Wide Range Of Process Conditions Research Articles

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.

Engineering Vertically Aligned Carbon Nanotube Growth by Decoupled Thermal Treatment of Precursor and Catalyst

We study synthesis of vertically aligned carbon nanotube (CNT) "forests" by a decoupled method that facilitates control of the mean diameter and structural quality of the CNTs and enables tuning of the kinetics for efficient growth to forest heights of several millimeters. The growth substrate temperature (T(s)) primarily determines the CNT diameter, whereas independent and rapid thermal treatment (T(p)) of the C(2)H(4)/H(2) reactant mixture significantly changes the growth rate and terminal forest height but does not change the CNT diameter. Synchrotron X-ray scattering is utilized for precise, nondestructive measurement of CNT diameter in large numbers of samples. CNT structural quality monotonically increases with T(s) yet decreases with T(p), and forests grown by this decoupled method have significantly higher quality than those grown using a conventional single-zone tube furnace. Chemical analysis reveals that the thermal treatment generates a broad population of hydrocarbon species, and a nonmonotonic relationship between catalyst lifetime and T(p) suggests that certain carbon species either enhance or inhibit CNT growth. However, the forest height kinetics, as measured in real-time during growth, are self-similar, thereby indicating that a common mechanism of growth termination may be present over a wide range of process conditions.

Infrared laser-based monitoring of the silane dissociation during deposition of silicon thin films

The silane dissociation efficiency, or depletion fraction, is an important plasma parameter by means of which the film growth rate and the amorphous-to-microcrystalline silicon transition regime can be monitored in situ. In this letter we implement a homebuilt quantum cascade laser-based absorption spectrometer to measure the silane dissociation efficiency in an industrial plasma-enhanced chemical vapor deposition system. This infrared laser-based diagnostic technique is compact, sensitive, and nonintrusive. Its resolution is good enough to resolve Doppler-broadened rotovibrational absorption lines of silane. The latter feature various absorption strengths, thereby enabling depletion measurements over a wide range of process conditions.

A Geometric Model for the Dynamics of Microchannel Emulsification

Microchannel emulsification is an interfacial tension driven method to produce monodisperse microdroplets, or microspheres. In this paper we introduce a model for describing the dynamics of microchannel emulsification based on simple time dependent geometric shape analysis. The model is based on mechanistic principles that simultaneously predicts both process and microchannel geometry effects. The model contains no adjustable (fit) parameters and is thus fully predictive for oil in water emulsification. The model is easy to use and does not require extensive computational time and/or memory. The model was validated by comparison with the experimental results published by Sugiura and co-workers and we found excellent agreement. It was found that the droplet size of oil in water emulsions could be fully predicted using only two dimensionless numbers, an adapted capillary number that also comprises effects of terrace width and height, and the ratio of terrace length over terrace height. Based on these findings, a dimensionless design map could be constructed for a wide range of process conditions and microchannel dimensions.

Kinetics of structure formation in PP/layered silicate nanocomposites

Polypropylene (PP)/organophilized montmorillonite (OMMT) and polypropylene/organophilized montmoril- lonite/maleic anhydride grafted polypropylene (MAPP) composites were prepared in an internal mixer under a wide range of processing conditions to study the kinetics of structure formation. Structure and properties were characterized by a vari- ety of techniques. The gallery structure of the organophilic silicate changed in spite of the fact that no compatibilizer was added to PP/OMMT composites. Silicate reflection shifted towards smaller 2θ angles, broadened and its intensity decreased indicating intercalation. Transmission electron microscopy (TEM) micrographs even showed individual platelets at long mixing times. However, the extent and direction of changes in the gallery structure of the silicate did not justify those observed in properties. The analysis of the results and additional experiments proved that the degradation of the poly- mer also takes place during processing leading to the formation of carbonyl and/or carboxyl groups, as well as to the decrease of molecular weight. The modification of the chain structure of the polymer influences interfacial interactions and the intercalation process. Some properties are directly determined by molecular weight (rheological properties, elongation). Both the clay and the MAPP seem to accelerate degradation. Thermooxidative degradation must have disadvantageous effect during the application of PP nanocomposites and needs further study.

