Intraparticle Diffusion Resistance Research Articles

Mg and Fe co-loaded biochar prepared by microwave-synergized K2FeO4 of marine biomass for efficient CO2 capture: Performance assessment and mechanism exploration

To overcome the limitations of complex preparation and suboptimal performance of CO2 adsorbents, the present work synthesized a polymetallic oxide-loaded biochar (MgO·FeOx@biochar) with good performance in one step using a green and simple method of microwave-synergized K2FeO4. MgO·FeOx@biochar-700–10-0.1 with a hierarchical porous structure, abundant adsorption sites and well-distributed basic sites was obtained by optimizing the preparation parameters, which had a good CO2 trapping performance of 4.92 mol/kg with a retention rate of 83.01 % over 20 cycles, and exhibited good selectivity for O2 and N2. CO2 capture by MgO·FeOx@biochar was predominantly driven by chemical interaction between surface adsorption sites and CO2, supplemented by microporous filling. The adsorption kinetics revealed that the CO2 adsorption rate of MgO·FeOx@biochar was influenced by the combined effect of membrane diffusion resistance and intraparticle diffusion resistance. This study established a theoretical basis and technical insight for the environmentally friendly and efficient preparation of high-performance biochar-based CO2 adsorbents.

Facile synthesis of amine hybrid silica aerogel globule via wet casting assisted self-catalysed sol-gel process for CO2 capture including direct air capture

Amine hybrid silica aerogel globule (AHSAG) for CO2 capture including direct air capture (DAC) was firstly synthesized via wet casting assisted self-catalyzed sol-gel process. AHSAG has abundant interpenetrating macropores, which favors diffusion of CO2 into internal amine sites and can enhance CO2 adsorption kinetics and capacity. The optimal CO2 adsorption capacity of AHSAG with dry 100% and 400 ppm CO2 are 3.82 (30 °C) and 1.86 mmol/g (55 °C), respectively. Corresponding amine efficiencies are 0.478 and 0.233. The effect of temperature on CO2 adsorption capacity is attributed to simultaneous enhancement of mass transfer kinetics and adsorption thermodynamics. The highest CO2 adsorption rate of AHSAG is achieved at 70 and 55 °C with 100% and 400 ppm CO2, respectively. The trend of CO2 adsorption rate with temperature is attributed to the synergistic effect of diffusion kinetics and desorption. Based on experimental CO2 adsorption kinetics, adsorption mechanism in 400 ppm CO2 was estimated with different diffusion models. Both film diffusion resistance and intraparticle diffusion resistance are involved in CO2 capture of AHSAG from air under given condition to control the overall adsorption process. Three kinetics models were used to fit the experimental data of AHSAG for DAC, and the Avrami model showed the best fitting within the whole adsorption period. Comparing with its state-of-the-art counterparts, AHSAG offers significant advantages for practical DAC, such as high adsorption capacity and amine efficiency, fast adsorption kinetics, and excellent cyclic stability.

Exploring kinetic and thermodynamic insights of graphene related two dimensional materials for carbon dioxide adsorption

Graphene related two dimensional materials (GR2Ms) are promising adsorbents for CO2 capture. However, the CO2 adsorption kinetics and mechanisms on these materials remain insufficiently explored and understudied. Recognizing the pivotal role of adsorption kinetics in assessing the practical applicability, this study comprehensively evaluates the CO2 adsorption kinetics, underlying mechanisms, and thermodynamic properties via gravimetric analysis on three distinct well-characterized graphene materials (few layer graphene-FLG, graphene oxide-GO, reduced graphene oxide-rGO) across temperatures from 25 to 75 °C under atmospheric pressure. Results reveal that Avrami’s fractional model offers the most accurate fit for CO2 adsorption kinetics among the three examined models (pseudo-first, pseudo-second, and Avrami’s fractional order). The interplay between the physico-structural-chemical properties of GR2Ms and the CO2 adsorption kinetics discloses that the morphology, crystallite size, specific surface area and porosity of GR2Ms greatly influence the CO2 adsorption rate as evidenced by the largest rate constant, kA value of rGO at 25 to 75 °C under atmospheric pressure. Analysis of activation parameters including activation energy, enthalpy of activation, entropy of activation, and free energy of activation derived from Eyring, Arrhenius, and Gibbs equations indicates a greater favorability of CO2 adsorption on GR2Ms at lower temperatures. Moreover, investigation into the underlying interaction mechanisms between CO2 molecules and GR2Ms, using rate-limiting kinetic models (Boyd’s film diffusion model, interparticle diffusion model, and intraparticle diffusion model), confirms that both film diffusion resistance and intraparticle diffusion resistance predominantly govern the CO2 adsorption rate.

