Multiplicity and uniqueness for binary,exothermic reaction in a non-adiabatic continuous stirred tank reactor

Exact multiplicity and uniqueness criteria for steady state in a non-adiabatic continuous stirred tank reactor are studied through simple tangent analysis for binary, exothermic reaction of the type A + bB → Products with rate expression r_A = kC_A^m C_Bⁿ, where A is the limiting reactant. Important parameters for multiplicity criteria are reaction orders m and n, stoichiometric coefficient b, the ratio p of feed concentration of A to that of B, dimensionless activation energy α, dimensionless heat of reaction β, dimensionless heat transfer coefficient γ and dimensionless coolant temperature. Necessary conditions for the system to have multiple exit conversions (temperatures) are defined in the (m, n, b, p, α, β, γ) space. Multiplicity is guaranteed by limiting the dimensionless space time ? in a proper range in addition to the necessary conditions. Effects of various parameters on multiplicity and uniqueness are numerically calculated and graphically represented. Theoretical prediction for multiplicity are further compared with multiplicity data reported in literatures.     

IR Spectroscopy in Rank and Group Assignment of Coal

The possibility of express determination of the characteristics V _IR ^daf , R_{o, IR}, y_IR, ΣLC_IR, and A _IR ^d used in the ranking of coal on the basis of IR spectroscopy is assessed for a specific example: Kuznetsk coals of different maceral composition and metamorphic development. The IR characteristics are compared with values obtained by standard methods (V^daf, R_{o, r, y}, ΣLC, and A^d).     

Effects of A-site ionic size on the phase transition behavior of lead-free niobate ceramics

Understanding the phase structure evolution is important for developing high performance lead-free piezoelectric materials. In this work, the effects of A-site ionic size of monovalent ions on the phase transition behaviors for the lead-free niobate ceramics ANbO₃ (A = Li, Na, Ag, and K) are investigated using XRD analysis and dielectric measurement. The iso-valent ionic doping restrains the relaxation behavior that usually appears in the hetero-valent ionic-doped niobate ceramics. The A-site average ionic size of R_A and its ionic radius differences of ΔR_A are found to be crucial influence factors on the phase transition behaviors of the ANbO₃ ceramics. Small Li⁺ doping stabilize tetragonal phase of the ANbO₃ ceramics with R_A > 1.47 Å, but stabilize rhombohedral phase of the ones with R_A < 1.47 Å. On the other hand, The ANbO₃ ceramics without Li⁺ doping prefer to orthorhombic phase due to indistinctive ionic size differences (ΔR_A < 0.25 Å). Our results suggest that a certain phase and phase transition boundary could be designed by appropriate ionic doping for developing the niobate-based lead free piezoelectric ceramics.     

Application of critical state to uniaxial compaction

From the radial stress σ_R and the normal stress σ_A, measured continuously during uniaxial loading and unloading on three compactable (sodium chloride, polyethylene and tartaric acid) and two non-compactable (polypropylene and polystyrene plastics) materials, characteristic compaction profiles of (σ_A ? σ_R) versus (σ_A + σ_R) can be observed. The uniaxial loading stress pathways for both compactable and non-compactable materials validated the assumption that the Coulomb yield criterion, which is usually applicable for the shear testing of soils, can be applied to the uniaxial compression of particulate materials. In addition, the unloading stress profiles for the compactable materials produced two characteristic parameters: a normal stress value at zero shear (σ_A + σ_R)_o and a minimum shear stress value (σ_A ? σ_R)_min. Correlation of (σ_A + σ_R)_o and (σ_A ? σ_R)_min values with either the tensile strength f_c or the Vickers hardness number H_V from the resultant compacts showed a linear logarithmic relationship. No such relationship was found, however, with non-compactable materials.     

Chemistry and kinetics of chemical vapour deposition of pyrocarbon: VII. Confirmation of the influence of the substrate surface area/reactor volume ratio

Carbon deposition from a methane–hydrogen mixture (p_CH4=17.5 kPa, p_H2=2.5 kPa) was studied at an ambient pressure of about 100 kPa and a temperature of 1100°C, using deposition arrangements with surface area/reactor volume ratios, [A_S/V_R], of 10, 20, 40 and 80 cm⁻¹. Steady-state deposition rates and corresponding compositions of the gas phase as a function of residence were determined. The deposition rates in mol/h increase with increasing [A_S/V_R] ratio at all investigated residence times up to 1 s. However, surface-related deposition rates in mol/m²h decreased. As the same results have been obtained in a preceding study using pure methane at a partial pressure of 10 kPa, it has been confirmed that all the kinetics can be determined by changing the [A_S/V_R] ratio.     

