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Journal ArticleDOI

Multiphase catalytic reactors: a perspective on current knowledge and future trends

TL;DR: In this paper, a review of the physical parameters for various multiphase reactors is presented, focusing on gas-phase catalyzed processes with an emphasis on unsteady state operation.
Abstract: Conventional and emerging processes that require the application of multiphase reactors are reviewed with an emphasis on catalytic processes. In the past, catalyst discovery and development preceded and drove the selection and development of an appropriate multiphase reactor type. This sequential approach is increasingly being replaced by a parallel approach to catalyst and reactor selection. Either approach requires quantitative models for the flow patterns, phase contacting, and transport in various multiphase reactor types. This review focuses on these physical parameters for various multiphase reactors. First, fixed-bed reactors are reviewed for gas-phase catalyzed processes with an emphasis on unsteady state operation. Fixed-bed reactors with two-phase flow are treated next. The similarities and differences are outlined between trickle beds with cocurrent gas–liquid downflow, trickle-beds with countercurrent gas–liquid flow, and packed-bubble columns where gas and liquid are contacted in coc...
Citations
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Journal ArticleDOI
TL;DR: In this paper, micro particle image velocimetry (μPIV) and fluorescence microscopy techniques were used to characterize microscale segmented gas-liquid flow at low superficial velocities relevant for chemical reactions with residence times of up to several minutes.
Abstract: We use micro particle image velocimetry (μPIV) and fluorescence microscopy techniques to characterize microscale segmented gas–liquid flow at low superficial velocities relevant for chemical reactions with residence times of up to several minutes. Different gas–liquid microfluidic channel networks of rectangular cross section are fabricated in poly(dimethylsiloxane) (PDMS) using soft lithography techniques. The recirculation motion in the liquid segments associated with gas–liquid flows as well as the symmetry characteristics of the recirculations are quantified for straight and meandering channel networks. Even minor surface roughness effects and the compressibility of the gas phase induce loss of symmetry and enhance mixing across the centerline in straight channels. Mixing is further accelerated in meandering channels by the periodic switching of recirculation patterns across the channel center. We demonstrate a new, piezoelectrically activated flow injection technique for determining residence time distributions (RTDs) of fluid elements in multiphase microfluidic systems. The results confirm a narrowed liquid phase RTD in segmented flows in comparison to their single-phase counterparts. The enhanced mixing and narrow RTD characteristics of segmented gas–liquid flows are applied to liquid mixing and in sol–gel synthesis of colloidal nanoparticles.

510 citations

Journal ArticleDOI
TL;DR: In this paper, the authors explored three major aspects of the wet oxidation and catalytic wet oxidation (WO) processes, with the major focus being on WO and CWO, using air or oxygen as an oxidant.
Abstract: This review article explores three major aspects of the wet oxidation (WO) and catalytic wet oxidation (CWO) processes (with the major focus being on WO and CWO, using air or oxygen as an oxidant). These aspects are (a) the fundamental chemistry of WO/CWO; (b) important aspects of catalysts, with regard to the CWO process; and (c) engineering aspects of the WO/CWO process. The applications of WO and CWO technology to treat industrial wastewater clearly illustrate the potential of these processes for treating wastewater from a wide number of industries. WO/CWO is a fertile area of research with significant scope for further research and innovation, particularly in the areas of catalyst development, the understanding of catalytic mechanisms, and the fundamental chemistry that occurs during WO/CWO. Selected examples of findings to date are discussed in this review.

437 citations

Journal ArticleDOI
TL;DR: An up-to-date overview of both technological and chemical aspects of liquid phase oxidation chemistry in continuous-flow microreactors is given, including the use of oxygen, hydrogen peroxide, ozone and other oxidants in flow.
Abstract: Continuous-flow liquid phase oxidation chemistry in microreactors receives a lot of attention as the reactor provides enhanced heat and mass transfer characteristics, safe use of hazardous oxidants, high interfacial areas, and scale-up potential. In this review, an up-to-date overview of both technological and chemical aspects of liquid phase oxidation chemistry in continuous-flow microreactors is given. A description of mass and heat transfer phenomena is provided and fundamental principles are deduced which can be used to make a judicious choice for a suitable reactor. In addition, the safety aspects of continuous-flow technology are discussed. Next, oxidation chemistry in flow is discussed, including the use of oxygen, hydrogen peroxide, ozone and other oxidants in flow. Finally, the scale-up potential for continuous-flow reactors is described.

402 citations

Journal ArticleDOI
TL;DR: In this paper, the authors measured the two-phase pressure drop in Taylor slug flow in a capillary and found that if the slug length was smaller than 10 times the capillary diameter, the length-averaged friction factor increased drastically from the single phase value (f = 16/Re) due to differences in curvature at the front and the back of the bubble.
Abstract: In a capillary, the two-phase pressure drop in Taylor slug flow was measured. A carefully designed inlet section for the capillary allowed the independent variation of gas bubble and liquid slug length. Gas and liquid superficial velocities were varied from 0.04 m/s to 0.3 m/s. If the slug length was smaller than 10 times the capillary diameter, the length-averaged friction factor for the liquid slug increased drastically from the single phase value (f = 16/Re) due to differences in curvature at the front and the back of the bubble. The use of different liquids allowed the independent variation of Re and Ca. The flow of elongated bubbles in capillaries was simulated using the CFD code FIDAP. It was found both numerically and experimentally that for Re ≫ 1, the extra pressure terms may be taken account using (Ca/Re) as a parameter. The numerical results agreed with the experimental data, provided that Marangoni effects of impurities are taken into account. The results allow the determination of slug length from pressure drop measurements in closed equipment where the slug length cannot otherwise be measured easily, such as monoliths and microreactors. © 2005 American Institute of Chemical Engineers AIChE J, 2005

