Alexandru Woinaroschy

Department of Chemical and Biochemical Engineering,Politehnica University Bucharest,Bucharest 011061,Romania

1.Introduction

The aim of this paper is to present the evolution of chemical engineering pointed to its general paradigms.We will start from the paradigm definition given by The American Heritage Dictionary of the English Language:“Paradigm is a set of assumptions,concepts,values,and practices that constitutes a way of viewing reality for the community that shares them,especially in an intellectual discipline”.An overuse of the word paradigm has led to some confusion over the meaning of the term.Villermaux[1]has considered paradigms as:mass,heat,momentum analogies,reaction-transfer coupling,effective media and properties,population balance,residence time distribution,axial dispersion,continuous stirred tank,non-linear dynamics,energy and entropy management,structure of condensed matter,etc.Nevertheless,specific techniques for solving various classes of chemical engineering problems are not new paradigms,they fall within the current chemical engineering way of thinking.Related to the overuse and confusion over the meaning of word paradigm,Hill[2]refers the Dilbertcomic strip where every engineer says his project is a paradigm,but no one seems to know what that means!

For the evolution of chemical engineering,the definition given by The American Heritage Dictionary of the English Language[3]is useful to be linked with that proposed by Kuhn[4],which defines a scientific paradigm as:“universally recognized scientific achievements that,for a time,provide model problems and solutions for a community of practitioners”.

From the ancient times applied chemistry meant an art,a trade for obtaining salt,caustic soda,soap,sulfuric acid,sugar,and glass-things in rudimentary workshops.Traditional recipes have been transferred with minor,empirical improvements gained from observation.This period can be considered as the empirical stage of chemical engineering.

The development of the variety and the amounts of the chemical products,mainly in the last quarter of the 19th century,imposed a new stage,respectively the rational stage of chemical engineering.The empirical rules and practices were abandoned for rational scientific methods.The transition to this stage is especially owing to the great progresses of physical chemistry.In 1885 prof.H.E.Amstrong has taught at Central College of London the first chemical engineering course.In this course fundamental scientific training was combined with technical practice for the design of chemical industry equipment.It may be considered that at this moment the rational stage of chemical engineering begins.

In 1887 prof.Geoge Davies from Manchester Technical College has taught a lot of chemical engineering lessons.These lessons were the roots of his further Handbook of Chemical Engineering published in 1901 and next in a second edition consisting in two volumes in 1904.The practical value of Davies lessons from this book consists in the variety and abundance of the technical end economical data.Due to the lack of scientific explanations,in fact this book belongs to empirical stage and is a document of what meant chemical engineering at that stage[5].

2.The first paradigm:unit operations

The Davies' book contained a novelty,which subsequently it appears to be more important as it incipiently looked:instead to describe each technological process existent at that time,Davies regards an industrial chemical process to be composed by distinct sections which are present-in different sequences and conditions in many other processes.As this Davies' priority was not explicitly announced,it was assigned to Arthur D.Little,which in a report to Massachusetts Institute of Technology has introduced the notion of unit operations.Much more lately,in 1958,Davies' priority about the concept of unit operations has been recognized[5].This concept and its application can be assumed to be the first paradigm of chemical engineering,namely the unit operations paradigm.Therefore,the explosion of chemical industrial applications at the end of 19th century and at the beginning of the 20th century imposed the requirements of the process details knowledge systematization.It can be considered that the first paradigm has appeared as a necessity of systematization.The representative book of this paradigm is“Principles of chemical engineering”,written by Walker et al.[6].

The tens of thousands of industrial chemical processes can't be individually treated to the detailed scale as imposed by design and operation of the corresponding plants.Nonetheless,these processes are made from a much smaller number(about 80)of unit operations.Based on unit operation paradigm,an enormous amount of information concerning both theoretical and experimental studies,as well as results about unit operations is systematized,in a huge literature(books,papers,and patents).

For each unit operation,the following are investigated:(1)the fundamental theoretical principles needed by the formulation of phenomena equations;(2)the laboratory and pilot experimental methods needed by the equations which cannot be theoretically formulated;and(3)the ways to equipment scale-up from laboratory or pilot scale to industrial scale.

