Microscale and Nanoscale Process Systems Engineering: Challenge and Progress

第8卷第3期过程工程学报Vol.8 No.32008年6月The Chinese Journal of Process EngineeringJune 2008Microscale and Nanoscale Process Systems Engineering: Challenge and ProgressYANG You-qi (杨友麒)(China National Chemical Information Center, Beijing 100029, China)Abstract: This is an overview of the development of process systems engineering (PSE) in a smaller world. Two diferentspatio-temporal scopes are identified for microscale and nanoscale process systems. Tbe features and challenges for eachscale are reviewed, and different methodologies used by them discussed. Comparison of these two new areas with traditionalprocess systems engineering is described. If microscale PSE could be considered as an extension of traditional PSE, nanoscalePSE should be accepted as a new discipline which has looser connection with the extant core of chemical engineering. Since“molecular factories" is the next frontier of processing scale, nanoscale PSE will be the new theory to bandle the design,simulation and operation of those active processing systems.Key words: process systems engineering; microchemical engineering; nanotechnology; molecular factoryCLC No: TQ021.8Document Code: AArticle ID: 1009- 606X(2008)03- 0616 -091 INTRODUCTION10000Eoolog, Indus pankAccording to Schumpeter's innovation wave theory,100we may now be living in the first half of bio/nan/infoTnodtonl PSEwave. We find there a shortage of knowledge iunderstanding the world of a smaller scale. For instance,Mcroscale PSE0.01in the nanoscale world only since. 1981 we havemanaged to measure the size of an atom cluster on a1E-4Pancscale PsEsurface, and only in 1991 we were able to move atomson a surface. Assembling molecules by physically1 1E-101E-8 1E6 1E4 0.01 1 100 100positioning their component atoms is an issue of theLength scale (m)21st centuryh-. Now we can say that we are enteringFig.1 The dfferent spatio temporal scopes of processan epoch of “molecular processing”. As Hegedus'lsysterns engineering (PSE)pointed out, there is a new overlap between chemicalengineering and chemistry in scales ranging from tensThe development of finechemical andof nanometers to hundreds of micrometers. This newpharmaceutical industries has promoted the demand ofoverlap is the focus of research to fill the knowledgespeedycommercialization of product innovation byvacancy in the small-scale world.shortening the period from laboratory to market.This small-scale world should be divided into two“Making your learming at a small scale and your profitscategories according to their spatial and temporalon a large scale” bas become the commoncharacteristics: microscale processsystems andunderstanding in the process industries. However,nanoscale process systems. Since there is a 1 000-time"learning at a small scale" used to mean lab and pilotdifference spatially between them, the research objects,plants, although now it means microscale and nanoscalemethodologies and dominating rules are quite different.experiments. This not only means that in recent researchThe characteristic length of the former systerms is 1~100environment, innovation could be accormplished muchum (microchannel size) and that of the latter systems isfaster, much cheaper and much better in smaller-scaleabout an nm (supramolecular size), the characteristicfacilities, but also means that many new processtime scale of the former systems is ms and that of thepossibilities could only be implemented in microscalelatter us. The spatial and temporal scopes of traditionalfacilities'process systems engineering (PSE), microscale PSE and中国煤化工re increasinglynanoscale PSE are shown in Fig.1. .challenodularization andYHCNMHGReeived date: 2008- 02- 18; Acepted date: 2008-04 -28Biograpby: YANG Youqi (1935-), male, native of Xiangtan City, Hunan Province, Bacbelor, Professor, major in process systems cogineering,E-mail: yang@pku.edu.cn.第3期YANG You-qi: Microscale and Nanoscale Process Systems Engineering Challenge and Progress617miniaturization. Process intensification also tends②The ratios of viscous force to inertial force and oftoward this direction. If in 1970~1980s the wholeinterfacial force to inertial force in microchannel arechemical industry tried reducing cost through enlargingseveral orders of magnitude higher than that in regularequipment size in order to gain competitive advantage,equipment, meaning that laminar flow always happenssince the end of last century, a contrary trend hasin microchannels and heat conduction with molecularemerged, because the high energy consumption of largediffusion dominates the transport phenomena. Thereforeplants, heavy pollution to environment, and lowheat and mass transfer will be significantly initensified;efficiency of traditional chemical industry could notfor example, the heat transfer coefficient for micro-heatmeet the requirements of sustainable development.exchanger could be as large as 25000 W/(m^."C), asCompared with the fast upgrading of micro-electronic-compared with that of regular heat exchanger of 200 W/mechnical systems (MEMS), the contrast is obvious.