Fixed-bed Process Research Articles

Highly mesoporous K2CO3 and KOH/activated carbon for SDBS removal from water samples: Batch and fixed-bed column adsorption process

This manuscript evaluates the behavior of activated carbon (AC) prepared from the cones biomass of Iranian pine trees, with high mesoporosity and a large specific surface area, as a high potential adsorbent for sodium dodecylbenzene sulfonate (SDBS) in batch and continuous systems. The AC samples were prepared from pine tree cones by chemical activation with different impregnation ratios of K2CO3 and KOH. The materials were characterized by Boehm titration, approximate elemental, SEM, FT-IR, TGA, XRF analyses and BET surface area measurement. In a batch process, the effects of various parameters such as adsorbent dose, pH, contact time and initial SDBS concentration and temperature were considered. Six different adsorption isotherms were applied to equilibrium data. Pseudo-first-order, pseudo-second-order and intraparticle diffusion models were used to estimate the adsorption kinetic data. The experimental data resulted in excellent fits with the Redlich-Peterson isotherm and that the pseudo-second-order described the best description of adsorption data. Thomas and Yan models were used in describing the experimental data in a continuous system. The thermodynamic parameters such as Gibbs free energy (ΔG°), enthalpy (ΔH°), entropy (ΔS°) and activation energy (Ea) were analyzed. The contrasting negative and positive values of ΔG° and ΔH°, respectively, indicated that adsorption was spontaneous and endothermic in nature, and the obtained Ea confirmed chemisorption of SDBS adsorption onto AC. The adsorptive behavior of AC was also investigated with different bed heights, flow rates and the initial concentrations of SDBS. These results, by the recovery of 88% after five successive cycles, indicated that the combination of sulfuric acid and ethanol with a ratio of 4:6 is suitable for desorbing SDBS from AC.

Modeling of Fixed Bed Column Studies for Iron Removal from Industrial Effluents Through Ion Exchange Process

The performance of a fixed-bed cation exchange process was examined for final purification of the iron load derived from catalyst usage in the secondary treatment of olive mill wastewater, which led to unacceptable iron levels. Results showed an increase in the pH value up to 4 enhanced the iron IE efficiency, which decreased upon higher pH. Furthermore, Thomas model provided utmost accurate dynamic behaviormodeling for all inlet concentrations studied (20, 50 and 100 mg L-1).

Phosphorus removal from aquaculture effluents at the Northeast Fishery Center in Lamar, Pennsylvania using iron oxide sorption media

Three different iron oxide-based sorption media samples were tested for removal of phosphorus (P) from fish hatchery effluents using fixed bed processing. Two of the media samples were derived from residuals produced by the treatment of acid mine drainage, which were then compared to granular ferric hydroxide (GFH), a commercially available sorption medium. All of the media types removed from 50 to 70% of the P from the incoming aquaculture wastewater over 70–175days of operation without regeneration. In some of the sorption trials, the GFH media showed superior adsorption in the earlier stages of the trial, but the GFH appeared to reach saturation more quickly, so that media performance was similar – at about 60% removal of P – over a longer time period of 175days. Media regeneration tests were also conducted for both the commercial and mine drainage media, and demonstrated longer term performance, with overall P removal of 50–55%, over 223days of total operation, with the advantages of phosphorus recycle and media reuse.

Iron removal and reuse from Fenton-like pretreated olive mill wastewater with novel strong-acid cation exchange resin fixed-bed column

The performance of a fixed-bed cation exchange process was examined for final purification of the iron load derived from catalyst usage in the secondary treatment of olive mill wastewater, which led to unacceptable iron levels. Results showed an increase in the pH value up to 4 enhanced the iron ion exchange (IE) efficiency, which decreased upon higher pH. Furthermore, Thomas model provided utmost accurate dynamic behavior modeling for all inlet concentrations studied (20, 50 and 100mgL−1). Additionally, up to 100% recovery efficiencies were maintained even after 10 complete cycles. Finally, an effluent with quality for irrigation reuse was obtained.

