Carbon Dioxide Medium Research Articles

Photocatalytic Properties of Tetraphenylporphyrins Immobilized on Calcium Alginate Aerogels

We have prepared photocatalytic systems based on tetraphenylporphyrins (TPP) immobilized on calcium alginate solid gels in the conditions of thermal drying on air (xerogel), freeze drying in vacuum (cryogel) and supercritical drying in the supercritical carbon dioxide (scCO2) medium (aerogel). As a test reaction to measure the prepared systems’ efficiency, we studied tryptophan photooxidation in the aqueous medium. We have demonstrated that the systems with aerogel as a carrier exhibited the highest photocatalytic efficiency. In that case, the rate constant for the test substrate (tryptophan) oxidation exceeds the corresponding rate constants of similar systems based on xerogel and cryogel by more than 5 times. Moreover, the aerogel-based photocatalytic systems demonstrated enhanced functional stability and a possibility of multiple use of such a catalyst in tryptophan oxidation. Based on the data of small-angle X-ray scattering and thermooxidative destruction, we have made a conclusion about the relationship between the high photocatalytic activity of aerogel-immobilized TPP and formation of a developed porous aerogel structure in the conditions of drying in the scCO2 medium, which is stabilized due to formation of additional complex bonds of calcium ions with fragments of glycoside rings.

The Formation of Functionally Active Polymer Materials in the Supercritical Carbon Dioxide Medium*

The Formation of Functionally Active Polymer Materials in the Supercritical Carbon Dioxide Medium*

Исследование антикоррозионных свойств ингибиторов, синтезированных на основе триглицеридов оливкового масла, в сероводородной и углекислотной средах

Исследование антикоррозионных свойств ингибиторов, синтезированных на основе триглицеридов оливкового масла, в сероводородной и углекислотной средах

Особенности коррозионно-электрохимического поведения сталей с различным содержанием хрома в углекислотных низкотемпературных средах

The effect of chromium on the corrosion rate of low-alloy steels in carbon dioxide media has been studied by the gravimetric method. The features of the electrochemical corrosion behavior of these steels in the media containing carbon dioxide have been determined

The structure of the soft drinks supply at the market of Yekaterinburg

Nowadays research of the regional markets and consumers’ preferences in the soft drinks segment are actual. This is associated with the saturation of the market and increasing competition within the segment. The research of the market is the base for the assessments of the prospects for the certain enterprise and for the sector development. Analysis of the assortment of the made and sold at the Yekaterin-burg soft drinks was realized. The article shows the position of the good relative to the all-marketing positions in the region. It has been established that assortment of the soft drinks is characterized by the diversity of the types and drinks on the basis of the aromatic staff prevail (41,6%), juice and juice-contained beverages (28,2%), mineral and drinkable bottled water (21,4%) with different trademarks prevail. Leaders of the market are two big foreign companies. “Coca-Cola Company” with trademarks “Coca-cola”, “Fanta”, “Sprite”, “Nestea”, “Dobriy”, “Bon Aqua” and the company “Pepsi Co Russia” representing trademarks “Pepsi” “Mirinda”, “7up”, “Tonus”, “Russkiy Dar”. According to strength saturation with carbon dioxide medium carbonated drinks (40,4%) and strong carbonated drinks (39,1%) prevail. The light carbonated drinks are much smaller and account 13,5%, and non-carbonated drinks are the smallest part of the market (6,96%). The reason of that structure that the carbon dioxide is actively used by the soft drinks producers as a preservative, regulator of the acidity and antioxidant. The research of the package show that the producers use polymeric materials, metal, glass and combined pack. The main trends of the market are increasing consumer requirements to the quality and information about the proposed drinks, the growth of the number of consumers that attend to the ingredients and the impact of “the healthy food choice” on the market.

