Change in viscosity of softening coal upon heating with its liquid content. Part I: linear relationship between logarithm of viscosity and liquid fraction

A variable-force-loading needle penetrometry and a proton magnetic resonance analysis were performed for in situ measurements of shear-rate-independent viscosity of softening coal pellet upon heating, η, and the fraction of mobile hydrogen existing in the liquid phase, φ_mh, respectively. During isothermal heating of the pellet at temperature in a range from 680 to 730 K, φ_mh changed with time via a maximum while η did inversely. At every temperature examined, the time for the maximum φ_mh coincided with that for the minimum η. This result qualitatively validated the experimental definition of the liquid fraction in the softening coal as a liquid/solid suspension by φ_mh. Further analysis of the results revealed that the logarithm of η, which changes in a range from 10¹⁰ to 10⁴ Pa s upon isothermal heating, is correlated linearly with the liquid fraction ranging from 0.1 to 0.5. For each of the pellets made of two different coals, it was found that the logarithm η and φ_mh varied being governed by a single linear relationship upon both isothermal heating and non-isothermal heating. Such a single relationship, which was valid over a temperature range from 600 to 800 K, suggested fairly small temperature dependency of the viscosity of liquid in the softening coal.     

Microbial desulphurization of coal containing pyritic sulphur in a continuously operated bench scale coal slurry reactor

Pre-combustion microbial desulphurization of coal containing total sulphur (3.90%) and pyritic sulphur (2.80%) has been evaluated in a coal slurry reactor. The coal slurry reactor operated at hydraulic retention time (HRT) of 96 h with a coal pulp density of 15 percent and remove 79 percent of pyritic sulphur and 76 percent of ash with an increase in the calorific value of coal from 4400 to 6800 kcal kg⁻¹ at a pyritic load of 1.9 kg pyritic sulphur kg⁻¹ MLSS d⁻¹. The treated coal yield is 72 percent. The biochemical kinetic coefficients, viz. yield coefficient (Y) and decay coefficient (K_d) in the coal slurry reactor system are 0.178 and 0.007 d⁻¹, respectively, while maximum growth rate (μ_max) and half saturation rate constant (K_s) are 0.025 h⁻¹ and 0.220 g l⁻¹ as pyrite, respectively.     

Macroscopic observation of thermal behavior of concentrated solution of coal extracts

The solvent extracts of Upper Freeport and Illinois No.6 coals were mixed with N-methyl-2-pyrolidinon (NMP) and annealed at 353 K to produce the gelatinous materials. Differential scanning calorimetric measurements revealed that the materials can hold significant amounts of nonfreezable NMP (as much as 3 g NMP per 1 g coal extracts) which disperse in the materials on a molecular scale, indicating the materials are not phase separated. The thermal behaviors were measured macroscopically as a function of the extract concentration using a needle penetrometer during heating from 223 to 360 K. The penetration-temperature curves were analyzed to estimate the apparent viscosity (η_a). During the penetrations, η_a was decreased very rapidly, approximately four orders of the magnitude by a temperature increase of 20 K, suggesting that the coal extracts-NMP mixtures undergoes a gel to sol transition. The heats of dissociation of crosslinks (ΔH_m) were estimated by applying Eldridge-Ferry equation. The ΔH_m of coal extracts-NMP mixtures was relatively small, i.e. approximately 10 kJ/mol, whereas the ΔH_m of polyvinyl alcohol-NMP gel in which the hydrogen bonds contribute the formation of the physical network structures, was about 65 kJ/mol. Not the specific interaction such as hydrogen bonds, but weak interactions such as van der Waals force were likely to contribute the formation of the coal extracts-NMP gel.     

Differential capacitance and frequency dispersion on solid and liquid mercury in liquid ammonia

The behaviour of solid and liquid mercury electrodes in 0·1 M ammonium nitrate solutions of liquid ammonia is investigated. The differential-capacitance/potential curves for the solid (at −40°C) and the liquid (at −38°C) are U-shaped and have a minimum of 11·2 μF/cm² at 0·45 V (vs Cd/satd. Cd(NO₃)₂ in liquid NH₃) for the solid of and 10·25 μF/cm² at 0·4 V for the liquid. The curves have no anodic hump. The values for the solid are about 10% higher than that for the liquid but this is still within the error of the surface area measurement. The frequency dispersion of the interfacial impedance was measured between 400 and 20,000 Hz at 0·60, 0·40, 0·10, and −0·25 V. Assuming de Levie's model of parallel grooves of depth l and aperture 2 β to be applicable, the parameter l/sin β was calculated from the data. Values obtained for the liquid mercury electrodes are 5·5–6·8 × 10⁻² cm and are attributed to shielding and solution creepage. For the solid electrodes l/sin β is 12–23 × 10⁻²cm. Although these numbers are too large, the increase in l/sin β by a factor of 3 when going from a liquid to a solid surface is parallel to an increase in roughness factor to about 3 expected for this case. This suggests that l/sin β may be a useful way to measure surface roughness and/or surface roughness changes.     