Hierarchical porous AlOOH hollow microspheres for efficient CO2 capture

In order to reverse the trend of increasing carbon dioxide (CO2) emissions, the development of efficient and economical CO2 trapping agents is an urgent necessity for the sustainable development of industry. In this paper, hierarchical porous hydroxyl aluminum oxide (AlOOH) hollow microspheres with controllable structure and morphology were prepared by conventional hydrothermal synthesis using malonic acid as a structure guiding agent. Then, potassium carbonate (K2CO3) based adsorbents were prepared using AlOOH hollow microspheres as supports, and their CO2 trapping performance was assessed by simulating industrial flue gas flow in a fixed bed. The results show that the loading of K2CO3, the pore structure, and the surface basic site of the adsorbent have a significant influence on the trapping performance of CO2. Among the prepared K2CO3/AlOOH adsorbents, 30 wt% K2CO3/AlOOH adsorbent has the best CO2 capture ability, which is about 2.15 times higher than that of K2CO3/C–Al2O3 adsorbent prepared from commercial alumina (C–Al2O3). There may be two explanations for this. Firstly, it may be due to the nanostructured shell and hierarchical porous structure of the adsorbent, which reduces the intra-particle diffusion resistance of CO2, and secondly, it may be due to the suitable surface basic sites of the adsorbent. In addition, the adsorbent was regenerated at 120 °C after trapping CO2, and then CO2 was captured in a cycle. It was found that the CO2 capture capability of the adsorbent did not decrease significantly after 10 cycles. In this work, an excellent technique for preparing porous honeycomb adsorbents with suitable surface basic sites has been devised, which provides a creative strategy for capturing and utilizing CO2.

A mathematical model for ammonium removal and recovery from real municipal wastewater using a natural zeolite

A study was carried out to remove/recover ammonium (NH4+) from residual effluents in tertiary treatment by sorption/desorption processes onto a natural clinoptilolite zeolite (NZ) in batch and fixed-bed column systems. Batch equilibrium and kinetic experiments were performed at different loading of NZ and contact time intervals, respectively. The results obtained in batch were fitted by the Freundlich and Langmuir isotherms and mass action law model. The Freundlich isotherm showed better agreement with experimental data than the Langmuir model. The isotherm studies revealed a type III with a maximum capacity of 2.8 ± 0.2 mg/g at 40 mgNH4+/L. Moreover, the data from the fixed-bed column studies was well fitted by a mass transfer model, considering the intraparticle diffusion resistance given by the linear driving force model (LDF). Finally, the capacity of NH4+ recovery of activated zeolite was measured experimentally and by a robust dynamic desorption model. The column desorption results demonstrated that higher recoveries (92–99.99%) were observed when increasing the flow rate to 0.12 mL/min. The uniqueness of this study is its capability to simulate both the sorption and desorption processes of the naturally derived sorbent for the effective removal and recovery of NH4+-N from real wastewater stream.