(m2."C). The mass transfer coefficient for multichannelMiniaturization of chemical lab and plant is becoming amicroreactor could be KLa≈5~15 s，which is tworealistic trend in this new centurys.orders of magnitude larger than those for macroscopicreactors, Ka~0.01~0.08 s [10. These characteristics2 MICROSCALE PROCESSforetell the possibility of high yields of chemicalSYSTEMS ENGINEERINGreactions under such microscale extreme conditions.③Since inertial force has much less influence in small2.1 Features and Advantages of Microscale PSEdimensions, space turbulence is avoided. The high heatSince 1980s of the last century, integrated circuitand mass transfer rates also allow reactions to beand MEMS have continued to develop, until in 1989performed under more uniform temperature conditions.Ciba Geigy published micro-total-analytical-systemAll of these make it feasible to fully characterize(μ-TAS) as a representative microdevice for applicationchemical reaction engineering parameters from sensorin combinatorial chemistry and high throughputdata.screening. In 1995 the first workshop on microsystemstechnology for chemical and biological microreactors inTable 1 Scaling ffect of transport properties周Germany has been credited for giving birth to a newPropertyLengh(Z)10-discipline: microreactor engineering°. Since thenSurfce area ([3)10-110-1210-16intemnational conferences on microreactor technologyVolume (巧)1010~18 10have been held almost every year. At about the sameSpecifc surfce area(C")Rate (xL)time, Du Pont published the. first demonstrationmicrochemical plant to synthesize a number ofhazardous chemicals including isocyanates which haveViscous force/inertial force (xL3)storage and shipping limitations'.Interfacial tension/inetial force (xL ,)Therefore, integrating the design idea of MEMSand principles of chemical engineering,and(2) Miniaturization brings signifcant reduction oftransplanting the micro-fabrication technology of sample amount required in tests, much faster and moreintegrated circuit and microsensor led to the birth of aaccurate. Microchemical systems for combinatorialnew high-technology, microchemical technology.synthesis and screening samples have reduced theMicrochemical technologystudies the design,detection time from 2~3 h to 50 s, and enhanced thesimulation, operation, control and application ofaccuracy to zmol (10 21 mole)"]. Contemporary DNAmicrochemical systems within the spatial range ofdetector and“pharmacy-on-a-chip" are good application1~100 μm and temporal range of 1~100 ms. Such kindexamples.of systems has many features different from traditional(3) Inherent safety and good controllability.chemical systems as follows:Because the characteristic scale of microstructure is(1) The miniaturization of length scale causessmaller than the fre-spread critical diameter ancsignificant effects on transport properties and actingpowerful heat transfer capability of microchannels,forces, as shown in Table 189:①The specific surfaceexplo中国煤化工microreactors couldarea increases 10*~10 times as the scale of flowbe saperation range andchannel reduces. The specific surface area of regularwith'YHC N M H Gxplosion happened,flow channel is not more than 1000 m/m', but that ofthere would be less serious results because of its smallmicrochannel could be as high as 10000~ 50000 m2/m3.holdup.618过程工程学报第8卷(4) Convenience in process scale-up to commercialmulti-phase, catalytic or non-catalytic， isolated orproductionof newproducts.Numbering-upintegrated with other unit operations， e.g.， heatmicroreactor units used in laboratory would eliminateexchanger, membrane separation, etc. Some criticalcostly and time-consuming pilot plant experiments,indices are found in trying to identify the threshold, e.g,thereby shortening the development time from lab toφ=reaction rate/diffusion rate, at which geometriccommercial production. This feature is very importantinfluence on reaction becomes insignificant' .for fine chemical and pharmaceutical industries,(2) Unit operations at microscale are quite differentbecause the lab-to-market time is a key performancefrom the regular ones. First, mixing becomes veryindex of competitiveness. Besides, 50% chemicalimportant when laminar flow and molecular difusionreactions used in existing fine chemical industry coulddominate to make mixing very slow, calling fore changed from batch production into continuousreduction of the diffusion length, such as the idea ofproduction by using microreactors in order to increasesplitting-recombination mixerl7.18. Secondly, fluidthe yield of high value added productsll2 -15].dynamics of microchannels deviates from classical fluid(5) Possibility of implementing distributeddynamics, for two-phase flow where interfacial tensionproduction mode in chemical industry. The features ofdominates. Thirdly, heat transfer efficiency inmicrosystems make modularization of production muchmicrochannels is higher for ceramic and glass heateasier, thus making