Inlet Partial Pressure Research Articles

Elucidating the impact of gas transport on high-performing air electrodes: a 1D physically based model unveiling the correlation between microstructure and impedance response

Abstract A 1D physically-based model on high performing air electrodes for Solid Oxide Cells is used to unravel the physical mechanisms lying behind the resistive peaks observed in experimental impedance data, posing particular attention to the low frequency contribution. In particular, the latter is commonly observed when analyzing the impedance response of high performing air electrode materials but its physical interpretation is still questioned. The model construction is grounded on the microstructural characteristics of conventional screen-printed electrodes. These properties were extracted by combining the statistical analysis of experimental 2D images taken with a scanning electron microscope and a validated microstructural model able to generate the synthetic 3D reconstructions of homogeneous electrode architectures. The implemented electrochemical model was tailored on the specific characteristics of a reference high performing SmBa0.8Ca0.2Co2O5+δ electrode material. Specifically, the model was used to reproduce its stationary and dynamic behavior between 650-750 °C, with an inlet oxygen partial pressure between 0.1-1 atm. The performed simulations unraveled the physical mechanisms lying behind the resistive contributions emerging from the impedance data. In particular, the effect of gas transport was analyzed in detail to understand the impact of the electrode microstructure on its electrochemical behavior. A sensitivity analysis on the effective gas diffusion coefficient highlighted that, in the investigated operating conditions, the electrochemical performance of classic screen-printed air electrodes is not limited by the gas diffusion. On the contrary, the low frequency contribution evidenced in the Nyquist plots was addressed to the impact of gas conversion. The developed electrochemical model successfully completed the correlation between microstructural and electrochemical properties and the results included in this work can be extended to different electrode materials tested in similar operating conditions.

Oxygen Concentration and Reaction Rate Profiles Analysis of Polymer Electrolyte Fuel Cell

Introduction A one-dimensional (1D) model of polymer electrolyte fuel cells (PEFCs) is especially suitable for performance diagnostics, design optimization, and material evaluation, due to its high computational efficiency. Uniform distributions of reactants are commonly assumed in 1D models, i.e., a single representative reactant concentration inside the gas channel is required. However, this concentration is strongly dependent on the flow field. Although plenty of 1D models with sufficient accuracy as 3D models have been reported, the effects of the flow field have not been sufficiently discussed in the literature. In this work, efforts have been put into developing a generalized theory suitable for various flow fields to quantitatively analyze the in-plane reaction rate profile, so that the flow-field-sensitive representative reactant concentration can be employed to further fill the gaps in the 1D models. Analytical model A series of a plug flow reactor (PFR) and a continuous stirred tank reactor (CSTR) was proposed to explain the unideal flow and the macromixing behaviors inside a gas channel coupled with a gas diffusion layer (GDL), as shown in Fig. 1(a).[1] The fraction of PFR’s space time to total space time was defined as the characterization factor γ, which should be the function of flow field shape and flow rate. Furthermore, under-rib oxygen concentration and current density profiles were taken into account by introducing the dimensionless moduli.[2] Especially, the under-rib convection can be evaluated by Péclet modulus Pe, by increasing which will improve the under-rib mass transfer and the effectiveness factor f. The in-plane profile of the ohmic resistance of the membrane was assumed uniform. The oxygen reduction reaction (ORR) was regarded as a surface reaction occurring on the interface of cathode catalyst layer (CCL) and GDL. The ORR rate was assumed to be proportional to oxygen partial pressure and independent of relative humidity (RH). Results and Discussion The characterization factors γ of different flow fields were determined according to the residence time distribution simulated by the computational fluid dynamics (CFD) model. The ORR rate constant at each electrical potential was obtained from the measured polarization curve of a parallel gas channel (PN0) with 0.35 mm channel depth, by employing the analytical model mentioned above. Fig. 1(c) shows the polarization curves of parallel channels with staggered 1-mm-long partially narrowed structures (PSN1) and PN0 with different channel depths. Compared to the PN0, the under-rib convection improves the oxygen mass transport and the cell performance, where f increases 17 % at 0.35 V in the case of the PSN1. On the other hand, increasing the channel depth restrains the oxygen diffusion and f decreases by 18 % at 0.35 V. The analytical model results show good agreement with experiment data, which indicates that the effects of the flow field can be summarized by the parameters γ and f.The analytical model provides the in-plane oxygen mole fraction and current density profiles. Fig. 2 shows the oxygen partial pressure distribution in a single gas channel calculated by the CFD model and analytical model. The mean oxygen partial pressure on the under-channel CCL-GDL interface calculated by the analytical model approximately equals the CFD result. By employing the ohmic resistance estimated according to the inlet conditions, although the current density is underestimated where RH is high, the integral mean of the in-plane current density offered by the analytical model has less than 5 % error compared to the CFD results, as shown in Fig. 3.The analytical model also gives an effective way to estimate the integral mean in-plane oxygen partial pressure. Fig. 4 demonstrates the relationships among integral mean, inlet, and outlet oxygen partial pressures. When the reaction rate constant and effectiveness factor are fixed, Fig. 4 also reveals the relationships between total and local current densities. If the parameters γ and f are determined, the integral mean of the oxygen partial pressure can be obtained when the outlet oxygen partial pressure or oxygen conversion is known. Conclusions The analytical model quantitatively demonstrates the effects of the flow field shape and provides a quick and effective way to estimate the reaction rate profile, based on the fixed in-plane ohmic resistance assumption. This model was verified by experiment and CFD model in case of the oxygen conversion less than 0.33 and can be applied to ORR kinetics determination and rapid performance prediction. Reference [1] Y. Ma et al., J. Electrochem. Soc., 170, 084506 (2023).[2] Y. Ma et al., ECS Meet. Abstr., MA2023-02, 1867 (2023). Figure 1

