Introducing Quantum Chemistry in Chemical Engineering Curriculum

Article Cite This: J. Chem. Educ. XXXX, XXX, XXX−XXX

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Introducing Quantum Chemistry in Chemical Engineering Curriculum Mohammednoor Altarawneh* and Bogdan Z. Dlugogorski School of Engineering and Information Technology, Murdoch University, Perth 6150, Australia

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S Supporting Information *

ABSTRACT: Due to the wide and the ever-increasing strategic applications of quantum chemistry in chemical industries, it is important to introduce chemical engineering students to illustrative case studies that deploy molecular modeling in the design of reactors and derivation of thermochemical functions. Herein, we demonstrate how quantum chemical calculations can be implemented within a unit on the chemical reaction engineering to obtain properties that are typically measured in the laboratory classes, namely, reaction rate constants, fractional conversion of reactants, and residence time. A rigorous coupling between quantum chemistry and chemical reaction engineering is expected to encourage students to appreciate the accuracy and the practicality of molecular calculations in process modeling and design of novel materials. KEYWORDS: Graduate Education/Research, Chemical Engineering, Physical Chemistry, Upper-Division Undergraduate

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INTRODUCTION Over the past two decades, molecular simulation has emerged as an insightful and accurate design tool in academic and industrial research. The availability of powerful computers and the development of very precise theoretical frameworks have enabled chemists, chemical engineers, and materials scientists to evaluate properties of molecules and materials accurately, map out prominent chemical phenomena, and design chemical operations based on atomic-level knowledge pertinent to the system under investigation. Literature provides numerous success stories1,2 in which molecular modeling has aided in all phases of chemical operations starting from the early stages in the plant design to the safe disposal of products at the end of their lifetimes. Quantum chemistry is now widely deployed in research and development departments of major chemical industries around the world to study the course of chemical reactions, to design catalysts with potent active sites, and to fine-tune properties of materials toward the desired optical and electronic attributes. Major applications of quantum chemistry in chemical industries include the following: • Optimizing the performance of reactors, i.e., the heart of chemical plants. • Interpreting the experimental results at the laboratory scale before proceeding to mass production. • Shortlisting chemicals and catalysts that warrant further experimental scrutiny. While the governing equations and approaches in quantum chemistry are of a purely theoretical and physicochemical © XXXX American Chemical Society and Division of Chemical Education, Inc.

nature, the questions that quantum chemistry attempts to answer are truly practical. For example, they comprise how to enhance the conversion of NOx into N2 in an internal combustion engine,3 how to increase the selectivity of ethene over ethane in catalytic processing of hydrocarbons,4 and how to minimize the emission of notorious pollutants during the manufacturing and the use of pesticides.5 Practical applications of quantum chemistry in chemical industries rest on the fact that properties of molecules and materials are directly linked with their atomic structures. Owing to the ever-increasing role of molecular modeling in chemical industries, it is essential to introduce chemical engineering students to this field and to elucidate how findings can be implemented in real-life scenarios. While quantum chemistry is widely deployed in all aspects of chemical research (i.e., in reaction mechanisms, thermochemistry, materials chemistry, and catalysis), it has also been implemented extensively as a teaching tool in undergraduate courses. (In Australia, we often employ a world “unit” to denote a “course”, and a word “course” or “major” to denote a “program”; we are adhering to “unit” in the present contribution.) Examples include derivations of mechanisms for typical reactions in organic synthesis,6 resonance in molecular structures,7 molecular orbitals, molecular energy levels,8 thermochemistry of reactions, and structures of nanoparticles9 and chemical species.10 Other contributions Received: June 5, 2018 Revised: June 30, 2018

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DOI: 10.1021/acs.jchemed.8b00422 J. Chem. Educ. XXXX, XXX, XXX−XXX

