Bed Adsorption Research Articles

Highly dispersive Cu species constructed in mesoporous silica derived from ZSM-5 for batch and continuous adsorptive desulfurization of thiophene

ZSM-5 zeolite with long narrow pore structure could restrict the adsorption of sulfur compounds from commercial fuels due to their larger molecular dimensions. Herein, ZSM-5 as silica precursor and CTAB as template was successfully employed using dissolution and self-assembly method to synthesize micro-mesoporous silica (MMZ). Compared with ZSM-5, MMZ materials could effectively overcome the diffusion pathway, enhance mesopores and enlarged the BET surface area (830 m2/g). After MMZ crystals were fabricated with 5-20 wt% Cu content by ultrasound facilitated impregnation strategy, the active sites were improved, which promoted thiophene adsorption capacity from 0.9 to 0.44 and 0.48 mmol/g via π-complexation conducted under dynamic (flow) conditions in a fixed bed adsorber and batch stirring tang reactor, respectively. And the desulfurization performances decline in the order 10Cu/MMZ >20Cu/MMZ > 5Cu/MMZ >10Cu/ZSM-5 > MMZ > ZSM-5. The higher adsorption capacity was tentatively linked with well dispersive Cu nanoparticles (NPs) and textural properties of MMZ. Furthermore, the ADS activity of Cu/MMZ towards thiophene can be recovered well without nominal loss.

A sustainable remediation of Congo red dye using magnetic carbon nanodots and B. pseudomycoides MH229766 composite: mechanistic insight and column modelling studies.

In the present investigation, a biocomposite, magnetic carbon nanodot immobilized Bacillus pseudomycoides MH229766 (MCdsIB) was developed and consequently characterized using SEM-EDX, FTIR, XRD, and VSM analyses to effectively biotreat hazardous Congo red (CR) dye present in water bodies. The adsorptive efficiency of MCdsIB for the detoxification of CR from wastewater was investigated both in batch and column schemes. Optimum batch parameters were found as pH 3, 50 mg L-1 dye concentration, 150 min equilibrium time, and 2 g L-1 MCdsIB dosage. The Freundlich isotherm model best fit the experimental data, and the maximum adsorption capacity of MCdsIB was observed as 149.25 mg g-1. Kinetic data were in accordance with the pseudo-second-order model where the adsorption rate reduced with the rise in the initial concentration of dye. Intra-particle diffusion was discovered as the rate-limiting step following 120 min of the adsorption process. Furthermore, despite being used continually for five consecutive cycles, MCdsIB demonstrated excellent adsorption capacity (> 85 mg g-1), making it an outstanding recyclable material. The CR dye was efficiently removed in fixed-bed continuous column studies at high influent CR dye concentration, low flow rate, and high adsorbent bed height, wherein the Thomas model exhibited an excellent fit with the findings acquired in column experiments. To summarize, the current study revealed the effectiveness of MCdsIB as a propitious adsorbent for CR dye ouster from wastewater.

Assessment of Appropriate Geometry for Thermally Efficient CO2 Adsorption Beds

Carbon capture is one of the recently raised technologies to mitigate greenhouse gas emissions. Adsorption was introduced as an energy-efficient carbon capture process, and the literature primarily shows the utilization of circular cross-sectional adsorption beds for this purpose. In this regard, this paper investigates different shapes of adsorbent beds to determine the thermal and adsorption uptake enhancements. Three geometries are considered: circular, square, and triangular cross-sectional beds. Mg-MOF-74 is used as an adsorbent, and numerical simulation is developed using a user-defined function coupled with ANSYS-Fluent. The results show that the triangular cross-sectional bed exhibits better adsorption capacity and thermal management compared to other beds. For example, the triangular cross-sectional bed shows 6 K less than the circular one during the adsorption process. It is recommended that the triangular cross-sectional bed be used for temperature swing adsorption when pumping power is not important. The square bed comes second after the triangular one with a lower pressure drop, suggesting such beds as good candidates for pressure swing adsorption. The square bed could be an excellent choice for compact beds when CO2 uptake and pumping power are both important.