Cyclohexane dehydrogenation: Critical evaluation of parameter estimation procedures for kinetic modeling

In the present paper a comparison between different parameter estimation procedures commonly used for the kinetic modeling of chemical reaction is performed, based on experimental measurements of the cyclohexane dehydrogenation to benzene. The obtained results show that, when the Arrhenius equation parameters are estimated from estimates of the rate constant taken at different temperatures, larger parameter uncertainties and correlations are obtained, particularly when the variances of the experimental measurements are not considered during the estimation process. It is also observed that an apparent kinetic compensation effect occurs when the experimental data are separated according to the inlet partial pressure and catalyst mass in the reactor, mainly due to the existing and unavoidable experimental uncertainties and parameter correlations. Additionally, it is shown that larger uncertainties and correlations are obtained when the parameter estimates are computed through the differential method, which can also lead to poorer model predictions of the experimental data. Finally, it is shown that the simultaneous one-step estimation of all model parameters through the integral method and considering the available experimental uncertainties can provide the most accurate parameter estimates, making use of mathematical expressions that describe how variances of the experimental measurements depend on the experimental conditions.

Kinetic study of propane ODH on electrospun vanadium oxide-based submicron diameter fiber catalyst

A rigorous kinetic study of the oxidative dehydrogenation (ODH) reaction of propane on a vanadium oxide-based submicron diameter fiber catalyst has been developed. The proposed kinetic model simulates the conversion-selectivity profiles, the surface coverage of the different adsorbed species and the oxidation state of the catalyst for the studied operating conditions of temperature, space–time and inlet partial pressures of propane and oxygen. The activation energy of the rate determining step (RDS), the first hydrogen abstraction from propane, is 104 kJ·mol−1. The model predicts that although the reaction seems to be pseudo-zero order with respect to oxygen in a broad range of conditions, the catalyst may not be fully oxidized during reaction. The accuracy of the model when predicting the oxidation state of the catalyst has been experimentally confirmed by analyzing the catalytic fixed bed after reaction. The reduction degree of the catalyst will depend on its intrinsic chemical nature and reaction conditions, increasing with the space–time and in detriment of the overall reaction rate. Consequently, the propane turnover frequency (TOF) will also depend on the reaction conditions and space–time, even changing along the fixed-bed reactor.