Kinetic and thermodynamic studies of H2S adsorption by lignin-based composite membranes

Abstract Two lignin-based composite films were prepared by solution casting, which were named Cu-CLA/PVA and CuO-LA/PVA/CNF, respectively. The kinetic and thermodynamic analyses of the deodorization process of the composite membranes were performed by using adsorption models. The results showed that both membranes had good adsorption performance for H2S with the adsorption amounts of 36.39 mg g−1 and 35.69 mg g−1, respectively. The adsorption processes were mainly following the pseudo-secondary kinetic model, intraparticle diffusion model, and Freundlich isothermal adsorption model, indicating that the intraparticle diffusion resistance controlled the H2S adsorption rate and H2S was adsorbed on the non-homogeneous surface of the membranes through multiple layers. The adsorption of H2S by Cu-CLA/PVA is an exothermic process, while the adsorption of H2S by CuO-LA/PVA/CNF is a heat-absorbing process, indicating that Cu-CLA/PVA is more suitable for H2S adsorption at low temperatures, but CuO-LA/PVA/CNF, at higher temperatures, is favorable for H2S adsorption reactions. △G is negative of both Cu-CLA/PVA and CuO-LA/PVA/CNF, indicating that both Cu-CLA/PVA and CuO-LA/PVA/CNF are spontaneous for H2S adsorption.

Comprehensive reverse flow reactor model for fluid–solid systems

A comprehensive model for a Reverse Flow Reactor was developed and implemented in the present article. The model consists of the combination of mass and energy balance equations written for a fluid–solid packed reactor, where the feed and outlet positions are alternated periodically using dedicated boundary conditions. Several non-idealities were considered, dealing with both the particle and the fluid phases. Different chemical systems were simulated numerically to investigate the behavior of the reverse flow reactor and to determine the optimal operation policy. Intraparticle diffusion resistance allowed to predict concentration gradients in each case, while intraparticle heat transfer was demonstrated to be non-influent. The impact of the main kinetic and heat/mass transfer parameters was checked via a parametric investigation, demonstrating the high flexibility of the model, even predicting harsh operation conditions. The model was tested in the description of data taken from the literature, demonstrating a good descriptive power.

High Temperature CO2 Capture Performance and Kinetic Analysis of Novel Potassium Stannate.

For the first time, the use of stannate-based sorbents was investigated as high temperature CO2 sorption to evaluate their potential to contribute towards reducing carbon emissions. The sorption capacity and kinetics of commercial tin oxide, sodium, potassium and calcium stannates and lab synthesised potassium stannates were tested using thermogravimetric analysis. Commercial K2SnO3 was found to possess the largest CO2 uptake capacity (2.77 mmol CO2/g or 12.2 wt%) at 700 °C, which is among the highest for potassium sorbents, but the CO2 desorption was not successful. On the contrary, the in-house synthesised K-stannate (K-B) using facile solid-state synthesis outperformed the other sorbents, resulting in a CO2 uptake of 7.3 wt% after 5 min, an adsorption rate (0.016 mg/s) one order of magnitude higher than the other stannates, and stability after 40 cycles. The XRD and XPS analyses showed that K-B contains a mixture of K2SnO3 (76%) and K4SnO4 (21%), while the Scherrer crystal sizes confirmed good resistance to sintering for the potassium stannates. Among the apparent kinetic model tested, the pseudo-second order model was the most suitable to predict the CO2 sorption process of K-B, indicating that chemical adsorption is dominant, while film-diffusion resistance and intra-particle diffusion resistance governed the sorption process in K-B. In summary, this work shows that solid-state synthesised potassium stannate could be an effective sorbent for high temperature separation, and additional work is required to further elucidate its potential.

Capturing CO2 by ceria and ceria-zirconia nanomaterials of different origin.

