Carlos A. Grande

Adsorption of H2, CO2, CH4, CO, N2 and H2O in Activated Carbon and Zeolite for Hydrogen Production

Abstract The design of a layered pressure swing adsorption unit to treat a specified off-gas stream is based on the properties of the adsorbent materials. In this work we provide adsorption equilibrium and kinetics of the pure gases in a SMR off-gas: H2O, CO2, CH4, CO, N2, and H2 on two different adsorbents: activated carbon and zeolite. Data were measured gravimetrically at 303–343 K and 0–7 bar. Water adsorption was only measured in the activated carbon at 303 K and kinetics was evaluated by measuring a breakthrough curve with high relative humidity.

Electric Swing Adsorption for CO2 removal from flue gases

One of the most important sources of CO2 emissions are the fossil-fuel fired plants for production of electricity. Removal of CO2 from flue gas streams for further sequestration has been proposed by the International Panel on Climate Change experts as one of the most reliable solutions to mitigate anthropogenic greenhouse emissions. When natural gas is employed as fuel, the molar fraction of CO2 in the flue gas is lower than 5% causing serious problems for capture. The purpose of this work is to present experimental validation of an Electric Swing Adsorption (ESA) technology that may be employed for carbon capture for low molar fractions of CO2 in the flue gas streams. To improve energy utilization, an activated carbon honeycomb monolith with low electrical resistivity was employed as selective adsorbent. A mathematical model for this honeycomb is proposed as well as different ESA cycles for CO2 capture.

Advances in Pressure Swing Adsorption for Gas Separation

Pressure swing adsorption (PSA) is a well-established gas separation technique in air separation, gas drying, and hydrogen purification separation. Recently, PSA technology has been applied in other areas like methane purification from natural and biogas and has a tremendous potential to expand its utilization. It is known that the adsorbent material employed in a PSA process is extremely important in defining its properties, but it has also been demonstrated that process engineering can improve the performance of PSA units significantly. This paper aims to provide an overview of the fundamentals of PSA process while focusing specifically on different innovative engineering approaches that contributed to continuous improvement of PSA performance.

Adsorption and Desorption of Carbon Dioxide and Nitrogen on Zeolite 5A

The adsorption equilibrium data of CO2 and N2 at (303, 333, 363, 393, 423) K ranging 0-1 bar on zeolite 5A is reported. The pressure and temperature range covers the operating pressure in adsorption units for CO2 capture from power plants. Experimental data were fitted by the multi-site Langmuir model. The adsorbent is much more selective to CO2: loading at 303 K and 100 kPa is 3.38 mol/kg while loading of N2 at the same pressure is 0.22 mol/kg. The Clausius-Clapeyron equation was employed to calculate the isosteric enthalpy of adsorption. The fixed-bed adsorption and desorption of carbon dioxide and nitrogen on zeolite 5A pellets has been studied. A model based on the bi-LDF approximation for the mass transfer, taking into account the energy and momentum balances, had been used to describe the adsorption kinetics of carbon dioxide and nitrogen. The model predicted satisfactorily the breakthrough curves obtained with carbon dioxide–nitrogen mixtures. Desorption process (consisting of depressurization, blowdown, and purge) was also performed. Following the feasibility of concentration and capture of carbon dioxide from flue gases by Pressure Swing Adsorption (PSA) process was simulated. A CO2 recovery of 91.0% with 53.9% purity was obtained using a five-step Skarstrom-type PSA cycle.

Adsorption of propane and propylene onto carbon molecular sieve

Abstract Equilibrium data for propane and propylene adsorption on a carbon molecular sieve (CMS) 4A from Takeda are presented in the temperature range 343–423 K and 0–300 kPa pressure. The pellet adsorption loading is 0.9 mol/kg for propane and 1.2 mol/kg for propylene at 100 kPa and 373 K. The equilibrium selectivity for propylene in the low-pressure range are 2.3 (343 K) and 1.7 (423 K). Experimental data were fitted with the Toth and Dubinin models. Zero length column (ZLC) technique has been used to determine the controlling mechanism and estimate the diffusivity parameters. Transport of both hydrocarbons in the pellets is controlled by micropore diffusion. Breakthrough curves were measured in the same temperature range and atmospheric pressure, at the low partial pressure of adsorbate (linear region of the isotherm). Simple models have been used in the simulation of breakthrough curves.

Adsorption of Off‐Gases from Steam Methane Reforming (H2, CO2, CH4, CO and N2) on Activated Carbon

Abstract Hydrogen is the energy carrier of the future and could be employed in stationary sources for energy production. Commercial sources of hydrogen are actually operating employing the steam reforming of hydrocarbons, normally methane. Separation of hydrogen from other gases is performed by Pressure Swing Adsorption (PSA) units where recovery of high‐purity hydrogen does not exceed 80%. In this work we report adsorption equilibrium and kinetics of five pure gases present in off‐gases from steam reforming of methane for hydrogen production (H2, CO2, CH4, CO and N2). Adsorption equilibrium data were collected in activated carbon at 303, 323, and 343 K between 0‐22 bar and was fitted to a Virial isotherm model. Carbon dioxide is the most adsorbed gas followed by methane, carbon monoxide, nitrogen, and hydrogen. This adsorbent is suitable for selective removal of CO2 and CH4. Diffusion of all the gases studied was controlled by micropore resistances. Binary (H2‐CO2) and ternary (H2‐CO2‐CH4) breakthrough curves are also reported to describe the behavior of the mixtures in a fixed‐bed column. With the data reported it is possible to completely design a PSA unit for hydrogen purification from steam reforming natural gas in a wide range of pressures.