Plasma-chemical processes in microwave plasma-enhanced chemical vapor deposition reactors operating with C/H/Ar gas mixtures

Microwave (MW) plasma-enhanced chemical vapor deposition (PECVD) reactors are widely used for growing diamond films with grain sizes spanning the range from nanometers through microns to millimeters. This paper presents a detailed description of a two-dimensional model of the plasma-chemical activation, transport, and deposition processes occurring in MW activated H/C/Ar mixtures, focusing particularly on the following base conditions: 4.4%CH4/7%Ar/balance H2, pressure p=150 Torr, and input power P=1.5 kW. The model results are verified and compared with a range of complementary experimental data in the companion papers. These comparators include measured (by cavity ring down spectroscopy) C2(a), CH(X), and H(n=2) column densities and C2(a) rotational temperatures, and infrared (quantum cascade laser) measurements of C2H2 and CH4 column densities under a wide range of process conditions. The model allows identification of spatially distinct regions within the reactor that support net CH4→C2H2 and C2H2→CH4 conversions, and provide a detailed mechanistic picture of the plasma-chemical transformations occurring both in the hot plasma and in the outer regions. Semianalytical expressions for estimating relative concentrations of the various C1Hx species under typical MW PECVD conditions are presented, which support the consensus view regarding the dominant role of CH3 radicals in diamond growth under such conditions.

Anion exchange chromatography provides a robust, predictable process to ensure viral safety of biotechnology products

The mammalian cell-lines used to produce biopharmaceutical products are known to produce endogenous retrovirus-like particles and have the potential to foster adventitious viruses as well. To ensure product safety and regulatory compliance, recovery processes must be capable of removing or inactivating any viral impurities or contaminants which may be present. Anion exchange chromatography (AEX) is a common process in the recovery of monoclonal antibody products and has been shown to be effective for viral removal. To further characterize the robustness of viral clearance by AEX with respect to process variations, we have investigated the ability of an AEX process to remove three model viruses using various combinations of mAb products, feedstock conductivities and compositions, equilibration buffers, and pooling criteria. Our data indicate that AEX provides complete or near-complete removal of all three model viruses over a wide range of process conditions, including those typically used in manufacturing processes. Furthermore, this process provides effective viral clearance for different mAb products, using a variety of feedstocks, equilibration buffers, and different pooling criteria. Viral clearance is observed to decrease when feedstocks with sufficiently high conductivities are used, and the limit at which the decrease occurs is dependent on the salt composition of the feedstock. These data illustrate the robust nature of the AEX recovery process for removal of viruses, and they indicate that proper design of AEX processes can ensure viral safety of mAb products.

An Improved Non‐Isothermal Kinetic Model for Prediction of Extent of Transesterification Reaction and Degree of Randomness in PET/PEN Blends

AbstractAn improved non‐isothermal kinetic model was developed based on mass balance and Arrhenius laws using a second‐order reversible reaction capable of predicting the extent of transesterification reaction (X) and the degree of randomness (RD) in poly(ethylene terephthalate) (PET)/poly(ethylene naphthalene‐2,6‐dicarboxylate) (PEN) blends prepared by a twin screw micro‐compounder over a full composition range under different processing conditions. The experimental values of X and RD were determined by 1H‐NMR and a direct relationship between them developed. The model constants were tuned by an optimization method using half of the experimental data, with the other half used for verification. Good agreement was found between the experimental and theoretical data in the verification stage and, therefore, it was concluded that the model is capable of predicting the extent of transesterification reaction with a high level of confidence for a wide range of processing conditions. Similarly to the experimental results, the model showed that, among all parameters affecting the extent of transesterification reaction, the time and temperature play the major role, whereas the blend composition does not have a significant role.magnified image

Raman spectroscopy for spinline crystallinity measurements. II. Validation of fundamental fiber‐spinning models

