Wide Range Of Process Conditions Research Articles

Composite ionic liquid and polymer membranes for gas separation at elevated temperatures

In recent years, the utilization of ionic liquids supported on porous polymer membranes has been demonstrated to enhance gas separation performance by improving both permeability and selectivity for several industrially-relevant gas mixtures. However, the use of such supported ionic liquid membranes (SILMs) is normally not feasible at elevated process temperatures due to the resulting decrease in ionic liquid viscosity, which can lead to increased loss of ionic liquid from the membrane support during operation. In addition, many of the polymer membranes typically used in SILMs exhibit relatively poor mechanical and thermal stabilities at high temperatures. To overcome these problems associated with SILMs, thermally-stable composite ionic liquid and polymer membranes (CILPMs) have been fabricated in this study, thus exploiting the beneficial properties of ionic liquids for gas separation at elevated temperatures. Poly(pyromellitimide-co-4,4′-oxydianiline) (PMDA-ODA PI) and polybenzimidazole (PBI) in combination with the ionic liquid, [C4mim][NTf2] were used to fabricate the CILPMs. A measurement rig was designed and built to determine permeabilities and selectivities of the CILPMs for H2, N2, CO, CO2 and CH4 over a range of pressures and temperatures. The fabricated CILPMs were shown to maintain excellent mechanical and thermal stability over a wide range of processing conditions. Temperature was shown to greatly affect both permeability and selectivity of the membranes, whilst pressure had less influence. The incorporation of [C4mim][NTf2] into the membranes was found to significantly increase CO2 permeation and, therefore, it is anticipated that these CILPMs hold significant potential for CO2 separation applications.

Influence of shrinkage on convective drying of fresh vegetables: A theoretical model

The aim of the present work was the formulation of a theoretical model predicting the behavior of a convective drier over a wide range of process conditions. The proposed approach was based on the coupling of a transport phenomena model, describing the simultaneous transfer of momentum, heat and mass both in the drying chamber and in the food, and of a structural mechanics model aimed at estimating food sample deformations, as due to moisture loss. The effects of food shrinkage on drying performance were ascertained by analyzing the spatial distributions of temperature, moisture content, strain and stress, as a function of operating conditions. The agreement between model predictions and a set of experimental data collected during drying of cylindrical potatoes was good as far as the time evolutions of food average moisture content and of its main dimensions, i.e. length and diameter, were concerned.

Modeling of Fischer-Tropsch Product Distribution over Fe-based Catalyst

The kinetic models of Fischer-Tropsch synthesis (FTS) product distribution can be classified into two major groups: hydrocarbon selectivity models and detailed Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetic models. In this study the two approaches to FTS product distribution modeling are presented and compared using the experimental data obtained in a stirred tank slurry reactor with promoted iron catalyst over a wide range of process conditions. Positive deviations from the classical Anderson-Schulz-Flory distribution and an exponential decrease in olefin-to-paraffin ratio with carbon number are predicted by the inclusion of solubility-enhanced 1-olefin readsorption and/or chain length dependent 1-olefin desorption concepts. In general the agreement between the model predictions and experimental data was very good, and modeling approaches are discussed in terms of fit quality, physical meaningfulness and practical utility.

A new model for silicon nanoparticle synthesis

This work presents a novel multivariate particle model to simulate the synthesis of silicon nanoparticles across a wide range of process conditions. The gas-phase mechanism of Ho et al. (1994, J. Phys. Chem. 98, 10138–10147) is simultaneously solved with a stochastic population balance incorporated a detailed multidimensional particle model. A systematic parameter estimation procedure is used to adjust gas-phase and heterogeneous pre-exponential factors to obtain fits with experimental results. The model is tested against a six different experimental configurations, with excellent fit observed for the majority of cases. It was found that primary particles were too large under conditions of finite-rate sintering, leading to the recommendation that the model could be made more robust by development of accurate sintering kinetics for silicon nanoparticles.

The importance of specific mechanical energy during twin screw extrusion of organoclay based polypropylene nanocomposites

Abstract This study demonstrates how the specific mechanical energy (SME) can be used to describe the influence of extrusion parameters such as screw rotation speed, feed rate and barrel temperature on clay dispersion in organoclay (OMMT) based polypropylene nanocomposites. These materials were prepared by a melt mixing masterbatch process via twin screw extrusion with a wide range of processing conditions. Maleated polypropylene (PP-g-MA) was used as a compatibilizer to allow clay exfoliation. Characterization of the morphological evolution along the extrusion profile revealed that microscale dispersion primarily happens in the melting zone, whereas continuous exfoliation is observed all along the kneading zones, up to the die exit. The results indicate that exfoliation in the kneading zones is mainly issued from clay tactoids and small aggregates with characteristic size inferior to 10 μm, emphasizing the crucial role of primary microscale dispersion on the final structure and properties of the nanocomposites. Relevant quantitative prediction of the multiscale dispersion state along the extrusion profile was obtained using the melt state SME as unique parameter.