Rapid temperature swing adsorption using microwave regeneration for carbon capture

The use of microwave heating for the thermal regeneration of a porous carbon adsorbent in adsorptive carbon capture was evaluated. In this Microwave Swing Adsorption (MSA) process, a multimode microwave oven has been used to accelerate the desorption of CO2 after the adsorption of a CO2 / N2 (15/85 v/v) mixture. Starting from a commercial activated carbon (AC) material (MSP-20X), sorbent extrudates were prepared and loaded in a Teflon column. The heating of the sorbent bed inside the microwave (MW) cavity was characterised at different locations. Although the adsorption bed is not heated uniformly due to hot spots in the multimode MW cavity, flowing a purge gas reduces the non-uniform heating during the regeneration step. This study also reports that MSA regeneration achieves extremely fast total desorption (in 56 to 79 s), the quickest regeneration reported up to date in MSA, and very rapid desorption rates allowing swift adsorption–desorption cycles. This fast desorption is associated with the extremely high heating rates achieved (100 to 400 °C/min). We show that the desorption rate is faster when using higher powers at practically identical MW energy inputs. Complete CO2 desorption can be achieved at slightly longer durations when using 2-step MW heating. When comparing the MSA results with a reference TSA process, MSA outperforms TSA, due to the higher heating rates achieved by MSA. During eleven adsorption–desorption cycles, it is evidenced that the MSA process can regenerate the adsorption bed at a high reproducibility. The microporosity of the material remained intact during the MSA, revealing that localised heating and the high heating rates are not damaging the sorbent material.

Accumulation and Emission of Water Vapor by Silica Gel Enriched with Carbon Nanotubes CNT-Potential Applications in Adsorption Cooling and Desalination Technology

This paper presents a study of the application of the properties of water vapor as a gas with high potential energy, strongly dependent on temperature and pressure. Analyses of water vapor sorption on two types of silica gels (SG) (90 wt.%) enriched with carbon nanotubes (CNTs) (10 wt.%), in the context of their application in the design of adsorption beds in adsorption cooling and desalination systems were conducted. The sorption experiments were performed by gravimetric method at a relative humidity of 0% < RH < 100% and temperatures of 298 K, 313 K, and 333 K. The addition of CNTs to SG caused a decrease in the sorption capacity and depended on the temperature. As the process temperature increased, a lower SG/CNT mixtures sorption capacity to vapor was obtained. The highest influence of CNTs was observed at the highest temperature, and the average decrease of sorption capacity was several percent. The ratio of SG/CNT sorption capacity to pure SG values was below 1 in most measurements.

Column optimization of adsorption and evaluation of bed parameters-based on removal of arsenite ion using rice husk.

The objective of this study deals with column optimization of adsorption-based on removal of arsenite ion using rice husk. The parameters affecting the column adsorption study, i.e., influent-concentration, bed depth, and flow rate, were optimized. The range of parameters, i.e., influent-concentration (15-50mg/L), flow rate (20, 35, 45, and 60mL/min), and bed depth (15-60mm), were studied experimentally. Kinetics models Bohart-Adams and Hutchins were studied to measure the amount adsorbed, depth of mass transfer zone, saturated concentration, and time observed at 10% & 90% breakthrough. The percentage amount adsorbed qm enhanced with enhancement in bed depth but got reduced with influent ions concentration and volumetric flow rate. Established model Bohart-Adams and Hutchins equations were used for calculation of mass transfer zone which came out to be 51mm. An adsorption capacity (qm) of 4.5mg/g for arsenite ions was achieved at optimum parameter values of 60mm of bed depth, 20mL/min volumetric flow rate, and 50mg/L of influent ions concentration. The adsorption bed parameters were also evaluated using Hutchins and Michaels equations. The column study proved rice husk to be a potential adsorbent for the adsorption of arsenite.

Experimental evaluation of a solar-driven adsorption desalination system using solid adsorbent of silica gel and hydrogel.

