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Numerical methods were applied to the study of the behaviour of high moisture content foods during drying process. Finite difference techniques were used to obtain numerical solutions by three different methods. The process was found to... more
Numerical methods were applied to the study of the behaviour of high moisture content foods during drying process. Finite difference techniques were used to obtain numerical solutions by three different methods. The process was found to depend upon a linear relation between solid volume variation and moisture content. The results obtained for the numerical methods were presented and compared among them and with a theoretical law, experimentally verified. Results showed that a Yuen and Kleinman type method is superior to the others, both in its accuracy and computational efficiency. Introduction
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Reactor temperature manipulation to increase product yields of chemical reactions is a known technique used in many industrial processes. In the case of exothermic chemical reactions, the well-known Le Chatelier’s principle predicts that... more
Reactor temperature manipulation to increase product yields of chemical reactions is a known technique used in many industrial processes. In the case of exothermic chemical reactions, the well-known Le Chatelier’s principle predicts that a decrease in temperature will displace the chemical reaction toward the formation of products by increasing the value of the equilibrium constant. The reverse is true for endothermic reactions. Reactor temperature manipulation in an industrial system, however, affects the values of many variables, including physical properties, transport parameters, reaction kinetic parameters, etc. In the case of reactive absorption, some variables change with increasing temperatures due to solute absorption, while others change in such a way that the solute absorption rate decreases. For example, temperature drop increases product formation for exothermic reactions but reduces the value of transport parameters, leading to decreasing interfacial concentrations and...
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There is increased interest in many different processes based upon interactions between a charged solid surface and a liquid electrolyte. Energy storage in capacitive porous materials, ionic membranes, capacitive deionization (CDI) for... more
There is increased interest in many different processes based upon interactions between a charged solid surface and a liquid electrolyte. Energy storage in capacitive porous materials, ionic membranes, capacitive deionization (CDI) for water desalination, capacitive energy generation, removal of heavy ions from wastewater streams, and geophysical applications are some examples of these processes. Process development is driven by the production of porous materials with increasing surface area. Understanding of the physical phenomena occurring at the charged solid-electrolyte interface will significantly improve the design and development of more effective applied processes. The goal of this work is to critically review the current knowledge in the field. The focus is on concepts behind different models. We start by briefly presenting the classical electrical double layer (EDL) models in flat surfaces. Then, we discuss models for porous materials containing macro-, meso-, and micro-po...
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Capacitive deionization (CDI) for water desalination, capacitive energy generation, geophysical applications, and removal of heavy ions from wastewater streams are some examples of promising electrochemical processes. The CDI process can... more
Capacitive deionization (CDI) for water desalination, capacitive energy generation, geophysical applications, and removal of heavy ions from wastewater streams are some examples of promising electrochemical processes. The CDI process can be improved by using a flow-through electrode (FTE) cell architecture, where the input feed water is pumped through an open channel separated from a flowing aqueous slurry mixture by a suitable ionic membrane. In this work we simulate the operation of a symmetrical electrochemical cell where the ions removed in the water flow channel are stored in flowing porous particles located in the slurry mixture channel. We use a two steps volume averaging technique to derive the averaged transport equations for multi-ionic system in the slurry electrode. The complete model involves sections for simulating the ionic transport in the water channel, the ionic membrane, and the slurry electrode. A fixed reference control volume approach was used to deal with the two moving phases. The individual ionic concentrations equations are derived for a binary salt made up of identical ions. The equations for co-ion and counter ion can be combined yielding averaged equations similar to the ones developed by Rubin et al. (2016). The derivation of an acceptable model to simulate the operation of a slurry electrode can be used to design improved CDI processes.
