Showing papers in "Chemical Engineering Communications in 2009"

Reactive dividing-wall columns—how to get more with less resources?

Abstract: This work presents a novel integrated reactive-separation design based on a dividing-wall column (DWC) applied to an industrial case study within AkzoNobel Chemicals. To the best of our knowledge this is one of the first reported industrial applications of a reactive DWC. Due to changing market conditions, one of the by-products in a plant became more economically attractive than the main product. However, the design of the existing plant does not allow an increase of the by-product production rate at the cost of the main product. To solve this problem we developed a novel integrated design that combines reaction and separation into a feasible reactive DWC that allows 35% savings in capital and 15% savings in energy costs. This article describes the novel reactive DWC design, presents the rigorous simulation results, and makes a comparison with the base case alternative.

Beneficial role of surfactants as corrosion inhibitors in petroleum industry: a review article

Abstract: The objective of this review is to outline the beneficial role of surfactants as corrosion inhibitors in the petroleum field. After an introduction and brief notes on fundamentals of surfactants, the article shows the most important corrosion problems in the oil industry and the effective role of surfactants to solve these problems. The reported mechanisms of corrosion inhibition by surfactants are also considered. Key results are extracted from publications covering the past 50 years.

Advances in modeling of fluidized-bed catalytic reactors: a comprehensive review

Abstract: A number of fluidized-bed catalytic reactor models have been proposed during the past half-century based on conservation equations as well as empirical relations. This article presents a comprehensive review of these models, ranging from the classic and pioneering reactor models found in the literature to the current state-of-the-art. Each model incorporates a different set of assumptions, leading to different expressions for simulating reactor performance. Forty models are analyzed depending on the characteristics of their conservation equations and their underlying assumptions by reducing each model to a sequential combination of assumptions. This review contributes to the elucidation process for choosing the appropriate model to simulate a specific fluidized-bed reactor.

Forced convection boundary layer flow at a forward stagnation point with newtonian heating

Abstract: The steady forced convection boundary layer flow near the forward stagnation point of an infinite plane wall generated by Newtonian heating in which the heat transfer from the surface is proportional to the local surface temperature is investigated in this study. The governing partial differential equations are first transformed into a system of ordinary differential equations before they are solved numerically by a finite-difference scheme, namely the Keller box method. Numerical solutions are obtained for a large range of values of the Prandtl number.

REACTIVE EXTRACTION OF PROPIONIC ACID USING TRI-n-OCTYLAMINE

Abstract: Reactive extraction of propionic acid using tri-n-octylamine (TOA) in 1-decanol and 2-octanol was studied. Physical and chemical extractions from aqueous solution of acid were presented. The extraction of propionic acid from aqueous solutions using TOA in 1-decanol and 2-octanol, respectively, resulted in a degree of extraction as high as 92%. The effect of temperature was studied and it was found that as the temperature was raised from 305 to 353 K, KE decreased from 30.11 to 11.85 and 19.44 to 10.23 in the case of 30 and 40% TOA, respectively, in 1-decanol and 28.57 to 11.32 and 21.99 to 8.70 in the case of 30 and 40% TOA, respectively, in 2-octanol. TOA in both diluents was found to be more effective at pH values less than 4. Increasing the pH from natural pH to 7 was found to severely affect the extraction. Different salts (NaCl, Na2SO4, K2HPO4) and substrate sources (lactose and dextrose) were selected to study their effects on the reactive extraction of propionic acid. The presence of salts lowers t...

Investigation of the effect of multiwalled carbon nanotubes on the viscosity index of lube oil cuts

Abstract: In the present work, the influence of temperature and concentration on the viscosity index of oil-multiwalled carbon nanotube (MWCNT) nanofluids has been investigated theoretically and experimentally. Data were collected for temperatures ranging from ambient to 100°C and for concentrations ranging from 0.01 to 0.2 wt.% of MWCNT. The results show that viscosity is enhanced with increasing the MWCNT concentration and decreasing temperature. Experimental results emphasize that the maximum enhancement of the viscosity index is 14.11% for MWCNT-oil nanofluid. Stability examinations of the nanofluids have been performed by a UV-vis spectrophotometer. It has been found that the Einstein formula and those derived from the linear fluid theory are valid for relatively low particle volume fractions of MWCNT, and for higher MWCNT concentrations the discrepancy between these formulas and experimental data is significant, indicating that the linear fluid theory is no longer appropriate to represent the real behavior of...