Nowadays, the world is facing a shortage of fresh water. Utilizing adsorbent materials to adsorb air moisture is a suitable method for producing freshwater, especially combining the adsorption desalination system with solar energy devices such as solar collectors. The low temperature of solar collectors has caused some water to remain in the adsorbents in the desorption process and has reduced the possibility of using these systems. In this research, for the first time, an evacuated tube collector (ETC) is used as an adsorbent bed so that the temperature of the desorption process reaches higher values and as a result, more fresh water is expected to produced. In this study, two adsorption desalination systems (ADS) are experimentally investigated. In the first system, a laboratory experimental setup using silica gel and hydrogel adsorbents is used to investigate freshwater production using each of the two adsorbents. The effect of different parameters such as variable adsorption and desorption time, variable temperature and humidity of inlet air, and variable adsorbent mesh sizes on the desalination process is evaluated. Then, in the second system, an innovative configuration of the solar-driven adsorption desalination system with an ETC full of silica gel is studied. In the laboratory experimental setup, the maximum amount of water produced by silica gel is 0.36 L/kg and by hydrogel is 0.58 L/kg. In the solar-driven adsorption desalination system, the largest amount of accumulated water production, daily efficiency, and cost per liter (CPL) of produced water are 1.518kg/m2 day, 11.25%, and 0.0699 $/L, respectively. Therefore, this new configuration for an adsorption desalination system seems feasible.

Relay Upgrading of Biomass Producer Gas Via Shift-Methanation Plus CO2 Adsorption in a Symbiotic Fixed-Bed Reactor: Concept Proposition and Numerical Visualization

Abstract Producer gas from biomass gasification is a feasible supplementary source to overcome the shortage of energy supply. However, the relatively high CO content and low heating value greatly restrict raw biomass producer gas for extensive application. The technical combination of shift-methanation reaction and CO2 adsorption is proved to be an effective upgrading method. Different from the conventional tandem way of connecting shift-methanation and CO2 adsorption, this work first attempts to integrate the two units into a fixed-bed reactor to form a cooperative symbiotic relationship. The relay upgrading process of biomass producer gas is numerically investigated over Ni-based catalyst and mesoporous carbon adsorbent using computational fluid dynamics method. It is found that the CO content can be effectively reduced from 30.8% to below 5% and lower heating value on wet basis can be increased from 6.5 MJ/Nm3 to over 10 MJ/Nm3. The influence of catalyst and adsorbent bed volume on the composition of product gas is evaluated. Meanwhile, the effect of catalyst and adsorbent bed gap is also analyzed. Given the similarity of catalyst and adsorbent bed, the impact of their sequence on the upgrading performance is discussed. At last, for continuous run, a regeneration cycle involving reaction–adsorption coupled with N2 purge is designed and the cycle simulation is conducted to better understand the flow behavior and reaction/adsorption characteristic.

Ultra-pure hydrogen production via ammonia decomposition in a catalytic membrane reactor

In this work two alternatives are presented for increasing the purity of hydrogen produced in a membrane reactor for ammonia decomposition. It is experimentally demonstrated that either increasing the thickness of the membrane selective layer or using a small purification unit in the permeate of the membranes, ultra-pure hydrogen can be produced. Specifically, the results show that increasing the membrane thickness above 6 μm ultra-pure hydrogen can be obtained at pressures below 5 bar. A cheaper solution, however, consists in the use of an adsorption bed downstream the membrane reactor. In this way, ultra-pure hydrogen can be achieved with higher reactor pressures, lower temperatures and thinner membranes, which result in lower reactor costs. A possible process diagram is also reported showing that the regeneration of the adsorption bed can be done by exploiting the heat available in the system and thus introducing no additional heat sources.

Scaling analysis of large pressure jump driven adsorption of water vapour in columnar porous silica gel bed

Adsorption process can be initiated either by Large Temperature Jump (LTJ) or Large Pressure Jump (LPJ). In this study, a theoretical analysis of coupled heat and mass transfer process during LPJ driven adsorption has been carried out using scaling principles of the governing conservation equations. A columnar domain consisting of silica gel (adsorbent) and water vapour (adsorbate) pair has been considered with heat and mass transfer directions orthogonal to each other. This domain is subjected to a sudden LPJ with isothermal boundary condition. Adsorption process has been divided into three phases for scaling analysis viz. i) pressure equalization ii) adsorption accompanied by heat generation and iii) heat removal phase. From order of magnitude arguments, various important physical scales for each phase have been derived and validated with a 2-dimensional computational fluid dynamics (CFD) study. The temperature rise in the adsorber bed is found to be 14.5 K, and the time scale to attain peak temperature is ~100 s from the initiation of adsorption. This justifies the short cycle time deployed in practical PSA systems to operate near isothermal condition. The outcomes of this investigation serve as a fundamental insight into LPJ driven adsorption process and help identify the various factors which practically effect this mode of adsorption.

