incorporating environmental impact assessment into conceptual process design: a case study example

Incorporating EnvironmentalImpact Assessment intoConceptual Process Design: ACase Study ExampleJeffrey R. Seaya and Mario R. Edenba Department of Chemical and Materials Engineering, University of Kentucky, Paducah,KY 42002; [email protected] (for correspondence)b Department of Chemical Engineering, Auburn University, Auburn, AL 36849

Published online 10 December 2008 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ep.10328

The purpose of this contribution is to present acase study illustrating how environmental impactassessment using the U.S. EPA Waste Reduction Algo-rithm has been incorporated into conceptual processdesign. This will be achieved via the introduction ofa simple methodology for integrating environmentalimpact assessment into the standard heuristics of con-ceptual process design to ensure that environmentaland sustainability goals are met while maintainingeconomic viability. The case study presented to illus-trate the methodology is based on a process to manu-facture industrially important C3 compounds fromthe dehydration of bio-based glycerol. The selectedcase study is important from the perspective of sus-tainability because glycerol is produced as a byprod-uct of the manufacture of biodiesel from vegetableoils. � 2008 American Institute of Chemical Engineers Envi-ron Prog, 28: 30–37, 2009Keywords: environmental impact assessment, WAR

algorithm, process design, glycerol dehydration

INTRODUCTION

The impacts of chemical processes on the environ-ment are becoming increasingly important to industryand to the general public. This research will illustratehow environmental impact assessment has been inte-grated into the standard heuristics of conceptual

process development by use of a simple methodol-ogy. The developed methodology is illustrated usinga case study example based on the manufacture ofindustrially important C3 products from bio-basedglycerol. By integrating environmental impact assess-ment into the standard design heuristics used to de-velop and screen potential conceptual processes, thedesigner can ensure that the resulting process is notonly optimized in terms of overall performance, butalso is based on minimizing the environmentalimpact of the process.

PREVIOUS WORK IN PROCESS DESIGN AND INTEGRATION

This research will focus on the development of astructured approach to the integration of sustainabledesign principles, environmental impact assessment,and laboratory experimentation into conceptual proc-ess design. Early work on the development of a struc-tured approach to process design based on hierarchi-cal techniques and standard design heuristics hasbeen described by Douglas [1] in his book, Concep-tual Design of Chemical Processes. This concept hasbeen further advanced in widely used process designtextbooks by Seider [2] and Biegler et al., [3]. In gen-eral, these techniques rely on a knowledge-basedapproach. Although these techniques can be appliedquite successfully to systems based on well-estab-lished chemistry, they do not address the gathering of� 2008 American Institute of Chemical Engineers

30 April 2009 Environmental Progress & Sustainable Energy (Vol.28, No.1) DOI 10.1002/ep

the experimental data needed to design a processbased on newly developed chemistry.

The need for the inclusion of laboratory experi-mentation has begun to be addressed in otherongoing work in this area by Kiss et al. [4], regardingthe linking of experiments to modeling in biodieselproduction. Kiss et al. points out that the disconnectbetween the chemists who typically carry out thekinetic experiments and the design engineers whomust use the data to develop conceptual processmodels can lead to design failures because the condi-tions considered in the lab may not lead to feasibleconceptual processes.

Another key component of process design is proc-ess integration. Process integration is a holisticapproach to process design that emphasizes the unityof the process [5]. El-Halwagi defines three key com-ponents of process integration: process synthesis,process analysis, and process optimization. Energyintegration, an important subset of process integra-tion, has been introduced in recent years. Energyintegration has been defined by El-Halwagi [4] as: Asystematic methodology that provides a fundamentalunderstanding of energy utilization within the processand uses this understanding in identifying targets andoptimizing heat-recovery and energy-utility systems.

This systematic methodology is used to determinethe optimum utilization of heating and coolingenergy within a process. Thermal pinch analysis isthe principle tool for determining this optimum.

Recently, the idea of system-based environmentalmanagement has been proposed [6]. This idea isbased on the fusion of chemical engineering princi-ples with the tools of other disciplines, such as envi-ronmental sciences, toxicology, and economics. Eachof these tools is used in different ways to assess theeconomic performance of a process.

The research presented will draw on this previouswork and incorporate it into a cohesive methodologythat integrates safety, environmental impacts, sustain-ability, and economic considerations into the stand-ard heuristics of conceptual process design. Theapplication of this proposed methodology will beillustrated using a process development case study.