Ceria and ceria-zirconia nanomaterials of different origin were studied in order to elucidate the role of their structural and textural characteristics in controlling the performance towards CO2 capture. Two commercial cerias and two home-prepared samples, CeO2 and CeO2-ZrO2 (75% CeO2) mixed oxide, were investigated. The samples were characterized by a number of analytical techniques including XRD, TEM, N2-adsorption, XPS, H2-TPR, Raman and FTIR spectroscopy. Static and dynamic CO2 adsorption experiments were applied to assess the CO2 capture performance. The type of surface species formed and their thermal stability were evaluated by in situ FTIR spectroscopy and CO2-TPD analysis. The two commercial ceria samples possessed similar structural and textural characteristics, formed the same types of carbonate-like surface species upon CO2 adsorption and, consequently, demonstrated almost identical CO2 capture performance under both static and dynamic conditions. The thermal stability of the adsorbed species increased in the order bidentate (B) carbonates, hydrogen carbonates (HC) and tridentate carbonates (T-III, T-II, T-I). Reduction of CeO2 increased the relative amount of the most strongly bonded T-I tridentate carbonates. Preadsorbed water led to hydroxylation and enhanced formation of hydrogen carbonates. Although the synthesized CeO2 sample had a higher surface area (by 30%) it showed a disadvantageous long mass transfer zone in the CO2-adsorption breakthrough curves. Because of its complex pore structure, this sample probably experiences severe intraparticle CO2 diffusion resistance. Having the same surface area as the synthesized CeO2, the mixed CeO2-ZrO2 oxide exhibited the highest CO2 capture capacity of 136 μmol g-1 under dynamic conditions. This was related to the highest concentration of CO2 adsorption sites (including defects) on this sample. The CeO2-ZrO2 system showed the lowest sensitivity to the presence of water vapor in the gas stream due to the lack of dissociative water adsorption on this material.

Impact of the Non-Uniform Catalyst Particle Size on Product Selectivities in Consecutive Reactions

The analysis of consecutive reactions A→B→C in porous catalyst particles, where the simultaneous processes of diffusion and chemical reactions take place and both reactant and products are subjected to diffusion limitations, was performed for catalyst particles with non-uniform sizes, a fact that has not been considered so far. The system comprises first-order consecutive irreversible reactions that proceed on spherical catalyst particles with a log-normal volume particle size distribution (PSD), which is typical in many catalytic applications. Regardless of the prevailing diffusion regime (chemical control, transition situation or intraparticle diffusion control), the yield of the intermediate product (B) reaches a maximum value as a function of the conversion of reactant (A), then decreases as a consequence of the prevalence of the secondary reaction that converts it into the secondary product (C). If intraparticle diffusion resistances affect the reactant species, given the relationship between the kinetic constants and the mean particle size, the selectivity to the intermediate product is negatively affected by the dispersion in PSD. The larger the dispersion in PSD, the stronger the negative impact.

Adsorption Effect and Adsorption Mechanism of High Content Zeolite Ceramsite on Asphalt VOCs.

In order to meet the requirements of industrial-scale fixed beds and develop an excellent adsorbent for asphalt VOCs. Zeolite ceramsite containing binder was prepared and successfully applied to the inhibition of asphalt VOCs. The results showed that prepared zeolite ceramsite possessed a high degree of crystallinity, and its main crystal phase is zeolite. The micropores with a pore size of 0.88 nm dominated the pore size distribution of the material. The adsorption experiment of asphalt VOCs showed a lower VOCs adsorption effect of 8.72% at a small dosage of 5%, while at a large dosage of 50%, the adsorption effect of VOCs exceeded 45%. This might be caused by the quite small external specific surface area, which occupied only 8.3% of the total specific surface area, and the low intraparticle diffusion coefficient due to the micropores. Meanwhile, the kinetics diameters of most aromatic hydrocarbons, which were comparable to the pore size of micropores, and the increase in the intraparticle diffusion resistance of aliphatic hydrocarbon molecules were the important factors in obtaining high adsorption of aromatic hydrocarbons in asphalt VOCs. Furthermore, the results indicated that the particulate adsorbent with a microporous structure should be mixed into the asphalt as a fine aggregate rather than an asphalt modifier for better asphalt VOCs adsorption effect.

