TECHNOLOGY
Institute Gathers Chemical Engineering Data tentially applicable data, they are reliabilities of physical constants, often unsure about its reliability. temperature-dependent properties, Even large chemical firms cannot and environmental information on meet the costs of determining phys- 1025 compounds by 1985, and as ical properties and thermodynamic many as 5000 in later years. Members behavior of all the compounds and received final data on the first 197 mixtures in a plant. The consequence compounds at the Los Angeles may be the spending of excessive AIChE meeting in November. The sums on oversized motors, pumps, institute will issue data on these compressors, piping, columns, con- compounds to the general public late Stephen C. Stinson, C&EN New York densers, reboilers, and heat ex- this year. Meanwhile, the number of compounds compiled reached about Chemical engineers have begun sa- changers. voring the first fruits of a massive A company membership in DIPPR 300 in 1982, and members may see effort to gather, determine, and currently costs $750 per year. In ad- that total rise to 600 during 1983. evaluate data on physical properties dition, the institute requires com- "The data compilation project is the and predictive methods for large panies to cover budgets of projects in largest of all these projects and is numbers of compounds and mixtures which each firm participates. Partic- central to the overall DIPPR effort/' processed in the chemical industry. ipation in a project lets company says chemical engineer Alvin B. This centralized data source may lead representatives have a say in the Larsen of Monsanto, who is overto economic benefits for chemical form it takes. The institute will con- seeing this project for the institute. Principal investigators for the data processors, whose engineers no tinue work on seven projects in 1983 compilation project are chemical longer will need to spend so much at a total budget of $470,000. time in search of design data or to One project, called data compila- engineering professors Ronald build excessive safety factors into tion, seeks to search out and evaluate Danner and Thomas Daubert of plants. The first beneficiaries of this effort are engineers from the 52 firms that are members of the Design Institute for Physical Property Data (DIPPR), organized under the American Institute of Chemical Engineers to carry out the project. Under terms of their membership, these firms will receive newly evaluated data and predictive methods one year before they are released to the chemical engineering community at large. Petroleum refining engineers have enjoyed access to similarly collected data and predictive methods, thanks to an effort begun more than 20 years ago by the American Petroleum Institute. Though that information has been available to chemical engineers, they often worry whether and to what extent methods and data for hydrocarbons are applicable to polar compounds processed in chemical Stephen Newman (Foster Wheeler Synfuels Corp.), Thomas Daubert plants. In cases where chemical and and Ronald Danner (both of Penn State) and Alvin Larsen (Monsanto) synthetic fuels engineers find po- gather round the desktop computer used to test data correlations
The Design Institute for Physical Property Data is working on data compilation and prediction projects to benefit its member firms
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January 3, 1983 C&EN
Pennsylvania State University. In addition to searching the literature for data, their task includes uncov ering published evaluations of reli ability or carrying out such evalua tions at Penn State. To get as much information to chemical engineers as soon as possible in one source, Dan ner and Daubert include crude esti mates and numbers from unknown sources, and then label these ac cording to reliability. For example, the acentric factor of toluene (used to calculate the activity coefficient of toluene in mixtures) is 0.2566 and labeled ΧΕΙΡ. ΧΕ means experimentally determined and evaluated, 1 means that error is less than 1%, and Ρ means that the eval uation was done at Penn State. By contrast, the dipole moment of tolu ene is given as 1.03405 Χ 10" 30 , but labeled ?UO, which means that the value's origin is unknown and its reliability not evaluated. Even a rat ing of unknown origin or reliability is valuable to a chemical engineer who otherwise would have to con clude this after his own search. The Penn State team seeks 24 physical constants for each com pound and up to five coefficients each for equations that express the temperature dependence of 13 tem perature-dependent properties. For such properties, the coefficients and equations usually are specified as useful from the triple-point temper ature to the critical-point tempera ture. To ensure that this is so, Danner and Daubert are using a desktop computer with a high-resolution monitor to test data correlation. As they test each data point, the Penn State workers mark them either as reliable and used in the regression analysis; as reliable but not used for regression; or as rejected, together with literature references for each. Though published data might have been determined at temperatures or pressures other than those needed for a particular plant, chemical en gineers can calculate needed values with the equations, confident that the procedure is reliable. A second project of the institute is assembly of a data prediction manual. The manual will contain 12 chapters on recommended methods for using known data to predict values of properties that are unknown at the
