Effective Pore Diffusivity Research Articles

Sequential diethylaminoethyl dextran-grafting and diethylaminoethyl modification improve the adsorption performance of anion exchangers

Ion exchangers with high adsorption capacity, fast mass transfer, and high salt-tolerance synchronously are highly desired for high-performance protein purification. Here, we propose a sequential diethylaminoethyl dextran-grafting and diethylaminoethyl chloride modification strategy to achieve high-performance anion exchangers. The advantages of the double-modification strategy lie in: (1) the introduction of diethylaminoethyl in the second modification has no diffusion limitation due to the small molecular size, thus a high ionic capacity; (2) the grafting ligands not only provide three-dimensional adsorption space for high adsorption capacitybut alsofacilitate surface diffusion of protein by chain delivery. The maximum adsorption capacity of the obtained anion exchangers for bovine serum albumin reaches 333 mg/mL, the ratio of effective pore diffusivity (De) to free solution diffusivity (D0) reaches 0.69, and the adsorption amount reaches 97 mg/mL even in 100 mmol/L NaCl concentration,. All these results demonstrate the proposed sequential modification strategy are promising for the preparation of high-performance ion exchangers.

Adsorption of stable and labile emerging pollutants on activated carbon: degradation and mass transfer kinetic study

The design of adsorption processes for pharmaceuticals removal depends not only on the adsorption equilibrium but also on the mass transfer and adsorbate stability, being a problem still not solved the case of degradation products. By selecting different stable (amoxicillin, ciprofloxacin, carbamazepine and ibuprofen) and labile micropollutants (omeprazole) as case studies emerging pollutants, we have quantitatively analysed these effects on activated carbon. For stable compounds, the experimental data were fitted to equilibrium models to obtain information about the different adsorption mechanism depending on the characteristics of the molecules. Mass transfer effects were analysed for all the adsorbates, observing the control of intraparticle pore diffusion mechanism, since the effective pore diffusion coefficient is in the range from 10–8 to 10–10 cm2 h−1. As far as omeprazole is concerned, a kinetic model is proposed for predicting its degradation, identifying the reversibility of several degradation steps. The overall adsorption of OMP and derivates is calculated, observing the pore diffusion is considered as the rate-limiting step. For the first time, a combined model considering the chemical degradation and the adsorption of the degradation products is proposed and experimentally validated. This represents an important step in the modelling of processes leading to the purification of water from this type of pollutant.

Entrained-flow pyrolysis and (co-)gasification characteristics of Indian high-ash coals

Co-utilization in entrained-flow gasifiers is a potential solution to address the high ash-related problems persistent in fluidized-bed gasifiers. This work presents the hitherto unreported high-temperature (1000–1400 °C) entrained-flow pyrolysis and (co-) gasification characteristics of Indian high-ash coals and two candidate fuels (indigenous bituminous coal and petcoke) for possible co-utilization. Char analyses – TGA, FTIR, Raman, and SEM − are also performed to characterize the pyrolysis-induced structural changes. Volatile yields of candidate fuels matched with proximate values while those of high-ash coal exceeded by ∼12 wt%. Thermal deactivation was more pronounced for coal chars. High-ash coals achieved 100% carbon conversion at conditions exceeding 1300 °C and 20 vol% CO2. Bituminous coal showed comparable conversions, 70−90%, at identical conditions; further increase in conversion potential may be possible through steam addition due to enhanced char deactivation and pore diffusion effects at higher temperatures. Petcoke achieved lowest conversion of ∼30% even at the severest conditions; decreasing the average particle size by half showed an improvement of only ∼15%. Co-gasification of high-ash coal and petcoke blends showed no synergy. Considering closely matching carbon conversion, volatile release potential, and industry-standard slag tapping temperatures (1300−1500 °C), indigenous bituminous coals are more promising for co-utilization with high-ash coals in autothermal entrained-flow gasifiers.

Dynamic of CO2 adsorption in a fixed bed of microporous and mesoporous activated carbon impregnated with sodium hydroxide and the application of response surface methodology (RSM) for determining optimal adsorption conditions.

