt.%, as current regulations demand. Initially, the S-compounds in the fuel were oxidized using an oxidative mixture of H2O2 with carboxylic acid (either acetic or formic acid). Subsequently, the oxidized S-compounds were extracted from the fuel using a series of environmentally friendly deep eutectic solvents (DESs), the best of which was proven to be a mixture of choline chloride with ethylene glycol at a 1/2 molar ratio. The process was optimized by investigating the effect of several process parameters on the desulfurization efficiency, namely, the H2O2/S molar ratio, the H2O2/acid molar ratio, the acid type, the oxidation temperature and oxidation time, the solvent/fuel mass ratio, the extraction time, and the extraction temperature. A desulfurization efficiency of 75.7% was achieved under the optimized conditions, reducing the S content in the fuel to 0.33 wt.%. Furthermore, different methods to recycle the DESs were investigated, and consecutive desulfurization and solvent regeneration cycles were performed. The most efficient recycling method was determined to be the anti-solvent addition of excess water, which resulted in 89.5% DES purification by causing precipitation of the dissolved solids. After three cycles of desulfurization and regeneration using different recycling routes, it was found that the regeneration degree declines gradually; however, it is more than 79.3% in all cases.

Intensification of extractive desulfurization in micro-channels using triethylamine/propionic acid as deep eutectic solvent

In this study, the extractive desulfurization from the model fuel was investigated in different micro-channels using triethylamine/propionic acid with the molar ratio of 1 to 3 ([TEA:3Pr]) as DES. In this regard, the effect of operating parameters (i.e., extraction time, temperature, and fuel to DES volume ratio) and micro-channel geometrical parameters (i.e., the diameter of the micro-channel, and length of the micro-channel) on the sulfur removal and volumetric mass transfer coefficient was investigated. Moreover, the effect multiple extractive desulfurization cycles, regeneration of spent [TEA:3Pr] has been also investigated. It was found that the best geometry for the micro-channel is 0.6 mm in the diameter and 20 cm in length considering the sulfur removal and mass transfer. The slug and throat-annular flow regimes were observed in the different micro-channels through two-phase flow visualization. The achieved sulfur removal was 70.8%, 68.7%, and 44.4% from the model fuels containing dibenzothiophene (DBT), benzothiophene (BT), and thiophene (Th) in a very short residence time of 17 s, respectively. The overall volumetric mass transfer coefficient in the micro-channel was 0.679 s−1 in the fuel to DES volume ratio of 5. It was also found that deep sulfur removal can be achieved using multiple-extraction cycles.

Desulfurization of diesel via joint adsorption and extraction using a porous liquid derived from ZIF-8 and a phosphonium-type ionic liquid.

A type-III porous liquid based on zeolitic imidazolate framework-8 (ZIF-8) and an ionic liquid trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide ([THTDP][BTI]) was synthesized and used for the desulfurization of model diesel. The desulfurization effect by ZIF-8/[THTDP][BTI] combined both the adsorptive desulfurization by ZIF-8 and the extraction desulfurization by [THTDP][BTI]. The removal of the three chosen aromatic organic sulfides by the ZIF-8/[THTDP][BTI] porous liquid followed the order of dibenzothiophene (73.1%) > benzothiophene (70.0%) > thiophene (61.5%). It was further found that deep desulfurization could be realized by ZIF-8/[THTDP][BTI] through triple desulfurization cycles and ZIF-8/[THTDP][BTI] can be regenerated readily. The desulfurization mechanism was explored further in detail by conformation search and density functional theory calculations. Calculations supported that the large molecular volume of [THTDP][BTI] excluded itself from the cavities of ZIF-8, making the pores of ZIF-8 in the porous liquid unoccupied and accessible by other guest species, here the studied organic sulfides. These calculations indicate that the van der Waals interactions were the main interactions between ZIF-8/[THTDP][BTI] and specifically benzothiophene. This work supports that the porous liquid ZIF-8/[THTDP][BTI] could potentially be used for desulfurization of diesel in industry.

