Process Intensification, Transforming Chemical Engineering.pdf

8/10/2019 Process Intensification, Transforming Chemical Engineering.pdf

1/13

22 January 2000 Chemical Engineering Progress

oday, we are witnessing importantnew developments that go beyondtraditional chemical engineering.Engineers at many universities and

industrial research centers are working on novelequipment and techniques that potentially couldtransform our concept of chemical plants andlead to compact, safe, energy-efficient, and envi-ronment-friendly sustainable processes. Thesedevelopments share a common focus on processintensification an approach that has been

around for quite some time but has truly emergedonly in the past few years as a special and inter-esting discipline of chemical engineering.

In this article, we take a closer look at pro-cess intensification. We define what it involves,

discuss its dimensions and structure, and reviewrecent developments in process-intensifying de-vices and methods.

What is process intensification?

One of the woodcuts in the famous 16thcentury book by Georgius Agricola (1) illus-

trates the process of retrieving gold from goldore (Figure 1). The resemblance between someof the devices shown in the picture (for in-stance, the stirred vessels O and the stirrers S)and the basic equipment of todays chemicalprocess industries (CPI) is striking. Indeed,

Agricolas drawing shows that process intensi-

fication, no matter how we define it, does notseem to have had much impact in the field ofstirring technology over the last four centuries,or perhaps even longer. But, what actually isprocess intensification?

In 1995, while opening the 1st InternationalConference on Process Intensification in theChemical Industry, Ramshaw, one of the pio-neers in the field, defined process intensifica-tion as a strategy for making dramatic reduc-tions in the size of a chemical plant so as to

reach a given production objective (2). Thesereductions can come from shrinking the size ofindividual pieces of equipment and also fromcutting the number of unit operations or appa-ratuses involved. In any case, the degree of re-

duction must be significant; how significantremains a matter of discussion. Ramshawspeaks about volume reduction on the order of100 or more, which is quite a challengingnumber. In our view, a decrease by a factor oftwo already bears all attributes of a drasticstep change and, therefore, should be consid-

ered as process intensification.On the other hand, Ramshaws definition is

quite narrow, describing process intensifica-tion exclusively in terms of the reduction inplant or equipment size. In fact, this is merelyone of several possible desired effects. Clear-

ly, a dramatic increase in the production ca-

Emerging equipment, processing techniques,

and operational methods promise spectacularimprovements in process plants, markedly shrinking

their size and dramatically boosting their efficiency.

These developments may result in the extinction

of some traditional types of equipment, if not

whole unit operations.

Process Intensification:TransformingChemical Engineering

T

PROCESS DESIGN TRENDS

Andrzej I. Stankiewicz,

DSM Research/Delft University

of Technology

Jacob A. Moulijn,

Delft University of Technology

Copyright 2000

American Institute

of Chemical Engineers.

All rights reserved.

Copying and

downloading permitted

with restrictions.
http://www.aiche.org/publication/permiss.htmhttp://www.aiche.org/publication/permiss.htmhttp://www.aiche.org/publication/permiss.htm


2/13

Chemical Engineering Progress January 2000 23

pacity within a given equipmentvolume, a step decrease in energyconsumption per ton of product, oreven a marked cut in wastes or

byproducts formation also qualify asprocess intensification.

Not surprisingly, process intensifi-cation, being driven by the need forbreakthrough changes in operations,focuses mainly on novel methods and

equipment. But, it also encompasses

certain established technologies andhardware. Usually, these have beenapplied on a limited scale (at least incomparison with their potential) and

have not yet generally been recog-nized as standard by the chemical en-gineering community. A typical ex-ample is the compact heat exchanger(3,4). These exchangers have beenwidely used for quite a long time in

the food industry. In the chemical in-

dustry, however, process developers

still often opt for conventional shell-and-tube units, even in cases where

plate or spiral heat exchangers couldeasily be applied.

Process intensification concernsonly engineering methods and equip-ment. So, for instance, developmentof a new chemical route or a changein composition of a catalyst, no mat-ter how dramatic the improvementsthey bring to existing technology, donot qualify as process intensification.

We, therefore, offer the followingdefinition:

Process intensification consists of

the development of novel apparatusesand techniques that, compared tothose commonly used today, are ex-pected to bring dramatic improve-ments in manufacturing and process-ing, substantially decreasing equip-ment-size/production-capacity ratio,energy consumption, or waste pro-

duction, and ultimately resulting incheaper, sustainable technologies.

Or, to put this in a shorter form:any chemical engineering develop-ment that leads to a substantiallysmaller, cleaner, and more energy-efficient technology is processintensification!

As shown in Figure 2, the wholefield generally can be divided intotwo areas:

process-intensifying equipment,

such as novel reactors, and intensivemixing, heat-transfer and mass-trans-fer devices; and

process-intensifying methods,such as new or hybrid separations, in-

tegration of reaction and separation,heat exchange, or phase transition (inso-called multifunctional reactors),techniques using alternative energysources (light, ultrasound, etc.), andnew process-control methods (like in-tentional unsteady-state operation).

Obviously, there can be someoverlap. New methods may requirenovel types of equipment to be devel-oped and vice versa, while novel ap-paratuses already developed some-times make use of new, unconven-

tional processing methods.

Figure 1. 16th century technology for retrieving gold from ore (1).


3/13



Process-intensifyingequipmentOur earlier comment that Agricolaswoodcut shows how little stirringtechnology has progressed is not en-tirely true. In fact, the technology ofstirring has been greatly intensifiedduring the last 25 years, at least asfar as liquid/liquid and gas/liquid

systems. Surprisingly, this wasachieved not by improving mechani-cal mixers but, quite the opposite, byabandoning them in favor of stat-ic mixers (5). These devices are fine

examples of process-intensifyingequipment. They offer a more size-and energy-efficient method for mix-ing or contacting fluids and, today,serve even wider roles. For instance,the Sulzer (Winterthur, Switz.) SMRstatic-mixer reactor, which has mix-

ing elements made of heat-transfertubes (Figure 3), can successfully beapplied in processes in which simul-taneous mixing and intensive heatremoval or supply are necessary,such as in nitration or neutralization

reactions.

One of the more important disad-vantages of static mixers is their rela-tively high sensitivity to clogging bysolids. Therefore, their utility for re-actions involving slurry catalysts islimited. Sulzer solved this problem(at least partially) by developingstructured packing that has good stat-ic-mixing properties and that simulta-

neously can be used as the supportfor catalytic material. Its family ofopen-crossflow-structure catalysts,so-called KATAPAKs (6) (Figure 4a),are used in some gas-phase exother-

mic oxidation processes traditionallycarried out in fixed beds, as well as incatalytic distillation. KATAPAKshave very good mixing and radialheat-transfer characteristics (6). Theirmain disadvantage is their relativelylow specific geometrical area, which

is much lower than that of their mostimportant rival in the field, monolith-ic catalysts (7) (Figure 4b).

