Kinetic and Statistical Studies of Adsorptive Desulfurization of Diesel Fuel on Commercial Activated Carbons

Diesel fuel desulfurization by different commercial activated carbons was studied in a batch adsorber. Experiments, carried out to determine the sulfur adsorption dependency on time, were used to perform kinetic characterization and to screen the best performing activated carbon. The equilibrium characterization of the adsorption process was also performed. The statistical study of the process was undertaken by way of a two‐level one‐half fractional factorial experimental design with five process parameters. Individual parameters and their interaction effects on sulfur adsorption were determined and a statistical model of the process was developed. Chemviron Carbon SOLCARBTM C3 was found to be the most efficient adsorbent. The kinetic pseudo‐second order model and Freundlich isotherm are shown to exhibit the best fits of experimental data. The lowest achieved sulfur concentration in treated diesel fuel was 9.1 mg kg^–1.     

Preparation and Application of Perovskite Catalysts for Diesel Soot Emissions Control: An Overview

The diesel engines are energy efficient (1), but their particulate matter (soot) emissions are still a matter of concern even though major advances in their control are being made. For soot abatement, catalytic diesel particulate filter (DPF) technique is widely employed to trap and burn the soot. Many types of catalysts have been investigated for the soot combustion i.e. platinum group metal (PGM) based, perovskite-type oxides, spinel-type oxides, rare earth metal oxides, and mixed transient metal oxides etc. The cost of PGM catalysts is high and their availability is questionable. Further they are susceptible to poisoning and have low thermal stability. On the other hand perovskite catalysts show potential as effective soot oxidation catalyst for the DPF because of their low cost, high thermal stability and tailoring flexibility. Many papers related to soot oxidation over perovskite catalysts have been published but no review paper appears in the literature that is dedicated to soot oxidation. Thus, this article provides a summary of published information regarding pure and substituted perovskite catalyst, preparation methods, properties, and their application for diesel soot emission control.     

Epoxidation Processes by Pyridoxal Dioxomolybdenum(VI) (Pre)Catalysts Without Organic Solvent

Molybdenum(VI) pyridoxal thiosemicarbazonato complexes have proved to be efficient catalysts in the olefinic epoxidation of cyclooctene by aqueous TBHP in the absence of an organic solvent. High activity and selectivity have been obtained with a catalyst loading of just 0.05% molybdenum in the case of one mononuclear (pre)catalyst (TOF 3360 h⁻¹) under solvent‐free conditions. The influence of methanol on the activity and selectivity has been studied.     

Simple and efficient method for the oxidation of sulfides to sulfones using hydrogen peroxide and a Mo(VI) based catalyst

A simple and efficient method for the oxidation of sulfides to sulfones at room temperature using ammonium heptamolybdate and 30% H₂O₂ is developed. The reactions provide excellent yields within short time, also sensitive functional groups such as allyl, vinyl, propargyl, alcohol, ketone, ester, pyridine and nitrile are found to be tolerated.     

Polycyclic Aromatic Sulfur Heterocycles in Desulfurized Diesel Fuels and Their Separation on a Novel Palladium(II)-Complex Stationary Phase

The lowering of the legal concentration of sulfur in fuels (in the European Union from 150 ppm at present to 50 ppm in 2004) not only affects the concentration but also the pattern of the polycyclic aromatic sulfur heterocycles (PASH) in the fuels. This pattern was studied for 12 diesel samples, most of which have been desulfurized. A separation of the PASHs and the polycyclic aromatic hydrocarbons becomes necessary at such sulfur levels. An efficient liquid chromatographic method for this is presented and involves a Pd(II)-containing complex based on 2-amino-1-cyclopentene-1-dithiocarboxylate covalently bonded to silica. The resultant PASH fraction can be analyzed by gas chromatography/flameionization detection.     

