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1、Structured Catalysts and Reactors,K.RajalakshmiCH09M003,Structured Catalysts and React,An inherent feature of conventional packed-bed reactors is their random and structural maldistributions. Random maldistributions result in:(1) Non uniform access of reactants to the catalytic surface, worsening th
2、e overall process performance(2) Unexpected hot spots and thermal runaways of exothermic reactions.(3) Fouling and attrition,Structured-Catalysts-and-Reactors：结构化催化剂与反应器课件,Effect of liquid channeling on column efficiency for a system with a relative volatility of 1.07. Total number of theoretical pl
3、ates N of 10, 20, 40, and 100 at top liquid composition X of 90 and 60 mole percent.,Manning and Cannon, Ind. Eng. Chem., 49, 347 (1957),Effect of liquid channeling on,Structured catalysts (reactors) are promising as far as the elimination of these drawbacks of fixed beds is concerned.,Structured Ca
4、talysts and Reactors (2nd edition) 2019 Andrzej Cybulski and Jacob A. Moulijn,Structured catalysts (reactors,Monoliths,Monoliths are structures that contain various types of interconnected or separated channels in a single block of material.Monolithic reactors are those filled with monoliths that ar
5、e either made of porous catalytic material or the catalytic material is deposited (washcoated) in the channels of an inert monolithic support.In both arrangements, the channel walls function as catalyst and the channels provide space for flow of gas and/or liquid.,Ceramics: Cordierite, alumina,titan
6、ia,silicaMetal,MonolithsMonoliths are structu,AdvantagesNo filtering of catalyst necessaryNo attrition of catalystLow pressure dropHigh geometric surface areaEfficient mass-transferIn the case of internal diffusion limitations: more efficient use of catalyst due to thin catalytic layerEasy scale upD
7、isadvantagesRelatively high manufacturing costLittle practical experience in multi-phase applications,Advantages,History,Automotive Catalytic Converters,pellet filled catalytic converter,monolith catalytic converter,Monolith Key Features: no attrition high surface area low pressure drop rapid light-
8、off,HistoryAutomotive Catalytic Co,Hydrodynamics and mass transfer,For co-current gasliquid flow, several flow regimes can occur. The preferred one usually is the so-called Taylor or slug flow. This type consists of gas bubbles and liquid slugs flowing consecutively through the small monolith channe
9、ls. The gas bubble fills up the whole space of the channel and only a thin liquid film separates the gas from the catalyst.,Hydrodynamics and mass transfe,The rate of mass transfer in taylor flow is large due to the following reasons. First the liquid layer between bubble and catalyst coating is thi
10、n, increasing mass transfer. Secondly, the liquid slugs show an internal recirculation during their travel through a channel. Because of this, radial transfer ofmass is increased.The gas bubbles push the liquid slugs forward as a piston and a type of plug flow is created.Taylor flow can be induced i
11、n single-phase liquid phase reactions over monoliths by adding an inert gas component.,The rate of mass transfer in,Gas-liquid-solid system,Gas-liquid-solid system,Selectivity ImprovementBenzaldehyde hydrogenation,Batch slurry , monoliths or extrudates slurry 50 m, monolith 4 cm , extrudates 1.7x 5
12、mmPilot monoliths 1 cm - variation cell density trickle bed 4.7 cm , extrudates 1.7x 5 mm,Selectivity ImprovementBenzal,T. A. Nijhuis et al. Chemical Engineering Science 56(2019) 823-829,T. A. Nijhuis et al. Chemical,Benzaldehyde hydrogenation - selectivitiesat 50 % conversion,T. A. Nijhuis et al. C
13、hemical Engineering Science 56(2019) 823-829,Benzaldehyde hydrogenation -,Catalytic hydrogenation of anthraquinone SiO2 - used as the monolith support material Palladium - active catalyst component.,Structured-Catalysts-and-Reactors：结构化催化剂与反应器课件,Comparison of monolithic, slurry and packed-bed reacto
14、rs,R. Edvinsson Albers et al. Catalysis Today 69 (2019) 247252,Comparison of monolithic, slur,Membrane reactors,Catalyst-membrane systems are promising structured catalysts. The combination of reaction and membrane separation can result in increase in the reaction yield beyond what the reaction equi
15、librium allows and/or modifying the process selectivity.,Membrane reactorsCatalyst-memb,Classification of membrane reactor configurations according to membrane function and location,Structured Catalysts and Reactors” (2nd edition) 2019 Andrzej Cybulski and Jacob A. Moulijn,Classification of membrane
16、 rea,Based on material consideration,Membrane Reactors,Inorganic membrane reactors,Organic membrane reactors,Dense (metal)membrane,Porousmembrane,Based on material consideratio,Potential applications of Inorganic membrane reactors,Conversion enhancement of equilibrium limited reactions,Controlled ad
