Preparation and hydration of β-C2S without stabilizer

The preparation method of β-C ₂S without stabilizer, and their hydration characteristics were studied. β-C₂S is formed when γ-C₂S is heated at about 1000°C or about 1500°C. The hydration kinetics of β-C₂S produced from α′-C₂S is markedly different from that from α-phase. Ca(OH)₂ is hardly produced in the hydration of β-C₂S without stabilizer. Formed C-S-H has a composition of $\text{C/S}\text{? 2}$.     

Early hydration of β-C2S: Surface morphology

High-resolution Scanning Transmission Electron Microscopy (STEM) in the scanning mode has been used to study the changes in the surface morphology of β-C₂S immediately upon contact with water.     

Surface studies of hydrated β-C2S

ESCA (electron spectroscopy for chemical analysis) studies of β-C₂S in the early stages of hydration have yielded valuable information on the chemical changes on the hydrating surface. These changes are less pronounced than, but very similar to, those noted for C₃S. The data indicate that, although β-C₂S hydrates more slowly than C₃S, the same hydration mechanism applies to both. The studies also suggest surface hydroxylation as a first step in the hydration process.     

The influence of VTES on the hydration process of C3S

This paper investigated the hydration process of tricalcium silicate (C₃S) in which a small amount of vinyltriethoxysilane (VTES) was added by using the techniques of ¹H NMR, ²⁹Si MAS-NMR and XRD. In comparison with the hydration process of C₃S without adding any additives, not only the average molecular weight of hydrated calcium silicate in C₃S paste, but also the ordering of the silicon nuclei in it increased. This indicates that the VTES has joined effectively into the real hydration process of C₃S. These results imply some possible reasons why the intrinsic properties of low porosity hardened cement paste (HCP) in which a small amount of VTES was added could be improved. Besides, it has been found that in early stage hydration of C₃S with or without VTES, Ca(OH)₂ crystal in the paste appears earlier than Q₁ which shows that in the first several hours of hydration, there only exists Si(OH)₄ and other basic salts and no dimer and polymer of silicate anion when Ca(OH)₂ crystal begins to form.     

Hydrodeoxygenation of aliphatic esters on sulphided NiMo/γ-Al2O3 and CoMo/γ-Al2O3 catalyst: The effect of water

Water formed during hydrotreating of oxygen-containing feeds has been found to affect the performance of sulphided catalysts in different ways. The effect of water on the activity of sulphided NiMo/γ-Al₂O₃ and CoMo/γ-Al₂O₃ catalysts in hydrodeoxygenation (HDO) of aliphatic esters was investigated in a tubular reactor by varying the amount of water in the feed. In additional experiments, H₂S was added to the feed, alone and simultaneously with water.

Under the same conditions, the NiMo catalyst exhibited a higher activity than the CoMo catalyst. The ester conversions decreased with increase in the amount of added water. When H₂S and water were added simultaneously, the conversion increased to the same level as without water addition on the NiMo catalyst and reached a higher value on the CoMo catalyst. The conversions were highest, however, when only H₂S was added. Unfortunately, the conversions decreased with time under all conditions. On both catalysts, the total yield of the C₇ and C₆ hydrocarbons decreased with the amount of added water, while the concentrations of the oxygen-containing intermediates increased. The presence of H₂S improved the total hydrocarbon yield and shifted the main products towards the C₆ hydrocarbons. Thus, the addition of H₂S effectively compensated the inhibition by water.     

A multi-method study of C3S hydration

C₃S pastes hydrated at 25°C have been studied using QXRD (to determine uncreacted C₃S), TG (to determine CH and water), and trimethylsilylation (to determinemonomeric and dimeric silicate) and the results compared with ones obtained with analytical electron microscopy. Monomeric silicate is accounted for by unreacted C₃S. The silicate in the C-S-H formed during the first few days is entirely dimeric, but at later ages dimer and polymer are both present. A new hypothesis for the reaction mechanism is tentatively proposed.     