Adopting the Experimental Pressure Evolution to Monitor Online the Shrinkage in Injection Molding

In this work, a procedure is reported which is suitable to analyze online the quality of molded parts in terms of shrinkage. The procedure is based on the evaluation of the average solidification pressure, namely the average along the thickness of the pressure at which each layer solidifies, a parameter which is known to correlate well with shrinkage. The calculation of this parameter normally requires the estimation of the solidification history, information which is currently not reachable experimentally. The procedure reported in this work allows adoption of the pressure evolution measured by a piezoelectric pressure transducer to make an estimation of the solidification profile and thus of the average solidification pressure. The procedure is applied to the data of shrinkage measured on an amorphous PS and a semicrystalline iPP in a wide range of processing conditions.

Methodology for advanced measurement accuracy of the overall volumetric oxygen transfer coefficient with application to hydrocarbon–aqueous dispersions

AbstractAccurate quantification of the overall volumetric oxygen transfer coefficient (KLa) is essential for the success of aerobic bioprocesses. In hydrocarbon‐based bioprocesses where KLa is depressed at higher viscosities, this is particularly critical. In this study an accessible methodology for KLa determination has been developed and validated for alkane‐based systems under a wide range of process conditions. Critical to measurement accuracy in around 90% of the KLa values was the incorporation of the response lag. Neglect of the response lag resulted in errors greater than 5% above KLa = 0.3Kp to KLa = 0.6Kp (where Kp is the inverse response lag or probe constant), at least 1.5‐fold to 3‐fold lower than the analogous KLa in water. Further, Kp varied significantly with both alkane concentration and chain length. A sensitivity analysis confirmed − 25% to 90% error in KLa with 30% over‐ and under‐estimation of Kp respectively. When incorporating Kp values specific to the process conditions, accurate KLa values were confirmed in 0 to 20% (v/v) C10–13 and C14–20 aqueous dispersions over 600 to 1200 rpm agitation. Copyright © 2012 Society of Chemical Industry

Deformation inhomogeneity in roll drawing process

The deformation inhomogeneity of flat wires produced with roll drawing process is analyzed. The effect of main process parameters, i.e., initial wire diameter, forming roll dimension and thickness reduction on deformation inhomogeneity is established by means of experimental tests and a developed FE model. Vickers microhardness–strain relationship is developed for the analyzed material (low carbon steel AISI-1010) by correlating the microhardness measurements and effective strain fields as predicted by an axisymmetric numerical model of a compression test. A non-linear finite element model of roll drawing process is developed for a thorough understanding of process parameters effect on deformation inhomogeneity. Thus, in order to encompass the wide range of process conditions, an inhomogeneity index, calculated as the coefficient of variation of effective strain, is used. The numerical results showed that the inhomogeneity factor of flat wires produced with roll drawing is highly dependent on area reduction.

Anodic Ordered Titania Nanostructures and in-Situ Electropolymerized Poly-3-Methylthiophene Films for Hybrid Photovoltaic Solar Cells

In the field of hybrid photovoltaic cell technology, the present work aims studying titanium dioxide layers with ordered nanostructure and poly-3-methylthiophene (P3MT) films in-situ electropolymerized onto them. Nanotube arrays were synthesized by anodization technique using a wide range of process conditions, and the dimensions and morphology of the obtained nanotubes were thoroughly analyzed. This study allowed tailoring the nanotube dimensions as requested by the final application. In this case, arrays with low thickness and large pore diameter, obtained in the acidic water based electrolyte, were selected to carry out further electropolymerization onto them. The nanotube pore diameter was identified as the dominant parameter influencing the P3MT layer thickness. The P3MT layers with the lowest thickness were obtained onto the less porous morphologies with low nanopore diameter values.

