Adsorption Unit Research Articles

Adsorption Thermodynamics for Process Simulation.

Adsorption has rapidly evolved in recent decades and is an established separation technology extensively practiced in gas separation industries and others. However, rigorous thermodynamic modeling of multicomponent adsorption equilibrium remains elusive, and industrial practitioners rely heavily on expensive and time-consuming trial-and-error pilot studies to develop adsorption units. This article highlights the need for rigorous adsorption thermodynamic models and the limitations and deficiencies of existing models such as the extended Langmuir isotherm, dual-process Langmuir isotherm, and adsorbed solution theory. It further presents a series of recent advances in the generalization of the classical Langmuir isotherm of single-component adsorption by deriving an activity coefficient model to account for the adsorbed phase adsorbate-adsorbent interactions, substituting adsorbed phase adsorbate and vacant site concentrations with activities, and extending to multicomponent competitive adsorption equilibrium, both monolayer and multilayer. Requiring a minimum set of physically meaningful model parameters, the generalized Langmuir isotherm for monolayer adsorption and the generalized Brunauer-Emmett-Teller isotherm for multilayer adsorption address various thermodynamic modeling challenges including adsorbent surface heterogeneity, isosteric enthalpies of adsorption, BET surface areas, adsorbed phase nonideality, adsorption azeotrope formation, and multilayer adsorption. Also discussed is the importance of quality adsorption data that cover sufficient temperature, pressure, and composition ranges for reliable determination of the model parameters to support adsorption process simulation, design, and optimization.

Treatment of fluoride-contaminated water in a prototype adsorption unit using zirconium-activated carbon nanocomposites

ABSTRACT Zirconium-activated carbon nanocomposites (ZANC) are found to have high fluoride removal capacity and thus used as an adsorbent to perform column studies. The adsorbent was characterised using SEM-EDS and FTIR before and after the adsorption of fluoride. A packed bed adsorber prototype of 1 m length was fabricated to carry out defluoridation studies. The effect of varying initial fluoride concentration (2.5–10 ppm) and bed height (6–14 cm) was studied. The maximum fluoride removal was found to be 29.4% and uptake capacity was 4.72 mg/g at an initial fluoride concentration of 10 ppm, flow rate of 2 LPM, and bed height of 14 cm for synthetic samples. The Thomas, Yoon–Nelson and Bed Depth Service Time (BDST) models were employed and their results confirmed the experimental findings. The maximum fluoride adsorption capacities obtained from the Thomas model are 1.9 mg/g and from the BDST model, the N value was 20.979 mg/cm3. Regeneration studies were performed and found that the adsorbent can be regenerated for three cycles. Column studies were also performed using real-field groundwater samples collected from Pavagada of Tumakuru district. All the tested parameters of the treated water were found to be within the permissible limit.

Optimization of carbon dioxide adsorption from industrial flue gas using zeolite 13X: A simulation study with Aspen Adsorption and response surface methodology

One of the best ways to prevent further warming of the planet and reduce pollutants is to remove or adsorb and recover carbon dioxide gas from the exit of cement factory exhaust. So far, several methods have been proposed for this; In this research, zeolite 13X adsorbent is used considering the operational conditions. To remove CO2 gas from the desired gas mixture, an adsorption operation unit with a column filled with zeolite 13X adsorbent was simulated in Aspen Adsorption V14 software. Changes in parameters such as temperature, and pressure and their effects on adsorption rate, adsorbent saturation time, and output heat rate were investigated to achieve higher system efficiency and optimal operating conditions. The adsorption unit was optimized by RSM to achieve maximum CO2 adsorption. Temperature and mole fraction of CO2 were identified as key influencing factors determining the adsorption performance of zeolite 13X for CO2 adsorption. It was found that the system should be operated at a temperature of 28.07 °C and a pressure of 1.202 bar to achieve maximum adsorption. Finally, 2.784 mol% CO2 gas was captured by the said process in optimal operating conditions. Further analysis revealed higher temperatures slightly decrease CO2 adsorption capacity, while increasing pressure enhances it. Conversely, elevated flow rates reduce breakthrough time, indicating a trade-off between adsorption capacity and capture efficiency.

