Performance Study of Multiphase Catalytic Monolith Reactor

Performance Study of polyphase Catalytic Monolith ReactorPerformance study of multiphase catalytic monolith nuclear reactor and its comparison with the executing of separate out develop sex reactor (TBR)Xiaofeng WangIntroductionMultiphase reactors are found in diverse screenings such(prenominal) as in manufacture of petroleum-based fuels and products, in production of commodity and posture chemicals, pharmaceuticals, herbicides and pesticides, in production of materials and in pollution abatement 1. A key motivation for implementing multiphase reactor technology has largely been driven by the discovery and development of new or improved guns for any emerging or existing processes 2. A wealth of products are produced in multiphase catalytic reactions. Among the multiphase reaction systems, the monolith reactor, slurry talk column and the trickle contend reactor (TBR) (Figure 1) are being used most extensively.Figure 1. Schematic diagram of the pilot plateful trickle bed re actorFigure 2. Schematic diagram of the pilot scale monolith reactor 3In general, monolith reactors refer to reactors that contain accelerator pedals with certain structures or arrangements (Figure 2). match to this definition, there are many different types of monolith reactors, such as honeycomb, foam, and fiber reactors, etc. Usually monolith reactors refer to those containing catalysts with parallel straight convey inside the catalyst block. Monoliths stool carry active catalyst in two ways the show displace engender a washcoat of the active catalyst, or the structure can be impregnated with active catalyst. Monolith reactors offer several advantages over traditional random fixed beds or slurry reactors, such as better mass transfer characteristics, racyer(prenominal) volumetric productivity for a teensyer amount of catalyst, elimination of filtration step and disdain pressure drop.In youthfully years, monoliths as multiphase reactors to replace trickle-bed and slurry reactors have received more and more attention. The honeycomb monolith has been very successful in mess up phase reactors, most nonably as the structured support for the renewing of pollutants in vehicle exhausts. The potential of monoliths to act as a catalytic support for multiphase reactions has been recognized for over 20 years and much recent work has been done to extend the application of monoliths to liquid and gasliquid systems 4, 5. Monoliths offer the benefits of an absence of a need for filtering catalyst from the product, low pressure drop, steep geometrical surface area, safer operation and, perhaps most significantly, potentially easy scale-up. However, the latter is crucially dependent upon being able to achieve an even gasliquid distribution across the channels. Furthermore, maldistribution can lead to a wide residence time distribution across the radial section of monolith with consequently lower necessitateivity, ineffective catalyst usage and hot floater in the reactor 5, 6.Some of the applications that have been proposed or explored include hydrodesulphurization of oil, liquefied coal, and dibenzothiophene hydrogenation or dehydrogenation associated with various evocative compounds oxidation reactions. Applications of monolith structured packed beds used for distillation and adsorption have also been reported. Now inquiry has been done on monolith reactors in many areas, such as preparation and extruding techniques, applications and performance to various reactions, flow regime and hydrodynamics studies, mass and heat transfer, and modeling and trick including computational silver dynamics (CFD) simulation 7-10. This report will analyze and summarize the performance of catalytic monolith reactor on the different reactions, such as hydrogenation, dehydrogenation 11-18 and oxidation 19-22 reactions, and mostly focus on the studies published in the last 10 years.Advantages Of Monolith ReactorsFor multiphase reaction applications, di fferent types of conventional reactors have been used in industry. The major ones are the trickle bed reactor (TBR), slurry bubble column reactor and the stirred store slurry reactor. Each reactor type has its own advantages and shortcomings. A TBR is a convenient reactor compared to slurry bubble column reactor and the stirred tank slurry reactor, although larger particles must be used to guarantee moderate pressure drop. However, on the catalyst surface, where the liquid is either depleted or imperfectly covers the catalyst surface, dry areas are encountered these substantially reduce the liquidsolid reaching efficiency of the trickle-bed reactor 23. Besides, local hot spots may develop and cause runaways. Adding to the problem are the low gasliquid velocities required to avoid excessive pressure drop. This requirement results in high operational costs and low productivity. For the slurry bubble column reactor and stirred tank reactor, the slurry catalysts are very small, which needs the reactors offer very simple reactor geometry, high heat removal, excellent mass transfer characteristics, and a high effectiveness factor. Moreover, it is very difficult to separate product and catalyst, and catalyst attrition in these reactors. Another major drawback of conventional reactors for multiphase reactions is the difficulty of scale-up to industrial size