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Refinery Reactors
Published in James G. Speight, Refinery Feedstocks, 2020
In a fluidized bed, the finely crushed catalyst particles are fluidized because of the movement of the liquid. Three-phase fluidized beds usually operate in a concurrent mode with gas and liquid flowing upward. However, bubbles fill the cross-section of the channels. This flow type is called a slug flow. At higher gas flow rates, the smaller bubbles in a slug flow merge, and the resulting flow is called a Taylor flow or a churn flow. At even higher gas flow rates, the gas phase becomes continuous, and a gas-liquid dispersion develops. The flow is called an annular flow, and it is very inefficient and undesirable in three-phase systems. A monolith catalyst must always work under bubble flow or slug flow conditions; a slug flow gives the best mass transfer rates. Monolith catalysts are used in, for example, hydrogenation and dehydrogenation reactions.
Catalytic Three-Phase Reactors
Published in Salmi Tapio, Mikkola Jyri-Pekka, Wärnå Johan, Chemical Reaction Engineering and Reactor Technology, 2019
Salmi Tapio, Mikkola Jyri-Pekka, Wärnå Johan
Recently, a novel technology for three-phase processes has been developed: the monolith catalyst, sometimes also called the “frozen slurry reactor.” Similar to catalytic gas-phase processes (Section 4.1), the active catalyst material and the catalyst carrier are fixed to the monolith structure. The gas and liquid flow through the monolith channels. The flow pattern in the vertical channels is illustrated in Figure 6.14. At low gas velocities, a bubble flow dominates, and the bubble size distribution is even. At higher gas flow rates, larger bubbles fill the cross-section of the channels. This flow type is called a slug flow. At higher gas flow rates, the smaller bubbles in a slug flow merge, and the resulting flow is called a Taylor flow or a churn flow. At even higher gas flow rates, the gas phase becomes continuous, and a gas–liquid dispersion develops. The flow is called an annular flow, and it is very inefficient and undesirable in three-phase systems. A monolith catalyst must always work under bubble flow or slug flow conditions; a slug flow gives the best mass transfer rates. Monolith catalysts are used in, for example, hydrogenation and dehydrogenation reactions.
Design guidelines for Roller Compacted Concrete lift joints
Published in L. Berga, J.M. Buil, C. Jofré, S. Chonggang, Roller Compacted Concrete Dams, 2018
Monolithic block construction is similar to the placement method practiced for conventional mass concrete gravity dams in that the lift area is segmented into smaller “active” work areas or monoliths between transverse contraction joints. These smaller active work areas allow for more rapid vertical placement of lift layers. The axial length of the monoliths is based on both the maximum area that can be placed within the specified lift joint maturity criteria and the spacing of transverse contraction joints. An additional advantage to this approach is that by isolating RCC placement operations to a single or multiple monoliths, other construction activities such as foundation excavation or final cleanup, grout curtain drilling, and gallery installation can occur simultaneously in other portions of the dam. The main disadvantages to this approach are the need for temporary formwork at the contraction joints, temporary ramps or a large crane to move equipment from one monolith to the other, and added restrictions to the conveyor delivery system (Holderbaum 2000). These disadvantages will dictate the maximum practical vertical height differential between monoliths which is typically from 6 to 60 feet (1.8–18 meters).
Optimization of Activated Carbon Monolith Co3O4-Based Catalyst for Simultaneous SO2/NOx Removal from Flue Gas Using Response Surface Methodology
Published in Combustion Science and Technology, 2020
Kiman Silas, W.A. Wan Ab Karim Ghani, T. S. Y. Choong, Umer Rashid
Monolith is a structured adsorbent with long parallel channels separated by thin catalytic wall (0.5–4 mm) (Roy et al., 2004). Monolith is used as an active support component in gas–solid and gas–liquid–solid treatment (Kreutzer et al., 2001). The transition metal oxide, tricobalt tetraoxide (Co3O4), is one of the most efficient catalysts used in gas–solid application (Assebban et al., 2015); therefore, it can be supported on monolith for the purpose of developing a hybrid adsorbent where the monolith provides the geometry and the mechanical strength while the Co3O4 provides the adsorptive and catalytic properties in a dry sorption process (Groppi, and Tronconi, 2005; Neyestanaki et al., 2004). Moreover, the optimization of the independent variables that influence adsorption capacity is significant and response surface methodology (RSM) software can be utilized for that purpose. The RSM is a statistical tool that is used to study the effect of several factors at different levels and a regression model equation with optimized conditions according to an experimental design can be generated (Chaudhary and Balomajumder, 2014). Liu et al. (2010) used the RSM software to obtain the optimum values for independent variables (calcination temperature, calcinations time, and mass of sample) in decomposition rate of cobalt oxalate and found that the response was significantly affected by various factors. However, the study and other literatures could not report diverse synthesis methods of monolithic catalyst and study the adsorptive capabilities, optimization, and characterization.
Pseudoboehmite nanorod–polymethylsilsesquioxane monoliths formed by colloidal gelation
Published in Journal of Asian Ceramic Societies, 2019
It is known that the properties of porous monoliths can be controlled by their microstructure morphology [9–11]. We have reported, for example, that thermal conductivity can be controlled by changing the pore structure of PMSQ macroporous monoliths [12]. When macroporous monoliths are prepared through monomer reaction via a sol-gel process, the microstructures obtained by solid-liquid phase separation are somewhat similar regardless of the composition, which can be predicted by calculation [13]. If a colloid with an anisotropic shape is used as a starting material, however, a complicated structure can be formed [14]. The ability to fabricate monoliths from various forms of colloidal dispersion broadens the range and composition of available microstructures and permits the development of new materials with novel applications. In this study, fabrication of macroporous monoliths using pseudoboehmite nanorods (PBNRs) as the colloids and PMSQ derived from the precursor MTMS as the glue was investigated.