To achieve the results imposed by process research,design,and operation the unit operation paradigm use the following general theoretical principles:(1)momentum,energy and mass balances;(2)thermodynamic phase equilibrium relations;(3)momentum,energy and mass physical kinetic relations(transfer equations);and(4) financial conditions and the corresponding equations.In this way,if the material physical properties are defined,as well as technological and economic constraints,it is possible to obtain a quantitative solution for each specific industrial chemical process.It may be said that if the chemist is thinking in chemical reactions,the chemical engineer is thinking in unit operations.Subsequently,the paradigm of unit operations was adopted by other process industries,such as food industry or light industry.

3.The second paradigm:transport phenomena

While still useful to the present day,the unit operation paradigm proved inadequate for solving some important classes of problems[2].This awareness led to the emergence of chemical engineering science as a second paradigm in the late 1950s,as best exemplified by the Birds' textbook Transport Phenomena[7].This is the transport phenomena paradigm,an upper systematization and synthesis evolution.At the moment of issue of this book,the field of transport phenomena has not been yet recognized as a distinct engineering subject.The authors have considered that it is important to put more emphasis on understanding basic physical principles,than on the blind use of empiricism.Their thought has been that the subject of transport phenomena should rank along thermodynamics,mechanics,and electromagnetism as one of the key“engineering sciences”.The paradigm of transport phenomena approaches the three elementary physical processes,which take place in any kind of unit operation:momentum,energy,and mass transport.Thus,unit operations can be considered as specific applications of these three fundamental processes.As combinations of unit operations give technologies,combinations of transport processes give unit operations.

The paradigm of transport processes presses for the mechanisms of these processes,on the phenomena,which take place close to the border of two physical phases;the aim of the paradigm consists in the deep understanding of the elementary causes and effects which explain the features and applications of each unit operation.The transport phenomena paradigm extends the content of chemical engineering to a fundamental,theoretical science,closely linked with physics,mathematics,mechanics,thermodynamics,electromagnetism etc.The birth of the second paradigm was,therefore,the consequence of the need for a deep,scientific knowledge of the phenomena which explain what happened inside of unit operations.

Engineering,in the last analysis,depends heavily on heuristics to supplement in complete knowledge.Transport phenomena can,however,prove immensely helpful by providing useful approximations,starting with order of magnitude estimates,and going on to successively more accurate approximations,such as those provided by boundary layer theory[8].

At last,it appears the trend to gather all the three transport phenomena in a single concept,respectively the property transport[9].This very high systematization is justified by the analogy of the transport phenomena,respectively the structural similitude of differential equations and boundary conditions which describe them.In this treatment,each fundamental transport process becomes a specific case.

4.The third paradigm:chemical product engineering

In the second part of20th century the diversity of industrial products(in many cases with close properties and with the same utilization)has a huge growth,and correspondingly,very strong market fights have evolved between producer companies.The same things happened with chemical products.The importance of properties and qualities of chemical products has become essential.Until recently,the main purpose of chemical engineering has been to obtain the lowest cost process.Even process related issues like reliability,product purity,pollution control,etc.have been ultimately translated into costs that must be minimized.In contrast,chemical product design tries to obtain the most added values for a product through enhanced product properties.This is a more complex task than a mathematical treatment to maximize profit.The profit depends in some unidentified way upon the complex set of product properties.Therefore,product engineering problems can't be solved by traditional chemical engineering approaches.Their solution requires not just additional chemical engineering approaches,but even more fundamentally,and that is why product engineering should be recognized as a third paradigm of chemical engineering,as first hinted in 1988[10].Hill[2]substantiated the product engineering as a new paradigm,respectively the third paradigm of chemical engineering.Hill has considered that,“while the design of a chemical product and its manufacturing process is analogous,some critical differences are so fundamental that a new paradigm and new approaches are needed to successfully solve product design problems”.

It can be assumed that the third paradigm was imposed by the fight for technical and economical product performances generated by a strong competitive market environment.Nowadays,it is far more important what and how much is sold,than what and how much is produced.

