F. Carl Knopf

State‐of‐the‐art on the supercritical extraction of organics from hazardous wastes

Extraction by supercritical fluids (SCF) is a relatively new technology which offers several key advantages over traditional methods, especially enhanced solubility and rapid diffusion. Because the molecular properties of SCF are intermediate between those of liquids and gases, well‐known heuristic design rules may not apply to SCF systems. In the present, work progress in the areas of predicting and correlating thermody‐namic and transport properties of supercritical fluids are outlined. In addition, specific fruitful areas are delineated wherein proven applications have evolved. Some specific examples include SCF leaching of contaminated soil samples, oxidation of hazardous waste, and regeneration of adsorbents.

Algae attachment on carbonated cements in fresh and brackish waters - preliminary results

Abstract In order to evaluate the usefulness of different cements as substrates for artificial reefs, we have performed preliminary tests of both conventional and pH-neutral molded cements for attachment of microalgae populations. Neutrality was achieved by molding in the presence of carbon dioxide. It was verified through analysis of carbonate and hydroxide content and measurement of contact pH. Algae attachment tests were conducted at both brackish and freshwater conditions. We have found pH-neutral materials to which microalgae readily attach. These include silica-enriched (pozzolanic) cements, but also blast-furnace slag and fly ash, which are also silica-rich, and mixtures of these with Portland cement. In most cases the pH-neutralized, carbonated cements outperformed the conventional materials in rate of algae attachment, in some cases by wide margins. The high pH, conventional cements preferentially attached barnacles in brackish water. There was no evidence of weight loss in any of the test specimens.

Measurement and modeling of extraction of chlorinated hydrocarbons from water with supercritical carbon dioxide

Abstract Supercritical-fluid extraction (SCFE) for the removal of toxic chlorinated organics from water has been studied using a continuous-flow view-cell system. The solubilities of pure 1,2-dichloroethane, 1,1,2-trichloroethane, and 1,1,2,2,-tetrachloroethane in subcritical and supercritical C0 2 have been obtained at 313.2 and 323.2 K and over a pressure range of 6.2–8.27 MPa. All the compounds studied were completely miscible in C02 at the temperatures studied and at pressure > 9 MPa. Equilibrium data for the removal of these compounds from water using supercritical C02 were obtained at two temperatures (313.2 and 323.2 K) and over a pressure range 9.65-16.54 MPa. The distribution coefficients (K-values) of these three compounds between supercritical C0 2 and an aqueous phases were in the range of 20 to 200. These high distribution coefficients verify that extraction with supercritical C0 2 is an effective method to remove chlorinated hydrocarbons from water. The results have been modeled using a hardsphere, perturbation-theory-based Camahan-Starling-DeSantis-Redlich-Kwong equation of state and simple mixture rules.

Reactive extraction of lignin from wood using supercritical ammonia-water mixtures

Supercritical Fluid (SCF) extraction was used to selectively remove lignin from yellow poplar wood (Liriodendron tulipifera L). The process may serve as an alternative to conventional delignification techniques practiced by the pulp and paper industry. Extraction experiments were performed by flowing supercritical ammonia-water mixtures through a fixed bed of poplar wood. Extraction of cellulose, hemicellulose, and lignin was determined as a function of time (0–3 h), solvent composition (0–20 wt % water), temperature (160–200 °C), and pressure (136–272 atm). The percentage of water in the solvent and temperature were found to be the most important variables in determining extraction efficiency. A simple model involving these variables was developed. The most effective extraction was obtained using 20 wt % water in ammonia at 272 atm and 200 °C, at these conditions about 70% of the lignin, 50% of hemicellulose, and 15% of the cellulose initially present in the wood were extracted in one hour.

Supercritical fluid extraction of acetic acid, alcohols and other amphiphiles from acid-water mixtures

Common supercritical fluid solvents cannot effectively extract highly water-soluble contaminants from either soils or waters. Two questions then arise: (1) how effective is SCF extraction from aqueous solution of contaminants only slightly soluble in water, when highly soluble organics are present; and (2) how will the extractability of the highly soluble contaminant be affected by the slightly soluble one? We have explored SCF extractions of this type, the solvent being CO2 at 7–17 MPa and temperatures to 323 K, for a range of amphiphilic or surfactant compounds including simple alcohols (1-hexanol and 1-octanol), longer chain oxyalcohols (polyethylene glycol-200 and the methyl ether of polyoxyethylene-3), and a fluorinated polyether carboxylate. Acetic acid was used as the model contaminant of high aqueous solubility. We found that the presence of the amphiphiles decreases the already limited extractability of acetic acid from aqueous solution by SCF-CO2; this was especially true of materials regarded as nonionic or anionic surfactants. Meanwhile, the presence of acetic acid apparently decreased the extractabilities of alcohols by CO2, especially for alcohols of higher molecular weight. Possible reasons for this behavior and its implications for SCF extraction of natural waters are discussed.

