Adsorption equilibrium of carbon dioxide on zeolite 13X at high pressures

High-pressure adsorption of methane, carbon dioxide, and nitrogen on zeolite 13X was measured in the pressure range (0 to 5) MPa at (298, 308, and 323) K and fitted with the Toth and multisite Langmuir models. Isosteric heats of adsorption were (12.8, 15.3, and 37.2) kJ/mol for nitrogen, methane, and carbon dioxide respectively, which indicate a very strong adsorption of carbon dioxide. The preferential adsorption capacity of CO2 on zeolite 13X was much higher than for the other gases, indicating that zeolite 13X can be used for methane purification from natural gas or for carbon dioxide sequestration from flue gas.

Performance evaluation of clinoptilolite and 13X zeolites in CO2 separation from CO2/CH4 mixture

Adsorption equilibrium for sulfur dioxide, nitric oxide, carbon dioxide, nitrogen on 13X and 5A zeolites

Propylene and propane single-adsorption equilibrium isotherms and mass-transfer kinetics over 13X and 4A zeolite pellets have been investigated using gravimetry and zero length column techniques, respectively. The 13X zeolite shows a higher loading capacity and lower mass-transfer resistance while 4A zeolite shows the highest selectivity for propylene. The experimental adsorption equilibrium isotherms were adjusted with the Toth isotherm. Kinetic studies indicate that macropore diffusion controls the mass transfer inside 13X zeolite pellets while micropore diffusion controls the propylene adsorption on 4A zeolite pellets.

In the current study, the effect of modified zeolite using (3-aminopropyl) triethoxysilane in polybutylene succinate (PBS) and polylactic acid (PLA) blend was investigated. Two types of modified zeolite i.e., zeolite 5A and 13X at 3wt% of polymer blend between PBS and PLA were mixed together in twin-screw extruder and thin-films were produced by cast-film extruder. The thickness of each film is between 50 – 70 micron. Mechanical properties, thermal properties, morphological properties and permeability of oxygen, carbon dioxide as well as water vapour were investigated. Adding of zeolite 5A into PBS/PLA blend was found to increase more tensile strength and Young’s moduluswith the comparison to zeolite 13X whereas the zeolite 13X and 5A had increased the percentage of elongation at break more than PBS/PLA blend. The zeolite 5A and 13X tended to increase the thermal stability of the composite films. Gas permeation results showed that PBS/PLA with zeolite 5A allowed the permeation of carbon dioxide and oxygen more than 13X in composite films. Moreover, water vapour transmissionrate of PBS/PLA with zeolite 5A was higher than the one with zeolite 13X.

Adsorption isotherms are reported for pure carbon dioxide and water vapor on 5A and 13X zeolite beads and silica gel granules. These data were obtained using a volumetric method and cover the temperature ranges of (−45 to 175) °C for carbon dioxide and (0 to 100) °C for water. Also, pure carbon dioxide isotherms on silica gel at temperatures from (10 to 55) °C were measured using a gravimetric apparatus. All pure component equilibria are described well by Toth isotherms with parameters having temperature dependence. For carbon dioxide adsorption, zeolites 5A and 13X have similar loadings and show a much higher capacity than silica gel. However, for water vapor, zeolite 13X has a slightly higher capacity than zeolite 5A. Both zeolites have very good adsorption capacities for water vapor at low pressures but lose their advantages to silica gel when water pressures are high.

Experimental measurements and modeling of supercritical CO2 adsorption on 13X and 5A zeolites

