Rigorous Kinetic Model Research Articles

A Rigorous Mechanism-Based Kinetic Modeling Method for Optimization of Solid Oxide Fuel Cell

A Rigorous Mechanism-Based Kinetic Modeling Method for Optimization of Solid Oxide Fuel Cell

Exergoeconomic evaluation of fuel production from rice husk residue through the pyrolysis process

Some agro-industrial wastes are currently untreated, resulting in an increase in greenhouse gas emissions. Therefore, in relation to the pollution generated by fossil fuels, the study of the obtained fuels from agro-industrial and forestry residues has been promoted. Rice is a basic product for several families in the world, and its residue is a component that has enormous potential in Colombia due to its consumption. The objective of the present study is to conduct an exergoeconomic evaluation of the production of fuel from rice husks as agro-industrial waste by means of the slow and fast pyrolysis process. Using simulators like Aspen Plus, the simulation of the two processes was carried up, implementing a rigorous kinetic model. The yield values were validated with data from the literature, obtaining values of 42.3% and 41.4% for slow and fast pyrolysis, respectively, for pyrolytic oil. The total investment cost of the process is 2146.45 kUSD. According to the thermodynamic parameters of the simulator, an exergy analysis was conducted for the two processes. Overall exergy percentages of 73.84% and 78.19% were obtained for the slow and fast pyrolysis, respectively. The economic and exergy analysis was coupled to implement a specific exergy costing. The exergoeconomics factors obtained values of 72.21% and 76.78%, for the slow and fast pyrolysis reactors, respectively. The contribution of the present research is related to the rigorous kinetic model, in addition to its implementation in slow pyrolysis, involved in the exergoeconomic study of biomass pyrolysis processes.

Simple model for water wash performance in amine scrubbing for CO2 capture

In amine-based capture systems, a water wash is necessary to remove gaseous amine to minimize atmospheric emissions and maximize amine recovery. Water wash simulation requires rigorous thermodynamic and kinetic models like those for absorption and stripping systems. An offline water wash model has been developed based on simplified thermodynamic and mass transfer assumptions to simulate a single-stage water wash for flue gas from gas-fired turbines with little or no aerosol, and to expedite simulations without needing to utilize process modeling software. Calculation of activity coefficients using both Pitzer–Debye–Hückel and Debye–Hückel theory suggest that the liquid phase in a typical water wash will be ideal due to the dilute concentration of molecular and ionic species.Vapor phase piperazine (PZ) is predicted with a driving force based on the volatility of the free amine that has not reacted with other species or dissociated into its ionic form, and the predicted outlet concentration is nearly identical to that predicted by rigorous Aspen PlusⓇ simulations. The predicted UT FEED outlet concentration is 220 ppb compared to 260 ppb predicted by Aspen PlusⓇ.Single-stage water washes are predicted to have single ppm concentration of MEA leaving the wash outlet flue gas. Amino-methyl-propanol (AMP) is predicted to be reduced to 10–30 ppm by a single-stage wash, and is predicted to be a difficult-to-capture amine without further washing steps. This prediction correlates with published TCM data from an ALIGN-CCUS campaign. Amine compounds at a similar or lower volatility to that of PZ are predicted to be reduced to ppb levels via a single-stage wash.

Production of dimethyl carbonate by gas-phase oxidative carbonylation of methanol over Cu/Y zeolite: Mechanism and kinetics

Dimethyl carbonate (DMC) has become into an appealing fuel additive for reducing the formation of pollutants during combustion and, together with the post-combustion treatment, allowing to fulfill the most stringent environmental regulations. Although the production of this chemical is still an open issue, the oxidative carbonylation of methanol catalyzed by solids and with reactants and products in the gas phase has been proposed to replace the homogeneous commercial process (CuCl in aqueous phase). In this work, we propose the use of a Cu/Y zeolite (prepared by solid-state ion exchange with copper (I) chloride) as alternative catalyst for this purpose, optimizing the reaction conditions and proposing a rigorous kinetic model for this reaction. For accomplishing this aim, gas phase reaction was performed in a continuous fixed-bed reactor. Temperature (100–200 °C) played a critical role in product distribution, DMC being the main product at 120 °C. The influence of different reactant (CH3OH/CO/O2) concentrations on reaction rate and product distribution was determined at 120 °C. The experimental data have been successfully fitted to a kinetic model, derived from the mechanism of the reaction.

