Deep oxidative desulfurization of model fuel using ozone generated by dielectric barrier discharge plasma combined with ionic liquid extraction

The dielectric barrier discharge (DBD) is often used to prepare ozone. In this study, a novel room temperature oxidative desulfurization method involving ozone oxidation produced in the DBD reactor combined with ionic liquid (IL) [BMIM]CH₃COO ([BMIM]Ac) extraction was developed. The method was suitable for the deep removal of sulfur (S)-containing compounds from model fuel. By this desulfurization technology, 4,6-dimethyldibenzothiophene (4,6-DMDBT), dibenzothiophene (DBT), benzothiophene (BT) and thiophene (TS) were efficiently removed. Normally, the removal of TS and BT from fuel is highly difficult. However, using the proposed method of this study without any catalyst, the removal rate of TS and BT reached 99.9%. When TiO₂/MCM-41 was used as a catalyst, the S-removal of DBT and 4,6-DMDBT increased to 98.6 and 95.2%, respectively. The sulfur removal activity of the four sulfur compounds decreased in the order of TS > BT >> DBT > 4,6-DMDBT.     

Role of microporosity and surface chemistry in adsorption of 4,6-dimethyldibenzothiophene on polymer-derived activated carbons

Two carbon samples derived from poly(4-styrenesulfonic acid-co-maleic acid) based polymer by carbonization between 700 and 800 °C were oxidized to two different levels of surface acidity. The surfaces of resulting adsorbents were characterized by potentiometric titration, adsorption of nitrogen, FTIR, SEM/EDAX and thermal analysis. The materials were used as adsorbents of 4,6-dimethyldibenzothiophene (4,6-DMDBT) from hexadecane with initial concentration of sulfur between 10-150 ppmw. Although it was found that pores with diameter less than 10 Å govern the amount of 4,6-DMDBT adsorbed, that amount is enhanced when acidic groups are present in the larger pores owing to the contributions of specific interactions. Surface chemistry plays an important role in reactive adsorption and deposition of the products of surface reactions in the pore system.     

Desulfurization of high-sulfur jet fuel by mesoporous π-complexation adsorbents

Desulfurization of JP-5 jet fuel (1172 ppmw S) was investigated by π-complexation adsorption with AgNO₃ supported on mesoporous silica SBA-15 and MCM-41. The average pore sizes of AgNO₃/SBA-15 and AgNO₃/MCM-41 were 48.8 and 19.1 Å, respectively. The results of JP-5 desulfurization showed that significant sulfur breakthrough occurred at ∼10.0 and ∼15.0 mL/g by AgNO₃/SBA-15 and AgNO₃/MCM-41, respectively, at a space velocity of 1.25 h⁻¹. The spent AgNO₃/MCM-41 was regenerated by a simple process (heating in air at 200 °C) and ∼50% of the sulfur capacity was recovered after the first cycle. Molecular orbital calculations show that Cu⁺ (as that in CuY zeolite) formed stronger π-complexation bonding with the thiophenic compounds than Ag⁺ (in AgNO₃), as evidenced by experimental heats of adsorption. However, pore diffusion limitation of the large sulfur molecules (alkylated benzothiophenes) became an important factor for desulfurization of high sulfur jet fuels such that the AgNO₃-supported mesoporous sorbents yielded substantially better results than Cu(I)Y, although Cu(I)Y was better for a model fuel that contained only small sulfur molecules. Among all sorbents that have been investigated, the AgNO₃/MCM-41 sorbent showed the best desulfurization performance for high sulfur jet fuels.     

Inhibition of CoMo/HMS catalyst deactivation in the HDS of 4,6-DMDBT by support modification with phosphate

