Cylindrical Extrudates Research Articles

La-Doped ZnTiO3/TiO2 Nanocomposite Supported on Ecuadorian Diatomaceous Earth as a Highly Efficient Photocatalyst Driven by Solar Light.

Currently, there is great interest in the use of TiO2 for photocatalytic remediation of wastewater. Doping, heterojunction, and immobilization on porous materials are effective methods to improve the photocatalytic efficiency of this semiconductor oxide. In this study, ZnTiO3/TiO2 (ZTO) and ZnTiO3/TiO2/La (ZTO/La) nanocomposites were successfully prepared and immobilized on diatomaceous earth (DE). The composition and texture of the composites prepared were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM-EDX), and specific surface area (SSA). The adsorption capacity and photocatalytic activity of the composites were determined via degradation of methylene blue (MB) in batch reactors. The materials evaluated were prepared in the shape of 0.2 cm (diameter) and 1.0 cm (length) cylindrical extrudates. The results indicate that the ZTO/La-DE composite exhibited higher efficiency for the removal of MB under solar irradiation than both ZTO-DE and DE. The pseudo-second-order model and the Langmuir isotherm model were better suited to explain the adsorption process. The highest degradation percentage of MB obtained was 96% after 150 min of irradiation. The results indicate that synthesized composite could be used for the removal of cationic dyes in wastewater.

Mapping the coke formation within a zeolite catalyst extrudate in space and time by operando computed X-ray diffraction tomography

We have used operando X-ray diffraction computed tomography (XRD-CT) analysed by rigorous crystallographic methods to reveal the behaviour of a zeolite/alumina based catalyst extrudate in the methanol-to-hydrocarbon reaction under working conditions (Treaction = 440 °C; ambient total pressure; WHSV = 12 gMeOH gextrudate−1 h−1). By doing so, we demonstrate that it is possible to precisely monitor how the cylindrical extrudate is deactivated during the process by gradual filling with coke from the outer surface towards the core. The operando data thus collected are simulated by a model taking both the reaction kinetics and the diffusion within the extrudate into account, and this analysis provides the tools required for future optimization of the degree of utilization of the catalyst. Both the operando experiment and post mortem XRD-CT of fully deactivated extrudates from a test reactor show clearly that the core of the catalyst body, around 1/3 of its volume, remains completely untouched by the reaction, even when the reactor output indicates zero activity.

Enhanced CO2 utilization via methane tri-reforming over Ru incorporated Co/MgO-Al2O3 catalyst: Influence of La and Ce promoters

The catalytic efficiency of Ru incorporated Co-based catalysts supported on cylindrical extrudates of MgO-Al2O3 mixed oxide with promoters La and Ce were investigated for syngas production by methane tri reforming for the effective utilization of CO2 present in varied sources, including industrial waste flue gases. Ru was chosen as one of the active metal due to its characteristic hydrogen spillover phenomena and high coke resistivity. Moreover, Co and Ru coexistence plays a pivotal role in enhanced reactants’ conversion and catalyst stability via the bimetallic synergy. The activity study revealed that Co content, Co-Ru synergy and La, Ce-doping influenced the catalytic activity as the prepared catalysts evaluated at different operating conditions like temperature 600–800 °C, pressure 1 atm and GHSV 4000–10,000 ml gcat−1 h−1 under an optimized molar feed ratio of CH4:CO2:H2O:O2 = 1:0.75:0.75:0.1. The variation in feed composition was also tested over the Co-Ru catalyst and obtained a product syngas ratio 1–2. The other key factors that influenced the catalytic performance were Co crystallite size, Co3O4 reducibility, surface basicity and metal-support interface as observed from the stability studies and detailed physicochemical characterization of fresh and spent catalysts using N2 physisorption, XRD, H2-TPR, CO2-TPD, SEM, TEM, XPS, and TG-DTG. Further, the addition of La facilitated the formation of a large number of surface basic sites than Ce via better La-(Co-Ru)-support interface resulted in superior coke resistivity for the La-doped Co-Ru catalyst with high conversions of CH4 and CO2 during 100 h time on stream study.