Highly Efficient Catalytic Oxidative Desulfurization of Dibenzothiophene using Layered Double Hydroxide Modified Polyoxometalate Catalyst

Layered double hydroxide-modified polyoxometalate (ZnAl-PW) was prepared and used for the oxidative desulfurization of dibenzothiophene. XRD patterns of ZnAl-LDH and PW are still present in ZnAl-PW. The bands of ZnAl-PW in wavenumber 3276, 1637, 1363, 1050, 952, 887, and 667 cm-1. The typical surface of ZnAl-LDH and ZnAl-PW can be observed not smooth in different sized with irregular shapes. The average diameter distribution of ZnAl-LDH and ZnAl-PW is 14 nm and 47 nm, respectively. For dibenzothiophene with 500 ppm, conversion on ZnAl-LDH, PW, and ZnAl-PW was 94.71%, 95.88%, and 99.16%, respectively. Conversion of dibenzothiophene in line with the acidity of ZnAl-LDH, PW, and ZnAl-PW were 0.399, 1.635, and 3.023 mmol/gram, respectively. The most effective catalyst dosage for the desulfurization of dibenzothiophene on ZnAl-LDH, PW, and ZnAl-PW is 0.25 g. The unchanged dibenzothiophene concentration indicates a heterogeneous system. ZnAl-LDH, PW, and ZnAl-PW are truly heterogeneous catalysts. After 3 cycles of oxidative desulfurization, the percentage conversion of dibenzothiophene on ZnAl-LDH, PW, and ZnAl-PW were 77.42 %, 65.98%, and 86.38%, respectively. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Thick pore walls mesoporous silicon composites based on phosphomolybdic acid: An efficient catalyst for oxidation desulfurization reaction

Thick pore walls mesoporous silicon composites based on phosphomolybdic acid: An efficient catalyst for oxidation desulfurization reaction

Lindqvist@Nanoporous MOF-Based Catalyst for Effective Desulfurization of Fuels.

An effective and sustainable oxidative desulfurization process for treating a multicomponent model fuel was successfully developed using as a heterogeneous catalyst a composite material containing as an active center the europium Lindqvist [Eu(W5O18)2]9− (abbreviated as EuW10) encapsulated into the nanoporous ZIF-8 (zeolitic imidazolate framework) support. The EuW10@ZIF-8 composite was obtained through an impregnation procedure, and its successful preparation was confirmed by various characterization techniques (FT-IR, XRD, SEM/EDS, ICP-OES). The catalytic activity of the composite and the isolated EuW10 was evaluated in the desulfurization of a multicomponent model fuel containing dibenzothiophene derivatives (DBT, 4-MDBT and 4,6-DMDBT) with a total sulfur concentration of 1500 ppm. Oxidative desulfurization was performed using an ionic liquid as extraction solvent and aqueous hydrogen peroxide as oxidant. The catalytic results showed a remarkable desulfurization performance, with 99.5 and 94.7% sulfur removal in the first 180 min, for the homogeneous active center EuW10 and the heterogeneous EuW10@ZIF-8 catalysts, respectively. Furthermore, the stability of the nanocomposite catalyst was investigated by reusing and recycling processes. A superior retention of catalyst activity in consecutive desulfurization cycles was observed in the recycling studies when compared with the reusing experiments. Nevertheless, the nanostructure of ZIF-8 incorporating the active POM (polyoxometalate) was shown to be highly suitable for guaranteeing the absence of POM leaching, although structural modification was found for ZIF-8 after catalytic use that did not influenced catalytic performance.