Bad data can cause money losses, plant failures Chemical engineers know that plant costs can run up when uncertainties in design data lead to overdesigning to allow for errors. Though few instances of cost overruns or plant failures are ever recorded officially, anecdotes abound whenever chemical engineers gather. For example, to see how much stored ethylene a salt dome near Houston really contained, the owners decided to empty it. Pressure, volume, and weight rela tionships of ethylene vary widely near its critical temperature (about 50 °F), which is the temperature of a typical winter day on the Gulf. Because of this, the salt dome was found to contain much more ethylene than expected, despite engi neers' costly efforts over the months to meter additions and withdrawals at temperatures above 50 °F. The excess ethylene translated into discrepancies in amounts of money that area com panies should have paid or received. In another instance, a gas processing plant yielded less propane than ex pected because of incorrect vapor-liquid equilibrium constants estimated for methane. Correcting this problem re sulted in increased power use, the need for an extra pass through a cooling
tower, and lowered yields of ethane. Operating costs rose and efficiency declined, compared with plant design ers' projections. In a different case, designers of an amines plant erred in estimating the activity coefficient of water in the product stream. The error led to a greater water content than expected by the time the stream went to a lowpressure distillation for stripping. Excess water caused the amines to "distill" into the steam jets used to reduce column pressure. Then, excess organics in the wastewater from the steam jets pro duced frequent overloading of the acti vated charcoal used to treat the waste water before discharge. The firm had to live with increased costs of regenerating charcoal and recharging beds. In another case, a helium recycling plant was forced to run at two thirds of its rated capacity and later suffered turbine failure. Miscalculations of heattransfer coefficients led to excessive heat leakage into liquid helium transfer lines. In addition, a unit intended to ad sorb impurities was bypassed as the result of an associated change in flow pattern. Dirty gas continuously entered the turbine, eventually causing it to fail.
conditions that will arise in the plant "Enthalpies, along with densities, under design. Five chapters, cov dictate the liquid and vapor loadings ering general data, critical properties, and column diameter. Enthalpies and vapor pressure, density, and envi transport properties determine the ronmental data, have been released heater and cooler duties for the col to institute members, and will be umn and heat-transfer surfaces for made available generally in June tower condensers and reboilers. 1983. Danner and Dauber are devel Transport properties such as viscos ity, surface tension, and diffusivity oping the prediction manual. Chemical engineer Stephen A. assist the designer in translating Newman of Foster Wheeler Synfuels theoretical stages into real trays Corp., Livingston, N.J., described the through the calculation of massimportance of methods in the man transfer hydraulic efficiencies." ual to the Los Angeles AIChE meet As he notes, "most of the proper ing, using the example of a fraction ties contained in the prediction ating tower. Calculating parameters manual come in handy when de of the tower design requires the so signing a distillation column." lution of heat-and-material-balance But chemical engineers always equations, Newman says, and these have been uncertain whether the equations must be fed accurate va predictive methods evaluated by API porization constants and enthal for hydrocarbons would apply to pies. polar compounds. One of the Penn "Vaporization constants are the State workers' tasks is to investigate prime factors in determining the this, and to describe the amount of number of theoretical trays to effect error involved in doing so. a given separation/' he explains. "One surprise coming out of our January 3, 1983 C&EN
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Technology Completion for 1025 compounds to include variety of data Identification Name Synonyms Formula Structura Chemical Abstracts registry number Physical conet ante Molecular weight Critical temperature Critical pressure Critical volume Critical compressibility factor Acentric factor Melting point at 1 atm Triple-point temperature Boiling point at 1 atm Enthalpy of fusion at melting point Enthalpy of formation of ideal gas at 25 *C Gibbs energy of formation of ideal gas at 25 °C Absolute entropy of ideal gas at 25 °C Standard enthalpy of combustion at 25 °C Solubility parameter at 25 °C Liquid molar volume at 25 °C
