Adsorption Front Research Articles

Pressure swing adsorption process modeling using physics-informed machine learning with transfer learning and labeled data

Pressure swing adsorption (PSA) modeling remains a challenging task since it exhibits strong dynamic and cyclic behavior. This study presents a systematic physics-informed machine learning method that integrates transfer learning and labeled data to construct a spatiotemporal model of the PSA process. To approximate the latent solutions of partial differential equations (PDEs) in the specific steps of pressurization, adsorption, heavy reflux, counter-current depressurization, and light reflux, the system's network representation is decomposed into five lightweight sub-networks. On this basis, we propose a parameter-based transfer learning (TL) combined with domain decomposition to address the long-term integration of periodic PDEs and expedite the network training process. Moreover, to tackle challenges related to sharp adsorption fronts, our method allows for the inclusion of a specified amount of labeled data at the boundaries and/or within the system in the loss function. The results show that the proposed method closely matches the outcomes achieved through the conventional numerical method, effectively simulating all steps and cyclic behavior within the PSA processes.

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.

Simultaneous Recovery of Bovine Serum Albumin and Bovine Immunoglobulin G with Dual-Ligand Hydrophobic Charge-Induction Chromatography

This study investigated the potential of dual-ligand hydrophobic charge-induction chromatography for the simultaneous recovery of two high-value components (bovine serum albumin and bovine immunoglobulin G). Compared to single-ligand chromatography, dual-ligand chromatography offers greater flexibility and room for improvement. Tryptophan and tryptamine were used as ligands to prepare a series of single- and dual-ligand resins. Bovine serum albumin and bovine immunoglobulin G were used for adsorption and comparison in batch, frontal adsorption, and recovery experiments. The results showed that the dual-ligand mode had a stable coupling efficiency ratio (tryptamine to tryptophan, ∼2.30) during preparation and could break through the upper limit of the adsorption capacity of single-ligand mode. Additionally, it exhibited good adsorption performance for both bovine serum albumin and bovine immunoglobulin G from bovine serum (recoveries of 90.73 and 101.4%, respectively). The findings of this study confirmed that dual-ligand chromatography can be used as an effective strategy for biological separation.

Operando monitoring of gas drying by adsorption on supported ionic liquids: Determination of velocity of adsorption front by microwaves

For adsorption-based gas drying to reach very low dew points, ionic liquids (ILs) immobilized on solid porous supports are promising materials. Prior investigations with the IL 1-ethyl-3-methylimidazolium methanesulfonate ([EMIM][MeSO3]) show high absorption capabilities for water (vapour) and low regeneration (desorption) temperatures (< 100 °C). Due to the negligible evaporation losses of this IL combined with a high thermal stability and low melting point, [EMIM][MeSO3] is ideal for immobilization on highly porous supports. In this work, the IL covers at least a monolayer of the substrate (here silica), thereby filling about 30 % of the pores with the IL. Water then mainly (ab)sorbs in the IL and practically not adsorbs on the surface of silica. In the presence of water, the dielectric losses of the supported IL increase strongly and can therefore be measured by microwave perturbation methods. For this purpose, a quartz tube containing the fixed-bed of the supported IL was placed in the radial center of a microwave resonator operating in a mode so that the electric field strength varies in axial direction along the bed. During sorption experiments, the electrical signals measured with a network analyzer allowed to track the sorption front, to calculate the velocity of the moving front, and to detect the breakthrough of water vapor. The validation of this method was accomplished by simultaneously measuring the humidity of the carrier gas at the in- and outlet of the packed bed by humidity sensors. The water partial pressure (carrier gas N2), the temperature, and the gas velocity were varied in a range relevant for gas drying (5–15 mbar; 40–60 °C; 0.05–0.30 m s−1). The results demonstrate that microwave-derived parameters, like resonant frequency or quality factor, are suitable to locate the sorption front along the fixed-bed and to calculate the front velocity and the breakthrough time.

Simulation of conformality of ALD growth inside lateral channels: comparison between a diffusion-reaction model and a ballistic transport-reaction model.

Atomic layer deposition (ALD) has found significant use in the coating of high-aspect-ratio (HAR) structures. Approaches to model ALD film conformality in HAR structures can generally be classified into diffusion-reaction (DR) models, ballistic transport-reaction (BTR) models and Monte Carlo simulations. This work compares saturation profiles obtained using a DR model and a BTR model. The saturation profiles were compared qualitatively and quantitatively in terms of half-coverage penetration depth, slope at half-coverage penetration depth and adsorption front broadness. The results showed qualitative agreement between the models, except for a section of elevated surface coverage at the end of the structure, 'trunk', observed in the BTR model. Quantitatively, the BTR model produced deeper penetration into the structure, lower absolute values of the slope at half-coverage penetration depth and broader adsorption fronts compared to the DR model. These differences affect the values obtained when extracting kinetic parameters from the saturation profiles.