Microporous and mesoporous activated carbon produced from longan-seed biomass were impregnated with NaOH and used to capture CO2 from a simulated flue gas in a fixed-bed column. The process variables that were studied included types of activated carbon as characterized by the volume ratio of micropores and mesopores (Vmic/Vmes), adsorption temperature, NaOH loading, gas feed rate and the adsorbent amount. All five process variables affected the two important breakthrough parameters, namely the breakthrough time (tB) and CO2 adsorption capacity at breakthrough time (qB), with different trends and degrees. However, it was only the NaOH loading that showed a characteristic of an optimum loading that provided the maximum of the breakthrough parameters. It was found that an approximate 45% increase in the adsorbed amount of CO2 could be achieved with the activated carbon impregnated with around 1 weight % NaOH solution as compared to the case of the non-impregnated carbon. The response surface methodology (RSM) was applied to develop the correlations for both tB and qB and the maximum predicted qB of 33.58mg/g was derived at the NaOH loading of 76.5mg/g carbon, Vmic/Vmes of 2.83, adsorption temperature of 20°C, gas feed rate of 156kg/m2-h and adsorbent amount of 51kg/m2 of column cross-section area. The Klinkenberg's breakthrough model was able to describe the CO2 breakthrough curves reasonably well for all the tested conditions. The analysis of the two model parameters, the affinity constant (K) and the effective pore diffusivity (De), revealed that the optimum Vmic/Vmes that provided the maximum K value was around 2.90, corresponding to the activated carbon that contains 74% and 26% by volume of micropores and mesopores, respectively. The proper volume ratio of micropores and mesopores along with alkali addition into activated carbon can be effectively used for maximizing CO2 adsorption in a fixed-bed adsorption system.

Investigation of Corrosion Behavior of Oxygen-Free Copper Canisters in Groundwater Chemistry of Deep Geological Repositories.

The disposal of nuclear waste represents a paramount concern for human safety, and the corrosion resistance of containers within the disposal environment stands as a critical factor in ensuring the integrity of such waste containment systems. In this report, the corrosion behavior of copper canisters was monitored in Olkiluoto-simulated/-procured groundwater (South Korea) with different temperatures. The exposure of copper in the procured groundwater at 70 °C revealed a 3.7-fold increase in corrosion vulnerability compared with room temperature conditions, with a current density of 12.7 μA/cm2. During a three-week immersion test in a controlled 70 °C chamber, the canister in the Korean groundwater maintained a constant weight. In contrast, its counterpart in the simulated groundwater revealed continuous weight loss, indicating heightened corrosion. An X-ray diffraction (XRD) analysis identified corrosion byproducts, specifically Cu2Cl3(OH) and calcite (CaCO3), in the simulated groundwater, confirming its corrosive nature. The initial impedance analysis revealed distinct differences: Korean groundwater exhibits high pore resistance and diffusion effects, while the simulated groundwater shows low pore resistance. Consequently, the corrosion of copper canisters in the Korean environment is deemed relatively stable because of significant differences in ion concentrations.

Facile green synthesis of novel iron asparate (Fe-LAA) MOF for adsorptive mitigation of lead (Pb) from water

A newly reported metal organic framework (MOF), designated as Fe-LAA, was successfully synthesized through a one-step facile and green co-precipitation method. Subsequently, Fe-LAA showed effective adsorptive ability to remove the highly toxic inorganic lead (Pb2+) ions from water. The developed MOF with amine functionalization showed enhanced surface properties which were explored in detail employing various standard analytical techniques, namely, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, X-ray diffraction, energy dispersive X-ray, Brunauer-Emmett-Teller analysis, X-ray photoelectron spectroscopy and zeta potential analysis. The enhanced pore volume (vp = 0.24 cm3/g) and specific surface area (SBET > 250 m2/g) of the developed MOF compared to the non-modified structural counterpart, MIL88A (SBET: 91 m2/g, vp = 0.13 cm3/g), was successfully illustrated. The maximum Langmuir Pb uptake capacity was determined as 508.2 mg/g at 25 °C. An established mass transfer model, premised on pore-diffusion and adsorption, was utilized to analyze the adsorption kinetics and estimate the optimum effective pore diffusivity (Dp) as well as the mass transfer coefficient (kf). Furthermore, the convective and diffusive time scales (τc and τd) were evaluated to explain the transport characteristics of the solute contaminant. The adsorbent proved to be selective and reusable (over multiple cycles). The significant role of Pb groups in the MOF structure in maintaining strong electronic interaction with lead moieties was reported. Overall, the present study showcases the development and application of novel Fe-LAA MOF as an effective adsorbent for the treatment of Pb in contaminated aqueous medium.