Separation of methane and nitrogen by adsorption on carbon molecular sieve

Abstract Adsorption equilibrium of methane and nitrogen on CMS 3K from Takeda Corp. were gravimetrically measured at 298, 308, and 323 K and at pressures up to 2000 kPa. The most adsorbed gas is methane followed by nitrogen. The adsorption loading at 550 kPa and 308 K is 1.73 mol/kg for methane and 0.91 mol/kg for nitrogen. Experimental data were fitted with the multisite Langmuir model. Single component uptake of these gases at low pressures was used to determine the adsorption kinetics. Adsorption of nitrogen is much faster than methane, although this gas is preferentially adsorbed. The adsorption rate of both gases was controlled by a surface barrier resistance at the mouth of the micropore combined with micropore diffusion. Breakthrough curves of pure gases and their binary mixtures were measured at ambient temperature. A bi‐LDF (Linear Driving Force) model was used to predict the fixed‐bed behavior. Large differences in the adsorption kinetics were observed: at 308 K the LDF constant ratio was Kμ,N2 /Kμ,CH4 =133, although because of much higher adsorption of methane, the overall kinetic selectivity was 1.9 at 308 K. The data obtained in this work can be used for adsorption separation processes modeling for methane purification from nitrogen‐contaminated streams.

Vacuum Pressure Swing Adsorption to Produce Polymer-Grade Propylene

We have evaluated the Vacuum Pressure Swing Adsorption (VPSA) technology to separate propane–propylene streams to produce polymer-grade propylene. Zeolite 4A is used as kinetic adsorbent since propylene diffuses much faster than propane. A single VPSA process is able to produce propylene with purity higher than 99.6%. However, propylene recovery is only 67% and therefore a second stage is used. In this VPSA unit, zeolite 4A with smaller crystal radius is employed to reduce kinetic limitations. The second VPSA (tail unit) produces purified propane and recovers propylene that is recycled to the feed of the first VPSA (front unit). Linking these two VPSA units allows us to produce polymer-grade propylene (PGP) recovering 95.9% of the propylene. Comparing the performance of this process with distillation, there is a significant decrease in the separation volume. However, further efforts are necessary to reduce the power consumption of VPSA which is still slightly higher than for distillation.

Propane/Propylene Separation by Simulated Moving Bed I. Adsorption of Propane, Propylene and Isobutane in Pellets of 13X Zeolite

Abstract The separation of propane‐propylene mixture is the most energy consuming operation in the petrochemical industry. Various studies have been investigated to relieve the cryogenic distillation ordinarily used for this separation, and the adsorption technology appeared to be a promising option. Considering the encouraging results obtained by cyclic adsorption processes and notably by pressure swing adsorption, the simulated moving bed (SMB) has been suggested as a new and competitive alternative. The keystone of a SMB for a gas mixture separation is the choice of an adequate and pertinent adsorbent‐desorbent couple. In this work, isobutane has been tested as a potential desorbent over 13X zeolite. A gravimetric method has been used to measure the adsorption equilibrium isotherms of propylene, propane, and isobutane on 13X zeolite pellets over a temperature range from 333 K to 393 K and pressure up to 160 kPa. Experimental adsorption equilibrium isotherms were correlated with the Toth model. The 13X zeolite shows an intermediate loading capacity for isobutane at low pressures. Equilibrium capacities for propylene, propane, and isobutane at 373 K and 110 kPa were 2.12, 1.61, and 1.53 mol/kg, respectively. The heats of adsorption at zero coverage for propylene, propane, and isobutane were found to be 42.4, 36.9, 41.6 kJ/mol, respectively. Breakthrough curves of pure components were measured at 373 K and 150 kPa with different initial conditions (adsorbent bed saturated with nitrogen or isobutane). Experimental breakthrough curves were well‐predicted by an exhaustive mathematical model taking into account the energy balance in the three phases (gas, solid, and wall column). Multi‐component fixed bed adsorption experiments allowed us to observe that isobutane could displace an adsorbed propane/propylene mixture from the 13X zeolite and itself was fairly easily displaced from the adsorbent by this same mixture. These results confirmed the assumption that isobutane is a good desorbent for the adsorptive separation of C3H6/C3H8 mixture by a simulated moving bed.

Hydrotalcite Materials for Carbon Dioxide Adsorption at High Temperatures: Characterization and Diffusivity Measurements

Abstract Hydrotalcites are receiving considerable attention as adsorbents, catalysts, and catalyst precursors. However, the use of hydrotalcites as an adsorbent material for carbon dioxide has only been considered recently. In this work, three commercial hydrotalcites, Puralox MG30, MG50, and MG70, were used for the removal of CO2 at temperatures in the range 423–623 K. The adsorbent materials were characterized by use of scanning electron microscopy/energy dispersive x‐ray, mercury porosimetry, and N2 adsorption at 77 K, which indicated the presence of micropores. The HK plot suggested pore‐width values around 0.55 nm. The BET surface areas were 199, 154, and 144 m2/g for MG30, MG50, and MG70, respectively. The micropore areas calculated by the DR method were 206, 161, and 146 m2/g. The diffusivity of CO2 onto hydrotalcite adsorbents was measured by the zero length column method. Kinetic studies indicated that the controlling mechanism for mass transfer inside the extrudate was micropore diffusion. The reciprocal of the time constants for micropore diffusion (D c/l 2) were 8.5 × 10−3–15.3 × 10−3 s−1 for MG30, 8.0 × 10−3–10.4 × 10−3 s−1 for MG50, and 6.8 × 10−3–11.3 × 10−3 s−1 for MG70, in the temperature range 423–623 K.