Research of forming of the system of transport pores in the structure of carbon composites by their gasification

The structure of pores for carbonized carbon plastics is considered. Description of porous structure by the parabolic law of distribution on four local maximums is offered. Mechanism of forming for the system of transport pores are researched in the structure of carbonized carbon plastics taking into account oxidization of its lateral face and real distribution of porous structure on the size of radiuses at gasification in the medium of carbon dioxide. The task of carbon dioxide transfer on length of carbonizing carbon plastic pores, providing the given profiling of its structure in the process of gasification, is considered

Stable “coloured” states of spirooxazine photochrom molecules immobilized in polymer matrixes by supercritical carbon dioxide

Formation of long-lived coloured forms of indoline spirocompounds (spirooxazines and spiropyrans) molecules under matrix immobilization in polar polymer of different chemical structure using supercritical fluid impregnation is studied. Some of such systems acquire additional optical characteristics besides colour – they become fluorophores. Mechanisms of observed changes in optical properties and long-term stability of the resulting coloured forms of indoline spirooxazine in polymers are discussed. Electronic absorption spectra of such coloured forms were recorded in supercritical carbon dioxide medium as well as on air. The results can be applied for creation of optical, biomedical and electronic devices and stable fluorescence composite coverings.

Solubility of dialkylalkyl phosphonates in supercritical carbon dioxide: Experimental and modeling approach

Dialkylalkyl phosphonates have found renewed interest in the selective extraction of actinides from different matrices. In this context, two dialkylalkyl phosphonates, dibutylbutyl phosphonate (DBBP) and diamylamyl phosphonate (DAAP) were synthesised and their solubilities in supercritical carbon dioxide (SCCO2) medium were determined in the pressure range of 10–25 MPa at 313–333 K. Solubility studies were carried out to examine their utility as ligands during supercritical fluid extraction of actinides. Solubilities of dialkylalkyl phosphonates ranged from 0.06 to 0.12 mole fraction. Experimental solubilities were correlated using Mendez-Santiago, Chrastil, solution theory with Wilson activity coefficient model and association model based on van Laar activity coefficient model. Comparison among these models revealed that the association model with van Laar activity coefficient model provides better solubility predictions. SCCO2 containing DAAP was employed for the (i) selective extraction of uranium in the presence of simulated fission products and (ii) extraction of uranyl nitrate from acidic medium.

Formation of porous matrices from lactide and ε-caprolactone copolymers in supercritical carbon dioxide medium

A series of lactide and e-caprolactone copolymers containing 4–24 mol % of e-caprolactone with 20- to 30-kDa molecular weights are synthesized. Based on them, porous materials are produced by foaming in supercritical carbon dioxide. The pore size was shown to decrease with increasing e-caprolactone content in copolymer, while the porosity of the entire sample was not altered. The resulting pore size also decreases if 7 wt % polyethylene glycol is added to the initial monomer mixture. The Young’s modulus of the porous samples decreases with increasing e-caprolactone content and when polyethylene glycol is added.

Regeneration of an average temperature isomerization catalyst in supercritical carbon dioxide medium modified with C5–C6 isoalkanes

The regeneration of an average temperature isomerization catalyst with supercritical carbon dioxide together with a cosolvent was studied. An effect of regeneration conditions on catalytic activity of the studied catalyst has been defined.

Glycerol Dehydration to Acrolein Catalyzed by ZSM-5 Zeolite in Supercritical Carbon Dioxide Medium.

Supercritical carbon dioxide (SC‐CO2) has been used for the first time as a reaction medium for the dehydration of glycerol to acrolein catalyzed by a solid acid. Unprecedented catalyst stability over 528 hours of time‐on‐stream was achieved and the rate of coke deposition on the zeolite catalyst was the lowest among extensive previous studies, showing potential for industrial application. Coking pathways in SC‐CO2 were also elucidated for future development. The results have potential implications for other dehydration reactions catalyzed by solid acids.