Monitoring the Moisture Content of Solids in Fluidized Bed Dryers by Analysis of Pressure Fluctuations

Perusing the hydrodynamic changes of fluidized bed dryer is important for online monitoring of the drying process. The present study investigates the drying process of wetted rice particles. Air at ambient conditions with superficial velocity of 1 ms−1 was used for drying. Absolute pressure fluctuations were measured to monitor the fluidization status of the dryer. Fast Fourier transform, discrete wavelet transform, and statistical analyses of detailed signals were employed to evaluate the fluidization quality in the bubbling regime. Pressure fluctuations were decomposed by the wavelet transform to 10 subsignals. It was shown that the energy of subsignals is more sensitive to moisture changes than other studied parameters. Specifically, the energy of the subsignals corresponding to the macrostructure (large bubbles) can be used for determining the moisture content of the solids during the drying process. This method can be used for online monitoring of drying processes in a wide range of processing conditions in fluidized beds.

Effects of Roller Speed, Die Temperature, Volumetric Flow Rate, and Multiple Extrusions on Mechanical Strength of Molten and Solidified LDPE under Tensile Deformation

An experimental rig coupled with a high speed data-logging and recording system and a personal computer was specially designed and constructed for the real-time measurement of mechanical strength (in terms of drawdown force) as a function of volumetric flow rate and roller speed for virgin low-density polyethylene (LDPE) and reprocessed LDPE during a filament stretching process. The effect of the number of extrusion passes for the reprocessed LDPE was our main interest. The experimental rig was connected to the end of a single-screw extruder, which was used to melt and extrude the polymers. The LDPE filaments were then solidified and collected for studying the mechanical properties. The mechanical strength of the virgin LDPE and reprocessed LDPE were investigated in both molten and solidified states. The mechanical strengths of the virgin and reprocessed LDPEs under these two states are discussed and compared in terms of change in magnitude under a wide range of processing conditions (volumetric flow rate, die temperature, and roller speed). The results suggested that in the molten state the drawdown force for LDPE melts was dependent on volumetric flow rate, die temperature, roller speed, and the number of reprocessing passes. The drawdown force being affected by the number of reprocessing passes could be explained by molecular degradation and gelation effects when using high volumetric flow rates. In the solidified state, the tensile properties of the solidified LDPE increased with roller speed. The effect of the number of extrusion passes for the solidified LDPE was similar to that for the molten LDPE. In the case of volumetric flow rates, the mechanical properties of the solidified LDPE decreased with increasing volumetric flow rate, whereas those of the molten LDPE exhibited the opposite effect. Thus, the mechanical strength of the molten LDPE could not always be used to assess the mechanical properties of the solidified LDPE.

Soot formation in the pyrolysis of benzene, methylbenzene, and ethylbenzene in shock waves

Soot formation in the pyrolysis of benzene, methylbenzene, and ethylbenzene and in the oxidative pyrolysis of benzene in shock waves has been investigated using an absorption-emission technique. Even in the presence of small amounts of oxygen, soot formation in the pyrolysis of these hydrocarbons is accompanied by a decrease in the temperature of the reacting mixture. The soot yield has been measured as a function of temperature over wide initial reactant concentration ranges. A new, larger value was obtained for the coefficient of light absorption by soot particles at a wavelength of 632.8 nm. A revised, substantially modified kinetic model is suggested for soot formation. This model has been verified against experimental data available from the literature on the time profiles of the concentrations of some key components at the early stages of pyrolysis and oxidation of various hydrocarbons in a wide range of process conditions. The model reproduces fairly well the time dependences of the soot yield and soot particle temperature measured in this study for benzene, methylbenzene, and ethylbenzene pyrolysis.

Stochastic Approach for the Prediction of PSD in Crystallization Processes: Formulation and Comparative Assessment of Different Stochastic Models

A stochastic formulation for the description of antisolvent mediated crystal growth processes is discussed. In the proposed approach, the crystal size growth dynamics is driven by a deterministic growth factor coupled to a stochastic component. The evolution in time of the particle size distribution (PSD) is then described in terms of a Fokker−Planck equation. In this work, we investigate and assess comparatively the performance of the FPE approach to model the crystal size distribution based on different expressions for the stochastic component. In particular, we investigate the one-dimensional Fokker−Planck equation with a nonlinear diffusion coefficient to represent the crystal growth process. Validations against experimental data are presented for the NaCl−water−ethanol antisolvent crystallization system. It is shown that the stochastic model better suited to describe the experiments is given by the Geometric Brownian Motion (GBM), which gives an excellent agreement, with the experiments for a wide range of process conditions (i.e., antisolvent feed rate).

