Search

In the last decades, it has been observed that faults can slip both by slow aseismic creep and seismic events (i.e., earthquakes). Between these two slip modes, a wide variety of fault slip behavior can be observed, including low-frequency earthquakes, slow slip events and tremors. This wide variety of slip modes can radiate seismic energy at different frequencies whose content may be linked to the physical mechanisms at play. In the laboratory, it is possible to reproduce the entire spectrum of fault slip modes by modulating the loading stiffness of the apparatus depending on the critical fault rheologic stiffness (i.e. k/kc). This technique allows us to study, under controlled laboratory conditions, the acoustic signature of different fault slip modes to infer the physical mechanisms at their origin. To shed light on the nucleation mechanisms and seek for reliable precursors to failure of different slip modes, we performed friction experiments on powders that differ for granulometry and grain shape (i.e., glass beads with a grainsize < 150 µm; and quartz powders MinUSil with an average grain size of 10.5 µm), to simulate fault gouge. The experiments were conducted in a double direct shear configuration, instrumented with an array of piezoelectric sensors to record continuously Acoustic Emissions (AEs) at high recording rate (~10MHz). The experiments are performed at a constant displacement rate of 10 µm/s and using a spring to reduce the apparatus stiffness k, to match the critical fault rheological stiffness (kc). Following this procedure we obtain slow slip events (i.e., k = kc) and fast events (i.e. k

Earthquake nucleation has been understood as controlled by the frictional properties of fault zones. Mature fault zones host abrasive wear products, such as gouges, which result from the frictional sliding occurring in successive slip events. Shear localization in fault gouges is strongly dependent on, among others, fault mineralogical composition and grain size distribution, originating a wide variety of microstructural textures that may be related to different types of fault motion from aseismic creep, slow earthquakes to fast slip events. Additionally, within a fault, one can encounter different stages of maturity, ranging from an incipient and poorly-developed fault zone (i.e. discontinuous and thin gouge layer) to a mature fault zone that has experienced a lot of wear from previous sliding events (i.e. well-developed gouge layer). The localization of deformation within a mature gouge layer has been identified as possibly responsible for mechanical weakening and as an indicator of a change in stability within the fault.To gain insights on the role of grain size distribution, and thus fault maturity, in slip behavior and fault rheology, we performed friction experiments on quartz fault gouge in a double direct shear configuration using a biaxial apparatus (BRAVA at INGV in Rome, Italy). The experiments were performed at a constant normal stress of 40 MPa and under 100% humidity. We investigated different sliding velocities, from 10 µm/s to 1 mm/s, to assess time-dependent physical processes. Different bi-disperse mixtures of quartz were sheared to reproduce different initial grain size distributions within the fault (F110, average grain size and Min-u-sil, average grain size ). Samples were carefully collected at the end of the experiments to prepare thin sections for microstructural analyses.A first set of experiments was performed increasing the proportion between smaller and larger particles within a homogeneous blend. The friction evolves from a strain-hardening behavior for a sample with only F110 to a slip-weakening one for the one with only Min-u-sil. The difference in rheology is observable in the analyzed microstructures. Particularly, the two end members clearly show comminution and localization along boundary shear planes, whereas mixtures of the two sizes of particles only present a more diffused deformation. In the second set of experiments, we sheared gouges with a horizontal layering of the two grain sizes and observed different behaviors in terms of friction and rheology. These layered gouges present strain hardening behavior, with a strengthening part corresponding to the material of the layer in contact with the sliding block and a steady-state part with slightly higher friction than for the homogeneous mixtures.These results give important information on the connection between grain size distribution, shear localization, and the resulting fault slip behavior. In this context, the proportion between small/large particles and their distribution and percentages within the fault plays an important role in controlling fault rheology. We also complete our knowledge by using Discrete Element Method, simulating gouge sliding with different grain scale properties (size, distribution, cementation…), and observing a detailed evolution of shear localizations.

Fault zones usually present a granular gouge, coming from the wear material of previous slips. This layer contributes to friction stability and plays a key role in the way elastic energy is release...

Earthquakes happen with frictional sliding, by releasing all the stresses accumulated in the pre-stressed surrounding medium. The geological third body (i.e. fault gouge), coming from the wear of previous slips, acts on friction stability and plays a key role in this sudden energy release. A large part of slip mechanisms is influenced, if not controlled, by fault gouge characteristics and environment. We aim to link third body properties (geological, mechanical, physical…) to its rheological behavior by testing numerically different types of dense geological third body (% of porosity, % of cohesion, grains shapes…) with distinct contact laws. Different granular samples are generated to simulate a mature fault gouge with mineral cementation between particles. The gouge is then inserted between two rock walls to realize direct shear experiments with Discrete Element Modelling in the software MELODY2D (Mollon, 2016). A dry contact model is considered to investigate mechanisms without fluid (displacement-driven and under constant confining pressure). Researches are based here on a millimeter-scale portion of gouge, considering that the output values could be used in another model at larger scale.The peak strength can be sharp, short, and intense for dense and highly cohesive cases (angular particles, 15% initial porosity) and relatively low for ultra-dense samples (polygonal particles, 0% initial porosity). The observed regimes also correspond to an evolution of the amount of ductility within the sample. A very dense or highly cohesive sample behaves as a brittle material, whereas a typical cohesionless and porous geological layer tends to behave as a ductile material. The evolution of gouge characteristics truly influences the shape and formation time of Riedel shear bands. A change in contact laws between particles (%cohesion, friction) modifies the entire kinematics of Riedel bands formation. Indeed, with cohesion between particles, Riedel bands are directly linked to the importance of the dilation phase, depending itself on the initial porosity present within the sample (Casas et al., 2020). Then, increasing friction not only changes the principal orientation or Riedel bands but makes them more numerous within the gouge. It also leads to a more sudden post-peak weakening, which is prone to switch the fault behavior from a ductile aseismic response to a brittle seismic slip, depending on the stiffness of the surrounding medium. Global stiffness of the gouge also has an important role to play on Riedel bands formation, and it can be defined as a combination of multiple parameters such as initial porosity, shape and size of particles, numerical stiffness, gouge thickness… The local Breakdown energy, or energy needed to weaken the fault, is also calculated to be connected to Riedel bands formation.

