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Industrial Requirements for Thermodynamics and Transport Properties Eric Hendriks,*,† Georgios M. Kontogeorgis,‡ Ralf Dohrn,§ Jean-Charles de Hemptinne,| Ioannis G. Economou,⊥ Ljudmila Fele Zˇilnik,# and Velisa Vesovic∇ Shell Global Solutions, Shell Technology Centre Amsterdam, Grasweg 3, 1031 HW Amsterdam, The Netherlands, Centre for Energy Resources Engineering (CERE), Department of Chemical and Biochemical Engineering, Technical UniVersity of Denmark, DK-2800, Lyngby, Denmark, Bayer Technology SerVices GmbH, Process Technology, Kinetics, Properties & Modeling, Building B310, D-51368 LeVerkusen, Germany, IFP, 1& 4 AVenue de Bois-Pre´au, 92852 Rueil-Malmaison Cedex, France, The Petroleum Institute, Department of Chemical Engineering, P.O. Box 2533, Abu Dhabi, United Arab Emirates, National Institute of Chemistry, Department of Catalysis and Reaction Engineering, P.O. Box 660, SI-1001 Ljubljana, SloVenia, and Department of Earth Science and Engineering, Imperial College London, London SW7 2AZ, United Kingdom
This work reports the results of an investigation on industrial requirements for thermodynamic and transport properties carried out by the Working Party on Thermodynamic and Transport properties (http://www. wp-ttp.dk/) of the European Federation of Chemical Engineering, EFCE (http://www.efce.info/). A carefully designed questionnaire was sent to a number of key technical people in companies in the oil and gas, chemicals, and pharmaceutical/biotechnology sectors. Twenty-eight companies have provided answers which formed the basis for the analysis presented here. A number of previous reviews, specifically addressed to or written by industrial colleagues, are discussed initially. This provides the context of the survey and material with which the results of the survey can be compared. The results of the survey have been divided into the themes: data, models, systems, properties, education, and collaboration. The main results are as follows. There is (still) an acute need for accurate, reliable, and thermodynamically consistent experimental data. Quality is more important than quantity. Similarly, there is a great need for reliable predictive, rather than correlative, models covering a wide range of compositions, temperatures, and pressures and capable of predicting primary (phase equilibrium) and secondary (enthalpy, heat capacity, etc.) properties. It is clear that the ideal of a single model covering all requirements is not achievable, but there is a consensus that this ideal should still provide the direction for future development. The use of new methods, such as SAFT, is increasing, but they are not yet in position to replace traditional methods such as cubic equations of state (especially in oil and gas industry) and the UNIFAC group contribution approach. A common problem with novel methods is lack of standardization, reference data, and correct and transparent implementations, especially in commercially available simulation programs. The survey indicates a great variety of systems where further work is required. For instance, for electrolyte systems better models are needed, capable of describing all types of phase behavior and mixtures with other types of components. There is also a lack of data and methods for larger complex molecules. Compared with the previous reviews, complex mixtures containing carbon dioxide associated with a wide range of applications, such as capture, transport, and storage are becoming interesting to a number of survey participants. Despite the academic success of molecular simulation techniques, the survey does not indicate great interest in it or its future development. Algorithms appear to be a neglected area, but improvements are still needed especially for multiphase reactive systems (simultaneous chemical and physical equilibrium). Education in thermodynamics is perceived as key, for the future application of thermodynamics in the industry. A number of suggestions for improvement were made at all three levels (undergraduate, postgraduate, and professional development) indicating that the education is correctly perceived as an ongoing process. 1. Introduction Accurate knowledge of thermophysical properties of fluids plays an important role in cost-effective design and operation of chemical and biochemical plants. Broadly speaking, the thermodynamic properties determine the feasibility of a given process, while the transport properties have a major impact on sizing of the equipment. The requirement for accuracy and reliability varies depending on the application. For * To whom correspondence should be addressed. E-mail:
[email protected]. † Shell Technology Centre Amsterdam. ‡ Technical University of Denmark. § Bayer Technology Services GmbH. | IFP. ⊥ The Petroleum Institute. # National Institute of Chemistry. ∇ Imperial College London.
instance, for the design of separation processes the issue is acute, as often more than 40% of the cost of the process is related to the separation units.1 As well as having impact in the design and operation of processes,1 the importance of thermodynamics in product design,2-5 green and environmental engineering,6-8 applied nanotechnology/material science,9,10 and biotechnology11-14 was recently elucidated. Due to the diversity of products and applications, the need for accurate and reliable thermodynamic and transport property data, over a wide range of mixtures and conditions, is apparent. These observations led in 2007 to the creation of a new Working Party (WP) within the European Federation of Chemical Engineers (EFCE), with the following objectives: 1. To promote thermodynamic, transport, and physical property measurements, correlations, predictions, and simula-
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tions in the academic and industrial chemical engineering communities, the national societies, as well as among the national and international funding agencies; 2. To promote concerted education activities to Chemical Engineers in the areas of thermodynamics and transport properties; 3. To offer a suitable forum to Chemical Engineers for exchange of ideas, the development of new basic and applied research projects, and collaboration through the organization of conferences, workshops, and related activities; 4. To promote and coordinate research activities at the European level by identifying chemical systems and conditions that are important for novel chemical processes and for which data and/or correlations are nonexistent or inaccurate; 5. To publish quarterly an electronic newsletter summarizing recent developments in the field. So far, the new Working Party (WP), entitled “Working Party on Thermodynamics and Transport Properties” has published a review on the role of thermodynamics in the chemical engineering education in Europe and the USA.15 The objective of the current paper is to report on a second activity that was initiated by the WP, that is, to investigate the industrial needs for thermodynamic and transport properties. For this purpose, a WP task group on Industrial PerspectiVes prepared a questionnaire that was sent to a number of key technical people in major oil and gas, chemical, and pharmaceutical/biotechnology companies. The responses received to this questionnaire are analyzed and discussed in Section 3. To put the analysis in its historical perspective, we briefly summarize a number of previous reviews that have been published in the last 20 years. Reviews emanating from both academic and industrial sources are presented and analyzed. 