New chemical products have been created by combining a wide knowledge of existing chemical products with a big amount of scientific experimentation.A combinational explosion of product options will limit all experimental techniques.Therefore,it is desirable to minimize experimentation through a systematic consideration of product formulation prior to experimentation.Product engineering techniques is largely based on heuristics when data are limited,followed by detailed calculations when data become available,this being the essence of the third paradigm.The basics of the third paradigm have been stated in the book of Cussler and Moggridge(1st ed.[11]and 2nd ed.[12]).The general steps of product engineering propose by Cussler and Moggridge[12],followed by the general stages of process engineering are presented in Fig.1,where we put into evidence the distinction between the steps of product and those of process engineering.We consider that this distinction may be useful for a better discrimination between the terms“product”and“process”engineering,very frequently used nowadays in chemical engineering literature.

Fig.1.Product and process engineering.

Cussler and Moggridge[12],have proposed a generic framework for chemical product design,based on a 4-step algorithm:the first three steps are those indicated in Fig.1,where the fourth step was named as the manufacture the product.This step four contains all the stages of process design:batch vs.continuous process,inputs and outputs,reactor and recycles,and separations and process integration.The authors admit that this four step algorithm is a major simplification that affects effectiveness in specific cases.But,this procedure can be an excellent starting point,very useful to expand each specific case.Related to the controversy of the key to product design,management or technology,Cussler and Moggridge consider that the application of technology is central to chemical product design.

Hill[2]proposed a methodology for designing homogeneous chemical products when limited data are available.The methodology has the following eight steps:(1)product definition,(2)technical product requirements,(3)product performance relationships,(4)product candidate generation,(5)product candidate selection,(6)process design,(7)risk analysis,and(8) financial(business case)analysis.This methodology assumes that a homogeneous product can achieve all the required product properties.This approach ignores the class of structured products,which achieve their properties through a microstructure that is determinant by the interaction of its components and the manufacturing process[13].Product engineering for structured products is significantly more complex,as the product and process must be simultaneously designed[14].Two primary approaches have been proposed:(1)generation and systematic reduction of the number of alternatives through heuristics,and(2)optimization of the set of all potential alternatives through mathematical programming[2].

Severalnew developments have been conceived in the field of product engineering.Gani[15]provided a set of integrated methods and tools so that some of the chemical product design steps can be carried out faster,over a wider search space and using fewer resources.

Abildskov and Kontogeorgis[16]presented some current and future challenges in thermodynamic modeling towards chemical product design.

Seider et al.[17]suggested new perspectives and strategies of chemical product design.Starting from the innovation map[18]that links the critical technological advances required to meet customer needs,aspects of the product-development process are considered with emphasis on the concept,feasibility,and development stages.

In the 3rd edition of the book of Seider et al.[19],the social aspects and economics of product design are introduced,and the Stage-Gate Product Development Process is explored in parallel tracks for several chemical products.

Wu[21]took into consideration a supply chain that consists of an original equipment manufacturer producing first-hand products and a re-manufacturer recovering the used items,respectively.

The objective of the Ng,Gani and Dam-Johansen[22]book is to help form a more clear perspective of product design through case studies from people with different backgrounds.

Product engineering,or its more essential aspects are now taken into consideration in the new curricula of chemical engineers[23];[24];[25].

It may be accepted that,nowadays,product engineering has evolved from a concept to a paradigm.Hill[2],who is an outstanding researcher in this field,has entitled his paper:“Chemical Product Engineering-The third paradigm”.

Due to major changes in the chemical industry the product design role and merits are continuously increasing,however this is not an argument that process design should disappear.Product design and process design must be used together,in agreement with these changes in the chemical industry.

5.The fourth paradigm:sustainable chemical engineering

Nowadays the concept of sustainability is imposed in all human activity fields,especially in industrial domains.Chemical industry,as a huge materials and energy consumer,and with a strong ecological impact,could not remain outside of sustainability requirements.The basics of the fourth paradigm-sustainable chemical engineering-are now formulated.This new paradigm is set on the recognition of limitation of resources,the requirement for inter and transgenerational equity within human society and the need for preservation of life supporting natural systems[26].The contemporary discussion around the concept of sustainability started with the Brundtland report[27].In this report,sustainability or sustainable development is defined as“the development that meets the needs of the present without compromising the ability of the future generations to meet their own needs”.This report clearly frames the challenge of sustainability:it requires human society to live within the limitation of our planet in a way that allows infinite development in temporal terms.Sustainability becomes more and more important in the modern economy,and in 1999 the Dow Jones Sustainability Indices were started.Corporate sustainability is considered a business approach that creates long-term shareholder value by embracing opportunities and managing risks deriving from economic,environmental,and social development[28].Nowadays,these three dimensions constitute sustainability and are considered the three pillars carrying this concept.All these three parts are equally important in sustainable development.They are not independent of each others;on the contrary,there is manifold interaction between them.