Monolithic catalysts

Monolithic substrates used today

for catalytic applications are metallic

Equipment forCarrying Out

Chemical Reactions

Spinning Disk ReactorStatic Mixer Reactor

(SMR)Static Mixing Catalysts

(KATAPAKs)Monolithic ReactorsMicroreactorsHeat Exchange (HEX) ReactorsSupersonic Gas/Liquid

ReactorJet-Impingement

ReactorRotating Packed-Bed

Reactor

Static MixersCompact Heat ExchangersMicrochannel Heat

ExchangersRotor/Stator MixersRotating Packed BedsCentrifugal Adsorber

Supercritical FluidsDynamic (Periodic) Reactor Operation

Centrifugal FieldsUltrasoundSolar EnergyMicrowaves

Electric FieldsPlasma Technology

Membrane AbsorptionMembrane DistillationAdsorptive Distillation

Reverse-FlowReactors

Reactive DistillationReactive Extraction

Reactive CrystallizationChromatographic ReactorsPeriodic Separating

ReactorsMembrane ReactorsReactive ExtrusionReactive ComminutionFuel Cells

Equipment forOperations

not InvolvingChemical Reactions

MultifunctionalReactors

HybridSeparations

AlternativeEnergy Sources

OtherMethods

Equipment

Process Intensification

Methods

Examples

Figure 2. Process intensification and

its components.

Figure 3. Proprietary reactor-mixer is a clas-

sic example of process-intensifying equipment.

(Photo courtesy of Sulzer.)


4/13


or nonmetallic bodies providing amultitude of straight narrow channelsof defined uniform cross-sectional

shapes. To ensure sufficient porosityand enhance the catalytically activesurface, the inner walls of the mono-lith channels usually are covered witha thin layer of washcoat, which actsas the support for the catalytically ac-tive species.

The most important features of the

monoliths are: very low pressure drop in sin-

gle- and two-phase flow, one to twoorders of magnitude lower than that

of conventional packed-bed systems; high geometrical areas per reac-

tor volume, typically 1.54 times

more than in the reactors with partic-ulate catalysts;

high catalytic efficiency, practi-cally 100%, due to very short diffu-sion paths in the thin washcoat layer;and

exceptionally good perfor-mance in processes in which selec-

tivity is hampered by mass-transferresistances.

Monolithic catalysts also can beinstalled in-line, like static mixing el-

ements, using the latter as gas/liquid

dispersing devices. The in-line unitsoffer additional advantages:

low investment costs, becausein-line monolithic reactors are ready-to-use modules that are installed aspart of the pipelines;

compact plant layout (in-linemonolith reactors can even be placedunderground, say, in cement ducts see Figure 5);

ability to meet much highersafety and environmental standards

than conventional reactors (such as,for instance, by placing the reactorunit beneath ground level);

very easy and quick replacement(e.g., in case of catalyst deactivation)simply by swapping a piece ofpipeline, instead of having to unloadold and load new catalyst;

the possibility of distributingmultiple feed points along the reac-tor; and

easy attainment of a near-to-plug-flow regime.

In a modeling study of an industri-al gas/liquid process, Stankiewicz (8)

Heat Exchange (Optional) Reaction Dispersing, Mixing

Side-Stream (Optional)

Monolithic Catalyst

Figure 5. Cross-flow monolithic structure. (Illustration courtesy of Corning.)

Figure 4.

(a) Packing with

integrated catalyst

(photo courtesy of

Sulzer.), and

(b) monolithic

catalyst (photo

courtesy of

Corning).


5/13



gives a spectacular example of an ap-

proximately 100-fold reduction in re-actor size from replacing a conven-

tional system with an in-line mono-lithic unit.

One of the problems in monolithreactors, especially for gas-phase cat-alytic processes, is difficult heat re-moval due to the absence of radialdispersion. Monolith channels arefully separated from each other and,therefore, the only heat transportmechanism is the conductivity

through the monolith material. Forhighly exothermic gas-phase reac-tions, so-called HEX reactors devel-

oped by BHR Group, Ltd. (Cranfield,U.K.) (9) present a promising option.In these reactors, one side of a com-pact heat exchanger is made catalyti-cally active, either by washcoating orby introducing catalytically active el-ements (such as pellets or structuredpackings). A ceramic cross-flow

monolith structure developed byCorning Inc. (Corning, NY) (10)(Figure 6) also potentially can beused as a catalytic reactor/heat ex-changer, e.g., for carrying out twochemical processes (exo- and en-dothermic) within one unit. Com-pared to conventional fixed-bed reac-tors, such reactors offer much betterheat-transfer conditions namely,heat-transfer coefficients typically of3,5007,500 W/m2K, and heat-trans-

fer areas of up to 2,200 m2.

Microreactors

Even higher values of heat-trans-fer coefficients than those in the HEX

reactors can be achieved in microre-actors. Here, values of up to 20,000W/m2K are reported (11). Microreac-tors are chemical reactors of extreme-ly small dimensions that usually havea sandwich-like structure consistingof a number of slices (layers) with

micromachined channels (10100 min dia.). The layers perform variousfunctions, from mixing to catalyticreaction, heat exchange, or separa-tion. Integration of these variousfunctions within a single unit is one

of the most important advantages of

microreactors. The very high heat-

transfer rates achievable in microre-actors allow for operating highly

exothermic processes isothermally,which is particularly important in car-rying out kinetic studies. Very low re-action-volume/surface-area ratios makemicroreactors potentially attractive forprocesses involving toxic or explo-sive reactants. The scale at whichprocesses using batteries of multiplemicroreactors become economicallyand technically feasible still needs to

be determined, though.The geometrical configuration of

microchannel heat exchangers (stacked

cross-flow structures) resembles thatof the cross-flow monoliths in Figure6, although the materials and fabrica-tion methods used differ. The chan-nels in the plates of microchannelheat exchangers are usually around 1mm or less wide, and are fabricatedvia silicon micromachining, deep X-

ray lithography, or nonlithographicmicromachining. Over the past few

years, Pacific Northwest National

Laboratory (Richland, WA) hasdemonstrated microchannel heat ex-

changers in a planar sheet architec-ture that exhibit high heat fluxes andconvective-heat-transfer coefficients.The reported values of heat-transfercoefficients in microchannel heat ex-changers range from 10,000 to

35,000 W/m2K (4, 12).

Rotating devicesAlmost as high heat-transfer coef-

ficients are achievable in the spinningdisk reactor (SDR) (13). This unit(see Figure 7) developed by

Ramshaws group at Newcastle Uni-versity (Newcastle, U.K.) primarily isaimed at fast and very fast liquid/liq-uid reactions with large heat effect,such as nitrations, sulfonations, andpolymerizations (e.g., styrene poly-merization (14)). In SDRs, a very thin(typically 100 m) layer of liquid

moves on the surface of a disk spin-ning at up to approximately 1,000rpm. At very short residence times(typically 0.1 s), heat is efficiently re-moved from the reacting liquid atheat-transfer rates reaching 10,000W/m2K. SDRs currently are beingcommercialized.