Two-component irreversible adsorption with pore diffusion control – Experimental verification of a theory for protein adsorption on core–shell resins

The adsorption rates of mixtures of BSA monomer and dimer and of fibronectin and thyroglobulin are measured for core–shell adsorbents and compared with a pore-diffusion limited irreversible binding model. Measurements are conducted for individual particles, batch, and packed columns. The proteins in this work are irreversibly bound but have different binding capacities and effective pore diffusivities resulting in different one-component rates. Consistent with the theoretical model, mixture adsorption results in a single adsorption front within the particles, batch uptake curves with no overshoot in the amount adsorbed, and breakthrough curves without roll-up and with the stronger binding dimer emerging first from the column. Quantitatively, the model accounts for the different capacities and diffusivities and for the inert shell through a modified Biot number. Based on one-component measurements, the model accurately predicts mixture adsorption and is useful for describing flow-through purifications where multiple contaminants are removed from an unbound product.

Mercury removal from aqueous media by aminated polyacrylonitrile beads impregnated with nano-urchin bismuth sulfide particles: Experimental and theoretical analysis under batch and continuous mode

The present study encompasses a thorough analysis of aqueous Hg (II) adsorption using aminated polyacrylonitrile beads incorporated with high-capacity surfactant assisted bismuth sulfide nanoparticles. The porous beads provided effective contact between aqueous Hg and the inorganic nano-adsorbent (PBS2) that was encapsulated in the matrix. The macro-sized beads served as suitable packing material for designing a fixed bed adsorption column for continuous mode analysis without significant pressure build up and offered an easy solid–liquid separation after treatment. A marginal negative zeta potential of the adsorbent beads improved the interaction with Hg2+ facilitating the sorption. The incorporation of amine groups into the polymeric bead surface via amination increased the adsorption capacity further from 83.30 mg/g to 130.00 mg/g (∼56.00%) at 303 K. The associated parameters of batch kinetics (effective pore diffusivity and mass transfer coefficient) were determined using a first principle-based model available in literature. Mercury was chemisorbed via synergistic lone pair interactions of S and N atoms with Hg, leading to formation of coordination bonds (Hg-S and Hg-N). An established mass transfer model was utilized to generate simulated breakthrough curves for the continuous analysis using synthetic feed. Additionally, the adsorption column showed comparable performance using both synthetic and real water samples (synthetically spiked) maintaining high selectivity. The optimized values of axial dispersion coefficient (Ez) and fixed bed mass transfer coefficient (kfb) were estimated and subsequently used for the scale up studies to predict column life. The adsorbent beads were regenerated using 0.05 M EDTA aqueous solution and showed good reusability (>95.00%) after 5 cycles of operation. Overall, this work highlights a reusable Hg adsorbent possessing good selectivity and capacity and simultaneously demonstrating real-field applicability.