A series of CoMoS catalysts supported on hexagonal mesoporous silica (HMS) modified with different amounts of phosphate (0.5, 1.0, 1.5 and 2.0 wt.%) were prepared in order to study the influence of phosphate on catalyst deactivation. The catalysts were characterized by a variety of techniques (X-ray fluorescence, N₂ adsorption-desorption at 77 K, FT-IR study of the framework vibration and NO adsorption, NH₃-TPD, H₂-TPR, XPS, ³¹P NMR and TPO/TGA). The sulfided catalysts were tested in the deep hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DMDBT) performed in a fixed-bed flow reactor at 598 K, P = 5.0 MPa and WHSV = 46.4 h⁻¹. The catalyst with the largest phosphate content (2.0 wt.%) showed the best catalytic response linked with its low deactivation during on-stream reaction and a larger sulfidation degree of Co species. It was found that coking behavior is closely related with the location of the active sites in the support structure being a lower coke formation on the catalysts having active phases located within support structure. The catalysts modified with a large amount of phosphorous (1.5 and 2.0 wt.% of P₂O₅) were more susceptible to coking and produced a more polymerized coke than P-free sample, as confirmed by TPO/TGA experiments. The presence of P₂O₅ favours the sulfidation degree of Co species and the creation of medium strength acid sites leading to the enhancement of the 4,6-DMDBT HDS reaction toward the isomerization route.     

Adsorptive removal of tetrahydrothiophene (THT) and tert-butylmercaptan (TBM) using Na-Y and AgNa-Y zeolites for fuel cell applications

Adsorptive removal of tetrahydrothiophene (THT) and tert-butylmercaptan (TBM) that are widely used sulfur odorants in pipeline natural gas was studied using AgNa-Y zeolites at ambient temperature and atmospheric pressure. The AgNa-Y were obtained via Ag⁺-exchange with Na⁺ of Na-Y at various exchange levels, and the contributions of formed adsorption sites (Ag⁺, Na⁺, Ag⁰, H⁺, and Ag₂O) in the THT and TBM adsorption uptake and selectivity were characterized. THT adsorption strength on these sites followed an order of Ag⁺ > Na⁺ ∼ Ag⁰ > H⁺ > Ag₂O. The adsorption strength of THT on Na⁺ sites was sufficiently high, thus an increase in the Ag⁺-exchange level did not lead to a notable increase in the breakthrough THT uptake. Differently, adsorption of TBM on Na⁺ sites was weak, whereas that on Ag⁺ sites was strong. This resulted in a marked increase in the breakthrough TBM uptake with an increase in the Ag⁺-exchange level, showing an order of magnitude higher uptake on AgNa-Y compared with that on Na-Y. Noticeably, the adsorption strength of THT on these adsorption sites was higher than that of TBM. This resulted in an almost 100% adsorption selectivity for THT over TBM, when these two sulfur species coexisted in the feed stream.     

Hydrodesulfurization of hindered dibenzothiophenes on bifunctional NiMo catalysts supported on zeolite–alumina composites

A series of NiMo catalysts supported on HNaY(x)–Al₂O₃ composites with different amounts of HNaY zeolite (x = 0, 5, 10, 20 and 100 wt.% of HNaY) was prepared and tested in the hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4,6-dimethyl-DBT (4,6-DMDBT). The catalysts were characterized by N₂ physisorption, X-ray diffraction (XRD), FT-IR spectroscopy of pyridine and nitrogen oxide adsorption (Py and NO-FT-IR), temperature-programmed reduction (TPR), scanning electron microscopy (SEM-EDX) and high-resolution transmission electron microscopy (HRTEM). It was found that the increase in the zeolite content causes changes in the acidic properties of the catalyst (number of acid sites) as well as in the characteristics of the deposited metallic species (location and dispersion). Different activity trends with the amount of the zeolite were found for the DBT and 4,6-DMDBT hydrodesulfurization on NiMo/HNaY-Al₂O₃ catalysts. As for the HDS of DBT the alumina-supported catalyst presents the highest activity. The incorporation of the zeolite causes an initial drop and then the recovery of activity with zeolite content. In contrast, for the 4,6-DMDBT the HDS activity always increases with zeolite content. These two different catalytic behaviors seem to be due to two opposite effects, which affect the contribution of the reaction routes available for the HDS of each reactant, these effects are: (i) the decrease of MoS₂ dispersion caused by the incorporation of zeolite to the catalyst and (ii) the increase of the proportion of Brönsted acid sites with zeolite content. The reaction product distribution indicates that both types of sites, coordinatively unsaturated sites (CUS) of the MoS₂ and zeolite Brönsted acid sites, participate in the 4,6-DMDBT and DBT transformations.     