Other reactors especially dedicatedto fast and very fast processes worthmentioning include: the supersonicgas/liquid reactor developed at Prax-

air Inc. (Danbury, CT) (15) forgas/liquid systems and the jet-im-pingement reactor of NORAM Engi-neering and Constructors (Vancouver,BC) (16,17) for liquid/liquid systems.

Figure 6. Concept of an in-line catalytic

reactor (8).

Figure 7.

Schematic of the

spinning-disk

reactor.

Feed

Products

Heat Exchange


6/13


The former employs a supersonic

shockwave to disperse gas into verytiny bubbles in a supersonic in-line

mixing device, while the latter uses asystem of specially configured jetsand baffles to divide and remix liq-uid streams with high intensity.Rotor/stator mixers (18), which areaimed at processes requiring very fastmixing on a micro scale, contain ahigh-speed rotor spinning close to amotionless stator. Fluid passesthrough the region where rotor and

stator interact and experiences highlypulsating flow and shear. In-linerotor/stator mixers resemble centrifu-

gal pumps and, therefore, may simul-taneously contribute to pumping theliquids.

Rotational movement and centrifu-gal forces are used not only in SDRs.High gravity (HIGEE) technology,which Imperial Chemical Industries(London) started working on in the

late 1970s as a spinoff from a NASAresearch project on microgravity en-vironment (19,20), has developedinto one of the most promisingbranches of process intensification.HIGEE technology intensifies mass-transfer operations by carrying themout in rotating packed beds in whichhigh centrifugal forces (typically1,000 g) occur. This way, heat andmomentum transfer as well as masstransfer can be intensified. The rotat-

ing-bed equipment, originally dedi-cated to separation processes (such asabsorption, extraction, and distilla-tion), also can be utilized for reactingsystems (especially those that are

mass-transfer limited). It potentiallycan be applied not only to gas/liquidsystems, but also to other phasecombinations including three-phasegas/liquid/solid systems. Recently,Chong Zhengs group at the HI-GRAVITEC Center (Beijing) has suc-

cessfully applied rotating (5002,000rpm) packed beds on a commercialscale for deaeration of flooding waterin Chinese oil fields. There, rotatingmachines of 1 m dia. replaced con-ventional vacuum towers of 30 m

height (21).

Chong Zhengs group also hasachieved successes in crystallizationof nanoparticles: very uniform 1530

nm crystals of CaCO3 have beenmade in a rotating crystallizer at pro-cessing times 410 times shorter thanthose for a conventional stirred-tankprocess (22). Another interesting ex-

ample here, also undergoing commer-cialization, is a centrifugal adsorber(Figure 8) developed at Delft Univer-sity of Technology (Delft, TheNetherlands) (23). This is a new con-tinuous device for carrying out ion-exchange or adsorption processes.

Using a centrifugal field to establishcountercurrent flow between the liq-uid phase and the adsorbent enablesuse of very small (1050 mm) adsor-bent particles and design of extreme-ly compact separation equipment

with very short contact times and

high capacities (typically 1050m3/h).

Process-intensifyingmethods

As highlighted in Figure 2, mostprocess-intensifying methods fall intothree well-defined areas: integration

of reaction and one or more unit op-erations into so-called multifunction-al reactors, development of new hy-brid separations, and use of alterna-tive forms and sources of energy forprocessing. Lets now take a closerlook at each of these areas.

Multifunctional reactors

These can be described as reactorsthat, to enhance the chemical conver-sion taking place and to achieve ahigher degree of integration, combine

at least one more function (usually a

Liquid Feed

Liquid Feed

Liquid Effluent

Liquid Effluent

Axis

Adsorbent Effluent

Adsorbent EffluentAdsorbent Feed

w

Fresh Adsorbent

Centrifugal Field w2R

L

Figure 8.

Centrifugal adsorber

(23). (Drawing

courtesy of Bird

Engineering.)


7/13



unit operation) that conventionally

would be performed in a separatepiece of equipment. A widely known

example of integrating reaction andheat transfer in a multifunctional unitis the reverse-flow reactor (24). Forexothermic processes, the periodicflow reversal in such units allows foralmost perfect utilization of the heatof reaction by keeping it within thecatalyst bed and, after reversion of theflow direction, using it for preheatingthe cold reactant gases. To date, re-

verse-flow reactors have been used inthree industrial processes (24): SO2oxidation, total oxidation of hydrocar-

bons in off-gases, and NOx reduction.The recent introduction of inert pack-ing for heat exchange (25) has lead toa sandwich reactor; it consists ofthree zones a catalyst bed betweentwo beds of packing of heat-accumu-lating material. The reverse-flow prin-ciple also has been applied in rotating

monolith reactors, which are used in-dustrially for removal of undesiredcomponents from gas streams andcontinuous heat regeneration (26).Studies also have been carried out onemploying reversed-flow reactors forendothermic processes (27).

Reactive (catalytic) distillation isone of the better known examples ofintegrating reaction and separation,and is used commercially (28). In thiscase, the multifunctional reactor is a

distillation column filled with catalyt-ically active packing. In the column,chemicals are converted on the cata-lyst while reaction products are con-tinuously separated by fractionation

(thus overcoming equilibrium limita-tions). The catalyst used for reactivedistillation usually is incorporatedinto a fiberglass and wire-mesh sup-porting structure, which also providesliquid redistribution and disengage-ment of vapor. Structured catalysts,

such as Sulzers KATAPAK, also areemployed (29). The advantages ofcatalytic distillation units, besides thecontinuous removal of reaction prod-ucts and higher yields due to theequilibrium shift, consist mainly of

reduced energy requirements and

lower capital investment (30). Also, a

reverse process to the one describedabove, that is, combination of reac-

tion and condensation, has been stud-ied for benzene oxidation to cyclo-hexane and for methanol synthesis(31,32). The number of processes inwhich reactive distillation has beenimplemented on a commercial scaleis still quite limited but the poten-tial of this technique definitely goesfar beyond todays applications.

Numerous research groups are in-

vestigating other types of combined re-actions and separations, such as reac-tive extraction (33,34), reactive crystal-

lization (35), and integration of reac-tion and sorption operations, for in-stance, in chromatographic reactors(36,37,38) and periodic separating re-actors, which are a combination of apressure swing adsorber with a period-ic flow-forced packed-bed reactor (39).

