Innovative polymer processing in carbon dioxide

'This report summarizes the results of work done during the first 1.3 years of a three year project. During the first nine months effort focussed on the design, construction and testing of a closed recirculating system that can be used to study photochemistry in supercritical carbon dioxide at pressures up to 5,000 psi and temperatures up to about 50 C. This was followed by a period of work in which the photocatalytic oxidation of benzene and acetone in supercritical, liquid, and gaseous carbon dioxide containing dissolved oxygen was demonstrated. The photocatalyst was titanium dioxide supported on glass spheres. This was the first time it was possible to observe photocatalytic oxidation in a supercritical fluid and to compare reaction in the three fluid phases of a solvent. This also demonstrated that it is possible to purify supercritical and liquid carbon dioxide using photochemical oxidation with no chemical additions other than oxygen. The oxidation of benzene produced no intermediates detectable using on line spectroscopic analysis or by gas chromatographic analysis of samples taken from the flow system. The catalyst surface did darken as the reaction proceeded indicating that oxidation products were accumulating on the surface. This is analogous to the behavior of aromatic compounds in air phase photocatalytic oxidation. The reaction of acetone under similar conditions resulted in the formation of low levels of by-products. Two were identified as products of the reaction of acetone with itself (4-methyl-3-penten-2-one and 4-hydroxy-4-methyl-2-pentanone) using gas chromatography with a mass spectrometer detector. Two other by-products also appear to be from the self-reaction of acetone. By-products of this type had not been observed in prior studies of the gas-phase photocatalytic oxidation of acetone. The by-products that have been observed can also be oxidized under the treatment conditions. The above results establish that photocatalytic oxidation of organic compounds in supercritical carbon dioxide can be achieved. Until recently it was not possible for us to obtain high quality, quantitative kinetic data. The original flow cell used to obtain UV-Visible spectra on the recirculating fluid did not provide quantitative concentration data because the sapphire windows did not have adequate transmission characteristics below about 240 nm. A pair of windows with better transmission properties arrived as this report was being prepared. While waiting for the replacement windows for the flow cell, the concentration of reactants was monitored by withdrawing samples of the fluid stream for gas chromatographic analysis. This allowed progress to be made in determining some of the factors that affected the rates of reaction in a qualitative sense but the results had large error bars due to the difficulty in obtaining reproducible samples from the pressurized system using gas tight syringes. This problem was recently solved by incorporating a gas chromatograph with automatic sampling valves into the flow system. The two on line analytical methods will now result in reliable analytical data that can be used to follow the reaction kinetics and detect and identify reaction intermediates and by-products, if any are formed.'

This chapter describes several aspects of the use of carbon dioxide as a solvent or cosolvent in coating applications. The primary impetus for using carbon dioxide for this purpose has been the alleviation of volatile emissions and liquid solvent wastes. However, the special physical properties of liquid and supercritical carbon dioxide may offer some processing advantages over conventional organic or aqueous solvents. Liquid carbon dioxide is quite compressible, and a reduction in temperature results not only in a reduction in the operating pressure, but also in a significant increase in the liquid density to values of approximately 0.9 g/cm3. At these high liquid densities, carbon dioxide exhibits improved solvent performance, but with much lower viscosities and interfacial tensions than aqueous or organic liquid solvents. Under supercritical conditions, carbon dioxide also exhibits high densities, low viscosities, and improved solvent power. Low viscosities and interfacial tensions tend to facilitate the transport of the solvents into any crevices or imperfections on the surface to be covered, and this might prove advantageous in the coating of patterned or etched surfaces. Since carbon dioxide dissolves and diffuses easily into many different polymers and organic liquids, it can also be used to reduce the viscosity of coating solutions. Whether in the liquid or the supercritical state, the temperature and pressure of the mixture can be used to control its physical properties in ways that are impossible to achieve with traditional solvents. These distinguishing features have raised the level of industrial interest in carbon dioxide as a solvent for coating applications, beyond those based solely on environmental concerns. In this chapter, we will discuss current applications and research on the use of CO2 as a solvent for coatings. The first section deals with spray coating from supercritical CO2. Subsequent sections deal with the use of liquid coatings, such as spin and free meniscus coatings, and impregnation coatings. Since the start of the 20th century (ca. 1907), atomization has been the basis for conventional spray coating applications (Muirhead, 1974). Typically, atomization is caused by high shear of the coating fluid in air, leading to droplet or particle formation.