366 citations

Journal ArticleDOI
TL;DR: A comprehensive review of the literature on catalytic conditioning of biomass-derived syngas can be found in this paper, with an emphasis on tar destruction and steam reforming catalysts.
Abstract: Thermochemical conversion of biomass to create fuels and chemical products may be achieved through the gasification route via syngas. The resulting biomass-derived raw syngas contains the building blocks of carbon monoxide and hydrogen as well as undesired impurities, such as tars, hydrocarbons, hydrogen sulfide, ammonia, hydrogen chloride, and other trace contaminants. These impurities require removal, usually through catalytic conditioning, to produce a quality syngas for end-use synthesis of liquid fuels, such as mixed alcohols and Fischer−Tropsch liquids. In the past decade, significant research attention has been focused on these catalytic processes. This contribution builds on previous reviews and focuses on capturing the work on catalytic conditioning of biomass-derived syngas that have been performed since the Dayton review in 2002, with an emphasis on tar destruction and steam reforming catalysts. This review organizes and discusses the investigations of catalytic conditioning of biomass-derived ...

354 citations

References
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Journal ArticleDOI
TL;DR: In this paper, a predictive two-phase flow model was derived starting with the Boltzman equation for velocity distribution of particles, which is a generalization of the Navier-Stokes equations of the type proposed by R. Jackson, except that the solids viscosities and stresses are computed by simultaneously solving a fluctuating energy equation for the particulate phase.
Abstract: Detailed knowledge of solids circulation, bubble motion, and frequencies of porosity oscillations is needed for a better understanding of tube erosion in fluidized bed combustors. A predictive two-phase flow model was derived starting with the Boltzman equation for velocity distribution of particles. The model is a generalization of the Navier-Stokes equations of the type proposed by R. Jackson, except that the solids viscosities and stresses are computed by simultaneously solving a fluctuating energy equation for the particulate phase. The model predictions agree with time-averaged and instantaneous porosities measured in two-dimensional fluidized beds. Observed flow patterns and bubbles were also predicted.

1,583 citations

Book
01 Jan 1978
TL;DR: In this paper, the authors describe current industrial applications of organic chemistry and offer an excellent overview of industrial organic chemistry, covering the manufacture of the most important precursors and intermediates and their use in the development of commercial products.
Abstract: This book describes current industrial applications of organic chemistry and offers an excellent overview of industrial organic chemistry. It covers the manufacture of the most important precursors and intermediates and their use in the development of commercial products. It details chemical and physical data, aspects of energy and raw materials supply, and the production of chemicals in different countries. It also describes the possibilities for future developments in the manufacture of various chemicals.

1,529 citations

Journal ArticleDOI
01 Dec 1939-Nature
TL;DR: Chapman and Cowling as mentioned in this paper showed that the ultimate scope of the descendent of the kinetic theory of gases must be the whole field of the properties of matter in bulk, derived from the atomic constitution of matter and from properties of atoms and their interactions.
Abstract: SINCE the days when the kinetic theory of gases was founded by Clausius, Maxwell and Boltzmann, great changes have taken place in the scope and bearing of the descendent theory. Taking a wide view of its present field, the qualification “of gases” has become a misnomer. One can see that the ultimate scope of the descendent of the kinetic theory of gases must be the whole field of the properties of matter in bulk, derived from the atomic constitution of matter and from the properties of atoms and their interactions. The present scope of the theory falls short of such inclusiveness, but not so far short as to leave any doubts for the future. The Mathematical Theory of Non-Uniform Gases An Account of the Kinetic Theory of Viscosity, Thermal Conduction, and Diffusion in Gases. By Prof. Sydney Chapman and Dr. T. G. Cowling. Pp. xxiii + 404. (Cambridge: At the University Press, 1939.) 30s. net.

1,346 citations

Journal ArticleDOI
TL;DR: In this article, the authors focus on an idealized granular material comprised of identical, smooth, imperfectly elastic, spherical particles which is flowing at such a density and is being deformed at a rate that particles interact only through binary collisions with their neighbours.
Abstract: We focus attention on an idealized granular material comprised of identical, smooth, imperfectly elastic, spherical particles which is flowing at such a density and is being deformed at such a rate that particles interact only through binary collisions with their neighbours. Using general forms of the probability distribution functions for the velocity of a single particle and for the likelihood of binary collisions, we derive local expressions for the balance of mass, linear momentum and fluctuation kinetic energy, and integral expressions for the stress, energy flux and energy dissipation that appear in them. We next introduce simple, physically plausible, forms for the probability densities which contain as parameters the mean density, the mean velocity and the mean specific kinetic energy of the velocity fluctuations. This allows us to carry out the integrations for the stress, energy flux and energy dissipation and to express these in terms of the mean fields. Finally, we determine the behaviour of these fields as solutions to the balance laws. As an illustration of this we consider the shear flow maintained between two parallel horizontal plates in relative motion.

1,230 citations