Journal of Chemical Education

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classical point of view. For this reason in this contribution, we describe how students can be introduced to quantum chemical calculations of the reaction rate constants (Case 2). Recently, there has also been a shift in the chemical engineering education to focus more on product engineering.16 A large number of chemical engineers now work on fine chemicals rather than on commodity chemicals and in traditional chemical industries (such as oil and gas refineries). These new changes require that graduates of chemical engineering must be equipped with new dimensions that are not typically covered in the chemical engineering pedagogy, most notably, quantum chemistry. In most universities, chemistry departments teach the physical chemistry unit that might have not been adapted for needs of students in chemical engineering. Thus, while an introductory physical chemistry unit in the chemical engineering curriculum briefly covers aspects of molecular orbitals theory, chemical bonding, and electronic structure, direct applications of quantum chemistry in chemical engineering are typically not taught. Even for chemistry students, quantum mechanics is typically covered in the more advanced physical chemistry units, i.e., not as an introductory unit. Overall, graduates will need to have some knowledge on how to design a product based on its microstructure. Indeed, the latest versions of the curriculum and pedagogy of chemical engineering attempt to broaden their scope by adding chemical biology, nanomaterials, and product engineering to the traditional process engineering. The teaching of these areas will benefit from the ever-increasing use of quantum chemistry as a prominent research tool in academia and industry alike. Starting from 2015, we have been implementing simple case studies in the content of the unit titled Reactor Engineering at Murdoch University. In these cases, students apply results from quantum chemistry to predict the temperature profile along a packed bed reactor, to elucidate the effect of the residence time on the conversion and to plot the equilibrium concentration profiles of a gaseous reacting system. It is hoped that these simple projects inspire students to appreciate the novelty and exciting applications of quantum chemistry in diverse chemical engineering fields spanning catalysis,17 environment protection,18−21 and efficiency of fuel combustion.22 The emphasis throughout this paper is to provide worked out cases with stepby-step illustrations into thermochemistry, equilibrium, and kinetics of chemical reactions and to link the newly learned concepts within the unit on Reactor Engineering, a central topic in the curriculum of chemical engineering.

have also focused on training students on the foundational equations and formulations in quantum chemistry.11 A vast majority of these introductory examples, available in the literature, mainly deal with units on physical and organic chemistry, providing limited perspectives relevant to undergraduate students in chemical engineering. Murdoch University (Perth, Australia) offers a combined degree in chemical and metallurgical engineering. Thus, the program structure covers two closely related strands over a four-year period of study. In the current program structure, physical chemistry (the unit in which principles of quantum mechanisms are normally introduced) is not a required unit; the reader can refer to the program structure given in Table S1 of Supporting Information (SI). The students are also not learning concepts of quantum chemistry at any stage of their study. Thus, it is important to cover some aspects of quantum chemistry in the existing units. Surprisingly, physical chemistry (and quantum chemistry) is also not part of the chemical engineering curricula at other Australian universities such as The University of Sydney, The University of Newcastle, The University of Melbourne, and Monash University based on their online published unit descriptions. Due to the very complex mathematical expressions governing quantum chemistry, we think it is not important, nor it is feasible, for chemical engineering students to comprehend these equations. However, students must also be aware that computer codes of quantum chemistry are not to be utilized as “black boxes”. Students are encouraged to compare a sample of their calculated properties with relevant experimental values to set a benchmark of expected accuracy limits. These quantities typically include standard enthalpies of formation, bond dissociation energies, infrared (IR) spectra, solvation energies, pKa values, and reaction rate constants. Similarly, it is important to demonstrate to the students that the accuracy of quantum chemical calculations primarily depends on the deployed theoretical methodology and the relative size of the system. A trade-off always manifests itself between the desired accuracy and the size of the system; the latter is typically denoted by a number of non-hydrogen atoms.12 Chemical reaction engineering, physical chemistry, and chemical thermodynamics constitute the appropriate units in the chemical engineering curriculum to implement a practical introduction to quantum chemistry. Students across units of chemical engineering often refer to thermodynamics and kinetics handbooks to extract values. However, most of these references lack data on newly engineered materials and chemicals, or simply the required data are not available at the temperature domain of interest. Therefore, introducing an alternate, more pedagogically active approach would better prepare the chemical engineering students for many jobs in the 21st century. In this regard, Galano et al.13 illustrated the importance of quantum chemistry in understanding gas-phase reactions with an emphasis on atmospheric-type reactions. The authors described the theoretical basis of the transition state theory (TST) and provided reaction paths for sample reactions. The authors highlighted the satisfactory agreement between theoretically derived and experimental reaction rate constants. However, tutorial-like examples on the derivation of the acquired reaction paths and reaction rate constants were not provided. Likewise, Ge,14 and Revell and Williamson,15 described the temperature-dependent entropic and enthalpic decoupling effects on the reaction rate constants from a