The role of Heisenberg spin exchange and the quantum Zeno effect in the spin-selective reaction between spin-1/2 and spin-1 particles.

The kinetics of spin-selective reactions involving triplet molecules, such as triplet-triplet annihilation or electron transfer to dioxygen molecules in the ground triplet spin state, are strongly dependent on the dipole-dipole interaction (DDI) of electron spins in spin-1 particles. The effect of this interaction on the intersystem crossing in the reaction encounter complex of the paramagnetic particles was previously considered for some particular cases using oversimplified approaches. In this study, we consider a rigorous kinetic model of the irreversible reaction between the spin-1/2 and spin-1 particles in an encounter complex with the reactive doublet state. This model explicitly includes both isotropic exchange coupling of the reactants and spin dependence of the reaction rate in the form of the Haberkorn reaction term. For the time-independent DDI, an analytical expression for the reaction kinetics was derived. The effect of DDI fluctuations was analyzed using numerical simulations. It was found that increasing both the exchange coupling and the reaction rate constants can significantly slow down the quartet-doublet spin transitions and, as a consequence, the observed spin-selective reaction rate. Additionally, the presence of the irreversible reaction in the doublet states affects a coherent evolution in the non-reactive quartet subsystem.

Efficient and recyclable composite beads containing sodium alginate and EGDMA-AN cross-linked polymer for phenol removal: Kinetic and diffusion mechanisms

Adsorption, a ubiquitous technique used in the purification of pollutants streams, depends on the development of a suitable adsorbent wherein kinetic, equilibrium and diffusion phenomena are crucial aspects to ensure that the separation process will be feasible. Hence, in this study, an accurate isotherm in conjunction with rigorous kinetic and diffusion models was developed to investigate the adsorption mechanisms through independent equilibrium and transient experiments during the adsorption of phenol. To this end, dual cross-linked sodium alginate (SA)/ethylene glycol dimethacrylate (EGDMA) and acrylonitrile (AN) composite beads were prepared using a relatively simple gelation technique. The synthesized SA/EGDMA-AN composite material was characterized by FTIR, SEM-EDS, BET, TGA, XRD and the swelling factor. Additionally, the equilibrium was described by the Freundlich isotherm and the kinetics by the Langmuir model. The diffusion coefficients were found to be in the range 1.54 × 10-7 to 8.75 × 10-8 cm2·min-1 for bead diameters of 2.5 and 4.0 mm, respectively, which represent an effective diffusion behavior of the sorbent molecules. The synthesized SA/EGDMA-AN composite beads can be easily regenerated and separated from an aqueous solution. After regeneration, the SA/EGDMA-AN composite beads still present high adsorption capacity for up to four cycles of desorption and adsorption. These results led us to propose a suitable SA/EGDMA-AN composite adsorbent and a rigorous modeling approximation with good predictive ability that would guide the design of further separation processes for the removal of phenol in wastewater treatment.

Fuzzy logic control of a catalytic naphtha unit

This work examines the fuzzy logic-based control of a catalytic reformer. The control process requires development of an exact process model valid over a wide range of operating conditions. Two control methods, proportional integral derivative (PID) and Fuzzy-PID, were applied to determine the optimal operating conditions. The output temperature from the feedback fuzzy controller was sent to the PID controllers as a setpoint in the heating system loop, and two fuzzy logic systems, one in the forward path and one in the feedback path were developed to give setpoints for temperature control loops in the four reactors. A fuzzy logic-based optimal control scheme was established to increase the aromatics yield, subject to constraints on the inlet temperature of the reactors. A rigorous kinetic model was then developed by expressing the heat and mass balances under unsteady state conditions. This model was used to determine the temperature and concentration profiles of three main hydrocarbons, naphthenes, paraffins, and aromatics, across the four reactors. A reaction scheme involving 27 pseudo components connected using a network of 71 reactions for components in a wide range of carbon numbers was thus modelled. The simulation results for the model were compared with previous studies to validate the model, and good agreement was found between the reformate composition of the proposed model and the plant reformate composition and temperature. The simulation results also showed that the PID –Fuzzy controller is accurate but that it requires additional time to reach a steady state value.