EVALUATING POTENTIAL ENVIRONMENTAL IMPACTS

For the case study presented, the tool used to cal-culate the potential environmental impact, PEI, of theproposed conceptual processes is the Waste Reduc-tion (WAR) algorithm, developed by the U.S. Environ-mental Protection Agency [7, 8]. The PEI of a givenquantity of material or energy can be defined as theeffect this material or energy would have if it wereemitted directly to the environment [7, 8]. For thepurposes of this study, only the PEI of the streamsleaving the process is considered. It is assumed thateach of the conceptual process design alternativeswould subject to the same regulatory environmentalconstraints, so the PEI after waste treatment wouldnot provide a clear picture of the true impact of theproduction process itself.

There are some important limitations to using theWAR algorithm for an analysis of this type. Althoughthe WAR algorithm provides an effective means ofcomparing process options with a similar basis, itcannot evaluate the impacts of switching from acrude oil to a renewable, biomass derived feed stock.Therefore one should use caution when directly com-paring the PEI calculated for cases based on utilizingsustainable feed stocks with that calculated for proc-esses based on utilizing crude oil derived feed stocks.The use of biomass derived feed stocks have signifi-cant advantages regarding carbon dioxide generation,therefore their use as a feed stock has a potentiallysignificant advantage over crude oil derived feedstocks in terms of environmental impact. Because thisanalysis does not include a complete lifecycle assess-ment, any benefit gained by this switch in feed stockswill not be captured.

SUSTAINABILITY AND PROCESS DESIGN

Often the criteria used in developing conceptualoptions for a proposed process is based solely on itseconomic viability in terms of return on investment.Although the importance of economics should not beminimized, the environmental impacts of a new proc-ess should not be ignored. There are a multitude ofbenefits for minimizing the environmental impacts ofa process:� Potential new environmental regulations.� Emissions trading opportunities.� Potential increased costs of ‘‘after the fact’’ meansof emissions abatement.By taking an integrated approach, an optimized

design that considers viability in terms of both eco-nomic performance and minimum environmentalimpacts can be proposed. A flow chart has been gen-erated describing the general steps included in con-ceptual process design activities. This flow chart isillustrated in Figure 1.

In this generalized flowchart, the basic steps fromthe selection of the initial chemistry to final optimizedconceptual design are included. The inclusion ofenvironmental impact assessment and determinationof economic viability are included in Steps 2 and 4,application of simulation and optimization methodol-ogy. This additional methodology is described in asecond flowchart, which is illustrated in Figure 2.

In this flowchart, the simulation and modelingactivities of process design are grouped with environ-mental impact assessment. This is done to ensure thatdesign choices that lead to unacceptable results withregard to potential environmental impacts are elimi-nated at an early stage. Additionally, by applying thismethodology, process risk is also addressed. This riskis not simply limited to process safety, but alsoincluded the risk of potential releases to the environ-ment because of upset conditions.

By incorporating this methodology into the proc-ess design hierarchy as illustrated in Figure 1, thefinal conceptual will be not only economically opti-mized, but also require fewer external safeguards to

Environmental Progress & Sustainable Energy (Vol.28, No.1) DOI 10.1002/ep April 2009 31

minimize the environmental impacts, because of bothnormal operation and upset conditions.

This proposed methodology covers the entirerange of activities included in conceptual processdesign. This methodology has been applied to aprocess development project based on the sustain-able manufacture of specialty chemical products frombio-based glycerol. This process development projectwill be presented as a case study on the applicationof the proposed methodology to conceptual processdesign. In particular, the portion of the methodologyfocused on environmental impact assessments, Step Fin Figure 2, will be described in detail.

PROCESS DEVELOPMENT CASE STUDY

A Growing Market for BiodieselIn recent years, much attention has been focused

on the impact of human activities on the global envi-ronment. The effects of using of crude oil derivedfuels and feed stocks on the global climate, and theimportance of pursuing the use of sustainable rawmaterial feed stocks has been well documented [9,10]. In terms of energy production, biodiesel is theonly alternative with an overall positive lifecycleenergy balance [11]. Therefore use of biodiesel andits byproducts may have a positive impact on globalclimate change. In addition, according to the U.S.Department of Energy’s 2003 World Energy Report, at

current rates of consumption, crude oil reserves maybe depleted in 80 to 120 years [12]. This provides anincentive for replacing crude oil derived fuels sourceswith sustainable sources, such as biodiesel.