Decoration of multi-walled carbon nanotubes with metal nanoparticles in supercritical carbon dioxide medium as a novel approach for the modification of screen-printed electrodes

A supercritical carbon dioxide medium was used for the decoration of functionalized multi-walled carbon nanotubes (MWCNTs) with metallic nanoparticles. This procedure allowed the rapid and simple decoration of carbon nanotubes with the selected metallic nanoparticles. The prepared nanomaterials were used to modify screen-printed electrodes, improving their electrochemical properties and allowing to obtain a wide range of working electrodes based on carbon nanotubes. These electrodes were applied to the amperometric determination of vitamin B6 in food and pharmaceutical samples as an example of the analytical potentiality of the electrodes thus prepared. Using Ru-nanoparticles-MWCNTs as the working electrode, a linear dynamic range between 2.6×10−6 and 2×10−4molL−1 and a limit of detection of 0.8×10−6molL−1 were obtained. These parameters represented a minimum 3-fold increase in sensitivity compared to the use of bare MWCNTs or other carbon-based working electrodes.

Chitosan impregnation with biologically active tryaryl imidazoles in supercritical carbon dioxide.

The presented paper is focused on impregnation of chitosan and its derivatives with a biologically active triaryl imidazole model compound ((2-2-hydroxyphenyl)-4.5-diphenyl-1H-imidazole) in the supercritical carbon dioxide medium. Since initial chitosan represents a polycation-exchange resin and does not swell in supercritical carbon dioxide, the impregnation was carried out in the presence of water (0.15-3.0 vol%). The maximum 2-2-hydroxyphenyl)-4.5-diphenyl-1H-imidazole concentration in a chitosan film was achieved at the ~5 × 10(-3) g/cm(3) water content in the reactor. We also used hydroxy carboxylic acid derivatives of chitosan and its copolymer with polylactide as matrices for introduction of hydrophobic 2-2-hydroxyphenyl)-4.5-diphenyl-1H-imidazole. We have shown that unmodified chitosan contains the greatest amount of 2-2-hydroxyphenyl)-4.5-diphenyl-1H-imidazole, as compared with its hydrophobic derivatives. The kinetics of 2-2-hydroxyphenyl)-4.5-diphenyl-1H-imidazole diffusion from a chitosan matrix was studied in acidified water with pH 1.6. We found that the complete release of 2-2-hydroxyphenyl)-4.5-diphenyl-1H-imidazole into the aqueous phase from unmodified chitosan films occurred in 48 h, while its complete release from chitosan modified with hydroxy carboxylic acids occurred in 5 min or less.

Chemical Reaction CO+OH(•) → CO2+H(•) Autocatalyzed by Carbon Dioxide: Quantum Chemical Study of the Potential Energy Surfaces.

The supercritical carbon dioxide medium, used to increase efficiency in oxy combustion fossil energy technology, may drastically alter both rates and mechanisms of chemical reactions. Here we investigate potential energy surface of the second most important combustion reaction with quantum chemistry methods. Two types of effects are reported: formation of the covalent intermediates and formation of van der Waals complexes by spectator CO2 molecule. While spectator molecule alter the activation barrier only slightly, the covalent bonding opens a new reaction pathway. The mechanism includes sequential covalent binding of CO2 to OH radical and CO molecule, hydrogen transfer from oxygen to carbon atoms, and CH bond dissociation. This reduces the activation barrier by 11 kcal/mol at the rate-determining step and is expected to accelerate the reaction rate. The finding of predicted catalytic effect is expected to play an important role not only in combustion but also in a broad array of chemical processes taking place in supercritical CO2 medium. It may open a new venue for controlling reaction rates for chemical manufacturing.

Kinetics of coal char gasification in a carbon dioxide medium

Solid fuel samples with different carbon contents are gasified by successively subjecting to pyrolysis in argon and oxidation in carbon dioxide at various temperatures to determine the rate of the chemical reactions and the activation energy required for simulating and optimizing the operation of gas generators. The samples were prepared from bituminous coal, lignite, and anthracite of the Kuznetsk and Kansk-Achinsk coal basins. The gasification of coal char samples in a carbon dioxide medium at 900–1200°C is analyzed by thermogravimetry. The temperature dependences of the weight change rate and gasification time of coal char samples are measured and used to calculate the preexponential factor and activation energy of the carbon oxidation reaction. It is found that, with increasing oxidizing medium temperature from 900 to 1200°C, the gasification time of the coal char samples obtained from anthracite and bituminous coal decrease 8- and 22-fold, respectively. A physicomathematical model of coal char gasification in a fixed bed, with the oxidizing gas diffusing through the ash layer formed, is proposed.

