Artículo 1 - The future of chemical engineering

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Chemical Engineering Science 57 (2002) 46674690

www.elsevier.com/locate/ces

The triplet molecular processesproductprocess engineering:the future of chemical engineering ?

Jean-Claude Charpentier

Department of Chemical Engineering=CNRS, Ecole Superieure de Chimie Physique Electronique de Lyon, P.O. Box 2077,

69616 Villeurbanne Cedex, France

Abstract

Today chemical engineering has to answer to the changing needs of the chemical and related process industries and to meet the marketdemands. Being a key to survival in globalization of trade and competition, the evolution of chemical engineering is thus necessary. Its

ability to cope with the scientic and technological problems encountered will be appraised in this paper. To satisfy both the markets

requirements for specic end-use properties of products and the social and environmental constraints of the industrial-scale processes, it is

shown that a necessary progress is coming via a multidisciplinary and a time and length multiscale approach. This will be obtained due to

breakthroughs in molecular modelling, scientic instrumentation and related signal processing and powerful computational tools. For the

future of chemical engineering four main objectives are concerned: (a) to increase productivity and selectivity through intelligent operations

via intensication and multiscale control of processes; (b) to design novel equipment based on scientic principles and new methods of

production: process intensication; (c) to extend chemical engineering methodology to product focussed engineering, i.e. manufacturing

and synthesizing end-use properties required by the customer, which needs a triplet molecular processesproductprocess engineering;

(d) to implement multiscale application of computational chemical engineering modelling and simulation to real-life situations, from the

molecular scale to the overall complex production scale.

? 2002 Elsevier Science Ltd. All rights reserved.

Keywords: Future of chemical engineering; Multidisciplinary and multiscale approach; Triplet molecular processesproductprocess engineering;End-use property; Soft solids; Complex uids; Molecular modelling; Process intensication

1. Introduction

The world moves forward. Industry used to be king, now

the customer is. One key to survival in globalization of

trade and competition, including needs and challenges, is

the ability of chemical engineering to cope with the society

and economic problems encountered in the chemical and

related process industries. In this paper we would like toshow successively some of the challenges to be taken up by

chemists and consequently the waiting from chemical and

process engineering. Then it will be presented the new mul-

tidisciplinary and time and length multiscale approach of

chemical engineering and the necessary tools for assuring

the success of this integrated approach. And nally we

will propose four tracks for future researches in chemical

engineering involving tailoring of materials with control

structures, process intensication, product-engineering, and

Tel.: +33-472431702; fax: +33-472431670.

E-mail address: [email protected] (J.-C. Charpentier).

multiscale simulation and modelization from the molecule

scale to the overall complex product scale.

2. The world of chemical and related industries at the

heart of a great number of scientic and technological

challenges to be taken up by chemical engineering

The world of chemistry and related industries, includ-

ing process industries such as petroleum, pharmaceutical

and health, agro and food, environment, textile, iron and

steel, building materials, glass, surfactants, cosmetics and

perfume, electronics, etc., is considerably evolving at the

beginning of this new century due to unprecedent market de-

mands and constraints stemming from public concern over

environment and safety issues.

The chemical knowledge is growing rapidly as the rate

of discovery is increasing every day (Fig. 1). Over fourteen

million dierent molecular compounds have been synthe-

sized and about one hundred thousand can be found on the

0009-2509/02/$ - see front matter? 2002 Elsevier Science Ltd. All rights reserved.

PII: S 0 0 0 9 - 2 5 0 9 ( 0 2 ) 0 0 2 8 7 - 7


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4668 J.-C. Charpentier/ Chemical Engineering Science 57 (2002) 46674690

1900 1950 2000

years

12.000.000

10.000.000

8.000.000

6.000.000

4.000.000

2.000.000

14.000.000

numberofknowncompounds

Fig. 1. Chemical knowledge is growing rapidly in consumer goods busi-

ness.

market. Only a small of them are found in nature. Most of

them are and will be deliberately conceived, designed, syn-

thesized and manufactured to meet the human need or to

test an idea or to satisfy his quest of knowledge (see for ex-

ample the nowadays development of combinatory chemicalsynthesis).

Already chemistry plays an essential role in mans attempt

to feed the population of the planet, to tap new sources of

energy, to cloth and house humankind, to improve health

and eliminate sickness, to provide substitutes for rare raw

materials, to design necessary materials for the new infor-

mation and communication technologies and to monitor and

to protect our environment.

Thus to imagine reactions that will convert chemical sub-

stances we nd around us into substances or products that

serve the consumers needs, such is the business of chemists

and such are problems and challenges posed to and by the

chemical and related industries. But the evolution of the

needs has become such that the keywords associated with

the modern chemistry are life sciences, information and

communication sciences, and instrumentation in the 21st

century.

2.1. Intellectual frontiers of chemistry especially with life

sciences

Up to recently Chemists have wanted to understand the

atom and the structure of matter while Biologists have been

more concerned about the function of matter.

Now, Chemist starts to make molecules that have func-

tion, and Biologist needs to understand structure. In the past

chemical developments such as X-ray, NMR, sequencing

of nucleic acids, organic synthesis, genes and recombina-

tion methods leading to discoveries in chemistry have been

adopted by biology to enable biological discoveries. In the

next 20 years the simulation will be reversed and chemistrymay look very dierent in the post-genomic world (in-

volving proteomics and metabolomics). Actually the Human

Genome project, begun in 1985, may have led to the dis-

covery of 25 000 40 000 new genes or at least 40 000 new

chemical products which need to be investigated for both

structure and function. Indeed every gene and its products,

poly-ribonucleic acid (RNA) and proteins, can be classied

according to their elementary functions and their systemic

functions. This fascinating topic is a main eld of study in

biology and biochemistry research together with bioinfor-

matics: understanding the systemic properties of genes may

revolutionize life including new cures for disease, drugs cre-

ated specically for individuals (mining the genome for

drugs) involving nanoscale laboratories where matter is

sculptured each atom by each atom, and driving advances in

technology, diagnosis and agriculture. It is a huge problem

and challenge to understand and to build all the new ma-

terials and thus biology will more and more drive chemical

discoveries: it will become possible to alter genes in order

to alter function, to change proteins chemically to alter their

function by using small ligands. Such challenges are equally

posed to Chemists in biocatalysis with the design and the

use of enzymes (protein molecules used as biologys cat-

alyst to speed up the biochemical reactions in the cell) to

catalyse industrial reactions to make complex products un-der mild conditions with little waste. The problem posed to

chemists is to mimic the conditions of nature to design use-

ful enzymes in taking into account the fact that biological

systems have evolved over long periods to accomplish very

specic functions and thus to adopt the natures methods to

design catalysts by evolution of structure and stability. This

design necessitates rapid analytical screens obtained today

with the modern micro- or nanotechnology.

2.2. Natural intellectual frontiers of chemistry with

information and communication sciences and processingtechnologies

Electronics may have dominated the 20th century, but

the new century will see this technology superseded by one

using both electricity and light. As a result of the limitations

of both electronics and all-optical processing, the hybrid

technology of electro-optics, where the transmission of light

encoded with information through a material is manipulated

using electricity, is receiving increased attention.

Examples of potential applications include turning elec-

trical television signals into optical signals for long dis-

tance transmission by bre optics in the cable TV industry;


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J.-C. Charpentier/ Chemical Engineering Science 57 (2002) 46674690 4669

detecting electromagnetic radiation in radar applications;

voltage sensing in the electric power industry; fast switch-

ing in optical area networks; ultrafast analogue-to-digital

conversion; beam steering applications including at panel

displays, etc.

The extent to which applications are implemented and the

economic impact of electro-optic devices depends stronglyon materials now being developed. For a material to be

electro-optically active, it needs to have second-order opti-

cal non-linearity. An unusual requirement for second-order

optical non-linearity is non-centrosymmetric material sym-

metry, that is, all the optical species (chromophores) must

be dipolar in nature and pointing in the same direction. This

feature is rare in nature and preparing such materials is a

challenge for chemists and chemical engineers.