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Abstract CO2 capture from powerplant-generated flue gas via a phase-changing process involving absorption with aqueous amino acids (e.g., glycine or sarcosine) and bicarbonate crystallization with bis-iminoguanidines (e.g.,... more
Abstract CO2 capture from powerplant-generated flue gas via a phase-changing process involving absorption with aqueous amino acids (e.g., glycine or sarcosine) and bicarbonate crystallization with bis-iminoguanidines (e.g., glyoxal-bis-iminoguanidine or GBIG) is investigated in this paper. This process is of high interest due to its potential to decrease the energy penalty for CO2 capture by significantly reducing the solvent regeneration energy typically associated with aqueous amine solvents. A critical step in the proposed CO2 capture mechanism is the regeneration of the amino acid by removal of protons and bicarbonate ions from solution through crystallization of GBIGH22+ bicarbonate salt. Here, we investigated the thermodynamics and kinetics of glycine regeneration by crystallization of GBIGH22+(HCO3–)2(H2O)2. A theoretical model was developed and compared to experimental data to simulate and predict the glycine regeneration and determine its reaction mechanism. This combined experimental and theoretical study led to the conclusion that, while the GBIGH22+ bicarbonate crystallization step provides most of the thermodynamic driving force for the glycine regeneration, the rate-limiting step is the protonation of GBIG prior to crystallization. The CO2 loading and amino acid regeneration steps were combined into a single, intensified process using a bubble column reactor. The CO2 loading capacity of GBIG was experimentally determined to be roughly 1.36 mol CO2 per mol GBIG. These results provide the fundamental basis for developing an effective carbon capture technology with phase-changing amino acid/guanidine absorbents.
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Energy storage in capacitor porous materials, capacitive deionization (CDI) for water desalination, geophysical applications, and removal of heavy ions from waste streams are some examples of processes where understanding of ionic... more
Energy storage in capacitor porous materials, capacitive deionization (CDI) for water desalination, geophysical applications, and removal of heavy ions from waste streams are some examples of processes where understanding of ionic transport processes is very important. Most studies available in literature apply only to symmetric, binary electrolytes. A new model that computes the individual ionic concentration profiles inside porous electrodes is proposed to simulate ionic transport process. A volume averaging methodology has been used to derive the averaged equations from the point equations and appropriate boundary conditions. The transport parameters have been calculated for isotropic porous media. Finally, important issues to practically implement the proposed model are discussed.
ABSTRACT Carbon dioxide (CO2) absorption from power plant generated flue gas is investigated for CO2 emissions reduction. Amino acid alkaline solvents have the potential to reduce the energy required for solvent regeneration. This project... more
ABSTRACT Carbon dioxide (CO2) absorption from power plant generated flue gas is investigated for CO2 emissions reduction. Amino acid alkaline solvents have the potential to reduce the energy required for solvent regeneration. This project is focused on CO2 absorption by amino acid alkaline solvents in a bubble column. Important parameters characterizing the reactor, e.g., bubble size, liquid-phase dispersion coefficient, and gas holdup, are experimentally determined. A theoretical model based upon transient mass and energy balances for the chemical species involved is presented. Simulation results are compared to experimental data. The model can be used to predict, optimize, and control CO2 absorption in industrial-scale applications.
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Several carbon sequestration technologies have been proposed to utilize carbon dioxide (CO2) to produce energy and chemical compounds. However, feasible technologies have not been adopted due to the low efficiency conversion rate and... more
Several carbon sequestration technologies have been proposed to utilize carbon dioxide (CO2) to produce energy and chemical compounds. However, feasible technologies have not been adopted due to the low efficiency conversion rate and high-energy requirements. Process intensification increases the process productivity and efficiency by combining chemical reactions and separation operations. In this work, we present a model of a chemical-electrochemical cyclical process that can capture carbon dioxide as a bicarbonate salt. The proposed process also produces hydrogen and electrical energy. Carbon capture is enhanced by the reaction at the cathode that displaces the equilibrium into bicarbonate production. Literature data show that the cyclic process can produce stable operation for long times by preserving ionic balance using a suitable ionic membrane that regulates ionic flows between the two half-cells. Numerical simulations have validated the proof of concept. The proposed process ...
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Environmentally friendly amino-acid salt solutions are used for the absorption of carbon dioxide from concentrated flue-gas streams via chemical absorption. Process intensification reduces operating and capital costs by combining chemical... more
Environmentally friendly amino-acid salt solutions are used for the absorption of carbon dioxide from concentrated flue-gas streams via chemical absorption. Process intensification reduces operating and capital costs by combining chemical reactions and separation operations. Here, we present a new process-intensification approach that combines the CO2 capture and the amino-acid regeneration steps into a single process carried out in a slurry three-phase reactor. The absorbed CO2 precipitates as a solid carbonated guanidine compound. The cycle is completed by separation of the solid precipitate to strip the CO2 and regenerate the guanidine compound, while the liquid solution is recycled to the slurry reactor. The process was studied by modifying a model developed by the authors for a gas-liquid bubble column without the presence of the guanidine compound. The guanidine precipitation reaction was accounted for using kinetic parameters calculated by the authors in another study. The pr...