Granulation of alkaline metal nitrate promoted MgO adsorbents and the low-concentration CO2 capture performance in the fixed bed adsorber

Magnesium-based adsorbents with the modification of alkaline metal salts are considered the competitive candidates for CO2 capture at intermedium temperature. In this article, the NaNO3 promoted MgO adsorbents were prepared and granulated, and the characterization methods were used to detect the microstructure of the granular adsorbents, including NaNO3 distribution, BET specific surface area, micropore size and microcrystal aggregation. The thermogravimetric analyzer (TGA) tests were carried out to investigate the optimal CO2 adsorption and desorption temperatures and the cyclic stability of the NaNO3 promoted MgO granules. Moreover, the pretreatment of carbonization and calcination was adopted to improve the cyclic stability of the granular adsorbents. Furthermore, the fixed bed adsorber with 40 g NaNO3-MgO granules was used to capture CO2 from 50% CO2 mixture gas with N2 and from 20% CO2 mixture gas with N2, respectively, and the CO2 breakthrough behaviors in the fixed bed were investigated. It was found that NaNO3-MgO adsorbents were suitable for the middle and high-concentration CO2 capture (such as 50% CO2 feed gas) in fixed bed adsorber with the higher CO2 recovery efficiency, but the CO2 recovery efficiency was lower for the low-concentration CO2 capture (such as 20% CO2 feed gas) at ordinary pressure. Because about 10 kPa CO2 partial pressure in the gas phase was needed to overcome CO2 mass transfer resistance in the molten salt layer on MgO surface during adsorption, the appropriate pressurization would improve the low-concentration CO2 capture efficiency in the fixed bed adsorber.

Efficient separation of strontium ions from aqueous solution by dibenzo-18-crown-6 functionalized resin: Static and dynamic adsorption studies with computational DFT insights

The separation and utilization of radiotoxic 90Sr from liquid nuclear waste streams generated in the nuclear fuel reprocessing is highly desirable and challenging. Herein, we studied dibenzo-18-cown-6 functionalized chloromethyl-polystyrene (CMPS-DB18C6) resin which displays an excellent affinity toward Sr2+ion adsorption from aqueous solution. Adsorption behaviors were investigated as a function of solution pH, contact time, Sr2+ion concentration, temperature and presence of other metal ions. The prepared grafted resin exhibits high adsorption capacity of 141.37 mg/g at pH 6 with good selectivity in the presence of interfering coexisting ions such as Li+, Na+, Mg2+and Ca2+ions.The adsorption kinetics and isotherm were well fitted by the pseudo second order and Langmuir model, respectively. The adsorption efficiency was seen to be reduced with temperature. The regeneration of the used CMPS-DB18C6 resin was accomplished by 0.5 M HNO3acid and regenerated resin was reused up to four cycles with modest change in the adsorption capacity. The breakthrough curve analysis using a fixed-bed column showed 99.6% adsorber performance with bed capacity of 147.56 mg/g and 1.38 mbar pressure drop across the adsorber bed. The adsorbent showed good radiation stability as seen from the almost constant strontium distribution coefficient up to 500 kGy radiation dose. Further, the high adsorption and selectivity of Sr2+ ion was complimented using complexation Gibbs free energy by performing density functional theoretical calculations. The present work might provide an easy and efficient adsorptive removal process for the separation Sr2+ ions from radioactive waste stream for environmental remediation.