Study on the operating variables of sulcis coal hydroliquefaction

The hydroliquefaction of a high sulphur and bituminous Italian coal (Sulcis, Sardinia) was studied batchwise in a 1.5 dm³ autoclave to assess the influence of coal comminution (d_p = 45?664 μm), coal/solvent (c = 0.22 to 0.37 g coal/g solvent) and catalyst/coal (Y = 0?15 mg catalyst/g coal) ratios, and reaction time (t = 60?120 min) on the overall coal conversion (η_h), yields of oil (η_o) and asphaltene (η_a) and hydrodesulphurization (η_hs) by means of a composite design technique. Significant effects were observed on η_h by d_p, on η_o and η_a by Y, and on η_hs by Y and t, by means of an F-test on the basis of Yates's method. The variables were then fitted to a quadratic expression with an overall mean standard error of about 10%.The optimal range of the operating variables under the experimental conditions (i.e., 405°C, 150 bar) was derived by statistical treatment of the hydroliquefaction yield data and found to be d_p = 0.13 mm (100–150 mesh), c = 0.3 g coal/g solvent, Y = 13–15 mg catalyst/g coal and t = 100?130 min. Operating at these conditions results in an overall coal conversion approximately equal to 92%, oil and asphaltene yields ranging from 40 to 45%, and a 90% conversion of the initial sulphur into H₂S.     

Cell models for suspension viscosity

Cell models for the viscosity μ of a suspension of spherical particles in Newtonian fluid of viscosity μ₀ are discussed. Various boundary conditions on the outer boundary of the spherical cell lead to different results: the viscosity predicted for a zero velocity perturbation boundary condition is higher than those predicted with zero tangential stress perturbation. However, in all cases Einstein's prediction μ/μ₀=1+2.5φ+? holds in the limit of small solid volume fraction φ?1.     

Temperature-dependent aggregation of bio-surfactants in aqueous solutions of galactose and lactose: Volumetric and viscometric approach

Modulation in the aggregation behavior of bio-surfactants(bile salts), sodium cholate(NaC) and sodium deoxycholate(NaDC) in aqueous solutions of carbohydrates(galactose and lactose) have been investigated by measuring the density(ρ), speed of sound(u) and viscosity(η) of the mixtures at different temperatures293.15, 298.15, 303.15, 308.15 and 313.15 K. The density and speed of sound data have been used to calculate various volumetric and compressibility parameters such as apparent molar volume(V_φ), isentropic compressibility(κ_s), apparent molar adiabatic compression(κ_(s, φ)) to get a better insight into the micellization mechanism of bile salts. Further, the viscosity data have been studied in the light of relative viscosity(η_r) and viscous relaxation time(τ). Some derived parameters such as free volume(V_f), internal pressure(πi) and molar cohesive energy(MCE) of Na C and Na DC in aqueous solution of saccharides have also been calculated from viscosity data in conjunction with density and speed of sound values. All the calculated and derived parameters provide qualitative information regarding the nature of interactions i.e. solute–solute, solute–solvent and solvent–solvent in the solution.     

The influence of suspended solids on oxygen transfer to organic liquids in a bubble column

Volumetric mass transfer coefficients (k_La), and gas holdups (ε_G) were studied for the oxygen transfer into organic slurries. Aluminium oxide, polyvinylchloride and polyethylene were used as solid particles in ligroin and tetralin. It was found that the presence of particles can affect the mass transfer remarkably. Solids with high densities can increase k_La in small concentrations for liquids with low density and viscosity. When the density difference is small or the liquid viscosity is high, the slurry behaves as a pseudohomogeneous phase. Successful correlations were proposed for k_La and ε_G as a function of the effective suspension viscosity.     