Direct extraction of Mo(VI) from sulfate solution by synergistic extractants in the rotation column

Direct extraction of molybdenum from sulfate solution with synergistic extractants (mixture of D₂EHPA and TBP) was studied in the rotation column. The influence of extractant concentration and initial pH of aqueous phase was studied in the bench scale experiments. The outcomes demonstrated that the synergistic solvent extraction enhances the constancy of the extracted complexes for transfer into the organic phase. In the continuous experiments, the effect of different operating parameters such as speed of agitation, inlet solvent flow rate and inlet aqueous flow rate on the holdup, mean drop size, drop size distribution, slip and characteristic velocities and extraction percentage were examined. Modified correlations were proposed for prediction of hydrodynamic parameters with consideration of reaction extraction condition in the rotation column. Furthermore, these correlations were compared with the experimental data. According to the results, the direct extraction of Mo (VI) from aqueous solution and sulfuric media with extraction efficiency of 90.4% was obtained at higher rotor speed (240 r·min^-1 rpm) in this column.     

脱硫催化剂(四羧基酞菁铝键合MCM-41)的制备及催化活性研究

为了降低油品中的含硫化合物,合成了四羧基酞菁铝,然后将其键合在MCM-41的表面,通过红外光谱进行了表征,最后以四羧基酞菁铝键合MCM-41作为脱硫催化剂,测定了它去除乙硫醇的催化活性。结果表面:脱硫催化剂(四羧基酞菁铝键合MCM-41)对乙硫醇的去除率可以达到97.8%,而且反应速率快,持续时间长,具有良好的催化活性。     

Application of Magnetic Resonance Imaging (MRI) to Determine the Influence of Fluid Dynamics on Desulfurization in Bench Scale Reactors

The influence of fluid dynamics on the hydrodesulfurization (HDS) reactions of a diesel oil in bench‐scale reactors was evaluated. The porosities and liquid saturations of catalyst beds were quantified by using the MRI technique. The gas‐liquid systems used in the experiments were nitrogen diesel and hydrogen diesel. An apparatus was especially constructed, allowing in situ measurements of gas and liquid distributions in packed beds at elevated pressure and temperature up to 20 bar and 200 °C, respectively. The reactor itself had a length of 500 mm and an internal diameter of 19 mm. The packed beds used in this MRI study consisted of: (1) 2 mm diameter nonporous spherical glass beads and (2) 1.3 mm diameter porous Al₂O₃ trilobes having the same size as the original trilobe catalyst used in HDS bench‐scale experiments. The superficial gas and liquid velocities were set within the range of trickle flow, e.g., u_0G = 20–500 mm/s and u_0L = 0.1–6 mm/s. In parallel with the MRI experiments, the hydrodesulfurization of a gas oil was investigated in a bench‐scale plant. Its reactor had the same dimensions of the trickle‐bed column used in the MRI experiments and was filled with original trilobe catalyst. These catalytic experiments were carried out at a wide range of operating conditions (p = 30–80 bar, T = 300–380 °C, LHSV = 1–4 h^–1). The results of both fluid dynamic and catalytic reaction experiments were then combined for developing a simulation model to predict the HDS performance by accounting for fluid dynamic nonidealities.     

催化气化(一步法)煤制天然气催化剂研究进展

概述了煤制天然气工艺的研究现状,综述了煤-水蒸气催化气化制天然气(一步法煤制天然气)催化剂的最新研究进展,包括催化剂的分类、不同催化剂对煤催化气化碳转化率及产品气体组成的影响、各类催化剂在活性经济性等方面的优缺点等,并分析了导致催化剂失活的原因以及回收的方法。指出了一步法煤制天然气催化剂的研究方向。     

Destruction of trichloroethylene (TCE) and trichloromethane (TCM) in the presence of selected VOCs over Pt-Pd-based catalyst

Catalytic oxidation of trichloroethylene (TCE) and trichloromethane (TCM) oxidized alone and in two-component mixtures with selected volatile organic compounds (VOCs) such as toluene, n-hexane, ethanol or acetone was investigated over a Pt-Pd-based catalyst on a monolithic, metallic, γ-Al₂O₃-washcoated support. TCE and TCM were more difficult to oxidize than VOCs and temperatures of their 50% conversion (T_50%) amouted to 420 and 330 °C, respectively. All the VOCs added were found to enhance the conversion of the two chlorinated compounds, drecreasing T_50% by 20 °C, at the most, for TCM in the presence of toluene and by 50 °C for TCE in the presence of acetone. Both the chlorinated compounds lowered the conversion of the VOCs added (except that of toluene), and this lowering was particularly distinct with n-heptane; they also raised the concentration of acetaldehyde formed during the oxidation of oxyderivative compounds.     