Numerical Study of a Water Gas Shift Fixed Bed Reactor Operating at Low Pressures

Today, hydrogen has become one of the most promising clean energy. Several processes allow obtaining hydrogen, among them there is the Water Gas Shift (WGS) reaction. On an industrial scale, WGS reaction takes place at high pressure [25–35 bar]. At high pressure, the cost of the process rises due to the energy consumed by compression, and the reduction in the lifetime of the equipment and the catalyst. At low pressures, catalyst lifetime can reach many years and the energy cost is reduced. It is for this reason that we are interested in modelling and simulation of a WGS converter operating at low pressures close to atmospheric pressure. In this work, a numerical study was conducted in order to determine the conditions allowing good rector operating at low pressure. A number of drawbacks of the process were identified. These drawbacks are essentially the non-negligible pressure drops and the strong intraparticle diffusion resistances. The prediction of the concentrations and the reaction rate within the pellet showed that the active zone of the pellet is located near the particle surface. It has also been shown that the resistances to interfacial mass and heat transfer are insignificant. The study of pressure effect showed that the pressure increase reduces the required catalyst mass to achieve equilibrium. Finally, this work revealed that the decrease in temperature and the increase in the concentrations of the reactants by increasing their fluxes, make it possible to increase the effectiveness factor of the catalyst and the conversion of carbon monoxide. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Comparison of the intraparticle diffusion of DBT and 4,6-DMDBT in HDS over different mesostructured silica-based catalysts

Achieving ultradeep hydrodesulfurization (HDS) of diesel necessitates HDS catalyst optimization. Understanding the catalyst pore structure effects on the diffusion behavior of the organosulfur compound benefits the proper design of the HDS catalysts with maximized apparent reactivities. In the present study, we controllably synthesized three mesoporous silica-based catalysts (NiMo/Zr-SBA-15, FDU-12, and MCFs) with similar intrinsic reactivities (∼13 × 10-4 and ∼ 5 × 10-4 mol•g−1•h−1 for DBT and 4,6-DMDBT HDS) but different pore structures. The diffusion behaviors of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) in pore channels were systematically investigated via the reaction kinetic method. The pore channel/cage sizes rather than the pore mouth/window sizes dominated the intraparticle diffusion. The effective diffusion coefficient (De) decreased in the order of NiMo/Zr-MCFs (19.7 cm2•s−1) > NiMo/Zr-FDU-12 (18.2 cm2•s−1) > NiMo/Zr-SBA-15 (8.2 cm2•s−1) for DBT, while NiMo/Zr-MCFs (7.4 cm2•s−1) > NiMo/Zr-FDU-12 (4.4 cm2•s−1) > NiMo/Zr-SBA-15 (4.2 cm2•s−1) for 4,6-DMDBT. The corresponding correlation with pore size suggested that the intraparticle diffusion resistance can be greatly relieved when the catalyst pore/cage size is > 25x larger than the molecule size of the organosulfur-containing compounds. The findings present fresh opportunities for designing silica-based HDS catalysts for efficient HDS reaction.

Adsorption Beds: The Significance of Thermodynamic Properties and Particle Size on System-Level Heat Pump Performance

Abstract The performance of an adsorption heat pump is a function of the equilibrium uptake and diffusion resistances of a particular system, which determines the refrigerant throughput during a cycle. Previous studies have sought improved sorption bed performance by increasing heat transfer; however, some of the proposed heat exchanger enhancements represent costly alterations to the system. This work instead investigates a method for optimizing sorption bed mass transfer, which can be implemented as a low-cost alternative to heat transfer enhancement or in addition to it. The objective is to balance the intra-particle diffusion resistance, which increases with adsorbent particle diameter, with the inter-particle pressure drop, which decreases with adsorbent particle diameter. A silica gel–water system model is used to show that the optimal particle geometry in a packed bed yields a 48% improvement in cooling duty and over 50% increase in coefficient of performance compared with larger particles (dp = 1.42 mm).