ABSTRACTWhen separating volatile compounds from aqueous solution using supercritical carbon dioxide (SC CO2), methods to bring SC CO2 into contact with volatile compounds in the solution are very important. An extraction using micro bubble, gaseous, supercritical, and liquid CO2 generated by a filter nozzle was carried out. Under optimal conditions (20 MPa, 35°C), > 95% of volatile compounds consisting of 6 to 12 carbon atoms could be removed by extraction for 40 min at CO2 flow rate, 4.0 g/min. Extraction at 35°C could achieve either a selective or nonselective separation by adjusting the extraction pressure, since the effect of pressure on extraction ratio was most significant at 35°C.

The main goal of the present paper is to assess the available information so as to obtain a general procedure for dealing with the critical enhancement of the thermodynamic and transport properties of supercritical CO2 and CO2 containing binary mixtures for practical and scientific applications. The present review provides comprehensive analysis of the thermodynamic and transport properties of supercritical carbon dioxide and CO2 containing binary mixtures (experiment and theory) and their various technological and scientific applications in different natural and industrial processes. The available information for the thermodynamic and transport properties (experiment and theory) enhancement (anomaly) of supercritical carbon dioxide and SC CO2 + solute mixtures is comprehensively reviewed. The effect of long-range order parameter fluctuations on the thermodynamic and transport properties of supercritical fluids (SC CO2) will be discussed. Simplified scaling type equation based on mode-coupling theory of critical dynamics with two critical amplitudes and one cutoff wave number as fluid-specific parameters was used to accurately predict of the transport properties of supercritical carbon dioxide. The recommended values of the specific parameters (asymptotic critical amplitudes) of the carbon dioxide for practical (prediction of the thermodynamic and transport properties of the supercritical CO2 for technological applications) and scientific use were provided. The role of the critical line shapes of the carbon dioxide containing binary mixture (SC CO2+solvent) in determination of the critical behavior of the mixture near the critical point of pure supercritical solvent (CO2) is discussed. Krichevskii parameter concept for a description of thermodynamic behavior of dilute near-critical SC CO2+solute mixtures is also discussed. The structural and thermodynamic properties of the carbon dioxide containing binary mixtures near the critical point of pure solvent (CO2) are discussed.

We report the formation of self-assembled monolayers (SAMs) on gold substrates by exposure to n-alkanethiols [CH3(CH2)n-1SH; n = 8, 10, 12, 16, and 18] in liquid and supercritical carbon dioxide. The results of this novel study show that an environmentally friendly solvent can be used to form highly crystalline SAMs with few gauche defects and that pressure as well as exposure time can be used to affect the structural and barrier properties of the monolayer film. Reflectance infrared spectroscopy, electrochemical impedance spectroscopy, and wetting measurements were used to characterize the SAMs. The effects of pressure (76−300 bar) and adsorption time (3−90 min) on the formation of the SAMs were explored. The overall chain density of these SAMs was greater than that for SAMs formed in common organic solvents such as ethanol. The properties of the SAMs were slightly affected by the pressure during formation. At 35 °C, as the carbon dioxide pressure increased (from 76 to about 140 bar), the packing density and resistance of the SAM increased. SAMs prepared at higher pressures ranging from about 140 to 300 bar exhibited similar resistances, capacitances, and canted structures. There was also no significant difference in using liquid (25 °C and 103 bar) or supercritical (35 °C and 103 bar) carbon dioxide for SAM formation. Supercritical carbon dioxide also enabled the formation of SAMs using polar adsorbates (−OH- and −CO2H-terminated thiols) to prepare high-energy surfaces that are wet by water.

9.11 Dry-cleaning with liquid carbon dioxide

A flow-through method for the extraction of lithium-ion battery electrolytes with supercritical and liquid carbon dioxide under the addition of solvents has been developed and optimized to achieve quantitative extraction of the electrolyte from commercial 18 650 cells.

