A modified SAFT equation of state is developed by applying the perturbation theory of Barker and Henderson to a hard-chain reference fluid. With conventional one-fluid mixing rules, the equation of state is applicable to mixtures of small spherical molecules such as gases, nonspherical solvents, and chainlike polymers. The three pure-component parameters required for nonassociating molecules were identified for 78 substances by correlating vapor pressures and liquid volumes. The equation of state gives good fits to these properties and agrees well with caloric properties. When applied to vapor−liquid equilibria of mixtures, the equation of state shows substantial predictive capabilities and good precision for correlating mixtures. Comparisons to the SAFT version of Huang and Radosz reveal a clear improvement of the proposed model. A brief comparison with the Peng−Robinson model is also given for vapor−liquid equilibria of binary systems, confirming the good performance of the suggested equation of state. ...

Perturbed-Chain SAFT: An Equation of State Based on a Perturbation Theory for Chain Molecules

As particle design is presently a major development of supercritical fluids applications, mainly in the pharmaceutical, nutraceutical, cosmetic and specialty chemistry industries, number of publications are issued and numerous patents filed every year. This document presents a survey (that cannot pretend to be exhaustive!) of published knowledge classified according to the different concepts currently used to manufacture particles, microspheres or microcapsules, liposomes or other dispersed materials (like microfibers):

RESS: This acronym refers to ‘Rapid Expansion of Supercritical Solutions’; this process consists in solvating the product in the fluid and rapidly depressurizing this solution through an adequate nozzle, causing an extremely rapid nucleation of the product into a highly dispersed material. Known for long, this process is attractive due to the absence of organic solvent use; unfortunately, its application is restricted to products that present a reasonable solubility in supercritical carbon dioxide (low polarity compounds).

GAS or SAS: These acronyms refer to ‘Gas (or Supercritical fluid) Anti-Solvent’, one specific implementation being SEDS (‘Solution Enhanced Dispersion by Supercritical Fluids’); this general concept consists in decreasing the solvent power of a polar liquid solvent in which the substrate is dissolved, by saturating it with carbon dioxide in supercritical conditions, causing the substrate precipitation or recrystallization. According to the solid morphology that is wished, various ways of implementation are available:

GAS or SAS recrystallization: This process is mostly used for recrystallization of solid dissolved in a solvent with the aim of obtaining either small size particles or large crystals, depending on the growth rate controlled by the anti-solvent pressure variation rate;

ASES: This name is rather used when micro- or nano-particles are expected; the process consists in pulverizing a solution of the substrate(s) in an organic solvent into a vessel swept by a supercritical fluid;

SEDS: A specific implementation of ASES consists in co-pulverizing the substrate(s) solution and a stream of supercritical carbon dioxide through appropriate nozzles.

PGSS: This acronym refers to ‘Particles from Gas-Saturated Solutions (or Suspensions)’: This process consists in dissolving a supercritical fluid into a liquid substrate, or a solution of the substrate(s) in a solvent, or a suspension of the substrate(s) in a solvent followed by a rapid depressurization of this mixture through a nozzle causing the formation of solid particles or liquid droplets according to the system.

The use of supercritical fluids as chemical reaction media for material synthesis. Two processes are described: thermal decomposition in supercritical fluids and hydrothermal synthesis.

We will successively detail the literature and patents for these four main process concepts, and related applications that have been claimed. Moreover, as we believe it is important to take into account the user's point-of-view, we will also present this survey in classifying the documents according three product objectives: particles (micro- or nano-) of a single component, microspheres and microcapsules of mixtures of active and carrier (or excipient) components, and particle coating.

http://www.tuleoffice.com/images/editor/File/pdf/book/nano/s5%20im-web.pdf

Particle design using supercritical fluids: Literature and patent survey

Carbon dioxide is often promoted as a sustainable solvent, as CO 2 is non-flammable, exhibits a relatively low toxicity and is naturally abundant. However, injudicious use of carbon dioxide in a process or product can reduce rather than enhance overall sustainability. This review specifically examines the use of CO 2 to create greener processes and products, with a focus on research and commercialization efforts performed since 1995. The literature reveals that use of CO 2 has permeated almost all facets of the chemical industry and that careful application of CO 2 technology can result in products (and processes) that are cleaner, less expensive and of higher quality.

