Fixed-bed Experiments Research Articles

Sulphated zirconia catalysed conversion of high density polyethylene to value-added products using a fixed-bed reactor

A sulphated zirconia catalyst (SZ) was investigated for catalytic conversion of high density polyethylene (HDPE) to liquid and gaseous hydrocarbons using a fixed-bed reactor. The SZ catalyst reduced the onset of degradation from 337°C for HDPE alone to 187°C with 10wt% SZ added. At 450°C a complete weight loss was obtained with the SZ addition against only 4wt% loss for HDPE only. Fixed-bed reactor experiments using 2g of HDPE with 10wt% SZ catalyst with a 30min residence time showed a 98.0wt% conversion at temperature as low as 380°C. The liquid yield obtained was 39.0wt% with a composition of 16wt% paraffins, 21wt% olefins, 5wt% naphthenes and 58wt% aromatics. The carbon number distribution of the liquid was C7–C12, which is within the gasoline range. Equally, gaseous products ranging from methane up to different isomers of pentane which contained more paraffinic and naphthenic hydrocarbon were obtained. The sulphated zirconia catalyst was found to have high ammonia desorption (337.0μmolNH3g−1), BET surface area (116.0m2g−1), external surface area (112.0m2g−1) and mesoporous structure. The overall results indicate that sulphated zirconia had excellent properties for catalytic conversion at temperature as low as 380°C with significant liquid yield which could offer a solution to plastic waste problem by converting the waste back into value-added chemicals and fuel.

Decomposition of dimethyl carbonate caused by adsorption onto activated carbon

This contribution addresses the adsorptive cleaning of an exhaust gas released from a Lithium–Ion-battery recycling process. Adsorption in fixed beds is frequently used to clean off gases containing solvents, toxic components, or other contaminates. Well-established short-cut models are available to determine capacity and dynamics of such adsorber beds. However, uncertainties arise if the gas contains unknown trace components or if new components appear due to chemical reaction or decomposition processes. In the present study, the off gas mainly consists of dimethyl carbonate in a nitrogen gas stream. Dimethyl carbonate decomposes when contacted with activated carbon. The decomposition product methanol co-adsorbs together with dimethyl carbonate onto activated carbon and therefore decreases the adsorption capacity for DMC. This paper shows the influences of temperature, residence time, carbon mass and water on the decomposition of dimethyl carbonate. Additionally, first results of fixed-bed experiments including temperature profile and breakthrough curve are discussed to show the effect of decomposition occurring in fixed-bed adsorption.

Arsenate and phosphate removal from water using Fe-sericite composite beads in batch and fixed-bed systems

Abstract Natural sericite clay was modified with iron-oxide and then the modified sericite was encapsulated into beads by employing the ionic gelation method to obtain Fe-sericite composite beads. The materials were fully characterized by N2 adsorption–desorption isotherm, SEM-EDX, XRD, FT-IR and XPS analyses. Batch experiments showed that the composite beads showed a high uptake of As(V) and phosphate within a wide range of pH and the maximum sorption capacity determined by Langmuir isotherm were found to be 5.780 and 4.446 mg/g for As(V) and phosphate, respectively. The sorption kinetic data indicate that at least 12 h of contact time is necessary to attain the sorption equilibrium and intra-particle diffusion plays a significant role in the sorption process. The presence of background electrolyte (NaNO3) or other heavy metals ions could not significantly affect the uptake of As(V)/phosphate by Fe-sericite composite beads. Furthermore, a fixed-bed column experiment has demonstrated that Fe-sericite composite beads could remove As(V) and phosphate up to acceptable level with a high breakthrough volume even under dynamic conditions. XPS analysis results indicate the successful sorption of As(V)/phosphate and it is assumed that these two pollutants formed an inner sphere complexes with iron oxide present in the composite beads.

Stepped water isotherm and breakthrough curves on aluminium fumarate metal–organic framework: experimental and modelling study

Adsorption of water vapour on the Al-fumarate metal–organic framework (MOF) was studied in static and dynamic conditions, by performing gravimetric and fixed bed experiments. A two-step, type IV water isotherm is obtained, which reveals the complexity and the duality of the hydrophilic/hydrophobic behaviour of this MOF. Breakthrough experiments with feed conditions corresponding to three different zones in the water adsorption isotherm were performed to study the effect of isotherm shape on the column dynamics. At low partial pressure of water in the feed, a single breakthrough step is observed while a stepped profile is observed at higher partial pressure of water. These breakthrough curves could be described qualitatively with a simple model accounting for the isotherm shape.