Accommodation of impurities in α-Al2O3, α-Cr2O3 and α-Fe2O3

Atomic scale computer simulation was used to predict the mechanisms and energies associated with the accommodation of aliovalent and isovalent dopants in three host oxides with the corundum structure. Here we consider a much more extensive range of dopant ions than has previously been the case. This enables a rigorous comparison of calculated mechanism energetics. From this we predict that divalent ions are charge compensated by oxygen vacancies and tetravalent ions by cation vacancies over the full range of dopant radii. When defect associations are included in the model these conclusions remain valid. At equilibrium, defects resulting from extrinsic dopant solution dominate intrinsic processes, except for the largest dopant cations. Solution reaction energies increase markedly with increasing dopant radius. The behaviour of cluster binding energies is more complex.     

ESCA and SEM studies on early C3S hydration

Electron Spectroscopy for Chemical Analysis (ESCA) and high-resolution Scanning Electron Microscopy (SEM) have been used to explore the phenomena occuring on the C₃S¹ surface in the very early stages of hydration. Definite changes in the surface morphology and Ca to Si ratio were observed already after a few seconds of hydration.     

The influence of CaCl2 on the crystallization of calcium silicates in autoclave hydration of C3S

The influence of CaCl₂ on the autoclave hydration C₃S (5 hours at 190°C) after different precuring times (0–16 hours) at room temperature has been studied. The addition of calcium chloride retards the autoclave hydration of C₃S and prevents completely the formation of the crystalline hydrated silicates (-C₂SH and C₃SH_1.5). This result has been compared with that observed in the ball-mill hydration of C₃S in the presence of CaCl₂, i.e., the complete absence of crystalline afwillite.

Abstract

On a étudié l'influence du CaCl₂ sur l'hydratation en autoclave du C₃S (5 heures à 190°C) après différents temps de conservation (0–16 heures à température ambiante. L'addition de chlorure de calcium retarde l'hydratation en autoclave du C₃S et empêche complétement la formation des silicates cristallins hydratés -C₂SH et C₃SH_1.5. Ce résultat a été comparé avec le phenomene observé en étudiant l'hydration du C₃S dans un moulin à boulets en presence de CaCl₂, c'est à dire la disparition complète du composé crystallin afwillite.     

New ferrocene-derived hydroxymethylphosphines: FcP(CH2OH)2 [Fc=(η-C5H5)Fe(η-C5H4)] and the dppf analogue 1,1-Fc[P(CH2OH)2]2 [Fc=Fe(η-C5H4)2]

Reactions of the ferrocene-phosphines FcPH₂ and 1,1^′-Fc^′(PH₂)₂ with excess formaldehyde gives the new hydroxymethylphosphines FcP(CH₂OH)₂ 1 and 1,1^′-Fc^′[P(CH₂OH)₂]₂ 2, respectively. Phosphine 1 is an air-stable crystalline solid, whereas 2 is isolated as an oil. Reaction of 1 with H₂O₂, S₈ or Se gives the chalcogenide derivatives FcP(E)(CH₂OH)₂ (E=O, S or Se), whilst reaction of 2 with S₈ gives 1,1^′-Fc^′[P(S)(CH₂OH)₂]₂, which were fully characterised. Phosphine 1 was also characterised by an X-ray crystal structure determination.     

