Abstract
This work provides a series of methane adsorption isotherms and breakthrough curves on one 5A zeolite and one activated carbon. Breakthrough curves of CH
4
were obtained from dynamic column ...measurements at different temperature and pressure conditions for concentrations of 4.4 – 17.3 mol.‐% in H
2
/CH
4
mixtures. A simple model was developed to simulate the curves using measured and calculated data inputs. The results show that the model predictions agree very well with the experiments.
This work provides a series of methane adsorption isotherms and breakthrough curves on one 5A zeolite and one activated carbon. Breakthrough curves of CH4 were obtained from dynamic column ...measurements at different temperature and pressure conditions for concentrations of 4.4 – 17.3 mol.‐% in H2/CH4 mixtures. A simple model was developed to simulate the curves using measured and calculated data inputs. The results show that the model predictions agree very well with the experiments.
Breakthrough curves of methane were measured on 5A zeolite and activated carbon at different operating conditions. A simple mathematical model was used to simulate the dynamic behavior of the adsorbent bed using inputs of previously measured adsorption isotherms, heat of adsorption and physical properties evaluated according to literature reports.
A method based on the linear driving force (LDF) approximation is described to estimate the mass transfer coefficient of molecules adsorbing onto microporous carbons, by using independently measured ...uptake data. This parameter was determined from uptake curves derived from pressure increments during the measurement of isotherm data. To validate the method, simulations for batch uptake were performed and compared to the experimental data in order to obtain the values for the LDF constants. Such values were applied to predict breakthrough curves and compared to experimental data. The proposed method to estimate the LDF coefficient can be adequate to obtain a more physically meaningful value of the mass transfer coefficient.
A simple procedure to estimate the mass transfer coefficients for CO2 and N2 in microporous activated carbon was developed based on uptake experiments typically used to obtain equilibrium isotherms. The estimated parameters helped to simulate breakthrough curves, which were compared to experimental data. An excellent match was observed, indicating the good reliablity of the presented method.
Pure component adsorption equilibrium of CH
4
and CO
2
on activated carbon have been studied at three different temperatures, 298, 323, and 348 K within a pressure range of 10-2000 kPa. Binary ...adsorption equilibrium isotherm was described using extended Sips equation and ideal adsorbed solution theory (IAST) model. Experimental breakthrough curves of CO
2
/CH
4
(40:60 in a molar basis) were performed at four different pressures (300, 600, 1200, and 1800 kPa). The experimental results of binary isotherms and breakthrough curves have been compared to the predicted simulation data in order to evaluate the best isotherm model for this scenario. The IAST and Sips models described significantly different results for each adsorbed component when higher pressures are set. These different results cause a significant discrepancy in the estimation of the equilibrium selectivity. Simulated and experimental equilibrium selectivity data provided by IAST presented values of around 4, for CO
2
/CH
4
, and extended Sips presented values of around 2. Also, simulated breakthrough curves showed that IAST fits better to the experimental data at higher pressures. According to the simulations, in a binary mixture at total pressure over 800 kPa, extended Sips model underestimated significantly the CO
2
adsorbed amount and overestimated the CH
4
adsorbed amount.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
•Adsorption equilibria of Xe, Ar, Kr, and O2 on activated carbon and two separate zeolites simulated using ANN.•The MLP and RBF models were used 25 for the two hidden layers and 65 for the single ...layer, respectively.•The Bayesian Regularization algorithm with a tangent sigmoid transfer function was developed for adsorption prediction.•The generated ANN weight matrix can predict the adsorption behavior of adsorbents under different process conditions.
In the present study, the artificial neural network (ANN) has been used to predict the adsorbed amount of Ar, Xe, Kr, and O2 on zeolites and activated carbon. The experimental (data set 1400) on adsorbent type, gas type, and pressure of this adsorption, defined by the 303°K isotherm, have been applied as input datasets for ANN development. The adsorbed amount was used as an ANN's output dataset. The Bayesian Regularization (BR) algorithm was applied as the two-layer network training from a Multi-layer perceptron (MLP) technique with 25 neurons. Furthermore, it was compared to the Radial based functions (RBF) algorithm, which uses a single 60-neuron hidden layer. The MLP and RBF networks had the best Mean Square Error (MSE) validating the efficiency of 0.00004 and 0.00071, respectively, after 100 epochs. The square of the coefficient of correlations (R2) for the MLP and RBF models were 0.9998 and 0.9978, respectively. The generated network weight matrix can predict the adsorption behavior of different adsorbents under different process conditions with high efficiency (accuracy over 99%).
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This paper investigates multiple methods of machine learning for an application of surrogate modeling and optimization of an experimentally validated pressure swing adsorption model, evaluating their ...accuracy and precision compared to the more widely used method of artificial neural networks. In addition, some means of improving the machine learning model’s accuracy with at-hand process knowledge and parameters were explored, which was followed by the optimization of the purity and recovery parameters of the system, finishing with a quantification of the total computational time employed. All steps described were developed and finished successfully using the open-source Python programming language, and the expected and unexpected results were discussed.
•High quality zeolites were synthesized from coal fly ash.•The CO2 adsorption of the synthetic zeolites is similar to that of commercial ones.•The zeolites studied exhibited good stability after 5 ...adsorption-desorption cycles.