For the economic assessment there are already a number of books,especially in the chemical engineering field,that cover cost and profitability subjects in detail.Fromthese,Peters et al.[29]is the standard reference book.

3.1構建與患者以及醫(yī)護人員的交流平臺。臨床藥師在參與藥物治療工作的過程中應注意通過和患者以及醫(yī)護人員之間的有效溝通和交流來構建一種良好的醫(yī)患關系,堅持以人為本的人性化理念,對患者的用藥隱私以及知情權進行保障。同時還要注意和所在科室的醫(yī)護人員進行有效溝通與交流,以此促進一種良好的專業(yè)關系的形成,對所有醫(yī)護人員的工作予以充分尊重,學習他們優(yōu)良的醫(yī)德醫(yī)風和醫(yī)療知識。此外還應在參與醫(yī)療活動的過程中對本科室藥學監(jiān)護工作的特點以及醫(yī)療規(guī)范等進行了解并掌握,和所有患者之間都盡量建立一種專業(yè)的醫(yī)療關系,并將其生成詳細的記錄。

There are many published methods for environmental assessment.The method proposed by Heinzle et al.[28]provides an approach that allows the scientist or engineer in process development to make an environmental,health,and a safety assessment within a reasonable time.By this method,a global environmental index EI,which indicates the environmental relevance of a whole process,is calculated.The method requires material flows to compute Mass Indices(which is a metric for the material intensity of the process),and the so-called ABC classification(provided by user in order to compute individual Environmental Factors EFi—a metric for the environmental impact of each component i).The environmental index EI is now computed from Mass Indices and Environmental Factors.

The identification of relevant social aspects and a corresponding set of indicators is a very complex task.There are important differences between processes and products,countries specificities,national and international legislations,etc.For the social assessment of bioprocesses,by taking into account the results gained from the multi-perspective approach of technology assessment,including the implications of an international stakeholder survey,Heinzle et al.[28]have identified these eight significant aspects:health and safety;quality of working conditions;impact on employment policy;education and advanced training;knowledge management;innovative potential;customer acceptance and social product benefit;and societal dialog.

It is imperative to consider all three dimensions of sustainability in all stages of process development.As a consequence,process optimization evolves to multi-objective optimization[30].In traditional process optimization the objective function is a scalar one.In multiobjective optimization of sustainable processes the objective function is a vectorial one,with economical,ecological and social components[31,32].

Chemical engineering,with its strong systemic orientation and its function to link natural sciences,engineering and industrial practice,is in“pole position”among many other engineering sectors to meet the challenges of sustainable development.It is a key engineering discipline for adapting human society towards sustainability[26].

A main task of chemical engineering during its entire evolution was to reduce material and energy consumption.Chemical engineering is placed on the first positions among other engineering sectors related to these consumptions.Before sustainability era,reducing of material and energy consumption was imposed by economical reasons(increasing profitability,decreasing products cost).Environmental assessment modifies drastically the material and energy consumption,now these amounts are not the unique objective.The main feature consists in the change of material and energy resources base both in order to preserve the frequently used resources,but also to involve new sources,especially environmentally friendly ones.Related to the use of new raw materials an example in this direction is the book Bioprocessing for Value-Added Products from Renewable Resources[33].Related to energy resources,the limitation of fossil resources adds to the pressure on society to look for other sources.A particular challenge for chemical engineering is providing energy storage in a sustainable way.Renewable sources for energy and material will become more important and will require a massive re-structuring of industrial processes[26].

In the field of reducing of materialand energy consumption,increasing of research activities and applications of process integration[34]must not be omitted.