High capacity aluminium substituted hydroxyapatite incorporated granular wood charcoal (Al-HApC) for fluoride removal from aqueous medium: Batch and column study

In this study, aluminium substituted hydroxyapatite (Al-HAp) was synthesized in-situ on granular commercial wood charcoal at room temperature for fluoride removal from groundwater. Granular size (0.5–3.0 mm) of the carbon particles was selected considering the practical application of the final adsorbent in a packed-bed column filter. The adsorbent was characterized thoroughly. The Al-HAp phase was precipitated inside the pore channel as well as on the surface of highly porous wood charcoal matrix. The adsorbent had surface area of 442 m2/g and pHzpc value was 5. The maximum fluoride adsorption capacity at 303 K was achieved as 105 mg/g which is the highest for any granular adsorbent reported till date for adsorption of fluoride. Batch studies were used to deduce the effective role of pH, temperature and ion selectivity on adsorption efficiency. The reusability of the media was tested upto five cycles after consecutive regeneration with 1 M NaOH. Using the developed media, continuous column run experiments were conducted at different operating conditions, viz., bed volume, flow rate and feed concentration. The maximum number of bed volume was obtained as 1415 for a 30 cm bed height with flow rate 10 L/day and feed concentration of 3 mg/L. A fundamental mass transport model based on pore-diffusion was used to simulate breakthrough behavior in fixed-bed column runs with the synthetic and real contaminated groundwater. The relevant model parameters, namely, fixed bed mass transfer coefficient (kfb), effective pore diffusivity (Dp) and the coefficient of axial dispersion (Ez) were estimated.

Protein adsorption to diethylaminoethyl-dextran grafted macroporous cellulose microspheres: A critical pore size for enhanced adsorption capacity and uptake kinetic

To study the details of the effect of pore size on the performance of grafting-ligand ion exchangers, four diethylaminoethyl-dextran grafted macroporous cellulose microspheres with different pore sizes ranging from 164.57 to 281.96 nm were selected to investigate their adsorption equilibria and kinetics for bovine serum albumin (BSA) and γ-globulin. It was found that for whether adsorption equilibria or uptake kinetics, both the proteins showed increasing-then-decreasing trends with the decreasing pore size. More importantly, for a specific protein, the maximum adsorption capacity and fastest uptake rate were achieved on the same media, indicating the existence of a critical pore size (CPZ), at which the adsorption capacity and uptake kinetic are significantly enhanced synchronously. The CPZs of BSA and γ-globulin were identified to be 216.64 and 266.93 nm, respectively. Experimental results and analyses revealed that the high adsorption capacities at CPZ are attributed to the high utilization of binding sites in pores, and the uptake kinetics are enhanced by the combination of fast pore diffusion and chain delivery effect.

Pore-size dependent catalytic activity of supported Pd catalysts for selective hydrogenation of nitrile butadiene rubber

Pore diffusion effect plays a crucial role in heterogeneous hydrogenation of unsaturated polymers. However, how large pore size can eliminate the pore diffusion limitation remains a controversial issue. Herein, we prepared a series of Pd/SiO2 catalysts with graded pore sizes and investigated the effect of pore size on hydrogenation activity of nitrile butadiene rubber (NBR). It is found that when the catalyst pore size (Dcat) is 7 times of the diameter of NBR chains (DNBR), the Weisz modulus Φ can be reduced to < 0.3 thus the internal mass transfer limitation can be eliminated, making NBR easier to approach the active sites. Consequently, the catalysts with the Dcat/DNBR > 7 exhibit excellent catalytic activity (96.7%) and selectivity (100%) to C = C. This work emphasizes that the pore size of catalysts can regulate the pore transfer limitation and the accessibility of internal active sites, providing useful guidance for the design of efficient macromolecular hydrogenation catalysts.

Adsorptive remediation of aqueous inorganic mercury with surfactant enhanced bismuth sulfide nanoparticles

Heavy metal contamination in water is a growing threat, endangering the environmental stability. Mercury (Hg) is one of the most lethal heavy metals damaging the immune and nervous system irreversibly. A novel synthetic route to prepare bismuth sulfide (Bi2S3) nanoparticles in presence of the surfactant Pluronic (P123) was illustrated in this work. The sorption of Hg (II) by the nanoparticles was investigated. The surfactant assisted nanoparticles showed enhanced surface area and potential compared to the unmodified ones. The effects of adsorbent dose, pH, initial concentration, and temperature were investigated. The maximum Hg (II) adsorption capacity for the surfactant enhanced Bi2S3 was 832 mg/g at 303 K and pH 5. The distribution coefficient (Kd) of the order ∼106 ml/g indicated high selectivity of the synthesized adsorbent toward mercury ions. Chemisorption was identified to be the dominant mechanism of adsorption. The adsorbent also showed excellent reusability (>95%) after 5 cycles. The transport parameters involved in the adsorption, the effective pore diffusivity (Dp: 7.36 × 10−12 m2/s) and the mass transfer coefficient (kf: 1.52 × 10−6 m/s) were estimated from a first principle-based model.