First principle‐based simulation of ethane steam cracking

AbstractA consistent set of ab initio‐based kinetic and thermodynamic data is applied for the simulation of an ethane steam cracking furnace. The thermodynamic data are calculated using accurate quantum chemical CBS‐QB3 calculations including corrections for hindered internal rotation. The kinetics are obtained from CBS‐QB3‐based group additive models. With these thermodynamic and kinetic data, simulations for pilot and industrial ethane steam cracking reactors over a wide range of process conditions are performed. It is shown that, without adjusting any parameter, the main product yields can be predicted within 15% rel. of the experimentally observed cracking yields. This indicates the tremendous potential of integrating ab initio methods with engineering models for accurate reactor simulations. © 2010 American Institute of Chemical Engineers AIChE J, 2011

Shear and extensional rheology of polypropylene melts: Experimental and modeling studies

Non-linear correlations are found between the melt strength and fundamental shear flow properties such as low frequency loss tangent, crossover frequency, and zero-shear-rate viscosity for a series of polypropylene (PP) melts. The very good non-linear correlations suggest rheotens as a reliable rheological test to characterize extensional rheology relevant to fabrication, despite its non-homogeneous and non-isothermal flow kinematics. The rheotens model of Doufas [J. Rheol. 50, 749–769 (2006)] with a modified Giesekus (MG) viscoelastic constitutive equation is expanded to the case of PP melts. A single set of molecular parameters per material predicts the rheotens force curves very well over a wide range of processing conditions. The rheotens model is proposed as a tool for determination of rheological parameters of constitutive equations applicable to the simulation of complex polymer processes. Molecular considerations and predictions of the rheotens model are extensively discussed. A multi-mode MG model predicts the non-linear steady shear data (shear and first normal stresses) very favorably satisfying linear viscoelasticity. The oscillatory shear data and model predictions satisfy both the Cox–Merz [J. Polym. Sci. 28, 619–621 (1958)] and Laun [J. Rheol. 30, 459–501 (1986)] rules. The model exhibits stable numerical behavior without singularities or turning points in the prediction of steady shear viscosity even at quite high shear rates (e.g., on the order of 20 000 s−1), problems that have been reported for other constitutive equations.

Thermodynamic analysis of absorption refrigeration cycles using ionic liquid + supercritical CO 2 pairs

Absorption refrigerators are alternative systems to conventional compression cycles in which the energy necessary for the refrigeration is provided by heating instead of mechanical power. Commercial absorption refrigerators use two absorbent/refrigerant pairs: NH 3–H 2O and H 2O–LiBr. These systems have some limitations due to the difficulty of separating absorbent and refrigerant, the narrow refrigeration temperature range, or the possibility of corrosion and salt deposition. The application of ionic liquids as absorbents with supercritical carbon dioxide as refrigerant can solve some of these problems because separation of ionic liquid from CO 2 is easy due to the negligible vapor pressure of ionic liquids. In this work, suitable ionic liquids–CO 2 pairs have been selected considering their phase equilibrium properties, calculated with the Group-Contribution equation of state developed by Skjold-Jørgensen. The energetic efficiency of the process with ionic liquids has been estimated by calculation of the Coefficient of Performance (COP) of the process. It has been found that the process with ionic liquids has a lower COP than conventional NH 3–H 2O systems due to the necessity of operating with a higher solution flowrate. Nevertheless, near-optimum performance is obtained in a wide range of process conditions.

Effects of Noise, Nonlinear Processing, and Linear Filtering on Perceived Speech Quality

The purpose of this study was to measure subjective quality ratings in listeners with normal hearing and listeners with hearing loss for speech subjected to a wide range of processing conditions that are representative of real hearing aids. Speech quality was assessed using a rating scale in a group of 14 listeners with normal hearing and 15 listeners with mild to moderately severe sensorineural hearing loss. Controlled simulations of hearing aid processing were used to process speech that included speech subjected to (1) noise and nonlinear processing, (2) linear filtering, and (3) combinations of noise, nonlinear processing, and linear filtering. The 32 conditions of noise and nonlinear processing included stationary speech-shaped nose, multitalker babble, peak clipping, quantization noise, spectral subtraction, and dynamic range compression (in quiet, with babble, and with spectral subtraction). The 32 linear filtering conditions included high-pass filtering, low-pass filtering, band-pass filtering, positive and negative spectral tilt, and resonance peaks. Subsets of these conditions were used for the 36 conditions that combined noise and nonlinear processing with linear processing. Both listeners with normal hearing and listeners with hearing loss gave consistent (reliable) ratings. In both listener groups, sound quality was significantly affected by the noise, nonlinear processing, and linear filtering conditions. Compared with the listeners with normal hearing, the listeners with hearing loss showed significantly lower ratings of sound quality in nearly all of the processing conditions. For the conditions included in the current hearing aid simulation, noise and nonlinear conditions had a greater effect on quality judgments than did the linear filtering conditions. The data reported here provide a comprehensive dataset of speech quality ratings for simulated hearing aid processing conditions. The results indicate that quality ratings by listeners with hearing loss are significantly lower than quality ratings by listeners with normal hearing. In addition, quality ratings by listeners with hearing loss are impacted by signal processing at least as much as, and often more than, the quality ratings by listeners with normal hearing. Finally, quality ratings for speech processed with a simulated hearing aid are impacted more by noise and nonlinear signal processing than by linear filtering.