For several decades, lithium niobate (LiNbO3) crystals

have been the material of choice for making electro-optic

modulator devices, despite having only modest electro-optic

properties. Since LiNbO3 is crystalline, clever processing

and engineering are needed to make it useable with semicon-

ductor electronics and bre optic transmission lines. This,

coupled with the diculty of growing high-quality single

crystals, makes lithium niobate expensive to use and the

LiNbO3 technology has probably reached maturity.

Polymeric materials are now oering intriguing new pos-

sibilities for making and using electro-optic devices and for

commercialization on a broader scale. Indeed devices based

on polymeric materials show bandwidths (i.e, the ability

to process large amounts of information per unit time) of

greater than 100 GHz compared with those around 10 GHz

for inorganic materials and even smaller for purely elec-

tronic devices. Polymeric materials also oer improved pro-cessability and ease of integration into device-appropriate

shapes, that is, light conning waveguides (optical wires)

appropriately integrated with drive electronics (for exam-

ple semiconductor VLSI) and with silica bre transmission

lines. And polymeric electro-optic materials must be capable

of being processed into optical quality lms, poled, hard-

ened, processed in unit buried channel waveguide structures,

and integrated with VLSI electronics and silica bres.

These are challenges for both chemistry and for engineer-

ing sciences such as chemical engineering, including ad-

vances in microfabrication methods for chemical systems

and in microelectromechanical systems (i.e, Wise, 1998).

2.3. Instrumentation in the 21st century

To help the required multidisciplinary approach of

chemists, there exists instrumentation in all its forms:

laser, molecular beam, NMR, Temporal Analysis of Prod-

uct, X-ray diraction, mass spectrometry, surface acoustic

wave technique, spectroscopic ellipsometry, tomography,

trajectography, etc.

To analyse 10 000 samples a day especially in medi-

cal systems and in food production, Chemists have now

the possibility of using thin-layer chromatography and its

parallel-processing capabilities. Spy satellite infrared tech-

nology that can detail limits below a microgram is becoming

available in chemistry. This may be used to determine func-

tional groups without completely resolving the substances

on the thin layer plates. Mass spectrometry and ion-trap mass

spectrometers with the ability to store ions in the trap will

allow to do chemistry within the trap. This may develop intoa gas-phase synthesis tool.

Developments in holographic optical systems and new

optical components and array detector technology is of great

help for the development and the use of the quantitative

Raman spectrometry allowing very low detection limits, in

the ppm range, with the use of bulk samples with little sam-

ple preparation. Also the present day high-throughput syn-

thesis methodologies, such as combinatorial techniques, are

applied to the discovery of pharmaceuticals, catalysts, and

many other new materials.

So this developing instrumentation in all its forms at the

disposition of chemists will be of great help either for the de-

scription of molecular complexity or for obtaining an accu-

rate picture of chemical or enzymatic transformations. This

will be necessited for the modelling and simulation in chem-

ical and process engineering.

3. What are we waiting from chemical and process

engineering?

In fact there are two demands associated with the previ-

ous challenges in order to assure competitiveness and em-

ployment in such process industries:

(i) How to product and with the help of which pro-

cesses in order to compete in the new global economywhere the keywords are globalization of business and tech-

nologies, partnership and innovation (innovation means

discovery + development). This involves that the speed

of product innovation is accelerating. For example in the

fast moving consumer goods business to which the major-

ity of the food business belongs, the half-times of product

development has decreased from 10 years in 1970 to an

estimated 23 years in the year 2000 (Fig. 2). This means

that the high bonus on being rst with a product innova-

tion of substance is getting increasingly dicult to achieve,

0

2

4

6

8

10

1970 1980 1990 2000

Year

Half time

UUerf Unilever

Fig. 2. Acceleration of innovation time.


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and speeding up the product=process development cycle is

therefore of paramount importance.

(ii) How to answer to the evolution of market demands

involving a double challenge: for developing and industri-

alizing countries there is a low cost of manpower and less

constraining local production regulations. For industrialized

countries, there is a rapid development in consumer demandand constraints stemming from public and media concerns

over environment and safety issues.

To answer these dierent demands, chemical engineering

will be in charge:

(a) To research very innovative processes for the produc-

tion of commodity and intermediate products where

patents usually do not concern products but processes

(multi-step processes for intermediate products). This

leads to no longer selecting processes on the basis of

economic exploitation alone but seeking compensatory

gains resulting from the increased selectivity and sav-

ings linked to the process itself. Indeed the economic

constraint will no longer be dened as sale price mi-

nus capital plus operating plus raw material and energy

costs. But the problem becomes more complex and re-

quires valorization of safety, health and environmental

aspects, including the value of non-polluting technolo-

gies, reduction of raw material and energy losses and

products and by-products recyclability as well. Indeed

the customer will buy a process which is non-polluting,

defect-free and perfectly safe.

(b) To progress from traditional intermediate chemistry

to new specialities and active material chemistry and

related industries. This concerns industries involved

with food products, with products for human, ani-mal and vegetal health, along once again with the

chemistry=biology interface. This concerns also up-

grading and conversion of petroleum feedstocks and

intermediates, conversion of coal-derived chemicals or

synthesis gas into fuels, hydrocarbons or oxygenates.

The aim is characterized by new market objectives,

with sales and competitiveness dominated by the

end-use properties of a product linked to its quality

or shape and size (chemical and biological stability,

degradability, chemical, biological and therapeutic ac-

tivity, aptitude to dissolution, mechanical, rheological,

electrical, thermal, optical magnetics characteristicsfor solids and solid particles together with size, shape

colour, touch, handling, cohesion, friability, rugosity,

tastes, succulence, esthetics, sensory properties, etc.).

Control of this end-use property and expertise in the

design of the process, its permanent adjustments to

variety and changing demand along with speed in

reacting to market conditions will be the dominant

elements. Indeed for these new specialities and active

materials the client will buy the product which is the

most ecient and the rst on the market, thus strength-

ening the existing competition between the developed

country producers.

Such are examples of present day problems and challenges

posed by chemical and related industries to specialists of

chemical and process engineering. And what is the situation

concerning the participation and the implication of chemical

engineering?

4. Chemical and process engineering approach in year

2001

To satisfy the previous demands involves material and

energy transformations and to create again new industrial

processes with zero pollution, zero defects and complete

safety. Actually it needs to take into account or cope with

what are called today new or emerging technologies such as

biotechnology, microelectronics and microoptoelectronics,

biomedical, nanotechnologies, new materials, polymers, ce-

ramics, composites. And simultaneously, it requires to main-

tain competitive the classical technologies necessitated for

permanent recurrent and classical problems such as renew-

able energies, synthetic fuels, raw material and energy sav-

ings in order to break the infernal cycle from raw material

and energy to wastes in such a way that wastes constitute

the raw material of the following cycle (e.g. paper, textile,

sludges).

Fortunately, chemical engineering is evolving to satisfy

these numerous demands as the problem is not quite new

for chemical and process engineering specialists. Indeed

by denition, the objective of petroleum engineering, then

of chemical broadened to process engineering, is the syn-

thesis, design, scale-up or scale-down, operation, control

and optimization of industrial processes that change thestate, microstructure and chemical composition of material

through physico (bio) chemical separations (distillation,

absorption, extraction, drying, ltration, agitation, pre-

cipitation, uidization, emulsication, crystallization, ag-

glomeration, etc.) as well as through chemical, catalytic,

biochemical, electrochemical, photochemical and agro-

chemical reactions. Chemical engineering involves the

whole of scientic and technical knowledge necessary for

physicochemical and biological transformations of raw ma-

terials and energy into the targeted products required by the

customer. Thus it covers areas involving a wide variety of

technologies with increasing emphasis on the demand ofend-use properties.

However, it is important to note that today 60% of all

products that a chemical company sells to its customer are

crystalline, polymeric or amorphous solids. These materials

need to have a clearly dened physical shape in order to meet

the designed and the desired quality standards. This also

applies to paste-like and emulsied products. So instead of

classical basic and industrial chemicals, new developments

increasingly concern highly targeted and specialized mate-

rials, active compounds and special eect chemicals. These

are much more complex in terms of molecular structure than

classical chemicals.