Membrane reactors

Today, a huge research effort is de-voted to membrane reactors (40). Themembrane can play various functionsin such reactor systems. It, for in-stance, can be used for selective in-situ separation of the reaction prod-ucts, thus providing an advantageousequilibrium shift. It also can be ap-plied for a controlled distributed feedof some of the reacting species, eitherto increase overall yield or selectivity

of a process (e.g., in fixed-bed orfluidized-bed membrane reactors(41,42)) or to facilitate mass transfer(e.g., direct bubble-free oxygen sup-ply or dissolution in the liquid phase

via hollow-fiber membranes (43,44)).In addition, the membrane can enablein-situ separation of catalyst particlesfrom reaction products (45)). Finally,the membrane can incorporate catalyt-ic material, thus itself becoming ahighly selective reaction-separation

system. The scientific literature on cat-alytic membrane reactors is exception-ally rich (see, for instance, Ref. 46)and includes many very interestingideas (such as heat- and mass-integrat-ed combination of hydrogenation and

dehydrogenation processes in a single

membrane unit). Yet, practically no

large-scale industrial applications havebeen reported so far. The primary rea-

son for this most definitely is the rela-tively high price of membrane units,although other factors, such as lowpermeability as well as mechanicaland thermal fragileness, also play animportant role. Further developmentsin the field of material engineeringsurely will change this picture.

Multifunctional reactors may inte-grate not only reaction and heat trans-

fer or reaction and separation but alsocombine reaction and phase transi-tion. A well-known example of such a

combination is reactive extrusion.Reactive extruders are being increas-ingly used in the polymer industries.They enable reactive processing ofhighly viscous materials without re-quiring the large amounts of solventsthat stirred-tank reactors do. Particu-larly popular are twin-screw extrud-

ers, which offer effective mixing, thepossibility of operation at high pres-sures and temperatures, plug-flowcharacteristics, and capability of mul-tistaging. Most of the reactions car-ried out in extruders are single- ortwo-phase reactions. New types ofextruders with catalyst immobilizedon the surface of the screws, howev-er, may allow carrying out three-phase catalytic reactions (47).

Fuel cells present another example

of multifunctional reactor systems.Here, integration of chemical reactionand electric power generation takesplace (see, for instance, Ref. 48). Si-multaneous gas/solid reaction and

comminution in a multifunctional re-actor also has been investigated (49).

Hybrid separations

Many of the developments in thisarea involve integration of mem-branes with another separation tech-

nique. In membrane absorption andstripping, the membrane serves as apermeable barrier between the gas andliquid phases. By using hollow-fibermembrane modules, large mass-trans-fer areas can be created, resulting in

compact equipment. Besides, absorp-


8/13


tion membranes offer operation inde-pendent of gas- and liquid flow rates,without entrainment, flooding, chan-neling, or foaming (50,51).

Membrane distillation is probablythe best known hybrid, and is beinginvestigated worldwide (52,53). Thetechnique is widely considered as analternative to reverse osmosis and

evaporation. Membrane distillationbasically consists of bringing avolatile component of a liquid feedstream through a porous membraneas a vapor and condensing it on theother side into a permeate liquid.Temperature difference is the driving

force of the process. Foster et al.(54) name four basic advantages ofmembrane distillation:

100% rejection of ions, macro-molecules, colloids, cells, and othernonvolatiles;

lower operating pressure across

the membrane than in the pressure-driven processes;

less membrane fouling, due tolarger pore size; and

potentially lower operating tem-peratures than in conventional evapo-ration or distillation, which may en-able processing of temperature-sensi-tive materials.

Among hybrid separations not in-volving membranes, adsorptive dis-tillation (55) offers interesting ad-vantages over conventional methods.In this technique, a selective adsor-bent is added to a distillation mix-ture. This increases separation abili-

ty and may present an attractive op-tion in the separation of azeotropesor close-boiling components. Ad-sorptive distillation can be used, forinstance, for the removal of trace im-purities in the manufacturing of fine

chemicals; it may allow switching

some fine-chemical processes frombatchwise to continuous operation.

Use of alternative formsand sources of energy

Several unconventional processingtechniques that rely on alternativeforms and sources of energy are of im-portance for process intensification.

For instance, we already have dis-cussed the potential benefits of usingcentrifugal fields instead of gravitation-al ones in reactions and separations.

Among other techniques, researchon sonochemistry (the use of ultra-sound as a source of energy for

chemical processing) appears to bethe most advanced. Formation of mi-crobubbles (cavities) in the liquid re-action medium via the action of ul-trasound waves has opened new pos-sibilities for chemical syntheses.

These cavities can be thought of as

Figure 9. Task-integrated methyl acetate column is much simpler than conventional plant. (Drawing courtesy of Eastman Chemical (76).

Distillation

ExtractiveDistillation

AceticAcid

Catalyst

Methanol

Methanol

MethylAcetate

Solvent

SolventEntrainer

Water

Water

Azeo

Water

Heavies

Catalyst

Acetic Acid

MethylAcetate

Reaction

ReactiveDistillation

ReactiveDistillation

Distillation

Task-IntegratedConventional


9/13



high energy microreactors. Their

collapse creates microimplosionswith very high local energy release

(temperature rises of up to 5,000 Kand negative pressures of up to10,000 atm are reported (56)). Thismay have various effects on the re-acting species, from homolytic bondbreakage with free radicals forma-tion, to fragmentation of polymerchains by the shockwave in the liq-uid surrounding the collapsing bub-ble. For solid-catalyzed (slurry) sys-

tems, the collapsing cavities addi-tionally can affect the catalyst sur-face this, for example, can be

used for in-situ catalyst cleaning/re-juvenation (57). A number of sono-chemical reactor designs have beendeveloped and studied (58). Sono-chemistry also has been investigatedin combination with other tech-niques, e.g., with electrolysis for ox-idation of phenol in wastewater (59).

The maximum economically andtechnically feasible size of the reac-tion vessel still seems to be the de-termining factor for industrial appli-cation of sonochemistry.

Solar energy also may play a rolein chemical processing. A novel high-temperature reactor in which solar en-ergy is absorbed by a cloud of react-ing particles to supply heat directly tothe reaction site has been studied

(60,61). Experiments with two small-

scale solar chemical reactors in whichthermal reduction of MnO2 took placealso are reported (60). Other studiesdescribe, for example, the cycloaddi-tion reaction of a carbonyl compound

to an olefin carried out in a solar fur-nace reactor (62) and oxidation of 4-chlorophenol in a solar-powered fiber-optic cable reactor (63).

Microwave heating can makesome organic syntheses proceed up to1,240 times faster than by conven-

tional techniques (64). Microwaveheating also can enable energy-effi-cient in-situ desorption of hydrocar-bons from zeolites used to removevolatile organic compounds (65).

Electric fields can augment process

rates and control droplet size for a

range of processes, including painting,coating, and crop spraying. In theseprocesses, the electrically charged

droplets exhibit much better adhesionproperties. In boiling heat transfer,electric fields have been successfullyused to control nucleation rates (66).Electric fields also can enhance pro-

cesses involving liquid/liquid mix-tures, in particular liquid/liquid extrac-tion (67) where rate enhancements of200300% have been reported (68).