REVIEW OF RECENT ADVANCES IN TRANSITION AND LANTHANIDE METAL–DOPED GaN AND ZnO

Abstract: Wide band gap semiconductors such as GaN and ZnO have continued to be at the forefront of spintronics research due to the demonstration of room-temperature ferromagnetism in these materials. A goal of this research is the fabrication of a spintronic device that may provide easy incorporation into existing GaN and ZnO technologies, higher integration density, and less power consumption that its electronic counterparts while achieving similar speeds. The progression of the ferromagnetic metals incorporated into GaN has moved from transition metals to rare earth metals such as the lanthanides. The properties of transition metal–doped ZnO thin films for the two most studied transition metal dopants, namely Mn and Co, are also discussed in this review.

Slip boundary condition for viscous flow over solid surfaces

Abstract: A slip boundary condition is derived for the flow of a viscous fluid over a solid surface, using the theory of thermal activation process. The slip velocity is proportional to the hyperbolic sine of the shear stress on the solid surface, and the slip boundary condition reduces to Navier's slip boundary condition for the flow of Newtonian fluids under small shear stresses. There exists a critical shear stress determining the onset of the slip flow.

An asymptotic derivation of the thin-debye-layer limit for electrokinetic phenomena

Abstract: The thin-Debye-layer model for field-induced electrokinetic processes (e.g., electrophoresis) is driven using a systematic asymptotic methodology. Cox's method for analyzing the Debye-layer equations over curved interfaces (J. Fluid. Mech., 338, 1997) illuminates the subtlety in the prevailing assumption of a locally flat boundary.

Corrosion inhibition of carbon steel in acidic media by bifurcaria bifurcata extract

Abstract: The effect of extract of brown alga Bifurcaria bifurcata (Bb) on the corrosion of steel in 1 M HCl solution was studied using weight loss, potentiodynamic, and polarization resistance measurements. Experimental data revealed that Bb extract acted as an inhibitor in the acid environment. The extract was a mixed-type inhibitor, predominating as an anodic inhibitor at higher concentration. It was found that the inhibition efficiency increased with an increase in Bb extract concentration. The corrosion inhibition of Bb extract on carbon steel in 1 M HCl solution was also investigated by infrared and UV-visible spectrophotometry to obtain information on bonding mechanism between the metallic surface and the inhibitor. The process of inhibition is attributed to the adsorption of the extract molecules, the precipitation of Fe-chelates, and/or formation of complex at the electrode surface.

SYNTHESIS, CHARACTERIZATION, AND COMPARATIVE STUDY OF PYRIDINE DERIVATIVES AS CORROSION INHIBITORS OF MILD STEEL IN HCl MEDIUM

Abstract: Radical catalysis has been used to achieve addition of dodecanethiol and mercaptoacetic acid to 4-vinylpyridine (4VP), giving 4-(dodecylthiaethyl)pyridine (DTEP) and 4-pyridylethylthia-acetic acid (PETAA). The purified monoadducts have been characterized using 1H NMR and 13C NMR spectroscopy. Inhibition of the corrosion of mild steel in 1 M HCl by 4VP, DTEP, and PETAA has been investigated at 308 K using weight loss measurements, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) methods. The results obtained show that PETAA is the best inhibitor and its inhibition efficiency (E %) increases with the inhibitor concentration, reaching up to 93% for DTEP at 10−3 M. Potentiodynamic polarization studies clearly revealed that the inhibitors changed the mechanism of hydrogen evolution and that they acted as mixed inhibitors but most effectively in the cathodic range.