work is how well the API hydrocarbon correlations work for polar c o m p o u n d s / ' says Danner. "It's much better than could have been anticipated." Each chapter in the manual begins with an introductory discussion of the property to be correlated. Next, recommended procedures are described, noting whether calculator or computer methods are applicable, and at what operating conditions each is valid. Finally, there is a discussion of reliability, with literature references. The chapter on environmental data correlations is based on the Environmental Protection Agency's ambient and discharge multimedia environmental goals. This chapter contains methods for assigning numerical values of maximum permitted concentrations to individual compounds and for blending these values to obtain limits for stream mixtures. Chemical engineers may use these methods to evaluate alternative waste-treatment designs. Yet a third project taken up by the institute is assembly of a data book and manual of predictive methods for vapor-liquid and solid-liquid (solubility) equilibria of aqueous 36
January 3, 1983 C&EN
Dipole moment Radius of gyration Van der Waals reduced volume and area Refractive index Flash point Flammabillty limits Autoignition temperature Temperature-dependent properties Vapor pressure Enthalpy of vaporization Density of solid Density of liquid Second virial coefficient Heat capacity of solid Heat capacity of liquid Heat capacity of ideal gas Viscosity of liquid Viscosity of vapor Thermal conductivity of liquid Thermal conductivity of vapor Surface tension Environmental data Ambient and discharge multimedia environmental goals
electrolytes. The contract for this project is with Chemsolve, a Morristown, N.J., firm that specializes in developing computer programs to simulate processes involving aqueous electrolytes. If application of predictive methods for properties of hydrocarbons to polar compounds is tenuous, equilibrium and thermodynamic predictions for concentrated electrolyte solutions are almost unknown territory. Still, advances during the past five years make problems of electrolyte solutions appear more tractable than before. Semiempirical correlation methods have been developed for activity coefficients of up to 4M to 6M. Regulatory pressures from EPA have helped because they've led to the generation of much thermodynamic data. And computer programs now can solve higher-order equations for neutralization of polyprotic acids. Much work yet remains. Ionic strengths of industrial solutions can reach 20 molal. Pressures range from 1 to 25 atm. Temperatures vary from 25 to 200 °C. And calculations must work for solutions of many molecular and/or ionic species together.
Besides projects involving compilation of reliable data from centralized sources and systematic evaluations of predictive methods, the institute has commissioned a series of experimental projects to shed new light on particular systems of chemical engineering interest. Two of these involve determining vaporliquid equilibria and volumetric data for the acetic acid/water and ammonia/water systems at high pressures over a wide temperature range. This work, assigned to Wiltec, an industrial contract research lab in Provo, Utah, is largely complete. Another experimental project, expected to go on over a much longer period, is determination of vaporliquid equilibrium data for a number of binary liquid mixtures. Such data are valuable not only for the specific mixtures themselves, but also for estimation of functional-group contributions to equilibrium properties. Methods exist for predicting vaporliquid equilibria for mixtures by using number values for functional groups to express interaction of all structural and electronic features of molecules of one component in the mix with those of another. For example, workers at Purdue University have studied the mixture of propylene oxide and tert-butanol to generalize on how epoxy groups of any compound in mixtures interact with hydroxyl groups of any other compound. Contributions from the hydrocarbon features of both compounds were already known. A further experimental project is determination of vapor pressures of pure compounds between 0.2 psi and the critical point. Compounds selected in this project in 1982 for study by participant firms were 2-propanol, 4-ethyltoluene (the p-methylstyrene precursor), ethanolamine, vinyl acetate, triethylene glycol, phenol, methacrylic acid, 3,3,3-trifluoropropylene, N-cyclohexylpyrrolidine, and 3-mercaptopropanol. Danner and Daubert carried out these studies at Penn State. In 1983, the institute has asked them to determine methyl tert-butyl ether (the antiknock additive), diand triethanolamine, hexamethylenediamine, hexamethylenetetramine, hexamethyleneimine, and an aery late ester yet to be chosen. D