Sorption-enhanced methane synthesis in fixed-bed reactors

Production of synthetic methane as a substitute for natural gas has been widely discussed as a means of long-term energy storage with the potential of CO2 neutrality. While the maximum conversion of catalytic CO2 methanation is limited by the highly exothermic and pressure-dependent nature of the Sabatier reaction, high conversion at low pressure could be achieved at laboratory scale through sorption enhancement. The transient nature of this process requires new reactor designs and process engineering for large-scale reactors. We investigated pellet bed reactors from a process and reactor engineering perspective, particularly in the context of upscaling. Our results show that heat generation in the reactor remains a major challenge for process performance and product purity. The bed temperature is coupled with the water adsorption capacity of the catalyst, which in turn affects the reactor capacity. Consequently, this has an impact on the dynamics of the coupled adsorption and reaction front with implications for the design of larger reactors. The results provide a comprehensive understanding of the process and a guide for reactor engineering.

Mass transfer of proteins in chromatographic media: Comparison of pure and crude feed solutions

Elucidation of intraparticle mass transfer mechanisms in protein chromatography is essential for process design. This study investigates the differences of adsorption and diffusion parameters of basic human fibroblast factor 2 (hFGF2) in a simple (purified) and a complex (clarified homogenate) feed solution on the grafted agarose-based strong cation exchanger Capto S. Microscopic investigations using confocal laser scanning microscopy revealed slower intraparticle diffusion of hFGF2 in the clarified homogenate compared to purified hFGF2. Diffusive adsorption fronts indicated a strong contribution of solid diffusion to the overall mass transfer flux. Protein adsorption methods such as batch uptake and shallow bed as well as breakthrough curve experiments confirmed a 40-fold reduction of the mass transfer flux for hFGF2 in the homogenate compared to pure hFGF2. The slower mass transfer was induced by components of the clarified homogenate. Essentially, the increased dynamic viscosity caused by a higher concentration of dsDNA and membrane lipids in the clarified homogenate contributed to this decrease in mass transfer. Moreover, binding capacity for hFGF2 was much lower in the clarified homogenate and substantially decreased the adsorbed phase driving force for mass transfer.

Digging deep into a GAC filter – Temporal and spatial profiling of adsorbed organic micropollutants

A large pilot-scale granular activated carbon (GAC) filter was operated downstream in a full-scale wastewater treatment plant to remove organic micropollutants. To describe the spatial and temporal developments of micropollutant adsorption profiles in the GAC filter, micropollutants were extracted from GAC media taken at various filter depths and number of treated bed volumes. At a low number of treated bed volumes (2600 BVs), most micropollutants were adsorbed in the top layers of the filter. At increasing number of treated bed volumes (7300–15,500 BVs), the adsorption front for micropollutants progressed through the filter bed at varying rates, with sulfamethoxazole, fluconazole, and PFOS reaching the bottom layer before carbamazepine and other well-adsorbing micropollutants, such as propranolol and citalopram. Higher amounts of adsorbed micropollutants in the bottom layer of the filter bed resulted in decreased removal efficiencies in the treated wastewater. Mass estimations indicated biodegradation for certain micropollutants, such as naproxen, diclofenac, and sulfamethoxazole. A temporary increase in the concentration of the insecticide imidacloprid could be detected in the filter indicating that extraction of adsorbed micropollutants could provide an opportunity for backtracking of loading patterns.

Evaluation of hydrophobic charge-induction ligand efficiency for protein adsorption in one single cycle

Ligand is an essential part of the cost of adsorbent preparation, which needs to be carefully selected and evaluated. In this paper, we introduced ligand efficiency (Le) with three levels (recovery, preparation and cost) to form a selection strategy for evaluation of the efficiency of hydrophobic charge-induction ligand. These functions were calculated from static/dynamic binding capacity, desorption efficiency, coupling efficiency and ligand cost. Nine kinds of ligand were used to demonstrate this strategy. The coupling efficiency was determined by preparing the adsorbents with different kinds and densities of ligand. These adsorbents were characterized by FT-IR, SEM. Then adsorption equilibrium, adsorption kinetics, and frontal adsorption experiments were used to test the adsorption and desorption performance of these adsorbents. Finally, Les of recovery, preparation and cost were calculated. The results showed there were apparent differences in Les between ligand types and densities under static and dynamic adsorption conditions. 4FF-Tryptophan with 52 μmol/g adsorbent had the best performance with the lowest static/dynamic Le of recovery, preparation and ligand cost. Compared with those methods evaluated by static saturated adsorption capacity or dynamic binding capacity at 10% breakthrough, the selection strategy based on ligand efficiency is more suitable for subsequent research and industrial amplification.

