Evaluation of the performance of catalytic oxidation of VOCs by a mixed oxide at a semi‐pilot scale†

Volatile organic compounds (VOCs) are one of the main contributors to air pollution. To reduce anthropogenic emissions, it is necessary to improve existing techniques such as catalytic oxidation through the development of new cost‐effective catalysts. Although many studies deal with the development and testing of new materials, most are performed at laboratory scale, of which only a few study mixtures of VOCs. To assess their viability for industrial applications, further tests are required, namely, mixture tests at intermediate scale in relevant environment and extrapolated on an industrial scale. In this work, the catalytic performance of a new mixed oxide Co‐Al‐Ce was investigated towards the oxidation of the n‐butanol and toluene on a semi‐pilot scale (TRL 4). Single component and mixture experiments were performed for several concentrations at a fixed flow rate. A commercial catalyst Pd/γ‐Al₂O₃ was used as the benchmark to evaluate the performance of the mixed oxide. The Co‐Al‐Ce catalyst enables complete oxidation of n‐butanol at the same temperature as the reference catalyst. Moreover, it provides a better selectivity for n‐butanol, while providing an equivalent one for the oxidation of toluene. In mixtures, the presence of n‐butanol promotes the oxidation of toluene for both catalysts but more significantly for the Co‐Al‐Ce catalyst. The presence of toluene inhibits the oxidation of n‐butanol for the Co‐Al‐Ce and promotes it for high conversions of n‐butanol for the Pd/γ‐Al₂O₃ catalyst.     

Design of novel Pt-structured catalyst on anodic aluminum support for VOC’s catalytic combustion

Emission control of volatile organic compounds (VOCs) is one of the priorities for environmental catalysis. Catalytic combustion is one of promising technologies for elimination of VOCs. A novel platinum-structured catalyst was designed and is presented in this work. Aluminum was used as support for the catalyst after anodic oxidation treatment and in a shifted arrangement bent, short channels are applied in the design of the structured catalyst. The simulation results show that the novel design of the structured catalyst brings in the higher catalytic activity, compared with the traditional structured catalyst which has long, straight channels. Lastly, the novel structured catalyst was manufactured and its catalytic activity was evaluated with the catalytic combustion of VOC. The results show that the conversion obtained from the reactor with the structured catalyst is almost identical to that obtained from the tube reactor packed with the plate catalyst in which the reaction rate is controlled by surface reactions. Hence, it can be concluded that the mass transfer can be improved by the novel design of the structured catalyst and that the mass transfer in gas phase is not the rate-determining step for the catalytic combustion of VOC.     

Influence of citric acid on the hydration of Portland cement

Citric acid can be used to retard the hydration of cement. Experiments were carried out to investigate the influence of citric acid on the composition of solid and liquid phases during cement hydration. Analyses of the solid phases showed that dissolution of alite and aluminate slowed down while analyses of the pore solution showed that citric acid was removed almost completely from the pore solution within the first hours of hydration. The complexation of the ions by citrate was weak, which could also be confirmed by thermodynamic calculations. Only 2% of the dissolved Ca and 0.001% of the dissolved K formed complexes with citrate during the first hours. Thus, citric acid retards cement hydration not by complex formation, but by slowing down the dissolution of the clinker grains. Thermodynamic calculations did not indicate precipitation of a crystalline citrate species. Thus, it is suggested that citrate sorbed onto the clinker surface and formed a protective layer around the clinker grains retarding their dissolution.     

Influence of sulfate solution concentration on the formation of gypsum in sulfate resistance test specimen

The sulfate concentration, which is required to form gypsum from portlandite, was derived from thermodynamical calculations and experimental measurements. The obtained results were compared to the sulfate concentrations in laboratory solutions that are commonly used to test the performance of concrete exposed to sulfate attack and also to sulfate concentrations that can be expected under field conditions. It was derived that the formation of gypsum can strongly affect the performance of binders in the tests, but has a less marked impact under most field conditions. An SEM investigation of mortar bars that were exposed to different sulfate concentrations supports the suggestion made.     