Uncharacteristic Adsorption Breakthrough Behavior of a Core–Shell Copper Hydroxysulfate Metal–Organic Framework Against Gaseous Formaldehyde

AbstractCore–Shell structured microspheres with a packed nano‐platelet copper hydroxysulfate (CHS) core and an octahedral crystalized metal–organic framework‐199 (CHS@M199) shell are synthesized and tested as adsorbent for gaseous formaldehyde (FA). CHS@M199 outperforms reference materials (e.g., activated carbon (AC), CHS, and M199) with adsorption capacity (Q) of 8.13 mg g−1 and partition coefficient (PC) of 0.263 mol kg−1 Pa−1 against 10 Pa FA at 10% breakthrough (BT) level with the aid of large surface area and copper sites for coordinating with carbonyl group. Contrary to general expectations, CHS@M199 exhibits a unique adsorption behavior in that BT volume increases systematically with the rise in FA inlet partial pressure (e.g., 5–10 Pa). The 10% BT capacity of CHS@M199 decreases noticeably (8.13 to 2.08 mg g−1) with increasing relative humidity (0.016 to 10%), reflecting water‐FA competition for hydrophilic adsorption sites. Although FA adsorption on CHS@M199 diminishes with elevated RH levels, such reduction intensifies when simulating ambient conditions (through stepwise addition of competing components: O2, CO2, and H2O). The FA adsorption on CHS@M199 is well described by both pseudo‐first‐order (PFO) and pseudo‐second‐order (PSO) kinetics. Polymerization may play a pivotal role in the adsorption of FA on CHS@M199, as Qi‐LeVan isotherm best fits the experimental data.

Activation by O2 of AgxPd1-x Alloy Catalysts for Ethylene Hydrogenation.

A composition spread alloy film (CSAF) spanning all of AgxPd1-x composition space, xPd = 0 → 1, was used to study catalytic ethylene hydrogenation with and without the presence of O2 in the feed gas. High-throughput measurements of the ethylene hydrogenation activity of AgxPd1-x alloys were performed at 100 Pd compositions spanning xPd = 0 → 1. The extent of ethylene hydrogenation was measured versus xPd at reaction temperatures spanning T = 300 → 405 K and inlet hydrogen partial pressures spanning PH2in = 70 → 690 Torr. The inlet ethylene partial pressure was constant at PC2H4in = 25 Torr, and the O2 inlet partial pressure was either PO2in = 0 or 15 Torr. When PO2in = 0 Torr, only those alloys with xPd ≥ 0.90 displayed observable ethylene hydrogenation activity. As expected, the most active catalyst was pure Pd, which yielded a maximum conversion of ∼0.4 at T = 405 K and PH2in = 690 Torr. Adding a constant O2 partial pressure of PO2in = 15 Torr to the feed stream dramatically increased the catalytic activity across the CSAF at all experimental conditions and catalyst compositions without inducing catalytic ethylene combustion and without measurable O2 consumption. The presence of PO2in = 15 Torr more than doubled the maximum achievable conversion on Pd to ∼0.9 and activated alloys with as little as xPd = 0.6 for ethylene hydrogenation. Measurement of the reaction order with respect to hydrogen, nH2, showed that nH2 ≈ 0 when PO2in = 15 Torr on high xPd alloys but that nH2 increases to values between 0.5 and 1 as xPd decreases or when PO2in = 0 Torr. We attribute this PO2in-induced change in nH2 to a change in the reaction mechanism resulting from different functional catalyst surfaces: one that is O2-activated and Pd-rich and one that is Ag-capped with low activity. Both are extremely sensitive to the bulk alloy composition, xPd, and the reaction temperature, T. These results show that the activity of AgPd catalysts for ethylene hydrogenation depends strongly on the operational conditions. Furthermore, we demonstrate that the exposure of AgPd catalysts to 15 Torr of O2 at moderate temperatures leads to enhanced catalyst performance, presumably by stimulating both Pd segregation to the topmost surface and Pd activation for ethylene hydrogenation.