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Fig. 3. Chemical supply chain (Grossmann & Westerberg, 2000).

So the purpose of basic research in chemical and process

engineering is still the development of concepts, methods

and techniques to better understand, conceive and design

processes to change raw materials and energy into useful

products. But the complexity of phenomena involved in in-

dustrial processes now increasingly forces the engineer and

researcher to develop new concepts and methods sometimes

encountered in other industrial activities such as defense,

car, aeronautical and space or medical activities.Thus chemical and process engineering is today con-

cerned with the understanding and development of

systematic procedures for the design and optimal opera-

tion of chemical, pharmaceutical, food, cosmetics: : : pro-

cess systems, ranging from nano- and microsystems to

industrial-scale continuous and batch processes, as pre-

sented in Fig. 3 in using the concept of chemical supply

chain (Grossmann & Westerberg, 2000). This chain starts

with chemical or other products that industry must synthe-

size and characterize at the molecule level. Subsequent step

aggregates the molecules into clusters, particles, and thin

lms as single or multiphase systems that nally take theform of macroscopic mixturessolids, paste-like or emul-

sion products. Transitioning from chemistry or biology to

engineering, one move to the design and analysis of the

production units, which are integrated into a process that in

turn becomes part of an industrial site with multiple pro-

cesses. Finally, this site is part of the commercial enterprise

driven by market considerations and demands the inclusion

of the product quality.

In this supply chain, it should be emphasized that product

quality is determined at the micro and the nano level and

that a product with a desired property must be investigated

for both structure and function. This involves a thorough

Fig. 4. The length and time scales covered in the multiscale approach.

understanding of the structure=property relationship at both

molecular (e.g. surface physics and chemistry) and micro-

scopic levels. The ability to control microstructure forma-tion to obtain the end-use properties of a uid or solid

product is the key to success and will therefore help to de-

sign and control product quality and make the leap from the

nano level to the process level.

This requires an integrated system approach for a multi-

scale and multidisciplinary modelling of complex simulta-

neous and often coupled momentum, heat and mass transfer

phenomena and processes taking place on dierent scales

(Fig. 4):

dierent time scales (1015108 s) from femto- and pi-

coseconds for the motion of atoms in a molecule during


6/24


Scales and complexity levels in process engineering

Nano-scale Micro-scale Meso-scale Macro-scale Mega-scale

Molecular

Processes

Activessites

Particles

Droplets

Bubbles

Eddies

Reactors

Exchangers

Separators

Pumps

Production

Units

Plants

Environment

Atmosphere

Oceans

Soils

COMPLEXITY

between

MOLECULAR STRUCTURE

FLUID DYNAMICS

REACTION

COMPLEXITY

betweenPROCESS

BUSINESS

How TO UNDERSTAND and to DESCRIBE the relationship between events at NANO and MICRO-

scales to better convert MOLECULES onto USEFUL PRODUCTS at the PROCESS-scale

Fig. 5. Scales and complexity levels in process engineering: to understand and to describe the relationships between events at nano- and microscale to

better convert molecules into useful products on the process scale.

a chemical reaction and nanoseconds for molecular vi-

brations up to the scale of hours for operating industrial

processes and of centuries for the destruction of pollu-

tants in the environment.

dierent length scales (108106 m) in industrial prac-

tice (Fig. 5) with approaches on the nanoscale (molecular

processes, active sites), on the microscale (bubbles,

droplets, particles, eddies), on the mesoscale for unit

operations (reactors, exchangers, columns), on the

macroscale for production units (plants, petrochemical

complexes) and megascale (environment, atmosphere,

oceans, soils) e.g., up to thousands of kilometers fordispersion of emissions to the atmosphere.

So organizing scales and complexity levels in process

engineering is necessary to understand and to describe the

relationships between events at nano- and microscales to

better convert molecules into useful products at the process

scale. It is this approach which is required by chemical

engineering today.

Let us present three illustrations of this multiscale and

multidisciplinary approach.

(i) Transport phenomena in polyolen polymerization.

This example borrowed from polymerization engineering

illustrates the fact that even for processes in use on an in-

dustrial scale for quite some time, it may be necessary to

re-examine the fundamental mechanisms involved at the

microscopic level. This is presently the case of the poly-

merization of olens using highly active ZieglerNatta type

catalysts and more recently supported metallocene catalysts

that oer the possibility of producing tailor-made poly-

mers in rather mild, and therefore less expensive process

conditions.

For a proper reactor design, optimization and control,

many attempts have been made over the course of the past

to model the kinetics of polymerization, the evolution of the

morphology of particles formed by the catalyst and polymer

as well as the heat and mass transfer around these growing

particles. To put the problem into perspective, Fig. 6 presents

the dierent length scales and transfer phenomena involved

in both cases of gas-phase uidized-bed reactor (FBR) (left

side) and liquid phase slurry or liquid pool processes (SBR)

(right side).

Let us consider the gas-phase processes which are in the-

ory particularly interesting because they use no solvents and

because of the ease of separation of the nal product from the

reaction medium. If the models available in the literature are

used in conjunction with the classical transfer equations and

correlations for transfer coecients, they predict that exper-imentally observed polymerization kinetics are theoretically

impossible, as they would lead to temperature gradients so

high during gas-phase polymerization that the centre of the

polymer particles would melt. If this happened, the pores of

the growing particles would ll with molten polymer and

the resulting increase in mass transfer resistance would then

completely extinguish the reaction. This does not mean that

signicant temperature gradients at particle levels do not

exist. It means that the fundamental description currently

available for such situations are inadequate. Since the reac-

tion is very fast we do have very high levels of activity and

typical rates on the order of 3060 kg polymers=g catalyst=h

and we do encounter melt-downs in industrials: the models

simply do not tell us why or how.

If we consider the length scales shown in the schema

of Fig. 6, it is easy to see that events taking place on the

nanoscale (e.g. kinetics, Fig. 5), the microscale (e.g. internal

mass and energy transport), and the mesoscale (particle

particle, particlewall interactions) have a signicant impact

on macroscale events (e.g. global reactor behaviour), and

even on megascale issues such as reactor run away, use of

energy, etc. It is therefore absolutely critical that the process

engineer has a fundamental understanding of events at all

levels of complexity.


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Catalyst

Single Particle

Reactor

1-10 metres

100 m - 1cm

10 - 100 m

1 - 100 nm

LENGTHSCALES

Particle Swarm

Sub-particle

Electrostatic/ThermalAgglomeration

FlocculationCoalescence

Local Interactions

Interphase Transfer

Surface temperature

Surface coverage

Morphology, porosity

Arrangement of active sites

Distribution of microdomains

Mixing, RTD, Homogeneity

Molecular Phenomena

1 - 100 AChemistry, kinetics, macromolecular diffusion

Active site

Fig. 6. Problems to be solved and related length scales in the heterogeneously catalysed polymerization of olens.

For example, a fundamental analysis of mass and heat

transport equations reveals that convection might play a

very important role during polymerization, especially dur-

ing the early stages of the operation which are critical for

the development of particles (Fig. 7). After the rst few sec-

onds at most, the hydraulic forces created by the formation

of solid polymer inside the particle cause the original struc-

ture to rupture or fragment. The particle retains its original

shape because of the entanglement and=or crystallization of

the macromolecules formed in the porous structure of the

originally porous support. But values generally retained for

the heat transfer coecient around these particles growing

rapidly from an original size of 10 m for fresh catalyst

to a nal size on the order of 1 mm for polymer particles

have to be increased by a factor of at least 10 in order of

magnitude to account for experimental observations. Fur-

thermore, it seems necessary to revise the description of the

basic mechanism for heat transfer in the gas phase around

the particles because the correlations used up to recently are

based on the assumption that heat transfer takes place only

via convection. Classical chemical engineering correlations

indeed have been developed for particles diameter 400 m

whereas we are dealing with particles on the order of

2040 m in diameter during the critical stages of low pres-

sure olen polymerization. The use of a computational uid

dynamics software package to study heat transfer from

spherical particles of dierent sizes and under dierent heat

transfer conditions has shown that the classical heat transfer

correlations for the case where particles do not interact are

not true for densely packed systems such as those encoun-

tered in reactors commonly used in olen polymerization

(McKenna et al., 1999; McKenna & Soares, 2001). It was

also demonstrated that convection is not the only means of

removing heat from small highly active particles. Conduc-

tive heat transfer between large and small particles present

in the same reactor appears to help previous alleviate prob-

lems of overheating and explain why earlier models of heat

transfer in olen polymerization overpredict the tempera-

ture rise during early polymerization.