AbstractThe original Doufas–McHugh two‐phase microstructural/constitutive model for stress‐induced crystallization is expanded to polyolefin systems and validated for its predictive capability of online Raman crystallinity and spinline tension data for two Dow homopolymer polypropylene resins. The material parameters—inputs to the model—are obtained from laboratory‐scale material characterization data, that is, oscillatory dynamic shear, rheotens (melt extensional rheology), and differential scanning calorimetry data. The same set of two stress‐induced crystallization material/molecular parameters are capable of predicting the crystallinity profiles along the spinline and fiber tension very well overall for a variety of industrial fabrication conditions. The model is capable of predicting the freeze point, which is shown, for the first time, to correlate very well with the measured stick point (i.e., the point in the spinline at which the fiber bundle converts from a solid‐like state to a liquid‐like state and sticks to a solid object such as a glass rod). The model quantitatively captures the effects of the take‐up speed, throughput, and melt flow rate on the crystallization rate of polypropylene due to stress‐induced crystallization effects. This validated modeling approach has been used to guide fiber spinning for rapid product development. The original Doufas–McHugh stress‐induced crystallization model is shown to be numerically robust for the simulation of steady polypropylene melt spinning over a wide range of processing conditions without issues of discontinuities due to the onset of the two‐phase constitutive formulation downstream of the die face, at which crystallization more realistically begins. Because of the capturing of the physics of polypropylene fiber spinning and the very good model predictive power, the approximations of the original Doufas–McHugh model are asserted to be reasonable. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Optimization of a thin film deposition process using a dynamic model extracted from molecular simulations

This study presents and demonstrates an algorithm for computing a dynamic model for a thin film deposition process. The proposed algorithm is used on high dimensional Kinetic Monte Carlo (KMC) simulations and consists of applying principal component analysis (PCA) for reducing the state dimension, a self organizing map (SOM) for grouping similar surface configurations and simple cell mapping (SCM) for identifying the transitions between different surface configuration groups. The error associated with this model reduction approach is characterized by running more than 1000 test simulations with highly dynamic and random input profiles. The global error, which is the normalized Euclidean distance between the simulated and predicted states, is found to be less than 1% on average relative to the test simulation results. This indicates that our reduced order dynamic model, which was developed using a rather small simulation set, was able to accurately predict the evolution of the film microstructure for much larger simulation sets and a wide range of process conditions. Minimization of the deposition time to reach a desired film structure has also been achieved using this model. Hence, our study showed that the proposed algorithm is useful for extracting dynamic models from high dimensional and noisy molecular simulation data.

Two-dimensional population balance model with breakage of high aspect ratio crystals for batch crystallization

A two-dimensional population balance model was developed for the description of breakage of crystals with high aspect ratios for a potassium dihydrogen phosphate (KDP) batch crystallization process. Two physical assumptions were made for the modelling. Firstly, the rate of breakage is proportional to the product of the frequency and impact energy of the collisions between the crystals and crystallizer equipment. Secondly, crystals become prone to breakage only when their aspect ratio exceeds a certain limit. Parameters for the rate of breakage were determined by fitting the breakage function in agitation experiments of suspended crystals in a crystallizer. These obtained parameters were validated in batch crystallization experiments. Since the growth rate of KDP is affected by low concentrations of multi-valent ions, Fe 3 + ions were used to control the crystal growth rate resulting in crystals with high aspect ratios. To be able to describe the effect of the used concentrations of Fe 3 + ions on the crystallization process, growth rate equations were derived, which account for the inhibitory effect on the growth rates along widths and lengths of crystals. The results obtained by solving the two-dimensional population balance model accompanied by crystal breakage were compared with seeded cooling batch crystallization experiments at various concentrations of FeCl 3 . The model described crystal breakage very well at a wide range of process conditions. Some discrepancies were observed during initial period of the crystallization, which are most likely caused by the growth model used.