Multi-Fixed-Bed Bioreactor System Applied for Bioprocess Development of Immobilized Lactic Acid Bacteria

The multi-fixed-bed bioreactor“Multiferm”provides a downscaled system for the development of fixed-bed processes with immobilized microorganisms or cells. It consists of twelve single fixed-bed units that can be operated independently. Different bacterial strains, carriers used for immobilization, media or flow rates can be studied in one compact experimental set-up. Experiments can be run in parallel to allow for determination of experimental errors. In these studies several continuous cultivations were carried out withLactobacillus delbrueckiissp.bulgaricususing different dilution rates and culture durations as proof-of-concept for theMultiferm. Parameters relevant for process design such as reproducibility of simultaneously performed cultures, optimal dilution rate and long-term performance were determined by means of volume specific lactate and biomass productivity. First indications on a reduced growth rate of the cells due to immobilization were found.

Mathematical Modelling of the Fixed-Bed Biomass-Coal Co-Gasification Process

The paper considers mathematical modelling of downdraft fixed-bed gasification process of the mixtures of woody biomass and coal. Biomass/coal ratio, biomass moisture content and air equivalence ratio are varying parameters. Boundaries of the efficient gasification regimes are estimated.

Experimental Investigation and Reaction Kinetics Modeling of Biomass Formation, Substrate Consumption and Product Formation During Startup of Fixed-Bed Cultures with Immobilized Lactococcus lactis ssp. lactis

Lactic acid bacteria (LAB) like Lactococcus lactis ssp. lactis are used in food industry as well as for production of bacteriocins and optically pure lactic acid. Fixed-bed processes are highly productive but mathematical description is often complex. The aim of this work was to establish a mathematica model for process design. Biomass formation, lactose consumption and lactate production during start-up of fixed-bed cultures with immobilized L. lactis was investigated experimentally and described by a reaction kinetics model. Appropriate modeling and simulation of fixed-bed processes require biomass data. Therefore, a low-volume multiple fixed-bed reactor system (Multiferm) was used to investigate biomass formation of a L. lactis strain during the start-up phase of fixed-bed cultivation. The generation of data in parallel experiments was fast and easily compared to larger single reactor systems. Biomass data obtained from both fractions, retained and free suspended biomass, was used for modeling and simulation, together with data for lactose and lactate. The underlying Luedeking-Piret-like model structure was developed based on the results from suspension cultivations with the same strain. The fixed-bed system was described as perfusion culture with cell retention. For this, merely four additional parameters had to be defined to extend the suspension model to fixed-bed cultures. Experimental trends and steady states of both biomass fractions besides substrate and product could be described very well. Thus, this model could be used for process layout during process development.

Evaluation of the Parameters and Conditions of Process in the Ethylbenzene Dehydrogenation with Application of Permselective Membranes to Enhance Styrene Yield.

Styrene is an important monomer in the manufacture of thermoplastic. Most of it is produced by the catalytic dehydrogenation of ethylbenzene. In this process that depends on reversible reactions, the yield is usually limited by the establishment of thermodynamic equilibrium in the reactor. The styrene yield can be increased by using a hybrid process, with reaction and separation simultaneously. It is proposed using permselective composite membrane to remove hydrogen and thus suppress the reverse and secondary reactions. This paper describes the simulation of a dehydrogenation process carried out in a tubular fixed-bed reactor wrapped in a permselective composite membrane. A mathematical model was developed, incorporating the various mass transport mechanisms found in each of the membrane layers and in the catalytic fixed bed. The effects of the reactor feed conditions (temperature, steam-to-oil ratio, and the weight hourly space velocity), the fixed-bed geometry (length, diameter, and volume), and the membrane geometry (thickness of the layers) on the styrene yield were analyzed. These variables were used to determine experimental conditions that favour the production of styrene. The simulation showed that an increase of 40.98% in the styrene yield, compared to a conventional fixed-bed process, could be obtained by wrapping the reactor in a permselective composite membrane.