The utilization of adsorption processes operating at low temperatures can be interesting in the context of production of liquefied natural gas (LNG), where they can constitute a lower energy alternative as hybrid technologies with cryogenic distillation. This paper provides the necessary parameters to design an adsorption process for selective removal of CO2 from methane at low temperatures to satisfy LNG specifications, with particular emphasis on a temperature swing adsorption (TSA) process. Adsorption equilibrium of CH4 and CO2 on commercial zeolite 4A and zeolite 13X is reported at cryogenic temperatures: 198, 208, 223, 248, and 279 K. Carbon dioxide is much more adsorbed than methane, and CO2 isotherms are extremely steep at low temperatures. In the studied low-temperature range, it was observed that zeolite 4A has a very different behavior toward CH4 and CO2; adsorption of methane is entirely controlled by diffusion (kinetic control), while adsorption of CO2 is mostly controlled by the shape of the isotherm (equilibrium control). Adsorption breakthrough curves of a mixture of 1.5% CO2 and 98.5% CH4 were measured in the zeolite 4A adsorbent at 204 K to identify transport phenomena at such low temperatures and verify if adsorption equilibrium can be described on the basis of pure component data. Experiments were performed at different total pressures (1 and 10 bar) and different flow rates.

The excess adsorption of CO2 on 13X zeolite and of N2O on silica gel has been studied at high pressure using a magnetic suspension balance, i.e. a gravimetric method. Recently, a detailed study on the density distribution in the measuring cell of the magnetic suspension balance showed that a proper approach to thermostatting the unit should be used in order to obtain reliable and accurate excess adsorption measurements. This is particularly important in the vicinity of the critical point of the fluid, where the density is strongly dependent on pressure and temperature. In the past, several effects were observed in our laboratory when measuring near-critical adsorption on 13X zeolite and on silica gel, namely critical adsorption and critical depletion. In the present study, these effects have been checked using the balance in the new thermostatting configuration, and the conclusion can be drawn that the accuracy of the measurement is not sufficient to prove that they indeed occur. More accurate adsorption data for the two systems have been measured and reported.

All in an engineer’s life

Zeolites have long been considered as excellent candidate materials for gas separation and purification. Most of the worldwide industrial adsorption applications of molecular sieve zeolites utilize zeolites X, A and Y. Chabazite zeolite however, has pore dimensions between those for zeolites X, A and Y and hence has promising separation features for specific application but has not been utilized in any major industrial separation or purification applications to date. Some early work on alkali-exchanged chabazites revealed a diminished porosity and surface area due to pore blockage. This initial work was based on limited experimental data and preliminary analytical techniques and analysis. As a result, this initial pessimistic assessment of the merits of chabazite zeolite has led to a loss of interest in this material for adsorption applications. In this study, a pure phase chabazite was synthesized and ion-exchanged to produce potassium chabazite (KCHA), sodium chabazite (NaCHA) and lithium chabazite (LiCHA). Attempts were successful to produce a fully exchanged potassium chabazite, which is a unique product that has not been reported in the literature to date. The adsorption of nitrogen and carbon dioxide was studied since these gases are component of flue gas and the application to which chabazites were to be directed was CO2 capture form flue gas. Adsorption equilibrium isotherms for CO2 and N2 were measured at pressures up to 101.3 kPa and temperatures of 273, 303 and 333 K. More importantly, this work focused on determining fundamental properties of adsorbate-adsorbent interactions which require low pressure measurements hence low pressure isotherms, down to 0.001 kPa, were measured. These data provide valuable information to study the adsorption behavior in the Henry’s law region. The results showed that porosity characterization of KCHA using the conventional approach of nitrogen at 77 K reveals a surface area of only 17.82 m2 g-1 and a diminished pore volume (by density functional calculation) of 0.005 cm3 g-1, compared to 584.4 m2 g-1 and 0.214 cm3 g-1 using carbon dioxide at 273 K, respectively, calculated from the revised Toth model and CO2 isotherm data at 273K. These findings strongly suggested that KCHA is a highly porous adsorbent, in spite of the large size of K+ ions which block access of the N2 molecules to the pore space. It is concluded that traditional methods of characterization are not suitable in the case of pore blockage leading to incorrect interpretation of adsorbent properties. It was initially hypothesized that carbon dioxide molecules enjoy large freedom within the zeolite pores, however, virial plots developed from equilibrium isotherms showed anomalous behavior for carbon dioxide adsorption at 273 K on NaCHA and KCHA at loadings lower than 1.5 gmole kg-1, which correspond to pressure of about 0.15 kPa. This suggested that carbon dioxide molecules were not at true equilibrium condition, but rather were subject to steric hindrance due to partial pore blockage. Adsorbed phase densities calculated from van der Waals constants confirmed the pore blockage phenomenon on KCHA, however, it also reveals a slight blockage against nitrogen molecules on NaCHA. On the synthesized chabazites, carbon dioxide affinities and heats of adsorption were considerably higher than those for nitrogen for which their adsorption equilibria differ significantly due to screening against nitrogen molecules in KCHA and partially in NaCHA. Carbon dioxide entropy measurement revealed a concave trend, demonstrating an appreciable loss of degrees of freedom within increase in loading. Carbon dioxide desorption isotherms showed low pressure hysteresis at 273 K with residuals of 0.37 and 0.57 molecule cavity-1 on NaCHA and KCHA, respectively, at pressures lower than 0.05 kPa. This outcome confirmed the pore blockage occurrence suggesting a low pressure encapsulation. The combined use of the statistical theory of the radial distribution function (rdf) and the theory of the perfect 3D lattice gas to describe the encapsulation process underestimated the number of accommodated molecules compared to the experimental results. The individual implementation of Lennard-Jones and quadrupolar potentials to describe the adsorbate-adsorbate and adsorbate-host interactions, respectively, affected the performance of the models.