The effect of sulfur compound on the hydrogenation of tetralin over a Pd–Pt/HDAY catalyst

A composite metal catalyst with a Pd/Pt of 4:1 and an H-form dealuminated Y zeolite support for the hydrogenation of tetralin was investigated. The materials were characterized by XRD, NH₃-TPD, N₂ adsorption, TPR and FTIR. The activity for the hydrogenation of tetralin was investigated with a high-pressure fixed-bed continuous-flow reactor operating at 4.0 MPa. The thiotolerance was tested with feeds containing 200 ppm sulfur in the form of 4,6-dimethyldibenzothiophene and thiophene, respectively. It was found that thiophene was more effective for deactivating the catalyst than the former one. The diffusion barrier of the pores for the sulfur compound is likely the major reason for the different deactivation rate of catalysts. The products other than decalins were mainly decalin isomers and ring-opened products. Selectivity of cracking products for the feed with thiophene was lower than that for the other feed, while that of ring-opened and ring-contracted products with the two feeds was similar.     

Microbial desulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene in dodecane and straight-run diesel oil

The desulfurization of dibenzothiophene (DBT), 4,6-dimethyldibenzothiophene (4,6-DMDBT) and their mixture by lyophilized cells ofPseudomonas delafieldii R-8 was studied in the presence of dodecane. The desulfurization rate for 4,6-DMDBT was found to be about 40% in comparison with that for DBT. The desulfurization process for DBT and 4,6-DMDBT proceeded simultaneously without preference for either one. The desulfurization rate for each compound was decreased when they were mixed together. The extent of desulfurization of 4,6-DMDBT was increased with the increase of cell concentration and the decrease of the volume ratio of oil-to-water used. The specific desulfurization rate for 4,6-DMDBT could be reached to 10.4 mmol sulfur kg⁻¹ (cell) h⁻¹ [approximately 0.33 mg sulfur g⁻¹ (cell) h⁻¹].Pseudomonas delafieldii R-8 showed high desulfurization capability for straight-run diesel oil (containing 1,807 mg/L of sulfur). About 1,000 mg/L of sulfur in diesel oil was removed by resting cells of this strain in 24 h of reaction. The specific desulfurization rate was 8.75 mmol sulfur kg⁻¹ (cell) h⁻¹.     

High performance sorbents for diesel oil desulfurization

Sorbents with different Ni loading supported on silica–alumina (SiAl) and activated carbon (AC) were synthesized and tested for removal of sulfur compounds from a model diesel oil, containing nearly 250 ppmw S as benzothiophene (BT), dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT). A state-of-art Commercial Ni-based sorbent and two Norit activated carbons were also tested for comparison. Moreover, the influence on sorbents uptake capacity of the presence of aromatics in amounts representative of real diesel oils was studied. Both commercial and home-made materials performed worse in presence of aromatic compounds. Probably, the latter competed with the refractory sulfur compounds (DBT and 4,6-DMDBT) in the adsorption on active sites. As a first important result of the investigation the sorbents carrying 45% and 30% of Ni on SiAl showed a breakthrough uptake capacity of nearly, respectively, 2 and 2.6 times higher than Commercial sorbent as a consequence of their higher Ni dispersion and surface area. Moreover, activated carbons and the sample with 28%Ni on AC showed an even higher breakthrough uptake capacities. In particular, the deposition of nickel on activated carbon is an innovative approach which takes advantage of the selectivity of Ni towards S-species and the high adsorptive capacity of AC support.     

HDS reactivities of dibenzothiophenic compounds in a LC-finer LGO and H2S/NH3 inhibition effect

The hydrodesulfurization (HDS) reactivities and the inhibition effects of H₂S and NH₃ were experimentally investigated for 11 difficult-to-remove sulfur compounds contained in LC-finer light gas oil using a commercial NiMo/Al₂O₃ hydrotreating catalyst. Among these sulfur compounds, 4-MDBT was the most reactive while 4,6-DMDBT was the least reactive. It was found that the presence of methyl groups away from the sulfur atom slightly enhanced the HDS reactivities of the methyl substituted DBTs. The observed low reactivity of 4,6-DMDBT was mainly caused by the steric hindrance of the two methyls at the 4 and 6 positions. Both H₂S and NH₃ significantly inhibited the HDS reaction rates for all 11 sulfur species of interest, while 4,6-DMDBT was one of the most inhibited species. At the same concentration (1.0 vol%), H₂S showed a stronger inhibition effect than NH₃. Measurable catalyst deactivation was observed in the course of the experiment that had a relatively even effect on the HDS of all reactants investigated in this study.     