Kinetic and catalytic performance of a BI‐porous composite material in catalytic cracking and isomerisation reactions

Catalytic behaviour of pure zeolite ZSM‐5 and a bi‐porous composite material (BCM) were investigated in transformation of m‐xylene, while zeolite HY and the bi‐porous composite were used in the cracking of 1,3,5‐triisopropylbenzene (TIPB). The micro/mesoporous material was used to understand the effect of the presence of mesopores on these reactions. Various characterisation techniques, that is, XRD, SEM, TGA, FT‐IR and nitrogen sorption measurements were applied for complete characterisation of the catalysts. Catalytic tests using CREC riser simulator showed that the micro/mesoporous composite catalyst exhibited higher catalytic activity as compared with the conventional microporous ZSM‐5 and HY zeolite for transformation of m‐xylene and for the catalytic cracking of TIPB, respectively. The outstanding catalytic reactivity of m‐xylene and TIPB molecules were mainly attributed to the easier access of active sites provided by the mesopores. Apparent activation energies for the disappearance of m‐xylene and TIPB over all catalysts were found to decrease in the order: E_BCM > E_ZSM‐5 and E_BCM > E_HY, respectively. © 2012 Canadian Society for Chemical Engineering     

Solution properties of solids in the ettringite—thaumasite solid solution series

The thaumasite form of sulfate attack (TSA) has received considerable research attention since its discovery in several motorway bridge foundations in the UK in 1998. Its significance as a deterioration mechanism in concrete, leading to the fluidisation of the matrix in extreme cases, is now acknowledged. Despite the continuing uncertainties that exist with regard to mechanisms for thaumasite formation, there is now reasonable agreement on conditions that favour TSA, and, as with all deleterious reactions affecting concrete structures, there is a desire to be able to anticipate the likelihood of occurrence so that such problems can be ‘designed out’ in the formulation stage. Inevitably, this points to the development of suitable models and the generation of reliable data. It is towards this latter goal that this paper is focused. Building on our previous studies, which reported on the means of fixing intermediate compositions in the ettringite-thaumasite solid solution series, this paper describes the treatment of solubility data, which can be utilised in phase development and solubility models involving this system.     

Influence of the exchanged cation in Pd/BEA and Pd/FAU zeolites for catalytic oxidation of VOCs

0.5 wt% palladium supported on exchanged BEA and FAU zeolites were prepared, characterized and tested in the total oxidation of volatile organic compounds (VOCs). The BEA and FAU zeolites were exchanged with different cations to study the influence of alkali metal cations (Na⁺, Cs⁺) and H⁺ in Pd-based catalysts on propene and toluene total oxidation. The exchange with different cations (Na⁺, Cs⁺) and H⁺ led to a decrease of the surface area and the micropore volume. All Pd/BEA and Pd/FAU zeolites were found to be powerful catalysts for the total oxidation of VOCs. They were active at low temperature and totally selective for CO₂ and H₂O. However, their activity depends significantly on the type of zeolite and on the nature of the charge-compensating cation. The activity order for propene and toluene oxidation on FAU catalysts, Pd/CsFAU > Pd/NaFAU > Pd/HFAU, is the reverse of the activity order on BEA catalysts: Pd/HBEA > Pd/NaBEA > Pd/CsBEA. The catalytic activities can be rationalized in terms of the influence of the electronegativity of the charge-compensating cation on the Pd particles, the Pd dispersion, the PdO reducibility and the adsorption energies for VOCs.     

掺垃圾焚烧飞灰烧制的水泥熟料对水泥性能影响的试验研究

研究了城市生活垃圾焚烧飞灰的性质以及其用于水泥生料配料对水泥力学性能、工作性能和水泥制品环境安全性的影响,探讨了水泥工业协同处置城市生活垃圾焚烧炉渣的技术及其可行性。研究结果表明：掺烧飞灰的熟料的安定性、标准稠度用水量、凝结时间、抗折强度都和基准样相差不大,但是3d和28d抗压强度略微下降;由于掺入飞灰后生料的易烧性得到改善,因此可以稍微调高KH值来抵消强度下降;飞灰掺量为4．62％时,烧制的水泥熟料其制品的重金属极限溶出能够达到Ⅲ类地表水标准,重金属的长期浸渍溶出主要集中在早期,0—3d、3～7d龄期重金属浸渍液能够达到Ⅲ类地表水标准;7—28d、28～60d龄期重金属浸渍液能够达到Ⅱ类地表水标准。     

Model for a solid‐liquid airlift two‐phase partitioning bioscrubber for the treatment of BTEX

