Adsorption equilibrium for sulfur dioxide, nitric oxide, carbon dioxide, nitrogen 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.

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.

In a way to overcome challenges with global warming, the use of fossil fuels in producing environmentally friendly energy towards reducing the ozone layer depletion and greenhouse gas emissions by participating countries is of interest. The adsorption refrigeration system has the advantages of a long lifespan and its environmental friendliness; however, its major disadvantage is the low coefficient of performance, which is a function of adsorbent–adsorbate, with zeolite–water as the most common adsorbent–adsorbate working pair. Zeolites 4A and 13X are the most used zeolite classes due to their higher selectivity for separating mixtures of CO2/N2 and CO2/CH4/N2 and their high-water adsorption capability, respectively. In this study, for the first time, the synthesis of zeolites 4A and 13X from natural sources (Kankara kaolin) and the mixture optimization for solar adsorption refrigeration application were considered. Raw Kankara kaolin, beneficiated Kankara kaolin, calcined Kankara kaolin and synthesized zeolites 4A and 13X were characterized using X-ray fluorescence, while the synthesized zeolites 4A and 13X were characterized using X-ray diffraction. Using the mixture simplex lattice design of experiment, mixtures of zeolites 4A and 13X were developed and characterized using Brunauer, Emmett and Teller analysis to obtain their pore size, specific surface area and pore volume. The statistical analysis produced the mathematical models of the response that were significant for pore size and specific surface area. The analysis proposed an optimal solution of 75 wt% zeolite 4A and 25 wt% zeolite 13X, which gave a desirability of 0.944.

The performance of zeolites 5A and 13X is numerically investigated in oxygen separation from air by a two-bed PSA system. The effect of operating variables such as adsorption step time, P H /P L ratio and cycle time was investigated on product purity and recovery. The simulation results showed that nitrogen adsorption capacity on zeolite 13X was slightly more than the one on zeolite 5A. In the completely same operating conditions, zeolite 5A had a larger mass transfer zone than zeolite 13X. Therefore, the adsorption and desorption rate of nitrogen on zeolite 5A is less than zeolite 13X. Moreover, for the equal volume of adsorbed nitrogen on both adsorbents, zeolite 5A is more capable rather than zeolite 13X to desorb much more volume of nitrogen at certain time. Furthermore, for achieving oxygen with purity of 96%, utilizing zeolite 5A is more economical than zeolite 13X, when 5.5<P H /P L <7 and 75<cycle time≤90.

Adsorptive removal of ultra-low concentration H2S and THT in CH4 with and without CO2 on zeolite 5A and 13X pellets

The present study aimed to investigate the adsorption behavior of heavy metal ions (Cu 2+ , Cd 2+ , and Pb 2+ ) on zeolite 4A (26.9 m 2 /g) and zeolite 13X (550.1 m 2 /g) at neutral pH in batch experiments. Influencing parameters on the adsorption were studied, including equilibrium time, solution pH, and adsorbent dose. The metal removal efficiencies at neutral pH were considerably higher than those at acidic pH. Cu 2+ and Cd 2+ were more efficiently adsorbed on zeolite 4A, while the greater removal of Pb 2+ was achieved with zeolite 13X. With an initial concentration of 300 ppm and an adsorbent‐to‐liquid ratio of 0.2% w/v, the highest removal efficiencies were 91.1% for Cu 2+ and 95.2% for Cd 2+ with zeolite 4A, and 92.9% for Pb 2+ with zeolite 13X. The experimental data fitted well with the Langmuir isotherm and the pseudo‐second‐order models, indicating the monolayer formations and the dominance of chemisorption. Zeolite 4A showed higher pseudo‐second‐order rate constants than zeolite 13X. The intraparticle diffusion contributed more significantly to the adsorption of Cu 2+ and Cd 2+ than that of Pb 2+ on the zeolites. The findings from this study provide valuable insights into the adsorption behavior of heavy metals on different kinds of zeolites in neutral solution.

Zeolite filled P84 co-polyimide membranes for dehydration of isopropanol through pervaporation process

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.

Adsorption of methane, ethane and ethylene on molecular sieve zeolites

In this study, new monomers having silica groups were synthesized as an intermediate for the preparation of poly(imide siloxane)-zeolite 4A and 13X mixed matrix membranes (MMMs). The effects of membrane preparation steps, zeolite loading, precursor’s composition, and pore size of zeolite on the gas separation performance of these mixed matrix membranes were studied. The new diamine monomer was prepared from 3,5-diaminobenzoic acid (3,5-DABA), 3-aminopropyltrimethoxysilane (3-APTMS), and zeolite 4A and zeolite 13X in N-methyl-2-pyrollidone (NMP) at 180 °C. Poly(imide siloxane)-zeolite 4A and 13X MMMs were synthesized from pyromellitic dianhydride (PMDA) and 4,4-oxydianiline (ODA) in NMP using a two-step thermal imidization. SEM images of the MMMs show the interface between polymer and zeolite phases getting closer when surface modified zeolite is used. The increase in glass transition temperature (Tg) confirms the polymer chain becoming more rigid induced by the presence of zeolite. The experimental results indicated that a higher zeolite loading resulted in a decrease in gas permeability and an increase in gas pair selectivity. In terms of O2 and N2 permeance and ideal selectivity, the separation performances of poly(imide siloxane)-zeolite MMMs were related to the zeolite type and zeolite pore dimension.

