Chemical Engineering and Processing 84 (2014) 113

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Chemical Engineering and Processing:Process Intensication

j ourna l h o mepage: www.elsev ier .com/ locate /cep

Local and global process intensication

Jean-Francois Porthaa,b, Laurent Falka,b,, Jean-Marc Commenga Universit de Lorraine, Laboratoire Ractions et Gnie des Procds, UMR 7274, Nancy F-54001, Franceb CNRS, Labora

a r t i c l

Article history:Received 19 DReceived in reAccepted 5 MaAvailable onlin

Keywords:Process intensProcess systemProcess retroDebottlenecki

a comglobause o

e exmpaI focall uvery lensi

driveg ne

1. Introduction

Process intensication (PI), formally regarded as processimprovement strategy, consists, according to Stankiewicz andMoulijn [1], in novel equipment, processing techniques, and pro-cess develooffer substaand proceswhich replby devices Among the design of mtions, e.g. rerecent apprmore specisurface-to-vby several in which mpraised) ma

Abbreviatiotank reactor; intensicationengineering; R

Correspondes Procds,

E-mail add

eld of research. Every year, numerous patents are reported formicrotechnology-related areas. Focusing on microreactors, morethan 1500 patent publications in different elds of chemical appli-cations already exist, annually rising in number by more than 250new patents [6]. Then, from the numerous studies published in the

http://dx.doi.o0255-2701/ pment methods that, compared to conventional ones,ntial improvements in (bio) chemical manufacturing

sing. It is related to new and innovative technologiesace large expensive and energy-intensive equipmentwhich are smaller, less costly and more efcient [24].different strategies, a well-established approach is theultifunctional devices, which merge several unit opera-action and separation into one apparatus [2]. However,oaches in PI predominantly focus on equipment andcally on microstructured technologies, providing a higholume ratio, hence increasing mass and heat transfer

orders of magnitude [5]. The revolution-like mannersicrotechnology develops (and as which it is sometimesnifest themselves in the vast number of patents in this

ns: API, active pharmaceutical ingredient; CSTR, continuous stirredGHG, greenhouse gases; LCA, life cycle assessment; PI, process; PFR, plug ow reactor; PR, process retrot; PSE, process systemOI, return on investment time; RSR, reactor separator recycle.ding author at: Universit de Lorraine, Laboratoire Ractions et GnieUMR 7274, Nancy F-54001, France. Tel.: +33 383175094.ress: laurent.falk@univ-lorraine.fr (L. Falk).

literature, it is clear that PI focuses on the equipment improvement,which can be dened as a local approach of process improvementstrategy.

On the other hand, process system engineering (PSE), accordingto Grossmann and Westerberg [7], aims at improving decision-making for the creation and operation of the chemical supply chain,which deals with the discovery, design, manufacturing, and dis-tribution of chemical products. From this denition, PSE can beconsidered as a global approach of process improvement strategy.Recently, Moulijn et al. [8] felt that it was timely to attempt tobetter dene the place of PI in relation with other chemical engi-neering disciplines, such as PSE. Based on the preliminary approachby Grossmann and Westerberg [7] and Marquardt et al. [9], theyproposed to dene PI in conjunction with PSE. The focus and actionof PSE take place along the product creation chain, as a top-downapproach from the enterprise to the molecules, while the focus andaction of PI are on chemical engineering aspects of the process unitsseparately. PI has a more creative than integrating character andprimarily aims at higher efciency of individual steps in that chain,for instance by offering new mechanisms, materials, and structuralbuilding blocks for process synthesis.

In addition, the scales considered are different; PSE focuses lesson the scale of molecules, sites and (nano-) structure, whereas PI

rg/10.1016/j.cep.2014.05.0022014 Elsevier B.V. All rights reserved.toire Ractions et Gnie des Procds, UMR 7274, Nancy F-54001, France

e i n f o

ecember 2013vised form 19 April 2014y 2014e 13 May 2014

ication engineeringtng

a b s t r a c t

The present paper aims at proposing concepts of local intensication and classical approach of PI based on the efciency of a single unit or device. Sompresents several limitations when coglobal intensication. Indeed, when Petc.), the strong interactions among intensication of a single unit can be This paper identies that process intprocesses and has to consider severalto fulll the key objectives in designinea,b

plementary view of process intensication (PI) based on thel intensication. Local intensication is dened here as thef techniques and methods for the drastic improvement of theamples are given to illustrate that local process intensicationred to holistic overall process-based intensication, nameduses on single units (reactors, separators, hybrid separators,nits within the process are ignored and the impact of localimited, resulting in weak improvement of the whole process.cation is broader than technical improvement of devices orrs such as economics, safety, eco-efciency and sustainabilityw plants and retrotting existing units.

2014 Elsevier B.V. All rights reserved.

2 J.-F. Portha et al. / Chemical Engineering and Processing 84 (2014) 113

explicitly includes this level but often pays less attention to thehighest levels. It is clear that PI has consequences for the longitu-dinal action of PSE; for instance, development and application ofa reactive separation can inuence the PSE over the whole chain,from molec

The impcontext thaMost chemibe kept largefcient frocompetitiveefcient prtion of existhe end of thern countrifacilities.

Also, therequires thchanges in ucts. Accorof retrot ddesign of nealternativesate and useis by naturetechnical obnecking andnew feedstuct. Sustainsafety, the ing processand the higity).

Concernretrot (PRthe operatisame implein terms ofcess by chaalternative.a new colualso possibthe equipmical dimenscould incluheat-exchacolumns. Anment to rea

From this obvious conversion ronmental iengineeringbetween thlocal and gmay exist.

Howevesome limitabased intenbased inten

El-Halwholistic andever, procetwo main and plant ious deniti

intensication focuses on the improvement of the global process:maximize the throughput, minimize inventory, or minimize utilitymaterials and feedstock. In case of plant intensication, units thatwill be intensied are not pre-specied and more than one unit can

nsi press intd gloclassds foit or rcomics,

focuipmee ign

the pt, gln thech cThe

and ed und mctur. Thes duere bondl

wheabili

in mnica

ude that

the roposm too acagi

on prvironcle at to czatio

intenrkerslicatiexten.ther tensicatch o

procle an

answnsi

icathoulon crses?he pat thunit to houle to site, if not to enterprise.rovement of processes must also be examined in thet a major portion of the chemical industry has matured.cal plants were built at a time when prot margins coulde and thus were not typically designed to be the mostm an energy and raw material perspective. Nowadays,

pressures have greatly increased the need for moreocesses claiming for the redesign and the moderniza-ting facilities. Grossmann et al. [10] estimated that, ine 80s, 7080% of all process design projects in the west-

es dealt with the redesign, i.e. retrot design of existing

successful commercialization of specialty chemicalse ability to redesign processes quickly, to respond tonew technology and to the short life cycle of new prod-ding to Grossmann and Westerberg, the developmentesign strategies is a more difcult problem than thew processes because it includes a far greater number of

than the grassroots problem, due to the need to evalu- existing equipment. The nature of the retrot problem

complex and multidimensional. They propose a list ofjectives as the increase of the throughput by debottle-

by higher conversion of feedstocks, the processing of aock and the improvement of the quality of the prod-ability is also considered by the increase of processreduction of the environmental impact of an exist-, the reduction of energy input per unit of production,her operability of the process (exibility, controllabil-

ing economics and the major constraints of process), several approaches can be developed. The change ofng conditions of the process can enable to keep themented equipment which is obviously the least costly

investment. The change of architecture of the pro-nging the piping that connects the devices is another