Effects of combined temperature- and depth-dependent viscosity and hall current on an unsteady mhd laminar convective flow due to a rotating disk

Abstract: The present study investigates the effects of mixed temperature- and depth-dependent viscosity and Hall current on an unsteady flow of an incompressible electrically conducting fluid on a rotating disk in the presence of a uniform magnetic field. We assume that the fluid viscosity strongly depends on temperature and depth, which may be directly applicable to the earth's mantle and a uniform mid-ocean ridge basalt reservoir in whole mantle flow. The system of axial symmetric nonlinear partial differential equations governing the unsteady flow and heat transfer is written in cylindrical polar coordinates and reduced to nonlinear ordinary differential equations by introducing suitable similarity parameters. Solutions for the flow and temperature fields are obtained numerically assuming large Prandtl number by using Runge-Kutta and shooting methods. The nature of radial, tangential, and axial velocities and temperature in the presence of a uniform magnetic field is presented for changing various nondimensiona...

Selective removal of high-k gate dielectrics

Abstract: Continuous downscaling of integrated circuits brought an end to the era of SiO2. In gate dielectrics, it is being replaced by materials with high dielectric constant, so-called high-k dielectrics. One of the challenges in the integration of the high-k material is removal of those materials selectively over the substrate. This work is one of the first attempts to review current state of the art of the high-k removal. Two main approaches are discussed: dry (plasma) removal and wet removal. First, the fundamentals and limitations of both approaches are presented, then an overview of the existing experimental data is given. It is concluded that the best results could be obtained by combining the dry and wet approaches.

The effect of viscosity on particle suspension in an aerated stirred vessel with different impellers and bases

Abstract: The agitator speed required to suspend solids under gassed conditions, N JSg , has been studied in water and in corn syrup of 0.01 and 0.1 Pas giving Reynolds numbers from the full turbulent region down to ∼103. Of the impellers tested, the down-pumping, three-blade, axial flow hydrofoil impellers are generally unsuitable for this duty, and although six-blade, mixed flow down-pumping impellers require the lowest mean specific energy dissipation rates to suspend the solids, (ϵ T ) JSg , at low gas flow rates, they are still prone to flow instabilities and torque fluctuations. The latter poor characteristics are made worse by reducing the size of the impeller relative to the vessel and by increasing viscosity and gas flow rate, Q GV . Thus, they are of limited use for such systems. The Ekato InterMIG impeller has the highest (ϵ T ) JSg and tends to cause vessel vibrations when dispersing the gas, and this weakness is also enhanced by increasing viscosity and gas flow rate. Again, they are generally not appr...

Controlled growth of copper nanoparticles and nanorods in the channels of sba-15 by supercritical fluid deposition

Abstract: Copper nanoparticles and nanorods were prepared in the one-dimensional channels of SBA-15 supported by a modified supercritical fluid deposition (SCFD) method. In this approach, cheap and widely available copper nitrate, which is insoluble in supercritical CO2 (scCO2), was used as the copper source and ethanol as the co-solvent, thus avoiding the employment of expensive and less available scCO2-soluble precursors. The deposition was carried out at the pressure of 21–25 MPa and temperature of 50°C, followed by calcinations at 500°C and H2 reduction at 500°C. The results showed that highly dispersed Cu nanoparticles or nanorods were obtained controllably just by varying the deposition time, as characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). On the other hand, when Cu(acac)2 was used as the precursor and without any co-solvent, only nanoparticles were formed in the channels of SBA-15 no matter how long the deposition time.

Adsorption, kinetics, and equilibrium studies on removal of 4,4-ddt from aqueous solutions using low-cost adsorbents

Abstract: The removal of a chlorinated pesticide (4,4-DDT) from aqueous solutions by a batch adsorption technique using different low-cost adsorbents was investigated. Two adsorbents, wood sawdust (A) and cork wastes (B), were used to determine adsorption efficiency. The influence of the adsorbent particle size and the organic matter of water (humic acids) on the removal process was studied. The obtained results were compared to those obtained with a commercial powdered activated carbon (PAC, F400, Chemviron) (C). Kinetic studies were performed to understand the mechanistic steps of the adsorption process. The rate of the adsorption kinetics of 4,4-DDT on the low-cost adsorbents was found best fitted with a pseudo-second-order kinetic model. This is in contrast to the rate of the adsorption kinetics of the PAC F400, which was best fitted with the Lagergren model. The application of the Morris-Weber equation showed that the adsorption process of 4,4-DDT on these adsorbents was complex. Both the adsorption on the sur...