Operando Monitoring of Gas Drying by Adsorption on Supported Ionic Liquids: Determination of Velocity of Adsorption Front by Microwaves

Operando Monitoring of Gas Drying by Adsorption on Supported Ionic Liquids: Determination of Velocity of Adsorption Front by Microwaves

Shrinking-Core Model Integrating to the Fluid-Dynamic Analysis of Fixed-Bed Adsorption Towers for H2S Removal from Natural Gas

Natural gas sweetening is an essential process within hydrocarbon processing operations, enabling compliance with product quality specifications, avoiding corrosion problems, and enabling environmental care. This process aims to remove hydrogen sulfide (H2S), carbon dioxide, or both contaminants. It can be carried out in fixed-bed adsorption towers, where iron oxide-based solid sorbent reacts with the H2S to produce iron sulfides. This study is set out to develop a fluid-dynamic model that allows calculating the pressure drop in the H2S adsorption towers with the novelty to integrate reactivity aspects, through an iron sulfide layer formation on the solid particles’ external skin. As a result of the layer formation, changes in the particle diameter and the bed void fraction of the solid sorbent tend to increase the pressure drop. The shrinking-core model and the H2S adsorption front variation in time support the model development. Experimental data on pressure drop at the laboratory scale and industrial scale allowed validating the proposed model. Moreover, the model estimates the bed replacement frequency, i.e., the time required to saturate the fixed bed, requiring its replacement or regeneration. The model can be used to design and formulate new solid sorbents, analyze adsorption towers already installed, and help maintenance-planning operations.

A comparative adsorption kinetic modeling of fluoride adsorption by nanoparticles and its polymeric nanocomposite

Nanoparticles (NPs) of metallic oxides/hydroxides (oxyhydroxide) are highly efficient adsorbents for pollutants but tend to agglomerate readily. So, in recent years, NPs have been embedded inside the porous polymeric matrix to decontaminate pollutants more efficiently than NPs alone. But the roles of the polymeric barrier on the performance of composite adsorbent have not been explored in literature. In the present study, diffusivity coefficients (De) of fluoride ions (F-) for adsorbents mixed metal oxyhydroxides and nanocomposite were estimated using a kinetic model to understand the roles of the polymeric barrier on adsorbate diffusion from the external surface to interior pores of the nanocomposite. Adsorption kinetic modeling study of both adsorbent-F- systems reveals that Fe-Al-Mn@chitosan composite is a more efficient adsorbent than mixed metal oxide nanoparticles alone. Although, the mass fraction of metal oxides/hydroxide present in the polymeric composite is less. The kinetic model reveals that only 25% of adsorption front radius was accessible for the adsorption of fluoride ions in mixed metal oxyhydroxide (Fe-Al-Mn) NPs. But, More than 80% of the total adsorption front radius was accessible for Fe-Al-Mn@chitosan. The magnitude of De is found to be almost in the same order for both the adsorbents, proving that polymer layers in Fe-Al-Mn@chitosan composite provide minimum resistance to the internal pore diffusion of adsorbate ions from the external surface to interior pores.

Adsorption of iodine from aqueous solutions by aminosilane-grafted mesoporous alumina

Adsorptive removal of iodine from aqueous waste streams is an efficient way of minimizing the environmental footprints associated with radioactive species, however, developing highly efficient, durable, adsorbents is key to this technique’s success. Here, we investigated the iodine adsorption performance of aminosilane-grafted mesoporous alumina using various aminosilanes, including 3-Aminopropyl-triethoxysilane (APS), N-methylaminopropyl-trimethoxysilane (MAPS), and 3-N,N-dimethylaminopropyl-trimeth-oxysilane (DMAPS). The successful incorporation of amine moieties within the mesopores of alumina was confirmed by FTIR and elemental analysis. From the iodine adsorption tests, Al-APS, Al-MAPS and Al-DMAPS exhibited capture capacities of 124, 223 and 241 mg/g, respectively, while the bare alumina had a capacity of 107 mg/g. Assessing the iodine adsorption front on the Al-DMAPS sample revealed sharp adsorption kinetics from 0 to 4 h followed by a gradual increase from 4 to 24 h, indicating that the aminated Al2O3 had high affinity towards the contaminate. Increasing the Al-DMAPS loading from 30 to 50 wt% revealed only a 4% enhancement in iodine adsorption capacity, implying that the lower aminosilane concentration was optimal. The equilibrium uptake and kinetics of iodine adsorption over aminosilane-grafted mesoporous alumina were represented by Langmuir and pseudo-second-order models, respectively. Meanwhile, the leach test results revealed that amine grafting moderately enhanced the material’s ability to permanently trap iodine for safe geological disposal, however, further waste consolidation is required to improve the iodine retention in these adsorbents.