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The absorption of carbon dioxide is an important process in many practical applications such as reduction of greenhouse gases, separation and purification processes in the chemical and petroleum industries, and capture of radioactive... more
The absorption of carbon dioxide is an important process in many practical applications such as reduction of greenhouse gases, separation and purification processes in the chemical and petroleum industries, and capture of radioactive isotopes in the nuclear fuel cycle The goal of this research is to develop a dynamic model to simulate CO2 absorption by using different alkanolamines as absorption solvents. The model is based upon transient mass and energy balances for the chemical species commonly present in CO2 gas-liquid absorption. A computer code has been written to implement the proposed model. Simulation results are discussed. The reported model simulates well the response to dynamic changes in input conditions. The proposed model can be used to optimize and control the separation of carbon-14 in the form of CO2 in the nuclear industry.
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Hydrocarbons are the most important source for hydrogen production. A combined reaction-separation process using inorganic membranes can significantly increase the reaction conversion by shifting the equilibrium toward product formation.... more
Hydrocarbons are the most important source for hydrogen production. A combined reaction-separation process using inorganic membranes can significantly increase the reaction conversion by shifting the equilibrium toward product formation. Sulfur poisoning is a significant problem as it deactivates the most commonly used metallic membranes. The relationship of the membrane activity and surface coverage with the surface structure has been recognized in the literature. A theoretical model to simulate hydrogen transport in the presence of sulfur compounds is presented. This model accounts for active site deactivation and permanent structural damage to the membrane. Transport and reaction rate parameters used in the model have been estimated from experimental data. Qualitatively, the model represents well the behavior of inorganic membranes, including partial membrane activity regeneration after the sulfur source is removed.
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ABSTRACT Ion storage in porous electrodes is important in applications such as energy storage by supercapacitors, water purification by capacitive deionization, extraction of energy from a salinity difference and heavy ion purification. A... more
ABSTRACT Ion storage in porous electrodes is important in applications such as energy storage by supercapacitors, water purification by capacitive deionization, extraction of energy from a salinity difference and heavy ion purification. A model is presented to simulate the charge process in homogeneous porous media comprising big pores. It is based on a theory for capacitive charging by ideally polarizable porous electrodes without faradaic reactions or specific adsorption of ions. A volume averaging technique is used to derive the averaged transport equations in the limit of thin electrical double layers. Transport between the electrolyte solution and the charged wall is described using the Gouy–Chapman–Stern model. The effective transport parameters for isotropic porous media are calculated solving the corresponding closure problems. The source terms that appear in the average equations are calculated using numerical computations. An alternative way to deal with the source terms is proposed.
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Con el objetivo final de proponer una tecnología simple para la producción de•chips de mandioca deshidratados, se estudia la transferencia de materia controlada por difusión en el interior de un sólido que varía su volumen durante el... more
Con el objetivo final de proponer una tecnología simple para la producción de•chips de mandioca deshidratados, se estudia la transferencia de materia controlada por difusión en el interior de un sólido que varía su volumen durante el proceso. Se interpretan los resultados experimentales mediante un modelo apropiado, el cual se resuelve empleando el método de las diferencias finitas,obteniéndose un satisfactorio ajuste.
A rnethodology to generate discrete orthogonal rneshes in irregular regions bounded by analytical functions is presented. The technique includes the gene ratio n of the ortogonal grid and allow to obtain the transforrned differential... more
A rnethodology to generate discrete orthogonal rneshes in irregular regions bounded by analytical functions is presented. The technique includes the gene ratio n of the ortogonal grid and allow to obtain the transforrned differential equation in the new dornain. A rnethod to control the grid spacing is al so proposed. This rnethodology is extended to three dirnensions in two special cases.
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The mixing process of fresh water and sea water releases a significant amount of energy and is potentially an enormous source of renewable energy. The so called ‘blue energy’ or salinity gradient energy can be harvested by a device... more
The mixing process of fresh water and sea water releases a significant amount of energy and is potentially an enormous source of renewable energy. The so called ‘blue energy’ or salinity gradient energy can be harvested by a device consisting of carbon electrodes immersed in an electrolyte solution, based on the principle of capacitive double layer expansion (CDLE). In this study, we have investigated the feasibility of energy production based on the CDLE principle. Experiments and computer simulations were used to study the process. Mesoporous carbon materials synthesized at the Oak Ridge National Laboratory (ORNL), were used as electrode materials in our experiments. Neutron imaging of the blue energy cycle was conducted with cylindrical mesoporous carbon electrodes and 0.5 M lithium chloride as the electrolyte solution. For experiments conducted at 0.6 V and 0.9 V applied potential, a voltage increase of 0.061 V and 0.054V was observed respectively. A computer code to simulate th...