Evaluation of the structure and fuel properties of lignocelluloses through carbon dioxide torrefaction

Two typical lignocelluloses, pine and poplar, were torrefied in a tubular reactor under carbon dioxide medium at temperatures ranging from 220 to 340°C. The effect of torrefaction temperature on the structure and properties of the chars obtained was investigated to evaluate their fuel applications. As the temperature raised from 220 to 340°C, the mass yield decreased from 96.7% to 48.7% for pine, and from 97.1% to 43.8% for poplar. The higher heating value of the torrefied pine increased to 25.6MJ/kg for the sample torrefied at 340°C. An increase in reaction temperature resulted in a decrease in the contents of cellulose and hemicelluloses but notable increase of the content of lignin, especially for the sample subjected to the strongest torrefaction. The variation of C, H, and O contents of the samples after torrefaction suggested that a high temperature promoted the dehydration and deacetylation reactions. Thermal analysis indicated that the combustion activity of the sample was improved to a level of lignite after torrefaction. The hydrophobicity of lignocelluloses was notably increased with increased torrefaction severity, suggesting the prepared samples are good feedstocks for further processing.

Deformations and phase transitions on the swelling of fossil coals in a carbon dioxide medium

The swelling of fossil coals in an atmosphere of carbon dioxide was analyzed within the framework of a model of the elastic deformation of a medium with an internal volume under the conditions of sorption. The solutions obtained were adequate to experimental data. The possibility of phase transitions in the sorbate substance caused by changes in the sorption potential, which accompany the swelling of coal, was considered.

Swelling kinetics and impregnation of PLA with thymol under supercritical CO2 conditions

The present work was aimed to study swelling kinetics of polylactic acid (PLA) and its impregnation with thymol in supercritical carbon dioxide (scCO2) medium. The influences of temperature and soaking time on the swelling kinetics and impregnation yield of PLA cylindrical disc and film were investigated. Swelling experiments were performed in a high pressure view cell at 10 MPa and temperatures of 40°C, 60°C and 75°C for 2 to 24 h. On the basis of swelling kinetics, pressure of 10 MPa and temperature of 40°C were chosen for supercritical solvent impregnation (SSI) of the PLA samples during 2 to24 h. The highest swelling extent was observed for the PLA monolith after 24 h treatment with pure scCO2 (7.5%) and scCO2 with thymol (118.3%). It was shown that sufficiently high amount of thymol can be loaded into both PLA monolith and film using SSI after only 2 h (10.0% and 6.6%, respectively). Monolith and film of PLA impregnated with thymol could be suitable for active food packaging and sterile medical disposables.

Relative permittivity of monocomponent and binary solutions of N2O5 in liquid CO2 and their activity in nitration of cellulose

Static relative permittivity of liquid carbon dioxide solutions of dinitrogen pentoxide and its mixtures with nitric, acetic or trifluoroacetic acids is measured. The procedure for nitration of cellulose acquired from various natural noncotton sources (wood, linen, hemp) by mixtures of dinitrogen pentoxide and 100% nitric acid in a carbon dioxide medium is developed. A supercritical drying technique is implemented for dehydration of wet nitrocellulose.

Xenogenic bone matrix treated with supercritical carbon dioxide as a potential osteoplastic material

A multistage environmentally safe method for processing xenogenic bone matrix using suband supercritical media has been developed. This method provides fast matrix delipidization in a medium of supercritical carbon dioxide and deproteinization by treatment with a 3% hydrogen peroxide solution followed by washing with subcritical water for removal of polar substances. The final treatment with supercritical carbon dioxide serves to remove residual nonpolar components. A method to control the porosity of xenogenic bone matrix at different stages of its purification has been suggested. Preliminary data indicate that a cellular test system based on an allogenic osteoid cell line Th-1 could be used for evaluation of primary adhesion and proliferation of cells on the surface of purified bone matrix.