The effect of temperature on the fluorescence spectrum of pyrene in supercritical and liquid carbon dioxide and liquid organic solvents is systematically studied. The Py parameter (intensity ratio of vibronic bands 1 and 3) is found to increase with the density of supercritical carbon dioxide in the range from 0.54 to 0.75 g/cm3. This observation is consistent with the fact that dispersion forces, which represent the major interaction between pyrene and carbon dioxide, depend inversely on the sixth power of distance. However, the Py parameter of both supercritical and liquid carbon dioxide is also found to decrease with temperature at constant density, which is not consistent with expectations for dispersion forces. Carbon dioxide, which is generally regarded as a nonpolar solvent, shows a temperature effect comparable to that for polar liquid solvents. The origin of this temperature effect is examined in this study by computer simulation using both semiempirical molecular orbital and molecular mechanics methods. On the basis of these simulations, a strong electrostatic attraction arises between pyrene and carbon dioxide which is similar in magnitude to that with polar solvents. The temperature dependence of the Py parameter can be qualitatively explained by these simulation results.

In this work, the complex of shikonin-methyl-β-cyclodextrin and shikonin-2-hydroxypropyl-β-cyclodextrin were studied in supercritical carbon dioxide (sc CO2) at moderate pressure and temperature much lower than the melting point of shikonin. For comparing, the complex was also prepared by sealed heating method. Complex efficiency between shikonin and 2-hydroxypropyl-β-cyclodextrin (HPBCD) was quite low. Partly formation of shikonin—methyl-β-cyclodextrin (MBCD) was obtained by sealed heating method. Complete formation of shikonin—MBCD was obtained in sc CO2 media in short reaction time. This complexation was accelerated and enhanced by the rise in both the reaction temperature and carbon dioxide pressure up to 100 °C 100 bar. The physical state of cyclodextrins in complex reaction has remarkable influence on the complex. The aqueous solubility of shikonin could be enhanced about 75 times by complexing with MBCD. In this work, the complex of shikonin-methyl-β-cyclodextrin and shikonin-2-hydroxypropyl-β-cyclodextrin were studied in supercritical carbon dioxide (sc CO2) at moderate pressure and temperature much lower than the melting point of shikonin (SK). For comparing, the complex was also prepared by sealed heating method. Complex efficiency between SK and 2-hydroxypropyl-β-cyclodextrin (HPBCD) was quite low. Partly formation of SK—methyl-β-cyclodextrin (MBCD) complex was obtained by sealed heating method. Complete formation of SK—MBCD was obtained in sc CO2 media in short reaction time. This complexation was accelerated and enhanced by the rise in both the reaction temperature and carbon dioxide pressure. The physical state of cyclodextrins in sc CO2 has remarkable influence on the complex. The aqueous solubility of SK could be enhanced about 75 times by complexing with MBCD.

In the supercritical CO2 method of extraction of palm oil, many processes in conventional method, such as degumming, deodorization, refining and bleaching processes, are eliminated. The supercritical method allows palm oil to be extracted and fractionated simultaneously, which not only reduces the cost of processing, but also provides a more environmental-friendly processing alternative. In this research, the high-pressure phase behaviour of the binary system between supercritical carbon dioxide (SC CO2) and palm oil fatty acid components were investigated. The phase transition is observed from a camera which is connected to a high-pressure variable-volume view cell. Carbon dioxide has high solvating power, nontoxic, inflammable and low critical points. The determination of phase behaviour could offer an insight to the right operating condition of palm oil supercritical fluid carbon dioxide extraction process in order to acquire the desired extraction selectivity and an optimum yield. The phase boundaries of some fatty acids components, lauric acid (C12), stearic acid (C18), and oleic acid (C18) in compressed supercritical carbon dioxide were determined at temperatures of 313.15 K, 323.15 K, 333.15 K, 343.15 K and 353.15 K under pressures between 10 MPa and 60 MPa.

