Engelhard titanium silicate, ETS-4, is a promising new adsorbent for size-selective separation of mixtures of small gases, a leading industrially important example of which is methane-nitrogen separation. Single component equilibrium and kinetics of oxygen, nitrogen, and methane adsorption in Na-ETS-4 and cation-exchanged Sr-ETS-4, measured in an earlier study over a wide range of temperatures and pressures, are analyzed in this study. The adsorbent crystals were synthesized and pelletized under pressure (without any binder), thus giving rise to a bidispersed pore structure with controlling resistance in the micropores. Change in equilibrium and kinetics of adsorption of the aforementioned gases in Sr-ETS-4 due to pore shrinkage with progressively increasing dehydration temperature has also been investigated. Differential uptakes have been measured at various levels of adsorbate loading, which has allowed the elucidation of the nature of concentration dependence of micropore diffusivity. Both homogeneous and heterogeneous models are examined on the equilibrium data, while a bidispersed pore diffusion model is able to capture the differential uptakes very well. On the basis of chemical potential gradient as the driving force for diffusion, the impact of isotherm models on the concentration dependence of micropore diffusivity is also analyzed. It is shown that pore tailoring at the molecular scale by dehydration can improve the kinetic selectivity of nitrogen over methane in Sr-ETS-4 to a promising level. The models investigated are evaluated to identify essential details necessary to reliably simulate a methane-nitrogen separation process using the promising new Sr-ETS-4 adsorbent.
Efficient CO2 capture onboard ships is a vital step in mitigating maritime emissions. In our previous work, we showed that amine-based absorption is the best prospect for onboard capture, and ships powered by LNG are better suited than those using HFO. Hence, in this work, an extensive design for amine-based absorption onboard LNG-run ships with different flue gas conditions (flow rate, temperature, and composition) as well as maximum CO2 storage capacity and number of days at sea is presented. The design comprises discussions on the selection of key variables for separation, e.g., the dimensions of the absorber and regenerator column and solvent flow rate, as well as the selection of optimal CO2 storage conditions. Additionally, the best configuration for cold energy integration to minimize the extra power demand for the CO2 compression is also assessed. The design is based on 90% recovery of CO2 from the total flue gas to be processed, including emissions stemming from extra fuel burned to fulfill the energy deficit for solvent regeneration and the power demand for CO2 compression. To this end, a novel noniterative approach to calculate total flue gas to be processed as a function of the flue gas conditions under optimized design conditions is also developed. Lastly, cargo losses from the installation of the capture unit are also presented. In summary, the study intends to provide ship owners with a comprehensive design guide for the installation of an amine-based absorption unit. To illustrate the utility of the study, case studies are presented using reference ships available in the literature.
A dual resistance model with distribution of either barrier or pore diffusional activation energy is proposed in this work for gas transport in carbon molecular sieve (CMS) micropores. This is a novel approach in which the equilibrium is homogeneous, but the kinetics is heterogeneous. The model seems to provide a possible explanation for the concentration dependence of the thermodynamically corrected barrier and pore diffusion coefficients observed in previous studies from this laboratory on gas diffusion in CMS. The energy distribution is assumed to follow the gamma distribution function. It is shown that the energy distribution model can fully capture the behavior described by the empirical model established in earlier studies to account for the concentration dependence of thermodynamically corrected barrier and pore diffusion coefficients. A methodology is proposed for extracting energy distribution parameters, and it is further shown that the extracted energy distribution parameters can effectively predict integral uptake and column breakthrough profiles over a wide range of operating pressures.
Perovskite samples of the general formula La0.1A0.9CoyFe1-yO3-δ (where A = Ca, Sr, Ba; y = 0.1, 0.5, 0.9) were synthesized in our laboratory. Further substitution of Sr to a small extent by Ag and complete substitution of La by Sr were also studied. For a fixed perovskite composition (SrCo0.5Fe0.5O3-δ), samples obtained by carbonate coprecipitation and citrate methods of synthesis were compared. Use of helium as the carrier gas produced more weight loss (i.e., higher oxygen vacancy) than nitrogen in all the perovskite samples. Oxygen sorption equilibrium and sorption kinetics were thermogravimetrically studied in the temperature range 500−800 °C at atmospheric pressure using oxygen−nitrogen mixtures in which the oxygen fraction ranged from ∼5 to 50%. Desorption kinetics were studied by allowing the equilibrated sample to desorb in pure nitrogen. For a fixed B-site substitution, oxygen capacity varied with A-site substitution in the order Sr > Ba > Ca. Considering both equilibrium capacity and sorption−desorption kinetics, SrCo0.5Fe0.5O3-δ and La0.1Sr0.8Ag0.1Co0.5Fe0.9O3-δ were found to be the more promising candidates for further investigation.