COMPARISON OF EXACT AND APPROXIMATE SOLUTIONS OF TRANSIENT RESPONSE FOR LEACHING BY SCF IN CSTR

Abstract Leaching or extraction by supercritical fluids (SCF) is a relatively new technology which offers several key advantages over traditional methods, especially enhanced solubility and rapid diffusion. Because the molecular properties are somewhere in between those of either liquid or gas, the design of SCF systems does not fit the classical mold based on intuitive or well-known rules of thumb. In the present work, transient transport for dissolution of solutes filling granulated porous media is studied for SCF leaching in spinning basket or slurry reactors. We present an approximate model based on taking the intraparticle composition profile to be always parabolic. This leads to a simple one-term expression (transportable on the back of a postage stamp) which is shown to compare very favorably with the more tedious exact solution. The approximate solution thus allows designers to quickly delineate those conditions, such as sampling times, which are realizable in the experimental sense. Moreover, it ...

Bridging Excel and C/C++ code

Microsoft Excel provides a flexible pre‐ and post‐processor for low‐level languages such as C/C++. Here details are provided to allow single variables, vectors and matrices to pass from Excel ↔ VBA ↔ C/C++ programs. Passing single variables and vectors is straightforward. Passing matrices requires understanding of row‐major and column‐major storage strategies. Simple examples utilizing each data type are shown.

Catalytic oxidation of model waste aromatic hydrocarbons in a dense fluid

Abstract Aromatic compounds dissolved in dense COa (with stoichiometric air) were oxidized at 80-140 bar and 453-573 K. A range of behavior from partial oxidation to complete combustion was observed upon varying the active metal oxide on an Al2O3, support. This process can be joined to supercritical fluid extraction as a waste treatment technology; some of the rates of destruction observed here compare favorably to those obtained for similar compounds in supercritical water or wet-air oxidation processes. The results of experiments where pressure was varied, but reactant mole fractions held constant, suggest the absence of rate-limiting fluid-phase reactions, or of diffusional control; the catalyst itself appears to be the locus of the rate-limiting reactions at these conditions.

It's Not as Easy as it Looks: Revisiting Peng—Robinson Equation of State Convergence Issues for Dew Point, Bubble Point and Flash Calculations

The use of equations of state (EOS) is a ‘modern’ method of physical property prediction and here we present a detailed exposition of the use of the Peng–Robinson EOS for mixtures. This EOS can be used to determine whether a stream is in the vapor phase or liquid phase. However, for two-phase systems the approaches presented in standard textbooks for the calculation of the state frequently will not converge. We provide modifications to standard dew point, bubble point and flash algorithms to help improve the convergence of any EOS. Commercial software can show different values for stream energetic properties (entropy values) and here we utilize species formation from its elements as well as species ideal gas capacities and mixture departure functions to explain observed differences.

Data Reconciliation and Suspect Measurement Identification for Gas Turbine Cogeneration Systems

Data reconciliation is widely used in the chemical process industry to suppress the influence of random errors in process data and help detect gross errors. Data reconciliation is currently seeing increased use in the power industry. Here, we use data from a recently constructed cogeneration system to show the data reconciliation process and the difficulties associated with gross error detection and suspect measurement identification. Problems in gross error detection and suspect measurement identification are often traced to weak variable redundancy, which can be characterized by variable adjustability and threshold value. Proper suspect measurement identification is accomplished using a variable measurement test coupled with the variable adjustability. Cogeneration and power systems provide a unique opportunity to include performance equations in the problem formulation. Gross error detection and suspect measurement identification can be significantly enhanced by increasing variable redundancy through the use of performance equations. Cogeneration system models are nonlinear, but a detailed analysis of gross error detection and suspect measurement identification is based on model linearization. A Monte Carlo study was used to verify results from the linearized models.