Properties of the solid thermolysis products of brown coal impregnated with an alkali

The mechanism of formation of a porous active carbon framework is considered, and the properties of the solid thermolysis products of brown coal (Aleksandriisk deposit, Ukraine) with potassium hydroxide are studied. The yields of the solid thermolysis products (Y _STP, %) and potassium humates, the rate of the interaction of the solid thermolysis products with KOH at 700–900°C, the specific surface areas (S _BET, m²/g), the adsorption capacities for methylene blue (A _MB, mg/g) and iodine (A _I, mg/g), and the specific activities of surface areas A _MB ^′ = A _MB/S _BET and A _I ^′ = A _I/S _BET (mg/m²) are determined under variation of the KOH/coal ratio (R _KOH < 18 mol/kg) and temperature (110–900°C).     

The role of multiple gas—solid collisions in the catalytic decomposition of formic acid

An improved version of a low pressure free-molecular flow reactor is described. Use of a macroscopic, geometrically well-defined analog of a catalyst pore enables one to combine the multiple gas—solid collision effects of a high pressure supported catalyst with the detailed flow characterization available in a vacuum system. Simulations of the molecular trajectories within the reactor produce a relationship between an observed integral conversion and the probability of reaction when a gas molecule strikes the surface; low reaction probabilities are integrated experimentally in a manner which makes them readily observable. The Pt and Cu catalysed decomposition of formic acid was studied in two different reactor geometries at temperatures between 300°C and 450°C. The probability of reaction per collision on these surfaces was found to be independent of the collisional history and could be described by the relationships:Pr = 1.12 × 10⁴ exp (? 16000/R_gT) (platinum)Pr = 2.52 × 10⁵ exp (? 21600/R_gT) (copper). These probabilities are consistent with single collision experiments performed on various crystals and wires if the accommodation coefficient for the single collision is less than unity. No information on the molecular mechanism of decomposition was obtained.     

Multiplicity of photoluminescence in Raman spectroscopy and defect chemistry of (Ba1−xRx)(Ti1−xHox)O3 (R = La,Pr, Nd,Sm) dielectric ceramics

(Ba_1?xR_x)(Ti_1?xHo_x)O₃ (R = La, Pr, Nd, Sm; x ≥ 0.04) (BRTH) ceramics were prepared using a mixed oxides method. The solubility limits in BRTH with R = La, Pr, Nd, Sm were determined by XRD to be x = 0.11, 0.12, 0.06, and 0.14, respectively. The ionic radius of R at Ti-site plays a decisive role in the solubility limit in BRTH. Only BRTH with R = La satisfied Vegard's law. The multiplicity of photoluminescence (PL) signals of Nd³⁺/Ho³⁺ and Sm³⁺/Ho³⁺ in Raman scattering under 532-nm excitation laser and the high-permittivity abnormality for the denser BRTH with R = Sm and at x = 0.07 were reported. The PL provided the evidence of a small number of Ho³⁺ at Ba-site in BRTH and it was determined that the number of Ba-site Ho³⁺ ions increased from 0.05 at% at R = La to 0.19 at% at R = Sm with increasing atomic number of light rare earth. BRTH exhibited a much broadened dielectric-temperature characteristics, marked by ×5 T, ×6 T, ×7 T, and ×8 S dielectric specifications for BRTH with R = La, Pr, Nd, Sm and at x = 0.06, respectively, and they exhibited lower dielectric loss (tan δ < 0.015) at room temperature. The dielectric-peak temperature (T_m) of BRTH decreased linearly at a rate of less than ?21 °C/%(R/Ho). The defect chemistry, solubility limit, lower dielectric loss, and dielectric abnormality are discussed.     

Influence of geometry and solids concentration on the hydrodynamics and mass transfer of a rectangular airlift reactor for marine sediment and soil bioremediation

Hydrodynamics and mass transfer characteristics of a three-phase airlift reactor were studied in a rectangular split-vessel reactor and using an air-seawater-marine sediment system. Experiments were conducted over a range of downcomer to riser cross-sectional area ratios (A_D/A_R = 0.65 to 1.0) for two-phase systems and for five sediment concentrations (5 to 25% w/v) using marine sediments. The influence of higher sediment concentrations (30 to 50% w/v) was examined for A_D/A_R = 1. The presence of fine sediment particles in the system had little effect on hydrodynamic and mass transfer parameters compared to the two-phase systems up to 25% loading, decreasing at higher loadings. The airlift reactor was found to meet the dissolved oxygen demand needed for a contaminated sediment treatment process. Axial distribution of the particles was uniform along the riser and the downcomer. Correlations were developed that described the hydrodynamic and mass transfer behaviour for all experimental conditions examined.     