Given the increase in CO2 emissions, the adsorption process using zeolites are proposed to remove this compound from combustion gases in pulverized coal power plants. Besides it, these materials can also be synthesized using coal fly ash to reconcile environmental and economic concerns. The aim of this study was to measure the adsorption capacity of zeolites synthesized from coal fly ash compared with commercial zeolites and assess their performance in temperature swing adsorption processes. Two pelletized synthetic zeolites were selected, one NaX type (SZX) and one NaA type (SZA), and two commercial zeolites, one NaX (CZX) and one NaA (CZA). Zeolites were characterized by XRF, XRD and textural analysis (BET). Adsorption capacity tests were performed by thermogravimetric analysis using similar CO2 concentrations to those found in pulverized carbon combustion gases, without moisture. Isotherms were also obtained for synthetic and commercial zeolites type X. The XRD results showed substantial similarity between the commercial and synthesized zeolites, indicating a good degree of crystallinity. The CO2 adsorption capacity at 303 K for both samples showed values similar to those reported in the literature (1.97 mmol/g for SZX and 1.37 mmol/g for SZA), demonstrating their potential in commercial applications. After five cycles, the adsorption capacity of all samples remained practically unchanged, indicating the possibility of application in TSA processes. In the adsorption tests at different temperatures and in the isotherms, adsorption capacity declined as temperature increased for both samples, being similar to benchmark commercial 13X and 4A zeolite adsorbents.
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Monocomponent adsorption of hydrogen sulfide and multicomponent adsorption with CO2 and CH4 mixtures were predicted in two samples of commercial activated carbons. We perform Monte ...Carlo calculations in the grand canonical ensemble in representative slit-pores of each carbon material and proposed a new energy parameter for H2S-carbon interaction from experimental adsorption heat in selected activated carbons. Further analysis of adsorption in representative pores demonstrated the importance of ultramicropores in H2S retention and a cooperative effect of CO2 molecules favoring H2S adsorption. To the best of our knowledge this is the first time that a method based on molecular simulation is proposed to predict H2S adsorption on carbon. This study contributes to a better understanding of the role of pore size distribution and adsorption regimes in carbon materials.
In this study, the adsorption of CO2 and H2S has been investigated on commercial activated carbon Desorex K43 impregnated with K2CO3, NaOH, or Fe2O3 in order to assess their potential for “upgrading” ...and desulfurization of biogas or contaminated natural gas. Different chemical Fourier transformed infrared spectra (FTIR), X-ray fluorescence (XRF) and pH measurements and textural characterization techniques (N2 adsorption/desorption isotherms) were used to study the material surface and confirm the presence of K, Na, and Fe. Gravimetric experiments of single and binary gas sorption isotherms were used to evaluate CO2 uptake and selectivity with respect to CH4. Breakthrough curves under dry and humid conditions were performed to assess the adsorption of H2S. The materials studied showed high adsorption capacities for both gases: in the range from 0.85 to 4.58 mmol g–1 for H2S and from 1.61 to 1.88 mmol g–1 CO2, under dry conditions and 1 bar. Furthermore, the selectivity of the activated carbons for CO2 in relation to CH4 was in the range of 1.2–2.4, Desorex K43-BG being the material with higher adsorption capacity for gases under study. The data obtained by the adsorption experiments were correlated with the textural characteristics and the chemical properties of the materials, which allowed one to identify how promising an adsorbent is for the removal of acidic gases from biogas to obtain biomethane. The best compromise between H2S adsorption and CO2/CH4 selectivity was found for the sample containing Na (Desorex K43-Na), which benefited from both a basic surface chemistry and pore size distribution restricted to the micropore range.
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•CO2 capture capacity decrease reaches 10% at maximum typical SO2 concentration.•A model derived from reactive molecular dynamics can predict the adsorption of SO2.•A surprising ...cooperative effect between CO2 and SO2 is observed in a pore of 8.9 Å.•The use of activated carbons can exempt the use of a pre-treatment operation.•IAST and Langmuir models should be used with caution to estimate SO2/CO2 selectivity.
Carbon capture under post-combustion conditions has been the topic of numerous studies in the last decade. Although exhaust gases typically contain different components other than CO2, they are commonly neglected in these studies. The presence of sulfur dioxide, for example, tends to interfere in the carbon capture process through different mechanisms. The present work aimed to evaluate the effects of SO2 on the CO2 retention capacity through the integration of experimental evaluation, column dynamics modeling and molecular simulation (multiscale modeling) for an activated carbon sample under typical conditions found in the post-combustion environment. Results indicate that, under typical post-combustion flue gas conditions, SO2 has little influence on the CO2 retention capacity of the carbon in comparison to other adsorbent materials. The highest concentration of SO2 (5 000 ppmv) led to a decrease of approximately 10 % in the CO2 capture capacity. Significant deactivation (around 40 %) was observed experimentally and by molecular simulation only for very high concentrations of SO2 (50 000 ppmv). Additionally, no evidence of reactions with the material was found and both captured components could be completely desorbed by means of suitable regeneration methods. To access individual pore performance, molecular simulations were implemented for SO2 adsorption using, for the first time, a rigorous heterogeneous pore model (rMD). The results revealed a large deactivation for the 7.0 Å pore, a surprising cooperative effect for the 8.9 Å pore, and indifference for the larger 18.5 and 27.9 Å pores. For SO2 concentrations up to 5 000 ppmv, the use of carbon-based adsorbent could rule out the need of a pre-treatment operation to remove SO2 in carbon capture processes. For higher concentrations, molecular simulation showed that tailoring carbon porosity in the range of 7 Å to 8.9 Å considerably reduces the interference of SO2. Results also point out that the IAST and Langmuir models diverge from the molecular simulation results, particularly at low loadings (up to 5 000 ppmv SO2), indicating the need for caution when applying these models in systems where competitive interactions between molecules are relevant, as is the case with mixtures of CO2 and SO2.