it possible distributed production ofexchangers because of reduced axial heat transfer inchemicals right next to consumers. Such distributedceramic and glass heat exchangers as compared withpoint-of-use chemical synthesis of chemicals with lessmetallic oneslo.19. Many new unit operations have beenstorage and transport limitations not only eliminatescreated recentlyewhich need to be screened forpotential dangers, but also better utilizes local resources.practical applications at the microscale.Such prospect challenges traditional centralized mode of(3) Process integration and optimization. One ofchemical production. In the future, chemical industrythe most significant characteristics in a microchemicalmay produce single components to be distributed andsystem is its highly compact integration. Gavilidis etfinally “assembled" locally into products in the manneral.0o pointed out three kinds of integration architecture:of electronic and automobile industries!lo.vertical, horizontal and hybrid, and platforms to allow(6) Pursuing new reaction paths. Increased heatintegration of all components using “plug-and-play"conduction out of catalyst suppresses “hot spots” andmodules. Those microprocess integrations have so faropens mild reaction conditions typically not accessiblebeen made for fabrication concems, and generalin conventional reactors, thus making easiertheoretical methodology to guide these activities is notimplementation of highly exothermic reactions ingiven yet. Kirschneck et al.4n put forward a three-phasemicroreactors and opening new possibilities fordesign methodology: process stability study, flowsheetsearching environmentallybenign product andoptimization study and industrial plant design, as shown114.process'in Fig.2. Pfeiffer et a.2 tried to optimize microscale2.2 Challenges to PSEseparation systems by using distributed agents. Chow231Since 1996, research in microchemical systems haspointed out many yet unanswered theoretical problemscontributed more than 1 000 published papers, thoughin microchemical systems design. The difficulties invery few among them from engineering viewpoint,integration and optimization of microchemicalparticularly PSE one. The difference is primarily due to:processes could be hardly separated fom fabricationfirst, the pioneers in this field are mostly chemists, nottechnology.chemical engineers; secondly, at this initial stage ofmicrochemicalsystems, the crucial technology ismicroreactor fabrication and application rather thangeneral process design; thirdly, commercial productionusing microstructured devices has just started and notaccumulated enough scale-up experience. Therefore thisfield is full of challenges as follows:(1) Modeling of microreactor. Microreactor is theFig2中国煤化工nin poces saeul[1]nucleus of microchemical systems, and mathematicalCNMH Gmodels of microreactors form the basis for further(4) scaic-up pruulems Ior microstructured systems.research of PSE. Microreactors could be single-phase orThere are probably three major reasons for the第3期YANG You-qi: Microscale and Nanoscale Process Systems Engineering: Challenge and Progress619popularityofmicrochemicalsystems.First,response time. If model predictive control (MPC) ismicrostructures require highly clean flow in order toused, the model calculation must be sufficiently fast,avoid blockage; secondly, numbering-up is not as easye.g., calculation speed is 50~500 times faster than realas imagined, because distribution uniformity needs to beime'Palusinski et al.50J pointed out that processguaranteed; thirdly, it is difficult to persuade enterprisecontrol ofmicrochannelsystemsinvolvingmanagers to adopt new microstructured facilities tohigh-frequency signal processing is not suitable usingreplace existing traditional ones. Generally the onlypopular digital control techniques and is better usingopportunity for using microstructured systems is foranalog circuits. But the latter has been limited by thenew plants. Recent research showed that distributiondifficulty in implementing algorithms of highuniformity was probably not as serious as commonlycomplexity due to the finite accuracy of analogthought. Delsman et al. [24) proved by theoretical analysiscomponents. So it is desirable to have flexible,and experiments that the influence of maldistribution onprogrammable systems that allow the functionaloverall reactor conversion rate is relatively small k partitioning of analog and digital circuits to be changed0.5%), while the influences of channel diameter andduring processing. They put forward a new technologyamount of catalyst coating are more pronouncedof field-programmable analog arrays which could meet(3%~5% lower conversion rate). Rebrov et al.t5such requirements'5n. Another problem in operatingproposed a header consisting of a cone diffusermicrochannel systems is diagnosis of blocked channels,connected to a thick-walled screen, which improveswhich could be treated by the method developed bynonuniformity to less than 0.2%. Tonkovich et al.20]Kano et al.52 based on data base