Experimental Investigation of Sorbent for Warm CO₂ Capture by Pressure Swing Adsorption

A new sorbent for warm CO₂ capture containing magnesium oxide was developed using incipient wetness impregnation. The reversible adsorption isotherm, cyclic stability, and sorption rate were measured using a custom-built high-pressure microbalance system and a thermogravimetric analyzer. The experimental data indicate that the sorbent has a fairly large regenerable capacity in the 180–240 °C temperature range, fast kinetics, low heat of adsorption, and stable working capacity for at least 84 cycles. The new sorbent performs better than synthetic hydrotalcite and K₂CO₃-promoted hydrotalcite in the temperature range of interest. This makes the sorbent a very promising candidate material for warm CO₂ capture by pressure swing adsorption

Analysis of Adsorbent-Based Warm CO₂ Capture Technology for Integrated Gasification Combined Cycle (IGCC) Power Plants

Integrated gasification combined cycle with CO₂ capture and sequestration (IGCC–CCS) emerges as a promising method for reducing emission of greenhouse gases from coal without reducing efficiency significantly. However, the high capital costs of these plants have limited their deployment. The current solvent-based low-temperature CO₂ capture process is energy and capital intensive contributing to the problem. Warm CO₂ capture has been predicted to be a key enabling technology for IGCC–CCS. Here, we assessed the applicability of CO₂ removal technology to IGCC via a warm pressure swing adsorption (PSA) process based on our newly invented sorbent, which has good cyclic sorption–desorption performance at an elevated temperature. A 16-step warm PSA process was simulated using Aspen Adsorption based on the real sorbent properties. We used the model to fully explore the intercorrelation between hydrogen recovery, CO₂ capture percentage, regeneration pressure of sorbent, and steam requirement. Their trade-off effects on IGCC efficiency were investigated by integrating the PSA process into the plant-wide IGCC simulation using Aspen Plus. On the basis of our analysis, IGCC-warm PSA using our new sorbent can produce similar thermal efficiencies to IGCC-cold Selexol. In order to achieve this, warm PSA needs a narrow range of process parameters to have a good balance between the hydrogen loss, steam consumption and work requirement for CO₂ compression. This paper provides a rigorous analysis framework for assessing the feasibility of warm CO₂ capture by sorbents in an IGCC system

Correction to “Analysis of Membrane and Adsorbent Processes for Warm Syngas Cleanup in Integrated Gasification Combined-Cycle Power with CO₂ Capture and Sequestration”

Correction to “Analysis of Membrane and Adsorbent Processes for Warm Syngas Cleanup in Integrated Gasification Combined-Cycle Power with CO₂ Capture and Sequestration

Analysis of Hydroxide Sorbents for CO₂ Capture from Warm Syngas

Integrated gasification combined cycle (IGCC) with CO₂ capture and sequestration (CCS) is a promising technology to efficiently mitigate the emission of CO₂. Warm CO₂ removal has been predicted to make the CO₂ capture process more efficient. Here, we investigate the efficiency penalties associated with CO₂ removal via a pressure swing adsorption (PSA) process using metal hydroxide sorbents at elevated temperature. We use numerical models constructed in MATLAB and integrate these with Aspen Plus process simulations. We apply these models to both general metal hydroxides of variable enthalpy of adsorption and real metal hydroxides identified using density functional theory (DFT) calculations. We show that having an enthalpy of adsorption between 15 and 20 kJ/mol results in a PSA process that gives an overall IGCC–CCS efficiency that is competitive with the conventional IGCC–CCS process using (cold) Selexol. An enthalpy of adsorption of 20 kJ/mol is predicted to be the most favorable because it yielded a promising combination of HHV efficiency and higher working capacity. In addition, we identify Fe­(OH)₂, Co­(OH)₂, Ni­(OH)₂, and Zn­(OH)₂ as potentially favorable real materials, with IGCC–CCS efficiencies predicted to be within 1% HHV of that of Selexol

