Structured-Catalysts-and-Reactors：結(jié)構(gòu)化催化劑與反應(yīng)器課件

1、Structured Catalysts and ReactorsK.RajalakshmiCH09M003Structured Catalysts and ReactAn 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 o

2、verall process performance(2) Unexpected hot spots and thermal runaways of exothermic reactions.(3) Fouling and attritionStructured-Catalysts-and-Reactors：結(jié)構(gòu)化催化劑與反應(yīng)器課件Effect of liquid channeling on column efficiency for a system with a relative volatility of 1.07. Total number of theoretical plates

3、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 onStructured catalysts (reactors) are promising as far as the elimination of these drawbacks of fixed beds is concerned. Structured Catalysts

4、and Reactors (2nd edition) 2019 Andrzej Cybulski and Jacob A. MoulijnStructured catalysts (reactorsMonolithsMonoliths 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 are either ma

5、de 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,titania,silicaMet

6、alMonolithsMonoliths are structuAdvantagesNo 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 upDisadvantagesRe

7、latively high manufacturing costLittle practical experience in multi-phase applications AdvantagesHistoryAutomotive Catalytic Converterspellet filled catalytic convertermonolith catalytic converterMonolith Key Features: no attrition high surface area low pressure drop rapid light-offHistoryAutomotiv

8、e Catalytic CoHydrodynamics and mass transferFor 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 channels. The gas bubble fil

9、ls 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 thin, increasing mass tran

10、sfer. 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 in single-phase liquid p

11、hase reactions over monoliths by adding an inert gas component. The rate of mass transfer in Gas-liquid-solid systemGas-liquid-solid systemSelectivity ImprovementBenzaldehyde hydrogenationBatch slurry , monoliths or extrudates slurry 50 m, monolith 4 cm , extrudates 1.7x 5 mmPilot monoliths 1 cm - v

12、ariation cell density trickle bed 4.7 cm , extrudates 1.7x 5 mmSelectivity ImprovementBenzalT. A. Nijhuis et al. Chemical Engineering Science 56(2019) 823-829T. A. Nijhuis et al. ChemicalBenzaldehyde hydrogenation - selectivitiesat 50 % conversionT. A. Nijhuis et al. Chemical Engineering Science 56(

13、2019) 823-829Benzaldehyde hydrogenation - Catalytic hydrogenation of anthraquinone SiO2 - used as the monolith support material Palladium - active catalyst component. Structured-Catalysts-and-Reactors：結(jié)構(gòu)化催化劑與反應(yīng)器課件Comparison of monolithic, slurry and packed-bed reactorsR. Edvinsson Albers et al. Cata

14、lysis Today 69 (2019) 247252Comparison of monolithic, slurMembrane 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 equilibrium allows and/or modifying the p

15、rocess selectivity.Membrane reactorsCatalyst-membClassification of membrane reactor configurations according to membrane function and locationStructured Catalysts and Reactors” (2nd edition) 2019 Andrzej Cybulski and Jacob A. MoulijnClassification of membrane reaBased on material consideration Membr

16、ane ReactorsInorganic membrane reactorsOrganic membrane reactorsDense (metal)membranePorousmembraneBased on material consideratioPotential applications of Inorganic membrane reactorsConversion enhancement of equilibrium limited reactionsControlled addition of reactantCoupling of reactionsSelectivity

17、 increase of intermediate productsPotential applications of InorDense 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 hydrogenationsPorous membranes such as -alumina, modifie

18、s in an advantageous way the residence time and the concentration profile of the reactantsin the catalytically active zone .Dense membranes (e.g. Pd alloEsterification processes in a H-ZSM-5 membrane reactorA catalytically active zeolite membrane has been used to displace equilibrium by selective wa

19、ter 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 bed with the same amount of zeolite material.M. Pilar Bern