Removal of Pb(II) in Aqueous Solutions Using Synthesized Zeolite X from Ecuadorian Clay

Zeolite X was synthesized from clay using the alkaline fusion method and hydrothermal treatment to remove Pb(II) in aqueous solutions. Clay and zeolite were characterized through X-ray diffraction and fluorescence (XRD, FRX), as well as through specific surface area (SSA). The adsorbents were prepared as cylindrical extrudates using clay and a clay-zeolite combination (60-40%, respectively). The effects of pH, isotherm, and adsorption kinetics on the removal of Pb(II) in solutions of 80 mg Pb(II)/L were studied. It was possible to obtain a zeolite X from clay, with an SSA of 376 m2/g, 30 times greater than that of clay (12 m2/g). In the combined extrudate was present the zeolitic structure, with an SSA 12 times higher compared to the clay extrudate. The adsorption capacity, at 30 °C and V/m ratio of 1 g/L, is almost double compared to the clay extrudate (24 mg Pb(II)/g vs. 13 mg Pb(II)/g). Adsorption follows second order kinetics, and the Langmuir isotherm equation showed a good fit with the experimental equilibrium data for the two extrudates. The Webber-Morris and Bangham-Burt’s models suggest that pore and film diffusion influence the kinetic mechanism.

Structuring of ZnTiO3/TiO2 Adsorbents for the Removal of Methylene Blue, Using Zeolite Precursor Clays as Natural Additives.

Adsorption is an effective method of removing harmful pollutants from air and water. In the present study, zeolites prepared by sol-gel method from two Ecuadorian clays were combined with precursor clays and the ZnTiO3/TiO2 semiconductor for adsorbing methylene blue (MB) as a water contaminant. The synthesized compounds were characterized using powder X-ray diffraction, X-ray fluorescence, scanning electron microscopy, energy dispersive X-ray, and surface area measurement. These compounds were combined to form cylindrical extrudates of 0.2 cm (diameter) and 1.0 cm (length). The adsorption characteristics of the composites were measured using batch sorption studies as a function of pH, initial concentration, and contact time. The pseudo-second-order model and the Langmuir isotherm model were better suited to the adsorption process. The equilibrium state was achieved around 180 min of adsorption, and a pH of 7 was established as the optimal operating condition. The maximum adsorption values of the dye were obtained with the composites derived from G-Clay, whose average adsorption capacity was 46.36 mg g−1, in contrast with composites derived from R-Clay, whose average adsorption value was 36.24 mg g−1. The results reflect that synthesized composites could be used potentially for the removal of cationic dye from wastewater.

Modeling the breakage stage in spheronization of cylindrical paste extrudates

AbstractSpheronization of cylindrical extrudates on a rotating friction plate involves breakage and rounding. Little attention has been given to the breakage stage and quantitative modeling of this process is scarce. Two simple models are compared with experimental data obtained for the early stages of spheronization of microcrystalline cellulose/water extrudates. Tests were conducted for different times (t), rotational speeds (ω), initial loadings, and on pyramidal friction plates with different dimensions. The first model, describing the number of pellets, validated ω3t as a characteristic time scale for the breakage stage. The kinetic parameters obtained by fitting showed a systematic dependence on plate dimensions expressed as a scaled gap width. The second model, a simple population balance, described the evolution of the number and length of pellets. The pseudo rate constants provided insights into the kinetics: extrudates tended to break near the middle, while breakage of smaller pellets was slowed down by more pellet–pellet collisions.

Synthesis of the ZnTiO3/TiO2 Nanocomposite Supported in Ecuadorian Clays for the Adsorption and Photocatalytic Removal of Methylene Blue Dye.