Stirring free surface flows due to horizontal circulatory oscillation of a partially filled container

Abstract: Mixing in a partially filled beaker or conical flask using oscillator shaker tables is routinely used for cultivation of biological cells. The present study seeks to gain a better understanding of fluid flow inside a beaker on a shaker table and the fluid motion influence on the mixing of cells within the fluid medium used for their cultivation. The imposed oscillatory motion on the beaker induces free surface deformations, which may cause laminar and low shear flow environments thus uniformly mixing the fluid medium. The low shear and uniformly mixed cell culture medium are requirements necessary for optimum cellular growth. In this study, fluid flow due to periodic and horizontal circulatory oscillations at a beaker boundary has been analyzed both numerically and experimentally. A partially filled beaker was modeled as a circular cylinder, and the cell culture medium was modeled as an incompressible fluid with a free and deformable liquid interface. The three-dimensional numerical model that can resolve...

Inhibition of the corrosion of nickel and its alloys by natural clove oil

Abstract: The corrosion behavior of nickel, Inconel 600, and Inconel 690 in different concentrations of HCl solutions and its inhibition by clove oil was studied using potentiostatic polarization measurements. As the acid concentration increases, the rate of corrosion increases, indicating that HCl accelerates the dissolution of nickel and its alloys. The inhibition efficiency of the clove oil was found to increase with increase of its concentration. The inhibitive action of this oil was discussed in view of adsorption onto the metal surface. The adsorbed layer acts as a barrier between the metal surface and aggressive solution, leading to a decrease in corrosion rate. The adsorption process follows Langmuir adsorption isotherms. It was found that the clove oil provides good protection to nickel and its alloys against pitting corrosion in chloride-containing solution using potentiodynamic anodic polarization techniques.

Optimization of process conditions using response surface methodology (rsm) for ethanol production from waste cashew apple juice by zymomonas mobilis

Abstract: Ethanol has been known for a long time, being perhaps the oldest product obtained through traditional biotechnology. It is an attractive, sustainable energy source for fuel additives. Based on a four-level central composite design (CCD) involving the variables substrate composition (20–100%) X1, pH (4.5–6.5) X2, incubation temperature (28°–36°C) X3, and fermentation time (12–60 h) X4, a response surface methodology (RSM) for the production of ethanol using waste cashew apple juice as substrate by Zymomonas mobilis MTCC 090 was standardized. The design contains a total of 31 experimental trials with the first 16 organized in a fractional factorial design and 25 to 31 involving the replications of the central points. Data obtained from RSM on ethanol production were subjected to the analysis of variance (ANOVA) and analyzed using a second-order polynomial equation, which resulted in the optimized process conditions of 62% (v/v) as substrate concentration, pH of 5.5, temperature of 32°C, and fermentation tim...

Mechanical and thermal properties of nano-al2o3/nylon 6 composites

Abstract: Nano-Al2O3-reinforced monomer casting nylon (NA/MCN) composites were prepared by using in situ polymerization. The average molecular weight of the matrix nylon was measured using gel permeation chromatography. The thermal-mechanical properties of the NA/MCN composites were characterized by thermo-dynamic mechanical analysis, and the results were compared with micro-Al2O3-reinforced nylon (MA/MCN) composites. A tensile property test was conducted to investigate the mechanical properties of neat nylon and composites. Experimental results showed that the average molecular weight of the matrix nylon filled with nano-alumina had little change and was higher than that with micro-alumina. The glass transition temperature (Tg) and storage moduli of NA/MCN composites were higher than that of neat nylon. During the experiment, it was also found that the tensile strength increased up to 52% when 3 wt.% of nano-Al2O3 particles were added. The thermal and tensile properties of NA/MCN composites were better than those ...