Some aspects of structural transformations taking place in organic mass of Ukrainian coals during heating. Part 1. Study of structural transformations when heating coals of different caking capacity

The structure of the plastic layer in coals of different caking capacity was studied using the X-ray method and the influence of the plastic layer structure on the mechanism of coke formation was determined. It is shown that the transportation of the plastic mass in the gas-saturated zone of the plastic layer has a decisive influence on the decrease in volume of the coal charge and on obtaining a denser residue during carbonization. When heating poorly caking and non-caking coals an increase in the charge volume takes place.Using the quantitative X-ray phase analysis an ordered phase amount (C_cryst) was found in solid residues of carbonization and the parameters d₀₀₂, L_c and L_a were determined. It is shown that the gas-saturated zone is generated in the plastic layer only when structural transformations in coals take place at the pre-plastic stage without changing the ratio between the number of carbon atoms in the ordered and non-ordered phases. The transition of well caking coal into the plastic state is accompanied by the activation of segmental and conformal movement of side chains and separate macromolecular fragments of the coal organic mass. In the course of grain swelling of non-caking coal its crystallites degrade. The conclusions drawn on the basis of X-ray studies were confirmed by the EPR-spectroscopy of residues corresponding to plastic zones in coals of different caking capacity.     

Comparison of surface mechanical properties among linear and star polystyrenes: Surface softening and stiffening at different temperatures

In a previous study, we reported both surface softening and stiffening for poly(α-methylstyrene) (PαMS) over a temperature range from room temperature to 21 °C above the glass transition temperature (T_g) using the spontaneous particle embedment technique. In the present study, we have explored the surface mechanical responses of a linear polystyrene (PS), a 3-arm star PS, and an 8-arm star PS emphasizing the range of temperature from T_g −10 °C to T_g +10 °C, similar to that in which the prior study had shown a transition from surface softening (increased mobility) to stiffening (decreased mobility). We used atomic force microscopy for particle embedment depth estimation and the isochronal form of the Lee and Radok (LR) model for surface compliance determination. We observed both surface softening and stiffening for the linear PS and 3-arm star PS for the studied temperature range. However, surface softening was observed at all temperatures in this study for the 8-arm star PS. The surface compliance results for the different PS molecular architectures are compared with those for the linear PαMS from the previous study.     

Fusibility and flow properties of coal ash and slag

We studied the fusibility and flow properties of laboratory ash and Shell gasifier slag from the same coal sample (Chinese Huainan coal). The physical properties of ash and slag were analyzed with X-ray fluorescence, X-ray diffraction, and scanning electron microscopy. The fusion temperature and the experiment viscosity were measured for the ash and slag with the addition of fluxing CaO. Ash and slag have properties that were approximated by the SiO₂-Al₂O₃-‘FeO’-CaO system. The computer software package FactSage was used to predict the proportion of solid phase and the mineral phase formed as a function of the composition and the temperature of the SiO₂-Al₂O₃-‘FeO’-CaO system. The results show that the fusion temperatures and the temperature of critical viscosity (T_cv) of ash are always higher than that of slag. Also, the viscosity of ash is always higher than that of slag at the slag tapping temperature range of 1400-1500 °C, and the hysteresis between the heating and cooling cycles for ash is more obvious than that of slag because of different physical properties. The fusion temperature and T_cv of ash and slag decrease with increasing CaO content, whereas those values increase rapidly with CaO content higher than 35%. Also, the sensitivity of the viscosity of the ash and slag with temperature decreases with increasing CaO content because the sensitivity of the phase equilibria of in the SiO₂-Al₂O₃-‘FeO’-CaO system to temperature excursions decreases with increasing CaO content.     

Rheology of Concentrated AP/HTPB Suspensions Prepared at the Upper Limit of AP Content

Due to the requirements for the preparation of an ammonium perchlorate (AP)/hydroxy‐terminated polybutadiene (HTPB) based composite propellant, an upper limit content of AP applicable in the propellant, φ_max (wt%), exists. The rheology of concentrated AP/HTPB suspensions prepared at φ_max is investigated in this study. The relative viscosity, η_rφ(‐), of the suspensions prepared at φ_max is almost constant at approximately 200. For the suspensions prepared at φ_max, the HTPB layer thickness, H_φp (µm), on the AP particle, calculated from the specific surface area measured by the air‐permeability method, is closely related to the void fraction, ε_max(‐), for the loose packing of the AP powder. H_φp decreases with increasing ε_max. By reversal conclusion it was found that the relative viscosity of the suspension, of which the HTPB layer thickness is H_φp, will accordingly be η_rφ.     