Interesting results have been pub-lished concerning so-called GlidingArc technology, that is, plasma gener-

ated by formation of gliding electricdischarges (69,70,71). These dis-charges are produced between elec-trodes placed in fast gas flow, andoffer a low-energy alternative forconventional high-energy-consump-

tion high-temperature processes. Ap-

plications tested so far in the labora-tory and on industrial scale include:methane transformation to acetylene

and hydrogen, destruction of N2O, re-forming of heavy petroleum residues,CO2 dissociation, activation of organ-ic fibers, destruction of volatile or-ganic compounds in air, natural gas

conversion to synthesis gas, and SO2reduction to elemental sulfur.

Other methods

A number of other promising tech-niques do not fall within the threecategories we have discussed. Some

already are known and have beencommercially proven in other indus-tries. For instance, supercritical fluids(SCFs) are used industrially for theprocessing of natural products. Be-cause of their unique properties,

SCFs are attractive media for mass-

Coolling Water

Reflux

Steam

Condensate

Flooding Tank

Vacuum Pump

Direct Condenser

Cooling Water

Column

Product

Intermediate Product

Climbing Film Evaporator

Feed

Lamella-Type Separator

Figure 10.

Single-unit

distillation plant for

hydrogen peroxide

(77). (Drawing

courtesy of Sulzer.)


10/13


transfer operations, such as extraction

(72) and chemical reactions (73).Many of the physical and transport

properties of a SCF are intermediatebetween those of a liquid and a gas.Diffusivity in an SCF, for example,falls between that in a liquid and agas; this suggests that reactions thatare diffusion limited in the liquidphase could become faster in a SCFphase. SCFs also have unique solubil-ity properties. Compounds that arelargely insoluble in a fluid at ambient

conditions can become soluble in thefluid at supercritical conditions. Con-versely, some compounds that are

soluble at ambient conditions can be-come less soluble at supercriticalconditions. SCFs already have beeninvestigated for a number of systems,including enzyme reactions, Diels-Alder reactions, organometallic reac-tions, heterogeneously catalyzed re-actions, oxidations, and polymeriza-

tions. On the other hand, cryogenictechniques (distillation or distillationcombined with adsorption (74)),today almost exclusively used forproduction of industrial gases, may inthe future prove attractive for somespecific separations in manufacturingbulk or fine chemicals.

Dynamic (periodic) operation of

chemical reactors has interested re-searchers for more than three decades.

In many laboratory trials, the inten-tional pulsing of flows or concentra-tions has led to a clear improvement ofproduct yields or selectivities (75).Yet, despite a great amount of re-search, commercial-scale applicationsare scarce, and limited mainly to thereverse-flow reactors we have alreadydiscussed. One of the main reasons isthat dynamic operation requires in-

vestments to synchronize nonstation-ary and stationary parts of the process.So, in general, steady-state operation

is less expensive. There are cases,however, in which dynamic operationmay prove advantageous, despite thetradeoffs involved (76).

Unit operations an extinctspecies?

So far, we have highlighted a vari-

ety of equipment and techniques thatshould play a significant role in the in-tensification of chemical processes.This has not been a comprehensivecataloging, as new developments areregularly emerging from researchersworldwide. The examples do makeclear, however, that hybrid operations,

that is, combinations of reactions and

one or more unit operations, will playa dominant role in the future, process-

intensive, sustainable CPI. Has theevolution of chemical engineeringthus reached the point in which tradi-tional unit operations will give way tothese hybrid forms and become ex-tinct? Our answer to this question isboth no andyes.

No, because the development ofthese new, integrated apparatuses andtechniques is and will remain deeply

rooted in the knowledge of the basic,traditional unit operations. More thanthat, further research progress in pro-

cess intensification will demand aparallel progress in fundamental unit-operation-based knowledge. There-fore, traditional unit operations willnot disappear, at least not from chem-ical engineering research.

Yes, because some unit opera-tions simply may become too ex-

pensive or inefficient to continue tobe used commercially. These opera-tions may well be marked for ex-tinction in the industrial practice ofthe 21st century.

This scenario is even more likelyfor process equipment. Some typesof apparatuses used now probably

Figure 11. One vision of how a future plant employing processintensification may look (right) vs. a conventional plant (left) (78).(Rendering courtesy of DSM.)


11/13



Literature Cited

1. Agricola, G., De Re Metallica Libri XII,

Froben & Episopius, Basel, Switz. (1556).2. Ramshaw, C., The Incentive for Process

Intensification, Proceedings, 1st Intl. Conf.

Proc. Intensif. for Chem. Ind., 18, BHR

Group, London, p. 1 (1995).

3. Thonon B., Design Method for Plate

Evaporators and Condensers, Proceed-

ings, 1st Intl. Conf. Proc. Intensif. for

Chem. Ind., 18, BHR Group, London,

pp. 3745 (1995).

4. Thonon, B., and P. Mercier, Compact to

Very Compact Heat Exchangers for the

Process Industry, Proceedings, 2nd Intl.

Conf. Proc. Intensif. in Pract., 28, BHR

Group, London, pp. 4962 (1997).5. Mixing and Reaction Technology, Sulzer

Chemtech, Winterthur, Switz. (1997).

6. Stringaro, J.-P., P. Collins, and O. Bailer,

Open Cross-Flow-Channel Catalysts and

Catalysts Supports, in Structured Cata-

lysts and Reactors, A. Cybulski and J. A.

Moulijn, eds., Marcel Dekker, New York,

pp. 393416 (1998).

7. Irandoust, S., A. Cybulski, and J. A.

Moulijn, The Use of Monolithic Catalysts

for Three-Phase Reactions, in Structured

Catalysts and Reactors, A. Cybulski and J.

A. Moulijn, eds., Marcel Dekker, New

York, pp. 239265 (1998).

8. Stankiewicz, A., Process Intensification in

In-Line Monolith Reactor, ISCRE-16,

16th Intl. Conf. Chem. React. Eng., Cra-

cow, Poland, submitted to Chem. Eng. Sci.

9. Phillips, C. H., G. Lauschke, and H.

Peerhossaini, Intensification of Batch

Chemical Processes by Using Integrated

Chemical Reactor-Heat Exchangers,Appl.

Therm. Eng., 17 (810), pp. 809824

(1997).

10. Ketcham, T. D., and D. J. St. Jullien,

Method of Making a Cross-Flow Honey-

comb Structure, U.S. Patent 5,660,778

(Aug. 26, 1997).

11. Jckel, K.-P., Microtechnology: Applica-tion Opportunities in the Chemical Indus-

try, Monograph Series 132, Dechema,

Frankfurt, pp. 2950 (1995).

12. Tonkovich, A. L. Y., C. J. Call, D. M.

Jimenez, R. S. Wegeng, and M. K. Drost,

Microchannel Heat Exchangers for Chem-

ical Reactors,AIChE Symp. Ser., 92 (310),

AIChE, New York, pp. 119125 (1996).

13. Gibbard I., Spinning Disk Reactors. New

Opportunities for the Chemical Industry,

presented at Proc. Intensif.: Profits for the

Chem. Ind., Rotterdam, Netherlands Agen-

cy for Energy and the Env., Sittard, The

Netherlands (May 1998).

