bluuebunny/crossref_metadata_2025 huggingface dataset:
Inorganic Precipitated Silica Gel. Part 2: Fragmentation by Mechanical Energy
Authors: Quarch K. , Durand E. , Kind M.
Published: May 2010

Precipitated silica (SiO2) is industrially produced by mixing a silicate solution with acid in a semi‐batch process. Polycondensation of monomeric silica leads to the formation of particles which aggregate and eventually form a particulate gel. However, this is instantly fragmented by the mechanical energy input caused by the stirrer. Shrinkage and compaction of these fragments lead to the final product aggregates. It is the aim of this study to enable tailoring of the structure and size of these product particles via the process parameters. In the present paper this is achieved by varying the stirrer speed. It can be shown that there is an analogy between the behavior of the gel and that of highly viscous liquids. Unexpectedly, however, the fragment size can not be reversibly controlled by the power input. The influence of the process parameters on the strength of the gel has been described in the first part of this series [1].
Characterization of organic‐coated solids isolated from different oil sands
Authors: Adegoroye Adebukola , Wang Louxiang , Omotoso Oladipo , Xu Zhenghe , Masliyah Jacob
Published: May 2010

Solids isolated from weathered oil sands ores and those having low‐ and high‐fine solids content were studied. The organic matter (OM) adsorbed on the solids was found insoluble in most common solvents, contributing significantly to the change of solid surface properties. The surface properties of these solids were found to affect the entire process cycle of obtaining synthetic crude oil from surface‐mined oil sands using a water‐based extraction process, and managing the existing tailings ponds. In this study, the low‐fine solids ore possessed the lowest amount of organic‐coated solids and highest bitumen recovery. Siderite and pyrite, which tend to concentrate in the hydrocarbon phase were observed in the isolated solids from the weathered and high‐fine ores but were absent in the low‐fine ores. In all the ores studied, the solids from the bitumen froth possess less quartz, and more carbonates compared with solids from the tailings. Elemental analysis by energy dispersive X‐ray spectroscopy (EDX) and elemental analyser revealed the presence of more transition metals (iron and titanium), and carbon in the solids obtained from the bitumen froth when compared with those from the tailings. Infrared (IR) spectroscopy study substantiated the results obtained by X‐ray diffraction and elemental analysis. IR spectra showed a likely association between OM and carbonates in the organic‐coated solids isolated from bitumen froth. More organic‐coated solids were found in weathered oil sands than in other types of ores and observed to reduce bitumen recovery from oil sands.
Destabilisation of homogeneous bubbly flow in an annular gap bubble column
Authors: Al‐Oufi Fahd M. , Cumming Iain W. , Rielly Chris D.
Published: May 2010

Experimental results are presented to show that there are very significant differences in the mean gas void fractions measured in an open tube and a annular gap bubble column, when operated at the same gas superficial velocity, using a porous sparger. Measurements were carried out in a vertical 0.102 m internal diameter column, with a range of concentric inner tubes to form an annular gap, giving diameter ratios from 0.25 to 0.69; gas superficial velocities in the range 0.014–0.200 m/s were investigated. The mean gas void fraction decreases with increasing ratio of the inner to outer diameter of the annular gap column and the transition to heterogeneous flow occurs at lower gas superficial velocities and lower void fractions. Two reasons are proposed and validated by experimental investigations: (1) the presence of the inner tube causes large bubbles to form near the sparger, which destabilise the homogeneous bubbly flow and reduce the mean void fraction; this was confirmed by deliberately injecting large bubbles into a homogeneous dispersion of smaller bubbles, and (2) the shape of the void fraction profiles changes with gap geometry and this affects the distribution parameter in the drift‐flux model. Both of these effects serve to reduce the mean gas void fraction in an annular gap bubble column compared to an open tube at the same gas superficial velocity.
Phase distributions in a gas–liquid–solid circulating fluidized bed riser
Authors: Razzak S. A. , Barghi S. , Zhu J.‐X.
Published: May 2010

The distributions of the three phases in gas–liquid–solid circulating fluidized beds (GLSCFB) were studied using a novel measurement technique that combines electrical resistance tomography (ERT) and optical fibre probe. The introduction of gas into a liquid–solid circulating fluidized bed (LSCFB), thus forming a GLSCFB, caused the increase of solids holdup due to the significantly decreased available buoyancy with the lower density of the gas, even with a somewhat increased liquid velocity due to the decreased liquid holdup giving space for the gas holdup. The gas passed through the riser in the form of bubbles, which tended to flow more through the central region of the riser, leading to more radial non‐uniformity in radial holdup of the phases. The gas velocity has the most significant effect on the gas phase holdup. While the gas velocity also has an obvious effect to the solids holdups, the liquid flow rate had a much more considerable effect on the phase holdups. The solids circulation rate also had a significant effect on the phase holdups, with increasing solids circulation rate causing much more increased solids holdup in the central region than close to the wall. A correlation was developed for the relative radial distributions of solids holdup in GLSCFB, as such radial profiles were found similar over a wide range of operating conditions, like those in a typical gas–solid circulating fluidized beds (GSCFB). Finally, the axial solids profiles in a GLSCFB was found to be much closer to those in an LSCFB which are very uniform, than those found in a GSCFB which are less uniform and sometime having a S shape. Water was used as the continuous and conductive phase, air was the gas phase and glass bead and lava rock particles were used as the solid and non‐conductive phase.
A net draft tube slurry airlift bioreactor for 2,4‐D (2,4‐dichlorophenoxyacetic acid) pesticide biodegradation
Authors: Znad H. , Ohata H. , Tade M. O.
Published: May 2010