Elucidating Selective and Total Oxidation Elementary Reactions over a Ni-Based Catalyst for Sustainable Ethylene Production via Oxidative Dehydrogenation of Ethane: Microkinetic Analysis

This work develops a microkinetic model to investigate the selective and total oxidation elementary reactions involved in the Oxidative Dehydrogenation of Ethane (ODH-C2) over a SnO2-NiO based catalyst. The kinetic parameters were determined accounting for statistical significance and thermodynamic consistency. The pre-exponential factors were calculated using the Transition State Theory (TST) and statistical thermodynamics, while the activation energies were, first, approximated by using the UBI-QEP method and, then, tuned through regression analysis using experimental data at a temperature range of 603 to 753 K, inlet oxygen partial pressures between 3 and 12 kPa, inlet ethane partial pressures between 6 and 27 kPa, space-times (W/FC2H6,0) between 5 and 53 kg s/mol, and total pressures from 100 to 300 kPa. The microkinetic model adequately described experimental data. The model was able to predict the conversion of ethane and the selectivity to ethylene in the range of 4 % to 69% and 50% to 90%, respectively. Microkinetic analysis delivered a solid mechanistic hypothesis that elucidates the following: (i) the formation of nucleophilic and electrophilic oxygen species on the active metallic surface promote selective and total oxidation reactions, respectively; (ii) the hydrogen abstraction from ethane, double bond cleavage on ethylene, and water desorption are the energetically relevant elemental reaction steps during the ODH-C2; and (iii) O2/C2H6 ratios less than unity favor the formation of nucleophilic oxygen species, leading to increased ethylene selectivity. Overall, microkinetic analysis establishes the groundwork for future research aimed at both redesigning the catalyst and scaling up the ODH-C2.

A Portable Servoregulation Controller to Automate CO2 Removal in Artificial Lungs.

Artificial lung (AL) systems provide respiratory support to patients with severe lung disease, but none can adapt to the changing respiratory needs of the patients. Precisely, none can automatically adjust carbon dioxide () removal from the blood in response to changes in patient activity or disease status. Because of this, all current systems limit patient comfort, activity level, and rehabilitation. A portable servoregulation controller that automatically modulates removal in ALs to meet the real-time metabolic demands of the patient is described. The controller is based on a proportional-integral-derivative (PID) based closed-loop feedback control system that modulates sweep gas (air) flow through the AL to maintain a target exhaust gas partial pressure (target or ). The presented work advances previous research by (1) using gas-side sensing that avoids complications and clotting associated with blood-based sensors, (2) incorporating all components into a portable, battery-powered package, and (3) integrating smart moisture removal from the AL to enable long term operation. The performance of the controller was tested in vitro for ∼12 h with anti-coagulated bovine blood and 5 days with distilled water. In tests with blood, the sweep gas flow was automatically adjusted by the controller rapidly (<2 min) meeting the specified tEG level when confronted with changes in inlet blood partial pressure of (p) levels at various AL blood flows. Overall, the removal from the AL showed a strong correlation with blood flow rate and blood p levels. The controller successfully operated continuously for 5 days when tested with water. This study demonstrates an important step toward ambulatory AL systems that automatically modulate removal as required by lung disease patients, thereby allowing for physiotherapy, comfort, and activity.

Reaction chemistry of ethanol oligomerization to distillate-range molecules using low loading Cu/MgxAlOy catalysts

We study ethanol oligomerization to higher alcohols and other oxygenates with a 0.3 wt. %Cu/Mg2.9AlO catalyst. This reaction involves more than 130 products in a complicated reaction network. The selectivity towards diesel fuel precursor compounds (hereafter ‘DFPC’) increased with conversion until reaching a plateau at an ethanol conversion of ~70 %. Alcohol selectivity was found to follow Schultz-Flory distribution at all studied conversions. Larger sized alcohols then are formed mostly by chain-growth mechanisms via surface reactions of adsorbed oligomers with ethanol-based monomers. Higher esters are formed from alcohols and aldehydes in a series reaction mechanism. Moreover, C6+ ester and C4+ ketones selectivities increase as conversion increases. We also found that C4+ alcohols most likely undergo Guerbet coupling with the studied catalyst to form even higher alcohols once, and that the oxygen of these alcohols is active as a nucleophile, resulting in the selective formation of esters if the starting alcohol is branched. Finally, we performed several cofeed studies varying ethanol-to-H2 inlet partial pressures, and adding acetaldehyde and ethyl acetate as cofeeds to ethanol at different concentrations. We conclude from these experiments that acetaldehyde concentration controls reaction chemistry, with conditions favoring larger concentrations of the molecule promoting both alcohol coupling and ester formation, and conditions leading to lower concentrations of acetaldehyde resulting in higher alcohol selectivity at the expense of esters and higher aldehydes.