Currently, the study of semiconductor materials is very promising for the photocatalytic remediation of hazardous organic substances present in the air and water. Various semiconductors have been investigated in this interesting photo-assisted methodology, among them metal oxides such as ZnO, TiO2 and their derivatives. In this study, ZnTiO3/TiO2 was synthesized by the sol-gel method using Ti(OC3H7)4 and Zn(CH3COO)2 · 2H2O as reagents. The role of several conditions such as synthesis temperature and TiO2:ZnO proportion on the morphology and purity of compounds obtained was studied, and the suitable conditions for the synthesis of photocatalysts were determined. Various techniques were used to conduct a systematic investigation on the structural, morphological, and photocatalytic properties of ZnTiO3/TiO2. Scanning Electron Microscopy (SEM) images show that ZnTiO3/TiO2 have a typical particle size of approximately 100 nm with a quasi-spherical shape. The adsorption and photocatalytic activity were investigated by the decolorization of Methylene Blue (MB) as an organic contaminant under UV irradiation both in TiO2 and ZnTiO3/TiO2 supported over some Ecuadorian clays. The materials evaluated were prepared in the shape of 0.2 cm (diameter) and 1.0 cm (length) cylindrical extrudates. The degradation percentage of MB obtained was 85% approximately after 150 min of irradiation. The results obtained allow us to conclude that these synthesized materials can be used as adsorbents and photocatalysts.

Implementation of formation mechanisms in DEM simulation of the spheronization process of pharmaceutical pellets

In the production process of pharmaceutical pellets with a narrow size distribution and a high sphericity, a combined extrusion-spheronization technique is frequently used. The rounding of the wet cylindrical extrudates in the spheronizer after the extrusion step is influenced by various interfering mechanisms, in particular plastic deformation, breakage, attrition and coalescence. Due to the complexity of these mechanisms which depend on the particle dynamics, there is no sufficient description of the particle rounding process in the spheronizer. In this study, the Discrete Element Method (DEM) which runs on the micro scale is coupled with a Particle Shape Evolution (PSE) model on the macro scale to describe how the particle shape changes due to collisions. For the DEM simulation a new contact model was used which was developed to capture the cyclic, dominant visco plastic deformation behaviour. Based on the DEM collision data, the changing particle shape was described in the PSE model by applying the proposed submodels for the different formation mechanisms. The resulting particle shapes obtained with this simulation framework are in a good agreement with experimental data.

Convective Drying of Sewage Sludge Layer in Through-flow

Drying of the sewage sludge layer was investigated in a convective laboratory dryer at air temperatures of 65 °C and 80 °C and air speeds of 0.53 m/s and 0.83 m/s. The sludge layer was formed by loading cylindrical extrudates on a grate of 0.5 m × 0.5 m size. The drying air was directed through the layer, as typically encountered in industrial belt dryers. Under such setup, the sludge layer structure and porosity significantly affect the air flow conditions and thus the drying rates. Shrinkage and cracking of the material during drying caused changes in the layer’s porous structure, that affected the pressure drop and the drag force due to passing of air through the layer. The decreasing of drag force over time was modeled by a simple function that showed excellent agreement to the selected measured data. The sludge layer drying kinetics was determined by fitting the measured data to the most common drying models. Two models, the modified Nadhari and the Wang Singh model, were determined as most suitable for modeling of drying curves. The total drying time per kilogram of sludge was modeled as a function of drying air temperature, drying air velocity and initial sludge dry matter content. The coefficient of determination (R2) of the model is 0.944. Total drying times between 43 minutes per kilogram and 76 minutes per kilogram of sludge were obtained for the investigated range of drying air conditions.

Ductile damage and fragmentation of highly porous γ-alumina under multi-point crushing test

Mechanical behavior of highly porous alumina catalytic supports is investigated through a non-conventional approach consisting in a multi-point crushing of individual cylindrical extrudates. A ductile behavior characterized by irreversible deformation and fragmentation phenomena is observed and pointed out by experimental load-displacement curves. SEM fractographies of the fragments collected after the tests confirm the presence of dense micro-cracking and of local deformations under contact zones. A Finite Element analysis of the test shows that a Drucker-Prager strength criterion associated with a perfectly plastic flow rule mimics the global damageable behavior of the specimen under the multi-point crushing test. A correlation is proposed between the evolution of the mass of fine fragments and the plastic energy dissipation.