2. Literature Studies on Industrial Needs Some of the early review articles from industry including those of Tsonopoulos and Heidman16 (Exxon) and Zeck17,18 (BASF) are almost 20 years old. They focus on the needs of oil and gas and chemical industries, which have been traditionally the first industries to make wide use of thermodynamic data and models. Tsonopoulos and Heidman16 emphasized the then very dominant role of cubic equations of state which they consider to be largely adequate for the needs of the oil and gas industry, due to their applicability to high pressures and hydrocarbon-gas mixtures. The authors did not discourage the use of higher-order equations of state (EoS), which were appearing at the time (such as PHCT), but they were of the opinion that the petroleum industry would still use cubic EoS for years to come. Twenty-five years later, the cubic EoS remain a ubiquitous working tool in the oil and gas industry. However, association models such as SAFT and CPA are gaining ground, as the evidence is growing that they are successful for many petroleum engineering applications featuring water-hydrocarbon mixtures, especially in the presence of (antihydrate) cosolvents such as alcohols, as shown in the review of De Hemptinne et al.19 (IFP). In the early 90s, when interest in thermodynamics was regenerated by the new industrial sectors (materials, nanotechnology, and biotechnology), Zeck17 wrote: “There is still considerable potential for improVement for phase equilibrium thermodynamics eVen in long-established areas of the chemical industry. With all the enthusiasm about the possibilities of thermodynamics in new areas, it is necessary first to concentrate on performing the basic tasks”. The deficiencies of the thermodynamic models, as Zeck saw them, were often related
to insufficient precision in the description of vapor-liquid equilibria (VLE) and liquid-liquid equilibria (LLE), as well as multicomponent LLE, using a single model with a single parameter set. Many of the basic tasks noted by Zeck are related to traditional, but still difficult, separation processes like complex (azeotropic, extractive) distillations, adsorption, or extraction. About the same time, Mathias and Klotz20 (Air Products) also considered that main-stream traditional issues such as multicomponent liquid-liquid equilibria are far from solved. They stated: “RelatiVe merits of these (classical, etc.) mixing rules are uncertain at present because research is in progress, but it is clear that the methods should be judged by whether they can proVide good description of multi-component LLE e.g. for water-alcohol-hydrocarbons”. Almost ten years after Zeck’s review, Dohrn and Pfohl21 (Bayer) emphasized that the general needs for thermodynamic data may differ substantially even within the same industrial sector, in their case, the chemical industry. The answer to their question about the availability of thermophysical data elicited responses ranging from “we don’t haVe enough data” to “we haVe enough data” including even “we haVe too many data”. Each of these statements was “justified” based on the availability, or not, of relevant databases, of suitable models in process simulators or on the level of difficulty of a particular separation process. Data especially for multicomponent mixtures can be scarce and costly even for well-defined mixtures of industrial importance such as water-hydrocarbons-alcohols or glycols. Dohrn and Pfohl21 illustrated moreover, via examples, how similar models may yield different design when used in process simulators even for rather simple mixtures. For this purpose, they modeled a mixture of ethyl benzene-styrene with the Soave-Redlich-Kwong (SRK) EoS. More examples were given recently by Dohrn et al.22 showing that results may be sensitive to the specific parametrization used in models. So the evaluation of thermophysical property data should play an increasingly important role in industrial thermodynamics. Agarwal et al.23 (Virtual Materials Inc.) in their review focused their attention on what they called “less attractive” (or often neglected) properties such as heats of mixing, entropies, excess volumes, and heat capacities. Such properties could be used for additional validation and model development, and the authors investigated how cubic EoS (using either classical or advanced EoS/GE mixing rules) perform for these properties. They conclude: “Traditional actiVity coefficient models such as NRTL haVe limitations on the magnitude of the excess enthalpies they can predict. How these models behaVe inside cubic EOS for the calculation of deriVed properties is not well known and is disappointing sometimes. So, if you are modeling a system with significant excess enthalpies using a Gibbs free-energy-based EOS and you haVe a good VLE fit, this does not automatically ensure you haVe a good oVerall model from an energy balance point of View.” About the same time, articles on industrial needs specifically addressing polymer properties (from ASPEN24 and Bayer25) appeared, illustrating that a large variety of models may be required for designing polymer processes. Simulator developers and providers have also frequently published their opinions on thermodynamic requirements. Carlson26 (ASPEN) discusses the importance of using the so-called decision or selection trees for selecting appropriate models suitable for specific applications. He further discusses various techniques, such as family plots, for estimating missing parameters. In general, commercial simulators offer a lot of versatility
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to the end user, but this comes at a price of sometimes bewildering choice of models, model varieties, mixing rules, and parameter selection. Chen and Mathias,27 also from ASPEN, stated that in many industrial systems polymers, electrolytes, sometimes surfactants, and mixed solvents coexist, and this gives rise to multiple simultaneous interactions. One of the major messages of their investigation is that many existing models have been developed for each subsystem independently (for example, only for polymeric or electrolyte mixtures), and such independent developments should be abandoned if future models are to have wide applicability. They further emphasize that there is a great demand for thermodynamic models for complex products, such as consumer goods and bioprocesses. Another important issue that is discussed is the industrial response to the developments in the field. Chen and Mathias27 argue that industry rarely updates or replaces its thermodynamic models with newer and better correlations unless a clear advantage is evident. It often takes a long time, of the order of 10 years or more, for a new model to be conceived, developed, validated, and accepted by the industry. One of the most recent and extensive industrial articles on thermodynamic requirements is that by Gupta and Olson28 (Dow Chemical). In particular, they state: “Most past work focused on extensions of cubic VdWtype EoS ... This has occurred despite the now famous recommendation of Henderson. No matter how sophisticated a mixing rule, the use of Van der Waals-type cubic equations of state force their inherent limitations on the users. These are the ability to reasonably predict only the Vapour pressure of a select series of components and only an approximate modelling of the effect of liquid density and compressibility. Van der Waals-type cubic equations are unable to accurately model other liquid phase properties, for example, enthalpy and heat capacity also phase equilibria at high pressures, particularly the mixture critical locus.” Gupta and Olson illustrate, via examples (simultaneous VLE and LLE of alcohol-alkanes), that SAFT-type models should be preferred over cubic EoS for phase equilibria of polar mixtures. A report for the Eureka project written by Moorwood29 (InfoChem) discussed status and requirements for thermodynamic data for a very broad range of applications including metals and agrochemicals. In addition, Bruin30 (Unilever) discussed some thermodynamic needs specifically related to food industry. In the most recent joint industrial-academic work, O’Connell et al.31 analyzed in detail a number of specific cases from a thermodynamic perspective. Special emphasis was given to the need for simultaneous physical and chemical equilibria data, for solvent selection for pharmaceuticals, and for formaldehyde-water and CO2-water-alkanolamine mixtures. During the past decade, several articles have appeared from industrial sources (Astra Zeneza, Mitsubishi, ASPEN, Merck, etc.) on thermodynamic requirements of the pharmaceutical sector,32-37 particularly the need for accurate and reliable models for solvent screening. A variety of models have been tested, ranging from modifications of UNIFAC and solubility parameters to modern versions of local composition models, such as NRTL-SAC,38 and methods based on quantum chemistry like COSMO-RS39,40 and COSMO-SAC.38 The use of quantum chemistry methods in pharmaceutical industry has been also