Dichloro and dimethyl dioxomolybdenum(VI)-bipyridine complexes as catalysts for oxidative desulfurization of dibenzothiophene derivatives under extractive conditions

• Ligand effects for Mo VI -catalysed oxidative desulfurization (ODS) of a model diesel. • Ionic liquid-entrapped [MoO 2 X 2 (4,4′-R 2 –2,2′-bipyridine)] give >99% ODS in 1–2 h. • Highly IL-soluble complexes (R = t Bu, nonyl; X = Cl or Me) are the best catalysts. • The IL/catalyst mixtures showed good recyclability over three consecutive cycles. • Crystal structures reported for [MoO 2 Me 2 (4,4′-R 2 –2,2′-bipyridine)] (R = Me, nonyl). The complexes [MoO 2 Me 2 (2,2′-bipyridine)] ( 5 ), [MoO 2 X 2 (4,4′-dimethyl-2,2′-bipyridine)] (X = Cl ( 2 ), Me ( 6 )), [MoO 2 Me 2 (4,4′-di‑ tert ‑butyl‑2,2′-bipyridine)] ( 7 ) and [MoO 2 X 2 (4,4′-dinonyl-2,2′-bipyridine)] (X = Cl ( 4 ), Me ( 8 )) have been prepared and examined as catalysts in extractive and catalytic oxidative desulfurization (ECODS) of a simulated diesel fuel (3000 ppm S) containing dibenzothiophene, 4-methyldibenzothiophene and 4,6-dimethyldibenzothiophene. The molecular structures of 6 and 8 were characterized by 1 H NMR, FT-IR and FT-Raman, and X-ray crystallography. The ECODS reaction conditions were optimized for complex 5 by comparing different extraction solvents (MeCN, the ionic liquid (IL) 1‑butyl‑3-methylimidazolium hexafluorophosphate ([BMIM]PF 6 ), polyethylene glycol (PEG) and two PEG-based deep eutectic solvents), and by varying the catalyst and oxidant (H 2 O 2 ) amounts, and diesel/solvent volume ratio. Under the optimal conditions with [BMIM]PF 6 as the extraction solvent, the quantitative elimination of all sulfur compounds from the model diesel was achieved within 3 h at 70 °C. A comparison of initial ECODS rates for complexes 2, 4, 6 and 8 indicated that the equatorial N,N -chelate ligand was more important than the axial ligand (X) for the desulfurization catalytic performance, with the best results being obtained for the IL-soluble complexes 4 and 8 . The IL-entrapped catalyst from 4 showed a good capacity to be reused in consecutive desulfurization cycles. Synopsis: Ligand effects have been examined for dioxomolybdenum(VI)-bipyridine complexes used as catalysts in extractive and oxidative desulfurization. The ionic liquid (IL)-soluble complexes [MoO 2 X 2 (4,4′-dinonyl-2,2′-bipyridine)] (X = Cl, Me) allowed elimination of all dibenzothiophene derivatives from a model diesel and the IL-entrapped catalysts could be effectively reused in consecutive desulfurization cycles.

Membrane-Supported Layered Coordination Polymer as an Advanced Sustainable Catalyst for Desulfurization.

The application of a catalytic membrane in the oxidative desulfurization of a multicomponent model diesel formed by most refractory sulfur compounds present in fuel is reported here for the first time. The catalytic membrane was prepared by the impregnation of the active lamellar [Gd(H4nmp)(H2O)2]Cl·2H2O (UAV-59) coordination polymer (CP) into a polymethyl methacrylate (PMMA, acrylic glass) supporting membrane. The use of the catalytic membrane in the liquid–liquid system instead of a powder catalyst arises as an enormous advantage associated with the facility of catalyst handling while avoiding catalyst mass loss. The optimization of various parameters allowed to achieve a near complete desulfurization after 3 h under sustainable conditions, i.e., using an aqueous H2O2 as oxidant and an ionic liquid as extraction solvent ([BMIM]PF6, 1:0.5 ratio diesel:[BMIM]PF6). The performance of the catalytic membrane and of the powdered UAV-59 catalyst was comparable, with the advantage that the former could be recycled successfully for a higher number of desulfurization cycles without the need of washing and drying procedures between reaction cycles, turning the catalytic membrane process more cost-efficient and suitable for future industrial application.