Electrochemical formation of nanometric layers of tin selenides on Ti surface

Photoelectrically active tin selenide coatings of nanometric thickness were manufactured by electrodeposition from separate solutions of Sn and Se precursors. Sn was deposited from acidic SnSO₄ electrolytes and Se was deposited from H₂SeO₃ solutions. Fine-grained Sn coatings were deposited at potential φ = −0.3 V with 100% current efficiency. Se coatings were formed at two potentials: φ = −0.5 V, forming Se⁰, and φ = −0.85 V, forming Se²⁻ ions. After the Sn coating was immersed into H₂SeO₃ solution, small quantities (∼2 at.%) of SnSe were formed and SeO₃²⁻ was adsorbed on the surface. A short-time deposition of Se at φ = −0.5 V passivated the surface, so no Sn dissolution is observed upon anodic polarization. XPS and Auger data indicated that under those conditions 20 at.% of Se⁰ and only 2 at.% of SnSe were formed. Thickening of Sn and Se layers led to formation of larger quantities of Se⁰ (75 at.%) and SnSe (4-5 at.%) on the surface, whereas deeper layers contained up to 10 times more of SnSe phase. Upon deposition of Se at φ = −0.85 V, new SnSe₂ phase was formed and the quantity of SnSe phase is increased and that of Se⁰ was reduced. All coatings formed exhibited photoelectric properties.     

An empirical approach for predicting kinematic viscosities of biodiesel blends

Kinematic viscosity (η) is an important property of diesel fuels, including biodiesels, which are marketed mostly as the blends in many countries around the world. In this study, the free energy of viscous flow (ΔG_vis) for a non-associated liquid mixture is assumed to be the summed of ΔG_vis of individual components. Hence, the Eyring’s equation, η = Ae(−ΔG_vis/RT), is transformed to ln η_blend = a + bn₁ + c/T + dn₁/T (where, a, b, c and d, T and n₁ are thermodynamically related constants, absolute temperature and mole fraction of biodiesel, respectively). The transformed equation is used to predict kinematic viscosity of biodiesel blends (η_blend) of different degree of blending at any temperatures from pour point to 100 °C. The predicted kinematic viscosities are in good agreement with those reported in literatures at all temperatures. The highest deviation is ±5.4% and the average absolute deviation (AAD) is less than 2.86%. The transformed equation can also be used to predict kinematic viscosities of pure fatty acid methyl esters in diesel fuel. Methyl ricinoleate is an exception. The AAD is 4.50% and the deviation is as high as 12.80%. The high deviation suggests that molecular interactions between methyl ricinoleate and diesel fuel is high and cannot be ignored.     

Stress softening of multigraft copolymers

The hysteresis behaviour of multigraft (MG) copolymers, with a polyisoprene backbone and polystyrene (PS) side chains, was investigated by applying a modified softening model proposed by Elías-Zúñiga, which uses an approach of Ogden and Roxburgh. The model was combined with the non-affine tube model of rubber elasticity of Kaliske and Heinrich. Four parameters are obtained: chemical and physical cross-link moduli (G_c, G_e), the number of statistical segments between two successive entanglements (n_e/T_e) and a softening parameter (b). The model was proven to be valid by a comparison with other methods evaluating hysteresis behaviour. The characterization of the multigraft copolymers revealed a branch point and molecular architecture dependence of the softening parameter. b was low for tetrafunctional MG copolymers with cylindrical microdomains, and it was further reduced for a spherical morphology and for more complex molecular architectures. The magnitude of b also depends on the PS arm molecular weight for hexa- and tetrafunctional multigraft copolymers.     

Influence of coal thermoplastic properties on coking pressure generation: Part 2 - A study of binary coal blends and specific additives

