Near-critical adsorption of CO2 on 13X zeolite and N2O on silica gel: lack of evidence of critical phenomena

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

The adsorption isotherms of nitrous oxide (N2O) on zeolite 5A, 13X, activated carbon, ZSM-5, and silica gel were investigated by a static volumetric method. The pressure and temperature by measurement of adsorption isotherms ranged from 0 to 1 MPa and 298 to 358 K, respectively. In terms of the adsorption amount, zeolite 13X has the highest adsorption capacity at high pressure (>0.7 MPa), while activated carbon has the best performance at low pressure (<0.1 MPa). The Langmuir, Langmuir–Freundlich, and Toth models were employed to describe the isotherm data, and the Langmuir–Freundlich model showed the best correlation with experimental isotherm data on all adsorbents. In addition, the temperature-dependent Langmuir–Freundlich model was used to fit the N2O adsorption data on all adsorbents. The isosteric heats of N2O on all five adsorbents were calculated. The heat of N2O adsorption on 5A was up to 51.1 kJ/mol, which was the highest compared to 13X, activated carbon, ZSM-5, and silica gel.

Enhanced coalbed methane recovery (ECBM) increases the recovery of the methane present in a coal seam by injecting CO2 at high pressure. It is attractive from two perspectives, the valuable methane recovered and the storage of the greenhouse gas CO2 for geological times. In the framework of a feasibility study for the Sulcis Coal Province in Italy, the adsorption of pure CO2 and CH4 on dry coal has been measured at 45 and 60°C, using a magnetic suspension balance with in situ density measurement. The results show that the CO2 adsorption isotherms on coal are similar to those for other standard adsorbents such as silica gel and activated carbon. From the excess adsorption isotherms, the absolute adsorption is calculated using the assumption of constant volume of the adsorbed phase. As expected, CO2 get adsorbed more than CH4 in all cases. The Sulcis coal can uptake CO2 at the reservoir conditions in an amount of about 10% of its mass. © 2006 American Institute of Chemical Engineers Environ Prog, 2006

Interpretation of net and excess adsorption isotherms in microporous adsorbents

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

Due to the industrialization, it is urgent to reduce the carbon dioxide emissions. For that, diverse technologies can be applied. In adsorption processes, the development of new materials is an emerging challenge in order to increase the CO2 adsorption capacity of materials and the efficiency of the processes. In this work, a new hybrid honeycomb monolith composed by zeolite and activated carbon was produced by extrusion process. Single adsorption equilibrium isotherms of carbon dioxide and nitrogen were measured by a gravimetric method using a Rubotherm® magnetic suspension balance at three temperatures, 303, 333 and 373 K. The experimental points were well described by Dual-Site Langmuir model. The material presented a carbon dioxide adsorption capacity of 2.63 mol kg−1 at 1 bar and 303 K. Binary breakthrough curves were obtained at 298 K and 2.4 bar with different feed mixtures. The experimental results of adsorption equilibrium were validated with the Dual-Site Langmuir isotherm extended to multicomponent mixtures. A mathematical model was applied to predict the dynamic behaviour of the adsorption bed.

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.

The densities of two polymer/CO2 single‐phase solutions, poly(ethylene glycol) (PEG)/CO2 and polyethylene (PE)/CO2, were measured at temperatures higher than melting temperature of the polymer under CO2 pressures in the range 0–15 MPa using a newly‐proposed gravimetric method. A magnetic suspension balance (MSB) was used for the density measurement under the high pressure CO2: A thin disc‐shaped platinum plate was submerged in the considered polymer/CO2 single‐phase solution in the MSB high‐pressure cell. The weight of the plate was measured while keeping CO2 pressure and temperature in the sorption cell at a specified level. Since the buoyancy force exerted on the plate by the polymer/CO2 solution reduced the apparent weight of the plate, the density of the polymer/CO2 solution could be calculated by subtracting the true weight of the plate from its measured weight. Experimental results showed that the density of PE/CO2 solution increased with the increase of CO2 pressure and the density of PEG/CO2 solution decreased with the increase of CO2 pressure. To differentiate the effect of CO2 dissolution in polymer from that of mechanical pressure, the density of polymer/CO2 solution was compared with the density of neat polymer under the given mechanical pressure, which was calculated using the Sanchez–Lacombe equation of state and Pressure–Volume–Temperature data of the polymer. The comparison could elucidate that the dissolution of CO2 in polymer reduced density of both PEG/CO2 and PE/CO2 systems but the degree of CO2 induced‐density reduction was different between two polymer/CO2 systems. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