(ii) Transport phenomena in metallic material elabora-

tion. This integrated multiscale approach for the descrip-

tion, analysis, understanding and modelling of phenomena


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Fig. 7. Schematic transformation of a fresh catalyst particle into a polymer particle, and evolution of particle morphology and growth. (McKenna, Spitz,

& Cokljat, 1999).

occurring at dierent scales is also met in an other important

industrial case: the elaboration and processing of metallic

materials (metals, alloys, materials having noticeable prop-

erties and new functions such as nanophase materials andquasicrystals). For these metallic materials the steps of cast

and solidication play an important role, especially for the

quality and then for the end-use property. So for the step of

solidication this necessitates the homogeneization of ma-

terials at dierent scales, thus the organization of levels of

complexity, from the microstructure at the microscale of the

dendrite and of the grain for columnar or equiaxial struc-

tures up to the scale of the surface state of the rough-cast

product, characterized by chemical macrosegregation and

microsegregations. The controlled formation of these chem-

ical segregations during the solidication requires this new

approach in process system engineering in terms of coupled

transport phenomena and phase changes, and also in terms

of knowledge of the strong coupling existing between phe-

nomena occurring at dierent scales such as the mesosegre-

gation and the microsegregation.

(iii) Transport phenomena in biochemical engineering.

This multiscale approach is now encountered in the domains

of biotechnology and bioprocesses for the knowledge and

the control of biological tools (enzymes and microorgan-

isms) to manufacture products and services. In such cases it

is necessary to organize the levels of increasing complexity

from the gene with known property and structure up to the

productprocess couple by modelling coupled mechanisms

and processus at dierent length scales (Fig. 8): nanoscale

for molecular and genomic processus and metabolic trans-

formations, pico- and microscales for the enzymes and inte-

grated enzymatic systems, for the populations and cellularplant, mesoscale for the biocatalyst and active aggregates,

and macro- and megascales for the bioreactors, units and

plants involving interactions with the biosphere. So organiz-

ing levels of complexity at dierent length scales associated

with an integrated approach of phenomena and simultane-

ous and coupled processus underlie the new view of bio-

chemical engineering, i.e., understanding an enzyme at the

molecular level means that it may be tailored to produce a

particular end product (Engasser, 1998).

Also in food process engineering for the production of

man-made structured foods or for (bio) converted foods

there is today a signicant scope for such approaches in link-

ing scales to model process physics, process (bio) chemistry

and process microbiology from the molecular and cellular

scale to the full process plant scale (Bruin, 1997).

These examples underlie the new view of chemical and

process engineering: organizing levels of complexity by

translating molecular processes (that I call processus)

into phenomenological macroscopic laws to create and con-

trol the required end-use properties and functionality of

products manufactured by a continuous process.

This can be dened by le Genie du Triple processus

produitprocede (the triplet molecular processes

productprocess engineering) with an integrated system


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BIOCHEMISTRY AND BIOCHEMICAL ENGINEERING

From the GENE with known structure and function

to the end-use property (or function) PRODUCT (ecoproduct)

Nano-scale Micro-scale Meso-scale Macro-scale Mega-scale

Gene

Function

Micro-organism

enzyme

populationcellular plant

Biocatalyst

Environment

activeaggregat

Bio

Reactors

Separators

Units

plants

Interaction

biosphere

Organizing levels of complexity underlie new view

of biochemical engineering

Fig. 8. Biochemistry and biochemical engineering: organizing levels of complexity underlie new view of biochemical engineering.

approach of complex phenomena occurring on dierent

length and time scales.

This explains why, in addition to the basic notions of unit

operations, coupled transfers and classical tools of chemical

reaction engineering, that is, in addition to the fundamentals

of chemical and process engineering (separation engineer-

ing, chemical reaction engineering, catalysis, transport phe-

nomena, process control), this integrated multidisciplinary

and multiscale approach is a supplementary and of consid-

erable advantage for the development and the success of this

engineering science in terms of concept and paradigms.

So in the future, chemical and process engineering will

involve a strongest multidisciplinary collaboration amongphysicists, chemists, biologists, mathematicians and instru-

mentation specialists leading to the theoretical development

of the design of products with complex structures (emul-

sions, paste-like products, plastics, ceramics, soft solids,

etc.). Developing new concepts adapted to this idea of the

product, within the framework of what could be called

physicochemical (bio) engineering justies the quali-

cation of process engineering as an extension of chemical

engineering and takes on its full meaning (Charpentier &

Trambouze, 1998; Bacchin et al., 1999).

And improving both the design and evaluation of com-

plex systems for the production of real products requires fur-

ther research into strategies, methodologies and tools. These

should be oriented toward the acquisition of basic data in

thermodynamics, kinetics, rheology and transport, and to-

ward the conception of new integrated operations allowing

for coupling and uncoupling of elementary processus (trans-

fer, reaction, separation) or combining several functions in

one piece of equipment. This is clearing the way to smaller

and cheaper installations requiring improved knowledge in

process modelling, automation and control.

But this requires mathematical models and scientic in-

strumentation which aords useful basic data that can be

treated using powerful computational tools. For example,

the treatment of generalized local information necessitates

more and more the help of the computational uid dy-

namics as it is the case since a long time in combustion,

car, aeronautic and spatial applications especially for the

knowledge, control, stability of the ows and the charac-

terization and the improvement of the transfer phenomena.

Thus CFD, due to recent rapid advances in available soft-

ware (e.g. CFDLIB, FLUENT, PHOENICS, FLOW 3 D,

FIDAP, FLOW MAP, etc.) is daily becoming more im-

portant in scaling up new equipment or multifunctional

unit operations by simulation of ow phenomena and

processing generalized local information, i.e., for under-

standing the impact of complex ow geometries on mixingand reaction phenomena at the microeddy scale or for

the numerical simulation of the complex hydrodynamics

of multiphase catalytic gasliquidsolid reactors, or for

simulating ow in complex geometries such as reactor in-

ternals (industrial distributor devices). Indeed calculations

can be carried out for any geometric complexity and for

single- and two-phase ow, provided that physical models

are available. Nevertheless, the use of this tool becomes

possible only when the calculation time is acceptable,

i.e., less than few days. CFD is thus a good link between

laboratory experiments, conducted at small scale with com-

mon uids (air, water, organic, hydro-carbons, etc.), and

industrial operation (large scales, complex uids, severe

temperature and pressure conditions) (Kuipers & Van

Swaaij, 1997).

5. Necessary and indispensable tools for the success of

chemical and process engineering

It will be possible to understand and describe relation-

ships between events on the nano- and microscale to con-

vert molecules into useful products on the process and unit

scales thanks to signicant simultaneous breakthroughs in


10/24


three areas: molecular modelling (both theory and computer

simulations), scientic instrumentation and non-invasive

measurement techniques, and powerful computational tools

and capabilities. It may be cited as illustration:

5.1. Modelling at dierent scales

at nanoscale, the assistance of molecular modelling to

better control surface states of catalysts and activators,

to obtain increased selectivity and to facilitate asymmet-

rical syntheses (chiral technologies), or to explain the

relationships structure=activity at the molecular scale in

order to control the crystallization, coating and agglom-

eration kinetics, etc.

at microscale the computational chemistry is very use-

ful to a better knowledge of complex media such as

non-Newtonian liquids, melted salts, supercritical u-

ids, multiphase dispersions, and suspensions and more

generally all systems whose properties are controlled by

rheology and interfacial phenomena such as emulsions,

colloids, gels, froths, foams, hydrosoluble polymers and

particulate media such as powders, aerosols, charged

and viscous liquids. The computational chemistry is

also of great help for the knowledge of fractal struc-

tures of porous media and their inuence or mass

and heat transfer, and on chemical and biological

reactions.