17、dition of reactant,Coupling of reactions,Selectivity increase of intermediate products,Potential applications of Inor,Dense membranes (e.g. Pd alloys or solid electrolyte) can supply one of the reactants in a monatomic form, particularly active towards, for instance, partial oxidations or partial hy
18、drogenationsPorous membranes such as -alumina, modifies in an advantageous way the residence time and the concentration profile of the reactantsin the catalytically active zone .,Dense membranes (e.g. Pd allo,Esterification processes in a H-ZSM-5 membrane reactor,A catalytically active zeolite membr
19、ane has been used to displace equilibrium by selective water permeation during ethanol esterification. The acidic membrane both catalyzed the reaction and selectively permeated the water product, while reactants were fed at the other side. The catalytic performance was better than that in a packed b
20、ed with the same amount of zeolite material.,M. Pilar Bernal et al. Chemical Engineering Science 57 (2019) 15571562,Esterification processes in a,Methanol to olefin conversion,H-ZSM-5 membranes was used for the conversion of methanol to olefin.Olefins easily react further to aromatic products (MTG-p
21、rocess) over this catalyst, but with proper balancing of the reaction rate and the membrane permeation rate, olefin selectivities of 80 to 90% at methanol conversion levels of 60 to 98% were achieved.,T. Masuda et al. Chemical Engineering Science 58 (2019) 649 656,Methanol to olefin conversionH,N2 w
22、as flowed backward to sweep out molecules permeating from the feed side to the permeate side of the membrane.,T. Masuda et al. Chemical Engineering Science 58 (2019) 649 656,N2 was flowed backward to swee,Pressure drop was expected to enhance the diffusion rates of molecules through the membrane and
23、 to realize the direction of the diffusion from the feed side to the permeate side of the membrane.,Pressure drop was expected to,Membrane assisted fluidized bed reactor (MAFBR),An MAFBR is a special type of reactor that combines the advantages of a fluidized bed and a membrane reactor. This setup a
24、llows the coupling of the most typical properties of fluidized-bed reactors (good degree of mixing, high heat transfer coefficients allowing close-to-isothermal operation, etc.) with the separation properties of the membrane.,Membrane assisted,The Pd membranes, permselective towards hydrogen, are im
25、mersed in a fluidized bed of catalyst pellets.Perm-selective membranes are intended to break the thermodynamic barrier and shift the equilibrium forward to enhance hydrogen production while also purifying the product.Vacuum is applied to extract the permeatingcompound throughout the membrane.,Steam
26、reforming of methane,The Pd membranes, permselectiv,Parallel-Passage and lateral-Flow Reactors,Particulate catalysts can be arranged in arrays of any geometric configuration. In such arrays, three levels of porosity (TLP) can be distinguished. The fraction of the reaction zone that is free to the ga
27、s flow is the first level of porosity. The void fraction within the arrays is the second level of porosity. The fraction of pores within the catalyst pellets is referred to as the third level of porosity. Parallel-passage and lateral-flow reactors are examples of TLP reactors.,Parallel-Passage and l
28、ateral-F,Parallel-Passage and lateral-Flow Reactors,The parallel-passage reactor (PPR) and the lateral-flow reactor (LFR) are fixed-bed reactors suitable for the treatment of large volumes of gas at relatively low pressure.Since the PPR and LFR can use catalysts in the shape and size as used in conv
29、entional fixed beds, no dedicated catalyst manufacturing plants are generally required to fulfill the catalyst needs, and there are no special requirements for catalyst handling beyond those for traditional fixed-bed catalysts.,Parallel-Passage and lateral-F,The gas flows through these passages alon
30、g the catalyst layers, instead of through the bed as in a traditional fixed-bed reactor.,The straightness of the gas passages also prevents particulates present in the gas from being caught by impingement upon obstacles, and thus the PPR can be used for treating dust-containing gases, similarly to m
31、onolithic (honeycomb)-type reactors, which are also applied in treating flue gas.,The gas flows through these pa,In contrast to the PPR, where all the gas passages connect the inlet directly with the outlet by being open at both ends, the gas passages of the LFR are each closed off at one end, neigh
32、boring passages being open and closed at different ends.The gas is forced to flow through the layers of catalyst, instead of alongside them as in the PPR,Structured-Catalysts-and-Reactors：结构化催化剂与反应器课件,Industrial Applications The Shell flue gas desulfurization,The Shell flue gas desulfurization remov