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highlighted in industrial lectures (for example, by Natori, 2001, at the PPEPPD conference in Kurashiki, Japan). A systematic investigation on industrial needs for both thermodynamic and transport properties has been conducted under the so-called Forum 2000 project, and the results are documented in a detailed report41 and several publications.42,43 One important comment from Forum 2000, by Jim Olson (Dow Chemical), focuses on the need for reliable experimental data for families of compounds which have not been systematically studied: “We can neVer conduct all the necessary experiments but many data measurements are missing. For instance, multi-functional chemicals such as alkanolamines, glycol ethers, excess properties like excess Volumes at Various temperatures, amides, liquid phase heat capacities, enVironmental phase equilibrium, safety data e.g. flashpoint and auto ignition temperatures, simultaneous physical and chemical equilibrium, ...” The need for reliable experimental data is the message that is also strongly supported by other industrial-oriented reviews, e.g., by Rhodes44 (Union Carbide) and Richon.45 Other important comments from the Forum 2000 work are related to the need for accurate data and models for transport properties. For example, Bill Wakeham stated: “Thermal diffusion, although an abstruse transport property, will turn out to be extremely important in oil reserVoirs, due to the large T-differences”. He later added: “What’s the data in tissue engineering that we need? If you look at the way cancer tumours are sometimes remoVed, which is ultrasonic’s or microwaVes, this is all done by heating. The thermal conductiVity of the tissue you heat, the heat capacity of that tissue, matters and they don’t know it. Sometimes it is measured in Vitro neVer in ViVo.” P. Mathias stated: “Transport properties are becoming increasingly important, but little attention has been deVoted to them”. He further made a point on solids: “When one actually does modelling, with particle sizes, the issues of nucleation and growth are important. An area I think chemical engineers did many things 30 or 40 years ago, but there’s not been a lot recently”. So far, we have summarized some comments and opinions based on the reviews of articles from industrial sources. Several reviews emanating from academia have also been published. In particular, the review by Prausnitz and Tavares46 and more recently a book by Kontogeorgis and Folas38 review a large number of thermodynamic models and present an outlook for future developments. According to most of the academic reviews, important advancements in thermodynamics are needed to address issues related to “post-modernism”,47,48 life sciences/biotechnology,11-14,49,50 and chemical product development.2-5,9,10 Moreover, there is a need to connect closely with other disciplines of chemical engineering, such as mass and heat transfer, nucleation, and chemical kinetics. One example where such an interdisciplinary approach would pay great dividends would be in the design of controlled drug release systems. The postmodernism trends in chemical engineering encompass the need for more “human aspects” in the curriculum. They emphasize the role that chemical engineering plays in society and provide ample opportunity for thermodynamics. The nearfuture focus should be on addressing different environmental and safety related aspects, for example, the use of supercritical fluids, the optimization of processes related to CO2 capture and storage, as well as modeling of loss-prevention scenarios.6-8,47,48
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Many recent investigations39,40,51-53 point to the increasing importance of quantum chemistry especially in the form of models like COSMO-RS and COSMO-SAC for thermodynamic calculations and especially screening purposes for a wide range of situations, mostly at low pressures. The role that the molecular description increasingly plays in modern thermodynamics has been emphasized by Prausnitz:9 “Thermodynamics is often most useful when directed at deVeloping model for new situations, where our quantitatiVe understanding is seriously inadequate. Pioneering molecular thermodynamics is concerned not with improVements where primary understanding has already been achieVed, but with shedding light on situations where as yet, we know little. For many practical problems, old theories are sufficient proVided that they are used with courage and imagination.” 3. Questionnaire and the Survey The task group Industrial PerspectiVes appointed by the EFCE Working Party on Thermodynamics and Transport Properties (EFCE WP) prepared a questionnaire comprised of seven questions that are presented in Appendix 1. The questions ranged from simple yes/no answers to the ones that were openended where any issue related to thermodynamic and transport property requirements could be addressed. The overall purpose of the survey was to: • Review the situation in industry with respect to thermodynamics and transport properties requirements. The emphasis was primarily to collect information on European industry, although some companies from the USA, Japan, Thailand, Brazil, and South Africa were also included in the survey; • Identify limitations in current approaches; • Provide specific recommendations on R&D work (to be initiated by the EFCE WP and individual researchers in this area). A list of possible companies that could take part in our survey was created with the contact names collected by the coauthors of this paper, and the invitations were sent out. Fifty-nine companies in total from sixteen different countries were contacted, and the reminders were sent out to increase the number of responses. In total, 28 replies were received, which represents a 47% response rate. Most responses were from European but globally operating industries. Figure 1 illustrates the industrial sectors of the companies that have responded to the survey. 4. Results Although it is rather difficult to categorize and summarize an overwhelming number of answers received, an attempt is made to summarize the essential features by means of Figure 2. Figure 2 shows on the left the industrial requirements regarding thermodynamics and transport properties, summarized by a few keywords. The requirements are usually short-term, and this is probably why there is a resistance in trying out recently developed advanced tools, such as SAFT EoS and molecular simulation (“first concentrating on basic tasks”). Yet, the industrial requirements often relate to complex thermophysical systems, hence the reliance in some instances on simple “rule of thumb” approaches, which are believed by industry to give a good indication of trends. Finally, industrial needs require either (i) the knowledge of thermophysical properties at given operating conditions or (ii) in product design the ability to design
Figure 1. Responses to the questionnaire classified by industrial sector. Some responders work in more than one category.