At meso and macroscales, computer uid dynamics

is required for the design of new operating modes for

existing equipment such as reversed ow, cyclic pro-

cesses, unsteady operations, extreme conditions, i.e,high temperature, high pressure technologies, and su-

percritical media: : : : CFD is required for the designed,

or for the design of new equipment or unit operations

especially by seeking to render process step multifunc-

tional with higher yields in coupling chemical reaction

with separation or heat transfer which provides a con-

siderable economic benet. More generally CFD is

of previous assistance when it concerns the design of

new equipment based on new principles of coupling

or uncoupling elementary operations (transfer, reaction,

separation).

At the scale of production units and multiproduct plants,dynamic simulation and computer tools are more and

more required and applied to analyse the operating con-

ditions of each equipment of the production units, to

predict both the material ows and states and residence

times within individual pieces of equipment in order

to simulate the whole production in terms of time and

energetic costs. This allows for an interactive walk to

predict in a few seconds the new performances (product

quality and nal cost) obtained by any change due to a

blocking step or a bottleneck in the supply chain. Many

dierent scenarios may be tested within a short time,

thus allowing the rapid identication of an optimal solu-

tion. For instance, the simulation of an entire production

year takes within 10 minutes on a computer. It is clear

that such computer simulations enable the design of in-

dividual steps, the structure of the whole process at the

megascale and place the individual process in the overall

context of production.

But the previous modelization, simulation, transcription,translation and interpretation at dierent scales require also

the current breakthroughs in information collecting and pro-

cessing.

5.2. Breakthroughs in scientic instrumentation and

non-invasive measurement techniques

The development of a sophisticated instrumentation

and non-invasive measurement techniques leads to no-

table progress in the knowledge of matterradiation in-

teraction. In this context, the increased cooperation with

physicists and physical-chemists is essential since they

possess considerable expertise, especially in the applica-

tion of ne, precise and instantaneous methods, which are

not yet widely exploited in process engineering. For ex-

ample nuclear magnetic resonance (NMR), also used in

the medical world, allows one to characterize and mon-

itor chemical and physical phenomena that occur over

a wide range of length and time scales and thus pro-

vides information on structure and on structure dynam-

ics at the molecular or Angstrom scale (speed of parti-

cle agglomeration, rate of bubbles or drop coalescence,

speed of nucleation in crystallization, rate of coagulation

of colloids, etc.). Magnetic resonance imaging (MRI)presents a non-invasive means to obtain specic informa-

tion about structural heterogeneity of materials and porous

media and concentration, temperature and velocity pro-

les in such media. Thus with the help of performing

3D image analysis techniques such as laser scanning mi-

croscopy, one assesses local momentum, heat and mass

transfer.

Tomographic techniques, optical, acoustical and im-

pedance (both resistance and capacitance) are useful local

non-intrusive techniques for ow characterization and

on-line control of processus. Capacitance tomography al-

lows for the determination at microscopic scale of instanta-neous local velocities, mean lengths and shape coecients

of drops and bubbles and the local fraction of each phase

in multiphase ow in porous media. Also, the computed

gamma-ray tomographic technique is very promising for

the measurement of porosity and gasliquid ow distribu-

tion in trickle bed reactor of large diameter as well as the

utilization of the computer-assisted X-ray transmission to-

mography for liquid imaging in trickle ow columns. We

should also point out the positron emission particle tracking

technique that utilizes a radioactive tracer particle to obtain

the trajectories of solid or uid elements in real time either

inside rotating blenders or inside agitated vessels containing


11/24


Fig. 9. Computing speed acceleration.

non-Newtonian uids. Let us also add the spectroscopic

and monochromatic ellipsometry to characterize the struc-

ture parameters of solid surfaces in situ and in real time

at microscopic scale, i.e. porosities and thicknesses and

gas sorption behaviour in thin supported membrane layersand atomic force microscopy to nely analysed surface

structures.

It is even possible to imagine intelligent micro- and nan-

otransmitter that measure every processus and model pa-

rameter at any location and any time, with the help of, e.g.,

optical techniques using laser beams such as laser space

time resolution uorescence spectroscopy and applied par-

ticularly to real media (particulate or opaque). When will

micro- or nanoelectronic transmitters be implanted directly

on particles or catalytic sites to evaluate local parameters

values. When will piezo-electrical polymers that generate a

turbulence wake be able to continuously clean the surfaceof a membrane?

5.3. Breakthroughs in computational tools and capacities

The considerable breakthroughs in computation tech-

nology and microelectronics must be underlined (Fig. 9).

Already today informatics is of greatest importance for the

engineer or the researcher in chemical and process engi-

neering for design, control and operation of the process.

But if the eective speed of electronic hardware and soft-

ware development roughly doubled every year over the past

30 years, this acceleration in computing chip power is ex-pected to continue over the coming decade. Experts predict

that around 2010 the magneto-resistive storage technology

used will have reached a limit with a storage density of

1015 gigabyte=cm2 against about 0:25 gigabyte=cm2 to-

day. As previously mentioned as a challenge for chemists

and material science specialists, holographic memory tech-

nology may substitute the magneto-resistive technology

with potential storage densities of 150 gigabyte=cm2. Ma-

nipulating individual atoms is now envisioned and consid-

erable perspectives in molecular simulation are anticipated

because the current diculty for its use is the computer

calculation time which is approximately proportional to

N2 where N is the number of atoms which limit the

size of the molecules and the number of compounds of a

mixture.

These fantastic rapid increases in computational capabil-

ities enable to handle more complex mathematics which

permits the exhaustive solution of more and more detailed

models. This will help chemical and process engineers tomodel process physics, process (bio) chemistry and pro-

cess microbiology from the molecular and cellular scale to

the full process plant scale. In addition the developments in

expert systems and articial intelligence will enable more

and more the process engineer to have empirical, qualitative

information available virtually at his ngertips in a struc-

tured and easily accessible fashion. Fuzzy logic is of great

help in the control of processes as well as the neural net-

works for diagnosing on-line defects, for analysing trends

and for the design and the modelling of new processes. In-

deed the complexity of phenomena in many cases is such

that it might be too long before the obtention of the com-

plete model or the whole of necessary experimental param-

eters. For example concerning these necessary experimental

parameters it is interesting to utilize the advances in com-

puters and neural networks to train a neural net model based

on a huge set of available data and make predictions based

on such a model. Such an approach has been applied by

Larachi, Bensetiti, Grandjean, and Wild (1998) concerning

the accumulation of over 30,000 data for the uid dynamic

parameters in packed beds with two-phase ow. These au-

thors have shown that if one selects randomly about 60%

of the available data in concurrent upow xed bed re-

actors, a neural net can be trained to achieve a remark-

able t of the training set. The advantage of the approacharises when the neural net predictions are tested against

the remaining 40% of the data and very good agreement is

found.

And nally we should emphasize that the powerful com-

putational tools and capabilities largely contribute to the

breakthroughs in signal and image processing for visual-

ization and validation of models at dierent scales. Just to

mention the case of operation in real media (particulate or

opaque) and=or in complex multiphase ow conditions, the

present use of sophisticated techniques such as particle im-

age velocimetry, laser doppler anemometry, laser-induced

uorescence, computed tomography, computed automatedradioactive particle tracking, etc. (Chaouki, Larachi, &

Dudukovic, 1997).

6. Chemical and process engineering: quo vadis ?

The previous considerations on the future of chemical

engineering involving an integrated multiscale approach of

molecular processes, product and process engineering seem

to concern four main parallel objectives for engineers and

researchers.


12/24


6.1. Total multiscale control of the process to increase

selectivity and productivity

This requires the intensication of operations and the

use of precise nano- and micro technology design. Such is

the case of molecular information engineering encountered

for the supported organometallic catalysis or for supramolec-ular catalysis where instead of using porous support for

heterogeneous catalyst, synthetic materials with targeted

properties are now conceived and designed by chemical

engineers. Indeed, central to a successful catalytic process

is the development of an eective catalyst which is a com-

plex system in both composition and functionality. And the

ability to better control its microstructure and chemistry

allows for the systematic manipulation of the catalysts

activity, selectivity, and stability.