33、es sulfur oxides from flue gas in a PPR using a regenerable solid adsorbent (acceptor) containing finely dispersed copper oxide. The essential elements in the development of the SFGD process are the development of a mechanically and chemically stable active acceptor that can withstand thousands of a
34、cceptance/regeneration cycles and the Parallel flow reactor as a dust-tolerant system.,Industrial Applications The,Flow scheme of the SFGD process as applied for sulfur oxides removal from refinery furnace off-gas.,Groenendaal, W. et al., AIChE Symp. Ser., 72, 1222, 1976,Flow scheme of the SFGD proc
35、es,The PPR and LFR are also applied in the process for NOx removal from off-gases. The Shell low- temperature NOx reduction process is based on the reaction of nitrogen oxides with ammonia catalyzed by a highly active and selective catalyst, consisting of vanadium and titania on a silica carrier.The
36、 low pressure drop and dust tolerance of the PPR and LFR are of potential interest in many end-of-pipe treatments of waste gases to reduce emissions that meet with increasing environmental concern.,The PPR and LFR are also appli,Structured Packings for reactive distillation,The combination of chemic
37、al reaction with distillation of reactants in a single piece of process equipment is called reactive distillation.Since in a reactive distillation process the reaction products are continuously removed from the reaction mixture, chemical equilibrium limitations can be overcome and high reaction rate
38、s are maintained.Reactive distillation columns consist of three sections: a reactive section located between an upper enriching and a lower stripping section.,Structured Packings for react,The reactive distillation column can be regarded as a countercurrent gasliquid catalytic trickle-bed reactor op
39、erating at the boiling point.The column internals need to fulfill various functions: Immobilize catalyst of particle sizes typically 0.2 to 3 mm. Efficient liquid contacting of the catalyst. High capacity in countercurrent operating mode. Efficient gasliquid mass transfer for high separation efficie
40、ncy. Adjustable residence time. Mechanical stability and resistance to catalyst swelling.,Structured-Catalysts-and-Reactors：结构化催化剂与反应器课件,CDTech (Catalytic Distillation Technologies) has developed the so-called catalyst bales . This is a structure containing the catalyst within layers of fiberglass c
41、loth, being rolled up into bales together with a layer of stainless steel demister wire mesh. Bales are stacked in the column to form the reaction zone.,CDTech (Catalytic Distillation,Sulzer Chemtech and Koch Engineering have developed similar reactive distillation packing technologies: KATAPAK-S an
42、d KATAMAX , respectively. In these structures the catalyst is immobilized between two sheets of metal wire gauze forming pockets. Each of the wire gauze sheets is corrugated, resulting in a structure with flow channels of a defined angle and hydraulic diameter. The pockets are assembled with the flo
43、w channels in opposed orientation, so that the resulting combination is characterized by an open cross-flow structure pattern.,Sulzer Chemtech and Koch Engin,Structured catalyst-sandwiches. (a) Catalyst sandwiched between two corrugated wire gauze sheets. (b) The wire gauze sheets are joinedtogether
44、 and sewn on all four sides. (c) The sandwich elements arranged into a cubical collection. (d) The sandwich elements arranged in a roundcollection.,Structured catalyst-sandwiches,Applications of structured packings in reactive distillation,Hydrolysis of methyl acetateLarge quantities of methyl aceta
45、te are formed as a side product in the production of polyvinyl alcohol (PVA). By the hydrolysis of the methyl acetate, methanol and acetic acid are recovered and recycled back to the PVA production. CH3COOCH3+H2O CH3COOH+CH3OH Because of the small equilibrium constant of the reaction,conventional hy
46、drolysis processes can only reach low conversion of methyl acetate per pass (around 30%) and require large recycle streams.,Applications of structured pac,Sulzer Chemtech (Switzerland) has developed together with Wacker-Chemie (Germany) a new process for the hydrolysis of methyl acetate.The new meth
47、yl acetate hydrolysis process combines a reactor and a reactive distillation column containing Katapak-SP structured packing.The reactor outlet product is fed to the reactive distillation column, where reaction conversion is increased up to 97%.,Sulzer Chemtech (Switzerland),Structured ReactorsDriving forces, Pressure drop Mass transfer Surface area Catalyst Efficiency Fluid distribution Catalyst SeparationEquilibrium limiting reactions,Structured ReactorsDriving fo,Thank You,Structured-Catalysts-and-Reactors：结构化催化剂与反应器课件,