Effect of carbon black composite (CBC) support properties on hydrodesulfurization performance of sulfided Mo and Co, and carburized Mo, catalysts

Carbon black composites (CBCs) have been prepared by pyrolyzing mixture of a carbon black with polyfurfuryl alcohol and then pretreated by oxidation with nitric acid, gasification with water steam or ammoxidation. The effects of the chemical character of the carrier surface, nature of the active metal phase and pH value of the impregnation solution on the catalytic activity towards the hydrodesulfurization (HDS) of thiophene of the CBC supported Mo (Co) catalysts were determined. It was stated that the catalytic properties of the CBC supported sulfides of Mo or Co and of Mo carbides are affected by the chemical character of the carrier surface. Generally, catalysts supported over basic surface CBC exhibit higher activity than those ones supported over CBC possessing acidic surface character. Co catalysts supported on acidic surface show lower activity (per mol of active metal) than Mo based ones supported on the same carrier. In the case of catalysts supported on basic CBC, Co exhibits distinctly higher activity than Mo. At the experimental conditions adopted for this study, CBC surface properties, active phase nature, and catalyst impregnation pH were found to exert a relatively small influence on both HDS and hydrogenation activities.     

Opportunity to recycle chromium(VI) by in situ electro‐oxidation

BACKGROUND: Chemical oxidation is generally used to oxidise Cr(III) to Cr(VI) in aqueous effluents, but this leads to Cr(VI) solutions that are contaminated with oxidising agents, which reduces their recycle and reuse value. RESULTS: We now report an electrolytic method for the in situ oxidation of Cr(III). Complete oxidation of Cr(III) occurs anodically using an initial pH of 5.0 and a current of 3.0 A. CONCLUSIONS: Anodic oxidation is shown to achieve in situ oxidation of Cr(III) to Cr(VI) to permit the regeneration of Cr(VI) solutions for recycle in oxidising industrial processes. Copyright © 2008 Society of Chemical Industry     

Synthesis, Characterization and Catalytic Properties of Coordination Complexes Based on [Mo(CO)3(CH3CN)3] and Poly(4-vinylpyridine)

The synthesis, characterization, and catalytic properties of the zero-valent, group six metal complex formed by the reaction of [Mo(CO)₃(CH₃CN)₃] and poly(4-vinylpyridine) (P(4-VP)) is described in this work. The pyridyl groups of the organic polymer are covalently bonded to the Mo centers as suggested by X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and Fourier transform infrared (FT-IR) techniques. The polymer-immobilized metal catalyst was also characterized by DTA–TGA, differential scanning calorimetry (DSC) analysis and its morphology and elemental analyses were studied by scanning electron microscopy/energy dispersive X-ray (SEM/EDX) techniques. In the presence of 2-ethoxyethanol the solid is an active catalyst for the heterogeneous hydrogenation of styrene to ethyl benzene.     

Dehydrodimerization of Isobutene to 2,5‐Dimethyl‐1,5‐Hexadiene over Bismuth‐(III)‐Oxide and Various Additives

Bi₂O₃ and mixtures with different additives (Cr₂O₃, MoO₃, NH₄VO₃, SnO₂, and V₂O₅) have been chosen to study the oxidative dehydrodimerization of isobutene. The catalytic performances were investigated by variation of the residence time, isobutene to oxygen molar ratio, and pressure. The best results for 2,5‐dimethyl‐1,5‐hexadiene (DMH) yield (13 %) were achieved with Bi₂O₃ as the catalyst. The selectivity of DMH reaches values of over 90 %.     