Design of a fixed-bed ion-exchange process for the treatment of rinse waters generated in the galvanization process using Laminaria hyperborea as natural cation exchanger

In this study, the removal of zinc from galvanization wastewaters was performed in a fixed bed column packed with brown macro-algae Laminaria hyperborea, acting as a natural cation exchanger (resin). The rinse wastewater presents a zinc concentration between 9 and 22 mg/L, a high concentration of light metals (mainly Na and Ca), a high conductivity (0.5–1.5 mS/cm) and a low organic content (DOC = 7–15 mg C/L). The zinc speciation diagram showed that approximately 80% of zinc is in the form of Zn2+ and ≅20% as ZnSO4, considering the effluent matrix. From all operational conditions tested for zinc uptake (17 < bed height<27 cm, 4.5 < flow rate<18.2 BV/h, 0.8 < particle equivalent diameter<2.0 mm), the highest useful capacity (7.1 mg Zn/g algae) was obtained for D/dp = 31, L/D = 11, 9.1 BV/h, τ = 6.4 min, corresponding to a service capacity of 124 BV (endpoint of 2 mg Zn/L). Elution was faster and near to 100% effective using 10 BV of HCl (1 M, 3.0%, 363 g HCl/L of resin), for flow rates higher than 4.5 BV/h. Calcium chloride solution (0.1 M) was selected as the best regenerant, allowing the reuse of the natural resin for more than 3 saturation/elution/regeneration cycles. The best operation conditions were scaled-up and tested in a pre-pilot plant. The scale-up design of the cation exchange process was proposed for the treatment of 2.4 m3/day of galvanization wastewater, resulting in an estimated reactants cost of 2.44 €/m3.

Dynamic modeling of fixed-bed adsorption of flue gas using a variable mass transfer model

This study introduces a dynamic mass transfer model for the fixed-bed adsorption of a flue gas. The derivation of the variable mass transfer coefficient is based on pore diffusion theory and it is a function of effective porosity, temperature, and pressure as well as the adsorbate composition. Adsorption experiments were done at four different pressures (1.8, 5, 10 and 20 bars) and three different temperatures (30, 50 and 70 °C) with zeolite 13X as the adsorbent. To explain the equilibrium adsorption capacity, the Langmuir-Freundlich isotherm model was adopted, and the parameters of the isotherm equation were fitted to the experimental data for a wide range of pressures and temperatures. Then, dynamic simulations were performed using the system equations for material and energy balance with the equilibrium adsorption isotherm data. The optimal mass transfer and heat transfer coefficients were determined after iterative calculations. As a result, the dynamic variable mass transfer model can estimate the adsorption rate for a wide range of concentrations and precisely simulate the fixed-bed adsorption process of a flue gas mixture of carbon dioxide and nitrogen.

A highly efficient polyampholyte hydrogel sorbent based fixed-bed process for heavy metal removal in actual industrial effluent