Fault zone usually presents a granular gouge, coming from the wear material of previous slips. Considering a mature fault gouge with mineral cementation between particles, we aim to understand the ...

In the framework of EGS, using hydraulic stimulation increases pore pressure into the existing fracture networks and can be responsible for slip reactivations. In order to predict the seismic or as...

International audience; Earthquakes happen with frictional sliding, by releasing all the stresses accumulated in the prestressed surrounding medium. The geological fault gouge, coming from the wear of previous slips, acts on friction stability and plays a key role in this sudden energy release. A large part of slip mechanisms are influenced, if not controlled, by the characteristics and environment of this tribological “third body”. A 2D granular fault (mm scale) is implemented with Discrete Element Modelling (DEM). A displacement-driven model with dry contact is studied to observe kinematics and properties of the slipping zone. Increasing the length of the granular media increases the slip needed to weaken the friction from friction peak to steadystate. Low-angle Riedel shear bands are mostly observed. Their number increases with the inter-particle friction coefficient, which also influences shear bands formation in their orientation angle (higher friction leads to higher angle with the main slip direction).

How do earthquakes start? What are the parameters influencing fault evolutions? What are the local parameters controlling the seismic or aseismic character of slip?To predict the dynamic behaviour of faults, it is important to understand slip mechanisms and their source. Lab or in-situ experiments can be very helpful, but tribological experience has shown that it is complicated to install local sensors inside a mechanical contact, and that they could disturb the behaviour of the sheared medium. Even with technical improvements on lab tools, some interesting data regarding gouge kinematics and rheology remains very difficult or impossible to obtain. Numerical modelling seems to be another way of understanding physics of earthquakes.Fault zone usually present a granular gouge, coming from the wear material of previous slips. That is why, in this study, we present a numerical model to observe the evolution and behaviours of fault gouges. We chose to focus on physics of contacts inside a granular gouge at a millimetre-scale, studying contact interactions and friction coefficient between the different bodies. In order to get access to this kind of information, we implement a 2D granular fault gouge with Discrete Element Modelling in the software MELODY (Mollon, 2016). The gouge model involves two rough surfaces representing the rock walls separated by the granular gouge.One of the interests of this code is its ability to represent realistic non-circular grain shapes with a Fourier-Voronoï method (Mollon et al., 2012). As most of the simulations reported in the literature use circular (2D)/spherical (3D) grains, we wanted to analyse numerically the contribution of angular grains. We confirm that they lead to higher friction coefficients and different global behaviours (Mair et al., 2002), (Guo et al., 2004).In a first model, we investigate dry contacts to spotlight the influence of inter-particular cohesion and small particles on slip behaviour and static friction. A second model is carried out to observe aseismic and seismic slips occurring within the gouge. As stability depends on the interplay between the peak of static friction and the stiffness of the surrounding medium, the model includes the stiffness of the loading apparatus on the rock walls.The work presented here focuses on millimetre-scale phenomena, but the employed model cannot be extended to the scale of the entire fault network, for computational cost reasons. It is expected, however, that it will lead to a better understanding of local behaviours that may be injected as simplified interface laws in larger-scale simulations.

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

Micro- and nanoparticles of bio-compatible and bio-degradable polymers such as poly-lactic-co-glycolic acid (PLGA) are widely used as delivery devices for the administration of sensitive biopharmaceuticals such as proteins, peptides and genes. The purpose of this study is the investigation of supercritical fluid extraction of emulsions (SFEE) as a novel process for the production of such particles. By variation of PLGA concentration and stirring rate during emulsion preparation, particles of pure PLGA with average sizes ranging between 100 nm and a few μ m with very narrow size distributions have been produced in controlled and reproducible manner. Moreover, lysozyme has been used for the formation of composite particles with PLGA. Three different encapsulation methods have been investigated and evaluated by determining the corresponding encapsulation efficiencies. With the method of in situ suspension emulsions, an encapsulation efficiency of up to 48.5% has been achieved. The current study highlights the potential of SFEE as an attractive and scalable process for the manufacturing of drug–PLGA composite particles for pharmaceutical applications.

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.

Struktur-Eigenschaftsbeziehungen polydisperser fraktaler Stoffsysteme Dr. U. Katzel (E-Mail: uwe.kaetzel@merck.de), Dr. T. Gottschalk-Gaudig, Dr. M. Stintz, Dr. H. Barthel Merck KGaA, Zentrale Verfahrensentwicklung, ZVE-I, Frankfurter Strase 250, D-64293 Darmstadt Wacker-Chemie AG, Werk Burghausen, Johannes-Hess-Strase 24, D-84480 Burghausen Institut fur Verfahrenstechnik und Umwelttechnik, Arbeitsgruppe Mechanische Verfahrenstechnik, Technische Universitat Dresden, D-01062 Dresden DOI: 10.1002/cite.200750628