Deep desulfurization of gasoline using ion-exchange zeolites: Cu(I)- and Ag(I)-beta

Solid adsorbents Cu(I) and Ag(I) metal exchanged beta zeolites were prepared by solid-state ion-exchange (SSIE) method. Crystallographic structure of the prepared adsorbents has been characterized by XRD analysis. The texture of the prepared adsorbents was investigated using N₂ sorption. Pyridine IR measurements have been carried out to investigate the nature of the acid sites of the adsorbents. The deep-desulfurization performance of such adsorbents has been evaluated through fixed-bed adsorption technique with model gasoline containing thiophene and benzothiophene at ambient temperature and pressure. The obtained results revealed that the breakthrough capacities of Cu(I)- and Ag(I)-beta zeolite with the optimized Cu⁺ or Ag⁺ content are 0.239 mmol S/g and 0.237 mmol S/g, respectively. The remaining sulfur in the desulfurized gasoline is less than 1 ppmw. Their desulfurization capacity for actual FCC gasoline blend is reduced about 30% due to the competitive adsorption from olefins and aromatics. However, The capacity regeneration of Cu(I)- and Ag(I)-beta zeolite sorbents was carried out for 9 times. It is more than 95% recovery of desulfurization after the first regeneration, and it keeps little reduction after subsequent 8 times of regeneration. Such studies included the effect factors on desulfurization performance, such as metal exchange content, SiO₂/Al₂O₃ ratio, acidity, and other texture properties of the zeolite etc.     

Effects of olefin on adsorptive desulfurization of gasoline over Ce(IV)Y zeolites

Effects of olefin on adsorptive deep desulfurization of gasoline over Ce(IV)Y zeolites have been studied via a FT-IR spectrometry and a fixed-bed adsorption technique at room temperature and atmosphere pressure by using model fuels containing thiophene and 1-octene as model compounds. The adsorptive selectivity for thiophene decreases significantly as the concentration of 1-octene increases. The difference in the FT-IR spectra between the Ce(IV)Y zeolite samples adsorbing the model fuels with and without 1-octene can be attributed to the stronger adsorption interactions of 1-octene with the Ce(IV)Y zeolite than those for thiophene. For minor content (500 µg/g) of thiophene and 1-octene, the FT-IR spectra show that the Ce(IV)Y zeolites have the preference to adsorb thiophene rather than 1-octene. However with the content of 1-octene increasing in the model fuel up to 150 mg/g, 1-octene can be adsorbed on the Ce(IV)Y zeolites remarkably, resulting in a descending adsorptive selectivity of the Ce(IV)Y for removing thiophene from the model fuel.     

Adsorption of thiophene and toluene on NaY zeolites exchanged with Ag(I), Ni(II) and Zn(II)

The present study evaluates the adsorption capacity of thiophene and toluene and their competitive behaviour on zeolite NaY exchanged with transition metals (5 wt% Ni, Zn and Ag). The headspace chromatography technique was used to obtain monocomponent apparent adsorption isotherms of thiophene and toluene with NaY, NiY, ZnY and AgY using isooctane as an inert solvent at 30 and 60 °C. Selectivity between toluene and thiophene at saturation capacities were also measured at 30 °C. The adsorption capacity for thiophene increased for the studied adsorbents as follows: NaY < ZnY < NiY < AgY at 30 °C and NaY < NiY < ZnY < AgY at 60 °C. Toluene is less adsorbed, but within the same order of magnitude as thiophene and following the same sorbent order. All adsorbents were moderately selectivity for toluene. Nevertheless, the sulfur content was successfully reduced in the presence of aromatics and olefins in immersion tests with a model fuel mixture. These results show the importance of inserting transitions metals in the zeolitic structure to enhance the adsorption of both aromatic and sulfur containing compounds in organic liquid mixtures, which shows promise to meet environmental standards in transportation fuels.     