and models.proposed a scale-up methodology for commercial-scale3 NANOSCALE PSEsteam-methane reforming at a capacity of 8 m'/s. Theysuggested a uniform index Q=(Mmxt -Mmn)/Mmax≤20%3.1 Nanotechnology and Nanoscale Systemsis acceptable for industrial use. Hasebe et al.127,28]Nanotechnology, a high-tech developed since theproposed a six-step design and scale-up methodology:nd of last century, is devoted to the understanding,usingCFDsofware.An industrial-academiccontrol and manipulation of matter at the level ofconsortium involving 20 famous companies andindividual atoms and molecules as well as at theresearch institutes was established in the framework of"“supramolecular" level involving clusters of molecules.SUSTECH initiative of European Chemical IndustryIts goal is to create materials, devices and systems withCouncil (CEFIC)， called IMPULSE (integratedessentially new properties and functions because of theirmultiscale process units with locally structuredsmall structures. The development of this technologyelements)4，aiming to develop a methodology forserves to fill u mankind's knowledge of many newstructured multiscale chemical process design.phenomena and processes at the scale of individual(5) Development of simulation tools. Complexmolecules to 100 molecules, that is, 1~100 nm.coupling fodeveloping simulation models ofFrom an engineering viewpoint, Roco21 identifiedmicrochemical systems arises from the strongour generations of nanotechnology products andinteraction between electrical, mechanical, thermal,research since 1996:microfluidic, transport and chemical phenomena inFirst generation (~2001) dealt with passivecompactly configured microgeometries. As early asnanostructured products, ilurtrated by nanostructured1990s of the last century, MIT developed the softwarecoatings, dispersions of nanoparticles and bulk materials,MEMCAD to analyze MEMS and Lab- on-a-chip,e.g, nanostructured metals, polymers and ceramics.followed by COMSOLab which developed anotherSecond generation (~2005) consisted of activesoftware, FEMLAB. Recently the most popularnanostructured products, ilustrated by transistors,simulation tool used for microchemical systems is CFDamplifiers, targeted drugs and chemicals, actuators andbased on finite element analysis, which is capable of adaptive structures. Molecular tectonics was putsimulating geometric influences on reactions though notforward in this period, aimed at making preciseof simulating mass and heat balance of whole systems.functional supramolecules to build meso-/nano-scaleIn order to do so, it is necessary to nest CFD into specialunits,中国煤化工rs, molecular tubes,flowsheeting software for microchemical systems.motorEgates/channels for(6) Operation and control of microsysterms toselectiMHCN M H Gules. Key researchinsure that the microreactors are compactly integratedincludedmultiscalemodeling and simulation,with sensors and actuators in order to shorten theirnanobiosensors and devices, and tools for molecular620 .过程工程学报第8卷.medicine.(includingcatalyst). (2) Separators,includingThird generation (~2010) is to start with 3-Dnanoporous media, membranes, molecular sieves,nanosystems and nanosystems engineering, variousmolecular channels, ionic gates, etc., which have thesyntheses and assembling techniques such ascapability of selectively transporting ions or molecules.bio-assembling and networking at nanoscale and(3) Molecular mixer and sliter. (4) Energy formationmultiscale architectures. Research focus will shiftand dissipation.toward supramolcular systems engineering whichMaterial transporters: (1) Nanotubes, using variousincludesdirected multiscaleself- assembling,driving potentials (chemical/charge ditributions alongchemico-mechanical processing,and nanoscaletubes, etc.) to transport ions, molecules or isomers. (2)electronic -mechanical systems (NEMS), and targetedMolecular motors, pumps and shuttles.cell therapy with nanodevices.Control elements: (1) Signal carriers, molecularFourthgeneration (~2015) willconsiderelectrical wires, directional“effective”concentrations ofheterogeneous molecular nanosystems in which eachsurface charges, ions or molecules. (2) Actuators,molecule has a special structure and plays a differentmolecular switches, gates, valves, etc.role, and each system possesses a unique function. SuchThe research of molecular tectonics has alreadysystems approach the way that biological systems workmanaged to use simpler molecules assembling to unitin aqueous surrounding with relatively slow informationoperation supramolecules with the above complexprocessing. Emerging in this generation are thefunctions. Among those building components there aremolecularfactories,behaviorof complexmany simple and familiar molecules, porphyrins,macromolecular assemblies, nanosystem biology fofullerines,multifunctional heterocycles, metalhealthcare and agricultural systems, human-machinecomplexes, silsequioxanes, oxyanions, catechols,interface at the tissue and nervous system level.chalcogenide clusters and multi-hydrogen-bondingWith the