6.1.1. Nanotailoring of materials with controlled structure

Indeed through the control of pore opening and crystal-

lite size and=or a proper manipulation of stoichiometry and

component dispersion there exists now ability to engineer

via nanostructure synthesis novel structures at the molec-

ular and supramolecular levels, leading to the creation of

nanoporous and nanocrystalline materials. These materials

both possess an ultrahigh surface-to-volume ratio, which of-

fers a greatly increased number of active sites for carrying

out catalytic reactions.

Nanocrystalline processing includes the tailoring of

size-dependent electronic properties, homogeneous mul-

ticomponent systems, defect chemistry, and excellent

phase dispersion. This provides nanocrystalline catalystswith greatly improved catalytic activity over conventional

systems and multifunctionalities necessary for complex

applications. We should mention that vapour phase and

wet-chemical synthetic approaches have led to unpreceded

control of material structures at the atomic and molecular

levels, and brought about ensembles of such features in the

shape of nanocrystalline systems involving crystallite-size

tuning. Now complex nanocomposite systems can be built

to full various roles required for the reaction mechanism

and conditions and nanocomposite processing and tailor-

ing also lends itself readily to intelligent combinatorial

approaches in material design and rapid catalyst screening(Engstrom & Weinberg, 2000).

Beyond catalysis, nanoparticles may be dispersed in an

emulsion or a liquid for use in coating applications, food

processing, cosmetic products. And organic nanoparticles

can be used for drug delivery and gene therapy systems,

and quantum dots for medical imaging and diagnostics and

more generally for chemical, biochemical, electronic, opti-

cal, thermal and structural applications.

Also through supramolecular templating, nanoporous

systems can now be derived with well-dened porous size

and structure, as well as compositional exibility in the

form of particles and thin lms. Microporous materials

including zeolites and tailored with well-dened porous

structures for excellent surface areas and product selectiv-

ity are typically derived through templating with individual

molecules. The resulting zeolitic structure which consists

of pore opening ( 1:5 nm) allows only small molecules

to enter and react, this providing shape and selectivity in

separations and catalytic reactions. There exists now thesynthesis of well-dened mesoporous materials (250 nm

pores) with the development of supramolecular templating

which involves the use of molecular aggregates, instead

of individual molecules as the framework-directing agents.

Supramolecular templating processes are achieved with

surfactants to guide the formation of mesostructures from

solubilized silicate precursors. The anionic silicates are de-

posited around the posivitely charged surfactant templates

to form inorganicorganic mesostructures (with hexagonal,

cubic and lamellar ordering) via electrostatic interactions.

For illustration, silicates with hexagonally packed cylin-

drical pores are obtained with ultrahigh surface areas of

1000 m2=g. And by using surfactants with longer hydro-

carbon tails and by adding polar compounds, the diameters

of the mesopores can be systematically varied between 2

and 10 nm (Ying, 2000).

So nanoporous structures hold many possibilities in

materials applications with further development in

molecular engineering such as surface functionalization

of inorganic structures and extension of supramolecular

templating to organic systems. And self-assembly of nanos-

tructured building blocks (e.g, nanocrystals) combining

porosities on dierent length scales will lead to interesting

hierarchical structures. Indeed such systems with multiple

levels of intricacies and design parameters oer the possi-bility to simultaneously engineer molecular, microscopic

and macroscopic materials characteristics leading to the

construction of such advanced systems as biomimicking

medical implants or electronic=photonic devices.

We could also add that in the eld of homogeneous

catalysis a supramolecular ne chemistry has been recently

established extending the principle of self-organization of

the enzyme (catalyst) molecule to non-biological systems in

using supramolecular compounds as catalysts for the shape

selection of molecules. Such catalysts are formed in situ by

self-organization, i.e., chemical bionics (Kreysa, 2001).

So the latest advances in nanotechnology have generatedmaterials and devices with new physical characteristics and

chemical=biochemical functionalities for a wide variety of

applications. And chemical engineers and researchers are

uniquely positioned to play a pivotal role in this techno-

logical revolution with their broad training in chemistry,

physical-chemistry, processing, systems engineering, and

product design.

More generally, the previous approaches concerning the

tailoring of materials with controlled structure imply that

chemical engineers should and will go down to the nanoscale

to control events at the molecular level. Indeed at this level,

we have seen that new functions such as self-organization,


13/24


regulation, replication, and communication can be created

by manipulating supramolecular building blocks.

6.1.2. Increase selectivity and productivity by supplying

the process with a local informed ux of energy or

materialsAt a higher microscale level, detailed local tempera-

ture and composition control through staged feed and heat

supply or removal would result in higher selectivity and

productivity than does the conventional approach which im-

poses boundary conditions and lets a system operate under

spontaneous reaction and transfer processes. Finding some

means to convey energy at the site (supplying the process

with a local informed ux of energy) where it may be

utilized in an intelligent way is therefore a challenge. Such

a focused energy input may be achieved by using ultrasonic

transducers, laser beams or electrochemical probes but a

more fundamental approach is required to progress in this

direction. Indeed the need to convey the exact amount ofenergy at the precise location where it has to be utilized to

promote transfer or reaction requires some kind of feedback

between the process and the energy source, and to drive

the elementary processes within the unit is a challenge but

combining microelectronics and elementary processes, e.g.

tuning the selectivity by controlling catalytic reactions at

the surface of electronic chips should be a track to explore

for chemical engineering.

6.1.3. More clearly recognized is the necessity to increase

information transfer in the reverse direction, from process

to man

This means developing all kinds of intelligent sen-

sors, visualization techniques, image analysis and on-line

probes giving instantaneous and local information about

the process state. This opens the way to a new smart

chemical and process engineering requiring close com-

puter control, relevant models, and arrays of local sensors

and actuators. Field-programmable analog arrays coupled

with microreactor technology promise to change the way

plants are built, as well as the methods by which their

processes are designed and controlled. Rapid progress

is noticeable in this area, although sensors for opaque

materials and particulate solids in bulk systems are stillscarce.

6.2. Design of novel equipment based on scientic

principles and new operating modes and methods of

production: process intensication

The progress of basic research in chemical engineering

has led to a better understanding of elementary phenomena

and now makes it possible to imagine new operating modes

of equipment or to design novel equipment based on scien-

tic principles.

6.2.1. Process intensication using multifunctional

reactors

Such is the case with the multifunctional equipment that

couple or uncouple elementary processes (transferreaction

separation) to increase productivity, selectivity with the de-

sired product or to facilitate the separation of undesired

by-products. Indeed in recent years, extractive reaction pro-cesses involving single units that combine reaction and sep-

aration operations have received considerable attention as

they oer major advantages over conventional processes:

due to the interaction of reaction and mass and energy trans-

fer, thermodynamic limitations, such as azeotrope, may be

overcome and the yield of reactions increased. So the re-

duction in the number of equipment units leads to reduced

investment costs and signicant energy recovery or sav-

ings. Furthermore improved product selectivity leads to a

reduction in raw material consumption and, hence, operat-

ing costs. So globally, process intensication through use

of multifunctional reactors permits signicant reductions in

both investment and plant operating costs (10 20% reduc-

tions) by optimizing the process. In an era of emaciated

prot margins, it allows chemical producers more leverage

in competing in the global market place. There exist a great

number of reactive separation processes involving unit op-

eration hybridiztion.

The concept of reactive or catalytic distillation has been

successfully commercialized, both in petroleum process-

ing, where packed bed catalytic distillation columns are

used, and in manufacture of chemicals where reactive dis-

tillation is often employed. Catalytic distillation combines

reaction and distillation in one vessel using structured cata-

lysts as the enabling element. The combination results in aconstant-pressure boiling system, ensuring precise tempera-

ture control in the catalyst zone. The heat of reaction directly

vaporizes the reaction products for ecient energy utiliza-

tion. By distilling the products from the reactants in the reac-

tor, catalytic distillation breaks the reaction equilibrium bar-

rier. It eliminates the need for additional fractionation and

reaction stages, while increasing conversion and improving

product quality. The use of reactive distillation in the pro-

duction of fuel ethers or methyl acetate clearly demonstrates

some of the benets. Similar advantages have been realized

with the production of high-purity isobutene, for aromatics

alkylation, for the reduction of benzene in gasoline and in re-formate fractions, for the selective production of ethylengly-

col which involves a great number of competitive reactions

and for selective desulphurization of uid catalytic cracker

gasoline fractions as well as for various selective hydrogena-

tions. The next generation of commercial processes using

catalytic distillation technology will be in the manufacture

of oxygenates and fuel additives (Dudukovic, 1999).