the right product with specific thermophysical properties (i.e., solvent design). The “supply” from the thermodynamic community is presented in Figure 2 as a triangle that should respond to these needs: the response is the “package” that includes models, parameters, and algorithms. Ideally, this model should be unique, independent of the type of system or operating conditions. To construct this ideal package, the three vertices of the triangle must be considered: Upper left: what is the molecular system under inVestigation? There is a plethora of mixtures of industrial interest, and it is more or less impossible to include every conceivable combination. A reasonable approach would be to rely on good description of thermophysical properties of pure species and use modeling tools to obtain the properties of the mixtures. The industrial interest changes with time, as a result of new developments, new processes, and new products. Currently, there is an emphasis on CO2, electrolytes, and polyfunctional molecules. Many molecular systems are compositionally welldefined, but this is not always the case. For instance, for reservoir fluids the detailed molecular composition is usually not available, hence some additional characterization is needed. Upper right: what is the property required? Although VLE remains the most common, other types of phase equilibria (LLE, SLE) are nowadays also in demand. Furthermore, there is an increasing need for enthalpic properties (heat of mixing, heat capacities, etc.) and transport properties. The traditional cubic EoS is of limited use for this purpose,28 and one requires more sophisticated models that are not necessarily available in every package. Lower corner: data. The most traditional approach is to claim that there are not enough data or to use the available data without any analysis of their accuracy or reliability. Although it is true that for a large number of systems the data are scarce, when the data are available one should ask the question according to Dohrn and Pfohl:21 “do we have the correct data (that means useful in view of the applications)?” At the very right of Figure 2, the various state-of-the-art predictive tools that the thermophysical property community can use, to respond to the industrial needs, are illustrated. Molecular simulation plays an essential role, as well as quantum chemistry, as both have shown great advances in terms of both development and applications. In the near future, other com-
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Figure 2. Schematic illustration of the position of thermodynamic tools for the oil and gas, chemical, and process industries.
putational techniques might become available including, for example, the ones dealing with nonequilibrium thermodynamics or calculation of transport properties directly from intermolecular potential. Industry is not yet fully aware of the applicability of these computational techniques to address their requirements, which is why very few industrial comments on this issue were found in our survey. It is thus the role of the academic community to introduce the use of advanced computational techniques, by both further refining theoretical models and showing that the results can be used as alternative, pseudoexperimental data, or parameter provider. In the next set of subsections, we present and analyze the results obtained in the current survey. For ease of use, the main conclusions from the survey are presented in the bold font in the first paragraph of each section. 4.1. Data. There is an acute need for high-quality experimental data for both thermodynamic and transport properties, including the phase and chemical equilibrium data. The high-quality data can only be obtained in a wellcharacterized experimental apparatus with a well-defined uncertainty level, which cannot be demonstrated to be inconsistent with other data or with theory. Although such instruments do exist, their use requires knowledge of their full-working equation, and in some cases it requires a number of corrections, to account for the nonideality of the apparatus, to be made to experimental data. Thus, producing high-quality data is expensive and time-consuming, and not surprisingly, such data are scarce. It is important to emphasize that rather than focusing on the amount of data available for a particular system one should focus on gathering reliable data with well-defined uncertainty levels that cover the phase space of interest. Such sets of high-quality data, that are mutually consistent, can then be used as a benchmark data set for a particular system essential for validating or developing predictive models and tools. More specific comments that were made in the survey were as follows: (i) For complicated molecules, containing multiple functional groups (e.g., hyper-branched polymers, dendrimers, micelles) that are used for fine chemicals, crop protection, and bioapplications, very few phase equilibrium data exist in the open literature. So group contribution methods are less accurate for these molecules, as there are no data to fit the required parameters. (ii) For many traditional/bulk chemicals, a large number of data sets exist that do not agree with each other. Most of the data have been measured a long time ago in the apparatus whose description does not allow for their proper levels of accuracy to be established. There is a lack of high-quality reference data to which model parameters can be fitted for process simulation.