New Regulations in Linear Dynamics of Adsorption

A study of the behavior of the output curves in linear frontal adsorption dynamics is continued. The linearity of adsorption isopycnic lines (isopics) and their approximation to the origin in the newly discovered concentration ranges of 0.592 and 0.6 at different intervals of the relative length of the adsorbent layer were found. An algorithm is proposed for determining the adsorption and kinetic constants from the output curve. Using the model output curves as an example, the possibility of a fairly accurate solution of the inverse problem of linear adsorption dynamics is shown.

The Efficiency of the Removal of Naphthalene from Aqueous Solutions by Different Adsorbents.

The paper presents the results of laboratory tests on possibilities to utilize active carbons produced in Poland (AG-5 and DTO) and clinoptilolite for removing naphthalene from a water solution in the adsorption process. The concentration of naphthalene in the model solution was 20 mg/dm3. The effects of pH, dose and adsorption time were determined under static conditions. Adsorption kinetics were consistent with the pseudo-second-order model (PSO). Among the applied models, the best fit was obtained using the Langmuir isotherms. The maximum adsorption capacity for the activated carbons (AG-5 and DTO) equaled 24.57 and 30.28 mg/g, respectively. For clinoptilolite, all the analyzed models of adsorption poorly described the adsorption process. The flow conditions were realized by filtration method. On the basis of the obtained results, the breakthrough curves, so-called isoplanes, were prepared and served in turn to determine the adsorption capacities in flow conditions. The total adsorption capacities determined under dynamic conditions of the AG-5 and DTO activated carbons were 85.63 and 94.54 mg/g, respectively, and only 2.72 mg/g for clinoptilolite. The exit curves (isoplanes) were also utilized to determine the mass penetration zone (the adsorption front height), as well as to calculate the rate of mass-exchange zone advance.

Preparation of a novel hydrophobic interaction chromatography with higher selectivity by introducing spatial recognition

AbstractBACKGROUNDHydrophobic interaction chromatography (HIC), as a typical separation technology, often suffers from low selectivity because it has a single interaction mode. Herein, a novel HIC resin (Octyl@BSA) with imprinted layer was synthesized and used for protein adsorption. Bovine serum albumin (BSA) and bovine serum γ‐globulin (bIgG) were used as model competitive proteins in this study. The effects of pH, salt type, concentration, and mass ratio were then investigated.RESULTSThe data from the static and dynamic adsorption experiments indicated that the introduction of spatial recognition effectively reduced the adsorption of competitive proteins, leading to significant improvements in selectivity. In comparison with raw HIC resin, Octyl@BSA retained a high binding capacity for BSA but rejected other proteins through spatial recognition. The maximum selectivity factors (α) of this resin may be close to 5. The adsorption kinetics and frontal adsorption experiments further confirmed the improvement in selectivity in batch and column mode. In addition, the recyclability of Octyl@BSA was tested using ten continuous BSA adsorption–desorption cycles.CONCLUSIONThis study demonstrated that the introduction of spatial recognition was an effective strategy for enhancing the advantage of target proteins during competitive adsorption, leading to an improvement in selectivity for HIC. © 2020 Society of Chemical Industry

Improvement of Adsorption Selectivity of Ion-Exchange Chromatography through the Double-Recognition Mode

Ion-exchange chromatography (IEC) was combined with molecular imprinting technology (MIT) to prepare two kinds of double-recognition resins (DEAE@BSA and DEAE@bIgG) using bovine serum albumin (BSA) and bovine immunoglobulin G (bIgG) as the imprinting template proteins. New resins consist of ion-exchange interaction and spatial recognition and were characterized by Fourier transform infrared, scanning electron microscopy–energy-dispersive X-ray spectrometry, thermogravimetric analysis, and Brunauer–Emmett–Teller techniques. The static and dynamic adsorption behaviors of proteins on resins were investigated. In addition, the competitive adsorption between BSA and bIgG was also studied. It was found that the adsorbed protein density (Qc) of the target protein remained the same after imprinting, but the competitive protein dropped obviously. The selectivity factors (α) of DEAE@BSA and DEAE@bIgG could reach 3.56 and 2.56, respectively. The results of adsorption kinetics and frontal adsorption experiments furth...