Properties of adsorbents prepared by the alkali activation of Aleksandriisk brown coal

Highly microporous adsorbents (micropore fraction of ～70%) were prepared by the alkali activation-thermolysis (800°C, 1 h) of brown coal (C ^daf = 70.4%) in the presence of potassium hydroxide at the KOH/coal weight ratio R _KOH ≤ 2.0 g/g. The dependences of the specific surface areas and adsorption capacities of the adsorbents for methylene blue (A_MB, mg/g), iodine (A_I, mg/g), and hydrogen (\(A_{H_2 } \), wt %) on R _KOH were determined. The adsorbents obtained at R _KOH ≥ 1.0 g/g exhibited developed specific surface areas and good adsorption characteristics (A_I = 1000–1200 mg/g, A_MB = 200–250 mg/g, and \(A_{H_2 } \) ≤ 3.16 wt % at 0.33 MPa). The high capacity for hydrogen allowed us to consider brown coal adsorbents as promising materials for use as hydrogen accumulators.     

Calorimetric study of quinoline interaction with o-phenylphenol and coal-derived asphaltenes

A calorimetric method is presented for the simultaneous evaluation of equilibrium constant, K, and molar enthalpy, ΔH^o, for 1:1 adduct formation of quinoline (Qu) with coal-derived asphaltenes in solvent benzene. Asphaltene (A), together with its acid/neutral (AA), and base (BA) fractions used in this study were isolated from a centrifuged liquid product (CLP) sample prepared from Kentucky hvAb coal at 27.6 MPa hydrogen pressure and 723 K, with reactor charged with glass pellets. The computed K values for the interaction of Qu and A, AA, and BA are, within experimental error, the same, 18–19 dm³ mol^?1; whereas there is large variation in the ΔH^o values (Qu-A, ?16.92 ± 0.21 kJ mol^?1; Qu-AA, ?14.74 ± 0.04 kJ mol^?1; Qu-BA, ?11.76 ± 0.04 kJ mol^?1). For Qu-A and Qu-AA systems, hydrogen-bonding occurs between the aromatic phenols (present in A and AA) and quinoline, which is a strong hydrogen-bond acceptor, in addition to other molecular interactions. The hydrogen-bonding interaction in the Qu-BA system is lacking because both Qu and BA are hydrogen-bond acceptors. Since asphaltenes are really mixtures, we have taken a pure compound, o-phenyl-phenol (OPP), and obtained thermodynamic parameters for its interaction with quinoline (Qu). OPP was chosen to represent the aromatic phenols found in coal liquefaction products. Results obtained are: K (dm³ mol^?1): 10.4 (in CS₂), 6.2 (in CCl₄); ΔH^o (kJ mol^?1): ?31.40 (inCS₂) ?27.80 (inCCl₄). The solvent effect is apparent. By using o-phenylanisole as a model non-hydrogen-bonding donor (Dietz Blaha, Li J. Chem. Thermodynamics, 1977, 9, 783), the relative contribution of H-bond to π-interactions in the total enthalpy change for the OPP—Qu system is estimated to be 3:1.     

Internal cation mobilities in the molten binary system Li2CO3K2CO3

Internal mobility ratios of two cations in the molten binary system (Li, K)(CO₃)_0.5 have been measured with the Klemm method. From these and available data on the densities and conductivities, the internal mobilities of Li⁺ and K⁺ have been calculated. Except at a region of relatively high concentration of Li₂CO₃, the Chemla effect occurs, that is, the mobility of the large cation K⁺ is greater that of the small one Li⁺. The internal mobilities of Li⁺ ions are well expressed by b_Li = [A/(V − V₀)] exp (− E/RT), where A, V₀ and E are constants characteristic of the cation and independent of temperature T, V the molar volume of mixtures, and R the gas constant. Negative deviations from this equation at a small V region may be attributed to the free space effect. For b_K such a simple equation does not hold over an extended region of concentration, which suggests that the agitation effect and the free space effect would also play a role for the mobility.     