A contact model for the deformation behaviour of pharmaceutical pellets under cyclic loading

Spherical pharmaceutical pellets are commonly produced by an extrusion-spheronization process. In the spheronizer, the wet cylindrical extrudates are rounded into spheres due to multiple collisions. In order to model this rounding, a suitable contact model, which can predict the dominantly plastic deformation behaviour, is necessary. In this study, a novel cyclic model for wet and dry pellets was developed. Various single particle compression and impact tests with pellets produced from microcrystalline cellulose (MCC) and lactose were conducted to calibrate and validate this model. It was found that the model is able to predict the energy dissipation as well as the deformation during pellet impact in the velocity range which is relevant for the spheronization process. Since the pellets are loaded multiple times during this process, the model was designed in order to account for the increasing flattening and hardening in the contact area as a function of the number of loading cycles. Therefore, the presented model allows the description of the pellet deformation by repeated stressing.

Intensification of the convective drying process of Arthrospira (Spirulina) platensis by capillary draining: effect of the draining support

The aim of this work is to study the intensification of the convective drying process of Arthrospira (Spirulina) by capillary drainage. Capillary drainage effect was performed by the integration of different draining supports, namely cotton, microfibers, 30 μm fabric, and 80 μm fabric, between the biomass and the drying tray. Drying tests were carried out in a pilot-scale drying tunnel at a free-stream temperature between 39 and 42 °C, at air velocity of 0.5 m s−1 and at air relative humidity around 20%. The Arthrospira biomass was set at two different initial moisture contents on dry basis: 7 kg kg−1 and 5 kg kg−1. For each of these initial moisture contents, the fresh paste was spread over the different draining support, either in a thin layer (dimensions 80 × 80 × 3 mm3) or in cylindrical extrudates (3-mm diameter and 120-mm length) with two different spacings (10 and 20 mm). Drying experiments of biomass in thin layer after the integration of the different draining supports, particularly the 80-μm mesh fabric, lead to a significant drying time reduction compared to that performed without any draining support. For this most effective support, the percentage time reduction was around 30%. However, the percentage time reduction was around 35% for drying tests of biomass in cylindrical extrusions using 80 μm mesh fabric as a draining medium. For all drying tests, the drying kinetic coefficient kx was identified by fitting the falling rate drying period data by a first-order kinetic equation (Lewis model). This coefficient was significantly increased by the presence of the porous material. Its value was equal to 5.604 × 10−4 g dry matter s−1 for drying test without any support and reached a value of 11.556 × 10−4 g dry matter s−1 for drying test with 80-μm mesh fabric.

Hydrodynamics in a pilot‐scale cocurrent trickle‐bed reactor at low gas velocities

Hydrodynamic data obtained from laboratory‐scale trickle‐beds often fail to accurately represent industrial‐scale systems with high packing aspect ratios and column‐to‐particle diameter ratios. In this study, pressure drop, liquid holdup, and flow regime transition were investigated in a pilot‐scale trickle‐bed column of 33 cm ID and 2.45 m bed height packed with 1.6 mm × 8.4 ± 1.4 mm cylindrical extrudates for air‐water mass superficial velocities of 0.0023 – 0.094 kg/m2s and 4.5 – 45 kg/m2s, respectively, at atmospheric pressure. Significant deviation was observed from pressure drop and liquid holdup correlations at low liquid flows rates, corresponding to gravity‐driven flow limit. Likewise, liquid saturation is overestimated by correlations at high liquid flow rates, owing to significantly reduced wall effects. Lastly, trickle‐to‐dispersed bubble flow and trickle‐to‐pulsing flow regime transitions are reported using a combination of visual observations and analysis of the magnitude of local pressure fluctuations within the column. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2560–2569, 2018

Asphaltenes Transport into Hydroconversion Catalysts at High Temperature: Role of the Alumina Nanoporous Texture