Biodegradation of the pesticides 2,4‐D have been investigated in a net draft tube airlift bioreactor at different concentrations (10–160 ppm) and air flow rates (0.75–4 L min−1), employing acclimatised activated sludge. A modification for the glass draft tube airlift bioreactor was proposed in which the draft tube is made of non‐woven polypropylene textile net. The experiments were carried out as well in a bubble column (BC) for comparison. The results confirmed that immobilising the activated sludge on the net of the draft tube could enhance the substrates mass transfers and improve the biodegradation rate. A mathematical model was developed to simulate the biodegradation process. The simulated results were in good agreement with the experiments.
The effect of Pd‐catalyst wettability on hydrogenation of nitrate to hydroxylamine
Authors: Grote Claudia , Rosu Marius , Schumpe Adrian
Published: May 2010

In the HPO process of the DSM, nitrate is reduced to hydroxylamine on Pd/C catalyst in a 5 M salt solution. Pd/C catalyst increases the interfacial area by a coalescence hindering effect. Nevertheless, mass transfer limitation is encountered and Pd/C catalyst in the liquid bulk is not just useless but even catalyses product decomposition. In this study, the more selective Pd/Al2O3 catalyst was silanised with trichloromethyl silane to reduce its wettability and enrich the catalyst at the gas–liquid interface. The silanization did not affect the catalyst activity. In a stirred tank reactor, significantly higher hydrogen absorption rates were achieved for a flat interface but the effect decreased at higher stirring speed.
Trajectory planning for grade transitions: A restricted form approach
Authors: Gilbert W. A. M. , Lipsett M. G. , Forbes J. F.
Published: May 2010

Trajectory planning is of importance for controlling chemical processes under transient conditions. Many of the available techniques for trajectory optimization yield solutions that cannot be implemented. Furthermore, many transient processes are operated manually, which further reduces the classes of trajectories that may be used. In this article, input trajectories are restricted to step/ramp functions, which are easily implemented by manual control or simple control schemes. Direct transcription of the dynamic optimization problem was used to allow the solution to be found using algebraic optimization techniques. The proposed method serves as a useful control policy evaluation tool, where comparison of unrestricted and restricted trajectories gives insights into the gains associated with adopting a more sophisticated control scheme. The restricted inputs approach is applied to several benchmark problems, including gravity separation in an oilsands process.
Kinetics of non‐isothermal decomposition of basic cobalt carbonate
Authors: Liu Bingguo , Peng Jinhui , Zhang Libo , Li Wei , Zhou Liexing
Published: May 2010

The kinetics of the thermal decomposition of basic cobalt carbonate was investigated under non‐isothermal heating in air media using thermogravimetric analysis (TGA). TG‐DTG curves showed that the decomposition proceeded through two well‐fined steps in air. Weight loss of the thermal decomposition of basic cobalt carbonate was in good agreement with the theoretical weight loss. The isoconversional method has been applied to the data in order to evaluate a dependence of the effective activation energy on the extent of conversion, and the possible conversion functions have been estimated through the multiple linear regression method. The average apparent activation energies of the second steps (0.4 ≤ α ≤0.9) were 96.607–144.537 kJ/mol.
Effect of natural surfactants released from athabasca oil sands on air holdup in a water column
Authors: Zhou Zhiang , Xu Zhenghe , Masliyah Jacob
Published: May 2010

Natural surfactants released from Athabasca oil sands are a crucial component in water‐based bitumen extraction processes. The effect of natural surfactant released from estuarine and marine oil sands on air holdup was investigated using a water column. The air holdup in the resultant supernatant of the conditioned oil sands slurry was found to be much higher than that in de‐ionized water. A further increase in air holdup was observed with the supernatant obtained from the oil sands slurry conditioned with caustic. Aging of the ore prior to bitumen extraction caused an increase in air holdup. The presence of small amount of fine solids in the supernatant resulted in a higher air holdup for all the cases studied. The present study shows that the higher air holdup and poorer processibility of marine ores, compared with estuarine ores, could be accounted for by the release of larger amount of surface active species and the presence of more fine clays in the ores.
Factors affecting the aeration of small bitumen droplets
Authors: Moran Kevin , Masliyah Jacob , Yeung Anthony
Published: May 2010

Small bitumen droplets, roughly 10 to 40 μm in diameter, constitute a significant fraction of the total hydrocarbon in an oil sands flotation process. In this study, the aeration of such droplets is examined—both from a surface energetic perspective as well as from direct observations. The spreading coefficient associated with bitumen aeration is evaluated based on in situ measurements of interracial and surface tensions. In addition, micropipette techniques are employed to monitor the aeration process and to quantify the probability of aeration. Our results suggest that a positive spreading coefficient does not always guarantee the aeration of bitumen droplets, and that such a process may best be described from a statistical stand point.
Novel reactor for cyanide solution treatment
Authors: Fortin Luc , Kasireddy Vijaya K. , Soucy Gervais , Bernier Jean‐Luc
Published: May 2010