14. Boodhoo, K. V. K., R. J. Jachuck, and C.

Ramshaw, Spinning Disk Reactor for the

Intensification of Styrene Polymerisation,

Proceedings, 2nd Intl. Conf. Proc. Intensif.in Pract., 28, BHR Group, London,

pp. 125133 (1997).

15. Cheng, A. T. Y., A High-Intensity Gas-Liq-

uid Tubular Reactor under Supersonic Two

Phase Flow Conditions, Proceedings, 2nd

Intl. Conf. Proc. Intensif. in Pract., 28, BHR

Group, London, pp. 205219 (1997).

16. Hauptmann, E. G., J. M. Rae, and A. A.

Guenkel, The Jet-Impingement Reactor, a

New High Intensity Reactor for Liquid-Liq-

uid Reaction Processes, Proceedings, 1st

Intl. Conf. Proc. Intensif. for the Chem. Ind.,

18, BHR Group, London, pp. 181184

(1995).17. Rae, J. M., and E. G. Hauptmann, Jet

Impingement Reactor, U.S. Pat. 4,994,242

(Feb. 19, 1991).

18. Bourne, J. R., and M. Studer, Fast Reac-

tions in Rotor-Stator Mixers of Different

Size, Chem. Eng. Proc., 31 (5),

pp. 285296 (1992).

19. Ramshaw, C., Higee Distillation an

Example of Process Intensification, The

Chem. Eng., 389 (2), pp. 1314 (1983).

20. Ramshaw, C., and R. H. Mallinson, Mass

Transfer Apparatus and its Use, Eur. Pat.

0,002,568 (June 20, 1984).

21. Zheng, C., K. Guo, Y. Song, X. Zhou, D.

Al, Z. Xin, and N. C. Gardner, Industrial

Practice of HIGRAVITEC in Water Deaera-

tion, Proceedings, 2nd Intl. Conf. Proc. In-

tensif. in Pract., 28, BHR Group, London,

pp. 273287 (1997).

22. Chen, J., Y. Wang, Z. Jia, and C. Zheng,

Synthesis of Nano-Particles of CaCO3 in a

Novel Reactor, Proceedings, 2nd Intl. Conf.

Proc. Intensif. in Pract., 28, BHR Group,

London, pp. 157161 (1997).

23. Bisschops, M. A. T., L. A. M. Van der Wie-

len, and K. C. A. M. Luyben, Centrifugal

Adsorption Technology for the Removal of

Volatile Organic Compounds from Water,

Proceedings, 2nd Intl. Conf. Proc. Intensif.in Pract., 28, BHR Group, London,

pp. 299307 (1997).

24. Matros, Y. S., and G. A. Bunimovich, Re-

verse-Flow Operation in Fixed-Bed Catalyt-

ic Reactors, Catal. Rev.-Sci. Eng., 38 (1),

pp. 168 (1996).

25. Matros, Y. S., and G. A. Bunimovich,

Control of Volatile Organic Compounds by

the Catalytic Reverse Process, I. & E. C.

Res., 34 (5), pp. 1,6301,640 (1995).

26. Comprehensive Activities in the Engineering

and Installation of Efficient Energy Systems,

Leaflet 2016/3.0/8.90/Br, Kraftanlagen Hei-

delberg, Heidelberg, Germany (1990).

27. Kolios, G., and G. Eigenberger, Styrene

Synthesis in a Reverse-Flow Reactor,

Chem. Eng. Sci., 54 (13-14),

pp. 2,6372,646 (1999).28. DeGarmo, J. L., V. N. Parulekar, and V.

Pinjala, Consider Reactive Distillation,

Chem. Eng. Progress, 88 (3), pp. 4350

(Mar. 1992).

29. Kreul, L. U., A. Grak, and P. I.

Barton, Katalytische Destillation in Mod-

ernen Strukturiert-Katalytischen Packun-

gen, Jahrestagungen 98, II, Dechema,

Frankfurt, p. 913 (1998).

30. Stadig, W. P., Catalytic Distillation: Com-

bining Chemical Reaction with Product Sep-

aration, Chem. Proc., 50 (2), pp. 2732

(1987).

31. Halloin, V. L., H. Ben Armor, and S. J.Wajc, Reactor-Condenser, Proceedings,

5th World Congress of Chem. Eng., San

Diego, III, pp. 232237 (1996).

32. Ben Armor, H., and V. L. Halloin,

Methanol Synthesis in a Multifunctional

Reactor, Chem. Eng. Sci., 54 (10),

pp. 1,4191,423 (1999).

33. Minotti, M., M. F. Doherty, and M. F.

Malone, Design for Simultaneous Reaction

and Liquid-Liquid Extraction, I. & E. C.

Res., 37 (12), pp. 4,7464,755 (1998).

34. Samant, K. D., and K. M. Ng, Systematic

Development of Extractive Reaction Pro-

cess, Chem. Eng. Technol., 22 (10),

pp. 877880 (1999).

35. Kelkar, V. V., K. D. Samant, and K. M.

Ng, Design of Reactive Crystallization Pro-

cesses, presented at AIChE Ann. Mtg., Los

Angeles (1997).

36. Mazotti, M., A. Kruglov, B. Neri, D.

Gelosa, and M. Morbidelli, A Continu-

ous Chromatographic Reactor: SMBR,

Chem. Eng. Sci., 51 (10), pp. 1,8271,836

(1996).

37. Meurer, M., U. Altenhner, J. Strube, and

H. Schmidt-Traub, Dynamic Simulation

of Simulated Moving Bed Chromatographic

Reactors, J. of Chromatogr., 769 (1),

pp. 7179 (1997).38. Juza, M., M. Mazzotti, and M. Morbidel-

li, Simulated Moving Bed Technology

Analytical Separations on a Large Scale,

GIT Special. Chromatografie, 18 (2),

pp. 7076 (1998).

39. Vaporciyan, G. G., and R. H. Kadlec, Pe-

riodic Separating Reactors: Experiments and

Theory, AIChE J., 35 (1), pp. 831844

(1989).

40. Sirkar, K. K., P. V. Shanbhag, and A. S.

Kovvali, Membrane in a Reactor: A Func-

tional Perspective,I. & E. C. Res., 38 (10),

pp. 3,7153,737 (1999).


12/13


41. Tsotsis, T. T., A. M. Champagnie, S. P.

Vasileiadis, Z. D. Ziaka, and R. G.

Minet, Packed Bed Catalytic Membrane

Reactors, Chem. Eng. Sci., 47 (911),pp. 2,9032,908 (1992).

42. Adris, A.-E. M., and J. R. Grace, Char-

acteristics of Fluidized-Bed Membrane Re-

actors: Scale-up and Practical Issues,I. &

E. C. Res., 36 (11), pp. 4,5494,556 (1997).

43. Ahmed, T., and M. J. Semmens, Use of

Sealed End Hollow Fibres for Bubbleless

Membrane Aeration: Experimental Stud-

ies,J. Membr. Sci., 69 (1), pp. 110 (1992).