A simple desulfurization process to achieve high efficiency, sustainability and cost-effectivity via peroxotungstate catalyst

• Peroxotungstate presented higher desulfurization efficiency than peroxomolybdate. • The [BMIM]PF 6 was used as extraction solvent and as catalyst entrapment. • Peroxotungstate promoted high desulfurization efficiency using low amounts of oxidant, catalyst and solvent. • Complete desulfurization was achieved after 40 min using H 2 O 2 /S = 4. • Catalyst and [BMIM]PF 6 solvent were reused for consecutive cycles with high efficiency. The creation of more sustainable and high efficient desulfurization system, capable to operate under cost-effective conditions, led to the application of peroxopolyoxometalates as active oxidative catalysts. These compounds present active peroxo groups in their structure that promote easily the oxidation of sulfur compounds in the presence of low amounts of oxidant (H 2 O 2 /S = 4). The sustainability of the desulfurization of a multicomponent model diesel (2000 ppm S) was increased by the optimization of various parameters, such as nature and volume of extraction solvent, oxidant and catalyst. The Venturello peroxotungstate ((Bu 4 N) 3 PW 4 ) showed to be a catalyst able to complete desulfurize a model diesel (after only 40 min), under lower amounts of solvent, oxidant and catalyst, than the analogues peroxomolybdate ((Bu 4 N) 3 PMo 4 ) compound. Furthermore, the (Bu 4 N) 3 PW 4 /[BMIM]PF 6 system was able to be reused for six consecutive desulfurization cycles maintaining its efficiency. The oxidized sulfur compounds were removed from [BMIM]PF 6 phase in the end of each catalytic cycle. This simple procedure guarantees the cost-efficiency of the process, promoting the reuse of the catalyst and the solvent for various consecutive cycles, without the need of heterogenization techniques.

An Effective Magnetic Catalyst for Oxidative Desulfurization of Model and Real Fuels: Fe3O4/ZIF-8/TiO₂

In the current research, an advanced and innovative composite based in zeolitic imidazolate framework-8 (ZIF-8) incorporating magnetic and effective oxidative catalytic properties was successfully used to prepare ultra-low sulfur model and real fuels by oxidative desulfurization (ODS) process. To this purpose, the surface of ZIF-8 was decorated by TiO 2 and Fe 3 O 4 nanoparticles (NPs) to prepare the composite catalyst (Fe₃O₄/ZIF-8/TiO₂). Structural characterization was performed by XRD, FT-IR, SEM, EDS, TEM, N 2 adsorption-desorption isotherm and VSM. TEM images showed that the semi-spherical TiO 2 and Fe 3 O 4 NPs are fairly doped. The effect of TiO 2 and Fe 3 O 4 NPs incorporated in ZIF-8 support allowed an efficient catalytic oxidative desulfurization of model fuel (500 ppm of dibenzothiophene, DBT) and real fuels (gasoline, diesel, among others) using tert-Butyl hydroperoxide (TBHP) as oxidant under a solvent-free system. Optimization studies were performed and complete desulfurization of model fuel was found after 6 h using O/S = 3 at 80 °C, instead of the 33% of desulfurization obtained with the pristine ZIF-8. Under optimized conditions, sulfone was the only product observed. The stability and the recycle capacity of the Fe₃O₄/ZIF-8/TiO₂ composite catalyst was confirmed and after ten consecutive ODS cycles only a slight decrease of desulfurization efficiency was detected (around 10%). Therefore, the results here presented confirm that the magnetic catalyst conciliates efficiency, stability and easy recovery, that are essential properties for future industrial application. • Magnetic catalytic composite has been prepared based on ZiF-8 support. • Fe 3 O 4 /ZIF-8/TiO 2 presents high catalytic efficiency for oxidative desulfurization of model and real fuels. • Solvent-free oxidative catalytic system was successfully used. • Complete desulfurization was achieved after 6 h using O/S = 3. • Catalyst presented high stability and recycle capacity for 10 consecutive desulfurization cycles.

An Effective Hybrid Heterogeneous Catalyst to Desulfurize Diesel: Peroxotungstate@Metal-Organic Framework.