MOCVD of ZrO2 films from bis(t-butyl-3-oxo-butanoato)zirconium(IV): some theoretical (thermodynamic) and experimental aspects

The equilibrium concentrations of various condensed and gaseous phases were calculated from thermodynamic modeling of MOCVD of ZrO2 films using a β-ketoesterate complex of zirconium as precursor. This leads to the construction of the ‘CVD phase stability diagram’ for the formation of solid phases. In the reactive ambient of oxygen, the calculations predict carbon-free ZrO2 film over a wide range of process conditions. The thermodynamic yields are in reasonable agreement with experimental observations, though the removal of carbon from the MOCVD grown films is not as complete as the thermodynamic calculations predict.

Dispersion mechanism of nano-particulate aggregates using a high pressure wet-type jet mill

A high pressure wet-type jet mill was employed to disperse nano-particle suspensions. Commercially available nano-particles, fumed silica ( SiO 2 ) of primary particle diameter ( d 0 ) ranging from 7 to 40 nm, alumina ( Al 2 O 3 ) of d 0 = 12 nm and titanium oxide ( TiO 2 ) of d 0 = 21 nm were dispersed in the continuous phase up to viscosity η c = 1000 mPa s . Ion exchanged water, aqueous ethylene glycol and aqueous polyethylene glycol solutions with molecular weight up to 2 000 000, were used as the continuous phase. Particle size distribution, zeta potential and suspension viscosity were measured under a wide range of process conditions. The smaller the d 0 was, the harder it was to disperse the aggregates. Zeta potential was largely dependent on d 0 at any process conditions and became dependent on η c for η c > 450 mPa s . The energy barrier was evaluated by taking van der Waals attractive forces, electrostatic repulsive forces and dispersive forces into consideration. Cavitation measurements showed a negligible cavitation during the passage through the jet mill; therefore aggregate disruption was modeled for fully turbulent flow. Aggregate disruption occurred in inertia sub-range for η c ⩽ 300 mPa s and in viscous sub-range for η c ⩾ 450 mPa s . By balancing mechanical energy with turbulent disruptive energy, a mechanistic model was developed for each sub-range. The analysis of fractal dimensionality showed that nano-aggregates were made up by particle–particle collision in inertia sub-range and orthokinetic cluster–cluster collision in viscous sub-range. The rheological data obtained were expressed according to a modified Casson model.

Electroplating of Copper–Alumina Nanocomposite Films with an Impinging Jet Electrode

A circular, unsubmerged impinging jet electrode system was developed and used for a systematic investigation of the electrocodeposition of nanocomposite films of copper–alumina over a wide range of process conditions. The process variables investigated were current density of , electrolyte flow rate of , copper sulfate concentrations of with pH of either 0.8 or 1.5, and particle loading from . Particle incorporation increase linearly with particle loading for all process conditions studied up to a maximum of . An average grain size of was observed for a deposit formed at with .

Gas‐Assisted Mechanical Extraction of Oil Seeds

It is the objective of this thesis to show the general applicability of the Gas Assisted Mechanical Expression (GAME) process for recovery of oil from oilseeds with high yields. In this process, the oilseeds are saturated with supercritical CO2 before mechanical pressing. The CO2 displaces part of the oil during the pressing and therefore increases the oil yield. To prove the general applicability of GAME, a number of oilseeds with a wide range of properties was chosen: sesame, linseed, jatropha, palm kernel and rapeseed. These seeds all produce high added value oils with a low market volume and their properties range from soft (sesame) to hard (jatropha, palm kernel) and from high (sesame) to low oil contents (palm kernel). A lab scale hydraulic press was used to determine the oil yields and expression rates that can be obtained for both conventional expression and GAME expression under a wide range of process conditions.

Control of nano carbon substitution for enhancing the critical current density inMgB2

The effects on transition critical temperature, lattice parameters, critical current density, and flux pinningof doping MgB2 with carbon nanoparticles, were studied for bulk, wire and tape under a widerange of processing conditions. Under the optimum conditions, magneticJc was enhanced by two orders of magnitude at 5 K for a field of 8 T, and by a factor of 33 at 20 K for afield of 5 T for bulk samples, whereas enhancement by a factor of 5.7 was observed in the transportIc at 12 T and 4.2 K for a wire sample. Samples sintered at high temperature (900 and1000 °C) exhibitedexcellent Jc,approximately 10 000 A cm−2 in fields up to 8 T at 5 K. This result indicates that flux pinning was enhanced by thecarbon substitution for B with increasing sintering temperature. Highly dispersednanoparticles are believed to enhance the flux pinning directly, in addition to theintroduction of pinning centres by carbon substitution. Nano-C is proposed to be one of themost promising dopants besides SiC and CNT for the enhancement of flux pinning forMgB2 in high fields.