For example, with respect to the cost of purchasingmn, repiping typically incurs very modest costs. It isle to keep the process owsheet intact but to changeent sizing, sometimes in ways that the external phys-ions of the equipment are not altered. Such changesde installation of new tube bundles inside existingnger shells, closer packed trays or even packing insided nally, the last approach is the addition of new equip-ch the objectives.e denition proposed by Grossmann et al. [10], itthat PR shares numerous keywords (improvement ofand yield, reduction of energy consumption and envi-mpact, safety considerations, etc.) with process system

and process intensication. This large overlappingose three concepts shows also that PR is concerned bylobal intensication and that synergies between them

r, as stated by El-Halwagi and co-workers [11], there aretions in most of the previous works focused on unit-sication when compared to holistic overall process-sication.agi and co-workers identied process integration as a

systematic framework for intensication where, how-ss intensication has a broader scope. They denedclasses for intensication: single-unit intensicationntensication. Unit intensication refers to the previ-on of process intensication. On the other hand, plant

be inteThe

procestion anas the methogle unto ovedynammainlyof equcess arrest of

Firsview oapproaunits. zationachievheat aarchiteciencyprocestherefo

Secaspectsustaintationson techto incldesignreduce[12] pprobleing intEl-Halwmizatithe enlife-cyattempoptimiresentco-woits appof an design

Furcess inintensapproawholetainabshouldbe inteintensHow smizatiproces

In ttrate thsingle-pared ed simultaneously.ent paper aims at proposing a complementary view ofensication based on the concepts of local intensica-bal intensication. Local intensication is dened hereical approach of PI based on the use of techniques andr the drastic improvement of the efciency of a sin-device (reactors, separators, mixers, exchangers, etc.),e specic limitations that can be related to thermo-kinetics, heat or mass transfer and energy supply. Itses on the technical improvement of the performancesnt but the interactions among all units within the pro-ored and the impact of intensifying a single unit on therocess is not considered.

obal (or overall) intensication has a more general whole process, considering rst a multi-dimensional

onsisting in the simultaneous improvement of severalprocess is improved by inventory and utility minimi-by throughput maximization. Process intensication issing the classical methods of local intensication andass integrations meaning that a complex owsheet ore should be designed to increase the overall process ef-

impact of a local change will have an effect on the entire to the strong interactions between units and should

e studied at the whole process scale.y, global intensication possesses a multi-dimensionalre different drivers (economic, safety, eco-efciency andty) are included in the strategy. There are some limi-ost of the previous PI works as they focused mainly

l drivers but did not develop an holistic view, omittingthe different drivers. This is not the case with retrot

recently included various methods to evaluate andenvironmental impact of chemical processes. Sun et al.ed the formulation of a multi-objective optimization

determine sustainable chemical process designs tak-count economic, environmental and societal aspects.

and co-workers [13] presented a multi-objective opti-ocedure for the recycle and reuse networks includingmental implications of the discharged wastes using

ssessment. More recently, they developed [11] a rstouple an intensication strategy with a multi-objectiven problem, but the mathematical functions used to rep-sication lacked for realism. In a recent study, Gani and

[14] presented the development of a software tool andon to chemical processes, based on the implementationded systematic methodology for sustainable process

work is still needed to combine process retrot, pro-ication and process system engineering to dene anion strategy which takes into account both the localf PI and the global approach of PSE considering theess by multi-objective optimization to propose sus-d intensive chemical process designs. The strategyer the following questions. Which equipment should

ed in a process? What is the impact of local procession of a device on the overall process performance?d new process architecture be achieved? Which opti-iteria should be chosen? What are the criteria of safer

resent paper, some examples will be given to illus-e classical approach of process intensication based onintensication presents several limitations when com-listic overall process-based intensication.

J.-F. Portha et al. / Chemical Engineering and Processing 84 (2014) 113 3

Step 1 Step 2 Step 3 Step 4 Step 5

Fig. 1. Linear process composed of 5 steps, units or devices in series.

2. Multi-uthe overall

In most sto improve the conseqthe impact performanc

2.1. Equipm

Let us cseveral steptransformaestablish thdevice (for cess) and thand to derivsity (for excase study considered

The genesponds to thto the maxiferred in thientire procewhere G0 isux:

= G0 G1G0

In this pin series (1 G0 denotes

i =Gi1

G0

The globobviously asteps. The ris a key infobe intensiFor a complin some speand generafor processconsidered.sidered alonstirred tankof a specicthe reactanof that reacversion of tspecic reabe minimiz

The globcies. Indeedlocal inefc

1 g = GNG0

Table 1Comparison of two intensication strategies for a unique extensity in a cascade oftwo reactors.

Unit 1 Unit 2 Overall

ase icatiicati

con

N

i

umerjecti

tankentt co

unitouldstep ategy

show whiith thh the

secolong les i

he ovfcie

i

i

o-st in Tas re

onlyxten

n Tabcy is

s simity, t

whicprocy in nsifyvioubal es or

also

duct

threrall y

yielpact of efciency improvement then depends on the cho-p. In ne chemistry, the productivity of a chemical route

depends on the labor cost; indeed, an intense labor cost when many procedures are performed manually by work-e transition from a batch to a continuous process or the usenits aspects: impact of local intensication on efciency of a process

tudies dedicated to local intensication, the objective isthe reactor or the separator without taking into accountuences on the whole process. This section illustratesof improving single equipment on the whole processe.

ent efciency versus process efciency

onsider a batch or a continuous process unit E withs or units. In each of them a specic operation (i.e.

tion or transfer) is carried out. The objective here is toe relationship between the efciency of one specica continuous process) or step (for a discontinuous pro-e efciency of the whole process in different conditionse some intensication strategies. The concept of exten-ample the number of moles) is essential because theis different when identical or different extensities arein the analysis.ral denition of the efciency of a unit or a step corre-e ratio of the transformed or transferred extensity uxmal extensity ux which can be transformed or trans-s unit or operation step. The denition is identical for anss. The efciency is given by the following equation

the inlet extensity ux and G1 is the outlet extensity

(1)

aragraph, N process units or devices Ei are considered i N). Each one is characterized by an efciency and

the outlet extensity ux of equipment Ei (Fig. 1):

Gi (2)

al efciency of this serial arrangement of devices is combination of the local efciencies of all the devices orelationship between the local and the global efciencyrmation to select the local step or device which has toed to improve the performance of the global process.ex process, this relationship is not straightforward, butcic cases, the relationship can be analytically derivedl rules can be identied. Two cases are selected here,

units in series, with respect to the type of extensity The rst case arises when the same extensity is con-g the process. For example, when several continuous

reactors in series are used to perform the conversion molecule, the extensity ux is the molar ow rate oft and the efciency corresponds to the conversion ratetant. Typical cases concern depollution where the con-he pollutant must be maximal and the conversion of actant, whose concentrations in the nal product musted to get the right end-use specications.al efciency can be dened by considering inefcien-, the overall inefciency is equal to the product of theiencies:

G1 G2 GN

Base cIntensIntens

As a

ng = 1

A nThe obstirredequipmreactansecondunit shof the ing strresultsby 10%step wto reac