Prediction of CO2 freeze-out conditions and CO2 hydrate formation conditions with a single equation of state

Abstract: A recent study by Eggeman and Chaffin (2005), which showed large discrepancies in CO2 freeze-out conditions as predicted by several commercial simulators, prompted a reexamination of using the TBS equation of state for phase equilibrium calculations involving solids. Salim and Trebble (1994) had previously presented a methodology for extending the Trebble-Bishnoi-Salim (TBS) equation of state (Salim, 1990) to calculations involving a solid phase. In this study, the CO2 freeze-out conditions in CO2/CH4 and CO2/C2H6 mixtures are calculated from the TBS equation of state, and it is shown that they provide a better data fit than the traditional Poynting correction method. Furthermore, since the use of an equation of state in SLE/SVE calculations does not require the explicit assumption of a pure solid phase, the model was assessed for its ability to correlate CO2 gas hydrate equilibrium conditions. Gas hydrates were simply treated as an impure solid phase, and it was seen that the predictions of gas hydrate e...

Study of thin-layer drying of grape wastes

Abstract: The effect of drying temperature on grape wastes, the solid wastes of the wine and raki production processes, was investigated in a cabinet dryer. Drying experiments were performed three air temperatures of 70°, 90,° and 110°C, at constant air velocity of 1.2 m/s, and initial thickness of 1.8 cm for grape marc and 2.0 cm for grape pulp. Experimental data were fitted to Henderson and Pabis, Page, and logarithmic models, respectively. The performance of these models is evaluated by comparing coefficient of determination and reduced chi-square between the observed and predicted moisture ratios. The statistical analysis concluded that the best model was the logarithmic model. The effective moisture diffusivity varied from 8.55 × 10−10 to 3.32 × 10−9 m2/s over the temperature range. Temperature dependence of the diffusivity was well documented by an Arrhenius-type relationship. The activation energies for grape marc and grape pulp were calculated as 25.41 and 13.74 kJ/mol, respectively.

Evaluation of sulfated aluminas synthesized via the sol-gel method in the esterification of oleic acid with ethanol

Abstract: Sulfated aluminas were synthesized via the sol-gel method by means of the addition of different ions during the gelling of titanium alkoxide. Both the Lewis and Bronsted acid sites were formed, depending on the sulfate precursor. The catalytic activity of sulfated aluminas was tested by performing the esterification reaction of free fatty acids with ethanol at 86°C by using a fatty acid-alcohol with a molar ratio of 1:10 and 3 wt.% of catalyst. The selectivity towards ethyl ester was 100% in all the catalysts. Through this study, we found that sulfated aluminas showed a higher activity in the esterification reaction than unsulfated γ-alumina. It has been found that the conversion of oleic acid varies according to the sulfate precursor (NH4)2SO4 > H2SO4 > NiSO4, which affects both the acidity strength and textural properties of the catalysts.

Synthesis of well-crystallized zeolite beta at large scale and its incorporation into polysulfone matrix for gas separation

Abstract: Using a silica source with high specific surface area, aluminum zeolite beta was successfully synthesized in a very short crystallization period through the conventional hydrothermal route. The obtained materials were characterized by means of XRD, TEM, FESEM, EDS, TGA/DTG, and N2 adsorption/desorption techniques. It is found that the well-crystallized zeolite beta can be rapidly synthesized at 170°C in 9 h and the highly porous silica source used could be completely converted into zeolite beta. No difference results from the silica source used. Moreover, through this synthesis route, it is also possible to conveniently obtain zeolite beta at high yield for manufacturing composite membranes for gas separations. The gas permeation tests show that the incorporation of porous zeolite beta into a polymer has modified the gas permeation properties significantly, indicating industrial application potential of this new type of composite material.

Modeling and simulation of hydrogen sulfide removal from petroleum production lines by chemical scavengers

Abstract: The in-line scavenging of hydrogen sulfide is the preferred method for minimizing the corrosion and operational risks in offshore oil production. We model hydrogen sulfide removal from multiphase produced fluids prior to phase separation and processing by injection of triazine solution into their gas phase. Using a kinetic model and multiphase simulator, the flow regimes, amounts, and composition of three phases are determined along the horizontal and vertical flow path from subsea well to separator tank. The flow regimes were found to be slug flow or intermittent flow. The highly reactive triazine is destroyed on contact with water phase flowing near the wall. We have simulated the hydrogen sulfide concentration profiles for different amounts of gas injection. The results are compatible with the available field data from an offshore oil well and are useful in determining the injection rates of expensive chemical scavengers and optimal gas injection rates.