A peroxotungstate composite comprising the chromium terephthalate metal–organic framework MIL-101(Cr) and the Venturello peroxotungstate [PO4{WO(O2)2}4]3− (PW4) has been prepared by the impregnation method. The PW4@MIL-101(Cr) composite presents high catalytic efficiency for oxidative desulfurization of a multicomponent model diesel containing the most refractory sulfur compounds present in real fuels (2000 ppm of total S). The catalytic performance of this heterogeneous catalyst is similar to the corresponding homogeneous PW4 active center. Desulfurization efficiency of 99.7% was achieved after only 40 min at 70 °C using H2O2 as an oxidant and an ionic liquid as an extraction solvent ([BMIM]PF6, 2:1 model diesel/[BMIM]PF6). High recycling and reusing capacity was also found for PW4@MIL-101(Cr), maintaining its activity for consecutive oxidative desulfurization cycles. A comparison of the catalytic performance of this peroxotungstate composite with others previously reported tungstate@MIL-101(Cr) catalysts indicates that the presence of active oxygen atoms from the peroxo groups promotes a higher oxidative catalytic efficiency in a shorter reaction time.

Desulfurization Performance of Choline Chloride-Based Deep Eutectic Solvents in the Presence of Graphene Oxide

Extractive catalytic oxidative desulfurization (ECODS) is the one of the recent methods used in fuel desulfurization which involved the use of catalyst in the oxidative desulfurization of diesel fuel. This study is aimed to test the effectiveness of synthesized choline chloride (ChCl) based deep eutectic solvent (DES) in fuel desulfurization via ECODS method, with the presence of graphene oxide (GO) as catalyst and hydrogen peroxide (H2O2) as oxidant. In this study, 16 DESs based on choline chloride were synthesized using glycerol (GLY), ethylene glycol (EG), tetraethylene glycol (TEG) and polyethylene glycol (PEG). The characterization of the synthesized DES was carried out via Fourier transform infrared spectroscopy (FTIR) analysis, density, and viscosity determination. According to the screening result, ChCl-PEG (1:4) was found to be the most effective DES for desulfurization using ECODS method, with a removal of up to 47.4% of sulfur containing compounds in model oil in just 10 min per cycle after the optimization of the reaction parameters, and up to 95% desulfurization efficiency could be achieved by six cycles of desulfurization. It is found that the addition of GO as catalyst does not increase the desulfurization performance drastically; hence, future studies for the desulfurization performance of DESs made up from ChCl and PEG and its derivatives can be done simply by using extraction desulfurization (EDS) method instead of ECODS method, for cost reduction purpose and easier regulation of DES waste into environment.

Regenerable Co-ZnO-based nanocomposites for high-temperature syngas desulfurization

Abstract H2S is a common impurity in the syngas derived from municipal solid waste gasification. For power generation using advanced technologies, such as gas engines/turbines or solid oxide fuel cells, reducing the H2S content to acceptable levels is required. This work investigated the desulfurization performance of bimetallic particles by adding different metals (Fe, Cr, Co, Ni) into ZnO-based nanocomposites. At 400 °C, the Co-ZnO demonstrated 26.3, 5.0, 1.7 times higher sulfur uptake from a model syngas (composed of 100 ppmv H2S, 15 vol% CO, 5 vol% CO2, 15 vol% H2, 15 vol% H2O and N2 (balance)) than pure ZnO, Cr-ZnO and Fe-ZnO, respectively. This could be attributed to the formation of p-n heterojunction between the n-type ZnO and p-type Co3O4, accelerating surface reaction kinetics. Although the Ni-ZnO showed a better performance at 400 °C, at an elevated temperature of 600 °C, the Co-ZnO demonstrated 1.2 times higher sulfur capacity compared to Ni-ZnO. Furthermore, the Co-ZnO nanocomposite was subjected to 3 cycles of high-temperature desulfurization (600 °C) and regeneration. The results showed that its high desulfurization efficiency was retained after the tests. This could enable a high-temperature desulfurization of hot syngas and hence an increase in the electrical efficiency of waste-to-energy facilities.

