Mass transfer and deodorization efficiency in a countercurrent spray tower for low superficial gas velocities

The aim of this study was to characterize mass transfer and deodorization efficiency in a countercurrent spray tower for low superficial gas velocities. The influence of operating parameters (U_G = 0.005 to 0.025 m s^?1, U_L = 6.1 × 10^?5 to 2.4 × 10^?4 m s^?1) on the liquid retention (ε_L), the drop diameter (d_g), the interfacial area (a) and the overall liquid and gas phase mass transfer coefficients (K_La, K_Ga) were estimated. The spray efficiency of some malodorous compounds was also estimated. A negative influence of the superficial gas velocity was demonstrated, during the spraying of water or chemical neutralizing scrubbing solutions. There was also an increase with the liquid flow rate. Abatements obtained were very good with respect to ammonia (>90%), and acceptable for the other compounds.     

Gas‐Liquid Mass Transfer in a Slurry Bubble Column at High Slurry Concentrations and High Gas Velocities

The volumetric mass transfer coefficient k_La in a 0.1 m‐diameter bubble column was studied for an air‐slurry system. A C₉‐C₁₁ n‐paraffin oil was employed as the liquid phase with fine alumina catalyst carrier particles used as the solid phase. The n‐paraffin oil had properties similar to those of the liquid phase in a commercial Fischer‐Tropsch reactor under reaction conditions. The superficial gas velocity U_G was varied in the range of 0.01 to 0.8 m/s, spanning both the homogeneous and heterogeneous flow regimes. The slurry concentration ?_S ranged from 0 to 0.5. The experimental results obtained show that the gas hold‐up ?_G decreases with an increase in slurry concentration, with this decrease being most significant when ?_S < 0.2. k_La/?_G was found to be practically independent of the superficial gas velocity when U_G > 0.1 m/s is taking on values predominantly between 0.4 and 0.6 s^–1 when ?_S = 0.1 to 0.4, and 0.29 s^–1, when ?_S = 0.5. This study provides a practical means for estimating the volumetric mass transfer coefficient k_La in an industrial‐size bubble column slurry reactor, with a particular focus on the Fischer‐Tropsch process as well as high gas velocities and high slurry concentrations.     

Drift Flux Modelling for a Two‐Phase System in a Flotation Column

Using different two‐phase systems, a laboratory flotation column was operated over a wide range of bubble size from 250 to 1100 µm. The drift flux analysis for the tests was used to obtain a new correlation to relate the characteristic exponent m in the drift flux equation j_gf = U_tα_g(1 — α_g)^m, to bubble Reynolds number, where j_gf is the drift flux, U_t is the terminal velocity of an individual bubble, α_g is the gas volume fraction, and m is an exponent that depends on flow conditions. m = 20.26 + 1.89 Re_b/4.38 + Re_b.     

Bubble size and radial gas hold‐up distributions in a slurry bubble column using ultrafast electron beam X‐ray tomography

Gas hold‐up and bubble size distribution in a slurry bubble column (SBC) were measured using the advanced noninvasive ultrafast electron beam X‐ray tomography technique. Experiments have been performed in a cylindrical column (D_T = 0.07 m) with air and water as the gas and liquid phase and spherical glass particles (d_P = 100 μm) as solids. The effects of solid concentration (0 ≤ C_s ≤ 0.36) and superficial gas velocity (0.02 ≤ U_G ≤ 0.05 m/s) on the flow structure, radial gas hold‐up profile and approximate bubble size distribution at different column heights in a SBC were studied. Bubble coalescence regime was observed with addition of solid particles; however, at higher solid concentrations, larger bubble slugs were found to break‐up. The approximate bubble size distribution and radial gas hold‐up was found to be dependent on U_G and C_s. The average bubble diameter calculated from the approximate bubble size distribution was increasing with increase of U_G. The average gas hold‐up was calculated as a function of U_G and agrees satisfactorily with previously published findings. The average gas hold‐up was also predicted as a function of C_s and agrees well for low C_s and disagrees for high C_s with findings of previous literature. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1709–1722, 2013     