Theered amolecucase, tlocal e

g =N

A twsentedwhereare notunits. Egiven iefcien

Thiextensor unitwhole strategin intethe prethe gloof stepwould

2.2. Re

Theare oveoverallthe imsen stemainlyoccursers. Th=

G0 G1

GN1= (1 1)(1 2). . .(1 N) (3)

of advanced1 (%) 2 (%) efciencyg (%)

10 50 55on of the rst unit 20 50 60on of the second unit 10 60 64

sequence, the expression of the overall efciency is:

(1 i) (4)

ical example is given in Table 1 for a chemical reaction.ve is to convert the reactant by using two continuous

reactors in series. The considered extensity and the efciency correspond here to reactant ow rate andnversion, respectively. In this example, the rst and thes have an efciency of 10% and 50% (base case). Which

be improved uppermost? Intuitively, the intensicationwith the lowest efciency appears as the most promis-

in order to achieve the highest overall benet. But the that, when the local efciency of one step is increased

le keeping the efciency of the other step constant, thee highest efciency should be intensied rst in order

highest global efciency.nd case arises when different extensities are consid-the process, as for instance the conversion of severaln a multiple-steps reaction scheme A B C. In thiserall efciency is simply equal to the product of thencies:

(5)

ep continuous process is considered as an example pre-able 2. In the rst stage, the reaction (a) is performed,action (b) is carried out in the second stage. Both stages

reactors but can include other units, such as separationsities and denitions of efciencies for each stage arele 2 with a numerical example showing that the global

equal to the product of the local efciencies.ple illustration shows that, depending on the consideredhe intensication strategy, i.e. the selection of the steph must be intensied to improve the performance of theess, can be very different. In Table 2, the most promisingorder to achieve the highest overall efciency consistsing the stage having the lowest efciency contrary tos example in Table 1. The previous relations show thatfciency of a process is also a function of the numberunits in the process. Then, an intensication strategybe the reduction of the number of steps in the process.

ion of the number of steps

e main drivers for commercial production of chemicalsield, productivity and cost. As indicated previously, the

d of a process is a function of the local efciencies and process control may be solutions in order to reduce

4 J.-F. Portha et al. / Chemical Engineering and Processing 84 (2014) 113

Table 2Comparison of two intensication strategies for different extensities in a two stages process.

Stage 1 Stage 2 Whole process

Reaction performed A B (a) B C (b) A C (c)Extensity ux (mol/s) FAEfciency 1 = 1 FA

F0A

Molar ow rates (base case) F0A = 100 mol/s 1

Base case 50% Intensication of the rst stage 60% Intensication of the second stage 50%

the labor cost. The cost driver is mainly dependent on the chemicalroute. By a rough estimation, the decrease of manufacturing costsis proportional to the reduction of the number of synthesis steps.As mentionyield. Howeincrease of impact whethe beginnivery often, tions whensoftens reawith respecsynthesis rothroughput

The examthrough a mup step is c[16]. Convetransfer, mto maximizvery detrimdegradationsteps are ofas addition(micro heattleneck. In tcompared fTable 3 presve chemicthe couplinuous micromay have a time and thardous reacboth cases,the couplinthe intensiput and theresulting in

The yielis explainematerial sin

Table 3Overview of as

Campaign siBatch assetsCAPEX (M$)Operators ThroughputBottleneck Gain in yieldEconomical

pharmaceuintermediation may be

ctor eck tors proce

actio

ost whert tha

(RSRo extt sepratiappr]. Kothermr PFRetwoes frperstion

. .) arandnsiston (dary cnctiove r

ompd anen bol ecoraturr openg thing e

add

Globacyclied previously, the other driver is logically the overallver, it is important to point out that, economically, anthe yield for one individual step does not have the samether the step is located close to the nal product or atng of the synthesis route [15]. This also explains why,chemical reactors operate with higher dilution condi-

they are closer to the nal product. Higher dilutionction conditions and often favors selectivity and yieldt to throughput. Conversely, at the beginning of theute the costs of chemicals are generally low, and the/productivity becomes the driving force.ple of chemical synthesis of an intermediate productultistage organometallic reaction followed by a work-

onsidered here and has been studied by Roberge et al.ntional stirred tank reactors, limited by heat and massust very often operate with diluted reactants in ordere the selectivity. But these diluted conditions are alsoental to the reaction time which also contributes to the

of selectivity. Therefore, protection and de-protectionten used in ne chemical routes, which are consideredal steps of the process. The use of intensied reactors

exchanger-reactors) can be used to overcome this bot-he study of Roberge, different scenarios are studied andor a campaign producing ve tons of the intermediate.ents the reduction of the synthesis route from seven toal steps. Batch reactors, where the slowest reaction isg reaction (bottleneck), have been replaced by a contin--reactor. In this perspective, micro-reactor technologysignicant impact by allowing the decrease of residencee use of a higher temperature by safely performing haz-tions. As the workup operations remain unchanged in

the bottleneck of the whole process is then no longerg reaction, but the downstream step. Results show thated process enables to increase both the total through-

global yield, and to reduce the number of operators higher economical performances of 10%.d has a larger effect on cost than throughput whichd by the large cost contribution from the startingce the intermediate product lies closer to the active

sumptions and gain for two scenarios in commercial production [16].

cost fabottlenof reacof the

2.3. Re

In mrators reactanrecyclethe twefciencongubased [1820for isoCSTR orator n(recyclThe suconnecprot.Hildebthat coequatiboundtive fu[21] haThey ction anbetweoptimatempereactomeanifollowwill be

2.3.1. with reBatch process Continuous and batch

ze (tons) 5 5 (6 m3) 7 5

0

J.-F. Portha et al. / Chemical Engineering and Processing 84 (2014) 113 5

1 2G0G1

G2

G3

Fig. 2. Representation of an isothermal reactorseparator system with recycling.

The reactor (equipment 1) efciency (i.e. conversion) is given bythe following expression:

1 = 1 G1

G0 + G3(6)

where the sum G0 + G3 represents the extensity ux at reactor inletand G1 the extensity ux at reactor outlet. The separator (equip-ment 2) efciency is dened as the ratio between the recycledextensity ux G3 over the extensity ux G1 at the separator inlet.The separator efciency is given by the expression:

2 =G3G1

= 1 G2G1

(7)

The overall process efciency g can be calculated with respectto the two previous local efciencies and by using a material bal-ance on the

g1

1 2(1 The over

efcienciesthe overall eIt can be noof efciencihigh overalefciency ator efcienchigh global because the

001

001

0.05

0.05

005

0.1

0.1

0.1

0.

0.2

0.30.40.5

0.7

0.9

Sepa

rato

r ef

ficie

ncy

0.

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Fig. 3. Overall(equipment 2)

0.1

0.2

0.30.5

0.70.8

0.95

0.95

1

1.5

1.5

2

2

34

5

10

Sep arator intensification

Sepa

rato

r ef

ficie

ncy

0.