Low energy carbon capture via electrochemically induced pH swing with electrochemical rebalancing

We demonstrate a carbon capture system based on pH swing cycles driven through proton-coupled electron transfer of sodium (3,3′-(phenazine-2,3-diylbis(oxy))bis(propane-1-sulfonate)) (DSPZ) molecules. Electrochemical reduction of DSPZ causes an increase of hydroxide concentration, which absorbs CO2; subsequent electrochemical oxidation of the reduced DSPZ consumes the hydroxide, causing CO2 outgassing. The measured electrical work of separating CO2 from a binary mixture with N2, at CO2 inlet partial pressures ranging from 0.1 to 0.5 bar, and releasing to a pure CO2 exit stream at 1.0 bar, was measured for electrical current densities of 20–150 mA cm−2. The work for separating CO2 from a 0.1 bar inlet and concentrating into a 1 bar exit is 61.3 kJ molCO2−1 at a current density of 20 mA cm−2. Depending on the initial composition of the electrolyte, the molar cycle work for capture from 0.4 mbar extrapolates to 121–237 kJ molCO2−1 at 20 mA cm−2. We also introduce an electrochemical rebalancing method that extends cell lifetime by recovering the initial electrolyte composition after it is perturbed by side reactions. We discuss the implications of these results for future low-energy electrochemical carbon capture devices.

Modeling the performance of a metal-organic framework (MIL-101) for the adsorption of toluene in an industrial fluidized bed adsorber and comparison to other adsorbent materials

In the present study, the application of a metal–organic framework (MOF) is investigated for the adsorption of toluene in an industrial fluidized bed adsorber. A previously-validated steady-state model is used that takes into account interactions between bubble and emulsion phases. The change in overall removal efficiency and partial pressure profile along the bed is discussed for different design and operating parameters. The performance of MOF (MIL-101) is then compared to that of a beaded activated carbon (BAC), a porous styrene–divinylbenzene polymer (Dowex Optipore V503), and a zeolite (50:50 USY-ZSM-5). The results show an increasing trend for the removal efficiency with an increase in adsorbent feed rate, weir height, or the number of adsorber stages. Increasing gas flowrate or inlet toluene partial pressure decreases the removal efficiency. Examination of the corresponding partial pressure profiles reveals that the major contribution to toluene removal inside the bed shifts from the bottom stages (where the gas enters the bed) to the top stages (where the gas leaves the bed) with increased gas flowrate or inlet partial pressure, or with decreasing the adsorbent feed rate. Comparison of the removal efficiencies obtained with different adsorbent materials shows a general trend as MOF > BAC > polymer > zeolite, except when the adsorbent feed rate is very low or the inlet partial pressure is very high. In those cases, high apparent densities for BAC and zeolite (at constant adsorbent feed rate) create longer adsorbent retention times inside the bed and change the removal efficiency trend to BAC > MOF > zeolite > polymer. Improving the adsorbent retention time by increasing the weir height or the number of stages is suggested to remedy the removal efficiency for adsorbents with low apparent densities (e.g. MOF and polymer).