Ultra-sensitive low-temperature thermometer regulated by the crystal field strength

Developing novel optical thermometry with ultrahigh relative sensitivity and temperature resolution has become a cutting-edge topic. For this purpose, under obeying Boltzmann distribution, a series of Li₂Zn_0.9992-xA_xGe_3-yB_yO₈:0.08% Cr³⁺ (B= Sc³⁺, In³⁺, A = Si⁴⁺) phosphors were studied, which the luminescence intensity ratio between the transition of ⁴T_2g→⁴A_2g emission and the R line based on thermally coupled energy levels constitutes a temperature sensing work with a relative sensitivity of 9.46% K^?1, 9.73% K^?1, and 10.38% K^?1, respectively. It is worth mentioning that the luminescence intensity of the R line (peak 1) increases significantly with the increase of temperature, while the transition of ⁴T_2g→⁴A_2g (peak 2) with high intensity at low temperature gradually quenching, and this opposite trend is an important advantage for the design of excellent thermometers. Compared the best relative sensitivity of Li₂Zn_0.9992-xA_xGe_3-yB_yO₈:0.08%Cr³⁺ (B= Sc³⁺, In³⁺, A = Si⁴⁺) with the crystal field Dq/B, it can be concluded that relative sensitivity increasing gradually with decreasing the intensity of crystal field. Finally, by testing the stability of the sample at 50 K, a thermal resolution of 0.082 K, 0.080 K and 0.077 K was obtained, respectively, which is one of the best thermal resolutions so far, while the repeatability of the sample stability at 50 K and 300 K cycles was higher than 99%. Our work is expected to provide guiding insights for optimizing the sensitivity of Cr³⁺-based luminescence intensity ratio thermometers.     

Infrared spectral studies of nanostructured Co2+-substituted Li-Ni-Zn ferrites

Polycrystalline Li_0.5Ni_0.25–0.5x Co_0.5x Zn_0.5Fe₂O₄ ferrites (x = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) were prepared by standard auto-combustion method and characterized by XRD and IR spectra. The XRD results suggest that all samples were single-phase with a cubic spinel-type structure. The lattice constant, particle size, metal-oxygen bond length (R _A and R _B), cation radii (r _A and r _B) on A and B-sub lattices were found to increase while the X-ray density and porosity, decrease with increasing x. The IR spectra show two absorption bands, at ν₁ about 600 cm^?1 and ν₂ at about 425 cm^?1, which were attributed to tetrahedral (A) and octahedral (B) sites of the spinel structure, respectively. The band positions were found to depend on x. The force constants, K _t and K _o, were calculated and plotted against cobalt concentration x. Compositional dependence of the force constants is explained in terms of cation-oxygen bond distances and redistribution of cations.     

Heat transfer and kinetics in the low temperature pyrolysis of solids

New theory is developed to define the parameters controlling the pyrolysis rate of single particles. It is shown that the relative importance of internal and external heat transfer and of the intrinsic (first order) pyrolysis kinetics can be determined from the Biot number (hR/K) and, depending on the value of the Biot number, one of two Pyrolysis numbers defined by Py = (K/k?c_pR²) or Py′= (h/k?c_pR). On the basis of these groups four regions are defined, and appropriate and simple models of the kinetics of primary pyrolysis outlined. The models are tested against measurements of decomposition and temperature distributions in pyrolysing wood cylinders with diameters in the range 0.6–2.2 cm and at temperatures from 380 to 500°C. Good agreement with theory is found and it is concluded that, under these conditions, internal convection is unimportant and that with suitably large or small values of Bi, Py and Py′ very simple models are adequate. Some implications for reactor design are briefly discussed.     

Thermogravimetric investigations in prediction of coking behaviour and coke properties derived from inertinite rich coals

The coal quality, temperature, pressure, heating rate, various processes and reactor type affect coking behaviour of coal and resulting coke properties. Several petrographic and chemical methods were proposed earlier for prediction of coking behaviour of coals. Inertinite rich coal samples (I^mmf>30 vol%) having different petrographic compositions were selected for thermogravimetric investigations (DTA, DTG and TGA) and their coking behaviour was studied. The petrographic build up, micro-structural properties (porosity and cell wall thickness) and mechanical strength of the resulted cokes were also investigated. ΔH and ΔH_max (the main endothermic area of heat absorption and fast absorbing main endothermic area, respectively) were distinguished in DTA curves. ΔA and ΔA_max (the main decomposition area and fast disintegrating main decomposition area) under DTG curves were identified. ΔH_max/ΔA_max shows good correlation with Roga's indices (RI, caking properties) as well as with petrographic caking ratio (PCR). The coarse mosaic content of cokes seem to depend on LΔT_max/ΔT_max (ratio of weight loss during fast decomposing main reaction to temperature difference) under DTG. L^mΔT/ΔT (ratio of weight loss during main decomposing reaction to temperature difference) under DTG exhibits correlation with p₁ (mean pore size) and t₁ (mean cell wall thickness) of cokes. ΔA_max/(L^mΔT_max) also indicates good relationship with mechanical strength of cokes. (L^mΔT_A−T_B)/(L^mΔT) (i.e. ratio of weight loss during main endothermic reaction under DTA to weight loss during main decomposing reaction) appears to have relationship with DD (compactness) of cokes. The course of main endothermic reaction/main decomposition reaction under DTA, DTG and TGA seems to govern coking behaviour and the resulting coke strength, which in turn is controlled by microlithotypes.     

