Adsorption Equilibrium and Kinetics of Methane and Nitrogen on Carbon Molecular Sieve

Knowledge of adsorption equilibrium and kinetic data is essential for the design of an adsorption process. In this work, the adsorption equilibrium isotherms of methane and nitrogen are reported at 303, 323, and 343 K over the pressure range from 0 to 700 kPa by a gravimetric system on a carbon molecular sieve (CMS-131510). Methane is preferentially adsorbed. The adsorption capacity at 303 K and 700 kPa is 1.91 mol/kg for methane and 1.01 mol/kg for nitrogen. Experimental data obtained were fitted with the multisite Langmuir model and Toth model. The adsorption kinetics of pure gas was studied by a batch uptake experiment at several different surface coverages within the pressure range of 0–100 kPa and in the same temperature range covered by the equilibrium isotherm. The adsorption rate of both gases is found to be controlled by the surface barrier resistance at the mouth of the micropore and diffusion in the micropore interior. The dual resistance model employed in the simulation can successfully describe the uptake curves. The temperature and concentration dependences of kinetic parameters were also studied. A very high kinetic selectivity was observed. The effect of micropore distribution on the transport parameters is discussed in detail. Binary breakthrough curves were determined, and an enrichment of 50% for methane in the first few seconds was observed. The data reported in this work can be used for the future modeling of adsorption process for the separation of methane and nitrogen on this CMS material

Improving the Performance of a Simulated Moving Bed Reactor for the Synthesis of Solketal by Implementing Multifeed Strategy

The simulated moving bed reactor (SMBR) is a sorption-enhanced reactive technology that has been successfully applied to the synthesis of several organic compounds, due to its ability to overcome the thermodynamic limitations associated with reversible reactions. This work proposes the implementation of an innovative multifeed strategy that can considerably improve the performance of the SMBR, particularly for systems in which none of the reactants can be used as desorbent. A systematic design methodology based on the so-called “reactive-separation volumes” is developed and applied for the first time, and the results for the multifeed SMBR are compared to those obtained in a conventional SMBR. Due to its industrial relevance, the synthesis of solketal through the ketalization of glycerol and acetone was selected as a case study. The results demonstrated that the new SMBR operating mode can produce solketal with a purity of 97%, reaching a productivity of over 10 kgSolk LAds–1 day –1, while for a conventional unit this is barely possible. Moreover, it led to a reduction in desorbent consumption of 85%

Performance Evaluation of Pervaporation Technology for Process Intensification of Butyl Acrylate Synthesis

Pervaporation-based hybrid processes have been investigated to overcome the drawbacks of equilibrium-limited reactions. Pervaporation processes are strongly recommended for heat-sensitive products and azeotropic mixtures as in the butyl acrylate system case, since pervaporation can operate at lower temperatures than distillation. In this work, experimental pervaporation data for multicomponent mixtures in the absence of reaction were measured for the compounds involved in the esterification reaction of acrylic acid with <i>n</i>-butanol at different temperatures: 323, 353, and 363 K. A commercial tubular microporous silica membrane from Pervatech was used which is highly selective to water, and its performance was evaluated by studying several parameters, like the selectivity, permeate fluxes, driving force of species, and separation factor. The effects of temperature and feed composition were assessed for binary, ternary, and quaternary mixtures. Increasing the temperature increases significantly the total permeate flux as well as the separation factor, which is higher for quaternary mixtures. The presence of butyl acrylate and acrylic acid reduces the total permeate flux since these molecules hinder the water permeation. The permeance of each species was correlated with temperature according to the Arrhenius equation, and a mathematical model was proposed to develop an integrated reaction–separation process using the experimental data obtained. The reaction conversion of the fixed-bed membrane reactor at steady state achieved 98.7% at isothermal conditions, increasing by 66% the conversion obtained in a fixed-bed reactor (at the same operating conditions)

Synthesis, Pelleting, and Performance Evaluation of a Novel K‑Promoted γ‑Alumina/MgAl-Layered Double Oxide Composite Adsorbent for Warm Gas H₂/CO₂ Separation