Textural and chemical factors affecting adsorption capacity of activated carbon in highly efficient desulfurization of diesel fuel

Two synthetic, polymer-derived carbons, and two commercial carbons were investigated as adsorbents of dibenzothiophene and 4,6-dimethyldibenzothiophene from simulated diesel fuel in dynamic conditions. The total concentration of sulfur was 20 ppm. The surface features of the carbons were evaluated using adsorption of nitrogen, potentiometric titration, Boehm titration, thermal analysis and FTIR. The polymer-derived carbons outperformed the commercial micro- and micro/mesoporous carbons from the point of view of adsorption capacity and selectivity. The latter was evaluated based on the adsorption of naphthalene, which was also present in the fuel used. It was found that the presence of arenes did not affect significantly the capacity measured. The results suggest that the amount adsorbed is mainly governed by the volume of micropores, where dispersive interactions are predominant. Acidic groups located in larger pores are also important to attract additional molecules DBT and 4,6-DMDBT via specific interactions with the progress of adsorption. These groups may also contribute to the reactive adsorption leading to oxidation of DBT and 4,6-DMDBT.     

Removal of dibenzothiophenes in kerosene by adsorption on rice husk activated carbon

The capacity of rice husk activated carbon (RHAC) to adsorb refractory sulfur compounds of dibenzothiophenes (DBTs) from commercial kerosene was evaluated in terms of their textural and chemical characteristics. Rice husk activated at 850 °C for 1 h showed an acceptable adsorption capacity for DBTs, despite a much lower specific surface area (473 m²/g) and total pore volume (0.267 cm³/g), when compared to micro-porous activated carbon fiber with a large specific surface area (2336 m²/g) and total pore volume (1.052 cm³/g). The volumes of ultramicropores acting as DBTs adsorption sites, and of mesopores leading DBTs into the ultramicropores were closely related to the DBTs adsorption capacity of the RHACs.     

Efficient oxidative desulfurization (ODS) of model fuel with H2O2 catalyzed by MoO3/γ-Al2O3 under mild and solvent free conditions

An efficient process to remove organic sulfur compounds from model fuel has been explored. Dibenzothiophene (DBT) and 4, 6-dimethyldibenzothiophene (4, 6-DMDBT) can be completely oxidized into their corresponding sulfones by H₂O₂ over 14 wt.% MoO₃/γ-Al₂O₃ catalyst under mild conditions in 15 min. The effects of solvent, initial sulfide concentration, loading of MoO₃ and amount of catalyst on oxidative removal of DBT were studied. The employments of solvents have decreased the reaction rate of DBT, which can be attributed to the competitive adsorption between the sulfide and solvent. The oxidative reactivity increases in the order of thiophene (Th) < benzothiophene (BT) < DBT < 4, 6-DMDBT. The catalyst can be regenerated by methanol washing at 333 K.     

Synthesis, characterization, and hydrotreating activity of carbon-supported transition metal phosphides

A series of nickel, molybdenum, and tungsten metal phosphides deposited on a carbon black support (Ni₂P/C, MoP/C, and WP/C) were synthesized by means of temperature-programmed reduction. The samples were characterized by BET surface area, CO uptake, X-ray diffraction (XRD), elemental analysis, and extended X-ray absorption fine structure (EXAFS) measurements. The activity of these catalysts was measured at 613 K and 3.1 MPa in a three-phase, packed-bed reactor for hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) with a model liquid feed containing 500 ppm sulfur as 4,6-dimethyldibenzothiophene (4,6-DMDBT), 3000 ppm sulfur as dimethyl disulfide, and 200 ppm nitrogen as quinoline. The Ni₂P/C catalyst was found to exhibit the best hydroprocessing performance based on equal CO chemisorption sites (70 μmol) loaded in the reactor. An optimum Ni loading for HDS and HDN activity was found as 1.656 mmol g⁻¹ (11.0 wt.% Ni₂P) which gave an HDS conversion of 99% and an HDN conversion of 100% at a molar space velocity of 0.88 h⁻¹. These were much higher than those of a commercial Ni-Mo-S/γ-Al₂O₃ catalyst which gave an HDS conversion of 68% and an HDN conversion of 94%, and a previously reported best Ni₂P/SiO₂ catalyst which gave an HDS conversion of 76% and an HDN conversion of 92%. The use of carbon instead of silica as a support gave rise to other differences, which included smaller particle size, higher CO uptake, lessened retention of P on the support, and reduced sulfur deposition. The stability of the 11.0 wt.% Ni₂P/C catalyst was also excellent with no deactivation observed over 110 h of time on stream. The activity and stability of the Ni₂P/C catalyst were affected by the phosphorous content, both reaching a maximum with an initial Ni/P ratio of 1/2. EXAFS and elemental analysis of the spent samples indicated the formation of a surface phosphosulfide phase on the Ni₂P, which was beneficial for hydrotreating activity, while the bulk structure of the phosphides was maintained during the course of reaction as revealed from the XRD patterns.     