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CASE STUDIES Quantum chemical calculations are carried out via various computer codes; most notably, Gaussian09,23 ADF,24 VASP,25 Crystal,26 DMol3 ,27 and CASTEP.28 These codes are commercially available. Building pseudo (i.e., an approximate) molecular and structural arrangements is the first step in quantum chemistry calculations. This is followed by structural optimization. Desired properties are estimated on optimized structures, i.e., the minimum energy structures. The three presented cases are based on the Gaussian09 code. In addition to this code, instructors can also use the freely available GAMESS29 code to carry out the outlined basic quantum chemistry calculations, along with its graphical user interface for building structures. Auxiliary codes for deriving the thermochemical and kinetic parameters (i.e., ChemRate30 or B



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KiSThelP31) are also available free of charge from their respective distributors. The benefit of introducing these quantum-chemistry-based projects can be summarized as follows: • Students often devote a great deal of effort and time to finding relevant thermodynamic and kinetic data. In many cases, accurate data do not exist in the literature for many systems. The use of quantum chemistry permits to derive properties for any chemical system with ease and accuracy. • For simplification, major textbooks in reactor engineering (e.g., Fogler32) often deploy thermodynamic functions as temperature-independent quantities. Accurate modeling of nonisothermal reactors necessitates incorporating temperature-dependent functions of heat capacities and enthalpies of formation. As it will be demonstrated in the presented cases, students can readily use quantum chemistry techniques to derive these functions. • Introducing students to quantum chemistry aligns very well with the apparent push in chemical engineering worldwide to incorporate new dimensions in the pedagogy such as product engineering, chemical biology, and nanomaterials.

unwanted products (CO 2 , water, and acetaldehyde, C2H4O):33−35 C3H6 + O2 → C3H4O + H 2O

(1)

C3H6 + 4.5O2 → 3CO2 + 3H 2O

(2)

4C3H6 + 3O2 → 6C2H4O

(3)

Reactions 1−3 occur in the gas phase. Their rate expressions and the PolyMath code are included in Supporting Information. Production of acrolein from catalytic oxidation of propene presents an interesting case study for students in the Reactor Engineering unit. While carrying out this project, students will encounter several essential concepts including pressure drop, energy balance, and selectivity. Writing an energy balance equation requires acquiring accurate thermodynamic functions for species involved in reactions 1−3, as Scheme 1 demonstrates. The differential change of temperScheme 1. Energy Balance Equation along the PBR

Case 1: Catalytic Oxidation of Propene into 2-Propenal in a PBR

2-Propenal or acrolein (CH2CHCHO) is one of the most important industrial chemical intermediates. 2-Propenal is currently produced via selective catalytic partial oxidation of propene (or propylene: CH2CHCH3) in a packed bed reactor (PBR). PBR are tubular reactors that are packed with particles of solid catalysts.32 PBR operates continuously, with the reactants and products flowing in and out of the reactor, respectively. PBRs are typically used for high-temperature catalytic gas-phase reactions. Figure 1 shows a schematic diagram of a PBR.

ature across the PBR (as a function of the catalyst weight) varies according to the rates of reactions, heat of reactions, heat capacities of species, and the molar flow rates. The riΔHri(T) term accounts for the heat generated in the PBR while the UaT term signifies the removed heat. Likewise, Ua denotes the heat transfer coefficient of the heat exchanger integrated with the reactor. It is often very challenging for students to find thermodynamic values for compounds of interest, as a function of temperature. Quantum chemical calculations can be used in this regard. The procedure is shown in Scheme 2 and requires the use of any standard quantum chemical software, i.e.,

Figure 1. Schematic diagram of a PBR.