A new method for extracting discrete equilibrium data from a set of dynamic column breakthrough experiments is described. Instead of the classical approach where an isotherm model, i.e., a function, is used to describe the equilibrium, this approach represents the isotherm as a set of discrete points. For a given set of discrete fluid phase concentrations, an optimization method is used to determine the corresponding solid loadings that lead to the best-fit prediction of the experimental breakthrough profile. In this work, we develop the algorithm and validate it using single-component case studies, for a variety of isotherm shapes. The practical use of the method is demonstrated by applying it to experimentally measured breakthrough profiles taken from the literature.
Separation of propylene/propane mixture with new 8-ring zeolite, pure silica chabazite (SiCHA), has been studied in this work. Since the diffusion of propane molecules in SiCHA is extremely slow, thus equilibrium information for propane has been indirectly estimated using available uptake data at 80 °C and 600 Torr. Moreover, molecular simulation has been used to obtain equilibrium information of propylene and propane and verify our estimation. The ideal kinetic selectivity of propylene/propane mixture is ∼28 at 80 °C, which increases with decreasing temperature. A four-step, kinetically controlled pressure swing adsorption process has been suggested for this separation and studied in detail using a nonisothermal micropore diffusion model, developed and verified in an earlier study. In this model, Langmuir isotherm represents adsorption equilibrium and micropore diffusivity depends on adsorbate concentration in the micropores, according to chemical potential gradient as the driving force for diffusion.
Many cities have extensive distribution networks that supply natural or town gas to domestic, industrial, and power plant consumers. A typical network may have hundreds of pressure regulating stations that are of different types and capacities, but most legacy networks are sparsely instrumented. The reliability of these stations is the first priority for ensuring uninterrupted gas supplies; hence, condition monitoring and prescriptive maintenance are critical. In this study, mathematical models were developed for two types of commonly used regulators: spring-loaded and lever-type regulators. We also considered three faults that are typically of interest: filter choking, valve seat damage, and diaphragm deterioration. The proposed methodologies used the available measured data and mathematical models to diagnose faults, track prognoses, and estimate the remaining useful life of the regulators. The applicability of our proposed methodologies was demonstrated using real data from an existing distribution network. To facilitate industrial use, the methodologies were packaged into a user-friendly dashboard that could act as an interface with the operational database and display the health status of the regulators.
'/%3e%3cuse xlink:href='%23a' transform='translate(288.889 -214.211)'/%3e%3cuse xlink:href='%23a' transform='translate(108 342.749)'/%3e%3cuse xlink:href='%23a' transform='translate(469.189 342.749)'/%3e%3c/svg%3e)
'/%3e%3c/defs%3e%3cpath fill='%23012169' d='M0 0h10080v5040H0z'/%3e%3cpath stroke='%23fff' stroke-width='.6' d='m0 0 6 3m0-3L0 3' clip-path='url(%23b)' transform='scale(840)'/%3e%3cpath stroke='%23e4002b' stroke-width='.4' d='m0 0 6 3m0-3L0 3' clip-path='url(%23c)' transform='scale(840)'/%3e%3cpath stroke='%23fff' stroke-width='840' d='M2520 0v2520M0 1260h5040'/%3e%3cpath stroke='%23e4002b' stroke-width='504' d='M2520 0v2520M0 1260h5040'/%3e%3cg fill='%23fff'%3e%3cuse xlink:href='%23d' x='2520' y='3780'/%3e%3cuse xlink:href='%23a' x='7560' y='4200'/%3e%3cuse xlink:href='%23a' x='6300' y='2205'/%3e%3cuse xlink:href='%23a' x='7560' y='840'/%3e%3cuse xlink:href='%23a' x='8680' y='1869'/%3e%3cuse xlink:href='%23e' x='8064' y='2730'/%3e%3c/g%3e%3c/svg%3e)
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)
