Structred Catalysts and Reactors：結(jié)構(gòu)化催化劑與反應(yīng)器

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)

2、unexpected 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 perce

3、nt.manning 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) 2006 andrzej cybulski and jacob a. moulijnmonolithsmonoliths are structures tha

4、t contain various types 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 bo

5、th arrangements, the channel walls function as catalyst and the channels provide space for flow of gas and/or liquid.ceramics: cordierite, alumina,titania,silicametaladvantagesno filtering of catalyst necessaryno attrition of catalystlow pressure drophigh geometric surface areaefficient mass-transfe

6、rin the case of internal diffusion limitations: more efficient use of catalyst due to thin catalytic layereasy scale updisadvantagesrelatively high manufacturing costlittle practical experience in multi-phase applications historyautomotive catalytic converterspellet filled catalytic convertermonolit

7、h catalytic convertermonolith 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 m

8、ass 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 in single-phase

9、liquid phase reactions over 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 , ex

10、trudates 1.7x 5 mmt. a. nijhuis et al. chemical engineering science 56(2001) 823-829benzaldehyde hydrogenation - selectivitiesat 50 % conversiont. a. nijhuis et al. chemical engineering science 56(2001) 823-829catalytic hydrogenation of anthraquinone sio2 - used as the monolith support material pall

11、adium - active catalyst component. comparison of monolithic, slurry and packed-bed reactorsr. edvinsson albers et al. catalysis today 69 (2001) 247252membrane reactorscatalyst-membrane systems are promising structured catalysts. the combination of reaction and membrane separation can result in incre

12、ase in the reaction yield beyond what the reaction equilibrium allows and/or modifying the process selectivity.classification of membrane reactor configurations according to membrane function and locationstructured catalysts and reactors” (2nd edition) 2006 andrzej cybulski and jacob a. moulijnbased

13、 on material consideration membrane reactorsinorganic membrane reactorsorganic membrane reactorsdense (metal)membraneporousmembranepotential applications of inorganic membrane reactorsconversion enhancement of equilibrium limited reactionscontrolled addition of reactantcoupling of reactionsselectivi

14、ty increase of intermediate productsdense 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, modifies in an advantageous way the

15、 residence time and the concentration profile of the reactantsin the 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

16、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 bernal et al. chemical engineering science 57 (2002) 15571562

17、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 reaction rate and the membrane permeation rate, olefin selectivities of 80 to 90% at m

18、ethanol conversion levels of 60 to 98% were achieved. t. masuda et al. chemical engineering science 58 (2003) 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 (2003) 649 656pressur

19、e 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 the permeate side of the membrane. membrane assisted fluidized bed reactor (mafbr)an mafbr is a special type of reactor that combines the advantage

20、s of a fluidized bed and a membrane reactor. this setup allows 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.the pd membranes,

21、permselective towards hydrogen, are immersed 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 permeatingco

22、mpound throughout the membrane.steam reforming of methaneparallel-passage and lateral-flow reactorsparticulate catalysts can be arranged in arrays of any geometric configuration. in such arrays, three levels of porosity (tlp) can be distinguished. nthe fraction of the reaction zone that is free to t

23、he gas flow is the first level of porosity. nthe void fraction within the arrays is the second level of porosity. nthe 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

24、 and lateral-flow reactorsthe 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 conventional fixed beds, no de

25、dicated 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.the gas flows through these passages along the catalyst layers, instead of through the bed as in a

26、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 monolithic (honeycomb)-type reactors, which are also applied

27、 in treating flue gas. 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 flow through

28、the layers of catalyst, instead of alongside them as in the pprindustrial 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 (acceptor) containing finely dispersed copper oxide. the essen

29、tial 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 system.flow scheme of the sfgd process as applied for sulfu

30、r oxides removal from refinery furnace off-gas.groenendaal, w. et al., aiche symp. ser., 72, 1222, 1976the 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 b

31、y 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 many end-of-pipe treatments of waste gases to reduce emissions that meet with increasing environmental concern.str

32、uctured packings for reactive distillationthe combination of chemical 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, chem

33、ical equilibrium limitations can be overcome and high reaction rates are maintained.reactive distillation columns consist of three sections: a reactive section located between an upper enriching and a lower stripping section.the reactive distillation column can be regarded as a countercurrent gasliq

34、uid catalytic trickle-bed reactor operating at the boiling point.the column internals need to fulfill various functions: nimmobilize catalyst of particle sizes typically 0.2 to 3 mm.n efficient liquid contacting of the catalyst.n high capacity in countercurrent operating mode.n efficient gasliquid m

35、ass transfer for high separation efficiency.n adjustable residence time.n mechanical stability and resistance to catalyst swelling.cdtech (catalytic distillation technologies) has developed the so-called catalyst bales . this is a structure containing the catalyst within layers of fiberglass cloth,

36、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. sulzer chemtech and koch engineering have developed similar reactive distillation packing technologies: katapak-s and katamax , respectively. in these st

37、ructures 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 flow channels in opposed orientation, so that the resulting combination is characterized by an open cross-flow structure pattern.structured catalyst-sandwiches. (a) catalyst sandwiched between two corrugated wire gauze sheets. (b) the wire gauze sheets are joinedtoge