A number of coal blends and pitch/coal blends were evaluated using rheometry, thermogravimetric analysis and microscopy to confirm and further elucidate the coking pressure mechanism previously proposed by Duffy et al. (2007) [1]. We confirm that blending a low rank, high fluidity, low coking pressure coal, with a high rank, low fluidity, high coking pressure coal can significantly reduce the coking pressure associated with the latter. Interestingly, blending does not necessarily result in a fluidity that is midway between that of the two coals; sometimes the fluidity of the blend is less than that of the low fluidity coal, especially when the coals are significantly different in rank. This occurs because the increase in complex viscosity (η*) through resolidification of the low rank, high fluidity coal counteracts the reduction in η* resulting from softening of the high rank, low fluidity coal. It has also been confirmed that the η* of the resultant blend can be estimated from the η* of each component coal using a logarithmic additivity rule commonly employed for polymer blends.Polarised light microscopy has indicated that the degree of mixing between coals of different rank is minimal, with fusion restricted to the particle surface. It is therefore inappropriate to think of such a coal blend in the same way as a single coal, since each component coal behaves relatively independently. This limited fusion is important for understanding the coking pressure mechanism for blends. It is proposed here that the lower rank coal, which softens at lower temperature, is able to expand into the interparticle voids between the high rank coal that is yet to soften, and these voids can create channels for volatiles to traverse. Then, and importantly, when the high rank coal begins to expand, the pore structure developed in the resolidified structures of the low rank coal can facilitate removal of volatiles, while the resolidified material may also act as a suitable sorbent for volatile matter. This is considered to be the primary mechanism by which coal blending is able to alleviate coking pressure, and applies to addition of inert material also.Addition of a coal tar pitch was found to increase fluidity but also to extend the thermoplastic range to lower temperatures. This caused an increase in the swelling range, which was accompanied by a long plateau in η*, a feature which has previously been observed for certain high fluidity, high pressure coals. Elasticity and η* at the onset of expansion were also higher for both the pitch impregnated coals and the high pressure blends, which supports previous findings for singly charged high pressure coals, and confirms the potential use of such criteria for identifying potentially dangerous coals/blends.     

Molecular characteristics of poly(1-trimethylsilyl-1-propyne) in dilute solutions

Samples and fractions of a membrane-forming polymer, poly(1-trimethylsilyl-1-propyne) (PTMSP), were studied by methods of molecular hydrodynamics (velocity sedimentation, translational isothermal diffusion and viscometry) in cyclohexane in the molecular mass range 60<M×10⁻³ g mol⁻¹<430. The following molecular-mass dependencies of the hydrodynamic characteristics (intrinsic viscosity [η] (cm³ g⁻¹), sedimentation coefficient s₀(s) and translational diffusion coefficient D₀ (cm² s⁻¹)) were established: [η]=0.198 M^0.50±0.06; s₀=8.66×10⁻¹⁶M^0.50±0.04; D₀=9.30×10⁻⁵M^{−0.50±0.04}. On the basis of the hydrodynamics data the equilibrium rigidity and hydrodynamic diameter of PTMSP chains were evaluated. The equilibrium properties of the different disubstituted polyacetylenes molecules are compared on the base of the normalised scaling plots.     

Electrochemical investigation of LiMn2O4 cathodes in gel electrolyte at various temperatures

A composite lithium battery electrode of LiMn₂O₄ in combination with a gel electrolyte (1 M LiBF₄/24 wt% PMMA/1:1 EC:DEC) has been investigated by galvanostatic cycling experiments and electrochemical impedance spectroscopy (EIS) at various temperatures, i.e. −3<T<56 °C. For analysis of EIS data, a mathematical model taking into account local kinetics and potential distribution in the liquid phase within the porous electrode structure was used. Reasonable values of the double-layer capacitance, the exchange-current density and the solid phase diffusion were found as a function of temperature. The apparent activation energy of the charge-transfer (∼65 kJ mol⁻¹), the solid phase transfer (∼45 kJ mol⁻¹) and of the ionic bulk and effective conductance in the gel phase (∼34 kJ mol⁻¹), respectively, were also determined. The kinetic results related to ambient temperature were compared to those obtained in the corresponding liquid electrolyte. The incorporated PMMA was found to reduce the ionic conductivity of the free electrolyte, and it was concluded that the presence of 24 wt% PMMA does not have a significant influence on the kinetic properties of LiMn₂O₄.     

Thermogravimetric analysis and kinetics of coal/plastic blends during co-pyrolysis in nitrogen atmosphere

Investigations into the co-pyrolytic behaviours of different plastics (high density polyethylene, low density polyethylene and polypropylene), low volatile coal and their blends with the addition of the plastic of 5 wt.% have been conducted using a thermogravimetric analyzer. The results indicated that plastic was decomposed in the temperature range 438–521 °C, while the thermal degradation temperature of coal was 174–710 °C. The overlapping degradation temperature interval between coal and plastic was favorable for hydrogen transfer from plastic to coal. The difference of weight loss (?W) between experimental and theoretical ones, calculated as an algebraic sum of those from each separated component, was 2.0–2.7% at 550–650 °C. These experimental results indicated a synergistic effect during plastic and coal co-pyrolysis at the high temperature region. In addition, a kinetic analysis was performed to fit thermogavimetric data, the estimated kinetic parameters (activation energies and pre-exponential factors) for coal, plastic and their blends, were found to be in the range of 35.7–572.8 kJ/mol and 27–1.7 × 10³⁸ min^− 1, respectively.