Other commonly used reactors in chemical reactions include: • Batch reactor: It is a closed vessel commonly used in liquid phase reactions and in the small-scale production of fine chemicals. Reactants are initially charged into the reactor and while reaction is carried out; nothing else is introduced or withdrawn until the reaction is complete. • Continuous stirred tank reactor (CSTR): CSTRs are commonly deployed when agitation is required to provide a homogeneous mixing throughout the reacting mixture. Like the PBR, CSTRs are open systems where reactants are continuously entering the reactor, while products are continuously removed. The reaction of oxygen with propene branches into three channels with only one of them producing acrolein as the desired product while the two other channels generate

Scheme 2. Procedure for Deriving Thermodynamic Functions from Quantum Chemical Calculations

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Gaussian09 in this case.23 This is to be followed by straightforward “data processing” by the ChemRate free open-source software30 to convert the calculated vibrational frequencies, and rotational constants, into temperaturedependent thermodynamic functions. Supporting Information provides step-by-step tutorials that train students how to use Gaussian09 to find the minimum energy structures for compounds (i.e., optimization, Part A) and the ChemRate code to derive the thermodynamic values (Part C). All geometrical optimizations, energy calculations, and estimation of vibrational frequencies were executed at the composite chemistry model CBS-QB3.36 CBS-QB3 executes out initial optimization and computes vibrational frequencies at the B3LYP/CBSB7 level of theory.37 This is followed by successive single point energy calculations at very accurate theoretical levels. The students are encouraged to revisit the physical chemistry unit, which typically covers equations of statistical thermodynamics that derive the thermodynamic functions from molecular vibrational frequencies, rotational constants and standard enthalpies of formation. These mathematical formulations constitute the computing engine in the ChemRate code. An important aspect for the student to grasp is that thermodynamic properties of compounds at the macroscale level (i.e., moles) stem from their structures (i.e., a microscale level). Viewing the obtained spectra of vibrational frequencies will assist in conveying to the students that internal energy in a molecule is primarily stored as vibrational motions. Computed vibrational frequencies could be readily compared with analogous experimental values collected by a means of a Fourier-transform infrared spectroscope (FTIR). Following successful optimization and frequency calculations of all structures, the first step is to ask students to compare the optimized geometries with the starting structures and to plot the vibrational spectra. As an example, Figure 2 depicts the

On the basis of the estimated vibrational frequencies and rotational constants (explained in Part C of Supporting Information), ChemRate code calculates thermodynamic functions, namely, heat capacities, entropies, and enthalpies of formation as a function of temperature. Figure 3 plots heat capacities and entropies of selected species.

Figure 3. Calculated heat capacities (a) and entropies (b) for acetaldehyde, 2-propanol, and propene.

The enthalpies of reactions 1−3 are calculated on the basis of the difference in the summation of enthalpies of formation of products and enthalpies of formation of reactants. Figure 4 portrays the reaction enthalpies of reactions 1−3 (in the gas phase). As a benchmark of accuracy, students are asked to compare the calculated enthalpy of combustion of propene at 298.15 K (enthalpy of reaction 2) with the corresponding

Figure 2. Optimized geometries and calculated vibrational spectra of 2-propenal.

vibrational frequency spectra and the optimized structure of the 2-propenal molecule. While calculations, in this case, were performed on a gas-phase species, analogous computations in the aqueous phase are very similar and necessitate introducing a solvation model.38 The solvation model replaces explicit solvent molecules with a continuum that characterizes the appropriate bulk dielectric constant.