Intensification of Temperature Swing Adsorption

Temperature swing adsorption (TSA) is an energy intensive process as it needs heat for regenerating the adsorbent bed. Beds are regenerated and saturated simultaneously and are used cyclically. While one bed is undergoing adsorption, other is regenerated and vice versa. Regeneration of bed can be carried out by changing pressure or temperature. Former is called pressure swing adsorption (PSA) and later TSA. Heat is supplied for regeneration to desorb the impurities. Temperature required to regenerate the gas is high. Cycle time can be reduced and the process can be intensified by facilitating faster heat transfer in the bed. Normally the heat transfer coefficient of the adsorbent material is low which affects the cycle time. Better heat transfer can be obtained by increasing the heat transfer through packing by adding metal wires, strips or composite materials. Thus, metal fillings with good conductivity can be used in the bed. Technologies like TEPSA (Thermally Enhanced Pressure Swing Absorption) and TPSA (Temperature Pressure Swing Absorption) are developed for air pre-purification. TEPSA is a PSA process and TPSA is a TSA process. TEPSA is improved by addition of heat while in TPSA, adsorbate is removed by unheated regeneration gas. It is possible to make 20-60% power savings by moving to a TPSA cycle compared to TSA system. TPSA reduces not only cost of vessel but also pipe work involved in process. TPSA has a major advantage which is, without decreasing cycle time, thermal energy can be saved. This article explores various methods for intensification of Temperature swing adsorption. By combining advantages of pressure and temperature swing adsorption, solution to the problem of high energy demand and cycle time can be obtained. Proper selection of adsorbent material can be helpful in building economic process. Selection of adsorbent materials is based on various factors like cross-sectional area, strength, chemical inertness, etc. of the adsorbents. For TSA, thermal properties of adsorbent materials become significantly important while selecting the adsorbent.

A Review of Numerical Research on the Pressure Swing Adsorption Process

The pressure swing adsorption (PSA) process has been considered a promising method for gas separation and purification. However, experimental methods are time-consuming, and it is difficult to obtain the detailed changes in variables in the PSA process. This review focuses on the numerical research developed to realize the modelling, optimization and control of the cyclic PSA process. A complete one-dimensional mathematical model, including adsorption bed, auxiliary devices, boundary conditions and performance indicators, is summarized as a general modelling approach. Key simplified assumptions and special treatments for energy balance are discussed for model reliability. Numerical optimization models and control strategies are reviewed for the PSA process as well. Relevant attention is given to the combination of deep-learning technology with artificial-intelligence-based optimization algorithms and advanced control strategies. Challenges to further improvements in the adsorbent database establishment, multiscale computational mass transfer model, large-scale PSA facility design, numerical computations and algorithm robustness are identified.

Adsorptive removal of Pb(II) using nanostructured γ-alumina in a packed bed adsorber: Simulation using gPROMS.

In this work, convective-dispersive and pore volume and surface diffusion models have been used to analyze Pb(II) adsorption from an aqueous solution over a nanostructured γ-alumina adsorbent in a packed bed adsorber. The models encompassing partial differential equation and a linear algebraic equation coupled with isotherm have been simulated in gPROMS using the backward finite difference approach. The predicted breakthrough curves of Pb(II) adsorption concerning flow rate, initial metal concentration, and bed height were matched with the experimental data. The accuracy of model predictions was analyzed through statistical measures such as coefficient of determination (R2), root mean square error, and chi-squared value. The simulation results also predicted the axial dispersion, distribution coefficient, mass transfer coefficient, pore volume, and surface diffusion coefficient, which are, otherwise, difficult to measure experimentally and, in turn, have been used to assess the mass transfer characteristics of continuous Pb(II) adsorption. Additionally, the values of breakthrough time, exhaustion time, adsorption column capacity, and mass transfer zone were determined as a function of flow rate, bed height, and initial metal concentration. Surface and pore volume diffusions (10-11-10-10 m2/s) apparently controlled the continuous adsorption process, with surface diffusion being dominant. The transport parameters evaluated in the current study could be beneficial for the large-scale Pb(II)/nanostructured γ-alumina adsorption system. As evident from the successful simulation, the developed gPROMS program can also be applied to other adsorbate/adsorbent systems with a slight modification concerning the operating parameters.

Evaporator Performance for Water Refrigerant Adsorption Cooling System

Adsorption Cooling System gives an alternative to the commercial vapor compression refrigeration cycles due to their benefits of having a very environmentally friendly and promising energy-saving system. An adsorption cooling system consists of four main components which are thecondenser, evaporator, expansion valve, and adsorption bed for the system to effectively function. One of the factors that affect the efficiency of the system is the performance of the evaporator itself as the system operates at sub-atmospheric pressure and the performance is mediocre when using conventional evaporators. Due to the low-pressure condition, hydrostatic pressure may affect the saturated temperature of the water refrigerant in a flooded type evaporator. Therefore, in this study, the performance of the evaporator was investigated based on the water height variation. The highest heat transfer coefficient and evaporation heat transfer rate are achieved when the water is set at the heat exchanger tube diameter level. Furthermore, 0.1 kg of silica gel adsorbent is used to obtain the maximum of 250 W/kg of Specific Cooling Power when the heat transfer fluid is set to 20 ºC.