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Fig. 4. Preferewith respect telasticity of th

The relaefciency shusing a sen

f thecien

i on ity eq

i wcy. E

on:

lim

calcddit

can d elae impon thaps ral map with two areas: one area where the reactor is theg equipment and one area where the separator is the limitingent toward overall process efciency. These zones are pre-

in Fig. 4 where the border between both areas is drawn as black dotted line. Thin dashed lines represent the iso-value

of the elasticity of the overall efciency with respect to eachy and the units efciencies.s gure illustrates that the choice of intensication strate-en for this simple units layout, is not intuitive and can easilyo non-optimal decisions. Whatever the separator efciency50% (bottom half of the gure), strategies focusing on ther intensication should be favored since they have a more separator. The following expression can be derived:

1)(8)

all system efciency is represented with respect to local in Fig. 3. When the separator exhibits zero efciency,fciency is, as expected, equal to the reactor efciency.ticed that, for a given overall efciency, several coupleses (reactorseparator) are solutions of Eq. (8). Indeed, al efciency can be obtained either with a low separatornd a high reactor efciency, or reversely a high separa-y and a low reactor efciency. However, in most cases,efciency cannot be obtained at low reactor conversion

reaction product must be generated rst.

2

0.3

0.4

0.5

0.5

0.6

0.6

0.7

0.7

0.8

0.8

0.8

0.9

0.9

0.9

0.950.95

0.95

0.95

0.99 0.99

0.99

0.99

ticity othe efof unitelasticciencyefcienequati

e/i =

Thesome aticitiesto builrelativfocus two ma globlimitinequipmsenteda thickcurvesstrateg

Thigies, evyield tbelow reacto0.2

0.3

0.4

0.6

0.7

0.8

0.95

0.99

Rea ctor efficiency1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

RSR efciency as a function of reactor (equipment 1) and separator efciencies.

signicant values are areactor efcall efciencindicates ththe contrarresponds toreactors, seticity may r0.3

0.4

0.40

.5

0.5

0.6

0.6

0.6

0.7

0.7

0.7

0.8

0.8

0.8

0.9

0.9

0.9

0.90.9

0.95

0.95

0.95 0.95

1recomme nded

Reactor intensification re comme nde d

Rea ctor eff iciency1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

ntial intensication strategies to be applied to the reactor or separatoro their respective efciencies (dotted lines present the values of theese strategies).

tive impact of unit intensication on the whole processould then be quantied. The study can be performed by

sitivity analysis as for instance by calculating the elas- overall process efciency. The elasticity with respect tocy of unit i represents the relative intensication impactthe global process efciency, on a percentage scale: anual to 0.5 means that a relative 1% increase in unit ef-ill induce a relative 0.5% increase in the overall processxpression of elasticity e/i is given by the following

/

i/i= i

d

di= %

%i(9)

ulations of reactor elasticity and separator elasticity giveional information. Using the above relations, these elas-be calculated with respect to each equipment, enablingsticity maps, similar to Fig. 3. These maps indicate theact of local intensication strategies that would eithere reactor or on the separator. Then, by overlappingepresenting both elasticities, it is possible to establishimpact on the overall efciency. In this area, elasticitybove 0.5, indicating that a 10% relative increase in theiency will yield to a minimum 5% increase in the over-y. For most layouts, the elasticity is below unity, whiche absence of synergetic effects between the units. On

y, in the upper left-hand side corner of the map that cor- highly efcient separators coupled to low-conversionparator intensication strategies are favorable and elas-each values far above unity. In this area, a small increase

6 J.-F. Portha et al. / Chemical Engineering and Processing 84 (2014) 113S

peci

fic e

nerg

y co

nsum

ptio

n (J

oule

/ m

ole

prod

uced

)

106

0

diffi cul t separati on =1.5

105

104

Fig. 5. Impactdownstream s

in the separefciency. Fthat this nea large capi

2.3.2. Reactperformanc

The modreactor cona better cotivity gainsduring the tor conversseparator inratio, as wecorrespondequipment posed of a place followtheoretical umn head iscolumn (rerecycling raat the columreactor inteon the volaculty (i.e.

= 3 and a = 1.5; enth

The resunicantly dan increaseenergy are

3. Processimproveme

Among tof changingof devices aHowever, asequence o

of unit operations into multifunctional process units, respectively.In the examples presented here, it is shown that simple changesof the owsheet, as recycling or heat and mass integration can beused to intensify a process, even with conventional non-intensied

s.

acta

eachies [uoun thend a etersts sulity) ustr

prodet al.een s pre

contntensady-sinuouon oe thesionn reaxed r), th

regermal

is wic coundshas

netangeactor. Meerc

as toalyste th

rea 0.1 0. 2 0.3 0. 4 0.5 0. 6 0.7 0. 8 0.9 1

gain 40 %

gain 25%

reacto r con version (XA)

easy sep ara tion =3

Conventionalreactor Intensif ied re actor

of the intensication of a reactor on the energy consumption ofeparation by distillation. Inuence of the difculty of separation.

ator efciency yields to a large increase in the processrom a practical point of view, one should not forgetcessary increase in the separator efciency can requiretal expenditure if no new technology is considered.

ionseparation with recycling: impact of the reactore on the energy consumptiones of action offered by the local intensication of thecerns the improvement of reaction efciencies withntrol of operating conditions for efciency and selec-

[3,22], but also lead to reduced energy consumptiondownstream separation operation. Indeed, a high reac-ion increases the concentration of desired product atlet, leading, for a distillation column, to a lower reuxll as a lower energy consumption in the boiler. This cases to a debottlenecking approach when the volumes ofare xed. This is illustrated for a simple process com-continuous reactor where a rst-order reaction takesed by an existing distillation column comprised of 20

plates [23]. The purity of the desired product at the col- xed to 99%. Depending on the feed composition of theactor outlet), the power supplied at the boiler and the

device

3.1. Re

Forstrateg(continfeed (iuous aparamproducexibifor indhigherLomel It has bprocesusing awere i

Stea contvariatiincreasconveror whe

In reactorole ofexotheurationcatalytcompothesis using aical chring reing beda commtive wthe catimprovlimitedte are adjusted to satisfy the composition constraintsn outlet. The results illustrated in Fig. 5 show that the

nsication implies an energy saving. This gain dependstility of the species, indicated by the separation dif-an easy separation corresponds to a relative volatilitydifcult separation corresponds to a relative volatilityalpy of vaporization = 25 kJ/mol).lts illustrated in Fig. 5 show that the energy gain is sig-ifferent depending on the difculty of separation. For

of about 30% of the reaction efciency, the gains inabout 2540%.

intensication by owsheet architecturent

he different strategies of intensication, the possibility the architecture of the process and the use of a networkre very often forgotten or not even considered as PI.

great deal of process intensication is linked with thef the process operations and the potential integration

that a periopossible (fono energy iperature ofachieves a bconguratiout.