Simultaneous Optimization of a Heat-Integrated Coal-to-SNG/MeOH Polygeneration Process Based on Rigorous Kinetic Models

In this article, a novel simulation–optimization method is proposed for the simultaneous design of a heat-integrated coal-to-SNG/MeOH (CTSM) polygeneration process, aiming at exergy efficiency enha...

Swift, versatile and a rigorous kinetic model based artificial neural network surrogate for single and multicomponent batch adsorption processes

Rigorous and robust first principles-based Homogeneous Surface Diffusion Model (HSDM) is demonstrated for numerical simulation and estimation of surface diffusivities for single, binary and ternary systems involving dyes and pharmaceutical molecules. The current work's novelty lies in proposing a fast, reliable and efficient Artificial Neural Network (ANN) surrogate to the mechanistic HSDM. Repeated numerical integration of the model's partial differential equations during parameter estimation from batch adsorption kinetics data is highly time-consuming and is not required for the proposed approach. This ANN was trained by a small number of HSDM simulations and limited experimental batch kinetics data with different combinations of surface diffusivity (DS) values. ANNs were developed and tested against the experimentally obtained batch kinetics data for various systems. The trained ANN was able to capture the kinetics that was rigorously predicted using HSDM. A 99.9%, 98.6% and 99.3% similarity could be achieved between DS values estimated using HSDM and ANN for single, binary and ternary systems respectively. Similarly, the batch kinetics data was almost identically tracked by ANN. The computational time required for this novel ANN per simulation reduced spectacularly and was about 14 times lesser while the total parameter estimation time was about 17 times lesser than HSDM. The ANN developed for estimating parameters could be operated in reverse as well for simulating the multicomponent batch adsorption kinetics and tracking the increase in percentage removal of the solutes with time at different process conditions. Irrespective of number of components, the ANNs performances were consistent. The ratio of neurons and their total number in the hidden layers had a significant impact on the performance. Hence optimization of network parameters is essential to realize the benefits of ANN. The shortcomings of empirical kinetic models viz. Pseudo First Order model (PFO) and Pseudo Second Order model (PSO) were also demonstrated. This work demonstrates the utility of ANNS in rigorous multicomponent adsorption kinetics applications and has considerable potential in real time optimization and operation of wastewater treatment plants.

Simulating reactive distillation of HIx (HI–H2O–I2) system in Sulphur-Iodine cycle for hydrogen production

Abstract In this article, we develop a reactive distillation (RD) column configuration for the production of hydrogen. This RD column is in the HI decomposition section of the sulphur - iodine (SI) thermochemical cycle, in which HI decomposition and H2 separation take place simultaneously. The section plays a major role in high hydrogen production efficiency (that depends on reaction conversion and separation efficiency) of the SI cycle. In the column simulation, the rigorous thermodynamic phase equilibrium and reaction kinetic model are used. The tuning parameters involved in phase equilibrium model are dependent on interactive components and system temperature. For kinetic model, parameter values are adopted from the Aspen flowsheet simulator. Interestingly, there is no side reaction (e.g., solvation reaction, electrolyte decomposition and polyiodide formation) considered aiming to make the proposed model simple that leads to a challenging prediction. The process parameters are determined on the basis of optimal hydrogen production as reflux ratio = 0.87, total number of stages = 19 and feeding point at 8th stage. With this, the column operates at a reasonably low pressure (i.e., 8 bar) and produces hydrogen in the distillate with a desired composition (H2 = 9.18 mol%, H2O = 88.27 mol% and HI = 2.54 mol%). Finally, the results are compared with other model simulations. It is observed that the proposed scheme leads to consume a reasonably low energy requirement of 327 MJ/kmol of H2.