units 24.Monolith reactors, as novel reactors, can overcome the above-mentioned disadvantages with their excellent design. Monolith catalysts or monolith reactors have or so common features in most of the applications they are used for. These features or characteristics include (1) low pressure drop especially under high fluid throughputs (2) elimination of external mass transfer and internal diffusion limitations (3) low axial dispersion and backmixing, and therefore high product selectivity (4) larger external surface (5) uniform distribution of flow (gas phase) (6) elimination of fouling and plugging, and thu s extended catalyst lifetime (7) easy scale-up, etc 25. Monolith reactors with these features or characteristics can make up the shortcomings of conventional reactors and can be an attractive alternative to other conventional multiphase reactors.Monolith Reactor Performance And Comparison With TBRAmong the various chemical reactions occurring in broad range of industrial application areas, catalytic gas-liquid-solid reactions are widespread 10, 23. These reactions occur extensively in chemical, petroleum, petrochemical, biochemical, material, and environmental industrial processes for a wide variety of products (such as hydrogenation, oxidation, and alkylation). Recent research has shown that monolithic reactors with a gasliquid flow in small regular channels with an active component deposited on the walls can lead to performance enhancement in comparison with such conventional multiphase reactors as trickle bed 14, 26-28 and slurry reactors 29-31. The performance enhancement is mai nly attributed to the more intensive contact between all phases and better mass transfer inherent in the slug flow, which is characterized by the passage of elongated gas bubbles being separated by liquid slugs 32.As a rule, research on monolithic reactors is focused on two different options with regard to practical realization. The first one is the application of monolithic systems as alternative to batch reactors, where a fixed catalyst (instead of a suspended catalyst) is used at superficial velocities needed for maximum innovation 33, 34. The second one is the utilization of monolithic catalysts in the column type reactors, which usually employ randomly packed catalyst particles 35.In this section, I select two different kinds of reactions to discuss the performance of a monolith reactor. And the performance is compared with that of a TBR operated at conditions typically employed for TBR. Moreover, I will point out some potential research orientations on the basis of the main p roblems encountered in recent research.Selective Hydrogenation of 2-butyne-1,4-diol To Butane-1,4-diolCatalytic, multiphase hydrogenation has been carried out commercially for over a century. A spacious variety of reactions are accomplished via this process, using predominantly heterogeneous catalysts. In addition, product values and volumes vary enormously by several orders of magnitude. Given this kind it is therefore perhaps somewhat surprising that these reactions are carried out for the most part in just one reactor type the stirred tank reactor. Furthermore, this type of reactor has been at the core of industry for over a century 36. There are a number of other well-established alternatives used in the large-scale chemical industries 37 including the TBR, which is used almost exclusively in re ticketry hydroprocessing and extensively for hydrogenation in petrochemical plants. However, these reactor designs prove difficult to scaleup as key length-scales do not scale in a sim ilar fashion. Monolith reactors, as novel reactors, can overcome the drawbacks with their distinctive design.A comparison between the monolithic reactors with traditional trickle bed reactors was reported by Fishwick et al. for a model reaction in both terms of activity and selectivity 29. Besides, the scale-out of a angiotensin converting enzyme channel to larger monoliths of 1256 and 5026 channels is analyzed, demonstrating the potential for rate and selectivity enhancements whilst allowing ease of scale-out. The selective hydrogenation of 2-butyne-1,4-diol was studied as the model reaction. This is a consecutive reaction widely applied in the production of butane-1,4-diol, a raw material used in the polymers industry and in the manufacture of tetrahydrofuran (THF) 38. Several side reactions are possible, as illustrated in Figure 3, for example the 4-hydroxybutyraldehyde and its cyclical hemiacetal, 2-hydroxytetrahydrofuran, as a consequence of double-bond isomerisation and hydro genolysis reactions 15.Figure 3. Reaction scheme for hydrogenation of 2-butyne-1,4-diolConclusionThe monolith reactor achieved the highest selectivity towards the alkene intermediate in the hydrogenation of 2-butyne-1,4-diol when compared to trickle bed reactors. personnel casualty of selectivity is for the most part due to the formation of non-hydrogenation side products. The high selectivity observed in the monolith can be partly attributed to the high dispersion of palladium and small palladium particle size on the washcoat support. However, differences in product distribution between single- and two- phase modes of operation suggest that mass transfer of hydrogen to the catalyst surface also influences the selectivity. 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