Energy obtained by salinity-gradients (blue energy) is a promising renewable energy source. Mixing of a high-concentration saline solution, such as seawater, with fresh water (river water) to produce a brackish solution dissipates more... more
Energy obtained by salinity-gradients (blue energy) is a promising renewable energy source. Mixing of a high-concentration saline solution, such as seawater, with fresh water (river water) to produce a brackish solution dissipates more than 2.2 MJ of free energy per m3 of fresh water. The charging-discharging cycle inside the pores of the solid electrodes is strongly influenced by the pore size distribution. Macroporous materials behave like standard plate capacitors, while mesoporous materials behave like cylindrical capacitors. The goal of this project was to optimize the recovery efficiency of free energy change by using tailored-design carbon electrodes. Morphology, pore size, and carbon electrode composition were chosen to optimize the charge-discharge steps of the reversible cycle. The physicochemical processes inside the electrode and the corresponding effects on the reversible energy cycle were investigated. A proposed energy cycle comprises a charging step, a discharging st...
The mixing process of fresh water and sea water releases a significant amount of energy and is potentially an enormous source of renewable energy. The so called ‘blue energy’ or salinity gradient energy can be harvested by a device... more
The mixing process of fresh water and sea water releases a significant amount of energy and is potentially an enormous source of renewable energy. The so called ‘blue energy’ or salinity gradient energy can be harvested by a device consisting of carbon electrodes immersed in an electrolyte solution, based on the principle of capacitive double layer expansion (CDLE). In this study, we have investigated the feasibility of energy production based on the CDLE principle. Experiments and computer simulations were used to study the process. Mesoporous carbon materials synthesized at the Oak Ridge National Laboratory (ORNL), were used as electrode materials in our experiments. A proposed energy cycle comprises a charging step, a discharging step and two switching steps that replace a saltwater solution inside the pores by a fresh water solution and vice versa. A new model that calculates concentration profiles of individual ions has been derived to model the charging/discharging steps. Ioni...
The removal of CO2 from gaseous streams is a very important industrial technology with applications to mitigate greenhouse gas emissions from flue gases in coal-fired power plants and removal of radioactive C14 in the nuclear industry,... more
The removal of CO2 from gaseous streams is a very important industrial technology with applications to mitigate greenhouse gas emissions from flue gases in coal-fired power plants and removal of radioactive C14 in the nuclear industry, among others. One of the well-known technological alternatives for CO2 capture is absorption/stripping with aqueous solvents, such as alkanolamines and their mixtures. A dynamic model of the absorption process for dilute carbon dioxide mixtures in high alkaline solutions is proposed. Chemical reactions between CO2 and the high pH solution have been included in the model through the use of an enhancement factor for chemical absorption. Interfacial equilibrium constants have been calculated based upon Henry’s constant values for the different gas phase species calculated using fugacity ratios obtained by the Peng-Robinson equation of state. Mass and energy balances have been derived for all the species in vapor and liquid phases. Numerical techniques ha...
Porous electrodes are widely used in electrochemical applications such as, capacity deionization, high density supercapacitors and blue energy storage. Electrodes that present a combination of macro-micropores are sought because of the... more
Porous electrodes are widely used in electrochemical applications such as, capacity deionization, high density supercapacitors and blue energy storage. Electrodes that present a combination of macro-micropores are sought because of the high area available for ion storage. Mesoporous carbon materials have received attention recently due to their high surface area and pore sizes significantly larger than the size of hydrated ions. The volume averaging method has been used to simulate the charge-discharge process in porous materials that present a bimodal pore size distribution. The pore size distribution consists of macroporosity outside the particles through which the ions are transported and microporosity inside the particles, where the electrical double layers form. No assumption is made on the size of the ‘small’ pores; however, they should be significantly smaller than the ‘big’ pores outside. Based on this constraint we can say that ion adsorption will occur only in the small po...