ADSORPTION OF FLUORIDE FROM INDUSTRIAL WASTEWATER IN FIXED BED COLUMN USING JAVA PLUM (SYZYGIUM CUMINI)

ABSTRACTObjective: The quality of drinking water is important for public safety and quality of life. Thus, providing every person on earth safe drinking waterseems to be the biggest challenge in front of mankind. For this purpose, here we have investigated the fluoride removal capacity of java plum.Methods: In this study, removal of fluoride from industrial wastewater using fixed-bed reactor adsorption techniques by java plum seed (Syzygiumcumini) was investigated. Fixed-bed column experiments were carried out for different bed depths, influent fluoride concentrations, and various flowrates. The Thomas model and bed depth service time model were applied to the experimental results. Both model predictions verify the experimentaldata for all the process parameters studied, indicating that the models were suitable for java plum (S. cumini) seeds (Biosorbent) fix-bed columndesign.Results: The empty bed residence time (EBRT) model optimizes the EBRT, and the Thomas model showed that the adsorption capacity is stronglydependent on the flow rate, initial fluoride concentration, and bed depth and is greater under conditions of a lower concentration of fluoride, lowerflow rate, and higher bed depth.Conclusion: The experimental results were encouraging and indicate that java plum (S. cumini) seed is a feasible option to use as a biosorbent toremove fluoride in a fixed bed adsorption process.Keywords: Adsorption, Column experiment, Thomas model, Empty bed residence time, Java plum.

Experimental Study on Embankment Reinforcement by Steel Sheet Pile Structure Against Tsunami Overflow

This study proposes a new embankment reinforcement using steel sheet piles against tsunami overflow, which has been known as the main cause of the failures of the embankments by the 2011 Tohoku Earthquake Tsunami. Effectiveness of the proposed technique was discussed through a hydraulic experiment. A model of embankment was set in a horizontal open channel, and one or two steel plates are installed into the embankment from the top as vertical walls inside. Temporal variations of the shapes of the embankment and the sheet pile structures were obtained from video images. In most of the cases, the sheet pile structures started to rotate after the erosion of the landward slope of the embankment. However the rotation stopped at about 30° and 10° from the initial location with the single- and double-wall cases. Height of the embankment after overflow was less than 20% with no reinforcement, while more than 70% and 95% of the height were kept with the single- and double-wall structures, respectively. The performance of the embankment with the reinforcement was also discussed in terms of tsunami energy reduction with an additional fixed-bed experiment.

Influence of the natural organic matter in the removal of caffeine from water by fixed-bed column adsorption

The removal of caffeine from tap water by F-400 granular activated carbon in fixed-bed adsorption experiments was carried out. Textural and chemical characterization of the adsorbent through N2 adsorption–desorption isotherms, Fourier transform infrared spectrometry, isoelectric point determination and scanning electron microscopy studies was developed in studies previously reported. Caffeine breakthrough curves and total organic carbon profiles at different operation conditions (inlet concentration, volumetric flow rate and mass of adsorbent) were obtained. These experimental results showed a displacement of the natural organic matter from the active sites exerted by caffeine molecules due to their higher affinity to the surface carbon. This behavior led to an overshooting, a local outlet natural organic matter concentration higher than the feed quantity. A competitive effect seems to be observed in the removal of the target compound, decreasing the efficiency of the process. Axial dispersion coefficients and dimensionless numbers were estimated for the caffeine removal onto F-400 activated carbon. Therefore, the regeneration of the adsorbent by adsorption–desorption cycles was studied.