High sorption capacity, high sorption rate, and fast separation and regeneration for qualified sorbents used in removing heavy metals from wastewater are urgently needed. In this study, a polyampholyte hydrogel was well designed and prepared via a simple radical polymerization procedure. Due to the remarkable mechanical strength, the three-dimensional polyampholyte hydrogel could be fast separated, easily regenerated and highly reused. The sorption capacities were as high as 216.1 mg/g for Pb(II) and 153.8 mg/g for Cd(II) owing to the existence of the large number of active groups. The adsorption could be conducted in a wide pH range of 3–6 and the equilibrium fast reached in 30 min due to its excellent water penetration for highly accessible to metal ions. The fixed-bed column sorption results indicated that the polyampholyte hydrogel was particularly effective in removing Pb(II) and Cd(II) from actual industrial effluent to meet the regulatory requirements. The treatment volumes of actual smelting effluent using one fixed bed column were as high as 684 bed volumes (BV) (7736 mL) for Pb(II) and 200 BV (2262 mL) for Cd(II). Furthermore, the treatment volumes of actual smelting effluent using tandem three columns reached 924 BV (31,351 mL) for Pb(II) and 250 BV (8483 mL) for Cd(II), producing only 4 BV (136 mL) eluent. Compared with the traditional high density slurry (HDS) process with large amount of sludge, the proposed process would be expected to produce only a small amount of sludge. When the treatment volume was controlled below 209.3 BV (7103 mL), all metal ions in the actual industrial effluent could be effectively removed (<0.01 mg/L). This wok develops a highly practical process based on polyampholyte hydrogel sorbents for the removal of heavy metal ions from practical wastewater.

New Smopex® Ion Exchange Materials for the Removal of Selenium from Industrial Effluent Streams

This article discusses new Smopex® ion exchange materials which have been developed by Johnson Matthey Water Technologies, and highlights their performance relative to other commercially available materials for the removal of selenocyanate, selenate and selenite ions from aqueous solutions. The ion exchange mechanisms by which these materials sorb these ions are also explained and modelled in order to highlight the additional benefits that these materials offer that non ion-exchange materials do not, such as the ability to achieve the full material exchange capacities at feed concentrations lower than 1 mg l–1 selenium. The unique characteristics of these fibrous type materials are also discussed, including fast sorption kinetics, facile regeneration and enhanced selectivity for selenium ions against competing sulfate ions. Finally, the performance of these materials in a continuous stirred tank reactor setup is demonstrated, showing that performance levels as high as in fixed bed processes can be achieved, due to the high selectivity and mass transfer kinetics of Smopex® materials.

Analysis of hematite re-oxidation in the chemical looping process

Very little attention has been dedicated to the carrier re-oxidation in chemical looping systems. The work presented in this paper is for the re-oxidation of partially reduced hematite from a cyclic chemical looping fixed bed process. The underlying purpose of this work is to develop engineering rates and mechanisms for the re-oxidation of partially reduced hematite that can be included in CFD models for a chemical looping process. To this end, experiments were run using nominally 1000g of hematite material in a fixed bed reactor cycling between reduction and re-oxidation. The cyclic processing began with the reduction step then proceeded to the oxidation step repeating this analysis for several cycles ranging from 5 to 10. The re-oxidation process was conducted at temperatures ranging from 745°C to 825°C and oxygen concentrations ranging between 9% and 11%. The reduction was carried out at the same temperature as the re-oxidation step at various CH4 concentrations from 5% to 9%. In this paper, cyclic induced variations in performance are presented as well as the kinetic parameters for the first cycle. The re-oxidation of the depleted hematite occurs through a 2 step parallel process in which oxygen reacts to fill the surface of each grain within the particles and then migrates through oxygen vacancy diffusion to the depleted cores of each grain.

On the Choice of Batch or Fixed Bed Adsorption Processes for Wastewater Treatment

Newly emerged nanomaterials, such as graphene or carbon nanotubes, are of increasingly widespread importance in environmental remediation, especially in their ability to remove undesirable chemicals from hydrological systems. Despite recent advances, the high cost of these materials and the relative inability to regenerate them hinders their use at larger scales. Although it is commonly held that adsorption in fixed bed processes is more efficient than in batch processes, the definition of efficiency needs to be examined closely. In this paper, we show that there exists a critical effluent concentration above which batch processes are more efficient than fixed bed processes from this perspective. This work proposes a simple method to choose either batch or fixed bed processes when the goal is to minimize the quantity of adsorbent needed to remove contaminants to below a specified threshold level. It also provides a systematic set of self-consistency checks on experimental measurements that may be used for comparative studies of these methods.