Forced periodic operations of a chemical reactor for methanol synthesis – The search for the best scenario based on Nonlinear Frequency Response Method. Part II Simultaneous modulation of two inputs

The analysis of the potential to improve performance of a methanol synthesis reactor through forced periodical operations by Nonlinear Frequency Response method is presented. The methanol synthesis in an isothermal and isobaric lab-scale CSTR is considered. First, the analysis was performed for single input modulations (in Part I), which showed that significant improvements can’t be achieved. Here, the study is extended to analysis of simultaneous modulations of two inputs. All possible input combinations (6 cases) are analysed and the optimal forcing parameters, maximizing the time-average methanol production, were determined. For all combinations the improvement is possible, but for some cases it is not significant. The highest improvement is predicted for simultaneous modulation of the inlet partial pressure of CO and the inlet volumetric flow rate. This case, for which it is possible to achieve up to 33.51 % of methanol production, is analysed it detail and optimized using multi-objective optimization.

Detailed gas-phase kinetics and reduced reaction mechanism for methane pyrolysis involved in CVD/CVI processes

A detailed gas-phase kinetic model consisting of 37 species and 318 reactions is developed for methane pyrolysis involved in the chemical vapour deposition/infiltration (CVD/CVI) processes. The model was used to perform the simulations of CH4 pyrolysis in a hot-wall CVD reactor over a wide range of operating conditions and validated against the experimental data. The overall trend of the concentration profiles of notable species is in good agreement with experimental results. The sensitivity analysis and reaction path flux diagram revealed that CH4 pyrolysis directly proceeds without any induction period. C2 species are the primary intermediates for the formation of acetylene, ethylene, and benzene. Besides, the accuracy of the present model is better than the models available in the literature. The detailed kinetic model was then systematically reduced to a small mechanism comprising 13 species and 29 reactions. The predictions of reduced mechanism also agreed well with the detailed mechanism at low inlet partial pressure (<10 kPa). Although the error in the mole fraction of light species was minimal, the relatively large error for C6H6 species was observed at high inlet partial pressure of CH4.

Single-event kinetic model for methanol-to-olefins (MTO) over ZSM-5: Fundamental kinetics for the olefin co-feed reactivity

Methanol-to-olefins (MTO) is an alternative pathway to selectively produce lower olefins on demand. Acid zeolites like ZSM-5 convert methanol to dimethyl ether (DME) and water, followed by the formation of olefins as well as of paraffins and aromatics as side products. In this study, butene was used as model compound for the recycle in the industrial methanol-to-propylene (MTP) process and co-fed with methanol. During these kinetic experiments, both methanol and butene inlet partial pressures were varied as well as the total volumetric flow rates. Temperatures between 708 and 788 K were applied as the aim of this work is to model the fundamental kinetics of the MTO chemistry at olefin co-feed conditions. For the kinetic model, the single-event methodology is used in order to reduce the number of estimated parameters while depicting each surface reaction. Olefin interconversion as well as olefin methylation and oxygenate interconversion steps are all covered by the model. Only the formation of aromatics is described in a simplified and thus not fundamental way. Over 4000 reaction steps are modeled using only eleven estimated parameters. The resulting high numeric significance of the activation energies allows a mechanistic analysis of the different reaction pathways and an assessment of the most important propene production steps. This shows high temperatures to be advantageous for fast carbon transfer to the olefin hydrocarbon pool and subsequent cracking of mainly hexenes and heptenes to propene.

Facile synthesis of CuBTC and its graphene oxide composites as efficient adsorbents for CO2 capture