Assuring optimality in surrogate‐based optimization: A novel theorem and its practical implementation in pressure swing adsorption optimization

AbstractSurrogate‐based optimization has gained significant traction in several engineering fields, given its ability to handle complex systems without significant computational burdens. However, surrogate models are approximations and may have limitations, including the possibility of artificial minima. The main contribution of this work is the derivation of a robustness test that guarantees the optimality of surrogate‐based optimization. The derivation of this metric is based on the universal approximation theorem. The full framework proposed in this work is also composed by a sampling sizing methodology to randomly select samples within a feasible operating region (FOR) resulting from the optimization population, reducing the computational cost of the analysis and avoiding biases in the robustness calculation. The applicability and importance of this methodology are demonstrated through a case study of a complex chemical process—a pressure swing adsorption (PSA) unit—which presents a high computational cost to solve optimization problems. The results highlight the need and importance of evaluating the optimality of surrogate‐based optimization schemes.

Airborne Toluene Removal by Dynamic Adsorption on Fiber‐ and Granular‐Activated Carbon

AbstractThe selection of adsorbents is critical for developing an adsorption unit. In this study, a activated carbon fibers (ACF) and a granular‐activated carbon (GAC) were evaluated in dynamic toluene adsorption to determine their benefits and limitations. A variety of physicochemical approaches were used to characterize the samples. Adsorption under varied circumstances demonstrated that ACF has a larger adsorption capacity and a longer saturation time than GAC. The Langmuir isotherm suited equilibrium data well. Thermodynamic characteristics showed that adsorption was spontaneous and exothermic. The adsorption kinetics were found to be dominated by the pseudo‐first‐order model, with GAC having a greater sorption rate. Thermal regeneration appeared to be more favorable for ACF.

Scaling up a hollow fibre adsorption unit for on-board CCS applications using a real gasoline engine exhaust

Decarbonising road transport using on-board carbon capture and storage (CCS) is challenged by inherent space and energy limitations. Thus, to be technically and economically viable, robust and compact carbon capture units need to be developed. Hence, in this work, a scaled up hollow fibre adsorption unit was tested downstream of a real 90:10 gasoline-ethanol engine exhaust gas to evaluate its CO2 capture performance after 100 adsorption–desorption cycles. The scaled up hollow fibre adsorption unit consisted of 37 four-channel hollow fibre adsorption units coated with a thin carbon xerogel layer, referred to as the CX-coated hollow fibre module (HFM). It should be noted that this is the first study to report the results of a HFM tested under real conditions over 100 adsorption–desorption cycles and is one of the few studies that reports the desorption step. Furthermore, despite the presence of CO, THC, NOx, and H2O in the exhaust gas, the CX-coated HFM exhibited high CO2 capture stability and mechanical integrity. This was evidenced through the CX-coated HFM obtaining and maintaining an average total capacity of 1.2 mmol/g over 100 adsorption–desorption cycles, and showing no visible signs of deterioration or a loss of mechanical integrity.

High Selectivity and Adsorption Capacity of Cation-Exchanged Zeolites for Biogas, Syngas, and Flue Gas Separation in a Pressure Swing Adsorption Unit

High Selectivity and Adsorption Capacity of Cation-Exchanged Zeolites for Biogas, Syngas, and Flue Gas Separation in a Pressure Swing Adsorption Unit

Sulfonate-functionalized covalent organic frameworks for capacitive deionization

Abstract Capacitive deionization is an efficient and cost-effective technology for ion removal from brackish water. Here, we demonstrate a sulfonate-functionalized covalent organic framework as a novel faradaic cathode material for capacitive deionization applications. Due to its orderly arranged adsorption units in the covalent organic framework, the resulting covalent organic framework demonstrates a superior sodium cations removal capacity of 19.56 mg g−1 and a maximum desalination rate of 3.15 mg g−1 s−1 in a 500 ppm NaCl solution at 1.2 V.