Modeling CO2 adsorption dynamics within solid amine sorbent based on the fundamental diffusion-reaction processes

A rigorous dynamic adsorption model, considering the realistic diffusion-reaction processes of CO2 adsorption onto the amine functionalized mesoporous silica, was proposed in this work. Three fundamental adsorption steps at different length scales were took into account in model development and a numerical algorithm was developed to solve the coupled partial differential equations of the multi-scale model. TGA (Thermal Gravity Analysis) experiments at different temperatures and CO2 partial pressures were conducted to acquire the dynamic adsorption curves for model fitting and validation. The simulation results based on the proposed model agreed well with the experimental data under all conditions. Through the developed model, the species distribution, mass transfer phenomena and reaction mechanisms at different scales within the sorbent were quantitatively predicted. The results indicated that the bulk of the sorbent captured CO2 simultaneously, and no adsorption front was observed. After the very early stage, the whole sorbent reacted with CO2 uniformly. Further mass transfer resistance analysis showed that chemical reaction was the rate-limiting step, and CO2 diffusion in the amine layer would play an important role in the later stage of adsorption, especially at high temperatures or high CO2 partial pressures. These findings provided a quantitative insight into dynamic evolution of CO2 adsorption within the sorbent particle, which would guide the design of sorbents with optimal pore features and amine loadings.

Design of High‐Productivity Mixed Tocopherol Purification from Deodorized Distillates by Tandem Reverse Phase Chromatography

AbstractCurrently, there is a great demand for high‐purity natural tocopherols in food supplements due to their antioxidant and Vitamin E activity. Deodorized distillate (DOD), a by‐product of the vegetable oil refining process, is a major source of these natural tocopherols. Isolation of pure tocopherols from DOD is challenging due to their lower concentration and presence of large quantities of polar and hydrophobic components. Several multistep methods are known in the art for the purification of tocopherols from DOD and crude feed stocks. This work presents a single‐step tandem reverse phase chromatography method for high‐purity tocopherols from DOD containing 4–8% of tocopherols (mixture of α, β, γ, and δ isomers). Tandem chromatography involved two consecutive chromatography columns, in which the first column is operated in frontal adsorption mode for maximum loading with partial removal of impurities and the second column operated in step wise separation mode causing high purity. The Developed tandem two‐column process produces 60% and 95% purity tocopherol grades at a high loading of 381 (g of DOD) per (L of resin). The developed method recovers up to 77% of loaded tocopherols in purified form with a productivity of 3.4 g L−1 hour−1.

Hindered diffusion of proteins in mixture adsorption on porous anion exchangers and impact on flow-through purification of large proteins

Complex adsorption kinetics behaviors of proteins in mixtures hampers chromatographic process development and complicates model-based prediction of separation. We investigated the adsorption characteristics of mixtures comprised of a larger protein (secretory immunoglobulins or thyroglobulin) and a smaller protein (serum albumin or green fluorescence protein) on the small-pore anion exchanger Q Sepharose FF. Confocal laser scanning microscopy measurements revealed that binding of the large protein was extremely slow and eventually stopped completely after the adsorption front penetrated just a few μm into the particle. Binding capacities after 24 h of incubation were nevertheless around 35 mg/mL of particle which is relatively high when considering that only a fraction of the particle was saturated, suggesting that locally-high bound protein concentrations are attained in a layer close to the particle surface. During mixture adsorption, the bound protein layer also significantly hindered diffusion of the smaller proteins into the particles resulting in about three times slower adsorption kinetics compared to single component adsorption. The combined effects of restricted diffusion and protein binding explain why flow-through purification of these mixtures with the small-pore resin Q Sepharose FF is effective under practical conditions. In this resin, diffusion of secretory immunoglobulins (or thyroglobulin) is restricted in the small pores so that despite their intrinsically greater affinity for the resin, much less binds compared to small proteins. Using the large-pore resin POROS 50 HQ results in faster transport, but also in more binding of secretory immunoglobulins (or thyroglobulin) compared to smaller protein impurities, preventing effective flow-through purification.