Temperature- and frequency-dependent hysteresis scaling behaviour and phase transitions in a [001]c 0.73Pb(Mg1/3Nb2/3)O3-0.27PbTiO3 single crystal

The dielectric properties and bipolar polarization-electric field (P-E) and strain-electric field (S-E) dynamic hysteresis of a relaxor [001]_c 0.73Pb(Mg_1/3Nb_2/3)O₃-0.27PbTiO₃ (PMN-0.27PT) single crystal were investigated to reveal more details of the temperature-induced phase transitions. Different linear scaling relations for ferroelectric hysteresis area <A>, coercive field E_c, saturation polarization P_s and remnant polarization P_r versus temperature τ were measured in different temperature regions. For each measurement frequency f, all hysteresis parameters were found to decrease linearly with temperature in the temperature range of the single rhombohedral (R) phase or tetragonal (T) phase, and the rate of decrease in the T phase was observed to be much larger than the corresponding rate in the R phase. In the temperature range near the R-T phase transition, the exponent α in the power law <A>∝f ^α for the R phase was found to be smaller than that for the T phase, and the magnitude of α depended strongly on temperature when the crystal was in the R-T coexisting phase state. Our experimental and theoretical results indicate that the difference in the activation energy and dipole moment in the R and T phases may lead to the observed discrepancy for the P-E and S-E hysteresis behaviour in different temperature regions.     

Assessing the technological value of coal in coking

Coking coal of the same rank from different countries and fields may be distinguished in terms of use value by rating on the basis of seven technological and petrographic characteristics that determine the coke yield and properties: the ash content A^d; the total sulfur content S_t^d; the yield of volatiles V^daf; the plastic-layer thickness y; the vitrinite reflection coefficient R_o; the content of vitrinite-group macerals Vt; and the basicity index B_b. A range of values and a rating (on a scale from 1 to 10) are established for each of these parameters. Each rating corresponds to a particular score (from 0.1 to 1.0). Ranges of A^d, S_t^d, Vt, and B_b are established for the whole metamorphic series, while ranges of V^daf, y, and R_o are established for individual ranks and groups of ranks. Altogether, 105 coking coals from Ukraine, Russia, the United States, Australia, and Canada that are used at Ukrainian coke plants are investigated. The range of rating scores and their mean values are determined for individual coal ranks and groups. As an example, three bituminous coals from Ukraine, the United States, and Australia are compared by the proposed method. This method permits objective assessment of the technological value of coal within a single rank and the selection of the best purchase option.     

Modulating the structure,vacancy defects,magnetic and dielectric properties in multiferroic GdMnO3 ceramics by alkaline earth ion substitution

This investigation highlights the significant influences of alkaline earth ion substitution for Gd on the structure, vacancy defects, magnetic and dielectric properties in GdMnO₃ (GMO) ceramics synthesized using the solid-state reaction method. The structure measurements indicate that all of the Gd_0.90A_0.10MnO₃ (A = Ca, Sr, Ba) samples show a single phase structure, and the introduction of A²⁺ ion induces structure distortion. A²⁺ ions substitution increases the Mn⁴⁺ ion concentration in GMOs, but has no significant effect on the oxygen vacancy concentration. All samples with irregular grain shapes have dense microstructures, and A²⁺ ion substitution inhibits grain growth. Positron annihilation experimental results indicate that A²⁺ ion substitution can increase the vacancy size and concentration, while the vacancy concentration increases first and then decreases with increasing A²⁺ ion radius. The evolution of the temperature- and magnetic field-dependent magnetization curves shows that A²⁺ ion substitution could obviously affect the magnetic state of GMOs, and improve the magnetic transition temperature and magnetization of Gd_0.90A_0.10MnO₃. The dielectric measurements reveal that the A²⁺ ion substituted samples exhibit giant dielectric constant characteristics over a broad frequency range. It is found that the enhanced magnetization of Gd_0.90A_0.10MnO₃ has a close relationship with the vacancy concentration, and the giant dielectric constant behaviors in Gd_0.90A_0.10MnO₃ ceramics can be associated with the mixed-valent structure of Mn³⁺/Mn⁴⁺.