Development of stable solid adsorbent in pellet form is of importance for CO₂/H₂ separation at elevated temperature (250–450 °C). This study provides a novel synthesis method by adding K₂CO₃ solution into alumina sol soaked MgAl-layered double hydroxide paste. The delay time of K₂CO₃ addition is studied to demonstrate that the formation of K-promoted γ-alumina is facilitated by an immediate addition. Extruded adsorbent of higher CO₂ capacity (0.65 mmol/g) and radial crushing strength (75.6 N per pellet) is obtained. The existing crystalline phase of obtained adsorbent is screened by X-ray diffraction. The adsorption capacity and adsorption kinetics of the developed adsorbent is characterized by a thermogravimetric analyzer in terms of calcination temperature of both dominant constituent materials, MG63 hydrotacite, and K-promoted pseudo boehmite. Crystal transit temperatures of the constituents are considered in selecting the optimal calcinations temperature. The adsorbent pellets, pretreated with the optimal parameters studied, are packed in a fixed-bed to test breakthrough curves of CO₂, consistent dynamic capacity compared to that of thermogravimetric testing data were obtained. Results of multicycle CO₂ adsorption and desorption, steam sweeping, pressure change, and wear tests prove the stability of the adsorbent both in CO₂ capacity and mechanical strength

Propylene/Nitrogen Separation in a By-Stream of the Polypropylene Production: From Pilot Test and Model Validation to Industrial Scale Process Design and Optimization

Two industrial-scale pressure swing adsorption (PSA) processes were designed and optimized by simulations: recovery of only nitrogen and recovery of both nitrogen and propylene from a polypropylene manufacture purge gas stream. MIL-100­(Fe) granulates were used as adsorbent. The mathematical model employed in the simulations was verified by a PSA experiment. The effect of several operating parameters on the performance of the proposed PSA processes was investigated. For the nitrogen recovery, a 5-step 2-column PSA process produced a nitrogen stream of 95.4% purity with recovery of 85.2%, productivity of 6.0 mol N₂/kg adsorbent/h, and power consumption of 156 Wh/kgN₂. Nitrogen and propylene with 96.2% and 97.6% purity, respectively, were obtained from the 6-step 3-column nitrogen and propylene recovery PSA process. The nitrogen and propylene recoveries obtained are 98.4% and 91.0%, respectively. The nitrogen and propylene productivities were estimated as 4.61 and 1.83 mol product/kg adsorbent/h and the power consumption as 383 Wh/kgN₂

Syngas Purification by Porous Amino-Functionalized Titanium Terephthalate MIL-125

The adsorption equilibrium of carbon dioxide (CO₂), carbon monoxide (CO), nitrogen (N₂), methane (CH₄), and hydrogen (H₂) was studied at 303, 323, and 343 K and pressures up to 7 bar in titanium-based metal–organic framework (MOF) granulates, amino-functionalized titanium terephthalate MIL-125­(Ti)_NH₂. The affinity of the different adsorbates toward the adsorbent presented the following order: CO₂ > CH₄ > CO > N₂ > H₂, from the most adsorbed to the least adsorbed component. Subsequently, adsorption kinetics and multicomponent adsorption equilibrium were studied by means of single, binary, and ternary breakthrough curves at 323 K and 4.5 bar with different feed mixtures. Both studies are complementary and aim the syngas purification for two different applications, hydrogen production and H₂/CO composition adjustment, to be used as feed in the Fischer–Tropsch processes. The isosteric heats were calculated from the adsorption equilibrium isotherms and are 21.9 kJ mol^–1 for CO₂, 14.6 kJ mol^–1 for CH₄, 13.4 kJ mol^–1 for CO, and 11.7 kJ mol^–1 for N₂. In the overall pressure and temperature range, the adsorption equilibrium isotherms were well-regressed against the Langmuir model. The multicomponent breakthrough experimental results allowed for validation of the adsorption equilibrium predicted by the multicomponent extension of the Langmuir isotherm and validation of the fixed-bed mathematical model. To conclude, two pressure swing adsorption (PSA) cycles were designed and performed experimentally, one for hydrogen purification from a 30/70% CO₂/H₂ mixture (hydrogen purity was 100% with a recovery of 23.5%) and a second PSA cycle to obtain a light product with a H₂/CO ratio between 2.2 and 2.4 to feed to Fischer–Tropsch processes. The experimental cycle produced a light stream with a H₂/CO ratio of 2.3 and a CO₂-enriched stream with 86.6% purity as a heavy product. The CO₂ recovery was 93.5%