Recent estimates predict that the demand for bio-diesel will grow from 6 to 9 million metric tons peryear in the United States and from 5 to 14 millionmetric tons per year in the European Union in thenext few years [13]. However, for every 9 kg of bio-diesel produced, 1 kg of crude glycerol is formed asa byproduct [14]. Beacause of its high viscosity, glyc-erol must be removed from the biodiesel product,thus reducing the carbon utilization. Therefore,the identification of novel industrial uses for this glyc-erol is important to the economic viability of bio-diesel [15].

Case Study BackgroundThe process investigated in this research is the cat-

alytic dehydration of glycerol using an acid catalyst.The reason why this process has been chosen is thatglycerol dehydration can be used as a renewablefeedstock for industrial C3 chemical products that are

Figure 1. Flowchart of proposed process integrationmethodology.

Figure 2. Simulation and optimization methodologyflowchart.


currently manufactured via the catalytic partial oxida-tion of propylene. Some of these products include,1,2-propanediol, 1,3-propanediol, acrolein, hydroxya-cetone, and acrylic acid [14, 16–18]. The process foreach of these products is similar, differing only withregard to the feed composition, catalyst, and reactoroperating conditions. The process described in thiscontribution is generally applicable to any of theseproducts.

Previously published work on this research projecthas presented how an optimized conceptual processwas developed based on the glycerol dehydrationreaction [19–21]. In the process considered for thisresearch, the primary feedstock is considered to becrude glycerol from a biodiesel production process.This crude glycerol will contain some fraction ofwater, which must be considered in the processdesign. Additionally, the previous research has indi-cated that dilute solutions of glycerol lead to higherreactor conversions than do more concentrated feed

solutions. In this process, inert nitrogen will be usedto dilute the glycerol. A block flow diagram of theproposed conceptual process for glycerol dehydrationis illustrated in Figure 3.

This glycerol dehydration process will be used toillustrate how environmental impact assessment hasbeen incorporated into conceptual process design.However, to have a point of comparison, a concep-tual process design for the propylene based processmust also be developed. A block flow diagram for atypical propylene based process is illustrated in Fig-ure 4 [22, 23].

Reactor Optimization ResultsBased on the glycerol dehydration process previ-

ously described, laboratory experiments were carriedout to determine the optimum operating conditions.The integration of laboratory experiments with proc-ess simulation is an important part of the process

Figure 3. Glycerol dehydration process block flow diagram.


integration methodology illustrated in Figure 1. A lab-oratory scale model of the glycerol dehydration reac-tor was constructed to conduct the experiments. Aschematic of this reactor is illustrated in Figure 5.

Statistical Design of Experiments (DOE) techniqueswere applied to determine the laboratory conditionsat which to operate the glycerol dehydration reactor.Three variables were identified that had a significantinfluence on the reaction yield: Glycerol to water ra-tio in the crude glycerol feed, space velocity in thereactor, and operating temperature. Using a Box-Behnken technique, 13 experimental points werechosen. Based on the results of the analysis of the ex-perimental results, six additional experimental pointswere added. These results were then analyzed todetermine the conditions leading to the maximumreaction yield. In general, it was found that lower val-ues for operating temperature, space velocity, andglycerol to water ratio led to higher yield.

Overall Process Performance ResultsTo select the final operating conditions for the

glycerol dehydration process, the performance of theentire process was evaluated for each of the experi-mental cases. Considerations such as operating risk,as evaluated by a process hazard analysis, energy uti-lization, capital costs, operating costs, and environ-mental impacts are all part of the assessment metricsof a proposed conceptual process and are includedin determining the process performance index. Eachof these considerations is evaluated as part of thesimulation and optimization methodology illustratedin Figure 2.

Using the process simulation to model each of theexperimental cases, the overall performance indexwas determined. To accomplish this, each case wasput on an equal basis in terms of raw material feedrate. However, putting all cases on an equal basis forraw material feed leads to a different product rate for

Figure 4. Propylene partial oxidation process block flow diagram.


each case. To address the discrepancy in the massand energy balances caused by different productrates, the results for the each of the cases were calcu-lated per mass of product.