The relation between adsorption resistances during removal of colour in sugar mill effluent

Phenolic compounds are the major source of colour in sugar mill effluent. Details mechanism of diffusional resistances for removal of phenolic compounds namely: phenol, 2-4 dichlrophenol and 2-4 dinitrophenol by adsorption onto activated carbon rice husk (ACRH) was studied. The mechanism studied was based on three diffusional resistance models: external mass transfer, intraparticle diffusion and twin resistance mass transfer. The relationship of mass transfer coefficient versus time shows that the adsorption process follows two regimes started with high mass transfer and then low mass transfer, due to high diffusion from bulk to surface of ACRH particles then slow mass transfer into pores of ACRH. The comparison between the three models was followed up by using the relationship of mass transfer coefficient versus time (kα cn). It was found that adsorption of phenol in the intraparticle structure is 180% higher than adsorption on the external surface of the ACRH. The value of mass transfer coefficient of the twin resistance model is close to that of external mass transfer model and both are lower than that of intraparticle diffusion model. The experimental results proved that intraparticle diffusion is controlling step. Moreover, three adsorption isotherms were studied: Langmuir, Freundlich and Dubinini -Roduch (D-R) for the three phenolic compounds.

Modeling Riemann–Liouville fractional differential equations for diffusion and reaction in fractal porous media

In this article, Riemann–Liouville fractional differential equations for diffusion and reaction process in batch reactors are developed with Mittag-Leffler function. For first-order irreversible reaction under isothermal conditions, analytical solutions are derived for fractal porous catalyst by taking into account intraparticle diffusion and external mass-transfer resistances. Furthermore, a numerical method for Riemann–Liouville fractional differential equations is developed. Both analytical and numerical solutions are found in good agreement with each other. The general expressions for effectiveness factor for first-order reaction under isothermal conditions are derived for fractal porous catalyst. Lastly, the effects of different parameters are studied.

Mass Transfer Mechanism and Equilibrium Modelling of Hydroxytyrosol Adsorption on Olive Pit–Derived Activated Carbon

The rise in olive oil production coincides with an increase in olive oil side-streams, such as olive mill wastewater and olive pits, enabling the exploitation of higher value-added products through proper processes. Adsorption techniques, common in wastewater treatment, facilitate the recovery of valuable compounds found in these by-products, such as the strong natural antioxidant hydroxytyrosol present in olive mill wastewater. Owing to their chemical composition, olive pits are a promising precursor for activated carbon production intended for adsorption purposes. However, a complementary side-stream strategy requires an in-depth analysis of the equilibrium state and the governing mass transfer mechanism based on sophisticated mathematical models for a reliable investigation of the processes occurring during hydroxytyrosol adsorption on olive pit–derived activated carbon (OPAC). Here we show the technological suitability of OPAC for adsorption of hydroxytyrosol in comparison to an existing commercial activated carbon (CAC). We found that the removal efficiency of OPAC was superior to CAC with increasing initial concentrations of hydroxytyrosol. The Redlich-Peterson isotherm provided the best fit to the adsorption equilibrium data based on the Akaike Information Criterion (AIC). Elucidation of the adsorption kinetics by means of the pore volume and surface diffusion model (PVSDM) showed that intraparticle diffusion resistance dominated hydroxytyrosol adsorption on OPAC. In addition, investigations over a broad temperature and pH range revealed the versatile applicability of OPAC and indicated a physisorption governed interaction. Our results demonstrate the fundamental parameters associated with hydroxytyrosol adsorption on OPAC, crucial for the development of adsorption systems to convert by-products into opportunities.

