Performance Study of Multiphase Catalytic Monolith Reactor

mental process Study of Multi physique catalytic Monolith ReactorPerformance study of multiphase catalytic monolith nuclear nuclear reactor and its comparison with the movement of carry screw reactor (TBR)Xiaofeng WangIntroductionMultiphase reactors atomic number 18 found in diverse applications much(prenominal) as in manufacture of petroleum- base fuels and convergences, in achievement of commodity and specialty chemicals, pharmaceuticals, herbicides and pesticides, in production of reals and in pollution hiatus 1. A trace motivation for implementing multiphase reactor technology has more often than not been driven by the discovery and development of new or meliorate atom smashers for either emerging or existing processes 2. A wealth of products argon produced in multiphase catalytic replys. Among the multiphase reply systems, the monolith reactor, slurry emit column and the flow bum reactor (TBR) (Figure 1) atomic number 18 being utilize roughly extensivel y.Figure 1. Schematic diagram of the pilot scale trickle chouse reactorFigure 2. Schematic diagram of the pilot scale monolith reactor 3In general, monolith reactors refer to reactors that contain accelerators with certain social systems or arrangements (Figure 2). According to this definition, on that point are many different types of monolith reactors, such as h 1ycomb, foam, and fiber reactors, etc. Usually monolith reactors refer to those containing catalysts with parallel straight channels in side the catalyst block. Monoliths can carry restless catalyst in two ways the surface can have a bun in the oven a washcoat of the active catalyst, or the structure can be impregnated with active catalyst. Monolith reactors offer several advantages over traditionalistic random improve beds or slurry reactors, such as better can agitate characteristics, higher volumetric productivity for a smaller keep down of catalyst, elimination of filtration step and baseborner compress drop.In recently 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 shove along phase reactors, most notably as the structured support for the conversion of pollutants in vehicle exhausts. The latent of monoliths to act as a catalytic support for multiphase reactions has been accepted for over 20 years and much recent work has been through to extend the application of monoliths to luculent and bumbleliquid systems 4, 5. Monoliths offer the benefits of an absence seizure of a need for filtering catalyst from the product, low pressure drop, high geometrical surface area, safer operation and, perhaps most significantly, potentially easy scale-up. However, the latter(prenominal) is crucially dependent upon being able to achieve an even gasliquid distribution across the channels. Furthermore, maldistribution can lead to a enormous residence time distribution acr oss the radial section of monolith with because lower selectivity, ineffective catalyst usage and hot spots in the reactor 5, 6.Some of the applications that have been proposed or explored intromit hydrodesulphurization of oil, liquefied coal, and dibenzothiophene hydrogenation or dehydrogenation associated with various(a) aromatic compounds oxidation reactions. Applications of monolith structured packed beds used for distillation and adsorption have also been reported. Now research has been done on monolith reactors in many areas, such as preparation and extruding techniques, applications and performance to various reactions, flux regime and hydrodynamics studies, mass and heat transfer, and modeling and trick including computational smooth dynamics (CFD) simulation 7-10. This report will decompose 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 foc us on the studies published in the last 10 years.Advantages Of Monolith ReactorsFor multiphase reaction applications, different types of established reactors have been used in industry. The major ones are the trickle bed reactor (TBR), slurry eruct column reactor and the stirred ice chest 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 servingicles 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 contacting efficiency of the trickle-bed reactor 23. Besides, local anaesthetic 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 oper ational 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, smooth mass transfer characteristics, and a high effectiveness factor. Moreover, it is very thorny 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 smart reactors, can overcome the above-mentioned disadvantages with their excellent design. Monolith catalysts or monolith reactors have nearly 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 revealdoor(a) mass transfer and internal diffusion limitations (3) low axial dispersion and backmixing, and hence high product selectivity (4) larger external surface (5) uniform distribution of flow (gas phase) (6) elimination of fouling and plugging, and thus incr quilt 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 encompassingspread 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 performa nce enhancement in comparison with such conventional multiphase reactors as trickle bed 14, 26-28 and slurry reactors 29-31. The performance enhancement is mainly attributed to the more intensive contact between all phases and better mass transfer inherent in the gulp 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 focussed 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 involve for maximum conversion 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 compare d 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 problems 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 huge variety of reactions are accomplished via this process, using predominantly heterogeneous catalysts. In addition, product value and volumes vary enormously by several orders of magnitude. Given this diversity 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 refinery hydroprocessing an d extensively for hydrogenation in petrochemical plants. However, these reactor designs prove difficult to scaleup as key length-scales do not scale in a similar 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 single 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 cyclic hemiacetal, 2-hydroxytetrahydrofuran, as a consequence of double-bond isomerisation and hydrogenolysis reactions 15.Figure 3. Reaction scheme for hydrogenation of 2-butyne-1,4-diol ratiocinationThe 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. handout of selectivity is for the most part due to the formation of non-hydrogenation side products. The high selectivity ascertained 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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