This paper presents the treatment of cyanide solution being derived from the aluminum industry by direct contact with thermal plasma in a novel reactor. The energy is provided by a plasma submerged in the solution which allows direct contact between the plasma and the solution. The scope of this study was to determine the feasibility of treating free and complex cyanides in solution through bench‐scale operations. An innovative reactor was designed and fabricated to provide stable operating conditions. Many parameters were studied, such as the NaOH concentration (32 and 57 g/L), initial SPL (Spent PotLining) leachate concentration (154 and 354 mg/L), plasma power (10 and 19 kW) and relative reactor pressure (0 and 1.34 MPa). These experiments allowed us to evaluate the kinetics of complex cyanide decomposition under thermal plasma conditions. At atmospheric pressure (about 100°C), the rate of cyanide decomposition was 12 times greater than that of thermal hydrolysis occurring in a plug flow reactor at the same temperature. These improvements are attributed to the presence of both steep thermal gradients and reaction photocatalysis by the plasma UV radiation.
Effect of clays and calcium ions on bitumen extraction from athabasca oil sands using flotation
Authors: Kasongo Tshitende , Zhou Zhiang , Xu Zhenghe , Masliyah Jacob
Published: May 2010

A novel approach, based on the doping of rich estuarine oil sands with calcium and/or clays, was developed to study bitumen extraction. The batch flotation tests showed that the addition of either calcium ions up to 40 p.p.m., or kaolinite, illite and montmorillonite clays at 1 wt% of oil sands processed had marginal effect on bitumen recovery from the estuarine ores. A sharp reduction in bitumen recovery was observed only when calcium ions greater than 30 p.p.m. and 1 wt% montmorillonite clays were added together. While bitumen recovery correlated well with changes in water/air/bitumen contact angle, no correlation was found between bitumen recovery and measured zeta potential of clays or surface tension of the supernatants from the flotation slurry. The wettability of bitumen was identified as a key element in determining bitumen recovery. The aqueous solution analysis for calcium ions showed that most of the added calcium ions disappeared from the solution when montmorillonite clays were present. The addition of illite or kaolinite clays changed the calcium ion concentration in the slurry only marginally. Stronger adsorption of calcium ions on montmorillonite than on either kaolinite or illite is considered to be responsible for the increased bitumen wettability, and hence reduced bitumen recovery.
Aqueous sulphur dioxide leaching of Cu, Ni, Co, Zn and Fe from smelter slag in absence of oxygen
Authors: Ahmed Isaac B. , Gbor Philip K. , Jia Charles Q.
Published: May 2010

Smelter slag and sulphur dioxide are waste products of non‐ferrous pyrometallurgical processes. Dissolution behaviour of Co, Cu, Fe, Ni and Zn from smelter slag in aqueous sulphur dioxide was studied. Experiments were carried out in batch mode, under near ambient conditions. Under the conditions studied, 81% Co, 60% Fe, 35% Ni and 68% Zn extraction were achieved within 3 h, while Cu behaved very differently. The initial dissolution of Cu was rapid, but subsequent precipitation lowered its overall extraction. The precipitation of Cu was more temperature sensitive than its dissolution. At 65°C all the dissolved Cu was precipitated in 2.5 h. The successive precipitation was explained based on the solution chemistry of the Cu‐Fe‐S(IV) system. Dissolution kinetics of the other metals were evaluated using the shrinking core model. Diffusion through the product/ash layer appeared to be the rate controlling step. SEM‐EDS analysis was used to characterize the slag and to confirm the existence of a product/ash layer after leaching.
The effect of particle shape on pipeline friction for newtonian slurries of fine particles
Authors: Schaan Jason , Sumner Robert J. , Gillies Randall G. , Shook Clifton A.
Published: May 2010

Experiments have been conducted to assess the effect of particle shape on pipeline friction in turbulent flow, using laboratory pipelines of nominal diameter 50 mm and 150 mm. The experiments were intended to examine the extent to which a fluid model is appropriate for slurries of this type, especially at high solids concentrations. The experiments confirm that fluid friction at low and moderate solids concentrations is proportional to slurry density, with particle shape being of minor importance. At high solids concentrations, additional increases in friction are observed and these depend upon the ratio of the solids concentration to the maximum settled concentration. Although this friction increase is qualitatively similar to that which would result from increased slurry viscosity, the evidence suggests that particle‐wall contact is the mechanism. However, the transition from turbulent to laminar flow indicates that an effective viscosity should be used in calculating critical Reynolds numbers.
Anomalous friction in slurry flows
Authors: Schaan Jason , Shook Clifton A.
Published: May 2010

Experiments conducted with water slurries of 1 mm particles of specific gravity 1.59 in a laboratory pipeline 0.105 m in diameter have provided evidence of a change in the friction mechanism at velocities above 3 m/s. These flows were stratified and at low velocities the frictional pressure gradients were in satisfactory agreement with the predictions of the conventional two‐layer model. However at higher velocities the friction is substantially lower than predicted. Measurements of concentration and velocity distributions within the pipe show that no major change in flow regime occurs concurrently with the change in the friction mechanism. It appears that the effect is due to a change in the nature of the particle‐wall interaction, of a type which suggests that an inward‐acting force affects the particles adjacent to the wall.
Bitumen effects on pipeline hydraulics during oil sand hydrotransport
Authors: Sanders R. Sean , Ferre Alan L. , Maciejewski Waldemar B. , Gillies Randall G. , Shook Clifton A.
Published: May 2010