Life-cycle assessment of hydrogen produced through chemical looping dry reforming of biogas

Chemical looping dry reforming of methane (CLDRM) using perovskites as a catalyst is considered a promising option for producing hydrogen from biogas. In this work, the life-cycle performance of a system compiling a CLDRM unit paired with a water gas shift unit, a pressure swing adsorption unit, and a combined cycle scheme to provide steam and electricity was assessed. The main data needed to reflect the behavior of the reforming reaction was obtained experimentally and implemented in an Aspen Plus® simulation. Inventory data was obtained through process simulation and used to assess the environmental performance of the process in terms of carbon footprint, acidification, freshwater eutrophication, ozone depletion, photochemical ozone formation, and depletion of minerals and metals. Overall, the environmental viability of the production of green hydrogen from biogas was found to be heavily dependent on the biogas leakage in anaerobic digestion plants. The CLDRM system was benchmarked against a conventional DRM implementation for the same feedstock. While the conventional DRM plant environmentally outperformed the perovskite-based CLDRM, the latter might present advantages from an implementation point of view.

CO2 Removal in Hydrogen Production Plants

Hydrogen is an industrial raw material both for the production of chemicals and for oil refining with hydrotreating. It is the subject of increasing attention for its possible use as an energy carrier and as a flexible energy storage medium. Its production is generally accomplished in Steam Methane Reforming (SMR) plants, where a gaseous mixture of CO and H2, with a limited number of other species, is obtained. The process of production and purification generates relevant amounts of carbon dioxide, which needs to be removed due to downstream process requirements or to limit its emissions to the atmosphere. A work by IEAGHG focused on the study of a state-of-the-art Steam Methane Reforming plant producing 100 kNm3/h of H2 and considered chemical absorption with MethylDiEthanolAmine (MDEA) solvent for removing carbon dioxide from the PSA tail gas in a baseline scheme composed of the absorber, one flash vessel and the regeneration column. This type of process is characterized by high energy consumption, in particular at the reboiler of the regeneration column, usually operated by employing steam, and modifications to the baseline scheme can allow for a reduction of the operating costs, though with an increase in the complexity of the plant. This work analyses three configurations of the treatment section of the off gas obtained after the purification of the hydrogen stream in the Pressure Swing Adsorption unit with the aim of selecting the one which minimizes the overall costs so as to further enhance Carbon Capture and Storage in non-power industries as well.

Innovative and efficient integrations of desalination plants coupled absorption, adsorption, and humidification-dehumidification desalination units employing external heat recovery techniques

Thermal desalination technologies have been developed recently to solve some pressing problems, such as high energy expenditure, increasing fuel costs, and environmental problems related to conventional plants. However, these technologies still need to be enhanced in terms of water production and gain output ratio (GOR). This paper presents innovative and efficient combined thermal desalination plants consisting of absorption (ABDS), adsorption (ADDS), and humidification-dehumidification (HDH) desalination units to enhance energy utilization, water production, and overall system performance. Four innovative combined desalination plants employing different external heat recovery scenarios are presented and compared. The result from each scenario is evaluated and compared with those of the standalone ABDS and with other studies found in the literature at the same heat source temperatures. The heat source is mainly utilized to drive the ABDS plant. The ADDS and HDH are driven by the heat rejection from the ABDS components with different external heat recovery scenarios. Results illustrated that the maximum freshwater production generated from the proposed scenarios ranges between 1.57 and 2.94 m3.day−1 with a GOR of between 1.38 and 1.75 at 120 °C. Raising heat source temperatures from 55 to 120 °C decreased the improvement in the water productivity from 618.5 to 224 % and decreased the enhancement in the GOR from 222.8 to 99 %. In scenarios where the ADDS and HDH are driven by the heat rejection from the absorption and condensation process of the ABDS, the maximum freshwater production results from the ABDS unit. On the other hand, in scenarios where the ADDS and HDH are driven by the outlet hot water from the ABDS-generator, the maximum freshwater production is obtained from the HDH unit. The finding provided that the proposed innovative scenarios have an effective improvement in overall system performance indicators.