Abstract Easily regenerable adsorbents are highly desirable for CO2 capture. In this regard, a modified synthesis method for preparing CuBTC and its graphene oxide (CuBTC@GO) composites as adsorbents is developed using a mixed solvent strategy at 323 K for the first time. The addition of N, N-Dimethylformamide was vital for the crystallization of CuBTC at low temperature by accelerating the nucleation. The newly synthesized CuBTC showed much higher surface area and total pore volume, compared with CuBTC synthesized by conventional method. As a result, the as-synthesized CuBTC showed a CO2 adsorption capacity of 8.02 mmol/g at 273 K, 1 bar, which was 17–90% higher than the reported CO2 capacity of CuBTC prepared by conventional method. The fabrication of CuBTC@GO composites enhanced the CO2 adsorption capacity mainly through the improved porosity and dispersion force. Compared with CuBTC, an improved CO2/N2 selectivity for CuBTC@1%GO was obtained from the binary breakthrough experiments, which is beneficial to practical gas separations. The partition coefficient of CuBTC and CuBTC@GO composite were evaluated at different breakthrough levels, e.g., 5%, 10% and 100%, with an inlet CO2 partial pressure of 0.15 bar. CuBTC@1%GO displayed higher partition coefficient values than CuBTC at all three breakthrough levels. The cyclic adsorption experiments for regenerability evaluation showed that the CO2 adsorption reversibility for CuBTC@1%GO composite could maintain above 90%, while that of CuBTC dropped to less than 74% after five adsorption-desorption cycles. The CuBTC@GO composite would be a promising CO2 capture adsorbent with both high CO2 adsorption capacity and remarkable regeneration performance.

Assessment of open thermochemical energy storage system performance for low temperature heating applications

Owing to their high energy storage density, thermochemical energy storage (TCES) systems are promising alternatives for seasonal storage of heat, which can be charged with solar thermal energy during the summers, and employed for space heating application in the winter season. In the present work, an open TCES system with a single reactive bed of solid strontium bromide salt reacted with moist air flow is considered. A two-dimensional model considering diffusion effect of water vapour inside the reactive bed is developed and validated. Parametric studies are carried out for both the charging as well as the discharging phases using the two-dimensional model to evaluate the effect of inlet air temperature, inlet partial pressure of water vapour and inlet air flow rate on the performance of the open TCES system. A case study is carried out for the discharging phase for a single night during the winter season for Pune, India. The use of a suitable humidity control at the inlet of the reactive bed is found to increase the energy saving by 18.9% and is found to be an effective way in maintaining the temperature of the air at the outlet of the reactive bed within comfortable limits for space heating application.

Competitive adsorption of gaseous aromatic hydrocarbons in a binary mixture on nanoporous covalent organic polymers at various partial pressures

Covalent-organic polymers (COPs) are recognized for their great potential for treating diverse pollutants via adsorption. In this study, the sorption behavior of benzene and toluene was investigated both individually and in a binary mixture against two types of COPs possessing different –NH2 functionalities. Namely, the potential of COPs was tested against benzene and toluene in a low inlet partial pressure range (0.5–20 Pa) using carbonyl-incorporated aromatic polymer (CBAP)-1-based diethylenediamine (EDA) [CD] and ethylenetriamine (DETA) [CE]. The maximum adsorption capacity and breakthrough values of both COPs showed dynamic changes with increases in the partial pressures of benzene and toluene. The maximum adsorption capacities (Amax) of benzene (as the sole component in N2 under atmospheric conditions) on CD and CE were in the range of 24–36 and 33–75 mg g−1, respectively. In contrast, with benzene and toluene in a binary mixture, the benzene Amax decreased more than two-fold (range of 2.7–15 and 6–39 mg g−1, respectively) due to competition with toluene for sorption sites. In contrast, the toluene Amax values remained consistent, reflecting its competitive dominance over benzene. The adsorption behavior of the targeted compounds (i.e., benzene and toluene) was explained by fitting the adsorption data by diverse isotherm models (e.g., Langmuir, Freundlich, Elovich, and Dubinin-Radushkevich). The current research would be helpful for acquiring a better understanding of the factors affecting competitive adsorption between different VOCs in relation to a given sorbent and across varying partial pressures.

The potential of biochar as sorptive media for removal of hazardous benzene in air