Recent developments in adsorption heat pumps for heating applications

Adsorption heat pumps (AHPs) have gained noticeable attention in recent years. The review discusses significant research in the domain of adsorption heat pumps focusing on heating applications, the working principle, adsorption equilibrium and kinetics, the design of adsorbent beds, physical models, operating parameters, and physical and thermodynamic characteristics of adsorbents. A comparison is presented among AHPs and traditional heating technologies and systems for AHPs that certain market participants have created. The review focuses on the most appropriate conditions for each measurement technique and the constraints of the modeling processes that are an essential element for the comprehensive performance evaluation of adsorption cooling units. For adsorption bed applications, it is suggested to use various bed designs and heat exchanger structures. Moreover, significant literature gaps and constraints in designing AHPs for heating applications are identified and analyzed. The heat and mass transfer resistance should be reduced by developing novel adsorbent materials and an improved interface among the duct wall and the bed, where heat transfer fluid circulates to increase adsorption heat pump system performance. Furthermore, optimum operational modes for the intended application might significantly enhance system performance.

Application analysis of layered pressure swing adsorption method for offshore floating natural gas purification

In view of the particularity of offshore operations, a new layered pressure swing adsorption (PSA) method for natural gas purification was proposed. CH4 is enriched in the three-component CH4/CO2/N2 crude mixed gas. The pressure swing adsorption process is based on the traditional method. The adsorption bed is divided into two layers, which are the first layer with activated carbon as the adsorbent to remove CO2 impurities, and the second layer with molecular sieve as adsorbent to remove N2 impurities. The process of PSA was simulated by Aspen Adsorption software. The simulation results show that after the process of double layered PSA, the purity of the product gas CH4 reached 98.7%, and the recovery rate of gas production was 89%. The concentration of CO2 was successfully reduced to 0.23% in the activated carbon layer, and the concentration of N2 was reduced to 1.2% in the molecular sieve layer of the first Tower.

Performance and Mechanism of Gas‐Solid Adsorption in a Rotating Adsorption Bed

AbstractA rotating adsorption bed for adsorbing toluene by activated carbon was constructed. It was found that the adsorption capacity of the rotating bed was stronger than that of the fixed bed and showed a faster adsorption rate. The particle diffusion model showed that the adsorption process in a rotating adsorption bed was a combination of surface diffusion and particle diffusion. In the rotating adsorption bed, the contribution rate of intraparticle diffusion to the whole adsorption was the largest, and the adsorption rate of each stage of the rotary adsorption bed was higher than that of the fixed bed. The good external diffusion force of the rotating adsorption bed effectively realized the deep‐pore adsorption of the adsorbent and improved the utilization rate of the adsorbent.

An experimental study and Performance Evaluation of a small adsorption air-conditioning system with FAM Z05 Zeolite and water

The main purpose of this work is to focus on comparing a FAM Z05 Zeolite-water and silica gel-water for designing two adsorption beds and evaluating the performance of the system. Two adsorption beds are tested in this study, the first one is using Polyvinyl acetate (PVA) glue for coating Zeolite with a weight of 1.2 kg, the second one is using polyvinylpyrrolidone (PVP) glue for coating Zeolite with a weight of 1.4 kg. The cooling water temperature of 25 °C and the chill water temperature of 20 °C are fixed during the experimental work, whereas three different hot water temperatures of 60, 70 and 80 °C are tested and changed, and five cycle’ times of 20, 25, 30, 35 and 40 minutes are changed to investigate their effects on the performance of the system. The test results show that the Coefficient of Performance (COP) on PVA glue at hot water of 70 °C is higher than that on PVP glue and this can be explained by the fact that the PVP glue blocks the porosity of the Zeolite and then deactivates the active nucleation sites which results in decreasing the adsorption of the water vapor. It is also observed that COP increases with increasing the cycle time. In addition, comparing the performance of the Zeolite adsorption bed with PVA glue to the silica-gel adsorption bed, the desorption temperature is much lower, and SCP at hot water of 80 °C is better than other types of coating glues.