BACKGROUND: Airlift solid–liquid two‐phase partitioning bioreactors (SL‐TPPBs) have been shown to be effective for the treatment of gas streams containing benzene, toluene, ethylbenzene and o‐xylene (BTEX). The airlift SL‐TPPB is a low‐energy system that utilizes a sequestering phase of solid silicone rubber beads (10%v/v) that will uptake and release large amounts of BTEX in order to maintain equilibrium conditions within the system. This increases mass transfer from the gas phase during dynamic loading periods and improves degradation performance. This study discusses the development and analysis of a steady‐state, tanks‐in‐series mathematical model, arising from mass balances on BTEX and oxygen in the gas, aqueous and polymer phases to predict the performance of the airlift SL‐TPPB over various gas flow rates and BTEX loadings. RESULTS: An estimability analysis on model parameters determined that the parameters to which model output is most sensitive are those that affect biological activity, which were targeted for estimation. The developed tanks‐in‐series model was able to predict the removal of BTEX components and dissolved oxygen concentrations over various inlet loadings (20, 60 and 100 mg L^?1 h^?1) and gas flow rates (2,3 and 4 L min^?1) that resulted in a range of system performance from effective BTEX treatment to oxygen limiting conditions. CONCLUSIONS: The model developed, with estimated parameters, provides a valuable tool to determine operating conditions that will result in favourable performance of the airlift SL‐TPPB. Copyright © 2009 Society of Chemical Industry     

An investigation of the catalytic abatement of emissions from the combustion of diesel/bioethanol blends

In this study, we investigated the activity of pre-sulfated 1%Pt–2%Sn/γ–Al₂O₃ on the catalytic abatement of the combustion emissions of three fuels: pure diesel E(0), pure bioethanol E(100) and bioethanol blended diesel containing 10% bioethanol E(10). The emissions generated, by each blend combustion, were conducted continuously to the catalyst sample. The catalytic activity was determined by following the evolution of the outflow emissions concentrations by FTIR gas spectroscopy as a function of the catalyst temperature. Results showed that the addition of bioethanol to diesel may be necessary to enhance the catalytic oxidation of diesel unburned hydrocarbons and particulate matter on pre-sulfated 1%Pt–2%Sn/γ–Al₂O₃.     

The kinetics of ettringite formation and dilatation in a blended cement with β-hemihydrate and anhydrite as calcium sulfate

The phase formation, heat of hydration and dilatation in a blended cement consisting of 50 wt.% calcium aluminate cement, 25 wt.% Portland cement and 25 wt.% calcium sulfate were studied (w/c=1). The calcium sulfate was β-hemihydrate, anhydrite and mixes of the two. Kinetic expressions describing the ettringite formation in the pastes with the pure calcium sulfates were found. Hydration reactions were suggested and the phase development was compared to the hydration heat by mass and heat balances. When the calcium sulfate was 75 and 50 wt.% β-hemihydrate, the systems behaved as a linear combination of the 100 and 0 wt.% blends. At 25 wt.%, the hydration kinetics differed from the other blends. With only β-hemihydrate, the last 50% of ettringite formation was accompanied by expansion, mainly caused by interaction of crystals growing radially on cement grains. In the paste with only anhydrite, ettringite crystals grew in solution and produced no expansion.     

Thermodynamic modelling of the effect of temperature on the hydration and porosity of Portland cement

The composition of the phase assemblage and the pore solution of Portland cements hydrated between 0 and 60 °C were modelled as a function of time and temperature. The results of thermodynamic modelling showed a good agreement with the experimental data gained at 5, 20, and 50 °C. At 5 and at 20 °C, a similar phase assemblage was calculated to be present, while at approximately 50 °C, thermodynamic calculations predicted the conversion of ettringite and monocarbonate to monosulphate.Modelling showed that in Portland cements which have an Al₂O₃/SO₃ ratio of > 1.3 (bulk weight), above 50 °C monosulphate and monocarbonate are present. In Portland cements which contain less Al (Al₂O₃/SO₃ < 1.3), above 50 °C monosulphate and small amounts of ettringite are expected to persist. A good correlation between calculated porosity and measured compressive strength was observed.     

Influence of heat treatment on the space charge within an epoxy resin polymer material

The influence of heat treatment on the appearance and the evolution of the space charge repartition within an epoxy resin polymer material is investigated. The space charge measurements were made using the thermal step method (TSM) and the thermally stimulated depolarization currents (TSDC) method. The results obtained show the behaviour of the space charge density after heat treatment and, in particular, it can be concluded that the charges are stabilized in deep levels. © 2001 Society of Chemical Industry     

Electrochemical incineration of 1,2-dichloroethane: Effect of the electrode material

The electrochemical incineration of 1,2-dichloroethane (EDC) at Pt, Au, boron-doped diamond (BDD), Ebonex, stainless steel, Ti/IrO₂-Ta₂O₅ and PbO₂ has been studied in acid media by cyclic voltammetry and bulk electrolysis. It has been shown that the performances of the process dramatically depend on the anodic material. Higher current efficiencies were obtained at BDD. In particular, at proper values of applied current density, it is possible to obtain the almost complete conversion of EDC to CO₂ at BDD with current efficiencies higher than 40%.     