Cyanide removal from blast furnace effluent using layered double hydroxide based mixed matrix beads: Batch and fixed bed study

Effluent tailings from steel industries contain huge amount of cyanide either in free form or as metal complex. The nanoparticle-based technologies for treatment of cyanide effluent are limited in practical application due to leaching and causes severe operational problems. In this study, the synthesized nickel aluminium layered double hydroxide (NiAl LDH) was impregnated inside the polysulfone matrix at different loadings of 2, 4, 6 and 8 wt% to form mixed matrix beads (MMBs) that serve as an alternative for the upscaling of adsorptive column and thereby overcome the shortcomings adequately. The basal spacing of the LDH impregnated inside the MMB is 8.8 Å. The characteristic peak at 2120 cm−1 in the post-adsorption FTIR indicated the successful adsorption of cyanide in LDH. The mean free energy value suggested that adsorption occurs via ion-exchange. The morphological stability of the impregnated LDH nanoparticles at elevated loading (6 and 8 wt%) was asserted using Field emission scanning electron microscopy and Transmission electron microscopy analysis. The maximum adsorption capacity of the optimum MMB was 80 mg/g at 303 K. The adsorption mechanism was established based on the speciation chemistry of cyanide present in the actual steel plant effluent. A fundamental macroscopic transport model was used to predict the adsorption kinetics to evaluate the mass transfer and diffusion time scales. The information about the effective pore diffusivity obtained from kinetic macroscopic model along with the adsorption isotherm parameters were used in a first-principle based model to simulate the breakthrough behaviour of continuous column mode experiments and axial dispersion and mass transfer coefficient were estimated in due process. These parameters were used to scale-up the adsorption columns and a performance curve was generated correlating the life of the filter, flow rate, feed concentration and amount of adsorbent required.

Grafting diethylaminoethyl dextran to macroporous cellulose microspheres: A protein anion exchanger of high capacity and fast uptake rate

Ion exchangers with high adsorption capacity and fast mass transfer synchronously are highly desired for protein separation and purification. For this purpose, here, we develop a high-performance anion exchanger by grafting diethylaminoethyl dextran (DEAE-dextran) on macroporous cellulose microspheres (MCMs). Static adsorption experiments for bovine serum albumin (BSA) show that the DEAE-dextran grafted MCMs have a higher adsorption capacity of 192.6 mg/mL than traditional non-grafted DEAE modified anion exchangers at a similar ionic capacity. The high adsorption capacity is due to the three-dimensionally extended polymer chains in pores that provide more and easily accessible ligands. Uptake kinetic results reveal that the DEAE-dextran grafted MCMs have a fast mass transfer rate and the maximum ratio (De/D0) of effective pore diffusivity (De) to free solution diffusivity (D0) reach 0.96, which is over three times higher than traditional non-grafted DEAE modified MCMs (0.29) and over nine times higher than commercial DEAE Sepharose FF (<0.10). It is attributed to the synergistic effect of the macropores and grafting ligands. The macropores provide wide channels for intraparticle pore diffusion, and the grafting ligands facilitate the surface transport of BSA by chain delivery occurred between adjacent DEAE-dextran chains. All these results demonstrate the DEAE-dextran grafted MCMs are promising as high-performance ion exchangers.