The Voidage Function for the Drag Force Ratio in a Liquid‐Fluidized Bed

Di Felice (1994) has shown that the ratio of the drag coefficient, C_D, on a sphere in a liquid‐fluidized bed of uniform spheres to the drag coefficient, C_DS, on the same sphere in isolation and subjected to the same superficial liquid velocity, u, is given by a function ?^?β, where β was expressed as an empirical function of the particle Reynolds number, Re = duρ/µ. Here it is shown that C_D/C_DS is well approximated by ?^?mm, where the Richardson‐Zaki index n is a function of the terminal free‐settling Reynolds number, Re_t = du_tρ/µ, and m is 2 plus the slope of the standard log C_DS vs. log Re plot at plot at Re = Re_t. The present model, using the best experimentally confirmed equation for n and a new simple equation for and a new simple equation for m, is compared with that of Di Felice in their respective abilities to predict liquid‐fluidized bed expansion.     

Multiple effects of operating variables on heat transfer in three-phase slurry bubble columns

Characteristics of heat transfer were investigated in pressurized slurry bubble column reactors whose diameter was either 0.051, 0.076, 0.102 or 0.152 m (ID) and 1.5 m in height, respectively. Effects of gas velocity (U _G ), solid contents (S _C ), pressure (P), liquid viscosity (μ _L ) and column diameter (D) on the heat transfer coefficient (h) between the immersed vertical heater and the column were determined. Multiple effects such as UG and D, P and D, μ _L and D, and S _C and D on the value of heat transfer coefficient were discussed. Temperature fluctuations were also measured and analyzed by adapting chaos theory, which was used to explain the effects of operating variables on the heat transfer in the column. The heat transfer coefficient increased with increasing gas velocity, pressure or solid content in the slurry phase, but decreased with increasing liquid viscosity or column diameter. The decrease trend of h with increasing column diameter was somewhat sensitive when the gas velocity was relatively high (U _G ⩾12 cm/s). The effects of column diameter on the h value became almost linear when the operating pressure (P=4−10 kg _f /cm²), liquid viscosity (μ _L =20−38 mPa·s) or solid content in the slurry phase (S _C =10−20 wt%) was relatively high and gas velocity was relatively low, within these experimental conditions. The heat transfer coefficient was well correlated in terms of dimensionless groups as well as operating variables.     

Influence of the lift force closures on the numerical simulation of bubble plumes in a rectangular bubble column

Numerical Eulerian-Eulerian simulations of the unsteady gas-liquid flow in a centrally aerated two-dimensional bubble column were carried out in order to understand the effect of different formulations of the lift force coefficient (C_L) on the computational results. Three different values of the superficial gas velocity (U_G=2.4, 12.0 and 21.3 mm s⁻¹) that ensure the existence of different flow regimes were experimentally and computationally studied. The validation of the simulated results was based on visual observations and measurements of the global gas hold-up (ε_G) and the plume oscillation period (POP). The results presented reveal that, at U_G=12.0 and 21.3 mm s⁻¹, using C_L<0 results in under- and over-estimation of the ε_G and POP, respectively. On the other hand, taking C_L>0 does not affect the POP while it leads to increasingly higher ε_G values, which are different from those experimentally reported. At U_G=2.4 mm s⁻¹, the effect of the lift force is not so evident, although it slightly improves the prediction of experimental values. Particularly interesting is the case of C_L>0.4 at U_G=21.3 mm s⁻¹, producing a non-symmetric bubble plume oscillation. Since using Tomiyama's lift coefficient correlation does not improve the results, including the lift force into the simulation of bubble plumes is not recommended.     

Radial Liquid Dispersion and Bubble Distribution in Three‐Phase Circulating Fluidized Beds

The liquid dispersion and bubble distribution in the radial direction have been investigated in the riser of a three‐phase circulating fluidized bed whose diameter is 0.102m and 3.5m in height. Effects of gas and liquid velocities and solid circulation rate have been determined. It has been found that the radial distribution of bubbles is related closely to the liquid dispersion in the radial direction. The size and rising velocity of bubbles tend to increase as the radial position approaches to the center of the riser. The bubble size increases with increasing U_G, but it decreases with increasing U_L or G_S in all radial positions. The radial dispersion coefficient of the liquid phase increases with increasing U_G or G_S, however, it tends to decrease with increasing U_L. The value of Dr has been well correlated in terms of dimensionless groups based on the isotropic turbulence model.     