聚丙烯酸高级醇酯的合成及对柴油的降凝作用

采用溶液聚合法合成了聚丙烯酸高级醇酯类降凝剂。对聚合条件进行了研究。同时对单一聚丙烯酸酯和混合聚丙烯酸酯对0＃和10＃柴油的降凝作用进行了研究。     

Identification of Vegetable Oil or Biodiesel Added to Diesel Using Fluorescence Spectroscopy and Principal Component Analysis

In order to identify possible adulteration of onroad diesel with vegetable oil, fluorescence spectroscopy was used as the analytical technique to differentiate between vegetable oil and biodiesel in diesel blends. Diesel/oil and diesel/biodiesel blends made with different proportions of soy, canola or waste cooking oil were analyzed. The reduced cost of analysis using fluorescence spectroscopy together with the reliability of the results suggest that this technique could be of great use in differentiating between diesel, biodiesel and vegetable oil and could therefore be used for rapid identification or confirmation of adulterated diesel. Furthermore, a compact fluorescence spectrophotometer with an LED excitation source could be used in gas stations or fuel distributors for diesel quality control because of its practicality, low cost and reliability.     

Diesel and rapeseed methyl ester (RME) pilot fuels for hydrogen and natural gas dual-fuel combustion in compression-ignition engines

This paper presents experimental results of rapeseed methyl ester (RME) and diesel fuel used separately as pilot fuels for dual-fuel compression-ignition (CI) engine operation with hydrogen gas and natural gas (the two gaseous fuels are tested separately). During hydrogen dual-fuel operation with both pilot fuels, thermal efficiencies are generally maintained. Hydrogen dual-fuel CI engine operation with both pilot fuels increases NO_x emissions, while smoke, unburnt HC and CO levels remain relatively unchanged compared with normal CI engine operation. During hydrogen dual-fuel operation with both pilot fuels, high flame propagation speeds in addition to slightly increased ignition delay result in higher pressure-rise rates, increased emissions of NO_x and peak pressure values compared with normal CI engine operation. During natural gas dual-fuel operation with both pilot fuels, comparatively higher unburnt HC and CO emissions are recorded compared with normal CI engine operation at low and intermediate engine loads which are due to lower combustion efficiencies and correspond to lower thermal efficiencies. This could be due to the pilot fuel failing to ignite the natural gas-air charge on a significant scale. During dual-fuel operation with both gaseous fuels, an increased overall hydrogen-carbon ratio lowers CO₂ emissions compared with normal engine operation. Power output (in terms of brake mean effective pressure, BMEP) as well as maximum engine speed achieved are also limited. This results from a reduced gaseous fuel induction capability in the intake manifold, in addition to engine stability issues (i.e. abnormal combustion). During all engine operating modes, diesel pilot fuel and RME pilot fuel performed closely in terms of exhaust emissions. Overall, CI engines can operate in the dual-fuel mode reasonably successfully with minimal modifications. However, increased NO_x emissions (with hydrogen use) and incomplete combustion at low and intermediate loads (with natural gas use) are concerns; while port gaseous fuel induction limits power output at high speeds.     

Anodic behaviour of arsenopyrite and cathodic reduction of ferrate(VI) and oxygen in alkaline solutions

This paper presents the results of an electrochemical study of the anodic characteristics of arsenopyrite in strongly alkaline solutions and of the cathodic reduction of ferrate(VI) and of dissolved oxygen at an arsenopyrite surface at potentials which are relevant to the oxidation reactions. Cyclic voltammetry at both arsenopyrite disc and arsenopyrite disc/platinum ring electrodes has shown that arsenic(III) is the main product of the anodic process at potentials in the region of the rest potential during oxidation by either ferrate(VI) or oxygen. Evidence for partial passivation of both the anodic and cathodic reactions has been obtained from potentiostatic current–time transients. The initial stage of oxidation by ferrate(VI) has been shown to be mass-transport controlled and this is also true of the oxidation by oxygen in dilute solutions of sodium hydroxide.     

Molybdenum(VI) Amino Triphenolate Complexes as Catalysts for Sulfoxidation,Epoxidation and Haloperoxidation

Two molybdenum(VI) complexes bearing a C₃ symmetrical amino tris‐tert‐butylphenolate ligand have proved to be air‐ and water‐tolerant catalysts that efficiently catalyse, in high yields and selectivity, the oxidation of sulfides, olefins and halides. In particular high turnover frequencies and turnover numbers (TOF and TON) have been obtained for the cyclooctene epoxidation (catalyst loading down to 0.05%, TONs up to 88,000 and TOFs up to 7500 h⁻¹).