Removal of Cr(VI) by modified and immobilized Auricularia auricula spent substrate in a fixed-bed column

To remove the heavy metals from industrial wastewater and reclaim valuable materials from edible fungus production, Auricularia auricula spent substrate (AASS) modified by cetyltrimethyl ammonium bromide (CTAB) and immobilized by sodium alginate was used as a novel adsorbent (MIAASS) for Cr(VI) removal. The modification and immobilization did not change the surface morphology, but changed the property of the adsorbents revealed by SEM, BET and FT-IR analysis. Batch adsorption experiments showed the modification and immobilization had the uptake capacity improved 21.44 to 27.34% at influent Cr(VI) concentration ranging from 25 to 125mg/L. In fixed-bed column adsorption experiments, the breakthrough and exhaustion time were prolonged about 2 to 4.5 times with bed height increasing from 50 to 70cm, influent concentration and flow rate decreasing from 200 to 50mg/L and 40 to 20mL/min respectively. The concentration-time profile and the adsorption process was better predicted and described by Thomas model than Adams-Bohart model indicating that the external and internal diffusions were not the bottle neck of the process. The stability of MIAASS was validated through three cycles of adsorption-desorption processes, and the final regeneration efficiency amounted to 52.48%.

Heterogeneous Fenton degradation of organic dyes in batch and fixed bed using La-Fe montmorillonite as catalyst

The La-Fe montmorillonite (La-Fe MMT) composite was synthesized by a simple precipitation method and was used for the degradation of dyes in both batch and fixed bed experiments. X-ray diffraction (XRD) and high-resolution transmission electron microscope analysis (HRTEM) confirmed the existence of Fe2O3 and La2O3 in the composite. The presence of La enhanced the degradation efficiency of dyes by the composite at neutral pH and results in little iron leaching consequently increasing the lifetime. More than 97% and 96% removal of the MB and RhB (100mg/L each) by the La-Fe MMT Fenton system could be achieved in less than 1h. The catalyst also exhibited excellent efficiency in fixed bed reactor with 91% MB degradation corresponds to 65% COD removal, even after 200h of use. The factors such as solution pH, catalyst dosage, H2O2 dosage and temperature on the degradation of dyes were investigated. Fluorescence and quenchers experiments indicated that OH was the main reactive species for the degradation of dyes. Due to the low cost, efficient reactivity, high stability and low metal leaching, the La-Fe MMT possesses a great potential to be a green catalyst for the heterogeneous Fenton-like degradation of hazardous dyes.

Trace Lead Removal in Drinking Water Using High Capacity Polymeric Supported Hydrated Iron Oxide Nanoparticles

Ferric oxide nanoparticles are environmentally benign and can be selective toward lead, especially in neutral to mildly alkaline pH of groundwater. However, due to very fine particles and low mechanical strength, it prevents these materials to apply in point of use filter or large scale fixed-bed adsorption. In this study, polymeric gel cation exchanger, Purolite C100, supported ferric oxide nanoparticles, C100-Fe, was synthesized, characterized, and tested with challenging water according to NSF standards 53. From SEM-EDX studies, it can imply that high concentration of iron can be doped and distributed within the gel phase structure of the C100 approximately 22% by mass. The TEM micrographs confirm the size of hydrated ferric oxide fall into the nanometer range about 10-60 mm. The fixed-bed adsorption experiments demonstrated that C100-Fe can remove lead below the stringent standard of 0.05 mg/L up to 15,000 BVs, whereas the GAC, GAC-Fe, and C100 can treat the same test water only 1200, 1700, and 3500 BVs, respectively. The results confirm that C100-Fe can be efficiently substituted to the traditional GAC for lead removal in drinking water.

The influence of iron oxide on the oxidation kinetics of synthetic char derived from thermogravimetric analysis and fixed-bed experiments under isothermal and temperature-programmed conditions

The catalytic effect of iron oxide on the oxidation kinetics of synthetic char was investigated in a fixed-bed reactor and in a conventional thermobalance for comparison. Synthetic char doped with iron oxide was obtained by pyrolyzing hydrochar at 800°C, which had been synthesized by hydrothermal carbonization of cellulose in the presence of iron oxide. Isothermal char oxidation in the fixed-bed reactor resulted in the most reliable kinetic results. According to model-free kinetic analysis of these experiments at 15% conversion, iron oxide decreased the activation energy of char oxidation from 149kJ/mol to 133kJ/mol. Modeling of the conversion-time curves was first performed by using the uniform reaction model and then improved by using a n-th order power law. In the temperature range of 440–490°C a very good agreement with the experimental data was achieved using n=0.6. Activation energies amounting to 149kJ/mol and 134kJ/mol were derived for the undoped and iron oxide-doped char, respectively, well in line with the model-free analysis.