Efficient hybrid strategy for simultaneous design of refinery hydrogen networks and pressure swing adsorption unit

Refineries face increasing hydrogen demand due to the consumption of heavy and sour crude oil. This study presents a novel hybrid method to optimize hydrogen network configurations with a rigorous pressure swing adsorption (PSA) process model. This method utilizes Bayesian optimization to address the upper-level unknown constraints black-box optimization problem while employing deterministic algorithms to manage the lower-level nonlinear programming problem. Furthermore, infeasible regions are transformed into feasible ones by introducing a dummy stream, and the costs incurred during the transformation process are accurately calculated. The proposed method is validated using two literature cases. In Case 1, Bayesian optimization outperformed the Kriging model, resulting in a 7.84% reduction in total annual cost (TAC). In Case 2, a comparison of four search strategies revealed the developed two-phase strategy as the most effective one. This method offers a powerful and practical tool for optimizing real-world hydrogen networks with PSA processes.

Experimental study on radial suction flow and its effect in water vortex unit

A water vortex unit is a non-contact adsorption unit that utilizes water as a flowing medium. Negative pressure is generated on the adsorbed surface through the high-velocity rotation of the fluid, resulting in suction force. In comparison to the air vortex unit, the water vortex unit exhibits a substantial increase in suction force and has the capability to deliver greater power. However, the presence of the central bubble in the water vortex unit weakens the suction force. To address the impact of the central bubble, a suction hole was introduced on the vortex unit to remove them. Experimental results indicate that solely removing the central bubble has almost no effect on the radial pressure gradients in the gap flow path and chamber center of the water vortex unit. However, in the cylindrical neighborhood, the radial pressure gradient increases, leading to a certain degree of improvement in suction force. Further increasing the suction flow rate induces inward radial flow within the vortex chamber. This flow field further enhances the suction force. To analyze the reasons for this pressure distribution, we indirectly obtained the radial velocity distribution by examining the relationship between the pressure gradient and tangential velocity. The results of the tangential velocity distribution indicate that the radially inward suction flow significantly increases the rotational velocity of the fluid in the chamber center, enhancing the centrifugal inertial effect. This further reduces the negative pressure, resulting in a significant improvement in the suction of the vortex unit.

Multi-objective optimization of a hybrid carbon capture plant combining a Vacuum Pressure Swing Adsorption (VPSA) process with a Carbon Purification unit (CPU)

The imperative challenge posed by climate change requires urgent actions to counteract the harmful effects of greenhouse gas emissions, particularly CO2, which contributes to approximately 80 % of emissions responsible for global warming. A hybrid system combining Vacuum Pressure Swing Adsorption (VPSA) unit with a Cryogenic Carbon Purification Unit (CPU) is evaluated to enhance recovery and purity of CO2captured from flue gas containing CO2concentration ranging from 5 % to 20 %. VPSA preconcentrates the CO2and CPU completes the separation and purifies the CO2. The study uses surrogate models for multi-objective optimization, considering energy consumption, cost, and CO2recovery, providing a time-efficient approach for investigating computationally demanding processes. Results from the study indicate that the hybrid system achieves over 90 % recovery for flue gas concentration range considered, while ensuring the production of high-purity CO2(>99.99 %) suitable for transportation. A trade-off analysis reveals the balance between recovery, electricity consumption, and economic viability. A sensitivity analysis identifies parameters influencing recovery and energy consumption, providing guidance for future optimization efforts. The techno-economic analysis highlights the impact of electricity prices and carbon taxes on total costs, identifying an optimum towards higher recovery values under rising carbon taxes. Furthermore, the research underscores concentration-dependent economic feasibility, emphasizing the attractiveness of concentrations above 10 % compared with other technologies, which require higher concentrations. For an electricity price of 75 €.MWh−1, the total cost of the CO2 capture hydride system considering CO2 emissions with carbon tax of 100 €.tCO2−1 for concentrations ranging from 10 % to 20 % is from 123 to 80 €.tCO2−1, respectively. The analysis of the electricity source shows the importance of a low-carbon emission energy mix for optimal carbon emission reduction.