Simple examples mentioned in the survey include the inorganic acids, like sulfuric acid, hydrochloric acid, and nitrous acid. (iii) The participants of the survey felt that the emphasis should be given to more measurements on: (i) gas solubilities; (ii) high-pressure and high-temperature phase equilibrium data of nonideal mixtures; (iii) dilute conditions; (iv) solubilities and diffusion in polymers; (v) reactive multiphase systems (CO2, H2S-water-alkanolamines); and (vi) electrolytes. Essentially, there is a need for high-quality data for a wide range of systems and conditions. (iv) Data are also lacking in petroleum-related applications for: (i) gas hydrate systems, e.g., hydrate formation with CO2 and H2, with additives, and with loss of hydrate inhibitor such as methanol and glycols; (ii) properties of heavy oils; (iii) partition coefficient of gases in hydrotreatment conditions, especially in the presence of oxygenated fuels; (iv) heats of reaction and of adsorption; and (v) VLLE of complex natural gas mixtures including water and electrolytes. (v) There is an acute need for transport property data that include viscosity, thermal conductivity, and diffusion coefficient data. Especially, emphasis was put on the lack of data for electrolytes and ionic liquids. It was noted that even when some transport property data do exist they do not cover an extensive temperature and pressure range. (vi) The lack of data is made even more acute by the observation that there are fewer research groups (at least in Europe) that have well-equipped laboratories and have funding to devote time to measurements. The disappearance over the years of a number of research groups that were producing highquality data is a worrying trend, as without the high-quality data the existing databases will become less useful as the tendency to target quantity rather than quality will intensify. (vii) A number of participants indicated that when the data need is clearly identified in view of specific industrial requirement, companies do not hesitate to spend money to measure the relevant properties. However, as these data are often considered strategic, they are not always published. Note that policy of expecting to find a laboratory, when a particular need arises, that can perform the high-quality measurements is relatively short sighted. Producing high-quality data requires continuity in terms of both maintaining apparatus and even more importantly maintaining research expertise, as the high-quality measurements cannot be performed on a short-term basis by inexperienced researchers. (viii) The use of advanced computational tools, such as molecular simulation or quantum chemistry, is sometimes mentioned as an alternative to “producing” experimental data, but this approach is currently not commonly accepted by industry.
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4.2. Models. 4.2.1. Scope of the Models. There is a need for reliable thermodynamic and transport property models for a Wery wide range of systems. The participants of the survey put the special emphasis on: (i) Need for models for phase equilibria and transport properties, preferably within a single framework, that cover all the components and conditions of interest and with good interand extrapolation capabilities in temperature, pressure, and composition. (ii) The framework should be targeted toward making use of generalized and simple equations of state for nonpolar, polar, associating, and high boiling substances and their mixtures, with sufficient accuracy for industrial purposes. (iii) The number of available models in the literature should be reduced by recommending either a unique model or a small number of models. Today, specialists in industry are required to recommend the best modeling approach for a specific application, and the number of available models or versions of the same model are sometimes bewildering. More specifically, the survey results indicated: (i) The models should cover the requirements of very diverse industrial fields: (a) oil and gas including heavy oil, mercury compounds, syngas, asphaltenes (currently poorly characterized), and organic sulfur compounds; (b) chemicals including complex oxygenated chemicals related to biofuels, ionic liquids, surfactants, and polymers; (c) biotech including biopolymers, pharmaceuticals, and building blocks; (d) colloids including emulsions, surfactants, food additives, emulsifiers, adhesives, and gels; and (e) metal and mining. The applications were by and large dependent on the industrial sector, but the following processes were particularly emphasized as in need of good models: flow assurance (gas hydrates, asphaltenes, and wax); separation methods other than distillation/extraction, e.g., adsorption and chromatography; and crystallization. (ii) As can be seen from the above list, requirements and expectations for models are not only diverse but also very extensive. Clearly current models cannot cover or meet all areas of interest and expectations. However, an interesting issue is that there is a feeling that models are incomplete or lacking even in areas which might have been considered “mature”. For instance, for bulk chemicals it was felt that a very important system of ammonia-water-sulfuric acid is poorly addressed by any of the available models. In the oil and gas area, the presence of mercury and sulfur compounds was equally badly catered for by the modeling community. There is a feeling that an analysis of the different requirements and expectations carried out for each industry sector would be useful. (iii) A lack of high-precision EoS for a number of systems was noted. 4.2.2. Theoretical Foundation of the Models. Traditional and novel models are equally important, and developments in both should continue. Model approaches used in industry range from traditional group-contribution (GC) models especially UNIFAC to modern approaches such as COSMO-RS and SAFT. The general consensus is that: (i) The development of both UNIFAC and COSMO-RS should continue as they are both very useful for industrial applications. There was a suggestion that some work should be carried out to combine them, by for instance making use of group contributions for the sigma profiles of COSMO-RS. The prediction of UNIFAC and COSMO-RS should be compared as the actual range of applicability and accuracy appears to be very system-dependent. Molecular modeling should be further
developed to gain better understanding, and molecular simulations are suggested to improve the prediction of thermophysical properties and phase equilibrium. (ii) The GC models in general are used and are needed in many contexts that do not necessarily involve predicting phase behavior, for instance, for computer-aided product design, properties of heavy compounds (even for pure species: melting temperature, vapor pressures, etc.), solvent screening, emulsions, and oxygenated compounds. Thus, the full phasing out of GC models in favor of modern models is not yet imminent. (iii) SAFT-based models are promising tools, but the requests from the industrial community for these models are multiple: • Characterization methods for oils, asphaltenes, and similar complex mixtures; • Speed must be improved for routine applications (see also next point on standardization); • Recommended pure-component and binary parameters should be collected and made available; • True improvements over classical cubic EoS should be demonstrated, especially for multifunctional, complex, and associating compounds like oxygenated compounds (biofuels); • The model should be applied to truly important new areas including polymers and electrolytes; • Standardization is needed. This is further discussed in section 4.2.3. 