An analysis on each of the process options includ-ing heat integration based on thermal pinch analysis,the implementation of inherently safe design prac-tices and an assessment of the operating risk, asdescribed in the simulation and optimization method-ology illustrated in Figure 2 was conducted. From theresults of the analysis of the overall process, includ-ing separation systems and waste treatment systems,the trends of which conditions lead to a minimizationof the performance index function were evaluated.The trends indicate that, as with the results of the

product yield, the optimal performance occurs at thelowest values of temperature and flow rate, however,unlike the yield results, the optimal performanceoccurs at the highest value of glycerol : water ratio.

At this point, an analysis of the potential environ-mental impacts can be conducted. As illustrated inthe simulation and optimization methodology, thisanalysis is completed after the optimization of theoverall process performance. This is done to ensurethat the chosen optimum process is not based onoperating conditions that lead to poor environmentalperformance, relative to the performance of the otherprocess options. If the optimized process does varysignificantly from the other process options, modifica-tion can be made during conceptual process design

Figure 5. Schematic of laboratory equipment used in case study example.

Figure 6. PEI plot of GLY : WTR Ratio versus space-velocity.

Figure 7. PEI plot of space-velocity versus tempera-ture.


to reduce its environmental impacts, without degrad-ing its overall process performance.

Potential Environmental Impact ResultsAs described in the simulation and optimization

methodology illustrated in Figure 2, the potentialenvironmental impacts for each proposed conceptualprocess must be considered. The WAR algorithm is agood tool to use for this task because it is simple toapply though a spreadsheet with an interface to aprocess simulator.

Although the WAR algorithm is not the only avail-able measure of environmental performance, it wasthe best option for use during the conceptual phaseof chemical process development for two importantreasons. First, it provides a broad ‘‘snapshot’’ of envi-ronmental performance over a wide range of indica-tors. The WAR algorithm is a measure of 8 environ-mental indicators: Human toxicity: ingestion; humantoxicity: dermal/inhalation; aquatic toxicity; terrestrialtoxicity; global warming; ozone depletion; photo-chemical oxidation; and acidification [7, 8]. Thisbroad spectrum makes the WAR algorithm applicableto a wide range of chemical processes.

Secondly, the WAR algorithm is easy to use withregard to evaluating process options at the concep-tual design stage. Once conceptual design has begun,radical changes to processes chemistry are usuallynot possible. Therefore, the final PEI value calculatedusing the WAR algorithm is less important than therelative difference among several potential processoptions. This makes it an appropriate tool to use inconceptual process design.

Because a process simulation was prepared for theproposed conceptual process, determining the inputvalues for the application of the WAR algorithm wassimple. The simulation package used to model theprocess for this conceptual design case study is As-pen Plus [24]. By using the simulation data importfunctionality within the WAR algorithm graphical userinterface available for download from the US EPA,the PEI of each of the reactor operating cases couldquickly be evaluated. These results are illustrated inFigures 6–8.

These results illustrate that the region chosen as theperformance optimum, that is, the region of low tem-perature, low space velocity and high glycerol : waterratio is in the region of low environmental impacts.Although the point corresponding to the performanceoptimum is not the minimum PEI point, it is close tothe minimum. Because of the level of accuracy of thePEI calculation, this is deemed to be an acceptableresult. Only if the performance optimum were far fromthe minimum PEI would further study be warranted.

CONCLUSIONS

In conclusion, this research has illustrated how theprevious work done in the field of process design andintegration can be expanded to include sustainabilityand an assessment of potential environmental impacts. Acase study example has been used to illustrate how envi-ronmental impact assessment can be incorporated intothe standard heuristics of conceptual process design.

By applying the methodology presented in thiswork, it has been shown that environmental impactassessment can be made an integral part of conceptualprocess design. The ability to include environmentalimpacts into the overall evaluation of conceptualprocess options will only become more important asenergy costs increase and additional scrutiny from thepublic is applied to chemical processes. Therefore,by including the potential environmental impacts intothe optimization process, it is possible to choosedesigns that are optimized for all aspects of processperformance, not just for economic viability.

ACKNOWLEDGMENTS

Funding and facilities for this research were pro-vided by the Evonik Degussa GmbH Health andNutrition Business Unit. Additional equipment wasprovided by the University of South Alabama. Theauthors would like to also thank Prof. Tom Thomasof the University of South Alabama and EvonikDegussa intern students Maria Schley, Astrid Roesner,Mareike Schaum, Stephan Adelmann, and HolgerWerhan for their contributions to this research.

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Figure 8. PEI plot of GLY : WTR ratio versus tempera-ture.


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incorporating environmental impact assessment into conceptual process design: a case study example

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