A descriptive force‐balance model for droplet formation at microfluidic Y‐junctions

AbstractIn a previous article, we studied the basics of emulsification in microfluidic Y‐junctions, however, without considering the effect of viscosity of the disperse phase. As it is known from investigations on many different microstructures that viscosity and viscosity ratio are governing parameters for droplet size, we here investigate whether this is also the case for microfluidic Y‐junctions and do so for a wide range of process conditions. The investigated Y‐junctions have a width of 19.9 or 12.8 μm and a depth of 5.0 μm, and the formed monodisperse droplets (CV < 1%) are between 3 and 20 μm. We varied the disperse‐phase viscosity using different oils (1–105 mPa s), and continuous‐phase viscosity using glycerol–water and ethanol–water mixtures (1.0–6.2 mPa s), which corresponds to disperse‐to‐continuous‐phase viscosity ratios from 0.4 to 105.0. Through the variation of the liquids, also a range in interfacial tensions (12–55 mN m−1) is assessed. The disperse‐phase flow rate is varied from 0.039 to 18.0 μL h−1, the continuous‐phase flow rate from 1.39 μL h−1 to 0.41 mL h−1, and this corresponds to flow rate ratios from 1.1 × 10−3 to 0.14, which is once again based on wide range of conditions. For all these conditions, in which droplets are formed in the dripping and jetting regime, the droplet size could be described with a model based on the existing force‐balance model, but now extended to incorporate the cross‐sectional area of the droplet and the resistance with the wall. Surprisingly enough, it was found that the droplet size is not influenced by the disperse‐phase viscosity, or the viscosity ratio, but it is dominated by the resistance with the wall and the continuous‐phase properties. Because of this, emulsification with Y‐junctions is intrinsically simpler than any other shear‐based method as droplet size is only determined by the continuous phase. © 2010 American Institute of Chemical Engineers AIChE J, 2010

Detailed Kinetic Model for the Hydro-desulfurization of FCC Naphtha

A detailed kinetic model has been developed that describes the selective hydro-desulfurization chemistry of FCC naphtha at minimal olefin saturation. The FCC naphtha is represented by 348 molecular lumps measured by different gas-chromatographic methods. The reaction chemistry is specified in terms of reaction rules using the structure-oriented lumping (SOL) framework. A total of 15 reaction rules, which describe 444 individual reaction steps, have been used to model the governing chemistry. Relative reactivity relationships among different molecular lumps within the same rule have been derived using model feeds or established results from the literature. The kinetic parameters have been estimated from a comprehensive experimental data set comprising of both pilot plant and commercial refinery data spanning a wide range of process conditions and feed compositions. The kinetic model quantitatively predicts the product composition, product properties, extent of hydro-desulfurization, olefin saturation, and the associated octane loss. The modeling framework is generic to naphtha hydroprocessing technologies, and its specific application to the Selective CAtalytic Naphtha hydrofining (SCANfining) process, a proprietary technology of ExxonMobil, is demonstrated.

Estimation of Molten Content of the Spray Stream from Analysis of Experimental Particle Diagnostics

Particle melting is one of the key issues in air plasma spray processing of high temperature ceramics such as Yttria Stabilized Zirconia (YSZ). The significance of assessing, monitoring, and controlling the molten content in spray stream on achieving an efficient process and reproducible coating characteristics and properties is known. This study aims to estimate the molten content of the spray stream (as an ensemble) from experimental measurement of in-flight (individual) particle characteristics. In a previous study by Streibl et al. the presence of melting signature in the particle temperature distribution was observed, which has been confirmed by simulation and through independent experimental observation by Mauer et al. Based on this observation, the particle temperature distribution could be delineated into the different achievable particle states in-flight (unmolten, partially molten, and completely molten) to a first approximation. This in-turn would enable estimation of the molten content in the spray stream. Thus obtained percentage molten content (referred in this study as Spray Stream Melting Index—SSMI) has been observed to correlate well with the experimentally measured deposition efficiency for a wide range of process conditions and feedstock characteristics. The implications of estimating SSMI for other materials and processes are also discussed.