Oil sand hydrotransport technology has become increasingly important to Syncrude Canada Ltd. and the oil sands industry. Oil sand slurries are complex, multiphase mixtures of bitumen, coarse solids, fine solids, water and air that can exhibit time‐dependent behaviour, wherein pipeline friction losses increase drastically with time. Four separate experimental programs were conducted to study the effect of bitumen on pipeline hydraulics using 100 mm and 250 mm (I.D.) recirculating and once‐through pipeline loops. The results show that pipeline friction losses increase as a bitumen coating forms on the pipe wall. The effect is more pronounced at 50°C, but also occurs at lower temperatures.
The effect of sand‐clay slurries on the performance of centrifugal pumps
Authors: Sellgren Anders , Addie Graeme , Scott Stephen
Published: May 2010

The addition of clay to sand slurries has been found to reduce the pipeline friction losses, thus lowering the pumping head and power consumption. Pump water heads and efficiencies are decreased by the presence of solid particles. Experimental results are presented for a centrifugal pump with an impeller diameter of 0.625 m for three narrowly graded sands with average particle sizes of 0.64, 1.27, and 2.2 mm. Reductions in head and efficiency of up to 30% were observed for sand slurries with volume concentrations of up to 35%. Head and efficiency were lowered by about one‐third for sand‐clay mixtures with sand to clay mass ratios between 4:1 and 6:1. Comparisons are made with design criteria and a mechanistic model approach based on a prediction of the relative motion of the solids and water in the volute region of the pump.
An integrated approach for coal tailings management
Authors: Choung Jaewon , Xu Zhenghe , Szymanski Jozef
Published: May 2010

A detailed study on an integrated process featuring three distinct mechanisms (i.e., hydrophobic extraction, coagulation and flocculation) is presented. In this process, fine coals in the tailings stream are extracted into a mineral oil by hydrophobic extraction, while coagulant and flocculant are used to aid effluent clarification by coagulation/flocculation. With a single stage process, a coal‐in‐oil mixture is produced as a potential fuel, while clarifying the water for recycling. The hydrophobicity of coal is found to be a key parameter in coal extraction. The addition of mineral oil prior to flocculant and coagulant, especially in the presence of fine clays, is beneficial for recovering weakly hydrophobic fine coals. Fine clays are found to stabilize coal‐rich oil droplets, reducing coal recovery. The presence of hydrophobic coal enhances droplet coalescence and improves process performance. In a case study using a tailings stream from OBED coal preparation plant, it was found that re‐grinding of original tailings is necessary to expose fresh hydrophobic surfaces. Applying this single stage unit operation to a tailings containing 52% ash, a combustible recovery greater than 85% in the form of coal‐in‐oil mixture at product ash content less than 14 wt% was achieved.
Determining equivalent pore diameter for rigid porous spargers
Authors: Gomez Cesar O. , Escudero Ramiro , Finch James A.
Published: May 2010

Prediction of the properties of gas dispersions (e.g., bubble size) generated by porous spargers requires a knowledge of the pore diameter. Three methodologies for determination of an equivalent pore diameter De of a rigid SS sparger of the type used in column flotation have been developed. In the first, De is determined by fitting the bubble diameter predicted by the Kumar/Kuloor model to that measured. In the second, an estimation of bubble diameter is substituted. Estimation was tested using drift flux analysis and Molerus' uniform bubbling model: the former gave acceptable agreement with the measured. Fitting to the estimated bubble diameter offers a simplification over using the measured bubble diameter. The third approach was a further simplification. By combining the Kumar/Kuloor model with drift flux analysis, De is estimated by fitting predicted to measured gas holdup. The methodologies are evaluated on a set of SS spargers using water with a flotation frother, Dowforth 250C. All three methodologies give similiar estimates of De.
Une nouvelle technologie d'appareils de dépôt chimique en phase vapeur. Partie 2 : Modélisation du dépôt de silicium pur à partir de silane et de silicium dopé in situ au phosphore
Authors: Vergnes Huges , Duverneuil Patrick , Couderc Jean‐Pierre
Published: May 2010

La modélisation des réacteurs de CVD permet, d'abord, une meilleure compréhension des mécanismes conduisant au dépôt et constitue, ensuite, un outil très performant pour assister la conception d'appareils industriels et l'optimisation de leurs conditions d'utilisation. Elle autorise une recherche plus sure et plus rationnelle des variables opératoires permettant l'élaboration de dépôts conformes aux spécifications requises. La mise en équation est effectuée, ici, dans le cas du dépôt de silicium polycristallin à partir de silane pour une technologie nouvelle d'appareil de LPCVD. Les hypothèses et méthodes nécessaires à l'elaboration des logiciels de modélisation sont énoncées et discutées, avant la présentation des résultats et leur confrontation avec les données de l'expérience. Cette étude est finalement étendue au cas, plus complexe, des dépôts dopés in situ au phosphore.
A two‐phase model for variable‐density fluidized bed reactors with generalized nonlinear kinetics
Authors: Tafreshi Zahra M. , Opoku‐Gyamfi Kingsley , Adesina Adesoji A.
Published: May 2010

