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The results of breakthrough experiments in an adsorption column packed with commercial activated carbon for three binary CO2/N2 mixtures as well as for two ternary CO2/N2/H2 mixtures are presented. The experiments were carried out at two different temperatures (25 and 45 °C), four different pressures (1, 5, 10 and 20 bar) and three different flow rates. To analyze the experiments, the breakthrough profiles are simulated using a one-dimensional model consisting of material and energy balances together with the necessary constitutive equations. Transport parameters such as the heat and mass transfer coefficients are fitted to the results from the experiments with the binary mixtures (CO2/N2) and then compared to parameters obtained in a previous work (Adsorption 18: 143–161, 2012) for binary CO2/H2 mixtures. Furthermore, the parameters obtained for binary mixtures are used to predict the outcome of breakthrough experiments with ternary CO2/N2/H2 mixtures. These simulations are then tested by experiments, showing that their prediction capability is rather satisfactory for a large range of experimental conditions., Adsorption, 20 (2-3), ISSN:0929-5607, ISSN:1572-8757

Two new MOF materials, i.e. USO-2-Ni MOF and UiO-67/MCM-41 hybrid, are evaluated as regards their potential for pre-combustion CO2 capture within an IGCC power plant. Both materials have been formulated as particles, thus allowing for a meaningful characterization in view of process scale-up. This is done by first conducting fixed bed experiments, where the adsorbent material is packed into a column and exposed to three different CO2/H2 mixtures at a given temperature (25 °C) and in a broad range of pressures (1–25 bar) in order to determine the corresponding transfer parameters. Second, complete PSA simulations are conducted. More precisely, a multi-objective analysis is carried out having the CO2 purity and recovery as objectives. A fixed process configuration is considered and the optimization is repeated for different process conditions. The results of this analysis are then compared to a benchmark which has activated carbon as adsorbent. This comparison shows that the USO-2-Ni MOF indeed increases both the separation performance and the productivity of the PSA process with respect to activated carbon. UiO-67/MCM-41 hybrid exhibits a slightly worse separation performance, but a better specific adsorbent productivity than activated carbon. Furthermore, it is shown that the particle formulation is crucial, as it has a big impact on the packing characteristics, which in turn have a big impact on the process performance.

Pressure swing adsorption (PSA) experiments are carried out in a 2-column laboratory setup using activated carbon. As feed an equimolar CO2/H2 mixture is used. Adsorption pressures of 10, 20, and 30 bar are applied, whereas the desorption pressure and the feed temperature are fixed at 1 bar and 25 °C, respectively. During the experiments the temperatures at five different locations inside the columns are measured and the composition of the product streams is analyzed by a mass spectrometer. A one-dimensional, nonisothermal, nonequilibrium model is used to reproduce the experiments. The model was validated previously using breakthrough experiments, and the modifications required to describe full PSA cycles are highlighted. It is shown that the temperatures measured inside the columns provide an excellent possibility for comparison of experiments and simulations, whereas the measured concentration profiles are affected by the piping between column outlet and MS, which has to be considered carefully.

A PSA process for pre-combustion capture within an IGCC power plant is presented. The process specifications are a high purity and recovery of CO 2 , i.e. the more adsorbable component, which is not standard in PSA and requires the development of a new PSA cycle. In order to determine its separation performance, a multi-objective optimization is carried out having the CO 2 purity and recovery as objectives. The results of this optimization are presented graphically as sets of optimal operating points, i.e. the so-called Pareto set. Moreover, the CO 2 productivity is calculated for each point on the Pareto set, representing a further performance indicator. Different process configurations and conditions are optimized and the obtained Pareto sets are compared. The process configuration investigated in this study are the direction of the flow during the depressurization steps and the number of pressure equalization steps. It is shown that a co-current depressurization is beneficial in terms of CO 2 purity and capture rate, and that increasing the number of pressure equalization steps leads to a higher CO 2 purity, but has a negative impact on the specific adsorbent productivity. The separation performance was found to depend on the operating temperature, on the adsorption pressure, at which H 2 is produced, and on the desorption pressure, at which CO 2 is produced. It improves for decreasing temperature and decreasing desorption pressure, whereas changing the adsorption pressure does not affect it though leading to lower productivity.

The IGCC technology (Integrated Gasification Combined Cycle) with pre-combustion CO 2 capture is a promising approach for near-zero CO 2 emission power plants to be realized in the near future. A key challenge within this technology is the separation of the CO 2 /H 2 gas mixture resulting from the water gas shift reaction that follows the gasification of coal. For the CO 2 stream a purity of about 95% is required; additionally a CO 2 capture rate of 90% is desired, which implies that both streams, H 2 and CO 2 , are required at rather high purity (∼95%). In contrast to post- combustion capture from power plants, where a large gas stream at low pressure and low CO 2 content has to be treated, in pre-combustion capture a gas mixture at up to 40 bar has to be separated; therefore an adsorption based process, such as pressure swing adsorption (PSA), constitutes a promising method for CO 2 removal from H 2 . In this work, new materials, namely USO-2-Ni MOF, UiO-67/MCM-41 Hybrid and MCM-41, are characterized in terms of equilibrium adsorption isotherms. Excess adsorption isotherms of CO 2 and H 2 on these materials are measured at different temperatures (25 °C 140 °C) and in a wide pressure range (up to 150 bar). The experimental data are then described with a suitable isotherm model, in our case Langmuir, Sips and Quadratic. In addition, the cyclic working capacity of CO 2 on each material is computed as a further assessment of the suitability of these materials for pre-combustion capture.

Adsorption, 18 (2), ISSN:0929-5607, ISSN:1572-8757

Adsorption, 18 (1), ISSN:0929-5607, ISSN:1572-8757

Three different adsorbent materials, which are promising for pre-combustion CO2 capture by a PSA (Pressure Swing Adsorption) process, are synthesized, pelletized and characterized. These materials are USO-2-Ni metal organic framework (MOF), mesoporous silica MCM-41 and a mixed material consisting of UiO-67 MOF bound with MCM-41. On these materials, equilibrium adsorption isotherms of CO2 and H2 are measured at different temperatures (25–140 °C) in a wide pressure range (up to 15 MPa). From the experimental data the parameters of different isotherm equations (Langmuir, Sips and Quadratic) are determined, together with the isosteric heats of adsorption. Binary adsorption of CO2/H2 mixtures on USO-2-Ni MOF is additionally measured and compared to predicted values using IAST (Ideal Adsorbed Solution Theory) showing a good agreement. The potential of the materials for the application of interest is evaluated by looking at their cyclic working capacity and compared to those of a commercial activated carbon. From this evaluation especially the USO-2-Ni MOF adsorbent looks promising compared to the commercial activated carbon. For the other two materials a smaller improvement, which is limited to lower temperatures, is expected.