Revisiting glycerol esterification with acetic acid over Amberlyst-35 via statistically designed experiments: Overcoming transport limitations

The market is overflooded by unrefined glycerol with the production of biodiesel from vegetable oils. A recurrently studied alternative for its valorization is the production of acetins via esterification with acetic acid over acid catalysts in liquid phase. However, most of the published literature uses experimental methodologies that prevent a proper kinetic analysis of the reaction. This work revisits glycerol esterification with acetic acid catalyzed by Amberlyst-35 applying sequential statistically designed experiments. Following such approach, statistically meaningful data were collected providing insight into the catalytic reaction. Experiments were designed to test the influence of the quantity of active sites; assumed herein as the number of surface SO3H+ sites on Amberlyst-35, temperature, and the acetic acid to glycerol molar ratio over the turnover frequency of the catalyst. The collected evidence shows that, under the typical conditions employed in most open literature, heat and mass transport artifacts should not be neglected. In the present case, these limitations were overcome by reducing the particle size of the solid. Under such conditions, a straightforward relationship between the concentration of surface SO3H+ active sites and the glycerol turnover rates was established. Meanwhile, it was shown that the reaction temperature has a rather weak effect on the catalytic turnover. This trend concurred with the thermodynamic equilibrium of the reaction. Likewise, the already established effect of the acetic acid to glycerol molar ratio was also confirmed. Overall, the performed study serves a double purpose. First, it is a methodological guide to collect kinetically relevant information in liquid phase. Second, it reports intrinsic kinetic rates for the esterification reaction over the studied catalyst hence paving the way for a rigorous kinetic modeling.

Dynamic modeling of a dual fluidized-bed system with the circulation of dry sorbent for CO2 capture

In CO2 capture processes with the circulation of dry sorbents, the regeneration energy as well as the capture efficiency are the key factors determining the overall energy efficiency of the CO2 capture. In an aspect of repeated circulation and regeneration of a sorbent, a dynamic model for a dual fluidized-bed system was developed, which includes a fast fluidized-bed carbonator and a bubbling fluidized-bed regenerator. A potassium carbonate-based sorbent for CO2 capture was applied in the fluidized-bed system and rigorous kinetic models for the carbonation and regeneration reactions were adopted. The validity of the developed model was confirmed by accurately predicting the experimental results from the dual fluidized-bed system at various operating conditions. The CO2 removal performance was found to slightly deteriorate from 52.8 to 51.9% during continuous cyclic operation when the regeneration was carried out under a nitrogen atmosphere at 150 °C. However, when CO2 gas was used for the regeneration under the same conditions, the capture performance dropped to 18.6% owing to partial regeneration of the sorbent. A case study for the regeneration condition was conducted using a CO2-rich gas to find the effective regeneration condition. The regeneration conversion under CO2 atmosphere could be improved by increasing the regeneration gas velocity and regeneration temperature. At a regeneration temperature of 160 °C, the capture performance was found to be 73.2%, with the energy required to capture one mole of CO2 being 234.8 kJ/mol-CO2. To reduce the energy requirement to less than 200 kJ/mol-CO2 in the dual fluidized-bed system, a granulated sorbent, satisfying the physical and chemical stability for fluidized-bed operation, should be developed for the regeneration below 145 °C with the same working capacity (0.46 mol/kg-solid). Alternatively, the working capacity should be improved by 30% at the regeneration temperature of 160 °C. The developed model can be further used for improving capture performance and energy efficiency.