Enhanced kinetics and super selectivity toward Cs+ in multicomponent aqueous solutions: A robust Prussian blue analogue/polyvinyl chloride composite membrane

Developing effective adsorbents for 137Cs removal from complex wastewater systems has been a significant challenge. Although existing spheres adsorbents could improve the post-separation ability and practical operability, the adsorption kinetics are still significantly retarded due to the large intra-particle diffusion resistance. Here, we demonstrate the efficiency of a robust Prussian blue analogue/polyvinyl chloride composite membrane (PPM), which was easily prepared by a simple solvent evaporation method. In virtue of the less dense layer and ion-sieving functionality, it showed enhanced kinetics (5 h) and super selectivity (SF = 248.3–5388.6) towards Cs+. New PPM was robust within a wide pH range (2–10) and exhibited favorable removal capacity (152.8 mg/g), placing it at an outstanding material for Cs+ removal among other adsorbents. Moreover, PPM could be simply eluted and reused using a KCl solution as eluent. A study of the adsorption mechanism confirmed an ion-exchange action during the removal process. Thus, PPM is considered to be a promising candidate for the removal of Cs+ from multicomponent aqueous solutions

Analysis of equilibrium and dynamic adsorption of benzene vapor over unimodal and bimodal silica-based mixed-metal oxides

In this study, purification of a benzene-lean gas stream over unimodal and bimodal silica-based mixed-metal oxides was investigated for the purpose of understanding the effects of secondary metal oxide and support pore structure on the adsorption capacities and kinetics. The unimodal silica fell in the borderline of micropores and mesopores, i.e., they consisted of large micropores and small mesopores with large surface area, while the bimodal silica consisted of large micropores, small mesopores and large mesopores with large mesopore volume. The titania and zirconia mixed-metal oxides showed reduced surface area and pore volume as a result of partial blockage of the pores, however, they exhibited improved adsorption behavior relative to the bare silica. Equilibrium adsorption measurements revealed unimodal adsorbents are superior to their bimodal analogues by exhibiting higher benzene vapor uptake, with capacities reaching 10.05, 11.71 and 11.25 mmol/g for SiO2, TiO2/SiO2 and ZrO2/SiO2 samples at 25 °C and 101 kPa. In contrast, dynamic breakthrough tests with 465 ppm benzene vapor concentration indicated faster adsorption kinetics for bimodal adsorbents relative to unimodal materials as a result of their larger pores which produced lesser intraparticle diffusion resistance. It was also found that, while titania or zirconia incorporation enhances the equilibrium adsorption capacity of the bare silica, it deteriorates the adsorption rate. Similarly, all the adsorbents depicted partition coefficient in the range of 0.31–1.75 mmol/g/μM. The mass transfer coefficients estimated from concentration profiles of bimodal SiO2, TiO2/SiO2 and ZrO2/SiO2 samples were 0.58 and 0.45, and 0.41 s−1, respectively. Overall, the findings of this investigation indicated that the introduction of large mesopores in the structure of microporous-mesoporous silica is a facile approach in developing mixed-metal oxide adsorbents with improved adsorption capacity and kinetics for the abatement of benzene vapor emissions.

Computation of effectiveness factor for methanol steam reforming over Cu/ZnO/Al2O3 catalyst pellet

A mathematical model was developed for a diffusion–reaction process in a spherical catalyst pellet contained in a heterogeneous packed bed reactor. The model developed was solved to predict the effectiveness factor and also to perform sensitivity analysis for steam reforming of methanol on Cu/ZnO/Al2O3 catalyst a source of hydrogen fuel. The method of orthogonal collocation was used to solve the resulting differential equation. At temperature below 473 K the effect on intra-particle diffusion limitation is reduced to the minimum indicated by the effectiveness factor being almost equal to one but as the temperature increases above 473 K there is considerable increase in the diffusion limitation effect. The effects of thermal conductivity, diffusion coefficient, catalyst size and surface temperature on effectiveness factor for the reaction process were also considered. Result indicates that catalyst size of 1.623,, times ,,10^{ - 4} m eliminates the effect of intra-particle diffusion resistance in the pellet. The variation of effectiveness factor with Thiele modulus, showing the asymptotic values, using power law and Langmuir–Hinshelwood–Hougen–Watson (LHHW) kinetics, was predicted. The two reaction kinetics had almost the same magnitude of effectiveness factor at different Thiele modulus which indicates that they can adequately predict the reaction process.