Polyoxomolybdate based ionic-liquids as active catalysts for oxidative desulfurization of simulated diesel

Abstract This work compares the stability and the catalytic efficiency of different ionic liquid phosphomolybdates ([BPy]3[PMo12O40] and [BMIM]3[PMo12O40]) with a cationic (propylpyridinium) functionalized mesoporous silica nanoparticle composite (PMo12O40@PPy-MSN). These were used as solid catalysts for the oxidative desulfurization of a multicomponent model diesel using hydrogen peroxide as oxidant and a polar immiscible extraction solvent. Ionic liquid ([BMIM][PF6] was successfully used as solvent to extract sulfur compounds from model diesel. The ionic liquid phosphomolybdates showed partial solubility in the ionic liquid phase, occurring some decomposition of their Keggin structure in the soluble reaction media, probably caused by their interaction with oxidant. On the other hand, the phosphomolybdate composite PMo12O40@PPy-MSN presented high structural stability and only negligible leaching occurrence after various consecutive reaction cycles. The model diesel was near complete desulfurized after 3 h and consecutive desulfurization cycles were performed without loss of activity. Therefore, the immobilization of Keggin phosphomolybdate structure [PMo12O40]3− using cationic propylpyridinium silica nanoparticle is an assertive strategy to produce stable and active heterogeneous catalysts.

Evaluation of dry acid gas removal process on bench scale test facility coupled with syngas produced by O2/CO2-blown gasifier

Abstract Dry acid gas removal test facility that comprises of halide and sulfur control units was coupled with O2/CO2-blown gasifier to demonstrate performance and operability of the dry gas purification process for the oxy-fuel IGCC power generation with efficient carbon dioxide separation. The facility was operated for initial five desulfurization cycles of sequential operation of sulfidation, regeneration, and reduction. The duration of each step was fixed to three hours which includes the purge operation to change the gas condition from syngas to oxidative gas, and vice versa. The test facility has the sulfur removal unit equipped with three fixed-bed reactors. Honeycomb shaped desulfurization sorbent that was improved to prevent harmful carbon deposition was installed in those reactors. The cyclic operation results revealed that the unit could reasonably remove sulfur compounds in the sulfidation steps and released the absorbed sulfur during succeeding regeneration steps for the initial five cycles of operation. The spent sorbent did not suffered with carbon deposition and retained their performance on sulfur removal. The absorbed sulfur in the spent sorbent was adequately released in regeneration steps for further operation of desulfurization cycles. The performance and operability of the dry acid gas removal process was successfully demonstrated in the actual syngas operation test.

Deep oxidative desulfurization of diesel fuels using homogeneous and SBA-15-supported peroxophosphotungstate catalysts

Abstract A combination of catalytic oxidation and extraction was used for the desulfurization of a model diesel containing benzothiophene, dibenzothiophene and 4,6-dimethyldibenzothiophene, or a real diesel sample with a sulfur content of 2300 ppm. The catalysts used were the soluble peroxo compound (nBu4N)3{PO4[WO(O2)2]4} (PW4) and a supported material denoted as PW4@TMA-SBA-15 that was prepared by immobilization of PW4 in an ordered mesoporous silica (SBA-15) derivatized with propyltrimethylammonium groups (TMA). The supported catalyst was characterized by FT-IR, FT-Raman, 31P and 13C MAS NMR spectroscopies, powder X-ray diffraction and scanning electron microscopy. Under optimized conditions (H2O2/S molar ratio = 7, 70 °C, acetonitrile as extraction solvent), both catalysts led to complete desulfurization of the model diesel within a reaction time of 2 h. The desulfurization systems could be recycled 10 times with only a slight decrease in performance being observed between the 9th and 10th oxidative desulfurization cycles. Application of the PW4 system to the real diesel led to an outstanding desulfurization efficiency of 89% after a reaction time of 2 h.

Improving the Catalytic Performance of Keggin [PW12O40]3- for Oxidative Desulfurization: Ionic Liquids versus SBA-15 Composite.