Theory of two-component irreversible adsorption with pore diffusion control

• Theory of pore-diffusion controlled multi-component irreversible adsorption. • Shrinking core model for multi-component irreversible binding. • Closed-form expressions for batch uptake and column breakthrough. • Solutions validated by numerical simulation with the general rate model. This paper provides a theoretical analysis of the kinetics of two-component irreversible adsorption in porous spherical particles for conditions where pore diffusion is limiting. The two components are assumed to have the same binding capacity without the possibility of displacement of one component by the other but with different effective pore diffusivities. As a result, the amounts of each component adsorbed depend on the relative rates of mass transfer within the particles. Closed-form analytical expressions derived by solving the relevant conservation equations are obtained to describe adsorption from an infinite bath with constant concentrations at the particle surface, batch adsorption in a finite bath, and adsorption in packed columns, both under constant pattern and non-constant pattern conditions. In each case, the expression derived reduces to a single integral. These expressions are in good agreement with the numerical solutions of the corresponding general rate model for conditions where the kinetics of binding is fast and provide a simple means to predict two-component adsorption in many practical cases where strong adsorption conditions prevail. Generalizations to systems with more than two components, to cases where the external mass transfer resistance is important, and to unequal capacities are also provided.

Numerical Simulation on the Effect of Burner Bias Angles on the Performance of a Two-Stage Entrained-Flow Gasifier.

A 2000 t/day HNCERI (Huaneng Clean Energy Research Institute) entrained-flow pulverized coal gasifier suffers from the problem of a high ash–slag ratio. An appropriate bias angle of the burners is the key to solve this issue for the gasifier with a specific structure. A random pore model considering bulk and pore diffusion effects was extended by user-defined function to describe the gasification reactions. The simulation of the gas flow and char gasification characteristics under different bias angles (0, 1.5, 2.5, 3.5, and 4.5°) of the four burners in the first stage was conducted. The simulation results showed favorable agreement with the industrial data. The evaporation, devolatilization, and char oxidation mainly occurred in the first-stage jet zone, and the upflow and downflow zones are dominated by the gasification reactions. The bias angles of the burners mainly affect the scale of gasification reaction zones. As the bias angles increased from 0 to 4.5°, the gas temperature at the slag tap hole decreased from 1880 to 1500 K. The carbon conversion efficiency of the first stage decreases and that of the second stage increases with the bias angle increasing. An optimal bias angle of 2.5° is recommended for the HNCERI gasifier with a total carbon conversion efficiency of 98.16%.

A study on the adsorption behaviors of three hydrophobic quinolones by ordered mesoporous CMK-3

In this work, a series of ordered mesoporous carbon nanomaterials (CMK-3) have been synthesized by a hard-template method at temperatures of 80 °C, 100 °C and 130 °C, which can serve as adsorbents for efficient adsorption of quinolones in aqueous solutions. The physicochemical properties and the morphologies of these CMK-3 have been well characterized, showing mesoporous channels with the specific surface area reaching up to 1290 m2/g. Adsorption studies have been performed on three hydrophobic quinolones: norfloxacin (NOR), ciprofloxacin (CIP) and enrofloxacin (ENR), with the adsorption capacities of 403 mg/g, 479 mg/g and 510 mg/g, respectively, at room temperature. The adsorption kinetics of the three quinolones are in accordance with the pseudo-second kinetic model, and the adsorption isotherm curves conform to Langmuir isotherm model. Significantly, the adsorption thermodynamics confirms that the adsorption processes are spontaneous endothermic. Finally, the adsorption mechanism has been discussed, which can be attributed to the synergistic effect of pore diffusion, hydrophobic bond, and electron donor-acceptor interaction.

Performance modeling of layered double hydroxide incorporated mixed matrix beads for fluoride removal from contaminated groundwater with the scale up study