Heat and Mass Transfer of Water During Activated Carbon Adsorption

AbstractIn order to investigate the dynamic process of the heat and mass transfer phenomenon of water vapor on activated carbon, a fixed‐column adsorption unit and two kinds of activated carbon were used as adsorbent for water vapor adsorption under the adsorption temperature 293.15 K, 303.15 K and 313.15 K, respectively. A coupled model was developed by mass and energy balance, mass transfer and simplified DO adsorption equilibrium equation. The effects of physical parameters on heat and mass transfer were theoretically investigated. Results show that the numerical model match well with the experimental data (R2>0.993). The axial diffusion coefficient (DL) increases from 1.226×10−6 m2 s−1 to 4.062×10−6 m2 s−1 for RAC and 1.425×10−6 m2 s−1 to 4.030×10−6 m2 s−1 for MAC, mass transfer coefficient (k) increases from 8.171 s−1 to 27.083 s−1 for RAC and 9.499 s−1 to 26.864 s−1 for MAC. Concurrently, the breakthrough time of adsorption water vapor gradually shorten from 1000 s to 780 s with temperature increasing from 293.15 K to 313.15 K. The effect of axial diffusion coefficient (DL) on mass transfer is not obvious. Furthermore, the influence of the mass transfer coefficient (k) on temperature variation rate surpasses that of the internal heat transfer coefficient (h).

Process design and adsorbent screening of VSA and exchanger type VTSA for flue gas CO2 capture

Carbon capture, as a core technology for mitigating greenhouse gas emissions, the greatest challenge is the balance between separation performance and energy consumption. This study seeks to evaluate and screen the separation performance and energy consumption of four typical adsorbents (13X, Mg-MOF-74, activated carbon, and Lewatit VP OV 1065) in vacuum temperature swing adsorption (VTSA) and vacuum swing adsorption (VSA) through optimization approach, which will support in-depth research and decision-making on adsorption processes. A non-isothermal non-adiabatic numerical model was carried out to describe a novel 4-bed 10-step VTSA cycle developed on an exchange type adsorption unit (ETAU), and the model was validated by binary breakthrough and temperature swing experiments. A 4-bed 10-step VSA cycle was in turn established and investigated. Parametric analysis of the two cycles was performed by varying the operating variables including feed gas flow rate, recycle time, and purge-to-feed ratio. Process optimization of the multiplicative fraction evaluation function, simultaneously considering purity, recovery, and productivity, was achieved using a dual convergence algorithm. Results showed that all four adsorbents could achieve more than 90 % purity and recovery on the VTSA process employing the ETAU for post-combustion carbon capture, and the separation performance was substantially superior to that of the VSA cycle. Mg-MOF-74 obtained a CO2 product with 97.90 % purity, 98.48 % recovery, and 5.48 mol/kgads/hr productivity at a desorption temperature of 383.15 K; it has a specific heat consumption of 1.45 GJth/ton and a specific power consumption of 0.55 GJel/ton. The total energy consumption of 13X was slightly lower than that of amine adsorbents, giving 95.00 % purity, 97.60 % recovery, and 1.91 mol/kgads/hr productivity. Relatively low desorption temperature is expected to introduce ultra-low-grade waste heat for partial heat source substitution, contributing to the energy sustainability of adsorption carbon capture technology.