Role of O₂ + QOOH in Low-Temperature Ignition of Propane. 1. Temperature and Pressure Dependent Rate Coefficients

The kinetics of the reaction of molecular oxygen with hydroperoxyalkyl radicals have been studied theoretically. These reactions, often referred to as second O₂ addition, or O₂ + QOOH reactions, are believed to be responsible for low-temperature chain branching in hydrocarbon oxidation. The O₂ + propyl system was chosen as a model system. High-level ab initio calculations of the C₃H₇O₂ and C₃H₇O₄ potential energy surfaces are coupled with RRKM master equation methods to compute the temperature and pressure dependence of the rate coefficients. Variable reaction coordinate transition-state theory is used to characterize the barrierless transition states for the O₂ + QOOH addition reactions as well as subsequent C₃H₆O₃ dissociation reactions. A simple kinetic mechanism is developed to illustrate the conditions under which the second O₂ addition increases the number of radicals. The sequential reactions O₂ + QOOH → OOQOOH → OH + keto-hydroperoxide → OH + OH + oxy-radical and the corresponding formally direct (or well skipping) reaction O₂ + QOOH → OH + OH + oxy-radical increase the total number of radicals. Chain branching through this reaction is maximized in the temperature range 600–900 K for pressures between 0.1 and 10 atm. The results confirm that <i>n</i>-propyl is the smallest alkyl radical to exhibit the low-temperature combustion properties of larger alkyl radicals, but <i>n</i>-butyl is perhaps a truer combustion archetype

Role of O₂ + QOOH in Low-Temperature Ignition of Propane. 1. Temperature and Pressure Dependent Rate Coefficients

The kinetics of the reaction of molecular oxygen with hydroperoxyalkyl radicals have been studied theoretically. These reactions, often referred to as second O₂ addition, or O₂ + QOOH reactions, are believed to be responsible for low-temperature chain branching in hydrocarbon oxidation. The O₂ + propyl system was chosen as a model system. High-level ab initio calculations of the C₃H₇O₂ and C₃H₇O₄ potential energy surfaces are coupled with RRKM master equation methods to compute the temperature and pressure dependence of the rate coefficients. Variable reaction coordinate transition-state theory is used to characterize the barrierless transition states for the O₂ + QOOH addition reactions as well as subsequent C₃H₆O₃ dissociation reactions. A simple kinetic mechanism is developed to illustrate the conditions under which the second O₂ addition increases the number of radicals. The sequential reactions O₂ + QOOH → OOQOOH → OH + keto-hydroperoxide → OH + OH + oxy-radical and the corresponding formally direct (or well skipping) reaction O₂ + QOOH → OH + OH + oxy-radical increase the total number of radicals. Chain branching through this reaction is maximized in the temperature range 600–900 K for pressures between 0.1 and 10 atm. The results confirm that <i>n</i>-propyl is the smallest alkyl radical to exhibit the low-temperature combustion properties of larger alkyl radicals, but <i>n</i>-butyl is perhaps a truer combustion archetype

Chemistry of Alkylaromatics Reconsidered

To investigate upgrading crude oil, alkylaromatic compounds are often chosen as model compounds to better understand their reactivity. In recent kinetic models of this chemistry, the main reaction consuming the alkylaromatic is a four-membered ring “retro-ene” reaction. Here, the transition state of that reaction is discovered to be inconsistent with six-membered ring retroene reactions reported in the literature, leading to inaccurate conclusions. A new detailed kinetic model is constructed using Reaction Mechanism Generator (RMG), and thermodynamic parameters of key compounds and radicals are identified to limit model accuracy. Thermochemistry for key species in the chemistry of hexylbenzene, including hexylbenzene, alkylbenzenes, alkylbenzene radicals, aliphatic radicals, and styrene, was calculated using the CBS-QB3 quantum chemistry method to improve the accuracy of the hexylbenzene pyrolysis model. The kinetics of a key beta scission reaction were also calculated. The results of these calculations have led to an overall improvement in hexylbenzene pyrolysis model predictions