This study deals with the role of the alumina nanoporous texture in the accessibility of the asphaltene molecules to the active sites of resid hydroconversion catalysts. We have proposed in this contribution to investigate the diffusion and adsorption process into the porosity of various monomodal and bimodal alumina supports. It consists of immersing catalytic supports, under the form of extrudates, into an asphaltene solution in toluene. Optical microscopy observations of a cut of the cylindrical extrudates were carried out to follow the asphaltene penetration as a function of the contact time. We aimed at reaching a good asphaltene mass balance, taking into account (i) the evolution of the asphaltene concentration in solution and (ii) the precise determination of the amount of asphaltenes deposited into the support. The influence, on the mass transfer and the penetration depth, of various parameters such as temperature, asphaltene concentration of the solution, asphaltene size polydispersity, and alumi...

Effect of the particle shape on the particle dynamics in a spheronization process

Spherical granules with a narrow size distribution are widely used in many pharmaceutical applications. Extrusion-spheronization is a well-established process to produce such pharmaceutical pellets. The cylindrical extrudates from the extrusion step are rounded in the spheronizer. The formation mechanisms inside of a spheronizer depend strongly on the particle dynamics. To describe the complex particle flow and interactions, the Discrete Element Method can be used. In our previous works the spherical particles during the last part of the spheronization process were studied. Since the pellets have a cylindrical shape at the beginning and undergo different stages of deformation during the rounding process, the objective of this study was the description of the influence of the particle shape on the particle dynamics. To predict the interactions of the pellets, their dominant plastic behaviour was described with an appropriate contact model and the material parameters were calibrated with compression and impact tests.

High temperature CO2 sorption using Ca(OH)2 in pilot scale packed column

Carbon dioxide is the major content of greenhouse gases, which is released by many industries such as paper, cement and steel industries etc. Removal or separation of CO 2 from the atmosphere is a challenging task for the researchers as it related to the human health and affects environment. Many methods and techniques have been tried for the removal of CO 2 , among them sorption method was found to be more simple and economical. Majority of research work related to CO 2 sequestration was carried out using Thermo Gravimetric Analysis (TGA). In the present study an attempt was made to study high temperature CO 2 sorption using self-fabricated packed bed column in pilot scale. In this work the absorption column was designed to utilize the flue gas temperature for effective sorption of carbon dioxide using Calcium hydroxide [Ca(OH) 2 ] as a sorbent. The Ca(OH) 2 was made into cylindrical extrudates. The gas mixture containing nitrogen and carbon dioxide was heated and subjected to CO 2 sorption using Ca(OH) 2 . The sorption process for various temperatures was studied at a constant flow rate and fixed bed height. Concentration of CO 2 was measured using a flue gas analyzer (NDIR sensors). The temperature was found to be major factor affecting sorption process. The optimum temperature was found to be 300 °C. Increase in the temperature above 300 °C, resulted in sintering and weight loss of the sorbent. The conversion of Ca(OH) 2 to CaCO 3 is confirmed by FT-IR, Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Analysis(EDAX) and XRD.

Preparation of cylindrical extrudates of mesoporous silica-alumina without use of binder and their activity in cracking of cumene

A series of mesoporous silica–aluminas (MSA) containing 24–59 wt% Al2O3 was synthesized from sodium metasilicate and aluminum nitrate and extruded in 1/16″ cylinders without use of a binder. This was followed by slow hydrogel drying, extraction by water and calcination at 500 °C. This procedure gave stable hard extrudates and the absence of binder allowed to keep the surface area, mesoporosity and cracking activity of MSA at the original high values. The resistance to crushing was much better as compared to commercial molecular sieve 13X. The extrudates have average pore size around 3.5 nm. Their properties were affected by the contents of Al2O3 and residual sodium. The MSA containing 50 wt% Al2O3 possessed the maximum values of surface area, pore volume and activity in cumene cracking. The calcined extrudates showed good water sorption capacity and were stable in aqueous environment. This predestinates the MSA extrudates as the shaped mesoporous acidic carriers for preparation of different supported catalysts.