A model based on the classical two‐phase concept is developed for the simulation of variable‐density reaction with generalized nonlinear kinetics in a bubbling fluidized bed. The influence of reaction density parameter on the fluidodynamics and performance of the reactor for four general types of reactions was explored. The results show that the expansion factor has a significant effect on both fluidodynamic characteristics and reaction conversion. In all types of reactions, higher values of hydro‐dynamic variables were obtained when ϵ ≥ 0. Reaction conversion, however, dropped as the expansion factor increased. This trend was more pronounced for reaction orders higher than unity. This suggests that bubbling fluidized operations are probably not optimal and applicable for certain types of reactions. Comparative analysis between reaction type and implications for optimum fluidized bed reactor are discussed.
Mechanism of the ClO2 generation from the H2O2‐HClO3 reaction
Authors: Yin Guohong , Ni Yonghao
Published: May 2010

The development of chlorine containing species during the hydrogen peroxide‐based chlorine dioxide generation process has been determined. Accordingly, two distinct phases, namely the induction period and the steady‐state phase, were identified. In the induction period, it was observed that chloride and chlorous acid are generated, while chlorine, a byproduct from some methanol‐based processes, is not detectable. The absence of chlorine is explained by the fast reaction kinetics between hydrogen peroxide and chlorine, which results in the formation of chloride. In the steady‐state phase, due to the accumulation of chloride and chlorous acid during the induction period, the reaction between chloric acid and chlorous acid, which is responsible for the generation of chlorine dioxide in the hydrogen peroxide‐based ClO2 process, becomes possible. Chloride is a catalyst in such a reaction.
Analysis of gamma‐ray imaging data to describe hydrodynamic properties of gas–polyethylene fluidized beds
Authors: Zarabi Taghi , Kantzas Apostolos
Published: May 2010

A scintillation gamma camera was used for measuring the instantaneous velocity profile and average velocity as well as the trajectories of a radioactive particle in small laboratory scale air–polyethylene–fluidized beds. A large number of frames, with frequencies between 1 and 50 Hz, were analyzed to investigate the effects of bed height, gas velocity and particle morphology. Subsequently: (1) horizontal and axial variations of the particle velocity were found; (2) three different flow zones along the axis (i.e., entrance zone, circulation zone and free board) were quantified; and (3) a characteristic time and a new definition of circulation (cycle) period were introduced. It was also found that the particle sometimes oscillates in the free board or gets trapped in the entrance zone.
Continuous protein recovery using a liquid–solid circulating fluidized bed ion exchange system: Modelling and experimental studies
Authors: Lan Qingdao , Zhu Jing‐Xu (Jesse) , Bassi Amarjeet S. , Margaritis Argyrios , Zheng Ying , Rowe Gerald E.
Published: May 2010

In this study, a continuous protein recovery process using a Liquid–Solid Circulating Fluidized Bed (LSCFB) ion exchange system is described and a model with known kinetics has been developed. Experiments and computer simulations using Matlab™ are conducted at different operating conditions. The effects of hydro‐dynamic parameters and kinetic parameters on the performance of the LSCFB ion exchange system are discussed. The model is shown to be applicable for the design of LSCFB ion exchange systems for protein recovery.
Formation of drops at narrow slots in a centrifugal liquid–liquid contactor
Authors: Wadley Robert , Lee Jonathan G.M. , Wraith Albert E.
Published: May 2010

In experiments on the dispersion of organic phases into aqueous phases, drops were generated continuously at narrow slots of width 12 μm ≤ w ≤ 125 μm mounted peripherally and normal to the radius in a ‘Hi‐Gee’ centrifugal contactor. The drops formed at an array of sources attributed to the Rayleigh‐Taylor instability distributed an average distance
equation image
apart where σ is the interfacial tension of the phases, Δρ their density difference and g the applied centrifugal acceleration. Measured Sauter mean drop diameters were in the range 0.48 to 1.00 mm. The average drop size, d, was given by
equation image
where d̄* = 0.1538 ± 0.0016 m1/3 is a measured capillary factor. Drop size was marginally affected by inertial forces at the highest flow rates.
Adsorption of flavour esters on granular activated carbon
Authors: Ismadji Suryadi , Bhatia Suresh K.
Published: May 2010

This article reports on the liquid phase adsorption of flavour esters onto granular activated carbon. Ethyl propionate, ethyl butyrate, and ethyl isovalerate were used as adsorbates, and Filtrasorb 400 activated carbon was chosen as the adsorbent. Sips, Toth, Unilan, and Dubinin‐Radushkevich isotherm equations which are generally used for heterogeneous adsorbents were used to fit the data. Although satisfactory in fitting the data, inconsistency in parameter values indicated these models to be inadequate. On the other hand the Dubinin‐Radushkevich model gave more consistent and meaningful parameter values and adsorption capacities. By employing the Dubinin‐Radushkevich equation, the limiting volume of the adsorbed space, which equals the accessible micropore volume, was determined, and found to correlate with the value from carbon dioxide adsorption.
Selectivity engineering in the O‐ versus C‐alkylation of p‐cresol with cyclohexene over sulfated zirconia
Authors: Yadav Ganapati D. , Ramesh Pala
Published: May 2010