Electrodeposition from a fluidized bed electrolyte. II. Effects of bed porosity and particle size

Mass transfer from a fluidized bed electrolyte containing inert particles has been found to depend on bed porosity and particle size. The optimum porosity was found to vary from 0.52 – 0.57 with decreasing particle size but mass transport increased with particle size.A mass transfer entry length effect was observed on the cylindrical cathode but its position within the bulk of the bed was found not to be critical, thus indicating that the hydrodynamic entry length was small. The limiting current density was found to vary as (d _e/L _e)^0.15 whered _e is the annular equivalent diameter andL _e the electrode length.List of symbols Re_I modified Reynolds No. =U _o d _p /v(1–) - Re_II particle Reynolds No. =U _o d _p /v - Re_O sedimentation Reynolds No. =U _i d _p v (constant value) - Re_t terminal particle Reynolds No. =U _t d _p /v - Sc Schmidt No. =v/D - St_I modified Stanton No. =k _L /U _o - C _b bulk concentration, M cm^–3 - D diffusion coefficient, cm² s^–1 - d _t tube diameter, mm - d _e electrode equivalent diameter, mm - d _p particle diameter, mm - bed porosity - zF Faradaic equivalence - cd current density - i _L limiting current density, mA cm^–2 - i _LO limiting current density in the absence of particles - k _L mass transfer coefficient, cm s_–1 - L _e electrode length, mm - m, n constants or indices - v kinematic viscosity, cm² s^–1 - U _o superficial velocity, cm s^–1 - U _i sedimentation velocity, cm s^–1     

Phenoxaphosphino‐Modified Xantphos‐Type Ligands in the Rhodium‐Catalysed Hydroformylation of Internal and Terminal Alkenes

The solubility of the modifying ligand is an important parameter for the efficiency of a rhodium‐catalysed hydroformylation system. A facile synthetic procedure for the preparation of well‐defined xanthene‐type ligands was developed in order to study the influence of alkyl substituents at the 2‐, and 7‐positions of the 9,9‐dimethylxanthene backbone and at the 2‐, and 8‐positions of the phenoxaphosphino moiety of ligands 1 – 16 on solubility in toluene and the influence of these substituents on the performance of the ligands in the rhodium‐catalysed hydroformylation. An increase in solubility from 2.3 mmol⋅L⁻¹ to >495 mmol⋅L⁻¹ was observed from the least soluble to the most soluble ligand. A solubility of at least 58 mmol⋅L⁻¹ was estimated to be sufficient for a large‐scale application of these ligands in hydroformylation. Highly active and selective catalysts for the rhodium‐catalysed hydroformylation of 1‐octene and trans‐2‐octene to nonanal, and for the hydroformylation of 2‐pentene to hexanal were obtained by employing these ligands. Average rates of >1600 (mol aldehyde) × (mol Rh)⁻¹×h⁻¹ {conditions: p(CO/H₂) = 20 bar, T = 353 K, [Rh] = 1 mM, [alkene] = 637 mM} and excellent regio‐selectivities of up to 99% toward the linear product were obtained when 1‐octene was used as substrate. For internal olefins average rates of >145 (mol aldehyde)×(mol Rh)⁻¹×h⁻¹ {p(CO/H₂) = 3.6–10 bar, T = 393 K, [Rh] = 1 mM, [alkene] = 640–928 mM} and high regio‐selectivities up to 91% toward the linear product were obtained.     