How to adjust dexamethasone mobility in silicone matrices: A quantitative treatment

Silicone-based drug delivery systems offer a great potential to improve the therapeutic efficacy and safety of a large variety of medical treatments, e.g. allowing for local long-term delivery of active agents to the inner ear. Different formulation parameters can be varied to adjust desired drug release kinetics. However, often only qualitative information is available on their effects, and product optimization is cumbersome. The aim of this study was to provide a quantitative analysis, allowing also for theoretical predictions of the impact of the device design on system performance. Dexamethasone was incorporated into thin films based on different types of silicones (e.g. varying in the type of side chains and contents of amorphous silica), optionally containing different types and amounts of poly(ethylene glycol) (PEG) (5% or 10%). Furthermore, the initial drug content was altered (from 10% to 50%). In most cases, an analytical solution of Fick’s second law could be used to describe the resulting drug release kinetics from the films and to determine the respective “apparent” diffusion coefficient of the drug (which varied from 2×10−14 to 2×10−12cm2/s, depending on the system’s composition). Thus, the impact of the investigated formulation parameters on drug mobility in the polymeric matrices could be quantitatively described. Importantly, the knowledge of the “apparent” drug diffusivity can be used to theoretically predict the resulting release kinetics from dosage forms of arbitrary size and shape. For instance, dexamethasone release was theoretically predicted from cylindrical extrudates based on a selection of different silicone types. Interestingly, these predictions could be confirmed by independent experiments. Hence, this type of quantitative analysis can replace time-consuming and cost-intensive series of trial-and-error experiments during product optimization. This is particularly helpful, if long-term drug release (e.g., during several weeks, months or years) is targeted.

Properties of extruded chia–corn meal puffs

This study investigated the properties of extruded corn meal puffs containing chia. Mixtures of corn meal and chia seeds (0–20 g/100 g) were processed in a laboratory-scale twin-screw extruder at different moisture contents (18–22 g/100 g) and final heating zone temperatures (120–160 °C). Extrusion processing provides a simple method for grinding the seeds, which is necessary for making the fatty acids available. The expansion of cylindrical extrudates decreased with increasing chia content, increasing moisture and increasing final heating zone temperature. The hardness of the extrudates increased with increasing moisture content and decreased at intermediate chia levels. The specific mechanical energy of the extrusion process decreased with increasing chia content.

Shaping of mesoporous AISBA-15 as cylindrical nano reactor for tertiary butylation of phenol.

Mesoporous AISBA-15 with different n(Si)/n(Al) ratios (45, 136 and 215) in the powder (P) form were synthesized by hydrothermal technique. The powder materials were shaped into cylindrical extrudates (Ex) by compounding with additives such as bentonite (binder) and methylcellulose (plasticizer). The AISBA-15 materials were characterized by XRD, N2 adsorption, AAS, 27Al MAS-NMR and thermogravimetric analysis. The orderly growth of AISBA-15 is evidenced by its XRD patterns. The surface area and pore volume of AISBA-15 catalysts were around 950 m2/g and 1.3 cm3/g respectively. A decrease in surface area and pore volume were observed for AISBA-15 (Ex) materials in comparison to AISBA-15 (P) materials. This may be due to partial blocking of pore entry and surface area coverage of additives during the shaping of extrudates. Vapor phase alkylation of phenol with tert-butanol was carried out over AISBA-15 (P) and AISBA-15 (Ex) catalysts and the results revealed that both powder and extrudate samples showed similar activity for phenol conversion. The activity of AISBA-15 catalysts follows the order: AISBA-15 (45) > AISBA-15 (136) > AISBA-15 (215) for both powder and extrudate forms. The major products were 2-tert-butylphenol (2-TBP), 4-tert-butylphenol (4-TBP) and 2,4-di-tert-butylphenol (2,4-DTBP). The selectivity to para product is much higher than other products. The catalyst exhibited steady conversion, and deactivation by coke formation of the catalyst is much reduced in AISBA-15 materials.