The effect of coal sulfur on the behavior of alkali metals during co-firing biomass and coal

Biomass contains high amounts of volatile alkali metals and chlorine, which can cause deposition, corrosion and agglomeration during combustion. Meanwhile coal contains a certain amount of sulfur that produces serious environmental pollution following combustion. To investigate the effects of sulfur on the migration of alkali metals during biomass and coal co-combustion, thermodynamic equilibrium calculations were applied and experiments were performed in a laboratory scale reactor combining with a scanning electron microscope (SEM), X-ray powder diffraction (XRD) and other analytical approaches. The results indicate that inorganic sulfur FeS₂ addition significantly enhanced the formation of potassium sulfate when the S/K molar ratio was less than 2. Meanwhile increasing FeS₂ dosage reduced the formation of KCl(g) and KOH(g) and increased the release of HCl(g). In addition potassium sulfate can react with silica and aluminum to form potassium aluminosilicates and release HCl at the S/K molar ratio above 4.     

Cobalt-exchanged mordenites: preparation,characterization and catalytic activity for the abatement of NO with CH<Subscript>4</Subscript> in the presence of excess O<Subscript>2</Subscript>

The abatement of NO with methane in the presence of oxygen was studied on various commercial MOR in the Na-form (Na-MOR) and H-form (H-MOR), or exchanged to various extents with cobalt (Co-MOR). The sodium and cobalt contents were determined by atomic absorption. Samples were characterized by FTIR and volumetric measurements of CO adsorption. Chemical analysis indicated that one cobalt species replaced two Brønsted acid sites in H-MOR and two Na⁺ ions in Na-MOR. The IR analysis of the OH stretching region, evidencing an unexpected presence of Brønsted acid sites (band at 3610 cm^?1) in Co-MOR, indicated that the exchange process had a more complex stoichiometry. The adsorption of CO at RT on Co-MOR, in addition to the bands of the corresponding H-MOR and Na-MOR matrices, yielded two types of Co^II-carbonyls, the first type occupied the?mordenite main channels, and the second one the mordenite smaller channels. Brønsted acid sites in mordenites were active for the selective catalytic reduction of NO with CH₄. Co-MOR samples were far more active than Na-MOR and H-MOR samples, showing that acid protons play a negligible role when Co is present. Co-MOR catalysts showing the highest activity had the largest amount of Co^II-carbonyls in the main channels. This result strongly suggests that Co^II in the main channels of MOR are the active sites for the CH₄ + NO + O₂ reaction.     

Modelling decomposition and fire behaviour of small samples of a glass‐fibre‐reinforced polyester/balsa‐cored sandwich material

This publication presents the experimental and numerical methods to model the devolatilization process of a glass‐fibre‐reinforced polyester/balsa‐cored sandwich material on small scale. The fundamental modelling of the source term in pyrolysis‐based fire simulations requires as input data the thermochemical properties of solid fuel and the kinetic parameters of the devolatilization process. First, the thermal decomposition of both elements composing the sandwich structure was studied by thermogravimetry coupled with gas analysis, in air and pure nitrogen atmospheres at several heating rates, in order to define a comprehensive multi‐step reaction pathway. A differential equation system is defined to model these decomposition processes. The kinetic parameters were then estimated by solving the system of equations by an inverse problem. Second, the fire behaviour of each element was studied separately and then combined in the sandwich structure on the cone calorimeter. In addition, numerical simulations with Fire Dynamics Simulator were performed to gradually assess the ability of the model(s) to reproduce each element composing the sandwich structure. Numerical and experimental results are compared and then discussed. Overall, the model provides a good agreement with the experimental data and encourages to model higher scales. Copyright © 2012 John Wiley & Sons, Ltd.     

Towards a better understanding of the high-temperature oxidation of MAX phase Cr2AlC

High-temperature oxidation of bulk single crystal, fine and coarse grained polycrystals of Cr₂AlC has been performed from 800 °C to 1500 °C. In the temperature range T = [800;1400] °C, an α-Al₂O₃ scale with a Cr₇C₃ subscale are in-situ formed independently of the initial microstructure on top of the bulk Cr₂AlC. CALPHAD calculations were performed to explain the formation of Cr₇C₃ instead of the expected mixture of carbides, indicating a favourable driving force for Cr₇C₃ formation. The kinetic study of the oxidation is consistent with previous works with an activation energy of about 400 kJ.mol^?1. Oxidizing for a longer time (1000 h) or at higher temperature (1500 °C) leads to the formation of chromia in the former alumina scale, which correspond to the calculated equilibrium phases.