Supercritical and near-critical CO2 in green chemical synthesis and processing

A version of the statistical associating fluid theory (SAFT) is developed for chain molecules of hard-core segments with attractive potentials of variable range (SAFT-VR). The different contributions to the Helmholtz free energy are evaluated according to the Wertheim perturbation theory. The monomer properties are obtained from a high-temperature expansion up to second order, using a compact expression for the first-order perturbation term (mean-attractive energy) a1. Making use of the mean-value theorem, a1 is given as the van der Waals attractive constant and the Carnahan and Starling contact value for the hard-sphere radial distribution function in terms of an effective packing fraction. The second-order perturbation term a2 is evaluated with the local compressibility approximation. The monomer cavity function, required for the calculation of the free energy due to the formation of the chains and the contribution due to association, is given as a function of a1. We analyse the equation of state for ch...

Statistical associating fluid theory for chain molecules with attractive potentials of variable range

Carbon-based structures are the most versatile materials used in the modern field of renewable energy (i.e., in both generation and storage) and environmental science (e.g., purification/remediation). However, there is a need and indeed a desire to develop increasingly more sustainable variants of classical carbon materials (e.g., activated carbons, carbon nanotubes, carbon aerogels, etc.), particularly when the whole life cycle is considered (i.e., from precursor "cradle" to "green" manufacturing and the product end-of-life "grave"). In this regard, and perhaps mimicking in some respects the natural carbon cycles/production, utilization of natural, abundant and more renewable precursors, coupled with simpler, lower energy synthetic processes which can contribute in part to the reduction in greenhouse gas emissions or the use of toxic elements, can be considered as crucial parameters in the development of sustainable materials manufacturing. Therefore, the synthesis and application of sustainable carbon materials are receiving increasing levels of interest, particularly as application benefits in the context of future energy/chemical industry are becoming recognized. This review will introduce to the reader the most recent and important progress regarding the production of sustainable carbon materials, whilst also highlighting their application in important environmental and energy related fields.

Sustainable carbon materials

The authors cover virtually every facet of supercritical fluid (SCF) technology: the history of SCF extraction, its underlying thermodynamic principles, process principles, industrial applications, and analysis of SCF research and development efforts. A review of 75 major SCF extraction patents provides an important source of technical and business information. Computer programs that can be used to calculate critical mixture and phase border curves for binary and ternary liquid-SCF and solid-SCF mixtures are included in the appendix. The book discusses the following contents: Introduction . Historical perspective . Phase diagrams for SCF-solute mixtures at high pressures . Experimental techniques for high pressure studies - Thermodynamic modeling of SCF-solute phase behaviour . Process operations . Early industrial applications - SCF process studies: 1976-81 . Polymer and monomer processing with SCF . SCF processing of pharmaceuticals, natural products and chemicals . Reactions in SCF . Special applications of SCF solvents . References and Index.

Supercritical Fluid Extraction: Principles and Practice

Cloud-point data to temperatures of 270 °C and 3000 bar are presented for CO2 with the family of poly(acrylates) including methyl, ethyl, propyl, butyl, ethylhexyl, and octadecyl, with poly(butyl methacrylate), with poly(vinyl acetate), with statistically random copolymers of poly(ethylene-co-methyl acrylate) with 41, 31, and 18 mol % acrylate, with poly(tetrafluoroethylene-co-hexafluoropropylene) and poly(vinylidene-co-hexafluoropropylene) copolymers, each with ∼20 mol % hexafluoropropylene, and with Teflon AF. Over the same range of conditions, CO2 cannot dissolve polyethylene, poly(acrylic acid), poly(methyl methacrylate), poly(ethyl methacrylate), polystyrene, poly(vinyl fluoride), or poly(vinylidene fluoride). CO2 is a weak solvent that exhibits the temperature-sensitive characteristics observed with polar solvents. The solubility of a nonpolar hydrocarbon polymer or a copolymer in CO2 can be increased by at least partially fluorinating the polymer or by incorporating some polar groups into the backb...

Solubility of Polymers and Copolymers in Supercritical CO2

Phase Behavior of Polymers in Supercritical Fluid Solvents.

Solld solubllltles of naphthalene and blphenyl In supercrltlcal carbon dioxide were measured at varlous Isotherms above 31.06 OC-the crltlcal temperature of C0,-and over a range of pressures from 80 to 500 atm. The upper crltlcal end polnt for the naphthalene-carbon dloxlde system Is estlmated from the solublllty data to be 63 OC, 240 atm, and a naphthalene mole fractlon of 0.16. The upper crltlcal end-polnt temperature for the blphenyl-carbon dloxlde system Is -56 OC and at a pressure near 460 atm. The biphenyl mole fractlon at the upper crltlcal end polnt (UCEP) Is -0.16.

Mark A. McHugh

Papers

Supercritical Fluid Extraction: Principles and Practice

Solubility of Polymers and Copolymers in Supercritical CO2

Phase Behavior of Polymers in Supercritical Fluid Solvents.

Solid solubilities of naphthalene and biphenyl in supercritical carbon dioxide

Reactions in supercritical fluids - a review