Constrained optimal control of liquid level loop using a conventional proportional-integral controller

Abstract: An analytical design method for a conventional proportional-integral (PI) controller is developed for the optimal control of the liquid level loop in order to explicitly handle important control specifications. The constrained optimal control problem for the liquid level loop is formulated and converted into an unconstrained optimization problem to find an optimal PI controller tuning rule. The proposed PI controller minimizes the rate of change of the outlet flow and the deviation of the level subject to two important constraints in the level loop: the maximum allowable rate of change in the outlet flow rate and the maximum allowable deviation of the level. The simulation results show that the constrained optimal control of the liquid level loop can be successfully implemented using a simple PI controller with the proposed design method.

Cfd simulation on influence of superficial gas velocity, column size, sparger arrangement, and taper angle on hydrodynamics of the column flotation cell

Abstract: The use of flotation columns in the mineral processing industry has experienced a remarkable growth over the years. The detailed hydrodynamics study of a column flotation cell demands the solution of mass, momentum, phase-transfer, and turbulence quantities. Simulations have been carried out to examine the influence of superficial air velocity, column size, column taper angle, and sparger arrangement on hydrodynamics of the column flotation cell. A commercial CFD software package (ANSYS CFX 10.0) has been used to predict the complex unsteady air-water flow. The k-e turbulence model for shear-induced turbulence, Sato's eddy viscosity model for bubble-induced turbulence, and the effect of interfacial momentum transfer terms (lift force, wall force) were considered. Present findings suggest use of low height-to-diameter ratio, low airflow rate, small column taper angle, and uniformly distributed sparger to achieve good separation in a column flotation cell.

An investigation of microsegregation and liquid density redistribution during solidification of inconel 718

Abstract: In order to investigate micro-segregation behavior and liquid density variation during solidification, microstructure and alloy element concentration in liquid of remelted samples quenched at different temperatures in the freezing range were investigated by SEM and EDAX, and the densities at different locations in liquid were calculated. Mass fractions of liquid and different solid phases were calculated using the Thermo-calc program for two alloy composition, Inconel 718 and segregated liquid. It was found that the segregation of Nb in liquid prompts the precipitation of high-Nb phases of δ and Laves directly from the liquid, which results in the redistribution of Nb and density in the vicinity of these phases in the liquid. There is a region with low Nb content and density at the inter-precipitate that can change the mono-increasing distribution of liquid density in the mushy zone of Inconel 718; this phenomenon should be taken into account when considering liquid convection related to liquid density di...

Nitrous oxide formation during light-off over a commercial pd-containing three-way catalytic converter: the effect of low-sulfur gasoline

Abstract: In this work we report how the use of low-sulfur gasoline decreases formation of N2O as a by-product during light-off of commercial Pd-only three-way catalytic converters (TWC). Our results also show that even in the absence of sulfur a large quantity of N2O (reaching instantaneous concentrations up to 700 ppm) is produced at low temperature, between 200° and 400°C. At high temperature (400° to 600°C) and lean conditions we found an unexpected emission of N2O (200 ppm), which is apparently produced by reduction of NO with C3H8 on the TWC. The emission of N2O during light-off is practically independent of the air-to-fuel ratio but depends strongly of the sulfur content in gasoline. Under rich and stoichiometric conditions, the presence of SO2 promotes N2O formation (concentrations from 700 to 900 ppm) via NO reduction by CO. The presence of SO2 in a lean environment has no effect upon formation of N2O.

Analyses of characteristics of ring-shaped electrostatic meter

Abstract: This article describes the characteristics of ring-shaped electrostatic pulverized fuel meters and their applications. At the University of Teesside, UK, the electrostatic technique has been used to measure pulverized fuel flow concentration, velocity, and mass flow rate under lean-phase condition. The mathematic model has been developed to express the relationship between the root-mean-square (rms) value of the meter's output voltage and solids mass flow rate. The effects of solids velocity and particle size on measurements have also been reflected in the model. Furthermore, the model presents the sensitivity variations over the cross-sectional area of meter and along the pipe axis. The article also introduces the research carried out at Southeast University in China, where the technique has been extended to measure dense-phase flow of pulverized coal, which is common in gasification and blast furnaces.