Figure 4. Calculated enthalpies of reactions 1−3. D



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experimental value quoted in the NIST chemistry webbook.39 The calculated and experimental standard enthalpies of reaction 2 amount to −1924 and −2057 kJ/mol, respectively. A difference of only 6.4% serves to encourage students to appreciate the accuracy of the quantum chemical calculations in reference to experimental values. Estimation of reaction enthalpies in the aqueous phase, when water is present in the reaction, is very challenging. However, the Gibbs free energy of the reaction could be readily calculated by Gaussian09. The latter requires computing the Gibbs free energy of solvation for the species involved in the reactions. In this regard, we have demonstrated a computational approach to estimate Gibbs free energy of formation for a set of chlorinated compounds in a previous study.40 Obtained thermodynamic values are fitted into temperaturedependent equations (i.e., Cp(T) = a + bT + CT2) using either PolyMath or Excel codes. Equations for Cp(T) and ΔHr(T) enter in the energy balance equation for the PBR introduced in Scheme 1. Part B in Supporting Information provides a detailed description of the reacting system underpinning the catalytic oxidation of propene, and operational conditions governing four building blocks, and the PolyMath file. Figure 5 illustrates the temperature profiles along the PBR and the heat exchanger. For simplicity, textbooks in chemical

Figure 6. Values of conversion and yield (i.e., % mole fractions of consumed propene and % mole fractions of produced 2-propenal and acetaldehyde; in reference to the initial number of moles of propene) (a) and values of selectivity (S) toward the formation of the desired 2propenal (b).

to any material even if their Cp(T) values do not typically appear in thermodynamic textbooks, such as pesticides and pharmaceuticals, thus providing students with a tool to obtain thermodynamic values for any chemical species. This case was introduced in one semester as the Design Project component of the unit on Reactor Engineering. Table 1 gives a planned timeline of the project and itemizes some assessment criteria.

Figure 5. Modeled temperature of the reactor (T) and the heat exchanger (Ta).

reactor engineering (e.g., Fogler32) typically assume that Cp and ΔHr are constants (i.e., independent of temperatures) when modeling nonisothermal reactors. With quantum chemistry, students can introduce Cp and ΔHr as functions of temperature and, thus, achieve more accurate and realistic description of the nonisothermal reactors. Figure 6a presents the conversion and yields (i.e., % mole fractions of consumed propene and % mole fractions of produced 2-propenal and acetaldehyde, in reference to the initial number of moles of propene). Figure 6b displays the values of selectivity (S) toward the formation of the desired 2propenal. S=

Case 2: Reaction Rate Constants and Residence Time (in Plug Flow Reactor, PFR) for the Gas-Phase Dehydrochlorination Reaction of C2H5Cl

The laboratory component in the unit on Reactor Engineering often focuses on the measurement of reaction rate constant, k(T), and elaborates on the effects of residence time (τ), concentration, and temperature on conversion. Fitting k(T) versus 1/T yields the two terms in the Arrhenius equation, namely, the activation energy Ea and the pre-exponential factor A. Similarly, quantum chemical calculations can be used as a virtual laboratory to investigate the kinetics of chemical reactions. Locating the transition state structure that dictates the reaction rate constant represents the central point of these calculations. By carrying out simple quantum chemical calculations, students can generate the potential energy surfaces for single-step reactions. This energy surface characterizes the energy of the reaction and the barrier height. In view of the transient nature and the short lifetime of the

number of moles of the desired 2‐propenal ∑ number of moles of 2‐propenal, propene, and acetaldehyde

In addition to the units on chemical reaction and chemical thermodynamic, students enrolled in units on process design and chemical process safety often deal with thermodynamic properties of chemical species. The procedure can be applied E


Figure 7. Potential energy surface for the reaction C2H5Cl → C2H4+HCl, calculated at the B3LYP/6-31G(d) level of theory. The energies of the transition state and product, relative to the reactant, are in kJ/mol.

Successful determination of the structures of transition states signifies the most challenging task in theoretical physical chemistry. We advise training students on reactions with welldefined transition state structures such as HCl elimination from chloroalkanes with a reasonably accurate theoretical framework. When locating the transition state structure, students can link its geometry with analogous geometries of reactants and products. As in Case 1, the ChemRate code serves to obtain the enthalpies of formation and standard entropies for reactant and transition states. Scheme 3 depicts a procedure for deriving the two Arrhenius parameters, namely, the activation energy Ea and the pre-exponential factor A, based on the transition state theory (TST). Part D in the Supporting Information illustrates the procedure depicted in Scheme 3 with a numerical example (Table S2). Figure 8a shows the unimolecular rate constant obtained for this reaction. If the reaction is performed in a plug flow reactor and by assuming a first-order reaction, the residence time (τ) can be expressed in terms of k(T) and conversion X (refer to page S20 in the Supporting Information for the derivation of this equation): τ=