Desalination of high salinity solutions has been studied using a novel experimental technique and a theoretical model. Neutron imaging has been employed to visualize lithium ions in mesoporous carbon materials, which are used as... more
Desalination of high salinity solutions has been studied using a novel experimental technique and a theoretical model. Neutron imaging has been employed to visualize lithium ions in mesoporous carbon materials, which are used as electrodes in capacitive deionization for water desalination. Experiments were conducted with a flow-through capacitive deionization cell designed for neutron imaging and with lithium chloride (6LiCl) as the electrolyte. Sequences of neutron images have been obtained at a relatively high concentration of lithium chloride (6LiCl) solution to provide information on the transport of ions within the electrodes. A new model that computes the individual ionic concentration profiles inside mesoporous carbon electrodes has been used to simulate the capacitive deionization process. The volume averaging method has been used to derive the equations that simulate the charge-discharge process in mesoporous materials. An electroneutrality condition has been derived to rel...
The mixing process of fresh water and seawater releases a significant amount of energy and is potentially an enormous source of renewable energy. The so called ‘blue energy’ or salinity-gradient energy can be harvested by a device... more
The mixing process of fresh water and seawater releases a significant amount of energy and is potentially an enormous source of renewable energy. The so called ‘blue energy’ or salinity-gradient energy can be harvested by a device consisting of carbon electrodes immersed in an electrolyte solution, based on the principle of capacitive double layer expansion (CDLE). In this study, we have investigated the feasibility of energy production based on the CDLE principle. Experiments and computer simulations were used to study the process. Mesoporous carbon materials synthesized at the Oak Ridge National Laboratory (ORNL), were used as electrode materials in our experiments. A proposed energy cycle comprises a charging step, a discharging step and two switching steps that replace a saltwater solution inside the pores by a fresh water solution and vice versa. A new model that calculates concentration profiles of individual ions has been derived to model the charging/discharging steps. Ionic...
The electrical double layer (EDL) formation near a charged surface has significance in electrochemical processes, such as electrosorption of ions and energy storage in supercapacitors. Electrosorption of ions from aqueous solutions is... more
The electrical double layer (EDL) formation near a charged surface has significance in electrochemical processes, such as electrosorption of ions and energy storage in supercapacitors. Electrosorption of ions from aqueous solutions is utilized in the capacitive deionization (CDI) process for water desalination. The main objective of the present work is to study the transport of ions in mesoporous carbon materials during the CDI process and synthesize efficient carbon electrode materials for application in CDI. The electrodes used in this study are made of mesoporous carbon materials of 8-20 nm pore size, which are synthesized at Oak Ridge National Laboratory. Neutron imaging is employed to quantify ion transport in charged mesoporous carbon electrodes. Specifically, neutron imaging is used as a tool to visualize neutron-absorbing ions in carbon electrodes during the CDI process, and image analysis is used to extract the transient concentration profiles of ions. From the time-depende...
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ABSTRACT Journal of Materials Science
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The absorption of carbon dioxide is an important process in many practical applications such as reduction of greenhouse gases, separation and purification processes in the chemical and petroleum industries, and capture of radioactive... more
The absorption of carbon dioxide is an important process in many practical applications such as reduction of greenhouse gases, separation and purification processes in the chemical and petroleum industries, and capture of radioactive isotopes in the nuclear fuel cycle The goal of this research is to develop a dynamic model to simulate CO2 absorption by using different alkanolamines as absorption solvents. The model is based upon transient mass and energy balances for the chemical species commonly present in CO2 gas-liquid absorption. A computer code has been written to implement the proposed model. Simulation results are discussed. The reported model simulates well the response to dynamic changes in input conditions. The proposed model can be used to optimize and control the separation of carbon-14 in the form of CO2 in the nuclear industry.
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The absorption of carbon dioxide is an important process in many practical applications such as reduction of greenhouse gases, separation and purification processes in the chemical and petroleum industries, and capture of radioactive... more
The absorption of carbon dioxide is an important process in many practical applications such as reduction of greenhouse gases, separation and purification processes in the chemical and petroleum industries, and capture of radioactive isotopes in the nuclear fuel cycle The goal of this research is to develop a dynamic model to simulate CO2 absorption by using different alkanolamines as absorption solvents. The model is based upon transient mass and energy balances for the chemical species commonly present in CO2 gas-liquid absorption. A computer code has been written to implement the proposed model. Simulation results are discussed. The reported model simulates well the response to dynamic changes in input conditions. The proposed model can be used to optimize and control the separation of carbon-14 in the form of CO2 in the nuclear industry.