Correlation between current–voltage (I–V) characteristic in the electric–thermal equilibrium state and resistivity‐temperature behavior of electro‐conductive silicone rubber

In the electric–thermal equilibrium state the current–voltage (I–V) characteristics of conductive silicone rubbers above the percolation threshold are found to be nonlinear. A mathematic model as I = a₁U ± (a₂U² + C) has been built for the nonlinear I–V relations. Constant C and quadratic term a₂U² can be considered as deviation from Ohm's law. For the first time, a correlation is found for conductive silicone rubber between the I–V characteristic in the electric–thermal equilibrium state and the resistivity–temperature characteristic. Samples with positive temperature coefficient (PTC) resistivity effect exhibit negative deviation from linearity, with an I–V relation as I = a₁U ? (a₂U² + C). Samples with negative temperature coefficient (NTC) resistivity effect exhibit positive deviation, with an I–V relation as I = a₁U + (a₂U² + C). The higher the loaded voltage, the more pronounced the deviation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Graft copolymerization of methacrylic acid onto xanthan gum by Fe2+/H2O2 redox initiator

The graft copolymer of xanthan gum with methacrylic acid was synthesized in inert atmosphere by using Fentos reagent as a redox initiator. The effect of reaction conditions on grafting parameters [G(%), E(%), C(%), A(%), H(%), and R_g] was investigated. Similar trend was observed on increasing the concentration of ferrous ion and hydrogen peroxide from 4.0 to 20.0 × 10^?3 mol dm^?3 and 2.5 to 10 × 10^?3 mol dm^?3 respectively, i.e., initially grafting parameters increased and after a certain range of concentration grafting parameters showed decreasing trend. Hydrogen ion shows influenced result i.e., small increment of concentration in hydrogen ion presents much increment in percent of grafting. It was observed that the [G(%), E(%), C(%), A(%), and R_g] increased upto 6.67 × 10^?2 mol dm^?3 concentration of methacylic acid after that it decreased. Maximum G(%) was obtained at minimum concentration of xanthan gum i.e., at 40 × 10^?2 g dm^?3. The optimum temperature and time duration of reaction for maximum percentage of grafting were found to be 45°C and 150 min respectively. Thermogravimetric analysis showed that the xanthan gum‐g‐methacrylic acid is thermally more stable than pure gum. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Dynamic light‐scattering characterization of the molecular weight distribution of unfractionated polyimide

Using a developed laser light‐scattering (LLS) procedure, we accomplished the characterization of an unfractionated polyimide (UPI) in CHCl₃ at 25°C. The Laplace inversion of precisely measured intensity–intensity time correlation function from dynamic LLS leads us first to an estimate of the characteristic line‐width distribution G(Γ), and then to the translational diffusion coefficient distribution G(D). By using a previously established calibration of D (cm²/s) = 3.53 × 10^?4 M^?0.579, we were able to convert G(D) into a molecular weight distribution. The weight‐average molecular weight M_w, calculated from the molecular weight distribution, agrees well with that directly measured in static LLS. Our results indicate that both the calibration and LLS procedure used in this study are ready to be applied as a routine method for the characterization of the molecular weight distribution of polyimide. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1670–1674, 2001     

EDTA and pH‐sensitive crosslinking polymerization of acrylic acid, 2‐acrylamidoglycolic acid,and 2‐acrylamide‐2‐methyl‐1‐propanesulfonic acid

Network formation was monitored by shear storage modulus (G′) during free radical crosslinking polymerization to investigate the effects of pH and ethylenediaminetetraacetic acid (EDTA; a complex agent). Three types of acrylic monomers, acrylic acid (AAc), 2‐acrylamidoglycolic acid (AmGc), and 2‐acrylamido‐2‐methyl propanesulfonic acid (AmPS), were polymerized in the presence of a crosslinking agent. The ratio of crosslinking agent (methylene bis‐acrylamide; MBAAm) to monomer was varied as: 0.583 × 10^?3, 1.169 × 10^?3, 1.753 × 10^?3, and 2.338 × 10^?3. G′ of the hydrogel in crosslinking polymerizations of AAc and AmPS was effectively increased by addition of EDTA, which was not the case for the crosslinking polymerization of AmGc. The order of magnitude of G′ differed based on the acidity of monomer. The maximum values of G′ in crosslinking polymerizations of AAc, AmGc, and AmPS were ～20,000 Pa, 6000 Pa, and 400 Pa, respectively. G′ varied linearly with the molecular weight between crosslinks (M_wc). pH and EDTA‐complex affected the rate of intramolecular propagation during crosslinking polymerization. Our results indicated that G′ was primarily affected by the following factors in the order: (1) acidity of monomer, (2) M_wc, and (3) physical interactions induced by pH and EDTA. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41026.     