44. Shanbhang, P. V., A. K. Guha, and K. K.

Sirkar, Single-Phase Membrane Ozona-

tion of Hazardous Organic Compounds in

Aqueous Streams, J. Haz. Mat., 41 (2),

pp. 95104 (1995).45. Huizenga, P., The Continuously Filtering

Slurry Reactor, PhD Diss., University of

Twente, Enschede, The Netherlands (1998).

46. Falconer, J. L., R. D. Noble, and D. P.

Sperry, Catalytic Membrane Reactors, in

Membrane Separations Technology. Prin-

ciples and Applications, R. D. Noble and

S. A. Stern, eds., Elsevier, Amsterdam,

pp. 669712 (1995).

47. Ebrahimi-Moshkabad, M., and J. M.

Winterbottom, The Behaviour of an In-

termeshing Twin Screw Extruder with Cat-

alyst Immobilised Screws as Three-Phase

Reactor, Cat. Today, 48 (14),

pp. 347355 (1999).

48. Tagawa, T., K. K. Moe, M. Ito, and S.

Goto, Fuel Cell Type Reactor for Chemi-

cals-Energy Co-generation, Chem. Eng.

Sci., 54 (10), pp. 1,5531,557 (1999).

49. Uhde, G., K. Sundmacher, and U. Hoff-

mann, Simultaneous Gas-Solid Reaction

and Comminution: A Novel Multifunction-

al Reactor, Proceedings, 5th World

Congress of Chem. Eng., San Diego, I,

pp. 167172 (1996).

50. Jansen, A. E., R. Klaassen, and P. H. M.

Feron, Membrane Gas Absorption a

New Tool in Sustainable Technology De-

velopment, Proceedings, 1st Intl. Conf.Proc. Intensif. for the Chem. Ind., 18, BHR

Group, London, pp. 145153 (1995).

51. Poddar, T. K., S. Majumdar, and K. K.

Sirkar, Removal of VOCs from Air by

Membrane-Based Absorption and Strip-

ping,J. Membr. Sci., 120 (4), pp. 221237

(1996).

52. Lawson, K. W., and D. R. Lloyd, Mem-

brane Distillation: A Review, J. Membr.

Sci., 124 (1), pp. 125 (1997).

53. Godino, P., L. Pea, and J. I. Mengual,

Membrane Distillation: Theory and Ex-

periments,J. Membr. Sci., 121, pp. 8993

(1996).

54. Foster, P. J., A. Burgoyne, and M. M. Vah-

dati, A New Rationale for Membrane Dis-

tillation Processing, presented atIntl. Conf.

on Proc. Innov. and Intensif., Manchester,U.K., I.Chem.E., Rugby, U.K. (1998).

55. Yu, K. T., M. Zhou, and C. J. Xu, A

Novel Separation Process: Distillation Ac-

companied by Adsorption, Proceedings, 5th

World Congress of Chem. Eng., San Diego,

I, pp. 347352 (1996).

56. Mason, T. J., Practical Sonochemistry.

Users Guide to Applications in Chemistry

and Chemical Engineering, Ellis Horwood,

New York (1991).

57. Mikkola, J. P., and T. Salmi, In situ Ultra-

sonic Catalyst Rejuvenation in Three-Phase

Hydrogenation of Xylose, Chem. Eng. Sci.,

54 (10), pp. 1,5831,588 (1999).58. Horst, C., Y.-S. Chen, U. Kunz, and U.

Hoffmann, Design, Modeling and Perfor-

mance of a Novel Sonochemical Reactor for

Heterogeneous Reactions, Chem. Eng. Sci.,

51 (10), pp. 1,8371,846 (1996).

59. Trabelsi, F., H. At-Lyazidi, B. Ratsimba,

A. M. Wilhelm, H. Delmas, P.-L. Fabre,

and J. Berlan, Oxidation of Phenol in

Wastewater by Sonoelectrochemistry,

Chem. Eng. Sci., 51 (10), pp. 1,8571,865

(1996).

60. Ganz J., P. Haueter, A. Steinfeld, and D.

Wuillemin, A Novel Volumetric Solar Reac-

tor for Metal Oxides Reduction, Proceed-

ings, 7th Intl. Symp. Solar Thermal Conc.

Tech., Moscow, 4, pp. 826832 (1994).

61. Meier, A., J. Ganz, and A. Steinfeld,

Modeling of a Novel High-Temperature

Solar Chemical Reactor, Chem. Eng. Sci.,

51 (11), pp. 3,1813,186 (1996).

62. Pohlmann, B., H.-D. Scharf, U. Jarolimek,

and P. Mauermann, Photochemical Pro-

duction of Fine Chemicals with Concentrat-

ed Sunlight, Sol. Energy, 61 (3),

pp. 159168 (1997).

63. Peill, N. J., and M. R. Hoffmann, Solar-

Powered Photocatalytic Fiber-Optic Cable

Reactor for Waste Stream Remediation, J.

Sol. Energy Eng., 119 (3), pp. 229236(1997).

64. Gedye, R. N., F. E. Smith, and K. C. West-

away, The Rapid Synthesis of Organic

Compounds in Microwave Ovens, Can. J.

Chem., 66 (1), pp. 17-26 (1988).

65. Curtis, W., C. Lin, R. L. Laurence, S. Yn-

gvesson, and M. Turner, Microwave Sorp-

tion Reactor Engineering, presented at

AIChE Ann. Mtg., Los Angeles (1997).

66. Karayiannis, T. G., M. W. Collins, and P.

G. Allen, Electrohydrodynamic Enhance-

ment of Nucleate Boiling Heat Transfer in

Heat Exchangers, Heat Technol.(Bologna),

7 (2), pp. 3644 (1989).

67. Weatherley, L. R., Electrically Enhanced

Mass Transfer,Heat Recov. Sys. & CHP, 13

(6), pp. 515537 (1991).

68. Yamaguchi, M., Electrically Aided Extrac-tion and Phase Separation Equipment, in

Liquid-Liquid Extraction Equipment, J. C.

Godfrey and M. J. Slater, eds., Wiley, New

York, pp. 585624 (1994).

69. Czernichowski, A., and T. Czech, Plasma

Assisted Incineration of Some Organic

Vapours in Gliding Discharges Reactor,

Polish J. Appl. Chem., 39 (4), pp. 585590

(1995).

70. Czernichowski, A., and H. Leuseur,

Multi-Electrodes High Pressure Gliding

Arc Reactor and its Applications for Some

Waste Gas and Vapor Incineration, Pro-

ceedings, Plasma Appl. to Waste WaterTreat., Idaho Falls, ID, pp. 113 (1991).

71. Czernichowski, A., J. Polaczek, and T.

Czech, Cold-Plasma Reduction of Flue-

Gas SOx to Elemental Sulfur, Proceedings,

ISPC-11, 11th Intl. Symp. Plasma Chem.,

Loughborough, U.K., I. U. P. A. C., Re-

search Triangle Park, NC, pp. 674679

(1993).