Indirect selective laser sintering of an apatite-mullite glass-ceramic for potential use in bone replacement applications

The feasibility of using indirect selective laser sintering (SLS) to produce parts from glass-ceramic materials for bone replacement applications has been investigated. A castable glass based on the system SiO2 x Al2O3 x P2O5 x CaO x CaF2 that crystallizes to a glass-ceramic with apatite and mullite phases was produced, blended with an acrylic binder, and processed by SLS. Green parts with good structural integrity were produced using a wide range of processing conditions, allowing both monolayer and multilayer components to be constructed. Following SLS the parts were post-processed to remove the binder and to crystallize fully the material, evolving the apatite and mullite phases. The parts were heated to 1200 degrees C using a number of different time-temperature profiles, following which the processed material was analysed by differential thermal analysis, X-ray diffraction, and scanning electron microscopy, and tested for flexural strength. An increase in strength was achieved by infiltrating the brown parts with a resorbable phosphate glass, although this altered the crystal phases present in the material.

Dielectric response near the permittivity maximum in (Sr0.8Pb0.2)TiO3 ceramic solid solution

It is well known that the weak-field relative dielectric permittivity maximum ϵw(max) achieved at the paraelectric-ferroelectric phase transition in ceramic ferroelectric solid solutions in the perovskite structure family is a strong function of the processing conditions used in fabrications. Heretofore, the height and sharpness of the dielectric peak have often been regarded as good qualitative indicators of the quality and homogeneity of the solid solutions. In the SrTiO3–PbTiO3 solid solution system at low PbTiO3 concentrations, this sensitivity is again strongly evident. Now, however, even for samples with a very sharp ϵw(max) giving values >45000 at weak-field dielectric maximum temperature Tmax above the peak temperature, 1∕ϵw (ϵw: weak-field relative dielectric permittivity) departs from Curie-Weiss behavior more than 15°C above the Curie-Weiss temperature θ which now occurs above Tmax. The unusual condition Tmax<θ appears to occur for quite a wide range of processing conditions. Measurements of thermal contraction also show departure from linearity for more than 15°C above θ when measured over the same temperature range, suggesting the development of micro- or nanopolar regions as in a relaxor ferroelectric and this polar character has been confirmed by recent Raman spectroscopy. There is, however, no evidence of dielectric relaxation in the radio-frequency range as in the classic relaxors; however, earlier studies on similar compositions have shown strong dispersion in the gigahertz frequency range at temperatures near to but above Tmax. Preliminary studies of x-ray-diffraction linewidth also suggest that the highest permittivity peak samples are less homogenous, perhaps indicating that micropolarity may be associated with inhomogeneity in the lead cation distribution.

A Mathematical Model for the Reactive Extrusion of Methyl Methacrylate in a Co-rotating Twin-Screw Extruder

A mathematical model for the reactive extrusion of methyl methacrylate (MMA) is presented. Key variables, such as pressure, temperature, residence time, filling ratio, number-average, and weight-average molecular weights (Mn and Mw) along the extruder length can be calculated using the model. The flow in the extruder is modeled using a simplified approach; however, this approach is versatile enough to include any screw profile, such as right-handed and left-handed elements, and kneading disks. A polymerization kinetic model that considers a mixture (“cocktail”) of initiators is coupled to the flow equations. An effective model for the auto-acceleration effect is used. Second-order thermal self-initiation of MMA is considered in the reaction mechanism. The model can be easily performed on a personal computer, and a wide range of process conditions can be modeled, because of its flexibility.