Of course,today sustainability is involved in almost all fields and disciplines.In chemical engineering,sustainability exhibits a huge application potential.Moreover,a theoretical system applied in sustainable chemical engineering is in course of elaboration.In this respect the activity of sustainability division of the institution of chemical engineers IChemE should be mentioned.This endeavor was materialized in many reports(e.g.The sustainability metrics series),meetings(e.g.Sustainability in chemical engineering education,2011),web seminars,etc.(see http://www.icheme.org/resources/).An important workshop report is“Chemistry for a sustainable future”conceived in the frame of National Science Foundation Workshop on Sustainability and Chemistry[35].Also,the start of theoretical and practical foundations in the domain of sustainability in chemical engineering are to be found in the books of Heinzle et al.[28]and Klemes[34].

Sustainable development will generate formidable challenges and vast chances for chemical engineers in the actual century.

6.Conclusions

In the present paper,it has been shown that from the aspect of technical application the main paradigms have a strong influence in the development of chemical engineering.The first two paradigms,respectively unit operation and transport phenomena are the fundamentals of chemical engineer curricula.In these two paradigms,there are systematical theories and methodology of chemical engineering,so people think“Chemical Engineering”as a branch of science,or an independent discipline.

The third paradigm,chemical product engineering,has a paramount importance in the recent evolution and applications of chemical engineering.

Nowadays,we propose that a fourth paradigm,sustainable chemical engineering,must be taken into account.This personal opinion is based on a great deal of reasons that were exposed above.In fact,it is rather difficult for a new paradigm to be entirely accepted by the scientific community.The same happened with the transport phenomena paradigm that was initially contested by many scientists.

The needs in the evolution of chemical engineering and the corresponding paradigms are presented in Fig.2,where the fourth(proposed)paradigm is indicated in dashed line boxes.

Related to the paradigms role in the evolution of chemical engineering,it is relevant the Kuhn conception[4],respectively that even when paradigms are known to be inadequate,their inadequacies are frequently minimized,or even ignored by the scientific community.Nevertheless,if and when a paradigm reaches a crisis where its technical inadequacies are brought into focus,perhaps driven by social requirements,a new paradigm will arise to explain what the prior paradigm could not.During the evolution of chemical engineering each new paradigm was a step forward which has extended the manifold of the tasks that can be solved.However,no older paradigm is derelict.In fact,almost all paradigms must be used together in order to solve the complex chemical engineering problems.

Of course,the discussion about paradigms of chemical engineering cannot avoid the subjectivity.An important discussion can be raised by the question whether product design and sustainability should be considered as paradigms in chemical engineering,when compared with the fundamental concepts of unit operations and transport phenomena.The 3rd and 4th paradigms have not been established and/or universally accepted,and despite this fact they are reported here as paradigms;it is possible that some researchers and chemical engineers are to be considered only as paradigm shifts—meaning new levels of understanding,scope,significance,etc.An explanation for this can be their novelty,despite the fact that it was elaborated an important amount of literature and research in their fields.I consider that product design and sustainability,due to their important economic and,respectively social,significances may be accepted as paradigms,in course of time,by the majority of the people concerned in chemical engineering.

Fig.2.The needs in the evolution of chemical engineering and the corresponding paradigms.

Also,some other personal ideas of the author and the reference selection are,doubtlessly,questionable.There are hundreds of works that deal with the fundamentals of chemical engineering,with its past,present,and future.Here,I tried,very briefly,to emphasize the importance of the basic paradigms in chemical engineering evolution.

[1]J.Villermaux,Future challenges for basic research in chemical engineering,Chem.Eng.Sci.48(14)(1993)2525-2535.

[2]M.Hill,Chemical product engineering—The third paradigm,Comput.Chem.Eng.33(5)(2009)947-953.

[3]The American heritage dictionary of the english language, fifth ed.Houghton Mifflin Harcourt Publishing Company,New York,2013.

[4]T.S.Kuhn,The structure of scientific revolutions,University of Chicago Press,Chicago,1996.

[5]Bratu E.,Chemical engineering,reception speech to the Romanian Academy on 20 Dec.1974,Romanian Academy Press,Bucharest,1976.

[6]H.Walker,W.K.Lewis,W.H.Mc Adams,Principles of chemical engineering,Mc Graw-Hill,Inc.,New York,1923.

[7]R.B.Bird,W.E.Stewart,E.N.Lightfoot,Transport phenomena, first ed.John Willey&Sons,Inc.,New York,1960.