Thermodynamics,kinetics, and isotherms studies for gold(III) adsorption using silica functionalized by diethylenetriaminemethylenephosphonic acid

A novel hybrid material silica gel chemically modified by diethylenetriaminemethylenephosphonic acid GH-D-P has been developed and characterized. The results of the adsorption thermodynamics and kinetics of the as-synthesized GH-D-P for Au(III) showed that this high efficient inorganic–organic hybrid adsorbent had good adsorption capacity for Au(III), and the best interpretation for the experimental data was given by the Langmuir isotherm equation, the maximum adsorption capacity for Au(III) is 357.14 mg/g at 35 °C. Moreover, the study indicated the adsorption kinetics of GH-D-P could be modeled by the pseudo-second-order rate equation wonderfully, and the adsorption thermodynamic parameters ΔG, ΔH and ΔS were −20.43 kJ mol⁻¹, 9.17 kJ mol⁻¹, and 96.24 J K⁻¹ mol⁻¹, respectively. Therefore, the high adsorption capacity make this hybrid material have significant potential for Au(III) uptake from aqueous solutions using adsorption method.     

高分散纳米Y型分子筛负载Ni_2P催化剂的制备及其加氢脱硫性能

以无模板剂法合成的纳米Y型分子筛(35 nm左右)为载体,采用低温还原法制备了高分散Ni_2P/NY催化剂,同时制备了普通Y型分子筛担载的Ni_2P/Y催化剂作为对比。采用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)和X射线光电子能谱(XPS)等手段对载体和催化剂进行了表征,并在固定床反应器中考察了不同催化剂对4,6-二甲基二苯并噻吩(4,6-DMDBT)的加氢脱硫反应性能。结果表明,该催化剂的高活性来自纳米Y型分子筛上Ni_2P分散度的提高和高活性中心的暴露。在反应温度为340℃,反应压力为3.0 MPa的条件下,以Ni_2P/NY为催化剂,4,6-DMDBT的转化率达到了96.0%,高于CoMoS/Al_2O_3商业催化剂(77.2%)和Ni_2P/Y催化剂(67.0%)。     

Chitosan membranes filled by GPTMS-modified zeolite beta particles with low methanol permeability for DMFC

Uniform zeolite beta particles about 800 nm in diameter were synthesized by a hydrothermal method, and functionalized by γ-glycidoxypropyltrimethoxysilane (GPTMS). Subsequently, chitosan (CS) membranes filled by GPTMS-modified zeolite beta particles were prepared, and characterized by SEM, FT-IR, XRD and TGA. Compared with the pure CS and Nafion^®117 membrane, these CS/zeolite beta hybrid membranes show apparently the lower methanol permeability, which could be assigned to the better interfacial morphology and compatibility between the GPTMS-modified zeolite beta particles and chitosan matrix. In all the prepared CS/zeolite beta hybrid membranes, the CS membrane filled by 10 wt.% GPTMS-modified zeolite beta particles exhibits the lowest methanol permeability, which is 4.4 × 10⁻⁷ and 2.2 × 10⁻⁷ cm² s⁻¹ at 2 and 12 M methanol concentration, respectively. The proton conductivity of this hybrid membrane is 1.31 × 10⁻² S cm⁻¹, which is slightly lower than that of the pure CS membrane. The selectivity of CS/GPTMS-zeolite beta membranes is comparable with Nafion^® 117 at 2 M methanol concentration, and much higher at 12 M methanol concentration.