Airborne benzene is hazardous even at sub-ppm levels. Therefore, an effective strategy is required for its removal, such as the use of a sorbent with large adsorption capacity or high breakthrough volume. To meet the goal, the performance for the removal of benzene was assessed by loading benzene at 5 Pa inlet partial pressure against seven types of biowaste-derived biochar: (1) paper mill sludge, (2) conventional biochar with magnetic properties, (3) biochar composites with carbon nanotubes (CNTs), (4) gasification biochar from mixed feedstock, (5) gasification biochar from a single feedstock, (6) modified gasification biochar, and (7) activated carbon (AC) as a reference. The 298 K maximum adsorption capacities (mg g−1), when measured at a benzene inlet pressure of 5 Pa (or 50 ppm in ultrapure nitrogen) and flow rate of 50 mL atm min−1, varied widely for different biochars, from 0.35 (MS: Swine manure + plastic mulch film waste) to 144 mg g−1 (XC-1: biochar from mixed feedstock); their 10% breakthrough volumes (BTV) were in the range of 0.22–492 L g−1, respectively. The experimental data (capacity vs. benzene outlet partial pressure) could be fitted to either two or three linearized Langmuir isotherms with distinctive sorption mechanisms ((1) a retrograde region (Type III isotherm: 0 to ∼0.2 Pa), (2) an intermediate pressure region (0.2 and 2.0 Pa), and (3) a higher pressure region (>2 Pa)) which was also confirmed similarly by Freundlich, Dubinin–Radushkevich, and Elovich fitting. About 65% of the maximum capacity was achieved in the retrograde region. The strongest biochar sorbent, XC-1, showed similar performance as activated carbon to prove its feasibility toward air quality management (AQM) applications.

Effects of CO2 delivery on fatty acid and chitin nanofiber production during photobioreactor cultivation of the marine diatom Cyclotella sp.

Diatoms are single-celled algae that make cell walls of nanopatterned biogenic silica through metabolic uptake of dissolved silicon. The centric marine diatom Cyclotella sp. produces intracellular lipids and the valued co-product chitin, an N-acetyl glucosamine biopolymer that is extruded from the cell as pure nanofibers. The effect of CO2 delivery on the phototrophic production of biomass, lipids, and chitin from Cyclotella sp. was studied in a bubble-column photobioreactor by varying the inlet partial pressure of CO2 in the aeration gas (pCO2) from 0.5× ambient (200ppm) to 7.5× ambient (3000ppm) under silicon-limited growth conditions at fixed light intensity corresponding to 50% of saturation on the photosynthesis-irradiance curve. The cumulative consumption of CO2, determined the difference between the inlet and outlet pCO2 vs. time, showed that CO2-replete cultivation occurred at an inlet pCO2 of 800ppm. Both lipid and chitin production were triggered after silicon substrate depletion. The lipid production rate increased with increasing inlet pCO2 under CO2 delivery-replete conditions until saturation was achieved at an inlet pCO2 of 3000ppm. In contrast, chitin production was not strongly affected by pCO2. At pCO2 saturation, production rates were 195±21mgdry/L-day for biomass, 42±11mg/L-day for lipids, and 8.5±1.4mg/L-day for chitin. Final yields in the biomass were 23±0.9wt% for lipid, and 8.5±0.5wt% for chitin (all errors 1.0 S.E.). This study has showed that silicon and CO2 delivery can be manipulated to control the relative production of lipid and the valued chitin nanofiber co-product by the diatom Cyclotella, where silicon depletion initiates chitin formation, and inlet pCO2 enhances lipid production on top of chitin formation.

Interplay of Kinetics and Thermodynamics in Catalytic Steam Methane Reforming over Ni/MgO-SiO2

The steam methane reforming (SMR) reaction was studied on a Ni/MgO-SiO2 catalyst at 923 K (650 °C) and 0.40 MPa in a tubular packed-bed reactor. The partial pressures of CH4 and H2O were varied between 20 and 140 kPa and 80 and 320 kPa, respectively. Measurements were carried out without mass and heat transport limitations, as verified by the Weisz–Prater and Mears criteria. Experimentally, the CH4 conversion increased with the inlet partial pressure of H2O and decreased with the inlet partial pressure of CH4. However, at low CH4 inlet partial pressures, i.e., at 40 and 60 kPa, the conversion passed through a maximum. Rate expressions were derived based on a simple two-step sequence. A statistical analysis led to a globally significant, weighted regression and resulted in a good agreement between the model and the experimental data, as indicated by a low F value of model adequacy of 2.84. The rate and equilibrium coefficient parameters were statistically significant as indicated by narrow confidence inter...