Separation of [formula omitted] mixtures by layered pressure swing adsorption for upgrade of natural gas

Adsorption of [formula omitted] from dry gases on MCM-41 silica at ambient temperature and high pressure. 1: Pure [formula omitted] adsorption

Hypercrosslinked polymers (HCPs) synthesized by copolymerisation of p-dichloroxylene (p-DCX) and 4,4′-bis(chloromethyl)-1,1′-biphenyl (BCMBP) constitute a family of low density porous materials with excellent textural development. Such polymers show microporosity and mesoporosity and exhibit Brunauer–Emmett–Teller (BET) surface areas of up to 1970 m2 g−1. The CO2 adsorption capacity of these polymers was evaluated using a thermogravimetric analyser (atmospheric pressure tests) and a high-pressure magnetic suspension balance (high pressure tests). CO2 capture capacities were related to the textural properties of the HCPs. The performance of these materials to adsorb CO2 at atmospheric pressure was characterized by maximum CO2 uptakes of 1.7 mmol g−1 (7.4 wt%) at 298 K. At higher pressures (30 bar), the polymers show CO2 uptakes of up to 13.4 mmol g−1 (59 wt%), superior to zeolite-based materials (zeolite 13X, zeolite NaX) and commercial activated carbons (BPL, Norit R). In addition, these polymers showed low isosteric heats of CO2 adsorption and good selectivity towards CO2. Hypercrosslinked polymers have potential to be applied as CO2 adsorbents in pre-combustion capture processes where high CO2 partial pressures are involved.

In this research, the biodegradable film of poly (butylene adipate-co-terephthalate) (PBAT) would be used as the polymer matrix. The influence of zeolite (as the filler) type and content were investigated on the mechanical and barrier properties of film packaging. Zeolite was treated with (3-aminopropyl) trimethoxy silane. Films were produced by cast film extruder. Effects of different types of zeolite (5A and 13X) as well as zeolite loading (1-5 wt%) on mechanical properties and permeability of gases (oxygen, carbon dioxide and water vapor) of PBAT composites films have been extensively studied. Tensile properties of PBAT incorporated with zelolite 5A are higher than the one with zeolite 13X. In addition, increasing zeolite content into PBAT film is likely to improve Young’s modulus with the sacrifices of both tensile strength and percentage of elongation at break of PBAT film. For barrier properties, PBAT/zeolite 5A possessed lower permeation both of oxygen and carbon dioxide gases than PBAT/zeolite 13X. The effect of zeolite content plays a major role on oxygen and carbon dioxide permeability of composite films. PBAT/zeolite composite film could certainly extend the ripening period of Homthong bananas for approximately longer than one week.