Chemical-activated carbons from peach stones for the adsorption of emerging contaminants in aqueous solutions

Activated carbons from peach stones by chemical activation with H3PO4(s) have been prepared, leading to high surface area and well-developed mesoporous materials. Further oxidation and gas phase treatments were applied in order to analyze the influence of the chemical surface groups on the adsorption behavior. The adsorption of three emerging compounds: a stimulant (caffeine), an anti-inflammatory drug (diclofenac) and a psychiatric drug (carbamazepine) from ultrapure water through batch and dynamic tests was investigated. The characterization of the adsorbents was conducted by N2 adsorption–desorption isotherms, scanning electron microscopy (SEM), infrared spectrometry (FTIR), thermal programmed decomposition (TPD), zero charge and isoelectric points (pHZPC, pHIEP) determination and the evaluation of the total acidity by potentiometric titration with n-butylamine. TPD profiles and FTIR spectra revealed the presence of carboxylic, phenolic, carbonyl and quinonic functionalities in the carbonaceous surfaces. S-type adsorption isotherms, as Giles classification, were obtained, indicating a competitive effect between aqueous solution and the target adsorbates. Carbamazepine adsorption capacity was higher than caffeine and diclofenac, reaching 335mg/g, attributed to its hydrophobic character and water solubility properties. The oxidation of the activated carbon greatly enhanced the hydrophilic character of the material, decreasing the adsorption capacity and highly affecting on the breakthrough times and adsorption capacity values in the fixed-bed adsorption process.

Assessment of naproxen adsorption on bone char in aqueous solutions using batch and fixed-bed processes

An integrated analysis of naproxen adsorption on bone char in batch and packed-bed column conditions has been performed. Kinetic, thermodynamic and breakthrough parameters have been calculated using adsorption models and artificial neural networks. Results show that naproxen removal using bone char in batch conditions is a feasible and effective process, which could involve electrostatic and non-electrostatic interactions depending mainly on pH conditions. However, the application of packed-bed column for naproxen adsorption on bone char is not effective for the treatment of diluted solutions due to the low degree of adsorbent utilization (below 4%) at tested operating conditions. The proposed mechanism for naproxen removal using bone char could include a complexation process via phosphate and naproxen, hydrogen bonding and the possibility of hydrophobic interactions via π–π electron. This study highlights the relevance of performing an integrated analysis of adsorbent effectiveness in batch and dynamic conditions to establish the best process configuration for the removal of emerging water pollutants such as pharmaceuticals.

Removal of Cr(VI) from wastewater using activated neem bark in a fixed-bed column: interference of other ions and kinetic modelling studies

Continuous adsorption experiments are carried out in a fixed-bed to evaluate the performance of a newly developed low-cost adsorbent (activated neem bark, ANB) for the removal of Cr(VI) along with other metal ions (Cu & Zn) from aqueous solutions. The effect of initial Cr(VI) concentration, mass of adsorbent and flow rate on the breakthrough curve are studied. It is observed that as there is an increase in the initial concentration of Cr(VI) from 50 to 100 mg L−1, the mass of the adsorbent from 25 to 175 g, and flow rate from 5 to 15 mg L−1, the breakthrough time decreases from 24.78 to 13.875 h, increase from 9.25 to 111.66 h and decrease from 35.09 to 8.26 h, respectively. The effect on the performance of the ANB for Cr(VI) adsorption is also studied in the presence of Cu and Zn. The breakthrough time is achieved earlier in the presence of Cu and Zn in the feed stream. The fixed-bed adsorption process parameters such as saturation loading capacity, breakthrough time, total percentage removal of Cr(VI), the fraction of unused bed length, adsorption exhaustion rate and empty bed residence time are calculated for different experimental runs. The experimental results are likewise applied to the Yoon–Nelson and the Yan kinetic models. The kinetic parameters for both the models are calculated and reported in this study.