20、al et al. Chemical Engineering Science 57 (2019) 15571562Esterification processes in a Methanol to olefin conversionH-ZSM-5 membranes was used for the conversion of methanol to olefin.Olefins easily react further to aromatic products (MTG-process) over this catalyst, but with proper balancing of the

21、 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 656Methanol to olefin conversionHN2 was flowed backward to sweep out molecules permeating from the

22、feed side to the permeate side of the membrane.T. Masuda et al. Chemical Engineering Science 58 (2019) 649 656N2 was flowed backward to sweePressure drop was expected to enhance the diffusion rates of molecules through the membrane and to realize the direction of the diffusion from the feed side to

23、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 allows the coupling of the most typical properties of fluidized-bed

24、reactors (good degree of mixing, high heat transfer coefficients allowing close-to-isothermal operation, etc.) with the separation properties of the membrane. Membrane assistedThe Pd membranes, permselective towards hydrogen, are immersed in a fluidized bed of catalyst pellets.Perm-selective membran

25、es 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 reforming of methaneThe Pd membranes, permselectivParallel-Passage an

26、d lateral-Flow ReactorsParticulate 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 gas flow is the first level of porosity. The void fraction within the arra

27、ys 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 lateral-FParallel-Passage and lateral-Flow ReactorsThe parallel-passage re

28、actor (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 conventional fixed beds, no dedicated catalyst manufacturing plants are general

29、ly 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-FThe gas flows through these passages along the catalyst layers, instead of through the bed as in a traditional fixed-b

30、ed 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 monolithic (honeycomb)-type reactors, which are also applied in treating flue g

31、as.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, neighboring passages being open and closed at different ends.The gas is forced to fl

32、ow through the layers of catalyst, instead of alongside them as in the PPRStructured-Catalysts-and-Reactors：結(jié)構(gòu)化催化劑與反應(yīng)器課件Industrial Applications The Shell flue gas desulfurization The Shell flue gas desulfurization removes sulfur oxides from flue gas in a PPR using a regenerable solid adsorbent (acce

33、ptor) 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 acceptance/regeneration cycles and the Parallel flow reactor as a dust-tolerant sy

34、stem.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, 1976Flow scheme of the SFGD procesThe PPR and LFR are also applied in the process for NOx removal from off-gases. Th

35、e 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 low pressure drop and dust tolerance of the PPR and LFR are of potential interest in

36、 many end-of-pipe treatments of waste gases to reduce emissions that meet with increasing environmental concern.The PPR and LFR are also appliStructured Packings for reactive distillationThe combination of chemical reaction with distillation of reactants in a single piece of process equipment is cal

37、led 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 rates are maintained.Reactive distillation columns consist of three sections: a reactive sec

38、tion located between an upper enriching and a lower stripping section.Structured Packings for reactThe reactive distillation column can be regarded as a countercurrent gasliquid catalytic trickle-bed reactor operating at the boiling point.The column internals need to fulfill various functions: Immob

39、ilize 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 efficiency. Adjustable residence time. Mechanical stability and resistance to catalyst swelling.S

40、tructured-Catalysts-and-Reactors：結(jié)構(gòu)化催化劑與反應(yīng)器課件CDTech (Catalytic Distillation Technologies) has developed the so-called catalyst bales . This is a structure containing the catalyst within layers of fiberglass cloth, being rolled up into bales together with a layer of stainless steel demister wire mesh

41、. Bales are stacked in the column to form the reaction zone. CDTech (Catalytic DistillationSulzer Chemtech and Koch Engineering have developed similar reactive distillation packing technologies: KATAPAK-S and KATAMAX , respectively. In these structures the catalyst is immobilized between two sheets

42、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 flow channels in opposed orientation, so that the resulting combination is characterized by an open cross-flow structure pattern.Sulzer Chemtech and Koch EnginStructured catalyst-sandwiches. (a) Catalyst sandwiched between two corrugated wire gauze sheets. (b) The wire gauze sheets are joinedtoge