4.2.3. Availability of the Models. Standards are very important for thermodynamic models. The term “Standards” has been used and understood in different (sometimes complementary) contexts, both in implementation and model validation: (i) Models should be present in simulators for active use by industry, otherwise, they may be forgotten. CAPE-OPEN is a useful (and standard) tool for integrating user developed unit operations and thermodynamics packages in commercial process simulation programs, but it is still not fully developed and supported. One of the comments in the survey was that the analytical derivatives are needed. The tool should be improved further, allowing exchange of thermodynamic packages belonging to different process simulators. (ii) The number of new models is enormous, even within the same family. For instance, there are numerous versions of SAFT. Sometimes different results are obtained with what should be the same model. Proper coding and validation are extremely important to ensure full reproducibility of the results. This should also be performed by other researchers rather than just by those involved in the model development. The question arises how can this be accomplished? It is worth investigating some process that would lead to a proper comparison of models. A first step in such a process could be the agreement to use some standard well-accepted databases for validation purposes. A second step would be the agreement on criteria for model validation which could be used by all developers. In particular, the model developers should try to present, in a few comprehensive articles, all equations of their models including a thorough evaluation. The codes can be made publicly available, but a good accompanying documentation would be necessary. 4.2.4. Algorithms. Implementation of the thermodynamic models requires reliable flash and related algorithms, and although significant developments have been made in the past (e.g., Michelsen and Mollerup54), new challenges are appearing, in particular, the need for very fast and robust calculations for flashes, the presence of multiple phases, and reactive systems. Further, there is a need to improve the stability test, the most
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time-consuming element of the multiphase calculations. Unfortunately, the field does not seem to be of active interest to the thermodynamic community. 4.3. Systems. The most popular systems appear to be electrolytes, CO2, and larger, polyfunctional molecules. These systems appeared repeatedly in a survey in different contexts from a number of companies belonging to different sectors. In particular: (i) There is a need for improved description for electrolyte systems that go beyond e-NRTL.38 The emphasis should be on describing all types of phase behavior (VLE/LLE/SLE) covering also electrolyte mixtures with water, other organic chemicals (i.e., mixed solvents), and hydrocarbons (natural gas), over extensive temperature and pressure ranges, up to high salt concentrations. Electrolyte models are multiparameter models, and modern e-EoS38 may be a way to go; however, much remains to be done. There is a need to bring electrolyte thermodynamic models to a level comparable to other fields. The need for improved electrolyte models is common among a wide range of industries. (ii) There is a lack of data and models for larger molecules, complex molecules, biomolecules (biopolymers, proteins, pharmaceuticals, gels), or molecules that contain multiple functional groups (polar and associating ones) that are used as food additives. (iii) CO2 mixtures with water, polar chemicals (methanol, glycols) including mixed solvents, H2S, N2O, O2, hydrocarbons, and (alkanol) amines appear of importance to a wide range of applications (gas hydrates, oil and gas, CO2 capture, transport, and storage). Of special importance to a number of participants was that the description of the system covers very extensive temperature and pressure ranges. The CO2containing systems also include electrolytes, as CO2-brine (+ rock mineral) systems are of great interest in CCS (CO2 capture and storage) applications. A number of the systems described are chemically reactive which further complicates their thermophysical description. 4.4. Properties. Multiple thermodynamic properties are of importance. It was frequently stated in the survey that simultaneous description of different thermodynamic properties and phase equilibrium types is of great importance. Internal thermodynamic consistency of the generated data by a given model is nowadays as essential as accuracy and reliability. This is especially important as the thermodynamic models are often used as part of the simulator by a different set of software developers who are not necessarily aware of all the nuances of a particular thermodynamic model. Hence, thermodynamic modelers should no longer be satisfied with models that for instance give only good VLE results at low pressures but are either untested or fail for other properties and regions of the phase space. In particular, the results of the survey indicated that for equilibrium properties: (i) Simultaneous description of VLE and LLE (+ VLLE) is of interest with the same model and the same parameter set, especially for complex multicomponent mixtures. (ii) So is the simultaneous description of the phase behavior and derivative properties (e.g., heats of mixing). (iii) Special attention should be given to dilute systems (infinite dilution), and the description of the system should be mutually consistent with the description at higher concentrations.
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(iv) Extrapolations to high temperatures and pressures are often needed, for instance, for gas solubilities in waterhydrocarbon-CO2 mixtures that could involve salts and other chemicals. The proposed correlations should have sensible extrapolation behavior. A number of other properties were mentioned as important for specific applications: (i) SLE is crucial for a variety of separation processes, e.g., crystallization, as well as for mineral stability and hydrate formation in the oilfield. (ii) Surface phenomena (adsorption) are typically equilibrium phenomena that play an important role in a number of applications. (iii) Chemical reactions (formation properties). None of these properties are currently well catered for by the thermodynamic community. Nonequilibrium properties: combined thermodynamic/ transport effects and appreciation of nonequilibrium effects are important. (i) There is a need for combined models for predicting thermodynamic and transport properties, reaction rates, and diffusivities. There is a need for a good procedure to disentangle reaction kinetics and mass transfer where both processes contribute. (ii) Is it possible to predict transport properties from thermodynamic data alone? Can we reliably estimate thermal and transport properties from limited vapor pressure and density data? (iii) There is a need for models for predicting properties, especially transport properties of complex products present in many fields of process industry, such as viscosity index of lubricant base oils from composition and octane/cetane numbers. (iv) What is the effect of nonequilibrium behavior? It is not always clear whether a system is in thermodynamic equilibrium or not. (v) There are cases where thermodynamic predictions may be quite misleading because of slow reaction kinetics, or poor mass transfer, e.g., predicting inorganic scale deposition. (vi) In many processes, the nonequilibrium part can be of importance, e.g., nucleation in crystallization and gas hydrate formation. (vii) It would be of great industrial interest to develop fundamental nonequilibrium thermodynamic approaches for predicting transfer across boundaries (for replacing the empirical “transfer efficiency” equations). 4.5. Education. What is the role of education in thermodynamic modeling for process and product design? There is a clear agreement among the participants in the survey that education is the key for an appropriate use of thermodynamics in industry. Three different levels of education are relevant in this context, each with different requirements: (i) Undergraduate education: it is essential that engineers in operating companies know some basic thermodynamics but even more importantly that they are aware of the limitations of their understanding. This is especially relevant as black-box type simulators are routinely used these days. (ii) Professional development: with the advent of new technologies (simulators) or as a result of job changes, people may be confronted with new challenges after several years of professional experience. The field of thermophysical properties is evolving rapidly, and there is a need for industry professionals to keep up with the latest developments.