Kinetic studies of mercury adsorption in activated carbon modified by iodine steam vapor deposition method

The objective of this study was to develop a high efficiency activated carbon (AC) sorbent for mercury removal. The vapor deposition method was used to modify the raw AC. This method is relatively easy to carry out and uniformly modifies the AC. The results of this study indicate that AC modified by iodine steam vapor deposition has much better Hg capturing capacity than AC modified by bromide deposition under the same experimental conditions. London dispersion forces and exposure of the sorbent surfaces play important roles in elemental mercury (Hg0) adsorption. Adsorption kinetic behavior was also studied under different experiment conditions. Results indicated that the pseudo-second model was the best fit to the actual mercury adsorption behavior onto AC-I2 sorbent. The effect of adsorbent mass and gas flow rate on adsorption behavior were examined. Results indicated that increasing the sorbent mass led to an increase in Hg adsorption capacity, while increasing the gas flow rate resulted in a significant decrease in Hg adsorption capacity. Decreases in Hg adsorption capacity were likely due to a shorter contact time and lower partial pressure reducing the number of contact opportunities between the Hg atoms and the sorbent surface. Finally, a general dynamic equation was determined that can be used to help predict Hg adsorption curve of AC-I2 sorbent without completing a real fixed-bed Hg adsorption experiment.

Encapsulated Ionic Liquids for CO2 Capture: Using 1-Butyl-methylimidazolium Acetate for Quick and Reversible CO2 Chemical Absorption.

The potential advantages of applying encapsulated ionic liquid (ENIL) to CO2 capture by chemical absorption with 1-butyl-3-methylimidazolium acetate [bmim][acetate] are evaluated. The [bmim][acetate]-ENIL is a particle material with solid appearance and 70 % w/w in ionic liquid (IL). The performance of this material as CO2 sorbent was evaluated by gravimetric and fixed-bed sorption experiments at different temperatures and CO2 partial pressures. ENIL maintains the favourable thermodynamic properties of the neat IL regarding CO2 absorption. Remarkably, a drastic increase of CO2 sorption rates was achieved using ENIL, related to much higher contact area after discretization. In addition, experiments demonstrate reversibility of the chemical reaction and the efficient ENIL regeneration, mainly hindered by the unfavourable transport properties. The common drawback of ILs as CO2 chemical absorbents (low absorption rate and difficulties in solvent regeneration) are overcome by using ENIL systems.

On the turbulent flow structure around an instream structure with realistic geometry

We investigate the flow dynamics around a rock vane, a widely-used instream structure for stream restoration, by conducting laboratory flume experiments, and carrying out high-resolution Large Eddy Simulation (LES) taking advantage of parallel computing. The flume experiments are conducted under fixed- and mobile-bed conditions, where the velocities and bed elevations are measured, respectively. The LES is carried out for the fixed-bed experiment by directly resolving the details of the rocks that constitute the vane and the individual roughness elements on the channel bed. The LES-computed mean flow statistics show good agreement with the measurements, and the analysis of the computed flow field reveals the existence of two counter-rotating secondary flow cells downstream of the vane, which originate from the plunging of the three-dimensional streamlines onto a lower part of the sidewall downstream of the vane. To further examine the role of the secondary flow cells under a mobile-bed condition, the LES results are compared with the equilibrium bed elevation measured in the mobile bed experiment. The mobile-bed experiment reveals the existence of an oblique sand ridge downstream of the vane that is aligned with the line of flow convergence caused by the collision of the two secondary flow cells. The results indicate that the two counter-rotating cells downstream of the rock vane has a profound impact on the mean flow and bed shear stress as well as on the bed morphodynamics. This article is protected by copyright. All rights reserved.