The techto the addmanner alobe led throfeeding) oring, which ireactors haequilibriuminstance, Kmicro-strucallowing todrogenationand hydrognt injection strategies

reactant fed to the reactor, there are several injection24] to choose among one-shot (batch), step functions feed), pulsed feed injection and staged injection of the

sense of time or space). The choice between a contin-batch operation is probably one of the most important. Batch processes are more appropriate for high-valuech as ne chemicals (high operating costs, improved

whereas continuous processes are more advantageousial-scale production (low operating and labor costs,uction, safer production). For example, in the work of

[25], the case of the Grignard reaction was considered.shown that the transition from a batch to a continuoussented a considerable reduction of operating times byinuous micro-reactor in which mixing and heat transferied.tate operation is the easiest conguration to operates process but is not necessarily the optimal one. The

f the feeding ow rate (pulsed reactant injection) can process performance. This strategy can be benecial for

or selectivity when the reaction kinetics is non-linearction orders are different [24].

bed operation with periodic ow reversal (reverse owe top and the bottom part of the catalyst bed play thenerative heat exchangers for feed and efuent, allowing

reactions to be operated auto-thermally. The cong-ell suited for exothermal reactions, for instance thembustion of undesired compounds (volatile organic) [26]. The reverse ow operation for methanol syn-also been investigated in forced unsteady conditionswork of three catalytic xed bed reactors with period-

of the feed position [27]. This conguration is called and corresponds to the principle of a simulated mov-thanol synthesis is performed from CO, CO2 and H2 overial CuZnAl catalyst at 50 bars and 300 C. The objec-

save energy by using the thermal storage capacity of bed, and by applying an optimal temperature prole toermodynamic conditions for exothermal equilibrium-ctions. In this way, numerical simulations have showndic unsteady regime and auto-thermal processing arer a given range of optimized switching times) becauses needed except the moderate feed preheating at a tem-

100 C. It has been demonstrated that this congurationetter conversion rate than the equivalent reverse-ow

on by avoiding the inconvenient phenomenon of wash-

nique of staged injection of a reactant correspondsition of at least one of the reactants in a distributedng the reactor (reactant dosing). This technique canugh an inter-stage feeding reactor system (discrete

in a plug-ow membrane reactor (distributed feed-s a generalization of the rst conguration). Membraneve mainly been considered for the improvement of-limited reactions by selective product removal. Foriwi-Minsker et al. [28] have developed a two-zonetured system: the zones are separated by a membrane

eliminate the hydrogen produced by the propane dehy-, implying the shift of the thermodynamic equilibrium,

en is oxidized by air providing heat for the endothermic

J.-F. Portha et al. / Chemical Engineering and Processing 84 (2014) 113 7

dehydrogenation. For a network of irreversible reactions, optimallocal reactant concentrations are essential for a high selectivitytoward the target product. If undesired consecutive reactions canoccur, it is usually advantageous to avoid backmixing. The possi-bility to enserial irreveHamel et almembrane the individtion order othe side reation) if reacthe reactaning decreasresidence ti

3.2. Process

3.2.1. Compoptimization

Intensiprocess unieach procesand mass trintegrationmethods ha(Glasser, H[45]) and tworkers). Tinto accounrecycling a(modeled burations. Dconsidered work has bthen for nohereafter dethe yield ar

The optitor networkthis selectivment of theand concentions schemthe followintions in a spinvolving dsidered the that two optank and plof B as a funThe Van der

A1B 2C

2A3D

Fig. 6 illuof reaction tion of initiait is possibletR1/tR2 and and increastwo differena single plucade of a stexample sh

mpactg the

moran in

follo who

C

ctionve fu

optited vity irs with recycling and specic injection points. This example

that a simple architecture is not sufcient in order achieveerformances.

methodology of reactor network superstructure was thened to non-isothermal homogeneous operation [32] and forothermal multiphase reactor networks [34]. The example of

CSTR

PFR

100 L/h of pure A

10.8 L/h VPFR = 0.01 L

VCSTR = 500 0 L

Fig. 7. Reactor network for -pinene synthesis [31].hance selectivity and yield in network of parallel andrsible reactions has been theoretically investigated by. [29] and Thomas et al. [30] in an isothermal tubularreactor. It is demonstrated that the reaction order ofual reactions have to fulll some requirements (reac-f the reactant in main reaction lower than the one inction, case of heterogeneously catalyzed partial oxida-tant dosing is used. Then, it is advantageous to lowert concentration by means of dosing; the correspond-e in concentration can be compensated by increasingme.

intensication by heat and mass integration

lex reactor networks for multistep reactions

cation requires to design the optimal conguration ofts and to reach the optimal operating conditions fors unit. The optimal conguration also means that heatansfers should be managed judiciously thanks to heat

and optimal mass recycling policy. As indicated above,ve been developed as the attainable region methodildebrandt and co-workers Lakshmanan and Bieglerhe superstructure method (Kokossis, Floudas and co-he reactor network superstructure consists in takingt all ow and mixing patterns with different feeding,nd bypassing strategies around ideal CSTRs and PFRsy ve CSTRs) in series, parallel, series-parallel cong-ifferent techno-economic objective functions may beto perform the optimization. The complex reactor net-een determined for isothermal operation rst [31] andn-isothermal operation [32]. The examples presentedmonstrate that the optimal congurations maximizing

e not a unique reactor but a network of several reactors.mization of complex chemical schemes requires a reac-

to maximize products selectivity. In order to increaseity, local intensication strategy consists in the adjust-

operating conditions, such as temperature, pressuretration, to selectively change the kinetics of the reac-e, within the same process architecture. However, ing illustration, local intensication of chemical condi-ecic reactor may lead to different process structures

ifferent types of reactors. Chitra and Govind [33] con-classical Van de Vusse reaction scheme and determinedtimal reactors structures, based on continuous stirredug ow reactor, can be proposed to maximize the yieldction of the characteristic time of the three reactions.

Wusse reaction scheme can be written as:

(10)

strates the two reactors structures for different ratiostimes tR1/tR2 and tR1/tR3. Let us consider the intensica-l working conditions, denoted by point A in the gure:

to increase the yield of B from 0.3 to 0.6 by decreasingdecreasing tR1/tR3 (scenario B) or by decreasing tR1/tR2ing tR1/tR3 (scenario C). These two strategies results int process structures: scenario B can be performed with

g ow reactor whereas scenario C requires using a cas-irred tank followed by a plug ow reactor. This simpleows that local intensication of a specic device can

Fig. 6. Ideliverin

lead tois also

Thepinene

A EA DB DC 2D2A

ReaobjectiD. Theconnecselectireactoshowshigh p

Theextendnon-is of the intensication of chemical reactions on the process structure maximal selectivity (according to [33]).

e complex structures and that architecture modicationtensication lever.wing example concerns the isothermal synthesis of -se reaction scheme can be written as:

(11)

s are either rst-order or second-order reaction. Thenction intends to maximize the selectivity of C overmal conguration consists in one PFR and one CSTRin a complex way as described in Fig. 7. The maximals obtained with a complex structure combining several

8 J.-F. Portha et al. / Chemical Engineering and Processing 84 (2014) 113

Con

nfigu

20 C 210 CAdiabatic

Adiabatic20 C 210 C

2

ction

naphthalencatalyzed g(always in to be consta

A B CA C

The objeThe optimawith four inexcess. Thesecond stagof removedmaximum y

3.2.2. Reactnetwork

The casefor which ethe energy possibilitiescombined hminimizatioillustrative mass integrexothermalP denoting ttion cannotsolvent vapregime. Diffin Fig. 8, witmass to rea

Adiabatimass and/ochemical reheat (congdecrease th

t ma 5) wf vie

Proce follon theof a olidtion itatioConfigurati on 3 - 10 1.4 = kg

Configuratio n 5 -

210 C 210 CIsotherm

Configuratio n 1 - 10 16700 = Co kg

Adiabatic20 C

210 C

20 C

Fig. 8. Different intensication scenarios of a catalytic rea

e oxidation is considered as an exothermal reaction. Theas phase reaction between naphthalene A and oxygengreat excess so that oxygen concentration is supposednt) is represented by the following scheme:

D(12)

ctive is to maximize the yield of phthalic anhydride C.l conguration found consists in a cascade of four PFRtermediate heat exchangers in order to remove the heat

feed stream is split between the rst (53.8%) and thee (46.2%) and a recycle loop is added. An optimal prole

catalysurationpoint o

3.2.3. The

used iposed by a scentraprecip heat is determined by optimization in order to nd aield equal to 99.9% [32].

or intensication by heat and mass integration

study of exothermal reactions is a typical case of PInergy savings could be performed by judiciously usingproduced by the chemical reactions. Among the several

which can be used as mass recycling, heat recycling,eat and mass recycling, PI can also lead to a drasticn of volume of the reactors. The following example is ancase study that shows how intensication by heat andation can reduce drastically the catalyst amount of an

reaction. The irreversible reaction A + B P is assumed,he products. The feed is supplied at 20 C, whereas reac-

be performed above 210 C for safety reasons (risk oforization). The catalyst is assumed to operate in kineticerent process congurations are studied and presentedh the objective of saving energy and decreasing catalystch a conversion of 96%.c reactors are considered with different ways to recycler heat at reactor inlet in order to kinetically initiate theaction. The optimal solution is to recycle both mass anduration 4) because it enables to preheat the feed and toe global mean residence time. A drastic decrease in the

the reactorprecipitatioprocess straeters and represented (Fig. 9a), a rsludge is reprecipitatoprecipitatio

The recyincrease thgrowth, bythe specicbalances anproduced osize, agglomthe expressIt is then porecycle ratito the volum

Precipitatio

Intergratedfiguratio n 4 - 354 kg=

ration 2 - 10208 = kg

Adiabatic

10 C

by heat and mass integration.

ss is observed. An isothermal reactor at 210 C (cong-ould obviously present the best productivity from the

w of the catalyst mass.

ss intensication by recyclingwing illustration is taken from the precipitation domain

treatment of wastes. Classical installations are com-continuous stirred tank reactor (precipitator) followedliquid separation (clarier) device. Because the con-of the compound to eliminate is generally very low,n reactors have very large volumes. The decrease in volume is a key parameter to reduce the cost of then process, and Plasari and Muhr [35] proposed newtegies based on relationships between process param-actor volume. Three different tested congurations arein Fig. 9: the classical conguration described aboveecycling strategy (Fig. 9b) where an important part of thecycled from the clarier to the reactor and an integratedr-settler (Fig. 9c) which consists in a perfectly-mixedn zone coupled with a clarier.cling and the integration strategy enables to drasticallye kinetics of the limiting step, which is the particles

increasing the concentration of particles and then surface of solid per unit volume. From populationd by taking into account some hypotheses (particlesnly by nucleation, growth rate independent of particleeration and breakage negligible), the authors derive

ion of the mean residence time for each conguration.ssible to establish the following equations relating theo R = qR/Q and the liquidsolid separation ratio = Q/qes:

n with recyclingVrecyVclass

11 + R

precipationVintVclass

1

(13)

J.-F. Portha et al. / Chemical Engineering and Processing 84 (2014) 113 9

tion (a)

Integrated configuration (c)

Settling

Q-q

q

A B

A B

V

Q-q

q

and settling [35].

where VclassVrecy is the and Vint is grated conreactor voluthe liquids

4. Intensi

Global ialso a multient drivers sustainabilidesign of prmize protalocal intensonly, withonology. It issystems hagenerally, nsustainabilihealth and sof these eleally addrespresented hglobal apprbility.

4.1. Econom

The eldthe disparitcant. It is thgains in oplem in a simtime on theby the prod

tion This tion:

=G

Itotalthe

equear)ted he p

in 3Classical configura

Precipitation with recycling (b)

Precipitation

V

Precipitati on

Settling

Q-q

q

V

A B

qR

Fig. 9. Congurations for precipitation

is the reactor volume of the classical conguration (a),reactor volume of the conguration with recycling (b)the perfectly mixed precipitation volume of the inte-guration (c). These equations demonstrate that theme can be drastically reduced if the recycle ratio orolid separation ratios are large.

cation drivers

ntensication is not only a multi-units approach but-dimensional strategy which has to consider the differ-as economic, safety, eco-efciency and more generallyty. The importance of economic considerations in the

(transicess). calcula

ROItime

whereGannaulgain is(tons/yassociaship, t100 kDocess equipment and chemical plant facilities to maxi-bility is no longer to be demonstrated. However, mostication studies focus on the technical performanceut considering the cost of the new intensied tech-

often the case that projects based on nice improvedve been abandoned due to economic reasons. Moreot only production costs but other criteria of processty have to be considered, as environmental problems,afety hazard. Nevertheless, such integrated assessmentments into process intensication has not been gener-sed in the previous approaches. Several examples areere to show that it is necessary to develop a more

oach of PI to solve the complicated issues of sustaina-

ic drivers

s of applications of intensication are very vast andies among the various examples are sometimes signi-erefore difcult to derive general laws on the economiceration. It is, however, possible to approach the prob-ple way by estimating the return on investment (ROI)

investment coming from the nancial gain contributeductivity gain associated with the technological change

10 0

250500

Prod

uctio

n ga

in (%

)

1

5

10

15

20

25

30

35

40

45

50

Fig. 10. Produon the price o(tons/year) [23from the conventional process to the intensied pro-estimation can be made by the following simple

Itotal

annual(14)

denotes to the total amount of investment (D ) andannual nancial gain (D /year). This annual nancialal to the product of the annual nominal production, the product price (D /ton) and the productivity gainwith the intensied technology (%). From this relation-roduction gain necessary to pay off an investment of

years is presented in Fig. 10 as a function of the price of1

1

2

2

2

3

3

3

3

4

4

4

4

5

5

5

5

10

10

10

1010

20

20

2020 20

50

50

5050100

100

Price (/kg)

Tons/year

2 3 4 5 6 10 16 25 40 63 10 0

ction gain required for an investment of 100 kD in 36 months basedf the manufactured product and for different production capacities].

10 J.-F. Portha et al. / Chemical Engineering and Processing 84 (2014) 113

Table 4Scenarios for the chlorination process [17].

Scenario 1 Scenario 2 Scenario 3

Reactor network 3 CSTR in series 2 CSTR in seriesMedium recyclingratio

1 PFRLow recycling ratio

Separation n rios)Prot (M$) 1.166 0.667Annual cost 293 785Yield 0.46 0.565Conversion 0.501 0.617

the productnological in(products wwith a smalis a short timediate prtonnage reqFor a higherure, either or the gainaccordinglyproductionseveral dozThe simple is borne ennd other g

Howevemajor drivebased on annology, andeconomical0 D , the pos(for a constogy has to pproductionNPV, this sim

Techno-process inteious economimplicitly shintensicatthe nal prysis, takingKokossis an50 kmol/h o

C6H6 + Cl2C6H5Cl + C

Authorstive functiofunctions w

- to maxim- to minimi- to maxim

desired prnario 3).