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(iii) Postgraduate education: the complexity and the wide applicability of thermodynamics leads to a need for specialists within a given company, typically educated to a PhD level, to act as an internal expert on thermodynamic and transport property issues. 4.6. Collaborations. Data collected revealed that: (i) The R&D organization in the various companies is generally rather strong: 25 out of 28 companies have a research lab, and 9 of them have a research subsidiary. (ii) Most of the companies that took part in the survey have bilateral collaborations with universities. The average level of collaboration fulfills close to 10% of the total research need. Some companies rely quite heavily on it. (iii) 25 out of 28 companies participate in consortia. Yet, the willingness to participate in joint R&D programs is surprisingly conservative with only 14 out of 28 indicating a clear yes. (iv) The area for joint collaboration is rather diverse: from gathering new data to developing parameter tables (UNIFAC consortium is often cited as an example). 5. Conclusion: Discussion and Comparison to Previous Studies A short discussion is provided in this section contrasting the results of our industrial survey and those from the literature that were presented in section 2. An important common feature of current and previous investigations (see for example a recent discussion45) is the need for experimental work which will result in high-quality measurements that are accurate, reliable, and thermodynamically consistent. In many cases, the real accuracy of published experimental data is far lower than the accuracy given by the authors, as discussed by Peper et al.56 The importance of practical expertise of the experimentalists in obtaining high-quality data has been highlighted by Dohrn et al.55 in their recent review on experimental methods for high-pressure phase equilibria. Often, the qualification of the staff and their familiarization with the technique have a stronger influence on the accuracy of experimental results than the choice of the experimental method or the equipment. Our survey shows that there is a clear need for qualified laboratories with experienced staff to provide experimental measurements. As many companies seek to reduce in-house facilities for routine, nonexploratory type of measurements, this need will likely increase. Universities have also reduced their experimental activities. The key problem is that performing high-quality measurements requires accumulation of many years of experience for which funding has to be secured. The different funding bodies in many instances do not see this type of activity as leading edge research and in the present climate decline to fund it. Furthermore, the pain-staking effort leads to a rather limited publication output. Nevertheless, data are lacking for a wide range of systems from “simple” common mixtures up to multifunctional chemicals, complex compounds originating from biomass, ionic liquids, polymers, and pharmaceuticals. Surprisingly, the data are still very scarce for solubility of water in CO2 at high pressures and for mixtures that involve inorganic acids or ammonia. Another common feature of the current survey and the previous ones is that reliable models are needed and that the predictive character is essential, but many existing models are essentially correlative. Thus, SAFT, COSMO-RS, and UNIFAC (GC) approaches should be further developed, and it appears unlikely that a single tool will be sufficient in all
cases. Most models have serious problems when applied to (poly)electrolyte systems, mixed solvents relevant for gas treatment using amines, and new solvents like ionic liquids. The simultaneous presence of polymers, electrolytes, and biomolecules is also an area where none of the models perform adequately. These are areas where important revisions and improvements are needed. It is particularly interesting that deficiencies in current electrolyte models are apparent even for models used in commercial simulators, as illustrated in a recent joint academia-industry project.57 Emphasis on electrolytes and polymers is found in both previous and the current investigation. New in our survey is the special interest in predicting the thermophysical properties of mixtures containing CO2. This is a direct result of climate change concerns and the development of sustainable technologies, in particular, the CCS. Regarding the capabilities of thermodynamic models, we can state that the advent of SAFT-family models has certainly contributed to better representation of a wide range of systems (nonpolar, polar, associating, polymers, etc.) and the simultaneous representation of various phase equilibrium types, e.g., VLE and LLE. On the other hand, there is a clear impression from the survey that certain important issues, also emphasized in the earlier industrial studies, have been overlooked. Good examples are the multicomponent multiphase equilibria especially for prediction purposes and the accurate description of derivative properties (e.g., heat capacity, speed of sound, enthalpy of mixing) together with phase behavior. Clearly, these issues need to be considered and included in future development-model validations. Some of the previously published industrial reviews emphasized molecular simulation techniques as enabling technology which can supplement the experimental data or act as pseudoexperimental data at temperatures and pressures where experiments are difficult. However, the participants of the current survey were not particularly encouraging the further developments of molecular simulation, which is a rather disappointing state of affairs. Algorithms appear to be a neglected area in many of the previous publications, but the results of the current survey illustrate that the improvements are clearly needed, especially for multiphase and/or reacting systems (simultaneous physical and chemical equilibria). According to the current survey, implementation is an important issue to the industrial users. In the previously published reviews, this aspect was not emphasized greatly, although the importance of CAPE-OPEN58 standard has been mentioned. The issue of having standardized and validated models is particularly highlighted in the current survey. The new models are published very frequently, but unfortunately most, if not all, of these models are tested against only a few data sets. A large, standardized set of data against which all models may be tested will be of great benefit, as it will allow models to be compared on equal footing. It will also be of benefit to those developing the models, as the validation against agreed industry benchmarks could lead to the reduction of cycle time from development to industrial use. A final original issue raised by the current survey is the need for education and the possible role the EFCE WP can play in this. A number of suggestions of improving the undergraduate level courses were made. Thermodynamics of process simulation should be taught with the emphasis on how generic simulators work, without necessarily going into peculiarities of a particular simulator, unless a particular simulator is used in class. It is
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important to get across how to distinguish between reliable and unreliable thermodynamic data and practices. However, the main issue raised is how to make engineers more aware of the practical consequences of “right and wrong” thermodynamics. In particular what type of problems require initiation of proactive research and under what circumstances would quick empirical fixes suffice.
Acknowledgment
Overall, the gap between the industrial requirements and the data availability has not appreciably shrunk over the years. It is not immediately clear how this gap can be closed especially in the present economic climate. The first step is to once again try to bring the relevant stakeholders closer together.