i yz 1 1 zz lnjjjj k(T ) k 1 − X(T ) z{

From Table S2 in the Supporting Information, the calculated rate constant at 900 K amounts to 0.23 s−1. Thus, arranging the 1 terms in the above equation gives X = 1 − 0.23τ . Varying the e value of τ between 1 and 10 s changes the conversion value X accordingly. Figure 8b illustrates the dependency of τ values on the conversion at 900 K. Most students successfully plotted Figure 8b in a 1 h tutorial. A question in the following assignment in the unit was to replot Figure 8b considering T between 300 and 1200 K. In a nutshell, this case serves as a good example to train students on how to derive reaction kinetics using quantum chemistry and how to deploy the results in the reactor design.

2

1

1

transition state, quantum chemistry presents the sole methodology to locate the transition state. Part A (task 2) in the Supporting Information illustrates a tutorial on how to calculate the energy barrier of a reaction using the Gaussian09 code. As an illustrative case, we construct the potential energy surface for the dehydrochlorination reaction C2H5Cl → C2H4+HCl as shown in Figure 7.

Comparing the effect of using T-dependent versus T-independent values on the obtained temperature profiles of the reactor (to produce Figure 5 with and without the use of Gaussian09 code; an apparent difference between the temperature curves encourages the student to appreciate the benefits of using quantum chemistry in in design projects in chemical engineering)

Carrying out an energy balance for the PBR reactor

Using the Gaussian09 code to calculate the thermodynamic functions of all species involved as a function of temperature (i.e., to plot Figures 3 and 4)

Plotting the selectivity and yields as a function of the catalyst weight

Reviewing the literature Compiling the reaction networks, operational parameters, and the desired selectivity Writing a PolyMath code based on temperature-independent thermodynamic and kinetic values Estimation of T-dependent thermodynamic values Modifying the PolyMath code considering T-dependent values Writing and documentation 2 1

1

Tasks

Briefly describing the catalytic reactions and the already existing industrial operations Sketching the flowchart of the process while adding numerical values for molar flow rates, temperatures, pressures, conversion, and yield values

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Table 1. Time Line for Tasks in Case 1

Description


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Scheme 3. Procedure for Calculating Reaction Rate Constants for the Reaction C2H5Cl → C2H4+HCl

in which y, P, K, and v denote mole fractions, pressure, equilibrium constant, and the summation of the stoichiometric coefficients, respectively. The K value relies on the Gibbs free energy of the reaction, and hence it is a temperature-dependent quantity: i ΔGr(T ) zy zz K (T ) = expjjjj− RT z{ k

Thus, knowing the value of ΔGr(T) for a given reaction enables one to find thermodynamic equilibrium concentrations of the relevant species. If the temperature-depended polynomials for Cp are available in reference thermodynamic tables, students can follow a lengthy procedure to obtain ΔGr(T) as described in chemical engineering thermodynamics textbooks.41 Alternatively, quantum chemistry provides a straightforward, yet accurate approach to calculate ΔGr(T). Let us consider the following reaction: N2O4 (g) = 2NO2 (g)

Calculating ΔGr(T) for this reaction requires geometry optimization and frequency computations for the two species followed by derivation of their thermodynamic functions. Values of ΔGr(T) stem from computed enthalpies of formation and standard entropies as demonstrated in Part B of Supporting Information: ΔGr(T ) = 2ΔGfNO2(T ) − ΔGfN2O4(T )

Figure 8. Calculated reaction rate constant for the reaction C2H5Cl → C2H4+HCl (a) and residence time versus conversion at 900 K (b).