Solid acids are more widely used as heterogeneous catalysts, because they are eco‐friendly. This paper reports the results for the Friedel‐Crafts alkylation of p‐cresol with cyclohexene using solid acids sulfated zirconia, 20% w/w dodecatungstophosphoric acid (DTP) supported on K10 clay and ZnCl2/K10 (Clayzic). This reaction gave substantial amount of 1‐cyclohexyloxy‐4‐methyl benzene (O‐alkylated product) and 4‐cyclo‐hexyl‐4‐methyl phenol (C‐alkylated product). Both products are of commercial importance as perfume and insecticide respectively. Sulfated zirconia catalyst was shown to be better than others studied in terms of activity and selectivity to the O‐alkylated product. The kinetics were studied with sulfated zirconia as catalyst where the rate determining step was the surface reaction between chemisorbed cyclohexene and p‐cresol from the liquid phase within pores according to the Eley‐Rideal mechanism. The production of O‐alkylated p‐cresol is favoured at lower temperatures and C‐alkylated product at higher temperatures. The best operating temperature is 353 K. The activation energies for O‐ and C‐alkylation are 72.68 and 118.28 kj/mol, respectively.
Decarboxylation of rosin acids in fusion synthesis of Ca‐resinates—Thermogravimetric studies
Authors: Sundqvist Satu , Turunen Sari , Paatero Erkki
Published: May 2010

Fusion synthesis of Ca‐resinates was studied in a laboratory reactor and in a thermobalance. In the syntheses, the resination reaction takes place at 235°C and it is followed by the thermal decarboxylation of rosin acids at 265°C. The kinetics of the thermal decarboxylation was modelled in the synthesis reactor using calcium contents corresponding to the theoretical target acid values 50 to 90 mg(KOH)/g. In the thermobalance, the kinetics of the decarboxylation reaction could be continuously followed and accurate kinetic results were thus obtained in different reaction conditions. The oxidative and thermal decarboxylation were separately studied in the thermobalance at the reaction temperature range of 245°C to 275°C and in different atmospheres (air, N2, CO2) at 260°C. The oxidative decarboxylation was observed to be faster than the thermal decarboxylation during the first 2 h. After that, however, the oxidative decarboxylation was restricted by the apparent reaction equilibrium.
Optimization of beech wood pulping in catalyzed acetic acid media
Authors: Vila Carlos , Santos Valentín , Parajó Juan Carlos
Published: May 2010

Fagus sylvatica wood samples were treated in HCl‐catalyzed, acetic acid solutions. The effects of selected operational variables (catalyst concentration, reaction time and liquor to wood ratio) on pulp yield, composition of pulps and composition of pulping liquors were assessed using incomplete, second‐order, centred, factorial designs. Pulp composition was measured by the contents in cellulose, xylan and lignin. The concentrations of glucose, xylose and furfural in pulping liquors were also considered as experimental variables. Under selected conditions, pulps with 5.8% to 7.5% Klason lignin (kappa numbers in the range 25 to 33), 77.2% to 85.3% cellulose and 3.3% to 6.1% xylan were obtained at 45.8% to 50.0% pulp yield. The selected pulps showed good SCAN viscosity (723 to 814 mL/g) and alkaline resistances which were affected by the acetyl group content of samples (6.6 to 7.6 weight percent).
Influence of fibre length and filler particle size on pore structure and mechanical strength of filler‐containing paper
Authors: Kinoshita Noriyoshi , Katsuzawa Hideo , Nakano Satoko , Muramatsu Hiroki , Suzuki Jyunko , Ikumi Yuko , Toyotake Yukie
Published: May 2010

Test sheets were prepared by incorporating softwood pulp with silica filler, PW‐5 (diameter 4.5 μm) or PW‐20 (15 μm). Length‐weighted averages of fibre were 2.5 (uncut fibre) and 1.25 mm (short‐cut fibre). Pore sizes less than 150 urn were measured by mercury porosimeter. Sheets of short‐cut fibres and mixed with uncut fibres at ratio of 3:1 or 1:3 had larger pore volumes than others tested. When filler content increased, the total pore volume increased for PW‐20 sheets, but it did not for PW‐5 sheets with short‐cut fibres. Tensile index and folding endurance were very much affected by fibre length. Contact number on a fibre was calculated by computer simulation, and it had a linear relation with tensile index of sheet.
Gas holdup for high gas velocities in a gas–liquid cocurrent upward‐flow system
Authors: Lee Dong‐Hyun , Grace John R. , Epstein Norman
Published: May 2010

Gas holdup has been measured in an 83‐mm diameter, 2.2‐m high column at high gas superficial velocities — 0.22 to 2.7 m/s — and at liquid (water) superficial velocities of 0 to 0.47 m/s, by means of a differential pressure transducer. The equation of Hills (1976) based on the slip velocity gives good predictions of the gas holdup for 0.1 ≤ Eg ≤ 0.4. However, the holdups predicted by this approach are considerably higher than the experimental values at gas velocities high enough that Eg > 0.4. Other equations from the literature are also shown to be inadequate. The new data and earlier data at high gas velocities are therefore correlated with a new dimensional equation for Ul ≤ 0.23 m/s.
Characteristics of air–water two‐phase flow in a 3‐mm smooth tube
Authors: Wang Chi‐Chuan , Yang Kai‐Shing , Chang Yu‐Juei , Lu Ding‐Chong
Published: May 2010

Two‐phase flow pattern and friction characteristics for an air–water system in a 3.17 mm smooth tube are reported in this study. The range of mass flux is between 50 and 700 kg/m2s. The experimental data show that the two‐phase friction multipliers are strongly related to the flow pattern. For a stratified‐wavy flow pattern, a mass‐flux dependence of the two‐phase multipliers is seen. For a non‐stratified flow pattern, the two‐phase frictional multipliers are comparatively independent of mass flux. Correlations of the frictional multipliers are developed for stratified and non‐stratified flow. To use the appropriate correlation in different regime, a simple criterion is proposed.
The effect of impeller pumping and fluid rheology on solids suspension in a stirred vessel
Authors: Wu Jie , Zhu Yonggang , Pullum Lionel
Published: May 2010