Hydrodeoxygenation of methyl esters on sulphided NiMo/γ-Al2O3 and CoMo/γ-Al2O3 catalysts

Wood-derived bio-oil contains high amounts of compounds with different oxygen-containing functional groups that must be removed to improve the fuel characteristics. Elimination of oxygen from carboxylic groups was studied with model compounds, methyl heptanoate and methyl hexanoate, on sulphided NiMo/γ-Al₂O₃ and CoMo/γ-Al₂O₃ catalysts in a flow reactor. Catalyst performances and reaction schemes were addressed. Aliphatic methyl esters produced hydrocarbons via three main paths: The first path gave alcohols followed by dehydration to hydrocarbons. Deesterification yielded an alcohol and a carboxylic acid in the second path. Carboxylic acid was further converted to hydrocarbons either directly or with an alcohol intermediate. Decarboxylation of the esters led to hydrocarbons in the third path. No oxygen-containing compounds were detected at complete conversions. However, the product distributions changed with time, even at complete conversions, indicating that both catalysts deactivated under the studied conditions.     

Fe2O3/β-SiC: A new high efficient catalyst for the selective oxidation of H2S into elemental sulfur

Over the last decades, sulfur recovery from the H₂S-containing acid gases (issued from oil refineries or natural gas plants) has become more and more important due to the ever increasing standards of efficiency required by environmental protection pressures. The H₂S-tail gas was directly oxidized by oxygen to yield elemental sulfur. A significant improvement of the H₂S conversion and selectivity has been developed, however, the support which is the core of the process still needs to be improved. Recently, β-SiC has been reported to be an efficient and selective catalyst support for the H₂S-to-S reaction. One expected reason for this superior yield should be due to the high thermal conductivity of the support. The high thermal conductivity of the silicon carbide plays an important role in the maintenance of the high selectivity by avoiding the formation of hot spots on the catalyst surface which could favor secondary reactions. On the other hand, insulator supports such as alumina exhibit a poor selectivity due to catalyst surface temperature runaway.     

Effect of the hydrogen spillover on the selectivity of dibenzothiophene hydrodesulfurization over CoSx/γ-Al2O3, NiSx/γ-Al2O3 and MoS2/γ-Al2O3 catalysts

Dibenzothiophene (DBT) hydrodesulphurization (HDS) reaction at 3 MPa and 325–375 °C on Mo/γ-Al₂O₃ single-bed and Me/γ-Al₂O₃//SiO₂//Mo/γ-Al₂O₃ (Me = Co or Ni) double-bed catalysts were investigated. Results indicate that ratio cyclohexylbenzene (CHB)/biphenyl (BP) or selectivity is higher when using double-beds rather than a single-bed. Synergy in dibenzothiophene hydrodesulphurization on Co//Mo and Ni//Mo double-beds is also detected. Changes in selectivity and conversion are attributed to the action of spillover hydrogen (Hso) formed in the first bed that reaches the second bed.     

Analyses of the aqueous phase during early C3S hydration

The concentrations of calcium and silica in solution during the first 4 hours of C₃S hydration were measured. The results of these analyses indicate that a solid calcium silicate hydrate forms within 30 seconds of the start of hydration and that an equilibrium between the solution and the solid hydrate is rapidly established. A strong dependence of the rate of early hydration on the w:C₃S ratio was observed, while the dependence on the surface area of the C₃S was minimal.     

The hydration of Portland cement,C3S and C2S in the presence of a calcium complexing admixture (EDTA)

The effect of EDTA, a calcium chelating agent, on the early hydration of Portland cement, C₃Sand β-C₂S has been studied by solution analysis and electron microscopy. EDTA is a retarded of cement hydration. Under normal conditions of hydration, the silica levels in solution are very low (<0.05 M) but in the presence of EDTA an initial flush of silica appears in the bulk aqueous phase. On continued hydration, following the saturation of EDTA with calcium, the appearance of ‘free’ calcium causes precipitation of C-S-H gel from the bulk solution and changes in microstructure of the colloidal gel around clinker particles in C₃S and β-C₂S pastes are observed. The action of EDTA as a retarding admixture is explained in terms of the membrane model of cement hydration.     

Hydrodemetallation of a vanadylporphyrin over sulfided NiMo---γAl2O3, Mo---γAl2O3, and γAl2O3 catalysts - effect of the vanadium deposit on the toluene hydrogenation.