An alternative reaction-separation unit is the chromato-

graphic reactor, which utilizes dierences in adsorptivity of

the dierent components involved rather than dierences in

their volatility. It is, especially, interesting as an alterna-

tive to reactive distillation when the species involved exhibit


14/24


small volatility dierences or are either non-volatile and sen-

sitive to temperature, as in the case, for example, in small

ne chemical or pharmaceutical applications. There are sev-

eral classes of reactions to which reactive chromatography is

applied. The widest one is given by esterications reactions

catalysed by acidic ion-exchange resins or by immobilized

enzymes as the polarity dierence between the two prod-ucts (ester and water) make their separation easy on many

dierent adsorbents. Other applications include transesteri-

cations, alkylation, etherication, (de)hydrogenations and

reactions involving sugars. Reactive chromatography has

been also utilized for methane oxidation. In all these appli-

cations, special care has to be devoted towards the choice of

the solid phase (sorption selectivity, sorption capacity and

catalytic activity). Typical examples for the adsorbents used

are activated carbon, zeolites, alumina, ion-exchange resins

and immobilized enzymes (Lode, Houmard, Migliorini, Ma-

zotti, & Morbidelli, 2001).

Concerning the coupling of reaction and crystallization,

there exist myriads of basic chemical, pharmaceuticals,

agricultural products, ceramic powders, pigments produced

by reactive crystallization based processes (i.e., processes

that combine crystallization with extraction to solution

mine-salts). These separation processes are synthesized

by bypassing the thermodynamics barriers imposed on the

system by the chemical reactions and the solubilities of

the components in the mixture. By combining crystallizers

with other unit operations, the stream compositions can be

driven to regions within composition space where selective

crystallization can occur (Berry & Ng, 1997a).

The complementary nature of crystallization and distil-

lation is also explored. Indeed the hybrids provide a routeto bypass thermodynamic barriers in composition space

that neither the distillation which is blocked by azeotropes

and hindered by tangent-pinches in vapourliquid com-

position space nor the selective crystallization which is

prevented by eutectics and hampered by solid solutions and

temperature-insensitive solubility surfaces, can overcome

when used separately (Berry & Ng, 1997b). Another advan-

tage of such crystallizationdistillation hybrid separation

processes is that they do not require the addition of solvents

which may increase the process ows, create waste streams

and propagate throughout a chemical plant and necessitate

costly equipment to separate and recycle these solvents.Membrane technologies respond eciently to the require-

ment of the so-called process intensication because they al-

low improvements in manufacturing and processing, in sub-

stantially decreasing the equipment-size=production-capacity

ratio, the energy consumption, and=or the waste production

and resulting in cheaper, sustainable technical solutions.

The paper by Drioli and Romano (2001) documents the

start of the art well with respect to progress and perspec-

tives on integrated membrane operations for sustainable

industrial growth. The rst studies on membrane reactors

were devoted to the use of the membranes for a distributed

feed of one of the reactants to a packed bed of catalyst, such

as in partial oxidation reactions in order to improve selec-

tivity. Others have attempted selective removal of product

from the reaction site in order to increase conversion of

product-inhibited or thermodynamically unfavourable re-

actions, i.e., immobilization of biocatalysts on polymeric

membranes. With such membrane bioreactors, provided that

membranes of suitable molecular weight cut-o are used,chemical reaction and physical separation of biocatalysts

(and=or substrates) from the products can take place in the

same unit. Substrate partition at the membrane=uid inter-

face can be used to improve the selectivity of the catalytic

reaction toward the derived products with minimal side re-

actions. This technology can respond to the strongly increas-

ing demand for food additives, feeds, avours, fragrances,

pharmaceuticals, agrochemicals. Catalytic membrane re-

actors are also proposed to selective product removal to

remove equilibrium limitations, i.e., catalytic permselec-

tive or non-permselective membrane reactors, packed bed

(catalytic) permselective membrane reactors, uidized bed

(catalytic) permselective membrane reactors. The devel-

opment of such membrane reactors for high-temperature

applications became realistic only in the last few years with

the development of high-temperature-resistant membranes

(palladium membranes) mainly to dehydrogenation reac-

tions, where the role of the membrane is simply hydrogen

removal. For more general applications material scientists

must solve the problem of providing inorganic membranes

of perfect integrity involving mechanical and thermal stabil-

ity and membranes which will allow large uxes of desired

species. Also, chemical engineers must gure out the heat

transfer problem which now threatens successful scale-up.

Thus it might seem reasonable to expect membrane reactorsthat combine oxygen transfer membranes with selective

catalytic layers for partial oxidation of hydrocarbons. How-

ever, a continuous research eort in the process dynamics

of these processes and in the study of advanced control

systems applied to integrated multimembrane operations is

now necessary for a larger utilization of membranes in mul-

tifunctional operations combining advantageously reaction

and separation in the same vessel.

Conversely uncoupling the transferreactionseparation

processes may benet: i.e., in a precipitator a better control

of the property of the solid is obtained with the separation

of the nucleationgrowthagglomeration processes and thenin using an ad hoc chemical reaction, the desired product

precipitates in the solution which eliminates the further uti-

lization of a crystallization in the chain production.

Finally, though multifunctional reactors are not quite new

to the process industries, i.e., absorption or extraction with

chemical reaction, only recently reactors incorporating sev-

eral function in one reactor have been formally classi-

ed as being multifunctional and the large benets obtained

in integrating progress of knowledge at dierent scale and

time-lengths have been acknowledged by the process indus-

tries. This was illustrated by the rst international sympo-

sium on multifunctional reaction (Moulijn & Stankiewicz,


15/24


1999) with a presentation of research and development in

the main domains : reaction and heat exchange, reaction and

membrane separation, reaction and sorption, reaction and

power generation, reactions and distillation, reaction and

catalyst regeneration and the use of non-classical structured

packing. But to achieve optimal performance with multi-

functional reactors, it is important to lead a scientic ap-proach to understand where the integration of functionalities

occurs, as explained by Dautzenberg and Mukherjee (2001).

For example these authors have proposed a classication for

the case of a catalyst particle in a reactive medium.

However, we will mention more generally that the

present day use of hybrid technologies encountered in a

great number of multifunctional reactors is limited by

the resulting problems concerning control and simulation.

In fact, the interaction between simultaneous reaction and

distillation introduces more complex behaviour involving

the existence of multiple steady states and output multi-

plicities corresponding to dierent conversion and product

selectivity, compared to conventional reactors and ordinary

distillation columns. This will lead in the near future to

interesting challenging problems in dynamic modelling,

design, operation, and strong non-linear control.

6.2.2. Process intensication using new operating modes

The intensication of processes may also be obtained by

new modes of production which are based on scientic prin-

ciples. These new operating modes are in the laboratory

and=or pilot stage: reversed ow for reaction-regeneration,

countercurrent ow and induced pulsing ow in trickle beds,

unsteady operations, cyclic processes, extreme conditions,pultrusion, high temperature and high-pressure technolo-

gies, and supercritical media are now seriously considered

for practical application. Reactors can be operated advanta-

geously with moving thermal fronts that are created by peri-

odic ow reversal. For example, low level contaminants or

waste products such as volatile organic compounds can be

eciently removed in adiabatic xed beds with periodic re-

versal by taking advantage of higher outlet temperatures gen-

erated in earlier cycles to accelerate exothermic reactions.

Energy and cost savings are aected by this substitution of

internal heat transfer for external exchange (Dautzenberg &

Mukherjee, 2001).