Pumping velocities of different impellers were measured using laser Doppler velocimetry. It was found that there is a link between impeller pumping capacity and the 5 parameter in the Zwietering correlation. Measurements showed that Njs increases with impeller spacing for dual impeller configurations. A dual‐impeller configuration shows less sensitivity to solids loading change than a single‐impeller configuration, and the change in Njs is larger for small impeller spacing than for large impeller spacing. An increase in slurry cloud height and a reduction in Njs resulted at a small increase of non‐Newtonian viscosity.
Scalar mixing measurements in a continuously operated stirred tank
Authors: Distelhoff Markus F. W. , Marquis Andrew J.
Published: May 2010

An LIF (Laser induced flourescence) line scan system was used to obtain unobtrusive scalar concentration measurements in a continuously operated stirred tank agitated by a radial flow Rushton turbine and an axial flow 60°‐pitched blade impeller. A better blending process was generally achieved in the axial flow field, with macro‐ and micromixing in the radial flow field being most complete with fluid injected into the radial discharge jet, and in the axial flow field with fluid injected from above into the rotating impeller. Local concentration levels and fluctuations scaled with the feed pipe flow rate, and the degree of concentration uniformity throughout the tank scaled with the impeller speed and increased with the cube of the power input.
Optimization of low pressure chemical vapour deposition reactors using hybrid differential evolution
Authors: Lu Jhy‐Chang , Wang Feng‐Sheng
Published: May 2010

In this study, hybrid differential evolution (HDE) was applied to solve four low‐pressure chemical vapour deposition (LPCVD) reactor optimal design problems. The mathematical model for this reactor is described using a two‐point boundary value differential‐algebraic equation (TPBVP‐DAE) problem. HDE is not only applied to solve the optimization problems but also to obtain the solution to TPBVP‐DAE. Under this situation, the HDE subroutine should call itself to evaluate the optimal solution to the optimization problem and the solution to TPBVP‐DAE. In this study, Fortran 90 was used to implement the HDE subroutine to achieve the calling itself requirement. The recursive HDE subroutine can be efficiently applied to solve the four LPCVD reactor optimal design problems. From the computational results, we observed that the combined optimal design obtain the smallest axial uniformity variation. Furthermore, test function maximization problems were used to compare the performance of the HDE with other methods.
Formation de nano‐gouttelettes d'eau au sein d'un éjecteur à air induit: Une étude qualitative par visualisation de l'écoulement
Authors: Desevaux Philippe
Published: May 2010

Cet article traite de la formation de nano‐gouttelettes d'eau au sein d'un éjecteur à air induit. Les deux processus de formation qui interviennent simultanément lorsque l'éjecteur est alimenté avec de l'air humide sont clairement mis en évidence par des visualisations de l'écoulement. Une brève analyse du régime de diffusion lumineuse des gouttelettes formées par condensation au sein de l'écoulement montre que leur diamètre moyen n'excède pas 0.1 μm.
Gas recirculation rate and its influences on mass transfer in multiple impeller systems with various impeller combinations
Authors: Lu Wei‐Ming , Wu Hong‐Zhang , Chou Cheng‐Ying
Published: May 2010

Both the numerical and experimental approaches were used to study the effects of the gas recirculation and non‐uniform gas loading on the mass transfer rate for each impeller in a multiple impeller system. By combining the calculated gas velocity and local gas holdup, the gas recirculation rate around each impeller was estimated. The local mass transfer coefficients for systems equipped with various combinations of the Rushton turbine impeller (R) and pitched blade impeller (P) were determined by using the dynamic gassing out method. It is found that the Rushton turbine impeller has to be served as the lowest impeller in order to have a better gas dispersion and to give a higher overall KLa for a multiple impeller gas‐liquid contactor. The upper pitched blade impeller always enforces the circulating flow around the Rushton turbine impeller just beneath it and gives a higher overall average mass transfer rate. However, the system equipped with only the pitched blade impellers results in a much lower mass transfer rate than the other systems owing to the poor gas dispersion performance of the pitched blade impeller.
Monitoring of emulsion polymerisations: A study of reaction kinetics in the presence of secondary nucleation
Authors: Othman Nida , Mckenna Timothy F. , Santos Amilton M. , Févotte Gilles
Published: May 2010

A non‐linear state estimator that provides on‐line information on residual monomer concentration and radical concentration is experimentally validated under dynamic conditions, and in particular in the presence of secondary particle nucleation. The proposed estimator uses the heat of reaction as an input. Practical methods for determining the initial values of the parameters in the energy balance are also proposed and tested on laboratory and pilot scale installations. It is shown that this method provides a robust tool for the on‐line monitoring of batch (with and without shot additions of monomer, surfactant and initiator) and semi‐batch emulsion polymerisation reactors. The observer was shown to converge rapidly, even under conditions where the number of particles per litre of emulsion (Np) changed rapidly.
Diffusivity of CO2, CH4, C2H6 and N2 in athabasca bitumen
Authors: Upreti Simant R. , Mehrotra Anil K.
Published: May 2010