Carbon dioxide (CO 2 ) corrosion at low partial pressure has been widely recognized, but research on supercritical CO 2 (SC CO 2 ) corrosion is very limited. By far, investigations on steel corrosion under SC CO 2 conditions have mainly focused on the corrosion rate, structure, morphology, and composition of the corrosion scales as well as the electrochemical behaviors. It was found in aqueous SC CO 2 environment, that the corrosion rate of carbon steel was very high, and even stainless steels (13Cr and high-alloy CrNi steels) were subjected to some corrosion. Inhibitor could reduce the corrosion rate of carbon steels and stainless steels, but none of the tested inhibitors could reduce the corrosion rate of carbon steel to an acceptable value. Impurities such as O 2 , SO 2 , and NO 2 and their mixtures in SC CO 2 increased the corrosion rate of carbon steel. However, the existing studies so far were very limited on the corrosion mechanism of steels in SC CO 2 conditions. Thus, this paper first reviews the finding on the corrosion behaviors of steels under SC CO 2 conditions, points out the shortcomings in the present investigations and finally looks forward to the research prospects on SC CO 2 corrosion.

Simultaneous solubility of carbon dioxide and hydrogen in the ionic liquid [hmim][Tf 2N]: Experimental results and correlation

In this study we investigated fluid displacement water with supercritical (sc) CO2 in chalk under conditions close to those used for geologic CO2 sequestration (GCS), to answer two main questions: How much volume is available for scCO2 injection? And what is the main mechanism of displacement over a range of temperatures? Characterization of immiscible scCO2 displacement, at the pore scale in the complex microstructure in chalk reservoirs, offers a pathway to better understand the macroscopic processes at the continuum scale. Fluid behavior was simulated by solving the Navier-Stokes equations, using finite-volume methods within a pore network. The pore network was extracted from a high resolution 3D image of chalk, obtained using X-ray nanotomography. Viscous fingering dominates scCO2 infiltration and pores remain only partially saturated. The unstable front, developed with high capillary number, causes filling of pores aligned with the flow direction, reaching a maximum of 70% scCO2 saturation. The saturation rate increases with temperature but the final saturation state is the same for all investigated temperatures. The higher the saturation rate, the higher the dynamic capillary pressure coefficient. A higher dynamic capillary pressure coefficient indicates that scCO2 needs more time to reach capillary equilibrium in the porous medium.

Schultz and Randall published in 1970 the results of qualitative investigations into the extractability of lipophilic natural substances with liquid carbon dioxide [1]. They described the influence of molecular weight and functional groups of aroma compounds from fruit juices on the solubility in the liquid carbon dioxide. In 1976 Stahl and Schilz studied the extractability with supercritical carbon dioxide of numerous individual compounds from various classes (e.g. polyaromatics, phenols, aromatic carboxylic acids, anthraquinones, pyrones, hydrocarbons and other lipids [2]; this furnished the first clear picture of the solubilites of natural substances in dense carbon dioxide. This information, together with experience from recent years, has enabled the rules of thumb given below to be suggested for extraction with dense carbon dioxide: 1) easily extractable (up to 300 bar) are lipophilic compounds with a molecular mass of up to 300–400, such as hydrocarbons, ethers, esters, ketones and similar compounds. 2) the presence of polar functional groups lowers, and may even completely prevent, extraction. 3) not extractable are polar substances, such as sugars, glycosides, amino acids, lecithins, etc.; and polymers, including proteins, cellulose, polyterpenes and plastics. Non-polar oligomers are only sparingly soluble. 4) water is poorly soluble in liquid carbon dioxide (ca. 0.1% by weight, at 20 °C) but shows increasing solubility in supercritical CO2 with temperature increase (ca. 0.3% by weight at 50 °C). 5) fractionation is possible when the substances display differences in molecular mass, vapour pressure or polarity.

The phase behavior of five β-adrenergic blocking agents (acebutolol, atenolol, nadolol, pindolol, and propranolol) were explored in liquid and supercritical carbon dioxide at (298, 308, and 318) K and at pressures between (80 and 275) bar. The solubility of the solids in carbon dioxide was experimentally determined by observing the cloud point using a variable-volume stirred vessel with visual access. Although these compounds are very similar structurally, each containing a secondary amine, alcohol, aromatic ring, and ether group, only pindolol was soluble in carbon dioxide under the conditions explored. The other four β blockers were observed to form yellow-brown salt complexes with carbon dioxide and did not show any appreciable solubility. It is believed that pindolol's lower basicity (having a Kb an order of magnitude lower than the other four compounds) prevented it from reacting with carbon dioxide, a Lewis acid, and salting out as the other four β blockers did.