Cooperative sorption of weak and strong electrolytes in microporous adsorbents

Sorption of pure electrolytes and binary electrolyte mixtures in non-ionic microporous adsorbents was studied in batch and fixed-bed systems. Hypercrosslinked polystyrene (HCPS) and densely crosslinked dextran gel (G10) were used as adsorbents and the studied model systems were HCl/CaCl2/HCPS at 25 °C and Na2-tartrate/NaOH/G10 at 50 °C. The results were explained in terms of cooperative sorption and the experimental data were correlated using a generalized Donnan equilibrium model together with Pitzer model for evaluation of the ion-ion and ion-adsorbent interactions. Moreover, a model was included for partial ion dehydration at high concentrations.Non-linear sorption observed at very low and high concentrations of pure electrolytes was explained by electrostatic exclusion and partial ion dehydration. In binary mixtures, a more complex behavior was observed because of cooperativity and good separation of the electrolyte mixtures was obtained in the fixed-bed experiments involving pulse feed and elution with pure water. In the HCl/CaCl2/HCPS system, selective uptake of HCl was enhanced by increasing the total electrolyte concentration. This trend can be explained by taking into account both size exclusion of CaCl2 and the non-ideal behavior of the electrolyte mixture. Separation of Na2-tartrate and NaOH was dominated by size exclusion of the tartrate anion and well-defined separation is possible even at very high column loading. Moreover, the observed splitting of Na2-tartrate to NaH-tartrate and NaOH can be explained on the basis of cooperativity. The results suggest that the proposed model applies equally well to materials having rigid microporous structure and to densely cross-linked gels.

Rapid and efficient treatment of wastewater with high-concentration heavy metals using a new type of hydrogel-based adsorption process

In this study, a new type of double-network hydrogel sorbent was developed to remove heavy metals in wastewater. The amino-functionalized Starch/PAA hydrogel (NH2-Starch/PAA) could be conducted in a wide pH and the adsorption process could rapidly achieve the equilibrium. The adsorption capacity got to 256.4mg/g for Cd(II). Resultantly, even though Cd(II) concentration was as high as 180mg/L, the Cd(II) could be entirely removed using 1g/L sorbent. Furthermore, the desirable mechanical durability of the adsorbent allowed easy separation and reusability. In the fixed-bed column experiments, the treatment volume of the effluent with a high Cd(II) concentration of 200mg/L reached 2400BV (27.1L) after eight times cycle. The NH2-Starch/PAA overcame the deficiency of conventional sorbents that could not effectively treat the wastewater with relatively high metal concentrations. This work provides a new insight into omnidirectional enhancement of sorbents for removing high-concentration heavy metals in wastewater.

Adsorption behavior of bovine serum albumin on Zn–Al and Mg–Al layered double hydroxides

In this work, non-calcined Mg–Al and Zn–Al layered double hydroxides (LDHs) with molar ratio of 3:1 were investigated for the adsorption of bovine serum albumin (BSA). Both LDHs were synthesized using the co-precipitation method and were characterized by X-ray diffraction, N2 adsorption–desorption isotherm at −196 °C, elemental analysis and X-ray photoelectron spectroscopy. The adsorption of BSA was evaluated in a batch adsorption system to assess the influence of buffer solution and buffer pH, contact time and initial concentration. Fixed-bed adsorption experiments were also performed in order to evaluate the dynamic adsorption behavior of BSA on the LDH as well as the regenerability of this material. In the batch adsorption experiments, the maximum amount of BSA adsorbed was reached at its isoelectric point (pI = 4.8) with 50 mM acetate buffer for Mg–Al LDH and pH 6.7 with 50 mM 2-(N-morpholino)ethanesulfonic acid (MES) buffer for Zn–Al LDH. The Langmuir and Langmuir–Freundlich models provided maximum equilibrium adsorption capacity of 338.74 and 346.54 mg g−1for Zn-Al LDH, respectively, and 196.12 and 197.80, respectively, for Mg-Al LDH. Column experiments were carried out with a constant flow of 1 mL min−1, varying the feed concentration of BSA solutions from 1.0 to 2.0 mg mL−1. An average of 98 % of BSA injected into the column was retained, and a completely elution was reached using 50 mM sodium phosphate with pH 12.