Tribological properties of polyaromatic organics as lubricating grease

The tribological properties of polyaromatic organics (xPyE) as lubricating grease additives are studied by simulations and experiments. Molecular Dynamics (MD) simulations are used to simulate the mechanical properties of four kinds of polyaromatic organics (2P1E, 3P2E, 4P3E, and 5P4E) with different aromatic ring numbers and a mass fraction under 300 MPa and 5 m/s relative shear velocity of the two solid walls. The friction force, positive pressure, stress, and adsorption energy are calculated quantitatively. Meantime, the friction coefficient of lubricating grease and the wear morphology of the sample are measured by Multifunctional Friction and Wear Testing Machine. The results show that the organic additives adsorbed on the wall form a protective film during the shearing process, improving the bearing capacity and reducing friction and wear. Among them, the 3P2E organic additive has an appropriate number of aromatic rings. Its single molecular adsorption energy and unit adsorption energy are higher than other organic additives and can uniformly lay on the wall to form a stable, protective film. This demonstrates the best friction performance and improves the load-bearing capacity of the lubricating film, reducing maximum wall stress by 53.4 %.

Simulation of Olive Pomace Gasification for Hydrogen Production Using Aspen Plus: Case Study Lebanon

Biomass is a renewable energy source gaining attention for its potential to replace fossil fuels. Biomass gasification can produce hydrogen-rich gas, offering an environmentally friendly fuel for power generation, transportation, and industry. Hydrogen is a promising energy carrier due to its high energy density, low greenhouse gas emissions, and versatility. This study aims to develop a hydrogen generation plant using a dual fluidized bed gasifier, which employs steam as a gasifying agent, to convert olive pomace waste from the Lebanese olive oil industry into hydrogen. The process is simulated using Aspen Plus and Fortran coding, and it includes a drying unit, gasification unit, gas cleaning unit, steam methane reformer unit, water–gas shift reactor unit, and a pressure swing adsorption unit. The generated gas composition is verified against previous research. Sensitivity analyses are conducted to investigate the impacts of the steam-to-biomass ratio (STBR) and gasification temperature on gas composition, demonstrating a valid STBR range of 0.5 to 1 and a reasonable gasification temperature range of 700 °C to 800 °C. Further sensitivity analyses assess the impact of reformer temperature and the steam-to-carbon ratio (S/C) on the gas composition leaving the steam methane reformer.

The Design of a Process for Adsorbing and Eluting Chromium (VI) Using Fixed-Bed Columns of E. crassipes with Sodium Tripolyphosphate (TPP)

Proper water resource management is a critical global objective, both privately and in business, due to the continuous deterioration of this valuable resource. Scientific research in environmental sciences has made significant progress in the development and achievements of treatment. The use of transformed E. crassipes biomass with sodium tripolyphosphate (TPP) can help to achieve this important goal. The objective of this study was to develop an experimental process for the continuous adsorption and elution of chromium (VI) using fixed-bed columns of E. crassipes biomass modified with sodium tripolyphosphate (TPP). Additionally, design tools were created, and economic viability was assessed by analyzing adsorption capacity indicators and unit production costs of different biomasses. Treatment systems were designed and constructed to remove chromium from tannery wastewater, ensuring that the levels were below the current environmental regulations of 0.05 mg/L Cr(VI). The biomass had an adsorption capacity of 98 mg/g and was produced at a low cost of 8.5 dollars. This resulted in an indicator of 11.5 g Cr(VI)/(USD) when combined with the elution processes. The proposed strategy, which utilizes entirely green technologies, enables the recovery and valorization of water resources. This makes it an effective tool for the circular economy.

Research on magnetic influence factors and optimal design of wall-climbing robot

The adsorption stability and motion flexibility are one of the core problems restricting the development of wall-climbing robots. In order to solve the problem of wall-climbing robots, the basic structure of magnetic adsorption unit is introduced in detail. Secondly, the finite element analysis software was used to optimize the simulation of the relationship between the parameters of the magnetic adsorption unit and the magnetic adsorption force through the control variable method. After optimization, the magnetic adsorption force of the magnetic adsorption unit was significantly improved under the condition that its own volume was unchanged. Finally, the experiment is carried out to verify.