Database of Small Molecule Thermochemistry for Combustion

High-accuracy ab initio thermochemistry is presented for 219 small molecules relevant in combustion chemistry, including many radical, biradical, and triplet species. These values are critical for accurate kinetic modeling. The RQCISD­(T)/cc-PV∞QZ//B3LYP/6-311++G­(d,p) method was used to compute the electronic energies. A bond additivity correction for this method has been developed to remove systematic errors in the enthalpy calculations, using the Active Thermochemical Tables as reference values. On the basis of comparison with the benchmark data, the 3σ uncertainty in the standard-state heat of formation is 0.9 kcal/mol, or within chemical accuracy. An uncertainty analysis is presented for the entropy and heat capacity. In many cases, the present values are the most accurate and comprehensive numbers available. The present work is compared to several published databases. In some cases, there are large discrepancies and errors in published databases; the present work helps to resolve these problems

Role of O₂ + QOOH in Low-Temperature Ignition of Propane. 1. Temperature and Pressure Dependent Rate Coefficients

The kinetics of the reaction of molecular oxygen with hydroperoxyalkyl radicals have been studied theoretically. These reactions, often referred to as second O₂ addition, or O₂ + QOOH reactions, are believed to be responsible for low-temperature chain branching in hydrocarbon oxidation. The O₂ + propyl system was chosen as a model system. High-level ab initio calculations of the C₃H₇O₂ and C₃H₇O₄ potential energy surfaces are coupled with RRKM master equation methods to compute the temperature and pressure dependence of the rate coefficients. Variable reaction coordinate transition-state theory is used to characterize the barrierless transition states for the O₂ + QOOH addition reactions as well as subsequent C₃H₆O₃ dissociation reactions. A simple kinetic mechanism is developed to illustrate the conditions under which the second O₂ addition increases the number of radicals. The sequential reactions O₂ + QOOH → OOQOOH → OH + keto-hydroperoxide → OH + OH + oxy-radical and the corresponding formally direct (or well skipping) reaction O₂ + QOOH → OH + OH + oxy-radical increase the total number of radicals. Chain branching through this reaction is maximized in the temperature range 600–900 K for pressures between 0.1 and 10 atm. The results confirm that <i>n</i>-propyl is the smallest alkyl radical to exhibit the low-temperature combustion properties of larger alkyl radicals, but <i>n</i>-butyl is perhaps a truer combustion archetype

Role of O₂ + QOOH in Low-Temperature Ignition of Propane. 1. Temperature and Pressure Dependent Rate Coefficients

The kinetics of the reaction of molecular oxygen with hydroperoxyalkyl radicals have been studied theoretically. These reactions, often referred to as second O₂ addition, or O₂ + QOOH reactions, are believed to be responsible for low-temperature chain branching in hydrocarbon oxidation. The O₂ + propyl system was chosen as a model system. High-level ab initio calculations of the C₃H₇O₂ and C₃H₇O₄ potential energy surfaces are coupled with RRKM master equation methods to compute the temperature and pressure dependence of the rate coefficients. Variable reaction coordinate transition-state theory is used to characterize the barrierless transition states for the O₂ + QOOH addition reactions as well as subsequent C₃H₆O₃ dissociation reactions. A simple kinetic mechanism is developed to illustrate the conditions under which the second O₂ addition increases the number of radicals. The sequential reactions O₂ + QOOH → OOQOOH → OH + keto-hydroperoxide → OH + OH + oxy-radical and the corresponding formally direct (or well skipping) reaction O₂ + QOOH → OH + OH + oxy-radical increase the total number of radicals. Chain branching through this reaction is maximized in the temperature range 600–900 K for pressures between 0.1 and 10 atm. The results confirm that <i>n</i>-propyl is the smallest alkyl radical to exhibit the low-temperature combustion properties of larger alkyl radicals, but <i>n</i>-butyl is perhaps a truer combustion archetype