The toluene hydrogenation performances of Mo--- and NiMo---Al₂O₃ hydrotreating catalysts are modified by vanadium deposited through HDM of the Vanadylporphyrin. Bulk deposited vanadium sulfide of mean VS_1.1 stoichiometry does not greatly affect the intrinsic performances of the initial catalysts but it appears that a part of the deposited vanadium replaces Ni in the NiMoS phase and acts as a promoter of the supported MoS₂     

The effect of oxygen concentration on the reduction of NO with propylene over CuO/γ-Al2O3

The effect of oxygen concentration on the pulse and steady-state selective catalytic reduction (SCR) of NO with C₃H₆ over CuO/γ-Al₂O₃ has been studied by infrared spectroscopy (IR) coupled with mass spectroscopy studies. IR studies revealed that the pulse SCR occurred via (i) the oxidation of Cu⁰/Cu⁺ to Cu²⁺ by NO and O₂, (ii) the co-adsorption of NO/NO₂/O₂ to produce Cu²⁺(NO₃⁻)₂, and (iii) the reaction of Cu²⁺(NO₃⁻)₂ with C₃H₆ to produce N₂, CO₂, and H₂O. Increasing the O₂/NO ratio from 25.0 to 83.4 promotes the formation of NO₂ from gas phase oxidation of NO, resulting in a reactant mixture of NO/NO₂/O₂. This reactant mixture allows the formation of Cu²⁺(NO₃⁻)₂ and its reaction with the C₃H₆ to occur at a higher rate with a higher selectivity toward N₂ than the low O₂/NO flow. Both the high and low O₂/NO steady-state SCR reactions follow the same pathway, proceeding via adsorbed C₃H₇---NO₂, C₃H₇---ONO, CH₃COO⁻, Cu⁰---CN, and Cu⁺---NCO intermediates toward N₂, CO₂, and H₂O products. High O₂ concentration in the high O₂/NO SCR accelerates both the formation and destruction of adsorbates, resulting in their intensities similar to the low O₂/NO SCR at 523–698 K. High O₂ concentration in the reactant mixture resulted in a higher rate of destruction of the intermediates than low O₂ concentration at temperatures above 723 K.     

Preparation and hydration study of rich C2S cements

Three laboratory clinkers were made with variable C₂S content (28–57%), using industrial raw materials. These clinkers were cooled by air and studied by X-Ray Diffraction (XRD). It is concluded that by fast cooling, the active crystal forms of - and ′-C₂S were stabilized in the rich C₂S clinker.

The hydration phenomena were also studied in cements prepared from these clinkers by DTA-TG and XRD, at 2, 7, 28 and 90 days. The combined water and the liberated Ca(OH)₂ were quantitatively determined by means of thermogravimetry and the hydration rate was studied.

It is concluded that the hydration rate differs at the early ages, but it progresses with the same rate after 28 days. No significant differences in the formed hydration products of these cements were observed by XRD.     

η-Al2O3与γ-Al2O3在CS2催化水解反应中的性能比较

通过制备高纯度的前驱体湃铝石获得了η-Al₂O₃材料,采用XRD验证了η-Al₂O₃与γ-Al₂O₃在晶相结构上的差异,比较了两者的表面形貌、织构及酸碱性能,结果显示,η-Al₂O₃与γ-Al₂O₃的比表面积相当,但η-Al₂O₃具有更弱的弱碱位和较少的强碱位,并拥有丰富的中等强度酸性位。将η-Al₂O₃与γ-Al₂O₃作为催化剂应用于CS₂水解反应,结果表明,在(200~450) ℃测试温度范围内,η-Al₂O₃催化剂对CS₂的水解活性始终优于γ-Al₂O₃,两种催化剂上CS₂反应的浓度效应也明显不同,推测与它们的酸碱性质影响了对CS₂的吸附能力有关,导致两者催化CS₂水解反应遵循了不同的机制。