Fixed-Bed Column Process as a Strategy for Separation and Purification of Cephamycin C from Fermented Broth

Fixed-bed column processes using the anionic resin Q Sepharose XL were evaluated for cephamycin C (CepC) purification from fermentation broth. Breakthrough and desorption curves were obtained for different flow rates (2.5, 5.0, and 7.5 mL/min). The elution method consisted of a stepwise gradient using NaCl solutions (0.1%, 0.3%, and 0.5%), which resulted in the separation of CepC from other antibiotics. The flow rate did not interfere in adsorption during loading of the column, but band broadening was observed during elution as the flow rate was increased. After the ion-exchange process, the fractions containing CepC were subjected to solid-phase extraction using a C18 cartridge to remove salts. Analyses of the broth used to feed the column and of the salt-free fractions by LC–MS showed a reduction in the concentration of some contaminants (possibly penicillin N, deacetylcephalosporin C, and deacetoxycephalosporin C) compared to the concentration of CepC. In conclusion, ion exchange followed by adsorption on a C18 adsorbent was demonstrated to be a selective and efficient procedure for the purification of CepC from fermentation broth.

Large-scale clinical-grade retroviral vector production in a fixed-bed bioreactor.

The successful genetic engineering of patient T cells with γ-retroviral vectors expressing chimeric antigen receptors or T-cell receptors for phase II clinical trials and beyond requires the large-scale manufacture of high-titer vector stocks. The production of retroviral vectors from stable packaging cell lines using roller bottles or 10- to 40-layer cell factories is limited by a narrow harvest window, labor intensity, open-system operations, and the requirement for significant incubator space. To circumvent these shortcomings, we optimized the production of vector stocks in a disposable fixed-bed bioreactor using good manufacturing practice-grade packaging cell lines. High-titer vector stocks were harvested over 10 days, representing a much broader harvest window than the 3-day harvest afforded by cell factories. For PG13 and 293Vec packaging cells, the average vector titer and the vector stocks' yield in the bioreactor were higher by 3.2- to 7.3-fold, and 5.6- to 13.1-fold, respectively, than those obtained in cell factories. The vector production was 10.4 and 18.6 times more efficient than in cell factories for PG13 and 293Vec cells, respectively. Furthermore, the vectors produced from the fixed-bed bioreactors passed the release test assays for clinical applications. Therefore, a single vector lot derived from 293Vec is suitable to transduce up to 500 patients cell doses in the context of large clinical trials using chimeric antigen receptors or T-cell receptors. These findings demonstrate for the first time that a robust fixed-bed bioreactor process can be used to produce γ-retroviral vector stocks scalable up to the commercialization phase.

Mathematical modeling of the competitive sorption dynamics of acetone–butanol–ethanol on KA-I resin in a fixed-bed column

The recovery and purification of biobutanol based on the adsorption method were performed in dynamic conditions. Computational and theoretical modeling is an important tool in the characterization, development, and validation of fixed-bed columns. Relevant breakthrough curves provide valuable information for designing fixed-bed adsorption processes for field applications. In the present study, a general rate model (GRM), implementing convection/diffusion approach theory and a competitive isotherm model, was used to predict the competitive sorption dynamics of acetone–butanol–ethanol (ABE) on a KA-I resin in a fixed-bed column under different operating conditions, i.e., inlet feed flow rate, initial adsorbate concentration, and bed height. The model simulation was quantified by the absolute average deviation (AAD). The calculated AAD values, ranging from 0.05 to 0.1, indicated that the GRM gives a general prediction for experimental data. The axial dispersion, external mass transfer, and pore diffusion coefficients were calculated by a series of empirical correlations. Biot number was used to identify the rate controlling step for the adsorption process of ABE on the resin. And the pore diffusion coefficient was found to be major governing factor for adsorption of ABE. The data and modeling presented are valuable for designing the continuous chromatographic separation process and simulation of ABE.