72. McHugh, M. A., and V. J. Krukonis, Su-

percritical Fluid Extraction, Butterworth-

Heinemann, Boston (1994).

73. Savage P. E., S. Gopalan, T. I. Mizan, C.

J. Martino, and E. E. Brock, Reactions at

Supercritical Conditions: Applications and

Fundamentals, AIChE J., 41 (7),

pp. 1,7231,178 (1995).

74. Jain, R., and J. T. Tseng, Production of

High Purity Gases by Cryogenic Adsorp-

tion, presented at AIChE Ann. Mtg., Los

Angeles (1997).

75. Silveston, P. L, Composition Modulation

in Catalytic Reactors, Gordon & Breach,

Amsterdam (1998).

76. Zwijnenburg, A., A. Stankiewicz, and J.

A. Moulijn, Dynamic Operation of Chemi-

cal Reactors: Friend or Foe?, Chem. Eng.

Progress, 94 (11), pp. 3947 (1998).

77. Siirola, J. J., Synthesis of Equipment with

Integrated Functionality, presented at Proc.Intensif.: Profits for the Chem. Ind., Rotter-

dam, Netherlands Agency for Energy and

the Env., Sittard, The Netherlands (May

1998).

78. Meili, A., Practical Process Intensification

Shown with the Example of a Hydrogen

Peroxide Distillation System, Proceedings,

2nd Intl. Conf. Proc. Intensif. in Pract., BHR

Group, London, 28, pp. 309318 (1997).

79. Sustainable Technological Development at

DSM: The Future Is Now,DSM Magazine,

No. 83, pp. 410 (Feb. 1999).


13/13

will disappear from plants because

of process intensification. They willgive way to new task-integrated de-

vices. A spectacular example of suchtask integration already applied oncommercial scale is the new methylacetate process of Eastman ChemicalCo.; seven tasks have been integrat-ed into a single piece of equipment(77) as illustrated in Figure 9. A sin-gle-unit hydrogen-peroxide distilla-tion plant (Figure 10) developed bySulzer (78) is another example of

such changes already taking place inindustry.

The CPI skyline also is likely to

change. New, highly efficient devicesmay replace tens-of-meters tall reactorsand separation columns. And, plants inwhich reactions take place undergroundin pipeline reactors and products areseparated in 12 m dia. rotating devicesare certainly conceivable.

Will further developments in the

CPI resemble those in the electronicsindustry and will process plants andequipment become increasinglyminiaturized as has happened in thefields of information and communi-cation? The answer very much willdepend upon the existence of suffi-ciently strong drivers to stimulate orforce such changes. In case of infor-mation and communication, a signifi-cant number of such drivers existedin the past, the cold war and the

space race of the super powers tomention only two. This led to revolu-tionary changes, particularly in mate-rials technologies, that eventuallybrought to our desks computers

much faster and more powerful thantheir multistory-building-size ances-tors. In the case of the CPI, the mostprobable scenario is that society it-self will spur radical changes. Withever-increasing population densityand growing environmental con-

sciousness in society, there will be noroom (literally and figuratively) forthe huge, inefficient chemical facto-ries producing tons of wastes per tonof useful product. Miniaturizationand process intensification in general

will become inevitable.

The role of educationTo make these society-driven

changes come true, the teaching of

chemical engineering also will haveto undergo some essential revision.First, future chemical engineers willhave to be taught an integrated, task-oriented approach to plant design,not todays sequential, operation-ori-ented one. (Eastmans process in Fig-ure 9 clearly illustrates the differencebetween these two approaches.) Toachieve this goal, the education of

future engineers must place muchmore stress on creative, nonschemat-ic thinking, not confined to known

types of equipment and methods.Second, future chemical engineersmust gain a much deeper knowledgeand understanding of process chem-istry (and chemists must becomemuch more familiar with the relatedengineering issues) because, inthe highly efficient chemical process-

es of the coming decade, chemistryand engineering will be meeting eachother at the molecular level, not atthe apparatus level as they do today.Third, material engineering will playan essential role in the developmentof new chemical processes at themolecular level (e.g., engineering ofcatalysts) and, therefore, will becomea much more important part of thechemical engineering curriculum.

Meeting these demands will re-

quire concerted effort and somecrucial cultural changes from uni-versities to find the new ways ofteaching chemical engineering andchemistry. But, these steps are es-

sential if the CPI are to prosper andrealize industrial visions of com-pact, efficient, sustainable technolo-gies like the one recently presentedby DSM (79) (Figure 11) come true.

Epilogue: the legacyof Agricola

Now, looking again at Figure 1, wehave a different perspective. WhatAgricola showed in his woodcut is ahighly task-integrated and energy-ef-ficient continuous plant for gold re-

covery! The energy-efficient integra-

tion of three different processing tasks

takes place via the water-wheelA thatsimultaneously supplies power to

crush ore in the crusher C, grind it ingrinder K, and recover gold by mixingthe ore with mercury in the three-stage system of stirred vessels O.

And, perhaps only now at thevery end of our article, can we saywhat process intensification reallyis. It is thinking progressively aboutprocesses and viewing them inte-grally through the tasks they have to

fulfill and the results they have todeliver. CEP



A. I. STANKIEWICZ is a senior researcher with

DSM Research in Geleen, The Netherlands

(31 46 4760820; Fax: 31 46 4760809;

E-mail: Andrzej.Stankiewicz@dsm-

group.com) and associate professor in

the Industrial Catalysis Section of Delft

University of Technology, Delft,

The Netherlands (31 15 2785006,

Fax: 31 15 2784452, E-mail:

[email protected]).

He is author or co-author of over 60

papers on chemical reaction engineering

and industrial catalysis, and holds

several patents in the field. He received

a PhD in chemical engineering from the

Industrial Chemistry Research Inst., Warsaw.He is a member of AIChE.

J. A. MOULIJN is professor of industrial

catalysis at Delft University of Technology,

Delft, The Netherlands (31 15 2785008; Fax:

31 15 2784452; E-mail:

[email protected]). The editor of

five books, the author or co-author of over

400 professional papers,

and the holder of several international

patents in reactor design, zeolithic

membranes, and catalysis development,

he is a chief technical advisor to

the U. N. Devel. Org., and serves as

European editor of Fuel Processing

Technology. He holds a PhD in chemical

engineering from the Univ. of Amsterdam,and is a member of AIChE.

Related Web Sitewww.ncl.ac.uk/pin/ administered by the Dept.

of Chemical and Process Engineering of the

Univ. of Newcastle started up in April. This

site, under the guidance of Colin Ramshaw,

professor of intensive processing, will contain

research and industry news, technical infor-

mation, articles on new technologies, a direc-

tory of equipment makers, plus links to other

resources for process intensification.

Process Intensification, Transforming Chemical Engineering.pdf

Documents

Transcript of Process Intensification, Transforming Chemical Engineering.pdf