The capture of CO2 under high pressure and temperature is challenging and is required in a number for industrial applications including natural gas processing. In this work, we examine the use of benchmark hybrid ultraporous materials HUMs for their potential use in CO2 adsorption processes under high-pressure conditions, with three varying temperatures (283, 298 and 318 K). NbOFFOVE-1-Ni and SIFSIX-3-Ni were the selected HUMs given their established superior CO2 capacity under low pressure (0–1 bar). Both are microporous with highly ordered crystalline structures as compared to the mesoporous hexagonal silica (Santa Barbara Anhydrous-15 (SBA-15)). SBA-15 was previously tested for both low and high-pressure applications and can serve as a benchmark in this study. Sorbent characterization using XRD, SEM, FTIR and N2 adsorption were conducted to assure the purity and structure of the sorbents. TGA analysis were conducted to establish the thermal stability of the sorbents under various temperatures. High-pressure CO2 adsorption was conducted from 0–35 bar using magnetic suspension balance (Rubotherm). Although the SBA-15 had the highest surface (527 m3/g) are of the three adsorbents, the CO2 adsorption capacity (0.42 mmol/g) was an order of magnitude less than the studies HUMs with SIFSIX-3-Ni having 2.6 mmol/g, NbOFFIVE-1-Ni achieving 2.5 mmol/g at 298 K. Multistage adsorption isotherms were obtained at different pressures. In addition, results indicate that electrostatics in HUMs are most effective at improving isosteric heat of adsorption Qst and CO2 uptake. Higher temperatures had negative effect on adsorption capacity for the HUMs and SBA-15 at pressures between 7–9 bar. In SAB-15 the effect of temperature is reversed in what is known as a cross over phenomena.

Analysis of gas dehydration in TSA system with multi-layered bed of solid adsorbents

Carbon dioxide (CO2) capture is a widely studied topic, with carbon capture and storage (CCS) methods gaining prominence. However, the literature still lacks studies about the impact of contaminants from gaseous streams, such as SOx on CO2 adsorption. This work aims to study the effects of the presence of SO2 in gas streams on the performance of CO2 capture. For this purpose, a commercial 13X binder-free zeolite (13XBF) was used as adsorbent, and adsorption measurements were performed in a magnetic suspension balance (MSB). The presence of SO2 in the gas stream reduces the CO2 and N2 adsorption capacity of the zeolite, which may be related to the reduction of textural properties and the decline in crystallinity after SO2 exposure due to the irreversible SO2 adsorption under the studied conditions. Prolonged SO2 exposure, even at low partial pressures, leads to a decrease in the level of CO2 adsorption, consistent with the deterioration in textural properties.

In this work, adsorption isotherms and adsorption kinetics of CO2 on zeolite 13X and activated carbon with high surface area (AC-h) were studied. The adsorption isotherms and kinetic curves of CO2 on the adsorbents were separately measured at 328 K, 318 K, 308 K, and 298 K and with a pressure range of 0–30 bar by means of the gravimetric adsorption method. The mass transfer constants and adsorption activation energy Ea of CO2 on the adsorbents were estimated separately. Results showed that at very low pressure the amounts adsorbed of CO2 on the zeolite 13X was higher than that on the AC-h, while at higher pressure, the amounts adsorbed of CO2 on the AC-h was higher than that on the zeolite 13X since the AC-h has a larger surface area and a larger total pore volume compared to the zeolite 13X. The adsorption kinetics of CO2 can be well described by the linear driving force (LDF) model. With the increase of temperature, the mass transfer constants of CO2 adsorption on both samples increased. The adsorption activation energy Ea for CO2 on the two adsorbents decreased with the increase of pressure. Furthermore, at low pressure the Ea for CO2 adsorption on the zeolite 13X was slightly lower than that on the AC-h, while at higher pressure the Ea for CO2 adsorption on the zeolite 13X was higher than that on the AC-h.

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.

The SF6 adsorption isotherms on zeolite 13X, zeolite NaY, activated carbon, and silica gel were investigated over a temperature range of 298–358 K and at pressure from 0 to 1000 kPa. Experimental results demonstrated that the adsorption capacity of SF6 was in the order AC > NaY > 13X > silica gel under the same adsorption pressure and temperature conditions. Moreover, the equilibrium isotherm data of SF6 on different adsorbents were fitted with Langmuir, Langmuir–Freundlich, and Toth models. The agreement between the fitting isotherms and the experimental data increased with the increase of available fitting parameters in the equation of the isotherm model, and the Toth model was verified to be the best alternative for describing adsorption behaviors of SF6. Furthermore, the isosteric heats of adsorption of SF6 on adsorbents were calculated by the Clausius–Clapeyron equation. Heats of adsorption of SF6 on the four adsorbents first decreased and then increased with increasing SF6 loading.

The effect of pressure on the adsorption characteristics of spherical adsorbents of zeolite 13X and RD silica gel is numerically analyzed in this study. The numerical model considers simultaneous heat and mass transfer in a spherical desiccant particle, which accounts for diffusion of moisture into the particles by both Knudsen and surface diffusion. The calculations indicate a dramatic difference of the adsorption behaviors between silica gel and zeolite 13X at a higher pressure of 7.5 atm due to the capability of adsorption and the diffusive ability of adsorbate within the adsorbent. For a lower system pressure of 1 atm, the variation amid silica gel and zeolite 13X is opposite to that at P = 7.5 atm. This is because the amount of the adsorbate for silica gel at P = 1 atm is significantly reduced. At a higher system pressure of 7.5 atm, the initial water content casts a very small influence on the adsorption behaviors for silica gel. However, for a normal pressure of 1 atm, a detectable difference is encountered subject to initial water contents. On the other hand, the initial water content casts appreciable influence on the adsorption characteristics for zeolite 13X.