Structured-Catalysts-and-Reactors:结构化催化剂与反应器课件.ppt
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- Structured Catalysts and Reactors 结构 催化剂 反应器 课件
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1、Structured Catalysts and ReactorsK.RajalakshmiCH09M003An 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 the overall process performance(2)Unex
2、pected hot spots and thermal runaways of exothermic reactions.(3)Fouling and attritionEffect of liquid channeling on column efficiency for a system with a relative volatility of 1.07.Total number of theoretical plates N of 10,20,40,and 100 at top liquid composition X of 90 and 60 mole percent.Mannin
3、g and Cannon,Ind.Eng.Chem.,49,347(1957)Structured catalysts(reactors)are promising as far as the elimination of these drawbacks of fixed beds is concerned.Structured Catalysts and Reactors(2nd edition)2019 Andrzej Cybulski and Jacob A.MoulijnMonolithsMonoliths are structures that contain various typ
4、es of interconnected or separated channels in a single block of material.Monolithic reactors are those filled with monoliths that are 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 cha
5、nnel walls function as catalyst and the channels provide space for flow of gas and/or liquid.Ceramics:Cordierite,alumina,titania,silicaMetalAdvantagesnNo filtering of catalyst necessarynNo attrition of catalystnLow pressure dropnHigh geometric surface areanEfficient mass-transfernIn the case of inte
6、rnal diffusion limitations:more efficient use of catalyst due to thin catalytic layernEasy scale upDisadvantagesnRelatively high manufacturing costnLittle practical experience in multi-phase applications HistoryAutomotive Catalytic Converterspellet filled catalytic convertermonolith catalytic conver
7、terMonolith Key Features:no attrition high surface area low pressure drop rapid light-offHydrodynamics and mass transfer 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 thin,increasing mass transfer.Secondly
8、,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 in single-phase liquid phase reactions ov
9、er monoliths by adding an inert gas component.Gas-liquid-solid systemSelectivity ImprovementBenzaldehyde hydrogenationBatch slurry,monoliths or extrudates slurry 50 m,monolith 4 cm,extrudates 1.7x 5 mmPilot monoliths 1 cm -variation cell density trickle bed 4.7 cm,extrudates 1.7x 5 mmT.A.Nijhuis et
10、al.Chemical Engineering Science 56(2019)823-829Benzaldehyde hydrogenation-selectivitiesat 50%conversionT.A.Nijhuis et al.Chemical Engineering Science 56(2019)823-829Catalytic hydrogenation of anthraquinone SiO2-used as the monolith support material Palladium-active catalyst component.Comparison of m
11、onolithic,slurry and packed-bed reactorsR.Edvinsson Albers et al.Catalysis Today 69(2019)247252Membrane reactorsCatalyst-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 equil
12、ibrium allows and/or modifying the process selectivity.Classification of membrane reactor configurations according to membrane function and locationStructured Catalysts and Reactors”(2nd edition)2019 Andrzej Cybulski and Jacob A.MoulijnBased on material consideration Membrane ReactorsInorganic membr
13、ane reactorsOrganic membrane reactorsDense(metal)membranePorousmembranePotential applications of Inorganic membrane reactorsConversion enhancement of equilibrium limited reactionsControlled addition of reactantCoupling of reactionsSelectivity increase of intermediate productsDense membranes (e.g.Pd
14、alloys or solid electrolyte)can supply one of the reactants in a monatomic form,particularly active towards,for instance,partial oxidations or partial hydrogenationsPorous membranes such as -alumina,modifies in an advantageous way the residence time and the concentration profile of the reactantsin t
15、he catalytically active zone.Esterification processes in a H-ZSM-5 membrane reactorA catalytically active zeolite membrane has been used to displace equilibrium by selective water permeation during ethanol esterification.The acidic membrane both catalyzed the reaction and selectively permeated the w
16、ater product,while reactants were fed at the other side.The catalytic performance was better than that in a packed bed with the same amount of zeolite material.M.Pilar Bernal et al.Chemical Engineering Science 57(2019)15571562Methanol to olefin conversionH-ZSM-5 membranes was used for the conversion
17、 of methanol to olefin.Olefins easily react further to aromatic products(MTG-process)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 Eng
18、ineering Science 58(2019)649 656N2 was 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 656Pressure drop was expected to enhance the diffusion rates of molecules through the membrane and
19、to realize the direction of the diffusion from the feed side to the permeate side of the membrane.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 allows the coupling of the most typi
20、cal 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.The Pd membranes,permselective towards hydrogen,are immersed in a fluidized bed of catalyst pellets.Perm-selective
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