ΔGfNO2(T ) = ΔHfNO2(T ) − T ΔSoNO2(T ) + T ∑ So(elements) ΔGfN2O4(T ) = ΔHfN2O4(T ) − T ΔSoN2O4(T ) + T ∑ So(elements)

Case 3: Equilibrium Concentration

Finding the equilibrium composition of a reacting mixture is an essential topic in chemical engineering thermodynamic as well as in chemical reaction engineering. In most common examples, students are asked to obtain the equilibrium compositions for a given set of reaction(s) based on the method of equilibrium constants. For the reaction, aA+bB = cC+dD, the governing equilibrium equation is written as

Figure 9a plots values of ΔGr(T). If only 1 mol of N2O4 is initially present and the reaction proceeds at 1 atm, the final equilibrium equation can be expressed as follows: 2 yNO (T ) 2

ij P yz = jjj zzz K a b j Po z yA yB k {

yCc yDd

yN O (T )

= K (T ) = exp( −ΔGr(T )/(RT ))

2 4

−v

yNO (T ) = 2

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2ζ 1−ζ , yN O (T ) = 2 4 1+ζ 1+ζ DOI: 10.1021/acs.jchemed.8b00422 J. Chem. Educ. XXXX, XXX, XXX−XXX


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introduced in other units of the chemical engineering curriculum, including the following. Process Safety

Molecular modeling can be used here to obtain the combustion energies of materials in estimating their TNT equivalency numbers. The results afford determination of safe evacuation areas in chemical facilities that store dangerous chemicals. Likewise, accurate thermochemical values are essential input in thermal-runaway models. Unit operations

Molecular modeling can be used here to estimate infinite dilution activity coefficients of organic compounds in solvents and to calculate partition coefficients of solutes, and to estimate solvation and crystallization energies. These data are essential to design separation units. Quantum chemical calculations can also be used to complement experimental results in the thesis projects. Potential examples include the following: • Modeling emission of nitrogen species from biomass surrogates in experiments involving the thermogravimetric analysis (TGA) • Plotting ultraviolet−visible (UV−vis) spectra emitted from the photodecomposition of chemicals assisted by TiO2 • Contrasting the structures of minerals with the X-ray diffraction (XRD) measurements. • Constructing reaction mechanism for the pyrolytic decomposition of polymers treated with brominated flame retardants • Estimating the turnover frequency (TOF) numbers for catalytic reactions. In a nutshell, introducing quantum chemistry in the curriculum of chemical engineering at Murdoch University (and potentially at other Australian university) prepares graduates for emerging chemical industries that integrate molecular modeling in their day-to-day operations.

Figure 9. Estimated ΔGr(T) for the reaction N2O4(g) = 2NO2(g) (a), and the predicted equilibrium mole fractions (b).

where ζ signifies the extend of the reaction. Figure 9b portrays the equilibrium mole fractions of gaseous N2O4 and NO2 between 300 and 400 K. Most students successfully plotted Figure 9a,b in a 2 h tutorial.

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ASSOCIATED CONTENT

S Supporting Information *

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The Supporting Information is available on the ACS Publications website at DOI: 10.1021/acs.jchemed.8b00422. Further details of the cases introduced in the paper and course structure (PDF, DOCX) Gaussian09 input and output files and PolyMath input files (ZIP)

REFLECTIONS ON STUDENTS’ PERCEPTION An online survey was conducted after the final examination in the unit. The survey showed that the students felt that the cases introduced in the unit on Reactor Engineering added value to their learning and enhanced the educational outcomes. Most importantly, the student indicated that they would expect to use tools of molecular modeling in their future employment, and the cases covered in this article constitute basic training for this purpose. However, some students indicated that it would have been more appropriate to introduce the theoretical principles of quantum chemistry earlier in their study, for example, in one of the introductory units in chemistry.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

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Mohammednoor Altarawneh: 0000-0002-2832-3886 Bogdan Z. Dlugogorski: 0000-0001-8909-029X

OUTLOOK Molecular modeling based on quantum chemical calculations is a chief research and design tool in chemical engineering, environmental chemistry, and materials science. It is important for chemical engineering students to gain a hands-on experience by carrying out a few exercises within the chemical reaction engineering and chemical thermodynamics units. In addition to these two units, quantum chemistry can be

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work has been supported by computational-time grants from the Pawsey Supercomputing Centre in Perth and the National Computational Infrastructure (NCI) in Canberra. H



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