Adsorption of Polycyclic Aromatic Hydrocarbons from Heavy Naphthenic Oil Using Commercial Activated Carbons. 2. Column Adsorption Studies

Continuous adsorption and desorption of polycyclic aromatic hydrocarbons (PAHs) from heavy naphthenic oils (HNOs) were performed using commercial activated carbon on fixed bed experiments. In part 1, HNO samples with high PAH content (ca. 8 wt %) were treated in batch adsorption experiments, showing decrease in PAH concentration to ca. 3%. In this study, successive column experiments were carried out to study the reduction in capacity along continuous cycles and optimal operational conditions. A column simulation model, using the particle parameters obtained in the previous study, was applied to predict breakthrough curves for adsorption and desorption runs. After several cycles of adsorption/desorption, using solvent or inert gas, only a slight decrease in PAH adsorption capacity was observed. Selectivities for PAH adsorption in relation to aromatics adsorption were also estimated from the adsorption breakthrough curves data. A conceptual continuous process was simulated using the proposed model and evaluated based on productivity in terms of volume of treated oil per mass of adsorbent per time, showing a maximum value at space velocity of ca. 4 h–1.

Advanced landfill leachate treatment using iron-carbon microelectrolysis- Fenton process: Process optimization and column experiments

A novel hydrogen peroxide-enhanced iron-carbon (Fe-C) microelectrolysis reactor was proposed for the pretreatment of mature landfill leachate. This reactor, combining microelectrolysis with Fenton process, revealed high treatment efficiency. The operating variables, including Fe-C dosage, H2O2 concentration and initial pH, were optimized by the response surface methodology (RSM), regarding the chemical oxygen demand (COD) removal efficiency and biochemical oxygen demand: chemical oxygen demand (BOD5/COD) as the responses. The highest COD removal (74.59%) and BOD5/COD (0.50) was obtained at optimal conditions of Fe-C dosage 55.72g/L, H2O2 concentration 12.32mL/L and initial pH 3.12. Three-dimensional excitation and emission matrix (3D-EEM) fluorescence spectroscopy and molecular weight (MW) distribution demonstrated that high molecular weight fractions such as refractory fulvic-like substances in leachate were effectively destroyed during the combined processes, which should be attributed to the combination oxidative effect of microelectrolysis and Fenton. The fixed-bed column experiments were performed and the breakthrough curves at different flow rates were evaluated to determine the practical applicability of the combined process. All these results show that the hydrogen peroxide-enhanced iron-carbon (Fe-C) microelectrolysis reactor is a promising and efficient technology for the treatment of mature landfill leachate.

Three-Dimensional Reduced Graphene Oxide Coupled with Mn3O4 for Highly Efficient Removal of Sb(III) and Sb(V) from Water.

Highly porous, three-dimensional (3D) nanostructured composite adsorbents of reduced graphene oxides/Mn3O4 (RGO/Mn3O4) were fabricated by a facile method of a combination of reflux condensation and solvothermal reactions and systemically characterized. The as-prepared RGO/Mn3O4 possesses a mesoporous 3D structure, in which Mn3O4 nanoparticles are uniformly deposited on the surface of the reduced graphene oxide. The adsorption properties of RGO/Mn3O4 to antimonite (Sb(III)) and antimonate (Sb(V)) were investigated using batch experiments of adsorption isotherms and kinetics. Experimental results show that the RGO/Mn3O4 composite has fast liquid transport and superior adsorption capacity toward antimony (Sb) species in comparison to six recent adsorbents reported in the literature and summarized in a table in this paper. Theoretical maximum adsorption capacities of RGO/Mn3O4 toward Sb(III) and Sb(V) are 151.84 and 105.50 mg/g, respectively, modeled by Langmuir isotherms. The application of RGO/Mn3O4 was demonstrated by using drinking water spiked with Sb (320 μg/L). Fixed-bed column adsorption experiments indicate that the effective breakthrough volumes were 859 and 633 mL bed volumes (BVs) for the Sb(III) and Sb(V), respectively, until the maximum contaminant level of 5 ppb was reached, which is below the maximum limits allowed in drinking water according to the most stringent regulations. The advantages of being nontoxic, highly stable, and resistant to acid and alkali and having high adsorption capacity toward Sb(III) and Sb(V) confirm the great potential application of RGO/Mn3O4 in Sb-spiked water treatment.