Below are listed the questions asked in the EFCE Working Party Task group on Industrial Perspectives Questionnaire. All questions are to be considered in relation to physical properties, thermodynamics, and transport properties.
As an example of possible actions, the French working party Thermodynamique des proce´de´s organizes small scale one-day meetings on specific topics such as education, molecular thermodynamics, and use of databases. The objective is to create learning and exchange opportunities between the academic and the industrial communities. Specific potential actions from these meetings are the installation of a Web site for exchange between educators and a Web-based information system for molecular thermodynamics issues.
Question 1. Your company’s business
Other examples include the organization of workshops such as the one recently organized between our working party and the German ProcesNet working party. Such workshops should be tailored so that they address some of the numerous questions raised above. At the same time, they can act as a forward looking forum where the industry can articulate their medium- and long-term needs and open a dialogue with data and model generators. The issue of having large, standardized set of data against which all models may be tested is also a very pertinent one that needs addressing. Although, there are databases (NISTTRC, Dechema-Detherm, Danner and Gess59) that are used by individuals, their use is still not widespread enough. Of equal importance is the definition and availability of standardized models. In our view, this requires for each such model the publication of a paper, perhaps in a dedicated journal, containing all that is needed to perform the calculations and reproduce results. This includes all the equations and parameter values needed to achieve this and results for a number of defined input cases. However, discussions on the merits of the model and comparison to experimental data should be left out. The model can then receive a unique identifier which together with this definition paper can serve as the reference. It would also be very useful to publish the implementation of this model including the parameters as open source code, preferably together with the definition. The vendors of commercial software should refer to these standard models in their documentation and clearly state when and where they deviate from them. The same holds for authors discussing a comparison of their results against those obtained with standard models. We see this paper as the first step in reinitiating the dialogue between the interested parties which can lead to a more effective collaboration that can close the current gap between the requirements and the availability of thermodynamic and transport property data and models. We feel that the EFCE WP should play an important role in this process, acting as a conduit between the academia, industry, and decision makers.
We acknowledge the contribution from all industry experts who replied to the survey and thank them for their effort, without which this paper could not have been written. Appendix 1. The Survey Questionnaire
What are the main businesses of your company? (Put Yes or No) Exploration and production Refining Bulk chemicals Fine chemicals Natural gas Power generation Pharmaceuticals Agrochemicals
Question 2. Limitations in thermodynamics and transport properties What do you consider as the limitations in thermodynamics and transport properties in addressing your company’s challenges? Products Processes Data Models Process simulation Reservoir simulation CO2 sequestration Enhanced oil recovery Extraction and processing of discounted (opportunity) crudes (heavy oil, high sulfur crudes, high acid crudes...) Gas processing Long-range transport Add as many as you wish Question 3. R&D in thermodynamics and transport properties How is the R&D organized in your company? Do you have your own research laboratories? Do you have a research subsidiary? Do you subcontract your research? What proportion of the work is subcontracted to academic teams? Question 4. Collaboration Consortia or other collaborative work in thermodynamics and transport properties. Do you participate in consortia? If so, in which areas?
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Is your company willing to sponsor research work that is to be shared with the rest of the thermodynamic community? If so, in which areas? Question 5. Benefit Can you provide examples of achievements in Thermodynamic R&D where you can give an estimate of potential business or avoided risk? Question 6. Areas What are your ideas and opinions concerning the development in the following areas? Suggestions: Try to be concrete, so refer explicitly to elements such as components (carbon dioxide, sulfur), models (SAFT), phenomena (gas hydrates), experimental quantities (SLE, speed of sound), standards (CAPE OPEN), algorithms (multiphase flash, speed improvement), conditions (T > 500 K), applications (heavy oil, reinjection of hydrogen sulfide), procedures (characterization of well fluids), and so on wherever this is possible. Look at competing or complementary approaches, such as Group Contribution methods versus CosmoLogic. Is there a need for both? Do we have a preference? Look at the need for standardization versus flexibility. For example, do we want yet another equation of state, or should we devote all effort to extending the traditional ones now present in most process simulation programs? And if the latter holds true, which ones would we single out in this stage? Physical Data Phenomena Conditions and environments Models Algorithms Procedures Implementation Applications Process simulation Standards Add your own item(s) Question 7. Other thoughts Do you have any other thoughts on thermodynamics and transport properties that could be relevant to us? Literature Cited (1) Prausnitz, J. M.; Lichtenthaler, R. N.; de Azevedo, E. G. Molecular Thermodynamics of Fluid-Phase Equilibria, 3rd ed.; Prentice Hall Inc.: Englewood Cliffs, NJ, 1999. (2) Kontogeorgis, G. M.; Gani, R. Introduction to Computer Aided Product Design. In: Computer-Aided Property Estimation for Process and Product Design; Kontogeorgis, G. M., Gani, R., Eds.; Elsevier: Amsterdam, The Netherlands, 2004. (3) Abildskov, J.; Kontogeorgis, G. M. Chemical product design - A new challenge of applied thermodynamics. Chem. Eng. Res. Des. 2004, 82 (11), 1505–1510. (4) Villadsen, J. Putting structure into chemical engineering - Proceedings of an industry/university conference. Chem. Eng. Sci. 1997, 52, 2857–2864. (5) Favre, E.; Kind, M. Formulation engineering: towards a multidisciplinary and integrated approach of the training of chemical engineers. Paper presented in the 2nd European Congress of Chemical Engineering (Montpellier), 1999. (6) Sandler, S. I. Infinite dilution activity coefficients in chemical, environmental and biochemical engineering. Fluid Phase Equilib. 1996, 116, 343–353. (7) Sandler, S. I. Unusual chemical thermodynamics. J. Chem. Thermodyn. 1999, 31, 3–25.
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ReceiVed for reView June 6, 2010 ReVised manuscript receiVed September 17, 2010 Accepted September 20, 2010 IE101231B