Coupling gas flow pattern and kinetics for tyre pyrolysis modelling

A novel strategy has been proposed for the rigorous kinetic modeling of tyre pyrolysis in a conical spouted bed reactor. A kinetic model coupled with a gas flow model was used in the fitting of experimental results obtained in a bench scale unit in the 425–610 °C range. A gas flow model should be incorporated to account for the delay and mixing phenomena observed in tracer experiments, as these phenomena cause remarkable deviations in the assessment of the kinetic parameters. The gas flow pattern from the reactor to the measuring device was modeled using two different approaches based on ideal flow reactors. Furthermore, two kinetic schemes considering lumped products have been proposed; the first one is based on four parallel independent reactions accounting for the volatile products (gas, liquid, aromatics and tar). The second one considers an additional secondary reaction of aromatic formation from the liquid. The strategy proposed for coupling the kinetics and the flow model led to a suitable fitting of the experimental results, with the performance of the model considering a secondary reaction being slightly better than the simple one.

Comments on “Theoretical investigation on H abstraction reaction mechanisms and rate constants of sevoflurane with the OH radical” [Chem. Phys. Lett. 692 (2018) 345–352

This short communication discusses the role of the newly-found lowest-lying structures of the transition states (∼3.0 kcal/mol lower than those previously reported by Ren et al. (2018), together with the inclusion of the hindered internal rotation correction, in obtaining reliable kinetic data for the hydrogen abstraction from sevoflurane by OH radical. With the new structures and the more rigorous kinetic model, the calculated rate constants agree much better with the experimental data than those suggested by Ren and coworkers.

Overproduction of L‐tryptophan via simultaneous feed of glucose and anthranilic acid from recombinant Escherichia coli W3110: Kinetic modeling and process scale‐up

L-tryptophan is an essential amino acid widely used in food and pharmaceutical industries. However, its production via Escherichia coli fermentation suffers severely from both low glucose conversion efficiency and acetic acid inhibition, and to date effective process control methods have rarely been explored to facilitate its industrial scale production. To resolve these challenges, in the current research an engineered strain of E. coli was used to overproduce L-tryptophan. To achieve this, a novel dynamic control strategy which incorporates an optimized anthranilic acid feeding into a dissolved oxygen-stat (DO-stat) glucose feeding framework was proposed for the first time. Three original contributions were observed. Firstly, compared to previous DO control methods, the current strategy was able to inhibit completely the production of acetic acid, and its glucose to L-tryptophan yield reached 0.211 g/g, 62.3% higher than the previously reported. Secondly, a rigorous kinetic model was constructed to simulate the underlying biochemical process and identify the effect of anthranilic acid on both glucose conversion and L-tryptophan synthesis. Finally, a thorough investigation was conducted to testify the capability of both the kinetic model and the novel control strategy for process scale-up. It was found that the model possesses great predictive power, and the presented strategy achieved the highest glucose to L-tryptophan yield (0.224 g/g) ever reported in large scale processes, which approaches the theoretical maximum yield of 0.227 g/g. This research, therefore, paves the way to significantly enhance the profitability of the investigated bioprocess.

Phenomenological modeling and evaluation of formic acid pretreatment of wheat straw with an extended combined severity factor for biomass fractionation and enzymatic saccharification to produce bioethanol

Abstract Chemical pretreatment of lignocellulosic biomass is a complex system involving heterogeneity and complicated reactions. Rigorous kinetic modeling of this complex system is not possible, but phenomenological modeling with parameter of severity factor (SF) may provide useful information in a wide operational range. In the present work, an extended combined severity factor ( CSF ext ) was defined by involving the contribution of solvent concentration for modeling and evaluating formic acid pretreatment of wheat straw in order to achieve a fractionation of the biomass components and improve cellulose digestibility for bioethanol production. Two phenomenological models based on classical Arrhenius and modified Logistic equations were developed to describe the solubilization of the biomass polymeric components. Although the determined values of CSF ext were somewhat different based on Arrhenius and Logistic models, the tendency of the component solubilization with respect to CSF ext was similar. With integrated consideration of biomass components solubilization, formylation of cellulose and enzymatic glucan conversion, the pretreatment condition was suggested be controlled at Arrhenius-based CSF ext of 23–24 or Logistic-based CSF ext of 25–26. CSF ext thus can be applied as an integrated parameter involving the contribution of temperature, time and solvent concentration to the reaction severity for evaluating the pretreatment process.