Measurement of mass transfer coefficient in an airlift reactor with internal loop using coalescent and non‐coalescent liquid media

In this work the sulfite oxidation (SOM), dynamic pressure‐step (DPM) and gassing‐out (GOM) methods were compared for volumetric mass transfer coefficient measurement in an airlift reactor with internal loop. As a liquid phase both, non‐coalescent and coalescent media were used. Among the methods discussed here, the mass transfer coefficient (k_La) values obtained by the DPM appear as the most reliable as they were found to be independent of oxygen concentration in the inlet gas, which confirmed the physical correctness of this method. The difference between data measured using air and oxygen was not higher than 10%, which was comparable to the scatter of experimental data. It has been found that the sulfite oxidation method yielded k_La values only a little higher than those obtained by the DPM and the difference did not exceed 10%. Up to an inlet gas velocity (U_GC) of ?0.03 m s^?1 the GOM using oxygen as a gas medium gave k_La values in fact identical with those obtained by the DPM. At higher flows of the inlet gas, the GOM yielded k_La values as much as 15% lower. The enhancement in oxygen mass transfer rate determined in non‐coalescent media was estimated to be up to +15%, when compared with a coalescent batch. The experimental dependence of k_La vs the overall gas hold‐up was described by an empirical correlation. 1 Copyright © 2004 Society of Chemical Industry     

Synthesis,speed of ultrasound and associated acoustical parameters of epoxy acrylate of 9,9′‐bis (4‐hydroxy phenyl) anthrone‐10 solutions

Density (ρ), viscosity (η), and speed of ultrasound (U) (2 MHz) of pure solvents (chloroform, THF, and 1,4‐dioxane) and solutions of epoxy acrylate of 9,9′‐bis(4‐hydroxy phenyl) anthrone‐10 (EAAN) have been investigated at 303, 308, and 313 K. Specific acoustical impedance (Z), isentropic compressibility (κ_s), intermolecular free path length (L_f), classical absorption coefficient (α/f²)_cl, and viscous relaxation time (τ) have been determined from ρ, η, and U data and are correlated with concentration. Z, (α/f²)_cl, and τ increased with C and decreased with T, while κ_s and L_f decreased with C and increased with T in the solvent systems studied. A fairly good to excellent correlation between a given parameter and concentration is observed in solvent systems studied. Linear increase or decrease of acoustical parameters with concentration and temperature indicated existence of strong molecular interactions. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Thermal Expansion of Rare‐Earth Pyrosilicates

The use of RE₂Si₂O₇ materials as environmental barrier coatings (EBCs) and in the sintering process of advanced ceramics demands a precise knowledge of the coefficient of thermal expansion of the RE₂Si₂O₇. High‐temperature X‐ray diffraction (HTXRD) patterns were collected on different RE₂Si₂O₇ polymorphs, namely A, G, α, β, γ, and δ, to determine the changes in unit cell dimensions. RE₂Si₂O₇ compounds belonging to the same polymorph showed, qualitatively, very similar unit cell parameters behavior with temperature, whereas the different polymorphs of a given RE₂Si₂O₇ compound exhibited markedly different thermal expansion evolution. The isotropy of thermal expansion was demonstrated for the A‐RE₂Si₂O₇ polymorph while the rest of polymorphs exhibited an anisotropic unit cell expansion with the biggest expansion directed along the REO_x polyhedral chains. The apparent bulk thermal expansion coeficcients (ABCTE) were calculated from the unit cell volume expansion for each RE₂Si₂O₇ compound. All compounds belonging to the same polymorph exhibited similar ABCTE values. However, the ABCTE values differ significantly from one polymorph to the other. The highest ABCTE values correspond to A‐RE₂Si₂O₇ compounds, with an average of 12.1 × 10^?6 K^?1, whereas the lowest values are those of β‐ and γ‐RE₂Si₂O₇, which showed average ABCTE values of ~4.0 × 10^?6 K^?1.     