Experimental data for the diffusivity of carbon dioxide, methane, ethane and nitrogen in Athabasca bitumen are presented in the range 25–90°C at 4 and 8 MPa. The diffusivity of these gases has been determined as a function of gas concentration in bitumen using a non‐intrusive experim̀ental method. The diffusivity of gas in general is found to increase with temperature and pressure, and is a unimodal function of concentration. A correlation is provided for the average diffusivity of these gases as a function of temperature.
Liquid holdup in concentric annuli during cocurrent gas‐liquid upflow
Authors: Das Prasanta K. , Das Gargi , Purohit Nalani K. , Mitra Arun K.
Published: May 2010

In the recent paper, an in‐depth investigation of liquid holdup during air‐water upflow through concentric annuli has been reported. The liquid holdup has been determined experimentally for the bubbly, slug and churn flow regimes. The drift flux model has been adopted for the theoretical estimation of holdup in the bubbly, dispersed bubbly and slug flow regimes. The pronounced effect of flow regime on this parameter as observed from experiments has been incorporated in the model by adopting different values of U0, n and C0. The asymmetry of the Taylor bubbles has been incorporated in the slug flow regime. The theoretical predictions exhibit a good agreement with the experimental data of the present work and that available in literature (Caetano et al., 1989b). The Hughmark's correlation is observed to correlate the churn flow data of the present work reasonably well.
Extended kalman filter based nonlinear geometric control of a seeded batch cooling crystallizer
Authors: Xie Wei , Rohani Sohrab , Phoenix Aaron
Published: May 2010

A nonlinear dynamic model of a seeded potash alum batch cooling crystallizer is presented. The model of the batch crystallizer is based on the conservation principles of mass, energy and population. In order to maintain constant supersaturation, a nonlinear geometric feedback controller is implemented. It is shown that compared to a natural and a simplified optimal cooling policies, the nonlinear geometric control (NCC) leads to a substantial improvement of the final crystal quality. An extended Kalman filter (EKF) is used as a closed loop observer for this nonlinear system to predict the non‐measurable state variables. It is found that the EKF is capable of effectively predicting the first four leading moments of the population density function. The effectiveness of the EKF based nonlinear geometric controller in the presence of plant/model mismatch is also studied. Simulation results show that the EKF based nonlinear geometric controller is reasonably robust in the presence of modeling error.
Packed bed structure: Evaluation of radial particle distribution
Authors: Mariani Néstor J. , Salvat Wilson I. , Martínez Osvaldo M. , Barreto Guillermo F.
Published: May 2010

A model describing the radial distribution of monosized spheres in randomly packed beds up to distances of about two particle diameters from the vessel wall is presented here. The model is based on the existence of a highly ordered layer of particles adjacent to the wall followed by a more diffuse, but still identifiable, second layer. Expressions generated from simple geometrical concepts (intersection between a cylindrical surface and a sphere) straightforwardly allow calculating the radial voidage profile given the radial distribution of particle centers and vice versa. These expressions are employed to fit the model to measures of voidage profiles within a wide range of aspect ratios, a = (RT/RP). The model can be used to accurately predict radial voidage profiles, but it is stressed that the identification of particle distribution constitutes more valuable information than an empirical expression for describing voidage variations.
Reaction rate hysteresis in the hydrotreating of thiophene in wide‐ and narrow‐pore catalysts during temperature cycling
Authors: Fatemi Shohreh , Moosavian Mohammad A. , Abolhamd Giti , Mortazavi Yadollah , Hudgins Robert R.
Published: May 2010

The influence of capillary condensation of reagents in porous catalysts for hydrodesulfurization at temperatures below 195°C and at pressures around 0.95 MPa was investigated experimentally and by modelling. The rate of reaction of thiophene in a solution of n‐heptane was studied in steady and dynamic modes over two Ni‐Mo/γ‐Al2O3 mesoporous catalysts with mean pore diameters differing by 2.6‐fold. Pronounced rate hysteresis was observed under thermal cycling for the narrow‐pore catalyst, but less so for the wide‐pore catalyst. The process was modelled for a mixed‐flow reactor under steady and dynamic conditions by means of the Kelvin equation and introducing two kinetic models for liquid and vapour phase to estimate the concentration of reactant in both phases. The model exhibited good agreement with hysteresis results.
Comparison of experimental and computational results in a cyclic flow
Authors: Li Wei , Sullivan Pierre E. , Davis Jeffrey A.
Published: May 2010

An investigation of cyclic flow within an optical water analog engine oriented horizontally and with a square cross‐section has been carried out using a computational code, KIVA, and compared with particle image velocimetry results. The simulation results highlight the ambiguity with regard to the velocity direction in the experiment and provide more insight into the velocity profile at the latter part of the intake stroke. The computational work is found to not adequately capture the higher order turbulence statistics obtained in the experimental results. The study concludes that the Reynolds stress transport is the dominant component of the equation of motion near the piston surface and causes the turbulent mixing responsible for the mixing and combustion efficiency in an engine.
A simple correlation for gas bubbles rising in power‐law fluids
Authors: Rodrigue Denis
Published: May 2010

Recently, the author (Rodrigue, 2001 a, b) proposed a generalized correlation for the steady rise of gas bubbles in uncontaminated viscous Newtonian fluids of infinite extent. It is the purpose of this note to show that this model can be modified for inelastic non‐Newtonian power‐law fluids. Using data taken from six different studies, it is shown that the modified model can predict quite nicely the bubble velocity for these non‐Newtonian inelastic fluids.