Different methodologies were used to increase the oxidative desulfurization efficiency of the Keggin phosphotungstate [PW12O40]3− (PW12). One possibility was to replace the acid proton by three different ionic liquid cations, forming the novel hybrid polyoxometalates: [BMIM]3PW12 (BMIM as 1-butyl-3-methylimidazolium), [BPy]3PW12 (BPy as 1-butylpyridinium) and [HDPy]3PW12 (HDPy as hexadecylpyridinium. These hybrid Keggin compounds showed high oxidative desulfurization efficiency in the presence of [BMIM]PF6 solvent, achieving complete desulfurization of multicomponent model diesel (2000 ppm of S) after only 1 h, using a low excess of oxidant (H2O2/S = 8) at 70 °C. However, their stability and activity showed some weakness in continuous reused oxidative desulfurization cycles. An improvement of stability in continuous reused cycles was reached by the immobilization of the Keggin polyanion in a strategic positively-charged functionalized-SBA-15 support. The PW12@TM–SBA-15 composite (TM is the trimethylammonium functional group) presented similar oxidative desulfurization efficiency to the homogeneous IL–PW12 compounds, having the advantage of a high recycling capability in continuous cycles, increasing its activity from the first to the consecutive cycles. Therefore, the oxidative desulfurization system catalyzed by the Keggin-type composite has high performance under sustainable operational conditions, avoids waste production during recycling and allows catalyst recovery.

Sustainable Desulfurization Processes Catalyzed by Titanium-Polyoxometalate@TM-SBA-15

A titanium-polyoxometalate with a µ-hydroxo dimeric structure [(PW11O39Ti)2OH]7− ((PW11Ti)2OH) was used efficiently for the desulfurization of a model diesel containing a mixture of various refractory sulfur compounds present in real fuels. The catalytic performance of the µ-hydroxo dimeric compound was compared in its homogeneous form and also when immobilized in the trimethylammonium-functionalized SBA-15 ((PW11Ti)2OH@TM-SBA-15). An optimization study was performed using the homogeneous and heterogeneous catalysts to obtain high catalytic efficiency, sustainability and cost-effectiveness of the system. Different optimized conditions were found using the homogeneous and heterogeneous catalysts. Lower amounts of solvent extraction (MeCN, 175 µL), catalyst (0.5 µmol of active center) and oxidant (50 µL) were used to produce sulfur-free model diesel after 2 h at 70 °C, using the heterogeneous (PW11Ti)2OH@TM-SBA-15 catalyst. On the other hand, complete desulfurization was achieved with homogeneous (PW11Ti)2OH catalyst after only 40 min, although higher amounts of MeCN (750 µL), catalyst (1.5 µmol) and oxidant (75 µL) were used. Both systems combined liquid–liquid extraction and catalytic oxidation. Using the heterogeneous catalyst, adsorption of oxidized-sulfur compound was also observed. Both homogeneous and heterogeneous desulfurization systems presented a high capacity to be reused/recycled for consecutive desulfurization cycles.

In Situ Preparation and Regeneration Behaviors of Zinc Oxide/Red Clay Desulfurization Sorbents

High-temperature gas desulfurization is an efficient and environmentally friendly process for syngas cleanup. The present study investigated the in situ preparation of a zinc oxide/red clay desulfurization sorbent and its desulfurization–regeneration behavior in O2/N2 atmospheres. The effects of regeneration temperature, space velocity, and O2 concentration on the regeneration behaviors of ZnO/red clay sorbents were also investigated. The surface and structural properties of the sorbents before and after regeneration were characterized by thermogravimetric–differential scanning calorimetry, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, elemental mapping, and N2 adsorption–desorption analyses. According to the results, the highest regeneration rate was achieved under the conditions of 6 vol % O2 and a space velocity of 3000 h–1 at 650 °C. After four cycles of desulfurization–regeneration experiments, the breakthrough time of the regenerated sorbents reduced by 18.7% and...