The establishment of a coke-burn kinetic model for zeolite catalysts

The regeneration of coked samples of methanol-to-gasoline (MTG) catalyst applied in the commercial TIGAS (Topsoe Improved GAsoline Synthesis) process was studied by kinetic investigations of the coke-burn rate from temperature programmed oxidation (TPO) analysis of coked catalyst from a pilot plant reactor. The spent catalyst was unloaded, and samples covering the catalyst bed from reactor inlet to exit were analyzed by means of TPO. A rigorous kinetic model was fitted to the measured evolutions of CO2 and CO at the different catalyst bed heights. It was found that the diversity in oxidation reactivity of the coke observed along the axial reactor coordinate could be represented by lumping the various coke species into families characterized by having approximate the same oxidation reactivity. It was found that seven coke families were needed in order to obtain a satisfactory fit of the measured evolutions of CO and CO2. These seven coke families can roughly be divided into two categories; low-temperature (reactive) and high-temperature (less reactive) coke. Model testing is accomplished by applying the model to reconstruct a complete catalyst regeneration performed in situ in the pilot reactor. Model application illustrates that during the first step in an industrial regeneration, there is a risk of obtaining temperature excursions much higher than those expected, due to a combination of the amount of coke combusted as well as the cokes deposition along the catalyst bed length.

Sensitivity analyses and optimization of a gas sweetening plant for hydrogen sulfide and carbon dioxide capture using methyldiethanolamine solutions

The selective removal of hydrogen sulfide (H2S) in the presence of carbon dioxide using Methyldiethanolamine (MDEA) solutions is a significant process in the petroleum and natural gas industries. An industrial plant with an energy consumption of 3.36 GJ/mol CO2 was simulated and validated using rigorous kinetic and equilibrium models for H2S-CO2-MDEA-H2O system that are incorporated into the Amine Package in Aspen HYSYS®. A modified Murphee-type vapor tray efficiency of 15% for CO2 and 100% for H2S was utilized to account for the non-ideal behavior of the stages. Sensitivity analyses were performed on circulation rate (L/G = 0.6–2 kg/kg), stripper pressure (50–220 kPa), lean amine temperature (45–65 °C), number of absorber stages (8–14), and concentration of MDEA (15–50 wt%). These process variables were evaluated with respect to percentage recovery of sour gaseous components and normalized reboiler duty. The sensitivity analyses results showed that the circulation rate and the MDEA concentration are the two main factors improving process performance. The optimized scenarios exhibited better selective H2S absorption and higher energy savings.

Modeling Growth Kinetics of Gas Hydrate in Porous Media: Experimental Validation

In this contribution, a rigorous kinetic model is proposed for carbon dioxide (CO2) based gas hydrate formation in porous media in the presence of a promoter. This model introduces the difference in chemical potential between the water in hydrate phase and liquid phase as the driving force. The effective surface area of porous material is proposed for the growth of CO2 hydrate, and this parameter plays a major role in making the model different with the existing kinetic models. A parameter set is identified for each of the porous materials used involving a system with various components at a reasonably high pressure. The proposed kinetic model is finally evaluated for four different porous materials (cellulose foam, silica gel, silica sand, and polyurethane foam) by comparing it with the available models with reference to the experimental data sets taken from the literature. It is investigated that this kinetic model consistently outperforms the existing models for a wide variety of conditions.

A new rigorous two-phase kinetic model for accurate prediction of the asphaltene deposition rate during the oil flow in porous media of petroleum reservoirs

ABSTRACTAsphaltene formation and deposition in oil reservoirs are the most important problems in petroleum industry. A new rigorous two-phase kinetic model for simulation of flow behavior considering the asphaltene deposition process is presented in this work. All governing equations considering the proposed new adsorption kinetic model are solved by finite difference method. The presented model is validated using the most accurate available data and different oil samples. The proposed approach can be used for accurate evaluation of the effect of asphaltene deposition on the oil flowing condition in porous media of petroleum reservoirs.