The resufunction, dmaximizingimal prot separation n

l reactor for a consecutive reaction network with respect told criterion. The annualized cost and the prot (scenarios2) provide similar results with process based on CSTR pre-g a lower Capex and Opex. These results show the importanceng into account the coupling of the separation and the reac-workl sol

fety

com to einvenmen

eventhe er, aen inore

d thaces w

may corr

robug a . Am

of ttives

HNO

rsto sme ui

of tnablereact. Cle

n prinous mng a

s for bHigh recycling ratio

etwork 2 distillation columns (identical for the 3 scena1.224

(k$) 321 0.314 0.326

and the production capacity [23]. It is found that tech-novation mostly favors the pharmaceutical processesith high added value and low tonnage) because evenl overall gain in the productivity by a few percent, thereme to return on investment. The innovation for inter-oducts at a few euros per kilogram and higher annualuires a substantially higher overall productivity gain.

investment of several hundred kilo-euro (to use the g-the value of the nominal productivity at constant gain,

at constant nominal productivity must be multiplied), Fig. 10 indicates that the expected gain on the entire

line should not be incremental but should at least touchen percent, which is a much more difcult objective.hypothesis made here considers that the nancial gaintirely by the productivity gain and shows the need toains on operating costs in order to reduce the ROI time.r, Becht et al. [36] showed that Capex reduction is ar of process innovation. Their rough calculation was

overall Capex of 10 MD for setting an intensied tech- a return on investment time of 10 years. Even for anly pessimistic scenario, an overall net present value ofitive differential cash ow has to amount 1.63 MD /yearant interest rate of 10%) meaning that the new technol-rovide an economic net advantage of 163 D /ton if the

is 10 kt/year. Even for a rather poor project with a zerople example shows that the target is pretty ambitious.

economic analysis is a key issue in process design andnsication. As illustrated in the following example, var-ic scenarios lead to different technical solutions. Thisows that reversely, the way how improvement or local

ion of equipment is performed may strongly inuenceotability strategy. A complex techno-economic anal-

into account Capex and Opex, has been performed byd Floudas [17] for benzene chlorination (production off chlorobenzene). The reaction network is given by:

C6H5Cl + HCll2 C6H4Cl2 + HCl

(15)

have underlined that the optimization of various objec-ns imply various process networks. The objectiveere, respectively:

ize the total prot of the plant (scenario 1),ze the annualized venture cost of the plant (scenario 2),ize the overall yield (ratio of the molar ow rate of

optimathe yie1 and sentinof takitor netoptima

4.2. Sa

It islinkedof the enviroin theing to Howevbetweand a mclaimeturbanwhichbeforebe lesscreatindesignparisonalterna

C6H6 +

Theers twcool thversionratio eof the Table 5catiodangermeani

Table 5Scenariooduct over the molar ow rate of feed reactants) (sce-

lts, given in Table 4, show that for each objectiveifferent process congurations are obtained. Indeed,

the overall yield (scenario 3) will not lead to the max-because yield does not actually take into account theetwork and the recycling rate. As expected, a PFR is the

ConguratioVolume of e

(m3)Liquid holduU (BTU/h/ft2A (ft2) Temperatur

(responsebenzene and the need for a systematic methodology to extractutions.

drivers

monly accepted that process intensication is closelyquipment miniaturization. The resulting minimizationntory of hazardous material is so that the safety andtal consequences of loss of containment are reducedt of a large leak from the process equipment, lead-

concept of inherently safer process by intensication.ccording to Luyben and Hendershot [37], the direct linktensied process and inherent safety is not always true

global analysis of the process has to be performed. Theyt these small hold-ups may also be very sensitive to dis-hich can cause rapid changes within the process, and

be detrimental to safety and product-quality constraintsective action can be taken. The intensied process mayst to changes in the internal and external environment,conict with the concept of inherently safer processong their different examples, they considered the com-he irreversible and exothermal benzene nitration in two

scenarios, with the same objective of 96% conversion:

3 C6H5NO2 + H2O (16)

scenario is based on a large CSTR and the second consid-all CSTRs, each reactor being equipped with a jacket tod. The two small reactors can be viewed as an intensiedhe large reactor because the higher surface to volumes to increase the cooling heat ux per reacting volumeor. The two corresponding scenarios are presented inarly, in absence of dynamics consideration, the intensi-ciples would favor scenario 2 because the inventory ofaterials is smaller and the size of equipment is smaller

lower capital cost, and less required coolant.

enzene nitration process [37].

Scenario 1 Scenario 2n 1 CSTR 2 CSTR in seriesach reactor 122 14

p (%) 100 75) 150 150

1230 289e deviation (F)

to a step ofow)

+0.2 and 0.4 +1.7 and 3.6

J.-F. Portha et al. / Chemical Engineering and Processing 84 (2014) 113 11

Table 6Results of acetaldehyde production [11].

Variable Basecase

Scenario 1(no new

Scenario 2(with new

Reaction temReux ratio Ethanol inveProcess yield

The respis studied (inominal vature deviatiof the inlet small CSTR inertia for aciently fast,of concentrdespite of la

Despite rst small Clower liquitory, the temlarger in the

4.3. Invento

The minis a key issuconsideratiand expensbetween ththe inventoand feedsto

The prostudied by tration casewith respecprocess inteinventory foture optimior the minima catalytic rindustrial ethree distillacted ethan11,240 tonsstored for toptimizatioprocess inteto minimizeios were takequipment tillation coladdition of cess yield binventory wratio of theis higher leadecreased b

4.4. Environ

The envrelated to s

environmental impacts is generally costly but can also generatesavings due to a decrease of energy consumption for example.A typical example concerns the reduction of greenhouse gases(GHG) emissions in a factory. To reach the given constraints, some

entger el en

emiin toycleed insignd div

ition

yclet andcyclects bod, flts in

resuo the

assehenre ctionchemis, ececen

The LCAzatiotion

eacemicrged ethesure

ecoent cns amatilicatother

of dr conl, caors, ocesss to ion, e calic a

t theted a

toolase).units) units)

perature (K) 600 580 610(3rd column) 3.5 5 3ntory (tons) 11,240 7100 7080

0.589 0.315 0.648

onse of each conguration to a step in the benzene owncrease to 120% and decrease to 80% with respect to thelue of 100%). Results show that the maximal tempera-ons are larger when two small CSTRs are used. A changeow rate implies a larger variation of concentrations in a

than in a large CSTR due to different space times (lower small space time). If the controller response is not suf-

the kinetics of reaction being very sensitive to variationations, the system of two CSTRs is much more instable,rge heat transfer capacities.several advantages under steady-state operation, theSTR presents much poorer dynamics results due to a

d hold-up. The closed-loop response is more oscilla-perature deviations being about an order of magnitude

small reactor than in the large one.

ry drivers

imization of the inventories of reactants and productse in factories which is related to safety and economic

ons because stocks of chemicals are often hazardousive. Then, global intensication aims at the compromisee maximization of the throughput for a given process,ry minimization, or the minimization of utility materialsck, as proposed by El-Halwagi and co-workers [44].duction of acetaldehyde through ethanol oxidation,Ponce-Ortega et al. [11], is considered here as an illus-

to reduce process inventory. The main difference heret to the classical superstructure optimization is that thensication approach considers the minimization of ther a given production, whereas the classical superstruc-zation usually considers the maximization of the protization of the total cost. The owsheet is composed of

eactor, two scrubbers to remove some gases from thexhaust (using ethanol as a solvent), and a network ofation columns to separate acetaldehyde from the unre-ol, from light organic wastes and from water. About

of ethanol, that is a hazardous and ammable liquid, arewo weeks. Whereas the classical superstructure-basedn usually considers the maximization of the prot, thensication approach, developed by the authors, is used

ethanol inventory. To reach this objective, two scenar-en into account: one scenario without new intensiedand one scenario with an intensied reactor and a dis-umn. The main results are presented in Table 6. Thenew intensied units in scenario 2 implies a higher pro-ut does not provide a signicant reduction of ethanolith respect to scenario 1. By manipulating the reux

third column in scenario 1, the ethanol recovery rateding to ethanol savings. The ethanol quantity stored is

investmexchanlow levof GHGThe mais life cdescribcess demetho

- Denary).