In this study, calcium aluminium based layered double hydroxide (LDH) was synthesized in a controlled manner and its efficiency as a potential adsorbent in fluoride removal was explored. The LDH basal spacing of 8.2°A confirmed the planar orientation of the intercalated NO3–. The maximum adsorption capacity of LDH was 247.1 mg/g (at 308 K) and the adsorption was facilitated by the lower crystal radius and higher electro-negativity of F- compared to NO3–. For practical application in adsorption column, the LDH was incorporated in polysulfone to form spherical mixed matrix beads (MMB) of average diameter 2.8 mm. The elongated macrovoids inside the MMB promoted the diffusion of fluoride to the adsorption sites. The maximum adsorption capacity of the MMB was 90 mg/g (at 308 K). A fundamental mass transfer-pore diffusion-adsorption model linking convection, diffusion and adsorption was used to predict the adsorption kinetics and the breakthrough behaviour in the batch and continuous column mode experiments with the synthetic solution and contaminated groundwater. Different model-estimated transport parameters, like, effective pore diffusivity, mass transfer coefficient and the axial dispersion coefficient were used for scaling up of the column filters. The spent adsorbent was regenerated using 0.1(M) NaOH and 1(M) NaNO3.

The Use of High Surface Area Mesoporous-Activated Carbon from Longan Seed Biomass for Increasing Capacity and Kinetics of Methylene Blue Adsorption from Aqueous Solution.

Microporous- and mesoporous-activated carbons were produced from longan seed biomass through physical activation with CO2 under the same activation conditions of time and temperature. The specially prepared mesoporous carbon showed the maximum porous properties with the specific surface area of 1773 m2/g and mesopore volume of 0.474 cm3/g which accounts for 44.1% of the total pore volume. These activated carbons were utilized as porous adsorbents for the removal of methylene blue (MB) from an aqueous solution and their effectiveness was evaluated for both the adsorption kinetics and capacity. The adsorption kinetic data of MB were analyzed by the pseudo-first-order model, the pseudo-second-order model, and the pore-diffusion model equations. It was found that the adsorption kinetic behavior for all carbons tested was best described by the pseudo-second-order model. The effective pore diffusivity (De) derived from the pore-diffusion model had the values of 4.657 × 10−7–6.014 × 10−7 cm2/s and 4.668 × 10−7–19.920 × 10−7 cm2/s for the microporous- and mesoporous-activated carbons, respectively. Three well-known adsorption models, namely the Langmuir, Freundlich and Redlich–Peterson equations were tested with the experimental MB adsorption isotherms, and the results showed that the Redlich–Peterson model provided the overall best fitting of the isotherm data. In addition, the maximum capacity for MB adsorption of 1000 mg/g was achieved with the mesoporous carbon having the largest surface area and pore volume. The initial pH of MB solution had virtually no effect on the adsorption capacity and removal efficiency of the methylene blue dye. Increasing temperature over the range from 35 to 55 °C increased the adsorption of methylene blue, presumably caused by the increase in the diffusion rate of methylene blue to the adsorption sites that could promote the interaction frequency between the adsorbent surface and the adsorbate molecules. Overall, the high surface area mesoporous carbon was superior to the microporous carbon in view of the adsorption kinetics and capacity, when both carbons were used for the removal of MB from an aqueous solution.

Comparison of Protein A affinity resins for twin-column continuous capture processes: Process performance and resin characteristics

Continuous chromatography is a promising technology for downstream processing of biopharmaceuticals. The operation of continuous processes is significantly different to batch-mode chromatography and needs comprehensive evaluation. In this work, the performances of four Protein A affinity resins were studied systematically for twin-column continuous capture processes. A model-based approach was used to evaluate the process performance (productivity and capacity utilization) under varying operation conditions, and the objective was to reveal the crucial resin properties for continuous capture. The trade-off between productivity and capacity utilization was found, and it is necessary to select appropriate resins for different feedstock and operation conditions. The capacity utilization heavily depends on mass transfer, and steep breakthrough curves are favorable for high capacity utilization. The productivity is determined by both equilibrium binding capacity and mass transfer, and the balance of feed amount and feed time is critical. Moreover, the influence of binding capacity and mass transfer on process productivity and parameter sensitivity with two important resin properties (equilibrium binding capacity qmax and effective pore diffusion coefficient De) were assessed by the model, and suitable resin parameter ranges for twin-column continuous capture were determined. The model-based approach is an effective and useful tool to evaluate the complex performance of different resins and guide the design of next-generation resins for continuous processes.