Different synthetic zeolites can be obtained by varying the composition, porosity, and active centers, making them of great interest in industry, especially as adsorbents in gas separation and purification processes. On the other hand, adsorption separation processes are increasingly common in industrial applications due to the technical and economic advantages of this technology. In this context, zeolites have emerged as promising candidates for these processes due to their high temperature stability, resistance to harsh environments combined with unique molecular sieve characteristics, ion exchange, and selective adsorption. In this chapter, we will focus on two cases, paraffin/olefin separation (ethane/ethylene and propane/propylene) and carbon dioxide/methane separation.Some innovative alternatives to replace conventional distillation have emerged for paraffin/olefin separation, with emphasis on simulated moving bed (SMB) technology. A wide variety of zeolites has been studied for this process, such as zeolites 13X, 4A, and 5A. The second case study is the removal of carbon dioxide (CO2) from natural gas stream. Adsorption processes are considered a competitive solution, once the adsorbent can be regenerated either by TSA or PSA. Concerning the use of zeolites for CO2 removal, natural chabazite, zeolite 4A, H-mordenite, and zeolite 13X are the ones with more available information in literature.In this review, we will focus on the strategy and importance of the lab/pilot scale with perspectives of scaling up adsorptive gas-phase separations using zeolites. The main methods adopted in lab/pilot scale studies include adsorbent characterization, adsorption equilibrium, adsorption dynamic studies, and process simulation and optimization.

Adsorption and desorption experiments for the binary mixture (N2/O2; 79:21 vol%) on zeolite 5A, 10X, and 13X beds were performed to study the dynamic characteristics of air separation adsorption processes. Because the breakthrough and desorption curves showed a tail by temperature variance in the beds, a nonisothermal dynamic model incorporating mass and energy balances was applied to the simulation of adsorption dynamics using the Langmuir–Freundlich model and the LDF approximation. The breakthrough and desorption results were compared among three different beds with respect to the breakthrough and desorption times, tailing effect, and temperature variation with the effects of pressure and flow rate. On the basis of the similar bed density, the order of breakthrough time and desorption time was zeolite 10X, 13X, and 5A beds. Also, the O2 MTZ of the zeolite 10X bed was slightly sharper than those of the zeolite 5A and 13X beds due to more favorable N2 isotherm of zeolite 10X. Furthermore, the breakthrough curve of the zeolite 13X bed showed a relatively long tail. In addition, the breakthrough curves of the zeolite 5A and 13X were similar to adiabatic behavior, whereas that of the zeolite 10X bed showed an isothermal behavior. The N2 desorption experiments were performed by O2 purge under the high pressure conditions. The desorption behaviors were very similar to the results of the breakthrough study, while the thermal effect on the desorption curve was negligible at the beds. The tails of the desorption curves were prominent with a change in the purge flow rate and desorption pressure. In all the beds, the feed and purge rates were more important factors for deciding the breakthrough and desorption times than the adsorption and desorption pressures in the experimental range.

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.

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.

Data for the adsorption of CO2 on 5A (CaA) and 13X (NaX) zeolite are critically evaluated. In addition, fresh data for the adsorption of CO2 on 13X zeolite is reported. Three intrinsic properties are examined: q max , the saturation loading, K H , the Henry constant, and (−ΔH) q , the isosteric heat of sorption. Below a reduced temperature T r , of 0.9, the q max values for both 5A and 13X zeolites are similar to theoretical values that may be derived using zeolitic crystallographic properties and the sorbate density calculated using the Rackett equation. For the region 0.9 ≤ Tr ≤ 1.0, the calculated q max values exceed the theoretical values similarly calculated, indicating that the molecules have a smaller molar volume than in a similar liquid phase. This is a similar result to that observed in ionic liquids. Linear regressed equations are derived for q max for the region 0.9 ≤ Tr ≤ 1.25. The Henry constant values for 5A are remarkably consistent for the five studies examined, with a correlation coefficient, R, of 0.999 for the van’t Hoff equation, but for the seven studies examined in 13X the data is more disperse as indicated by a correlation coefficient R of 0.899 for the van’t Hoff equation. The values of (−ΔH) q , the isosteric heat of sorption are in agreement with the literature. An explanation is advanced for the discrepancy between the higher heats of sorption values obtained calorimetrically from those obtained from isosteric adsorption studies. Finally, the fresh data is observed to fit the Toth model with regression coefficients of 0.999. However, the parameters obtained for the Toth equation by regression are significantly different from the intrinsic properties derived earlier, indicating the difficulty of deriving intrinsic parameters from isotherm fits.