- Life cinpu

- Life impameth

- Resu

Thedata, timpactdure wliteratuproduca petroanalysbeen rbelow.ods is optimiintegrasentingand chdischalem togis meaand antreatmsolutiomatheits app

An eration[14] foing tooindicates prpoint ioperattors areconomaccoungeneraimpact(base cy approximately 37%.

mental drivers

ironmental impact of a chemical process is closelyocial, technical and economic issues. The decrease of

methodologenzyme: thmode and imary recovmain solutiAs water ps are necessary in order to save energy (optimized heatnetwork, use of more efcient equipment, recovery ofergy, etc.) whose production is often the main sourcessions. Energy saving is also benecial in the long term.ol to determine the environmental impact of a process

assessment (LCA). This methodology has been widely the literature and is now considered as a tool for pro-

, selection and optimization [38]. LCA is a standardizedided in four main steps [39]:

of the scope of the study (objectives and system bound-

inventory analysis (determination of mass and energy output uxes by mass and energy balances).

impact assessment [calculation of environmentalased on mass and heat uxes with an impact assessmentor example Eco-Indicator [40]].terpretation (improvement analysis).

lts of LCA are subjected to the quality of the collected hypotheses considered in each scenario, to the chosenssment method and to the selected allocation proce-

co-products are obtained. LCA has been used in theoupled with process integration to analyze a biofuels

process [41], or coupled with exergy analysis to analyzeical process [42]. The coupling between environmental

onomic analysis and process integration techniques hastly developed by different research teams as describedenvironmental method consistently used in these meth-. Ponce-Ortega et al. [13] establish a multi-objectiven model for the synthesis of recycle and reuse mass

networks. Sources (inlet ow rate), interceptors (repre-h available unit with conversion factor based on physicalal properties) and sinks (exit ow rate or waste streamto environment) are dened and used to build the prob-r with constraints. An environmental objective functiond by an impact evaluation method (Eco-Indicator 99)nomic objective function considers fresh sources andosts. Solution is represented by a set of Pareto optimalnd a network is also obtained. This approach requirescal models to represent all process alternatives, makingion difcult and time consuming.

methodology for systematic process analysis and gen-esign alternatives has been developed by Carvalho et al.tinuous or discontinuous processes. The correspond-lled SustainPro, determines a set of mass and energyestablishes operational and design targets and identi-

alternatives matching the design targets. The startingdene the process specications (prices, conditions ofand process owsheet) of the base case. Then, indica-culated to identify process bottleneck. A general safety,nd environmental evaluation is performed to take intose issues in the design. Finally, design alternatives arend each alternative is evaluated using environmentals and safety indices with respect to the reference design

This method is especially useful for process retrot. Thisy has been applied to the production of an intracellular

e -galactosidase. The basic process operates in a batchs divided into three main sections: fermentation, pri-ery and purication. By applying the methodology, twoons were found: water purication or water recycling.urication was not economically viable, the recycle of

12 J.-F. Portha et al. / Chemical Engineering and Processing 84 (2014) 113

water was chosen. An important decrease of eutrophication andacidication indexes was observed and the investment was fullyrecoverable making the new design an economically sustainablealternative.

5. Conclus

In the prto illustratebased on siseveral limbased intenand global on a two-scan be perperformancthe elementechnique tby using rtion or reaSecondly, lmicrostructof innovatiperformed devices.

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Appendix A. Nomenclature

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esent contribution, several examples have been given that the classical approach of process intensicationngle-unit improvement (local intensication) presentsitations when compared to holistic overall process-sication (global intensication). In fact, a joint localintensication strategy needs to be developed, basedtep approach. Firstly, global intensication approachformed to get a drastic improvement of the wholee of the global process. The appropriate selection oftary unit operations that have to be intensied is onehat can be used. Optimization of process architectureeactant injection strategies, heat and mass integra-ctants recycling is another complementary approach.ocal intensication by classical techniques, such asuring to avoid heat or mass transfer limitations, useve driving forces or multi-functional systems, can beto reach the expected technical performances of the

on, it has been shown that process or device improve- only based on technical criteria but several drivers suchc, safety, eco-efciency and sustainability have to beto fulll the key objectives in designing improved pro-ew plants or in retrotting existing units. For instance,rocess safety is submitted to PI. As the inventory andzardous substances are lowered, the process risk isduced. Additionally, conservation of natural resources,etter utilization of mass and energy, may be linked to

ctive of the paper was not to oppose local and globalion but to show the complementary aspects betweends. Local intensication is essential because it consid-ical and chemical phenomena taking place in a system.s, the focus is also made at the scale of unit operationsidering the interactions between them. Global intensi-hniques will consider these interactions and constitutevant tool that can validate the addition of intensiedin a global process.e complexity of a typical process and the variousseveral authors [11,14] have already developed anamework for generating and pursuing valid opportu-rocess intensication. In both approaches, Gani andgroups propose to couple an intensication strategyi-objective optimization problem where the units thatnsied are not pre-specied and more than one unitsied simultaneously and where additional intensiede considered in the strategy. Optimization criteria aree previously cited drivers (economic, safety, sustaina-Following the same objectives, Freund and Sundmachereveloped a methodology not based on the classical unitoncept but on the basic functional principles encoun-hemical process. Process intensication is led at threehase level, the unit level and the plant level and inter-ween levels are taken into account. In these works,erformance of the different devices have an important

in this framework. The results obtained by the two are promising but however the challenge is to proposeeliable models that enable to consider local intensica-pment.

Latin lee/i

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[12] L. SuncCon437

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[14] A. anaChe

[15] T.YRev

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[20] X. Wsep

[21] L.GsysIndasticity taking into account the impact of i variations olar ow rate of component j (mol/s)olar ow rate of component j at unit inlet (mol/s)tensity uxnual nancial gain (D /year)tal amount of investment (D )mber of process unitstual owing volume (m3 s1)tual owing volume (m3 s1)cycle ratioit volume (m3)

sciency of a process or an equipment ierall efciencyuidsolid separation ratio

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Local and global process intensification1 Introduction2 Multi-units aspects: impact of local intensification on the overall efficiency of a process2.1 Equipment efficiency versus process efficiency2.2 Reduction of the number of steps2.3 Reactionseparation with recycling2.3.1 Global intensification strategy of a reactionseparation with recycling2.3.2 Reactionseparation with recycling: impact of the reactor performance on the energy consumption

3 Process intensification by flowsheet architecture improvement3.1 Reactant injection strategies3.2 Process intensification by heat and mass integration3.2.1 Complex reactor networks for multistep reactions optimization3.2.2 Reactor intensification by heat and mass integration network3.2.3 Process intensification by recycling

4 Intensification drivers4.1 Economic drivers4.2 Safety drivers4.3 Inventory drivers4.4 Environmental drivers

5 ConclusionAppendix A NomenclatureReferences