birth of nanoscale process systermsmolecules(34.engineering, Stephanopoulos et al.5) at MIT proposedFacing this kind of“molecular factories", what are“nanoscale factories" as the next frontier of processingthe challenges for PSE? Probable problems are thescale and nanoscale PSE as the new theory to handle thefollowing: (1) The accuracy of scale description indesign, simulation and operation of those activenanoprocessing is quite different from that of traditionalprocessing systems.PSE; the position precision requires an accuracy of a3.2 Features and Challenges for Nanoscale PSEfew A to nanometers. (2) Using average bulk value toBiological cell is a prototypical model ofdescribe the properties is not suitable innanosystems,“supramolecular factory": the plasma membrane definesbecause that is based on the assumption of“continuitythe boundaries of the "factory", allowing for selectiveof the material". However, this assumption only keepsflow of molecules in and out of the cell. The cell'svalid for thickness of liquid layers larger than 10organelles, such as nucleus, endoplasmic reticulum,molecules, while in molecular factory made bymitchondria, lysosomes, endsomes, etc., represent thesupramolecules, it is no longer valid. (3) The principles"supramolecular unit operations".of design and fabrication are different from those ofA typical nanoscale processing system is composedtraditional PSE. The philosophy of design and)f the following components: molecular scaffold,manufacture for regular systems is a top-downsupramolecular unit operations, material transporthierarchical approach. But for nanoprocessing, systemselements, monitoring and controlling signals. Whilecan be fabricated with such positioning accuracy thatbiologists are exploiting the mechanism of fundamental only through guided bottom-up self-organization offunctions,chemists are synthesizing serial newmolecules and supramolecules can make it possible. (4)structured supramolecules which possess the simulatedThe principles of operation and control are different.biological functions34. Those typical nanoscaleThe control of traditional process systems is based onprocessing units are listed as follows:central control, distributed control or loops- centerScaffolds: (1) Biological molecules (DNA, viruses).coordination control, but control of a nanoscale process(2) Inorganic scaffolds (branched nanocrystals, crossedsyster中国煤化Ielf-regulation andnanowire grids).secon_nals. Self-regulationoperations:(1) Reactors, variety ofat aCN M H Ge ahieved throughconfigurations (circle, loop, ube) and reaction functions judicious interactions among the supramolecular units第3期YANG You-qi: Microscale and Nanoscale Process Systems Engineering Challenge and Progress621 .acting as independent agents, since very limited extermnalnovel materials acrossorganic and inorganicmanipulations are technologically possible to effectchemistry,[37,38]on-system operation. (5) The mechanism ofSystem biology is a new discipline to study thenanoprocess systems is essentially the engineering 0relationships between overall functions and constructedcomplex systems because of their self-assembly,components and the new interface between molecularself- organization, self-replication and self-regulation. Asbiology and physiology. Nano-PSE is using the researchOttino5J has identified, “what is a complex system?results of system biology to design and manufactureComplex systems can be identified by (1) what they do,artificial biological systems, such as silicon cllsl94 .hey display organization without central organizingSince Adleman put forward the idea that DNAprinciple (emergence), and (2) how they may or may notcould be used to construct a generic computer in 1994,be analyzed, decomposing/analyzing subparts do notthe molecular computer was borm as a branch ofnecessarily give a clue as to the behavior of the whole."computational life science. There are two ways in theThe tools for study of complex systems are nonlineardevelopment of the molecular computer: (1) thedynamics and chaos, statistical physics (includingbiological way, exploiting the computational capabilityprobabilistic approach)， agent-based modeling, andof biological molecules and trying to create fasternetworks theory (including small-world network andcomputation speed (massively parallel), smaller sizescale-free network)1S,36.