[8]R.B.Bird,W.E.Stewart,E.N.Lightfoot,Transport phenomena(2nd edition),John Willey&Sons,Inc.,New York,2002.

[9]R.S.Brodkey,H.C.Hershey,Transport phenomena.A unified approach,Mc Graw-Hill,Inc.,New York,1987.

[10]Committee on Chemical Engineering Frontiers,Frontiers in chemical engineering:Research needs and opportunities,National Academy Press,Washington,1988.

[11]E.L.Cussler,G.D.Moggridge,Chemical product design, first ed.Cambridge University Press,New York,2001.

[12]E.L.Cussler,G.D.Moggridge,Chemical product design,second ed.Cambridge University Press,New York,2011.

[13]M.F.Edwards,The importance of chemical engineering in delivering products with controlled microstructure to customers,IchemE North Western Branch Papers,91988.

[14]M.Hill,Product and process design for structured products,AIChE J.50(2004)1656-1661.

[15]R.Gani,Computer-aided methods and tools for chemical product design,Chem.Eng.Res.Des.82(A11)(2004)1494-1504.

[16]J.Abildskov,G.M.Kontogeorgis,Chemical product design.A new challenge of applied thermodynamics,Chem.Eng.Res.Des.82(A11)(2004)1505-1510.

[17]D.Seider,S.Widagdo,J.D.Seader,D.R.Lewin,Perspectives on chemical product and process design,Comput.Chem.Eng.33(2009)930-935.

[18]S.Widagdo,Incandescent light bulb:Product design and innovation,Ind.Eng.Chem.Res.45(25)(2006)8231-8233.

[19]W.D.Seider,J.D.Seader,D.R.Lewin,S.Widagdo,Product and process design principles:Synthesis,analysis and evaluation,third ed.Wiley,Hoboken,2009.

[20]L.Candido,W.Kindlein,R.Demori,L.Carli,R.Mauler,R.Oliveira,The recycling cycle of materials as a design project tool,J.Clean.Prod.19(2011)1438-1445.

[21]C.H.Wu,Product-design and pricing strategies with remanufacturing,Eur.J.Oper.Res.222(2012)204-215.

[22]K.M.Ng,R.Gani,K.Dam-Johansen,Chemical product design:Toward a perspective through case studies,Elsevier,Oxford,2007.

[23]A.W.Westerberg,E.Subrahmanian,Product design,Comput.Chem.Eng.24(2000)959-966.

[24]P.M.Saraiva,R.Costa,A chemical product design course with a quality focus,Chem.Eng.Res.Des.82(A11)(2004)1474-1484.

[25]L.Kavangh,P.Lant,Introduction to chemical product design.A hands-on approach,Trans.IChemE Part D 1(2006)66-71.

[26]M.Narodoslawsky,Chemical engineering in a sustainable economy,Chem.Eng.Res.Des.91(10)(2013)2021-2028.

[27]World Commission on Environment and Development,Our common future,Oxford University Press,Oxford,1987.

[28]E.Heinzle,A.Biwer,C.Cooney,Development of sustainable bioprocesses,John Willey&Sons,Inc.,West Sussex,2006.

[29]M.Peters,K.Timmerhaus,R.West,Plant design and economics for chemical engineers(5th edition),Mc Graw-Hill,Inc.,New York,2003.

[30]G.P.Rangaiah,Multi-objective optimization,World Scientific Publishing,Singapore,2009.

[31]S.Taras,A.Woinaroschy,Simulation and multi-objective optimization of bioprocesses with Matlab and SUPERPRO Designer using a client-server interface,Chem.Eng.Trans.25(2011)207-212.

[32]S.Taras,A.Woinaroschy,An interactive multi-objective optimization framework for sustainable design of bioprocesses,Comput.Chem.Eng.43(2012)10-22.

[33]S.T.Yang,Bioprocessing for value-added products from renewable resources,Elsevier,Amsterdam,2007.

[34]J.Klemes,Sustainability in the process industry:integration and optimization,Mc Graw-Hill,Inc.,New York,2011.

[35]National Science Foundation Workshop on Sustainability and Chemistry,Chemistry for a sustainable future Grant CHE0633038,Arlington VA 2006.