Some attractive options for improved catalytic reactor per-

formance via novel modes of operation are periodic (sym-

metric) operation of packed beds with exothermic reaction,

and coupling of an exothermic and endothermic reaction in

a periodically operated (asymmetric) packed bed. The in-

duced pulsing liquid ow in trickle beds is also proposed

to improve liquidsolid contacting at low liquid mass ve-

locities in the cocurrent down ow mode. Also when high

conversions are required and the gaseous by-product of the

reaction is known to inhibit the rate, such as in hydrodesul-

phurization, countercurrent ow mode of operation of tra-

ditional trickle beds is now preferred.

6.2.3. Process intensication using microengineering and

microtechnology

Current production modes are and will be more and

more challenged by decentralization, modularization and

miniaturization. Indeed microtechnologies recently de-

veloped, especially in Germany (i.e., IMM, Mains and

Forschnungszentrum, Karlsruhe) and in USA (i.e., MIT andDuPont), lead to microreactors, micromixers, microsepa-

rators, micro heat-exchangers, and microanalysers, making

possible accurate control of reaction conditions with respect

to mixing, quenching, and temperature prole.

Microfabrication techniques and scale-up by replication

have shown spectacular advances in the electronics indus-

try and more recently in microanalysis by biological and

chemical applications referred in Section 2. Microfabricated

chemical systems are now expected to have a number of

advantages for chemical kinetic studies, chemical synthesis,

and more generally for process development. Indeed the re-

duction in size and integration of multiple functions has the

potential to produce structures with capabilities that exceed

those of the conventional macroscopic systems and to add

new functionality while potentially making possible mass

production at low cost. Miniaturization of chemical analytic

devices in micro-total-analysis-system (TAS) (Berg, Van

den Olthuis, & Bergveld, 2000) represents a natural exten-

sion of microfabrication technology to biology and chem-

istry with clear applications in combinatorial chemistry,

high throughput screening, and portable analytical mea-

surement devices. Also the merging of TAS techniques

with microreaction technology promises to yield a wide

range of novel devices for reaction kinetic and micromecha-

nism studies, and on-line monitoring of production systems(Jensen, 2001).

Microreaction technology is expected to have a number

of advantages for chemical production as the high heat and

mass transfer rates possible in microuidic systems allow

reactions to be performed under more aggressive conditions

with higher yields that can be achieved with conventional

reactors (Ehrfeld, Hessel, & Lowe, 2000). Also new re-

action pathways considered too dicult in conventional

microscopic equipment, e.g., direct uorination of aromatic

compounds, could be pursued because if the microreactor

fails, the small amount of chemicals released accidently

could be easily contained. And the presence of integratedsensor and control units could allow the failed microreactor

to be isolated and replaced while other parallel units con-

tinued production. Also these inherent safety characteristics

could allow a production scale systems of multiple microre-

actors enabling a distributed point-of-use synthesis of chem-

icals with storage and shipping limitations, such as highly

reactive and toxic intermediates (cyanides, peroxides,

azides).

Moreover scale-up to production by replication of

microreactors units used in the laboratory would elimi-

nate costly redesign and pilot plant experiments, thereby

shortening the development time from laboratory to


16/24


Fig. 10. The IMM micromixer: the two scanning electron microscopy images show the 2 15 interdigitated microchannels with corrugated walls (deBellefon et al., 2000).

commercial-scale production. This approach would be par-

ticularly advantageous for pharmaceutical and ne chemi-

cals industries where production amounts are often less than

a few metric tons per year.

Small size reactors are already used in testing process

chemistries, e.g., catalyst testing. Indeed the small dimen-

sions imply laminar ow, making it feasible to fully char-

acterize heat and mass transfer and extract chemical kinetic

parameters from sensor data. Also the high heat and mass

transfer rates possible in microuidic systems that are one ortwo order-of-magnitude greater than current heat exchang-

ers or multiphase reactors, allow reactions to be performed

under more uniform temperature conditions.

For illustration of all these potentialities for process

intensication using microtechnology, in the publication

by Jensen (2001), chemical processing advantages from

increased heat and mass transfer in small dimensions are

demonstrated with model gas, liquid, and multiphase re-

action systems: thin-walled microreactors (realized by

MEMSmicroelectromechanical systems) for heteroge-

neous gas-phase reaction, membrane microreactors for

hydrogenation or dehydrogenation reactions, packed bed

microreactor with high gasliquid interfacial area and high

surface-to-volume ratios, and low pressure drop, and mi-

crofabricated liquid-phase reactor that integrates laminar

mixing, hydrodynamic focusing, rapid heat transfer, and

temperature sensing.

As another illustration, recently de Bellefon, Tanchoux,

Caravieilhes, Grenouillet, and Hessel (2000) proposed a

new concept for high-throughput screening (HTS) exper-

iments for rapid catalyst screening based on dynamic se-

quential operations with a combination of pulse injectionsand micromachined elements. They describe a new concept

to achieve HTS of polyphasic uid reactions for two test re-

actions, a liquidliquid isomerization of allylic alcohols and

a gasliquid asymmetric hydrogenation. The principle used

for the test microreactor is a combination of pulse injec-

tions of the catalyst and the substrate, an IMM micromixer

with negligible volume and residence time less than 102 s,

and a tubular reactor (Fig. 10). The two scanning electron

microscopy images show the micromixer with 2 15 in-

terdigitated microchannels (40 m width) with corrugated

walls. The pulses mix perfectly in the micromixer and the

liquids or the gasliquid mixtures thereby emulsify and


17/24


Comparison with traditional equipment (batch reactor)

0

10

20

30

40

50

60

70

80

Conversion

One catalyst against several substrates

Catalyst pulse 0.2 cm3 of a [Rh] 0.004 kmol/m3 solution equivalent to 80 g of Rh for

each test. Catalyst : RhCl3/TPPTS/NaO H. Rh/T PPTS = 5. Selectivity > 95%. 70 C. Flow

rate: Aqueous phase 5 cm3/min Organic phase 1 cm3/min. [Substrate ] 0.1 kmol/m 3.

Residence time 100 s.

OH

OO

9

OH

10

HO

1HO

2

HO

3

HO

4

OH

5 OH

6

OH

7

OH

8

Batch

Micro

Fig. 11. Comparison with traditional equipment (batch reactor): one cat-

alyst against several substrates (de Bellefon et al., 2000).

behave as a reacting segment, which then travels along the

tubular microreactor. Collection at the outlet of the reac-

tor and analysis aord the conversion and selective data.

Application of this principle has been possible by using a

static micromixer mounted in a dynamic microactivity test.

The catalyst library was then screened. The results led to

the selection of the best catalyst showing activity towards

a large class of allylic alcohols. Similar results which were

obtained in a microreactor and in traditional well mixed

batch reactor (40 cm3) proves the validity of the concept

(Fig. 11).

In terms of catalyst and time consumption per test, thenumerous tests for the liquidliquid isomerization were per-

formed twice, to test for reproducibility, using only one or

two micromoles of metal and over a total screening time

of one hour. The test for the gasliquid asymmetric hydro-

genation showed similar features (down to 0:2 mol of cat-

alyst, and 35 min per test). Throughput testing frequencies

of more than 500 per day are thus achievable, albeit with

computer control of the apparatus. Using these microreac-

tors for dynamic, high-throughput screening of uidliquid

molecular catalysis oer considerable advantages over tra-

ditional parallel batch operations: ensuring good mass and

heat transport in a small volume, reduced sample amounts(to g levels), a larger range of operating conditions (tem-

perature, pressure) and fewer, simpler electro-mechanical

moving parts.

The examples shown here represent a small fraction of

the many designs for microreactors being pursued or envi-

sioned by dierent research groups. But in developing mi-

croreaction technology for process intensication, it will be

essential to focus on systems where microfabrication can

provide unique process advantages resulting from the small

dimension, not only the high transport rates, but forces as-

sociated with high surface area-to-volume ratio. And in

order to move beyond the laboratory into chemical produc-

tion, microreactors must be also integrated with sensors and

actuators, either on the same chip, or through hybrid inte-

gration schemes ultimately resulting in integrated chemical

processors for chemical synt

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Artículo 1 - The future of chemical engineering

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