(nanoscale) and more cost effective (energy saving)3.3 Nanoscale PSE as a Periphery Disciplineinformation processing systems, and (2) the molcularAs Ottinol3l pointed out in the period 1960s~1970s,elctronics way, trying to design and manufactureperiphery disciplines were developed as expansions ofdigital computers with more precise circuits. This istheir core: ideas flew from the core to the periphery.only miniaturization of the traditional digital computer,However, since 1990s the periphery was only looselythe principles remaining the samel42.43).connected to the core, a shift from where tools unifiedhe picture to a stage in which the periphery4 COMPARISION OF MICRO-,overpowered the core. Nanoscale PSE could be realizedNANO- AND TRADITIONAL PSEas a cross-discipline, as demonstrated in Fig.3, whereComparing the features of micro, nano- andone may find the PSE, system biology, moleculartraditional PSE systems, Table 2 delineates the bigtectonics and molecular computer are all fueling thedifferences between them. We can realize that thedevelopment of nanoscale PSE.principles of microscale PSE are more or less similar tothat of traditional PSE， making microscale PSEPSEsomewhat an extension of macroscale PSE. Howevernanoscale PSE is quite different from macroscale PSEin terms of methdologies of design, manufacturing andSystemMolecularNanoscaleoperation of the systems, having rather loosebiologytectonicsconnections with the core chemical engineering andPSE, as shown in Fig.4.This kind of multi-scale process systermsengineering study is entering the research scope Ccomputercomplex systems, as studied by Li et a.4.45J andKwaukl46. Correlation betweendifferent scales,Fig3 The feature of nanoscale PSE as a periphery disciplinecoupling between time and space dependencies andMolecular tectonics as a new branch of modemidentification of dominant mechanisms are becomingchemistry studies how molecules construct thosethe important steps in studying complex systems.complex molecular networks driven by differentFinding spatio-temporal compromise between dominantfunctional forces and how supramolecules are generatedmechanisms is crucial in process integration. That alsowith specific functions. This discipline has alreadycalls中国煤化工atial and temporalobtained many interesting research results from porouschangYHdifferences ofmetal-organic compounds to engineered crystals. It hasextremC N M H Gocal instantaneousgiven the way to design principles that arm thevariables and spatio-temporal average variables.imaginative architect with blueprints for constructing622过程工程学报第8卷Table2 Comparison of PSEs in different scalesMacro-process systemMicrostrucwured systcmNanoscale factoriesTypical systeChemical plantμTAS (Micro total analysis systcm)Biological cell,l silin cellScale from a few 10 few hundred nm,Size measured in metersSize measured in mm, but poeitionalpositional accuracy in few A to fewScale of manufacturing andConfigunation driven by cost,accuracy could be in um,nm; Oreriding consideration oftopological confgurationenvironmental and safetyconfiguration driven by efctivetopological flowsbeet is overall-systemconsiderationsspace uility and process eficicncy.functinalityAs long as the critical size of liquidmedia is of order 10 molcular layers,the continoum assumpion holds. ThePropety of poessed materialBulk characterization of processed materialschancterization of suprunolecular wnit(average over whole or local systems)operations, transporters and molecularcontrol structures cannot be based onaveraged bulk properties, but on secificatomic and molccular confgurations.Design approach is top-down, hierarchical approach.Only through a free and/or guidedDesign and fabricationMarufacuing is also through top-down, man- machine contolledbottom-up selforganization of moleculesconstruction.and supramolecular structuresTime- constants are from minutes to Timeconstants are fom seonds tohours, operating cycle times areminutes; operating cycle times areTime constants are miliseconds,from hours to years.from seconds to minutes.operating cycle times are scconds,Operational control structureControl systems: multivariableControl Systems: mulivariableprimary control mechanism iscentralized control or centralizedself-egulation.coordination of local control los.__ coordination oflocal control loops.Mcroscalemicrochemical systems challenge traditional PSE inPSEterms of fluid dynamics of microreactors and micro-unitoperations, process integration and industrial scale-up,but microscale PSE could be considered an extension ofCoretraditional PSE.Chem Eng(3) As“molecular factories" are the frontier ofnext generation manufacturing, traditional PSE is notvalid in this area. Because there are essential differencesbetween molecular factories and traditional chemicalplants in terms of position precision, description 0Fig.4 The diferent relationships between core discipline and newphysical properties, and principles of design anbranch discipline [(a) The methodologies and tools ofbranch disciplines are mostly the same as those of coreoperation. Nanoscale PSE could be realized as ardiscipline; (b) The methodologies and tools of branchinter-discipline, where one may find the PSE, systemdisciplines only have loose connection with those of core biology, molcular tectonics and molecular computerdiscipline.]are all fueling the development of nanoscale PSE.Nanoscale PSE should be acepted as a new discipline5 CONCLUSIONSwhich has looser connection with the extant core of(1) One of important development directins of chemical engineering.PSE in new century is exploring the new features of.(4) As both microchemical systems andsmaller world. 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