Rheological and thermal properties of saponified cassava starch‐g‐poly(acrylamide) superabsorbent polymers varying in grafting parameters and absorbency

Cassava starch‐graft‐poly(acrylamide) superabsorbent polymers (SAPs) with varying absorbencies were synthesized. Weight average molecular weight (M_w) of the hydrolyzed starch‐graft‐copolymers ranged from 1.6 × 10⁶ to 2.8 × 10⁶ g/mol, the largest being shown by the sample with highest percentage grafting. The storage (G′) and loss modulus (G″) of hydrogels were determined as a function of frequency. G″ was larger than G′ for the hydrogels with higher absorbencies and exhibited a liquid‐like behavior. However, hydrogels with lower absorbencies showed a reverse viscoelastic behavior. The viscosity of hydrogels determined using a Brookfield viscometer at different shear rates was found to be larger for the hydrogels with higher absorbencies. The melting temperature (T_m) and enthalpy change of fusion (ΔH_f) of the SAPs ranged from 149.7 to 177.7°C and 65 to 494.9 J/g, respectively and showed a positive correlation with grafting parameters and M_w. Heavy metal ion removal capacity of hydrogel followed the order Cu²⁺ > Pb²⁺ > Zn²⁺. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40368.     

Synthesis and characterization of chitosan‐g‐methacrylic acid and studies of its additional physicochemical properties,such as swelling,metal‐ion sorption,and flocculation behavior

The aim of this study was to examine the synthesis of a graft copolymer of chitosan and methacrylic acid (MAA) by free‐radical polymerization with a potassium peroxymonosulfate/cyclohexanone (CY) redox system in an inert atmosphere. The optimum reaction conditions affording maximum grafting ratio (%G), grafting efficiency (%E), add on (%A), and conversion (%C) were determined. The grafting parameters were found to increase with increasing concentration of MAA up to 24 × 10^?2 mol/dm³, but thereafter, these parameters decreased. With increasing concentration of peroxymonosulfate from 0.6 × 10^?2 to 1.2 × 10^?2 mol/dm³, %G, %A, and %E increased continuously. All of these grafting parameters increased with increasing concentration of CY up to 1.2 × 10^?2 mol/dm³, but beyond this concentration, the grafting parameters decreased. With various concentrations of chitosan from 0.6 to 1.4 g/dm³, the maximum %G, %A, and %E were obtained at 1.4 g/dm³. %G, %A, and %C decreased continuously with various concentrations of hydrogen ions from 2 × 10^?3 to 6 × 10^?3 mol/dm³. The grafting parameters increased with increasing temperature up to 35°C, but thereafter, these parameters decreased. With increasing time period of reaction from 60 to 180 min, %G, %A, and %E increased up to 120 min, but thereafter, these parameters decreased. The graft copolymer was characterized by Fourier transform infrared spectroscopy and thermogravimetric analysis. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Hydrodynamic characteristics of cold-bed circulating fluidized beds for the methanol to olefins process

The effects of the riser inlet velocity (2.2–3.9 m/s), seal-pot inlet velocity (2.4–7.1 U _mf ), aeration flow rate (2.5×10^?7–3.7×10^?6 m³/s) in seal-pot, and solid inventory (0.15–0.2 kg) on the hydrodynamic characteristics of a 9 mm-ID×1.9 m-high cold-bed circulating fluidized bed for methanol to olefins (MTO) process were investigated. FCC (Engelhard; 82.4 μm) particles were used as bed particles. Most of the experimental flow regimes were observed in fast fluidization and pneumatic transport regimes. The axial solid holdup in a riser increased with increasing solid mass flux and solid inventory. Solid mass flux increased proportionally until reaching a maximum value and then decreased with increasing seal-pot inlet velocity. The obtained hydrodynamic characteristics in the cold-bed circulating fluidized beds were compared with previous results.