Enthalpy of mixing of liquid (carbon dioxide + ethane) at the temperature 230.8 K and of liquid (carbon dioxide + n-butane) at 221.4 K and 241.4 K

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.

Exergy and economic analyses of a novel hybrid structure for simultaneous production of liquid hydrogen and carbon dioxide using photovoltaic and electrolyzer systems

We considered the method of carbon dioxide processing and recycling which is suitable for the use in food, refrigeration and other industries; moreover it provides a high level of carbon dioxide recycling and processing and its further use. The analysis of being in demand for this method was carried out in the field of processing liquid and solid carbon dioxide. A special feature of the method concept is the principle of solidification and the possibility of producing solid carbon dioxide with full use of raw materials without losses to the environment. A plant for producing solid carbon dioxide has been designed. The article presents the plant process flow diagram and describes its operation principle. We also mark the plant competitive advantages over analogues. Despite relatively small overall dimensions, the carbon dioxide return was anticipated by means of liquefaction back into the technological cycle. Feed connection can be carried out both from the cylinders with liquid carbon dioxide, and by connecting the liquid carbon dioxide pipeline from the liquefaction process flow at the enterprises.

'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.'

Dissolution process of a spherical rising supercritical or liquid CO2 droplet in water

The use of liquid and supercritical carbon dioxide was explored for the blending of poly(vinyl acetate) and citric acid as a basis for developing a new process for making chewing gum which would allow for flavorings to be released slower during chewing. Mixtures of 75% of polymer and 25% citric acid by mass were blended with carbon dioxide from 5 to 60 min over a temperature range of 25 to 55 °C and a pressure range of 83 to 241 bar in a batch process. Samples were then artificially chewed and citric acid dissolution monitored. Comparisons were made with samples prepared without carbon dioxide. In all cases, carbon dioxide blending produced polymers which retained the critic acid longer and hence produced more desirable products. With carbon dioxide, temperature had the largest effect on citric acid retention while pressure (or density) had only a modest effect. To make the flavoring be retained the longest in the polymer, the highest temperature and pressure (density) should be used with the longest blending time in carbon dioxide.

Carbon Dioxide-Water Emulsions for Enhanced Oil Recovery and Permanent Sequestration of Carbon Dioxide

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

Liquid (as well as supercritical) carbon dioxide can be used in deactivation. Solutions of TBP and phosphorus-and fluorine-containing acids in CO2 in the presence of alcohols make it possible to achieve the deactivation coefficients equal to 50 and above for surfaces polluted with weakly fixed α-, β-, and γ-radiating nuclides by two successive treatments. When performing the double treatment of metals contaminated with strongly fixed nuclides using solutions of chelating agents in CO2, it is possible to achieve deactivation coefficients equal to 2–3 for aluminum, 10–20 for brass (90–95 of radionuclides are removed), and 10–30 for stainless steel (90–97% of radionuclides are removed). Using an enlarged pilot apparatus, the possibility of deactivating protective clothes and metal products in liquid carbon dioxide down to the natural radioactive background is shown.

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.

X-band (9.5 GHz) time-resolved electron paramagnetic resonance (TREPR) spectra of a 1,9-acyl−alkyl biradical were obtained at room temperature in benzene and in liquid (950 psi) carbon dioxide (CO2) solutions. The spin exchange interaction (J) in this biradical is negative and larger in magnitude than the hyperfine interaction (q). This leads to the observation, in both solvents, of spin-correlated radical pair (SCRP) spectra which are net emissive. Spectra obtained at later delay times (>1.5 μs) in CO2 exhibit alternating intensities of their SCRP transitions due to spin relaxation but do not show any significant change in line width. The same effect is observed in benzene, but on a slower time scale. Q-band (35 GHz) experiments in benzene showed that the phenomenon was found to be both field and temperature dependent. It is also chain-length dependent, being much stronger in short biradicals (<C10). A Redfield theory analysis of the spin-state populations is presented and discussed that includes J modul...

Cooling capability of liquid nitrogen and carbon dioxide in cryogenic milling

It has been demonstrated that the pharmaceutical molecule, Ibuprofen, can be loaded into mesoporous silica using liquid (near-critical) carbon dioxide as the solvent, and that the resulting material had a high Ibuprofen content (300 mg Ibuprofen/g SiO2). A high enrichment (300 times) of Ibuprofen in the pores was observed in comparison to the Ibuprofen concentration in the solution. When similar experiments were performed in CO2 (l) mixed with minor amounts (5 mol-%) of other organic cosolvents (cyclohexane, acetone or methanol), a significantly lower loading capacity of Ibuprofen into the mesoporous material was achieved. The drug-loaded mesoporous silica material was analyzed with Thermogravimetric Analysis (TGA), confocal Raman microscopy, X-ray Powder Diffraction (XRPD) and Scanning Electron Microscopy (SEM). It was found that the Ibuprofen loaded into the mesoporous silica host was amorphous and that Ibuprofen was present both at the surface and in the centre of the mesoporous silica particles. Furthermore, the SEM images did not reveal any large flakes of Ibuprofen molecules outside the mesoporous silica particles.

The scheme of carbon dioxide cogeneration and trigeneration plant with the use of secondary energy resources in the form of combustion products or flue gases that enables to produce electricity, thermal energy and cold for centralized and decentralized supply of consumers simultaneously, is presented. In addition, the plant can produce liquid and gaseous carbon dioxide. The main elements of the plant are a heating unit, a turbodetander unit and a carbon dioxide unit for the production of cold, liquid and gaseous carbon dioxide. A thermodynamic calculation and a brief exergy analysis of the plant were carried out. In the proposed plant, off-gases from glassmelting, metallurgical furnaces, heat power facility and other energy facilities with a secondary energy temperature of 250–400 °C and above can be used as secondary energy resources. The heating unit of the installation has been designed to produce thermal energy for heating and hot water supply systems. The carbon dioxide unit has been designed for the production of cold, electric energy and carbon dioxide in liquid and gaseous form in order to ensure the operation of the plant and the use for commercial purposes. The cold in the plant can be obtained in two evaporators operating at different boiling temperatures. At a higher boiling point of carbon dioxide, cold is used in air conditioning systems and in centralized cooling and storage systems, while at a lower boiling point of carbon dioxide – in freezing and storage systems. For the implementation of the reverse carbon dioxide cycle, a three-stage carbon dioxide compressor with a receiver after the third stage is used. To reduce compression performance of the compressor, complete intermediate cooling of carbon dioxide between stages should be provided.

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.